Source rock and reservoir qualities of middle Jurassic Lianggaoshan lacustrine shale at fuxing area, Sichuan Basin: Implication for shale-oil enrichment

Abstract

The shale oil exploration, in the Middle Jurassic Lianggaoshan Formation in the Fuxing area of Sichuan Basin, is in preliminary stage, requiring further in-depth study on shale oil and gas enrichment conditions. The lithological, organic geochemical, and reservoir characteristics of the Lianggaoshan Formation shale were analyzed using a suite of tests, including common thin section observation, organic carbon determination, pyrolysis experiment, combined N₂-high pressure mercury test and argon ion polishing-scanning electron microscope, to elucidate source rock and reservoir qualities and their variation in vertical. Results suggest that the medium-carbon argillaceous shale, medium-carbon shell calcareous-argillaceous shale, and low-carbon argillaceous shale facies were mainly developed in Member 1 and Member 2 of the Lianggaoshan Formation. The medium-carbon argillaceous shale facies in the sub-layer ④ was rich in organic matter, with abundant sapropel, chitinous and secondary organic components, which were considered as a set of medium-quality source rocks. The medium-carbon shell calcareous-argillaceous shale and low-carbon argillaceous shale in the sub-layers ② and ③ have relatively low organic matter abundance, with vitrinite and inertinite as major organic microscopic components, revealing poor hydrocarbon generation potential. The porosity of shale reservoirs in sub-layers ②‒④ was higher than 3.0%, with predominant mesopores, followed by macropores, consisting of mainly clay mineral pores, organic pores, and microfractures related to organic matter. The medium-carbon argillaceous shale facies at the Lianggaoshan Formation is high-quality source rocks and reservoirs and is thus a potential target for lacustrine shale oil exploration in the Fuxing area of the Sichuan Basin.