The impacts and other issues related to CBM development and coal mining in the Powder River Basin, Wyoming will be observed and addressed at 4 stops in this field conference.  The stops will demonstrate the effects of drilling for CBM, CBM production, surface drainage of co-produced water, water quality,  gas collection, and coal mining operations.  Activities at all 4 stops are co-sponsored by gas and coal developers that collaborate with the USGS-BLM CBM cooperative project. 

Stop 1: Jacobs Ranch Coal Mine (Leaders: Rob Livingston, Jacobs Ranch Coal Co., Kennecott Energy, Gillette Wyoming and Romey Flores, USGS) 

At Reno Junction TURN RIGHT onto Highway 59 (mile marker 75.06; see Fig. 1).  About 3 miles south on Highway 59 TURN LEFT (mile marker 72.39) onto Highway 450 (mile marker 66.2) and proceed about 12 miles to Jacob Ranch Coal Company (a subsidiary of Kennecott Energy) headquarters (mile marker 54.4).  Thunder Basin Coal Mine (Arch Mineral) is located south of Highway 450.  The Jacobs Ranch Coal Mine (Fig. 22) opened in 1978 and produced about 300 million short tons of coal during the first 20 years of operation.  The mine produces from the Wyodak-Anderson coal zone, which is locally named Wyodak by the operator.  Here the coal zone consists of three coal beds; the lower, middle, and upper Wyodak seams; separated by shale beds.  The lower Wyodak seam is 5 ft thick and is not economic.  The middle Wyodak seam varies from 35 ft thick in strip pit 2 to 50 ft thick in strip pit 1 (Fig. 23).  The upper Wyodak coal seam varies from 7 to 10 ft thick and is also being mined.  The strip ratio (thicknesses of overburden rocks and coal and) is from 2.5:1 to 3:1 with the overburden or rocks above the coal zone varying from 150 to 200 ft thick.  The overburden consists of mainly sandstone and mudstone (Fig. 23). 

The coal is subbituminous in rank with an average calorific value of about 8,700 Btu/lb and an average of 0.45 percent total sulfur and 5.4 percent ash yield.  Jacobs Ranch Coal Mine is permitted to produce 35 million short tons of coal annually, however, last year the total annual production of was about 30 million short tons.  Jacobs Ranch is served by two railroads and a top-off precision loading system, which permits two trains to load simultaneously.  The coal is shipped to electric power generating plants in the southern and southeastern United States (Texas, Alabama, Georgia, and Tennessee).  The projected life of the coal mine is to the year 2006.  The remaining coal reserve is estimated at 240 million short tons and the coal has an average thickness of 55 ft.  Presently the coal mine has applied (Lease By Application) for a lease tract that contains as much as 530 million tons of coal reserve, which should extend the life of the mine beyond 2006.

The Jacob Ranch Coal Mine was involved in the “lost gas” issue and the company cored 2 wells for the USGS-BLM CBM project to determine the gas content of the Wyodak-Anderson coal zone in their mine property west of strip pit 1 (see Fig. 22).  RIM Operating, Inc. in their lease area west of the Jacobs Ranch Coal Mine property, for our study, cored an additional 2 wells.  The average gas content sampled about 500 ft from the mine highwall is about 1-2 standard cubic feet per ton of coal (scf/t) compared to 12 scf/t about 3 miles to the west of the mine highwall. 
 

Stop 2: Dry Fork CBM Field (Leaders: Tom Doll, Barrett Resources Corporation, Gillette, Wyoming; Joe Meyer, BLM, Casper, Wyoming, and Romey Flores, USGS, Denver, Colorado)

Return to Highway 450 from the parking lot of Jacobs Ranch Coal Company (see Fig. 1).  TURN RIGHT (west) on Highway 450 and proceed about 8.6 miles. TURN RIGHT (north) about 0.7 mile after the Highlight Road on a “scoria” road (mile marker 63) and proceed about 1 mile.  This stop is at the Dry Fork CBM field (Fig. 24), which has been operated by Barrett Resources Corporation for about a year. The Dry Fork field is one of three fields (Dry Fork, Greater Black Thunder, and Little Black Thunder) operated by Barrett in this area. The field consists of 80 producing wells that are more than 700 ft deep (Fig. 24).  These CBM wells produce gas from the Wyodak-Anderson coal zone, which is locally identified as Wyodak coal by the gas operator.  Here the Wyodak-Anderson coal zone is more than 70 ft thick and consists of as many as 6 coal seams interbedded with thin carbonaceous shale and mudstone partings (Fig. 25 and Fig. 26).  Toward the basin center the coal zone is locally split, and contains shale and mudstone beds that are thicker than the coal seam above and below.  Fluvial channel sandstones and associated floodplain-crevasse splay mudstones, siltstones, and sandstones overlie the coal zone.  The CBM wells within the 4-township area currently produce a total of 40 million cubic feet per day (MMCF/day).  The gas from the CBM wells is piped to pod stations, where it is metered.  Each pod station serves as many as 8 wells.  The gas is comingled and is piped to a rotary compressor which compresses the gas to about 80 pounds per square inch (psi).  The gas is then piped to a main line compressor where the gas is compressed to about 1500 psi.  Western Gas (Lance Oil and Gas Company) operates the pipeline infrastructure in this area.  The CBM wells in this area produce an average of 400 barrels of water per day per well.  The co-produced water is discharged into the North Fork of the Dry Fork of Little Thunder Creek, which eventually feeds into the Cheyenne River.

