With grants from the National Science Foundation and the National Energy Technology Laboratory, mining and minerals engineering assistant professor Cheng Chen is finding new ways to reduce the impacts of global climate change. His work is focused on Carbon Sequestration by examining how CO2 can be injected in subsurface geological formations for long-term storage. Results of his work can have a significant impact on cutting back carbon emissions around the globe, providing a safe, secure means of storing it.
Both of the funded projects address broad challenges associated with carbon sequestration—the ability to remove greenhouse gasses in the atmosphere and store them in underground geologic structures. However, each project is distinct and seeks to develop completely different methodologies.
DOE-NETL Grant: Machine-Learning Based Model
In the first project Chen received a $480K grant from the DOE-National Energy Technology Laboratory (NETL)'s University Coalition for Fossil Energy Research (UCFER) Program. The 2-year project seeks to develop a machine-learning-based, scale-bridging, data assimilation framework with applications to geologic carbon sequestration.
The work proposes to develop a less time-consuming approach to analyzing the permeability of geologic rock formations, which are based on large amounts of visualization data, such as from CT scans and which are critical to understanding a rock’s permeability and its affect on CO2 injection. “Normally this data is analyzed with computer modeling,” explains Chen, “however; it can be very slow and time consuming.” The objective a machine-learning based approach is to collect only a specified quantity of sample data. “Once there is enough mapping between the rock geometry and the fluid mechanics properties of the rock, a model can be trained to predict the fluid mechanics properties of new samples,” says Chen.
According to Chen, the project offers a good collaboration with NETL, which possesses the expertise and the facilities to generate data via x-rays and CT scans. “Our work complements the national laboratory because NETL has advanced CT imaging facilities and image processing methods and Virginia Tech has expertise in numerical modeling and machine learning.”
The next steps for Chen and his team are to collect a tremendous amount of image data, including from Nino Ripepi’s field scale injection site, and then develop a number of machine-learning models to analyze that data.
“The pore water near the top cap rock of the aquifer is saturated with dissolved CO2 and thus is denser than the underlying water not saturated with CO2, which can therefore cause miscible density-driven downward convection. The miscible density-driven downward convection transports dissolved CO2 away from the cap rock. This process reduces the risk of CO2 leaking at the cap rock and also has the potential to enhance subsequent CO2 dissolution from the supercritical phase into the aqueous phase.
National Science Foundation Grant: Convection in Porous Media
The second project is a National Science Foundation, $368K grant from the Division of Earth Sciences (EAR). For this 3-year project Chen and his team will study the fundamentals of miscible density-driven convection in porous media, which is encountered in geologic carbon sequestration.
This project entails laboratory experiments in which researchers can control and study the process of miscible density-driven convection. A possible means for storing CO2 is by injecting it into deep saline aquifers. Once injected, the CO2 is in a supercritical state—somewhere between a gas and a liquid. Over a period 10-100 years, the CO2 begins into dissolve into the water.
According to Chen, “the pore water near the top cap rock of the aquifer is saturated with dissolved CO2 and thus is denser than the underlying water not saturated with CO2, which can therefore cause miscible density-driven downward convection." This process effectively improves the long-term security of geological CO2 storage. “The miscible density-driven downward convection transports dissolved CO2 away from the cap rock,” Chen adds, "and reduces the risk of CO2 leaking at the cap rock and also has the potential to enhance subsequent CO2 dissolution from the supercritical phase into the aqueous phase."
In the field it is widely known that the salinity of underground aquifers has an influence on the convection of CO2. However, Chen’s approach is novel in that it seeks to design well-controlled laboratory testing methods for testing the process and numerous models used to understand it.
Chen and his team will first improve existing numerical models by carrying out simulations. “Our next step will be to setup lab experiments to confirm our hypothetical models surrounding density-driven convection,” Chen says. To do this, the team will construct a 1 x 1 meter porous media replica, or analog model. “The analog model enables us to control permeability distribution and the porous media, and its glass panel construction enables the flow of the dyed fluid to be observed and recorded with a high speed camera.”
For both projects a number Virginia Tech research faculty provide expertise as CO-PIs. For the NSF project, Chen is working with Yang Liu, associate professor in mechanical engineering's nuclear energy program. “The DOE-NETL project requires a big team, which includes Dr. Nino Ripepi, from mining and minerals engineering,” notes Chen.
In addition, Heng Xiao, assistant professor in aerospace and ocean engineering, and James McClure, a Computational Scientist at Virginia Tech’s Advanced Research Computing (ARC), also serve as CO-PIs.
The project has also enabled the hiring of graduate students to participate in the research. The NSF project provided funding for two graduate students, one from mining engineering and another from mechanical engineering, while the NETL project brought on one mining engineering and one aerospace and ocean engineering graduate student.
At the Laboratory for Flow and Transport in Porous Media
“Geological sequestration is perhaps the only viable technology to mitigate global climate change while continuing large scale use of fossil energy.”
The potential correlation between CO2 emissions and global climate change are critical issues that have a significant impact on society, communities and economies. Chen’s research, while fundamental in its scope, has wide reaching benefits. “Geological sequestration is perhaps the only viable technology to mitigate global climate change while continuing large scale use of fossil energy,” explains Chen. The capacity to store CO2 in underground geologic formations is vast. “If, as a society, we still depend on fossil fuels in the foreseeable future, our understanding of density-driven convection in porous media, and the ability to better predict and model the fluid mechanics of deep saline aquifers, might allow us to safely reduce or even eliminate greenhouse gasses from the atmosphere.”