Iraq petroleum geology

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Petroleum systems of the Tethyan region
Series AAPG Memoir
Chapter Iraq
Author George J. Grabowski Jr.
Link Web page
Store AAPG Store

UNDER CONSTRUCTION


There are more than 100 oil and gas fields in Iraq, containing more than 137 billion barrels of recoverable oil and more than 106 TCF of recoverable gas. Of this large resource, about 25 billion barrels of oil and 11 TCF of gas have been produced as of 2014.

Introduction[edit]

Nearly all of the oil and gas occurs in fields located within the Mesopotamian foredeep, Gotnia Basin, and Zagros foldbelt. Minor discoveries and shows have been found on the Arabian platform along the western flank of the Mesopotamian foredeep. There is one gas discovery (Akkas field) on the Arabian platform in western Iraq.

Ninety-eight percent of the oil and gas occurs in reservoirs of Cenozoic and Cretaceous age. The largest reserves occur in: 1) carbonate rocks of the Kirkuk Group (Lower Miocene–Oligocene), in fields within the Zagros foldbelt of northeastern Iraq, the largest being Kirkuk field; 2) carbonate rocks of the Mishrif Formation (Turonian–Cenomanian), in fields within the Mesopotamian foredeep and Zagros foldbelt in southern and central Iraq, including Rumaila, West Qurna, Majnoon, Halfayah, Zubair, and Buzurgan fields; and 3) siliciclastic rocks of the Zubair Formation (Albian–Barremian), in fields within the Mesopotamian foredeep and Zagros foldbelt in southern and central Iraq, including East Baghdad, Rumaila, West Qurna, and Zubair fields. Large reserves also occur in carbonate rocks of the Upper Cretaceous above the Mishrif Formation and in the Lower Cretaceous below the Zubair Formation. Smaller reserves occur in other Neogene and Paleogene carbonates and siliciclastics, in Jurassic and Triassic carbonates, and in Ordovician siliciclastics.

Most of the oil and gas that have been discovered were generated from organic-rich, oil-prone carbonates of the Jurassic Sargelu and Naokelekan Formations. These source rocks are widely distributed and mature for oil and gas generation across the Mesopotamian foredeep and Zagros foldbelt. Lesser amounts of oil and gas are derived from: 1) Upper and Lower Cretaceous oil-prone source rocks within the Zagros foldbelt; 2) Triassic oil-prone source rocks in northwestern Iraq; and 3) Silurian gas-prone source rocks in western Iraq. The oil generated from the Jurassic source rocks migrated vertically to fill stacked reservoir intervals in many fields. Lateral migration of oil occurred along the western margin of the Mesopotamian foredeep, as proven by small fields and large seeps that are located where source rocks are absent or immature for oil or gas generation.

Figure 1  Topographic map of Iraq, showing major cities and rivers, along with major oil and gas fields. Points of high elevation are indicated.

Physiography[edit]

The southern and western parts of Iraq are part of the broader Arabian platform of adjacent Syria, Jordan, Saudi Arabia, and Kuwait (Figure 1). This is a sparsely populated area of desert and low hills, mostly 300–500 m (984–1640 ft) above sea level (msl). The highest elevation here occurs at Jabal ‘Unayzah, in the southwestern corner of the country, at 940 msl. Bedrock is exposed in these areas, largely Cenozoic but Mesozoic and Paleozoic in western Iraq.

The land slopes down to the floodplains of the Al Furat (Euphrates) and Dijlah (Tigris) Rivers, which flow from Turkey and Syria through the length of Iraq to the Gulf of Arabia via the Shatt al Arab. The elevation at the Iraq–Syria border is 300–400 msl. Al Furat follows the Anah Graben until it reaches the subsiding Mesopotamian foredeep (Figure 1). The Dijlah flows around the uplifted Sinjar Graben to flow across the low portion of the Zagros foldbelt to the Mesopotamian foredeep. The floodplains are covered by alluvium, terrace gravels, and eolian sands. There are many towns and cities, including Baghdad, An Nasiriyah, and Basrah, in the floodplains of these rivers.

Elevations rise in northeastern Iraq. Most of the Kirkuk embayment of the Zagros foldbelt is covered by Neogene sediments, except for elongated northwest-trending anticlines that expose older strata. Surface elevations rise up to 850 m (2788 ft) on the Qara Chauq Dagh anticline (Figure 1). There are many towns and cities in this region, including Mosul and Kirkuk.

