Deformation and Failure Mechanism of Ultra-Deep Dolomite and FDEM Numerical Simulation

Abstract

ABSTRACT: The mechanism of rock deformation and failure in ultra-deep reservoirs is unclear, so this article takes ultra-deep dolomite as the research object and conducts rock mechanics experiments. Based on the damage variable theory model of Weibull distribution, the combined finite-discrete element method (FDEM) is used to numerically simulate the deformation and failure of dolomite. The results show that: (1) The compressive strength of ultra-deep dolomite is relatively high, and the failure is mainly brittle shear failure. Under high temperature and low confining pressure, the failure of dolomite exhibits a high angle shear fracture, accompanied by the development of secondary fractures. Under high temperature and high confining pressure, the failure mode of dolomite is often accompanied by other shear fractures in addition to one main shear fracture. (2) In the initial deformation stage, the linear characteristics of ultra-deep dolomite are more obvious. As the compression deformation deepens, the internal damage of the rock intensifies, gradually transitioning from elastic deformation to plastic deformation. The maximum damage rate occurs near the peak failure point and the fractures are formed at the macro level. In the post peak stage, the internal damage rate of the rock rapidly slows down and gradually reaches the residual strength. 1. INTRODUCTION The first ten thousand meters geological exploration well in China, "Deep Taco 1 Well," was drilled on May 30, 2023 in the Tarim Oilfield in the hinterland of the "Sea of Death" Taklamakan Desert. However, the current drilling technology for ultra-deep and complex wells remains one of the global drilling challenges (Li et al., 2018; Li et al., 2020). The ultra-deep formation has characteristics such as high temperature and high pressure, brittle transition of rock mechanical properties, poor wellbore stability, poor drillability of the formation, and low drilling production efficiency. Among them, obtaining the mechanical characteristics of ultra-deep rock and studying the deformation and failure mechanism of deep rock are important theoretical and technical foundations to solve these problems, and basic research needs to be carried out in advance.