Coal Characterization in CBM/ECBM Processes Using X-Ray CT Analysis

ABSTRACT

This paper presents the results of coal characterization during primary CBM and CO2-ECBM experiments using x-ray CT techniques. The coal density and density distribution varied with the gas type and gas pressure are investigated. A coal core sample from Alberta Manville formation with the rank of SubB was used in this work. Core flood experiments in coal have been conducted in inert gas (helium) flow, methane production, methane displacement by CO2 and inert gas flow after CO2 desorption. The x-ray CT experiment was carried out parallel to the core flood experiment to provide x-ray images of coal core saturated with different gases at different system pressures. 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 type and gas pressure were obtained.

The results show that net overburden pressure, 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 and Enhanced Coalbed Methane (ECBM) processes. The shrinkage and swelling of coal matrix due to adsorbing gases were also measured during production. The results from this study provide laboratory coal characterization techniques using x-ray imaging analysis.

A full version of this paper is available on CSEG Online.