关键词: 塔西南山前地区, 石炭系—二叠系, 恰探1井, 碳酸盐岩, 成藏条件

Abstract: A major breakthrough has been made in the Carboniferous-Permian carbonate rocks in Well Qiatan 1 in Wuqia structural zone in the West Tianshan Thrust Belt, marking the discovery of a major replacement formation in the piedmont southwestern Tarim Basin. Combined with the regional geological data, studies on field outcrops, drilling, and seismic data, as well as the comprehensive analysis of laboratory experimental and test data in wells Qiatan 1 and Kuntan 1, hydrocarbon accumulation conditions in the Carboniferous-Permian in the piedmont southwestern Tarim Basin are re-recognized. The study results show that a “horseshoe-shaped” platform margin zone was developed in the Late Carboniferous-Early Permian in the piedmont southwestern Tarim Basin, and a favorable high-energy beach sedimentary facies zone was formed in belts, in which source rocks of bay lagoon facies were deposited in the Permian Qipan Formation, with a thickness of up to 500 m, type Ⅰ-Ⅱ organic matter, and high organic matter abundance. Jointly controlled by sedimentary facies and karstification, the fractured-vuggy type carbonate reservoirs were developed in the Late Carboniferous-Early Permian, forming a favorable reservoir and cap rock assemblage with the overlying thick mudstone in the Permian Qipan Formation. As a result, a new hydrocarbon accumulation pattern of “lower source rock and upper reservoir, hydrocarbon transport by fault and near-source accumulation” is established. The comprehensive analysis indicates that the fault anticline traps in the Carboniferous-Permian are distributed in rows and belts, which have the advantage of near-source hydrocarbon accumulation, and a number of favorable exploration targets such as wells Yetan 1 and Abei 1JS are optimally selected after evaluation, showing good exploration prospects, which are expected to be the major replacement field for large-scale gas exploration and discovery.