DATA COLLECTION SURVEY FOR GEOTHERMAL DEVELOPMENT …

JRIL

15-088

The Republic of Djibouti

DATA COLLECTION SURVEYFOR GEOTHERMAL DEVELOPMENT

IN THE REPUBLIC OF DJIBOUTI(GEOPHYSICAL SURVEY)

FINAL REPORT

AUGUST 2015

JAPAN INTERNATIONAL COOPERATION AGENCY(JICA)

NIPPON KOEI CO., LTD.

JMC GEOTHERMAL ENGINEERING CO., LTD.

SUMIKO RESOURCE EXPLORATION ANDDEVELOPMENT CO., LTD.

The Republic of Djibouti

DATA COLLECTION SURVEYFOR GEOTHERMAL DEVELOPMENT

IN THE REPUBLIC OF DJIBOUTI(GEOPHYSICAL SURVEY)

FINAL REPORT

AUGUST 2015

JAPAN INTERNATIONAL COOPERATION AGENCY(JICA)

NIPPON KOEI CO., LTD.

JMC GEOTHERMAL ENGINEERING CO., LTD.

SUMIKO RESOURCE EXPLORATION ANDDEVELOPMENT CO., LTD.

Sonalia

Gulf of Tadjoura

Eritrea

Ethiopia

Dikhil

Survey Area

Hanle Djibouti

Lac Abhe

Lac Asal

Red Sea

Arta

Obock

Gaggade

Djibouti- Awrofoul

AsalRift

Sakalol

Rouweli

Lac Abhe

Djibout

Nord Goubet

Survey Area Hanle

Hanle -1

Hanle-2

Gas Sampling Point

Garabbayis-2

Garabbayis-1 Teweo -1

Existing Test Well Tracking Record Contour (20 m)

Dug Well Fumarole Rock

Acidic Altered Rock Weaky Acidic /Propyritic altered

Legend

Survey Area

Abbreviations

ASTER Advanced Spaceborne Thermal Emission and Reflection Radiometer

CERD Centre de Recherche et des Etudes de Djibouti (Centre for the Study and

Research of Djibouti)

DEM Digital Elevation Model

EDD Electricite de Djibouti

ESIA Environmental and Social Impact Assessment

EIS Environmental Impact Statement

GENZL Geothermal Energy New Zealand Ltd.

GRMF Geothermal Risk Mitigation Facility

ICEIDA Iceland International Development Agency

IPP Independent Power Producer

ISOR Iceland Geosurvey

JICA Japan International Cooperation Agency

a.s.l Above Sea Level

MT Magneto-Telluric

NCG Non-condensable Gas

ODDEG Djiboutian Office for Development of Geothermal Energy

ORSTOM Office de la Recherche Scientifique et Technique Outre-Mer

PPP Public-Private Partnership

R gas Residual Gas

TD Total Depth

TEM Transit Electro-magnetic

TOR Terms of Reference

TVD True Vertical Depth

USAID United States Agency for International Development

WB The World Bank

Data Collection Survey for Geothermal Development in Djibouti (Geophysical Survey) Final Report

Japan International Cooperation Agency S - 1 Nippon Koei Co., Ltd. Sumiko Resource Exploration and Development Co., Ltd.

JMC Geothermal Engineering Co., Ltd.

Data collection Survey for Geothermal Development in Djibouti

(Geophysical Survey)

Final Report

Executive Summary

1. Background of the Project

1.1 Background

Geothermal development has been conducted since 1970 in the Republic of Djibouti. However, geothermal

energy has not been smoothly developed partially because high salinity geothermal fluid was encountered.

Under such circumstance, the President of Djibouti requested the Prime Minister of Japan when he visited

Djibouti in August 2013 for possible technical assistance on geothermal energy development. In response

to this request, the Government of Japan expressed its intention to provide support. In accordance with this,

the Japan International Cooperation Agency (JICA) carried out the Data Collection Survey on Geothermal

Development (hereunder referred to as “JICA Survey (2014)”) in 2014 to collect and analyze geological

and geochemical information of all existing and conceived geothermal manifestation sites. As a result,

development priority was proposed.

1.2 Purposes

The purposes of the survey are as follows:

- To evaluate the geothermal resource of Hanle for consideration of possible future detailed surveys, i.e., test drilling; and

2. Review of Existing Surveys

2.1 Collected Data

The surface surveys (geological/geochemical/geophysical survey) and test well drilling had been

carried out in Hanle Region.

Based on the survey results, Aquater (1989) and Jalludin (2009) described the presence of geothermal

system in the Hanle Plain is contradicted. However, the presence of fumaroles on the plateau side

suggests the possibility of the existence of geothermal system.

Based on the existing survey results described above, the following are assumed for the geothermal

system of the Hanle Region.

1. The results of temperature distribution of the test wells indicated that a heat source causes the

fumaroles at the surface, which is believed to suggest the presence of heat source in the plateau

side. This is consistent with the fact that fumaroles are observed on the plateau.

2. The reason of low temperature of wells that have been drilled in the Hanle Plain is inferred to be




due to the presence of groundwater flow in the Hanle Plain. In addition, hydraulic gradient

indicates the possibility that the source of groundwater is in the Hanle Plain side.

3. In the geochemical survey under the JICA Survey (2014), the possibility of a temperature of

about 250 ºC on the reservoir has been pointed out.

From the above, the presence of geothermal system may exist under the plateau that extends to the

northeast of the Hanle Plains. Therefore, the Magneto-Telluric (MT) and Transit Electro-magnetic

(TEM) surveys were performed on the plateau, in order to reveal this assumption.

3. Geophysical Survey

3.1 Objectives

In one of the target fields for geothermal development in the project, the Magneto-Telluric (MT) survey,

which is one of the electromagnetic survey methods, was conducted to study the subsurface resistivity

structure. The Transit Electro-magnetic (TEM) survey was carried out to have static correction of MT

data. The acquired data were processed and analyzed to clarify the underground resistivity structures

of the target field. The geology and geological structures were deduced from the subsurface resistivity

distribution and the geophysical information of deep zone to contribute to the creation and estimation

of geothermal reservoir model and the planning of test drilling survey was obtained.

3.2 Results of 2D Inversion

The following are the characteristics of the resistivity structure in Hanle Geothermal Field. And the

panel diagrams of resistivity cross section and plan map are shown in Figures 3-14 and 3-15,

respectively:

・ The resistivity structure consists of three zones, namely: conductive overburden, resistive

intermediate thick zone, and conductive deeper zone at a depth from the surface to -10,000 m

elevation. The resistivity distribution is roughly ranging from 1 ohm-m to 2,500 ohm-m.

・The contour line, as the boundary of 100 ohm-m resistivity between conductive overburden and

resistive intermediate zones, is located from -1,500 m to -2,000 m elevation at the southwest side of

the survey site, and its location becomes shallow to the northeast direction and is roughly ranging from

-500 m to -1,000 m elevation at the northeast side of the survey site.

・In a large sense, resistivity distribution may change from conductive to resistive from the southwest

side to the northeast side. From -1,000 m to -2,000 m elevation, the interval of contour lines is

relatively narrow. It suggests the resistivity discontinuity which shows drastic change of resistivity

value.

・The conductive overburden is thin in the graben part of the survey site and thick in the horst part

while the intermediate resistive zone shows a large value in the horst part and a small value in the




標高100m

標高-500m

標高-1000m

標高-2000m

標高-4000m

標高-10000m

graben part of the survey site. The location of resistivity discontinuity, which shows drastic change of

resistivity, mainly coincides with the boundary between the graben and the horst.

・In all the profiles, the highest resistivity (>2,500 ohm-m) is observed from -4,000 m to -5,000 m

elevation and this high resistivity is distributed widely with a central focus on HNL200 and HNL300

profiles.

Source: The Survey Team

Figure1 Panel Diagram of Resistivity Maps 4 Supplementary Surveys

4.1 Overview of Geology and Topography

the geological and topographic feature of the survey area is as follows.

Quaternary volcanic rocks (Afar Stratoid) are widely distributed in the survey area. Major geological

layers are the lower basalt layer (2.0-2.7 Ma), upper basalt layer (1.8-2.2 Ma), and uppermost basalt

layer (1.25 is a -1.65 Ma). Rhyolite layer (1.9-2.6 Ma), which is almost the same age as the lower

basalt layer, is developed in the north.

Basalts form a plateau, covering a wide range including the MT/TEM survey area. In addition, the

uppermost basalt layer develops as volcanic corns in the NW-SE direction on the plateau.

4.2 Site Survey and Laboratory Analysis

In order to confirm the distribution of geothermal manifestations in the survey area, geological

reconnaissance was conducted in parallel with the geophysical surveys. As a result, the fumarole area

has been confirmed in the three sites around the geophysical survey area.




The survey conducted this year is an additional survey, to study more precisely the area and chemical

change of the geothermal steam supplied. For this purpose, two fumaroles including the one surveyed

last year were examined. As a result, geothermal steam producing the geothermal manifestations can

be steadily supplied from a geothermal reservoir which has the highest temperature of 260 °C. Based

on this interpretation, it follows that Garabbayis is an appropriate location for new test drilling to

prove the presence of a geothermal reservoir.

5 Geothermal Reservoir Model and Target for Geothermal Test Wells

5.1 Preliminary Geothermal Reservoir Model

The observations/information and interpretations necessary for the construction of preliminary

geothermal reservoir model are summarized in Table1, based on the past survey results and the

geophysical survey conducted.

Table1 Summary of Observations and Interpretations

Observation Geothermal System Interpretation

Temperature at 500 m depth of the past 5 test wells increases from the plain side to the plateau side (40 ºC 90 ºC 120 ºC) Heat source The heat source may exist under the

plateau area. Fumaroles are observed only in the plateau area.

The confirmed fumaroles seem to be on the extension line of the major faults. Reservoir

Fumaroles may emerge along the faults in rhyolite and/or lower basalt layer.

The confirmed fumaroles exist on the margin of the upper basalt. Reservoir The upper basalt may act as the cap

rock of the reservoir.

The fumarole includes mantle origin gas, and the geothermometer indicates 260 ºC Fluid Fluid with high temperature may exist.

Groundwater level in the Hanle Plain is higher than that in the plateau area. Fluid recharge There may be recharging from the

plain side to the plateau side.

There is a distinct difference of resistivity structure between the plain side and the plateau side.

Regional geological structure

There may be major fault between the plain and the plateau.

Ultra high resistivity zone (1,000 Ωm or more) is identified below elevation -3,000 m in the plateau side. Heat source This may be an intrusion body that

retains high temperature.


Based on the above information and interpretation, the following three cases are proposed as the

preliminary geothermal reservoir model.




Table2 Preliminary Reservoir Conceptual Models Case (a)

Figure 2 Case (b) Figure 3

Case (c) Figure 4

State of reservoir Not passed much time from the heat source intrusion High temperature reservoir is present locally

Geothermal system is fully developed Geothermal fluid circulates, and reservoir is formed over a wide range

Heat supply from the heat source is attenuated, and reservoir temperature decreases

Res

ervo

ir

Area/zone Under the plateau Along faults Along major faults only where fumaroles are confirmed

Permeability (hosted rock)

High Low Low

Temperature 260 260 260

Flu

id Origin Originated from the Hanle

Plain Originated from the Hanle

Plains Originated from the Hanle

Plain Upflow Along fractured faults Along fractured faults Along the major fault only

Heat source An intrusive rock below 3 km



Figure 2 Geothermal Conceptual Model: Case (a)


Figure 3 Geothermal Conceptual Model: Case (b)

SW NE

SW NE





Figure 4 Geothermal Conceptual Model: Case (c) A preliminary reservoir assessment with information on the target area based on the survey shows the

following results:

Capacity (MW)

80% Most Probable 20% 16.9 32.8 86.4

5.2 Target for Geothermal Test Wells

(1) Target Position on the Map

In that zone, the locations of the most active manifestations can be a candidate for the target position

on the map, as shown by a red circle in Figure 5.

Figure 0 Map for Planning of a New Test Well Drilling in Garabbayis

(2) Target Depth

Target depth should correspond to the depth of a high temperature in the models. The altitude of the

SW NE





isotherm of 250 °C is set at around -1,200 mASL in the models; thus, the target depth should be at

least 1,500 m from the surface whose altitude is ca. 300 mASL. Considering more the uncertainty of

the isotherm in the models, the target depth should be set at the depth ranging from 1,500 m to 1,800

m (-1,500 mASL) as shown in Figure 6.

Figure 6 Target Depth in the Geothermal Reservoir Model

(3) Wellhead Location

The well pad of the Garabbayis-1 well can be used for a new test well. The well pad is made of

concrete, offering a rigid and flat base for the drilling rig.

(4) Preliminary Drilling Plan

On the basis of the location of targets, preliminary drilling plan was examined. In the case where the

well pad for Garabbayis-1 is used also for the new test well, the deviation should be 300 m to reach

the farthest target. This deviation and targeted TVD (1,800 m) require a TD of 2,000 m with an

inclination of the well less than 30 °. This plan is sufficiently acceptable with a normal 2,000 m class

drilling rig.

