Experimental study on nonlinear mechanical behavior and sampling damage characteristics of rocks from depths of 4900–6830 m in Well Songke-2

Based on the deep cores of Well Songke-2 (SK-2), uniaxial compression tests of deep rock from 8 different depths in the 4900–6830 m range were carried out, and deformation and failure characteristics were analyzed in detail. It was found that in the range of 4900–6830 m, the mechanical parameters of uniaxial compression tests of rocks changed nonlinearly with depth, and the strength was positively correlated with the hard mineral content. Comparing the rock failure of these samples with the 4500–7000 m core disc segment in SK-2, it was found that the failure of magmatic rock samples in both cases was smoother than that of sedimentary rock, indicating that deep magmatic rocks more easily released energy during the failure process. From depths of 4900–6000 m, prepeak characteristic stresses increased with increasing depth, while from depths of 6000–6830 m, they decreased with increasing depth. Fracture closure stress was used to characterize rock sampling damage at depths of 1000–6830 m, and it was found that sampling damage varied linearly with burial depth in sedimentary strata, while in igneous strata, sampling damage remained stable with increasing burial depth.