Water shutoff and conformance improvement: an introduction

R.S Seright, B. Brattekas – 2021

Abstract

This review paper provides an introduction to water shutoff and conformance improvement. After indicating the volumes of water produced during oilfield operations, a strategy is provided for attacking excess water production problems. Problem types are categorized, typical diagnosis methods are mentioned, and the range of solutions is introduced for each problem type. The concept of disproportionate permeability reduction is introduced — where polymers and gels may reduce permeability to water more than to oil or gas. The properties of formed gels as they extrude through fractures are described and related to treating conformance problems caused by fractures. The efficiency with which gels block fractures after placement is covered, including the impact of fluids injected subsequent to the gel treatment.

Key Takeaways

  • A systematic strategy for attacking excess water production should begin with problem diagnosis — distinguishing channeling, coning, behind-pipe flow, and fracture-dominated pathways — before committing to a treatment type.
  • Disproportionate permeability reduction (DPR) is the property whereby polymers and gels reduce water permeability more than oil or gas permeability; this is valuable for production well treatments where zone isolation is not available.
  • Formed gel extrusion through fractures is characterized by mobile gel wormholing through concentrated dehydrated gel — a mechanism that limits matrix invasion and aids fracture plugging selectivity.
  • The efficiency of fracture blocking by gels after placement is high in narrow fractures (washout pressure equals placement pressure) but decreases in wider fractures where gel can be mobilized at lower pressure gradients.
  • The volume of water produced in oil field operations is enormous — an estimated 3 barrels of water per barrel of oil globally in 2000 — making the economic stakes of conformance improvement very large even for modest per-barrel treatment savings.
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