Poroelastic modeling of cutting rock in pressurized condition

Cutting rock in pressurized conditions is essentially different as compared to the ambient conditions. Under pressurized condition, cutter is not only fragmenting the rock matrix, but also driving pore fluid to flow forward. Due to the coupling of stresses and pore pressure, the pore pressure change caused by cutter will affect effective stresses in the rock and eventually affect mechanical specific energy (MSE). The change in stresses and pore pressure caused by cutter movement are the poroelastic effects in cutting process. To study pressurized cutting process, we developed a cutting model based on the theory of linear poroelasticity. The model can predict coupled stresses and pore pressure in the rock and give a better understanding of the poroelastic effect in the cutting process. To obtain the desired solution, a Fourier Transform is employed. After the analytic solution in Fourier space is obtained, a Discrete Fourier Transform is employed to numerically invert the solution back to the real space. The Mohr-Coulomb failure criterion is also introduced to determine failure of the rock ahead of the cutter. Eventually, the model can predict cutting forces and MSE in pressurized cutting process. The model is also compared to the published experimental data and a good consistency between model and experiment results was found. The influence of hydrostatic pressure and the existence of cuttings on MSE are studied and poroelastic effect during cutting process is also discussed. The results in this paper can be applied to bit-rock interaction in well drilling.