Shale Characteristics and Gas Bearing Controlling Factors in Wufeng Formation and Longmaxi Formation in Southeast Chongqing, China

Tieya, Jing; Jinchuan, Zhang; Xuan, Tang

Southeast Chongqing, one of the most potential shale gas accumulation areas in China, lies on Upper Yangtze eastern trough-like structural belt, having experienced strong tectonic movements. Due to the afterward uplift, the target shale formations are characterized by shallow burial depth and abundant fractures. Wufeng Formation of Upper Ordovician and Longmaxi Formation of Lower Silurian deposited successively under deep and shallow shelf facies with abundant pyrites and graptolite fossils. The lithology of the formations includes black carbonaceous shale, calcareous shale, siliceous shale and so on. The thickness of the shale varies greatly from 40 to 200 m. TOC ranges from 2% to 4% and decreases upward along the intervals owing to the change of sedimentary facies. The organic matter reaches mature and post mature stage. The porosity ranges from 0.77% to 4.7%, and the average permeability is about 0.0116 mD. Abundant fragile minerals exist in the shales which benefit the hydraulic simulation. Isothermal adsorption and on-site desorption experiments are conducted which show that the gas content of shale ranges from 1 to 3 m3/t and reaches the standard of commercial exploitation. Factors impacting gas bearing characteristics are analyzed using mathematical statistics method. It demonstrates that TOC is the most important factor, especially to absorbed gas content. Meanwhile, clay content, fracture development degree, thermal maturity, the type of kerogen, microscopic components and so on are also the significant factors regarding to gas bearing characteristics.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013