The Influence of Viscoelasticity on Displacement Efficiency--From Micro- to Macroscale

Abstract

The displacement efficiency (De) in porous media is usually analyzed by the ratio of the macro pressure gradient driving force and interfacial tension (IFT) between the driving fluid and residual oil. However, when the pressure gradient is constant, macro forces cannot explain the increase in De by driving fluids with elastic properties. Therefore, the change of micro forces acting on residual oil between driving fluids with and without elastic properties is analyzed.This paper shows the influence of viscoelasticity on De; the difference in the stress of non elastic fluids and fluids with elastic properties when flowing is analyzed; the effect of this stress difference on the micro flow lines in pores is mathematically simulated; the affect of the changes in micro forces caused by the change in micro flow lines on residual oil is shown; this enhanced micro force (without changing the macro pressure gradient) mainly acts on the protruding portion of different types of residual oil in pore(s), causing the protruding portion to change shape and move (mobilize); results on visualization core models confirm the above calculation and analysis; the displacement results on cores by fluids with different elastic properties in the lab are shown; the results of considering the phenomena that elasticity increases the De in numerical simulation are shown and compared with field results; large scale field results on polymer flooding and pressure coring are also shown.The above mathematical simulation, analysis, lab tests and field results all show that the micro forces acting on residual oil is different when the elastic properties of the displacing fluid varies, resulting in an increase in De for viscoelastic displacing fluids at constant pressure gradient conditions. This method of micro flow line and force analysis and its conclusions should be useful to further understand the mechanism of De in porous media; should be useful in designing, screening and developing better chemical flooding products, methods and projects to further increase oil recovery; should be useful in the analysis of phenomena associated with injecting non Newtonian fluids and gels.

Advances in Polymer Flooding

“…It was found that if an elastic fluid flows over dead ends, normal stresses between oil and polymer solution are generated in addition to the shear stresses resulting from the long molecular chains [36,37]. Therefore, polymer molecules impose a larger force on oil droplets and thus pull them out of dead ends.…”

“…For oil-wet porous media, residual oil is attached on the rock surface in the form of a continuous oil film (Figure 3(2)). Wang et al [8,36] compared the velocity profile of a Newtonian and a non-Newtonian fluid in a capillary and observed that the velocity gradient near the capillary wall for the elastic fluid is noticeably higher than that for the Newtonian fluid (Figure 7). Therefore, a stronger force is produced during flow of polymer solutions compared to water, which thus facilitates stripping the oil films off rock surface and eventually promotes the microscopic displacement efficiency [39][40][41][42].…”

Capillary breakup extensional rheometry of associative and hydrolyzed polyacrylamide polymers for oil recovery applications

“…While traversing through the constricted pore throat region of the reservoir, the injected slug would generate extensional, viscoelastic stress that led to the difference in their behavior. Several types of research were carried out to investigate the role of viscoelasticity in additional recovery during chemical flooding . It was concluded that viscoelasticity is an additional recovery mechanism that could mobilize some of the residual oil.…”

Enhanced displacement of a liquid pushed by a viscoelastic fluid

“…In oil recovery, the viscoelasticity of the pushing fluid has been considered through its extensional viscosity [6] which can induce significant increase of flow resistance in a porous medium. Recently it has been suggested that 1 the development ofsignificant normal stress differences could be at the origin ofenhanced oil recovery [7][8][9][10][11][12]. This normal stress effect has nevertheless not been demonstrated yet, and the physics at work not understood either:…”