In-situ stress distribution and its influence on the coal reservoir permeability in the Hancheng area, eastern margin of the Ordos Basin, China

( )During the coalbed methane (CBM) exploration and development, in-situ stress and permeability are two vital reservoir evaluation parameters. In this work, with the injection/falloff well test and in-situ stress data of 11 CBM wells in the Hancheng area, eastern margin of the Ordos Basin, China, the distribution of in-situ stress and its influence on the coal reservoir permeability were investigated. Results show that the maximum (S-H, 10.80-53.84 MPa) and minimum horizontal (S-h, 9.96-31.88 MPa), and vertical principal stresses (S-v, 14.37-36.46 MPa) increase with the increasing burial depth. However, the coal reservoir permeability (0.01-0.54 mD) shows a decreasing tendency accompanied by increasing stresses. Three stress fields (I, II, and III) between 532.28 and 1350.55 m could be divided: I is in a compression zone (<700 m, S-H>S-h approximate to S-v, reverse or strike-slip stress regimes); II is in a tension zone (700-850 m, S-v > S-H > S-h, normal stress regime); III is in a compression zone again ( > 850 m, S-H > S-v > S-h, strike-slip stress regime). The top-down in-situ stress regimes result in a "decreasing - increasing - decreasing" permeability variation. Meanwhile, the lateral stress coefficient, stress ratios decreased slowly while the reservoir pressures and temperatures show a positive correlation with increasing burial depth.