Novel thermo-associating polymer/silica nanocomposite as a temperature-resistant rheology modifier for bentonite-free water-based drilling fluids

Thermo-associating polymers have emerged as the promising agent to regulate the rheological properties of bentonite-free drilling fluids (BFDF). However, the application of thermo-associating polymers in high temper-ature drilling was still limited due to its unsatisfactory thermal stability. In this study, the method of combine the advantages of thermo-associating polymers and nanoparticles into an organic/inorganic hybrid system has been used to further enhance the thermal stability of thermo-associating polymers. In detail, the novel thermo-associating polymer/silica nanocomposite (AMS-CGBA) was prepared by in situ polymerization under optimal synthesis conditions. Different techniques (FT-IR, 1H-NMR, Elemental analysis and TGA) were used to charac-terize the structure and the thermal stability of AMS-CGBA. Rheological performance of the AMS-CGBA in BFDF was comprehensively studied and compared with that of thermo-associating polymer (CGBA). The TGA results showed that AMS-CGBA had excellent thermal stability probably due to incorporation of amino-grafted nano -silica (AMS) into thermo-associating polymer. Results from rheological tests revealed that AMS-CGBA exhibited much better performance than CGBA in improving the thermal stability of BFDF under high temperature and high salt (HTHS). Especially at the concentration of 1.5 wt% AMS-CGBA, the AMS-CGBA based BFDF showed nearly 16 times higher values of rheological parameters (AV, PV and YP) than that of CGBA-containing fluid after aging at 200 degrees C. And the dynamic light scattering tests revealed that the stability temperature of AMS-CGBA molecular was higher than 160 degrees C, while that of the CGBA was lower than 150 degrees C. Moreover, the AMS-CGBA-containing fluids exhibited a weakened thermo-thickening viscosity over a wide temperature range (80-180 degrees C), which was favorable for the "flat" rheology characteristic of BFDF. And the thermo-associative mechanism of AMS-CGBA was investigated through differential scanning calorimetry experiments to analyze the rheological stability of AMS-CGBA-containing fluids at high temperatures. The nanocomposite with the characteristic of both thermosensitive polymers and nanoparticles showed potential application in rheological regulation of bentonite-free drilling fluids at high temperatures.