Placement of Gels To Modify Injection Profiles

R.S Seright -1988

Abstract

This study investigates how flow profiles in injection wells are modified when zones are not isolated during placement of gelling agents. Mathematical models examine gel penetration and injectivity loss in zones of different permeability. Key conclusions: zone isolation is far more likely to be needed in unfractured wells than in fractured wells; productive zones in unfractured wells may be seriously damaged without isolation; gel placement causes least damage when (a) gelant resistance factor is low, (b) water-oil mobility ratio is high, (c) the most-permeable layers are watered-out, and (d) water fronts are not close to the production well in productive zones. Parallel linear corefloods overestimate the degree of profile modification achievable in radial systems. Chemical retention, dispersion and diffusion will probably not significantly mitigate injectivity losses from gelant penetration into low-permeability zones.

Key Takeaways

  • Zone isolation is far more likely to be needed during gel placement in unfractured injection wells than in fractured wells — this is the primary determinant of whether productive zones will be seriously damaged during treatment.
  • In unfractured injection wells without zone isolation, gelant causes least damage when: (a) the gelant has a low resistance factor during placement; (b) the water-oil mobility ratio is relatively high; (c) the most-permeable layers are watered-out; and (d) waterflood fronts are not close to the production well in productive zones.
  • Parallel linear corefloods substantially overestimate the degree of profile modification achievable in radial (field) flow systems — laboratory results from corefloods cannot be directly translated to field performance expectations.
  • Chemical retention, dispersion, and diffusion will probably not significantly reduce injectivity losses caused by gelant penetration into low-permeability zones — these phenomena do not provide the protective effect often assumed.
  • A need exists to determine the permeability and velocity dependencies of gelling-agent resistance factors and gel residual resistance factors — these are the critical design parameters that determine treatment selectivity.
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