HYDRAULIC FRACTURING:

When 2 wells meet, spills can often follow

When a geyser of oil and fracking fluid spewed out of an oil well on a farmer's field in Innisfail, Alberta, it coated 100 trees with a fine mist. About 20,000 gallons of oil and fluid collected on a snow-covered field and had to be cleaned up.

The spill was caused by hydraulic fracturing -- not the activities surrounding drilling. A series of similar incidents are being reported across the United States and Canada.

Drillers call it a "frack hit" or "downhole communication," and it could also contaminate groundwater aquifers.

A basic review by EnergyWire of oil spill reports from various states, as well as phone interviews with regulators, revealed more than 10 cases of frack hits that have resulted in spills ranging from 300 gallons to 25,700 gallons. The events were recorded in states from Montana to Texas.

The incidents are called frack hits because they happen when the fractures of two wells intersect. The communicating wells have, in cases, been as far apart as 1.8 miles, though it is more common for the wells to be less than 3,000 feet apart. That is too close for comfort because most states allow adjacent horizontal well bores to be about 600 feet from each other.

"Our concern is where the communication results in a loss of well control," said Ron Gusek, vice president of an Alberta-based oil and gas company and chairman of an Alberta industry task force set up to examine frack hits. "In other words, there's a fluid spill on the surface or loss of well control underground that could lead to contamination of a water aquifer."

The incidents generally go unrecorded by state regulators, but traces are found in oil spill databases as instances where operators report an overflowing production tank that spilled a few barrels into the environment.

Frack hits will be more common in the future as companies drill multiple wells in close proximity on each well pad.

They are a result of technological advancements in the industry since companies began combining directional drilling and fracking to split apart shale rock and extract oil and gas. The oil and gas development brought concerns about groundwater, set off by "Gasland," a documentary that showed water from a tap being set on fire due to the presence of methane. Since then, contamination worries have surfaced in Pavillion, Wyo., where U.S. EPA and the U.S. Geological Survey have found propane, methane and ethane -- all components of natural gas -- in groundwater aquifers.

Industry has argued that fracking is not a threat to groundwater resources and that there is no path for methane or fracking fluid in formations deep underground to contaminate groundwater aquifers. And surface spills are generally tied to human carelessness rather than drilling.

Frack hits could be a path of contamination, particularly in cases where the cementing is below standards.

In New Mexico on Feb. 9, 2012, Devon Energy Corp. was fracking a well when an older producing well 600 feet away started spouting 7,000 gallons of oil and wastewater. The fracks had hit the older well and pushed fluids out.

If the well had not been properly cemented -- a possibility with older wells -- the fluids could have migrated outside the well bore and directly entered groundwater aquifers.

"Everyone thinks cement is this magic; it's not," said Michael Beck, president of Surface Solutions Inc. and a consultant for the oil and gas industry in Canada who is helping companies including Encana Corp. deal with downhole communication issues. "Cement is not 100 percent perfect, it cracks."

The mechanism

Fracking involves pumping water, sand and chemicals into the well bore at high pressures to fracture shale. The well bores are horizontal, extending thousands of feet at times, and fractures extend a few hundred feet into the surrounding rock, like cracks embedded in an ice cube. That's the assumption, at least.

The truth can be messier. Some fractures get away from the drillers, extending even as far as adjacent formations. Using microseismic technology, researchers in Pennsylvania recently found one extending as far away as 1,800 feet, as reported by the Associated Press.

In the case of the Alberta spill, regulators found that an oil well 3,000 feet away was being fracked, and it had communicated with the well that lost control. About 20,000 gallons of fracking fluid and oil had to be cleaned up.

The fractures move toward the regions of lowest pressure, which can be a nearby well bore. Once a channel is established, the pressures of around 10,000 pounds per square inch travel rapidly across the formation to the older well. It pushes fracking fluid and whatever is at the bottom of the producing well -- oil, gas and produced water -- up the old well bore, which is not equipped to handle high pressures.

"The frack fluid crosses the path of least resistance," said James Amos, supervisory environmental protection specialist with the Bureau of Land Management in New Mexico. It runs up the well bore and can cause the production tank that's collecting the oil to overflow.

