A propellant-based technology, High Energy Gas Fracturing (HEGF), has been applied to fracturing through perforations in cased boreholes. The use of propellants that deflagrate or burn, rather than high-order explosives that detonate, permits controlled buildup of pressure in the wellbore. The key to successful stimulation in cased and perforated wellbores is to control the pressure buildup of the combustion gases to maximize fracturing obtained, without destroying the casing. Eight experiments have been conducted in a tunnel complex at the Department of Energy's Nevada Test Site. This location provided a realistic in situ stress environment (7 MPa [1000 psi] overburden stress) and access for mineback to directly observe fracturing obtained. Primary variables in the experiments include propellant burn rate and amount of propellant used; presence or absence of liquid in the wellbore; in situ stress orientation; and perforation diameter, density, and phasing. Fracture surfaces propagate outward along lines of perforations, then gradually turn toward the hydraulicfracture direction. Fracture lengths of 3m (10 ft) or more are observed. It is shown that such fractures, with proper choice of propellant and perforation design, can be created with no attendant casing damage.

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