Abstract
A method is proposed for using sequentially-fired, shaped charges to drill deep, small-diameter holes in rock more efficiently. Using this method, penetration in igneous rock can be increased from 10 times the diameter of a single, copper-lined charge to 18 or more times this diameter when two or more charges are fired sequentially. Design calculations for a shaped-charge drilling system can be performed using Bernoulli's equation; however, this simple mathematical model has several shortcomings. Shaped-charge penetration, therefore, should be computed using a scaling technique and available experimental data. This allows the penetration efficiency of a sequence of shaped charges to be determined. A shaped-charge drilling device is presented which uses two or more staged charges. Hydrodynamic evaluation of this device, especially the mechanics of slug deflection, indicates that this design overcomes some of the weaknesses of earlier designs. A major improvement is the use of explosive cylindrical lenses, initiated by mild detonating delay fuses, to ensure proper symmetrical firing of the second-and third-stage explosives.
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