Background
Scott Detrow / StateImpact Pennsylvania
A Leroy Township, Bradford County resident lights a sample of methane gas on fire. The gas has been bubbling into puddles and creeks for more than two months.
One of the most iconic symbols of the fracking debate is the video of a man setting his tap water on fire in the anti-drilling documentary Gasland.
Fracking, which refers to hydraulic fracturing, is a technique used to extract natural gas, and has become synonymous with all things gas drilling. It involves shooting water, sand and a mix of chemicals at high pressure deep into a wellbore to help split the shale rock and release the gas that lies tightly squeezed into the rock. Some worry fracking fluid will leak out of a well and contaminate aquifers. But the tap water blow torch seen in Gasland has nothing to do with hydraulic fracturing. Instead, it’s related to a problem called methane migration.
Methane migration is what it sounds like – methane gas migrating from deep underground to the surface. It leads to methane-filled drinking wells, flammable faucets, and even a 30-foot geyser of water and gas, in one Tioga County instance.
Methane can naturally migrate to the surface — reports of migration date back to the 1800′s – but natural gas drilling can speed up the process.
“Natural gas wants to migrate up,” Penn State University geologist Dave Yoxtheimer, who works at the Marcellus Center for Outreach and Research, tells StateImpact Pennsylvania. “It’s lighter, it’s less dense. And it finds itself getting trapped in these shallower, more porous formations. And during the drilling process you can go down through these shallower formations. As you’re drilling through, suddenly you’ve created a conduit for those gasses to escape.
If a driller doesn’t surround a gas well with the proper steel and cement casing, the gas can escape, and migrate up to the surface through faults and water wells. “What you’ve done,” Yoxtheimer explained, is “catalyzed the process of natural gas drifting up over geologic time.”
Pennsylvania’s Methane Migration Problems
State environmental regulators blame methane migration for Pennsylvania’s most high-profile drilling problem: contaminated water wells in Dimock, Susquehanna County.
Migrating gas is also the prime suspect for two problems that sprang up in May and June 2012: in Tioga County, a 30-foot geyser appeared along a road in Union Township, Tioga County. Private water wells also began overflowing, and gas puddles were discovered in a nearby creek.
Similar problems surfaced 13 miles away in Leroy Township, Bradford County, where flammable puddles were discovered near a well drilled by Chesapeake Energy:
State regulators suspect gas leaking from nearby Marcellus Shale operations caused both problems.
How Methane Migration Happens, And How It Can Be Prevented
Tracing the source of stray gas appearing at the surface, can be complicated and mysterious. Investigators often use isotope identification to get a “fingerprint” of the gas. But just like in law enforcement, fingerprints can be tricky. In the case of Dimock, Pennsylvania, the vertical wells drilled by Cabot Oil and Gas were fracked. But the Pennsylvania Department of Environmental Protection did not connect the flaming water taps to fracking, they blamed poor well construction and over-pressurization. When a wellbore is drilled, a steel casing is sent down the hole. Then cement is poured down, and pushed upward to seal the open space between the steel casing, and the rock. That cement seal is supposed to prevent any gas, or fluid, from migrating into or out of the wellbore, and from using that space between the rock and the newly drilled well as a conduit. But that cement job doesn’t always work. And in the case of Dimock, it failed miserably.
Fred Baldassare worked as an inspector for DEP, where he spent six years investigating methane migration and helped out on the Dimock case. He was the guy who looked at the geochemistry of those flaming taps. In other words, he looked at the gas fingerprint. Baldassare says the evidence linking the flaming tap water to gas drilling by Cabot is overwhelming. But where that gas actually came from, whether it was from deep in the Marcellus formation, or whether it was from a more shallow formation, is unclear.
“The gas was nearly an exact match to the gas coming from the Marcellus wells,” said Baldassare. But we couldn’t say it came from there because there are gas deposits above the Marcellus that have the same fingerprint.”
Baldassare says drilling, along with a bad cement job, can cause any gas pocket that has been stable for thousands of years, to start moving. That’s because methane, under high pressure, wants to go to an area of lower pressure. And drilling, whether it’s a vertical well, horizontal well, deep well, or shallow well, can provide that opportunity. But other things can too, such as coal mining. It can also happen naturally. And that’s where that fingerprint comes in. Baldassare says he spent a lot of time tracking methane migration before the first Marcellus Shale gas well was even drilled.
“There are examples of [methane migration] throughout the northeast that have nothing to do with gas activity,” says Baldassare. “And there are others that do happen because of drilling or mining activity.”
When gas migrates, it will dissolve in water, but once the water reaches a lower pressure zone, it wants to get out. That’s why people experiencing methane in their water supplies will first notice a spurting at the tap, or bubbles in a glass of water. If that happens, the concentration is high enough to be combustible and the presence of methane becomes dangerous. If the colorless and odorless gas has a concentration above 28 milligrams per liter, it needs to be vented. When triggered it could explode. That’s what happened when Dimock resident Norma Fiorentino’s water well blew up.
Drinking water that contains methane is not considered harmful. But there are few studies of the longterm health impacts of drinking water with high levels of methane.
So once methane migrates into water supply, what then? Baldassare says proper venting and aeration does work. Here’s a look at some of the equipment Leroy Township resident Michael Leighton has installed in his basement, to combat leaking methane gas:
Some homeowners suffering from methane in their water wells have expressed doubts about the venting and filtration systems. Baldassare also says if the source of the methane is halted, eventually, the water will be free of the gas through natural processes. But it’s unclear how long that could take.
