Methane Migration, also known as a gas leak, methane leak, or collectively as fugitive emissions, is a highly-contentious concern related to all oil and gas extraction. Methane migration is a result of methane finding its way up out of the bedrock and to the surface, often through water wells or pipelines dug into the ground.

While methane migration happens naturally, natural gas activities—and especially, fracking, which releases gas when it breaks up the shale below—can greatly increase the possibility of migrations happening. Wells which utilize horizontal drilling, as hydraulic fracturing does, tend to be at a higher risk for this type of danger. A recent study has estimated that a minimum of 7% of all hydraulic fracturing wells are currently leaking.

For a list of all known leaking wells in WellWiki's database, see Impaired Wells.

How It Happens

Source: Alberta Energy Utilities Board

Wells are typically pipes lined with cement casing. When that casing is fractured or otherwise poured incorrectly, this can result in a methane leak, the natural gas going not up the pipe for the driller but into local wells and water supplies, where the methane dissolves into the water.

Methane is a light gas—it naturally wants to go upwards. It will follow naturally-existing or industry-created fractures in the rock formations in order to find its way to the surface following the path of least resistance. As it does so, it finds its way into local streambeds, water wells, and basements, where it will build up until it reaches saturation point, finds its way up into the atmosphere, or combusts. Depending on the source of the migration (fracking or naturally-occurring), gas operators will either take responsibility for the resultant contamination or not. Frequently, though, it can be hard to ascertain what precisely triggered the migration.

Two ways that have been used to try to identify causes are dating the gas as young or old, or by taking a signature of the gas emerging with a gas chromatographer. There are two types of gas—biogenic and thermogenic.

• Biogenic gas is produced by microbial respiration, and is almost entirely methane. Biogenic gas is also typically younger, and produced near the surface.
• Thermogenic gas is a mixture of methane and other hydrocarbons produced by pressure and heat, and is older in nature. Thermogenic gas has its origins deep underground, but subsequent geological events and sloping beds mean that thermogenic gas can pocket either deep underground, or towards the surface.

The argument for cause rests on the idea that this differentiation indicates different sources—if it is found to be thermogenic, it is presumed it was related to oil and gas activity, versus biogenic gas being naturally-caused. The common rebuttal to this is that drilling and hydraulic fracturing can liberate biogenic natural gas into a fresh water aquifer. That is, just because gas is biogenic does not necessarily indicate that it reached a well by natural means.

Associated Dangers

Contaminated water itself is not considered undrinkable by the gas industry, though use can result in rashes and other health concerns.

When dissolved methane hits a saturation point, it will begin off-gassing, in which the water will begin to bubble with methane. This is frequently the point at which evidence of methane migration is obvious. Because methane is highly flammable and, in high concentrations, explosive, this causes serious danger to residents in areas with methane leaks. In cases of high methane buildup, it is common practice to evacuate the residents until the methane is vented off or given an alternative path to go through.

News Coverage

High profile cases of methane contamination include Dimock, PA, in which residents are able to light their tapwater on fire as a result of Cabot Oil & Gas activities, and Bradford County, PA, in which local puddles were reported to be flammable. The story of Cabot's activities in Dimock is highlighted by the 2010 film, Gasland, a documentary by Josh Fox nominated for “Best Documentary” in the 2011 Academy Awards.

See Also

• Impaired Wells
• Hydraulic Fracturing-Associated Concerns