Cementation-Controlled Mechanical Response and Failure Evolution of Naturally Fractured Dolomite

Reservoirs containing cemented natural fractures are widely developed in deep subsalt formations and play an important role in controlling rock mechanical behavior and failure evolution. However, the influence of fracture cementation on strength degradation, deformation response, and failure mode remains insufficiently understood, limiting the mechanical basis for evaluating hydraulic fracturing behavior in fractured dolomite reservoirs. A laboratory experimental framework is established to investigate the mechanical effects of cemented natural fractures in Cambrian subsalt dolomite from the Tarim Basin. CT scanning is used to characterize pore structure, fracture distribution, and cementation features of the samples. Based on these observations, Brazilian splitting tests and triaxial compression tests under a confining pressure of 40 MPa are conducted to analyze tensile strength, compressive strength, deformation characteristics, pore structure evolution, and failure modes under different cementation conditions. The results show that cemented natural fractures significantly weaken the tensile resistance of dolomite, and failure during Brazilian splitting mainly occurs along pre-existing fracture interfaces. Under triaxial compression, well-cemented samples exhibit limited porosity increase and relatively stable mechanical responses, whereas poorly cemented or heterogeneously cemented samples show more pronounced pore structure evolution, stronger nonlinear deformation, and unstable failure behavior. Cementation condition appears to influence fracture activation and failure path within the tested specimens. In the tested specimens, weaker cementation was associated with preferential opening and propagation along natural fractures, whereas stronger cementation was associated with relatively enhanced structural integrity and reduced fracture coalescence. These findings clarify the mechanical role of cemented natural fractures in dolomite failure and provide mechanical insights into the potential response of cemented natural fractures during hydraulic fracturing.