川滇黔邻区龙马溪组页岩气富集主控因素与勘探方向

The main controlling factors of shale gas enrichment and exploration prospect areas in the Sichuan-Yunnan-Guizhou border areas, southwestern China

关键词:  川滇黔邻区  五峰组-龙马溪组  页岩气  主控因素  构造保存  有利区优选

Key words:  Sichuan-Yunnan-Guizhou border area  Wufeng-Longmaxi Formation  shale gas  controlling factors  tectonic preservation  favorable areas selection

摘要:

中国的页岩气资源评价必须立足于中国主要陆块的地质条件与构造演化特点之上,对于不同层系、不同地区的页岩气选区评价,也必须抓住关键因素。川滇黔邻区的五峰组-龙马溪组富有机质页岩发育,但保存条件较渝东南地区更为复杂。印支期以来,该区经历了多期次构造应力场转换,断裂、褶皱发育,因此,建立针对性的页岩气选区评价参数体系是该区页岩气勘探走出困局的当务之急。本文在分析该区已有页岩气钻井成效的基础上,立足于扬子海相层系页岩气勘探应是基于保存条件的"连续型甜点区"的选区评价基本思路,结合前人研究成果,系统梳理出一套评价指标体系。该体系涵盖5大因素(区域盖层、直接盖层、底板条件、页岩层自身条件、构造改造强度)、4个等级、17个选区评价参数。另外,根据已有相关钻井数据,总结提出了5个页岩气层评价表征参数(含气量、孔隙度、电阻率、氮气组分含量和压力系数)。根据该指标体系,对川滇黔邻区的主要构造单元进行了梳理分析,优选出5个有利区,提出了各有利区的首选可能突破点。本研究对复杂构造区页岩气有利区带优选具有一定的指导意义。

Abstract:

The evaluation of shale gas resources in China must be based on the geological conditions and tectonic evolution of major continental blocks in China. Similarly,the critical factors must be stressed for shale gas selectedarea evaluation in different layers and regions. The organic matter shales well developed in the Wufeng Formation-Longmaxi Formation in the Sichuan-Yunnan-Guizhou border areas. However,the preservation conditions herein are more complicated than those in southeast Chongqing. Since the Indosinian period,the Sichuan-Yunnan-Guizhou border areas have experienced multi-phase transformation of tectonic stress fields,and the development of faults and folds. Therefore,it is imperative to construct a suit of evaluation index system for the shale gas selected-area evaluation aiming at contributing to the shale gas exploration in the study areas. Referenced to the existing shale gas drilling results in this area,a suit of evaluation index system has been established in the present paper on the basis of the basic ideas that the exploration evaluation of the marine shale gas in Yangtze Craton should be the selectedarea evaluation of the "continuous desserts area". The evaluation index system covers five types of factors including regional cap-rock,direct cap-rock,floor rocks,shale formation itself condition,structural transformation strength, four grades and seventeen selected-area evaluation parameters. In addition,five diagnostic parameters for the shale gas evaluation are outlined,including gas-bearing property,porosity,resistivity,nitrogen contents and pressure coefficient of shale gas reservoirs. Finally,the tectonic analysis is made for the Sichuan-Yunnan-Guizhou border areas,and five favourable areas for the shale gas exploration and potential break through points are delineated according to the index system mentioned above. The results of research in this study may be significant for the optimal selection of shale gas favourable areas in structurally complicated areas.