The impact of time-dependent deformation on coal permeability and gas drainage efficiency​​​​​​​

Abstract

Coal as a soft rock experiences a time-dependent deformation induced by continuous change in effective stress in reservoir during Coal Seam Gas (CSG) production and during well shut-in at static reservoir pressure. This deformation results in compaction of coal microstructure and loss of porosity and permeability over the course of gas production. Limited studies have considered the impact of time-dependent deformation (i.e. consolidation and creep) on coal permeability that may play a key role in determining the efficiency of CSG production. Negligence of the impact of consolidation and creep on coal permeability may result in overestimation of level of drained gas. This research aims to characterize time-dependent deformation in the coal injected with gas and investigate its impact on permeability and gas drainage efficiency. This has been achieved via implementation of two triaxial tests and development of governing equations (i.e. permeability models and mass balance equation) required for simulation of gas transport in coal. In the first test, V