Resercoir space characteristics and pore structure of Jurassic Lianggaoshan Formation lacustrine shale reservoir in Sichuan Basin, China: Insights into controlling factors

The Jurassic Lianggaoshan Formation lacustrine shale oil is the most potential exploration target of unconventional hydrocarbon resource in Southwest China. In this study, nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), low-temperature N-2 adsorption (LTNA), and high pressure mercury intrusion mercury injection capillary pressure are intergrated to reveal pore structure and its controlling factors of Lianggaoshan Formation lacustrine shale reservoir. Results indicate that three types of lithology combination are classified in the Jurassic Liangggaoshan lacustrine shale reservoir. Type A comprises pure shale. Type B is characterized by frequent shell limestone interbedding. Type C is characterized by frequent siltstone interbedding. The Type C shale is characterized by relatively high proportion of organic pores, high development and good connectivity of nanopores, and highest pore volume and Surface area. The nanopores of Lianggaoshan lacustrine shales are mainly dominated by mesopores and part of the macropores. Among them, the PV and SA are both mainly dominated by micropores. The enrichment of organic matter has little effect on the development of micropores, and does not affect the mesopore and macropore development. Quartz particles in Lianggaoshan lacustrine shale do not clearly facilitate the development of micropore and mesopore-macropore. Intraparticle pore in feldspar clast is an important component of mesopore and macropore. Clay minerals has no positive effect on the formation of micropore and mesopore-macropore.

Automated summary

The Jurassic Lianggaoshan Formation lacustrine shale oil is a highly potential unconventional hydrocarbon resource in Southwest China. This study used various methods to analyze the pore structure and its controlling factors in the Lianggaoshan Formation lacustrine shale reservoir, including NMR, SEM, LTNA, and high pressure mercury intrusion mercury injection capillary pressure. The results showed that the shale reservoir can be categorized into three types based on lithology combination, with Type C shale having the highest organic pores proportion, nanopore development, and pore volume and surface area. The nanopores in Lianggaoshan lacustrine shales are mainly mesopores and some macropores, dominated by micropores in terms of pore volume and surface area. The enrichment of organic matter has little effect on micropore development but affects the development of mesopores and macropores. Quartz particles and clay minerals do not significantly contribute to the development of micropores and mesopores-macropores, while intraparticle pore in feldspar clast is an important component of mesopores and macropores.