Modified Dubinin–Astakhov Model for the Accurate Estimation of Supercritical Methane Sorption on Shales

Abstract

In order to evaluate the total shale gas-in-place (GIP) resources in deep formations, it is important to study the sorption of supercritical methane in shales. At present, the Dubinin−Astakhov model is used to describe sorption isotherms. However, it still has some shortcomings. The main objective of this study is to establish an optimized model for supercritical methane sorption in shales. A series of high-pressure methane sorption isotherms were measured at different temperatures (from 293 to 333 K) for shale samples collected in the Cengong block, Guizhou, China. The characteristics and causes of shale gas sorption capacity changes were analyzed. By comparing the fitting results of several conventional sorption models, the characteristics and applicable scope of these models are obtained. A four-parameter (V 0 , D, m, and ρ a ) modified supercritical D−A model was developed to accurately estimate the sorption of supercritical methane on shales based on Polanyi sorption potential theory. The results show that the sorption characteristic curve of methane on the shale surface under high pressure is obviously different from that under low pressure. The density of the sorption phase and the virtual saturated vapor pressure have a great influence on the fitting results of the sorption models. The density of the adsorption phase directly determines the ultimate sorption capacity of the shale sample. Also, the modified D−A model can improve the accuracy of the prediction of supercritical methane sorption on shales, and it can accurately describe the isothermal sorption law of gas in the supercritical state.

Adsorption Capacities of Ammonia‐Activated Carbon Pairs in a Single‐Bed Adsorption Cooling System

“…For all adsorbents at low pressure, the amount of ammonia adsorbed increases sharply and tends to become constant at higher differences in operating pressure. This supports that the adsorbents follow typical Langmuir‐type adsorption behavior 26. The Langmuir isotherm sorption model (Eq.…”

“…This supports that the adsorbents follow typical Langmuir-type adsorption behavior [26]. The Langmuir isotherm sorption model (Eq.…”

Methane Adsorption Equilibrium on Marine Gas-Bearing Shale Matrices: The Polanyi Potential Theory Approach

“…36 Among them, the D−A model proposed in 1971 is widely applied to the CH 4 − shale system. 28,65 The mathematic form of the D−A model is 26 where n abs is the absolute adsorption capacity of CH 4 , cm 3 /g. n m is the maximum saturation adsorption capacity of CH 4 , cm 3 / g. ε is the adsorption potential, J/mol, which is defined as eq 3.…”

“…Instead, the pseudosaturated vapor pressure (P s , MPa) is recommended. 66−68 Until now, the Antoine equation, 34 the Reich equation, 65 the Dubinin equation, 66 and the Amankwah equation could calculate the pseudosaturated vapor pressure. 69 Particularly, the Amankwah equation involves parameter k (eq 4), which is capable of characterizing various adsorption systems.…”

Impact of Ionic Liquid Structure and Loading on Gas Sorption and Permeation for ZIF-8-Based Composites and Mixed Matrix Membranes

“…Table 1 gathers the textural properties of these materials, along with pristine ZIF-8. Total pore volume (V p ), specific BET surface area (A BET ), and micropore volume (V micro , calculated using the Dubinin-Astakhov equation [50]) were determined for a relative pressure (p/p 0 ) of 0.97. The textural properties of IL@ZIF-8(low) composites are very similar, though slightly inferior, to the ZIF-8 ones.…”