Polyanionic cellulose/hydrophilic monomer copolymer grafted silica nanocomposites as HTHP drilling fluid-loss control agent for water-based drilling fluids

The objective of this study is to improve the performance of water-based drilling fluids for high temperature, salt and calcium resistance in the exploration of deep and ultra-deep wells. In this study, poly(anionic cellulose), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), diallyldimethyl ammonium chloride (DMDAAC), N,N-dimethylacrylamide (DMAA), sodium p-styrene sulfonate (SSS) and silica nanoparticles were used as raw materials to form copolymer PAC-DDAS-SiO2 by free radical copolymerization in aqueous solution. Using X-ray photoelectron spectroscopy (XPS), Monomers were polymerized successfully. The rheological properties of the drilling fluid were maintained after the addition of copolymers to the drilling fluid, the filtration volume after aging at 260 ℃ is only 8 mL. At the same time, the 35 wt% Cacl2 copolymer base slurry aged at 200 ℃ showed a filtration loss of only 14.4 mL. The polymer helped the drilling fluid resist 10 wt% Nacl at 260 ℃. Analysis of the filter cake after ageing, the microscopic morphology of clay-polymer interactions in the drilling fluid after ageing and the particle size of the drilling fluid was carried out. The presence of a large number of anionic groups in the chains on the copolymer spheres formed hydrogen and ionic bonds with the clay, adsorbed Na+ and Ca2+ and prevented the intrusion, thus ensuring the normal size of the clay particles, resulting in the formation of a wider particle size distribution phenomenon in the drilling fluid, dense filter cake and reduced filtration volume.