Sedimentary micro-facies analysis of Huanglong Formation in the Shuangjiaba gas field, northeast Chongqing

Abstract：The Upper Carboniferous Huanglong Formation in the Shuangjiaba gas field of northeast Chongqing is the principal producing formation of natural gas pool. Based on the drilling, cores, thin slice and logging information,, in combination with a comprehensive study of petrology, paleobiology and well logging, the authors established a sedimentary model of Huanglong Formation. Studies show that the Huanglong Formation consists of two types of sedimentary systems, i.e., sabkha and continental shelf. The water bodies of two sedimentary systems deepened gradually and expanded, forming a transgression sequence. Six subfacies and eight microfacies were recognized based on the signature of sedimentary facies. On the basis of sedimentary facies of each well, the plane distributive map of sedimentary micro-facies about the first Member (C2hl1), the second Member (C2hl2) and the third Member (C2hl3) of the Huanglong Formation was compiled. Composite particles beach, calcarenite beach and bioclast beach are the most favorable microfacies. The second section of Huanglong Formation was the main gas-producing area in the upper Carboniferous period.