Geochemical Evaluation of (Late Jurassic) Naokelekan Formation /Zagros Fold Belt, North Iraq

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1 Proceeding of 3 rd scientific conference of the College Al-Ahmed Proceeding of 3 rd of Science, University of Baghdad. scientific conference, 2009, PP to 26 March Geochemical Evaluation of (Late Jurassic) Naokelekan Formation /Zagros Fold Belt, North Iraq Ahmed Asker Al-Ahmed Department Of Chemistry, College of science, University of Al Nahrain Baghdad Iraq Expert in Arab Petroleum Training Institute, OAPEC - Baghdad Iraq. Abstract Techniques used to assess the petroleum potential of source rocks may put into two broad categories, optical and chemical. Each has its respective strengths and limitations.in rigorous exploration programme neither would be used in isolation; rather both would be applied in a complementary fashion. Chemical and optical analysis where carried out to evaluate hydrocarbon potential of Naokelekan Formation within zagros fold belt north Iraq. Core and cutting samples recovered from encountered subsurface layers of three exploratory wells, Makhul-2, Taq Taq -1, and Kirkuk 109, further more samples recovered from the type locality of the studied formation. Both chemical and optical analysis corresponding kerogen type II within maturity zone and the organic matter extracted by palynological processed samples are declared on slides, shows amorphous organic matter (AOM) of type A, deposited in distal, anoxic basin. Almost all subsurface samples contain over (20 wt %) value of total organic carbon (TOC) with Rock Eval hydrogen indices between (20-600) corresponding Tmax value (440 c) within the oil generative window. Accordingly, very good hydrocarbon generation potential is predicted for this source rock formation Introduction The Naokelekan Formation was first recognized and described by Wetzel and Morton (1950), near Naokelekan, Rawanduz district, north east Iraq, at roadside and stream bed, 500m north west of Naokelekan village, at approximately 36 36' 00" N ; 44 44' 10" E. The type section is 14m thick (Bellen et al., 1959), (Fig1). Lithology of the formation consist of laminated shaly Limestone, at the top, the next underlying 4 meters are limestone's hard, dark grey, the lower most 7 meter are of thin bedded, extremely bituminous limestone's and dolomites with intercalated,black, bituminous calcareous shale's (coal horizons).based on palynological study the age is assigned to lower kimmeridgian at the base and no indication age was to determine the age at the top of the formation. (Bellen et al, 1959). Naokelekan Formation is overlying Sargelu Formation (Middle Jurassic ) With contact apparently conformable,both yielded the bulk of the oil that charged reservoir rocks in the Mesopotamian Basin and Zagros fold Belt (Beydoun et al., 1992 ; Sadooni, 1997 ; Alshididi et al., 1995, Pitman et al.,2004 and Al Ahmed, Barsarin Formation overlying Noakelekan (not clear in type section) in subsurface definitely in Taq Taq-1, Makhul-2 and Kirkuk-109 wells, Naokelekan Formation overlying with Gotnia Formation in Qarachuq-1 and AJeel-8 oil wells, whilst Naokelekan is completely obscured in Jabal Kand-1, Butmah-15 oil wells ( final well reports). The underlying (Posidonia bed), (plate 1,2) of the Sargelu Formation are certainly of middle Jurassic age (Al-Ahmed, 2001), and the upper most Callovian faunally represented. Palynostratigraphical show sequence and conformable layers, so no hiatus has been observed in the field, between Sargelu and Naokelekan Formations. Coal horizon 9671

2 comprising limestone and shale's are so rich in bitumen are well identified in the slides.the formation is named from the Naokelekan section, which is readily accessible. The most fossiliferous beds yet encountered in the formation are those of the (Coal horizon) at Naokelekan (Wetzel, et al, 1950) (unpublished report) Fig-1-Map shows location of studied wells and a photo of out crop within Zagros Fold Belt Plate 1 (Posidonia) Plate 2 :(Posidonia bed)

3 Jurassic Total Petroleum System(JTPS) Passive margin condition a long the Arabian plate during the Jurassic through late Cretaceous periods produced a broad stable shelf environment. Flooding of this platform in warm equatorial latitudes allowed for continued deposition of shallow-marine carbonates over the greater Arabian basin (Murris, 1980; AL- Husseini, 1997). In particular, Jurassic geologic condition of the Arabian subcontinent resulted in deposition of the following ideal sequence of primary petroleum system elements thick oil prone source rocks, extensive reservoir facies, and excellent seals, with secondary elements, widespread Early and middle Jurassic marine transgression deposited a thick sequence of shallow marine shelf carbonates and plat from evaporites. late Jurassic differential subsidence and sea level rise resulted in the formation of broad, intra shelf sub basins Fig 2 these intra shelf sub basins were depocenters for the main Jurassic rocks(upper Jurassic) Middle and upper Jurassic Source rocks are recognized in the Sargelu and Naokelekan Formation of Iraq. These source rocks were deposited in the Gotnia / Garau intra shelf basins were probably tectonically controlled these source levels are capped by persistent top Jurassic evaporites (Gotnia Formation) beydoun el at Fig.2 prograding sargelu Najmah ramp system (Hydro) Oil and gas accumulated in middle to upper Jurassic, high energy calcarenites and oolites of shelf margin origin. These reservoirs are cyclic and inter bedded with organic rich (2-5 wt% TOC), muddy lime source rocks that were deposited under anoxic and dysoxic condition in the restricted, inter shelf Gotnia sub basin (fig3) (USGS 2000). Fig-3 Schematic Section through the Middle-Late (Gotnia Basin) Hydro