Surface water discharge from CBM wells along the Caballo and Upper Belle Fourche Creeks (see Fig. 19) have been monitored for the last few years by the Casper District Office of the BLM (Meyer, 2000).  A major issue concerning the discharge of water on the surface by CBM wells concerns the volume of water produced and the effect on flow rates in nearby streams.  BLM has investigated this problem and monitored water gages from 1993 to 1999 along the Caballo Creek  and Belle Fourche drainages (see Fig. 19).  Streamflow volumes at the gaging stations show little or no increase that can be related to the introduction of CBM co-produced water (Meyer, 2000).  Streamflow events in the Caballo and Upper Belle Fourche drainage basins are mainly related to precipitation (e.g., rain and snow), with streamflow returning to near zero flow during periods of little or no precipitation.  Creeks in these drainage basins are ephemeral with flow occurring in response to storm events and snowmelt.  On average, flow on Caballo Creek during periods of significant precipitation represents less than 2 percent of the total volume of water produced from CBM wells (Meyer, 2000).  The Upper Belle Fourche Creek exhibits flow very similar to that of Caballo Creek; that is the flow averages less than 3 percent from co-produced water.  Thus, none or very little of the water discharge from CBM wells makes it to the stream gage locations on the Caballo and Upper Belle Fourche Creeks.  During periods of little or no precipitation evapotranspiration and infiltration losses may be greater than 90 percent (Meyer, 2000).  Similar trends have been observed in the Little Powder River drainage basin.
 

Stop 3: Peabody Natural Gas Drill Site (Leaders: Gary Stricker and Romey Flores, USGS, Denver Colorado; Craig Jennings. Peabody Natural Gas LLC, Gillette, Wyoming) 

Return to Highway 450 and proceed west to Highway 59 (see Fig. 1).  TURN RIGHT (north) toward Gillette, Wyoming.  CBM development is extensive for a distance of about 35 miles, from north of Wright to south of the city of Gillette.  Most of the development is west of Highway 59, where there are numerous CBM fields operated by several gas operators (e.g., Barrett Resources Corporation, Western Gas, Huber JM Corporation, Peabody Natural Gas LLC, Yates Petroleum Company, Devon Energy Corporation, Pennaco Energy, Inc., Ocean Energy Resources, Inc.).  The coalbed methane is produced from the Wyodak-Anderson coal zone, which averages about 50 ft thick and is as much as 100 ft thick.  The net total thickness of coal beds in the Wyodak-Anderson coal zone is shown in Figure 27.  The vertical and lateral variations of coal beds in the Wyodak-Anderson coal zone between Wright and Gillette are illustrated by a east-west cross section (see Fig. 11)

Some of the CBM fields that were developed in the 1980’s and early 1990’s, are gradually being depleted of gas such that some operators are using vacuum pumps to prolong the life of these wells.  The average life of a CBM well is about 7 to 8 years.  In this area, several gas operators have plans to explore and develop a zone of coal beds  (e.g. Cache, Wall, Pawnee, and Kennedy) below the Wyodak-Anderson coal zone (Fig. 28).  This zone of coal beds below the Wyodak-Anderson has net coal thickness of over 200 ft in the east-central part of the Powder River Basin (see Fig. 28), where the uppermost coal beds in this zone occur from 1,000 to 2,000 ft below the surface.  This is shown by the thickness of overburden rocks to the top of the uppermost coal bed in this zone (Fig. 29).

TURN left (mile marker 96.95) on Hoe Creek road and proceed west for about 4 miles.  This stop is to visit a site of Peabody Natural Gas drill site to observe drilling operations prior to CBM development.  Peabody is drilling for coalbed methane from coal bed below the Wyodak-Anderson coal zone.  The CBM wells are drilled by truck mounted rigs as shown in Figure 30.  The truck-mounted rig can drill to about 3,000 ft below the surface.  The drill rig is operated by at least 2 to 3 people (a driller and 1 or 2 assistants).  Because the CBM wells are shallow in the Powder River Basin, the drilling equipment is smaller than what is required for a conventional oil and gas well.  There are about 108 truck-mounted rigs operating in the Powder River Basin with about 70 of these operating at any given time.  With this many drilling rigs, the basin currently has the highest level of drilling activity of any onshore basin in the United States.  What makes the CBM wells economical is that they are shallow (?1,000 ft from the surface) allowing inexpensive (about $25,000 for wells less than 1,000 ft deep) drilling and well completion in only a few days (McGarry, 2000). Drilling and completion costs of deeper CBM wells average about $68,000 (Shirley, 2000).
 

