Stress geomechanical model construction in Nankai Trough subduction zone

Analyzing the in-situ stress state during the drilling is one of major challenges for evaluating earth crust and formation conditions. Stress magnitude is especially essential to comprehend stress heterogeneity, significant structural anisotropy, or preexisting fracture systems. Stress state is influenced by rock strength, structural properties, and near-field principal stresses, which impact borehole integrity during drilling. Factors that we can measure through Logging While Drilling (LWD) and Measure while Drilling (MWD) to better understand borehole conditions, including mud weight, overburden weight and velocity. The LWD resistivity images in Site C0002 indicate that most of the drillings in stable environments in Hole C0002A and C0002F. However, the bottom hole assembly became stuck in Hole C0002P. We created a geomechanical model and numerical model for Site C0002 to evaluate the mud weight and stress state required to drill a stable borehole. Our analysis inferred that the instability of Hole C0002P might have been caused by weak rock and an overpressure drilling fluid state. Furthermore, we developed an optimally oriented plane (OOP) model to constrain the stress state in the vicinity of Site C0002 in the Nankai Trough subduction zone. The modeled normal faulting stress regime is consistent with the observed borehole data. The optimized drilling processes for future deep drilling could be illustrated based on the simulation results from these studies.