A Thermal-Responsive Zwitterionic Polymer Gel as a Filtrate Reducer for Water-Based Drilling Fluids

Area of Science:

• Polymer Chemistry
• Materials Science
• Petroleum Engineering

Background:

• Water-based drilling fluids (WDFs) degrade in high-temperature, high-salinity deep oil/gas wells.
• Developing temperature and salt-resistant filter reducers is critical for drilling fluid performance.

Purpose of the Study:

• Synthesize and characterize a novel copolymer gel (PAND) for WDFs.
• Evaluate PAND's performance under harsh downhole conditions (high temperature and salinity).
• Investigate the mechanism behind PAND's filtration reduction capabilities.

Main Methods:

• Free-radical polymerization to synthesize PAND using acrylamide, N-isopropyl acrylamide, and a zwitterionic monomer.
• Characterization using FTIR, NMR, TGA, and elemental analysis.
• Rheological and filtration tests on WDFs with PAND under simulated downhole conditions (180°C, 30 wt% NaCl).
• Zeta potential and SEM analysis to elucidate filtration reduction mechanisms.

Main Results:

• PAND exhibited temperature and salt-responsive rheological behavior due to hydrophobic association and anti-polyelectrolyte effects.
• WDFs with 1 wt% PAND showed excellent rheological and filtration properties even at 180°C and 30 wt% NaCl.
• PAND enhanced bentonite colloidal stability, prevented aggregation, and promoted compact mud cake formation, reducing filtration volume.

Conclusions:

• PAND is a highly effective additive for stabilizing WDFs in extreme environments.
• The copolymer's unique properties make it suitable for deep and ultra-deep drilling applications.
• This research offers insights into using zwitterionic polymer gels for smart WDF development.