Stop 4: The Gap Gas Gathering Complex (Leader: Pierce Norton, Bear Paw Energy, Denver, Colorado)

Return to Highway 59 and TURN LEFT (north) towards Gillette, Wyoming (see Fig. 1).  Proceed to the Gap gas-gathering complex of Bear Paw Energy about 10 miles south of Gillette (Fig. 31).   About 6.3 miles TURN LEFT on McCreery road and proceed  about 1-1.5 miles to South Jim Wolff (first stop; see Fig. 31) and Antelope Valley compressor stations (second stop; see Fig. 31).  These compressor stations started in November, 1999.  The South Jim Wolff station gathers gas from Pennaco Energy (Marathon Oil Company), Coleman Oil and Gas Inc., and Torch Oil and Gas Company) wells to pod stations, which in turn is compressed to 75-80 psi by Screw compressors.  This gas is then moved to the Antelope Valley station where reciprocating compressors compress it to about 1,200 psi.

The Gap gas-gathering complex has been in operation for about 2 years and started flowing gas in May 1999.   Bear Paw Energy gathers gas in the Gap from 449 CBM wells.  The gas gathering system consists of 10 pod stations with each station serving 20 to 60 CBM wells.  The gas from each well is metered in the pod station and is commingled prior to being piped to screw and reciprocating compressors.  The gas is put into pipelines interconnecting to the Fort Union and Thunder Creek 24-inch pipelines (Fig. 32).  The gas is either moved north to North Dakota through the Williston Basin Interstate pipeline or it is moved to the south (Nebraska, Kansas, the Front Range of Colorado and California) through the Glenrock pipeline.

The Gap gas-gathering complex moves a total of 46 MMCFG/day through 535 miles of low pressure lines (from wells to pod stations), 35 miles of intermediate gathering system (from pod stations to the reciprocating compressors), and 18.5 miles of high pressure lines (from the reciprocating compressors to the main pipelines).  It cost about $45,000,000 to build the Gap gas-gathering complex.  Since 1999 the pipeline infrastructure (see Fig. 32) in the Powder River Basin has been expanded to 550 miles of 16, 20 and 24 inch pipelines at a cost of $443 million (Bear Paw Energy, personal communication, 2000).  The new pipeline infrastructure (e.g., Thunder Creek, Fort Union, and Medicine Bow) is 7 to 84 percent utilized.

The major impact demonstrated by this last stop in the Gap gas-gathering complex is its effect on the “urban interface environment.”   CBM development has encroached south of the city limit of Gillette.  In addition, CBM development has impinged on residential subdivisions west and north of the city limits of Gillette.  Drilling for CBM near or in residential areas is a conflict between landowners and gas operators because of possible invasion of privacy and devaluation of residential properties. In order to avoid devaluation of property, CBM wellheads and metering equipment are housed in tan fiberglass well covers to blend in with the environment.  Also, safe collection of the gas is an issue especially because the coal reservoir extends below residential areas.  This issue is particularly important because of potential hazardous migration of CBM inside homes as exemplified in the Rawhide Village subdivision (10 miles north of Gillette) 
(Jones and Taucher, 1989).  Based on field and laboratory studies of methane and hydrogen sulfide gas concentrations underlying the Rawhide Village subdivision, Glass and others (1987) and Jones and others (1987) reported that the entire subdivision was underlain by potentially explosive concentrations of methane (defined between 5 and 15 percent methane).  The Rawhide Village subdivision was subsequently abandoned.  Dewatering of coal lowers the water table, which in turn, may allow gas to seep.  However, gas collection may help prevent gas seepages.

Return to Casper

Two optional routes can be taken on the return to Casper.  One route (longer) is to return to Highway 59 and TURN LEFT (south) toward Wright/Reno Junction and turn west on Highway 387 toward Midwest/Edgerton.  The other route is to TURN RIGHT or north toward the City of Gillette and TURN left or west on Skyline Road through the southern city limits.  TURN LEFT or south on Highway 50, which intersects with Highway 387 at Pine Tree, about 19.5 miles west of Wright/Reno Junction.  The second route (shorter) may be delayed by construction along the highway.  Taking Highway 50 presents an opportunity to observe activities along the western limit of CBM development.  From Gillette to the Pine Tree intersection is about 50 miles.