The High Zagros Nappe zone further to the northeast is characterized by large anticlinal mountains that expose Cenozoic to Paleozoic sediments as well as igneous and metamorphic rocks. Elevations are higher across this region, reaching 3586 m (11765 ft) on the Iraq-Iran border east of Rowandaz (Figure 1). Major gorges cut by rivers, such as the Zab River that runs into the Dijlah River near Jabal Qara Chauq Dagh, form exposures that are the type sections for many formations. One effect of the surface relief of Iraq is the flow of groundwater deeply within the sediments of the Mesopotamian foredeep, from the somewhat higher Arabian platform in western and southern Iraq, as well as within synclines in the Kirkuk embayment of the Zagros foldbelt. Freshwater extends far into the subsurface because of these flows.

Figure 2 Bouguer gravity (right) and total magnetic field (left) maps of Iraq, from Jassim and Goff,[1] compiled by GEOSURV. The gravity map shows low values in the Zagros foldbelt and Mesopotamian foredeep due to the thick sedimentary section. Orientations of features trend to the north and northwest in southern, western, and northwestern Iraq, interpreted in part to be caused by the structural grain of Precambrian accreted terrains. 200 km (124.3 mi).

Tectonic setting[edit]

Iraq is located in the northern part of the Arabian tectonic plate. The basement rocks are presumed to be accretionary rocks assembled during the Late Precambrian Pan-African orogeny, although no wells reach the basement rock in Iraq. Bouguer gravity values are low in the northeast, presumably due to the extreme thickness of sedimentary rocks (Figure 2), and become progressively higher to the west onto the Khleisia High (Rutbah subzone of Jassim and Goff[1]) along the Iraq–Syria border. North- and northwest-trending basement grains are interpreted from gravity and magnetic data in southern, western, and northwestern Iraq as shown in Figure 2.

Figure 3 Map of tectonic provinces of Iraq, showing major structural features. Fields and significant wells with oil and/or gas shows are shown; numbers refer to Tables 1–5. Red lines are approximate locations of stratigraphic charts in Figure 4 and Figure 5.

Northeastern Iraq, contiguous with Iran and Turkey, is part of the Zagros foldbelt, consisting of two zones (Figure 3). The High Zagros Nappe zone is a topographically high region characterized by tightly folded rocks and by ophiolite which was obducted onto the Arabian plate in the Late Cretaceous (Figure 4). Cretaceous and older sedimentary rocks and a suite of igneous and metamorphic rocks crop out in this region (Figure 5). There are no oil and gas discoveries in the High Zagros Nappe zone, although rocks containing bitumen and organic-rich rocks are exposed.

Figure 4 Regional geologic cross section, which extends NE across central Iraq, from the Arabian platform of southwestern Iraq, at the border with Saudi Arabia, across the Mesopotamian Foredeep and Zagros foldbelt in eastern Iraq and adjacent Iran, and ending at the Sirjan-Sanandaj zone in Iran.
Figure 5 Regional geologic cross section which extends NE across western Iraq, from the Arabian platform at the border with Jordan, across the Mesopotamian Foredeep and Zagros foldbelt in northwestern Iraq, and ending in adjacent Turkey.

The main part of the Zagros foldbelt is topographically lower and is characterized by large anticlines trending to the northwest. In the southwestern part of the foldbelt, synclinal areas are covered by Neogene sediments. In the northwestern part of the foldbelt, Paleogene strata are exposed in synclines. The Zagros foldbelt forms a large structural embayment, called the Kirkuk embayment, in the overall Zagros foldbelt. Many oil and gas fields occur within this zone, as shown in Figure 3, including the super-giant Kirkuk field.

The central portion of Iraq is the Mesopotamian foredeep, an area of relatively deep-water deposition in the Mesozoic and Cenozoic that formed in front of, and which is less deformed than, the Zagros foldbelt (Figure 6). Structural features trend to the northwest in the Mesopotamian foredeep, parallel to the Zagros foldbelt trends, and are formed by both detached and basement-involved faults (Figure 4, Figure 6). Bouguer-gravity values are low in this foredeep (Figure 2), reflecting the thick sedimentary section. There are many oil and gas fields in the Mesopotamian foredeep (Figure 3), including the large East Baghdad field.

