Evidence abounds that industry interest in nodal seismic technology continues to escalate – for both land and marine applications.
There’s a wow factor here – even though the concept of autonomous ocean bottom seismograph data acquisition is somewhat old hat.
It originated decades ago in both academic and government circles, prompted by their interest in deep crustal studies and nuclear test monitoring, respectively.
Many years later, in the late 1990s, SeaBird Geophysical developed the first commercial autonomous OBN (Ocean Bottom Node) system.
FairfieldNodal has played a high-profile role in the commercial development of autonomous OBN seismic technology, following years of experience manufacturing and applying systems that initially were nodal only in concept.
Today, its efficient yet complex no-cable nodal systems are quite straightforward in application.
The autonomous battery-powered nodes are deployed on the seabed or dry land, where they record data continuously for pre-determined lengths of time before being retrieved to download and QC the acquired data prior to redeployment.
With no cables to contend with and the flexible deployment capability of the autonomous nodes – even in the marine environment, via remotely operated vehicles – the nodal seismic systems are designed to meet a number of needs, according to Keith Matthews, sales director, systems division at FairfieldNodal:
- More flexible acquisition geometries, e.g., wide and full azimuth for land surveys.
- Reduced downtime and maintenance.
- Improved depth imaging.
- Increased productivity.
- Insignificant footprint.
“I think we’re headed for a non-cable land world in 10 years or less,” Matthews predicted. “I expect a big chunk of the industry to switch to nodal systems without cables in that time frame.”
Thus far, marine nodal seismic surveys have been implemented in the Gulf of Mexico, West Africa, North Sea and the Middle East.
“From my personal reading of the tea leaves, I see interest in nodal technology picking up, with four early adopter majors – Total, Chevron, BP and Shell – obviously having an interest in it and leading the way,” said Bob Rosenbladt, Shell’s geophysical operations team leader-Americas.
Autonomous nodal seismic acquisition attracted considerable industry attention in 2005 when FairfieldNodal’s no-cable Z3000® marine deepwater system was first used for commercial application at the BP-operated Atlantis Field in the deepwater GOM.
Shell hopped onto the commercial nodal bandwagon in 2007, deploying the same deepwater system at its Deimos Field in about 1,000 meters of water in the GOM. The successful 3-D program included a small scale 2-D node repeatability study, aptly demonstrating that OBN data acquired with autonomous nodes exhibit repeatability, making them ideal for 4-D implementation.
“The uptick in the data quality was greater than originally expected,” Rosenbladt said. “We were thinking about the long offset and wide azimuth helping with illumination issues subsalt, and it turned out noise suppression characteristics were better than expected.”
Shell also used the deepwater system to conduct a seismic survey in the Mars area in the GOM and now has the crew working elsewhere. The core part of the Mars area program was a 4-D monitor survey that extends over a larger area than the original survey.
“Because you can replace those nodes back very accurately, it works nicely for 4-D applications as compared to streamer applications,” Rosenbladt noted.
“We’re seeing in many areas that nodal is cost effective and highly desirable, and what we’re seeing looking down the road is if you can drive costs down, there will be even more areas of application,” he said. “The more you get the costs down, the more fields where it will be economic.”
OBN costs have proven to be acceptable at the development or appraisal scale in most instances, and they also can be crucial assists in exploration surveys, e.g., where a platform sits in the middle of a survey area restricting access.
But when it comes to competing with the costs of large-scale streamer WAZ surveys over, say, 200 OCS blocks, nodal technology is not there – yet.
“It will take a step change to compete with streamer on something like that,” Rosenbladt said. “But it’s still an evolving technology, and we’re all learning.
“It’s a big aspiration to see nodes used for large exploration areas, and we’d like to see if that can be made to happen,” he said. “That’s what we call a stretch goal.”
Something For Everyone?
If you’re fretting that nodal seismic data acquisition might be beyond your reach, it ain’t necessarily so.
“The big boys get to play first,” Matthews noted. “But we already see an increase in the number of smaller companies starting to see the benefit of using nodes.”
This is especially true on land, where the use of no-cable nodes in particular means absolutely no troubleshooting. This translates into faster shooting and higher productivity, resulting in lower overall cost and the potential for fewer HSE incidents.
A number of nodal land systems are available to industry. Bearing designations that include no-cable, cable-free and cableless, these systems include FairfieldNodal ZLand® system, ION FireFly®, Sercel UNITE, Ascend Geo Ultra, and OYO GSR.
Unobtrusive nodes are particularly suited for congested, environmentally sensitive urban environments.
An example is the recently completed successful 2-D survey in the midst of the Long Beach and Signal Hill municipalities in California. Signal Hill Petroleum employed the no-cable ZLand® system there, using buried nodes to record over a part of the giant Long Beach/Signal Hill oil field, where it is the principal operator. (See October 2009 Explorer.)
Both civic officials and residents expressed approval at the conclusion of the project.
Survey operator SISCO then moved on to acquire both a 4-D and a surface micro-seismic survey for another client in a different geographic area. An identical system was used to acquire the high resolution, closely spaced data near two wells that were being perfed and fraced.
Look for land nodal seismic systems to be in higher demand as the BLM tightens access to certain locales – particularly in the Rocky Mountain region, where the agency controls considerable acreage attractive to the industry.
“The BLM just issued new restrictions for archaeological areas, where they really don’t want crews on the ground at all,” Matthews said. “It’s getting tougher to get permits for seismic crews because of these sites, and a lot of crews have professional watch crews to be sure they don’t disturb archaeological sites.
“The land permitting challenge is in addition to complying with restrictions such as mating season for grouse, worm reproduction and other such issues,” Matthews added.
“It’s easier to get permits with minimal impact no-cable nodal systems rather than using external geophone strings, cables and such as these things pile up, increasing the chance for damage,” he noted. “A no-cable nodal seismic system is very low impact as you only make two passes because of the way of deploying and retrieving nodes.”
‘Smaller, Lighter, Cheaper …’
If you think urban environments and issues such as ancient remains, wildlife hanky-panky, etc., discourage the use of cable acquisition systems, consider the jungle.
Imagine carrying copious amounts of heavy cables and equipment into these areas of dense vegetation.
Surveys using lightweight nodal systems comprised of fewer pieces of equipment require fewer crewmembers traipsing in and out of these sensitive locales. This results in far less environmental impact.
Vegetative cutting and clearing are minimalized, along with the number of fly camps and potential helicopter support flights, according to comments made by BP during a fairly recent presentation at the Indonesian Petroleum Association annual confab.
The company noted that added benefits are expected from autonomous nodes based on the simplicity and flexibility of the system.
For instance, internal timing and positioning via GPS means obstructions are much simpler to address, without sacrificing subsurface sampling and redundancy.
Steve Mitchell, vice president, systems division manager at FairfieldNodal summarized the principle issues that must be addressed in order for nodal systems to meet the coming demands and needs of industry.
“The next generation node must be smaller, lighter, cheaper, more plentiful and longer lived,” Mitchell said.
“Much of the mass of the OBN unit is in the batteries,” he noted. “Reducing power requirements is key to extending deployment longevity and reducing size and unit cost.
“Smaller, cheaper and longer-lived nodes will make larger 2C surveys or denser 4C surveys cost effective.
“In the deep water, ROV operations represent a significant portion of overall cost structure,” Mitchell noted. “Innovative deployment and retrieval methods that reduce this cost could facilitate the expansion of OBN technology into more markets.”