A Covalently Micro-Crosslinked Anionic Copolymer-Based Microgel for High-Temperature and Salt-Tolerant Water-Based...

Area of Science:

• Materials Science
• Chemical Engineering
• Petroleum Engineering

Background:

• Fluid-loss additives are crucial for water-based drilling fluids (WBDFs) in high-temperature, deep drilling.
• Developing additives with high thermal stability and salt tolerance is challenging for harsh drilling conditions.

Purpose of the Study:

• To synthesize and evaluate a covalently micro-crosslinked anionic copolymer-based microgel (PAAN) as a fluid-loss additive.
• To assess the thermal stability and salt tolerance of PAAN in WBDFs under simulated deep drilling conditions.

Main Methods:

• Free-radical copolymerization of acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, and N-vinylpyrrolidone with N,N'-methylenebisacrylamide crosslinker.
• Characterization of PAAN's chemical structure, thermal stability (decomposition temperature 297 °C), and molecular weight (1.3396 × 10^6 g/mol).
• Evaluation of PAAN-containing WBDF performance via high-temperature, high-pressure filtration tests after aging at 220 °C with 15 wt% NaCl for 168 hours.

Main Results:

• Synthesized PAAN exhibited excellent thermal stability and chemical structure integrity.
• PAAN-containing WBDF showed low filtration loss (15.6 mL) after aging at 220 °C/15 wt% NaCl, and 46.0 mL after 168 hours.
• Mechanistic analysis revealed PAAN enhances colloidal stability via electrostatic interactions and hydrogen bonding, forming a compact filter cake.

Conclusions:

• Microgel structural design is effective for enhancing WBDF filtration control under high-temperature and high-salt conditions.
• PAAN demonstrates significant potential as a high-performance fluid-loss additive for deep and ultra-deep drilling applications.