Figure 6 Interpretation from megaseismic line 7 (reproduced from Mohammed,[2] by permission from GeoArabia), which extends from the Arabian platform of southwestern Iraq across the Mesopotamian Foredeep to the Zagros foldbelt in eastern Iraq. 50 km (31.1 mi).

The southern part of the Mesopotamian foredeep is contiguous with the northern extension of the Gotnia Basin, an area of subsidence and deep-shelfal salt deposition during the Jurassic that extends into adjacent Kuwait. The Gotnia Basin (called the Zubair zone by Jassim and Goff[1]) is characterized by broad, low-angle anticlines that trend and plunge to the north. These anticlines form many oil and gas fields, including the super-giant Rumaila, West Qurna, Zubair, and Majnoon fields (Figure 3). Values of both Bouguer gravity and total magnetics are low (Figure 2), indicating a thick sedimentary sequence with a non-magnetic basement.

The Zagros foldbelt and Mesopotamian foredeep end at the Khleisia High (Rutbah subzone of Jassim and Goff[1]), a region of shallow basement and thin sedimentary cover, as interpreted from the high values of the Bouguer gravity map (Figure 2) and from the deep Khleisia 1 well which drilled to the Ordovician (Figure 5). Several east-trending extensional grabens that formed in the Late Cretaceous cut across and form the northern and southern boundaries of the Khleisia High (Figure 3). These include the Anah and Ashtar Grabens to the south (Figure 5), which appear as relatively low in the total magnetics map (Figure 2), and the inverted Sinjar Graben to the north, which is a low on Bouguer gravity. There are only a few small fields in northwestern Iraq (Figure 3).

Western and southern Iraq is part of the Arabian platform, a tectonically stable area which is only mildly deformed (Figure 4). The Ga’ara uplift in western Iraq is a large basement-involved high area where erosion has exposed Paleozoic strata. There are some small oil and gas discoveries on the Arabian platform in Iraq, mostly along the eastern edge, which is a structural monocline that flexes downward into the Mesopotamian foredeep (Figure 3). The most significant discovery is the Akkas field, located south of the Anah Graben, which contains gas in Paleozoic rocks.

Oil and gas fields[edit]

Table 1 lists the discoveries in Iraq (information in part from Jassim and Goff[1]; Verma et al.[3]), along with the hydrocarbon type and age of the main reservoir. The numbers refer to the locations of the fields as shown in Figure 3. Table 2 lists the fields by hydrocarbon type, structural province, structural style and trap type, source name, age and strata type, and volumes of in-place, estimated ultimate recoverable (EUR), produced, and remaining ultimate recoverable (RUR) oil and gas. The volumes data for oil and gas come mainly from Verma et al.[3] and Jassim and Goff,[1] except as noted in other references in this article.

