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

Abstract

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 (SH, 10.80–53.84 MPa) and minimum horizontal (Sh, 9.96–31.88 MPa), and vertical principal stresses (Sv, 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, SH〉Sh ≈ Sv, reverse or strike-slip stress regimes); II is in a tension zone (700–850 m, Sv > SH > Sh, normal stress regime); III is in a compression zone again (>850 m, SH > Sv > Sh, 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.