Lignin-containing cellulose nanofibers as stabilizers in Pickering emulsion-based drilling fluids

Conventional emulsion drilling fluids raise serious environmental concerns due to their reliance on mineral oils and surfactants, while research on eco-friendly alternatives remains limited. In response, this study developed a sustainable Pickering emulsion drilling fluid system using mechanically treated lignin-containing cellulose nanofibers (MLCNFs) as stabilizers and environmentally friendly biodiesel as the base oil. The physicochemical properties of MLCNFs were thoroughly characterized, and the emulsion stabilization mechanism was elucidated via scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Results demonstrate that the MLCNF-stabilized Pickering emulsion drilling fluid outperforms commercial emulsifiers in emulsion stability, rheological properties, filtration performance, and environmental compatibility. At a concentration of 0.1 wt%, the MLCNF-stabilized Pickering emulsion drilling fluid exhibits an emulsion stability of 78 mV, apparent viscosity (AV) of 20.5 mPa•s, plastic viscosity (PV) of 13 mPa•s, yield point (YP) of 7.5 Pa, API fluid loss volume (FL_API) of 4.5 mL, EC₅₀ of 9.48 × 10⁴ mg/L, and BOD₅/COD_Cr of 42.7 %. Mechanistic investigations reveal that lignin nanoparticles and cellulose nanofibers within MLCNFs synergistically stabilize the emulsion by reinforcing the interfacial film and constructing a three-dimensional network. This cooperative mechanism imparts the drilling fluid with superior rheological properties. Moreover, the interpenetrating network formed between lamellar bentonite particles and fibrous components contributes to the development of a compact filter cake, thereby improving filtration performance.