Prediction and zoning evaluation of in-situ stress field in deep tight sandstone reservoirs of Western Sichuan Depression, Sichuan Basin: a case study of the second member of Xujiahe Formation in Xinchang and Fenggu area

Abstract

The second member of the Triassic Xujiahe Formation (Xu 2 Member) in the Xinchang structural belt of the Western Sichuan Depression in the Sichuan Basin contains tight gas reservoirs with enormous resource potential. However, the geological structure is complex, presenting significant challenges for exploration and development. In particular, the current understanding of its in-situ stress state and distribution patterns is insufficient, severely restricting the selection of sweet spots for engineering, wellbore trajectory optimization, and reservoir fracturing modification. To clarify the current in-situ stress distribution characteristics in the tight gas reservoirs of the Xu 2 Member, the paper analyzed data from core tests, field tests, and well logging interpretation to determine the stress characteristics at individual wells. Considering the disturbances to the stress field caused by tectonic deformation and faults, Rhinoceros and FLAC3D software were used to precisely model and predict the three-dimensional in-situ stress field of the Xu 2 Member. Based on the stress distribution predictions, the minimum principal stress and stress differential, which significantly impacted fracturing and production, were selected as evaluation indicators. The stress field characteristics were zoned and evaluated, and preliminary suggestions were provided for well location deployment, well trajectory, and fracturing modification design in different in-situ stress zones. The results show that the current maximum horizontal principal stress direction in the Xu 2 Member of the Xinchang structural belt mostly ranges from N85° to 108°E, with an overall counterclockwise rotation as burial depth increases. The current in-situ stress regime corresponds to a strike-slip stress mechanism, with the central Hexingchang area showing significantly higher triaxial stress than the Xinchang and Fenggu areas. Moreover, local in-situ stress fields are disturbed by tectonic deformation and faults. The stress zoning results show that the low stress differential and low in-situ stress zones, which are favorable for fracturing modification, mainly develop near the third-order east-west-trending faults and the fourth-order north-south and northeast-trending faults in the Xinchang and Hexingchang areas, as well as in the extensional disturbance areas in the Fenggu area.

Keywords

• current in-situ stress
• stress field simulation
• stress zoning
• tight sandstone
• xujiahe formation
• xinchang structural belt
• sichuan basin