6. Preliminary Economic Analysis for IPP Participation

With information available at this stage, the reservoir resource of the Hanle geothermal prospect was

evaluated at 15 MWe as the probable occurrence 80% that should be considered when IPP project is to

be planned. This capacity is as a similar size as of a small hydropower plant. However, the Hanle

Fault-1





geothermal power station will be economically superior to the existing oil thermal power plants if the

transmission line should be constructed without financial burden to EDD.

Presently, a significant part of the electricity is being purchased from Ethiopia. Although Ethiopia still

has a large capacity of hydropower energy, the power purchase agreement between the two countries

have entered into only for a period of Ethiopia wet seasons. On the other hand, power plants within

Djiboutian territory are all of oil thermal power plant. Therefore, Djibouti does not actually have any

power plants of indigenous energy source.

Under this circumstance, constructing the Hanle geothermal power station, though the capacity is 15

MWe together with transmission line will be justifiable not only from economical point of view but

also energy security point of view too.

7. Procedure of Environmental and Social Considerations

7.1 Environmental and Social Impact Assessment Study

Decree 2011-029/PR/MHUEAT (2011) shall be referred to for the Environmental Social Impact

Assessment (ESIA), which describes the procedures to be followed. The decree classifies the

assessment into two categories: (1) basic and (2) detailed. The detailed assessment is required for test

well drilling and plan construction.

Assessment of the terms of reference (TOR) by the competent office needs about one month at least,

Survey and report preparation may take two months,

Assessment and approval of the report needs about three months, and

A total of about six months are required to start the test well drillings. 8. Proposal of Additional Surface Survey

8.1 Issues to be Solved to Realize Test Well Exploration

The following are the issues to be solved before implementation of test well exploration:

・To verify the appropriateness of the interpretation of geological structure (geological characteristics

of the Hanle Plain and the plateau).

A number of faults have been objectively confirmed by the lineament analysis using DEM data.

The MT/TEM survey identified one major fault between the Hanle Plain and the plateau.

Distribution of fracture together with regional geological structure has to be clarified.

・To improve knowledge on the characteristics of reservoirs

The resistivity structure of Hanle is different from that of a typical geothermal reservoir. Even

though, the Survey Team proposed three reservoir models based on the fact that there are

geothermal manifestations. The appropriateness of these models, however, has to be verified

with additional surface survey before test well exploration because the information at hand is

considered not to be enough to confidently propose the reservoir model which could allow more




reliable resource estimation. The drilling target may also be refined with the additional

information.

・To understand the extent of the sheeted high resistivity zone below, and the very low resistivity zone

in the surface zone of the northeast side of the plateau

The high resistivity zone below is considered to be the heat source that would originate from

intrusive rock; and the low resistivity zone in the surface zone of the northeast side of the

plateau may form the cap structure of the reservoir. These resistivity structures extend beyond

the present MT/TEM survey area. Since these are considered to be very important to examine

the geothermal system, the survey area has to be widened. This is also important to review the

size of the reservoirs.

8.2 Proposal for Additional Survey

The following three surface surveys are proposed: (1) gravity survey, (2) additional MT/TEM survey,

and (3) micro-seismicity monitoring. In addition, the following surveys are proposed which are

necessary for smooth implementation of test well exploration in the shortest time period: (4) ESIA for

test well drilling and (5) preparatory survey for test well drilling works.

8.3 Preliminary Work Schedule Up to Test Well Drilling

A preliminary work schedule up to test well drilling is proposed in Figure 7 below.


Figure 7 Preliminary Work Schedule up to Test Well Drilling

9. Activities of Other Donors

9.1 USAid

- A workshop was conducted on independent power producers (IPP) and public private partnership (PPP) for the energy sector in October 2014.

- An expert was appointed in 2014 to promote IPP or PPP projects in the energy sector. It is

Work Item

1. Gravity Survey

Preparation

Observation 300 points

Analysis/Reporting

2. Microseismic Survey

Preparation

Installation 5 points

Observation 3 months

Analysis/Reporting

3. Additional MT/Tem Survey

Preparation

Observation 36 points

Analysis/Reporting

4. Comprehensive Analysis

5. ESIA

Scoping

TOR Review

Site Survey

Review

6. Preliminary Study for Test Drilling

Market Research

Civil Engineering Planning

Specification

Cost Estimation

7th 1st 2nd 3rd 4th 5th 6th




understood that an aim of this support is to build a consensus for implementation of Power Africa under the Obama Initiative. The expert had left the country in February 2015.

- An alternative expert has been selected. The expert is not stationed in Djibouti and visits the country intermittently to conduct information collection and exchange. It is explained that the subject appears to be centered on the Asal Project in connection with investment opportunities from the country, and that specific proposals on institutional matters seem not to be made by the expert.

-

9.2 Support to Asal Geothermal Project by WB and Other Donors

- The Assal Geothermal Project is being handled by the EDD. The ODDEG and CERD serve like a technical support. Much information therefore is not available.

- Information given by ODDEG that needs to be confirmed are as follows:

The project director has been selected as of July 2015.

Procurement of drilling contractor is ongoing. The project seems to be moving.

However, every procedure has to go through the seven donors one by one, which will take a longer process.

Information on the actual implementation of drilling is yet to be made available to the Survey Team

9.3 Support from ICEIDA

The support from the Icelandic International Development Agency (ICEIDA) is categorized in the

following four sections according to the information given by ODDEG:

- Improved project management capacity for geothermal projects and project management system is in place at ODDEG (from May 2015)

- Geothermal drill training (2016)

- Improved capacity for surface exploration - Lac Abhe (from October 2015)

- Technical assistance (finalization of Geothermal Risk Mitigation Facility (GRMF) application and other matters, as applicable)

ICEIDA supported ODDEG in the preparation of the application to GRMF for the surface survey in

Nord Goubet. Although the expression of interest (EoI) was accepted, the preparation of the full

application was suspended.

9.4 GRMF

The ODDEG submitted the full application to GRMF for the surface survey of Arta geothermal

prospect with the assistance of a Japanese consultant group. The result will be notified by GRMF by

January 2016. If the application is accepted, the surface survey will be conducted by the staff of

ODDEG with the technical advice of the Japanese consultant group.

10. Activities with the National Fund

The Government of Djibouti is now in the process of procuring a drilling rig from Turkey. The present

conditions are as follows:

- Contract negotiation for purchasing a drilling rig with 2,000 m capacity. The machine would be




made available in Djibouti in 2017.

- A second-hand drilling rig with 900 m capacity will be provided from Turkish company, and will be made available in Djibouti in the coming September 2015. The ODDEG intends to conduct training of their staff with this machine.

- Information is yet to be made available to the Survey Team on how these rigs are to be operated when the Asal Project or other projects are to be implemented.

11. Conclusions and Recommendations

11.1 Conclusions

【 Geothermal Resource Assessment】

(1) The Hanle Plain has a main fault in its northwest plateau.

(2) The heat source and geothermal reservoir exist underneath the northwest plateau.

(3) The resistivity structures obtained by the geophysical survey do not show a similar pattern to the

typical geothermal resistivity structure of a geothermal reservoir. This is the reason why it is

considered that the hydrothermal alteration is not yet well advanced in Hanle.

(4) However, the Survey Team considers the geothermal system, which represents that manifestations

in field should consist of the heat source, reservoir, and fluid.

・ Heat source should be a body that shows high resistivity and is considered to be an intrusion

body.

・ Reservoir should be fractured faults themselves or together with permeable layers in the

lower basalt, with capping structure made up of upper basalt. The reservoir could be 260 °C

according to the geochemical survey that the Survey Team conducted.

・ Geothermal fluid should be recharged from the Hanle Plain where groundwater level is

higher than in the plateau.

(5) A preliminary reservoir assessment with information on the target area based on the survey shows

the following results:

Capacity (MW)

80% Most Probable 20%

16.9 32.8 86.4

However, there will be issues that need to be clarified as described in Section 11.2 below, and this

preliminary estimation shall be reviewed through the clarification of these issues.

【Environmental and Social Impact Assessment (ESIA)】

An ESIA is required by the Government of Djibouti before implementation of test well drillings as

well as before construction of geothermal plant. The process from the application with TOR to the

approval of ESIA for drilling works will need at least six months. To facilitate the implementation of

the works, the Survey Team has prepared the proposed TOR based on the one for the geothermal

development project in Asal, which is now in the process of project implementation.




【Preliminary Economic Analysis Assuming IPP Project】

The ODDEG intends to invite an IPP to the Hanle geothermal prospect after the geothermal resources

are confirmed by test wells, in principle. The Survey Team conducted a preliminary economic

assessment of a 15 MW geothermal power plant operated by an IPP which resulted in a breakeven

tariff of US$12.96/kWh for the power plant as against the estimated levelized cost of electricity

(LCOE) of US$19.0/kWh of a diesel power plant as an alternative case.

Although the breakeven tariff is higher than the energy price imported from the Ethiopia Hydropower

System, the Survey Team considered that the estimated breakeven price of the 15 MW geothermal

power project would be attractive for EDD taking into account energy security. Thus, an IPP project in

Hanle would be a promising option.

11.2 Issues and Recommendations

【Reservoir Estimation and Decision for Test Well Drilling】

Issues:

The next step after the geophysical survey would be the test well drilling based on a standard project

sequence. However, the resistivity structure of the Hanle Reservoir has been revealed to be different

from the typical resistivity structure. On the other hand, the Survey Team considered the need to have

a geothermal reservoir because clear and strong geothermal manifestations are observed on site. The

Survey Team considers it prudent and necessary to conduct the additional 3-G survey which will

contribute to the clarity of the geothermal system. With these information, a decision of ‘Go’ or

‘No-go’ for test well drilling could be made.

Recommendations:

The following additional surveys have been proposed in this report:

Gravity survey for consideration of geological structure in connection with geothermal reservoir system,

Additional MT/TEM survey for identification of the possible extent of geothermal reservoir,

3D inversion analysis for MT/TEM data, and

Micro-seismicity monitoring for identification of geothermal fluid movement.

【Environmental and Social Impact Assessment ESIA】

Issues

An ESIA process for test well drilling will need at least six months, which may retard the process of a

speedy development.

Recommendations:

It is recommended to conduct such process together with the proposed additional 3-G survey in order




to implement the test well drilling immediately after the additional 3-G survey.

【Survey on Procurement for Drilling Works】

Issues

Djibouti has experiences in conducting test well in the 1980s. but since then, the activities were

suspended. There is actually few information regarding availability of drilling machines, drilling

contractors, and modes of contract together with cost information.

Recommendations:

It is therefore necessary to conduct a survey on procurement matters for the drilling works.

【Preliminary Economic Analysis for an IPP Project】

Issues

The ODDEG intends to invite an IPP for the Hanle geothermal prospect after the confirmation of

geothermal resources. This report conducted a preliminary economic analysis focusing on IPP project

through desk study with available information at hand. The results of this analysis should be refined

with the information on economic factors as well as the results or reassessment of geothermal resource

with additional information to be obtained from the additional 3-G survey.

Recommendations:

It is recommended to conduct a preliminary economic assessment assuming an IPP project that the

ODDEG intends to introduce.

*** end of report **


Japan International Cooperation Agency i Nippon Koei Co., Ltd.Sumiko Resources Exploration & Development Co., Ltd.


DATA COLLECTION SURVEY

FOR GEOTHERMAL DEVELOPMENT IN DJIBOUTI

(GEOPHYSICAL SURVEY)

FINAL REPORT

Table of Content

Location Map

Abbreviations

Summary

Chapter 1 Background of the Project ..................................................................................................... 1-1

1.1 Background ............................................................................................................................... 1-1

1.2 Purpose and Scope .................................................................................................................... 1-2

1.2.1 Purposes ............................................................................................................................ 1-2

1.2.2 Survey Areas ..................................................................................................................... 1-2

1.2.3 Scope ................................................................................................................................. 1-2

Chapter 2 Review of Existing Surveys .................................................................................................. 2-1

2.1 Collected Data ........................................................................................................................... 2-1

2.2 Surface Survey .......................................................................................................................... 2-1

2.2.1 Geological and Geochemical Survey ................................................................................ 2-1

2.3 Drilling Data of Existing Wells ................................................................................................ 2-4

2.3.1 Overview ........................................................................................................................... 2-4

2.3.2 Geological Structure ......................................................................................................... 2-6

2.3.3 Alteration Minerals ........................................................................................................... 2-6

2.3.4 Distribution of Permeability .............................................................................................. 2-7

2.3.5 Wellbore Temperature ...................................................................................................... 2-7

2.4 Summary of Existing Surveys ................................................................................................... 2-9

2.4.1 Conclusion of Existing Survey ......................................................................................... 2-9

2.4.2 Interpretation of the Survey Team .................................................................................... 2-9


Japan International Cooperation Agency ii Nippon Koei Co., Ltd.Sumiko Resources Exploration & Development Co., Ltd.


