Tuesday, May 10, 2011

Methane in Well Water from Gas Fraccing

Many of you may have seen this kind of video, showing the effects of methane in drinking water near some shale gas extraction wells:

Before now, I've never known what to make of this kind of thing. Is this a very rare, if spectacular occurence, or is it common where shale gas drilling goes on?

Now, there is a paper in this week's PNAS, Methane contamination of drinking water
accompanying gas-well drilling and hydraulic fracturing
by Osborn et al, researchers at Duke University. It appears to answer the question, and the answer is not good.

Basically, they sampled well water from 68 private wells above the Marcellus and Utica shales in Pennsylvania and New York.  About a third were in an "active extraction area", defined as within 1km of a gas well, while the rest were further away.  They then measured the concentration of methane in the water.

The results are as follows:
You can see that there's an extremely strong effect, with water wells close to gas wells much more likely to show high levels of methane.  Nor are these levels trivial.  Note the scale from 0 to 70 mg/L of methane.  There are no regulations on methane in drinking water (which seems a remarkable fact in itself), but the paper refers to a publication of the Office of Surface Mining, Technical Measures for the Investigation and Mitigation of Fugitive Methane Hazards in Areas of Coal Mining. That report establishes the following guidelines for action:

You can see that a good number of the samples above fall into the above 28mg/L category that is potentially explosive and calls for immediate mitigation.  Meanwhile, a considerable majority are above at least the 10mg/L threshold for concern and warning.

There are a number of other interesting points in the paper that I'll briefly mention:
  • They do isotopic analysis to establish that the source of the excess methane near gas wells is thermogenic methane from sediments, not biological methane from near the surface.
  • They also tested the water for various possible toxic chemicals from the fracking fluid, but didn't find anything.
  • They also didn't find evidence of high levels of salt or radioactivity suggesting of deep saline aquifer water intruding into the shallow aquifers, at least not in the areas they sampled.
The sample area was as follows:

I have just one potential caveat with the paper.  They don't say anything about exactly how they selected private wells to sample.  They report probability numbers suggesting that they treated it as a random sample.  That could be reasonably implemented, for example, by selecting houses in the study area at random and approaching the homeowners to see if they'd agree to testing.  However, something like advertising in the local paper for people who'd like to have their water tested risks a self-selected population that already suspected problems with their water.  The results would still be interesting, but much less statistically meaningful.  In the absence of any description in the paper, I'm giving them the benefit of the doubt, but I have an email in to the authors querying this point.

At any rate, if this paper holds up, it appears that drilling within 1km of household wells presents an unacceptable risk to the residents.


Derwein said...

Stuart you write: ”You can see that there's an extremely strong effect, with water wells close to gas wells much more likely to show high levels of methane”. However, if you divide the data points according to active and inactive areas the correlation between methane concentration and distance to well seem to vanish. (At least for the eye, but one would need separate plots for the two situations to see that more clearly.) As far as I can (?) see the plotted data only show an association between active contra passive extraction area and methane concentrations, which of course is highly interesting by itself.

Of course questions regarding sampling methodology are relevant. However, it is not totally obvious that self-selection can explain the data. Obviously self-selection would tend to result in higher methane concentration than some form of random sampling. But I wonder if it necessarily would result in an association with active contra passive areas!

From the physical side of it one wonders how the drilling activity would affect methane transport to water wells. Are there any theories for that? If this data shows some form of transport associated with drilling it would not seem to be just in very special occasions, but rather according to the rule.

Jan W

bordoe said...

Interesting read.

Any good books to recommend on this topic?

I've got zero background in oil geology, much less in 'fracking' but I'm hearing so much about it I think I should give it a go.

Know of good resources on the subject?

rjs said...

"There are no regulations on methane in drinking water"

as far as i know, there are no regulations on water quality for private wells...most around here use bottled water for drinking...

"At any rate, if this paper holds up, it appears that drilling within 1km of household wells presents an unacceptable risk to the residents."

that doesnt leave much area in PA to drill in, does it?

brett said...

I'm glad I do not live in an area with shale gas potential.

James said...


The intense focus on "fracking" may be somewhat misplaced. What we have seen in western Colorado is that poor cementing is often the culprit
in situations like these.

Remember the Deepwater Horizon--the annulus of the wellbore, if not properly cemented, provides a direct link between methane producing zones miles below the surface and surface aquifers. In effect, you are trying to perfectly grout a mile or two of cement pipe, not always successfully.

buck smith said...

James has it correct, cement jops are key as well as having a more than one casing run with seals. This problem is easy to mitigate. The risk of methane in drink water in a small zone around a well is small price to pay to for low cost energy. There are many risk posed to society and the economy by energy becoming too expensive.

Stuart Staniford said...

buck - easy to say when it's not your water supply...

Mike said...

One thing to notice is how rapidly the effect dies out as you move more than about 800 meters from an active well (or if the well is inactive). Most likely it will be the property owner who is most affected and possibly immediate neighbors. To the extent owners are affected, the contract between the developer and the property owner is probably the most efficient remedy (and if property owners can effectively insist on mitigation, then the potential harms to neighbors likely also reduced).

Also interesting is that a number of water wells very near active gas development show only background levels of methane. It would be interesting to know what is the difference between these locations and the others (maybe just a good cementing job!).

rjs said...

mike's comment just brought some of my old memories back...i was involved in an investigation of landfill pollutants leaching into groundwater in my county in the 80s'; one thing the hydrogeologist stressed was that the pollution plume moved underground at a glacial pace, and that if one well a few thousand feet from the source was contaminated, it was almost certain that those farther away would become contaminated in a similar time equal to the distance from the source, and at a magnitude equal to the inverse of the square of the distance...

what i mean is that if a well 800 meters away is contaminated in one year, a well 1600 meters away will be contaminated in two years, at one fourth the degree of pollutant of the first well...