Estimation of stress magnitude and physical properties for coal seam of Rangamati area, Raniganj coalfield, India

Well log analysis has been carried out to evaluate resistivity and density log data of about seven wells distributed over 3.5 sq. km area of Rangamati, Raniganj coalfield, India. Geological logs of these boreholes have recorded occurrence of four major consistent coal seams (A, B, C and D) at different depths, varying between 52 to 200 m in the area. Cleat volume/porosity ranges from 1% to about 3% in this area. Vertical stress magnitude ranges from 0.55 to 4.59 MPa from 52 to 202 m and increases with depth. The gradient of vertical stress magnitude decreases within coal seams compared to the stress gradient at roof and floor of the same seams. 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 from Rangamati area. Permeability value ranges from 0.5 md at a depth of 193–200 m to 18 md at a shallower depth of 45–53 m while vertical stress decreases from 4.566 MPa to 1.254 MPa respectively. Permeability values of four coal seams have been correlated with effective horizontal stress to infer the maximum horizontal stress orientation.