Chapter 3 Geophysical Survey .............................................................................................................. 3-1

3.1 Objectives ................................................................................................................................. 3-1

3.2 Survey Results .......................................................................................................................... 3-1

3.2.1 Outline of Survey .............................................................................................................. 3-1

3.2.2 Results of Survey .............................................................................................................. 3-2

3.2.3 Results of 2D Inversion ..................................................................................................... 3-2

3.2.4 Conclusions of 2D Inversion ............................................................................................. 3-5

Chapter 4 Supplementary Surveys......................................................................................................... 4-1

4.1 Overview of Geology and Topography ..................................................................................... 4-1

4.1.1 Geological Structure ......................................................................................................... 4-1

4.1.2 Fault Distribution .............................................................................................................. 4-1

4.2 Site Survey and Laboratory Analysis ........................................................................................ 4-4

4.2.1 Surface Manifestation ....................................................................................................... 4-4

4.2.2 Geochemical Survey ......................................................................................................... 4-6

Chapter 5 Geothermal Reservoir Model and Target for Geothermal Test Wells .................................. 5-1

5.1 Construction of Conceptual Model ........................................................................................... 5-1

5.1.1 Geothermal Reservoir and Resistivity Structure ............................................................... 5-1

5.1.2 Resistivity Structure of Hanle Site .................................................................................... 5-2

5.1.3 Preliminary Geothermal Reservoir Model ........................................................................ 5-3

5.1.4 Preliminary Evaluation of Geothermal Potential .............................................................. 5-8

5.2 Target for Geothermal Test Wells .......................................................................................... 5-10

Chapter 6 Preliminary Economic Analysis for IPP Participation .......................................................... 6-1

6.1 Assumptions .............................................................................................................................. 6-1

6.2 IPP Breakeven Power Sales Prices at the Power Station .......................................................... 6-1

6.3 Transmission Cost ..................................................................................................................... 6-2

6.4 Power Purchasing Cost at Ali Sabieh Substation. ..................................................................... 6-2

6.5 A comparison with the power generation cost at the existing power plants ............................. 6-3

6.6 Conclusions ............................................................................................................................... 6-3

Chapter 7 Procedure of Environmental and Social Considerations ....................................................... 7-1

7.1 Environmental and Social Impact Assessment Study ............................................................... 7-1

7.2 Review of Existing Surveys（ESIA for Asal Geothermal Project） ....................................... 7-2

7.3 Draft Terms of Reference ......................................................................................................... 7-2

Chapter 8 Proposal for Additional Surface Survey ............................................................................... 8-1

8.1 Issues to be Solved to Realize Test Well Exploration .............................................................. 8-1


Japan International Cooperation Agency iii Nippon Koei Co., Ltd.Sumiko Resources Exploration & Development Co., Ltd.


8.2 Proposal for Additional Survey ................................................................................................. 8-2

8.3 Preliminary Work Schedule up to Test Well Drilling ............................................................... 8-6

Chapter 9 Activities of Other Donors .................................................................................................... 9-1

9.1 United States Agency for International Aid (USAID) .............................................................. 9-1

9.2 Support to Asal Geothermal Project by the World Bank (WB) and Other Donors .................. 9-1

9.3 Support from ICEIDA ............................................................................................................... 9-1

9.4 Geothermal Risk Mitigation Facility (GRMF) ......................................................................... 9-2

Chapter 10 Activities with National Fund ............................................................................................. 10-1

10.1 Procurement of Drilling Machines .......................................................................................... 10-1

10.2 Construction of the New ODDEG Office at PK 12 ................................................................ 10-1

Chapter 11 Conclusions and Recommendations ................................................................................... 11-1

11.1 Conclusions ............................................................................................................................. 11-1

11.2 Issues and Recommendations ................................................................................................. 11-2

Figures and Tables

Table 1-1 Proposed Development Priority in JICA Survey (2014) ............................................... 1-1

Table 2-1 Existing Information ...................................................................................................... 2-1

Table 2-2 Data of Existing Wells ................................................................................................... 2-5

Table 2-3 List of Aquifer Depth .................................................................................................... 2-7

Table 4-1 List of Geothermal Manifestation .................................................................................. 4-4

Table 4-2 Results of the Chemical Analysis for Fumarolic Gas in Garabbayis ............................. 4-8

Table 5-1 Relation between Resistivity and Alteration Minerals and Temperature ...................... 5-1

Table 5-3 Summary of Observations and Interpretations .............................................................. 5-3

Table 5-4 Preliminary Reservoir Conceptual Models .................................................................... 5-4

Table 5-5 Parameters for the Volumetric Method ......................................................................... 5-9

Table 5-6 Preliminary Resource Assessment ................................................................................. 5-9

Table 6.1 Assumptions for Examination of IPP Breakeven Power Price ......................................... 6-1

Table 6.2 IPP Breakeven Power Sales Prices Sold-out at the Hanle Geothermal Power Station .. 6-2

Table 6.3 Assumptions for Transmission Cost Calculation ........................................................... 6-2

Table 6.4 Power Purchasing Cost at the Ali Sabieh Substation ..................................................... 6-3


Japan International Cooperation Agency iv Nippon Koei Co., Ltd.Sumiko Resources Exploration & Development Co., Ltd.


Figure 1-1 Geothermal Development Stages ................................................................................. 1-2

Figure 2-1 Fluid Circulation in the Hanle Plains based on Geochemical Analysis ....................... 2-2

Figure 2-2 Fluid Flow System of Fumaroles ................................................................................. 2-2

Figure 2-3 Location Map of Electrical Survey in Hanle Plains ..................................................... 2-3

Figure 2-4 Results of Electrical Survey and Interpretation ............................................................ 2-4

Figure 2-5 Location Map of the Existing Wells ............................................................................. 2-5

Figure 2-6 Distribution Chart of Altered Minerals ........................................................................ 2-7

Figure 2-7 Contour Map of Underground Temperature（- 500 m a.s.l） ..................................... 2-8

Figure 2-8 Temperature Profiles in the Existing Wells .................................................................. 2-8

Figure 3-1 Location Map of MT Survey Site ................................................................................. 3-6

Figure 3-2 Location Map of MT Stations ...................................................................................... 3-7

Figure 3-3 Resistivity Cross Section (HNL100) ............................................................................ 3-8

Figure 3-4 Resistivity Cross Section (HNL200) ............................................................................ 3-9

Figure 3-5 Resistivity Cross Section (HNL300) .......................................................................... 3-10



Figure 3-8 Resistivity Plan Map (-100 m elevation) .................................................................... 3-13

Figure 3-9 Resistivity Plan Map (-500 m elevation) .................................................................... 3-13

Figure 3-10 Resistivity Plan Map (-1,000 m elevation) ............................................................... 3-14



Figure 3-13 Resistivity Plan Map (-10,000 m elevation) ............................................................. 3-15

Figure 3-14 Panel Diagram of Resistivity Plan Maps .................................................................. 3-16

Figure 3-15 Panel Diagram of Resistivity Plan Maps .................................................................. 3-17

Figure 4-1 Geological Map of the Survey Area ............................................................................. 4-1

Figure 4-2 Inclination Distribution Map and Inclination Direction Map ....................................... 4-2

Figure 4-3 Fault Distribution Map ................................................................................................. 4-3

Figure 4-5 Location Map of Geothermal Manifestation ................................................................ 4-4

Figure 4-6 Distribution Map of Geothermal Manifestation ........................................................... 4-5

Figure 4-7 Geochemical Survey Area ............................................................................................ 4-6

Figure 4-8 Photographs of Geothermal Manifestations in Garabbayis .......................................... 4-7


Japan International Cooperation Agency v Nippon Koei Co., Ltd.Sumiko Resources Exploration & Development Co., Ltd.


Figure 4-9 He-Ar-N2 Ternary Diagram for Garabbayis Fumarolic Gases ..................................... 4-9

Figure 5-1 Geothermal Reservoir and Resistivity Structure .......................................................... 5-1

Figure 5-2 Resistivity and Alteration Mineral ............................................................................... 5-3

Figure 5-3 Geothermal Conceptual Model: Case (a) ..................................................................... 5-5

Figure 5-4 Geothermal Conceptual Model: Case (b) ..................................................................... 5-6

Figure 5-5 Geothermal Conceptual Model: Case (c) ..................................................................... 5-7

Figure 5-6 Map for Planning of a New Test Well Drilling in Garabbayis ................................... 5-10

Figure 5-7 Target Depth in the Geothermal Reservoir Model ..................................................... 5-11

Figure 7-1 ESIA Procedures .......................................................................................................... 7-1

Appendices

Appendix -1 List of Collected Documents

Appendix -2 Record Photographs

Appendix -3 Data of Existing Wells

Appendix -4 Geophysical Survey


Japan International Cooperation Agency 1-1 Nippon Koei Co., Ltd.Sumiko Resources Exploration & Development Co., Ltd.


Chapter 1 Background of the Project

1.1 Background

Geothermal development has been conducted since 1970 in the Republic of Djibouti.

However, geothermal energy has not been smoothly developed partially because high

salinity geothermal fluid was encountered. Under such circumstance, the President of

Djibouti requested the Prime Minister of Japan when he visited Djibouti in August 2013 for

possible technical assistance on geothermal energy development. In response to this request,

the Government of Japan expressed its intention to provide support. In accordance with this,

the Japan International Cooperation Agency (JICA) carried out the Data Collection Survey

on Geothermal Development (hereunder referred to as “JICA Survey (2014)”) in 2014 to

collect and analyze geological and geochemical information of all existing and conceived

geothermal manifestation sites. As a result, development priority was proposed as shown in

Table 1-1.

Table 1-1 Proposed Development Priority in JICA Survey (2014)

Site Name

Geothermal Resources Workability Socio-Environmen (Reference)

Priority

Survey for the Next Stage

Others

Re- sources

CL (mg/L)

Accessi- bility Landform

Well DrillingWater

NaturalConditions

Inha-bitant

Distance to

ransmissio

DjiboutianPriority

Hanle A A

±1,000 C

B Plain-

ragged hill

A GroundwaterIn Hanle Plain

A Barren

A None

45 km to Dikhil

2 1 MT Survey

Arta A D

>30,000 B

B Plain-

ragged hill

C Sea

A Barren

B A few

6 km to N.1

4 2 MT Survey

Applicationpending

for GRMF

Nord Goubet A

D >30,000

C-D C

Plain- ragged hill

C Sea

A Barren

B A few

50 km to P.K. 51

1 2 Review ofCERD’s

MT Survey

Applicationpending

for GRMF

Gaggade A B

<5,000 D

D Ragged hill

A GroundwaterIn Hanle Plain

A barren

A None

40 km to P.K 51

2 3 MT Survey

Obock B C

10,000～20,000

A A

Plain C

Sea B

Coastal

D NearTown

Isolated 3 4 Review ofCERD’s

MT Survey

Djibouti- Awrofoul C

A ±1,000

A A

Plain C

Sea - - - - 5 MT Survey

A:Excellent, B:Good, C:Fair, D:Poor Source: The Survey Team

There are seven stages in geothermal development in general. Among these seven, the JICA Survey

(2014) corresponds to the “Surface Survey Stage” (Figure 1.1). In order to proceed to the “Test

Drilling” stage, it is necessary to select/identify drilling targets by detailed surface surveys

(geophysical survey followed by construction of geothermal conceptual model). Under this

circumstance, the JICA Survey (2014) (geophysical survey) has thus been instigated by JICA.





Figure 1-1 Geothermal Development Stages

1.2 Purpose and Scope

1.2.1 Purposes

The purposes of the survey are as follows:

- To evaluate the geothermal resource of Hanle for consideration of possible future detailed surveys, i.e., test drilling; and

- To assess the requirement for environmental assessment for drilling and future plant construction.

1.2.2 Survey Areas

Hanle Garabbayis, Republic of Djibouti

The survey location is shown after the cover page.

1.2.3 Scope

The scope of work of the survey is as follows:

① To implement geophysical survey,

② To evaluate the geothermal resource through construction of a conceptual geothermal model

of Hanle’s geothermal prospect,

③ To assess the necessity of test well drilling, and

④ To select drilling targets.

Next SurveyGeological, Geochemical and Geophysical Surveys




Chapter 2 Review of Existing Surveys

2.1 Collected Data

The existing surveys that had been carried out in Hanle Region are shown in Table 2-1.

Table 2-1 Existing Information No Name Author Year Geo-

logy Geo-

chemistry Geo-

physicsDrilling

1 PROJET POUR L’EVALUATION DES RESSOURCES GEOTHERMIQUES

Aquater 1981

2 RESSOURCES GEOTHERMIQUES ETUDES EFFECTUEES PAR AQUATER 1980 - 1982

Aquater 1982

3 INTERPRETATION OF GRADIENT WELLS DATA – HANLE PLAIN

Geotermica 1985

4 GEOTHERMAL EXPLORATION PROJECT HANLE-GAGGADE REPUBLIC OF DJIBOUTI – HANLE 1 REPORT

Aquater 1987 a

5 GEOTHERMAL EXPLORATION PROJECT HANLE-GAGGADE REPUBLIC OF DJIBOUTI – HANLE 2 REPORT

Aquater 1987 b

6 CARTE GEOLOGIQUE DE LA REPUBLIQUE DE DJIBOUTI A 1:100000 - DIKHIL

ORSTOM 1987

7 DJIBOUTI GEOTHERMAL EXPLORATION PROJECT REPUBLIC OF DJIBOUTI – DRAFT FINAL REPORT

Aquater 1989

8 DATA COLLECTION SURVEY ON GEOTHERMAL DEVELOPMENT IN THE REPUBLIC OF DJIBOUTI

JICA 2014


2.2 Surface Survey

2.2.1 Geological and Geochemical Survey

Based on Aquater (1981), geological and geochemical survey was carried out in the Hanle Plains. About 22 rock samples were collected, observed, and analyzed. In the geochemical survey, hot spring water, spring water, and fumarolic gas were collected and analyzed.

