Hydrocarbon source rock characteristics and shale gas potential of Permian marine shales in the Lower Yangtze region of South China

Abstract

Considerable progress has been made in shale gas exploration and development in China. However, apart from the Wufeng–Longmaxi Formation shales in the Sichuan Basin, large-scale commercial exploitation of shale gas has not yet been achieved. Permian marine shales in the Lower Yangtze region have long been considered prospective targets for unconventional reservoirs, but few detailed evaluations of their source rock characteristics have been undertaken. Based on a geological survey of shale gas in this region, we used geological and geochemical data to undertake a comprehensive assessment of the source rock characteristics of the Permian shales in the Gufeng and Dalong Formations, and then evaluated their shale gas potential by comparing them with the world’s prolific shale gas plays. Both Gufeng and Dalong shales have good thicknesses (average = 43.50 m [143 ft] and 30.80 m [101 ft], respectively), high quartz contents (average = 51.42 and 31.96 vol. %), low clay contents (average = 32.16 and 36.23 vol. %), high organic matter contents (average = 4.07 and 3.27 wt. %), favorable kerogen types (II1 and II2), and suitable maturity (average = 1.61% and 1.52%). Both shales exhibit similar geological and geochemical characteristics to those of commercially developed shale gas systems. The calculated total gas in the shales is ∼93 BCF/section (1013 m3/m3) and 47 BCF/section (512 m3/m3), respectively. Therefore, the shales are good source rocks, with the Gufeng Formation having the better shale gas potential. In addition, lateral intrabasinal comparisons suggest the southern Anhui Province has better shale gas-prone source rock potential than the southern Jiangsu Province.