Sandia LabNews

Carbon sequestration: Can we bury or store global-warming greenhouse gas underground?

Can we pump carbon dioxide underground and store it there to avoid warming the atmosphere? That is the question researchers at Sandia, teaming with 40 industrial partners and 10 technical partners (including state geologists, oil conservation departments, geological surveys, and the like) will attempt to answer over the next several years.

Following a phase one study, which showed a number of potential storage sites in the Southwest region, work toward phase two demonstrations is now under way, says David Borns, manager of Sandia’s Geotechnical and Engineering Dept. 6113. “Phase two will demonstrate at the field scale that sequestration really is possible with power plant outputs of CO2 injected in several types of geologic environments. In fact, multiple projects are possible in the region,” says David.

The Southwest Regional Partnership for Carbon Sequestration, which includes Arizona, New Mexico, Colorado, Utah, Texas, Oklahoma, Kansas, and Wyoming, has proposed a series of validation tests of the most promising sequestration technologies, including three major geologic tests and two terrestrial pilot tests.

Storage options

Geologic options include pumping CO2 into: (1) oil reservoirs to increase oil recovery rates, (2) coalbed methane zones where coal absorbs the carbon dioxide and releases methane gas, and (3) aquifers, where the CO2 combines with water stored in pore spaces in the rock. Terrestrial tests will determine if natural photosynthesis activity can be increased to tie up more CO2 from the atmosphere, David says.

DOE, spurred by a presidential goal of reducing carbon emissions by 18 percent, began an evaluation of sequestration two years ago, funding regional studies in seven regions. Three regions were selected for phase two projects. The Southwest regional project is funded at $16 million over four years, with New Mexico Tech acting as coordinator for the work.

“If carbon sequestration proves effective in managing global warming impacts, some of the first options are likely to coincide with existing CO2 transportation infrastructure,” says David. The Southwest region is home to an extensive CO2 pipeline network, transporting more than 30 metric tons of natural CO2 from the central Rockies to the Permian Basin, where it is used for enhanced oil recovery.

“Our phase one study concluded that the ‘lowest hanging fruit’ for sequestration would be to supplant the natural CO2 with power-plant sourced CO2,” says David. The partnership’s proposal includes:

  • sequestration in a saline aquifer and enhanced oil recovery in Utah,
  • enhancing coal bed methane production in the San Juan Basin in New Mexico,
  • a two-year enhanced oil recovery project using CO2 from a nearby power plant in West Texas, and
  • a terrestrial pilot test in the San Juan Basin and a regional analysis of terrestrial options.

A complex issue

Technically speaking, CO2 sequestration is a complex issue spanning a wide range of scientific, technological, economic, safety, and regulatory issues, says John Lorenz (6116). John and a team of Sandians will conduct detailed studies on the long-term geologic impacts of CO2 on the host reservoir to determine what characterization work will be needed before sequestration can be deployed.

“The overall objective of the project is to better understand CO2 sequestration-related processes and to predict and monitor the migration and ultimate fate of CO2 after it’s injected into a reservoir,” says John. Although saline aquifers, deep coal seams, depleted gas reservoirs and several other potential reservoirs are available, depleted oil reservoirs make an attractive option for immediate sequestration for a variety of reasons, says John.

A key reason is that many oil reservoirs have potential for incremental oil recovery with CO2 injection that can improve the overall economics for sequestration projects. Geophysical and geochemical modeling after injection will demonstrate methods to monitor injections to make sure CO2 stays in the ground. John, following up on the recently retired Norm Warpinski’s work in this area, will be joined by Dave Aldridge, Bruce Engler (both 6116), and Jim Krumhansl (6118).

Peter Kobos (6010), has been at work developing a high-level computer model to analyze physical, economic, and policy requirements needed to understand carbon sequestration in the region. “We’ve got a prototype right now,” says Peter. “We’re trying to integrate all the information so that both experts and interested parties can understand how we assess a project. We’ve got geologists, regulators, academics, and people from industry all involved. The model is a way we can see all of the issues quickly and address them in an integrated way.”

Model components

Len Malczynski (6115) is also a key player on the modeling project, developing much of the software that will tie large amounts of data from the Partnership team to the model itself. Several workshops developed the model’s key parts. An example is screening criteria for underground storage of CO2. A team of geologists helped identify what would be needed to create a successful storage reservoir, Peter said.

Identifying sources of CO2 and how they would flow to these reservoirs, or “sinks,” and some of the economics associated with the project were other model components. Currently, the team is working with a New Mexico test case, but Peter plans to expand it to a regional scope for the future.

“Our goal is an integrated assessment of the costs of the components parts,” says David. “If someone proposes to site a power plant, they will know the costs of carbon sequestration going in. They can look at the infrastructure availability to connect the plant to the sequestration options to help determine the best place to put the plant.”

The concept of carbon avoidance by industry is already being practiced in Europe and is catching on in the US, says David. Colorado has a $9/ton tax credit for CO2 avoided. “This is something that can tip the scale on the type of power plant you might build,” he says. More than 1,000 kilometers of pipeline cross northwestern New Mexico to eastern New Mexico and Texas, moving 25 tons of CO2 a year across the state. This is equivalent to the carbon emissions of about five million people. “We inject and we move it now. The question is how much of a solution is it to the overall problem?”