Hydrocarbon accumulation in deep ancient carbonate-evaporite assemblages
The Ediacaran-Ordovician strata within three major marine basins(Tarim,Sichuan,and Ordos)in China are analyzed.Based on previous studies focusing on the characteristics of the Neoproterozoic-Cambrian strata within the three major basins(Siberian,Oman,and Australian)overseas,the carbonate-evaporite assemblages in the target interval are divided into three types:intercalated carbonate and gypsum salt,interbedded carbonate and gypsum salt,and coexisted carbonate,gypsum salt and clastic rock.Moreover,the concept and definition of the carbonate-evaporite assemblage are clarified.The results indicate that the oil and gas in the carbonate-evaporite assemblage are originated from two types of source rocks:shale and argillaceous carbonate.The characteristics of the argillaceous carbonate in the saline platform environment are analyzed,and the results confirmed the capability of gypsum salt in the saline environment to drive the source rock hydrocarbon generation.The dolomite reservoirs are classified in two types:gypsum-bearing dolomite flat,and grain shoal & microbial mound.This study clarifies that the penecontemporaneous or epigenic leaching of atmospheric fresh water mainly controlled the large-scale development of reservoirs.Afterwards,burial dissolution transformed and reworked the reservoirs.The hydrocarbon accumulation in carbonate-evaporite assemblage can be categorized into eight sub-models under three models(sub-evaporite hydrocarbon accumulation,supra-evaporite hydrocarbon accumulation,and inter-evaporite hydrocarbon accumulation).As a result,the Cambrian strata in the Taizhong North Slope,Mageiti Slope and Mazatag Front Rise Zone of the Tarim Basin,the Cambrian stata in the Chuandong-Shunan area of the Sichuan Basin,and the inter-evaporite Ma-4 Member of Ordovician in the Ordos Basin are defined as favorable targets for future exploration.
万方数据
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