In situ stress field in the FZ Block of Qinshui Basin,China: Implications for the permeability and coalbed methane production

Abstract

In situ stress affects reservoir permeability and stimulation, and thus coalbed methane (CBM) recovery. In this study, the in situ stress field measured from 238 CBM wells in the FZ Block of Qinshui Basin, China, was investigated. The vertical stress, horizontal maximum and minimum principal stress are 5.92–20.08 MPa, 8.03–41.75 MPa, and 5.38–21.24 MPa, respectively. The in situ stress magnitudes increase with burial depth of the coal seams. The FZ Block is dominated by reverse and strike-slip faulting stress regimes. Most of reverse fault stress regimes appear within burial depth less than 500 m, whereas normal and strike faulting stress regimes are deeper than 500 m. The relation between the coefficient of lateral stress and burial depth shows that shallow strata are characterized by horizontal stresses, whereas deep strata are generally hydrostatic pressures that approximately equal to the principal stresses. Low gas and high water production are associated with vertical hydraulic fractures, wherein the horizontal minimum principal stress is the minimum stress. High gas and low water production are associated with horizontal hydraulic fractures, wherein the vertical stress is the minimum stress. This results are attributed to the enhanced permeability of the coal seam and the communication with overlying or underlying aquifers because the minimum stress varies between vertical and horizontal minimum stress. The orientation of the horizontal maximum principal stress is ∼NEE–NE and is locally distorted by faults, which can be used to optimize the drilling, completion, and stimulation of CBM wells in the study area.