The Stress and Gas Absorptive Effect on Coal Densities in Laboratory CBM/ECBM Processes

ABSTRACT

Density is an important coal property that determines the potential of gas resources in CBM reservoir. This paper aims to investigate coal density and structure variation during primary CBM and CO2-ECBM experiments. A coal core sample from Alberta Mannville formation with the rank of SubB was used to conduct the core flooding experiments covering the stages of inert gas flow, methane production, methane displacement by CO2 and inert gas flow after CO2 desorption. The x-ray CT experiments were carried out parallel to the core flooding experiment to provide x-ray images of coal core saturated with different gases at different stress conditions. The x-ray techniques were used for visualization and mapping of larger fractures and mineral streaks, as well as identification of flow paths. The coal density and density distribution changed with the gas adsorptive capacity and the stress condition were obtained.

The results show that net stress, gas adsorption capacity, and the production history are all key factors affecting coal core structure, leading coal density and density distribution variations. Hence, the core flow path, which contributes to the coal permeability, changes with those factors during CBM/ECBM processes. The results from this study provide laboratory coal characterization techniques using x-ray imaging analysis.

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