Cleanup of Oil Zones After a Gel Treatment

R.S. Seright – 2006

Abstract

A mobility-ratio model predicts cleanup times for gel-treated oil zones in both fractured and unfractured production wells. Key findings: (1) cleanup time is similar for radial vs. linear flow; (2) cleanup varies approximately with the cube of gel penetration distance — shallow penetration cleans up orders of magnitude faster; (3) cleanup varies inversely with pressure drawdown; (4) cleanup varies inversely with water permeability in the gel-treated region; (5) cleanup is not sensitive to the final oil permeability at residual water saturation after gel dehydration. Although oil permeability after gel dehydration does not affect cleanup time, it strongly determines how much of the original oil productivity is ultimately recovered.

Key Takeaways

  • Cleanup time varies approximately with the cube of gel penetration distance — doubling the gelant penetration depth increases cleanup time by approximately eightfold, making shallow penetration (a few feet or less) the critical operational target for acceptable cleanup.
  • Cleanup time is similar for radial and linear flow geometries — simplifying cleanup time estimation since measurements in linear core experiments can be used to predict radial well performance.
  • Cleanup time varies inversely with pressure drawdown — maximizing production pressure differential after gel treatment accelerates oil zone cleanup and restores productivity faster.
  • The water permeability in the gel-treated region (the residual water permeability) determines cleanup rate — lower post-gel water permeability (stronger gel) paradoxically slows cleanup, creating a tradeoff between DPR effectiveness and cleanup speed.
  • The ultimate oil productivity recovered after cleanup depends strongly on the final oil permeability at residual water saturation (after gel dehydration) — gel formulations that dehydrate more completely to a lower Frro provide better long-term oil productivity recovery.
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