Geophysical companies continue to demonstrate they’re going after the latest ‘n’ greatest when it comes to seismic data acquisition applications.
Creativity and innovation abound as new technologies, e.g., land node systems, roll out along with advanced applications for existing equipment, such as those hulking seismic vibrator machines.
In fact, Global Geophysical Services established some industry firsts on its recently completed 2,800-square-kilometer land seismic data acquisition program for BP Oman.
The application of a BP technology “Distance Separated Simultaneous Sweeping (DS3)” as the vibroseis recording methodology coupled with a modified slip sweep technique and Sercel’s state-of-the-art 428/464 instrumentation – enabled a record setting survey for a land seismic crew, according to Global president Richard Degner, an AAPG member.
“We provided a new world record for productivity for a land seismic crew,” Degner said. “Our best day was 12,200 VPs (vibrator points), and we averaged 50,000 VPs a week – these numbers are unheard-of.
“It’s just, frankly, staggering,” Degner exclaimed. “In terms of progressive vibroseis applications, this thing is rewriting the book.”
Simultaneous Shaking
Simply put, DS3 is a high efficiency vibroseis technique whereby two or more vibrators record seismic data at the same time.
In addition, multiple fleets of these separated vibrators can utilize slip sweep techniques, where one vibroseis cycle slips over the top of another one.
“Vibrators customarily shake in sequence one after the other,” said Maurice Flynn, Global’s vice president for Europe, Africa and the Middle East.
“With this source separation technique, you record multiple VPs at the same time,” he said, “and by incorporating slip sweep you start another vibrator fleet before the first is finished. It’s just another way of getting more productivity in a given amount of time.
“We utilized 15 vibrators on the project deployed in five fleets of three, with the three vibes in each fleet separated spatially by 12 kilometers, and one cluster of three vibrators shaking simultaneously at any one time,” Flynn added. “By maximizing the number of vibrators you have out there, there’s always one fleet ready to start shaking.
“In addition, if you slip it – in other words, it starts shaking at a given time – into another vibrator’s sweep then you’re double dipping on the time,” he said.
“You basically have parts of two VPs – or in this case, six VPs – being shot simultaneously.”
‘A Big Area’
The 15 vibrators on site were separated by a distance of as much as 24 kilometers. While one was shaking, another was shaking 12 kilometers away and a third one 24 kilometers distant – the distance allowed for the data recorded from each vibrator not to interfere with each record.
“Slip sweep historically has been limited to two fleets of vibrators shaking at any one time,” Degner said. “In this case we treated 15 vibrators each as their own fleet, enabling Global to break 12,000 VPs in a day.”
The crew operated on a 24-hour basis for the last four months of the five-month project – the first time for a crew in Oman to be operational around the clock, according to Flynn. The HSE guidelines were in place to enable the continuous operation that proceeded without incident.
The round-the-clock operational time in combo with the DS3 and slip sweep methodology enabled the crew to maximize the number of VPs within the time period, Flynn said.
The crew recorded into almost 8,000 live channels deployed over 180 square kilometers, which he emphasized “is quite a big area over which to maintain an active recording spread.”