Sweep Improvement Options for the Daqing Oil Field

R.S. Seright – 2008

Abstract

This paper investigates the potential of various approaches for improving sweep in parts of the Daqing oil field that have been EOR targets. Studies indicated that the polymer flood should have provided excellent sweep throughout the majority of patterns considered. However, because ASP flooding is being considered to increase recovery efficiency, mobility control and sweep improvement will be especially important. Fractures present in some Daqing wells aided reservoir sweep rather than causing channeling, because they were narrow and far from the wellbore. Near-wellbore fractures substantially increased injectivity index during polymer injection and oil-productivity index in production wells. Mechanical shear degradation is the greatest polymer degradation concern; near-wellbore fractures mitigate it effectively. Several new polymers show potential at Daqing. Other approaches investigated include colloidal dispersion gels, foams, ASP foams, steam, microbes, and reduced-salinity polymer solutions.

Key Takeaways

  • Polymer flooding provided excellent sweep throughout the vast majority of Daqing patterns studied — suggesting that additional sweep improvement technologies provide marginal incremental benefit over polymer alone for most existing patterns.
  • Fractures in Daqing wells aided sweep rather than causing channeling because they were narrow (not severely conductive) and located far from the wellbore — a favorable geometry contrast with fracture-dominated channeling problems seen in other fields.
  • Near-wellbore fractures substantially increased both injection well injectivity index and production well oil-productivity index during polymer injection — a positive operational outcome specific to Daqing’s fracture characteristics.
  • Mechanical (shear) degradation is the dominant polymer degradation mechanism of concern at Daqing; near-wellbore fractures reduce entrance pressure gradients and thereby mitigate mechanical degradation effectively.
  • Colloidal dispersion gels, foams, ASP foams, and microbes were all assessed — none provided a clear sweep improvement advantage over polymer flooding in Daqing-representative conditions.
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