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Deep Thinking in a Shallow Way

GOM Results Could be Profound

Geophysical contractors are riding a whole new wave of popularity these days, fueled by rising energy demands that have spurred the need for new seismic data.

One of the hotbeds of activity on the domestic front is in the shallow shelf waters of the Gulf of Mexico and adjacent coastal regions of Texas and Louisiana. Indeed, there's some sizzling seismic action here.

The driving force for all the activity is the operators' hunger for new data to help evaluate structures and define drilling targets at depths far greater than the plethora of past discoveries in the region, which ordinarily maxed out at 12,000-15,000 feet subsea.

A diverse throng of contractors is on the scene to accommodate the explorers' needs, applying new technology and new acquisition techniques in many cases.

"Our clients have indicated they need coverage on the very shallow shelf right up to the barrier islands and across the barrier islands and across the estuaries in the whole Gulf of Mexico," said Richard Degner, president of Global Geophysical Services.

"They need surveys with a very large seismic source of 75 to 100 bar-meters and very long offsets of 30,000-plus feet," he said, "and to ensure they properly image their objectives of varying depths and steep dips, they also need tight spatial sampling -- something with very high resolution and reasonably small cell size."

Global recently deployed its fourth seismic crew since the company's operational start less than six months ago. That crew is acquiring a high density, long offset 3-D program for Seismic Exchange Inc. (SEI); the shoot is in shallow state and federal waters from High Island to the West Cameron area.

"We'll tie it to the recently drilled Joseph well at High Island Block 10 and with some of the deep discoveries recently made in the West Cameron state waters area," said Randy Johns, vice president marketing offshore division at SEI. "There's the potential for a new trend out there, and that's what we're trying to chase back toward Louisiana."

Image Caption

Photos courtesy of Global Geophysical

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Geophysical contractors are riding a whole new wave of popularity these days, fueled by rising energy demands that have spurred the need for new seismic data.

One of the hotbeds of activity on the domestic front is in the shallow shelf waters of the Gulf of Mexico and adjacent coastal regions of Texas and Louisiana. Indeed, there's some sizzling seismic action here.

The driving force for all the activity is the operators' hunger for new data to help evaluate structures and define drilling targets at depths far greater than the plethora of past discoveries in the region, which ordinarily maxed out at 12,000-15,000 feet subsea.

A diverse throng of contractors is on the scene to accommodate the explorers' needs, applying new technology and new acquisition techniques in many cases.

"Our clients have indicated they need coverage on the very shallow shelf right up to the barrier islands and across the barrier islands and across the estuaries in the whole Gulf of Mexico," said Richard Degner, president of Global Geophysical Services.

"They need surveys with a very large seismic source of 75 to 100 bar-meters and very long offsets of 30,000-plus feet," he said, "and to ensure they properly image their objectives of varying depths and steep dips, they also need tight spatial sampling -- something with very high resolution and reasonably small cell size."

Global recently deployed its fourth seismic crew since the company's operational start less than six months ago. That crew is acquiring a high density, long offset 3-D program for Seismic Exchange Inc. (SEI); the shoot is in shallow state and federal waters from High Island to the West Cameron area.

"We'll tie it to the recently drilled Joseph well at High Island Block 10 and with some of the deep discoveries recently made in the West Cameron state waters area," said Randy Johns, vice president marketing offshore division at SEI. "There's the potential for a new trend out there, and that's what we're trying to chase back toward Louisiana."

Going Deeper

It is perhaps fitting testimony to the resurgence of the only-recently-beleaguered seismic industry that a shiny new, custom-designed vessel is being used for the project -- and that a relatively new company brought it to market.

"The James H. Scott, which was recently christened by Global, is designed specifically for shallow water, and it's the ideal situation for what we're trying to do at this time," Johns said. "It's basically a catamaran that can get into about four feet of water and can give us the energy we need with its 100 bar-meter seismic source.

