Reservoir Modeled From Outcrop

Virtual Field Trip Studies Real Geology

There's nothing closer to a rockhound's heart than the historically edifying field trip, where legions of geologists spend days scurrying up and down the outcrop with rock hammer, hand lens and notebook in hand.

But now, laser technology and high-end computer applications are being used to produce three-dimensional representations of outcrops that have the potential to provide far greater info than ever possible from the old-time surface study.

The basic technology to acquire 3-D outcrop data uses a GPS and a laser-pulse emitting system that receives and measures the laser beam as it bounces off the outcrop. A multitude of points are sent and received, providing an image of the outcrop face. Digital photographs are then draped on the digital terrain models (DTMs also called digital elevation models, or DEMs).

One of the groups pushing the envelope at the forefront of virtual outcrop technology is Norsk Hydro, working in conjunction with the University of Texas at Dallas (UTD).

"We feel our methodology takes this work another step or two further (than others)," said Ole Martinsen, head geologist-sedimentary geology, Norsk Hydro research center. "One reason is that our ambition all the time has been not just to visualize outcrops … but to utilize that information for reservoir modeling that would directly address critical issues such as upscaling of geological complexity (where some of the geological reality is lost) and producibility of reservoirs."

Martinsen calls the methodology Virtual Geological Reality, "to capture that what we work with in the virtual world is primary, real geological data."

The Norsk Hydro-UTD effort was detailed in a poster that was presented at last fall's AAPG international meeting in Barcelona, Spain. That effort earned the meeting's best poster award, and Martinsen and his team of researchers were presented with the Ziad Beydoun Memorial Award during the opening ceremony at the recent AAPG Annual Meeting in Dallas.

Image Caption

Researchers are finding that lasers and high-end computers are making photorealistic 3-D digital outcrop models valuable tools.
Photos, images courtesy of Ole Martinsen

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There's nothing closer to a rockhound's heart than the historically edifying field trip, where legions of geologists spend days scurrying up and down the outcrop with rock hammer, hand lens and notebook in hand.

But now, laser technology and high-end computer applications are being used to produce three-dimensional representations of outcrops that have the potential to provide far greater info than ever possible from the old-time surface study.

The basic technology to acquire 3-D outcrop data uses a GPS and a laser-pulse emitting system that receives and measures the laser beam as it bounces off the outcrop. A multitude of points are sent and received, providing an image of the outcrop face. Digital photographs are then draped on the digital terrain models (DTMs also called digital elevation models, or DEMs).

One of the groups pushing the envelope at the forefront of virtual outcrop technology is Norsk Hydro, working in conjunction with the University of Texas at Dallas (UTD).

"We feel our methodology takes this work another step or two further (than others)," said Ole Martinsen, head geologist-sedimentary geology, Norsk Hydro research center. "One reason is that our ambition all the time has been not just to visualize outcrops … but to utilize that information for reservoir modeling that would directly address critical issues such as upscaling of geological complexity (where some of the geological reality is lost) and producibility of reservoirs."

Martinsen calls the methodology Virtual Geological Reality, "to capture that what we work with in the virtual world is primary, real geological data."

The Norsk Hydro-UTD effort was detailed in a poster that was presented at last fall's AAPG international meeting in Barcelona, Spain. That effort earned the meeting's best poster award, and Martinsen and his team of researchers were presented with the Ziad Beydoun Memorial Award during the opening ceremony at the recent AAPG Annual Meeting in Dallas.

Picture Perfect

One of the unique aspects of the group's work centers around methodology developed by UTD, where the draping process is accomplished with a resolution of less than five centimeters, according to Martinsen.

"The UTD procedure makes it possible to decimate/simplify the DEMs and still drape the photography on," Martinsen said, "so that the geological detail is kept in the photographs and not in the terrain models. This makes the photorealistic model possible to handle easily in the (CAVE) visualization center.

"We scan all the points and then cut down on the number of points so the model is much coarser, and the detail is filled in by photographs," said UTD Ph.D candidate John Thurmond, a key player in the ongoing project.

"When you're actually trying to get 3-D, you need a 3-D model behind it," Thurmond said. "The trick is to make the model coarse enough so you can actually use it on a computer, which is what we do."

Despite the buzz about 3-D outcrop scanning work the past couple of years, the consensus among many industry participants has been "this is great, but what do we do with it?"

"That's why the poster we won the award for was so important," Thurmond noted. "We used the data to do some interesting things — for the first time building a reservoir model directly from a 3-D model of the outcrop.

"The bottom line is to be able to use the outcrop data effectively and incorporate it with other pieces of data, such as wells behind the outcrop," Thurmond said. "With our approach everything is globally positioned, so we can combine all the data all the way up to regional data and seamlessly drop it all together.

"The poster showed we were able to tie all the data sets together into the same framework and bring it up all at one time," he said, "and interpret all at the same time, which no one had done before."

The Ainsa Basin Example

The data used in the project came from the Ainsa Basin in Spain. Noted as one of the better deepwater outcrops in Europe, the Ainsa outcrops are comparable to some of Norsk Hydro's offshore fields and prospects.

Martinsen noted the actual geological complexity in the Ainsa dataset can be used to model reservoirs offshore, such as Angola and Norway.

Thurmond summarized the importance of building reservoir models from outcrop data:

"We're using the data to understand the sensitivities when you build a reservoir model of the subsurface," he said.

"Typically when you build this model, you build it with very coarse pixels. We're able to use all the detail on the outcrop and all the detail from other data we have," Thurmond said, "and build a very fine resolution model, because we have all the data in 3-D.

"What we're working on now — and will be in the future — is to take that very fine model and pretend this is the truth, and then build coarser models out of it that you would typically build in the subsurface," Thurmond said.

That will allow them to "see where the important factors are and what you really need to understand about the outcrop to build an accurate model in the subsurface," he added.

During a presentation at the AAPG Annual Meeting in Dallas, Tor Loseth, sedimentologist/reservoir modeler at Norsk Hydro, detailed the results gleaned from both a fine and a coarse model built from the Ainsa data:

"When you compared the two, the coarse one had twice as much oil in place as the fine one, where water breakthrough occurred 10 times quicker," Thurmond said. "This would be a pretty scary thing to any oil company, because if you estimate reserves as twice what you have, that's pretty bad.

"The companies want to accurately understand what's going on," he continued, "and the way to do this is to look at it in detail and figure out where you can coarsen and where you can't."

Better reserves estimates and better recovery for the oil and gas companies are the principle goals of the work being done by the team, according to Thurmond.