By Bill Chameides
New study finds lots of methane coming from oil and gas operations.
Talk about the future of energy or climate these days, and the subject of natural gas is sure to surface. Thanks to advances in technologies such as horizontal drilling/hydraulic fracturing (often referred to as simply fracking), natural gas (and oil) resources previously thought to be unrecoverable have been moved to the recoverable column, catapulting the potential supply of natural gas and, in the process, radically changing America's and the world's energy future. Suddenly tomorrow seems to be replete with an abundant supply of relatively cheap natural gas.
Natural Gas's Green Side
Accepted wisdom has been that this would be good from an environmental point of view:
- When it comes to air pollution, natural gas is the cleanest of the fossil fuels;
- When it comes to preserving habitat, it's hard to imagine anything worse than miles of landscapes scarred and denuded from extracting coal via mountaintop removal; and
- When it comes to the climate, burning natural gas produces less carbon dioxide emissions than the burning of oil or coal.
Natural Gas's Not-So-Green Side
But the accepted wisdom of natural gas's environmental bona fides has taken a significant hit of late. For example, serious concerns have arisen over the environmental impacts of fracking.
Perhaps even more damaging has been recent work arguing that expanding the production and use of natural gas will actually exacerbate rather than help mitigate global warming. The reason: the main ingredient in natural gas is methane, a greenhouse gas some 20 times more potent than carbon dioxide. If significant amounts of methane leak during the extraction and transport of natural gas, the warming from that methane added to the atmosphere could cancel out or even outweigh any benefit gained from burning natural gas instead of oil or coal.
The Unknown Quantity: Leakage
But how large could natural gas leakage be? The truth is we're not sure. The Environmental Protection Agency's recently updated estimates [pdf] suggest that wellhead leakage from unconventional resources is significant. It's not clear whether these revisions [pdf] will be enough to negate the apparent advantage natural gas has over coal when it comes to climate change. But some, most significantly Bob Howarth of Cornell University and colleagues, have argued just that: They maintain that emissions from natural gas leakage across the whole system (including storage and distribution) are likely to be in the range of 3.6 to 7.9 percent over the entire natural gas life cycle (which includes emissions at the well as well as losses during distribution and storage).
If Howarth et al are correct, then a full-bore leap to natural gas is a climate-change non-starter. We would be far better served to slow down our rush to natural gas until we've figured out a way to stop up the leaks in the whole natural-gas extraction-delivery system. However, lots of folks out there remain unconvinced by the Howarth et al analysis, and question their underlying assumptions, and/or out-and-out reject their conclusions.
New Study Examines Methane Leakage in Colorado
Now along comes a new study, in press at the Journal of Geophysical Research, that adds fuel, if you'll pardon the pun, to the controversy. Gabrielle Petron of the University of Colorado, Boulder, and colleagues used an extensive data set of ambient concentrations of methane and related hydrocarbons from 2008 in the vicinity of oil and gas operations north of Denver, Colorado, along with the known emissions profiles for these gases from oil and gas operations to infer the emissions from the these operations.
The method Petron et al adopted may seem complex, but it is actually quite straightforward and even elegant in its conception. Imagine for a moment you were concerned about the emissions of two gases, X and Y, from a given operation O1. Also suppose that X and Y have other sources, say O2 and O3. But O1 is unique in one important aspect -- the ratio of the emissions of X and Y from O1 is 2 to 1. All the other sources have different ratios. If all your measurements of X and Y in the atmosphere have a ratio of 2 to 1, you would have a pretty strong case for concluding that O1 is the principal source of X and Y in the atmosphere.
Now Petron et al's actual application of this method to the problem of methane and related hydrocarbons in Colorado is a whole lot more complicated than this simple example, but that's the general idea. The beauty of this approach is that while most emission inventories are largely accounting exercises summing up estimates of emissions from bits and pieces of the overall process, this method is fundamentally based on actual atmospheric data -- in this case, concentration measurements.
Lots of Leakage Found in Colorado Study
So what did they find?
They found evidence of large sources of methane from the oil and gas operations in the Denver Julesburg Basin. How much larger? They estimate that the amount of gas leaked from the field during production is between 2.3 and 7.7 percent -- with a best guess of about 4 percent. This is about a factor of two larger than the official inventory for leakage rates in the area. And puts Petron et al's estimate slightly higher than Howarth's estimate of losing 2.2 to 3.8 percent at the wellhead during both well completion and production. (The Petron et al study does not really include emissions from other parts of the natural gas lifecycle such as distribution and storage.)
Now, this is one study looking at a single oil and gas field during a single year, but it should raise a few red flags somewhere. I'm sure there will be those in the industry who will want to batten down the PR hatches by criticizing and questioning the Petron et al study. That's a fair game, and some of those criticisms and questions may be cogent and valid. But perhaps there might be a more constructive approach: battening down the operational hatches. Leaking natural gas can't be good for the PR line or the bottom line -- why not develop an aggressive and transparent program to search out leaks and batten down those?