**2.5.1 Injection in exhausted or declining oil reservoirs**

The option for injection in oilfields where production is waning serves another function besides carbon sequestration: it maximizes oil recovery. This process is called enhanced oil recovery (EOR). The standard production process always involves injection of water to maintain the producing pressure. The EOR process, shown in Figure 10, involves injection of water and CO2 in alternation. The CO2 injection increases the oil's fluidity, releasing the oil stuck in the rock pores, while the water, which is by nature not compressible, pushes the oil toward the producing well.

An example of the injection of CO2 in EOR projects is the Weyburn project, located on the border between Canada and the United States. It has been in operation since 2000. The CO2, with 95% purity, captured in a coal gasification plant in Beaulah, North Dakota, is carried by a pipeline to an oil production field in Weyburn, Saskatchewan, where it is injected (Zouh et al., 2004). Figure 11 shows the pipeline in yellow that connects Beulah and Weyburn. The red dots show possible derivations for use of the CO2 in new EOR projects in the region.

Carbon Capture and Storage – Technologies and Risk Management 249

Fig. 12. Weyburn Historical Oil Production - Source: Cenovus Energy (2011)

Statoil in its Sleipner natural gas field in the North Sea.

prompted Statoil to develop the geological capture project.

MtCO2 had already been stored by the end of 2008 according to Statoil.

Saline aquifers exist in the great majority of the world's regions. Since this water cannot be used for drinking or farming, the option to store CO2 in these aquifers appears very promising. The first project to capture carbon of this type was developed by Norway's

According to Statoil, the percentage of CO2 in the natural gas of its Sleipner field is approximately 9% (BGS, 2011), which is above the level tolerated by its consumers. In 1991, the Norwegian government introduced a tax of US\$ 50 dollars per tonne of CO2 emitted. These two aspects combined (standards required by consumers and government taxation)

Physically the project is composed of two platforms. On the first one the natural gas rich in CO2 is extracted. This gas is sent to the second platform where the CO2 is separated by chemical absorption, then compressed and injected into a saline aquifer located 1000 meters beneath the seabed. According to the projections of a special report of the IPCC (IPCC, 2005), the total storage capacity of the Sleipner project is 20 MtCO2, of which nearly 11

For the storage of CO2 in coal beds to be feasible, this process must be associated with the production of methane from the bed. The injection of CO2 enhances the production of methane, hence the name enhanced coal bed methane recovery (ECBM). The process is being studied by, among others, the Swiss Federal Institute of Technology (ETH) and other research organizations funded by European Commission and US Department of Energy (US DOE). These studies aim to obtain the necessary knowledge to apply the

**2.5.2 Saline aquifers** 

**2.5.3 Coal beds** 

technology in large scale.

Fig. 10. Enhanced Oil Recovery (EOR) Process

Fig. 11. Carbon pipeline linking Beulah and Weyburn – Source: Cenovus Energy (2011)

Figure 12 presents a graph of oil production in Weyburn since the start of the operation in December 2010. The brown area represents the increase in output because of the EOR process if the process had not begun in 2000, production in December 2010 would have been approximately 10 thousand barrels per day (10 kbopd). The EOR boosted this output in December 2010 to roughly 28 kbopd.

Fig. 12. Weyburn Historical Oil Production - Source: Cenovus Energy (2011)
