SEQUENTIAL EXTRACTION - A USEFUL TOOL FOR RESERVOIR GEOCHEMISTRY

Little is known about the microscale distribution and potential molecu lar fractionation of bitumen residing in reservoir rocks. Few data exi st on the comparative organic geochemistry of hydrocarbons in authigen ic inclusions formed in reservoir rocks and the bitumen in the pore sp ace. A three step sequential extraction technique has been applied to elastic petroleum reservoir samples, using a suite of solvents with in creasing polarity, in order to address these questions. In the analyze d samples the following main trends were observed: (i) the first extra ct represents >95% of the total extract; (ii) the relative polar compo und content increases going from the first to; the last extract; (iii) the last extract has generally a slightly lower apparent maturity as assessed using biomarker parameters. Additionally a reduction in the d egree of biodegradation from the first to the last extracts was observ ed, implying tentatively that biodegradation takes place dominantly in the center of the pores. Fluid inclusion extracts show distinct sourc e characteristics, however the last extract appears to approach the fl uid inclusion extract signature in some aspects. The use of sequential extraction as a routine tool in the reservoir geochemical context is judged to be limited: however it may help to solve specific problems. Copyright (C) 1996 Elsevier Science Ltd.