Coal Seam Gas—Dirtier than Coal,
Worse than Shale
In the land of desperate excuses, coal seam gas is king. The new boom industry of the Queensland and New South Wales hinterlands contaminates ground and surface waters, while taking rich farmland out of food production.
But at least, its promoters argue, coal seam gas (CSG) is a weak hitter among sources of greenhouse pollution. When burnt in modern power plants, the story goes, CSG can be as much as 70 percent “cleaner” than coal.
But that’s just an excuse. New evidence strongly indicates that when the whole greenhouse “footprint” of various fuels is taken into account, CSG is considerably more polluting than coal.
A peer-reviewed study of a related technology, shale gas production, has provided important insights. Work by engineers in the U.S. state of Wyoming has revealed huge emissions that current CSG practice fails to prevent.
The new study, published in April by the U.S. journal, Climatic Change, was conducted by a team under Cornell University environmental biologist Robert Howarth. It concludes: “Compared to coal, the footprint of shale gas is at least 20 percent greater and perhaps more than twice as great on the 20-year horizon.”
Firms developing CSG stress differences between their industry and shale gas extraction.
But the technology that accounts for most of the greenhouse footprint of shale gas—hydraulic fracturing, or “fracking”—is routinely used for CSG as well. And the end product is identical—the powerful greenhouse gas, methane, (the main component of natural gas).
Shale gas is found trapped in the pores of shale, a relatively tight rock that underlies much of the eastern U.S.
To free the gas, the shale must be fractured by pumping in a high-pressure mix of water, sand and various (often toxic) chemicals.
This process opens fissures in the shale and allows the gas to flow to the surface—hopefully through the borehole, but at times by way of geological faults that allow it to vent to the atmosphere or end up in water supplies.
But recent work that explores the interaction between methane and atmospheric aerosols concludes that during those 20 years, methane has a “global warming potential” a staggering 105 times that of an equivalent amount of carbon dioxide.
CSG, of which Australia has vast resources, is initially bonded within the matrix of coal in underground seams, where it is held by the pressure of groundwater. To extract CSG, wells are sunk into the seams and the water is pumped out. With the pressure reduced, gas then begins flowing to the surface.
Coal seams are fairly porous, and in the early days of CSG development fracking was used only occasionally. But expanding fissures in the seams can allow gas to flow much faster and from a wider area, meaning that fewer wells need be sunk.
A February 2011 National Toxics Network briefing paper said fracking will be used in up to 80 percent of Australian gas wells in the next ten years.
Once fracking has taken place, Howarth and his co-authors explain, a significant amount of the mix of water and chemicals “returns to the surface as flow-back within the first few days to weeks after injection and is accompanied by large quantities of methane … The amount of methane is far more than could be dissolved in the flow-back fluids.”
Additional methane is then emitted as plugs inserted in the well to allow fracking are drilled out. Once the well is in production, methane is routinely vented from pressure-relief valves. Further losses occur from leaks during transport, storage and distribution.
In all, Howarth and his collaborators calculate, methane losses during the several decades that a shale gas well operates are 3.6 percent to 7.9 percent of production.
Unlike shale gas, CSG extraction requires water to be pumped from the well throughout its operating life. This “produced water”—generally saline and laced with contaminants—also contains methane, mostly “entrained” as gas bubbles. In Australia, the usual practice is to pipe this water to evaporation ponds.
How much methane reaches the atmosphere this way? Engineers working on CSG technologies in Wyoming have found that the amount lost as entrained gas varies from two percent of total well yield to a mind-blowing 30 percent.
An improved gas separator, now awaiting patent, is claimed to remove all but 2-3 percent of the entrained methane from the water. But with a typical well, at present losing 15 percent of its output as entrained gas, the new equipment would still fail to catch emissions representing about 0.4 percent of total well yield.
Moreover, the new separator does not remove dissolved methane.
The produced water can be pumped back underground, but this is expensive and is not always convenient.
Otherwise a significant figure, probably about 0.5 percent, must be added for CSG emissions on top of the figure for shale gas methane emissions of 3.6 percent-7.9 percent.
That is supposing the new separator equipment reaches the market, and that energy companies are moved to install it. If not, the evidence from Wyoming suggests, typical losses of CSG methane from borehole to power plant would be at least 18 percent.
The implications of all this are ominous. Methane is relatively short-lived in the atmosphere. After 20 years it is virtually all gone, oxidized to water and carbon dioxide.
But recent work that explores the interaction between methane and atmospheric aerosols concludes that during those 20 years, methane has a “global warming potential” a staggering 105 times that of an equivalent amount of carbon dioxide.
If methane is burnt to produce a megawatt-hour of electricity, the amount of carbon dioxide that goes up the exhaust flue is indeed less than if the electricity were produced from coal.
But to the combustion emissions, we have to add the warming impact of the methane that escapes from the wells, produced water, fittings and pipelines. Over a 20-year period, a global warming potential of 105 means that leakage of even one percent more than doubles the cost in warming of gas-fired power.
The credible leakage figures for CSG start at about four percent.
And it gets worse. If the CSG is liquefied for export, as a great deal of Australia’s output will be, we need to add on carbon dioxide emissions corresponding to about 20 percent of the energy value of the methane, to power the liquefaction process.
Account should also be taken of emissions released by other factors listed in a fact sheet on Lockthegate.org.au: “Purging, boil-back from cryogenic transfers, leakage during LNG transfers, boil-back in transit, powering of LNG ships; and finally, re-gasification before use.”
We have to conclude that CSG extraction and use, as practiced in Australia, is much filthier—probably by several times—than either shale gas or coal.
That is not an argument for burning coal, or even for spending the money that could sharply cut CSG’s greenhouse footprint.
Even with best industry practice, CSG is still a fossil fuel. If humanity’s greenhouse dilemma is to be solved, all net carbon emissions must end around mid-century.
That implies a huge expansion of renewable energy, and it is on renewables that the scores of billions of dollars slated for CSG development in Australia should instead be spent.
—GreenLeft (Australia), June 4, 2011