Montana Earth Science Picture of the Week

An issue that has created a lot of controversy in Montana recently is the possible removal of coalbed methane gas from layers of coal beneath the eastern part of the state . On the one hand, the methane could provide a substantial amount of energy for heating homes and water. On the other hand, the removal of the methane requires that significant quantities of groundwater be pumped to the surface.

Understanding coalbed methane . . .
As plant material is changed into coal large amounts of methane gas are produced. The presence of this gas in coalbeds is what can cause explosions in underground coal mines. With coalbeds found beneath eastern Montana, large amounts of methane are contained in the groundwater that fills the cracks and spaces within the coal. Pressure caused by the weight of rock layers above keeps this "coalbed methane" dissolved in the same way that pressure keeps carbon dioxide gas dissolved in an unopened cola. With a bottle of cola, the pressure is decreased as it is opened, causing bubbles of carbon dioxide to form. With coalbed methane, wells are drilled and the water is pumped to the surface. As the water is approaches the surface, the pressure decrease allows the methane to form bubbles that can be collected.

So what's all the fuss about? . . .
While economic quantities of methane can be produced, what to do with the water is a major source of debate. Since water from the coal seams often contains dissolved salts and sodium, it may not be feasible to use the water for irrigation. If it were used to water crops, salts from the product water could accumulate in the root zone, adversely affecting plant growth. Saline conditions stunt plant growth because plants must work harder to extract water from the soil.

Another possibility, direct stream discharge won't work either because of the adverse affect that the salts would have on the quality of water in the streams. In fact, earlier this month (October 2003), the U.S. Supreme Court declined to review an appeals court ruling that determined "water released from coalbed methane wells is a pollutant under the federal Clean Water Act". The decision is significant because it establishes that coalbed methane water is a pollutant and subject to regulation.

A third option is to construct ponds in which the water would be stored. There are several terms for these impoundments: "holding ponds" "zero discharge ponds" or "infiltration ponds." Although they do not directly discharge water on the land surface, most impoundments are not lined and discharge to the subsurface. In addition, seepage flow from impoundments is likely to reach some stream channels via subsurface flow.

More about coalbed methane . . .
Methane (CH4) is the major component of natural gas. Coalbed methane is the same compound as the methane in natural gas. Currently, natural gas from coalbeds is approximately 7% of the total natural gas production in the United States, nearly one-third of the estimated 184 trillion cubic feet (tcf) of gas in the Rocky Mountain Region is in coal seams. An estimated 24 tcf of recoverable coalbed methane resources may lie below the Powder River basin of Montana and Wyoming.

Right: This map shows the Powder River Basin of Montana and Wyoming where coalbed methane gas is most likely to be taken from the ground. The map was designed by John Potter of the Billings Gazette. His source was the Montana Bureau of Mines & Geology and CMS Energy Oil and Gas.

Below: This arial photo taken near Sheridan, Wyoming, illustrates another concern related to drilling coalbed methane wells. As roads and evaporation ponds are built, the appearance of the landscape will be changed.

Photo courtesy of
Extension Water Quality Program
Montana State University

Terms: discharge, infiltration