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International Geoinformatics Research and Development Journal

Vol. 5, Issue 3, September 2014

Using Remote Sensing Techniques and GIS to Study Hydrocarbon Leakage

from Oilfields in Urban Areas

(A Case Study of Masjed-Soleiman City)

Khedri Gharibvand L. 1 *, Rangzan K.

2

1Department of engineering, Dezful Branch, Islamic Azad University, Dezful, Iran

Email: [email protected]

2Department of Geology, Shahid Chamran University, Ahwaz, Iran

Abstract

To examine gas and hydrocarbon leakage from oilfields of Masjed-Soleiman city, information layers such as

surface and subsurface structures, locations of gas leakage, stratigraphy, status of population density, and

topographic altitude of the region were prepared. Information from field investigations and remotely sensed

data have been analyzed and were entered into geographic information systems (GIS) software for mapping. By

using analytical functions in GIS, the layers were overlaid, and the zoning of gas leakage risk was accomplished

through Boolean logic. The results indicated high fracture density at the intersection of major faults

corresponding to the location of a deep anticline hinge in Masjed-Soleiman. It is a factor of decreasing the

impermeability of the Asmari Reservoir cap rock. Gas leakage occurs through these fractures; as a result, the

highest risk of leakage in Masjed-Soleiman was detected in its urban areas, including Siberenj and Naftun

districts. In addition to the high density of fractures, the gas cap depth is low. These areas also have the highest

amount of gas leakage and the highest population density. In other areas, the leakage risk was lower than

average due to lower population density, increased depth of gas cap, and lower fracture density.

Keywords: Masjed-Soleiman, Gas leakage, Remote sensing, GIS

Introduction

Hydrocarbon leakage has been observed in surface sediments of reservoirs in close proximity to the mountainous

Khuzestan province in southwest Iran. In most of these reservoirs, such leakage occurs in the south wing of

reservoirs with somewhat distance from the crest line of anticlines, which is due to the structural conditions of

these areas. In 1908, after drilling well number Mis1, Masjed-Soleiman reservoir was the first to be explored for

economic potential in the Middle East. The crest of this reservoir is at a depth of 183 m, which makes it one of

the shallowest reservoirs in Khuzestan province. As a result, several leakages have occurred. The first led to the

discovery of oil; however, recent changes in reservoir conditions have altered these leakages to a gaseous state.

H2S gas leakage in various areas of Masjed-Soleiman has created the potential for environmental disaster; any

factor that allows the exit of this gas can put the city at substantial risk [1]. Attempts have been made to

determine the origin of this gas and the cause of these leakages. In a 1994 report, number 73.3-2.438, the

National Iranian Oil Company probed the status of hydrocarbon leakage in Masjed-Soleiman city; the

investigation only identifying these leakages. The next report determined the type and concentration of the

pollutants and examined their environmental effects [2].

Similarly, the third report identified the origin rock and determined an inorganic nature for these gasses [3]. The

fourth attempted to determine the relationship between gas exit points and structural factors such as the depth of

the gas cap and its fault zones [4]. In other parts of the world, the high importance of maintaining the ecosystem

has dictated the implementation of certain conditions to avoid gas leakage from oilfields in urban areas, resulting

in the closure of several oilfields. Researchers have examined the surface and semi-deep migration patterns of

hydrocarbons in California and investigated the rates and mechanisms of the gas leakages [5]. In addition, an

attempt was made to determine the amount of leakage and hydrocarbon migration using remote sensing and

International Geoinformatics Research and Development Journal 2


three-dimensional seismology [6], and hyper spectral remote sensing was applied to recognize hydrocarbon

leakage [7].

General Geology of the Region

Masjed-Soleiman is located between 49°0'26" and 49°34'39" eastern longitude and 31°40'8" and 32°11'43"

northern latitude and is the major population center in the northeast region of Khuzestan province. This city is

bordered by Dezful to the north, Chaharmahal-o-Bakhtiary province and Izeh to the east, Ramhormoz to the

south, and Shushtar to the west (Figure 1).

Figure 1. Geographical position of Masjed-Soleiman region

The Masjed-Soleiman region is located in Zagros Mountains. The Zagros orogenic belt, which was folded in the

final stages of the Alpine orogenic phase to receive its current shape, is composed of three main zones of thrust

Zagros, folded Zagros, and Khuzestan plain. The region is located in the western part of the folded Zagros

region, west of the Kazeroun fault. The folding pattern of this oilfield is a disharmonic type. Reverse functioning

of faults with a N120–130 trend has resulted in the formation of a pressure zone and the creation of fault-related

folding (Masjed-Soleiman anticline) in hard layers. In addition, the existence of a formable layer of the

Gachsaran Formation is a factor for folding differences at several surfaces, which ultimately converted the

Masjed-Soleiman anticline into a substantially wide syncline at higher horizons (Figure 2) [8].