Table 1 List of oil and gas fields and wells with oil and/or gas shows, giving the dominant hydrocarbon type (oil or gas) and reservoir age. Field number refers to locations shown in Figure 3
Field # Field name Hydrocarbon type Age of main reservoirs Field # Field name Hydrocarbon type Age of main reservoirs Field # Field name Hydrocarbon type Age of main reservoirs Field # Field name Hydrocarbon type Age of main reservoirs
1 Tawake Oil Cretaceous 31 Chemchemal Gas Triassic 61 Tel Ghazal Gas Cenozoic 91 Nasiriyah Oil Cretaceous
2 Sufaiyah Oil Cretaceous 32 Kirkuk Oil Cenozoic 62 Balad Oil Cretaceous 92 Samawa Oil Cretaceous
3 Mushorah Oil Cretaceous 33 Ismail Oil Cenozoic 63 East Baghdad Oil Cretaceous 93 Diwan Oil Cretaceous
4 Boheira Oil Cretaceous 34 Bai Hassan Oil Cenozoic 64 Nahrawan Oil Cretaceous 94 Ghalaisan Oil Cretaceous
5 Abtakh Oil Cretaceous 35 Qara Chauq Oil Triassic 65 Fallujah Oil Cretaceous 95 Shawiyah Oil Cretaceous
6 Ain Zalah Oil Cretaceous 36 Khabbaz Oil Cenozoic 66 Nafatah Oil Cretaceous 96 Safawi Oil Cretaceous
7 Gullar Oil Cretaceous 37 Sadid Oil Cenozoic 67 Hit Oil Cenozoic 97 Ubaid Oil Cretaceous
8 Gusair Oil Cretaceous 38 Khanuqah Oil Cenozoic 68 Awasil Oil Cretaceous 98 Majnoon Oil Cretaceous
9 Jabal Kand Oil Cretaceous 39 Makhul Oil Jurassic 69 Abu Jir Oil Cretaceous 99 Nahr Umr/Bin Umar Oil
10 Raffan Oil Jurassic 40 Kor Mor Gas Cenozoic 70 Badrah Oil Cretaceous 100 Sindbad Oil Cenozoic
11 Butmah Oil Triassic 41 Jambur Oil Cenozoic 71 Dhafriya Oil Cretaceous 101 Siba Oil Cretaceous
12 Alan Oil Triassic 42 Pulkhana Oil Cenozoic 72 Ahdab Oil Cretaceous 102 Umm Qasr Oil Cretaceous
13 Sarjoon Oil Cretaceous 43 Judaida Oil Cenozoic 73 Afaq Oil Cretaceous 103 Zubair Oil Cretaceous
14 Ain Ghazal Oil Cenozoic 44 Hamrin Oil Cenozoic 74 Musaiyib Oil Cretaceous 104 Jabal Sanam Oil Cretaceous
15 Tel Hajar Oil Cenozoic 45 Ajil Oil Cenozoic 75 Kifl Oil Cretaceous 105 Tuba Oil Cretaceous
16 Ibrahim Oil Triassic 46 Tikrit Oil Cretaceous 76 West Kifl Oil Cretaceous 106 West Qurna Oil Cretaceous
17 Atshan Oil Triassic 47 Samarra Oil Cretaceous 77 Merjan Oil Cretaceous 107 Rumaila Oil Cretaceous
18 Adaiyah Oil Triassic 48 Mileh Tharthar Oil Triassic 78 Abu Ghirab Oil Cenozoic 108 Ratawi Oil Cretaceous
19 Qalian Oil Triassic 49 Khleisia Gas Paleozoic 79 Jabal Fauqi Oil Cenozoic 109 Subba Oil Cretaceous
20 Qasab Oil Cenozoic 50 Anah Oil Triassic 80 Buzurgan Oil Cretaceous 110 West Luhais Oil Cretaceous
21 Jawan Oil Cenozoic 51 Akkas Gas Paleozoic 81 Noor Oil Cretaceous 111 Luhais Oil Cretaceous
22 Najmah Oil Cenozoic 52 Chia Surkh Oil Cenozoic 82 Huwaiza Oil Cretaceous 112 Rachi Oil Cretaceous
23 Qaiyarah Oil Cenozoic 53 Qamar Oil Cenozoic 83 Halfayah Oil Cretaceous 113 Jerishan Oil Cretaceous
24 Hibbarah Oil Cenozoic 54 Gilabat Oil Cenozoic 84 Amara Oil Cretaceous 114 Khidr Al Maa Oil Cretaceous
25 Makhmour Oil Cretaceous 55 Injana Oil Cretaceous 85 Rifae Oil Cretaceous 115 Abu Kheima Oil Cretaceous
26 Hawler (Benenan) Oil Jurassic 56 Khashm Al Ahmar Gas Cenozoic 86 Muhainya Oil Cretaceous 116 Shaikan Oil Jurassic
27 Demirdagh Oil Cretaceous 57 Jaria Pika Gas Cenozoic 87 Kumait Oil Cretaceous 117 Miran West Oil Cretaceous
28 Quwair Oil Cenozoic 58 Nau Doman Oil Cenozoic 88 Dujaila Oil Cretaceous 118 Kurdamir Gas Cenozoic
29 Binabawi Gas Triassic 59 Naft Khaneh Oil Cenozoic 89 Rafidain Oil Cretaceous 119 Shakal Oil Cenozoic
30 Taq Taq Oil Cretaceous 60 Mansuriya Gas Cenozoic 90 Gharraf Oil Cretaceous 120 Bijeel Oil Jurassic
121 Bazian Oil Cretaceous
Table 2 List of oil and gas fields and wells with oil and/or gas shows. Field number refers to locations shown in Figure 3. Structural province refers to regions shown in Figure 3. Source name and age given only where proven by biomarkers. Volumes of oil and gas in-place, estimated ultimate recoverable (EUR), produced, and remaining ultimate recoverable (RUR) age given in millions of barrels of oil (MMBO) and billions of cubic feet of gas (BCFG). Condensate included in oil volumes. Information mainly from Verma et al.[3] and Jassim and Goff.[1] Additional references as shown. Comments reflect the impression of the author.
