Investigating the Potential Cuttings Transport Behavior of Ionic Liquids in Drilling Mud in the Presence of sII Hydrates

Water-based mud used for drilling hydrate sediments is often challenged with hydrate related wellbore instability and geohazards. Ionic liquids are believed to improve the rheological and hydrate management properties of water-based mud for drilling hydrate sediments. However, the effect of hydrates and ionic liquids of the viscoelastic properties of polymer water-based mud is not well understood in gas hydrate sediment drilling operation. In this study, the amplitude sweep, frequency sweep and flow curves of tetrahydrofuran hydrate and four imidazolium ionic liquids in polymer water-based mud system were evaluated at 271.15 K using a vane geometry in a Discovery HR-1 rheometer. The ionic liquids in this study were chosen to allow a clear understanding of their alkyl chain length and anion effect and were tested at 1 wt %. The studied ionic liquids are 1-ethyl-3-methylimidazolium chloride [C-2 mim][Cl], 1-butyl-3-methylimidazolium chloride [C-4 mim][Cl], 1-butyl-3-methylimidazolium tetrafluoroborate [C-4 mim][BF4], and 1-hexyl-3-methylimidazolium chloride [C-6 mim][Cl]. The study revealed that the storage modulus (G') and loss modulus (G) of the polymer water-based mud were reduced in the presence of tetrahydrofuran hydrate, while its viscoelastic range was increased from 13% to 25%, due to the solid nature of hydrate present in the mud. Generally, the presence of ionic liquids in the base mud (without THF) negligibly affected the viscoelastic properties of the base mud. However, the presence of hydrates affected the viscoelastic properties of the base mud and ionic liquid systems by changing its responses a fast deformation from elastic dominance to viscous at high frequencies (>50 rad/s). Ionic liquids with longer alkyl chains ([C-4 mim][Cl] and [C-6 mim][Cl]) best inhibited tetrahydrofuran hydrate formation in the mud and provided suitable viscoelastic and hydraulics properties for drilling fluids. [C-2 mim][Cl] and [C-4 mim][BF4] promoted hydrate formation and provided minimal drilling hydraulics properties of the THF water-based mud slurry. The presence of ionic liquids in the tetrahydrofuran hydrate mud slurry increased the consistency index and decreased the yield stress, flow index and YP/PV index of the THF water-based mud slurry suitable for ensuring the safe transportation of hydrate crystals and drill cutting out of the wellbore.