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

Abstract

The understanding of the adsorption and thermodynamic characteristics of methane adsorbed by shale under high pressure and high temperature (HPHT) is of great significance for evaluating deep shale gas reserves and for optimizing shale gas development. In this study, a strict framework for analyzing the adsorption−thermodynamic characteristics of methane adsorption in shale under HPHT conditions was proposed. Further, data processing and explanation of the framework were carried out through reference to published experimental data. When real gas behavior and phase density changes were considered, the temperaturedependent parameters were corrected on the dual-site Langmiur model (DSL) model to reflect the absolute adsorption isotherm at each temperature. These were successfully calculated by combining those with the global fitting method. Compared with other adsorption models that reflected surface heterogeneity, the modified DSL model was found to well characterize the adsorption behavior of shale under HPHT conditions. The thermodynamic potentials of the methane adsorption process were further calculated from the results obtained from the modified DSL model. It was found that in the two groups of shale samples with different total organic carbon (TOC) contents, the change law of isosteric enthalpy with adsorption capacity was different. The abnormal entropy change behavior of methane adsorption in shale with higher TOC content was explained, and a new position concerning the long-standing controversy relating to entropy change was put forward. In addition, both the total entropy and internal energy during the methane adsorbed phase under HPHT increased with an increase in adsorption capacity, and the total entropy in the adsorbed phase revealed a positive relationship with temperature. By introducing a thermodynamic graphic method to draw a clearer and more intuitive U a −n a −S a three-dimensional surface, more thermodynamic potential information could be obtained. The framework proposed in this study could also be used to help future research on the influence of basic physical parameters on adsorption and thermodynamic properties and to provide a foundation for improving the evaluation of deep shale gas reserves.

Study on Adsorption Characteristics of Deep Coking Coal Based on Molecular Simulation and Experiments

“…(2) L−F model (5) (3) BET multimolecular layer model (6) (4) D−R model (7) (5) D−A model (8) where n ab is the excess adsorption capacity, cm 3 /g; n 0 is the limit adsorption capacity, cm 3 /g; b is a constant related to the adsorbent, adsorbate properties, and temperature, MPa 10 shows the methane adsorption corresponding to different burial depths in the Xingwu Coal Mine and Pingdingshan Coal Mine.…”

“…For a long time, the focus of gas control has mainly been on highly metamorphic coal represented by anthracite, and there are few studies on coking coal. In particular, lack of research on the gas adsorption characteristics of coking coal under high-temperature and high-pressure conditions seriously restricts the development of coalbed methane, gas disaster control, and safe mining in coking coal mining areas. − Therefore, it is necessary to study the adsorption characteristics of coking coal on methane under high-temperature and high-pressure environments.…”

Cardiovascular Change in Athletes at Different Training Status Levels

“…Improving heart function is one of the main training goals of many sports events (especially endurance events). 1 Therefore, grasp the characteristics of the adaptability changes of the athlete's heart function to long-term training and the stress changes caused by different loads, for sports selection, evaluate the training effect, improving training methods has very important theoretical and practical significance. 2 The cardiovascular response caused by exercise is very complicated.…”

Methane/Carbon Dioxide Adsorption and Diffusion Performances at Different Mineral Compositions and Buried Depth Conditions

“…25,26 Moreover, the MD method is also employed to investigate the adsorptions of organic matter pores for methane and carbon dioxide; as a result, the adsorptions of methane and carbon dioxide on shale are physical adsorptions. 27 Certain achievements have been attained regarding the mechanisms underlying the adsorption and diffusion behaviors of methane; 28,29 however, most studies focus on the adsorption and diffusion behaviors of methane in single minerals. In actual practice, shale is usually jointly constituted by multiple minerals with significant differences in the sizes of pores that can store gas, which means that the adsorption capacities of minerals for methane are different.…”

“…Certain achievements have been attained regarding the mechanisms underlying the adsorption and diffusion behaviors of methane; , however, most studies focus on the adsorption and diffusion behaviors of methane in single minerals. In actual practice, shale is usually jointly constituted by multiple minerals with significant differences in the sizes of pores that can store gas, which means that the adsorption capacities of minerals for methane are different. , At the same time, X-ray diffraction (XRD) and total organic carbon (TOC) measurements show that illite, montmorillonite, and calcite are the major components of the clay types in the shale. , Therefore, based on the above research and the problems to be solved, this paper adopted the molecular simulation method to comparatively analyze the methane and carbon dioxide adsorption and diffusion performances in these three minerals and to explore the influences of different buried depths on their adsorption and diffusion performances.…”