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.

Assessment of Polymer Injectivity with Regards to Viscoelasticity: Lab Evaluations towards Better Field Operations

“…This method is preferred and used by different authors such as Wang et al (2007) and Xia et al (2004). A quantitative measurement of elasticity during flow is the first normal stress difference.…”

More Residual Crude Oil Can Be Displaced Out by Micro-Forces in Chemical Flooding

“…Because the span of cluster type residual oil is larger, and the pressure gradient remains constant, so the macro driving forces upon the cluster are higher than those on "oil droplets" and "oil columns" (the macro driving forces are proportional to length), the protruding portion on the forepart of the cluster will change shape and tend to form a droplet. Due to the "Expanding Piston Effect" [1] , with higher velocity and higher mass flow rate at the edges of the flow lines, the change in kinetic energy at these locations is greater for visco-elastic fluids compared to Newtonian Fluids, therefore the micro pushing force acting on the protruding portion is also greater, which is favorable to the mobilization of the residual oil.…”

“…Numerous test results in the lab and field show that the oil recovery ratio of polymer flooding is higher than that of water flooding [1][2][3][4] . Through flooding experiments on simplified pore models, Reference [4] studied the influence of Newtonian fluids and visco-elastic fluids with same viscosity on residual oil in dead ends.…”

Stability, seepage and displacement characteristics of heterogeneous branched-preformed particle gels for enhanced oil recovery

“…The elastic stress causes the protruding portion of residual oil to change shape and move. 10 Research shows that high elastic polymer solutions can result in higher sweep efficiency and lower residual oil saturation compared with low elastic polymer solutions. 11,12 Thus, a new viscoelastic displacement theory is put forward: the higher the viscoelasticity of the uid, the higher the oil recovery.…”