Maximum Horizontal Stress Validation Based on Wellbore Breakout Model

Abstract

Maximum horizontal stress is one of the most critical parameters that affect the stability of the wellbore during drilling operations. Currently, no direct measurement of the maximum horizontal stress is available to validate its magnitude obtained from existing solutions. It is usually estimated from an extended leak-off test or from equations that depend on other parameters such as the minimum horizontal stress, rock properties and the overburden stress. Borehole breakout is a function of in-situ stresses, pore pressure, elastic and plastic properties. These parameters are calculated from sonic logs and calibrated by triaxial tests and mini-frac jobs for wellbore stability design. In this study, four-arm caliper data is used to determine the breakout length in the wellbore. The breakout data is compared with simulation results using 2D numerical model to validate the maximum horizontal stress magnitude. The material law is based on elastoplastic model to capture the rock deformation process in the region based on an iterative process until the same extent of the breakout from the caliper log is attained. The results showed that the estimated magnitude of the maximum horizontal stress by the wellbore breakout model is 5% higher than corresponding values obtained from the existing solutions. This study determines how accurate can the existing equations estimate the maximum horizontal stress compared to numerical breakout model. The numerical model incorporates more physics and simulate realistic process of progressive breakout failure while drilling. The accuracy of maximum horizontal stress magnitude influences the overall wellbore stability design to estimate safe mud weight window for an oil and gas well.