Abstract: Clay-Membrane Filtration as Mechanism for Primary Accumulation of Hydrocarbons

C. R. Lewis

Oil and gas originate from decomposition of organic matter. Primarily the smaller hydrocarbon-precursor molecules are able to escape from the source shale. Higher hydrocarbons hypothetically may be built up by polymerization from these smaller molecules after they leave the source shale and enter sand layers. Large molecules thus formed in aqueous solution in the large pore spaces of the sand would remain free to migrate with compaction waters. Hydrocarbon deposits might occur when the dissolved molecules are filtered from laterally flowing water in sand layers. Generally, the filter would be a semipermeable membrane of shale through which the water could pass but higher hydrocarbon molecules and minute gas bubbles could not. These points of filtration would be at fault faces, sand-shale pinchouts, or other places where water flowing in sand layers must flow for short distances through hale. This hypothesis would suggest that exploration in new areas should pursue those traps which had faults or shale barriers downstream of the flow of compaction waters during the time such waters were flowing.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA