Judy Maksoud
International Editor
A recent survey off Nova Scotia has yielded more than 3,500 line km of new, ultra-deep 2D seismic data that could dramatically alter perception of the province's offshore.
According to GX Technology, NovaSpan is the first program of its kind covering offshore Nova Scotia and was specifically designed to provide a basin-wide understanding of the regional geology offshore.
If GXT is right about the value of this survey, NovaSpan will help geologists understand the overall architecture of the Scotian basin, which could significantly change industry's view of the region.
The big picture
"NovaSpan is really trying to answer the sorts of questions geologists get very excited about," Larry Scott, GXT's vice president of integrated seismic solutions, says. "We want to determine what happened millions of years ago, not just to find the container where oil lies today."
GXT is not doing a conventional 2D spec survey, which is a mapping type spread. "We're really trying to answer some fairly fundamental geologic questions," Scott says. The objective is an understanding of the overall basin architecture and how it evolved.
Though NovaSpan is not quite on a tectonic scale, Scott says, it lies between what an academic institution might do in trying to understand plate tectonics and what most operators do when they are trying to do detailed exploration. "This is one of the more interesting scales because it allows us to understand how the basin evolved over time and to determine if all of the ingredients that are needed for a productive petroleum system are present," he says.
According to Mark Noble, NovaSpan program manager, "NovaSpan is a truly revolutionary program because it provides exploration companies with a unique insight into the basin geology on a regional level. NovaSpan will provide an enhanced understanding of the Nova Scotia basin's tectonic and structural history, which will reduce drilling risks and uncertainties from the continental shelf to deepwater."
GXT has gathered new seismic data over offshore areas in Atlantic Canada that have never before been evaluated.
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The next step
NovaSpan is a framework for painting the bigger picture. The program could help to explain why drilling results have been disappointing in some areas. "NovaSpan will help us to understand if petroleum was generated and to infer where, in general, it would have gone," Scott says.
The complex geology off Nova Scotia presents imaging challenges. Drilling results have been disappointing, but that fact should be placed in context. It is still early days, in exploration terms, for Atlantic Canada.
Piers Gormly, vice president of marketing, draws a parallel between the exploration history of offshore Nova Scotia and the early days of the North Sea. "It was many years and many dry holes before the North Sea came onstream," he says.
Quite possibly, the promise of data generated by NovaSpan will encourage operators to stay the course off Nova Scotia and to uncover heretofore hidden reserves.
The team
Part of what GXT has brought to offshore Nova Scotia is the right combination of players to get the best data results, Scott says.
The team was put in place when the concept of NovaSpan was still in its infancy. "GXT hired consultants familiar with the area, got an understanding of the regional geology, and reprocessed existing data to understand the challenges," Scott says.
In the final program, GXT is providing imaging expertise and the ability to get those images at great depth, he says.
Other experts include the Geologic Survey of Canada, the Canada-Nova Scotia Offshore Petroleum Board, and Dr. Mark Rowan of Rowan and Associates. Together, they hope to arrive at a final product that will illuminate the history of Nova Scotia's offshore.
The data
NovaSpan includes data imaged to depths far below that of any previous regional seismic program, Scott says. "Existing data is very restricted in terms of its offset and record length." The deeper imaging provided by NovaSpan will allow a broader understanding of the region as a whole.
"We're imaging the basement and the source rock structure. We are trying to get a feel for the architecture and from that to infer how the deep structure has evolved so estimates can be made as to how and when it was buried, how petroleum was generated, and how it has moved," Scott says.
To accomplish that, GXT stipulated a cable length of 9,000 m and 18-second record length. The long offset and long record length combination is the longest cable and record length ever recorded offshore Nova Scotia and yields different information from a standard 2D survey.
Dr. Chris Willacy, who is responsible for the technical management and processing of this survey, points out that every aspect of the survey has been designed to take environmental noise conditions into account. He also notes that the flow for imaging is more consistent with an image-driven proprietary survey as opposed to existing standards for the non-exclusive market.
As an example, Willacy points to de-multiple technology, which has been applied to this data. Dealing with the varied and complex multiples has been the challenge in imaging the data, Willacy says. "We have achieved some remarkable results."
GXT planned to have much of the new data ready in August 2004. According to GXT, NovaSpan has elicited substantial interest from just about everyone working off of Nova Scotia. If the survey indicates the significant prospectivity geoscientists expect to see, operators will even have more reason to continue drilling.
