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Pseudo-Source Rock Characterization

Abstract

Pseudo-Source rocks are those naturally occurring rocks which appear to be good source rock by conventional analysis but actually these rocks do not contribute hydrocarbon in the basin. These pseudo–sources thus generate entirely wrong evaluation of hydrocarbon potential of the basin. It is therefore necessary to distinguish these pseudo-sources for proper evaluation of the petroleum potential of the basin. A pseudo-source rock contain appreciable organic carbon (TOC), show high generation potential during the pyrolysis experiment and kerogen in the pseudo-source rock may also show high maturity but it will not generate hydrocarbon till the rock maturity is less than the kerogen maturity. This is possible if already matured kerogen is somehow incorporated in the rock during deposition. This happens when a matured coal is weathered and deposited with fresh sediments or if sediments are deposited through an oil column. In this work a synthetic rock is prepared by depositing clays through a long oil column such that the clays can adsorb sufficient petroleum before being deposited. Sediments are then pressurized and simultaneously heated to convert the sediments to synthetic rock. Heating continued at low temperature such that the rock cannot be matured to generate hydrocarbons. After the clays are converted to rock a detailed geochemical analysis is carried out to find out the source potential of the rock. Results indicate reasonably good source potential of this synthetic rock and also a perfect oil source correlation using GC and GCMS results. This suggests such rocks may also be available in nature which appear as good source but cannot contribute to petroleum generation.