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The understanding of new measurements is becoming more routine, but integrating them into the big picture is still a challenge.
One thing the oil and gas industry has gotten very good at is using measurements to describe what cannot physically be seen in the subsurface. Over the years such technologies as gravity, magnetics, seismic, and well logs have helped operators better understand their reservoirs and, ultimately, get more out of them.
But this understanding has come at a price. Acquiring and interpreting these complex measurements has made specialists out of oil company workers, and a seismic specialist might not know much about gravity, magnetics, or well logging. This has hampered the industry's ability to integrate disparate forms of datasets to attain better subsurface understanding.
Many feel the industry is on the threshold of a leap that will push the boundaries of current data integration into full "multiphysics," where physical data can be merged together meaningfully to tell a more accurate story about the subsurface. In the May 2011 issue of The Leading Edge, John Eastwood, secretary-treasurer of the Society of Exploration Geophysicists, wrote, "There has not been a new tool or workflow during the past 15 years that has revolutionized interpretation. Interpreting on 2-D lines in a 3-D survey still represents the lion's share of interpretation done by the industry and, quite frankly, is stuck in the 1990s.
"I want (we all should want) a new, revolutionary user interface – a volume-based interpretation in which the interpreter evolves the 3-D interpretation or earth model that actually looks like the earth model." Eastwood is not alone in clamoring for a better model in which to work.
"It does feel like we've been sitting on a plateau," said Chris Friedemann, chief marketing officer for NEOS Geosolutions. "Seismic technology continues to get better over time, but it feels like we've been riding that wave and working the seismic to death."
Many companies are working on pieces of the puzzle. But it will be a while before those pieces can be fit together.
Part of the renewed interest in multiphysics comes from the emergence, or perhaps reemergence, of nonseismic measurement technologies. Two of the key technologies that have been introduced recently are controlled-source electromagnetics (CSEM) and gravity gradiometry. While both EM and gravity predate seismic as measurement tools, seismic (particularly 3-D seismic) was such a preemptive technology that many of the older methods fell by the wayside.
"In the old days, gravity equipment was relatively portable, the instrumentation was readily available, and seismic was big and complicated and required crews," said Neil Dyer, vice president of geophysical services for ARKeX Ltd. "Now we've gotten used to the big crews, and everyone has forgotten that the simpler acquisition methods are still valid and useful."
He added that the industry is now "reaching the edges" of the seismic method. "It's time to reawaken our old expertise," he said.
Gravity gradiometry measures the rate of change of rock density, while CSEM measures resistivity contrasts in the subsurface. While both technologies have been treated with some skepticism from the industry, Friedemann said most of the independent testing is done, and companies are now seeking ways to incorporate these measurements with seismic. "I think people are starting to think, 'OK, how do these pieces arrange themselves to pursue our opportunities?'" he said.
Quantitatively integrating these measurements with seismic will take time. Richard Cooper, CEO of Rock Solid Images, said it might be wise to start with qualitative integration. For instance, early CSEM datasets were simply overlain on top of seismic sections rather than being mathematically integrated with them, he said.
"We used eyeballs to interpret them," he said. "To be honest, that's the way you would want to start today. But if you're trying to tease out the reservoir properties, then you have to do it quantitatively." This will require algorithms, he said, which the industry already is improving.
Fugro Jason and others have had success with this concept in integrating seismic data with well log data. "We have integrated different key earth modeling disciplines like rock physics, geostatistics, and seismic inversion in a manner that people can understand," said Denis Saussus, product champion for geostatistical inversion at Fugro Jason. "One of the keys to integrating data from multiple disciplines is to have software that gives users control over the reliability and uncertainty of each data component." For instance, users can identify areas of poor seismic data quality and rely more on well log data in those areas. Additional data sources can be plugged in as modules – production rate information, for instance. It is a matter of finding statistical correlations between the different data types. TGS also has specialized in integration, starting with well logs and seismic. John Adamick, senior vice president for Geological Products and Services, said well logs are probably the best measurement available because the logs are actually in contact with the rocks when they take their measurements. Trying to merge two remote datasets such as seismic and CSEM is a bigger challenge," he said.
