Supercritical Methane Adsorption on Shale over Wide Pressure and Temperature Ranges: Implications for Gas-in-Place Estimation

Abstract

Methane adsorption experiments over wide ranges of pressure (up to 30 MPa) and temperature (30–120 °C) were performed using a gravimetric method on the Longmaxi shale collected from the northeast boundary of Sichuan Basin, China. Organic geochemical analyses, shale composition determination, and porosity tests were also conducted. The experimental supercritical methane excess adsorption isotherms at different temperatures initially increase and then decrease with increasing pressure, giving a maximum excess adsorption capacity (G ex m = 1.86–2.87 cm3/g) at a certain pressure P m (6.71–12.90 MPa). The excess adsorption capacity decreases with increasing temperature below 28 MPa, while this effect reversed above 28 MPa. However, the absolute adsorption capacity decreases as the temperature increases over the full pressure range. Supercritical methane adsorption on shale is of temperature dependence because it is a physical exothermic process supported by calculated thermodynamic parameters. P m is positively correlated with the temperature, while the decline rates (0.021–0.058 cm3 g–1 MPa–1) in excess adsorption negatively correlate with the temperature. Meanwhile, Langmuir volume G L (3.07–4.04 cm3/g) decreases while Langmuir pressure P L (1.44–4.31 MPa) increases with temperature elevation. In comparison to the actual adsorbed gas (absolute adsorption), an underestimation exists in the excess adsorption calculation, which increases with increasing depth. The conventional method, without subtracting the volume occupied by adsorbed gas, overestimates the actual free gas content, especially for the deep shale reservoirs. In situ adsorbed gas is simultaneously controlled by the positive effect of the reservoir pressure and the adverse effect of the reservoir temperature. Nevertheless, in situ free gas is dominated by the positive effect of the reservoir pressure. Low-temperature overpressure reservoirs are favorable for shale gas enrichment. Geological application of gas-in-place estimation shows that, with increasing depth, the adsorbed gas content increases rapidly and then declines slowly, whereas the free gas content increases continuously. There was an equivalence point at which the contents of adsorbed and free gas are equal, and the equivalence point moved to the deep areas with increasing water saturation. Moreover, the adsorbed gas and free gas distribution are characterized by the dominant depth zones, providing the reference for shale gas exploration and development.

Effect of Cryogenic Liquid Nitrogen on the Morphological and Petrophysical Characteristics of Tight Gas Sandstone Rocks from Kirthar Fold Belt, Indus Basin, Pakistan

“…Developed countries such as the United States, China, and Europe have already addressed numerous apprehensions about the status and hurdles. They have also recommended practices for unconventional natural gas resource exploitation and development to solve the energy crisis via different enhanced oil and gas recovery pathways − and smart drilling techniques. − Figure shows the status of production of unconventional natural gas from coalbed methane, shale gas, and tight gas around the globe. , Among the developing countries, Pakistan needs considerable natural gas in order to develop its infrastructure. Surging energy consumption in different industry sectors such as power-generating plants and cement industry has also increased natural gas consumption.…”

Synergetic Effect of Water, Temperature, and Pressure on Methane Adsorption in Shale Gas Reservoirs

“…The molecular simulation found that increasing temperature reduces the isosteric heats of adsorption, 43 while methane adsorption sites tend to shift from low-energy sites to high-energy sites, resulting in a decrease in methane adsorption. 36,43 Langmuir pressure P L is a temperature-dependent parameter related to the enthalpy of adsorption, and the relationship between P L and temperature can be expressed as 86,87…”

“…This indicates that an increase of 50 °C leads to a 23.05% reduction in the maximum adsorption capacity. The molecular simulation found that increasing temperature reduces the isosteric heats of adsorption, while methane adsorption sites tend to shift from low-energy sites to high-energy sites, resulting in a decrease in methane adsorption. , Langmuir pressure P L is a temperature-dependent parameter related to the enthalpy of adsorption, and the relationship between P L and temperature can be expressed as , where T is the temperature in K; Δ H is the adsorption enthalpy, J/mol; Δ S 0 is the standard adsorption entropy, J/mol/K; R is the ideal gas constant of 8.3145 J/mol/K; and P 0 is the atmospheric pressure of 0.101 MPa. The negative linear relationship between ln P L and 1/ T can be observed in Figure a, which indicates that the higher the temperature, the higher the P L .…”

Study on the Adsorption and Thermodynamic Characteristics of Methane under High Temperature and Pressure

“…The shale samples were taken from the Silurian Longmaxi Formation in the Sichuan Basin, China, and the adsorption isotherms of methane were measured by a gravimetric approach within the pressure range of 0−30 MPa and temperature range of 303− 393 K. The total organic carbon (TOC) content in this sample was 3.65%, and the detailed information of other physical parameters can be found in the original publication. 48 Here, only the adsorption isotherms at different temperatures have been displayed (Figure 2). These data have been substituted into eq 4, and the parameters of the adsorption model were obtained by the global fitting method, as shown in Table 1.…”