Lower Palaeozoic Petroleum Systems of Western Iraq with Reference to Jordan*
The Lower Palaeozoic of northwest Arabia is characterised by similar major chrono stratigraphic rock units, covering vast areas of eastern Jordan, northwest Saudi Arabia, eastern Syria and western Iraqi deserts. It is the most under explored succession in Iraq, but it is considered to have significant exploration potential. The Lower Silurian marine (hot) shale is the main proven source rock for the Palaeozoic hydrocarbons discovered in the area of study. However, some Upper Ordovician black shales (of the Khabour Formation of Iraq and its equivalent in Jordan) are also expected to be additional local source rocks within the region. Conversely, the Lower Ordovician Hiswah graptolitic shales of Jordan are originally lean, where analysed, and are not considered a major hydrocarbon source rocks. Similarly, preliminary geochemical results show that the Middle Cambrian Burj limestone does not have significant source potential in the marginal Jordanian wells, although it may have some potential where deposited in a more basinal settings such as in western Iraq. Several promising sandstone reservoir rocks (of Cambrian, Ordovician, and Early Silurian ages) are present across the study area. However, the reservoir quality is a major exploration risk as most of these sandstones have been severely affected by quartz overgrowth and clay cementation. Only some Upper Ordovician Dubaydib subsurface sandstones of Jordan have chlorite clay coatings, which prevented formation of the quartz overgrowth, preserving good reservoir quality. Seals are also available all over the region both on local and regional scales; these include (but are not limited to) the shales and carbonates mentioned above as potential source facies. The widespread occurrence of potential source, reservoir and seal rocks suggests that Lower Palaeozoic prospects below the deserts of western Iraq are quite promising frontiers for future hydrocarbon exploration. References Al Haba, Y.K. A. Al Samarrai, F. Al Jubouri, N.N. Georgis, and I.M. Ahmed, 1994, Exploration for the Paleozoic prospects in western Iraq, Part 1: exploration of the Paleozoic system in western Iraq: Second Seminar on Hydrocarbon Potential of Deep formations in the Arab Countries (OAPEC) Cairo, p. 1 21. Al Hadidy, A.H. 2007, Paleozoic stratigraphic lexicon and hydrocarbon habitat of Iraq: GeoArabia, v. 12/1, p. 63 130. Aqrawi, A.A.M. A.D. Horbury, 2010, Aqrawi, A.A.M. 1998, Paleozoic stratigraphy and petroleum systems of the western and southwestern deserts of Iraq: GeoArabia, v. 3/2, p. 229 248. Jassim, S.Z. 2006, Palaeozoic megaquences (AP1 AP5) in S.Z. Jassim, and J.C. Goff, (eds. Geology of Iraq: Dolin, Prague and Moravian Museum Brno, Czech Republic, p. 91 103. Jassim, S.Z. and M. Al Gailani, Hydrocarbons in S.Z. Jassim, and J.C. Goff, (eds. Geology of Iraq: Dolin, Prague, and Moravian Museum Brno, Czech Republic, p. 232 250. Konert, G. A.M. Al Afifi, S.A. Al Hajri, and H.J. Droste, 2001, Paleozoic stratigraphy and hydrocarbon habitat of the Arabian Plate: GeoArabia Manama, v. 6/3, p. 407 442. Sharland, P.R. R. Archer, D.M. Casey, R.B. Davies, S.H. Hall, A.P. Heward, A.D. Horbury, and M.D. Simmons, (eds. 2001, Arabian Plate Sequence Stratigraphy: GeoArabia Special Publication, v. 2, Gulf PetroLink, Bahrain, 371 p. Sharland, P.R. D.M. Casey, R.B. Davies, M.D. Simmons, and O.E. Sutcliffe, 2004, Arabian plate sequence stratigraphy; revisions to SP2: GeoArabia Manama, v. 9/1, p. 199 214. Verma, M.K. T.S. Ahlbrandt, and M.B. Al Gailani, 2004, Petroleum Reserves and undiscovered resources in the total petroleum systems of Iraq: Reserve growth and production implications: GeoArabia Manama, v. 9/3, p. 51 74.