Simulation of methane adsorption in diverse organic pores in shale reservoirs with multi-period geological evolution

Abstract

In shale reservoirs, the organic pores with various structures formed during the thermal evolution of organic matter are the main storage site for adsorbed methane. However, in the process of thermal evolution, the adsorption characteristics of methane in multi type and multi-scale organic matter pores have not been sufficiently studied. In this study, the molecular simulation method was used to study the adsorption characteristics of methane based on the geological conditions of Longmaxi Formation shale reservoir in Sichuan Basin, China. The results show that the characteristics of pore structure will affect the methane adsorption characteristics. The adsorption capacity of slit-pores for methane is much higher than that of cylindrical pores. The groove space inside the pore will change the density distribution of methane molecules in the pore, greatly improve the adsorption capacity of the pore, and increase the pressure sensitivity of the adsorption process. Although the variation of methane adsorption characteristics of different shapes is not consistent with pore size, all pores have the strongest methane adsorption capacity when the pore size is about 2 nm. In addition, the changes of temperature and pressure during the thermal evolution are also important factors to control the methane adsorption characteristics. The pore adsorption capacity first increases and then decreases with the increase of pressure, and increases with the increase of temperature. In the early stage of thermal evolution, pore adsorption capacity is strong and pressure sensitivity is weak; while in the late stage, it is on the contrary.

Permeability Enhancement Technology for Soft and Low-Permeability Coal Seams Combined with Hydraulic Perforation and Hydraulic Fracturing

“…The coal and gas outburst dynamics are the result of the combined effects of ground stress, gas pressure, and coal mechanical properties [1][2][3][4][5][6]; it always threatens the safety of underground production as a serious mine disaster [7][8][9][10][11][12]. In some soft outburst coal seams with low permeability in China, the coal seam has suffered from strong structural compression deformation due to the influence of multistage geological structure, and its primary structure has been damaged seriously, and the coal body strength and coal seam permeability are low [13][14][15][16][17].…”

Mesoscopic Mechanism of Permeability of Coal Rock Mass with Increasing Temperature in the Range of Room Temperature to 350°C

“…In recent years, many experiments on the permeability of coal rocks under thermal action have found some special phenomena and laws [15][16][17][18]. In the experiments on the permeability of lignite under the e ect of temperature and triaxial stress, Hu et al [19] found that the permeability of coal samples showed a monotonic decreasing pattern in the range of room temperature to 300 °C with the increase of temperature, although the axial pressure and the surrounding pressure applied to the coal samples always kept constant pressure.…”

Pore Structure in Shale Tested by Low Pressure N2 Adsorption Experiments: Mechanism, Geological Control and Application

“…Pore systems in shale are important for gas storage and transport [3][4][5][6]. From the start of shale gas development and production, pore structure has been one of the key research topics [7,8], and numerous studies have been carried out on pore systems in shale [9,10]. These have shown that shale contains organic pores and inorganic pores, e.g., within clays or formed by carbonate dissolution [11,12].…”