Drilling for natural gas can be safely conducted one-half mile from the site where a nuclear device was detonated 40 years ago in the Piceance Basin of western Colorado, according to a draft report released by the U.S. Department of Energy (DOE) last Thursday.
DOE recommends that natural gas developers adopt a "conservative, staged drilling approach, allowing gas reserves near the Rulison [nuclear] site to be recovered in a manner that minimizes the likelihood of encountering contamination. This staged approach calls for collecting data from wells outside of the half-mile zone before drilling closer, and then drilling within the half-mile zone in a sequential manner, first at low contamination probability locations and then moving inward.
"This approach is DOE's recommendation for drilling in this area that will protect public safety while allowing collection of additional data to confirm that contamination is contained within the 40-acre institutional control boundary," the draft report said.
In September 1969, the U.S. Atomic Energy Commission, the predecessor agency to DOE, detonated a 43-kiloton nuclear device more than 8,000 feet below the ground surface in the Williams Fork Formation at the Rulison site, 40 miles northeast of Grand Junction, in an attempt to release commercially marketable quantities of natural gas, according to DOE.
The DOE reported that four production tests conducted on a reentry well between October 1970 and August 1971 produced a total of 455 MMcf, which was approximately 10 times that of a conventionally stimulated well in the same production zone.
"An increase in drilling for natural gas near the site has raised concern about the possibility of encountering residual radioactivity from the area of the detonation," the draft said.
The DOE said it issued the draft report as guidance for operators and the Colorado Oil and Gas Conservation Commission (COGCC), which has final authority over applications for permits to drill oil and gas wells in Colorado. The COGCC has imposed administrative controls on drillers in the vicinity of the Rulison site. The commission notifies DOE of any drilling permit activity within three miles of the nuclear site.
"The results of the most recent conservative modeling provide confidence that wells at the half-mile radius...are safe for gas production. The half-mile radius is 2,640 feet from the detonation, yet no significant amount of tritium [an isotope of hydrogen] reached the hypothetic gas well for any simulation with a well 1,310 feet from the detonation," the draft said. It cited tritium as the only contaminant of concern for gas production.
"Almost all of the tritium...would be captured at the wellhead where the water vapor condenses and is removed from the gas prior to entering the gas distribution systems. Despite the low risk, a cautious approach to gas development near the Rulison site is recommended."
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