Abstract: The study on the shale reservoirs in the Lower Cambrian Shuijingtuo Formation in western Hunan-Hubei region are relatively less, and their heterogeneity severely limits the exploration of the shale gas. Taking the Shuijingtuo Formation shale as a target, and through analysis of thin sections, mineral content, organic geochemistry and SEM on profile and drilling data, the distribution and heterogeneity characteristics of the shale reservoirs in the Shuijingtuo Formation were studied. The result shows that the favorable facies for the development of the shale reservoirs is the deep water shelf, while dominated by carbonaceous shale and siliceous shale in the study area. The Shuijingtuo Formation is divided into two third-order sequences:the Sq1 is dominated by siliceous continental shelves, and the Sq2 is carbonaceous continental shelves more widely distributed. Macroscopically, siliceous and carbonaceous shales are developed in the transgressive system tract, which constitute an organic-rich shale zone; while calcareous and silty mud shales are developed in the highstand system tract. Microscopically, the shale reservoirs in the transgressive system tract have the features of increasing clay minerals and organic carbon content and decreasing brittle mineral content, and the reservoir space evolved from matrix pores to dissolved and organic pores, showing increasing total porosity; the shale reservoirs in the highstand system tract change in the opposite. The heterogeneous distribution of the shale reservoirs may be controlled by changes in sea level, source supply and biological effects, as well as diagenetic, tectonic and hydrogeological effects during the sedimentation.

Key words: western Hunan-Hubei region, Shuijingtuo Formation, shale reservoir, heterogeneity