Polymer flooding: Current status and future directions

R.S. Seright, Dongmei Wang – 2023

Abstract

This review presents our perspective on the factors that have brought polymer flooding to its current
state. Insights are provided on why HPAM is the dominant polymer used as well as what is needed to make alternative polymers and mobility-control methods viable. Explanation is given for why large polymer banks are needed for polymer flooding, and design of the injected polymer viscosity is detailed for cases with/without crossflow. The role of fractures and horizontal wells are discussed for improving injectivity and extending polymer flooding to recover oils with viscosities as high as 10,000 cP. Operational improvements are described to minimize mechanical and oxidative stability to allow HPAM polymers to be viable to 70 C and ATBS polymers to 120 C. Key factors affecting polymer retention are summarized. The paper points out unresolved issues and future directions for polymer flooding.

Key Takeaways

  • Polymer banks must exceed 50% pore volume to be effective — once water injection resumes, it fingers through the polymer bank in the most permeable pathway and the flood is effectively over.
  • The correct polymer viscosity to inject is determined by multiplying the endpoint water/oil mobility ratio by the permeability contrast between reservoir layers — a base-case design that many current projects underachieve.
  • Endpoint relative permeability to water (k_rwo) must be measured with sufficient throughput (potentially hundreds of pore volumes) — insufficient waterflooding during lab tests produces artificially low k_rwo values that lead to underdesigned polymer floods.
  • Open fractures are essential for acceptable injectivity in vertical polymer injection wells — they eliminate shear-thickening and mechanical degradation of HPAM that would otherwise make vertical injection impractical.
  • Residual resistance factors greater than 2 should be viewed with suspicion in rock above 200 mD — reported high values are usually an artefact of insufficient post-polymer brine flushing in short laboratory cores.
  • HPAM can be stable to 70°C and ATBS copolymers to 120°C under low-oxygen conditions, substantially expanding the reservoir temperature range where polymer flooding is technically feasible.
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