Demonstrating carbon sequestration

Click image to enlarge ENCANA The Weyburn researchers are using 4-D seismic surveys, such as this one, to infer the movement of the CO2 injected into the underground reservoir.

Initial findings from the largest carbon sequestration project in North America show that the oil industry can cost-effectively recycle waste carbon dioxide (CO₂) gas to recover petroleum from underground reserves at the end of their productive life span. Although the industry has used CO₂ in this manner for 40 years, this is the first major project to recycle waste gas from another energy source, pioneering the process that experts expect to become the main route for carbon sequestration in the future.

The Weyburn CO₂ Monitoring and Storage project now under way in Canada’s Saskatchewan province involves pumping waste CO₂ gas from the Dakota Gasification Co. in Beulah, N.D., up over the U.S.–Canadian border to the Weyburn oil field through a 320-kilometer pipeline. John Gale, program manager for geological storage at the International Energy Agency’s Greenhouse Gas R&D Programme (IEA GHG) in Cheltenham, England, says the Weyburn project is as important as the Sleipner project run by Statoil in Norway, where waste CO₂ from natural gas is being injected into deep saline aquifers on the sea floor (Environ. Sci. Technol. 1999, 33, 66A-70A).

The Weyburn site is notable for using waste CO₂ gas rather than tapping into naturally occurring CO₂ from underground reservoirs, which is how the oil industry historically harvested the gas to help capture the last remaining oil in underground deposits, says Howard Herzog of the Massachusetts Institute of Technology, who is leading his university’s Carbon Sequestration Initiative. The traditional approach actually “unsequesters” carbon, he explains.

The Weyburn project is expected to sequester 14 million metric tons (t) of CO₂ during its lifetime—about 77% of the gas pumped into the reservoir. The 1 million t of CO₂ captured per year are equivalent to the amount generated by a 150-megawatt coal-fired power plant, says Scott Clara of the U.S. Department of Energy’s (DOE) Office of Coal and Environmental Systems. The CO₂ is injected into the oil field through 29 injection wells, and there are 4 observation wells in the area. Funding for the project comes from 20 international organizations, including IEA; DOE; the European Community; and seven industrial sponsors from Canada, the United States, and Japan.

There are a growing number of geologic carbon sequestration projects around the world, but the Weyburn project is one of only four large, long-term active or planned projects that will sequester 1 million t of CO₂ annually, points out Herzog. In addition to Weyburn and Sleipner, Statoil is planning a second project in Norway and British Petroleum has one planned in Algeria.

The other three large projects involve sequestering the waste CO₂ that is routinely separated from natural gas to make it burn more efficiently. Rather than following the traditional approach of venting the unwanted carbon into the atmosphere, Statoil is injecting the waste gas into underground reservoirs, Herzog says.

Herzog argues that because the oil industry always makes an effort to use some kind of technology to enhance oil recovery at the end of its wells’ life spans, projects like Weyburn offer some of the best opportunities for scientists to study the value of geologic sequestration. The injection is taking place already and therefore scientists must simply monitor it more extensively, rather than having to drill a network of injection wells (Environ. Sci. Technol. 2001, 35, 148A-153A).

Another advantage of Weyburn, say scientists, is that the Saskatchewan province’s records on the geophysical, production, and injection activities in the oil field are among the most extensive available. The project’s organizers are using 4-D seismic technology to map the movement of the injected CO₂ through the underground reservoir, which helps scientists determine how much of the sequestered CO₂ stays underground (Environ. Sci. Technol. 1999, 33, 66A-70A). By showing how the CO₂ moves through the reservoir, the 4-D technology is helping researchers determine if they can direct CO₂ storage, explains Koorosh Asghari, an assistant professor of petroleum systems engineering with the University of Regina, one of the organizations involved in the monitoring effort.

IEA GHG estimates that 120 gigatons of CO₂ could be stored in depleted oil fields, approximately 13% of the total set forth by the Kyoto Protocol to stabilize emissions at 550 parts per million, Gale says. However, he says that the figure may be pessimistic because it is based on the assumption that 50% of the CO₂ injected into an underground reservoir stays there. Studies conducted to date show that the amount varies based on the miscibility of the CO₂ in petroleum, but anywhere from 33 to 50% of the gas may be taken up by the oil it is used to recover, Gale says. However, the oil industry has good technologies for separating this CO₂ from the oil pumped out of the wells, Asghari says.

It is too early to calculate the percentage of CO₂ being permanently sequestered at Weyburn, but the seismic studies are showing that the CO₂ is not escaping from the underground formation, says Mike Monea, the project’s executive director at Petroleum Technology Research Centre in Regina, Saskatchewan. Observers are concerned about the possibility that CO₂ will migrate up through wells or casings that have been bored into the rock. “I’m not worried about that…if we in the oil industry know anything, it’s how to plug holes,” Monea says.

“The only way to breach this reservoir is with fractures,” Monea notes. The project’s scientists are currently using models to calculate how much CO₂ could escape through fractures in the rocks over the next 5000 years.

Monea is particularly pleased because the project is thus far recovering significantly more oil from the Weyburn field than the 15% improvement predicted with modeling. “We have seen a 25% increase in oil production…of 5000 more barrels of oil per day,” Monea says. He expresses confidence that the project will prove profitable.

Gale agrees that the project will be a moneymaker, but he points out that the cost of the CO₂ used in the project is relatively low. Asghari says that Dakota Gasification is charging $1/t. The cost of capturing CO₂ is generally $35/t, Gale explains. However, Dakota Gasification had already constructed equipment for capturing the gas, so it could sell CO₂ for significantly less and still make a profit. DOE’s goal is to reduce the cost of capturing CO₂ to $10/t within the next few decades.

The cost of capturing CO₂ needs to come down before energy companies will be able to cost-effectively collect it from major sources like power plants, which are responsible for 33% of the global CO₂ emissions, Herzog says. But IEA GHG has identified more than 200 plants, like Dakota Gasification, at which CO₂ is present as a high-purity gas and could be captured and transferred to nearby oil fields to help enhance oil recovery, Gale says. In addition, the operators of the numerous oil fields in the vicinity of Weyburn could be interested in buying Dakota Gasification’s waste gas to increase their oil production, he adds.

The first official progress report on the Weyburn project is due out early next year. —KELLYN BETTS