conference call with analysts.
Occidental declined to comment for this story, referring questions to the petroleum association.
Drillers have been pouring acid down oil wells for more than a century, using it to dissolve the underground drilling debris that surrounds new wells. Acid can also clean out hydrocarbon deposits that gum up older wells.
In the Monterey Shale, however, oil companies are using larger amounts of hydrofluoric and hydrochloric acids to open tiny channels in the rock around each well. Those channels allow oil trapped within the rock to flow into the well.
Fracking also creates channels within shale, but does so by blasting the rock with a high-pressure mixture of water, sand and chemicals. Acidizing doesn't require high pressure or sand. It can, however, be combined with fracking in a process called fracture acidizing, or acid frack.
Hydrofluoric acid in particular is a powerful corrosive, capable of eating through steel as well as rock. So companies blend it with water and other chemicals to protect their wells. Mark Nechodom, director of the Department of Conservation, said drillers in California have used acid concentrations as high as 15 percent, although it's typically in the single digits.
Companies go out of their way to keep the exact composition of their acidizing fluids secret. At an industry conference in Bakersfield this spring, energy policy consultant Robert Collier watched oil company representatives try to discuss acidizing without divulging their own processes or plans.
"They were trying to get information from each other without giving any up," said Collier, a former Chronicle journalist who has written several reports about acidizing for the Next Generation think tank. "People weren't talking about exact percentages, their formulas. You don't give up your special sauce."
Hydrofluoric acid can damage lungs and cause severe skin burns. Above 67 degrees, it can form a vapor cloud that stays near the ground, according to Collier. A hydrofluoric acid accident last September at a South Korean chemical plant killed five people.
No serious accidents
State officials say they are unaware of any serious accidents involving acidizing in California oil wells. Nor have they seen cases of acid from a well seeping into groundwater.
"At least in our reading of current well histories or reporting, there's no evidence that we currently have a problem to solve," Nechodom told Pavley and other state legislators at the acidizing hearing in June. "But I think there's good purpose in taking a hard look at this to see if perhaps we have missed something or if we should add something to our regulatory oversight."
David R. Baker is a San Francisco Chronicle staff writer. E-mail: email@example.com Twitter: @DavidBakerSF
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