AE Method to In-Situ Stress Measurement Base on Core's Axial Trajectory Projection Orientation Technology

ABSTRACT: Rock cores are important physical evidence for obtaining geological information, but the complex construction environment of deep drilling poses severe challenges to core orientation and also limits the application of acoustic emission method for measuring in-situ stress. Based on the principle of consistency between drilling and core bending, a technical method for core reorientation based on drilling inclinometer data was proposed, and a core reorientation prototype was developed based on this technical method. The rock core obtained from the deepest well in China was oriented on the ground, and the in-situ stress was measured based on acoustic emission method. Meanwhile, the in-situ stress was measured by stress relief method. The results showed that the azimuth and trend of principal stress changes measured by the two methods were in good agreement. This study can provide some new insights for obtaining geological information of rock cores. 1. Introduction Rock core is a physical material that must be collected for geological research or mineral exploration (Stigsson 2016; Mingzhong et al. 2022; Xie et al. 2023). In many geotechnical engineering, it only requires sufficient sampling rate and representativeness, regardless of its true orientation, so the cores taken out from the borehole are mostly non-orientated. However, in modern refined underground engineering research, it is often required to collect orientated cores or reorient the cores on the ground (Nelson et al. 1987; Paulsen et al. 2002). Because not only the general geological structures information (e.g. faults, joints, crevices, and other planar structures) but also special geological characteristics (e.g. in situ stress and stratigraphic occurrence) are required to provide (Yamamoto 2009; Annavarapu et al. 2012; Azimian 2016; Diaz et al. 2017). However, the existing core orientation methods all have their shortcomings, such as the paleomagnetic method only applicable to sedimentary rocks (Opdyke et al. 1966; Sager and Carvallo 2022), the scoring method requiring non-magnetic drill bits (Nelson et al. 1987), the inclinometer method relying on identifiable structural planes (Lau 1983), and drilling imaging method requiring expensive instruments (Paulsen et al. 2002; Guo et al. 2017). The current status of rock core orientation technology makes it difficult to promote and apply several rock core-based stress measurement methods, such as anelastic strain recovery (Matsuki 2008), differential strain analysis (Sanada et al. 2013), deformation rate analysis (Yamamoto 2009), and acoustic emission methods (Seto et al. 1999).