Measurements, Modeling and Analysis of High Pressure Gas Sorption in Shale and Coal for Unconventional Gas Recovery and Carbon Sequestration

In order to exploit unconventional gas and estimate carbon dioxide storage potential in shale formations and coal seams, two key questions need to be initially answered:

1. What is the total gas-in-place (GIP) in the subsurface reservoirs?
2. What is the exact ratio between bulk gas content and adsorbed gas content?

Both questions require precise estimation of adsorbed phase capacity of gases (methane and carbon dioxide) and their adsorption behavior in shale and coal. This dissertation therefore analyzes adsorption isotherms, thermodynamics, and kinetics properties of methane and carbon dioxide in shale and coal based on experimental results to provide preliminary answers to both questions.

It was found that the dual-site Langmuir model can describe both methane and carbon dioxide adsorption isotherms in shale and coal under high pressure and high temperature conditions (up to 27 MPa and 355.15K). This allows for accurate estimation of the true methane and carbon dioxide GIP content and the relative quantity of adsorbed phases of gases at in situ temperatures and pressures representative of deep shale formations and coal seams. The concept of a deep shale gas reservoir is then proposed to optimize shale gas development methodology based on the successful application of the model for methane adsorption in shale.

Based on the dual-site Langmuir model, the isosteric heat of adsorption is calculated analytically by considering both the real gas behavior and the adsorbed phase under high pressure, both of which are ignored in the classic Clausius–Clapeyron approximation. It was also found that the isosteric heat of adsorption in Henry's pressure region is independent of temperature and can serve as a quantified index to evaluate the methane adsorption affinity on coal.

In order to understand the dynamic response of gas adsorption in coal for carbon sequestration, both gas adsorption kinetics and pore structure of coal are investigated. The pseudo-second order model is applied to simulate the adsorption kinetics of carbon dioxide in coals under different pressures. Coal particle size effects on pore characterization of coal and carbon dioxide and nitrogen ad/desorption behavior in coal was also investigated.