The explosive fracturing technique analysis for highly low permeable reservoirs using analytical, displacement discontinuity and finite difference coupled method

Crack propagation in the low permeable reservoir rock as an explosive fracturing technique can be used to increase the permeability and productivity of unconventional reservoirs. This technique is the same as hydraulic fracturing but uses blast-induced shock waves and gas pressure to generate and propagate radial cracks around the wellbore in a particular reservoir. In this study, we want to simulate the explosion-induced crack initiation and propagation around a wellbore as a stimulation method of unconventional reservoirs using an analytical-numerical technique. Therefore, the dynamic crack initiation and propagation process of deep rock caused by the explosion is considered both analytically and numerically. The mechanical process of rock cracking under the action of an explosion stress wave is theoretically analyzed and simulated with a finite difference method. Then the coupling effect of explosion load in the form of shock wave and gas pressure is established numerically based on the two-dimensional explicit finite difference and displacement discontinuity methods, respectively. The analytical method involved the solution of the Lame-Navier equation in elasto-dynamics based on the Green’s function solution. The simulation procedure consists of coupling the explicit finite difference method with the displacement discontinuity method in the form of higher-order displacement discontinuities along the boundaries of the problem. All of the mentioned processes have been done in an oil field with a density of 2.5 gr/cm3, Poisson’s ratio of 0.2, and elastic modulus of 20 GPa. The numerical results of this research show that shock waves are responsible for the initiation and propagation of radial cracks around the wellbore which in turn is filled with pressurized gas due to explosion. Then, these shock wave-induced radial cracks are propagating in the reservoir rock because of the explosive gas pressure inside them. This rock fracturing mechanism can help to improve the permeability and productivity of the highly low-permeable reservoirs in horizontal wells.