Behavior And Mechanism Of Fracturing And Enhanced-permeability Of Coals With Electric Pulse Stress Waves

Fracturing and enhanced-permeability of coals with electric pulse stress wave is a new reservoir stimulation measure based on pulsed power technology. However, the fracturing process and enhanced permeability mechanism about this technology are unclear. In this paper, a self-designed experimental platform was established, taking large block fat coal, lean coal and anthracite coal samples as objects of study, repeated impulses were tested on 13 large block coal samples under four kinds of pulse loading ways, electrical wire load and 5g, 10 g, 15 g energetic mixture load respectively. After that, the coal samples under different times of impulsion were collected, and then the pore fracture structure and permeability of coal samples were tested. The change characteristics of pore structure and evolution laws of macro and micro fractures were analyzed under the action of electric pulse stress waves. The fracturing results and influencing factors of electric pulse stress waves to fracture coals were discussed by the numerical simulation. In the end, the mechanism of electric pulse stress wave to fracture coal rocks and enhance permeability was preliminarily revealed. The results show that electric pulse stress waves could improve coal pore fracture structure, increase connectivity between the pores, and enhance coal reservoir permeability, which really is an effective technology for enhanced coal reservoir permeability. There are three kinds, and four kinds of evolution models of pores and fractures respectively. The growth and evolution of fractures has stage features, new fissures mainly from the further expansion of existing fractures, the extension of micro-fractures are controlled by macerals. Fractures mainly on extend mode in the early stages, and bifurcation mode later. There are optimal range values of stress wave peak pressure and shock times on fracturing results. Geostress has a strong inhibitory effect on fracturing results. Elastic modulus and tensile strength are the main coal mechanical parameters that influence fracturing effects. Fracture and vibration zones could be formed under the action of electric pulse stress wave, fracture zone is the core area of permeability modification. It is possible to reduce the capillary irreducible effect and improve the fluid mobility depend on repeated impulsion.