Experimental study on an alternative oil stimulation technique for tight gas reservoirs based on dynamic shock waves generated by Pulsed Arc Electrohydraulic Discharges

This article deals with the development of a technique to stimulate low-permeability reservoirs, a potential alternative to hydraulic fracturing. The practical objective is to increase the intrinsic permeability of rocks around the oil well by dynamic shock waves. Laboratory experiments were carried out on small hollow cylinder specimens under different confinements, which mimic in situ conditions. Shock waves are generated in water by Pulsed Arc Electrohydraulic Discharges (PAED), which then propagate in water and into the specimens. The specimen is damaged by the pressure waves and its permeability increases with the evolution of damage. Specimens were tested mechanically under three stress levels, corresponding to different depths underground. Then the overall permeability to gas of the specimens was measured and correlated to the electrical energy involved into the PAED. For each stress level, the threshold of energy was observed. From the threshold, the increase of permeability is linear. The thresholds of injected electrical energy increase with confinement level. The effect of repeated shocks on permeability is also considered. Tomography X ray scans have been used to analyze the evolution of the microstructure of representative specimens qualitatively. A good correlation is observed between the X-ray tomography results and the permeability. The evolution of cracking and damage due to dynamic mechanical loads are correlated with the intrinsic permeability of the material and with its microstructure.