4 Optical analysis Palynological process carried out to isolate organic matters (Batten, 1999) (Plate 2).The isolated organic matter could well identify as Amorphous Organic Matter of type A(Thompson et al., 1986) which generates oil according to the characteristic features, this method consider as the initial assessment to reduce risks, and to determine the promising potential areas that generates hydrocarbons Hydrocarbon Potential Rock-Eval analysis supplied by Oklahoma University and GeoMark Research, LTD of Houston, Texas (2006) show that the analyzed samples of Naokelekan Formation declared that quantity of petroleum generated and expelled increases as atomic hydrogen-to-carbon H/C ratio of the organic matter increases (Hunt,1995). Quality indicated accordingly of type II oil prone usually marine (Fig. 3), hydrogen index potential attained 600 mg HC/g Toc (Fig. 4). Plate- 2: shows AOM extracted from Mk-2 oil well (Mag x 400 With maturation calculated vitrinite reflectance from Tmax referred to MK-2 samples within oil Zone, while Taq-1 within condensate-wet Gas zone (Fig. 5). Fig-3- kerogen quality

5 Fig -4- kerogen type and maturity Fig-5- kerogen conversion and maturity

6 Table- 1 results of Rock Eval pyrolysis Conclusion Microscopic and chemical approach refers to the studied formation as a good source potential for hydrocarbons since the recent studies focusing on middle and upper Jurassic age as either the main source for petroleum or may consider as a good reservoir rocks meantime almost all total petroleum system consequences referred to certain typical section generating and migrating then accumulating super giant oil with subordinate gas not even in Iraq but in the surrounding countries.the studied Formation is added to such potential unit rocks that injects oil among other generative ones.

7 References 1. Bellen V., Dunnington R., Wetzel H., Morton D., 1959.Lexique stratigraphique international, 0310 Asie (Iraq). 333P. Reprinted by Gulf petrol link (2005). 2. Al Ahmed A., 2001 "Palynofacies indications of depositional environment and source potential for hydrocarbon (middle Jurassic) Sargelu Formation Northern Iraq ". M sc Thesis (Unpublished) College of Science. Univ. of Baghdad 100P (in Arabic). 3. AL Ahmed A., 2006" Organic Geochemistry, Palynofacies and Hydrocarbon Potential of Sargelu Formation (middle Jurassic) Northern Iraq. PhD Thesis (Unpublished) College of Science. Univ. of Baghdad 116 p. 4. Beydoun Z., Hughes Clark. Stoneley R., Petroleum in the Mesopotamian basin. A Late tertiary foreland basin overprinted on to the outer edge of a vast hydrocarbon-rich Paleozoic Mesozoic passive-margin shelf. In R. W. Mac queen and D. A. Leckie (Eds.), Foreland Basin and Fold Belt. AAPG Memoir 55.P Sadooni F., 1997 Stratigraphy and petroleum prospects of upper Jurassic carbonates in Iraq.petroleum Geosciences: v.3, P Alshididi, S., Thomas G., Delfaud J., 1995 Sedimentology, digenesis and oil habitat of lower cretaceous Qamchuqa Group, North Iraq AAPG Bulletin: V.79 P Pitman J., Stienshouer D., Lewan M., 2004, Petroleum generation and migration in the Mesopotamian Basin and Zagros fold Belt of Iraq result from a basin modeling study Vol. 9 No.4, Gulf Petrolink Bahrain P Al-Husseini M., 1997, Jurassic sequence stratigraphy of the western and southern Arabian Gulf, Geo Arabia, V.2, P Batten D., 1999 Palynofacies analysis, in Jones, T.P. Rowe & N. P. (eds) Fossil plant spores, modern techniques. Geological society, London, Thompson C., Dembicki H, 1986 Optical characteristics of amorphous kerogens and the hydrocarbon generating potential of source rocks int. Journal of coal Geology V.6, Hunt J., Petroleum Geochemistry and Geology. W. H. Freeman and company, New York 743 P.