Gilles Pijaudier-Cabot / Professor, University of Pau, director, Institute for the sustainable engineering of fossil ressources / January 14th, 2013
Electric fracturing
The second approach is dynamic loading. In statics, the surface of crack created in a material is proportional to the energy transferred to the volume of material that will break. Dynamic loading brings a large amount of energy to a small volume of material. In this volume, there is such an amount of energy, that a large area of cracks will be created. As the loading wave spreads inside the material, it will create fragmentations, thereby connecting the initial and newly created network of cracks. Dynamic loading can be induced for example by explosives placed at the bottom of wells or by electrical impulses, an original technique inspired by tunnel drilling methods. The load applied to the rock in the proximity of the drilling site is a pressure wave generated by an electrical discharge between two electrodes placed in a wellbore filled with water. The amplitude of this wave of pressure can reach up to 200 MPa (2000 times the atmospheric pressure) while its duration is around a hundred of microseconds. This pressure wave will be transmitted to the rock by the fluid inside the wellbore, and will create micro-cracks of decreasing density, according to the distance from the well. Models indicate rock permeability increases only up to several meters from the wellbore. Electric pulse fracturing could facilitate the reactivation of existing cracks by focusing more easily on the concerned rock volumes and avoiding important needs for water. However, the relevance of this process remains to be seen.
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