As a result, it indicated the presence of three aquifers, namely: sedimentary rock (chlorinated alkaline water), alluvial aquifer (bicarbonate-alkaline earth water), and volcanic aquifer (bicarbonate-alkaline sulphate chlorinated water) (Figure 2-1). Also, the upflow of fluid containing CO2 from deep underground was suggested. The model shown in Figure 2-2 was proposed for the source of fumarole.




Source: Modified from Aquater (1981)

Figure 2-1 Fluid Circulation in the Hanle Plains based on Geochemical Analysis


Figure 2-2 Fluid Flow System of Fumaroles




In Hanle Region, electrical survey was carried out in the entire Hanle Plains by Aquater (1982). The

survey point arrangement is shown in Figure 2-3; the fumarole points that have been confirmed by the

JICA Survey (2014) are located at the southeast end of the survey area.

The analysis result of the resistivity cross section (NE-SW direction) is shown in Figure 2-4. Low

resistivity layer in the shallow part (a few Ωm) and high resistivity layer in the deep part (tens Ωm) are

confirmed, and it was concluded that each of these parts corresponds to sedimentary/alluvium layer and

volcanic rock layer, respectively. Discontinuity of resistivity structure was confirmed in the center of the

Hanle Plains, which suggests fault structure. The exploration well drilling was proposed to aim at these

faults.


Figure 2-3 Location Map of Electrical Survey in Hanle Plains

Survey Area

Cross-section of Figure 2-4





Figure 2-4 Results of Electrical Survey and Interpretation

2.3 Drilling Data of Existing Wells

2.3.1 Overview

In Hanle Region, five wells were drilled in the 1980s. These wells were drilled on the plain area

according to the results of surface survey described in the previous section (Figure 2-5). Table 2-2

shows the main data of existing wells.

Garabbayis-1, Garabbayis-2, and Teweo-1 are structural drilling wells about 450 m deep to assess the

underground temperature. The results of these exploration wells were presented in Aquater (1982) and

Geotermica (1985). Deep exploration wells Hanle-1 (drilling depth of 1,623.8 m) and Hanle-2 (drilling

depth of 2,038 m) were carried out to reflect the results of the structural drilling wells. These results

were reported in Aquater (1987 a, b; 1989).

Alluvium

Volcanic Rock

Geological Interpretation




Table 2-2 Data of Existing Wells Item Well Name

Garabbayis-1 Garabbayis-2 Teweo-1 Hanle-1 Hanle-2 Coordinate N11º24’26.0”

E42º10’44.3”

Elevation : 299m

N11º24’17.5”

E42º10’06.0”

Elevation : 245m

N11º26’36.2”

E42º05’11.9”

Elevation :142m

N11º26’33.0”

E42º07’26.0”

Elevation :210m

N11º24’07.1”

E42º09’54.7”

Elevation: 236.8m

Depth 437m 452.2 m 452 m 1623.8 m 2038 m Drilling Period 1982

(Period is unknown)

1984/11/9 –

1984/11/28

(20days)

1984/10/30 –

1984/11/08, 1984/11/29 –

1984/12/15

(27days)

1987/01/02 –

1987/03/02

(32days)

1987/03/11 –

1987/04/23

(44days)

Well Diameter (Bottom)

5-5/8” 5-7/8” 5-7/8” 8-1/2” 8-1/2”

Temperature at Bottom hole ()

121.7 80.8 43.7 72 122.7

Contractor Genie Rural* GENZL GENZL INTAIRDRIL INTAIRDRIL *Now called Direction de l’eau Source: Compiled by the Survey Team


Figure 2-5 Location Map of the Existing Wells

Garabbayis-1

Teweo-1 Hanle-1

Hanle-2

Garabbayis-2




The features of the existing wells are discussed below.

2.3.2 Geological Structure

The features that can be deduced from the geological data are as follows:

In the exploration well, basalt layer has thick distribution.

In Teweo-1 and Hanle-1, the rhyolite layer appeared between the basalt layers. Distribution depth is as follows: Teweo-1: 257-278 m, Hanle-1: 98-220 m, 230-310 m, 610-680 m.

Alluvium was confirmed in the surface portion of Teweo-1, Hanle-1, and Hanle-2.

Mudstone layer was confirmed on Teweo-1 at the depth of 65 m-257 m.

The geological column of each exploration well is attached.

2.3.3 Alteration Minerals

The alteration minerals occurrence depth in each exploration well is shown in Figure 2-6.

Documentation indicating the alteration mineral occurrence for Garabbayis-1 was not available.

As a feature of the whole alteration minerals, low-grade alteration is observed characterized by

occurrence of zeolites. The following issues are presumed by the combination of alteration mineral

occurrence;

The transition zone between heulandite (He) – laumontite (Lm) is located at GL-1400m in Hanle-1, GL-1000m at Hanle-2, presumed that the zone was approximately 140 degrees of alteration environment.

Smectite is disappeared and chlorite is commonly observed at the depth of 1400m in hanle-2, presumed that the alteration environment is 180 to 200 degrees.

Epidote (EP) and Hematite (Hm) is observed at the limited depth of 200m and 300m. The appearance temperature of those minerals are approximately 200 degrees, therefore those minerals are originated by vein-let hydrothermal alteration.

Pyrite is intermittently observed at the depth from GL-1000m to 1900m, indicates hydrothermal alteration caused by acidic fluid.

Occurrence of zeolite and chlorite is described, but the detail is not identified in Garabbayis-2 and Teweo-1, indicates that the data may not be reliable.

Combination of alteration minerals deeper than the depth of GL-1500m may indicate more than 200

degrees of alteration environment.




Source: Compiled from Geotermica (1985) and Aquater(1989)

Figure 2-6 Distribution Chart of Altered Minerals

2.3.4 Distribution of Permeability

On each exploration well, the depths of high permeability and presence of aquifer are shown in Table

2-3. The aquifer is observed at depths of 80-90 m, 130-200 m, and 250-350 m in the shallow part for

several wells. This indicates that the aquifer is continuous in the horizontal direction. In the deeper

part (deeper than 1,000 m), an aquifer was only identified at the depth of 1,300 m in Hanle-1, and was

supposed to low permeability (Aquater (1987 b)). But because deep well was drilled only two sites,

this fact is not enough to conclude the permeability of Hanle area is low.

In addition, the groundwater levels of Garabbayis-1, Garabbayis-2, and Teweo-1 observed in December

1984 were 113 m, 60 m, and 17 m, respectively. This indicates a decrease of groundwater level in the

direction from the plain side to the plateau side.

Table 2-3 List of Aquifer Depth Garabbayis-1 Garabbayis-2 Teweo-1 Hanle-1 Hanle-2

Shallower than 1000 m

83 m 95 m 150 m 180 m

90 m 130 m 364 m

95 m 130-200 m

310 m 680-800 m

140-170 m 260 m 405 m

Deeper than 1000 m

- - - About 1300 m -


2.3.5 Wellbore Temperature

Figure 2-7 shows the temperature contour in -500 m a.s.l, which is assumed from the confirmed

underground temperature distribution in each well. It was assumed to be consistent with the structure of

NNW-SSE. It is confirmed that there is a tendency of temperature increase from the Hanle Plain side to

the plateau side. The underground temperature distribution of each well is summarized in Figure 2-8.

Si Hm Ch Ze Si Hm Qz Ze Ep Cc Sm Si Ch Qz He Lm Cc Sm Si Py Ch Qz He Lm

Cc Ch Ep He Hm Lm Py Qz

Si Sm Ze

Pyrite Quartz

SiO2 Smectite Zeolite

Calcite Chlorite Epidote Heulandite Hematite Laumontite

DepthGarabbayis-2 Teweo-1 Hanle-1 Hanle-2

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000





Figure 2-7 Contour Map of Underground Temperature（- 500 m a.s.l）


Figure 2-8 Temperature Profiles in the Existing Wells




2.4 Summary of Existing Surveys

2.4.1 Conclusion of Existing Survey

Based on the survey results, Aquater (1989) described the following conclusions:

The Hanle Plains can be characterized as a low temperature system where the temperature is controlled by groundwater circulation.

The zone with an almost constant temperature from about 400 m to 1,000 m in Hanle-2 could be related to the local thermal anomaly originated by the upflow of hot fluids at the Garabbayis fumaroles.

The possibility of finding high enthalpy fluids for electric power generation within the Hanle Plains was very low.

In addition, Jalludin (2009) concluded the following:

Any shallow thermal anomalies related to intrusions or magma chamber do not exist in the Hanle Plain.

The fumaroles of Garabbayis would represent an exceptional situation, where the major fault system is connected to some very deep thermal anomalies.

From the results of existing studies, the presence of geothermal system in the Hanle Plain is

contradicted. However, the presence of fumaroles on the plateau side suggests the possibility of the

existence of geothermal system.

2.4.2 Interpretation of the Survey Team

Based on the existing survey results described above, the following are assumed for the geothermal

system of the Hanle Region.

1. As to the results of test well drilling, temperature of the deep part of Hanle Plain is low and the

wells located in the northeastern part of the plain have slightly higher temperature (Figure 2-7).

2. The results of temperature distribution of the test wells indicated that a heat source causes the

fumaroles at the surface, which is believed to suggest the presence of heat source in the plateau

side. This is consistent with the fact that fumaroles are observed on the plateau.

3. The reason of low temperature of wells that have been drilled in the Hanle Plain is inferred to be

due to the presence of groundwater flow in the Hanle Plain. In addition, hydraulic gradient

indicates the possibility that the source of groundwater is in the Hanle Plain side.

4. In the geochemical survey under the JICA Survey (2014), the possibility of a temperature of about

250 ºC on the reservoir has been pointed out.

From the above, the presence of geothermal system may exist under the plateau that extends to the

northeast of the Hanle Plains. Therefore, the Magneto-Telluric (MT) and Transit Electro-magnetic

(TEM) surveys were performed on the plateau, in order to reveal this assumption.


Japan International Cooperation Agency 3-1 Nippon koei Co., Ltd.Sumiko Resources Exploration & Engineering Co., Ltd.

JMC Geothemal Engineering Co., Ltd.

Chapter 3 Geophysical Survey

3.1 Objectives

In one of the target fields for geothermal development in the project, the Magneto-Telluric (MT) survey,

which is one of the electromagnetic survey methods, was conducted to study the subsurface resistivity

structure. The Transit Electro-magnetic (TEM) survey was carried out to have static correction of MT

data. The acquired data were processed and analyzed to clarify the underground resistivity structures of

the target field. The geology and geological structures were deduced from the subsurface resistivity

distribution and the geophysical information of deep zone to contribute to the creation and estimation of

geothermal reservoir model and the planning of test drilling survey was obtained.

3.2 Survey Results

3.2.1 Outline of Survey

The following are the contents of MT survey and TEM survey carried out in the project. The location

map and stations map of MT and TEM surveys are shown in Figures 3-1 and 3-2, respectively. The list

of the coordinate system of the stations is at the back of the report.

・Survey Method

MT method with far remote reference site

TEM method with central loop system（for static correction of MT data）

・Survey Site

The survey area was decided by referring to the existing geological information and well drilling exploration. In this survey, the deployment of MT/TEM stations was decided with a central focus on the horst where manifestations of fumaroles are observed in the northeast part of Hanle Plateau.

・Operation Date

March 28, 2015 ~ May 5, 2015

・Number of Stations

30 stations, Remote reference station in Dikhil

・Acquired Data

MT method: Three components of magnetic field (Hx, Hy, Hz) and two components of electric field (Ex, Ey) in time series data

(Measurement time: More than 14 hours per one station)

TEM method: One component of magnetic field (Hz) of transient response

・Number of Frequency for Data Processing and Analysis

MT method: 80 frequencies ranging from 320 Hz to 0.00034 Hz

TEM method: Two kinds of repeat rate: 2.5 Hz and 25 Hz




3.2.2 Results of Survey

(1） TEM Survey

TEM survey was conducted at all stations of the MT measurement. Regarding the acquired data quality,

although data scatters were observed in a few windows at later times in several stations, good quality

data applicable to 1D inversion analysis were acquired. 1D inversion analysis of resistivity layer was

executed using the observed data at each station. Layered resistivity structures, which show the

resistivity variation of high-low-high from surface to deep zone were obtained at almost all stations.

From these results, MT responses were calculated and the apparent resistivity and phase curves were

created; and the offset values for static correction were estimated. After applying the offset values to the

apparent resistivity curves observed through the MT method, 2D inversion analysis of resistivity

structure was executed. The list of offset values for static correction and the results of 1D inversion

analysis of resistivity layer are at the back of the report.

