The Influence of Failure Criterion on the Estimation of In-Situ Stress Using the Wellbore Breakout of Inclined Well

Abstract

ABSTRACT: The accurate information of in-situ stress at depth is critical for oil and gas drilling and hydraulic fracturing operations. The technique of estimating the maximum horizontal stress using the wellbore failure detected from imaging logging has been widely recognized, but the influence of different rock failure criteria on the calculation results has always been neglected. Therefore, according to the linear poroelastic mechanics theory and different failure criteria of rock, the maximum horizontal stress in southwest Sichuan of China is calculated using the wellbore breakout of an inclined well from literature. The calculation results show that magnitudes of the maximum horizontal stress calculated with different failure criteria vary greatly. The frequent earthquakes in southwest Sichuan indicate that the preexisting faults in this area are close to the friction limit state under the in-situ stress, which agrees well with the results calculated by using Mogi-Coulomb criterion. 1. INTRODUCTION In-situ stress is very important for oil and gas drilling and hydraulic fracturing stimulation operations. Accurate knowledge of stress magnitude and orientation can help us to design reasonable drilling fluid density and borehole trajectory for preventing wellbore failure and associated underground complexity. Wellbore shape reflects the stress state that the wellbore wall is being or has been subjected. Thus, according to the wellbore shape and drilling history data, we can determine the stress distribution around the wellbore wall and calculate the magnitude of the in-situ stress. Although the final shape of wellbore may be different from the shape after the initial wellbore breakout, the breakout width remains unchanged (Zoback et al., 1985; Barton et al., 1988). Therefore, the breakout width can reflect well the initial stress state of wellbore when breakout occurs. Many authors preferred using wellbore failures to calculate the in-situ stress, even established several models to calculate the maximum horizontal stress combining Mohr-Coulomb criterion (Barton et al., 1988; Vernik & Zoback, 1992; Zoback et al., 2003; Frydman & Ramirez, 2006), but these models are only suitable for the failures of vertical wellbore. Peska and Zoback (1995) also adopted Mohr-Coulomb criterion to determine the maximum horizontal stress magnitude according the wellbore failure of inclined well. However, the effect of intermediate principal stress on rock strength is ignored in Mohr-Coulomb criterion, which may lead to unrealistic calculation results of in-situ stress. Although Tang et al. (2021) chose Mogi-Coulomb criterion in the analysis of the influence of thermo-poroelastic coupling operation on the calculation results of in-situ stress, the author did not analyze the differences caused by other criteria, which may have significant influence on in-situ stress estimation.