The Impact of Microemulsion Viscosity on Oil Recovery

Abstract

The physical structure of microemulsions and the degree to which ultra-low IFT is achieved is dependent on a number of parameters including the types and concentrations of surfactants, co-solvents and alkali, crude oil composition, brine composition, temperature and to a lesser extent, pressure. Modifying any one of these variables creates a microemulsion with different properties. The rheological properties of the microemulsion must be adjusted appropriately to achieve good performance under practical reservoir conditions. Two microemulsion properties of primary concern are undesirably high viscosity relative to oil viscosity and non-Newtonian behavior. The broader implications of injecting microemulsions with high viscosities or non-Newtonian behavior in the field include high surfactant retention, unsustainably high pressure gradients, reduced sweep efficiency and microemulsions that stagnate in the field due to high viscosity at low shear rates. The most common ways to reduce microemulsion viscosity are to optimize the surfactant formulation with a good co-solvent and/or by adding more branching to the surfactant hydrophobe. Adding co-solvent in appropriate concentrations makes a microemulsion much less viscous. However, co-solvents increase the cost and complexity and also tend to increase the IFT. A less conventional solution involves increasing the temperature of the injection water thereby lowering both the oil and microemulsion viscosity. This approach has been tested successfully in core floods using both surrogate and reservoir cores.

Use of Co-Solvents to Improve Alkaline-Polymer Flooding

“…Figure 4 shows crude #2 emulsions are as viscous as the crude at 68°C when the oil content is 30%, while adding just 1% co-solvent reduces their viscosity over ten-fold. This pattern is seen whenever a tailored co-solvent is added to viscous macroemulsions (Walker et al, 2012).…”

“…Macroemulsions can be extremely viscous, and can hurt coreflood performance in terms of oil recovery and excessive pressure drop (Walker et al, 2012). Addition of certain light co-solvents has the effect of destabilizing macroemulsions and encourages the formation of thermodynamically-stable microemulsions with low viscosity (Bourrel and Schechter, 1988;Sahni et al, 2010;Walker et al, 2012). The use of viscous macroemulsions for mobility control has generally not been successful (Mayer et al, 1983).…”

“…The light co-solvents used in this study are small, non-ionic molecules showing no issues with adsorption and/or chromatographic separation. Such light co-solvents tend to reduce the microemulsion viscosity, which is particularly important with heavy crude oils (Walker et al, 2012, Kumar et al, 2012.…”

An experimental and numerical study of chemically enhanced water alternating gas injection

“…As is well known, a microemulsion is a thermodynamically stable and clear dispersion of oil and water, in combination with surfactant molecules (Ruckenstein 1981;Walker et al 2012). Winsor (1985) identified that for a microemulsion system with a fixed surfactant concentration, selected crude oil, and different salinity, the phase behavior of microemulsion can be classified into three different classes: microemulsion Type I (or lower phase microemulsion), microemulsion Type II (or upper phase microemulsion), and microemulsion Type III (or middle phase microemulsion).…”

Application of Low Concentration Surfactant Enhanced Water-Alternating-Gas Flooding

“…Microemulsions are thermodynamically stable and clear dispersion of water and oil when combined with surfactant solution (Walker et al, 2012) Windsor (1985) discussed the classification of microemulsion phases. Microemulsion was classified into three different types; type I also known as the lower phase microemulsion, type II (upper phase microemulsion) and type III (middle phase microemulsion).…”