(2） MT Survey

After the acquired data were processed using the local reference method or the remote reference

technique, the apparent resistivity and phase curves were created, and the data quality of each measuring

station was evaluated. The data qualities of almost all stations from high frequencies to low frequencies

were good. Although at some stations, the apparent resistivity curve shows a little scatter in local

reference data processing, noises were reduced and data quality was improved after remote reference

data processing and data editing.

3.2.3 Results of 2D Inversion

The location map and stations map of MT and TEM surveys are shown in Figures 3-1 and 3-2,

respectively. The list of the coordinate system of the stations is at the back of the report.

As described above, the good data has been acquired from the high frequencies to low frequencies, and

the resistivity structure between -10,000 m elevation and the surface was estimated. But in the following,

the characteristics between -5,000 m and the surface were described. This range is important to

construct the geothermal reservoir model. And in order to explain the trend of resistivity distribution,

resistivity value of 100 ohm-m was used as a criterion.

(1） Resistivity Cross Section Map

The following are the characteristics of the resistivity structure from each cross section of the profile.

HNL100 profile (Figure 3-3)

The shallow zone is conductive, and the deep zone is resistive from the ground surface to the deep zone

of -5,000 m elevation. From 4 ohm-m to more than 2,500 ohm-m resistivity is distributed on the whole

cross section. The low resistivity of less than 100 ohm-m is distributed from the surface to about -1,500




m elevation in the southwest part and from the surface to about -800 m elevation in the northeast part.

This low resistivity layer of less than 100 ohm-m tends to become thin gradually from southwest to

northeast. At around -5,000 m elevation, the highest resistivity is shown in the northeast side and from

northeast to southwest, the resistivity value is decreasing. From -5,000 m elevation to the downward

direction, the resistivity value is becoming lower.


Same as the case of HNL100 profile, the shallow zone is conductive, and the deep zone is resistive. The

range of resistivity is from 2 ohm-m to more than 2,500 ohm-m. The low resistivity of less than 100

ohm-m is distributed from the surface to about -1,800 m elevation in the southwest part and from the

surface to about -900 m elevation in the northeast part. This low resistivity layer of less than 100 ohm-m

tends to become thin gradually from southwest to northeast. At around -5,000 m elevation, the highest

resistivity is observed in the northeast side and from northeast to southwest, the resistivity value is

decreasing same as in the HNL100 profile.


Same as HNL100 and HNL200 profiles, the shallow zone is conductive, and the deep zone is resistive.

The range of resistivity is from 1 ohm-m to more than 2,500 ohm-m. The lowest resistivity is around the

surface at HNL-306 station. The low resistivity of less than 100 ohm-m is distributed from the surface to

about -1,700 m elevation in the southwest part and from the surface to about -900 m elevation in the

northeast part. This low resistivity layer of less than 100 ohm-m tends to become thin gradually from

southwest to northeast. At around -5,000 m elevation, the highest resistivity is observed in the northeast

side and from northeast to southwest, the resistivity value is decreasing same as in the HNL100 and

HNL200 profiles.


Same as HNL100, HNL200, and HNL300 profiles, the shallow zone is conductive, and the deep zone is

resistive. The range of resistivity is from 2 ohm-m to more than 2,500 ohm-m. Around the surface at

HNL-403~HNL-404 and HNL406 stations, the lowest resistivity is observed. The low resistivity of less

than 100 ohm-m is distributed from the surface to about -1,500 m elevation in the southwest part and

from the surface to about -1,000 m elevation in the northeast part. Although this low resistivity layer of

less than 100 ohm-m tends to become thin gradually from southwest to northeast, the contour line of

100 ohm-m shows a little sign of increasing and decreasing. At around -4,500 m elevation, the highest

resistivity is observed in the northeast side and from northeast to southwest, the resistivity value is

decreasing similar with HNL100, HNL200, and HNL300 profiles.


The shallow zone is conductive, and the deep zone is resistive, same as with the HNL100, HNL200,




HNL300 and HNL400 profiles. The range of resistivity is from 3 ohm-m to more than 2,500 ohm-m.

The lowest resistivity is distributed around the surface at HNL-506 station. The low resistivity of less

than 100 ohm-m is distributed from the surface to about -1,400 m elevation in the southwest part and

from the surface to about -800 m elevation in the northeast part. This low resistivity layer of less than

100 ohm-m tends to become thin gradually from southwest to northeast. At around -4,500 m elevation,

the highest resistivity is seen in the northeast side and from northeast to southwest, the resistivity value

is decreasing similar with HNL100, HNL200, HNL300 and HNL400 profiles. The distribution of more

than 2,500 ohm-m resistivity is small in extent compared with the other profiles.

(2） Resistivity Plan Map

The following are the characteristics of the resistivity structure from the resistivity plan map at each

elevation.

100 m elevation (Figure 3-8)

Less than 16 ohm-m resistivity is distributed in the whole survey area. In a large sense, the resistivity

value is going down from west to east of the survey site. At the edge of the northeast part, the lowest

resistivity of 4 ohm-m is observed.

-500 m elevation (Figure 3-9)

The range of resistivity distribution is from 10 ohm-m to 100 ohm-m. From the west side to east side of

the survey site, the resistivity value gradually becomes higher and is highest at the northeast side of the

HNL100 profile. The contour lines extend in the northwest to southeast direction and the contour

interval is almost equal. It means resistivity varies gradually.

-1,000 m elevation (Figure 3-10)

The range of resistivity distribution is from 25 ohm-m to 600 ohm-m. The resistivity value is becoming

higher from the west part to the east part. The contour lines mainly extend in the northwest to southeast

direction same as in the plan map of -500 m elevation. From the center to northeast side of the HNL300

and HNL400 profiles, the contour interval is narrow and this indicates resistivity discontinuity structure.


The range of resistivity distribution is from 160 ohm-m to more than 2,500 ohm-m. The lowest

resistivity value is seen at the southwest side of HNL300 profile and from west to east, the resistivity

value increases. The contour lines mainly show the northwest to southeast direction same as the plan

map of -1,000 m elevation. From the center to the northeast side of HNL300 and HNL400 profiles, the

contour interval is narrow and it indicates resistivity discontinuity structure.





More than 400 ohm-m resistivity is distributed in the whole survey area. The lowest resistivity is shown around at the southwest edge of HNL200 and HNL300 profiles and from southwest to northeast, the resistivity value increases. In the northeast part of the survey site especially, more than 2,500 ohm-m resistivity is largely distributed.


The range of resistivity distribution is from 250 ohm-m to more than 2,500 ohm-m. In comparison with

the plan map of -4,000 m elevation, the value of the resistivity distribution is totally lower. Less than

400 ohm-m resistivity is distributed widely in the southwest part of the survey area and the resistivity

value increases to the northeast. The contour lines mainly show the northwest to southeast direction.

3.2.4 Conclusions of 2D Inversion

The following are the characteristics of the resistivity structure in Hanle Geothermal Field. And the

panel diagrams of resistivity cross section and plan map are shown in Figures 3-14 and 3-15,

respectively:

・The resistivity structure consists of three zones, namely: conductive overburden, resistive intermediate thick zone, and conductive deeper zone at a depth from the surface to -10,000 m elevation. The resistivity distribution is roughly ranging from 1 ohm-m to 2,500 ohm-m.

・The contour line, as the boundary of 100 ohm-m resistivity between conductive overburden and resistive intermediate zones, is located from -1,500 m to -2,000 m elevation at the southwest side of the survey site, and its location becomes shallow to the northeast direction and is roughly ranging from -500 m to -1,000 m elevation at the northeast side of the survey site.

・In a large sense, resistivity distribution may change from conductive to resistive from the southwest side to the northeast side. From -1,000 m to -2,000 m elevation, the interval of contour lines is relatively narrow. It suggests the resistivity discontinuity which shows drastic change of resistivity value.

・The conductive overburden is thin in the graben part of the survey site and thick in the horst part while the intermediate resistive zone shows a large value in the horst part and a small value in the graben part of the survey site. The location of resistivity discontinuity, which shows drastic change of resistivity, mainly coincides with the boundary between the graben and the horst.

・In all the profiles, the highest resistivity (>2,500 ohm-m) is observed from -4,000 m to -5,000 m elevation and this high resistivity is distributed widely with a central focus on HNL200 and HNL300 profiles.





Figure 3-1 Location Map of MT Survey Site

Legend

：MT survey site

：Reference station




Legend HNL-501

：Location of Station


Figure 3-2 Location Map of MT Stations




Figure 3-3 Resistivity Cross Section (HNL100)




Figure 3-8 Resistivity Plan Map (-100 m elevation)

Figure 3-9 Resistivity Plan Map (-500 m elevation)




Figure 3-10 Resistivity Plan Map (-1,000 m elevation)





Figure 3-14 Panel Diagram of Resistivity Cross Sections




Figure 3-15 Panel Diagram of Resistivity Plan Maps

100m Elev.

-500m Elev.

-1000m Elev.

-2000m Elev.

-4000m Elev.

-10000m Elev.




Chapter 4 Supplementary Surveys

4.1 Overview of Geology and Topography

4.1.1 Geological Structure

The geological map of the survey area (ORSTOM, 1987) is shown in Figure 4-1. Quaternary volcanic

rocks (Afar Stratoid) are widely distributed in the survey area. Major geological layers are the lower

basalt layer (2.0-2.7 Ma), upper basalt layer (1.8-2.2 Ma), and uppermost basalt layer (1.25 is a -1.65

Ma). Rhyolite layer (1.9-2.6 Ma), which is almost the same age as the lower basalt layer, is developed in

the north. Basalts form a plateau, covering a wide range including the MT/TEM survey area. In addition,

the uppermost basalt layer develops as volcanic corns in the NW-SE direction on the plateau.

From ORSTOM (1987), there are some fumaroles on the plateau of the study area. They appear at the

boundary portion of the lower and upper basalt layers. However, there are no fumaroles on the area

covered by the upper basalt layer.

Source: ORSTOM (1985)

Figure 4-1 Geological Map of the Survey Area

4.1.2 Fault Distribution

For obtaining the fault structure constituting the geothermal system in the study area, the Survey Team

analyzed the fault distribution using terrain data. The ASTER GDEM 30 m grid data has been used in

the analysis to create the inclination distribution and direction maps (Figure 4-2). The parts that are

Survey Area

LEGEND

Alluvium

Basalt (uppermost AfarStratoid: βSIII,1.25-1.65Ma)

Basalt (upper Afar Stratoid:βSII,1.8-2.2Ma)

Basalt (lower Afar Stratoid:βSI,2.0-2.7Ma) and lower

Rhyorlte

N




considered faults were extracted from the inclination distribution map, and the slope of each fault was

estimated using the inclination direction map.

The estimated fault distribution is shown in Figure 4-3. Fault strike is dominant in the NW-SE direction.

In particular, large-scale fault is recognized in the northeast and southwest end of the lava plateau,

which is inclined to the plain side. Lava plateau forms a horst structure. The main features are described

below.

The fault that developed in the rhyolite layer is not continuous to the upper basalt areas of the lava plateau.

On the geological map, the fault was drawn in the boundary part of upper and lower basalt layers (Figure 4-1). But in Figure 4-2, it is not observed. It is considered that the lower basalt is covered by the upper basalt.

Formation history of the terrain in this region is estimated: (i) the formation of the fault located on the southwest edge of rhyolite, (ii) effusion of the lower and upper basalt, and (iii) formation of large-scale fault that separates the northeast edge of the lava plateau.


Figure 4-2 Inclination Distribution Map and Inclination Direction Map

Inclination Distribution

Inclination Direction





Figure 4-3 Fault Distribution Map

Based on the geological structure and lineament estimation results, geological conceptual cross sectional

map including the study area were created (see Figure 4-4).


Figure 4-4 Conceptual Geological Cross Section

NESW

Hanle PlainGaggade PlainFumarole

(Not in Scale)

MT Survey Area

Legend

IV. Alluvium

III. Basalt (uppermost Afar Stratoid:βSIII,1.25-1.65Ma)

II. Basalt (upper Afar Stratoid:βSII,1.8-2.2Ma)

I. Basalt (lower Afar Stratoid:βSI,2.0-2.7Ma) and lower

IV

IV

I

II

I

II

III

IIII

III

Plateau




4.2 Site Survey and Laboratory Analysis

4.2.1 Surface Manifestation

In order to confirm the distribution of geothermal manifestations in the survey area, geological

reconnaissance was conducted in parallel with the geophysical surveys. As a result, the fumarole area

has been confirmed in the three sites around the geophysical survey area. Location map is shown in

Figure 4-5.

The maximum temperature and the extent of geothermal manifestations are summarized in Table 4-1.

The largest manifestation is point ③; the distribution of the surface high temperature area is about 500

m (Figure 4-6). It should be noted that the fumarole located at the southern end of point ③ has been

subject to gas analysis in the JICA Survey (2014).


