Abstract
Development of the nuclear explosive fracturing concept and Project Gasbuggy and other proposed gas reservoir stimulation tests are reviewed. Areas suitable for the technique and estimates of potential gas recovery are shown. Economics of future application are considered. The paper points out the desirability of utilizing the results of Project Gasbuggy in planning additional gas-stimulation projects. projects
Introduction
The nuclear explosive fracturing experiments, particularly Project Gasbuggy, have received so particularly Project Gasbuggy, have received so much "glamor" publicity that their experimental nature sometimes has been overlooked. Journalists frequently omit the qualifying phrases and assumptions used by technical participants in these projects. Reference is made to the feasibility reports projects. Reference is made to the feasibility reports on Project Gasbuggy, Project Bronco, and Project Ketchs that may be obtained at low cost from the Clearinghouse for Federal Scientific and Technical Information, Bureau of Standards, Springfield, Va. These reports and other articles published in authoritative journals, such as the journal of Petroleum Technology, provide the material to give Petroleum Technology, provide the material to give a realistic slant on this field of research.
The purpose of this paper is to review some of the background on the projects to evaluate nuclear source of low permeability gas reservoirs and to comment on possibilities for future commercial application.
TECHNICAL CONCEPT
Ten years ago, the petroleum producing industry thought of the nuclear explosive primarily as a heat source. For example, in 1958 one company proposed that nuclear explosives be used in the McMurray oil sands of Alberta, Canada, where the reservoir is saturated with cold oil of high viscosity. The heat liberated by the explosive was supposed to reduce the viscosity of the oil and allow it to be pumped to the surface. It was recognized that on an operational basis it might be necessary to provide for injection of additional heat to continue the recovery process. The report on this proposed application mentioned that, in addition to liberating a tremendous amount of heat, the explosive had the advantage of fracturing a large area in and below the sand. About this same time, another company expressed interest in trying a nuclear explosive in a shallow, high-viscosity-oil reservoir in Wyoming.
A review of the effects on oil production of the heat produced by nuclear explosives indicated this application to be unattractive. Although most of the energy of the explosion remains in the rock as heat, the increase in temperature outside the rubble zone or "chimney" is small, as shown by measurements following two underground tests. Five months after a 1.7-kiloton shot in tuff, the rock 100 ft from shotpoint (35 ft outside the chimney) was 5F above normal. Thirteen months later, the temperature had declined, leaving only a 3F temperature increase at this point. One year after a 5-kiloton shot, also in tuff, a 3F temperature rise was found 160 ft from the shotpoint (68 ft outside the chimney). The temperature of chimney gas rapidly approaches the temperature of steam at the particular chimney pressure. Withdrawal of gas along with dissipation of heat into cooler rock would bring about further cooling.
Discouragement over the lack of benefit to be derived from heat soon was reversed when it became evident that fractures produced by nuclear explosives could be of great benefit. A search was begun immediately to learn of oil reservoirs that fit the criteria for shooting jobs of such magnitude. Attention was first directed to oil because, per unit volume of reservoir, it is more valuable than gas, and it was obvious that nuclear stimulation would be difficult to justify economically.
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