Figure 2. Structural section of Masjed-Soleiman anticline

The trend of the Masjed-Soleiman anticline is N120–130. On the basis of controlled stratification status, the

anticline is asymmetric in the upper side of the Asmari Formation, and its axial plane slopes approximately 70°

toward the northeast. Oil and gas hydrocarbons are aggregated in the upper region of the Asmari Formation. The



stratigraphy of outcrop formations, including the Asmari Formation as the oil reservoir, is described in the

following subsections.

Asmari Formation

This formation with Oligocene–Miocene age (Oligomiocene) composition consists of cream-colored limes

among marly limestone layers. Due to its rather high resistance, an in-depth folding pattern has been determined.

Lower and upper borders of this formation are isoclinic with Pabdeh marls and halite and Gachsaran anhydrites,

respectively. This formation has no surface outcrop and has been solely determined by core drilling.

Gachsaran Formation

This formation with lower Miocene age is composed of sequence of anhydrite, halite, and green and red marls.

Due to its low resistance, this formation has become a detached layer as a result of non-harmonic folds in the

region. The upper border of this formation is isoclinic with marls and sandstones of the Aghajari Formation.

Aghajari Formation

This formation was built from the sequence of marl and red sandstones; it has altered to siltstone and marl in the

upper part and contains a Lahbari member. This formation has the age of middle to upper Miocene, and special

angular discontinuities can be observed between the formation and upper side (Lahbari member). This formation

comprises the major part of the surface outcrops in the studied region. Its upper border can be observed as an

unconformity due to conglomerates and sandstones of Bakhtiari Formation.

Bakhtiari Formation

This formation, composed of sequences of conglomerate, sandstone, siltstone, and a low quantity of marl layers,

has a Pliocene–Pleistocene age and is the youngest surface outcrop in the southwestern region [8].

Methodology

The research materials included the following elements: a) Geological map of the studied area: 1:100000 scale,

National Iranian Oil Company; b) Digital topographic maps at a scale of 1:25000 with digital graphic number

(DGN) format related to blocks 58531 NW, 58534 NE, 58542 SW, 58543 SE obtained from Iran Mapping

Organization; c) Underground Contour Map (UGC) related to the upper side of Asmari Formation with a scale of

1:50000 obtained from National Iranian South Oil Company; d) Maps of the city, roads, and countryside with a

scale of 1:15000 prepared by Sahab Geography and Cartography Institute, e) Statistics of the regional population

obtained from the last population census in 1991 by the management and planning organization of the province;

f) Annual statistics of weather stations adjacent to the studied area by Khuzestan; g) water and power

organization; h) Landsat 7-ETM satellite data, 166.038 transmission in 2002 prepared by Iran Remote Sensing

Center with the reference datum “WGS84” and Imaging System “UTM” Zone: north 39; i) ArcGIS 9.0,

Microstation, ArcView 3.2, Rivertools2.4, ENVI 4.0, and ER Mapper 6.1 software; j) Global Positioning System

(GPS) device, model ETREX, with geographical and altitudinal accuracy of ± 1m and ± 50 m, respectively.

Preparing the Required Layers

To prepare the zoning map of gas leakage risk, the following layers were required: fractures, lithology, condition

of underground structures, gas leakage points, demographic data, and altitude and land use. After preparing each

layer, a grid with dimensions of 1 km x 1 km was prepared; on this basis, isopotential surfaces were made for

each layer. Collection, entrance, and preparation methods of these layers are described in the following

subsections.

Structural Factors

To prepare the layers of fractures and faults, we were able to use proper filters for determining structural factors.

Therefore, in the ENVI software, directional filters with various angles of 45, 90, 135, and 190° were used in

different directions to determine faults and fractures. The final purpose of preparing such a layer was for

development of the isofracture potential map. To accomplish this task, a grid was made on the fractures and For

each cell of this grid, the total length of the fracture was calculated, and isofracture potential surfaces were

obtained for the region (Figure 3).



Figure 3. Map of isofractures in Masjed-Soleiman region

Position of Subsurface Structures

To prepare the deep layer of the reservoir gas cap, isodepth maps of the upper region of Asmari Formation were

arranged. The map was then corrected from a georeference geometric and included coordinates and pixel size.

After the digitizing process, a layer was prepared by a vector format from the curves related to deep alignments.

On the basis of depth, they were then classified in five ranks as follows: 100–200 m, 201–350 m, 351–500 m,

501–700 m, and above 700 m. For each cell of this grid, depth expansion was determined, and isodepth potential

surfaces of gas caps were specified (Figure 4).

Figure 4. Isopotential map of gas cap depth in Masjed-Soleiman region



Gas Leakage Locations

To prepare this layer, points of gas exit were identified after field investigations and questioning the local people.

