江西萍乐坳陷中部赣丰地1井上二叠统乐平组页岩气聚气条件

江西萍乐坳陷普遍发育上二叠统乐平煤系,是下扬子地区页岩气勘探突破的重点区域。为查明萍乐坳陷中部页岩气聚集条件及勘探潜力,以坳陷首口地质调查井完整钻遇乐平组各套主力页岩的赣丰地1井岩心资料为研究对象,通过不均匀采样,对200余块岩心样品开展了薄片鉴定、有机地球化学分析、全岩及黏土矿物X衍射分析、氩离子抛光扫描电镜观察和页岩现场解析。萍乐坳陷中部乐平组黑色碳质页岩厚度大、有机碳含量高、有机质类型好且处于高成熟生气阶段,有利于页岩气的生成和聚集;另外,其脆性矿物含量高(脆性指数Ⅰ为26%～53.5%,均值为37.3%;脆性指数Ⅱ为23.3%～52.6%,均值为39.0%),指示页岩层段具备良好的可压性;有机孔和黏土矿物粒内孔较为发育,孔隙内部连通性好,有效增大了矿物比表面积,有利于页岩气的赋存;微裂缝主要起到沟通导流作用,改善页岩渗透性。通过分析乐平组4段地层(官山段、老山段、狮子山段和王潘里段)的勘探潜力参数指标,认为王潘里段和老山段页岩在气测显示、厚度、TOC、有机质孔隙和矿物组成等各方面更加有利,可作为萍乐坳陷中部地区乐平煤系下一步页岩气勘探开发的重点层段。

Shale gas accumulation in the Upper Permian Leping Formation: a case study of well Ganfengdi-1 in the central Pingle Depression,Jiangxi Province

The Upper Permian Leping coal measures are widely developed in the Pingle Depression, Jiangxi Pro-vince, which is a key area for shale gas exploration in the Lower Yangtze region. The core data of well Ganfengdi-1, the first geological survey well in the Pingle Depression, which drilled through the main shale of Leping Formation, were studied in order to determine the shale gas accumulation conditions and exploration potential in the central Pingle Depression. More than 200 core samples were analyzed using non-uniform sampling. By means of thin section observations, organic geochemical analysis, X-ray diffraction analysis of whole rock and clay minerals, argon ion polishing scanning electron microscopy and in situ analysis of shale, it was determined that a large thickness of the black carbonaceous shale of the Leping Formation in the central Pingle Depression has a high content of organic carbon. The type of organic matter is good, and the stage of high maturity gas generation is favorable for shale gas generation and accumulation. In addition, the content of brittle minerals is high. The brittle index I is 26%-53.5%, averaging 37.3%, while the brittle index Ⅱ is 23.3%-52.6%, averaging 39.0%, which indicates that the shale formation has a good compressibility. Organic pores and intragranular pores in clay minerals are well-developed. The internal connectivity of the pores is good, and the specific surface area of the minerals is high, which is of great significance for the occurrence of shale gas. The micro-cracks mainly play a role of communication and diversion to improve the permeability of the shale. By analyzing the exploration potential parameter indexes of the 4 sections of the Leping Formation (Guanshan, Laoshan, Shizishan and Wangpanli), it is considered that the Wangpanli and Laoshan shale have more outstanding gas show, thickness, TOC content, organic matter pore and mineral composition, which can be regarded as favorable shale gas exploration targets in the Leping coal-bearing system in the central Pingle Depression.