Since its discovery almost three weeks ago, a leak at Sempra Energy Southern California Gas Co.’s (SoCalGas) 100 Bcf Aliso Canyon underground storage field has tied up the utility and a cadre of outside well experts who have so far been unable to stop the seepage.

Initial work to plug and abandon the well will begin in the next few days, utility and state officials told NGI.

Gas is escaping in a remote part of the storage field in the Santa Susana Mountains, about a mile from the nearest residences on the north edge of the suburban San Fernando Valley.

The prolonged nature of the incident, which a SoCalGas spokesperson told NGI Wednesday night was under control and of no threat to public safety, has heightened concerns of area residents, who can smell the escaping gas. An engineer from the California Division of Oil, Gas and Geothermal Resources (DOGGR) has been onsite since the leak was discovered, and the head of DOGGR, Steve Bohlen, told NGI there have been no public health or safety risks.

Bohlen praised SoCalGas for taking a proactive approach to dealing with residents, none of whom have been endangered, but some could be sensitive to mercaptan, the odorant placed in natural gas so leaks can be detected.

"The leak is outdoors at an isolated area of our mountain facility more than a mile away from and more than 1,200 feet higher than homes or public areas," a SoCalGas spokesperson said. "We are now preparing and planning our approach to stop the flow of gas," using the advice of some of "the world's best experts.”

Well control experts from Halliburton's Boots and Coots last Friday began using a coiled tubing rig (typically used in offshore operations) to clear through an ice plug before running multi-day diagnostics tests that are required before filling the well with fluid.

"Current indications are that the well is clear, the tubing is intact and there is access into the storage zone at around 8,500 feet," the spokesperson said.

Through the diagnostic work using the protection of the coiled tubing, a leak was identified in the well liner at 480 feet, according to Bohlen, who said the plan is now to kill the well with weighted brine and cementing the casing and that work will take place tomorrow (Friday). "The division has had an engineer onsite continuously to witness the work and expedite any state permitting needed for the work," he said.

SoCalGas officials said plans were to begin the procedure to stop the flow of gas within the next few days.

"While officials maintain that air samples taken to date show that the leak does not present acute health impacts, known toxic chemicals are obviously being released and something in the air has been making many people near the site sick," Tim O’Connor of the Environmental Defense Fund wrote in a blog published Wednesday.

"Natural gas continues to leak from the well and is emanating from the ground areas near the well," the SoCalGas spokesperson said. "It can best be described as 'seepage,’ and it is not blowing at high pressure."

O'Connor alleged that the source of the leak was a 40-year-old pipe failure 1,000 feet underground that allowed natural gas stored under pressure to migrate to the surface, but Sempra's spokesperson initially could not confirm or deny this.

The Aliso Canyon facilities were developed at an abandoned oilfield site and opened for gas storage in 1972. It is the state's largest underground storage field and one of the largest in the nation.