Synthesis and evaluation of polymer microspheres (P-FLA) synthesized by inverse emulsion polymerization as a filter loss reducer for water-based drilling fluid

With the continuous advancement of oil exploration and drilling technologies, water-based drilling fluids have become increasingly effective in protecting oil and gas reservoirs. To address the challenge of conventional filter loss reducers losing effectiveness at high temperatures, a novel polymer microsphere-based filter loss reducer was synthesized via inverse emulsion polymerization. The primary monomers used were β-cyclodextrin and soluble starch, with epichlorohydrin serving as the crosslinking agent. Sorbitan monooleate and polyoxyethylene sorbitan monooleate were employed as emulsifiers. The structure of the synthesized polymer microspheres was characterized using various analytical techniques, including scanning electron microscopy (SEM), optical microscopy, Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and particle size analysis. The performance of the microspheres was then evaluated in terms of rheology, filtration loss, and sealing ability using a six-speed rotational viscometer, static fluid loss (API) filtration apparatus, and a medium-pressure sand bed apparatus, respectively. Experimental results demonstrated that incorporating the polymer microspheres into water-based drilling fluids had minimal impact on the rheological properties before and after hot rolling aging at 150°C. Furthermore, both filtration loss and sealing performance were significantly improved. These findings indicate that the synthesized polymer microspheres possess excellent high-temperature resistance and sealing capability, making them a promising candidate for use as a filter loss reducer in water-based drilling fluids. Compared to conventional filtration loss reducers such as starch, CaCO 3 , and 2-acrylamido-2-methylpropane sulfonic acid (AMPS)-based copolymers, the polymer microspheres (P-FLA) microspheres exhibit superior high-temperature resistance, broader particle size distribution, and enhanced filtration control efficiency, making them more effective under deep well conditions.