Pressure Modification or Barrier Issues during Polymer Flooding Enhanced Oil Recovery

This paper examines when the pressure-barrier concept limits the size and viscosity of the polymer bank during a polymer flood. If the polymer bank is too large or too viscous, pressure drops from the injection well to the polymer front may act as a pressure barrier, usurping most of the downstream driving force for oil displacement. Using analytical and numerical methods, the paper examines pressure-barrier relevance across oil viscosities from 10 to 1,650 cp, vertical versus horizontal wells, single versus multiple layered reservoirs, permeability contrast, and crossflow between layers. In single-layer or no-crossflow multilayer reservoirs, the pressure-barrier concept only limits optimum polymer viscosity if the polymer bank mobility is less than the displaced oil bank mobility — meaning the optimum polymer viscosity is typically dictated by the oil bank mobility. For multilayer reservoirs with free crossflow between layers, a compromise between polymer viscosity and recovery efficiency is required. For viscous oil reservoirs like Pelican Lake and Milne Point where the target polymer/oil mobility ratio is near one, pressure barrier development is unlikely.