A Comparison of Polymer Flooding With In-Depth Profile Modification

R.S. Seright, Guoyin Zhang, Olatokunbo O. Akanni, Dongmei Wang

Abstract

This paper investigates when in-depth profile modification (using a blocking agent that places a deep plug in the high-permeability zone) is superior to conventional polymer flooding for stratified reservoirs with free crossflow. Using simulation and analytical studies, oil-recovery efficiency was examined as a function of permeability contrast, relative zone thickness, oil viscosity, polymer-solution viscosity, bank size, and relative costs. In-depth profile modification is most appropriate for high permeability contrasts (10:1), high thickness ratios (less-permeable zones 10 times thicker than high-permeability zones), and relatively low oil viscosities. Because of the high cost of the blocking agent relative to conventional polymer, economics favor small blocking-agent-bank sizes (e.g., 5% of high-permeability pore volume). Even though short-term economics may favor in-depth profile modification, ultimate recovery may be considerably less than from a traditional polymer flood. In radial flow, polymer flooding gains a relative advantage over in-depth profile modification compared with linear flow.

Key Takeaways

  • In-depth profile modification is most appropriate under specific reservoir conditions: high permeability contrast (10:1 or greater), high thickness ratio of less-permeable to high-permeability zones (10:1), and relatively low oil viscosity.
  • Because the blocking agent costs substantially more than conventional polymer, economics favor small blocking-agent banks (approximately 5% of high-permeability pore volume) — but these small banks also limit ultimate recovery.
  • Short-term economics may favor in-depth profile modification, but ultimate oil recovery may be considerably less than from a traditional polymer flood — requiring a longer-term view of economics.
  • In radial flow (typical of real field well patterns), polymer flooding gains a relative advantage over in-depth profile modification compared to the linear flow simulations commonly used to evaluate in-depth methods.
  • Retreatment with in-depth profile modification is compromised by previous blocks in the high-permeability layer, whereas polymer flooding allows successive retreatments without this constraint.
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