Field # Field name Hydrocarbon type Structural province Structural style Trap type Source name and age Source strata type In-place MMBO In-place BCFG EUR (Proved) MMBO EUR (Proved) BCFG Produced MMBO Produced BCFG RUR MMBO RUR BCFG Reference Comments
5 Abtakh Oil Zagros Foldbelt Anticline Show
78 Abu Ghirab Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 1040 572 6 3 1034 569 A bit low
69 Abu Jir Bitumen Arabian Platform Basement-involved fold Faulted anticline Bitumen shows
115 Abu Kheima Oil & gas Arabian Platform Basement-involved fold Anticline 100 75 Small
18 Adaiyah Oil Zagros foldbelt Detached fold-thrust Anticline 10 0 Small
73 Afaq Oil Mesopotamian foredeep Anticline Show
72 Ahadab Oil Mesopotamian foredeep Anticline 1200 500 0 CNPC in The World Energy Weekly Low to IP
14 Ain Ghazal Oil Khleisia high Anticline Show
6 Ain Zalah Oil & gas Sinjar Trough Detached fold-thrust Anticline Triassic Basinal marine 295 90 194 54 101 36
45 Ajil Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 3000 5000 500 500 3 4 497 496 APS Review Downstream Trends 12/02/2002 Low to IP
51 Akkas Gas Arabian Platform Basement-involved fold Faulted anticline Akkas Marine shale 7000 100 2500 www.investorsiraq.com Low to IP
12 Alan Oil and gas Zagros Foldbelt Detached fold-thrust Anticline Triassic Basinal marine 165 55 Small
84 Amara Oil Mesopotamian Foredeep Anticline 250 0
50 Anah Oil Arabian Platform Basement-involved fold Faulted anticline Show
17 Atshan Oil Zagros Foldbelt Detached fold-thrust Anticline 70 0 Small
68 Awasil Bitumen Arabian Platform Basement-involved fold Faulted anticline Bitumen shows
70 Badrah Oil Zagros Foldbelt Detached fold-thrust Anticline 109 150 0 MoO (in EIG 2008)
34 Bai Hassan Oil & gas Zagros Foldbelt Detached fold-thrust Anticline Naokelekan Basinal marine 2200 9200 473 284 1727 8916
62 Balad Oil & gas Mesopotamian Foredep Basement-involved fold Faulted anticline Naokelekan Basinal marine 1380 400 8 2 1372 398
121 Bazian Oil Zagros Foldbelt Detached fold-thrust Anticline 100 30
120 Bijeel Oil Zagros Foldbelt Detached fold-thrust Anticline 100 30
29 Binabawi Gas Zagros Foldbelt Detached fold-thrust Anticline 0 80 Estimated
4 Boheira Oil Zagros Foldbelt Anticline 100 0 Estimated
11 Butmah Oil & gas Zagros Foldbelt Detached fold-thrust Anticline Triassic Basinal marine 80 40 42 21 38 19
80 Buzurgan Oil & gas Mesopotamian Foredeep Anticline 1800 1080 125 81 1675 999
31 Chemchemal Gas Zagros Foldbelt Detached fold-thrust Anticline Balambo Basinal marine 25 2154
52 Chia Surkh Oil Zagros Foldbelt Detached fold-thrust Anticline 40 0 Small
27 Demirdagh Oil & gas Zagros Foldbelt Detached fold-thrust Anticline Naokelekan Basinal marine 40 40
71 Dhafriya Oil Mesopotamian Foredeep Anticline 130 0
93 Diwan Oil Arabian Platform Basement-involved fold Anticline 150 0
88 Dujaila Oil Mesopotamian Foredeep Anticline 260 0
63 East Baghdad Oil & gas Mesopotamian Foredeep Basement-involved fold Faulted anticline 8108 16,000 2500 13 2 15,987 2498 MoO (in EIG 2008) MoO smaller
65 Fallujah Oil Mesopotamian Foredeep Anticline 180 0
94 Ghalaisan Oil Arabian Platform Basement-involved fold Anticline Show
90 Gharraf Oil Mesopotamian Foredeep Anticline 863 500 0 MoO (in EIG 2008) Low to IP
54 Gilabat Oil Zagros Foldbelt Detached fold-thrust Anticline Mixed Balambo/Naokelekan Basinal marine 98 120 0 MoO (in EIG 2008)
7 Gullar Oil Sinjar Trough Detached fold-thrust Anticline 10 0 Estimated
8 Gusair Oil Sinjar Trough Detached fold-thrust Anticline 35 0 Small
83 Halfayah Oil & gas Mesopotamian Foredeep Anticline 4098 700 700 MoO (in EIG 2008) Low to IP
44 Hamrin Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 1780 750
26 Hawler (Benenan) Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 100 100 Estimated
24 Hibbarah Oil Zagros Foldbelt Detached fold-thrust Anticline Show
67 Hit Bitumen Arabian Platform Basement-involved fold Faulted anticline Bitumen shows
