The use of organophilic clays as additives for providing proper rheological and filtration properties in non-aqueous drilling fluids (NADFs) has long been a topic of study. Currently, most of these clays are based on the modification of bentonite with quaternary ammonium salts. As new NADF systems emerging, novel clay-modification technologies are needed urgently to obtain more effective organophilic clays for specific drilling fluids. This paper introduced a modified rectorite designed for biodiesel-based drilling fluid (BBDF). Through a suspension production technique, rectorite, a clay mineral formed by dioctahedral mica layer and dioctahedral smectite layer with a 1:1 type of layer structure and a peculiar banded structure, was modified by non-ionic surfactants. The swell behavior of the modified rectorite in invert biodiesel emulsion was investigated. Effects of this novel organophilic clay on the electrical stability, rheological parameters and suspendability of biodiesel emulsion were also tested. The results showed that some non-ionic surfactants can be intercalated into the structure of rectorite, altering the wetting characteristic of the clay surface. Compared to traditional organophilic bentonite, modified rectorite has better swell performance in biodiesel emulsion. The abilities of modified rectorite to improve yield point (YP) and low end rheology (e.g., 6 rpm reading) of biodiesel emulsion are also significantly stronger than those of traditional organophilic bentonite, suggesting a higher efficiency of adjusting rheology and suspendability. Combined with appropriate rheological modifiers (RMs), the modified rectorite can provide formulated BBDF a great suspendability, which is evidenced by static barite-sag test. Electrical stability of biodiesel emulsion was also enhanced with the addition of the modified rectorite due to the forming of Pickering emulsion. This novel modified clay is a reliable guarantee of steady properties of BBDF. The origin of its good performance can be attributed to the selection of suitable surfactants and the rational preparation technology. Rectorite is widespread all around the world and there are some rectorite mining areas in various countries although the degree of utilization for this clay is still low at present. In view of the relatively lower price of rectorite compared to bentonite, modified rectorite can be considered as a high-performance, cost-effective viscosifier for BBDF and perhaps, other NADFs.

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