With three natural gas transmission pipelines down and Aliso Canyon underground gas storage operations limited, an updated assessment of winter energy supplies issued Tuesday indicated the Southern California region faces greater uncertainty than a year ago, with gas curtailments to large industrial users more likely.

The latest “Aliso Canyon Winter Risk Assessment Technical Report” was compiled by state energy agencies and the Los Angeles Department of Water and Power (LADWP). Officials concluded the biggest new hurdle for the gas-dependent region is the absence of the Southern California Gas Co. (SoCalGas) transmission pipelines, a factor that is coming to light belatedly, considering that one of the idled lines ruptured Oct. 1 and now has an “uncertain” future in terms of its return to service.

“The uncertain return to operation of that pipeline raises significant concerns,” said the report, which was previewed the California Energy Commission (CEC) and California Public Utilities Commission (CPUC) at a press briefing on Tuesday.

Officials predict that supplies from Aliso Canyon, the state’s largest gas storage facility, will be needed this winter.

“Under extreme cold weather events, there may be insufficient gas supplies to meet demand even relying on withdrawals from all of the other storage fields,” the report noted.

Spot market prices at SoCal Citygate reported in NGI’s Daily Gas Price Index survey have proved exceptionally volatile in recent weeks, with frequent day/day moves of more than $1.00/MMBtu. Anxiety over potential supply shortages has manifested in NGI’s Bidweek and NGI’s Forward Look prices as well, with potential December demand increases looming on the horizon.

Bidweek trades at SoCal Citygate surged as high as $7.55/MMBtu Tuesday and have averaged $6.19 through three days. Meanwhile, fixed price forwards at SoCal Citygate jumped 10.21% day/day Monday and averaged $6.374 Tuesday, according to Forward Look.

SoCal Citygate prices for December have now surpassed the perennially constrained Algonquin Citygate, where fixed price forwards traded at $5.887 on average Monday, Forward Look data show.

“It makes sense that December would be coming in higher given the continued restrictions at those import points and the continued limitations at Aliso, when also considering that December and January have historically been two of the most significant demand months for SoCal,” Genscape Inc. analyst Joseph Bernardi told NGI Tuesday.

“Other than the continued unavailability” of imports through Otay Mesa, “which had previously served as an outlet for SoCal to continue receiving some rerouted Permian Basin molecules, we aren’t seeing any additional current maintenance events.”

Noting that the utility is reviewing the latest assessment, a SoCalGas spokesperson said federal, as well as state and local regulators, have expressed concerns about energy reliability this winter in Southern California.

“Last month we expressed our concerns about state policy decisions that limit the use of local natural gas storage and enhance the risk of service interruptions this winter,” she said.

Factoring in the same 4.5 Bcf/d maximum SoCalGas system sendout, the latest assessment lowers that overall sendout capacity by 200 MMcf/d to account for the fact that the SoCalGas Line 2000 operates at lower pressures, and adds further reductions caused by the Line 235-2 rupture and its simultaneous damaging of nearby Line 4000.

“The resulting outages further reduce maximum system capacity by 800 MMcf/d, decreasing maximum system sendout to 3.56 Bcf/d,” according to the updated assessment. In addition, maintenance work at one of the remaining underground storage fields through Dec. 18 further reduced the maximum sendout another 260 MMcf/d to the 3.3 Bcf/d level.

SoCalGas expects Line 4000 to return to service Dec. 30, which would bring back 350 MMcf/d to overall sendout capacity, but it has not provided an estimate on the ruptured Line 235-2, the update said.

As a result, the Sempra Energy gas-only utility has implemented two mitigation measures. It plans to temporarily increase interruptible capacity by 150 MMcf/d at its Kramer Junction interstate interconnection point and use full capability at its Southern Zone interstate interconnection point at Otay Mesa at the southern end of the state near the Mexican border.

By the start of the new year, SoCalGas expects to have overall sendout capacity of 4.1 Bcf/d without relying on any supplies from Aliso Canyon.

The California Independent System Operator joined the CEC, CPUC and LADWP in completing the latest assessment, their fourth since Aliso Canyon was shut down by a massive storage well leak two years ago.

“Our natural gas system was designed to use our storage facilities — including Aliso Canyon — to mitigate reliability risks, maintain reliable service during unplanned equipment/pipeline outages, like the ones we are facing this winter, and help ensure uninterrupted service to all our customers,” the utility spokesperson said.

“Southern Californians have played a role in timely reducing energy use in past peak-demand seasons, and they will be called upon again,” said CEC Chair Robert Weisenmiller.

CPUC President Michael Picker said it was unclear if similar actions this coming winter would be enough to avoid gas service curtailments to noncore customers in Southern California. There are no concerns about the issues causing any residual shortages in Northern California. So far, Pacific Gas and Electric Co.’s gas operations have been unaffected.