FERC has approved Transcontinental Gas Pipe Line’s (Transco) request to abandon four of seven caverns at its Eminence Salt Dome Storage Field in South Central Mississippi.
On Dec. 26, 2010, Transco detected a large, unexpected pressure drop in Cavern No. 3 — 357 pounds per square inch in one minute. The pipeline determined that gas was leaking from the cavern. A few days later. on Dec. 31, it discovered that gas was escaping from the ground around the wellhead of Cavern No. 1. By Jan. 24, 2011, Transco told the Federal Energy Regulatory Commission (FERC) that it had taken Cavern Nos. 1 and 3 out of service and began filling Cavern No. 1 with water.
Transco, a pipeline subsidiary of the Williams Cos., said it retained the consulting firm of Subsurface Technology Inc. to conduct an overall evaluation of Cavern Nos. 1, 2, 3 and 4. Subsurface Technology concluded “that, given the age of the four caverns and their documented history and condition, including damage caused by salt creep, none of the four caverns should continue to be used for long-term natural gas storage services.” According to Transco, the consultant’s findings prompted it to seek the abandonment of the facilities.
In approving Transco’s abandonment request, the FERC order said the pipeline experienced a “catastrophic incident within Cavern No. 3, and that event affected the integrity of Cavern Nos. 1,2 and 4…Transco took immediate steps to contain the events at the Eminence Storage Field, and…shut-in three caverns (Cavern No. 4 was already shut-in and water filled).”
Transco noted that it ceased using Cavern No. 4 for service in 2004 and filled it with water when its well casing failed at a depth of 5,379 feet. Transco had originally planned to review the possibility of salvaging Cavern No. 4, but changed its mind based on the findings from Subsurface Technology’s report.
Transco estimated that it had lost 1,868,382 Dth of top gas as a result of the incidents at the Eminence Storage Field, but noted that the pipeline would not seek to recover gas losses from storage customers through the fuel tracker provisions in Section 38 of the tariff.
The storage field’s current capacity is 20.5 Bcf, of which 15 Bcf is working gas capacity. But with the abandonment of the four caverns, the total capacity of the storage field would drop to 15.025 Bcf, of which 10.05 would be working gas.
Transco estimates that abandonment activities will cost $76 million.
Following the abandonments, only Caverns Nos. 5, 6 and 7 will remain in service at the Eminence Storage Field. The pipeline proposed that FERC establish 3,600 psia (pounds per square inch absolute) as the certificate maximum operating pressure for Cavern Nos. 5 and 6, and 2,775 psia for Cavern No. 7.
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