Publication Date:
2005-10-01
Description:
Silurian organic-rich (hot) shales were the source of large amounts of hydrocarbons in northern Gondwana, with supergiant and giant fields in the Middle East and North Africa. A study of these black shales has been conducted in Jordan, where they represent the source for the Risha gas field. Two organically enriched horizons occur in the Silurian in Jordan, termed the lower hot shale and the upper hot shale. Deposition of the transgressive lower hot shale occurred during the early Llandoverian and was restricted to the earliest Silurian paleodepressions. Three lower hot shale depocenters have been identified in Jordan; they are located in the western Risha, eastern Wadi Sirhan, and Jafr areas. The eastern Risha area was part of a larger scale paleohigh covering northeast Jordan, most of Syria and Iraq, and north-central Saudi Arabia (Qusaiba area). At least in Jordan, the high coincides with the depocenter of the latest Ordovician glaciation. Sedimentation of the upper hot shale occurred around peak sea level during the late Llandoverian and/or early Wenlockian and was limited to the distal parts of the shelf (Risha area), in front of the prograding silty-sandy deltaic front. Thermal maturity increases from immature in the Southern Desert outcrops to late or postmature in northern Jordan. Organic richness and pyrolysis data deteriorate significantly with increasing thermal maturity because of hydrocarbon generation. Prior to maturation, maximum organic richness is interpreted to have considerably exceeded 10% with good S2 (remaining generative potential) yields, as reflected in the values of the immature lower hot shale in the shallow borehole BG-14 in the Southern Desert outcrop area and exploration well Hunt JF-1 in the Jafr area. Identification and isopach mapping of the lower hot shale is based on its characteristic uranium enrichment. The gamma-ray/total organic carbon correlation coefficient increases with increasing maturity, suggesting that uranium is less vulnerable to maturity effects than the organic matter itself. The gamma-ray log, therefore, can be used as a proxy for the prematuration organic richness, representing a suitable basis for cross-basin comparisons of original organic richness trends. A two-phase generation of hydrocarbons is interpreted for both the Risha and Wadi Sirhan areas, with the first as a pre-Hercynian phase in the Carboniferous and the second as a less intense generation phase during the Mesozoic to early Tertiary. In contrast, gas generation of the Silurian-sourced giant fields in the central part of the Arabian Peninsula and Iran was restricted to the post-Hercynian. In Jordan, both structural and stratigraphic play concepts are envisaged, including fault, paleohigh, and channel plays. Key elements that need attention in future exploration of the Silurian plays in Jordan are Ordovician reservoir quality and timing of maturation. Poor permeabilities have been reported from wells in both the Risha and Wadi Sirhan areas. Sebastian Lüning studied geology and paleontology at the University of Göttingen, Germany, and completed his studies with a thesis on terrane tectonics in northwest Thailand. For his Ph.D. project at the University of Bremen, he investigated Upper Cretaceous sequence stratigraphy, biostratigraphy, and geodynamics of the Sinai Peninsula (Egypt). Since 1997, Lüning's research interest has focused on play elements and the petroleum potential of Paleozoic sedimentary basins in North Africa and the Arabian Peninsula. Initially, these studies were carried out on assignment for the former London-based independent Lasmo plc (now ENI). Subsequent projects were funded by the German Research Foundation (Deutsche Forschungsgemeinschaft) and, since 2002, by the international research consortium North Africa Research Group as well as individually by other companies, such as Shell and Exxon. Lüning also produces exploration training videos that are published through Seven-Continents.com Science Productions.Yosef Shahin studied geology at the University of Jordan (B.Sc.) and completed a master's degree in geology from Queens College, the City University of New York. His master's thesis discusses the Silurian stratigraphy of northeast Jordan. Since 1985 and during his work with the Natural Resources Authority (NRA) of Jordan, Shahin's studies and interests have been on the stratigraphy and hydrocarbon potential of Paleozoic rocks in Jordan and their correlation with their similar sections in Saudi Arabia and western Iraq. Shahin participated in studies on the Paleozoic hydrocarbon potential of Jordan and the neighboring countries, sponsored by Futyan, Jawzi and Associates (1994) and NRA and Petronas (1996–1997). In 1998, he worked with Anadarko as senior stratigrapher in their project in Jordan (1998). Shahin is currently the head of Petroleum Studies and Contracts at NRA and a geological consultant with Trans Global Petroleum Jordan Ltd. David Loydell is a senior lecturer at the University of Portsmouth, United Kingdom. He received his Ph.D. in 1989 for a study of the graptolites biostratigraphy of the Aberystwyth Grits and associated turbidite systems of mid-Wales and taxonomic work on Llandoverian graptolites from Sweden. Loydell's more recent work has been on Silurian sea level changes, with the erection of a new sea level curve for the Early Silurian, and on integrated biostratigraphy—correlating deeper water graptolitic sequences with shallower water sequences bearing conodonts and chitinozoans. His current research focuses on the graptolite biostratigraphy of hot shales in the Middle East and North Africa. David is the vice president of the Palaeontological Association, is a titular member of the International Union of Geological Sciences Subcommission on Silurian Stratigraphy, and currently chairs the Subcommission's working group on the Llandoverian–Wenlockian boundary. Hisham Al-Rabi received his engineering degree in mining and geology from Belgrade University in 1976. Between 1976 and 1983, he worked as an exploration geologist in the Iraq National Oil Company (Southern Petroleum Organization). Since 1983, he has been working as an exploration geologist with focus on log evaluation and stratigraphic correlation with the Natural Resources Authority of Jordan, where he is currently the director of Information and Investment. Ahmed Al Masri received his master's degree and D.I.C. in structural geology from Imperial College in the United Kingdom. He has had training in structural geology and remote sensing in the United Kingdom. Since 1985, he has been working as a field geologist in the 1:50,000 National Mapping Project with the Natural Resources Authority of Jordan, where he has concentrated on the Jordan rift valley. His research interests include stratigraphy and stress analysis. Bassam Al Tarawneh received his B.Sc. degree in geology from Baghdad University in Iraq. He has had training in sedimentary rocks, structural geology, paleontology, and remote sensing. Since 1981, he has been working as a field geologist for Gympsum Exploration and the 1:50,000 National Mapping Project with the Natural Resources Authority of Jordan. Currently, he is the head of the Geological Mapping Division (NRA). His research interests include stratigraphy and sedimentology. Sadat Kolonic obtained his diploma in geology in 2000 and his Ph.D. in petroleum geology and geochemistry in 2003 from the University of Bremen, Germany. In his Ph.D., he mainly worked on Cenomanian–Turonian black shales from the Tarfaya-Layoune basin (southwest Morocco). After his Ph.D., he joined ENI as postdoctoral fellow and became the coordinator and main contributor of a multidisciplinary study dealing with infra-Cambrian basins in the Sahara. In August 2004, Kolonic joined Shell Exploration and Production Research and Development as exploration geochemist in the Hydrocarbon Prediction and Detection Group, working within an integrated geology and geophysics team on exploration
Print ISSN:
0149-1423
Electronic ISSN:
1943-2674
Topics:
Geosciences
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