'Seeing Through Clouds,' 'Squeezing Data'

New Technologies Hit the Market

By LOUISE S. DURHAM
EXPLORER Correspondent

Photo courtesy of WesternGeco

The deepwater OBC 4-C Bluefin, a floating example of technological advances designed to meet exploration demands.

Deeper targets? Deeper water? Maturing fields?

Whatever the challenge, the oil and gas folks keep coming up with the technology needed to meet the most complex and demanding scenarios head-on.

Much of the tech know-how originates within the seismic industry, which currently is laboring to regain at least some semblance of its former robust health.

Yet, ongoing R&D efforts belie this struggle -- at least for now.

WesternGeco alone spends $50 to $60 million a year on R&D, according to Jim White, vice president multi-client data worldwide.

They have plenty to show for it.

The company's new Multi-Vision™ regional program in the Gulf of Mexico (GOM) incorporates both the old stand-by technology, 2-D, and the new 4-C, or multicomponent technology -- a survey concept developed by project partner AIM Geophysical, according to Robert Hubbard, manager North and South America new ventures for multi-client at WesternGeco.

"From a regional understanding, the 2-D with 10,000 meter offsets we have is important to tie key fields throughout the shelf into the deepwater," Hubbard said.

"Doing this with OBC technology, we know exactly where the cable is versus a 2-D streamer boat," he said, "and we feel this is a great advantage for looking at the deeper potential targets on the shelf that people are starting to chase.

"We're pleased with the data we're getting, both pressure and shear," Hubbard added, "and we think the images we'll get will be excellent with the cable on the bottom."

He noted the shear wave data will enable them to see through some of the shallow gas clouds that have plagued the industry on the GOM shelf for years.

The plan is to come up with a contiguous grid shot in phases with an average of two crews working over the life of the project

Besides this long-term undertaking, the company is busy with projects using its new "Q-Marine*" technology. This fully calibrated single-sensor marine seismic acquisition and processing system provides high-resolution, and low noise data for enhanced reservoir management.

It's part of the Q-technology package for both land and water, designed to afford improved reservoir images as well as reliable pictures of subsurface areas that previously could not be imaged.

The repeatability levels of Q-Marine technology mean the data are 4-D ready, i.e., every survey can be a baseline time lapse survey -- a plus for the oil finders who increasingly are wanting 4-D surveys to get a better handle on what's happening in the reservoir over time.

When used on land, Q-technology has a 30,000-channel capacity. Q-Marine, however, boasts 4,000 channels per streamer, up to a maximum 20 streamers. The system uses point-receiver recording with a 3.125m interval between individual hydrophones, and the output from each hydrophone is digitized and recorded separately on tape.

'Q' Case Study

Q-Marine was the topic of a case study paper presented by Jeff G.S. Pan, senior advisor at Kerr-McGee Oil & Gas, in the Convention Theater at the recent AAPG Annual Meeting in Houston. Nick Moldoveanu, geophysical support manager at WesternGeco, co-authored the paper.

Kerr-McGee acquired and processed a data set provided via five 2-D single sensor (Q) lines from a multi-client Q-2D program conducted over a recent field discovery in the deepwater GOM. The initial discovery occurred via conventional 3-D multi-client seismic data.

The objective, according to Pan, was to determine the benefit of single sensor data for reservoir characterization and field development.

He noted the project results showed the Q data enabled:

• Effective coherent noise attenuation.
• Preservation of broader frequency bandwidth.
• Proper spatial sampling of the seismic wavefield.
• Preservation of accurate amplitude.
• Applicability to AVO analysis.

Kerr-McGee is conducting a 3-D Q survey in the North Sea as part of its ongoing evaluation of the single sensor technology.

Spectral Decomposition

The GOM is a prime example of the challenges facing operators in the quest to create value. The shelf area is dotted with highly mature fields that demand evermore sophisticated technology to detect remaining reserves.

Then there's the "frontier" deepwater region with its tantalizing potential for big finds, at the same time calling for the newest technology available to key in on reservoir detail and avoid a super-pricey dry hole in this complex arena.

One of the techniques being used to depict the intricacies of the reservoir is spectral decomposition, which affords unique high resolution seismic images of both stratigraphic and structural reservoir traps (see Geophysical Corner). Resolution of reservoir boundaries, heterogeneities and thickness is much greater than what is possible with traditional broadband seismic displays.