Figure 4-5 Location Map of Geothermal Manifestation

Table 4-1 List of Geothermal Manifestation Site Number Max. Temp. Length Width Direction

① 96.2 About 140 m Max. 30 m NNW-SSE ② 96.4 About 80 m Max. 30 m NE-SW ③ 99.8 About 500 m Max. 130 m NW-SE






Figure 4-6 Distribution Map of Geothermal Manifestation

500m

Garabbayis-1

50.9

90.8 94.7

90.7

93.8

99.292.6

80m 140m

Site ① Site ②

Site ③




4.2.2 Geochemical Survey

(1) Objectives

Last year, a gas geochemical survey was conducted for a fumarole located in Garabbayis, Hanle under

the JICA Survey (2014). The survey conducted this year is an additional survey, to study more precisely

the area and chemical change of the geothermal steam supplied. For this purpose, two fumaroles

including the one surveyed last year were examined. Also, the distribution and temperature of spots of

hot and wet soil were investigated. The spots of the hot and wet soil mean that the small area lacks

steam but is wet by the hot water condensed from the fumarolic steam at the surface.

(2) Survey Area

The survey area is shown in Figure 4-7. The area contains an existing test well "Garabbayis-1 (435 m

depth) and geothermal manifestations (fumaroles and spots of hot and wet soil) located east of the well.

Figure 4-8 shows photographs of the geothermal manifestations, and Figure 4-7 depicts the distribution

of temperature of the manifestations. Among these fumaroles, the two strongest fumaroles were

sampled.

Fumarole (FR) No. 1: A fumarole that was examined last year. Fumarole (FR) No. 2: A fumarole about 130 m away from FR No. 1 in the NNW direction.

Figure 4-7 Geochemical Survey Area Source: The Survey Team





Figure 4-8 Photographs of Geothermal Manifestations in Garabbayis

(3) Results and Discussion

Table 4-2 shows the results of chemical analysis for fumarolic gas sampled in the last two years (FR No.

1 in 2014 and 2015, and FR No. 2 in 2015). The He-Ar-N2 trilinear diagram, which is based on the

analytical results, is shown in Figure 4-9. In this figure, other fumarolic gas samples taken in other

geothermal fields in Djibouti are plotted.

As seen in Figure 4-9, FR No. 2 and FR No. 1 (2014) show the same chemical composition even though

the two samples were taken from different fumaroles in different years. Because the composition shows

less contribution of atmospheric component, the fumaroles are obviously supplied with geothermal

steam originating from a geothermal reservoir. In addition, other fumaroles and spots of hot and wet soil

are distributed around the two fumaroles sampled. These geothermal manifestations are distributed in

the NW-SE direction with length of about 500 m and maximum width of 130 m (Figure 4.1). As a result,




it can be said that the geothermal steam found in the FR No. 2 and FR No. 1 (2014) are supplied in the

500 m long area of the manifestations.

Although FR No. 1 (2015) was sampled at the same position of FR No. 1 (2014), the sample showed

almost same composition as the atmospheric one in Figure 4-9. This indicates that the mixing ratio of

atmospheric component in the gas sampled in 2015 is larger than that in 2014. This might be because

the supply of geothermal steam could have been somewhat less during the survey in 2015.

Table 4-2 Results of the Chemical Analysis for Fumarolic Gas in Garabbayis





Gas geothermometers were applied to the gas composition of FR No. 2, and the results were

compared with that of FR No. 1 (2014). The geothermometers used are H2/Ar, CO2/Ar, and CH4/CO2.

Calculated temperatures are described as tHA, tCA, and tMC, respectively. These gas geothermometers are

influenced by changes in temperature and redox state while the steam ascends. The response to those

changes can be more rapid in the order of H2/Ar, CO2/Ar, and CH4/CO2 geothermometers. Consequently,

it is expected that the tMC geothermometer indicates a temperature of the deepest portion of the reservoir

(generally the highest temperature), and tHA geothermomter offers a temperature of the shallowest

temperature (generally the lowest temperature).

Figure 4-9 He-Ar-N2 Ternary Diagram for Garabbayis Fumarolic Gases

As can be seen in the calculated temperatures in Table 4.1, the temperatures are higher in the order of

tMC, tCA, and tHA, which indicates the expected characteristics of the thermometers mentioned above.

Calculated tHA, which is about 70 °C, is much lower than the temperature measured at fumaroles. For

this reason, tHA is excluded from the estimation of reservoir temperature. Calculated tCA shows a range

from 120 °C to 160 °C, and tMC ranges from 230 °C to 260 °C. From these results, it can be assumed

that there is a geothermal reservoir with the highest temperature of 260 °C at the depth of Garabbayis.

(4) Conclusion

In the east side of an existing test well, Garabbayis-1, fumaroles and spots of hot and wet soil are

distributed in the NW–SE direction with a length of 500 m. Geothermal steam producing the geothermal

manifestations can be steadily supplied from a geothermal reservoir which has the highest temperature

of 260 °C. Based on this interpretation, it follows that Garabbayis is an appropriate location for new test

drilling to prove the presence of a geothermal reservoir.





Chapter 5 Geothermal Reservoir Model and Target for Geothermal Test Wells

5.1 Construction of Conceptual Model

5.1.1 Geothermal Reservoir and Resistivity Structure

Examples of typical underground resistivity structure observed in geothermal area, refer to the findings

of Iceland (Arnason et al (1987): Figure 5-1).

As a feature of this resistivity structure, the following three points are stated: 1) the resistivity

structure is divided into three zones such as the upper high resistivity zone, lower resistivity zone,

and high resistivity zone, 2) discontinuous structure (vertical fault) appears in horizontal direction,

and 3) the range of resistivity shows from several ohm-m to several hundred ohm-m.

Figure 5-1 Geothermal Reservoir and Resistivity Structure

This resistivity structure is correlated with hydrothermal alteration zoning and corresponding

temperatures as shown in Table 5.1.

Table 5-1 Relation between Resistivity and Alteration Minerals and Temperature Resistivity Relation with Alteration Mineral (Zone) Estimated

TemperatureUpper zone

Several hundreds – several thousands Ωm

<Non alteration zone.> Volcanic ash, surface deposit, non-alteration volcanic rocks 50-100 oC

Low resistivity zone

Below 10 Ωm (or 5 Ωm)

<Clay zone (Cap rock)> Alteration zone including smectite, Mixed layer clay mineral, zeolite

100-250 oC

High resistivity zone

Several tens to several hundreds Ωm

<Chlorite – epidote zone (Reservoir)> Alteration zone including chlorite, illite, epidote (and garnet) 250-300 oC

Source：METI (2010) supplemented by The Survey Team

Árnason et al. (1987)




The resistivity structure of Hanle shows larger resistivity, which does not necessarily correspond to

the typical pattern. Table 5-1 may not be adopted in the case of the Hanle site. This may be because

that alteration in Hanle has not been developed well yet.

However, from the fact that there is a clear geothermal manifestations in Hanle site, the presence of

a geothermal reservoir of different resistivity structure is estimated.

The resistivity structure revealed by the survey in Hanle is interpreted as follows: the topmost

several tens Ωm may correspond to alteration zone (cap rock structure); the lowest zone of 1,000

Ωm or more may be an intrusion, which may be interpreted as a heat source; and the zone in

between the two may be the reservoir. For this reason, distribution area of reservoir was estimated

by shown in following chapter.

5.1.2 Resistivity Structure of Hanle Site

The correlation between resistivity and geothermal reservoir structure was examined in reference to

the past test wells drilled in Hanle in the 1980s. The drilling record of one previous well, Hanle-2

(2,038 m), indicates smectite and chlorite, which are good indications of cap rock and reservoir,

respectively. The depths and resistivity were correlated.

The lowest depth of cap rock is correlated with 40 Ωm, which corresponds to the lowest depth of

smectite emerging; whereas the depth of reservoir is correlated with 160 Ωm, which corresponds to

the bottom depth of the Hanle-1 well, at the bottom of which chlorite emerges.

Table 5-2 Geothermal Structure and Resistivity Zone Resistivity Geothermal Structure Elevation

Upper low resistivity zone 40 Ωm or less Cap rock -500 m or shallower

High resistivity zone From 40 to 160 Ωm Geothermal reservoir -500 m to -2000 m

Ultra high resistivity zone 1,000 Ωm or more Heat source -2000 m or deeper Source: The Survey Team





Figure 5-2 Resistivity and Alteration Mineral

5.1.3 Preliminary Geothermal Reservoir Model

The observations/information and interpretations necessary for the construction of preliminary

geothermal reservoir model are summarized in Table 5-3, based on the past survey results and the

geophysical survey conducted.

Table 5-3 Summary of Observations and Interpretations Observation Geothermal System Interpretation

Temperature at 500 m depth of the past 5 test wells increases from the plain side to the plateau side (40 ºC 90 ºC 120 ºC) Heat source

The heat source may exist under the plateau area.

Fumaroles are observed only in the plateau area.

The confirmed fumaroles seem to be on the extension line of the major faults.

Reservoir Fumaroles may emerge along the faults in rhyolite and/or lower basalt layer.

The confirmed fumaroles exist on the margin of the upper basalt.

Reservoir The upper basalt may act as the cap rock of the reservoir.

The fumarole includes mantle origin gas, and the geothermometer indicates 260 ºC

Fluid Fluid with high temperature may exist.

Groundwater level in the Hanle Plain is higher than that in the plateau area.

Fluid recharge There may be recharging from the plain side to the plateau side.

There is a distinct difference of resistivity structure between the plain side and the plateau side.

Regional geological structure

There may be major fault between the plain and the plateau.




Ultra high resistivity zone (1,000 Ωm or more) is identified below elevation -3,000 m in the plateau side.

Heat source This may be an intrusion body that retains high temperature.


Based on the above information and interpretation, the following three cases are proposed as the

preliminary geothermal reservoir model.

Table 5-4 Preliminary Reservoir Conceptual Models Case (a)

Figure 5-2 Case (b)

Figure 5-3 Case (c)

Figure 5-3 State of reservoir Not passed much time from

the heat source intrusion High temperature reservoir is present locally

Geothermal system is fully developed Geothermal fluid circulates, and reservoir is formed over a wide range

Heat supply from the heat source is attenuated, and reservoir temperature decreases

Res

ervo

ir

Area/zone Under the plateau Along faults Along major faults only where fumaroles are confirmed

Permeability (hosted rock)

High Low Low

Temperature 260 260 260

Flu

id Origin Originated from the Hanle

Plain Originated from the Hanle

Plains Originated from the Hanle

Plain

Upflow Along fractured faults Along fractured faults Along the major fault only Heat source An intrusive rock below 3 km






Figure 5-3 Geothermal Conceptual Model: Case (a)

Elevation: -1,000 m

SW NE





Figure 5-4 Geothermal Conceptual Model: Case (b)

Elevation: -1,000 m

SW NE





Figure 5-5 Geothermal Conceptual Model: Case (c)

Elevation: -1,000 m

SW NE




5.1.4 Preliminary Evaluation of Geothermal Potential

The reservoir resource assessment was conducted with volumetric method together with Monte

Carlo simulation, based on the conceptual case (a).

(1) Volumetric Method

The prevailing calculation methods include parameters that may not have been clearly defined and

therefore users are having difficulty in finding the appropriate specific digits for them. The

following equation was proposed by the paper (S. Takahashi and S. Yoshida, 2015) assuming a

single flash cycle, thereby parameters except the underground related parameters may be clearly

defined.

)()(ζ FLTTCVRE refrgex [kJ/s] or [kW] (1)

ffrr CCC )1( [kJ/s] or [kW] (2)

Where ηex: energy coefficient of turbo-generator, ζ：Effective energy allocation function, φ：

porosity of the reservoir rock, ρr：Density of the reservoir rock, Cr: Specific heat of the reservoir

rock, ρf：Density of geothermal fluid in the porosity of the reservoir rock, and Cf: Specific heat

of the geothermal fluid in the porosity of the rock.

Temperatures of the separator and the condenser are assumed as 151.8 ºC (5 bar) and 50 ºC,

respectively, taking into account the heated conditions of Djibouti. In addition, since the term

RgρCV(Tr-Tref) in the equation (1) represents the heat collected at the well head and cast into the

separator through heat insulated pipe system without losing heat energy, Tref=0.01 . The effective

energy allocation function is given below.

132538 1059.41019.41013.11014.1ζ rrr TTT (3)

The energy efficiency is given by an approximate equation obtained from the data of existing power

plants. When the separator temperature and condenser temperature are 151.8 ºC and 50 ºC,

respectively, the efficiency is:

ηex= 0.77 ± 0.05 (4)

Recovery factor is:

Rg= 0.05 ～0.20 (5)

(2) Probabilistic Method - Monte Carlo Simulation

Crystal Ball of Oracle Inc. was used for the Monte Carlo Simulation. The variable parameters are (1)

reservoir temperature and (2) porosity and reservoir volume with triangular distribution.




(3) Assumed Parameters

Parameters used for the calculation are shown in Table 5-5. The major parameters are as follows:

Reservoir Volume: The minimum reservoir volume was set as zero since there will be a possibility that the reservoir may not be identified.

Average Reservoir Temperature: The average reservoir temperatures are set from 200 ºC to 260 ºC with the median of 230 ºC, based on the geothermometer analysis results.

Table 5-5 Parameters for the Volumetric Method


(4) Preliminary Resource Assessment

The assessment results are shown in Table 5-6.

