Fluid-solid-thermal coupling analysis of pressure-holding coring tool for 10,000-meter deep wells

ABSTRACT: Closed pressure maintaining coring is a specialized technique utilized in core extraction that aims to maintain or closely approximate formation pressure, thereby preserving the original state of fluids and gases within the core. The tool is widely applied in deep wells to determine rock mechanical properties under in-situ pressures and temperatures. However, as drilling depth increases, the pressures and temperatures of drilling fluid increase significantly, exerting substantial effects on the stability and reliability of tools. Additionally, high-velocity jet also influences the safety of tools. In the present study, a multi-physics model is developed to analyze the distribution of pressure and velocity within the fluid subdomain and tools. Constant velocity and pressure are loaded on the inlet and outlet of fluid respectively, thus simulating the constant displacement of drilling fluid and bottomhole pressure. The evolution of stress in the solid subdomain is analyzed as well, which is applied to evaluate the effects of fluid pressure and thermal stress. At last, the structure of the tool is optimized depending on theoretical analysis. The results indicate that the maximum fluid pressure and velocity can reach 142 MPa and 40m/s respectively. Correspondingly, the maximum stress in the tools is 186.48 MPa, significantly below the critical value for the damage of materials. Higher inlet velocity and smaller diameter of nozzles leads to an increase in the fluid velocity. However, the pressure in the fluid only changes slightly. Consequently, the stability of tools is rarely affected. The findings of this study provide guidance for tool optimization and validate their stability.