Numerical simulation of diametrical core deformation and fracture induced by core drilling

Rock core-based stress measurement has been accepted as one kind of important in situ stress measurement method, particularly for deep boreholes. Diametrical core deformation analysis (DCDA) is a core-based method that estimates in situ stress through accurate core diameter measurements in different directions. However, core deformation can be significantly affected by elastic anisotropy, heterogeneity, and microcracks due to stress release. This study first analyzes the core deformation due to core drilling and compares it with the theoretical value. Further, the spherical inclusions and random elemental properties using a secondary development of ABAQUS are employed to simulate different mineral components’ elastic heterogeneity and effect. The rock core’s cracking and fracture behaviors due to core drilling are analyzed using brittle cracking and cohesive fracture models. Results show that the elastic homogenous model fits perfectly with the DCDA theory. Rock minerals affect the core deformation and fracture or cracking behaviors caused by stress release. A significant deviation of core deformation microcracks or even macrocracks may appear and significantly affect the application of DCDA for stress measurement.