Introduction :
No body can argue in a fact that the Iraq oil huge reserves and its development to produce these reserves is the future of Iraq and Worldwide , however the reserves unless produce in right time& in right price ; the oil worth will be disperse with no significant achievement to Iraqi peoples .
The Iraqi oil reserves is mostly concentrated mainly in the south of Iraq of about ( 70%) & in the north the rest of reserves , which range in its cost from the south to the north depending on depth of reservoirs and type of rock & geological region.
The North region is geologically is located tectonically in three part ; High folded, foothill (Unstable Shelf ) , musol upleft, the middle and the south is located in past sea flooded zone.
The north zone geologically composed of faulted due to tectonically movement of this part as an Arabian platform to strike the Indian ocean ( middle Asia ) platform which created a Zagros up left .
The north zone composed of several reservoirs in each field with a rocks range from basalt to sedimentary rocks , while the southern Iraq composed of several reservoirs in each field with a rocks composed mainly of sedimentary.
Geological and Tectonic background:
The Middle East region of hydrocarbon riches falls between the Arabian Shield on the one side and the Zagros mountains on the other.
The stratigraphy of the region is simplified by the fact that clearly recognizable rock units can be followed for long distances without unduly abrupt changes in facies.
The majority of the oil reservoirs in the Middle East (ME) range in geological age from the Tertiary Oligo-Miocene period to the Middle Jurassic period. Within some countries, hydrocarbons have been found in reservoir rocks of widely different ages. Thus, in Iraq, oil reservoir formations range from the Oligo-Miocene period to the Triassic. Iraq could be considered as a wide NW-SE oriented trough, the centre of which contains the youngest strata with a sedimentary cover having a thickness in the range of 5-13 kilometer.
Iraq Geology :
Iraq occupies the north-eastern corner of the Arabian Plate and over 95% of its territory lies within the Arabian Shelf units, whereas the rest, a narrow strip along the Iraqi-Iranian border, represents the Zagros Suture unit which separates the Arabian and Eurasian Plates.
Looking at the tectonic framework of Iraq, virtually all of Iraq is part of the Arabian sedimentary basin extending from the Arabian-Nubian platform in the
west and the Alpine folded geosynclinals units of the fore deep in the east. This vast sedimentary basin dates from pre-Cambrian.
Iraq is made up of two main divisions of Stable and Unstable Shelves of about equal areas. The Stable Shelf occupies the West and SW parts of Iraq and the Unstable Shelf in the East, North and NE parts of the country. Each is divided into a number of tectonic zones and some of these are divisible into sub-zones. Iraq is additionally dissected by a number of major NE-SW trending transverse faults, which cut across both Stable and Unstable Shelves and carry a strike-slip component of movement as well as a vertical component ( Figure No.1 ) .
Fig.2: Tectonic subdivision of North Iraq (Simplified Al-Kadhimi et al., 1996) showing the studied area. The Inner and outer platform terms are from S. F. Fuad: Personal communication
There are various structural plays which can be divided according to their prospects, geological age and tectonic setting to coincide with the tectonic framework:
Figure 3. Location map of Iraq showing northeast Arabian Peninsula, with locations of basins and oil fields.
The Stable Shelf :
The Stable Shelf roughly coincides with the Western and Southern Desert geographic divisions of Iraq. It is tectonically divided into a western Rutba-Jezira Zone and an 4 eastern Salman Zone separated by the N-S trending Salman-
Sharaf Divide where the basement is at its shallowest (about 5-6 km below sea level).
Through gravity modeling and magnetic, seismic (though very limited) and supplementary oil and water well data (with only few exploration well), the Stable Shelf is shown to possess thick sedimentary successions on either side of the Salman-Sharaf Divide. The successions principally consist of Paleozoic sediments.
The Unstable Shelf :
It is divided into two main zones. The NW-SE trending Mesopotamian Zone extends across the alluvial plains of the Euphrates-Tigris valleys continuing from the Salman Zone to the Iranian border and wedging out in the NW in an apex. The second main zone is the Folded Belt which is subdivided into a Foothills Zone, a High Folded Zone and an imbricated Zone, extending over the foothills and ranges of Zagros and Taurus Mountains.
