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The middle Permian Maokou Formation in the Longnüsi area in the central Sichuan Basin is currently a key formation for exploration and development. The evaluation of the current in situ stress in this area is of great significance for fracture prediction, well pattern deployment, drilling and construction, and fracturing stimulation. This study clarifies the current direction and magnitude distributions of the in situ stress by evaluating the Maokou Formation in the Longnüsi area using finite-element numerical simulation, acoustic emission experiments, and logging data (including data from imaging logging, array acoustic logging, conventional logging, and cross-dipole acoustic logging). Specifically, the current maximum horizontal stress of the Maokou Formation in the Longnüsi area is mainly in the NW‒SE direction, and the stress direction is greatly affected by the local fault zone. The current minimum horizontal stress magnitude of the Maokou Formation obtained by acoustic emission experiments is between 96.29 and 114.36 MPa, the current maximum horizontal stress magnitude is between 126.01 and 145.10 MPa, and the current horizontal stress difference is between 25.59 and 32.58 MPa. The current minimum and maximum horizontal stress magnitudes both decrease from north to south. The current horizontal stress parameters calculated by Huang’s model are not significantly different from those experimentally measured: there is a difference of less than 8% in the current minimum horizontal stress magnitude, a difference of less than 9% in the maximum horizontal stress magnitude, and a difference of less than 15% in the current horizontal stress difference. Therefore, Huang’s model has good applicability in terms of calculating the current horizontal stresses in the Longnüsi area. The current horizontal stress parameters, which are numerically simulated with the finite-element method, are also not much different from those experimentally measured: there is a difference of less than 11% in the current minimum horizontal stress magnitude, a difference of less than 10% in the maximum horizontal stress magnitude, and a difference of less than 20% in the current horizontal stress difference. The numerically simulated current horizontal stress also decreases from north to south. Therefore, the simulated results are highly accurate. This study clarifies the directions and magnitudes of the current in situ stress state of the Maokou Formation in the Longnüsi area of the central Sichuan Basin and provides a basis for the formulation of exploration and development plans for the Maokou Formation reservoir in the study area.

In-situ stress plays a crucial role in governing various parameters such as the distribution of oil and gas accumulation zones, the fracture pattern of reservoirs, formation fracture pressure, and collapse pressure. Understanding the distribution characteristics of current in situ stress of reservoirs has significant implications for exploration and development of oil and gas. This paper focuses on the characterization methods for current in situ stress of oil and gas reservoirs, discussing the research progress in testing methods, computational approaches, numerical simulations, and seismic prediction methods. The results indicate that the testing method including the on-site testing method and the laboratory testing method offer the relatively high accuracy, but this method only provides point-specific magnitude and direction of current in situ stress. The Computational approaches can obtain continuous profiles of current in situ stress along individual wells. After using the testing method for calibration, we can obtain relatively accurate calculation results. The numerical method can predict current in situ stress over large areas, but it requires rigorous model setup, boundary definition, and parameter selection. The seismic prediction method also can predict broad distribution of current in situ stress, but this method is influenced by many factors and we had better apply this method in conjunction with other methods. In the future, engineers and researchers should innovate testing technologies and instruments, and establish models and processes for joint use of multiple methods, and explore the development of novel current in situ stress prediction models based on artificial intelligence and big data.