In-Situ Horizontal Stress Inversion and Error Analysis Based on Borehole Deformation Monitoring

ABSTRACT: In-situ measurement is one of the most accurate and effective methods, but it is challenging to measure directly in the deep well. Therefore, a new horizontal in-situ stress inversion method was proposed based on the relationship between the borehole deformation and the in-situ stress state under nonuniform horizontal in-situ stress. The accuracy of the inversion model is validated by finite element simulation. The sources of measurement errors and their control method were discussed. The results indicated that the inversion error for the maximum and minimum horizontal principal stress is 0.001% and 0.052%, respectively. The results and errors of the horizontal principal stress inversion are significantly influenced by the measurement deviation of the borehole diameter, the borehole deformation, the wellbore pressure, and the elastic parameters of the rock. If the deviation from the borehole diameter measurement is less than 0.5 cm or the percentage deviation from the borehole deformation, the wellbore pressure and the elastic parameters of the rock is within ±5%, the horizontal stress inversion error is less than 4%, and thus the horizontal principal stress inversion results are deemed acceptable. This study can provide new ideas for in-situ stress measurement in the petroleum industry. 1. INTRODUCTION In-situ stress is a natural stress that exists in formation without engineering disturbance. Accurate measurement of the magnitude and direction of in-situ stress is a prerequisite for determining the mechanical properties of engineering rock, for analyzing the stability of the surrounding rock, and for the scientific design and decision-making of rock engineering excavations (Cai, 1993; Wang et al., 1991; He et al., 2000). In petroleum exploration and development, in-situ stress plays a very important role (Ma et al., 2022a, 2022b). In-situ measurement is one of the most accurate and effective methods (Wu, 2012). Currently, the hydraulic fracturing method has been widely used in petroleum, mining, and underground engineering. However, it can only directly measure the minimum horizontal principal stress (Duan et al., 2023). In mining and underground engineering, some in-situ measurement methods can directly measure both the minimum and maximum horizontal principal stresses, but it is very difficult to measure them directly in the deep well.