Cuderman, J.F., Sandia Natl. Laboratories
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 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 (8 MPa (1000 psi) overburden stress) and access for mineback to psi) overburden stress) and access for mineback to directly observe fracturig 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 hydraulic-fracture direction. Fracture lengths of 3 m (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.
Many gas and oil wells require stimulation after drilling to obtain commercially economic production. For uncased wells, the traditional techniques have been hydraulic and foam fracturing, or high-order explosive fracturing. More recently, tailored-pulse fracturing technology has been developed, which utilizes propellants that burn or deflagrate rather than propellants that burn or deflagrate rather than detonate.
The High Energy Gas Fracturing (HEGF) technique served to establish the important parameters of such tailored-pulse fracturing in uncased, liquid-free wellbores. By proper choice of propellants, available in a range of grain sizes and burn rates multiple radial fractures are created that emanate from the wellbore. Unlike the case of hydraulic fractures linked with the wellbore. The multiple fractures are also free of the wellbore crushing often obtained with high-order explosives.
For c ases and perforated wells, the fracturing technique of choice is usually hydraulic or foam fracturing. The resulting fractures, regardless of perforation phasing, are normal to the minimum in situ perforation phasing, are normal to the minimum in situ principal stress and generally parallel existing principal stress and generally parallel existing natural fractures. The present work using the HEGF technique is the first detailed study of dynamic tailored-pulse-fracturing techniques. These experiments were conducted in the Department of Energy's (DOE's) G-Tunnel Complex at the Nevada Test Site (NTS). The experiments at G-Tunnel (1000 psi) overburden stress). The fracturing obtained in G-Tunnel is readily observed posttest mineback.
The objectives of the research were to determine (1) whether one could obtain multiple fracturing through perforations, (2) the extent of such fractures, (3) pressure rates required for optimizing fracturing, and (4) attendant casing damage.