Abstract
In the late 1970s and early 1980s in conjunction with other oil and gas well stimulation studies, personnel from the Dynamic Effects Laboratory performed model testing to demonstrate the effectiveness of utilizing an open section of borehole just before a plug. We called the process stem induced fracturing. The open section beneath the stem was used to increase the pressure magnitude and spread out the duration of the pressure pulse. This technique was later utilized by Frank Chiapetta [Chiappetta, R.F. and Mammele, M.E., Citation1987, Analytical high-speed photography to evaluate air decks, stemming retention and gas confinement in pre-splitting, reclamation and gross motion applications. Proceedings of 2nd International Symposium on Rock Fragmentation by Blasting, Keystone, Colorado, USA, 257 – 309] in the fracture and fragmentation of rock in quarry blasting situations. He called his technique air deck blasting. In fact, Frank found that the Russians had previously discovered the same technique. There is currently interest in utilizing the same technique with an open hole beneath the explosive at the bottom of the bore hole to better remove the toe in a fragmentation shot. This paper reviews the development of stem induced fracturing and describes a series of model tests conducted to measure borehole pressure at points along a borehole when an explosive charge is detonated at the midpoint of the borehole. Tests were conducted in both stiff boreholes (aluminum) and less rigid boreholes (PMMA). Pressure time profiles were measured at the charge site, midway between the charge and the bottom of the hole, at the stemming at the top of the borehole, and at the bottom of the borehole. Crack initiation sites and crack propagation were also determined in the PMMA models. Some high speed pictures were taken of the event in the PMMA.