Abstract:

Based on the latest drilling data, the laboratory test results of shale core samples from Well Maye1 and combined with the geologic survey of field outcrops, this paper systematically studies the reservoir characteristics of the Lower Cambrian Qiongzhusi shale in the Malong block of eastern Yunnan Province from organic geochemical characteristics, mineral constituents, reservoir properties and fracture characteristics. The Qiongzhusi shale of study area is characterized by high organic content with TOC over 2%. The black shale was all highover mature because of the old Qiongzhusi Formation. The major mineralogical compositions of shale are detrital minerals, carbonatite minerals and clay minerals. The black shale has a high brittleness mineral content and the brittleness index averages at 0.62. Clay minerals are mainly composed of illite, followed by the I/S layers and chlorite, and the kaolinite content is low. Qiongzhusi shale is characterized by low porosity and permeability and various pore types dominated by inkbottleshaped pores, platelike pores and slitshaped pores. Nanoscale mesopores in shale play an important role. The specific surface area and total pore volume are low with an average of 9.18 m2/g and 10.38×10-3cm3/g, respectively. The fissures of shale reservoir are mainly of high angle crack. Carbonaceous shale in the upper part of target layer is characterized by welldeveloped fissures and silty shale in the lower part of target layer possesses undeveloped fissures. TOC and brittle minerals contents promote the development of fissures. Compared with typical marine shale from home and abroad, the shale from Qiongzhusi Formation in the Malong block of eastern Yunnan Province is mainly composed of silty shale with some thin carbonaceous shale. Barnett shale from Fort Worth, Longmaxi shale from Jiaoshiba area and Niutitang shale from Cengong block are mainly carbonaceous and siliceous shale. So the lithofacies of Qiongzhusi shale is poorer than that of the other three kinds of marine shale. The TOC content of Qiongzhusi shale is moderate, lower than that of the other three kinds of marine shale. The brittleness minerals content of Qiongzhusi shale is similar to that of Longmaxi shale and slightly lower than that of Niutitang shale. Qiongzhusi shale is characterized by good brittleness. The reservoir property and development of organic matter pores of Barnett shale and Longmaxi shale are better than those of Qiongzhusi shale and Niutitang shale. The organic matter pores in Qiongzhusi shale mainly develop in the mixture of organic matter and clay. The fissure development of Qiongzhusi shale is poorer than that of Barnett shale, Longmaxi shale and Niutitang shale. In addition, the gas content of Qiongzhusi shale is lower than that of other three kinds of marine shale, and Qiongzhusi shale has a strong adsorption ability.

Key words: Malong block, Maye1 well, Qiongzhusi Formation, marine shale, reservoir characteristics, comparison analysis