Complex in-situ stress distributions in ultra-deep marine carbonate reservoirs: 3D numerical simulation in the Yuemanxi Block, Tarim Basin

Abstract

Marine carbonate reservoirs are widely distributed across the globe and present significant opportunities for hydrocarbon exploration. However, inherent heterogeneity in rock mechanical properties, coupled with the presence of fractures and cavities, results in complex in-situ stress variations that pose a challenge to hydrocarbon production. This study focuses on the Yijianfang Formation within the Yuemanxi Block of the Tarim Basin, employing core samples, well logging data, rock mechanics testing and 3D numerical simulations to quantitatively assess in-situ stress variations in ultradeep fracture-cavity reservoirs. A novel approach to predicting 3D rock mechanics parameters is introduced, advancing beyond previous methodologies. By analyzing stress simulation outcomes, the study identifies key factors controlling the behavior of ultra-deep marine carbonate fracture-cavity reservoirs, offering critical insights for well placement, fracturing optimization, and broader reservoir development strategies. Core analysis reveals the Yijianfang Formation to be highly fractured, with fractures classified into structural and diagenetic types. Triaxial rock mechanics experiments show a static Young's modulus ranging from 36 to 44 GPa and a static Poisson's ratio between 0.22 and 0.24. Based on seismic data, five distinct fracture and cavity types were identified, enabling the creation of a comprehensive rock mechanics parameter model. Formation MicroScanner Image (FMI) data indicate a maximum horizontal principal stress orientation of NE17° in the Yuemanxi area. Wellbore analysis and 3D stress field simulations reveal a complex stress distribution in the Yijianfang Formation, with stress decreasing in proximity to faults and cavities. Factors such as the characteristics of strike-slip faults, cavity connectivity, and the development of fractures and cavities significantly influence in-situ stress distribution within these fracture-cavity reservoirs.