(112c) Modeling the Temperature Dependence of Supercritical Gas Adsorption: A Comparative Study

Simulations of enhanced coalbed methane (CBM) recovery and carbon dioxide sequestration in coalbeds require reliable adsorption models to describe the gas adsorption behavior under wide ranges of temperature and pressure. Due to the geothermal gradients in coalbed reservoirs, a significant variation in temperatures may exist in these reservoirs. Thus, a robust CBM adsorption model should be capable of describing the temperature dependence of supercritical gas adsorption expected in these systems.

In this work, we investigate the adsorption prediction capabilities of the simplified local-density (SLD) model.  The SLD model is used to investigate systematically the predictions of supercritical gas adsorption behavior, examine the temperature dependence and extend the model’s applicability to a wider temperature range.

To conduct this study, an expanded database was compiled that comprised of experimental adsorption measurements of pure- and mixed-gas adsorption. Emphasis was placed on data on gas species that are found typically in natural gas systems. The database comprised of measurements on activated carbons at several temperatures. The SLD adsorption model was then used to both correlate and predict the pure-gas adsorption over wide ranges of temperatures. The temperature dependence relations were incorporated in the model to improve the predictive capabilities. Using the parameters obtained from pure-gas adsorption, a priori predictions were obtained for mixture gas adsorption. The temperature dependence relations developed were found capable of reliable predictions of pure-gas adsorption. Further, the model was found capable of providing a priori predictions of mixed-gas adsorption for the systems studied.