Properties of N2- and CO2-foams as a function of pressure

In enhanced oil recovery (EOR) operations foam has been applied to improve sweep during gas injection or for gas shut-off. Field experiences for North Sea reservoirs involve foams using hydrocarbon gas for conformance control and gas blocking in high pressure and high temperature fields. Generally foam field applications have utilized CO2 and N2 in addition to hydrocarbon gas. ervoir conditions vary significantly it is important to understand foam properties on a broad experimental basis. The large changes in physical properties with temperature and pressure may affect CO2-foam properties and these are discussed by varying pressure from 30 to 280 bar in an outcrop Berea sandstone core material at 50 °C. The CO2-foam properties were compared to N2-foams. Foam was generated by co-injection of surfactant solution (AOS) and N2 or CO2 at 80% foam quality (fraction gas) at a total injection rate of 40 ml/h. N2-foams were generated both at 30 and 280 bar. In general, N2-foams were stronger than CO2-foams. Comparing CO2-foams at different pressures showed that CO2-foams at 30 bar were strong (MRF ~50–75) whereas supercritical CO2-foams gave MRFs in the range of 3–6. The visual foam structure observations from a sight glass at the core outlet showed denser N2-foams compared to CO2-foams. ing seawater after N2-foam showed that relative seawater permeability was low and remained low (<0.1) after injecting more than 10 pore volumes of seawater. Indeed, similar and positive results were obtained both for experiments run at 30 and 280 bar. ransfer was found to be very important for CO2-foam stability. Results from two CO2-foam flooding experiments with equilibrated fluids at 30 bar and 50 °C showed improved foam strength, even though the largest improvement was observed for foams ability to block seawater. ter relative permeability was strongly reduced in the presence of foam, thus providing the reservoir engineer with another tool for water blocking.