A preliminary study of the present-day in-situ stress state in the Ahe tight gas reservoir, Dibei Gasfield, Kuqa Depression

Abstract

Knowledge of the present-day in-situ stress state has significant applications in the exploration and development of tight gas reservoirs. The Ahe Formation is an important tight gas reservoir in the Dibei Gasfield of Kuqa Depression. However, prior to this study, little attention has been paid to the present-day in-situ stress field within the formation. In the present study, the in-situ stress orientation and magnitudes were investigated based on well log calculations and geomechanical modeling. The horizontal maximum principal stress (SHmax) orientation was determined from interpretations of drilling-induced tensile fractures (DITFs) and borehole breakouts in imaging logs, which showed variations between NNW-SSE-trending and NNE-SSW-trending in the Dibei Gasfield. The in-situ stress magnitudes were calculated in four wells based on well logs, the results indicated a normal faulting stress regime within the Ahe tight gas reservoir. Numerical simulation of the present-day in-situ stresses showed that the magnitudes of vertical stress (Sv), SHmax and horizontal minimum principal stress (Shmin) were −105.5 MPa∼-191.0 MPa, −88.9 MPa∼-142.9 MPa, and −79.1 MPa∼-127.7 MPa within the Ahe Formation, respectively. In addition, considering the present-day in-situ stress state in the Ahe Formation of Dibei Gasfield, natural fractures in directions parallel/sub-parallel to the SHmax orientation with high fracture angles showed great contributions to subsurface fluid flow. Borehole instability may become a potentially significant problem when drilling vertical wells and horizontal wells deviated toward the SHmax orientation in the Ahe tight gas reservoir of Dibei Gasfield.