History of Well Shooting
Oil and gas wells have been stimulated with high-energy explosives since the late
1800’s. It appears, however, that the term “well shooting” originated many years before this in days when a water well was sometimes rejuvenated by shooting a rifle down the well. Well shooting as discussed herein refers to any rapid release of energy from a chemical reaction in a wellbore for the purpose of stimulating production, presumably by fracturing the reservoir rock. This includes explosives (solid, liquid, and gas) and propellants that deflagrate rather than explode. In a broad sense, well shooting has been applied in several geotechnical fields; e.g., preparation of oil shale beds for true in situ processing, preparation of underground mineral deposits for solution mining, etc.
Problems of wellbore damage, safety hazards, and unpredictable results have reduced the relative number of wells stimulated by high-strength explosives. In recent years hydraulic fracturing has been favored, and sophisticated techniques, equipment, fracturing fluids, and proppant have been developed to optimize the hydraulic fracturing process.
Unfortunately, similar efforts toward general understanding and process optimization have been lacking for well shooting. However, recent finding have shed new light on the process of dynamic wellbore fracturing. These findings indicate that vast improvements are achieved using “tailored-pulse” loading techniques.
Several tailored-pulse concepts rely on the use of propellants which deflagrate rather than detonate. Unlike explosives, the burn front in these materials travels slower than the sound speed, and the burning rate can be varied over a wide range. Pressure-time behavior of propellants differ from explosives in that peak pressures are lower, and burn times are longer. These concepts are more fully described in SPE/DOE 8934 which is a detailed technical paper written about tailored-pulse well shooting studies conducted by Sandia National Laboratories.