Unconventional Resources (Jan 2024)
The present-day in-situ stress field and its effect on shale gas development in Zigong area of southern Sichuan Basin
Abstract
The Zigong area in southern Sichuan Basin is one of the key shale gas production areas in China, and the Longmaxi and Wufeng Formations within it are currently the key exploration and development layers. The present-day in-situ stress field has a significant impact on well trajectory deployment, horizontal well construction, hydraulic fracturing and other aspects. However, it has not been finely quantified in shale gas reservoirs of Zigong area, making it difficult to effectively guide development practice. Therefore, this study constructed a geomechanical model of the target layer in the Zigong area, quantitatively characterized the distribution of present-day in-situ stress, and explored its shale gas development effects. The results show that: (1) Based on the analysis of drilling induced fractures obtained from rock acoustic emission experiments and imaging logging interpretation, the dominant orientation of the maximum horizontal principal stress in the target layer is mainly NW-SE-trending; (2) The horizontal principal stress difference in the Layer S1l1-1−1 and Wufeng Formation is 5–30 MPa (the majority is 6–15 MPa) and 5–35 MPa (the majority is 6–18 MPa), respectively. Low stress difference values are mainly concentrated in the southeastern and northern parts. The overall prediction accuracy is high, with an error rate of less than 8% for the Layer S1l1-1−1 and less than 10% for the Wufeng Formation; (3) Based on rock acoustic emission experiments and finite element model simulation results, the study area is mainly under strike-slip stress faulting mechanism; (4) Due to the influence of the strike-slip faulting stress mechanism, when deploying horizontal wells in the area, priority should be given to selecting areas with low stress mechanism factor (Aφ) and low stress differences, to achieve better fracturing and transformation effects and reduce the risk of casing deformation and wellbore instability.