To the lay observer, it appears to be a surface spill. But in reality, such spills are caused by fracking hundreds or even thousands of feet away.

Communication between wells is not always bad. Sometimes companies want the fracks to communicate to effectively stimulate the rock. But problems arise when the communication is unintended and unexpected.

The worst-case scenario is when the fluids, propelled by high pressure, travel outside the steel pipe casing the producing well, through a bad cement job, and the brine enters groundwater aquifers. The risk is high when the frack hits communicate with older producing wells or abandoned wells.

In the New York State Department of Environmental Conservation alone, there are 4,000 unreported or abandoned wells to be plugged and 35,000 wells for which there are no records.

"If it doesn't get inside the well bore, it can migrate up the outside of the well bore; there are water aquifers up there," Beck said. He described aging cement as a layer of bubble gum wrapped around the steel pipe casing a well. It separates from the well bore with time, especially in areas where the geology is sandy or swampy, and provides a path to the groundwater aquifer.

How probable is it?

EnergyWire documented more than 10 cases of frack hits that resulted in blowouts or spills since 2010, and most state regulators said they are rare but would be more common in the future as additional wells get drilled.

"We've drilled 4,500 wells in our particular area, the wells are all closely spaced, you are drilling in areas where there are pre-intersecting fractures in the rock; I wouldn't expect it not to happen," said Lawrence Bengal, director of the Arkansas Oil and Gas Commission.

In the Montney Formation of Alberta, about 30 percent of the well bores that are up to 1,500 feet apart experience frack hits, Beck said. The Montney is similar in geology to the Bakken Shale of North Dakota.

The hits are common enough on New Mexico federal lands that some operators are temporarily shutting down their producing wells while new wells are being fracked, Amos said. They install cast-iron plugs downhole to prevent the fracking fluid from shooting up the well bore and damaging the producing well, he added.

Predicting frack hits

Industry is getting better at predicting the behavior of fractures underground, but the challenge will only increase as more wells get drilled, Pat Handren, an engineer with Denbury Resources Inc., wrote in a brief to EPA, which is conducting a study on fracking.

"As well density increases, it becomes increasingly probable that wells will communicate either through previously created fractures or through adjacent wellbores and then into previously created fractures," he wrote.

Anthony Ingraffea, an engineering professor at Cornell University and a critic of the oil and gas industry, described communication, and any resulting environmental impact, as a matter of probability.

"The industry can say there is less than a 1 percent probability this is going to happen," he said over the phone. "If you roll the dice 100 times, it is going to happen once. If you roll the dice 1,000 times, it is going to happen more than once."

Regulation

Frack hits are usually not reported to state regulators unless there is a spill of fracking fluid from the producing well.

In such cases, the incidents masquerade in state databases as production tank overflows due to an unexpected increase in pressure -- a "kick." That seems innocuous until one pauses to examine why, exactly, a producing well that should experience stable pressures would experience a kick.

"They [frack hits] periodically occur, but they don't necessarily put down the exact or the surmised cause. Most of the time we'll just get a spill report that says all of a sudden we overran the tanks 100 barrels to the bermed area," said Steve Sasaki, chief field inspector at the Montana Board of Oil and Gas.

State regulators disagree on whether a frack hit is a significant problem. Most, such as Bengal of the Arkansas Oil and Gas Commission, believe they are an issue for companies to resolve among themselves because it affects production. If there is a surface spill, it will be cleaned up and contained, he said. Additional regulation is not necessary, especially because wells are cased and cemented very stringently in his state, he added.

He acknowledged there could be a problem with fracks communicating with older wells.

Other regulators, such as Amos with the BLM in New Mexico, see all spills, including ones that can be contained at the surface, as a problem.

In Canada, the industry has put together a set of best practices to deal with the problem before it gets more prevalent.

"We just want to make sure that people have taken steps to ensure that they eliminate the risk of anything happening," said Gusek of the Alberta task force. "We saw that it has a potential to be a high-consequence event when and if it happened."