Table 5-6 Preliminary Resource Assessment Capacity (MW)


16.9 32.8 86.4


The estimated preliminary resource is classified into the Inferred Geothermal Resource that shall be examined by a test well drilling supported by supplemental subsurface survey.

Min. M.L Max.

Volume V m3 0 9.50E+09 1.50E+10 Triangle

Reservoir temperature Tr ºC 200 230 260 Triangle

Rock density ρr kg/m3 - 2600 - fixed

Rock volumetric specific heat Cr kJ/kg - 1 - fixed

Fluid volumetric density ρf kg/m3 - 950 - fixed

Fluid specific heat Cf kJ/kg - 5 - fixed

Porosity Φ % 5 - 10 Uniform

Recovery factor Rg % 5 20 Uniform

Reference temperature forflash type

Tref ºC - 0.01 - fixed

Rejection temperature(condenser temperature) *

T0 ºC - 50 - fixed

Separator temperature* - ºC - 151.8 - fixed

Exergy efficiency for flash ηex % 72 77 82 Triangle

Plant factor F % - 90 - fixed

Plant life L year - 30 - fixed

Parameter Symbol UnitRange Probabilistic

distribution

Min.: Minimum; Max.: Maximum, M.L.: Most likely; tbp: to be proposed; *: given in the heat allocationf i




5.2 Target for Geothermal Test Wells

A test well target is examined using a probable geothermal system model. Test well drilling is

expected to meet fractures with high temperature and permeability, and the fractures can be

associated with faults. For this reason, targets for a new test well in Garabbayis are examined using

the three geothermal models that include inferred faults as mentioned in Section 5.1.

Each of the models shows the distribution of geothermal reservoir along with the faults. Among

them, Fault #1 is recognized as a main reservoir in any of the models. Furthermore, the fault is

beside active surface manifestations, which means that Fault #1 is the highest priority as a target for

the new test drilling in Garabbayis, Hanle. Design of drilling targets comprises three factors, i.e.:

target position on the map, target depth, and wellhead location. For this design, the Garabbayis map

shown in Figure 5-6 was used. The map contains Fault #1, geothermal manifestations, and the well

pad for the existing Garabbayis-1 test well.

(1) Target Position on the Map

As seen in Figure 5-6, a part of Fault #1 overlapping the geothermal manifestations can be the target

zone. In that zone, the locations of the most active manifestations can be a candidate for the target

position on the map, as shown by a red circle in Figure 5-6.

Figure 5-6 Map for Planning of a New Test Well Drilling in Garabbayis





(2) Target Depth

Target depth should correspond to the depth of a high temperature in the models. The altitude of the

isotherm of 250 °C is set at around -1,200 mASL in the models; thus, the target depth should be at

least 1,500 m from the surface whose altitude is ca. 300 mASL. Considering more the uncertainty of

the isotherm in the models, the target depth should be set at the depth ranging from 1,500 m to 1,800

m (-1,500 mASL) as shown in Figure 5-7.

Figure 5-7 Target Depth in the Geothermal Reservoir Model

(3) Wellhead Location

The well pad of the Garabbayis-1 well can be used for a new test well. The well pad is made of

concrete, offering a rigid and flat base for the drilling rig.

(4) Preliminary Drilling Plan

On the basis of the location of targets, preliminary drilling plan was examined. The plan has to deal

with total drilling depth (TD), total vertical depth (TVD), and deviation of the well track. In the case

where the well pad for Garabbayis-1 is used also for the new test well, the deviation should be 300

m to reach the farthest target. This deviation and targeted TVD (1,800 m) require a TD of 2,000 m

with an inclination of the well less than 30 °. This plan is sufficiently acceptable with a normal 2,000

m class drilling rig.


Fault -1




Chapter 6 Preliminary Economic Analysis for IPP Participation

The government of Djibouti intends to introduce IPP for construction, operation and maintenance of

geothermal power station, once geothermal resources are confirmed. This chapter describes an

analysis of economic viability for a case where an IPP should participate in the project as the power

generation operator.

The preliminary reservoir assessment conducted with probabilistic approach resulted in 32 MWe,

86.4 MWe and 16.9 MWe for the most probable occurrence, 20 % probable occurrence and 80 %

probable occurrence respectively. Out of these, the assessment results of the probable occurrence of

80% shall be taken as the installed capacity when we examine an economic viability for the IPP

participation. We thus assume the capacity of the Hanle geothermal power station at 15 MWe.

The examination of economic viability was conducted through a comparison between the IPP

breakeven power sales price sold out at the Hanle power station and the power purchase price by

EDD at the substation of Ali Shabieh, with an assumption that the Hanle geothermal power station is

connected with the existing substation at Ali Shabieh via overhead power transmission line.

6.1 Assumptions

For the examination, assumptions are presented in Table 6-1 as follows.

A plant factor 80% is assumed that is recommended to use for planning purposes by the Ministry of Economy, Trade and Industry of Japan, while a 90 % is assumed in ESMAP (2010).

IPP shall bear the construction cost, except for the cost for test well drilling.

Two cases of 60% and 70% as the well successful rate, since success of failure of well will have a significant impact on project economics.

Costs for test wells are not included in the examination. Grant assistance from other sources is expected. Test wells are not to be converted to production wells even if successful.

Table 6-1 Assumptions for Examination of IPP Breakeven Power Price Items Assumptions Notes

Plant capacity 15 MW P = 80 % Plant factor 80 % Standard of Japan Cost bearing body IPP except for cost of test wells Well success rate 60 %, 70 % (for 2 cases) Cost of test wells Grant (8.4 M USD) 3 slim holes Use of test wells Not used for production wells

Source: JICA Survey Team

6.2 IPP Breakeven Power Sales Prices at the Power Station

The IPP breakeven power sales prices sold out at the Hanle geothermal power station are shown in




Table 6-2 below. Construction costs were determined with reference to past records around the

world, taking into account scale effects of capacity. The calculation sheets used are included in the

attachments.

As the results, the IPP breakeven power sales prices were calculated as 0.616 USD/kWh and 0.145

USD/kWh for each well successful rate of 60 % and 70 % respectively.

Table 6-2 IPP Breakeven Power Sales Prices Sold-out at the Hanle Geothermal Power Station Well Successful Rate 60 % 70 %

Construction cost 104.5 M-USD (7.0 M-USD/MW) 98.4 M-USD (6.6 M-USD/MW)Breakeven price at power station 0.161 USD/kWh 0.151 USD/kWh


6.3 Transmission Cost

The Hanle geothermal power station will be connected to the nearest substation of 63/20 kV at Ali

Sabieh approximately 70 km from the Hanle geothermal power station; the Ali Sabieh substation

being connected to the main substation at PK12 via 63kV transmission line. The following

assumptions in Table 6-3 are made in order to calculate the transmission cost from the Hanle

geothermal power station (15 MWe) to the substation at Ali Sabieh.

Table 6-3 Assumptions for Transmission Cost Calculation Items Assumptions

From and to From Hanle to Ali Sabieh Distance 70 km Capacity 63 kV Construction cost 17.5 M-USD (0.25 M-USD/km) Cost bearing body EDD


The transmission line will be of 63 kV, and approximately 70 km long; construction cost is

estimated at 0.25 m-USD/km; EDD will be the responsible body for the construction and, operation

& maintenance. Calculation sheets used are included in the attachment. As the result, the

transmission cost was calculated at 0.021 USD/kWh/

6.4 Power Purchasing Cost at Ali Sabieh Substation.

From the calculation results explained above, the power purchasing cost at Ali Sabieh substation by

EDD are shown in Table 6-4.

If the power plant is constructed with a successful rate 60% of production wells, the power purchase

cost at Ali Sabieh substation by EDD will be 0.182 USD/kWH; whereas the cost will be 0.172

USD/kWh if the successful rate should be 70 %.




Table 6-4 Power Purchasing Cost at the Ali Sabieh Substation Well successful rate 60 % 70 % Note

IPP breakeven cost (USD/kWh) 0.161 0.151 IPP minimum sailing price of electricity at power stationTransmission cost (USD/kWh) 0.021 0.021 63 kV, 70 km EDD bearing cost (USD/kWh) 0.182 0.172 Minimum cost of electricity at Ali Sabieh substation

from Hanle geothermal Source: JICA Survey Team

6.5 A comparison with the power generation cost at the existing power plants

Euei odf (2013)1 reports that the fuel cost accounting to a significant part of the power generation

cost was 180.4 USD/ MWh (0.180 USD/kWh) in 2013. A comparison of the Hanle geothermal

power plant (15 MWe) with the existing power plants thus results in:

When the well successful rate is 60%, both case will have similar economic implication,

When the well successful rate is 70%, the Hanle geothermal power station will economically superior to the existing power plants.

If the transmission should be constructed with a financial arrangement that should exempt EDD

from bearing or repaying, the Hanle geothermal power station will superior to the existing thermal

plants in both cases of the well successful rate 60% and 70 % will.

6.6 Conclusions

With information available at this stage, the reservoir resource of the Hanle geothermal prospect was

evaluated at 15 MWe as the probable occurrence 80% that should be considered when IPP project is

to be planned. This capacity is as a similar size as of a small hydropower plant. However, the Hanle

geothermal power station will be economically superior to the existing oil thermal power plants if

the transmission line should be constructed without financial burden to EDD.

Presently, a significant part of the electricity is being purchased from Ethiopia. Although Ethiopia

still has a large capacity of hydropower energy, the power purchase agreement between the two

countries have entered into only for a period of Ethiopia wet seasons. On the other hand, power

plants within Djiboutian territory are all of oil thermal power plant. Therefore, Djibouti does not

actually have any power plants of indigenous energy source.

Under this circumstance, constructing the Hanle geothermal power station, though the capacity is 15

MWe together with transmission line will be justifiable not only from economical point of view but

also energy security point of view too.

1 Page 45, “Elaboration d’une strategie nationale et d’un plan d’action pour le developpement du secteur electrique a Djibouti”; Rapport Scenarios (Version Finale)




Chapter 7 Procedure of Environmental and Social Considerations

7.1 Environmental and Social Impact Assessment Study

Decree 2011-029/PR/MHUEAT (2011) shall be referred to for the Environmental Social Impact

Assessment (ESIA), which describes the procedures to be followed. The decree classifies the

assessment into two categories: (1) basic and (2) detailed. The detailed assessment is required for

test well drilling and plan construction. Figure 7-1 shows the flow of procedural instruction.

Source: JICA Survey (2014)

Figure 7-1 ESIA Procedures

Project Proponent

National Government

Expert Team

Technical Committee

Citizens

Draft Terms of Reference

Order to check the Terms of Reference

Site survey

Opinion

Final Terms of Reference

Survey, Forecast, Evaluation

Draft EIS Report

EIS Report

Public hearing Opinion

Order to check theEIS report

Publicity

Opinion

Grant for Environment

Clearance

Opinion

Final EIS

Desk study andDetail study

Evaluation

Monitoring and taking measures to

protect the environment

Periodical report

Environment Audit Report

END

Inspection

Opinion

Implementation of EIA




Assessment of the terms of reference (TOR) by the competent office needs about one month at least,

Survey and report preparation may take two months,

Assessment and approval of the report needs about three months, and

A total of about six months are required to start the test well drillings.

7.2 Review of Existing Surveys（ESIA for Asal Geothermal Project）

The Government of Djibouti is now in the process of conducting test well drilling in the Asal

Geothermal Project with financial arrangement from the World Bank and others. ESIA was

conducted by Fichiner in 2012 and the report is on the website of the Word Bank.

The ESIA report conducted a field survey for the social conditions, and referred to the past well

drilling record for the natural environmental assessment together with interview survey.

7.3 Draft Terms of Reference

Since an ESIA is required before test well drilling in Hanle, a TOR has been drafted based on the

results of the ESIA report for Asal in order to realize smooth implementation of the test well drilling.




Chapter 8 Proposal for Additional Surface Survey In the previous sections of this report, three types of geothermal reservoir models were proposed

based on the MT/TEM survey conducted together with the information from past investigations. The

resistivity structure obtained in Hanle has been revealed to be different from that of a typical

geothermal reservoir. Although the next step for geothermal development is test well drilling, the

Survey Team considers it prudent and necessary to verify the appropriateness of the proposed three

geothermal reservoir models through additional surface survey. By this additional survey, the well

target could also be refined. In addition to the scientific survey, data collection and analysis will also

be necessary to prepare for the drilling works.

This chapter describes the issues to be solved as well as proposes survey to solve these issues in

order to realize test well exploration.

8.1 Issues to be Solved to Realize Test Well Exploration

The following are the issues to be solved before implementation of test well exploration:

・To verify the appropriateness of the interpretation of geological structure (geological characteristics

of the Hanle Plain and the plateau).

A number of faults have been objectively confirmed by the lineament analysis using DEM

data. The MT/TEM survey identified one major fault between the Hanle Plain and the plateau.

Distribution of fracture together with regional geological structure has to be clarified.

・To improve knowledge on the characteristics of reservoirs

The resistivity structure of Hanle is different from that of a typical geothermal reservoir. Even

though, the Survey Team proposed three reservoir models based on the fact that there are

geothermal manifestations. The appropriateness of these models, however, has to be verified

with additional surface survey before test well exploration because the information at hand is

considered not to be enough to confidently propose the reservoir model which could allow

more reliable resource estimation. The drilling target may also be refined with the additional

information.

