The Resource Evaluation of Jurassic Shale in North Fuling Area, Eastern Sichuan Basin, China

Light oil and natural gas are commonly found in Jurassic shales in the North Fuling area of Sichuan Bain in China. The main source rocks of the study area are shales from Lower-Middle Jurassic lacustrine layers including the Lianggaoshan Formation (J(2)l) and the Ziliujing Formation (J(1)z), which are further divided into the Da'anzhai (J(1)zD), Ma'anshan (J(1)zM), and Dongyuemiao (J(1)zDY) members. Multiple geochemical approaches and tests including kerogen elements, kerogen composition, vitrinite reflectance (VR), total organic carbon (TOC) content test, Rock-Eval pyrolysis, gas chromatography and gas chromatography-mass spectrometry, methane concentration, gas composition, and stable isotopes were employed to determine the geochemical characteristics of the source, oil and gas samples. J(1)zD shale demonstrates the best abundance and type of organic matter among all four strate and tends to be the most favorable source of hydrocarbons in this area. Crude oil in Jurassic strata is a waxy light oil. Oil samples and shale extracts are nonbiodegraded, and dominated by short-chain n-alkanes, maximizing around C-12-C-15. Natural gas in Jurassic shales can be categorized as wet gas. delta C-13 values in different components indicate the gas samples are oil-associated gas which probably originated from the cracking of crude oil. Source correlations suggest the oil and gas are probably generated from J(1)zD shale. The analysis leads to the general conclusion that the Jurassic shale is more favorable for conventional resources than shale gas.