CO2 value chain
The expression CO2 value chain is used to describe the process of capturing CO2 and transporting it back to the oil field, where it is injected in order to force more oil out of the reservoir. In this way, a problematic greenhouse gas becomes a tool for additional value creation, so-called Enhanced Oil Recovery (EOR).
A CO2 value chain consists of the following links:
- A processing plant that captures CO2
- Infrastructure for transport and intermediate storage
- Injection facilities
The petroleum industry already has experience from some links of the value chain. At the Sleipner field in the North Sea, Statoil has since 1996 been separating CO2 from natural gas and stored the CO2 underneath the ocean floor. The same is being done at the Snøhvit field, in the desert of Algeria and many other places around the globe.
For many years, the industry has been injecting water, gas or chemicals into the oil reservoirs to enhance oil recovery. CO2 injection is used on many onshore oil fields. In the USA alone there about 80 such projects. At the Weyburn field in Canada, CO2 from coal-fired power plants has been injected into the reservoir since 2000. According to plans, a total of 20 million tons of CO2 are to be injected into the Weyburn reservoir. So far, however, there are no complete CO2 value chains for Enhanced Oil Recovery at sea.
How CO2 injection affects oil yields
When CO2 is injected into an oil reservoir, it mixes with the oil, causing the oil to swell. In addition, CO2 reduces the surface tension between oil and water. The result is that the oil flows more easily, making it easier to pump the oil and increasing the reservoir's performance. However, this method requires that that the pressure in the reservoir exceeds the solution pressure of CO2, otherwise CO2 will not mix with the oil.
It is also possible to inject immiscible CO2 on top of an oil reservoir, in which case the pressure exerted by the CO2 forces the oil towards the oil wells.
Experts assume that CO2 injection into Norwegian offshore oil reservoirs could enhance oil recovery by 3-7 percent. CO2 injection is most appropriate in reservoirs that are becoming depleted, and thus the method can extend the productive life of an oil field.
Challenges related to CO2 injection
It can take from many weeks to even years before oil recovery actually increases after having injected CO2. Onshore facilities in the USA have shown that even wells located close to each other can behave differently.
Another challenge is that some of the CO2 injected into the reservoir is pumped up together with the oil. The facilities must therefore have equipment for re-capturing CO2 and pumping it back into the reservoir, which leads to considerable extra costs.