Investigators hired to pinpoint the cause of the nation's largest uncontrolled natural gas leak said in a new report that they found extensive corrosion on the casing of the well that broke open at the Aliso Canyon Natural Gas Storage Facility near Porter Ranch.
When one of Southern California Gas Company’s 114 gas wells failed in late October 2015, it released more than 100 metric tons of natural gas and other substances into the atmosphere and onto thousands of homes. Before the well was finally sealed in February 2016, more than 8,000 households had evacuated from Porter Ranch and adjacent neighborhoods. Thousands of individuals and companies have sued SoCal Gas alleging physical or financial damage.
The California Public Utilities Commission recently posted a Feb. 15 report by Blade Energy Partners, an independent firm hired to investigate the well’s failure. The report contains the first publicly available photos of the ruined well casing. One of the most significant findings was that the well casing had extensive corrosion on the outside, where the casing ruptured.
To get at the rupture point, 892 feet below the earth’s surface, investigators pulled about 1,000 feet of steel casing out of the earth and shipped them, under careful security to maintain the chain of evidence, to Blade’s warehouse in Houston.
The photos show the casing with a 19-inch vertical tear at a point where the casing blew apart. Photos also show what Blade investigators describe as severe corrosion at that point, and at several other places closer to the surface. The corrosion is more severe the deper the casing, the report said.
Following extensive testing and equipment overhauls, fewer than half the company’s wells have been permitted to resume injecting gas into the underground rock formations at Aliso Canyon, with limits on the amount of gas that may be stored to keep the pressure on the field and equipment fairly low.
In 23 instances during that testing phase, well casings either failed or required repairs for other reasons before they were permitted to come back on line, according to records of the state Division of Oil, Gas and Geothermal Resources (known as DOGGR). Two tests conducted from inside the casing can detect thinning walls from corrosion both inside and out, DOGGR spokesman Don Drysdale said.
“I hope that DOGGR will take a second look at what this means to their assertion about the safety of the wells,” said Issam Najm, president of the Porter Ranch Neighborhood Council, an elected city board supports the permanent closure of the Aliso Canyon storage field.
“If this is happening at this casing from the outside, which basically is corrosion that's caused from the soil around the casing, it could mean that it's happening at any of the other casings as well,” Najm said.
DOGGR officials have said the field overhaul has made it one of the most thoroughly tested and safest underground gas storage fields in the nation.
SoCal Gas spokesman Chris Gilbride declined to respond to questions about what might have caused corrosion on the outside of the casing or what it means for the safety of other wells at Aliso, because the investigation isn’t complete.
Prior to the well blowout , it was common practice at Aliso Canyon and other gas storage fields to move gas through both the inner tube of the wells as well as the space between the tube and the outer casing. That practice left no safety buffer if a break developed in the casing. State regulators now bar the practice.
“Recall that under new regulations, natural gas no longer flows through the casing. It only flows through brand new steel inner tubing. The outer casing now only serves as a secondary barrier of protection against leaks,” Gilbride said in an email statement.
Oil and gas well casings are generally made from carbon steel, and they can corrode when the gases underground come into contact with water, said Yoon-Seok Choi, research professor in the Department of Chemical and Biomolecular Engineering at Ohio University. He has published research on well casing corrosion.
It’s more common for casings to corrode from the inside, he said.
“Corrosion from the outside means that there was some sort of water source,” Choi said. "The most important thing is the environment. How much water is there, and what kind of gases.”
Carbon dioxide and hydrogen sulfide are two corrosive gases found in oil and gas fields, and when they are mixed with water, corrosion can result. He said the corrosion depicted in the Blade Energy Partners report on the outside of the casing probably did not develop over just the four months that the gas well blowout was active.
“Four months is too short unless there is a very severe environment around the casing,” Choi said.
“Corrosion has always been a problem,” said Patricia Oliver, one of the attorneys representing plaintiffs suing SoCal Gas. “It has always been something that’s on everyone’s mind,” she said.
The report does not pinpoint the exact cause of the well blowout, because the investigation still has several steps remaining. The casing must be subjected to digital and microscopic photography, laser analysis and other types of tests. One question is whether the rupture of the well occurred in one or two events.
The well, known as Standard Sesnon 25 or just SS-25, was drilled in 1953 as an oil extraction well. It is one of dozens of wells that dot the 3,600-acre oil field in the Santa Susana Mountains that rise north of Porter Ranch at the north end of the San Fernando Valley.
When the oil field was depleted in the 1970s, the Aliso Canyon field and its many wells dating back to the 1940s and 50s were converted by new owner Southern California Gas Company to store natural gas. The company has since drilled its own wells for injecting and withdrawing gas underground.
At least four gas wells at Aliso Canyon that are older than the ruptured well passed all tests and remain in operation.Twenty-two other well that predate SS-25 were shut down, according to data on the state Division of Oil, Gas and Geothermal Resources website.
Of the wells drilled after SS-25, at least 42 passed all tests and remain in service, and 19 were taken out of service.
The well record filed with DOGGR in 1954 for SS-25 indicates that a 4.5-inch drill pipe was left inside the well nearly 4,000 feet below the surface in 1953. It's unclear the role the lost equipment played in the blowout.
Blade Energy Partners estimates it will be November before its report on the well failure is complete.
This story is part of Elemental: Covering Sustainability, a new multimedia collaboration between Cronkite News, Arizona PBS, KJZZ, KPCC, Rocky Mountain PBS and PBS SoCal.
Correction, April 9, 2019: This story has been updated to correct the location of equipment that was lost inside the ruptured well.