The creation of multiple fractures from a wellbore has been demonstrated for a high-energy gas fracturing concept. In this concept, the gas pressure pulse due to the deflagration of a propellant is designed to give (1) pressure-loading rates sufficient to initiate multiple fractures, (2) peak pressures below the flow stress of the formation to avoid rock compaction, and (3) a duration of burn sufficient to allow gas penetration and extension of the fractures. Three experiments were conducted adjacent to a mine drift and the results were observed directly by mineback through the experimental areas. Tests with three different propellants to give different burning rates and, hence, different pressure loadings and pulses resulted in phenomenologically different behavior. Mine ack of the intermediate test (pressure loading rate of 20 psi (138 kPa)/msec, peak pressures of 13,800 psi (95,151 kPa), and burn time of 9.0 msec) indicated 12 separate fractures from 0.5 to 8.0 ft (0.15 to 2.4 m) long for the 20-lb (9 kg) propellant charge. Tests with a faster and slower burning propellant yielded only single fractures less than 5 ft (1.5 m) long and features normally associated with explosive and hydraulic fracturing, respectively.

Multiple fracturing alleviates many of the postulated limitations of explosive and hydraulic fracturing techniques for the effective stimulation of Devonian shales. An expected test series is being conducted as part of the Eastern Gas Shales Program to examine several techniques for multiple fracturing based on this controlled-pressure-loading concept. Test results will be evaluated with respect to the application of such techniques for formation evaluation and stimulation of that resource.

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