下扬子丰城——乐平地区二叠系乐平组页岩气潜力综合评价

Comprehensive Evaluation of Shale Gas Potential of Permian Leping Formation in Fengcheng-Leping Area of Lower Yangtze Region

下扬子区萍乐坳陷丰城—乐平地区发育二叠系乐平组海陆过渡相泥页岩。在深入调研其构造、沉积背景的基础上,综合利用多种实验手段对岩心有机地球化学特征、岩石类型和矿物特征、物性条件、储集空间类型和含气性进行了系统归纳,并进一步探讨了影响其含气性的沉积和构造因素。研究认为:丰城—乐平地区二叠系乐平组泥页岩厚度差异较大且非均质性较强,王潘里段和下老山亚段为好烃源岩,上老山亚段和中老山亚段为中等烃源岩;其有机质类型以Ⅱ2型为主,东区倾油而西区倾气;成熟度具有"东低西高"的特征;孔隙空间以微孔隙和微裂缝为主,物性整体表现为特低孔低渗。研究区二叠系海陆过渡环境为有利烃源岩的发育提供了基础,适中的埋藏深度保障了页岩气的赋存并可降低开采成本;但东区受推覆带改造使得该区构造复杂,变形强烈,页岩气保存条件差,西部丰城地区则构造稳定,具有较好的页岩气勘探前景。

The shale in sea-land transitional facies of Permian Leping Formation is developed in the Lower Yangtze region.Based on the investigation of structure and sedimentary background in this areathrough some experiment measures,we analyzed the organic geochemical characteristics,rock and mineral characteristics,physical conditions and storage space types of cores,and then discussed the main sedimentary and structural factors affecting gas content of shale.The research results show that the shale thickness of Permian Leping Formation in Fengcheng-Leping area is very different and heterogeneous;The Wangpanli and Lower Laoshan Subsections are good hydrocarbon source rocks,and the Upper and Middle Laoshan Subsections are medium hydrocarbon source rocks;the main organic matter type of shales is II2,which is the main gas source in the west area,the maturity of organic matter is characterized by'low in the east and high in the west';the micro-pores and micro-cracks are the main pore spaces;the whole physical property is ultra-low porosity and low permeability.The Permian sea-land transitional environment in the study area provided the basis for the development of hydrocarbon source rocks;the moderate burial depth guarantees the high content of shale gas and low production cost;the complicated structure and intense deformation in the eastern area is not conducive to the preservation of shale gas;the structure of western area is stable,and has a good prospect for gas exploration.