Tamar Hallerman
GHG Monitor
09/28/12
The Department of Energy’s National Energy Technology Laboratory is rolling out a series of models meant to cut down on the time it takes to predict and quantify the potential risks associated with long-term CO2 storage. In recent months, NETL, along with several national lab and university partners, has been releasing a series of methodologies meant to help generate first-generation ‘risk profiles’ for specific storage sites—tools which could help storage project operators predict the probability of any complications that could arise from sequestering CO2 into the subsurface. Grant Bromhal, one of NETL’s leads for the effort, said in an interview that NETL has built an integrated assessment model (IAM) aimed at quantifying reservoir performance by simulating the entirety of a subsurface system. From there, the team developed what it calls reduced order models, meant to allow for the quick evaluation of the behavior of several different factors such as wellbores, seals and groundwater across varying conditions that feed into the larger IAM to predict the overall risk profiles of different sites. “The first thing we’re trying to do is to develop this methodology that will allow anyone to take these tools and apply them to their site,” Bromhal said.
Bromhal said the profiles center on calculating the probability of 1 percent of CO2 sequestered at a site leaking into the atmosphere over the long term—over the course of 100 to 1,000 years—by looking at different metrics such as the amount of CO2 that could be released into the atmosphere, changes to groundwater pH, aquifer salinity and potential seismic hazards. By then plugging in some of their own site-specific data, CO2 storage project operators can answer many key questions surrounding risk and their chosen reservoirs, he said. The effort is part of DOE’s stimulus-funded National Risk Assessment Partnership, tasked with developing a science-based quantitative methodology for determining risk profiles of CO2 storage sites. Bromhal said NETL began testing first-generation profiles internally and with specific partners earlier this spring and that the labs hopes to make the information publically available by next year. There are also plans to release one or two more generations of increasingly complex profiling measures to help site operators more accurately calculate risk, he said.
Methods Could Help Save Operators Time
Bromhal said that while risk assessment is already part of typical siting and monitoring protocol for CO2 storage projects, these risk profiles could help save storage project operators lots of time given that typical modeling software can take hours to give single predictions about CO2 behavior. In order to get a more accurate look at the larger risk picture for a particular site, simulation tests may need to be run hundreds of times and could take months before an accurate reading can be made. “Once you develop that reduced order model, you can make significant predictions and actually quantify the uncertainty from that, which you couldn’t easily do [before],” he said. “If you have your reservoir model, then you need to run that reservoir simulator hundreds if not 1,000 times in order to predict what’s going to happen there and understand the uncertainty better. Doing that can take an extremely long time, and trying to do that for the entire system, that’s not very realistic. What we’ve done is developed reduced order model techniques where you may have to run your reservoir model only five or 10 times.”
NETL said the risk profiles could help offer more detailed assessments of sites, which could provide scientists with more information to help minimize potential liabilities. According to Bromhal, the profiles could help reduce what he said is the biggest barrier for CO2 storage—uncertainty. “The benefit of that is really that the biggest barrier to implementation of CO2 storage on the storage side is really uncertainties in risks and liabilities and being able to value those over the long term. What we hope to do is to break down that barrier so that implementation can go forward,” he said.