The Hydrocarbon Prospect :
The hydrocarbon prospects of Iraq or the ME are specifically addressed by their petroleum systems, geological ages of the reservoirs housing the accumulations, and sedimentological history from early Paleozoic to the Miocene , For oil occurrence there are conditions which need to be met .
These define a total of four reservoir plays in the Early-Middle Palaeozoic, seven in the Permo-Liassic, six in the Cretaceous, and one in the Cenozoic. Successful traps proven to date comprise Late Tertiary inversion anticlines, which have
been drilled to the virtual exclusion of other trap types. By analogy with nearby countries and as inferred from the database contained in this report, palaeostructures and a variety of stratigraphic traps are likely to exist Of these, tilted fault blocks that sit between inversion anticlines, are probably the most interesting new opportunity. Successful exploration for these will open up new play fairways across wide areas of northern Iraq. It is reasonable to assume that further accumulations remain to be discovered within northern Iraq. Until seismic mapping, volumetrics and play/prospect risk is assessed, it is difficult to put a precise figure on yet-to-find.
The focus is, in particular, on the presence and maturation of the source rock levels charging the reservoir rock of the structural anomalies (Traps) available to trap and preserve them under suitable seals.
The hydrocarbon prospects of Iraq, however, have been enriched by the presence of numerous plays of identified petroleum systems, geological ages of the reservoirs housing the oil accumulations and the sedimentology history which extends from early Paleozoic to the Miocene providing the right conditions for the occurrence of oil.
Figure No.4 Showing North Zone Isotopic Section
The various tectonic zones in Iraq are dominated by one or more petroleum systems. Generally, the stable shelf is dominated by the older system whereas the unstable shelf is dominated by the younger ones. The presence and maturation of the source rock, the ‘kitchen’, charges these reservoirs, from within or a far, of the structural anomalies (or the like) available to trap and preserve the hydrocarbon under suitable seals.
Our Petrolog & Associates (P&A) in-house study of 1997 included, among others, hydrocarbon prospectivity shown by typical lithology columns for each
tectonic zone. They help to show at a glance the main source level charging the targets and help to find the formation that would seal the accumulation being explored for. In addition, other productive or potentially productive objectives in the tectonic zones are identified.
North Iraq Geological Zone :
The prospectivity of northern Iraq is significant. It sits on margin of two known
hydrocarbon provinces, firstly the Mesopotamian basin with its major Jurassic
source rocks and Cretaceous to Oligo-Miocene reservoirs in late Tertiary anticlinal traps to the SE (Kirkuk-Makhul-Hamrin area) and secondly, the ‘NW
Iraq / NE Syria’ hydrocarbon province with likely Triassic source rocks and Triassic-Middle/Late Cretaceous reservoirs in inverted half-grabens to the north.
The Khleisia High is largely unexplored, but possesses many strong geological similarities with the Euphrates Graben system of Syria, in which
Silurian, Triassic and Late Cretaceous source rocks charge tilted fault-block
traps in which reservoirs, consisting of a variety of lithologies, range in age
from Carboniferous to Neogene.
In immediate vicinity, there are in-place recoverable reserves in the tens of billions of barrels, in Kirkuk (INOC est. 24 Billion recoverable), Jambur, Bai
Hassan, Kabbaz, Ain Zalah, Butmah, TaqTaq, Chemchemal, Qaiyarah, Qasab, Najmah, and Jawan Figure No.( 2 ) .
Prolific source rocks, mostly of Middle Jurassic-Early Cretaceous age with
average yields in the order of 10kg/tonne, are distributed widely across the
Mesopotamian Basin and Kurdistan. These are usually oil prone but some
gas generation is occurring at the present day in more deeply buried areas of
Kurdistan.
