关键词: 塔里木盆地, 库车坳陷, 南部斜坡带, 寒武系, 潜山成藏模式, 重大突破

Abstract: A major breakthrough has been made in the Cambrian buried hill dolomite reservoir in Well Tuotan 1 in Wensu-Xiqiu area on the south slope of Kuqa Depression in Tarim Basin, which is of great significance to the exploration of multi-target buried hill on the hydrocarbon facing side on the south slope of Kuqa Depression. Due to the complex geological conditions, there is a lack of clear understanding on hydrocarbon enrichment law, and it is difficult to identify geological structures and characterize traps, which restrict the petroleum exploration in the buried hills in the study area. Based on the systematic analysis of structural features, stratigraphic distribution in buried hill, source rock-reservoir-cap rock assemblage, hydrocarbon transport system, and exploration practice, a new pattern of hydrocarbon accumulation in the buried hill has been established. The Paleozoic structure in Wensu-Xiqiu area is a back thrust structure controlled by the front thrust Shajingzi-Xiqiu Fault and recoil thrust Wushinan Fault, which is further complicated by two secondary back thrust faults F1 and F2, forming three rows of Paleozoic buried hill structures, with the stratigraphic age from old to new from the near fault to the far fault area in each row of structures. Among them, the Cambrian buried hill strata have the largest distribution range in a NEE direction. The buried hill reservoirs are mainly composed of dolomite of restricted platform granular beach facies, and the high-quality fractured-vuggy type dolomite reservoirs are contiguously distributed after reconstructed by multi stage tectonic activities and long-term exposure and erosion. The hydrocarbon accumulation assemblage of the buried hill oil and gas reservoirs is composed of dual hydrocarbon supply by mudstone source rocks in the Triassic Huangshanjie Formation and the Jurassic Chakmak Formation, fractured-vuggy type dolomite reservoir, and cap rock of the overlying Paleogene gypsum salt rock; The hydrocarbon accumulation is characterized by “distant hydrocarbon supply from Kuqa Depression, hydrocarbon transport by unconformity surface, and hydrocarbon enrichment in structures on the hydrocarbon facing side”, with the main hydrocarbon accumulation period in the late Himalayan (4-1Ma). The successful drilling of Well Tuotan 1 has confirmed the huge exploration potential of multi-row and multi-type buried hills in Wensu-Xiqiu area, with the re delineated buried hill trap area of 840km², and the discovered oil resources of about 2.0×10⁸t and natural gas resources of about 590×10⁸m³, which is expected to be a new strategic replacement area for increasing oil and gas reserves and production.