Follow Highway 387 from Midwest through Edgerton, which is on the Cody Shale (mile marker and associated Shannon Sandstone (mile marker 100.5; see Fig. 3).  The origin of the sandstone is controversial and has been interpreted to be shelf ridge, lowstand facies tract (erosional-based shoreface), and paleovalley (tidal bars, estuarine) sand bodies (Bergman and Snedden, 1999). 

The Shannon Sandstone is an important oil and gas reservoirs in the Heldt Draw Field in the west-central part of the Powder River Basin (Todd Davis, 1976; Spearing, 1976).  As many as three sandstones (silty and fine-grained) serve as stratigraphic traps for hydrocarbons. 

The coal-bearing Parkman Sandstone of the Mesaverde Formation (see Fig. 3) is exposed immediately north of Edgerton (mile marker 103).  In the next 12 miles, we begin a gradual ascent from the Upper Cretaceous section (see Fig. 3) of the Cody Shale through the Mesaverde Formation (mile marker 102.5-103.8), Lewis Shale (mile marker 105-107), Fox Hills Sandstone (mile marker 109), and Lance Formation (mile marker 110-112).  The Lance Formation is coal bearing and is conformably overlain by the Paleocene Fort Union and overlying Eocene Wasatch Formations.  Coals of the Fort Union Formation are the principal coalbed methane producing beds in the Powder River Basin. A few coal beds in the Wasatch Formation also produce coalbed methane.

After leaving the Lance Formation, we cross the Pine Ridge (mile marker 113.2), which marks sandstone outcrops of the Fort Union Formation.  Pine trees commonly grow on these sandstones, which serve as aquifers.  Descend into the drainage basin of the Powder River that drains the south-central part of the basin and flows to the northeast joining the Yellowstone River in southeast Montana, which in turn, drains into the Missouri River.

In the next 36 miles to Wright-Reno Junction, the basin is covered by the Wasatch Formation, which is overlain by the Oligocene White River Formation (see Fig. 3), exposed in the Pumpkin Buttes to the north.  The White River Formation consists of volcaniclastic sandstones, siltstones, conglomerates, and tuffaceous rocks.  Uranium occurrences in the Pumpkin Buttes were first reported by Love (1952).  In 1954 two major areas in the southern part of the Powder River Basin were identified to contain potential uranium resources: 1) Pumpkin Buttes-Turnercrest area in parts of Johnson, Campbell, and Converse Counties, and 2) Monument Hill-Box Creek area in Converse County (Curry and Crews 1976).  Uranium ores in the form of uraninite occur in permeable arkosic fluvial channel sandstones in the uppermost part of the Fort Union and Wasatch Formations (see Fig. 3).  The ores were formed as roll front deposits resulting from a geochemical front that precipitated the minerals along a facies change of coarse to fine clastic sediments (Buturla and Schwenk (1976). 

Grasslands that mainly support cattle ranching cover the Powder River Basin.  The creeks that run through these grasslands are intermittently dry.  In this part of the basin land use is mainly agricultural and range land.  The majority of the surface here is privately owned (e.g., Iberlin, Moore, and Taylor Ranches).  About 55 percent of the subsurface minerals, such as coal, in the Powder River Basin are Federally owned and managed by the U.S. Bureau of Land Management (Fig. 4).  The rest of the subsurface mineral ownership is State or private. 

The southernmost extent of Powder River Basin CBM development in Campbell County occurs immediately south and north of Highway 387 and east of Highway 50 (mile marker 123-147; Fig. 5).  The Fort Union coal beds (Fig. 6) that are producing coalbed methane in this part of the Powder River Basin are shown in a composite stratigraphic column and a series of north-south and east-west cross sections (Figs. 7-11).  Figures 8, 9, 10 and 11 show the thick coal beds of the Wyodak-Anderson coal zone (sometimes informally named as Big George and Sussex coal zones), which produce coalbed methane.  These coal beds mainly occur from 1,000 to 2,000 ft below the surface (Fig. 12).  The CBM well spacing in the Powder River Basin varies from 40 (16 wells per section) to 80 (8 wells per section) acres.  The Wyoming Oil and Gas Conservation Commission recently issued an order of 80-acre spacing basinwide unless a gas operator requests and justifies an exception of this well spacing.

Five CBM fields are being developed along Highway 387 (see Fig. 5).  These fields include from southwest to northeast (towards Wright), the Pine Tree (mile marker 123-129; Devon Energy Corporation), Allnight Creek (mile marker 137.6-143.4; Barrett Resources Corporation), K Bar (Yates Petroleum Company), House Creek (mile marker 146-146.7; Devon Energy Corporation), and North Wright (Barrett Resources Corporation).  The Pine Tree and House Creek fields are both conventional oil and gas, and CBM fields.  These CBM fields were discovered in 1997 and are the youngest to be developed in the Powder River Basin.  The oldest CBM fields (e.g., Marquiss) occur between Wright and Gillette and Highways 59 and 50 (Fig. 13).  In that area, development began in the early 1990’s in the old Lighthouse and Marquiss coalbed methane project areas.  Since then development rapidly expanded from that project area in all directions, but  especially toward the north, west, and south.  These areas of early development by Barrett Resources Corporation and Lance Oil and Gas Company (Western Gas) were identified by the U.S. Bureau of Land Management (BLM) as the Gillette South Assessment Area (Bureau of Land Management, 1999).  That area and an area of additional development in the Gillette North Assessment Area located in central Campbell and northern Converse Counties, within the eastern Powder River Basin were named by BLM as the Wyodak CBM project Environmental Impact Statement (EIS) area (see Figs. 1 and 2).  During the last several years, development has extended westward outside the Wyodak CBM (EIS) project area.

The amount of methane produced from all wells and from wells on federal leases in billions of cubic feet of gas (BCFG)/month as well as the average amount of gas per well per day in thousand cubic feet of gas (MCFG) from January, 1990 to October, 2000 is shown in Figure 14.  The number of wells in production over the same time period is shown in Figure 15.  As of October 30, 2000, the total CBM production was about 15 billion cubic feet of gas or bcf/month and the rate was about 120 MCF/day/well.  CBM production from Federal leases was about 2.5 bcfg/month at a rate of 25 MCF/day/well (see Fig. 14).  A rapid increase of CBM production occurred last year (2000).  This increase may be explained by the astronomical rise of producing wells of about 3,000 wells, in one year (see Fig. 15).  The range in depth of producing CBM wells is from less than 200 to greater than 2,200 ft (see Fig. 16).  Fifty percent of the CBM producing wells have depths ranging from 400 to 800 ft.  Water co-produced with coalbed methane in the Powder River Basin, Wyoming is shown in Figure 17.  As of October 30, 2000, the total co-produced water was about 37 million barrels/month at a rate of about 370 barrels per day per well.  Co-produced water from Federal leases is about 4 million barrels/month at a rate of about 400 barrels per day per well.  During the ten-year period from January, 1990 to January, 2000) the rate of production, water ranged from 30 to 480 barrels per day per well.  However, one well in the west-central part of the basin produced as much as 4,800 barrels of water per day.