Novel Application of Citric Acid Based Natural Deep Eutectic Solvent in Drilling Fluids for Shale Swelling Prevention

Abstract

Shale swelling in clastic reservoirs presents a significant challenge, leading to instability issues in wellbores. Using water-based drilling mud with specific shale inhibitors is better for the environment compared to using oil-based mud. Although there's been interest in using ionic liquids (ILs) as shale inhibitors due to their customizable nature and strong electrostatic properties, however, research reveals that widely used imidazolium based ILs in drilling muds are toxic, non-biodegradable, and are expensive. Deep Eutectic Solvents (DES), often seen as a more economical and less toxic IL alternative, still lack true environmental sustainability. The latest development in this area is Natural Deep Eutectic Solvents (NADES), known for their genuine eco-friendliness. This study uses NADES formulated with citric acid (Hydrogen Bond Acceptor) and glycerine (Hydrogen Bond Donor) as a drilling fluid additive, prepared according to API 13B-1 standards and compares its efficacy with KCl, imidazolium based ionic liquid and Choline Chloride:Urea based DES. The research assesses various mud properties, revealing that NADES improve the yield point to plastic viscosity ratio (YP/PV), reduce mudcake thickness by 26%, and decrease filtrate volume by 30.1% at a 3% concentration. Remarkably, NADES achieve an impressive 49.14% inhibition of swelling, attributed to their ability to modify surface activity, zeta potential, and clay layer spacing. NADES emerge as non-toxic, cost-effective, and highly efficient shale inhibitors, offering a promising alternative to ILs and DES for environmentally conscious drilling operations.