46th U.S. Rock Mechanics/Geomechanics Symposium,
2012. American Rock Mechanics Association
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CO2 is commonly injected at lower temperature than that of the targeted coal seams in the field for sequestration. Under this condition, coal matrix swelling due to the thermal expansion and shrinkage induced by the decreasing adsorption capacity with increasing temperature complicate the permeability evolution and may lead to acceleration or delay of the permeability switch from reduction to recovery depending on the reservoir boundary conditions. In this study, a permeability switching model for CO2 sequestration in coal has been developed to represent the evolution of coal permeability under variable temperatures. The combined effects of coal deformation, gas flow and transport are evaluated through explicit simulations of the dynamic interactions between coal matrix swelling/shrinking and fracture aperture alteration, and translations of these interactions to permeability evolution for a series of hypothetical CO2 injection cases. Our results have revealed the transition of coal matrix swelling from local swelling to macro-swelling as a novel mechanism for the simultaneous switching of coal permeability from the initial reduction to the late recovery.
Geological CO2 sequestration in coal seams is one of the promising ways to reduce anthropogenic greenhouse gas emissions due to the relatively high excess sorption capacity coal exhibits and the simultaneous recovery of coal bed methane (CBM). Of all the aspects related to this problem, temperature variation in the coal seams and its effect on gas flow and coal properties during the injection and sequestration process are not well studied. A comprehensive understanding of these interactions is essential for the successful enhanced coalbed methane (ECBM) production and CO2 storage in coal seams, under particular in-situ pressure and temperature conditions. A number of experimental and numerical studies have been performed to predict the permeability change during CO2 geological sequestration under isothermal conditions.
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