Mechanisms of Reversible Transition in Emulsions Stabilized by Modified Nanocrystalline Cellulose

Reversible emulsion drilling fluids integrate the advantages of water-based and oil-based systems, offering solutions to critical challenges in shale oil and gas development. However, conventional reversible emulsions face limitations including poor stability, high cost, and material scarcity. This research introduces widely available, eco-friendly modified nanocrystalline cellulose (MNCC) as a sustainable alternative. While current reversible drilling fluids primarily depend on organoclays and adopt aqueous phases containing 20–25% CaCl2 for shale inhibition, pH-responsive MNCC was validated as an effective reversible emulsifier capable of stabilizing emulsions through 48 consecutive phase-inversion cycles. Enhanced emulsion stability was achieved with organoclay at an optimal dosage (≤2.5 g/100 mL), and a composite interfacial film superior to the film formed by pure MNCC was fabricated via the combination of organoclay and MNCC. Increasing the organoclay content elevated the acid requirements for phase inversion (due to its lipophilicity) but reduced the alkali needs. Finally, higher CaCl2 concentrations in the aqueous phase reduced the acid demand for inversion yet increased alkali consumption and diminished stability in both oil-in-water (O/W) and water-in-oil (W/O) emulsions. These effects are attributed to the dual role of CaCl2 in compressing the electrical double layer and modifying phase density differences, synergistically governing reversible inversion behavior. This research provides a foundation for applying nanocrystalline cellulose-stabilized reversible emulsion drilling fluids, offering practical solutions for efficient development of sensitive reservoirs like shale.