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TRAINING ON SURFACE EXPLORATION STUDIES FOR GEOTHERMAL RESOURCES AND

DEVELOPMENT OF CONCEPTUAL MODELS

UNDER THE AUSPICES OF INTERIM PROJECT COORDINATION UNIT OF THE AFRICA

GEOTHERMAL CENTER OF EXCELLENCE

HEAT FLOW MEASUREMENTS IN GEOTHERMAL MAPPING

Antony Wamalwa, Geothermal Development Company-KenyaEmail:- awamalwa@gdc.co.ke

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OUTLINE

INTRODUCTION

HEAT TRANSFER

HEAT FLOW SURVEY

METHODOLOGY

EQUIPMENT

CHALLENGES

CASE STUDIES

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GEOTHERMAL SYSTEM

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Geothermal energy is

heat from the earth; Geo - Earth

Thermal – Heat

•The Earth is composed of a number of

different layers:-

The core (7000km)

The mantle (2900km)

The crust (Oceanic crust

(5-100km), Continental

Crust (20-100km)

INTRODUCTION

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Earth’s interior temperature remain relatively constant over time

except near the surface

Temperature difference between cool crust and hot molten magma

establishes temperature gradient

Normal temp gradients range between 15 – 30 °C per km

Geothermal active regions exhibit higher temperature gradient

Areas with elevated temperature gradient - targets for geothermal

utilization

EARTHS TEMPERATURE

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RIFTING PROCESSES

Geophysical tomographic studies have

shown that the asthenosphere rises

beneath the rift hence the temperature

anomaly

The convective process in the

asthenosphere promotes the rifting

process

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•Tectonic plate movement results in faulting

•Hot rocks are brought close to the surface

•Water seeps through deep faults

• It’s heated by the hot rocks

•Faults serve as plumbing systems for fluid

and magma

•Results to geothermal manifestations

WHY HEAT FLOW MEASUREMENTS

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• To estimate amount of heat energy being lost naturally

• To analyze the distribution of heat loss features - hidden

fracture zones

• To help prioritize geothermal prospects for development

• It serves as an input for conceptual and volumetric models

• To estimate the extent of leakage of the reservoir

WHY HEAT FLOW MEASUREMENTS

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HEAT LOSS MEASUREMENTS & Other studies

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HEAT LOSS MEASUREMENTS & Other studies

Assist in quantifying amount of heat being lost on the surface

Complements other disciplines in determining the reservoir temperature

Assists or complements other discipline in identification of active

structures

Suggest possible orientation of fractures in the prospect area

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Heat is transferred from the geothermal system to the atmosphere

•Mechanisms include:

Conduction

Convection

Radiation

•Heat loss in geothermal systems is mainly through

Conduction

Convection

HEAT LOSS PROCESSES

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Free electron diffusion or proton vibration

No flow of medium or material

Occur mainly in solids

Transfer of energy is from high to low temperature

Hot grounds experience conductive heat loss

Boreholes serve as temperature gradient holes

Results can be used to estimate temperatures at depth

CONDUCTIVE HEAT FLOW

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Q = Ak dT/ dy

(One dimension heat equation

Where;

•Q = Conductive heat flow (watts),

•A = Surface area of hot ground (m2),

• k = Thermal conductivity of rock (w/m°C),

•T = Temperature (0C),

•y = Depth (m)

CONDUCTIVE HEAT FLOW

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Natural convection triggered by density variations due to heating

Involve the transfer of heat energy by fluids

Convective heat flow is often faster than conduction

Fluid moves from high pressure to low pressure due to pressure diff

Fluid transports the heat from one point to another

In geothermal systems hot springs, fumaroles, steaming grounds

transport heat & mass to the surface

CONVECTIVE HEAT FLOW

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Equation used; Qc = Vf ρf hf

Qc – convective heat flow (watts)

Vf - volumetric flow rate (m3/s)

ρf - density (kg/m3) (steam ~0.4753, water ~1000kg/m3 )

hf – enthalpy of fluid (~117kj/kg water at ambient and 2670kJ/kg for

steam )

f - denotes the fluid

d- Venturi Diameter~ 0.054m and dt – Diameter throat 0.00635m

Cd- Coef of discharge ~0.96

CONVECTIVE HEAT FLOW

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Desk top study

•Conduct literature review (gather existing relevant

information - geological, geochemical, heat loss,

geophysical) and generate necessary maps

(topographical, base maps).

This helps in;

•Avoid duplication of work.

•Defining objectives and scope of fieldwork.

DATA COLLECTION

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Spacing of the gradient holes depend on the

surface geothermal activity in the prospect

Area, time and resource available

Geologic formation of the area

Social constraints

DATA COLLECTION PLAN

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Global Positioning System (GPS) device

•Digital thermometer probe

•Mechanical soil auger

•Winch

•Venturi meter

•Manometer

•V-notch (weir box)

•Pitot tube

•Jembe, spade, panga, plastic basins

•Field map

•Satellite phone

FIELD TOOLS

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Global Positioning System (GPS) device

•Digital thermometer probe

•Mechanical soil auger

•Winch

•Venturi meter

•Manometer

•V-notch (weir box)

•Pitot tube

•Jembe, spade, panga, plastic basins

•Field map

•Satellite phone

FIELD TOOLS

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Hostile Climate

Poor communication (no roads)

Remote and undeveloped places

Equipment failure

Heavy equipment to be carried

Community acceptance of the project

Likely Challenges

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CASE STUDIES

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Temperatures range 23 –

96°C

•Anomalous thermal area

was approximately 35km2

•Total conductive heat loss

estimated at 1,130MWt

SILALI PROSPECT

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• Temperatures at 1m

depth varied 30 – 84°C

• Anomalous thermal area

was approximatelt 90km2

• NE-SW orientation of

thermal features

• Estimated heat loss

3,420MWt

• 10MWt convective

component

PAKA PROSPECT

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Temperatures range

from 23 - 97°C

•Anomalous thermal

area covered

approximately 85km2

•Total heat loss

2,870MWt

KOROSI_CHEPCHUK PROSPECT

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• Presence of anomalous heat flow supports existence of a

heat source

• Thermal anomalous areas can be used to infer presence

faults and geologic structures

• The use of thermal Gradient – Approximate Reservoir

temperature

• Thermally anomalous areas suggests resource area

CONCEPTUAL MODEL INPUT

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Thank you