"We're going after deep structures, so we need that energy."

The program is utilizing the Sercel 408 ULS recording system, which ties continuous and contiguous lines from the shallow marine environment to the 408 UL in land and swamp, according to Degner.

"The lines can run from 200 feet water depth up onto the shore," he said, "and we can record with a patch with the same power configuration, the same power structure and the same continuous coverage all the way across."

Johns noted the data acquired also will be used to improve the subsurface definition for smaller companies still looking for targets shallower than 12,000 feet. This will be achieved via much tighter bin size, higher fold and longer offsets.

Other Players

Specialized seismic acquisition technology of a whole different kind is being deployed in the Gulf by RXT (Reservoir Exploration Technology), which became a U.S. entity in 2004 after its original launch as Terra Seismic Services in Norway in 2002.

The company works exclusively with I/O's VectorSeis Ocean (VSO) system, which is a redeployable ocean bottom cable imaging system using VectorSeis® full wave sensors for multi-component data acquisition on the seabed.

RXT has completed several full wave surveys in the Gulf for a major oil company, according to vice president Larry Wagner. GX Technology served as project manager for the program. While declining to be specific about the objectives, Wagner noted it was highly likely some of the work was for deep targets.

"(The technology) is very valuable for both deep and shallow targets," Wagner noted. "It's a highly configurable system in the sense we can establish some acquisition geometry because of the way the system is constructed.

"The signal fidelity we get from the sensor technology is probably the real key to being able to image the reservoir better than in the past."

Fairfield Industries, which has been active in the shallow water GOM for more than two decades -- it kicked off its first 2-D transition zone program in Louisiana in 1976 -- bet on the future when it began shooting its deep shelf long offset 3-D data program a few years back.

"We started this back before the MMS granted royalty relief and when natural gas was about $3," said Steve Mitchell, vice president operations. "Our deep shelf program is doing real well and going strong as ever.

"We're doing long offset recording, and we shot 250 new blocks last year," Mitchell said. "We'll do at least that much this year."

Different Perspectives

Just as the Gulf clearly has many lives, so too are there many ways to look at it. For instance, 3-D seismic is not necessarily de rigueur for evaluating the challenging deep gas play.

Granted, there's 3-D seismic coverage aplenty over the shelf and adjacent transition zone. The problem is these earlier data were acquired using short offsets and short record lengths, meaning they are ill-suited to adequately define the deep structures currently of interest.

Today, long offset 2-D data are in demand to provide a better image in the deep area, particularly on a regional basis. They can help to tie in areas of interest and also to high-grade areas when looking for deep prospects. Proprietary, prospect-specific 3-D data can be acquired later as needed.

"Quite often the regional structural imaging on 2-D can be quite good and useful when it complements older shorter 3-D surveys acquired," said Kenneth Mohn, exploration vice president at Fugro. "It can be beneficial in an exploration program."

Although an "old" name in the industry with a worldwide presence, Fugro is just now implementing its first spec survey in the Gulf. It's a regional long offset (10,000 m) 2-D program on the shelf extending from about 30 feet of water depth out to 300 feet.

"Client interest was the determining factor in doing the program," Mohn said. "The data will be used to help image the deep targets, and we're seeing good results in the far offsets on the deep records. You can process the data to get maximum benefit out of the far offsets."

Sharing the enthusiasm for long offset 2-D data is PGS Onshore, which launched its Deep Shelf Gas Play Imaging Program in mid-2004 in response to the operators' professed need for a more sophisticated evaluation tool for the deep play. The program is designed to tie the Lower Tertiary Wilcox sediments onshore to the expanded Wilcox offshore. This geologic section has been prolifically productive in southeastern Texas and into southwestern Louisiana.

To image the subsurface at a depth greater than 40,000 feet, the program is using ultra-long offsets of 41,000 feet max, 20 second records and a nominal fold of 125 onshore and 250 offshore.

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