Numerical Investigation of Rock Breaking Mechanism With Supercritical Carbon Dioxide Jet by SPH-FEM Approach

Abstract

As a novel technology in the field of petroleum exploitation, rock breaking with supercritical carbon dioxide (SC-CO2) has considerable social and economic benefits. To investigate the rock breaking mechanism under SC-CO2 jet impacting in terms of mass and energy conservation, a fluid-solid coupling numerical model was established using smoothed particle hydrodynamics (SPH) method coupled with the finite element method (FEM). Jet movement feature and the stress distribution rule of impact target were obtained. Moreover, the space-time evolution of erosion cavity and failure process of elements were analyzed. The numerical research results are as follows: (1) the hybrid algorithm of SPH-FEM was effective for obtaining the numerical representation of rock breaking process under SC-CO2 jet impacting, and the simulation results were in good agreement with the experimental data. (2) The asymmetrical distribution characteristics of monitored points caused the erosion cavity to deviate from the geometrical center of the target face. (3) Soft rock under SC-CO2 jet impacting presented two failure forms: erosion and exfoliation. (4) The process of rock breaking with SC-CO2 jet was as follows: when the jet came into contact with the target plane, the pressure stress on the mating face and shear stress on the contact edge dominated the evolution of initial compression-shear failure zone. Thereafter, the high diffusivity-driven SC-CO2 penetrated into tiny cracks or pores near the failure zone, and strong air wedge effect caused tensile failure. With continuous high-speed impacting, the initial failure zone extended to a larger primary failure zone. Moreover, a few discrete failure zones were formed due to the high uncertainties of particles' motion trajectories, which mutually contributed to the main failure zone, and the erosion cavity was formed. When the jet became steady, quasi-static action was applied to the rock sample, and the erosion range expanded continuously.