Investigations of Stress-Dependent Petrophysical Properties of Coalbed Methane (CBM)

Abstract The increase of successful exploration and economical importance of coalbed methane makes the understanding of petrophysical properties-stress-dependent more essential. The influences of net stress on porosity, permeability, and reservoir quality index of Australian coalbed methane (CBM) formation are experimentally investigated. Two groups of low permeability from 0.01 to 1.5 md and medium permeability from 5.21 to 13.22 md actual CBM samples were used to perform this study. The variation of porosity, permeability, permeability-porosity ratio (K/φ) and reservoir quality index (RQI) under different stress conditions is studied. Current permeability-porosity models under stress are tested using the newly-attained experimental results from this study. New correlations were developed capable to be used as simple tools for predicting changes of petrophysical properties with stress. Attained results also indicated that the reduction rate of porosity of low and medium permeability CBM samples can be represented by a straight-line equation form while the permeability reduction of low and medium permeability CBM formations is confidently followed an exponentially reduction mode. The increase of net stress causes a reduction in both ( K/φ) and RQI values. The results also revealed that the effect of stress is more dominant for low permeability samples than that ones for medium permeability CBM.