Development of temperature- and salt-resistant viscosifier with dual skeleton structure of microcrosslinking and hydrophobic association structures and its application in water-based drilling fluids

In the process of developing deep oil and gas resources, the problem of high temperature and high salinity in deep strata has become a serious challenge faced by water-based drilling fluids. Under high temperature and high salinity conditions, drilling fluids must maintain good rheological properties to ensure safe and efficient drilling work. In this study, a temperature- and salt-resistant viscosifier (DASL) was synthesized using N, N-dimethylacrylamide, 2-Acrylamido-2-methylpropane sulfonic acid, sodium p-styrene sulfonate, and lauryl methacrylate as monomers with a double backbone structure of micro crosslinking and hydrophobic association structures. The results of pyrene fluorescence probe test and transmission electron microscopy observation showed that DASL has an obvious hydrophobic associative structure. Moreover, due to the presence of microcrosslinked structure, DASL exhibits good shear thinning property and thixotropy in aqueous solution. Under the conditions of 200 celcius and 35 wt% NaCl, the apparent viscosity of the drilling fluid with 2 wt% DASL added was 24.5 mPa ⸱s, and the filtration was only 9.2 mL. In addition, mechanism studies have shown that the dual skeleton structure of DASL improves its temperature and salt resistance. DASL can adsorb and bridge with bentonite particles, increase the internal friction and structural viscosity of the drilling fluid, enhance the internal mesh structure of the drilling fluid, improve the colloidal stability of the drilling fluid, and maintain a reasonable particle size distribution of the bentonite particles, which enable DASL to significantly increase the viscosity of the drilling fluid while reducing the filtration loss of the drilling fluid. This work demonstrates that polymers with dual skeleton structures of micro crosslinking and hydrophobic association have good application effects as temperature- and salt-resistant viscosifier for water-based drilling fluids.