Relationship of coal bed permeability with vertical stress from well log data: A case study from Raniganj coalField, India

Abstract

Characterization of coal in term of its physical properties like porosity and permeability has generally been performed on limited sample volumes such as plugs or cores. A methodology is proposed for estimation of permeability for a macro‐cleat system of coal from well log derived porosity and from known cleat spacing for Rangamati area of Raniganj Coalfield, India. Data of seven numbers of wells were available from the study area. Geological logs of these boreholes recorded occurrence of four major consistent coalseams (A, B, C & D) at different depths, varying between 53 to 200m in the area. Permeability values of four coalseams with thickness varying between 2–5 m encountered in the seven wells have been correlated with vertical (overburden) stress. Permeability value ranges from 0.5 md at depth of 200 m to 18 md at shallower depth of 53 m while vertical stress decreases from 4.566 MPa to 1.254 MPa respectively. Permeability value of coalseam decreases with increase in vertical stress. Regression analysis between permeability & vertical stress of the coalseams show 2nd order polynomial, as the best fit curves. Goodness of fit for the 2nd order regressions between vertical stress and permeability for individual coalseams varies between 0.86 and 0.99.