Lithologic sequence and exploration significance of Longtan Formation shale in eastern Sichuan Basin
Longtan Formation in eastern Sichuan Basin has large potential for shale gas exploration and development.This formation deposited under marine-continental environment has complex rock types and rapidly changing sedimentary sub-facies,which leads to the problems on how to identify and classify the rock-combinations by normal means.However,the present classification of rock-combination is not precise enough.These problems set limits and troubles on identifying the favorable rock-combinations and exploration activities for Longtan Formation in this area.On the basis of core observation,field profile measurement and thin section identification,combined with the mud-to-ground ratio and single-layer lithology thickness of the well,seven lithological combination types were established for the first time,namely:shale,rich shale containing sandstone,rich shale containing limestone,shale-limestone interbedding,rich limestone containing shale,dense limestone and igneous rock types.Based on the characteristic parameters of shale reservoirs such as TOC,porosity,gas content and brittleness index,the planar distribution of different lithological combinations in each section of the Longtan Formation was studied.The results show that the longitudinal dominant lithology combinations are mainly rich shale containing limestone and shale in Longtan section,and the second section of Longtan is mainly shale,shale-limestone interbedding and rich limestone containing shale.On the plane,the dominant lithological combination of mud-rich and mud-containing types in Longtan is mainly distributed in the Kaizhou-Yunyang area,and the shale is mainly distributed in the Chongqing-Qijiang area.The dominant shale type of Longtan Section Ⅱis distributed in the Banan-Qijiang area,the shale-limestone interlayer is distributed in the Dazhou area,and the mud-rich limestone is distributed in the Wanzhou-Liangping-Shizhu area.The research results provide an important basis for the exploration of shale gas in the Longtan Formation in eastern Sichuan.
Eastern SichuanLongtan FormationLithological associationDominant reservoirsSignificance of exploration
万方数据
维普