Afterwards, coordinates of the place were measured and recorded by GPS device based on UTM coordinates

system. A data bank was prepared from the mentioned coordinates and was turned to a point layer in the GIS;

accordingly, isodensity potential surfaces of gas exit points was prepared (Figure 5).

Figure 5. Map of density of gas leakage points in Masjed-Soleiman region

Stratigraphy

Through field sampling and analysis of satellite images in the region, surface outcropping of the formations was

determined. While digitizing layer borders, a map of surface outcrops was prepared in GIS. Stone layers of the

region were divided into five categories of very soft, soft, medium, hard, and very hard, and development of each

lithology was determined. On this basis, isodensity potential surfaces were prepared for the hardness

development of stones (Figure 6).

Figure 6.Map of expansion of rock hardness in Masjed-Soleiman region



Digital Elevation Model (DEM) of the Region

To prepare this layer, 1:25000 digital topographic maps of Mapping Organization were used. After correcting the

errors and performing required edits, the maps were used for basic altitudinal data. A digital elevation model

(DEM) of the region was developed by using the reverse internal distance weigh (IDW) method and cell size of

30 x 30 m. This layer contained five altitudinal classes of 100–201, 200–300, 301–500, 501–700 and 701–1200.

To prepare the map of altitude density, new values were determined for each cell (Figure 7).

Figure 7. Map of elevation density in Masjed-Soleiman region

Land use

To arrange this layer, urban digital maps of Mapping Organization with a scale of 1:25000 were used.

Accordingly, available functions of the region such as schools, hospitals, and health centers were determined,

and each was digitized as a separate layer and entered into GIS.

Population

To prepare this layer, urban digital maps of Mapping Organization were used with a scale of 1:25000 related to

blocks 58534 NE, 58542 SW, 58543 SE, and 58531 NW, and a vector layer was formed in GIS. By determining

residential area, the unit of population per area was calculated, and a population layer was prepared on the basis

of land use. Thus, the populated regions with such important features as schools were determined in the available

network, and population weight was determined in each district. Isopotential layers of population density were

prepared from this region with consideration of the new values (Figure 8).

Figure 8. Map of population density in Masjed-Soleiman region



Weighing the Layers

In this stage, each map was divided into the following five levels in terms of available density and effects of gas

leakage in the region: very high density, high density, medium density, low density, and very low density.

Considering the point that most layers have vector quantities and are given equal importance in zoning, an equal

weight system (Boolean logic) was applied to these layers [9]. The following three main placement techniques

were developed: Boolean logic, binary comparison method, and fuzzy logic. The effective factors in method

selection involve identification of priority and importance of elements and parameters that determine placement.

For zoning gas leakage risk, which is the purpose of this research, the involved parameters and factors are

considered equally important; whenever effective parameters and factors have equal importance or are

considered to be equivalent, the proper method would be Boolean logic. Finally, the following levels were

assigned: Very high density had the highest weight and risk (weight number: 5), high density had high weight

and high risk (weight number: 4), medium density had medium weight and medium risk (weight number: 3), low

density had low weight and low risk (weight number: 2), and very low density had very low weight and low risk

(weight number: 1).

Overlaying of Layers and Preparing Zoning Map

After selecting Boolean logic for placing the indexes, the prepared vector layers were overlaid according to risk

classification: very high risk (5), high risk (4), medium (3), low (2) and very low (1). After overlaying the layers,

the algebraic sum of weights of different layers of each grid cell was calculated, this was obviously in the range

of 6–30 for each cell. This range was then divided to the following five risk rankings: very high risk (26–30),

high risk (21–25), medium risk (16–20), low risk (11–15), and very low risk (6–10). On the basis of the

algebraic sum of layers of each cell, isopotential surfaces were finally prepared to develop the zoning map of gas

leakage risk (Figure 9).

Figure 9. Map of risk zoning of gas leakage in Masjed-Soleiman region.

Results and Discussion

A separate examination of data the layers revealed that the map of fracture density (Figure 3) indicated that the

highest density was related to the collision point of two structural trends of the Niayesh fault and the fault zone

of Masjed-Soleiman. A structural wedge is located in the central and southern regions of Masjed-Soleiman; as a

result, fracture density exhibited its highest value in this district and was assigned a high risk weight. An

additional center of fracture aggregation was discovered at the collision point of the Lahbari fault and a fault

trend of N 70°, which corresponds to the location of Batvand Village.

The map of expansion of stratigraphic units implied that major surface coverage of the region consists of the

Gachsaran, Aghajari (including the Lahbari member), and Bakhtiari formations. Controlling surface outcrops in

the urban area of Masjed-Soleiman indicated that the northern region of the city is located on the Aghajari

Formation, and the central and southern regions are situated on the Gachsaran Formation. By classifying these



outcrops to five rankings on the basis of rock hardness and preparing a map accordingly (Figure 6), it was

determined that the most expansion of hard rocks, which are easily broken under tension, occurs in the northwest

districts of the city, from its northwest border to Lali, and in Tembi valley. Regarding the layer of lithology data,

the city proper is located in the zones of very low to low density, which is regarded to carry a low risk for

environmental hazards.