This is the system that is important in charging central Iraq , However, for this system to be important in NW Iraq, long-distance migration would be required, and evidence suggests that these oils have reached the Jawan-Najmah structures and maybe not spilled beyond these traps.
Figure No.5 North Of Iraq area marked by its giant oil fields in Kirkuk and Musol area.
Triassic source rocks remain unquantified but geochemical data (sulphur isotopes ) and rare earth geochemical fingerprinting, in addition to the position of known production and shows outside of the Jurassic source kitchen) indicates that an active Triassic source system must exist, although it is likely to be of moderate rather than world-class ranking. A Palaeozoic source rock system , relying mostly upon the basal Silurian (Akkas Formation) and Tournaisian
(Ora - Shale Formation) may be sufficiently mature to have generated oils in more positive areas such as around the Khleisia High where there was insufficient burial of either Triassic or Jurassic source rocks.
There are cap rocks throughout the stratigraphy, typically present as flooding surface shales in Palaeozoic clastic systems, basinal marls developed as drowning units over karstified Mesozoic shelf limestones, or restricted salina/sabkha evaporites developed above porous, dolomitised reefal and platform margin carbonates of Mesozoic and Cenozoic age{ Fig.No. (2)}
Southern Iraq Gelogical Zone :
The Iraqi southern zone is mainly a sedimentary rocks type , hydrocarbon -charge modeling and source-rock characterization of the Lower Cretaceous and Upper Jurassic underlying the prolific Cretaceous and Tertiary reservoirs in the oil fields in southern Iraq with strong prospective of oil reserves in Iraq , well data of the Majnoon (Mj), West Qurna (WQ), Nahr Umr (NR), Zubair (Zb), and Rumaila (R) oil fields. Burial histories indicate complete maturation of Upper Jurassic source rocks during the Late Cretaceous to Paleogene followed by very recent (Neogene) maturation of the Low/Mid Cretaceous succession from early to mid-oil window conditions, consistent with the regional Iraq study of Pitman et al. (2004). These two main phases of hydrocarbon generation are synchronous with the main tectonic events and trap formation associated with Late Cretaceous closure of the neo-Tethys; the onset of continent-continent collision associated with the Zagros orogeny and Neogene opening of the Gulf of Suez / Red Sea.
Palynofacies of the Lower Cretaceous Sulaiy and Lower Yamama formations and of the Upper Jurassic Najmah/Naokelekan formations confirm their source rock potential, supported by pyrolysis data. To what extent the Upper Jurassic source rocks contributed to charge of the overlying Cretaceous reservoirs remains uncertain because of the stratigraphically intervening Upper Jurassic Gotnia evaporate seal. The younger Cretaceous rocks do not contain source rocks nor were they buried deeply enough for significant hydrocarbon generation.
The southern region in Iraq is well known for its giant oil fields. It is situated in what is known as the Mesopotamian Basin near the eastern edge of the Arabian plate (Figure 1).
The Mesopotamian Basin is the NW-trending foredeep to the Zagros fold and thrust belt that formed in response to the continental collision of the Arabian and Eurasian plates. Collision started during the Late Cretaceous and increased in intensity during the Paleogene/Neogene (Beydoun et al., 1992). The Mesopotamian Basin is relatively unaffected. Deformation increases in intensity from west to east towards the Zagros Mountains. The fields in the Basrah region occur along N-S trending folds in the southern part of the basin (Figure 4). N-S striking, basement-cored anticlines in this part of the basin began forming in the Paleozoic, with continued but with more limited growth throughout the
Mesozoic and Early Cenozoic. At least some of the structures may be related to salt diapirism of the Precambrian to Cambrian Hormuz Formation (Al Sharhan and Nairn, 1997; Sharland et al., 2001, and Jasim and Goff, 2005).
The Jurassic and the Cretaceous of the Arabian plate host the most prolific hydrocarbon systems in the world. Widely developed platform and basinal carbonates separated by a thick evaporate unit (the Upper Jurassic Gotnia
Formation) provide multiple source-rock, reservoir, and seal combinations. In combination with the subsequent development of a large foredeep with deep burial, and Zagros tectonics, this creates the right ingredients and timing for late source-rock maturation, large-scale structural development, and hydrocarbon entrapment.
