Shiyou shiyan dizhi (Nov 2022)
Thermal evolution characteristics of Triassic source rocks and their petroleum geological significance on the southern slope of Kuqa Depression, Tarim Basin
Abstract
According to the latest three-dimensional seismic stratification data, the Triassic source rocks are recognized to be deeply buried on the southern slope of Kuqa Depression, Tarim Basin, making it possible to develop local source rocks. Based on geochemical data and basin simulation, the burial history, thermal history and maturity evolution history of Triassic source rocks in this area were simulated and analyzed. By discussing the thermal evolution and maturity process of source rocks, the maturity stage and hydrocarbon generation stage of source rocks were proposed and their reservoir forming significance was further discussed. The source rocks of the Triassic Karamay Formation are distributed on the southern slope of Kuqa Depression. The burial depth in the southern area of Xinhe is generally about 6 700 m, which tends gradually to deepen in the north and reaches themaximum depth over 8 000 m, showing an overall characteristics of "shallowly buried in the south and deeply buried in the north". The southern slope of Kuqa Depression has the same overall subsidence amplitude, which has experienced the tectonic evolution process of stable burial in the early stage, continuous subsidence in the middle stage and rapid burial in the late stage. During the Triassic period, the strata were deposited stably and the burial depth was small. From Cretaceous to Paleogene, continental clastic rocks were mainly deposited, and the strata continued to deposit. From Neogene to present, the southern slope of Kuqa Depression entered the stage of rapid thermal subsidence, and the burial depth reached the largest. The evolution degree of Triassic source rocks on the southern slope of Kuqa Depression is characterized by "high degree in the north and low degree in the south". The northern region matured early, which entered the hydrocarbon generation threshold at the beginning of Paleogene (Ro=0.5%), evolved to mature stage by the end of Paleogene (Ro=0.7%) and to high maturity stage in the middle Neogene (Ro=1.0%) and till now (Ro=1.30%), mainly generating gas. The southern region matured relatively late, which entered the oil window in the early Neogene, reached mature stage in the middle Neogene (Ro=0.7%), and till now (Ro=0.86%), mainly generating oil. There are two oil and gas transportation of far-source and near-source on the southern slope of Kuqa Depression, which provides sufficient sources for oil and gas accumulation. This area has the overall characteristics of dual source hydrocarbon supply.
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