Analysis of Adsorption Characteristics and Influencing Factors of Wufeng-Longmaxi Formation Shale in Sichuan Basin

Shale gas resources provide a new impetus to alleviate the contradiction between China's oil and gas supply and demand. As an important part of shale gas, understanding the occurrence mechanism of adsorbed gas can help shale gas resources to be better developed and used. This time, a series of experiments, such as low-temperature nitrogen adsorption and methane isotherm adsorption, were conducted to discuss the pore structure, adsorption performance, and adsorption mechanism of shale. The results show the following: (1) Shale pores are dominated by nanopores, and pores with a pore width of less than 2 nm have the best relationship with the shale surface area and adsorption capacity. (2) Total organic carbon (TOC) plays an important role in controlling the specific surface area and methane adsorption capacity of shale. This is mainly due to the large number of micropores (pore size of <2 nm) developed in organic matter. Micropores provide the main specific surface area and adsorption sites for methane adsorption. (3) A variety of models were used to fit shale methane isotherm adsorption data. The results show that the SDR model and Langmuir model have the best fit. The methane adsorption performance of shale is controlled by many factors; the adsorption capacity becomes weaker as the temperature rises; and this influence is also affected by TOC. (4) In comparison to the adsorption capacity, the change of the adsorbed phase density is more complicated: overall, there is a weak positive correlation with TOC; as the temperature increases, the adsorbed phase density decreases. However, this law is not stable, and there are different performances in different experiments. (5) The adsorption comparison results show that the shale methane adsorption is mainly multilayer adsorption and micropore filling.

Automated summary

Shale gas resources provide new impetus for alleviating the contradiction between China's oil and gas supply and demand. Understanding the occurrence mechanism of adsorbed gas can help in the better development and utilization of shale gas resources. The experiments conducted in this study revealed that nanopores dominate shale pores, with Total Organic Carbon (TOC) playing an important role in controlling specific surface area and methane adsorption capacity. Micropores in organic matter provide the main specific surface area and adsorption sites for methane adsorption, which is mainly multilayer adsorption and micropore filling in shale.