Isothermal Adsorption and Desorption Properties of Marine Shales on Longmaxi Shale in South China

Abstract

The investigation of adsorption and desorption properties of shale are important for estimating reserves and exploitation. The shale samples used in this paper were from the marine shale on Longmaxi shale in Sichuan and Hubei province, China. A series of analyses, such as organic carbon content test, vitrinite reflectance test, rock pyrolysis, X-ray diffraction, and N 2 /CO 2 adsorption were performed. Gravimetric method with magnetic suspension balance was used to conduct isothermal adsorption and desorption experiments. The Langmuir, Freundlich, Langmuir-Freundlich, D-R, semi-pore, and Tothequations were used to fit the isothermal adsorption and desorption curves. And adsorption potential theory was used to explain the adsorption and desorption process. According to the results, the shale samples have a high level of organic carbon content with the same organic matter type II1 and high degree of maturation. The volume of adsorption increases rapidly and slows down to stable with the pressure increasing. Desorption is the inverse process of adsorption and 10 MPa -0.5 MPa is the main period of shale gas desorption. The fitting results show that three-parameter isotherm equations are better than the two-parameter ones. The adsorption temperature has a great influence on adsorption volume, little effect on potential energy. Adsorption potential varies under different TOC to affect adsorption properties. Moreover, a large adsorption potential means that the gas molecule is easy to adsorb but difficult to desorb.

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

“…The experimental investigation suggested that higher temperature results in a lower gas sorption content in the Devonian shale reservoir . Zhang believed that methane adsorption in both shale and isolated kerogen decreased with increasing temperature, which is in line with the conclusions obtained from other investigations. − It is widely reported that methane excess adsorption in shale and coal does not increase monotonically but first increases and then decreases with increasing pressure. ,,− However, the absolute adsorption increases monotonically and is greater than the excess adsorption. , The difference between absolute adsorption and excess adsorption is related to the ratio of the free gas density to the adsorbed gas density. , The density of free gas in the low-pressure stage is much lower than the density of adsorbed gas; therefore, the excess adsorption is approximately equal to the absolute adsorption. With the increase of pressure, when the increasing rates of the free gas density and the adsorbed gas density are equal, the excess adsorption reaches the maximum .…”

Effect of Surface Coverage of Water Molecules on Methane Adsorption on Muscovite and Pyrophyllite: Molecular Dynamics Study

“…Several factors contributing to the adsorption amount have been reported to date (for example, ref ). According to previous experimental studies, total organic carbon (TOC), − thermal maturity, and clay content ,, are positively correlated with the adsorption amount, while temperature − and moisture content ,− have a negative correlation with the adsorption amount.…”