The natural gas storage well that has leaked for weeks at California’s largest underground gas storage facility is being plugged and eventually will be abandoned in the days ahead, but it is only one of 115 similar wells at the Southern California Gas Co. (SoCalGas) 86 Bcf Aliso Canyon underground site that was once a producing oilfield.

Dealing with the rarely occurring leak comes at a time when the Los Angeles-based Sempra Energy gas utility finds itself in the middle of a multi-year, multi-million-dollar effort to upgrade its underground storage fields around Southern California.

The facility is a key part of the SoCalGas infrastructure that serves the largest contingent of retail natural gas consumers in the nation and it is within a mile of the Los Angeles suburban sprawl 35 miles northwest of downtown. Utility officials have given a detailed description of efforts to pinpoint the leak, diagnose the options for stopping it and establish an implementation plan, erring on the side of caution because large volumes of gas are involved.

With no imminent public safety or public health risks since discovering the well leak Oct. 23, SoCalGas and outside well control experts have worked methodically to control the problem. Once the utility engineers had a clearer understanding of the situation, they called in experts, including Halliburton Inc.’s Boots and Coots.

“Because these wells can be thousands of feet below ground, it is a complex process,” a SoCalGas spokesman told NGI. “Safety is our first priority in any gas leak situation, and we are working as quickly as safety [considerations] will allow to stop the flow of the gas.”

Last Friday, three weeks after the leak was discovered, SoCalGas and the well control experts decided they would cut off the gas flow with a heavy brine solution. Once the leak is stopped, they plan to cement the well at its base 8,500 feet below the surface and cap it.

The well was drilled in 1953 when the field was producing commercial quantities of oil, and it was converted to storage in 1973 when SoCalGas developed the Aliso Canyon facility. It sits at a 3,000-foot elevation in the Santa Susana Mountains. The casing inside the well was last replaced in 1979, and the well was inspected in October 2014, not showing any problems at the time, according to the spokesman.

In addition to a $200 million program to expand Aliso Canyon’s injection capacity by 150 MMcf/d two years ago (see Daily GPI, Nov. 18, 2013), SoCalGas currently has a $180 million, six-year proposal to spend additional funds on both operations/maintenance and capital investment in underground storage facilities, which collectively represent 137.1 Bcf of capacity.

The storage integrity management program (SIMP) is similar to what’s being done with pipeline systems in the state, the multi-year effort will identify and prioritize risks and then repair or replace infrastructure to mitigate the risks.

SoCalGas has estimated it would take $5.6 million annually for operations and maintenance, and another $24.2 million annually for capital improvements. “The six years is the estimated time required to inspect all of the wells and mitigate any identified conditions,” the spokesman said.

Asked how SoCalGas officials are sure there aren’t other leaks ongoing at Aliso Canyon, the spokesman said leaks “are not common; the these types of events are very rare.” Eventually, the cause of the current leak will be identified, he noted.

The site remains a key part of “an integrated natural gas energy storage infrastructure,” and the old oilfield where it is located also includes 19 active oil-producing wells, but they do not have access to the storage zones in the field.

So far this year, the producing wells have averaged 111 b/d per well, equating to overall production of 35,888 bbl, the spokesman said.

Aliso Canyon’s three 1970s-era gas compressors are being replaced with electric motor-driven compressors, but they would not be installed until additional electricity infrastructure is built on the site.

Last week, utility and third-party well control crews began pumping heavy brine into the leaking well to eventually smother the gas flow, but that work had to be curtailed earlier this week in response to high winds that raked Southern California as part of a Pacific storm system. The process should take a few more days when conditions allow resumption of the work, the spokesman said.

“We brought in the leading experts in well management,” he said. “SoCalGas works with several different kinds of consultants, including engineering and electrical specialists, for expertise in relevant fields. In this case, one of the experts we brought in is an expert in well containment.”