In response to a continuing natural gas pipeline leak under Cook Inlet, Hilcorp Alaska has shut in its Middle Ground Shoal oil field, the company has announced.
“Shutting in wells and idling lines and equipment in very cold temperatures creates a known risk of freeze up and potential rupture,” Hilcorp said March 25. “Warmer ambient temperatures now permit a safer shut in process of the wells along with the associated lines and equipment.”
The shut-in procedures were completed over the weekend of March 26, company spokeswoman Lori Nelson told Petroleum News in a March 27 email. With the gas pipeline operating at a reduced pressure of just 65 pounds per square inch, the leakage rate is now estimated to be in the range of 85,000 to 115,000 cubic feet per day, Nelson said.
Gas flow had been slowed
Having discovered a breach in the pipeline that supplies fuel gas to the field’s offshore platforms, the company had already stopped non-essential operations on the platforms, so that the pressure in the fuel line could be reduced. The company had been reluctant to completely shut-in the field. Given the cold winter conditions in the inlet, stopping the flow of oil through the subsea oil export line from the field posed the risk of the oil line freezing and thus incurring damage to the line. At that point the gas line was leaking at rate of about 229,000 cubic feet per day.
After discussions with Gov. Bill Walker and the Alaska Department of Environmental Conservation, the parties involved agreed on a reduction of the pressure in the gas line to 65 pounds per square inch, a pressure level that necessitates shutting in oil production from the field, the company said.
According to a press release from Gov. Walker, Hilcorp executives committed to the governor that they will not start production at the platforms again until federal and state regulators are satisfied that the oil and gas lines can be operated safely, in accordance with all applicable laws.
“I appreciate that the company officials are implementing a prudent plan of action,” Gov. Walker said. “Alaskans want peace of mind that our waters are protected.”
Nelson said that pumps are circulating filtered sea water through the subsea oil pipeline from the field to eliminate the risk of that line freezing up.
Preparing for repair
Hilcorp plans to send divers down to repair the broken gas line but has not yet been able to do so because sea ice conditions in the inlet currently render diving operations unacceptably dangerous. Based on current weather forecasts and ice conditions Hilcorp anticipates mobilizing equipment and deploying divers to begin repair operations within the next 10 days, Nelson said.
Meanwhile the company has been implementing a plan of environmental sampling and monitoring, to gauge any environmental impacts from the leak.
The federal Pipeline and Hazardous Materials Safety Administration has proposed two orders relating to the pipeline leak. The first order would require Hilcorp to repair the leak by May 1. The second order would require the company to conduct an inspection of the subsea oil pipeline, to ensure that the oil line is not also damaged. PHMSA has suggested that the likely cause of damage to the gas line is abrasion against rocks on the seafloor.
