Synthesis of hydrophobic associative polymers to improve the rheological and filtration performance of drilling fluids under high temperature and high salinity conditions

With the acceleration of deep oil and gas development, the problem of high temperature and high salinity in the formation is prominent, which seriously affects the rheology and filtration performance of water-based drilling fluid and causes drilling accidents such as formation collapse and wellbore instability. Therefore, in this work, a novel thickening and fluid loss control additive (i.e., ASML) with significant hydrophobic association characteristics as well as outstanding temperature- and salt-resistance was synthesized using acrylamide, sodium p-styrenesulfonate, maleic anhydride and lauryl methacrylate as monomers. The experiments of fluorescence spectroscopy, SEM, Zeta potential, rheology and filtration show that ASML makes the drilling fluid have more networked structure under the conditions of high temperature and high salt through hydrophobic association. At the same time, it also brings more negative charge to the bentonite by adsorbing ASML on the surface of bentonite, which effectively maintains its uniform colloidal dispersion, leading to higher viscosity, denser mud cake, and lower fluid loss under high temperature and high salinity conditions. Under the condition of 200 °C and 30 wt% NaCl, the fluid loss of ASML-based drilling fluid is only 5 ml, which is 94.3% lower than that of carboxymethyl cellulose-based drilling fluid. This study provides a new strategy for the development of temperature- and salt-resistant drilling fluid treatment agent, which is important for accelerating the efficient development of deep oil and gas.