​​​​​​​​Aliso Canyon Storage Facility

On December 4th, with CalGEM’s approval, Southern California Gas Company began drilling relief well Porter 39A as an alternative in case top-kill attempts at SS-25 continued to be unsuccessful. A relief well is a well specially drilled to intercept another well to address an issue, such as an uncontrolled release. 

When drilling was completed, Porter 39A intersected SS-25 at depths from 8492’-8500’. Fluids of heavy drilling mud followed by cement were pumped through Porter 39A and into SS-25.  This stopped the flow of gas from the reservoir and stopped the SS-25 gas leak.  On February 15, 2016, CalGEM confirmed SS-25 was sealed, and the well was subsequently plugged and abandoned. 

You can watch Blade Energy’s history of the Standard Sesnon 25 leak here: https://www.youtube.com/watch?v=Z3D1DvqBcgU​

On March 4, 2016, the Supervisor issued Order 1109, which ordered: a comprehensive safety review, plugging and abandonment of wells in accordance with Public Resources Code section 3208 for all wells in the gas storage injection project that had not been tested and remediated to the Division's satisfaction, equipping all gas storage injection wells with real-time pressure monitors as well as tubing and packer, and requiring the Operator to submit a Spill Contingency Plan and Risk Management Plan. 

In consultation with nationally recognized experts from the Lawrence Livermore, Lawrence Berkeley, and Sandia National Laboratories, CalGEM completed a comprehensive safety review of the 114 wells at the facility. 

On July 19, 2017, the California Public Utilities Commission (CPUC) and CalGEM concurred that the Aliso Canyon natural gas storage facility in Los Angeles County could reopen at a greatly reduced capacity. The State Oil & Gas Supervisor issued Order No. 1118, requiring the Southern California Gas Company to conduct aerial and ground surveys to measure total site methane emissions before injection resumed, and to report daily measurements to CalGEM after injection resumed.  

The order also required Southern California Gas Company to provide CalGEM with a work plan for completing a seismic risk study and for each well to either pass a battery of tests to potentially be eligible to resume gas injection or be taken out of operation and isolated from the reservoir. Wells that were isolated from the reservoir were ultimately required to be plugged and abandoned−that is, filled with cement and permanently sealed. 

Test results and abandonments related to Order No. 1118 have been completed. ​

• ​The leak’s direct cause was from a rupture of the outer 7-inch well casing due to external microbial corrosion from contact with groundwater.

• Southern California Gas Company did not conduct detailed follow-up investigations or failure analyses despite more than 60 casing leaks at Aliso Canyon between the 1970s and the October 2015 incident.  

• Southern California Gas Company lacked any form of risk assessment focused on well integrity management and lacked systematic practices of external corrosion protection and well surveillance through a real-time continuous pressure monitoring system.  
  
  

• identifying and assessing all modes of potential failure for gas storage wells,  

• evaluating consequences using quantitative risk assessment,  

• identifying, evaluating, and implementing protocols to prevent or mitigate identified hazards, 

• conducting a suite of mechanical integrity testing for each well to determine well integrity,  

• conducting ongoing monitoring of pressure, temperature and flow data,  

• submitting documents or reports for well integrity, testing, and monitoring results, and 

• plugging and abandonment procedures specific to underground gas storage wells. 

Further new regulations, Senate Bill 463: Chemical Inventory & Root Cause Analysis Regulations (Rulemaking), took effect July 1, 2025. These regulations require an operator to track in an inventory the chemicals that could be emitted from an underground gas storage well during a reportable leak, and address root causes identified in the Aliso Canyon SS 25 Root Cause Analysis by expanding the corrosion evaluation, mitigation, and monitoring requirements and requiring well-specific well control plans. 

CalGEM continues to inspect wells and production facilities for potential hazards and leaks, review well tests, witness abandonment operations, and review risk management plan submissions at Aliso Canyon and all other gas storge projects. Pursuant to Public Resources Code section 3185, CalGEM is also required to perform unannounced random onsite well inspections of some gas storage wells annually. Results of these inspections can be found through the CalGEM Underground Gas Storage Page.  

To view all current and past records, testing, and abandonments, please visit CalGEM’s Well Statewide Tracking and Reporting System WellSTAR. Short instructional videos on how to navigate within WellSTAR can be found here. 

The California Public Utilities Commission (CPUC) also has jurisdiction over aspects of underground gas storage operations. The CPUC has information about its actions and others have taken related to Aliso Canyon on its website. ​