Wormhole Stabilization Bernard Tremblay Ray Exelby

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Wormhole StabilizationBernard TremblayRay
Exelby
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Objectives

• Develop a method of strengthening wormholes for
  post cold production recovery methods
• Test method in the lab

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Post Cold Production

• 85 to 95 of OOIP remaining in reservoir after
  Cold Flow (Production)
• Several oil companies have suggested injecting
  solvents (methane/propane) into oil reservoirs
  after cold production
• Some proposed processes are based on cyclic
  solvent stimulation of wormholed reservoirs (ex
  Metwally, JCPT Vol 37, No 2, 1998)
• Other processes are based on using cold
  production wells as injector and producers (ex
  Miller et al., JCPT Vol 42, No 2, 2003)
• In these processes wormholes are assumed to be
  open (sand-free)

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Wormhole Stabilization Method

• Reinforce Sand surrounding Wormholes
• Principle
• First flood with Water Based-Polymer Gel
• (Gel coats sand grains and fills pores)
• Immediately Afterwards Flood with Heavy Oil
• (Some water-based gel coats the sand grains
  but
• oil pushes gel further until pores are free
  of gel)

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Regions around Open Channel

• 1 open channel
• 2 gel-reinforced region
• 3 dilated region (un-reinforced)
• 4 un-dilated (formation) region

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Wormhole Stabilization Experiment

• Water-wet sand saturated with Plover Lake oil
• Injected 1.6 pore volumes of 7 wt Maraseal
  (polyacrylamide) gel
• Immediately afterwards, 2.1 pore volumes of
  Plover Lake oil injected
• flooded with propane ( 150 pore volumes (_at_ Pres
  780 kPaa)
• (55 kPa below dew point pressure)
• flooded with 1 pore volume of Plover Lake oil
• removed screen at end of sand pack
• measured oil, water and sand

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Permeability Reduction and Critical Pressure
Gradients
Kabs absolute permeability Ko oil
permeability dP/dr radial pressure gradient
reduction in permeability
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Oil Production Rate Loss

• Sand in zone 3 is dilated (12.5 darcies) compared
  to zone 4 (3 darcies)
• Net reduction in oil production rate only 24

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Erosion Test

• For un-cemented oil sand, an arch (borehole or
  wormhole) collapses at critical pressure gradient
  (pressure drawdown)
• Critical pressure gradient at surface of cavity
  one order to two orders of magnitude larger than
  at the surface of open channel in field

cavity
injection
production
41 cm
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Oil and Sand Production

• First sand production occurs after 22 hours (11.6
  MPa/m pressure gradient at surface of cavity)

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Yield Stress (Cohesive Strength)

• Gel-reinforced oil sand three times stronger than
  un-reinforced oil sand
• Permeability reduction as in previous experiment
  (without propane)

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Numerical Simulation Fluid Placement
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Numerical Simulations STARS

• First 5 m3 of 7 wt MarasealSM (polyacrylamide)
  Gel (1,000 cP) was injected (3.6 hours)
• Then 6.8 m3 of heavy oil (10,000 cP) injected
  (11.5 hours)
• Total duration of fluid injection (15 hours)

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Numerical Simulation Gel Placement

• Fluid rates required to maintain injection
  pressure of 1,000 kPa

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Conclusions
For gravity drainage cyclic-solvent type process
using existing cold production wells wormhole
stabilization method is needed to keep wormholes
open

• Results
• Initial wormhole stabilization treatment
  successfully applied in a sand pack
• Permeability reduced by 46 but
• Oil Production Loss only 24
• Sand resistant to erosion at field pressure
  gradients
• Cohesive strength (yield stress) three times
  greater for gel-reinforced oil sand compared to
  oil sand
• Wormhole Stability Visualization Experiment
  Recommended before Going to Field

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ACKNOWLEGEMENTS

• BP Exploration (Alaska) Inc.
• Canadian Natural Resources Limited
• Canetic Resources Inc.
• Husky Oil Operations Limited
• Nexen Inc.
• Shell International Exploration Production B.V.
• Total EP Canada Ltd.