Oil spill is solved
Hilcorp says spill in water next to Anna platform came from flare system
Hilcorp has solved the mystery of an oil spill that happened at the Anna platform in the Cook Inlet on April 1. Apparently the oil had come from the platform’s fuel gas flare system, following a jolt to the platform caused by ice on the water of the inlet.
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After isolating the fuel gas flare on the platform for maintenance, an alternative fuel gas source for the pilot was drawn from an adjacent well, David Wilkins, Hilcorp Alaska senior vice president, has told Petroleum News. Then, during the repair, small amounts of liquid hydrocarbons were able to drop out and accumulate in the flare system. Later, when the platform was jolted by ice, the fluid was forced out of the flare system line and into the water of the inlet, Wilkins said. Hilcorp estimates that less than three gallons of oil was released, he said.
Hilcorp has taken corrective measures and, in future, to prevent a re-occurrence, the company will use a gas source upstream of the fuel gas scrubber for this type of operation, Wilkins said.
Hilcorp had originally thought that the leak originated from a subsea pipeline between the Anna and the Bruce platforms. But divers determined that the pipeline was intact, a finding confirmed by the successful pressure testing of the line. And the incident management team assembled to respond to the leak stood down while Hilcorp continued to investigate the cause of the leak.
Gas leak stoppedMeanwhile divers have successfully stopped the release of gas from the subsea pipeline that supplies fuel gas to Hilcorp’s Middle Ground Shoal field on the west side of the Cook Inlet. The divers fitted a clamp over a gash in the line that had been causing the leak, Hilcorp Alaska announced April 14. Hilcorp discovered the leak in early February and in late March shut down the oil field, to enable the gas pressure in the line to be reduced to a minimum level. The company has said that it will not return the gas line to service until the completion of a permanent repair, the conducting of pressure testing of the line and the approval of the restart by government regulators.
Hilcorp had been unable to commence repair operations until winter sea ice in the inlet had receded sufficiently to enable safe diving operations.
Multiple diving operationsThe company said that locating the leak and preparing the gas line for repair involved 12 diving operations. The leak point was found to be on the bottom of the pipeline, where the line rested on a boulder embedded in the seafloor. A visual inspection suggested a breach about 2 inches long, but exact measurements determined an actual size of three-sixteenth inches by three-eighth inches, Hilcorp said. After cleaning and preparation of the damaged area, divers installed a steel and rubber clamp over the leak, thus assuring a gas- and liquid-tight seal that will reinforce the pipeline, Hilcorp said. According to the Alaska Department of Environmental Conservation, dive boat operators confirmed that the bubbling of gas from the leak stopped after the clamp had been installed.
The federal Pipeline and Hazardous Materials Safety Administration has expressed concern about the condition of the subsea pipeline that delivers oil from the Middle Ground Shoal field to onshore. The oil line is of similar construction to the gas line and both lines are 8 inches in diameter. PHMSA has said that previous issues with damage to the subsea pipelines in the area appear to have resulted from the vibration of the lines against rocks on the seafloor, as a consequence of water currents in the inlet. The agency wants Hilcorp to inspect the oil line for damage.
Hilcorp said that it has provided details of the repair operation on the gas line to both ADEC and PHMSA. The company said that it was going to conduct further inspections and stabilization of both the gas and the oil pipelines, as weather permits.
“Neither pipeline will be returned to regular service until Hilcorp, along with state and federal regulators, agree it is safe to do so,” Hilcorp said.
Environmental samplingAccording to ADEC, Hilcorp has been conducting air sampling in the area of the leak to test for the presence of methane, carbon dioxide and volatile organic compounds. The damaged pipeline carries fuel gas, consisting of almost pure methane. However, the line had previously been used to carry oil. Hilcorp has also been conducting water sampling in the area of the leak, to check for concentrations of methane and dissolved oxygen in the water. And on March 24 Hilcorp initiated sampling to monitor methane, carbon dioxide and oxygen levels at the water surface, ADEC said. Hilcorp has been delivering reports from its sampling operations to ADEC.
The company is also investigating a metering discrepancy for gas flowing through the gas pipeline that connects the Steelhead platform to shore.
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