Geology of Wagon Wheel Nuclear Stimulation Project: ABSTRACT

Abstract

Project Wagon Wheel, if executed will be an attempt to stimulate gas reservoirs of the Pinedale anticline by means of nuclear explosives. The Pinedale field, located in the northern Green River basin of southwest Wyoming, is potentially productive from a section totaling nearly 10,000 ft of lower Fort Union, Lance-Lewis, and Mesaverde sandstone equivalents. Attempts to produce the field conventionally have proved uneconomical due to low permeability. Because its requirements exceeded the state of nuclear technological development, Wagon Wheel was not selected for the first gas stimulation experiment. Project Gasbuggy, in northwest New Mexico, was detonated in 1967 using a 26 kiloton device. Data produced in Gasbuggy were utilized in planning Wagon Wheel, which is an actual attempt at economic use of nuclear energy. Wagon Wheel No. 1 was drilled to 19,000 ft to evaluate the entire Mesaverde section. Gas was detected by mud-logging equipment below 7,972 ft depth throughout the basal Fort Union, Lance-Lewis, and Mesaverde. The well has been plugged back to 11,700 ft leaving approximately 3,700 ft of proved gas-bearing section available for stimulation. This interval will accommodate the 5 100-kiloton explosives planned. In-place End_Page 652------------------------------ gas reserves for this section are calculated at 252 billion cu ft/sq mi. Extensive logging, coring, and testing have been carried out in the program, including special logs for rock mechanics study. Cores were compared with those from Gasbuggy as to compressive strength, shear behavior, and potential for fracturing. Petrographic analyses indicate better fracture potential at Wagon Wheel due to a higher degree of grain to grain contacts and lower clay content. Environmental protection studies include examination of surface waters, springs and wells, man-made structures, mines, flora, fauna, and general land use. The most important aspect from a geologic standpoint is protection of the extensive groundwater aquifers above the gas reservoir. Two wells, in addition to the Wagon Wheel No. 1, were drilled for the purpose of evaluating those aquifers. Potable water extends to a depth of approximately 3,600 ft. Salt water occurs from 3,600 to approximately 5,200 ft. Low quality subpotable water extends from 5,200 to about 7,200 ft. The saltwater zone is interpreted to be in a tongue of Wasatch Formation extending from the west into Eocene arkoses derived from the Wind River Range on the east. Plans call for sequential detonation of 5 explosives spaced at intervals from 9,220 to 11,560 ft to produce a more or less continuous chimney from about 8,700 to about 11,600 ft. There will be a safety margin of 1,500 ft between the top of fractures and the bottom of known aquifers. End_of_Article - Last_Page 653------------