MODELING OF FLOW AND TRANSPORT INDUCED BY PRODUCTION OF HYDROFRACTURE-STIMULATED GAS WELLS NEAR THE RULISON NUCLEAR TEST

The Project Rulison test in Western Colorado was conducted in 1969 to determine if a nuclear device could be used to fracture low permeability, gas-bearing rock to enhance natural gas production. The presence of radionuclides (specifically tritium) in the produced gas persisted above acceptable levels, and the test was abandoned. Advances in hydraulic fracturing technology have made it feasible to extract natural gas from low-permeability reservoirs, and drilling activity near the Rulison site has raised concerns that remnant radioactivity in the detonation zone could migrate to nearby producing wells and enter the natural gas distribution system. The site was modeled using the massively parallel version of TOUGH2, TOUGH2_MP-EOS7R, with over 1,000,000 elements. The majority of the tritium is present as tritiated water, and since the gas permeability of the native formation is several orders of magnitude higher than the liquid permeability, any significant migration occurs with the gas phase. In the model, tritium partitions between the aqueous and vapor phases in relation to the Henry’s Law constant. The Henry’s constant for tritiated water vapor is simply the water vapor pressure. The model domain includes the entire targeted gas-bearing section and gas production wells installed in 2010 1.2 km (0.75 mile) from the Rulison site. The model was calibrated to historical production and pressure data from the Rulison reentry well and to data from the recently installed gas wells. The model was used to simulate the effects of current wells and of future wells that could potentially be installed nearer the Rulison site.