Methodology for the Quantitative Prediction of Abnormal Pressure in Ultradeep Fracture-Vuggy Reservoirs: Geomechanical Modeling Driven by Seismic Data

Abstract Overpressure in oil and gas basins, often referred to as abnormal pressure, is closely associated with the generation, migration, and accumulation of hydrocarbons. It plays a crucial role in controlling drilling safety and the success rate of drilling operations. To predict the three-dimensional (3D) distribution of abnormal pressure, correlations were established between parameters measured under laboratory conditions, data derived from well logging and seismic surveys, and formation pressures. However, in ultradeep carbonate reservoirs, conventional empirical models often face the challenge of accurately estimating the magnitude of abnormal pressures. This difficulty arises from insufficient consideration of specific influencing factors, such as fractured-vuggy bodies and rock mechanics parameters. To address these challenges, this study employs a geomechanical heterogeneity modeling approach and uses a two-floor modeling square law to improve the accuracy of abnormal pressure assessment. The 3D geometry of the fractured-cavity body is precisely defined, with the rock mechanics parameters of a single well calculated on the basis of well log data. To construct a geomechanical heterogeneity model for the fractured-cavity reservoir, these parameters were integrated with 3D seismic data, allowing the retrieval of 3D distributions. Using single-well data and the magnitude and direction of geostress at the well site, we established boundary displacement and stress application conditions for the model. This led to the development of a geomechanical heterogeneity‒anisotropy model for fractured-vuggy reservoirs. A numerical finite-element stress field simulation was then performed to analyze the effective stress within the fractured-vuggy reservoir. In addition, drilling data were used to delineate the depth range of pressure anomalies, which enabled the prediction of the 3D distribution of abnormal pressure within fractured-vuggy reservoirs. The methodology proposed in this study can serve as a reference for predicting abnormal pressures in fractured-vuggy reservoirs and for geomechanical modeling of ultradeep reservoirs in other regions.