Groundwater Contamination with Natural Gas

The Texas Railroad Commission recently issued a Water Well Complaint Investigation Report (Regulators Close Case on Flaming Texas Water, Researcher Says Not So Fast | StateImpact Texas) for a water well in the Silverado on the Brazos neighborhood in Parker County. The subject well of the report has been experiencing high (and increasing) levels of methane gas, originally noted in 2010. Since publication of the report, there has been considerable controversy (RR Commission credibility slips | Editorials | Fort Worth, Arlington, Northeast Tarrant edito…), including reports that some scientists doubt the validity of the Railroad Commission’s conclusions (Scientists: Tests prove fracking to blame for flaming Parker County wells | Dallas – Fort Worth).

What are Texas citizens (and voters) to believe? Those of us who are reasonable and open-minded (particularly when it comes to complex technical issues) are not well served by the he-said-she-said game that tends to driven by those with axes to grind. So let me try to shed a bit of light on this subject for your consideration, starting out with a brief discussion of the technical issues.

First, it is not uncommon for natural gas to exist either dissolved in or adjacent to groundwater zones. Two different processes are generally considered to produce hydrocarbon gases: biogenic and thermogenic. Biogenic processes occur at low temperatures largely through bacterial decomposition of organic material. Thermogenic gas is formed at deeper depths as a consequence of elevated pressure and temperature for long periods of time.

I’ll try to stay away from much geochemistry (since I’m certainly no expert in the area), but suffice it to say that  biogenic gas can be distinguished from thermogenic gas on the basis of composition (thermogenic natural gases typically contain large amounts of compounds in addition to methane) and isotopic analysis (more carbon atoms have an extra neutron in thermogenic gas). Different gas sources (e.g., geologic layers) will also have different compositions and isotopic ratios.

Another consideration with regard to methane existing in groundwater is the amount of methane that is dissolved in the water. At ambient surface conditions, the maximum amount of methane that can be dissolved in water is around 28 mg/L. But at elevated pressures in the subsurface (if deep enough) methane solubility can exceed 1000 mg/L. At a depth of 200 ft (from where the Lipsky well seems to be producing), maximum methane solubility could be as high as 200 mg/L.

Two factors make it difficult to know the true amount of methane that’s actually dissolved in groundwater. First, unless water sampling is done under pressure (downhole), excess dissolved methane will be released upon exposing the water sample to lower pressures than in the groundwater zone. Second, some of the gas in the groundwater zone may exist as a “free” gas phase, totally separate from the water itself. The methane gas produced from a water well’s wellhead will at least have been partially separated from the water downhole, making an analysis of the total amount of gas that has migrated to a particular well very difficult to discern.

And even when it has been determined that groundwater gas is of thermogenic origin (which it appears to be in this case) there’s the problem of attempting to determine the exact source of that gas … i.e., which well(s), which zone(s), and when in time.

Don’t be surprised if you’re confused by now. It’s a complicated problem. Add to this the difficulty in inferring the state of things deep within the earth when there is sparse and sometimes unreliable data. Much must be inferred and estimated to arrive at reasonable (often speculative) conclusions. Uncertainty about such matters is typically dealt with through multi-disciplinary data and analyses, in this case geochemistry to determine possible stratigraphic sources of the gas along with geology, petrophysical analysis, and fluid flow calculations to determine the location of potential migration paths.

I find the Railroad Commission report on this matter (Regulators Close Case on Flaming Texas Water, Researcher Says Not So Fast | StateImpact Texas) to be unconvincing. In particular, it fails to adequately convince the claimant (not to mention the Texas public) about the adequacy of its analysis. The real question (where’s the gas in the homeowner’s well coming from) remains unanswered. It’s time for both more transparency and more rigor at the Railroad Commission.

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