In EOR projects with chemical, flooding the core by several chemicals is a In EOR projects with chemicals, flooding the core by several chemicals is a must. The chemicals whether surfactant, polymer, alkaline, or the mixtures, is chosen based on a thorough evaluation of the reservoir system and properties. The oil-recovery of every chemical will be compared to brine oil-recovery. The chemical stability can be improved by adding nano particles into the chemical. The chemical with the highest oil recovery will be chosen.
It is also required to provide a driving fluid behind EOR chemical to push hydrocarbon into production wells. Some oil and gas companies use brine and others use polymers or emulsion. The viscosity of driving fluid of 2 or 3 times of oil viscosity is better.
The emulsion as a driving fluid has some advantages compared to other driving fluids. An emulsion for driving fluid can be water in oil emulsion (WO emulsion) or oil in water emulsion (OW emulsion). Some scientists go further to find that the emulsion of oil in water in oil (OWO) has better performance in which the viscosity is lower than the counterpart emulsion for the same rates. This will decrease the cost to push the fluid into production wells. Figure 1 and Figure 2 show a comparison of viscosities between the OWO emulsion and WO emulsion.
It is believed, driving fluid stability against shear is important for improve sweeping. The emulsion of oil-in-water in oil is better than water in oil emulsion. The viscosity of oil-in-water in oil emulsion is much lower than the viscosity of water in oil emulsion (Figure 1). Therefore the pressure loss and viscosity reduction during driving by the emulsion of oil-in-water in oil are lower. For more stable emulsion, nano particles can be added into the emulsion of oil-in-water in oil. If the oil being displaced has asphaltene, nano-particles are not required.
The produced liquid from the production well will have an emulsion phase. Emulsion breaking is required to separate the water and salts from the oil. A combination of the mechanical and chemical methods is generally utilized to break the emulsions. Some system injects demulsifier (emulsion breaking chemical) into flowline before heater and storage tanks and others inject demulsifier after the heater but before the storage tanks. A heater is required to control the temperature above the crude cloud point since emulsion is less stable above cloud point temperature. The demulsifier function as solvents, change surface tension, and flocculant. The demulsifier will act to solve the water and break the surface film oil-water and then flocculate the broken water into a water droplet to facilitate coalescence. Before applying the appropriate demulsifier, the service company is required to do a bottle test in the field to determine the most suitable demulsifier.
Recommended reading, emulsion for anti-aging, and emulsifier to male soap: