The decisive role of filtration reducers' surface charge in affecting drilling fluid filtration performance.

[Display omitted] • SiO 2 @polymer nanoparticles with different surface charges are prepared for drilling fluid loss reduction. • Electrostatic forces between SiO 2 @polymer and bentonite play the decisive role in reducing fluid loss. • Electrostatic repulsion induces slow formation of thin and compact filter cake. • Electrostatic attraction induces fast formation of thick and loose filter cake. To elucidate the effects of filtration reducers' surface charge on drilling fluid filtration performance, three kinds of SiO 2 @polymer nanoparticles with different surface charges are prepared. When these nanoparticles are added into bentonite-based drilling fluids as filtration reducers, the negatively charged nanoparticles show the best filtration reduction performance while the positively charged nanoparticles show the most inferior filtration reduction performance. Moreover, more negative charges induce better filtration reduction performance. Conversely, more positive charges induce more inferior filtration reduction performance. The filtration performance of drilling fluids is decided by the compactness of the filter cake. And the interactions among the particles in the drilling fluids play an important role in affecting the compactness of filter cake. The electrostatic attraction forces between the positively charged nanoparticles and negatively charged bentonite particles promoted the aggregation before the formation of incompact filter cake, and the electrostatic repulsion forces between the negatively charged nanoparticles and negatively charged bentonite particles slowed down the aggregation of particles to form more compact filter cakes. These findings demonstrate the decisive role of surface charge of filtration reducers, which could provide guidance for searching suitable filtration controlling additives for drilling fluids in the future. [ABSTRACT FROM AUTHOR]