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

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.