Diesel fuel has been used to "frack" at least 138 wells in the United States in the past year and a half, according to data filed by drillers with the FracFocus.org registry.

But if the definition of diesel proposed by U.S. EPA were used, that figure would rise to 408, according to an EnergyWire analysis of FracFocus data provided by PIVOT Upstream Group.

The data from PIVOT's D-Frac database show that diesel fuel is still used in hydraulic fracturing, despite industry reassurances that it had been all but discontinued.

They also define the terms of the disagreement between EPA and the companies that do the fracking as they try to figure out regulations for fracking with diesel. EPA's definition would have covered about 270 more wells.

Environmental groups say federal law requires a permit for hydraulic fracturing with diesel, so each instance is an environmental violation.

"They're violating the law, and EPA ought to be enforcing it," said Dusty Horwitt of the Environmental Working Group.

Oil and gas companies note they cannot get a permit because EPA has never created one. And, they say, there is no indication that fracking with diesel has damaged the environment.

"The question is, did you create an environmental problem by using it, and the answer is 'no,'" said Lee Fuller of the Independent Petroleum Association of America.

It is a relatively small number of wells. But the FracFocus data likely understate the amount of time diesel has been used because the registry is still voluntary in some states and has only recently been mandated in others. The registry includes information on about 25,000 wells, but significantly more than that have been drilled since FracFocus was launched in 2011.

PIVOT, a small Houston-based energy consulting firm, managed to do what others have tried to do without success -- unlock the privately held fracturing recipe data and turn them into a database that can be analyzed.

"It took a lot of trial and error," explained Joe McCord, who developed the D-Frac database for the firm. "I found it to be a personal challenge."

For its clients, the company has woven those FracFocus data in with drilling and production data from other sources to enhance the quality of its information.

EPA and industry disagree about how to define diesel. The oil and gas industry thinks it should be limited to two substances, diesel fuel No. 1 and diesel fuel No. 2. They have other names but are distinguished by their unique "chemical abstract service," or CAS, numbers (68334-30-5 and 68476-34-6).

EPA has proposed adding four other chemicals to that definition. They have four other distinct CAS numbers but are commonly known as fuel oil, fuel oil No. 2, kerosene and petroleum distillate. But the only one of those four that shows up in the FracFocus data, 270 times, is kerosene.

The issue stems from a provision in a 2005 energy law that environmentalists call the "Halliburton loophole." It exempted hydraulic fracturing from regulation by EPA under the Safe Drinking Water Act, unless diesel fuel is in the mix.

Diesel is a complex and relatively small part of the debate about fracturing, but it has raised questions about the credibility of both industry and regulators.

As Congress debated the exemption in 2005, industry representatives said the use of diesel was nearly nonexistent, and EPA officials never moved to regulate. But congressional inquiries showed diesel was, in fact, used many times in fracture treatments.

In 2010, EPA posted rules about fracturing with diesel on its website without notice. That prompted a legal challenge from industry that was settled earlier this year. In May, EPA issued proposed "guidance" on how fracturing would be regulated when diesel is part of the mix (E&ENews PM, May 4).

Industry officials had been concerned that EPA would use an overly broad definition of diesel fuel, banning substances as benign as mineral oil. The agency sought to resolve that by defining diesel fuel with six CAS numbers.

Using EPA's definition, the most fracture treatments involving diesel were in Arkansas, with 168. Texas was second at 115. New Mexico was third with 54, and Pennsylvania, with 40, was fourth. About 30 entries in the FracFocus registry explicitly list diesel as an ingredient in the fracturing process. Other entries list it as "petroleum distillates" or "carbohydrate polymer."

Other states where diesel was used include Colorado, Kansas, Louisiana, North Dakota, Oklahoma, Utah and West Virginia.

Most of the wells where diesel was used produce primarily gas. There are 342 gas wells listed as using diesel, while 66 produce primarily oil.

Revising ingredients

Industry officials have opposed the release of the full FracFocus database to the media or the public, saying it could be misused. The organizations that manage the registry, the Ground Water Protection Council and the Interstate Oil and Gas Compact Commission, have refused to release it in that format. They have stated that the information is intended to be reviewed one well at a time (EnergyWire, Aug. 13).

They have maintained that position even as states mandate disclosure of fracturing fluids through FracFocus, meaning that government-mandated information is being kept in private hands (EnergyWire, May 21).

But the kind of detailed scrutiny made possible by PIVOT's aggregation of the data allowed EnergyWire to determine that diesel or kerosene may not have been used even when FracFocus indicates that it was.

Several companies said they were revising their FracFocus data after being contacted by EnergyWire, because diesel or kerosene was incorrectly listed as an ingredient. The FracFocus site that companies use to enter data has a "remove" link next to each entry that allows companies to revise and resubmit entries.

FTS International, formerly Frac Tech Services, and EP Energy, formerly known as El Paso, said a typographical error resulted in the wrong FTS International product being listed for an EP Energy well.

A spokesman for XTO Energy Inc., a subsidiary of Exxon Mobil Corp., said XTO Energy revised one entry for an Oklahoma well that incorrectly listed diesel as an ingredient. FracFocus lists 31 other XTO Energy wells with diesel, as defined by EPA, among the fracking ingredients.

Also, the Independent Petroleum Association of America's Fuller checked with the maker of one of the products listed as containing diesel, Plexgel 907 LE. He found out that the company's diesel-based slurry was discontinued in 2009 and replaced with a mineral-oil-based slurry.

Southwestern Energy Co.'s board of directors earlier this year explicitly banned the use of diesel, as defined by EPA, in fracking its wells. The ban included contractors. But the data show that SEECO Inc., an Arkansas subsidiary, used a corrosion inhibitor that contains diesel on about 165 wells.

The amount of diesel used was a little more than 1 gallon for frack jobs entailing nearly 6 million gallons of fluid each. But Mark Boling, Southwestern Energy's general counsel and president of its V+ Development Solutions division, said company officials were upset to learn that a contractor had used the additive. He said that will change immediately.

"I can tell you it has been resolved," Boling said. "We appreciate you bringing this to our attention."

He said company officials were especially upset because the contractor has another corrosion inhibitor that is just as effective and does not contain diesel.

Energy Corporation of America, starting this year, moved away from using any diesel products in its frac fluids, said spokeswoman Jennifer Vieweg. The company has found another liquid to replace its use of Plexgel 907 LE.

"We made this change because we routinely seek out products that are effective, but more environmentally friendly," Vieweg said in an email. "So beginning this year and moving forward, diesel products are not included in our frac fluids."

All of Energy Corporation of America's wells listed as being fracked with Plexgel 907 LE were completed in 2011.

PIVOT's McCord said the most surprising interest in his data came from investment bankers seeking information about the ingredients of fracturing fluid to guide their investments in the makers of those ingredients. But he says there are numerous uses for the data.

"I like that people can use it to keep companies in line," McCord said. "But to me, it's really a way to pay the bills."

Click here to read PIVOT's explanation of its D-Frac database.