Sandia LabNews

Underground disposal of carbon dioxide

Sandia helps research team study underground disposal of carbon dioxide at New Mexico oil field

Sandia is helping the US government take the first small steps toward reducing net US fossil-fuel emissions by examining how some human-produced CO2 could be put back where it came from — the oil patch.

Since late December a multi-organizational research team has been pumping CO2 gas into a depleted oil reservoir near Hobbs, N.M. As the reservoir fills, they listen to what is happening thousands of feet underground with the help of instruments that measure subtle subterranean changes.

The team’s goal is to improve existing models that help researchers predict where CO2 will go after it is pumped into a reservoir, how far and how fast it will move, and what chemical reactions occur as the gas interacts with underground minerals.

They also want to identify remote sensing techniques that are sensitive enough to measure these changes.

And they want to know what the capacity of the reservoir is and how close that capacity matches their estimates.

"This is an experiment," says Hank Westrich (1011), former manager of Geochemistry Dept. 6118. "We don’t know if it is going to stay in the reservoir or migrate to an adjacent oil or gas reservoir immediately, or whether it might vent to the surface. We need to know that."

US power plants each year pump into the atmosphere some 2.4 gigatons of carbon dioxide produced in the burning of fossil fuels. Automobile emissions account for many more gigatons per year.

It’s a health hazard to those who breathe it, and if global climate change is real, emissions of man-made CO2 are probably a leading cause.

The southern New Mexico collaboration is one of several regional partnerships that make up DOE’s Carbon Sequestration Program, funded by the Office of Fossil Energy.

The larger program is exploring all the ways carbon dioxide could be captured at the smokestack and disposed of in a safe place.

It supports the President’s Global Climate Change Initiative (GCCI), which seeks to slow the increase of CO2 concentrations in the atmosphere and to ensure that a suite of commercially ready sequestration technologies are available by 2012.

DOE-funded teams, for instance, are exploring the possibility of injecting CO2 into aquifers or the deep ocean, where the gas would be harmlessly dissolved in water.

Others are studying how to speed or improve the natural carbon absorption processes of forests and the ocean’s surface.

The total capacity of US geologic repositories — depleted oil and natural gas reservoirs, aquifers, and unmineable coal beds — is estimated to be between 300 and 3,200 gigatons of carbon dioxide.

The DOE program proposes a combination of various carbon sequestration efforts to significantly lower net carbon dioxide emissions long enough for the US to transition to cleaner energy sources.

The oil reservoir project is led by DOE’s National Energy Technology Lab and includes researchers from Sandia, the Colorado School of Mines, the Petroleum Resource Recovery Center at New Mexico Tech, Los Alamos National Laboratory, and Kinder Morgan, an enhanced-oil-recovery company.

Using a small, one-mile-square depleted oil reservoir near Hobbs, donated as a test bed for the project by Strata Production Company, the team pumped about 30 tons of CO2 per day into the reservoir from early December until mid February.

As the gas was injected, downhole geophones much more sensitive than the human ear listened for the snap, crackle, and pop that occurred as the gas induced very small earthquakes called microseisms. Such sounds, it was hoped, would help the researchers follow the CO2 front as the gas spread underground.

Other seismic monitoring was done before and after the gas injection using lines of geophones laid out on the surface above the reservoir. As a truck with a large gas-driven thumper, parked at various locations on the surface, created vibrations, the surface instruments measured seismic waves that reflect off underground features.

Seismic surveys also are being performed between wells that straddle the reservoir. A pressurized air gun creates vibrations from one well while sensors in the other record the vibration signatures. Readings are being taken as the sensors are moved up the borehole in 10-foot increments.

With the gigabytes of data they are producing, the team will create three-dimensional images of the underground geology. The data will be compared with those from similar measurements taken before the CO2 was injected into the reservoir.

Changes between the two sets of images will provide clues about what is happening underground. Los Alamos and the Colorado School of Mines are performing the data analysis.

The data also will be used to adapt 3-D geophysical computer models used for oil and gas exploration to models that will help predict results of future geologic carbon sequestration efforts.

"The current models depend on some assumptions," says Norm Warpinski (6116), Sandia carbon sequestration program manager. "We don’t know where those assumptions are wrong."

"We might raise more questions than we answer," he says. "But that’s OK. This is a stepping stone to larger projects."

Sandia’s role is to provide technical support of the geologic modeling effort and study in detail the chemical reactivity and fate of the CO2 in laboratory tests.

During the past year Sandia researchers have conducted a series of lab experiments on core samples from the reservoir to study the expected chemical interactions between the CO2, a brine, and the underground minerals. They’ll test post-CO2 core samples, as well.

The Strata reservoir near Hobbs is the first US site dedicated to CO2 sequestration rather than enhanced oil recovery. (The oil industry pumps CO2 into active oil reservoirs as a way to recover remaining oil that is difficult to extract.)

Sandians involved in the project include Norm, Jim Krumhansl (6118), Carlos Jove-Colon (6851), John Lorenz, Scott Cooper (both 6116), and Hank.