The property development of drilling fluids strongly relies on the emergence of novelty additives and the formulation design of drilling fluids. Few studies focus on the influences of preparation technology on various properties of drilling fluids. At present, high-speed mechanical agitation is still the only method of formulating drilling fluids in the industrial community. In the paper, two kinds of sulfonated drilling fluids that were used frequently in China were prepared by the combination of high-power ultrasound and high-speed mechanical agitation. After the mechanical agitation, we exerted ultrasonic oscillations on the sulfonated drilling fluids and intensified the input of ultrasonic energy by increasing ultrasonic time or power. In addition, the superposition of mechanical agitation during ultrasonic oscillations could further help the sulfonated drilling fluids to absorb more ultrasonic energy when the time and power of ultrasonic oscillations remained unchanged. The effects of ultrasonic oscillations on the colloidal properties of sulfonated drilling fluids were investigated. The results show that the introduction of ultrasonic energy into sulfonated drilling fluids is able to cause the formation of thinner and denser mudcakes on borehole walls and further reduce the low temperature and low pressure (LTLP) and high temperature and high pressure (HTHP) filtrate volume. The HTHP accumulative filtrate volume within 30 minutes can be decreased by a maximum of 24.7%. Simultaneously, various Bingham-type rheological values, particularly yield point, get decreased. The ultrasonic improvement of filtration and rheological properties benefits from the formation of the stable colloidal structure of drilling fluids under acoustic cavitation. According to the total organic carbon (TOC) measurements, it is found that ultrasonic oscillations promote the adsorption of sulfonated additives on bentonite clays. The analysis of particle size and zeta potential also confirms that ultrasonic oscillations not only decrease the average clay particle size but also enhance the zeta potential absolute value. In our experimental range, all the colloidal properties acquire the continuing improvement with the increase in ultrasonic energy input, which cannot be achieved only through the high-speed mechanical agitation. Compared with our previous research works, the subject investigated in the paper is the given drilling fluid system, but not the bentonite suspension containing one single additive. It indicates that we take a step forward in the field application of ultrasound-assisted mud preparation technique.

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