A pumpjack is not a coal mine

Eight things you need to know about coalbed methane mining.

 

A pumpjack is not a coal mine.

No, that’s not the opening line to an avant garde poem. It’s another way of saying: Coalbed methane mining is not mining for coal.

Jonathan Thompson
In fact, it’s quite different. Coalbed methane is natural gas found in coal seams, and to “mine” it is to drill into the coal seam and extract it, much as one does with conventional natural gas. To many this may seem a rather simple concept, but since the coalbed methane industry’s emergence in the 1980s, there has been ample confusion surrounding the term. In the last couple of years, coalbed methane has hit the headlines again, this time for its contribution to the Four Corners Methane Hot Spot, as well as for the thousands of abandoned wells the industry left behind after the 2008 bust.


The misunderstanding is back, too, as was evident in national media stories about the Four Corners Hot Spot, many of which conflated coalbed methane mining with coal mining. That the befuddlement spread to the larger public was evidenced by a tweet sent to HCN in response to a story that mentioned the oil and gas industry’s contribution to the hot spot: “Early findings suggest coalbed methane may contribute more to the Four Corners Hot Spot than O&G (oil and gas).”

And on that note, the first of the seven things you need to know about coalbed methane, natural gas and methane emissions:

Coalbed methane is oil and gas, or at least a subset of the industry.

Methane is a combustible hydrocarbon and a potent greenhouse gas, though a relatively short-lived one: When in the atmosphere, methane breaks down after about 12 years. As a result, its global warming potential is 87 times that of carbon dioxide over a 20 year span, but about 31 times carbon dioxide’s over 100 years. That’s according to the Intergovernmental Panel on Climate Change; the Environmental Protection Agency adheres to an earlier figure of 21 to 25 times the potential over 100 years.

Natural gas is methane, accompanied by relatively small amounts of other hydrocarbons. “Conventional” natural gas occurs in reservoirs, usually in sandstone, thousands of feet under the surface, and is typically drilled with vertical drilling technique, and the well is “stimulated” with single-stage hydraulic fracturing. The pressure of the gas then forces it to the surface. Oil and natural gas, along with briny water, often occur together, so a typical well produces oil, natural gas and water. The water, usually contaminated, must be disposed of. In oil fields, the natural gas is vented or “flared” when there is no infrastructure to capture it.

Methane is in coal seams. And that can be hazardous for underground coal miners. If the methane concentration exceeds five percent, then it can explode. Higher than that and it starts to displace oxygen, so miners can asphyxiate. So underground coal mines typically drill wells into the coal seam from the surface to vent the methane. That’s why coal mines are some of the nation’s largest single sources of methane emissions. When those coal seams breach the surface, at “outcrops,” they can spontaneously leak the methane into the air or water (ditto if you drill a water well through a coal seam). Sometimes the methane concentration from these geologic seeps is high enough to ignite water or air. The methane can also displace soil oxygen, killing vegetation around the seep.

Coalbed methane is natural gas, though typically more pure — i.e. it has a higher concentration of methane. And so, it’s only natural that drillers have tried to go after it. Since coal formations are typically shallower than conventional oil and gas reservoirs, drilling for coalbed methane (CBM) should be easy. It’s not. That’s because…

A coalbed methane well is a water well. Methane is adsorbed, or bonded, to the coal by water pressure. In order to “liberate” the methane, the water first must be removed. The pumpjacks you see at coalbed methane wells are actually pumping up water — anywhere from 1,000 to 17,000 gallons per day. The gas then follows, and is gathered up and piped off to be processed. Dealing with that water in a responsible manner can be expensive. It’s trucked from the wells to disposal sites. In some places it’s injected deep underground, in others it’s put in evaporating ponds or run through treatment facilities.

Sucking the water out of the ground and then sticking it back in can cause the earth to do strange things. Commercial production of coalbed methane got its start in the San Juan Basin in southern Colorado and northern New Mexico in the late 1980s, as producers rushed to meet a 1992 deadline for tax credits for “unconventional” oil and gas drilling. By the early 1990s, the weirdness had begun.

Methane started showing up in domestic wells and the crawlspaces of homes; huge swaths of trees and shrubs and grass died off along parts of the coal outcrop; in one area, methane emanated from the earth with such force that it blew particles of sand into the air; and a freshwater spring, miles from the nearest coalbed methane well, became so hot that its waters could no longer be used for domestic purposes or for irrigation.

It’s generally accepted that the increase in methane oozing from the earth and into wells and homes was the result of the vast dewatering of the coal formation from all those wells. In just those first years, billions of gallons of water were pulled out of the coal seam aquifer, thus liberating huge quantities of methane. What wasn’t captured by the wells sought the path of least resistance, toward the outcrop. Besides killing vegetation and posing explosion dangers for those affected, the geologic seeps have collectively become one of the biggest sources of methane emissions, and thus contributors to the Four Corners Hot Spot, in the region.

As for the new hot spring? It was most likely caused by the injection of water into a deep disposal well some nine miles from the spring. These sorts of injection wells have also caused earthquakes in Oklahoma, the Raton Basin in Colorado and New Mexico and elsewhere.

The takeaway? Coalbed methane mining is just another form of natural gas drilling, albeit with its own set of ups and downs. Along with the rest of the natural gas industry, coalbed methane has had it rough since natural gas prices crashed in 2007, and that has brought along its own set of problems: Abandoned wells, thousands of them.

Jonathan Thompson is a senior editor of High Country News. 

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