Polymer Solution Extension Viscosity Effects During Reservoir Flooding

Abstract

Abstract Both shear and extensional viscosity properties of a polymer solution must be characterized as a function of macromolecular structure and solvent-polymer interactions if fluid mobility performance during reservoir flooding can be predicted. When the flow rate through a porous medium exceeds a critical value, polymer coils can elongate and produce additional resistance to flow. Extreme extensional flow conditions can increase the fluid's resistance by two or three orders of magnitude greater than that due only to the shear flow field. The conditions needed to produce high extensional fluid resistance depend upon 1) polymer properties, 2) porous media geometry, 3) fluid flow rates and 4) solvent composition. For a fixed porous medium geometry and flow rate, resistance increases with increasing macromolecular contour length and hydrodynamic polymer coil size. In turn, contour length and coil size depend upon macromolecular structure. Thus macromolecular structure can be adjusted to alter fluid resistance to extensional flow fields. Introduction When using a polymer solution to flood an oil reservoir the displacing fluid should have a high resistance to flow within the porous medium. High displacing fluid flow resistance increases movement of residual oil to a producing well and thus enhances oil recovery productivity. To be economically acceptable the water soluble polymers used to produce displacing fluids must significantly increase solution viscosity or resistance to flow when added in very small quantities to an aqueous solvent. Fluid resistance results from polymer coil molecular distortions during flow through the small and tortuous channels of the porous medium. These macromolecular distortions convert energy to heat and are caused by both shear and elongational forces produced by the flow field. In general increasing shear forces on polymer coils decreases flow resistance; however, increasing coil elongational forces increases resistance. This paper discusses how macromolecular structure properties and polymer-reservoir interactions affect fluid resistance during flow through a porous medium. P. 447^