Preparation, characterization and filtration control properties of crosslinked starch nanospheres in water-based drilling fluids

With increasingly stringent environmental regulations, an environmentally friendly and high performance filtration loss reducer for water-based drilling fluid is essential. This study aims to investigate the potential of utilizing starch nanospheres (SNSs) in this capacity. SNSs were fabricated by a crosslinking reaction between soluble starch and methylene-bis-acrylamide (MBA) using an inverse emulsion polymerization. The structure of SNSs was characterized with Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), particle size distribution measurement and thermogravimetric analysis (TGA). The effect of SNSs on the rheological and filtration properties of bentonite-based drilling fluid was investigated according to American Petroleum Institute (API) standards. Three-dimensional nearly spherical particles about 100–300 nm with smooth surface were formed after the inverse emulsion polymerization. SNSs had little influence on the rheological properties of bentonite-based drilling fluids. After subjected to thermal aging at 150 °C, SNSs still exhibited stable and effective filtration control. Viscosity and filtration loss were lower as well, and the performance after aging was better than currently used modified starch filtration reducers that were tested. The nano particles readily plugging micropores of filter cake and water absorbency ability as well as deformability and elasticity resulted in the effective filtration control. SNS has the potential to be used as biodegradable filtration loss reducer in elevated temperature formations replacing commercially available starch derivatives. •Crosslinked starch nanosphere was synthesized as filtration reducer in drilling fluid.•Starch nanosphere outperformed conventional starch derivatives after 150 °C aging.•Crosslinking and nano size contributed to thermal stability and better performance.