Polymer Gels Formulated With a Combination of High- and Low-Molecular-Weight Polymers Provide Improved Performance for Water-Shutoff Treatments of Fractured Production Wells

R.D. Sydansk, A.M. Al-Dhafeeri, Y. Xiong, and R.S. Seright – 2004

Abstract

A laboratory study showed improved performance for fracture water-shutoff polymer gels formulated with a combination of high- and low-molecular-weight (MW) polymers. These gels are intended for applications to fractures or high-permeability anomalies in direct contact with production wells — especially when large drawdown pressures or large-aperture fractures (>1.5 mm) are encountered. The combined high-MW and low-MW gel formulation exhibited an effective viscosity of approximately 500 cp during placement in a 1-mm fracture, withstood 92 psi total differential pressure (26 psi/ft) for 24 hours with no detectable brine flow, and achieved a 30,000x permeability reduction factor when the differential pressure was increased to 175 psi (88 psi/ft).

Key Takeaways

  • Combining high-MW and low-MW polymers in a single gel formulation provides improved performance for large-fracture or high-drawdown water shutoff applications compared to single-MW polymer gels.
  • A 1.5% high-MW and 2.0% low-MW combination gel exhibited approximately 500 cp effective viscosity during placement in a 1-mm fracture — indicating adequate injectivity while still in partially formed state.
  • The high+low-MW gel withstood 92 psi total differential pressure (26 psi/ft) for 24 hours with no detectable brine flow through the 1-mm fracture — demonstrating exceptional mechanical blockage strength.
  • When the differential pressure was increased to 175 psi (88 psi/ft), the gel provided a permeability reduction factor of 30,000 in the fracture — among the highest reported values for any polymer gel water shutoff system.
  • This high+low-MW formulation is specifically suited for large-aperture fractures (>1.5 mm) and large-drawdown production well applications where single-MW gels provide insufficient mechanical strength.
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