Effects of Nuclear Explosions on Oil Reservoir Stimulation

Abstract

Abstract A general description of Project Plowshar's Gnome atomic explosion near Carlsbad, N. M. is given from the point of view of possible application to oil reservoir stimulation. Post-shot exploratory mining and drilling into the explosion environment and blast cavity are discussed. Petroleum reservoir core and crude oil samples placed near the explosion were subjected to shock energy, high pressures and radiation from the atomic blast. These samples were recovered, analyzed and compared with unexposed, duplicate samples. Additional investigations, which must be undertaken to resolve problems that will be encountered in the use of an atomic device in an oil reservoir, are discussed. Introduction With the advent of nuclear explosions a new, concentrated source of energy bas become available. One promising use for this compact power source is in increasing oil reserves and oil production. This could be accomplished by using the shock energy from the nuclear explosion to change or upgrade the properties of oil reservoir rock. Project Gnome was the first scientific experiment with nuclear explosives to yield information on what effects such a blast would have on reservoir rock and oil samples. The major purposes of the Gnome experiment were:to study the effects of an underground nuclear explosion in salt;to determine the feasibility of recovering radioisotopes produced by the nuclear explosion;to measure neutron activation cross sections and resonance fission characteristics of several isotopes as a function of the neutron energy spectrum produced by the explosion;to make measurements to determine if heat energy could be recovered from the molten salt; andto make seismic measurements to aid in understanding differences between natural disturbances and nuclear explosions. An additional experiment was to subject a variety of rock and organic samples to a range of shock pressures to study the effect of the explosion on the samples. Among the samples incorporated in the experiment were a number of reservoir rocks (limestones, dolomites and sandstones) and typical crude oils. These samples were submitted by the Bureau of Mines and several major oil companies. This phase of the experiment was coordinated by the Bureau of Mines. Gnome was detonated in the Salado rock formation of Permian age (Fig. 1). This 3.1-kiloton nuclear shot was fired in bedded salt 25 miles southeast of Carlsbad, N. M. The working point, or location of the device, was at a depth of 1,184. ft. The region affected by the detonation was composed of 89 per cent halite (rock salt), 7 per cent polyhalite, 1 per cent anhydrite and 3 per cent silt or clay. The Gnome nuclear device was placed at the end of a buttonhook- shaped drift 987 ft from the shaft (Fit 2).The small reservoir rock and oil samples discussed in this paper were located in Drill Holes 3 and 15 (Figs. 2 and 3). The cores were grouted into thin-walled metal containers using saltcrete cement with the same acoustical properties as the surrounding salt. Small oil samples were placed in brass machined containers. The cores and oil samples were attached to a 1 -in. pipe and the assembly placed in Hole 3. Additional saltcrete cement was pumped in through the pipe in an attempt to make contact between the main salt body and the samples. Larger oil samples were placed in accumulators with working pressures of 1,500 psi. These were placed in Hole 15, which was ungrouted. The shot was fired on Dec. 10, 1961. Environment Created by the Explosion Following the detonation, the environment created by the explosion was explored in considerable detail by five vertical drill holes from the surface, six exploratory holes drilled from underground, in addition to mining exploration near the working point. While mining, the shock-effects samples were recovered from Drill Hole 3 (Fig. 2) and irradiated samples recovered from Hole 15. In attempting to recover samples that were exposed to shock pressure greater than about 45 kb, mining advanced directly into the standing cavity produced by the explosion (Fig. 4). JPT P. 473^