6:15 PM - 7:30 PM
[SSS30-P11] Stress concentration in the C0002 borehole of the NanTroSEIZE Project, Nankai Trough
Keywords:NanTroSEIZE, LWD, Breakout, Drilling, Borehole Instability
Wellbore instability is a major challenge for the engineer evaluating borehole and formation conditions. Instability is especially important to understand in areas with high stress variations, significant structure anisotropy, or pre-existing fracture systems. Borehole (in)stability is influenced by rock strength, structural properties, and near-field principal stresses. During drilling, the borehole conditions also impact borehole integrity. Factors that we can measure in the borehole during with logging while drilling (LWD) to understand these conditions include Mud Weight, mud loss, ROP (Rate of Penetration), RPM (Rotation Per Minute), WOB (Weight on Bit), and TORQ (Power swivel torque value). By observation the resistivity images, we can utilities the significant features under the interactions of effective stresses and formation. We conducted stress analysis for Site C0002F of the Nankai Trough transect based on riser and riserless drilling data during IODP Expedition 338. Rock strength and basic physical properties, including velocity, density and porosity are obtained from core samples. The borehole shape, determined from LWD resistivity images, indicates that most of drilling occurred in stable environments, however, in a few instances the bottom hole assembly became stuck. We used our stress profile model to evaluate the mud weight required to drill a stable borehole for the measured rock strength and physical properties. Based on our analysis, we constrained the stress magnitude and possible orientation during IODP Expedition 338 by the drilling parameters. The enlargement and collapse in the borehole indicated that mud weight plays the essential role in the drilling.