四川盆地西南部平探1井中二叠统栖霞组天然气勘探新突破及其意义

2020年,四川盆地西南部地区(以下简称川西南部)平探1井在中二叠统栖霞组钻遇台缘带孔隙型白云岩储层并获得高产工业气流,实现了该区中二叠统天然气勘探的新突破。为了深化对栖霞组的地质认识,指导该区带天然气勘探,在分析平探1井钻探成果的基础上,对该区的烃源条件、储层特征、保存条件等油气成藏要素开展了研究,探讨了该区栖霞组天然气的勘探潜力及下一步的勘探方向。研究结果表明:①川西南部栖霞组储层以中、细晶白云岩为主,储集空间主要为溶蚀孔洞、晶间孔、粒间孔和裂缝,为低孔、中—低渗透裂缝—孔隙型储层,局部发育高孔高渗储层;储层横向展布受台缘滩控制,主要沿邛西—平落坝—名山—汉王场一带大面积分布;②该区栖霞组天然气的来源与双鱼石构造类似,由下寒武统筇竹寺组泥页岩和中二叠统泥灰岩混源构成,主要来源于前者;③该区纵向上不仅具有"双层构造"特征,而且三叠系盐膏层具有区域封盖条件,二叠系的构造圈闭及构造—岩性复合圈闭形态完整、保存条件良好,为栖霞组天然气聚集成藏提供了有利的场所。结论认为,川西南部中二叠统具有较好的天然气成藏条件,平探1井的突破展示了该区栖霞组台缘带白云岩储层良好的天然气勘探潜力。

New breakthrough of natural gas exploration in the Qixia Formation of Middle Permian by Well Pingtan 1 in the southwestern Sichuan Basin and its implications

In 2020, Well Pingtan 1 in the southwestern Sichuan Basin drills into porous dolomite reservoirs of marginal platform belt in the Qixia Formation of Middle Permian and produces high-yield industrial gas, which indicates a new breakthrough of Middle Permian natural gas exploration in this area. In order to further understand the geological conditions of Qixia Formation and provide guidance for the natural gas exploration in this area, this paper studied hydrocarbon accumulation elements of this area (e.g. hydrocarbon source conditions, reservoir characteristics and preservation conditions) after analyzing the drilling results of Well Pingtan 1. Then, exploration potential and direction of Qixia Formation natural gas in this area were discussed. And the following research results were obtained. First, the Qixia Formation reservoirs in the southwestern Sichuan Basin are dominated by moderate and fine crystalline dolomite, and their reservoir spaces are mainly acted by dissolved vugs, intercrystalline pores, intergranular pores and fractures. They are fractured-porous reservoirs of low porosity and middle–low permeability, with locally developed high-porosity and high-permeability reservoirs. Their lateral distribution is controlled by marginal platform shoal and they are extensively distributed in the area of Qiongxi, Pingluoba, Mingshan and Hanwangchang. Second, the source rocks of Qixia Formation natural gas in this area are similar to those in Shuangyushi structure, and they are mainly composed of mud shale of Lower Cambrian Qiongzhusi Formation and marl of Middle Permian, among which the Qiongzhusi Formation is dominant. Third, this area is characterized by "double-layer structure" vertically, and the Triassic salt gypsum has regional sealing conditions and the Permian structural traps and structural-lithological traps are morphologically completed with good preservation conditions, which provide favorable sites for the accumulation of Qixia Formation natural gas. In conclusion, the Middle Permian in the southwestern Sichuan Basin is better in hydrocarbon accumulation conditions, and the breakthrough of Well Pingtan 1 reveals a good natural gas exploration potential of Qixia Formation dolomite reservoirs of marginal platform belt in the southwestern Sichuan Basin.