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

Abstract

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.

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

“…The isotherm adsorption experiment of the Longmaxi Formation shale shows that isothermal adsorption curves of shale samples of the Longmaxi Formation in the Dingshan area, southeast Sichuan Basin are approaching the IV type curve according to the international IUPAC classification standard. The pressure can be split into three stages, including “low pressure”, “medium pressure”, and “high pressure”. , Specifically, the relative pressure between 0 and 0.45 is determined as the “low pressure” stage, the relative pressure between 0.45 and 0.9 is determined as the “medium pressure” stage, and the relative pressure between 0.9 and 1 is determined as the “high pressure” stage. When the adsorption and desorption curves are greater than 0.45 at P / P 0 , a significant noncoincidence can be observed.…”

“…The pressure can be split into three stages, including "low pressure", "medium pressure", and "high pressure". 55,56 Specifically, the relative pressure between 0 and 0.45 is determined as the "low pressure" stage, the relative pressure between 0.45 and 0.9 is determined as the "medium pressure" stage, and the relative pressure between 0.9 and 1 is determined as the "high pressure" stage. When the adsorption and desorption curves are greater than 0.45 at P/P 0 , a significant noncoincidence can be observed.…”

Adsorption behavior and mechanism of CO2in the Longmaxi shale gas reservoir

“…Micropores are widely developed in the Longmaxi shale and dominate the specic surface area of pores which control the adsorption capacity of shale. 36,37 This is because the organic matter in the Longmaxi shale is in the stage of high-over maturity. The source rock reached the generation peak of gaseous hydrocarbon and formed a great amount of expansion micropores in organic matter.…”

Characteristics and Influencing Factors of Supercritical Methane Adsorption in Deep Gas Shale: A Case Study of Marine Wufeng and Longmaxi Formations from the Dongxi Area, Southeastern Sichuan Basin (China)

“…Values of methane adsorption at different temperatures on shale samples from previous works were also collected and compared in this work ,− (Table ; Figure ). The slopes of the correlation between the maximum methane absolute adsorption and temperatures are different for various shale samples, but all show significantly negative correlations.…”