Expanded Single and Multicomponent Adsorption/Desorption Isotherm Research

Abstract

Within unconventional reservoirs, gas is stored in a free gas phase (occupying the reservoir’s pore space), in an adsorbed gas phase (where gas is stored on the surface of the rock matrix), and as diffused gas within kerogen (which is outside of the scope of this thesis). Because adsorbed gas exhibits a liquid-like density, significantly more gas can be stored in the adsorbed phase compared to the free gas phase. It is essential to consider these two mechanisms of gas storage when evaluating reservoirs for original gas in place calculations or the implementation of enhanced gas recovery (EGR) techniques. The following thesis aims to further the literature’s comprehension of the effects of multiple parameters simultaneously on adsorption capacity and gas recovery in two comprehensive sets of experiments. The first set of experiments evaluated single component adsorption/desorption isotherms for five different gases (methane, ethane, propane, nitrogen, and carbon dioxide) on activated carbon at three distinct temperatures (30 °C, 45 °C, and 80 °C) up to 1500 psi. The isothermal adsorption and desorption data was calculated using the Gibbs sorption method and modelled with the Langmuir isotherm, where Langmuir parameters for each experiment were determined. The effects of pressure, temperature, gas type, and process (adsorption vs. desorption), as well as the fit of the Langmuir model, were assessed. The second set of experiments expanded upon the previous set, where binary-component mixtures were tested in conjunction with activated carbon, at the three aforementioned temperatures to highlight the effects of competitive adsorption. In this set of experiments, methane was injected into an activated carbon sample and following a “primary production” phase, was displaced by either nitrogen or carbon dioxide in five subsequent injection/production cycles, simulating a huff-n-puff-like displacement. Sorption capacities, changing adsorbed/free gas compositions, selectivity ratios, and recovery factors were determined, and the effects of displacement gas type and temperature were compared. Further, the Langmuir parameters from the first set of experiments were utilized to generate Extended Langmuir models for the binary mixtures and the quality of the model fits were evaluated. The numerous results of both studies are presented in the Conclusions section of this thesis.