中国南方五峰组-龙马溪组页岩气差异富集特征与控制因素

中国南方地区五峰组-龙马溪组页岩气2019年产量154×10~8m^3,已成为全球第二大页岩气产区。基于来自中国南方威远、长宁、涪陵及巫溪等地区典型钻井与露头剖面的1 000余件五峰组-龙马溪组页岩样品数据,综合分析页岩气差异富集特征,探讨其主要控制因素。研究表明我国南方五峰组-龙马溪组页岩气在纵向上和区域上均具有一定差异富集特征,具体表现在:纵向上集中发育甜点段,区域上甜点段厚度、含气量、TOC含量等关键参数存在着较大变化,其中长宁与涪陵地区较优;不同地区的五峰组-龙马溪组页岩含气量与TOC含量均具有较好正相关性,指示着有机质丰度(TOC含量)是影响页岩气富集程度(含气量)的关键因素;五峰组-龙马溪组页岩沉积时期的海洋表层水体总体高生产力,是有机质大量生成的重要前提条件;在断裂带发育较弱的构造稳定区域,硫化缺氧的水体条件是控制页岩气纵向上甜点段及区域上甜点区形成的关键因素,即页岩气差异富集的关键因素。

Discussion on characteristics and controlling factors of differential enrichment of Wufeng-Longmaxi formations shale gas in South China

In 2019,the annual output of Wufeng-Longmaxi formations shale gas in South China reached 154×10~8 m^3,making China the largest shale gas production region outside North America. Based on data of about 1 000 Wufeng-Longmaxi formations shale samples collected from typical cores and outcrops of Weiyuan,Changning,Fuling and Wuxi areas in South China,characteristics of differential enrichment of shale gas were analyzed,and its controlling factors were discussed. It is concluded that enrichments of Wufeng-Longmaxi formations shale gas in South China show differential vertically and laterally,respectively. In vertical orientation,the sweet-spot intervals of shale gas developed concentratedly,and the thicknesses,gas and TOC contents varied largely in different regions,of which in Changning and Fuling are high quality. For these four areas of shale gas exploration or development,gas contents are well correlated with TOC contents,suggesting that organic matter abundance is one of key factors controlling the enrichment of shale gas. When the Wufeng-Longmaxi formations shale deposited,the ocean surface had high productivity in general,providing prerequisites for formation of abundant organic matter. However,in the relatively stable tectonic zone,euxinic bottom water condition is the key factor controlling the formation of the sweet-spot interval of shale gas vertically and the distribution of sweet-spot area laterally,that is the key factor for differential enrichment of Wufeng-Longmaxi formations shale gas.