One of the boldest claims made by the shale gas industry goes like this: oil and gas companies have drilled and fractured a million oil and gas wells with nary a problem.
In other words fracture fluid or methane leaks are "a rare phenomenon."
But industry data disproves this dubious claim says Cornell University engineer Anthony Ingraffea, the main source for this series, who has studied the non-linear science of rock fractures for three decades.
Moreover industry studies clearly show that five to seven per cent of all new oil and gas wells leak. As wells age, the percentage of leakers can increase to a startling 30 or 50 per cent. But the worst leakers remain "deviated" or horizontal wells commonly used for hydraulic fracturing.
In fact leaking wellbores has been a persistent and chronic problem for decades. Even a 2003 article in Oil Field Review, a publication of Schlumberger, reported that, "Since the earliest gas wells, uncontrolled migration of hydrocarbons to the surface has challenged the oil and gas industry."
Methane, by its very lightness, wants to go up. Where ever drillers have not properly sealed and cemented wellbores in deep shale rock, the gas will escape and move through rock fractures (existing or industry-made ones) into groundwater, stream beds, water wells and even the basements of houses.
Aging can affect leakage too. Old and decaying cement jobs largely explain why offshore oil wells in the Gulf of Mexico report leakage rates as high as 60 per cent after 16 years of service. Abandoned wells also can become major pollution portals.
The Norwegian Petroleum Safety Authority reports that 18 per cent of its deep offshore oil and gas wells have integrity problems, while Australia struggles with chronic leaks from fractured coal bed methane wells.
"Anything that ages starts to fail," explains Ingraffea. "I'm 65 and I've had a knee replaced."
How much of Alberta is leaking?
Based on industry reports to regulators as opposed to independent audits, about five per cent of Alberta's 300,000 oil and gas wells now leak. But a 2009 study by Alberta scientists Stephan Bachu and Theresa Watson found that so-called "deviated wells" (the same kind right angling used for fracturing shale gas and tight oil formations) typically experienced leakage rates as high as 60 per cent as they age. Moreover "high pressure fracturing" increased the potential to create pathways to other wells, the atmosphere and groundwater.
Theresa Watson, now a member of Alberta's Energy Resources Conservation Board, also disclosed that an increase in the number of water wells in heavily fractured oil and gas fields would increase "the likelihood that gas, due to migration through shallow zones, can accumulate in buildings."
Alberta's energy regulator does not yet keep track of leaking wells in a rigorous or transparent fashion but it does note in a 2011 Field Surveillance Report that leaks and methane migration are routine items of "high risk noncompliance" that companies voluntary disclose to the regulator. In Alberta the industry remains largely self-regulated.
Leaking of toxic fracture fluids is also common because only 25 to 60 per cent of diluted chemicals and water used to blast open shale or coal formations are ever recovered.
In a 2004 report the U.S. Environmental Protection Agency factually noted that "if fracturing fluids have been injected to a point outside of the well's capture zone, they will not be recovered through production pumping and, if mobile, may be available to migrate through an aquifer."
The failure rates of shale gas wells in heavily fractured jurisdictions with transparent regulation has now become a significant issue. During the shale gas rush in Pennsylvania more than 75 companies drilled thousands of wells and fractured rock formations throughout the state in 2007. Due to a rising number of accidents, spills and leaks, the Department of Energy started to compile and publish open public statistics.
What 16,017 inspection reports said
In 2012 Ingraffea and colleagues read through 16,017 inspection reports filed over the last four years. What they found was a significant and steady rate of methane leaks at the wellbore or what is known in industry jargon as "bubbling in the cellar."
In 2010, 111 of 1,609 wells drilled and fracked failed and leaked. That's a 6.9 per cent rate of failure. In 2012, 67 out of 1,014 wells leaked -- a seven per cent rate of failure.
"We looked at violations and not comments," adds Ingraffea. Quite often inspectors would note that a well was leaking like a sieve but that violation was pending. As a consequence the seven per cent figure represents a dramatic underestimate of methane leaks, says Ingraffea.
Moreover, the seven per cent figure only includes leaks at the wellhead. It does not include leaks that sprouted up in stream beds, water wells, or ponds often 2,000 feet away from the well site after steady fracking operations.
'That's a lot of leaking wells'
In 2009, Cabot Oil and Gas drilled 68 new Marcellus wells in Pennsylvania that the state's Department of Environmental Protection concluded resulted in extensive groundwater contamination for nearly a dozen families in the town of Dimock. State regulators cited the company seven times for "Failure to report defective, insufficient or improperly cemented casing within 24 hours or submit plan to correct within 30 days."
But this common problem will only get worse. Industry has proposed between 150,000 to 200,000 new wells to develop the Marcellus Shale in Pennsylvania, West Virginia and New York. Given current practices that means 10,000 to 20,000 new wells leaking methane into the atmosphere or groundwater and many more over their lifetimes. "That's a lot of leaking wells," says Ingraffea.
Evidence is also growing that toxic fluids used for hydraulic fracturing can also migrate into adjacent water bodies. A 2012 study in the journal Ground Water warned that hydraulic fracturing opens more pathways for the movement of both fluids and methane. And a recent study by the US Environmental Protection Agency in Pavilion, Wyoming, found that toxic fluids had contaminated local water supplies.
So what is it, myth or reality, when industry claims that leaks are rare?
The scientific truth is irrefutable says Ingraffea: "Fluid migration from faulty wells is a well-known chronic problem with an expected rate of occurrence." Inadequate well construction and monitoring remains a persistent industry problem.
The health implications are also serious. The migration of methane or fracking fluid has repeatedly contaminated groundwater across North America or polluted the atmosphere with methane, a potent greenhouse gas.
Tomorrow, last in the series: How clean is natural gas?