Southern California Gas Co. (SoCalGas) sought state permission to reinject natural gas into its Aliso Canyon storage facility, shut over a year ago after a massive methane leak forced the evacuation of thousands of people in the Porter Ranch area of Los Angeles.

The utility said 29 of the 114 wells at the site passed state safety tests, making them fit for gas reinjection if authorization was granted. The balance remains temporarily sealed.

Before the leak, Aliso Canyon was able to deliver almost 1.9 billion cubic feet per day (Bcf/d). SoCalGas could not immediately say on Nov. 2 how much gas it may be able to withdraw from the wells that passed the tests.

SoCalGas said it added new inner metal tubing in every well approved for injection, installed around-the-clock pressure monitoring of all wells and built an infrared fence-line methane detection system.

The remaining 85 wells that have not passed safety tests must do so within one year or be permanently sealed, California's Division of Oil, Gas and Geothermal Resources (DOGGR) said.

"Over the last year we have made extensive physical upgrades and deployed advanced technologies to enhance safety at Aliso Canyon," SoCalGas President and Chief Operating Officer Bret Lane said in a statement late on Nov. 1.

SoCalGas cannot inject fuel into the field until California's Division of Oil, Gas and Geothermal Resources (DOGGR) and Public Utilities Commission (PUC) confirm the field is safe.

The utility, owned by California energy company Sempra Energy, could not say when it may be able to start injecting gas into the facility, noting it was up to the state agencies.

In a statement, Ken Harris, state oil and gas supervisor at DOGGR, said: "We will thoroughly review all the information and data, conduct independent site inspections, seek public feedback and the opinion of outside experts before making any determination."

Since DOGGR must give the public 15 days' notice before a meeting, SoCalGas cannot start injecting gas into Aliso Canyon until some time in mid- to late-November at the earliest.

The leak was discovered on Oct. 23, 2015, and not plugged until February. The California Air Resources Board said in September that it was the biggest methane leak in state history.

The state required SoCalGas to keep 15 Bcf of gas in the 86-Bcf facility to minimize risk of gas shortages that could result in electricity outages. The PUC required the utility to be able to withdraw 207 MMcf/d of gas for this purpose.