| Permian marine shale is widely distributed in Hefeng area, western Hunan-Hubei fold belt. It is rich in organic
matter and is a set of high-quality source rock. Compared with the shale gas of Niutitang Formation and Wufeng
Formation-Longmaxi Formation, the research degree of marine shale gas of Middle-Upper Permian is relatively low.
Survey well HD1 reveals the reservoir characteristics of the Gufeng-Dalong shale of Middle-Upper Permian and its gasbearing
properties in the core of Chenjiawan anticline, Hefeng area. So taking the Well HD1 as the research target,
analysis of organic geochemistry and data of X-ray diffraction whole rock mineral, SEM, high pressure mercury intrusion,
isothermal adsorption and on-site experimental permit to characterize the marine shale heterogeneity of Gufeng
Formation-Dalong Formation in Middle-Upper Permian in Hefeng area. The results show that four types of lithofacies
are developed in Gufeng-Dalong marine shale as siliceous shale facies, mixed shale facies, calcareous shale facies and
clay shale facies. Controlled by lithofacies, the linear density of fracture diversities among different lithofacies, and the
micro pore-fracture structures of different types and scales are developed. Siliceous shale in the lower part of Dalong
Formation and Gufeng Formation has high organic carbon content, large specific surface area and total pore volume. The
differential, onrush and variation coefficient of permeability show that the heterogeneity of mixed and calcareous
lithofacies in Dalong Formation is weak, while that of siliceous lithofacies is strong. Different types of lithofacies in
Xiayao Formation and Gufeng Formation show strong heterogeneity. The heterogeneity of gas generation capacity and
reservoir capacity result in the gas content having the characteristics of strong heterogeneity in different lithofacies. In
general, the shale layers with high organic carbon content, relatively well developed brittle minerals, natural macro
fractures, micro organic pores and micro fractures in minerals, with good reservoir physical properties and high gas
content are all siliceous shale facies, and located in the bottom part of Dalong Formation and Gufeng Formation. |