The lithostratigraphy of the Jurassic to Lower Cretaceous in Iraq was first described by van Bellen et al. (1959, 2005). Aqrawi et al. (2010) provide a detailed compilation of the stratigraphy, structural geology, and petroleum systems. The regional basin modeling study by Pitman et al. (2004) provides a good framework for this study while the main oil source rocks for this region were assessed by Al-Ameri et al. (1999, 2009) and Abeed et al. (2011) to be mainly of Upper Jurassic-Lower Cretaceous Sulaiy Formation with some other sources of Middle Jurassic Sargelu Formation (Al-Ameri et al., 2011) and Lower Cretaceous Zubair Formation (Al-Ameri and Batten, 1997). Figure 3 provides a summary of the stratigraphy of the region from the Late Jurassic to the Neogene.
The Southern Iraqi oil fields data was correlated between several fields and wells , the data and burial history and formation was taken from wells Mj-8 and Mj-19 (Majnoon Field), WQ-15 and WQ-23 (West Qurna Field), NR-7 and NR-9 (Nahr Umr Field), Zb-40 and Zb-47 (Zubair Field) and R-172 (Rumaila Field). The ages of depositional and erosional events were designated, based on the geologic time scale of Sharland et al. (2001). Lithologies are modeled as end-member rock types or as compositional mixtures of rock types assigned to each unit, using software default parameters of Pitman et al. (2004).
Core-rock samples for source-rock characterization and palynofacies assessment were taken from wells R-172 (Rumaila North Field) and WQ-1 (West Qurna Field) for the Upper Jurassic Najmah/Naokelekan, Sargelu, Upper Jurassic to Lower Cretaceous Sulaiy, and Lower Cretaceous Ratawi and Zubair Formations. Palynological analysis was done in the department of geology, College of Science, University of Baghdad, where the samples are stored. Source-rock pyrolysis was done by Geomark Research Ltd in Houston-Texas.
1D Petromod requires calibration of the thermal regime at each model location, based on crustal heat-flow parameters, calculated thermal conductivities of the rock succession and burial history tied to present-day surface and subsurface temperatures (Pitman et al., 2004). Type IIS kerogen kinetics were used for
source-rock maturation because extracts of the kerogen for the Jurassic Lower Cretaceous source rocks have considerable amounts of Sulfur (NSO=1-34%).
Iraq Oil Reserves :
In the Middle East and North Africa, an area of more than 14 million square kilometres, shallow water carbonates are very common both in outcrop and the stratigraphic sequence. This immense, largely desert region is the largest marine carbonate province in the world (Fig. 9) extending over a maximum east-west width of 8370 km and up to 4180 km from north to south. In this vast area of dominantly limestones and dolomites, petroleum exploration has already revealed a number of significant reef, and reef related oil and gas reservoirs.
These consist of fringing reefs in the Eocene and Oligocene of giant Kirkuk oil field in Iraq, where fore reef and back reef limestone are also productive, and fringing reefs in some of the oil fields of southern Iran. Known barrier reefs are limited to Middle Eocene limestone reservoirs of the western Kirkuk Field, and
The only possible case of a reef wall reservoir to-date is in the Oligocene limestones of the Bai Hassan oil field of Iraq.
Oil Reserves of Iraq :
Few definitions are given here by way of acquainting the non-technical readers and to denote their usage in the discussion that follows.
A reservoir is that portion of a trap which contains oil and/or gas as a single hydraulically-connected system. Although the hydrocarbons, oil or gas in place are fixed quantities, the recoverable portion of the hydrocarbons in place (that is the reserves) depends upon the reservoir characteristics and the method by which they are produced. The ratio of the proven reserve to the oil in place is called recovery factor.
Proven Reserves:
The proven reserves define the recoverable oil from
reservoirs that are reasonably well delineated and have normally been in production long enough so that sufficient data becomes available to permit material balanced calculations to be applied, in order to achieve a greater degree of accuracy.
