Summary
Viscoelastic-surfactant (VES) systems are the preferred gelling and
viscosity-generating agents for fluids used in the production zone because of
their nondamaging effects on the reservoir. Polymer gels have relatively higher
rock-retention values and can often damage the invaded zone, in most cases
requiring acid treatment to remove. In contrast, VES systems behave as
"equilibrium" or "living" polymers, and their viscosity can be reduced by
contact with the produced hydrocarbons or with an internal breaker. This can
eliminate the need for remedial treatments, greatly reducing operating
cost/time and damage to the formation.
Cationic, anionic, and cationic/anionic VES systems have historically
demonstrated limitations in high-density brines. Electrostatic screening
generally reduces the viscosity or causes phase separation. Many surfactants
generally have low salt tolerance and minimal to zero tolerance of divalent
brines. Most surfactants exhibit a dramatic decrease in viscosity after a
certain concentration of salt is reached and even phase separation in some
cases.
A novel method has been developed to stabilize different VES packages in
high-density completion brines. By controlling the curvature of surfactant
aggregates using low-molecular-weight surfactant polymers, nanometer-scale
manipulation of the phase behavior is achieved. We have viscosified mono- and
divalent high-density brines using cationic, anionic, and catanionic mixtures
that were previously considered ineffective. This unlocks a vast range of
surfactants for use in high-density completion brines,
fracturing/stimulation/acidizing fluids, and sand-control operations.
This paper details the laboratory work performed to develop VES packages for
fluids ranging from fresh water to completion brines. Extensive rheology
experiments have been run on several fluids, showing the viscoelasticity of
these systems. The self-breaking nature of VES systems when in contact with
hydrocarbons or exposed to a built-in breaker has also been demonstrated by
laboratory experiment.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
17 May 2011
- Meeting paper published:
11 April 2011
- Revised manuscript received:
14 September 2011
- Manuscript approved:
22 September 2011
- Published online:
19 December 2011
- Version of record:
27 December 2011
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