• News Center
• :
• About Us
• :
• Gas Pipeline
• :
• Gasification
• :
• Products
• :
• CO2 Capture and Storage
• :
• Clean Energy

• How It Works
• :
• Pipeline Information

How It Works

Capturing CO2

When coal is burned, it produces sulfur dioxide and nitrogen oxide as well as particulate matter and mercury. Under the Clean Air Act, those pollutants must be removed from exhaust gases that come out of the smoke stack. Coal combustion also produces carbon dioxide, which is not currently regulated. When coal is gasified, the process removes the sulfur dioxide, mercury and carbon dioxide from the syngas before it is combusted, making the "syngas" cleaner than raw coal. The other gases are lowered in the process, and the carbon dioxide is more concentrated, which makes it easier to capture.

Delivering CO2

The Great Plains Synfuels Plant has built a 205-mile long, 14-inch and 12-inch carbon steel pipe through western North Dakota into southern Saskatchewan. During construction, the pipeline had to cross the Little Missouri River and Lake Sakakawea.

At first, two compressors pushed the CO2 to Canada. In 2006, a third compressor was added, so more CO2 could move through the pipeline.

Storing CO2

Sequestration means to set apart something for safekeeping. Carbon sequestration encompasses the processes of capture and storage of CO2 that would otherwise reside in the atmosphere for long periods of time.

In the case of CO2, many consider it to be a greenhouse gas that contributes to the phenomenon of global warming. There is much debate over this issue with popular opinion supporting the theory that capturing human-produced CO2 emissions is a step in the right direction. On that basis, enhanced oil recovery via CO2 flooding is an example of how one project can be a benefit to both industry and the environment.

How enhanced oil recovery works

The gas in the pipeline is at very high pressure (about 152 bar), which makes it a supercritical fluid. Supercritical fluids are gases under such high pressures that the vapor (gas) phase becomes as dense as the liquid phase. Supercritical fluids have high density, but flow easily like gases, so are ideal for transporting through pipelines. The Weyburn oil field has a total of 720 wells. The vertical wells were drilled in a 9-spot grid pattern – eight producing wells in a square around an injection well and typically have a spacing of around 150 meters. The high pressure CO2 is pumped into 37 injection wells, helping oil to flow towards 145 active producer wells.

The level of purity of the CO2 supplied is ideal for use in enhanced oil recovery. This is because CO2 dissolves more readily into oil when small impurities are present. Hydrogen sulphide (H2S), which makes up 1.0 percent of the injection gas, is particularly beneficial at helping CO2 to mix with oil.

When CO2 supercritical fluid is pumped at high pressure into the reservoir, the CO2 mixes with the oil, causing it to swell and become less viscous. The swelling forces oil out of the pores in the rocks, so that it can flow more easily. Water is pumped into the injection wells, alternating with CO2, to push the released oil towards producer wells. Some CO2 comes back out of the ground at producer wells; this is recycled, compressed and re-injected along with gas from the pipeline.

It is predicted that the CO2 enhanced oil recovery operation will enable an additional 130 million barrels of oil to be produced, extending the field’s commercial life by around 25 years. It is also anticipated that about 20 million tons of CO2 will be injected and become permanently stored 1,400 meters underground over the lifetime of this project.

Although using CO2 to increase oil production is not new, prior to the Dakota Gas and Cenovus Energy project, the CO2 primarily came from natural sources. Because the naturally occurring ground source CO2 was removed and injected into the geological structure, there was no net reduction in CO2 emissions in the atmosphere. Dakota Gas is unique in that its CO2, which would have previously been emitted into the atmosphere, is permanently injected into a geological sink, thereby reducing the total annual emissions of CO2.

Top of page

• The CO2 Story

National Treasure

“The gasification plant is a national treasure and I think it should be recognized as such. It is absolutely amazing…the combination of the gas plant, Antelope Valley Station and the {Freedom} mine right next to each other – there is just no other facility complex like it – it’s unmatched in the world. You should be proud of that fact.”

– Dr. Robert Peltier, editor-in-chief, POWER magazine