Date of Award
Master of Science
Cleat permeability of coal is the most critical parameter affecting the amount of production from a coalbed methane (CBM) reservoir. As a result, there have been many studies about how cleat permeability changes over the life of a reservoir, leading to the development over time of several different permeability models. Most permeability models used today consider volumetric strain as an input parameter; however, permeability is impacted primarily by the increase in cleat aperture, resulting from matrix shrinkage in the horizontal direction. Recent work has shown that coal exhibits transverse isotropy, with total strain in the vertical direction being significantly higher than either horizontal direction. Hence, the inclusion of vertical strain through use of the volumetric strain parameter could be predicting inaccurate permeability variation results. The objective of this study was to determine the difference in permeability modeling with volumetric strain compared to permeability modeling with only horizontal strain, and assess the degree to which different parameters affect results from modeling using only horizontal strain. Experimental results showed that matrix strain remained consistent with transversely isotropic results of previous works. When included into the Palmer and Mansoori (P&M) permeability model, modeling results showed that permeability with horizontal strain is significantly lower than that with volumetric strain. The three unmeasured parameters in the Palmer and Mansoori permeability model have a major effect on the final results and need to be history matched in order to improve the level of accuracy in their estimation.
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