The Study Of Depsitional Characteristics And Potential Of Shale From Late Carboniferous To Permian Period

Qinshui basin is the main coal-abundant basin with about ten percentage of the whole coal resources in China.It is also the most developed basin for the exploration and production of coal bed methane.from late Carboniferous to Permian period,the Formations of Taiyuan,Shanxi and Xiashihezi are rich of organic shale,which give a good prosperity of the exploration of shale gas in Qinshui baisn.This study is based on the theory of petrography and sedimentology,combined with investigation in fields,analysis of cores,and geochemical identifications for samples.Single well data analysis,the correlation of wells,horizon analysis were done to study the distribution of strata in space,the depositional environment,and other influencing factors for shale formation.Thus,a general assessment of is given for the potential of shale resources and the possible formations with shale gas in Qinshui basin.The formations of Shanxi and Taiyuan in the study area thickened from the south to north,and the sediment sources came from the ancient land of Yinshan in the northern part and that of Zhongtiao in the mid-west part of the basin.The distribution of limestone showed multiple times of transgression from the south-east direction.The Taiyuan formation showed mainly the sedimentary facies of delta-plain,lagoon,barrier bar,marine carbonate platform and their subfacies,the Shanxi formation with sedimentary facies of delta-plain,lagoon,barrier bar,and their sub-facies,and the Xiashihezi formation with sedimentary facies of fluvial,delta-plain,lakes and their sub-facies.The shale in Qinshui basin has a good potential of hydrocarbon generation based on the values of TOC and Ro of shale in the study area much larger than the oil threshold of shale.Based on observations in filed,the thickness of shale between the Xiami in Taiyuan formation and the 3# coal in Shanxi formation is large and its continuation is good,while the shale in Xiashihezi formation only appeared in local area with less continuation and smaller thickness.