Quantitative Prediction of in situ Stress in Ultradeep Fracture-Cave Reservoirs and Its Applications

Abstract

Fracture-cave reservoirs are widely developed in carbonate formations and account for over 55% of global petroleum reserves. The productivity, formation mechanisms, and in-situ stress states of these reservoirs, characterized by fault-fracture-cave systems, are inherently interconnected. However, solely relying on geometric characterizations of natural fractures and cavities fails to meet the demands of modern petroleum exploration and development, particularly due to their complex structures, significant spatial heterogeneity, and strong geomechanical anisotropy. A critical challenge remains: how to safely and efficiently drill high-yield wells through highly fractured and cavernous zones while mitigating drilling risks. Consequently, establishing geomechanical models for fracture-cave reservoirs and predicting 3D stress fields are imperative for well trajectory optimization and reservoir reconstruction. This study integrates seismic interpretations of strike-slip faults with multi-attribute inversions of fracture-cave reservoirs. Using ANSYS 21.0 software, a homogeneous geomechanical model was constructed based on finely characterized geometries of fracturecave systems. Rock mechanics parameters, interpreted from conventional logging data and seismic attributes, were inverted to generate 3D distributions. These parameters were subsequently incorporated into the homogeneous model to develop a heterogeneous geomechanical framework. In-situ stress orientations were calibrated using drilling-induced fracture data, enabling predictions of the contemporary stress field in complex fracture-cave reservoirs. The methodology was validated in the Yueman Block of the Tarim Basin’s deep carbonate reservoir. Results revealed stress distribution patterns and key controlling factors, which were applied to evaluate wellbore stability, fracture reactivation risks, and optimize well trajectories. This approach provides a technical foundation for safe and efficient exploration-development of fracture-cave reservoirs worldwide.

Keywords

fracture-cave reservoirs / in situ stress / numerical simulation / geomechanics / carbonate rock / Tarim Basin / petroleum geology

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