On the map provided, which was based on the depth of the gas cap and introduced as a map of gas-cap density

(Figure 4), it was determined that the shallowest part of the gas cap is located in the southeastern region of

Masjed-Soleiman city. The city proper was placed in zones with low to medium depth; thus, the southeast region

was assigned a medium to high risk weight, and the center of the city was assigned a ranking of high density and

high risk probability.

An examination of gas leakage points revealed that most leakage occurred in the central region of Masjed-

Soleiman city in districts of Siberenj, Dare-Khersan, and Naftun. On the basis of this information, isodensity

potential surfaces were prepared (Figure 5). This map attributed the highest density and risk to the central part of

the city; thus, it carries high weight in terms of risk probability.

A study of population distribution in Masjed-Soleiman city revealed that most of its population resides in the

urban area. A population density map was developed that considered the population number relative to the

residential area (Figure 8). On the basis of this map, Masjed-Soleiman city has a linear shape from northwest to

southeast, and the highest population density is located in the northwest and southeast regions of the city; the

central region has a lower density. Nevertheless, the entire city is located in very high to high density zones,

which indicates very high to high risk probability.

An examination of altitude conditions of the region (Figure7) revealed that Masjed-Soleiman city is in a

relatively low altitude area (200–350 m) and that the central and eastern regions of the city are approximately

150 m higher in altitude than its western region situated in the valley of the Tembi River. Therefore, the western

region carries the highest weight with a very high risk probability, and the central and eastern regions have lower

risk probability and high risk. Altitudes adjacent to Masjed-Soleiman are 500–1000 m and carry medium to very

low weight.

Conclusion

After an examination of the zoning map of gas leakage risk, the following results were obtained: Considering the

point that most urban regions of Masjed-Soleiman are located on outcrops of the Gachsaran Formation, it carries

low weight in terms of lithology data. Thus, no zone of very high risk was assigned to Masjed-Soleiman city.

Due to high density of fractures, gas exit points, and population, the highest risk probability was assigned to

Naftun and Siberenj districts; the high weight of these two data layers demonstrated its effect on zoning patterns.

In addition, Other urban points of Masjed-Soleiman were assigned zones of medium to high risk probability,

which was affected by their relatively high population density, gas leakage points, and shallow gas cap depth. It

is also concluded that in other regions of Masjed-Soleiman, gas leakage risk probability ranged from very low no

risk according to low population density, high UGC depth, low fracture density and lower density of gas leakage

points. After examining altitude conditions of the region (Figure 7) and determining its relationship with gas exit

points, it was clear that regions with lower altitudes located in the gas cap area showed the highest pollution rates

due to the leakage of heavier gases. Therefore, these regions were assigned the highest weight and risk

probability; regions at higher altitudes carried lower risk probability.

References

[1] National Iranian Oil Company, Conditions of hydrocarbon leakages of Masjed-Soleiman city,73.3-2.438, 19

(1994).

[2] Shishegar A., Bioenvironmental problems arising from oil leakage in Masjed-Soleiman, Iran

Bioenvironmental Crises and Their Improvement Strategies seminar,1, 17 (2001).

[3] Rezaei Kavenrudi Z., Examining geochemical reasons of pollutant of hydrogen sulfide gas of Asmari

reservoir in Masjed-Soleiman oil field, Master's thesis of geology, Oil, Shahid Chamran university of

Ahwaz(2005).

[4] Safari H.and Rangzan K. and Khedri Gharibvand L., Effect of faulting zones on gas leakage pattern in

Masjed-Soleiman region using remote evaluation techniques and GIS, Iranian geology seminar,10, 175(2006).



[5] Jones V.T.and Coleman D.D. and Becker D.F. and Anderson T.H. and Witherspoon P.A. and Robbins G.A.,

Surface and near-subsurface hydrocarbon migration patterns associated with a macroseep. AAPG: Successful

application of non-seismic techniques to exploration, Houston, AAPG annual convention, (2002).

[6] O’brien G.W., Constraining hydrocarbon migration and seepage rate using a combination of 3d seismic data

and multiple, independent remote sensing technologies. Australia, Canberra(2004).

[7] Van der worff H., Detection of hydrocarbon microseepages with hyperspectral remote sensing, Department

of Earth systems analysis, (2005).

[8] Motiyee H., Geography in Iran, Zagros stratigraphy, tehran, Iran Geology Organization press, 536(1995).

[9] Aronoff S., Geographic information system. A management perspective, Ottawa, Canada ,WDL press,

190(1989).

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