Gas quality and geochemical studies in gas-stimulation experiments

Gas produced following the Gasbuggy and Rulison gas-stimulation nuclear explosions had a different composition than the natural gas produced in the same areas before nuclear stimulation. The principal difference was the presence of substantial amounts of CO2, CO, H2, and H2O in the post-explosion gas. There also were changes in ratios of hydrocarbons. Because CO2 reduces the heating value of the gas, and steam presents a troublesome disposal problem due to the trace of tritium it carries, an understanding of the geochemical effects produced by these types of nuclear explosions is needed. Samples of gas-bearing shales were heated under a variety of conditions evolving CO2 at temperatures as low as 5000C, even under a CO2 pressure of 50 atm, due to reactions between fine-grained carbonates and silicates. In other experimental studies evidence was obtained that regions of high temperature (approximately 4000C), rather than radiation, caused the changes in gas composition observed in the Gasbuggy chimney during the 6-mo ''shut-in'' period. In looking ahead to the geochemical effects that occur when multiple explosions are used to form interconnecting chimneys, it is concluded that less CO2 will be produced per unit yield than for a single explosion in the same rock. This is because the intensely heated rock is cooled rapidly by convecting gas before it can heat the adjacent rubble, which results in less rubble being heated hot enough to release CO2. Steam production, however, will be greater in the case of multiple explosions than for single explosions because a higher fraction of the total yield is deposited as heat in the chimney, thus increasing the average chimney temperature. The average chimney temperature, and thus the steam pressure, increases as the distance between multiple explosions is decreased. The steam pressure will also increase as the depth of nuclear explosions is increased