Dolphin and Shell to Rewrite Seismic Record Books of Orange Basin, South Africa
Dolphin Geophysical really needed to ‘think big’ for its recent 3D seismic survey with super-major Shell in the Orange Basin, South Africa. A huge survey area and limited timeframe led the Norwegian firm to adopt a radical approach to get the job done – it created, and successfully operated, the ‘world’s largest floating object’.
Dolphin, working with Shell for the first time, won the task of surveying an 8,000km2 deepwater basin, lying between 150 and 250km off the western coastline of South Africa, in July 2012. The potential in this under-explored sector, with evidence of source rocks suggesting possibilities of significant oil and gas deposits, is huge…but so are the challenges in realising it.
The weather is key. Bad weather, and there’s no shortage of that locally, can create serious safety issues for seismic vessels and equipment. In addition, surface (wave) disturbances disrupt the operation of vessel streamers and impact upon data quality, creating unwanted noise.
Dolphin’s team therefore had a limited weather window of four months to operate in. They decided that, in this particular case, size matters.
On October 25th 2012 the Polar Duchess mobilised with a configuration of seismic equipment that had never been seen before.
The firm created the ‘world’s largest floating object’ – eight streamers measuring 8km in length and separated by a distance of 200m, constituting a moving width of 1.4km of equipment through the water. As such the total area of the apparatus being towed by the Duchess was 11.2km2 (or the surface area of roughly 1,569 football pitches). Prior to this point the largest surface area of streamer equipment that had been utilised was between 8 and 9km2.
Phil Suter, Dolphin’s VP Marketing and Sales, explained the thinking behind the bold move: “In order to get 8,000 km covered in the limited weather window we needed as wide a tow as possible.”
“If we’d attempted this with a standard streamer configuration, of say 100m separation, it is unlikely that we would have got anywhere near the number of square kilometres covered in the same timeframe.”
The immense power of the Polar Duchess – propulsion of 2 x 7100kw (engine shaft power) and a bollard pull capacity of 210 tonnes – meant that, unlike the huge majority of seismic vessels, it could tackle the challenges of successfully navigating this heavy, wide-tow configuration through the water. Meanwhile, the processing capacity of Shell, working from its base in Houston, ensured that the best quality results could be interpreted from the acquired data, despite the fact that the streamers were so far apart.
“It really was a powerful partnership, leading to fantastic results in what was a very demanding project,” states Suter. “We, and Shell, are extremely happy with one of the first true, exploratory, wide-tow 3D surveys.”
Stuart McGeoch, Shell’s Regional Ventures Exploration Manager, Sub-Saharan Africa, adds: “Despite the remote nature of the area and the challenging metocean conditions, the survey has been executed safely, efficiently and with a low down time. We have been impressed with the quality of acquisition data.”
He concludes: “A significant contributor to this was the focus provided by Dolphin’s management team on this survey and the high quality of communication with Shell’s operational team.”
As a result of this successful first survey, Dolphin Geophysical has now entered into a three-year call-off agreement with Shell in Europe.
The two are looking forward to more large-scale success together in the near future.
Project in brief:
What: 3D seismic survey of an 8,000km2 deepwater basin, lying between 150 and 250km off the western coastline of South Africa. Conducted by Dolphin Geophysical’s Polar Duchess vessel for Shell.
When: October 2012 to February 2013.
Solution: The Polar Duchess pulled an 11.2km2 configuration of seismic equipment to acquire data within a limited window of opportunity. 11.2km2 is equivalent to the area of approximately 1,569 football pitches, or the combined surface area of three Vatican Cities, two Principalities of Monaco and two Cities of London.
Press Release, March 22, 2013