Variation in horizontal stress with pore pressure depletion in coal under uniaxial strain conditions: An update on the modelling of laboratory data

Building upon the previous modelling work on coalbed methane reservoirs by the authors, recently reported experimental horizontal stress data for two coal samples tested under uniaxial strain conditions have been analysed. As well as CH4, non-adsorbing Helium has also been used in the experiments. Deviation between the model and the experimental CH4 stress data at low pore pressures (< 3 MPa) are observed, which, as in the previous study, may be attributed to the onset of shear failure experienced by the coal samples. In addition, CO2 was also used on one of the samples after the CH4 experiment. The post-failure CO2 stress data could be matched using a combination of a reduced Young's Modulus and an increased Poisson's ratio. The results of this study have provided further evidence for the validity of the equation for computing the changes in the effective horizontal stress in producing coalbed reservoirs, which forms an integral part of the Shi and Durucan permeability model.