Sandia researchers are sharing a four-year, $12 million DOE contract that continues funding into research on the long-term geologic sequestration of carbon, considered a key element in reducing greenhouse gas emissions to the atmosphere.

The Energy Frontier Research Center (EFRC) contract from the department’s Office of Science, which went into effect Aug. 1, funds research by the Center for Frontiers of Subsurface Energy Security, a joint carbon sequestration program between The University of Texas, Austin, the lead partner, and Sandia. Sandia researchers will get $5.6 million of the total, which renews a five-year, $7 million contract awarded in 2009. The latest award was one of 32 EFRCs chosen from more than 200 proposals.

Upcoming work focuses on three technical challenges: sustaining large storage rates for decades; increasing efficient use of pore space in the geologic formations, or reservoirs, where carbon dioxide (CO2) would be stored; and making sure it doesn’t leak from the reservoir, says Sandia geochemistry researcher and assistant center director Susan Altman (6915).

“We’re not going to solve all these problems; they’re huge,” she says. “But we’re doing the basic science behind them so that we can inform decisions and move forward. We want to make sure our science will have impact on those three challenges.”

Marianne Walck (6900), associate director for the joint center, who also heads Sandia’s Geosciences Research Foundation, says the contract renewal validates the work done by Sandia and the university in the program’s first five years and positions the center to have major impact in subsurface storage research and development. “We are proud to be among the 22 EFRCs that DOE chose to continue for another four years,” she says. “The technical and programmatic reviews of our proposal with UT were superb; they speak to the quality of research at both institutions.”

Multidisciplinary effort centers on studies in deep saline aquifers

The effort concentrates on deep saline reservoirs, studying problems from the atomic to the full reservoir scale in a multidisciplinary approach that brings in chemistry, microbiology, geomechanics, geophysics, and computer sciences. The team includes researchers from Sandia and The University of Texas Cockrell School of Engineering and Jackson School of Geosciences.

The program so far has published 80 papers, including the featured article in the July 17 issue of the Journal of Physical Chemistry, “Chemical and Hydrodynamic Mechanisms for Long-Term Geologic Carbon Storage.”

The original EFRC focused on multiscale, multiphysics processes to ensure safe storage of CO2 without harming the environment. Researchers now will work to integrate physics across length scales. For example, they will look at the integrity of the caprock, the low-permeability mudstone that helps keep buoyant CO2 underground, Susan says. They will work at the atomic scale to see if there is significant storage space in the clay layers. They will work at the core scale to measure the caprock’s mechanical properties to better understand how the rock could fracture under pressure. Then team members will integrate knowledge and measurements from the core scale to model the caprock itself — the reservoir scale — to understand how fractures develop in the reservoir.

The center also studies how CO2 dissolves into resident brines over time. During injection, CO2 is trapped by the caprock, which is critically important but the least secure of four trapping mechanisms. After that comes residual trapping, in which CO2 bubbles are caught in pore space; solubility trapping, when CO2 dissolves in the brine or other fluids underground; and finally, mineral trapping, where carbon becomes a solid, such as calcite, the most secure mechanism but the one that takes longest.

Researchers also are working in the field at northeastern New Mexico’s Bravo Dome, a natural reservoir of CO2 trapped underground. They’re trying to calculate long-term dissolution rates at the site to understand how important solubility is to CO2 trapping, Susan says.