Preparation of Surface Modified Oil Soluble BaSO4@SiO2-OTMS Nanoparticles Used as Additive in Oil-Based Drilling Fluid
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Abstract
Oil soluble BaSO4@SiO2-OTMS nanoparticles were prepared by a sol-gel and in-situ surface modification method. The morphology and structure of the as-prepared BaSO4@SiO2-OTMS nanoparticles were analyzed by transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectrometry. The thermal stability of BaSO4@SiO2-OTMS nanoparticles was evaluated by thermogravimetric analysis, and its effects on the lubrication performance and rheological behavior of an oil-based drilling fluid were investigated with a reciprocating friction and wear tester and a six-speed rotational viscometer. Results show that the as-prepared BaSO4@SiO2 nanoparticles consisted of BaSO4 nano-cores with an average diameter of 30 nm and nano-silica shell with a thickness of about 8 nm. Thanks to the surface-modification of nano-silica by oleophilic octadecyltrimethoxysilane (denoted as OTMS), the as-prepared BaSO4@SiO2-OTMS nanoparticles can be well dispersed in liquid paraffin. In the meantime, BaSO4@SiO2-OTMS nanoparticles as the additive in the oil-based drilling fluid can reduce the flow resistance, abate the wear of the bit, and increase the drilling speed. When BaSO4@SiO2-OTMS nanoparticles were added in the oil-based drilling fluid at a relatively low concentration, the viscosity of the drilling fluid tended to decline with increasing additive content. At an additive concentration of 0.8% (mass fraction), the viscosity of the drilling fluid and the friction coefficient of the steel ball-shale disc sliding pair and the width of wear track of the shale disc reached the minimum.
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