Contrast test of different permeability improvement technologies for gas-rich low-permeability coal seams

摘要

To select an optimal gas stimulation technique for gas-rich low-permeability coal seams, contrast tests were conducted to study the permeability improvement effects of blasting and hydraulic fracturing techniques based on the same geological units of coal seams. A contrast test of three shaped charge blasting groups with different charging coefficients showed that when the radial decoupling charging coefficient was 1.5, a stress wave with low dominant frequency produced the strongest stimulation effect, and the combined action of the blasting gas and the stress wave on the coal mass effectively increased the volume fraction of gas in the extraction boreholes by 2.0-3.4 times. A contrast test of two hydraulic fracturing groups with different fracture parameters showed that increasing the duration of hydraulic fracturing continuously could effectively compensate for the injected pressure in the target coal seam and increase the gas permeability coefficient of the original coal mass by 6 times. A contrast test between the two permeability improvement techniques, namely, shaped charge blasting and hydraulic fracturing, showed that the effective range of permeability improvement by hydraulic fracturing was 1 m wider than that by shaped charge blasting, and that although shaped charge blasting provided a higher initial peak of the gas volume fraction in the extraction boreholes, the gas volume fraction under hydraulic fracturing had a lower decay rate. (C) 2016 Elsevier B.V. All rights reserved.