FORT UNION DEEP Page: 3 of 17
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ABSTRACT
Coalbed methane (CBM) is currently the hottest area of energy development in the Rocky
Mountain area. The Powder River Basin (PRB) is the largest CBM area in Wyoming and has
attracted the majority of the attention because of its high permeability and relatively shallow depth.
Other Wyoming coal regions are also being targeted for development, but most of these areas have
lower permeability and deeper coal seams.
This project consists of the development of a CBM stimulation system for deep coal resources
and involves three work areas: (1) Well Placement, (2) Well Stimulation, and (3) Production
Monitoring and Evaluation. The focus of this project is the Washakie Basin. Timberline Energy,
Inc., the cosponsor, has a project area in southern Carbon County, Wyoming, and northern Moffat
County, Colorado.
The target coal is found near the top of the lower Fort Union formation. The well for this
project, Evans #1, was drilled to a depth of 2,700 ft. Three coal seams were encountered with
sandstone and some interbedded shale between seams. Well logs indicated that the coal seams and
the sandstone contained gas. For the testing, the upper seam at 2,000 ft was selected.
The well, drilled and completed for this project, produced very little water and only
occasional burps of methane. To enhance the well, a mild severity fracture was conducted to
fracture the coal seam and not the adjacent sandstone. Fracturing data indicated a fracture half-
length of 34 ft, a coal permeability of 0.2226 md, and permeability of 15.3 md. Following
fracturing, the gas production rate stabilized at 10 Mscf/day within water production of 18 bpd.
The Western Research Institute (WRI) CBM model was used to design a 14-day stimulation
cycle followed by a 30-day production period. A maximum injection pressure of 1,200 psig to
remain well below the fracture pressure was selected. Model predictions were 20 Mscf/day of air
injection for 14 days, a one-day shut-in, then flowback. The predicted flowback was a fourfold
increase over the prestimulation rate with production essentially returning to prestimulation rates
after 30 days.
The physical stimulation was conducted over a 14-day period. Problems with the stimulation
injection resulted in a coal bed fire that was quickly quenched when production was resumed. The
poststimulation, stabilized production was three to four times the prestimulation rate. The methane
content was approximately 45% after one day and increased to 65% at the end of 30 days. The gas
production rate was still two and one-half times the prestimulation rate at the end of the 30-day test
period. The field results were a good match to the numerical simulator predictions. The physical
stimulation did increase the production, but did not produce a commercial rate.iii
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Jr., Lyle A. Johnson. FORT UNION DEEP, report, March 1, 2002; United States. (https://digital.library.unt.edu/ark:/67531/metadc785812/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.