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Statoil and TGS plan Chukchi surveys Statoil wants modern 3-D seismic data to assess its Chukchi Sea leases while TGS plans a more regional scale 2-D survey on spec Alan Bailey Petroleum News
Since the $2.6 billion Chukchi Sea outer continental shelf lease sale in 2008, Shell and ConocoPhillips have led the charge to determine whether this remote region of the Arctic offshore holds the huge oil and gas resources that many people think exist beneath its often ice-covered waters. Now Norwegian oil major Statoil wants to conduct a seismic survey during the summer and fall of 2010, to start testing its 16 leases purchased in the sale — Statoil owns most of these leases in partnership with Italian major ENI, with Statoil as operator.
“We’re planning a 3-D seismic survey over those leases in this open water season,” Martin Cohen, exploration manager for Statoil, told the National Marine Fisheries open-water meeting on March 22.
And, at around the same time, geophysical company TGS wants to shoot a 2-D survey across a broad area of the Chukchi Sea, with the intention of subsequently licensing this regional-scale data to entities interested in the regional geology, Michaele Cerf, TGS acquisition and quality control project manager, told the open-water meeting.
3-D survey A 3-D marine survey involves bouncing air-gun sounds off subsurface rocks and then gathering the resulting echoes using water-borne microphones known as hydrophones, towed in a grid configuration. The recorded echoes enable the construction of detailed three-dimensional images of the subsurface rocks, so that oil and gas explorers can pinpoint underground oil and gas prospects as targets for exploration drilling.
In fact, the planning and design of a modern exploration well typically depends on detailed information gleaned from a 3-D survey.
In a 2-D, or two-dimensional, survey the hydrophones are strung on a single, long line, rather than across a grid, thus enabling relatively large areas of territory to be covered quite quickly. However, the resulting seismic images are not as detailed as those from a 3-D survey and are more appropriate to gaining an understanding of broad geologic features than necessarily to the planning of specific wells.
Cohen said that Statoil expects its 3-D survey to cover a total of about 915 square miles, with almost all of that area lying more than 100 miles from the coast. If time permits, and depending on ice and weather conditions, the seismic crew may follow the 3-D survey with a broader 2-D survey across the locations of some exploration wells drilled in the 1980s, Cohen said.
“The existing seismic data in the area are quite old — they’re quite sparse and widely separated and they’re of inadequate quality to carry out modern exploration,” Cohen said.
Fugro-Geoteam will conduct the survey work, planned for early August to early October, using survey vessel Geo-Celtic supported by two smaller vessels for marine mammal monitoring and for conducting crew changes, he said. All three vessels involved in the survey will carry marine mammal observers — air-gun operations would shut down if the seismic vessel comes too close to a marine mammal.
“The vessels will arrive in Dutch Harbor towards the end of July and we’ll then have a safety program on board the vessels for both crews that we plan to use,” Cohen said, adding that Statoil anticipates just a single crew change through Nome around early- to mid-September.
The seismic vessel will tow six arrays of air guns and 12 lines, or “streamers,” of hydrophones. This configuration involves more streamers than have been used to date in Chukchi Sea 3-D surveys but will somewhat reduce the total time required for the survey operation, Cohen said.
Acoustic monitoring Statoil anticipates participating in a subsea acoustic monitoring program already established by Shell and ConocoPhillips. This program involves the placement of arrays of acoustic recording devices on the seafloor to monitor the sounds of marine mammals and hence track their movements — Statoil plans to install a grid of acoustic recorders in the area of its leases.
The company hopes to improve the accuracy of future marine mammal monitoring by cross-referencing the results of vessel-based observations with the results of the acoustic monitoring, Cohen said.
Cohen said that since October Statoil has been discussing its plans with various Chukchi Sea stakeholders, including the North Slope Borough wildlife department and community leaders from North Slope villages. The company submitted applications for necessary approvals and permits in December. And earlier in 2009 Statoil hosted a visit to Norway by people from the North Slope Borough, giving people an opportunity to meet with Norwegian government officials and fishermen from northern Norway, to discuss how the Norwegians approach offshore oil and gas exploration and development.
Statoil is still considering its response to a subsistence hunting conflict avoidance agreement revised by the Alaska Eskimo Whaling Commission, Cohen said.
TGS survey The TGS survey will involve towing a single streamer, three to four miles in length, along about 3,100 line-miles of 2-D seismic lines across a broad swath of the Chukchi Sea. Some of the longer lines extending north-south through the region may take as long as two days to transit, Cerf said.
“We will have one seismic vessel that will tow one source (air-gun) array and one (hydrophone) streamer,” Cerf said.
TGS is using feedback from coastal communities to refine the exact positions of the lines that it expects to follow. As currently envisaged, all lines will be at least 50 miles offshore, but that minimum distance may prove to be too close to land and require adjustment, Cerf said.
The company has already reduced the planned strength of the air-gun array that will be used, and may yet decide to change that strength further.
And, although in a perfect world it might be possible to complete the survey in 30 to 35 days, factors such as ice conditions, the presence of marine mammals and the need to coordinate with other offshore operators will likely extend that timeframe. With Shell planning to drill in the Chukchi at around the same time and Statoil planning its seismic survey, TGS will meet with these two companies to make sure that their operations do not clash, Cerf said.
Five to seven weeks “We will start no earlier than July 22. More than likely it’s going to be around Aug. 1,” Cerf said. “… We have planned a five- to seven-week duration. That takes us from August to about mid-September. … We would like to be in and out as quick as possible but we are permitting to the end of October.”
In addition to the seismic vessel, the TGS operation will involve two scout vessels, with one of these vessels assisting the seismic vessel and monitoring the area relatively closed to the air guns, while the other scout vessel will be stationed further out, watching for wildlife. All vessels will have marine mammal observers on board.
“One neat thing about such a regional survey is that, as we collect this data on (wildlife) distribution and abundance, we’re collecting it over a very large area in the Chukchi Sea,” Cerf said.
And TGS plans to do refueling, resupply and crew changes through Nome — the vessels will not conduct refueling at sea. TGS has been discussing its plans with North Slope communities and has just received for review a draft subsistence hunting conflict avoidance agreement, Cerf said.
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