Using Chemicals to Optimize Conformance Control in Fractured Reservoirs – 2000

Abstract

Second year of the conformance optimization project. The gel propagation mechanism in fractures is advanced: mobile gel forms wormholes through concentrated immobile dehydrated gel. The average leakoff rate follows ul = 0.05t^(-0.55) across fracture widths of 0.02 to 0.16 inches and injection fluxes of 129 to 66,200 ft/day. Pressure gradient during gel extrusion is insensitive to injection rate for a given fracture width. A field case involving a horizontal production well intersected by a fault is analyzed: downhole pressure measurements are used to infer fracture width and gel penetration depth. CMT imaging at Brookhaven National Laboratory begins to provide pore-scale evidence of gel distribution.

Key Takeaways

  • Mobile gel wormholes through concentrated immobile dehydrated gel advancing the gel front — the definitive mechanistic description of gel propagation in fractures.
  • The average gel leakoff rate during fracture extrusion follows ul = 0.05t^(-0.55) across a wide range of fracture widths, heights, lengths, and injection fluxes.
  • Pressure gradient during gel extrusion is insensitive to injection rate for a given fracture width — maximize injection rate to maximize gel penetration distance along fractures.
  • For narrow to moderate fractures, required gel volume scales approximately with penetration distance raised to the 1.5 power — a key treatment sizing relationship.
  • A detailed field case analysis demonstrates how downhole pressure data before, during, and after gel injection can infer fracture width, gel penetration depth, and treatment effectiveness.
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