82 Huwaiza Oil Gotnia Basin Basement-involved fold Faulted anticline 100 0
16 Ibrahim Oil Zagros Foldbelt Detached fold-thrust Anticline 30 0 Small
55 Injana Oil & gas Zagros Foldbelt Detached fold-thrust Anticline Balambo Basinal marine 140 20
33 Ismail Oil Zagros Foldbelt Detached fold-thrust Anticline 200 0 Estimated
79 Jabal Fauqi Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 730 450 3 2 727 448
9 Jabal Kand Oil Zagros Foldbelt Detached fold-thrust Anticline 30 0 Small
104 Jabal Sanam Oil Gotnia Basin Salt-supported dome Faulted dome Show
41 Jambur Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 3100 9200 115 174 2985 9026
57 Jaria Pika Gas Zagros Foldbelt Detached fold-thrust Anticline 0 918
21 Jawan Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 100 25
113 Jerishan Oil Gotnia Basin Basement-involved fold Anticline 80 0 Small
43 Judaida Oil Zagros Foldbelt Detached fold-thrust Anticline 200 0
36 Khabbaz Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 2000 3000 20 30 1980 2970
38 Khanuqah Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 100 200
56 Khashm Al Ahmar Gas Zagros Foldbelt Detached fold-thrust Anticline 1765 75 1413 MoO (in EIG 2008 )
114 Khidr Al Maa Oil Arabian Platform Basement-involved fold Anticline Show
49 Khleisia Gas Khleisia High Basement-involved fold Anticline Show
75 Kifl Oil Arabian Platform Basement-involved fold Anticline 209 400 0 MoO (in EIG 2008) High to IP
32 Kirkuk Oil & gas Zagros Foldbelt Detached fold-thrust Anticline Naokelekan Basinal marine 25,000 8220 14,177 5425 10,823 2795
40 Kor Mor Gas Zagros Foldbelt Detached fold-thrust Anticline 4500 30 1760 0 15 30 1745 EIA Country Brief Low to IP
87 Kumait Oil Mesopotamian Foredeep Anticline 140 0
118 Kurdamir Gas Zagros Foldbelt Detached fold-thrust Anticline 523
111 Luhais Oil & gas Gotnia Basin Basement-involved fold Anticline 1060 500 49 23 1011 477
98 Majnoon Oil & gas Gotnia Basin Basement-involved fold Anticline 12,580 7600 5600 MoO (in EIG 2008)
25 Mokhmour Oil Zagros Foldbelt Detached fold-thrust Anticline 100 0 Estimated
39 Makhul Oil Zagros Flowbelt Detached fold-thrust Anticline 30 0 Small
60 Mansuriya Gas Zagros Foldbelt Detached fold-thrust Anticline 4100 50 3284 EIA Country Brief
77 Merjan Oil & gas Arabian Platform Basement-involved fold Anticline 156 200 100 MoO (in EIG 2008)
48 Mileh Tharthar Oil Arabian Platform Basement-involved fold Anticline Show
117 Miran West Oil Zagros Foldbelt Detached fold-thrust Anticline 1000 100
86 Muhainya Oil Mesopotamian Foredeep Anticline Show
74 Musaiyib Oil Mesopotamian Foredeep Anticline Show
3 Mushorah Oil Zagros Foldbelt Anticline Show
66 Nafatah Oil Mesopotamian Foredeep Anticline Show
59 Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 430 340 114 99 316 241
99 Nahr Umr/Bin Umar Oil & gas Gotnia Basin Salt-supported dome Faulted Dome 6500 9900
64 Nahrawan Oil Mesopotamian Foredeep Basement-involved fold Faulted anticline 250 0
22 Najmah Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 858 200 45 MoO (in EIG 2008) Low to IP
91 Nasiriyah Oil Mesopotamian Foredeep Anticline 2000 500 0 APS Review Gas Market Trends 12/2/2002 Low to IP
58 Nau Doman Oil Zagros Foldbelt Detached fold-thrust Anticline 104 50 0 MoO (in EIG 2008) Low to IP
81 Noor Oil Mesopotamian Foredeep Anticline 500 0
42 Pulkhana Oil Zagros Foldbelt Detached fold-thrust Anticline 145 0
23 Qaiyarah Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 807 450 65 26 4 424 61 MoO (in EIG 2008) Low to IP
19 Qalian Oil Zagros Foldbelt Detached fold-thrust Anticline 15 0 Small
53 Qumar Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 73 200 250 MoO (in EIG 2008)
35 Qara Chauq Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 200 80
20 Qasab Oil & gas Zagros Foldbelt Detached fold-thrust Anticline 200 50
28 Quwair Oil Zagros Foldbelt Detached fold-thrust Anticline Show
112 Rachi Oil Gotnia Basin Basement-involved fold Anticline 870 0
10 Raffan Oil Zagros Foldbelt Detached fold-thrust Anticline 10 0 Small

