Petroleum Geology and Potential Hydrocarbon Plays in the Gulf Of
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Petroleum geology and potential AUTHOR A. S. Alsharhan ϳ Faculty of Science, hydrocarbon plays in the Gulf United Arab Emirates University, P.O. Box 17551, Al-Ain, United Arab Emirates; of Suez rift basin, Egypt [email protected] A. S. Alsharhan is professor of geology and A. S. Alsharhan dean of the Faculty of Science at the United Arab Emirates University. He holds a Ph.D. (1985) in petroleum geology from the University of South Carolina. He has authored ABSTRACT and published more than 80 scientific articles. He coauthored Sedimentary Basins and The Gulf of Suez in Egypt has a north-northwest–south-southeast Petroleum Geology of the Middle East (1997) orientation and is located at the junction of the African and Arabian with A. E. Nairn and Hydrogeology of an Arid plates where it separates the northeast African continent from the Region: Arabian Gulf and Adjacent Areas Sinai Peninsula. It has excellent hydrocarbon potential, with the (2001) with Z. Rizk, A. E. Nairn, D. Bakhit, and prospective sedimentary basin area measuring approximately S. Al-Hajari. He co-edited Quaternary Deserts 19,000 km2, and it is considered as the most prolific oil province and Climate Change (1998) with K. W. rift basin in Africa and the Middle East. This basin contains more Glennie, G. Whittle, and C. Kendall and than 80 oil fields, with reserves ranging from 1350 to less than 1 Middle East Models of Jurassic/Cretaceous million bbl, in reservoirs of Precambrian to Quaternary age. The Carbonate Systems (2000) with R. W. Scott. lithostratigraphic units in the Gulf of Suez can be subdivided into His research interests include Holocene three megasequences: a prerift succession (pre-Miocene or Paleo- coastal sabkhas of the Arabian Gulf region and the geology and hydrocarbon habitats of zoic–Eocene), a synrift succession (Oligocene–Miocene), and a the Middle East and North Africa. He is a postrift succession (post-Miocene or Pliocene–Holocene). These member of the AAPG, SEPM, International units vary in lithology, thickness, areal distribution, depositional Association of Sedimentologists, and environment, and hydrocarbon importance. Geological and geo- Geological Society of London. physical data show that the northern and central Gulf of Suez con- sist of several narrow, elongated depositional troughs, whereas the southern part is dominated by a tilt-block terrane, containing nu- ACKNOWLEDGEMENTS merous offset linear highs. I would like to thank M. G. Salah, who Major prerift and synrift source rocks have potential to yield oil sparked my enthusiasm for the fascinating ge- and/or gas and are mature enough in the deep kitchens to generate ology of the Gulf of Suez rift basin and coau- hydrocarbons. Geochemical parameters, sterane distribution, and thored with me many of the articles on this biomarker correlations are consistent with oils generated from ma- subject. I also thank A. Fowler, who read the rine source rocks. Oils in the Gulf of Suez were sourced from po- early draft of this article and offered valuable tential source rock intervals in the prerift succession that are typi- suggestions. Thanks go to P. E. Binns and R. P. cally oil prone (type I), and in places oil and gas prone (type II), or Martinsons who reviewed this article for are composites of more than one type (multiple types I, II, or III AAPG. for oil prone, oil and gas prone, or gas prone, respectively). The reservoirs can be classified into prerift reservoirs, such as the Precambrian granitic rocks, Paleozoic–Cretaceous Nubian sand- stones, Upper Cretaceous Nezzazat sandstones and the fractured Eocene Thebes limestone; and synrift reservoirs, such the Miocene sandstones and carbonates of the Nukhul, Rudeis, Kareem, and Be- layim formations and the sandstones of South Gharib, Zeit, and Copyright ᭧2003. The American Association of Petroleum Geologists. All rights reserved. Manuscript received February 28, 2001; provisional acceptance December 5, 2001; revised manuscript received May 23, 2002; final acceptance June 20, 2002. AAPG Bulletin, v. 87, no. 1 (January 2003), pp. 143–180 143 post-Zeit. The majority of oil fields in the region in- the eastern side of the Gulf of Suez and discovered the corporate multiple productive reservoirs. Miocene noncommercial Abu Durba oil field. Ras Gharib was evaporites are the ultimate hydrocarbon seals, whereas the field providing the first commercial oil and is the the shale and dense limestones of the prerift and the most prolific in the area. It was discovered in 1938 on synrift stratigraphic units are the primary seals. Struc- the western side of the Gulf of Suez by the Standard tural, stratigraphic, and combination traps are encoun- Oil Company of Egypt. Drilling ceased during the Sec- tered in the study area. The Gulf of Suez is the most ond World War and recommenced in 1946. The ex- prolific and prospective oil province in Egypt, and