Abstract

The Upper Paleocene-Lower Eocene clastic reservoirs contribute one of the most important hydrocarbons producing horizons in the North Assam Shelf of Assam & Assam Arakan Basin. These reservoirs are characterised by the presence of normal gravity oil, low to intermediate gravity oil, gas and light oil/condensates. The sand stone reservoirs show complex wire line log signature, which are commonly misleading. Geochemical analysis of sidewall core extracts by thin layer chromatography with flame ionisation detection (TLC-FID) and gas chromatograph (GC) provide valuable, cost effective input for reservoir fluid characterisation. The important parameters needed to identify the nature and composition of the reservoir fluid include (1) the bulk composition of the sidewall core extract ( content of saturate, aromatic and nitrogen, sulphur and oxygen (NSO) compounds ) (2) amount of extract in mg/g of rock (3) GC finger print and (4) the ratio of pristane (Pr) to nC17 . These parameters integrated with geological and geophysical (wire line logs) evidence, yield more accurate and reliable formation evaluation criteria.