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ABSTRACT: Inferred Oil Migration in the Zhu I Depression, Pearl River Mouth Basin, South China Sea

C. R. Robison, K. K. Bissada

Integration of geophysical and geochemical data has revealed a possible migration path within a Tertiary sequence in the Zhu I Depression of the Pearl River Mouth basin, South China Sea. Placing the geochemical attributes of several oils from four commercial and subcommercial fields in stratigraphic relationship to one another within the regional framework provided clues as to the origin and migration of the oils and explained differences in their physical/chemical properties. Depocenters within the Zhu I subbasin contain organic-rich lacustrine facies. Source rocks in such settings would, upon thermal maturation, generate high-wax oils such as those discovered in the Zhu I. Primary migration would move oil out of source rocks and into a massive sandstone carrier system t at is sealed by a widespread tight limestone. Secondary migration through the carrier system would be focused toward the SSE in the direction of the Dongsha Massif. Unless oil is entrapped in antiform structures within the subbasin it would probably migrate out of the subbasin and into carbonate reservoirs on the Dongsha Massif. Because these carbonate reservoirs are often shallow, oil in them could undergo varying degrees of biodegradation. Such an effect would significantly influence the oil's composition as well as its economic value.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990