Stray Gas Plagues NE Pa. Marcellus Gas Wells

Binghamton NY
10 July 2011
By Laura Legere

SCRANTON, Pa. -- Methane that caused a blast in a Dimock water well, forced a family to evacuate a Terry Township home, and bubbled up in the Susquehanna River was unsettled from porous rock between the surface and the Marcellus Shale as drillers searched for deep gas.

In high-profile cases affecting 35 drinking water wells in Bradford and Susquehanna counties, state investigators have linked the stray methane to faulty drilling practices that did not account for the gas-rich and highly fractured shallow geology in northeast Pennsylvania -- a hazard that has made the region one of the most difficult places in the state to drill safely into the Marcellus Shale.

As shale gas drilling has increased in Pennsylvania, so has the prevalence of methane migrating into water supplies as a result of the exploration.

The number of new Marcellus wells nearly doubled between 2009 and 2010, but the rate of methane migration more than quintupled: In 2009, there were 1.26 cases of gas migrating into groundwater for every 1,000 new Marcellus wells drilled, according to the Department of Environmental Protection.

Last year, there were more than seven cases for every 1,000 new wells.

Of the 10 confirmed Marcellus Shale stray gas cases since early 2008 -- each of which may include more than one affected water well or flawed gas well -- all of them have been recorded in this corner of the state.

Seven of the cases were in Bradford County and one each in Wyoming, Susquehanna and Lycoming counties.

Why here?

Geologists suspect that a lack of historical drilling in the region, combined with a large amount of methane generated deep underground created a gas-charged environment in shallow sandstone layers.

For more than 100 years in western Pennsylvania, formations similar to those now considered a nuisance to Marcellus Shale drillers in the Northeast were targeted by shallow well drillers hoping to draw out the gas.

The geology in Northeast Pennsylvania is also complicated and, in some rural regions, rarely studied, meaning there were few good historical maps for the drillers' reference, said Fred Baldassare, a former stray gas inspector with DEP who now owns Echelon Applied Geoscience Consulting.

"It's a very complex system with deep-seated fractures and deep-seated thrust faults that come to the surface," he said.

The shallow methane is not necessarily uniform in the layers above the Marcellus.

It is present in "a variety of strata -- very shallow all the way down through," said Scott Perry, the director of DEP's Bureau of Oil and Gas Management.

Natural gas wells are built with a nested series of cemented steel casings that each extend deeper underground to protect groundwater from the gas and fluids in the well.

The cement and casing is also supposed to isolate gas and fluids encountered in rock formations on the way down from migrating up the outside of the wellbore.

Problems with the barriers are common.

There have been 47 violations issued on 33 Marcellus wells in the first five months of 2011 for casing and cementing problems, according to DEP records.

In 2010, there were 90 violations issued on 64 faulty wells.

Not all of the cement and casing problems led to gas migrating into groundwater.

But in cases where methane migration has been tied to Marcellus Shale drilling, state regulators say the most likely cause is that the high-pressure shallow gas is channeling up small gaps or flaws in the cement.

Earlier this year, updated DEP regulations took effect that require a third string of steel casing, cement with gas-blocking additives in areas with known shallow gas-bearing zones, and a longer period to let the cement harden.

Because methane also reaches aquifers through natural fractures or spreads through the breakdown of organic materials without any man-made interference, gas is present in many water wells before drilling occurs.

The industry has worked to publicize the widespread presence of pre-existing methane in Pennsylvania water wells, but that campaign has sometimes served to create public doubt that drilling is ever responsible for residents' bubbling or flammable water.

Efforts by the industry to downplay or deny the migration problems often mask the efforts it is making to solve the problems.

Even before the strengthened state rules took effect, some operators were going beyond the requirements to find hazards and prevent problems before gas made its way into water, say scientists.

Several operators began using mud rather than air to drill into the shale.

Operators are also studying the isotopic signatures -- chemical fingerprints of the gas -- to help determine its provenance.