Comparative study on accumulation conditions of the tight gas in the upper paleozoic of the Qinshui Basin and Ordos Basin and its exploration potential

To discuss the exploration potential of tight gas in the Upper Paleozoic of Qinshui Basin,a systematic analo- gy analysis on difference about tectonic-sedimentary evolution,source-storage conditions,and accumulation regulation in Ordos and Qinshui basin was made. Some conclusions are as follows:(1) Qinshui Basin and Ordos Basin have ex- perienced tectonic stability,differentiation and finalization phase with similar sedimentary evolution mainly composed of transitional and continental sediments in carboniferous-Permian. (2) The total coal seam thickness in the Upper Pa- laeozoic of Qinshui Basin is about 3-17 m,as same as in the Ordos Basin;and its vitrinite reflectance is about 2． 0% -4． 5% with higher thermal evolution and stronger hydrocarbon-generating intensity than that of Ordos Basin. (3) Taiyuan,Shanxi and Xiashihezi Formations are the main targets,and the next are Shangshihezi and Shiqianfeng Forma- tions in the Ordos Basin. 103 well logs were reinterpreted in the Qinshui Basin,which indicates that there are 72 ques- tionable tight gas bearing layers accounting for 64. 9% of the totals in the Taiyuan and Shangshihezi Formations,followed by Shanxi and Xiashihezi Formations. (4) Based on the comprehensive analysis,two gas accumulation models of primary migration and secondary migration are presented in the Upper Paleozoic of the Qinshui Basin,preservation condition is the key factor in the tight gas accumulation,and the syncline core and wing with little fault in the south- central basin are favorable exploration areas.