South Piney coalbed methane: a primer

by Cat Urbigkit

The Bureau of Land Management has begun the public participation process for the South Piney natural gas development project, involving the drilling of 100 to 210 coalbed methane wells along the east flank of the Wyoming Range.

The gas development proposal, which will be subject to an environmental impact statement, was brought forth by Infinity Oil and Gas of Wyoming, Inc. and Williams Production RMT Company. An initial public scoping meeting on the proposal will be held Monday, Feb. 24, at 6:30 p.m. in the Marbleton fire hall.

Infinity Oil and Gas of Wyoming (Infinity-Wyoming) is a subsidiary of Infinity, Inc. Infinity-Wyoming controls leases on 28,000 acres in the Wyoming Range, of which it has drilled five exploratory wells. The company controls an equal acreage in the LaBarge area and has drilled one exploratory well there. According to the company's website, Infinity, Inc. is an independent energy exploration company focused on coalbed methane. The Kansas-based company is said to have "evolved from a small oilfield services company into a natural resources exploration and development company," and operates in Kansas, Oklahoma and Wyoming. According to a PR Newswire report last September, Infinity engaged First Albany Corporation as a strategic advisor for possible sale or merger of the energy company.

The Infinity-Wyoming and Williams partnership on the 31,230-acre leasehold in the South Piney area provides for an interesting development plan. Infinity-Wyoming will drill wells to a maximum depth of 5,000-acre feet to test the Mesaverde Formation for methane production, while Williams will be drilling wells to a maximum depth of 10,000 feet to test the Frontier Formation for natural gas production. Proposed well spacing ranges from four to eight wells per section. The companies propose to drill an average of 30 wells per year over a seven-year period.

While much what's in the news about coalbed methane production comes from development in the Powder River Basin, the situation in the Wyoming Range appears to be much different. Here's a primer on what exactly coalbed methane is, taken from the pages of the Mineral Occurrence and Development Potential Report prepared for the BLM's use in revising the Pinedale Resource Management Plan.

According to the report, the presence of methane in coal seams has long been recognized as a potential hazard in the mining of coal, so extraction of the methane was conducted as a safety measure. It was eventually recognized that there was a potential significant gas resource in coals and a federal tax incentive, now expired, successfully encouraged the development of technologies to produce coalbed methane.

CBM occurs as a result of coalification - the process that turns plant material into coal, according to the report. As the plant material is buried and subjected to increased temperatures and pressures, it is transformed into varying ranks of coal. This process generates gases, including methane, nitrogen and carbon dioxide.

According to the report, the methane generated in the coalification process can be stored in several ways: as free gas in pores and fractures of the coal; as a dissolved phase in interstitial water in the coal; or is absorbed onto the surface of the coal.

"Because most coals have abundant microfractures, or cleat, there is a large amount of surface area on which gas can be absorbed," the report stated. "This feature of gas storage allows coals to store a much higher volume of gas than conventional gas reservoirs.

"In order to extract the gas from the coal, it is necessary to lower the hydrostatic pressure in the coal," the report stated. "Lowering the pressure is accomplished by producing the water that is in the coal." This means pumping large amounts of water in the initial stages of development.

As much as 6,000 barrels of water per day have initially been produced from a single well, but once wells reach economic production, water production rates can be substantially lower, according to the report. Water quality varies greatly, with water quality better if the coal seam is closer to the surface.

Water disposal options, which are dependent on water quality and economics, can include discharging at the surface or re-injection into disposal wells or aquifer recharge wells.

The Management Situation Analysis for the Pinedale RMP revision notes that the disposal method currently used in the Pinedale RMP area is to re-inject produced water, into deeper formations with poorer water quality. Discharge into surface water features, including ephemeral channels, would not be allowed, according to the BLM document.

The mineral potential report noted that while no commercial quantities of CBM have been produced in the Pinedale RMP area, "there are indications that CBM may be an important resource." In 1992, experts with the Wyoming Geological Survey indicated that coal from a drill hole in the Mesaverde Formation in the Riley Ridge area just south of the South Piney project had methane values range from 434 to 539 cubic feet per ton, compared to the Powder River Basin coal gas content of 65 CFPT.

Infinity-Wyoming anticipates the need to install up to 20 central production facilities within the South Piney project area for the collection and compression of methane produced from the wells, as well as water collection and disposal. Each well location would have an access road and buried gas line as well as a buried line for transporting produced water to a central disposal facility. Each central production facility site would include a water disposal/injection well for the subsurface disposal of water produced from the Mesaverde Formation.

For more information on the South Piney gas development project, contact the Pinedale BLM office or attend the Feb. 24 public scoping meeting in Marbleton. Public comments during this initial scoping phase will be accepted until April 1 and should be sent to South Piney EIS, BLM, Pinedale Field Office, P.O. Box 768, Pinedale, Wyo., 82941.