The Petroleum Technology Research Centre (PTRC), a Canadian group comprising both government and industry oil industry interests, is researching the Enhanced Oil Recovery (EOR) operations at the Weyburn and Midale oil fields in Saskatchewan to learn more about how CO2 behaves underground, acting executive director Brian Kristoff told Gasification News.
So far, the data received from the first phase of the project from the Weyburn site, which has a CO2 intake of 5,000 tons/day, shows no cause for concern, Kristoff said.
"It is still early, but in the tests that we have done – and we've done surface monitoring also, in addition to seismic and chemical monitoring – haven't shown anything coming back to the surface. These are subsurface geological formations that have held oil and gas for millions of years at relatively high pressures, so they should be fairly competent," he said.
Three-dimensional map showing the location of the Weyburn study area in southeastern Saskatchewan. The dashed cube represents the area where the geoscience framework is being constructed. Lower inset shows the location of the International Energy Agency geoscience framework study area within the Williston Basin. Courtesy of PTRC.
Research at the Weyburn site encompasses Phase I of the study, which started in 2000. Phase II includes research recently started at the adjacent Midale site which is about one third of the size of the Weyburn field and takes in about 1,400 tons/day of CO2.
CO2 from the Great Plains gasification plant in North Dakota is compressed and pipelined a couple of hundred miles to the fields for injection to aid in EOR activities.
Kristoff said about 30% of the CO2 injected comes out with the oil. It is recaptured at the surface and reinjected.
Courtesy of PTRC
Monitoring EOR sites is expected to be more difficult than monitoring a pure sequestration site as the mature oil fields have not only been worked over for decades, but also are still operating.
The Weyburn and Midale sites were first developed in the 1950's and originally had 1.4 billion and 515 million barrels of oil in place respectively. They have both been through primary production, water flooding, in-fill drilling as well as some horizontal drilling. Weyburn has been flooding with CO2 since 2000 and Midale since 2005.
The seismic work at the 70 square mile Weyburn field is also tricky in that "you are injecting at one point and producing at another, and the CO2 is supposed to move across that distance," Kristoff said. But he added that the seismic work done so far "shows how 70% the CO2 is trapped as the oil is produced. You can actually see it in the seismic data and from chemical monitoring."
Ultimately, at the end of its life, the Weyburn field will have injected with more than 30 million tons of CO2, which is the equivalent of taking more than 6 million cars off the road for a year, PTRC said. The 40 square mile Midale field will have injected some 10 million tons of CO2, the equivalent of removing more than 2 million cars from the roads for a year.
The CO2 is injected at many sites on the fields and there are also hundreds of wells bringing oil up, so the fields have been likened to giant pincushions, which makes surface monitoring for CO2 all the more critical.
The CO2 is injected to a level 2,000 to 2,500 meters deep. "In terms of the radius (of the CO2 pool) we learned in Phase I how far it migrated out from the injection wells," Kristoff said.
He plans to compare the Weyburn data to the Midale data when it is complete. "From that we can make some assumptions as to how we might operate in other areas, whether other EOR fields or pure geological sequestration. The outcome of the next phase is a best practices manual. That will tell us how to really develop this kind of process for other reservoirs and geological settings."
As far as the costs involved with getting and injecting CO2 for EOR, that information is closely held by the participating companies, Kristoff said.
--Suzanne McElligott