Hydrocarbon enrichment effects in the non-foreland area of the Tarim Basin under the coevolution control of the Tethys and Paleo-Asian oceans
The Phanerozoic evolutionary processes of the Tethyan and Paleo-Asian tectonic domains have delivered profound impacts on the Tarim Basin,including the formation of prototype basins and sedimentary filling processes,as well as hydrocarbon accumulation and later adjustment and modification.Both the ProtoTethys and Paleo-Asian oceans experienced phases of expansion,subduction,closure,and collisional orogenesis.Specifically,the Tethyan tectonic domain progressed through the Proto-,Paleo-,and Neo-Tethys stages in a row.Meanwhile,the Paleo-Asian Ocean underwent a complex extension-convergence process within a Neoproterozoic-Paleozoic framework involving multiple continents,islands,and oceans.Due to the coevolution of the Tethys Ocean(the Kunlun-Altyn Tagh branch)and the Paleo-Asian Ocean(the South Tianshan Ocean as a branch),the Tarim Basin experienced two extension-convergence megabasin cycles from the Neoproterozoic to the Eopaleozoic and from the Neopaleozoic to the Cenozoic.These cycles,along with eustatic sea-level changes and climatic cycles,facilitated the formation of high-quality source rocks and various large-scale reservoirs and cap rocks,which jointly created a superior material foundation for hydrocarbon generation and accumulation.The hydrocarbon accumulation effects ncontrolled by the coevolution of the Tethys and Paleo-Asian oceans are manifested in the following aspects:differential hydrocarbon accumulation and enrichment across different parts of the non-foreland area(i.e.area covered by Paleozoic marine sediments)in the Tarim Basin under a variety of basin prototypes and later tectonic modifications;high-quality source rocks widely seen in the northern depression serving as the foundation for large-scale hydrocarbon enrichment in the northern Tarim,Shuntuoguole low uplift and Tazhong area;two types of large-scale reservoirs with distinct characteristics:fault-controlled fractured-vuggy and fractured-vuggy karst types formed under tectonic fracturing and paleokarstification associated with multi-phase tectonic movements;and the differential evolution of structures and geothermal fields in the accumulation zone dictating the regular changes in hydrocarbon phase state and secondary alterations.Favorable hydrocarbon exploration targets in the non-foreland area include large paleo-uplifts,unconformities,strike-slip fault zones,high-energy facies tracts,and areas where these three factors overlapping.
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