Modeling of hydrofacture Stimulated gas wells near the Rulison Nuclear Test

Rex Hodges, Art Keinrath, and Rick Hutton

The 1969 Project Rulison test in western Colorado, the second natural gas stimulation experiment in the Plowshare Program, was conducted to determine if a nuclear device could be used to fracture low-permeability, gas-bearing rock to enhance gas production. The re-entry well produced gas at rates significantly greater than those of conventional wells of the time; however, the presence of radionuclides in the produced gas persisted above acceptable levels, and the test was abandoned. Advances in hydrofacturing technology has led to increased drilling activity near the Rulison site, raising concerns that remnant radioactivity in the detonation zone could migrate to nearby producing wells and enter the natural gas distribution system. Numerical modeling can be used to make predictions about a site's flow system and contaminant transport potential by quantitatively replicating the site conceptual model and various aspects of the system, allowing past, current, and future scenarios to be tested. The domain of this Rulison modeling effort includes current gas production wells 0.75 mile west of the site and the entire productive interval targeted by the test. Radionuclides that can exist in the mobile gas phase, have a relatively long half-life, and were created in significant amounts by the detonation are of primary concern. Gas-phase radionuclides other than tritium were largely removed by production testing. The depletion of tritiated methane by the production testing leaves tritiated water vapor as the primary mobile contaminant at Rulison. This study confirmed the results of previous Rulison modeling in that it predicts that contamination, in the form of tritiated water, is contained within the institutional control boundary of Lot 11. Simulations of future wells producing in the lot adjacent to the site do not induce migration, though a small pressure gradient develops between the detonation zone and the hydrofactured intervals at the same depth as the detonation zone. The modeling provides quantifiable results that allow the effects of gas production on the flow system and the potential for contaminant migration to be visualized at the Rulison site.

AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012