Laboratory-scale fracturing of cement and rock specimen by plasma blasting

Abstract

Although hydraulic fracturing is the most commonly used method for fracturing of shale-gas-bearing rock, there are some problems with this method. As plasma blasting can fracture rock without these problems, laboratory-scale fracturing of cement and rock specimens by plasma blasting was performed to investigate the possibility of using this method in shale gas development. Specimens were fractured by plasma blasting under various stress conditions. First, specimens were fractured under uniform pressure, and the discharge energies required for fracturing and fracture development were investigated. As uniform pressure increased, the energy increased as a parabolic curve. Fewer fractures were developed as uniform pressure increased for the same discharge energy. Second, plasma blasting was performed for specimens subjected to three different stresses. Fractures both perpendicular and oblique to the minor stress direction were developed with a differential stress of 3 MPa; however, only fractures perpendicular to the direction of the minor stress were developed with an 8 MPa differential stress. More fractures with diverse directions were developed with the same stress conditions but higher energy. Several long fractures were developed by multiple low-energy blasts, the same result as for one highenergy blast. Proppants were injected effectively into fractures by plasma blasting, resulting in a hydraulic conductivity increase. In sandstone, the geological structure controlled the direction and characteristics of fracture development by plasma blasting. All these results indicate that plasma blasting can be a possible method for fracturing shale gas formation. However, more researches are necessary to apply this method in shale gas development in field.

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