The holy grail
Is it a challenge worth pursuing? Many industry experts think so. Cooper said the goal is to have a central earth model that all scientists work from rather than having multiple iterations of models that often are conflicting. Adamick added that, while integrating CSEM data with seismic can be challenging, it is worth it to the oil companies.
But it will not be easy.
A key concern is cost. Saussus said adding more data to the model will result in longer run times, even with today's modern compute power. "If you want the algorithms to do more work, it's going to come at a cost," he said.
There also is a cost-benefit ratio when it comes to the amount of time needed versus the value of the additional information.
"Let's say you have to do a 3-D survey, and you want a full-azimuth survey. You'll need wide-azimuth acquisition, which is expensive," said Jacques Leveille, senior vice president and technology advisor for ION. "Then you want to drop it on top of a full gravity gradiometry survey, which is going to be expensive, and then you want to throw in a CSEM survey and log the bejeebers out of the wells. And you don't know what you're going to get out of it.
"It would be difficult to propose that to oil company management, although ultimately it may solve the problem."
Add to that the time element. Large-scale 3-D seismic surveys alone can take years to process and interpret, not even taking into account ultimate integration with gravity or EM data. For a company that has a rig on location, this time frame is simply not acceptable.
These two elements will have a significant impact on the ultimate value proposition. "Time, unfortunately, is the one commodity that we're all running out of," said Leveille. "It's going to take major investment by companies that can afford it.
"It goes back to when the information is so valuable to you that you're willing to invest," he added. "At the end of the day, this is a business . It's a business based on a heavy dose of science, but it's still a business."
Adamick said there are two ends of the spectrum where the value case is easiest. "The more frontier the area is, the less that is known, and the less data that there is available," he said. "You are more likely to throw the kitchen sink at it with a wide variety of regional tools (gravity, magnetics, 2-D seismic, ocean bottom core sampling, etc.) to try to understand the basic plays in the region.
"When you've got a major producing field, the game is trying to maximize production. In that situation you've got a lot of cash flow and will happily spend some of it to increase production."
Other barriers to change
Integration between disciplines is one of the biggest hurdles the industry faces despite attempts to adapt to an asset team approach. "I think the key problem in the way to data integration is simply the cross-disciplinary nature of it," said Saussus. "The fact that we have to have geophysicists talking to geologists talking to reservoir engineers – that has been a huge obstacle."
He added in many instances different disciplines use different names for the same concept – facies, for example. "They can be called facies, lithofacies, rock types, rock categories, rock classes, and so on," he said. "Sometimes they mean the same thing, and sometimes they don't, which is the real killer."
Added Leveille, "It's not very often that you get all of the disciplines representing the various physics together in one meeting room. We need to get all of these people talking on the same subject and understanding each other's language. That has proven to be a very difficult thing to do."
Another issue that is not new but still problematic is the issue of scale. Reservoir measurements can be taken with anything from an airplane to an electron microscope. Can properties found at the pore scale be statistically relevant at the seismic scale?
The answer is most likely "no," but many see a new development known as "digital rock physics" (DRP) to be a promising start.
DRP is a staged analysis that studies cores, plugs, and pore scales. Each stage provides visual and quantitative information that can be used to select a smaller but representative volume for the next stage of analysis.
Leveille said DRP provides a perfect way to integrate the microscopic with the macroscopic.
Added Jim Sledzik, partner and president of Energy Ventures, "The introduction of DRP helps us go from pore to core to log to seismic to all of the other nonseismic methods and start to realistically link them. But the upscaling issue has not been, nor will it continue to be, a trivial task."
A brave new world
Despite the challenges, multiphysics appears to be a trend that refuses to be ignored. While the business model is still amorphous, oil and service companies are preparing to be involved in the process in whatever way possible.
"Like it or not, we're going to get dragged into this new world," said Cooper. "We just aim to be there sooner than some."