Synthesis of a network-structured polymer with low viscosity effect and its use as filtrate reducer for water-based drilling fluids

With the development of deep formations, high temperature and high salinity seriously affect the rheology and filtration performance of water-based drilling fluids. Therefore, in this study, a network-structured polymer (DSD-beta-CD) with low viscosity effect was synthesized using beta-cyclodextrin (beta-CD) as the backbone and N,N-dimethylacrylamide (DMAA), sodium p-styrene sulfonate (SSS), and dimethyl diallyl ammonium chloride (DMDAAC) as monomers. The polymer was analyzed by transmission electron microscope, Fourier transform infrared spectrum, nuclear magnetic resonance, and thermogravimetric analysis. The filtrate reducer in this study showed excellent temperature and salt resistance, the filtration loss of the water-based drilling fluid containing 3.5% DSD-beta-CD and 18% NaCl was 5.1 mL after hot rolling at 220 degrees C for 16 h. Additionally, its viscosity was 0.2 mPa s higher than that of the water-based drilling fluid with 18% NaCl, showing an excellent low viscosity effect. The filtration loss reduction mechanism of DSD-beta-CD was investigated by viscosity analysis, mud cake analysis, particle size distribution, hydration swelling of bentonite, and Zeta potential. The results showed that DSD-beta-CD could be adsorbed on the surface of bentonite particles through hydrogen bonds and ionic bonds, which increased the dispersion of bentonite particle and the compactness of the mud cake, thus reducing the filtration loss.