Geomechanical twin modeling for ultradeep fractured-vuggy carbonate reservoirs and its application in the Tarim Basin

Fault-controlled fractured-vuggy reservoirs are extensively developed in ultradeep carbonate strata, and their formation and distribution are closely related to the in situ stress state. Since fractured-vuggy carbonate reservoirs exhibit the characteristics of both discrete and continuous media, conventional methods for geomechanical modeling often struggle to accurately predict stress fields in these complex reservoirs. Using seismic attribute-based inversion, we establish a model to characterize the distribution of rock mechanical parameters of fractured-vuggy reservoirs. Then, a geomechanical heterogeneity model for these reservoirs is developed, achieving both geometric and mechanical similarities between the geological and geomechanical models of fractured-vuggy rock masses (i. e., twin modeling). Accordingly, the in situ stress field distribution and activity of complex fractured-vuggy reservoirs are predicted. The geomechanical twin modeling technique enables the reproduction of actual geometric morphologies of subsurface fractured-vuggy rock masses using finite element software. The results indicate that different fractured-vuggy rock mass types exhibit distinct stress field characteristics. Among these, uplifted fractured-vuggy rock masses show strong stress heterogeneity in the compressional segments of major faults, resulting in distinct stress segmentation. Similarly, embedded fractured-vuggy rock masses exhibit significant differences in vertical stress, also suggesting strong stress heterogeneity. In contrast, combined fractured-vuggy rock masses display moderate stress heterogeneity, while chaotic and isolated fractured-vuggy rock masses show uniform stress distribution. Fractured-vuggy rock masses exert significant impacts on rock mechanical strength and stress magnitude. Specifically, karst caves show the highest decreased magnitude of stress at their periphery, followed by fractured-vuggy rock masses, with the periphery of fractures exhibiting the lowest decreased magnitude. Additionally, different types of fractured-vuggy rock masses exhibit varying activity. The domed and down-dipping types exhibit the strongest activity, succeeded by the combined type, while the chaotic and isolated types prove the least active.