Often the mere mention of transition zone (TZ) 3-D seismic surveys brings to mind oppressive heat, mosquito swarms and other unpleasant thoughts.
After all, many of these surveys occur along coastal zones in various parts of the world where heat, humidity and predatory critters can make life miserable for seismic crews much of the year.
But is this worse than the challenge posed by acquiring data in a frozen TZ?
It’s likely a toss-up.
There was ice aplenty for MGM Energy’s TZ 3-D program conducted during the winter of 2007-08 in the Canada’s Mackenzie Delta region, Northwest Territories, including portions of the Ellice and Langley islands, Mackenzie River channels and the shallow Beaufort Sea.
The 144-square-kilometer survey, dubbed the North Ellice 3-D, was located on the northwest edge of the Mackenzie Delta, with the TZ between onshore and offshore frozen during acquisition.
The data were acquired during a 111-day stretch beginning Dec. 10, 2007. Field operations kicked off the previous September in order to pre-position the equipment and camp prior to freeze-up of the Mackenzie River.
Over the course of the survey, about 65 percent of the source points were dynamite shotholes drilled through floating sea ice, according to Fred Kierulf, geophysicist at MGM.
Vibroseis was used on land.
Once a survey is completed in this part of the world, operators submit a report to the government describing the work accomplished and how it was done. In other words, the parameters of past surveys are all in the public domain.
“This is not high tech, but it’s a tough environment, so we have to use proven technology,” Kierulf said. “It’s an area where technology continues to develop based on everyone’s input.
“We read about all that had been done and used all the hard work that had already been done in the Delta,” he noted. “There are about a hundred past surveys we read through to see what the guys did and problems that were encountered.”
He likened it to heading out to wild, wooly parts of the world, reading journals of those who went before.
There are only a couple of seismic operators in this area, and they bring all their skills to this challenging part of the world.
“Everyone uses the same group of guys who know the equipment that works there as there are not a lot of options,” Kierulf noted. “It’s not state-of-the-art, but it’s close.”
A Short Window
The end product is good quality seismic data, but the effort required to get there appears to be almost archaic in these times when business – owing to all the high tech electronic communications gadgets and gizmos – sometimes is accomplished essentially in an instant.
“Getting the information organized and down from north of the Arctic Circle to the computers that can process it takes a long time,” Kierulf said. “We were shooting in February and March and had to decide before the middle of summer where to drill the wells the next year.”
He emphasized there are only a few winter months to acquire seismic and to drill wells. Not only do sensitive species use both land and marine portions of the area in the summer, but drilling crews need to exit the ice before it begins melting.
“There’s time pressure to get it all done and to get the tapes and such down from there on a weekly flight,” he emphasized. “The processing had to be done quickly, and this is harder to do when there are long distances involved and you don’t have the Internet.
“We were essentially trying to do real time processing even though we had to wait for the tapes to come down almost by dog sled,” Kierulf commented humorously.
He explained that Internet access of a sort actually was available, emphasizing that the connection shared by 150 people was like a dial-up, which was not conducive to sending shot records.
In fact, everyone there was completely out of touch with the world for days at a time during big storms.
‘Ugly Seismic’
In its raw state, Kierulf said the acquired data doesn’t look like seismic from anywhere else. Not surprisingly, there were significantly different seismic responses recorded on the ice compared to data collected over the islands.
“It’s ugly seismic with strange noises,” he noted, “and you can’t just run it through standard computer processing. You must spend a lot of time to make it look good yet rather quickly.”
The seismic data processing was contracted to WesternGeco, and Kierulf had high praise for the processing folks, emphasizing that they did a great job.
MGM has drilled two wells based on the processed seismic, but they failed to encounter significant hydrocarbons. A third well went down based on earlier seismic data; it was a gas discovery.
There have been commercial discoveries in the region, but they await development seeing as how the product can’t be sold because construction of the Mackenzie Gas Project Pipeline has been delayed repeatedly, according to Kierulf.
He noted that a consortium of the majors is going through regulatory and environmental reviews to build a pipeline.
Meanwhile, MGM intends to go back later to drill, as they believe there are other opportunities based on the 3-D seismic just acquired – but absent the pipeline, there’s no rush.
As Kierulf said: “We’ll wait until there’s a better economic reason to do it.”