Semi Proven Reserves:
Semi-proven reserves often refer to the reserves of discovered reservoirs which have not been sufficiently delineated or put into production to permit calculations to the degree of accuracy obtainable in the case of proven reserves. The reserves of such formations, for example, other than the main producing reservoir (although well delineated but not put in production) are sometimes also called Semi Proven.
Potential reserves:
The potential reserves are the probable reserves that could be estimated from knowledge of past exploration history and knowledge of the geology of the basin under consideration. Again, reserves are meant to be the recoverable portion of hydrocarbons in place. The economics of finding and its development dictates the exploration effort in search for additional reserves.
Reserves Growth:
The reserve estimate of any one reservoir improves with time as a result of further delineation of the reservoir’s extent, the oil zone thickness and the recovery factor from better understanding of the recovery mechanism and sweep efficiency. Generally, reserve estimates made towards the latter part of the production history of the reservoir are much higher than those made during the early part, partly because of improved knowledge, partly because of professional attitudes which are conservative whilst dealing with uncertainties and, occasionally, because of policy reasons concerning market or political conditions.
The IPC‟s published reserves throughout the 1960s were based on conservative recovery factors, by and large, and semi-proven reserves were excluded.
As knowledge of the reservoirs advances with time, revision is justifiably introduced. In the case of the southern Iraq oil fields, for example, Zubair reserves of 1.9 B bbl and North Rumaila reserves of 5.0 B bbl of earlier years
were increased to 4.5 B bbl and 8 B bbl respectively. Likewise, as knowledge of semi-proven reserves advances, their reserves may be upgraded and/or turned into proven reserves.
Estimate of Potential Oil Reserves:
Potential reserves are estimated from knowledge of past exploration history and knowledge of the geology of the basin under consideration. Again, reserves are meant to be the recoverable portion of hydrocarbons in place.
I have made a few estimates for Iraq‟s proven and potential reserves over the last 45 years. The results are such as I must say I have good reason to believe in the richness of Iraq reserves and the figures given below quantifying them and
that would not be surprised if the future exploration would reveal much larger ultimate total reserves.
These are being covered below in chronological as follows:
INOC Founded in 1964:
In 1966, under my supervision as the Executive Director in charge of the technical departments, the INOC geological and petroleum engineering departments, jointly with a credible team of American consultants from Frank Cole Engineering, carried out a study of potential oil reserves covering an area of approximately 215,000 sq km south of a horizontal line passing through the centre of the country near Baghdad and bound by the Iraqi boundaries from the south, east and west, but excluding the area surrounding the major producing fields of Rumaila and Zubair. Only 18 wells were drilled in the area. Ten found oil in commercial quantities and another two had encouraging shows.
References :
1. Formation evaluation upper Qamchuqa reservoir in Khbbaz Oil Field of Kirkuk , Northeastern Iraq , a Ph.D thesis by Fuad Mohammad Qdir , College of science , department of Gelogy , Bagdad University 1999.
2. Hihgh Resolution SEQUENCESTRATIGRAPHY AND PETROLEUMSYSTEM OF PALEOZOIC SEQUENCESIN WESTERN Iraq , an MS thesis presented by Ghazi Hassan Al Shara’a to College of Science , department of Geology , University of Baghdad 1978.
3. Practical geology of Iraq / 3rd year students course book For the Academic year 2010-2011 by Fadhil Ahmad Lawa & Taher Hama , University of Sulaimani , College of Science , Department Of Gelogy.
4. Hydrocarbon Generation Modeling of the Basrah Oil Fields, Southern Iraq , Thamer K. Al-Ameri1, Mohamed S. A. Jafar², and Janet Pitman , an AAPG Annual Convention and Exhibition, Houston, Texas, April 10-13, 2011.
5. Iraq's fourth bid round is scheduled for April 2012, as announced in May 2011 , an article published by Wood Mackenzie Upstream Service in December 2010 by Muhammed Abed Mazeel .
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