Abstract

The Surma Basin is situated in the north-eastern part of Bangladesh and forms a portion of the Bengal Basin. About eight TCF of gas and thirty four MMSTB of condensate have been estimated as recoverable reserve from six gas/condensate fields of the Surma Basin. The recent discovery of oil in Sylhet-7 has opened a new avenue for the exploration geologists to establish the geological condition in the basin responsible for generation, migration and accumulation of liquid hydrocarbon. An extensive geological and geophysical (mostly seismic) survey have been carried out in order to describe stratigraphy, regional setting, structural evolution, condition of deposition of sediments and paleogeography of the basin. The present paper comprises the detail geological and geochemical studies to evaluate the hydrocarbon prospects of the area under reference.

Geochemical analyses of oil, oil seep, condensate, gas core and cutting samples of six wells have been studied. The results are integrated with the regional geological information to identify the probable source rock of the hydrocarbon discovered and to locate the new areas of high potential for concentrated petroleum occurrence.

The study reveals that all the gases discovered in the Surma Basin are genetically similar to each other and are generated probably from terrestrial kerogen at various levels of maturity equivalent to approx. 0.6 to 1.30% vitrinite reflectance (Ro). Condensates produced with the gases may have originated from terrestrial kerogen as well as maturity greater than 1.0% Ro. Oil from Patharia and Sylhet-7 have similar characteristics and may have sourced from the Oligocene sediments. On the basis of the limited data, Oligocene sections penetrated in Atgram contain 0.6–1.59% organic carbon derived from terrigenous source and may have good potential for oil generation together with significant quantities of gas. Good possibilities exist for moderate oil accumulation in the undisturbed Oligo-Miocene reservoirs close to the generative depressions.