四川盆地西南部中二叠统沉积特征与勘探目标

四川盆地中二叠统大中型气藏的勘探方向和目标是目前研究的热点和难点，而川中高石梯—磨溪地区下寒武统龙王庙组大气田的成功勘探经验表明，有利的沉积相带是大气田形成的基础。为此，基于地震资料、地表露头资料及钻井资料，对该盆地西南部中二叠统的构造格局和沉积特征进行了综合研究，从沉积相控的角度提出以下观点：①该区中二叠统沉积时处于浅水缓坡高能带，发育大规模礁滩相沉积；②中二叠世时期基底抬升，茅口组顶部遭受剥蚀，形成不整合面风化壳，盆地西南部处于岩溶斜坡带，古表生岩溶作用强烈；③礁滩相沉积叠加风化壳岩溶有利于形成大规模礁滩相岩溶型储层。进一步结合研究区资源条件和成藏条件的综合研究结论指出：四川盆地中二叠统基础地质条件优越，有望寻找到大规模礁滩相岩溶型气藏；该盆地西南部龙门山前隐伏构造带、川西坳陷斜坡带中二叠统圈闭发育，成藏条件好，是寻找大规模礁滩相岩溶型气藏的有利目标区。

Sedimentary features and exploration targets of Middle Permian reservoirs in the Southwestern Sichuan Basin

The exploration direction and targets for the large-scale Middle Permian gas reservoirs in the Sichuan Basin are hotspots and challenges in current exploration researches. The exploration successes of large gas field of Cambrian Longwangmiao Formation in Gaoshiti-Moxi region, the Central Sichuan Basin, indicated that prospective sedimentary facies belt was the basis for the formation of large gas fields. In this paper, based on seismic data, outcrop data and drilling data, the tectonic framework and sedimentary features of Middle Permian in the Southwestern Sichuan Basin were comprehensively studied. The following conclusions were reached from the perspective of sedimentary facies control: (1) during Middle Permian, this region was in shallow water gentle slope belts with high energy, where thick reef flat facies were deposited; (2) the basement was uplifted during Middle Permian, resulting in the unconformity weathering crust at the top of Maokou Formation due to erosion; the Southwestern Sichuan Basin was located in karst slope belt, where epigenic karstification was intense; and (3) reef flat deposits superimposed by karst weathering crust was favorable for the formation of large-scale reef flat karst reservoirs. Based on the combination of the resources conditions and hydrocarbon accumulation conditions in this region, it was pointed out that the Middle Permian has great potential of large-scale reef flat karst gas reservoir due to its advantageous geological conditions; the Middle Permian traps with good hydrocarbon accumulation conditions were developed in the Longmen Mountain front closed structural belt in the Southwestern Sichuan Basin and Western Sichuan Basin depression slope belt, which are favorable targets for large-scale reef flat karst reservoirs.