Table 3 lists the reservoir horizons and seals in fields that have produced oil and gas. The same information is shown for undeveloped fields in Table 4 and for small discoveries and wells with shows in Table 6. Table 5 lists information by show number and show structure.

There are 107 oil discoveries and nine gas discoveries in Iraq. The majority of these are in the Zagros foldbelt (53), the Mesopotamian foredeep (22), and the Gotnia Basin (18), and they account for over 98% of the oil and gas discovered.

The oil discoveries contain recoverable reserves of about 137 billion barrels of oil (gbo) and 93 trillion cubic feet of gas (tcfg). The largest oil fields are Rumaila (30 gbo), Kirkuk (25 gbo), and East Baghdad (16 gbo). Oil (and minor condensate) is about 89% of the per-barrel oil equivalent in Iraq.

The nine gas discoveries contain recoverable reserves of about 13 tcfg and 280 million barrels of liquid (mbl). The largest gas fields are Mansuriya (3.3 tcfg) and Akkas (2.5 tcfg).

To date, about 25 gbo and 11 tcfg have been produced from about 23 fields. The most has been from the Kirkuk (about 14 gbo) and Rumaila (about 8 gbo) fields.

The major reservoirs in Iraq are Cretaceous, and these are the main reservoirs in 69 discoveries. The recoverable reserves in Cretaceous reservoirs in all fields are estimated to be between 59 and 101 gbo and 15 to 55 tcfg. Similar, there are 32 discoveries with mainly Cenozoic reservoirs, with 24–46 gbo and 14–41 tcfg recoverable in all Cenozoic reservoirs. Only 10 discoveries are mainly in Triassic reservoirs, with recoverable reserves of 400–500 mbo and up to 6 tcfg, and three discoveries mainly from Jurassic reservoirs, with 580–1500 mbo and no gas. Estimates of up to 6 tcfg of gas occur in the Paleozoic at Akkas field, with shows in Khleisia 1.

Several conclusions can be drawn from these data:

  • Iraq is an oil province, with a lot of oil generated in superb source rocks.
  • The Cretaceous and Cenozoic are the most important reservoir intervals, and there are fewer discoveries in Jurassic and older rocks.
  • Some accumulations are very large, with large trap and reservoir volumes, commonly in stacked reservoir-seal pairs.

See also[edit]

References[edit]

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Jassim, S. Z. and Goff, J. C., 2006, Geology of Iraq: Dolin, Prague, and Moravian Museum, Brno, 341 p.
  2. ↑ Mohammed, S. A. G., 2006, Megaseismic section across the northeastern slope of the Arabian plate, Iraq: GeoArabia, v. 11, no. 4, p. 77–102.
  3. ↑ 3.0 3.1 3.2 Verma, M. K., Ahlbrandt, T. S., and Al-Gailani, M., 2004, Petroleum reserves and undiscovered resources in the total petroleum systems of Iraq: Reserve growth and production implications: GeoArabia, v. 9, no. 3, p. 51–74.

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