Shiyou shiyan dizhi (Jan 2020)
Research progress on marine oil and gas accumulation in Tarim Basin
Abstract
In recent years, great achievements have been made in the exploration of ultra-deep marine oil and gas in the Tarim Basin. New oil and gas discoveries have been achieved in the Shunbei Ordovician, Tazhong Cambrian and Tahe deep strata, which provide abundant basic data for studying the marine oil and gas accumulation in the Tarim Basin. The marine oil and gas in the Tarim Basin are mainly distributed in the platform-basin area. There are various types of reservoirs, and the physical properties of crude oil vary greatly, showing the complexity of hydrocarbon accumulation. Through the analysis of a large number of samples, simulation experiments and extensive geology and geochemistry analysis, combined with the research results of tectonic evolution, sequence stratigraphy, sedimentary facies and sedimentary environments, some significant progress has been achieved such as the distribution and evolution of source rocks, oil and gas geochemistry characteristics, and the distribution characteristics of marine oil and gas reservoirs. The following achievements have been made: 1) clarification that the marine oil and gas in the Tarim platform-basin area mainly come from the Lower Cambrian-Middle/Lower Ordovician source rocks formed under strongly reducing environments, especially the Lower Cambrian Yuertusi Formation in the platform-basin. Two alterations types of ultra-deep marine reservoirs, namely, TSR and thermal cracking are defined, and the corresponding identification indicators are proposed. 2) by establishing the sedimentary development mode of the gentle slope-type high-quality Yuertusi source rocks, through well-seismic calibration, forward modeling, regional survey line interpretation of seismic facies, 3D area attribute analysis and seismic inversion, the distribution of source rocks in the Yuertusi Formation may be predicted, and their evolution characteristics clarified: the "high-pressure hydrocarbon generation evolution inhibition mode" under the long-term low geothermal background since the Yanshan period has delayed the thermal evolution of Shuntuoguole low uplift Cambrian source rocks, and the Shuntuoguole area still has the formation conditions of late high-maturity liquid hydrocarbon. 3) by comparing the hydrocarbon accumulation characteristics of the platform-basin area, the Ordovician oil and gas distribution characteristics have been clarified, further delineating the Cambrian Yuertusi in situ source rocks there, and identification of the light oil-gas reservoirs matching with the active strike-slip faults in the late Yanshan period and charged by the late hydrocarbon supply, which provide an key direction for oil and gas exploration in the ultra-deep carbonate rocks of the Tarim platform-basin area.
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