Methane/CO₂ Sorption Modeling for Coalbed Methane Production and CO₂ Sequestration

Abstract

A thorough study of the sorption behavior of coals to methane and carbon dioxide (CO 2 ) is critical for carbon sequestration in coal seams and enhanced coalbed methane recovery. This paper discusses the results of an ad/de-sorption study of methane and CO 2 , in single gas environment, on a set of coal samples taken from the San Juan and Illinois Basins. The results indicate that, under similar temperature and pressure conditions, coals exhibit higher affinity to CO 2 as compared to methane and that the preferential sorption ratio varies between 2:1 and 4:1. Furthermore, the experimental data were modeled using Langmuir, BET, and Dubinin-Polanyi equations. The accuracy of the models in quantifying coal-gas sorption was compared using an error analysis technique. The Dubinin-Radushkevich equation failed to model the coal-gas sorption behavior satisfactorily. For methane, Langmuir, BET, and Dubinin-Astakhov (D-A) equations all performed satisfactorily within comparable accuracy. However, for CO 2 , the performance of the D-A equation was found to be significantly better than the other two. Overall, the D-A equation fitted the experimental sorption data the best, followed by the Langmuir and BET equations. Since the D-A equation is capable of deriving isotherms for any temperature using a single isotherm, thus providing added flexibility to model the temperature variation due to injection/depletion, this is the recommended model to use.

Methane Adsorption Rate and Diffusion Characteristics in Marine Shale Samples from Yangtze Platform, South China

“…The value of P L can also be a measure of the isotherm curvature: the smaller the value of P L , the greater the initial slope of the isotherm [43]. A least-squares fit of methane adsorption isotherms based on the Langmuir model was applied to determine the Langmuir parameters, including V L and P L .…”

Data Preprocessing and Its Influence on the Adsorption Capacity of Calculated Shale. Comparison of Selected Methods: A Case Study

“…A description of this method is often found in the literature (Kroos et al 2002;Harpalani et al 2006;Lutyński 2014). The data for calculation was collected from high-accuracy pressure and temperature transducers, connected to a computer and working in continuous mode online.…”

Comparative Experiment Study on Nitrogen Injection and Free Desorption of Methane-Rich Bituminous Coal Under Triaxial Loading

“…The adsorption energy of solid to gas forms the first molecular layer and the adsorption energy of gas to gas forms the second and the rest adsorbed molecular layers. Actually, the BET model can describe the different types of isothermal adsorption curves (Lowell & Shields, 1984;Harpalani, 2006).…”

“…P 0 is the saturation vapor pressure of the adsorbate at temperature T, and P is the equilibrium vapor (or free gas) pressure (Harpalani, 2006). Dubinin and Radushkevich suggested that the value of n = 2 may be appropriate for some cases, and the equation (D-R equation) can be modified as…”