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Ion doing early winter Beaufort survey Company using in-ice technique to gather offshore basin-wide seismic data after the end of the fall subsistence whaling season Alan Bailey Petroleum News
Ion Geophysical is carrying out an early winter 2-D seismic survey in Alaska’s Beaufort Sea using a technique that the company has developed for gathering offshore seismic data in sea-ice conditions. The survey will cover the entire length of the Beaufort Sea and is designed to enable deep, basin-wide imaging of the regional offshore geology.
“The work’s progressing in good ice conditions,” Joe Gagliardi, vice president Marine-GeoVentures for Ion Geophysical, told Petroleum News Nov. 1.
In-ice system In 2006 GX Technologies, a division of Ion, conducted a regional survey in the U.S. Chukchi Sea during the summer open water season using conventional marine surveying techniques. But the company later decided to rethink its method of collecting seismic data in the Arctic and developed the in-ice system that it is now using. The company has successfully used the technique in ice-laden waters offshore Greenland and Canada.
The in-ice system enables Ion to gather seismic in the early winter, after the winter sea ice has started to form, thus enabling the company to avoid conflicts other offshore activities, especially subsistence bowhead whale hunting.
The company had originally planned to conduct its Alaska Beaufort Sea survey in 2010 but deferred the survey both that year and the following year.
The survey, conducted by seismic vessel the Geo Arctic, supported by an icebreaker, started in the second half of October and could continue until Dec. 15. Ion is starting its survey at the eastern end of the Alaska Beaufort, moving progressively west and eventually shooting a couple of seismic lines across into the northern Chukchi Sea — Ion planned to survey the eastern part of the Beaufort, to the east of the Colville River Delta, in October, moving to the western part of the Beaufort in November, after the Barrow bowhead whale hunt. The Chukchi Sea lines will enable the images from the 2006 Chukchi Sea survey to be correlated with the new images from the Beaufort.
Survey technique In a marine seismic survey a seismic vessel tows arrays of air guns that periodically discharge sound through the ocean water and into the rocks below the seafloor. The vessel also tows “streamers” of special microphones called hydrophones that detect echoes from the air-gun sounds, reflected from rock strata deep below the seafloor.
According to the Bureau of Ocean Energy Management’s environmental assessment for Ion’s Beaufort Sea survey, the in-ice system involves towing a single streamer, either 2.8 or 5.6 miles long. Equipment attached at intervals along the streamer will maintain the streamer at a depth of about 31 feet below the surface, thus enabling the streamer and geophones to run below the bottom of any sea ice. An icebreaker moves ahead of the seismic vessel, clearing a route through the ice. Ion has said that the system can operate in conditions where ice covers up to nine-tenths of the sea surface.
Wildlife monitoring The environmental assessment says that wildlife observers on the vessels will monitor for marine mammals during daylight hours. Night vision equipment will be available to watch for wildlife after dark. And the icebreaker has an infrared imaging system for detecting seals and polar bears on the ice. Ion has said that it will not ramp up the survey air guns after dark unless it has established that there are no marine mammals within appropriate exclusion zones around the guns.
The Bureau of Ocean Energy Management, or BOEM, has determined that the seismic program will have negligible environmental impacts. In the environmental assessment BOEM says that many bowhead and beluga whales and other marine mammals will already have departed the survey area for the winter at the time of the survey. Polar bears and seals which live on and around the ice during the winter could experience small and temporary disturbance from vessel noise and seismic sound, BOEM says in a finding of no significant impact. And the overall impact of the seismic operations on sea ice, the polar bear’s critical offshore habitat, would be slight, given the small area of ice affected and the relative rapidity with which ice would reform behind the vessels conducting the survey, BOEM says.
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