Some Calculations For Effecting Oilfield Stimulation By Nuclear Means
Authors: Higgins Gary H. , Rodean Howard C. 
Published: December 2007

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Nuclear explosions in underground rock formations form large cavities surrounded by a substantial region of crushed and fractured rock. The cavity generally collapses to form a rubble-filled chimney that is very porous and highly permeable. The surrounding crushed and fractured zone is also increased in permeability to such a degree that the effective well radius of a natural-gas well stimulated by a nuclear explosion may be several times the chimney radius. The relations between yield, depth of burial, and the geometry of chimneys and fractured regions indicate that the effect of explosion yield on the number of wells required in a given region should be investigated from the standpoint of economics. Similarly, the relations between thermal energy deposition and yield indicate that heating of the chimney rubble (and, therefore, the natural gas) is independent of yield, but the thermal time constant of the chimney rubble varies directly with yield and inversely with production rate. A representative value for this time constant is eight years. The radioactivity concentration present in natural gas from a well stimulated by a nuclear explosion is independent of yield only if the design parameters such as fission-to-fusion ratio are held constant. The radio nuclides which might be product contaminants are tritium, carbon-14 and krypton-85. These materials will be concentrated in the rubble-filled chimney, so as production proceeds, the contaminants will be purged from the reservoir and the contamination will continuously decrease. The initial concentration of Kr85 might be about 100 pc/cm3 of gas. After a few hundred million standard cubic feet of gas have been removed (equivalent to about two to five chimney volumes of gas), ninety percent of the contaminants will have been removed from the well. The average contamination for the entire production period will be about 3 pc/cm3. When these values are compared to stated standards for the general population, these average concentrations do not lead to air contamination in excess of permissible levels.

Introduction

It is a common practice in the petroleum industry to stimulate the production of oil and gas wells by fracturing the oil-or gas-bearing rock formations adjacent to the wellbore. These fractures serve to increase the effective permeability of the medium in the vicinity of the wellbore, and thereby increase the effective well diameter.