Abstract
Abstract
Water flooding has been used for many decades as a way of recovering more oil. Historically, the salinity of the injection water has not been regarded as a key variable in determining the amount of oil recovered. Crude oil/water/rock chemical interactions can lead to large variations in the microscopic displacement efficiency of water flood. There is increasing evidence, as reported in the literature, that injecting low salinity brines has a significant impact on the amount of oil displaced, but the exact mechanism by which this occurs is an unsettled issue. The main objective of this paper is to determine the effects, advantages, and practicalities of using low salinity water flood to displace more oil in both carbonates and clastics formations. Another objective is to understand the main mechanisms in low salinity waterflood, and to determine the effects of salinity level on oil recovery.
In the present study, we measured the interfacial properties between oil n-dodecane and brines with various salt contents. The interfacial tension between oil and brines was measured using the Pendant Drop Apparatus. The effects of salinity, temperature, pressure and aging were examined in details.
The results obtained indicated that there is a critical salt concentration where the interfacial tension between brine and oil is low. We believe that this salt concentration will enhance oil recovery, and therefore, should be considered when designing water floods. Aging time has a significant effect on the interfacial properties and it depends on the temperature and pressure conditions. Interfacial tension decreased linearly with temperature.
Introduction
Sixty percent of the oil remained entrapped in the porous rock of the formation after secondary recovery process. For extraction of this valuable residual oil, associated gas lift, water or aqueous chemical solution flooding are the most efficient methods in practice. The tertiary oil recovery is mainly dependent on the properties of oil/aqueous/formation interfaces. These are capillary forces, contact angle, wettability, viscous forces and interfacial tension. These properties are represented by a dimensionless group called the capillary number, Nc, which is a measure of the mobilization of the occluded oil to enhance the oil recovery:
Equation
where µ is the dynamic viscosity of the liquid, v is the velocity, ? is the contact angle, and s is the interfacial tension (IFT) between the water phase and the oil phase.
For better EOR efficiencies, the capillary number, Nc, has to be maximized by either increasing viscosity or reducing interfacial tension. Viscosity can be increased by flooding with chemical solutions of high apparent viscosity while interfacial tension is reduced by injection surfactant solution or water with an optimum salinity. This decrease in interfacial tension between crude oil and formation water lowers the capillary forces, facilitates oil mobilization, and enhances oil recovery. Therefore, IFT of any hydrocarbon-water systems is an important thermo-physical property in oil recovery process.