any ploration activity in the Gulf of Suez and in Egypt has open acreage, or relinquished area, will be of great in- been affected by changes in the political environment terest to the oil industry. and has passed through several phases of activity. From 1970 onward, the Egyptian government encouraged foreign oil companies, leading to continuous and inten- INTRODUCTION sive exploration. At present, the Gulf of Suez oil basin has more than 1000 exploration wells, resulting in 240 The Gulf of Suez is bounded by long. 32Њ10Ј and 34ЊE oil discoveries in more than 80 oil fields (Figure 2), and lat. 27Њ and 30ЊN (Figure 1) and is known to be a with reserves from 1350 to less than 1 million bbl, in Clysmic Gulf (Robson, 1971), a rejuvenated, slightly reservoirs ranging in age from Precambrian to Quater- arcuate northwest-southeast–trending taphrogenic de- nary. The purpose of this article is to illustrate the com- pression. It is an intracontinental, late Oligocene rifted parative influences of geology, hydrocarbon potential, basin but was originally formed during the early Paleo- and tectonism on hydrocarbon generation, migration, zoic as a narrow embayment of the Tethys that was and accumulation within the basin and to clarify the intensively rejuvenated during the rifting phase of the controls on hydrocarbon occurrences and hydrocarbon great East African rift system in the Paleogene (see also potential in the Gulf of Suez onshore and offshore Bosworth et al., 1998; Montenat et al., 1998; Jarrige regions. et al., 1990). The Gulf runs in a northwest-southeast direction and forms an elongated graben measuring about 320 km in length, with width ranging between LITHOSTRATIGRAPHY 30 and 80 km, and water depth only 40–60 m. It is bounded by two major sets of marginal faults. Paleo- The stratigraphy, age, and lithological characterization zoic–Tertiary strata and huge Precambrian basement of rock units described in this article from the Gulf of blocks are exposed on both sides of the Gulf of Suez. Suez region (i.e., western Sinai Peninsula, offshore the Surface hydrocarbons are uncommon and found Gulf, and Eastern Desert) relies on data from measured only in the southern part of the Gulf of Suez. Asphaltic stratigraphic sections and subsurface cores, electric logs impregnations have been found in alluvial sands, and tied to microfaunal and palynological studies of ditch seeps exist mainly in Pliocene and Pleistocene lime- samples, and rock thin sections. These data are incor- stones. Oil was first found in the Gulf of Suez in 1886, porated with reference to previous studies, such as Sa- when crude oil seeped into tunnels that had been dug dek (1959), Abdallah et al. (1963), Egyptian General to extract sulfur in the Gemsa area, on the western Petroleum Corporation Stratigraphic Committee coast of the Gulf of Suez (Schlumberger, 1995). Sub- (1964), Issawi (1973), Mazhar et al. (1979), Beleity sequently, drilling was conducted close to the surface (1982), Webster (1982), Sellwood and Netherwood oil seeps in the west coastal strip of the southern Gulf (1984), Beleity et al. (1986), Barakat et al. (1986, of Suez, resulting in the discovery of the Gemsa oil 1988), Darwish (1992), Darwish and El-Araby (1993), field in 1907, the first oil discovery in the Middle East and Alsharhan and Salah (1994, 1995). The lithostrat- and Africa. Oil also was found in 1918, when the An- igraphic units in the study area range from Precambrian glo Egyptian Oil Company drilled near an oil seep on to Holocene in age and have been divided into three Figure1. Tectonic setting and major tectonic developments. Successive group of tilt blocks with regional dips. The homogeneous tilt provinces are separated by tectonic boundaries (transform faults), which are the effects of Aqaba faults that acted as strike-slip faults during the early stage of the rift structuration (compiled from Jarrige et al. [1990]; Alsharhan and Salah [1994, 1995]; and Montenat et al. [1998]). Insert figure shows location map of Egypt and Gulf of Suez study area. 144 Hydrocarbon Potential in the Gulf of Suez Rift Basin (Egypt) Alsharhan 145 Figure2. Major oil fields in the Gulf of Suez. 146 Hydrocarbon Potential in the Gulf of Suez Rift Basin (Egypt) major sequences relative to the Miocene rifting event: strata known as Tayiba red beds were deposited in the postrift lithostratigraphic units (post-Miocene units), late Oligocene and are sporadically distributed, having synrift lithostratigraphic units (Miocene units), and accumulated during the early stages of rifting in the prerift lithostratigraphic units (pre-Miocene units). central and northern Gulf of Suez regions. The Mio- These units vary in thickness and other facies attributes cene sequences were previously subdivided into two within the Gulf of Suez. A generalized lithostrati- main groups, the Gharandal and Ras Malaab (Table 2). graphic scheme of the study area is given in Figure 3 The term “Gharandal” was introduced by the An- and Tables 1, 2, and 3.