A new rock mechanical behavior evaluation method reconstructed based on the digital core model

In the process of oil and gas well drilling, the cores drilled from the overlying non-target strata is limited in quantity, which, to some extent, limits the researches on rock mechanical behaviors and is not beneficial for safe and efficient drilling. To this end, this paper applies the digital core model to conduct inversion research on the rock mechanical behaviors of the overlying non-target strata in the long hole section. Then, with the Xujiahe Formation of Upper Triassic in the Tianfu Gas Field of the Sichuan Basin as an example, the three-dimensional Voronoi body model of digital core for characterizing the mechanical behaviors of the Xujiahe Formation cores is established on the basis of the cuttings component test results of the target layer and the Voronoi theory. In addition, the spatial distribution of mineral compositions, clay and pores are restored. Finally, the mechanical properties and damage evolution of the rocks are analyzed from a microscopic perspective. And the following research results are obtained. First, the uniaxial compression deformation of digital core is divided into four stages, i.e., pore compaction, elastic deformation, plastic deformation and post failure, with shear failure as the main failure form, which is highly consistent with the experimental result. Second, under the action of axial pressure, mineral particles are compressed to generate strain. When the strain exceeds the yield strain of the mineral itself, mineral damage begins, and the pressure beyond the bearing capacity is transferred to the neighboring mineral particles to form crack and fracture surface gradually. Third, the spatial distribution of minerals only influences the damage evolution and crack propagation of digital core, and particle size affects the mechanical behaviors in elastic, plastic and post failure stages. Fourth, with the increase of the confining pressure, compression strength and residual strength increase significantly. In addition, the larger the core size, the lower the elastic modulus and peak strength. In conclusion, the analysis results by this method are consistent with the experimental results, which means this method provides a new idea for studying the mechanical properties of the overlying strata in the drilling process without enough cores, and is of great significance for understanding rock breaking mechanisms and optimizing the selection and design of drill bits. © 2024 Natural Gas Industry Journal Agency. All rights reserved.