Key Aspects of Project Design for Polymer Flooding at the Daqing Oil Field

Dongmei Wang, R.S. Seright, Zhenbo Shao, Jinmei Wang – 2008

Abstract

This paper describes the design procedures that led to favorable incremental oil production and reduced water production during 12 years of successful polymer flooding at the Daqing oil field. Key design factors include: (1) recognizing when profile modification is needed before polymer injection and when zone isolation is valuable; (2) establishing optimum polymer formulations and injection rates; and (3) time-dependent variation of molecular weight in injected slugs. Oil recovery can be enhanced by 2–4% OOIP with profile modification before polymer injection in some wells. Injecting polymer separately into different layers improved profiles, sweep, injection rates, and reduced water cut. Bank sizes grew from 240–380 mg/L·PV in early pilots to 640–700 mg/L·PV in recent industrial sites. Economics and injectivity behavior can favor changing polymer molecular weight and concentration during injection. Polymers of 12 to 35 million Daltons Mw were designed. The optimum polymer injection volume was approximately 0.7 PV, with average concentration around 1,000 mg/L.

Key Takeaways

  • Profile modification before polymer injection can increase oil recovery by 2–4% OOIP in Daqing wells with highly heterogeneous permeability — a prerequisite step often skipped in field-scale projects.
  • Injecting polymer separately into layers with significant permeability differential and no crossflow improved flow profiles, reservoir sweep, injection rates, and production well water cut simultaneously.
  • Bank sizes grew from 240–380 mg/L·PV in early Daqing pilots to 640–700 mg/L·PV in recent industrial sites — larger banks consistently yielded better performance.
  • Changing polymer molecular weight and concentration during injection can improve economics and injectivity: polymers of 12 to 35 million Dalton Mw were designed for different reservoir geological conditions at Daqing.
  • The optimum polymer injection volume at Daqing was approximately 0.7 PV at an average concentration of about 1,000 mg/L, though individual injection stations used concentrations up to 2,000 mg/L.
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