"It's analogous to what you do with remote sensing or satellite data on the surface," said Greg Partyka, staff geophysicist at BP. "There you use frequency bands of infrared and visible wavelengths to get subtle details.

"With seismic data, you have a seismic bandwidth with much lower frequencies than used in remote sensing," he said, "but you can leverage this by looking at the information provided by discrete frequencies just like you do with satellite imaging data."

Using spectral decomposition, a suite of amplitude maps is acquired from a range of frequency slices in the reservoir zone. Images from certain frequencies are combined selectively to depict the unique geologic relationships within the zone. The amplitude maps can be animated to aid in the interpretation process.

When tied in with all other information, spectral decomposition is an effective risk reduction tool, according to Craig Cooper, manager of imaging technology at BP.

It's a novel -- but relatively inexpensive -- way to use seismic data to try to extract details about a particular zone in a seismic volume, according to Partyka.

"All you need is a seismic data set plus some kind of guide horizon to help you identify the zone of interest," he said. "Once you have that, for a fairly large 3-D survey it's a matter of running over a few hours and looking at the results.

"You have nothing to lose and everything to gain," Partyka noted. "It lets you squeeze out that added bit of information from the seismic."

He offered one note of caution: If there's no contrast in the rock properties or fluid properties in the zone of interest, spectral decomposition won't be a magic bullet. It only reveals what's in the seismic, so if there's a bunch of noise, it will display noise.

Although spectral decomposition deservedly carries the "cutting edge" label, it is not a new application.

Partykya has been working on it since 1991 at Amoco, and BP, which has established a track record for successful use of the technique, acquired the patent in 1996. Apache also has had a version of the technology for some time.

Now, however it appears to be on the cusp of widespread useage.

Deepwater Driving

Besides the role it plays in the demand for more advanced reservoir interpretation processes, the ever-increasing activity in the deepwater GOM is helping to hasten the development/commercialization of a number of exciting tools to operate in this often-hostile environment.

Perhaps one of the most intriguing gizmos is the autonomous underwater vehicle (AUV), which already has proven its merits in the research milieu.

The AUV is a far more sophisticated tool for acquiring remote data than its predecessor, the remotely operated vehicle (ROV). The ROV requires a skilled surface pilot for operation, and it has a tendency to veer off course and depth configuration during a deep tow survey because of the extreme length of the tether. Turning is difficult, sometimes requiring a second towing vessel.

In contrast, because it is autonomous, the AUV is agile. It can be programmed to avoid obstacles and to maintain a constant distance from the seabed and only needs a crew and vessel for the launch and recovery process.

Needless to say, the AUV requires some ultra-sophisticated programming technology. Boeing has been developing this kind of software for a number of years, and the company recently formed a partnership with Oceaneering and Fugro to provide an AUV for commercial use.

The machine, which is rated to 3,000 meters, currently is being tested off the California coast and will be available commercially the second quarter of this year, according to Carl Sonnier, AUV program manager, Fugro Geoservices.

"The purpose of the tool is mainly deepwater construction planning, like big offshore platforms, pipelines and such," Sonnier said, "so the initial payload is designed as a survey tool and targeted at that specific market."

Initially, the machine will collect side scan data -- basically conducting acoustic mapping of the seafloor -- and will be used for bathymetry to develop terrain contours. Sonnier said it's also equipped with a shallow seismic system called a sub-bottom profiler used to map the top 100 feet or so beneath the mudline.

"The vehicle is designed to handle multiple payloads," he said, "so we intend to do other types of things, like gravity for instance. There's a variety of other oceanographic sensors we can carry, and I view the vehicle as a sort of truck where we can slap on different payloads."

The analogy is apt, given that once the cage containing the AUV is lowered into the water, the vehicle backs out much like a car out of a garage. It dives to the seafloor, goes through a calibration process and begins its work.

Once the mission is complete, the machine returns to the surface, is pulled back into the cage and brought onto the boat -- an offshore work-class vessel will suffice.

The cost of the equipment tallies several million dollars, but the overall throughput is much higher compared to alternative deepwater techniques, according to Sonnier.

"The net effect," he said, "is you can reduce the cost of these type surveys by 25 percent over previous tools to collect deepwater data."