Abstract
In surfactant flooding, low interfacial tensions (IFT's) are required for recovery of additional significant quantities of crude oil from a reservoir rock. This paper indicates the usefulness of perspective plots to facilitate comparison of sets of IFT data. Such perspective plots simplify the process of screening various surfactant systems for enhanced oil recovery.
Introduction
Numerous articles have been written about the effects and/or importance of IFT between oil and aqueous phases in determining ultimate oil recovery during a phases in determining ultimate oil recovery during a secondary (waterflooding) or tertiary oil-recovery process. In the area of micellar/polymer or surfactant process. In the area of micellar/polymer or surfactant flooding, IFT has been studied extensively both by industrial and by academic investigators. A simplistic summary of this work is that low IFT's (generally corresponding to high capillary numbers ( are required for recovery of additional significant quantities of crude oil from a reservoir rock.
Method Development
Several variables influence between an oil-rich phase and a surfactant-containing aqueous phase. During phase and a surfactant-containing aqueous phase. During a surfactant flood, variations in surfactant concentration and salt concentration will occur as a result of mixing of the chemical slug with the pre flush (or formation brine) and polymer drive (" rear mixing" ). Nelson investigated salt concentrations required during a chemical flood to achieve efficient oil displacement. Since these variables (and others) change during the progress of a flood, it is desirable to determine the impact of these changes on the IFT between the oil- and water-rich phases. To assess the importance of changes in these two key variables (surfactant concentration and salinity) on IFT, an x-y plot may be constructed with values of each variable along the axes. The IFT for a particular surfactant concentration and salinity then is obtained experimentally and the numerical value placed at the corresponding (x, y) point on the plot. The resultant figure/table can be referred to as an IFT map. Points of equal, or about equal, IFT can be connected to produce an IFT contour map. In the investigation of the effect(s) of temperature on a given surfactant system and crude oil, IFT maps might be constructed for each of the pertinent temperatures. IFT's might be determined at six different sodium chloride concentrations (e.g., 1.0, 1.5, 2.0, 3.0, 4.0, and 5.0 wt%) and four surfactant concentrations (e.g., 0.085, 0.064, 0.042, and 0.021 meq/mL), resulting in IFT maps (for each temperature) each consisting of 24 IFT values. A comparison of the values of one map to the values of a second map (measurements made at different temperature) then is required to determine the impact of the temperature change. A single value for IFT for a given salinity and surfactant concentration assumes that the system is two-phase, because two IFT's can be measured for a three-phase system consisting of an oil-rich phase, a water-rich phase, and a microemulsion phase. phase. A method to allow easier comparison for the relatively large number of IFT data points that may be obtained during the study/screening of various surfactant systems at various conditions is described in this paper. The technique consists of interpolating between IFT values and then plotting the data with a perspective plotting routine. The method allows comparisons of IFT values for different crude oils, temperatures, cosolvent types, surfactant types, hardness ion concentrations, etc., through visual scanning of a perspective plot ranter than through trying to judge or compare numerical IFT values of an IFT map.
SPEJ
p. 350
Characterization of Complex Crude Oil Microemulsions-DSC Contribution