・To understand the extent of the sheeted high resistivity zone below, and the very low resistivity

zone in the surface zone of the northeast side of the plateau

The high resistivity zone below is considered to be the heat source that would originate from

intrusive rock; and the low resistivity zone in the surface zone of the northeast side of the

plateau may form the cap structure of the reservoir. These resistivity structures extend

beyond the present MT/TEM survey area. Since these are considered to be very important to




examine the geothermal system, the survey area has to be widened. This is also important to

review the size of the reservoirs.

8.2 Proposal for Additional Survey

The following three surface surveys are proposed: (1) gravity survey, (2) additional MT/TEM survey,

and (3) micro-seismicity monitoring. In addition, the following surveys are proposed which are

necessary for smooth implementation of test well exploration in the shortest time period: (4) ESIA

for test well drilling and (5) preparatory survey for test well drilling works. The explanation for each

survey is as follows:

(1) Gravity Survey

The gravity survey is proposed to identify regional geological structure, detailed geological anomaly

in and around the reservoirs, and distribution of the deep sheeted high resistivity geology.

A set of 300 measuring points are proposed with an interval of 1,000 m for regional investigation

and 500 m in and around the geothermal reservoir. The layout of the measuring points is shown in

Figure 8-1.


Figure 8-1 Layout of Gravity Survey Measuring Stations




(2) Additional MT/TEM survey

The additional MT/TEM survey is proposed to grasp the distribution of the deep sheeted high

resistivity zone and the low resistivity zone of the surface area in the northeast of the plateau.

About 36 measuring points are proposed in the area neighboring the northern boundary of the

previous MT/TEM survey points with an interval of approximately 1 km as shown in Figure 8-2.

The additional survey will cover the fumarole points shown in the geological map in the north of the

previous survey area. The survey will provide an underground information on a wider area of the

plateau.

3D inversion method is proposed to analyze the obtained data.


Figure 8-2 Layout of the Additional MT/TEM Survey Points

(3) Micro Seismicity Monitoring

Micro seismicity monitoring is proposed to investigate the structure, extension, and fluid activity

area of the geothermal reservoirs. This would provide information on the size of reservoirs.




A set of five monitoring points is proposed that encompasses the expected reservoir area in the

middle as shown in Figure 8-3. Access conditions to the monitoring points are also considered. A

minimum of three months are allocated for the monitoring.

Based on Lépine and Hirn (1992), microseismicity monitoring has been conducted twice on Hanle site.

The first monitoring has been carried out using the 7 seismometers in the period of March 1985 to June

1986 (Figure 8-4). At that time, swarm considered to be due to geothermal activity was observed below

the fumarole area (Figure 4-5, ①) in depth of 3km. The second monitoring was performed using 30

seismometers in late 1986 (about three months). At this time, 10 events has been observed in depth of

8km or deeper.


Figure 8-3 Layout of Monitoring Station of Micro Seismicity




Source: Lépine and Hirn (1992)

Figure 8-4 Location of Micro Seismicity

(4) ESIA ESIA for test well drilling is proposed in accordance with the proposed TOR. It will take at least six

months from the submission of TOR to the competent governmental authority for final approval.

This is important if the test well drilling should be implemented at earliest convenience.


Figure 8-5 ESIA Process for Test Well Drilling

MT/TEM Survey Area

Swarms




(5) Preparatory Survey for Test Well Drilling Works (Contractual and Procurement Matters)

Djibouti has experiences in conducting test well in the 1980s; but since then, the activities were


contractors, and modes of contract together with cost information. For smooth implementation of

the test well drilling works, the following survey is proposed:

Information collection and analysis on payment terms for drilling works

Proposal for the most optimal contract conditions

Availability of drilling contractors

Work planning

Preliminary drilling works plan (drilling program, material procurement, etc.)

Preliminary civil works plan (Access road, water supply, electricity, etc.)

Preliminary cost estimation for test well drilling works

8.3 Preliminary Work Schedule up to Test Well Drilling

A preliminary work schedule up to test well drilling is proposed in Figure 8-6 below.


Figure 8-6 Preliminary Work Schedule up to Test Well Drilling

SpecificationPreparationMeasurment 300 pointsAnalysis Reporting

PreparationSetting up 5 monotoring postsMeasurment 3 monthsAnalysis Reporting

3　Additional MT/TEM surveyPreparationMeasurment 36 pointsAnalysis Reporting

ScopingTOR apprisalFeid surveyApprisal

6 Preparation survey for test well drilling planingMarket surveyContractual aspectPreliminary PlaningPreliminary cost estimation

4　Integrated analysis5　ESIA

6th 7th1　Gravity Survey

2　Micro scismisity monit

Moths 1st 2nd 3rd 4th 5th




Chapter 9 Activities of Other Donors

Information on other donors’ activities are described below based on the interview survey with

ODDEG, because the donors concerned are not stationed in Djibouti.

9.1 United States Agency for International Aid (USAID) - A workshop was conducted on independent power producers (IPP) and public private

partnership (PPP) for the energy sector in October 2014.

- An expert was appointed in 2014 to promote IPP or PPP projects in the energy sector. It is understood that an aim of this support is to build a consensus for implementation of Power Africa under the Obama Initiative. The expert had left the country in February 2015.

- An alternative expert has been selected. The expert is not stationed in Djibouti and visits the country intermittently to conduct information collection and exchange. It is explained that the subject appears to be centered on the Asal Project in connection with investment opportunities from the country, and that specific proposals on institutional matters seem not to be made by the expert.

9.2 Support to Asal Geothermal Project by the World Bank (WB) and Other Donors

- The Assal Geothermal Project is being handled by the EDD. The ODDEG and CERD serve like a technical support. Much information therefore is not available.

- Dr. Jalludin, the former director of the Centre for the Study and Research of Djibouti (Centre de Recherche et des Etudes de Djibouti: CERD), and Dr. Kayad of ODDEG are now in charge. The Survey Team did not have the opportunity to conduct an interview with them.

- Information given by ODDEG that needs to be confirmed are as follows:

The project director has been selected as of July 2015.

Procurement of drilling contractor is ongoing. The project seems to be moving.

However, every procedure has to go through the seven donors one by one, which will take a longer process.

Information on the actual implementation of drilling is yet to be made available to the Survey Team

9.3 Support from ICEIDA

The support from the Icelandic International Development Agency (ICEIDA) is categorized in the

following four sections according to the information given by ODDEG:

- Improved project management capacity for geothermal projects and project management system is in place at ODDEG (from May 2015)

- Geothermal drill training (2016)

- Improved capacity for surface exploration - Lac Abhe (from October 2015)

- Technical assistance (finalization of Geothermal Risk Mitigation Facility (GRMF) application and other matters, as applicable)




ICEIDA supported ODDEG in the preparation of the application to GRMF for the surface survey in

Nord Goubet. Although the expression of interest (EoI) was accepted, the preparation of the full

application was suspended.

9.4 Geothermal Risk Mitigation Facility (GRMF)

The ODDEG submitted the full application to GRMF for the surface survey of Arta geothermal

prospect with the assistance of a Japanese consultant group. The result will be notified by GRMF

by January 2016. If the application is accepted, the surface survey will be conducted by the staff of

ODDEG with the technical advice of the Japanese consultant group.




Chapter 10 Activities with National Fund

10.1 Procurement of Drilling Machines

The Government of Djibouti is now in the process of procuring a drilling rig from Turkey. The

present conditions are as follows:

- Contract negotiation for purchasing a drilling rig with 2,000 m capacity. The machine would be made available in Djibouti in 2017.

- A second-hand drilling rig with 900 m capacity will be provided from Turkish company, and will be made available in Djibouti in the coming September 2015. The ODDEG intends to conduct training of their staff with this machine.

- Information is yet to be made available to the Survey Team on how these rigs are to be operated when the Asal Project or other projects are to be implemented.

10.2 Construction of the New ODDEG Office at PK 12

It was informed that the construction has almost been completed. The staff are about to move to the

new office.




Chapter 11 Conclusions and Recommendations

Based on the geophysical MT/TEM surveys together with the review of the past surveys conducted

in the 1980s, and the supplemental geological and geochemical surveys in the Hanle geothermal

site, which the JICA Survey (March 2015) recommended as the first priority for development, the

conclusions and recommendations of this report are as follows:

11.1 Conclusions

【Geothermal Resource Assessment】

1) The Hanle Plain has a main fault in its northwest plateau.

2) The heat source and geothermal reservoir exist underneath the northwest plateau.

3) The resistivity structures obtained by the geophysical survey do not show a similar pattern to the

typical geothermal resistivity structure of a geothermal reservoir. This is the reason why it is

considered that the hydrothermal alteration is not yet well advanced in Hanle.

4) However, the Survey Team considers the geothermal system, which represents that manifestations

in field should consist of the heat source, reservoir, and fluid.

(a) Heat source should be a body that shows high resistivity and is considered to be an

intrusion body.

(b) Reservoir should be fractured faults themselves or together with permeable layers in the

lower basalt, with capping structure made up of upper basalt. The reservoir could be

260 °C according to the geochemical survey that the Survey Team conducted.

(c) Geothermal fluid should be recharged from the Hanle Plain where groundwater level is

higher than in the plateau.

5) A preliminary reservoir assessment with information on the target area based on the survey shows

the following results:

Capacity (MW)


16.9 32.8 86.4

However, there will be issues that need to be clarified as described in Section 11.2 below, and

this preliminary estimation shall be reviewed through the clarification of these issues.

【IPP Breakeven Power Sales Prices and Economic Comparison with the Existing Power plants】

The government of Djibouti intends to introduce an IPP for construction and operation of the

Hanle Geothermal Power Station, once the geothermal resources should be confirmed by test




well drilling that the ODDEG expects financial assistance from donors.

The Survey Team conducted a preliminary economic analysis, assuming that the installed

capacity should be 15MWe, EDD should purchase the electricity at Ali Sabieh substation by

constructing the transmission line from Hanle to Ali Sabieh. The analysis has resulted that the

Hanle geothermal power plant is superior to the existing diesel power plants if the successful

rate of the production wells should be 60% or more.

If the EDD should be exempted from the construction cost of the transmission line from the

Hanle geothermal power station to Ali Sabieh substation, the Hanle geothermal power station

will be much more superior to the existing power plants.

Although the prices of the electricity imported from Ethiopia is much more lower, Djibouti

does not have any indigenous energy sources for electricity; which should be a serious issues

from energy security point of view. It is therefore concluded that the Hanle geothermal

development should be justifiable.

【Environmental and Social Impact Assessment (ESIA)】

An ESIA is required by the Government of Djibouti before implementation of test well drillings

as well as before construction of geothermal plant. The process from the application with TOR

to the approval of ESIA for drilling works will need at least six months. To facilitate the

implementation of the works, the Survey Team has prepared the proposed TOR based on the

one for the geothermal development project in Asal, which is now in the process of project

implementation.

11.2 Issues and Recommendations

【Reservoir Estimation and Decision for Test Well Drilling】

Issues:

The next step after the geophysical survey would be the test well drilling based on a standard

project sequence. However, the resistivity structure of the Hanle Reservoir has been revealed to be

different from the typical resistivity structure. On the other hand, the Survey Team considered the

need to have a geothermal reservoir because clear and strong geothermal manifestations are

observed on site. Although the Survey Team proposed three cases of geothermal reservoir, they do

not have reliable bases for these interpretations and these should be supported with additional 3-G

information. Because the investment costs of test well drilling are considerably large, the Survey

Team considers it prudent and necessary to conduct the additional 3-G survey which will contribute

to the clarity of the geothermal system. With these information, a decision of ‘Go’ or ‘No-go’ for

test well drilling could be made.




Recommendations:

The following additional surveys have been proposed in this report:

Gravity survey for consideration of geological structure in connection with geothermal reservoir system,

Additional MT/TEM survey for identification of the possible extent of geothermal reservoir,

3D inversion analysis for MT/TEM data, and

Micro-seismicity monitoring for identification of geothermal fluid movement.

【Environmental and Social Impact Assessment ESIA】

Issues

An ESIA process for test well drilling will need at least six months, which may retard the process of

a speedy development.

Recommendations:

It is recommended to conduct such process together with the proposed additional 3-G survey in

order to implement the test well drilling immediately after the additional 3-G survey.

【Survey on Procurement for Drilling Works】

Issues

Djibouti has experiences in conducting test well in the 1980s. but since then, the activities were


contractors, and modes of contract together with cost information.

Recommendations:

It is therefore necessary to conduct a survey on procurement matters for the drilling works.

【Preliminary Economic Analysis for an IPP Project】

Issues

The ODDEG intends to invite an IPP for the Hanle geothermal prospect after the confirmation of

geothermal resources. This report conducted a preliminary economic analysis focusing on IPP

project through desk study with available information at hand. The results of this analysis should be

refined with the information on economic factors as well as the results or reassessment of

geothermal resource with additional information to be obtained from the additional 3-G survey.

Recommendations:




It is recommended to conduct a preliminary economic assessment assuming an IPP project that the

ODDEG intends to introduce.

*** end of report **

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