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Hilcorp plans a new 3-D seismic survey in lower Cook Inlet area
Alan Bailey Petroleum News
Hilcorp Alaska has applied to the federal Bureau of Ocean Energy Management for a permit to conduct a 3-D seismic survey in the federal waters of lower Cook Inlet during the summer of 2019. The survey would take place within an approximately 374 square-mile area, about halfway between Kachemak Bay in the lower Kenai Peninsula and the Iniskin Peninsula on the west side of the inlet. Hilcorp purchased 14 leases in BOEM’s 2017 lower Cook Inlet lease sale - the area of the proposed 3-D survey appears to encompass eight of these lease tracts.
Prospective area The area of the survey is prospective for oil and gas. Although some distance south of the producing Cook Inlet oil and gas fields, the area is north of the Augustine-Seldovia arch, a geologic structure to the south of which the thick Tertiary rock sequence hosting the producing fields thins out. There are known oil seeps on the Iniskin Peninsula. In 2013 Hilcorp shot a 2-D seismic survey on the peninsula, following up on that survey with some on-land fieldwork.
Hilcorp has recently applied to the National Marine Fisheries Service for an incidental take authorization, to allow the unintended disturbance to marine mammals in lower Cook Inlet during oil and gas exploration and development activities over a five-year period. In addition to offshore 3-D seismic surveying, that application envisages a future offshore geohazards survey, and exploration and development activities on the Iniskin Peninsula in the summers of 2019 and 2020.
Seismic vessel, steamers and airguns Hilcorp anticipates contracting Polarcus Ltd. to conduct the planned offshore 3-D seismic survey. The survey operations would involve a seismic vessel towing eight to 10 recording streamers, approximately 1.5 miles in length about 26 feet below the sea surface. The streamers would be placed about 165 feet apart.
A dual airgun array would generate the seismic signals. The survey plan says that Hilcorp has opted to use the lowest possible sound source for the survey operations. The airguns would fire every 2.5 to 6 seconds.
There would also be one support vessel, to assist with the logistics of the operations. One or two chase vessels would monitor the in-water equipment and maintain a security perimeter around the streamers.
45 to 60 days to complete Active data collection would take about 30 days, but the survey program is expected to last for 45 to 60 days, depending on weather conditions and interruptions to accommodate marine mammal activity. Hilcorp has asked for permission to start as early as March 23, to enable the surveying to be completed in early summer. Presumably the actual start date would depend on sea-ice conditions in the inlet.
Survey operations will be active 24 hours per day, with the seismic array being towed at a speed of about 4 knots. The seismic vessel and its towed array would move parallel to the shorelines, into the tidal currents that characterize the inlet. Each data acquisition run would take three to four hours to complete. It would then take one to one-and-a-half hours to turn and reposition the vessel for the next run. Crew changes, by helicopter or support vessel, would take place every four to six weeks, Hilcorp’s survey plan says.
Assessment of environmental impacts Hilcorp’s plan includes an assessment of the survey’s potential environmental impacts.
The plan says that the shallow water depth, the soft seafloor and high levels of background noise from currents and glacial silt in the Cook Inlet limit the distance that sound tends to travel in waters of the inlet. But there are a number of marine mammal species that may be encountered in the survey area, including endangered Cook Inlet beluga whales and Steller sea lions. Hilcorp plans mitigation and monitoring measures that would minimize impacts of the seismic surveying on mammals. Those measures include, for example, the use of trained protected species observers and the implementation of exclusion zones, where the entry of a marine mammal would trigger an operational shutdown.
There are both commercial and sport fisheries in the Cook Inlet region. The plan says that sounds from the seismic surveying may temporarily displace fish from the area in which airguns are in use, but that fish will likely backfill the area rapidly, following the transit of the seismic vessel. Impacts on birdlife is anticipated to be limited and temporary, the plan says.
The plan also suggests that the surveying would likely have only a limited impact on subsistence hunting and fishing, with, for example, brief disturbance to marine mammals such as harbor seals.
- ALAN BAILEY
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