In-situ stress orientations in the Xiagou tight oil reservoir of Qingxi Oilfield, Jiuxi Basin, northwestern China

Abstract

Knowledge of the present-day in-situ stress orientation is important for borehole stability, fluid flow in fractured reservoirs, and hydraulic fracture stimulation, etc. The Qingxi Oilfield of Jiuxi Basin, northwestern China, is an old oilfield; however, within which there were no systematic investigations into the present-day in-situ stress orientation prior this study. In the present study, the orientation of horizontal maximum stress (SHmax) in the Qingxi Oilfield was interpreted and analyzed based on 149 borehole breakouts (BOs) and 131 drilling induced fractures (DIFs) from electrical borehole imaging logs in 23 wells. Our interpretations revealed a prevailing ∼ NE-SW-trending (14.94°N∼52.74°N) SHmax orientation in the Xiagou tight oil reservoir of Qingxi Oilfield. However, the SHmax orientation indicated various tendencies both laterally and with burial depth within single wells, which were influenced by well-developed faults, natural fractures and bedding planes. The presence of these structures caused great contrasts of rock mechanical properties, influencing stress orientation variations. In addition, the effects of present-day in-situ stress orientation on natural fractures, hydraulic fracture stimulation and borehole stability were discussed. In the Qingxi Oilfield, ∼NE-SW-trending natural fractures indicated favorable contributions to subsurface fluid flow. Hydraulic fractures would propagate vertically following ∼ NE-SW-trending. Wells were more likely to experience borehole instability issues if they were deviated towards ∼ NE-SW-trending. The results can provide geological references for subsequent tight oil production in the Qingxi Oilfield of Jiuxi Basin.