An understanding of how CO2 foam flows through a reservoir rock is useful for many subsurface applications, including enhanced oil recovery and CO2 storage. There are economic and environmental benefits in identifying surfactants that exhibit good foaming behavior with CO2 at both low concentrations and high foam qualities. Core flood experiments have been carried out to investigate the behavior of supercritical CO2 foams flowing through a high-permeability Indiana Limestone. The foaming behavior and concentration response of two surfactants, a betaine and a sultaine, were investigated. For the two surfactants, the transition foam quality and the maximum apparent foam viscosity both decreased with reducing surfactant concentration. A comparison between the foaming behaviors of these surfactants with CO2 and N2 was also carried out. It was found that the N2 generated stronger foam at low foam qualities, but the CO2 was better at maintaining good foaming behavior at high foam qualities.

The efficiency of oil processes depends on the product of volumetric sweep and microscopic sweep. In oil recovery by steam injection the microscopic sweep is generally good; however, obtaining a good volumetric sweep can be challenging. This is caused by low density and viscosity of the injected steam combined with the reservoir heterogeneity, in particular existence of thief zone. Consequently, the steam utilization factor measured by steam-to-oil ratio (SOR, kg steam/bbl of oil) for many steam-flooding projects becomes poor. All these issues can be addressed by a successful application of steam foam technology. In steam foam applications, steam (plus a non-condensing gas) is injected simulateneously with a surfactant solution. Under the favorable injection conditions a foam is formed inside the reservoir leading to significant reduction of steam mobility and can eventually improve sweep efficiency. In the literature many successful steam foam pilots have been reported. However, most of these applications are at relatively shallow reservoirs with low pressures and thus low temperatures. In our paper we investigate if steam foam can also be effectively used for applications at high steam temperatures, significantly exceeding 200°C. To test the viability of steam foam technology at high temperatures, we have tested the stability of multiple surfactants at reservoir conditions. For those surfactants that showed good stability, core flood tests have been carried out to test the ability to form foam and to assess the resulting foam strength. Steam foam tests have also been carried out at temperature up to 240°C.

The efficiency of the dimethyl ether (DME) enhanced oil recovery (EOR) technique in a fractured chalk reservoir core plug was investigated. The coreflood experiment showed that DME EOR could lead to 44.2% additional oil recovery, amounting to 80.6% of the ultimate oil recovery. A comprehensive set of laboratory experiments, including density measurements of miscible fluids, DME-induced oil swelling factor, and partition coefficient of DME between the aqueous and oleic phase, were performed. The experimental results show that the partition coefficient of DME for the mixture of DME-brine-oil can reach up to 18.3. The oil swelling factor for such a system can reach up to 2.7 under realistic reservoir conditions. Comparing this data set to the available data for other mutually soluble solvent-based EOR techniques shows that the oil swelling caused by DME is far stronger than for other common solvents. Due to the strong partitioning of DME between the phases, the DME from the DME-brine solution rapidly partitions into the bypassed oil in the low permeability matrix, which leads to strong oil swelling and production.

Foam structure evolves with time due to gas diffusion between bubbles (coarsening). In a bulk foam, coarsening behaviour is well defined, but there is less understanding of coarsening in confined geometries such as porous media. Previous predictions suggest that coarsening will cause foam lamellae to move to low energy configurations in the pore throats, resulting in greater capillary resistance when restarting flow. Foam coarsening experiments were conducted in both a model-porous-media micromodel and in a sandstone core. In both cases, foam was generated by coinjecting surfactant solution and nitrogen. Once steady state flow had been achieved, the injection was stopped and the system sealed off. In the micromodel, the foam coarsening was recorded using time-lapse photography. In the core flood, the additional driving pressure required to reinitiate flow after coarsening was measured. In the micromodel the bubbles coarsened rapidly to the pore size. At the completion of coarsening the lamellae were located in minimum energy configurations in the pore throats. The wall effect meant that the coarsening did not conform to the unconstricted growth laws. The coreflood tests also showed coarsening to be a rapid process. The additional driving pressure to restart flow reached a maximum after just 2 minutes.

Gas trapping is an important mechanism in both Water or Surfactant Alternating Gas (WAG/SAG) and foam injection processes in porous media. Foams for enhanced oil recovery (EOR) can increase sweep efficiency as they decrease the gas relative permeability, and this is mainly due to gas trapping. However, gas trapping mechanisms are poorly understood. Some studies have been performed during corefloods, but little work has been carried out to describe the bubble trapping behaviour at the pore scale. We have carried out foam flow tests in a micromodel etched with an irregular hexagonal pattern. Image analysis of the foam flow allowed the bubble centres to be tracked and local velocities to be obtained. It was found that the flow in the micromodel is dominated by intermittency and localized zones of trapped gas. The quantity of trapped gas was measured both by considering the fraction of bubbles that were trapped (via velocity thresholding) and by measuring the area fraction containing immobile gas (via image analysis). A decrease in the quantity of trapped gas was observed for both increasing total velocity and increasing foam quality. Calculations of the gas relative permeability were made with the Brooks Corey equation, using the measured trapped gas saturations. The results showed a decrease in gas relative permeabilities, and gas mobility, for increasing fractions of trapped gas. It is suggested that the shear thinning behaviour of foam could be coupled to the saturation of trapped gas.