Experimental study of rheological characteristics of bentonite-based drilling fluids

Bentonite and polymer-based drilling slurries are widely used in numerous geotechnical applications such as Slurry Shield TBM tunnelling, MicroTunnelling, Horizontal Directional Drilling and other trenchless technologies, piles and diaphragms constructions. In all cases, the rheological characteristics of the fluids must be correctly adjusted to ensure the stability of the excavation, proper lubrication and transportability of the excavated material. To date, there are several international standards and many best practices, empirical abacuses and indications for the definition of rheological properties of drilling fluids. However, there is often a lack of correlation between the results of different tests or measurements that can be carried out in laboratories using rheometers, viscometers and other sensitive and accurate equipment, and the rapid measurements that are widely used on site. The study presented in this paper involves the systematic performance of laboratory tests and rapid measurements on a natural bentonite used in the construction of tunnels and other underground works. The aim is to provide a broad overview of the rheological characteristics of drilling fluids prepared at different bentonite dosages, a series of correlations between the results of laboratory tests carried out using different mixing speed and mixing time. The results of the study support a better selection of the correct properties during drilling, an informed choice of the most appropriate measuring instruments and a more accurate measurement and control of the rheological properties of drilling fluids.