Abstract
Wagon Wheel is a project planned to stimulate a well in gas reservoirs of the Pinedale anticline by means of nuclear explosives. The Pinedale field, in the northern part of the Green River basin of southwest Wyoming, is potentially productive from almost 10,000 ft of lower Fort Union, Lance-Lewis, and Mesaverde sandstones. Attempts to produce the field conventionally have proved uneconomic because of low permeability.
The first nuclear stimulation experiment, Gasbuggy, in northwest New Mexico, was detonated in 1967 using a 29-kiloton explosive. Technical questions answered by Gasbuggy resulted in the program at Wagon Wheel, which will be an attempt to define the economics of use of nuclear stimulation. Project Rulison was the second test to stimulate natural gas reservoirs and utilized a device of approximately 40 kilotons. The most recent test, Project Rio Blanco, used three 30-kiloton explosives fired simultaneously. Project Rulison and Project Rio Blanco are in the Piceance basin of western Colorado.
Wagon Wheel 1 was drilled to 19,000 ft to evaluate the entire Mesaverde section. Gas was detected on mud-logging equipment throughout the basal Fort Union, Lance-Lewis, and Mesaverde, below the top of the gas reservoir at 7,972 ft. The well has been plugged back to 11,700 ft as a possible emplacement hole in which five 100-kiloton explosives will produce a chimney from 9,000 to 11,650 ft. Reserves in this interval are calculated at 207 Bcf of gas in place per square mile.
Extensive logging, coring, and testing were carried out in the program, including special logs for rock-mechanics study.
Two special wells in addition to the Wagon Wheel 1 were drilled to evaluate the aquifers above the gas reservoir. Potable water extends to a depth of 3,730 ft. Salt water is present from 3,730 to 5,630 ft. Low-quality subpotable water extends from 5,630 to 7,140 ft. The saltwater zone is interpreted to be a tongue of Wasatch extending from the west into Eocene arkose derived from the Wind River Range on the east.
Plans call for sequential detonation of five explosives spaced at intervals from 9,220 to 11,570 ft, to produce a continuous chimney from 9,000 to 11,650 ft. There will be a safety margin of 1,600 ft between the top of fractures and the bottom of the known aquifers.
