Effect of capillary number and work of adhesion on oil displacement by aqueous solutions of surfactants
This article deals with the physical foundations of the displacement processes and the main parameters characterizing the physicochemical properties of the phase separation surfaces and the patterns of their interaction, such as the work of adhesion, wetting, and interfacial tension. This required the analysis of the published studies on oil displacement with aqueous solutions of surfactants. The authors have performed a series of experimental studies on oil displacement from the composite core (sandstone) with sample mineralized water (2% NaCl in distilled water) and surfactant solutions under thermobaric conditions: mountain pressure <i>p</i>=25 MPa and temperature <i>t</i>=60°C with filtration rate 1.7 m/day by stationary filtration. This analysis required an interfacial tension at the “oil - water surfactant solution” interface, as well as oil adhesion to a model solid surface (a plate made of quartz glass) in water and water surfactant solutions. The results show that the oil recovery coefficient depends not only on the capillary number <i>N<sub>c</sub></i>, but also on the adhesion of oil to the surface of rocks <i>W</i>. The authors suggest to evaluate the effect of surfactants on the adhesion of oil to rock with a dimensionless parameter <i>W*</i>=<i>W<sub>w</sub>/W</i>, equal to the ratio of specific works adhesion of oil when displaced by water (<i>W<sub>w</sub></i>) and with the use of surfactants (<i>W</i>). The mass transfer during oil displacement with surfactant aqueous solutions is characterized by the equation K<sub>dis</sub>=<i>C</i>·(<i>N<sub>c</sub></i>·<i>W*<sup>n</sup></i>)<i><sup>m</sup></i>, the empirical coefficients of which are found by the equation of the linear trend line lg(K<sub>dis</sub>) from the logarithm of the modified capillary number <i>N*<sub>c</sub></i>=<i>N<sub>c</sub></i>·<i>W*<sup>n</sup></i>. The reliability of the linear approximation <i>R</i><sup>2</sup> of the experimental data obtained in this work is 0.9999, that is very close to 1. For the reagents and rock considered in the work, the empirical coefficients were the following: <i>С</i>=268.16; <i>m</i>=0.1080, <i>n</i>=0.25.