Long-lasting ultra-high-temperature salt-resistant filtration control agents based on nano-hydrophobic composites

With advancements in drilling technology, oil and gas drilling is increasingly extending into ultra-deep and extra-deep wells. Consequently, the drilling environment is becoming more complex. High-temperature and high-salinity formations pose severe challenges, often causing excessive filtration loss in drilling fluids. These filtration losses can lead to critical safety hazards, including severe leakage and borehole instability. Therefore, elucidating the failure mechanisms of drilling fluids under extreme conditions and developing targeted additives are essential for ensuring operational success. To address these technical challenges, a novel nano-composite filtration control agent was synthesized via emulsion polymerization by incorporating hydrophobically modified titanium dioxide nanoparticles into a polymer system comprising 2-acrylamido-2-methylpropane sulfonic acid, dimethyl diallyl ammonium chloride, N-vinyl-2-pyrrolidinone, and N, N-dimethylacrylamide, namely, ANDT-70 (2-acrylamido-2-methylpropane sulfonic acid, N-vinyl-2-pyrrolidinone, N,N-dimethylacrylamide, dimethyl diallyl ammonium chloride, and titanium dioxide nanoparticles). The performance and filtration control mechanism of ANDT-70 were evaluated through filtration loss tests, temperature and salt resistance tests, and microscopic analysis using scanning electron microscopy and transmission electron microscopy. The results demonstrated that the incorporation of hydrophobically modified titanium dioxide significantly enhanced the thermal stability of ANDT-70 and improved the dispersion of bentonite. Consequently, ANDT-70 was confirmed to exhibit superior resistance to high-temperature and high-salinity environments. Bentonite slurry containing 2.0% ANDT-70 was aged at 260 °C for 16 h, resulting in an American Petroleum Institute (Abbreviation: API) filtration loss of only 10.2 ml with negligible viscosity change. Furthermore, even after 72 h of aging at 260 °C, the bentonite slurry with ANDT-70 effectively withstood the effects of saturated sodium salt and 5% calcium salt. Thus, this study provides valuable insights for the future development of nano-composite drilling fluid filtration control agents designed for high-temperature and high-salinity environments.