What Are the ‘Geological Challenges’ of WV Coal?

The State Journal
24 September 2012
By Taylor Kuykendall, Reporter

It seems just about every coal company operating in Appalachia has been talking about "geologic challenges" in their financial reports. What does that mean?

The State Journal asked experts at Marshall University and West Virginia University what exactly are some of these challenges to mining coal in the region. Christopher J. Bise, professor in the Department of Mining Engineering at West Virginia University, said some mine roofs are more difficult to stabilize and varying conditions affect the thickness of a coal seam.

He added that while the coal is found in thinner beds than coal in some Western basins, it has a higher BTU count, which makes the coal more valuable.

"As a mining engineer, we use the terms 'minability' of coal seams: coals seams that can be mined safely and economically," said Anthony B. Szwilski, the director of the Center for Environmental, Geotechnical and Applied Sciences at Marshall University. "There are many factors that govern the minability of a coal seam … "

Szwilski said the "easy coal" in West Virginia — coal seams with thick deposits near the surface —were mined out years ago.

"The minability of coal seams in West Virginia, in general, are better than any of the coal mining countries I have worked in or visited: coal seams generally of good thickness, continuous, flat, of high quality coal, competent coal seam rock strata," he said. "The coal outcrops (exposed coal seams) at the sides of the mountains have provided easy access to the coal reserves."

Now, Szwilski said, coal seams mined today and in the future are getting deeper and getting thinner, increasing the cost per ton to mine. Techniques such as longwall mining have enabled more efficient mining of thinner seams, but safety issues at increasing depths are inherent because of "increasing pressure in the rock strata around the coal seams," he said.

The increasing pressure can result in methane outbursts and roof falls into work places.

Ronald Martino, a professor of geology at Marshall University, said many seams over 1,000 feet deep are considered "too deep to mine," but some mining difficulties can and have been addressed.

"Underground mining can be impacted by poor roof conditions, coal seam irregularities and discontinuities like channel washouts, splits, rapid changes in quality," Martino said. " Engineering innovation in mining techniques often overcome some of these challenges."

Now, there is easier coal to be mined in Wyoming's Powder River Basin, but its lower BTU rank and higher moisture content makes it less attractive on a pound-for-pound basis.

"Mined by underground and surface mining methods, Wyoming coals are geologically younger and softer, and of less quality sub-bituminous coal of lesser heating value," he said.

Therefore, Szwilski said, the seams are generally very thick and near the surface. The surface is typically flat, and it is surface mined.

So why is the coal in West Virginia so different than in the Powder River Basin, aside from the fact it has been mined over a longer period of time?

"Seams are thickest where there was a balance between the rate of subsidence of the earth's crust and the rate of peat accumulation," Martino explained. "The longer these were in balance, the thicker the seam that will form.

"Seam thickness can be influenced by the ancient landscape: low-lying areas may have thicker coals whereas hills or uplands have thin or no coal. Seams also tend to thin toward the edge of the swamp as it changed to a lake or coastal tidal flats."

Seam thickness and accessibility isn't the only challenge to mining in the region.  

"An interesting  feature of mining coal seams in the Appalachian mountains is mining the coal above or below the water table, or termed mining above or below drainage," Szwilski said. "Generally, coal methane gas content increases with depth below drainage. The water in the coal pores and fractures (cleat) traps the coal methane, thus the methane gas in the coal seams above the water table (drainage) has had a greater opportunity to escape into the surrounding rocks over geological time, resulting (in) the underground mine (above drainage) being much less gassy."

Those gases can have potential value, but the economics of increased natural gas supplies has reduced interest in coal bed methane supplies.

"Many West Virginia coal beds have considerable potential for natural gas production," Martino said. "Prior to the development of the Marcellus Shale, CBM was a fast-growing industry. This same potential makes them hazardous to underground mining if not degassed by drilling ahead of mining or if the mine is not properly ventilated (as was apparently the case in the Upper Big Branch mine disaster)."