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AAPG Bulletin, V.
Origin of petroleum in Bangladesh
1Unocal Corporation, 14141 Southwest Freeway, Sugar Land, Texas, 77478; email: [email protected]
2Unocal Corporation, 14141 Southwest Freeway, Sugar Land, Texas, 77478
3Unocal Corporation, Lake View, House 12, Road 137, Dhaka, Bangladesh 1212
414431 Broadgreen Avenue, Houston, Texas, 77079
5Bangladesh Oil, Gas and Mineral Corporation (Petrobangla), 3 Kawren Bazar, Dhaka, Bangladesh 1215
Joseph A. Curiale is a senior consulting geochemist with Unocal Corporation in Sugar Land, Texas. He received his B.A. degree in chemistry with a specialization in the earth sciences from the University of California at San Diego in 1977 and his Ph.D. in geology from the University of Oklahoma in 1981. He joined Unocal in 1981 and has evaluated petroleum and source rock geochemical data from numerous basins worldwide. His interests include the application of isotope and molecular marker geochemistry to the problems of petroleum exploration, development, and production. Since 1993 he has served as co-chief editor of Organic Geochemistry.
George Covington is a geologist with Unocal Gulf Region USA in Sugar Land, Texas. He graduated with a B.S. degree in geological engineering and an M.S. degree in geology from the Colorado School of Mines. He joined Unocal as an exploration geologist in 1967, where he worked on a variety of exploration projects in the basins of the Rocky Mountains. Transferring to Midland, Texas, he held several positions, ranging from regional exploration manager to South Permian asset manager. In 1994 he transferred to Sugar Land, Texas, in international exploration, where he worked on a variety of exploration projects in the Middle East, Mexico, Venezuela, and Brazil. Since 2000, he has worked in the Gulf of Mexico as a development and exploitation geologist. His focus is on generating viable oil and gas prospects.
A. H. M. Shamsuddin has worked with Unocal Corporation as a consulting geologist-geochemist since 1995, and he is chief geologist of Unocal Bangladesh. Before joining Unocal, he worked about nine years in the Research Laboratory Division of Bangladesh Oil, Gas and Mineral Corporation (Petrobangla), where his work focused on source rock geochemistry, basin evaluation, and the petroleum systems of Bangladesh. He received his M.Sc. degree (1980) in applied geology and his Ph.D. (1986) in petroleum geology from Moscow State University. He was also a postdoctoral fellow at the Institute Francais du Petrole (IFP), France, in 1992, where he spent more than a year researching organic geochemistry and basin modeling.
Javier Alejandro Morelos-Garcia received his B.S. degree in geology from the Instituto Politecnico Nacional in Mexico and his Ph.D. in organic geochemistry from the University of Texas at Dallas in 1995. He now works at Humble Geochemical Services (HGS) in Humble, Texas. Prior to his current position at HGS, he worked with Unocal's deep-water assessment team. His research interests are integrated petroleum basin and reservoir assessment, petroleum systems analysis, and source rock and petroleum fluid characterizations.
A. K. M. Shamsuddin is currently working as a managing director of Western Gas Company Ltd. (WES GAS), a subsidiary of Bangladesh Oil, Gas and Mineral Corporation (Petrobangla). Prior to being posted to WES GAS, he worked in different departments of Petrobangla, including the petroleum concession division. He has also worked for the Ministry of Petroleum, Government of Iraq (1982-1983). He graduated in mining engineering in 1969 and obtained his M.Sc. degree in 1975. In 1980, he received his postgraduate diploma on mineral exploration from Delft University, the Netherlands.
We gratefully acknowledge the release of geochemical data from the Bangladesh Oil, Gas and Mineral Corporation. Some of the data contained herein were originally obtained by APTI Geosciences, GeoMark Research, Geochem Group Ltd., Core Laboratories, Bundesanstalt fur Geowissenschaften und Rohstoffe, the Anglo Scandinavian Petroleum Group, and the Welldrill Group, and we appreciate the ability to use these data. We benefited from technical discussions with A. G. Douglas and with the Bangladesh resource assessment team at Unocal. We also thank Frank Wright for drafting assistance and Unocal and Petrobangla for permission to release and publish these data and interpretations. We appreciate the important and helpful comments of our AAPG reviewers, W. J. Wade and P. K. Mukhopadhyay. Finally, and most importantly, we sincerely thank AAPG reviewer G. E. Claypool, whose insightful comments caused us to rethink-for the better-our interpretations and conclusions.
Fewer than 70 exploration wells have been drilled in Bangladesh (207,000 km2), mostly in the eastern onshore and offshore areas, making it one of the least explored countries in the world. Tectonic developments have controlled the accommodation space available for sediment deposition since the Early Cretaceous. Collision between the Indian plate and Eurasia to the north of Bangladesh and between the Indian plate and the Burma platelet on the east provided favorable conditions for development of Oligocene-Miocene source rocks and Miocene reservoir sands in eastern Bangladesh. The resulting Jenam-Bhuban Boka Bil petroleum system is the most active system identified to date and is dominant in eastern Bangladesh. Hydrocarbons likely also have been generated from the organic-rich shales of the Miocene Bhuban formation. The Jenam-Bhuban Boka Bil petroleum system alone is responsible for the generation of more than 16 tcf of gas in place discovered to date, mostly in the Surma basin of the Chittagong-Tripura fold belt. Several other petroleum systems have been postulated in Bangladesh. Together, the best technical estimate of the total resource base is about 61 tcf, including reserves within the discovered fields, anticipated field growth, and new field discoveries.
With the exception of small bacterial contributions in some surface seep gases and two subsurface accumulations, the gases of Bangladesh are thermogenic. Modeling results indicate that the gases and associated condensates are sourced at peak generation depths of at least 6 km. Many of the gas accumulations are associated with retrograde condensates whose compositions are defined by two distinct source facies and by the solution/exsolution effects of vertical migration. Most of the condensates possess molecular signatures that indicate a major hydrogen-rich, angiospermous (flowering land plant) contribution to the organic matter of their source rock(s). The carbon isotope ratios of the methane in the gases and the isotopic and molecular characteristics of the associated condensates indicate a distinct source facies for petroleums of the northern Surma basin relative to those in the south. These isotopic and molecular results, when interpreted in light of the geological framework and our basin models, suggest that the Oligocene Jenam formation is the major contributor north of 24.4 degreesN and that the Miocene Bhuban formation is the major contributor to the south.
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