While many are focusing on
atmospheric solutions to reduce greenhouse gases, some researchers are setting
their sights on the ground—deep underground. Li Li, an assistant professor of
energy and mineral engineering at Penn
State, is investigating
geologic carbon sequestration as a way to reduce the amount of carbon dioxide
in the atmosphere.
The process, which at this point
is in early stages of development with a few pilot tests, would involve the
collection of carbon dioxide from stationary sources such as power plants, the
compression of carbon dioxide into a supercritical fluid form with a density
similar to a liquid, and the injection of the supercritical liquid into various
formations deep below the Earth’s surface (at about one kilometer or deeper).
Because of the high pressure underground, the injected fluid will maintain its
supercritical form and could be stored underground for long periods of time in
deep saline aquifers (which cannot be used as a source for drinking water),
coal seams and depleted oil and gas reservoirs.
Li’s research, with partial
funding from the U.S. Department of Energy’s National Energy and Technology Laboratory
(NETL), is focused on the possibility for and potential impact of the leakage
of carbon dioxide from underground sequestration sites. For example, her group
is studying the effect of carbon dioxide and brine on wellbore cement
integrity, and also is studying the potential impact of carbon dioxide leakage
on the quality of drinking water.
In paper published in Environmental Science & Technology,
her graduate student Evan Frye and coauthors have shown that the leakage of
carbon dioxide into aquifers can cause heavy metals to mobilize. The extent of
the mobilization depends on several factors, including the velocity and amount
of carbon dioxide leaking from underground storage areas, and the properties of
the aquifer into which the gas is leaking.
NETL is working with researchers
to pioneer the Carbon Sequestration Program, whose goal is the development of
“a technology portfolio of safe, cost-effective, commercial-scale carbon
dioxide capture, storage and mitigation technologies that will be available for
commercial deployment beginning in 2020.” The goal of Li’s research is to
quantify the risks associated with carbon sequestration, understand the coupled
processes in the complex subsurface, and determine the optimal injection
conditions and sequestration sites.
Li said a primary challenge for
researchers is that the scale of the work is so large, both in terms of time
and space.
“Typically it is much easier
for researchers to fully understand the scope of their work when the scale is
small, in a laboratory where scales range from microns to meters and within
time frames from seconds to years,” she said. “However, geologic
carbon sequestration involves areas of tens or hundreds of kilometers and time
scales of hundreds or thousands of years. The issue of scaling is a big
challenge as we work to quantify and predict the ultimate fate of carbon
dioxide stored deep beneath the Earth’s surface.”
Also, it is prohibitively
expensive to drill wells and take samples from the depths that would be
involved in carbon sequestration, so research often relies heavily on
mathematical models. Li uses a combination of numerical simulations and
experimental work that aims to mimic relevant underground conditions. She and
her team, composed of a few graduate students and post doctoral scholars, split
their time between experimental work and numerical simulation to better
understand the subsurface complexities associated with geologic carbon
sequestration.
