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The AAPG/Datapages Combined Publications Database

Southeast Asia Petroleum Exploration Society (SEAPEX)


Proceedings of the South East Asia Petroleum Exploration Society Volume X, 1992
Pages 159-169

An Organic Geochemical Study of the Oil, Condensate and Seep Samples from the Bengal Basin, Bangladesh

Mahaboob Alam


Seventeen oil, condensate, seep and oil soaked sandstone samples over a wide range of geographic region from the Bengal Basin, Bangladesh were studied using computerised gas chromatography and mass spectrometry The major aim of this study is to classify crude oils and seep samples from the Bengal Basin into genetically related families based on their biomarker composition. Therefore, for the purpose of this study, distributions of various classes of biomarker compounds have been used as the primary tool for the classification of oil types and the determination of possible source racks.

As part of the process of assessing the petroleum potential of an area, any liquid (oil, condensate) or oil seeps are exhaustively analysed. Their chemical properties are examined in detail to determine whether or not they have a common origin, what kind of source rocks they were derived from and how mature or deeply buried those source rocks were when migration began. In modern day petroleum exploration, organic geochemistry, particularly the biomarker geochemistry has proven to be an essential tool in assessing key exploration parameters, such as thermal maturity, organic facies, oil-oil, oil-source rock correlation and biodegradation.

Bengal Basin oils can be divided into two groups on the basis of biomarker distribution (i) Group I, those occurring in Surma Basin in the north with abundant bicadinanes, and (ii) Group II oils, occurring in the foredeep region without any bicadinanes. The Surma Basin oils are parafinic waxy oils with a varying amount of high molecular weight n-alkanes typical of generation from source rocks rich in land plant materials. The oil samples from Surma Basin have broadly similar maturity indicating that they had been generated at around peak oil maturity of the source. The condensate and oil-sand samples from the foredeep region are of lower maturity and had been generated at the early stage of oil generation also from a definitely terrestrial source rock.

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