Impact of multi-branched ionic liquid on shale swelling and hydration for high temperature drilling applications

Shale swelling and hydration during the drilling operation have adverse effects on the stability of a wellbore. Hydrophilic interactions of shale results in swelling and disintegration of the shale formation. This paper discusses wettability changes and hydration characteristics of shale to improve the wellbore stability. The use of multibranched ionic liquid as drilling fluid for high temperature applications was investigated. The novel multibranched ionic liquid (Trihexyltetradecyl phosphonium bis (2,4,4-trimethyl pentyl) phosphinate, denoted as Tpb-P) water-based drilling fluid was prepared by mixing different concentrations of ionic liquid and other additives such as filtration controller, rheological modifier, and pH controller. The wettability of bentonite powder was determined using a contact angle in the presence of various concentrations of ionic liquids. Several other experimental techniques, such as linear swelling, hot rolling recovery, and bentonite swell index, were used to examine the inhibition performance of ionic liquid. The rheology and filtration properties of ionic liquid-based drilling fluid were also examined. Various concentrations of multibranched ionic liquid were used to formulate the drilling fluids ranging from (0.1 to 0.5 wt.%), and their performances were compared with the base drilling fluid prepared without ionic liquid. The hydrophobicity of the shale surface was determined by measuring the contact angle, and results showed that drilling fluid having 0.1 wt.% concentration of ionic liquid has a maximum contact angle indicating the highly hydrophobic shale surface. The hot rolling shale recovery experiment was conducted at 150°F, and it was observed that adding ionic liquid improved the shale recovery (24.4%) compared to the base fluid recovery (12.8%). The linear swelling was evaluated over the time of 24 hours, and the least swelling of bentonite was noticed with 0.1 wt.% ionic liquid (98.1%) compared to linear swelling in deionized water (125%). The results suggested that the ionic liquid in the drilling fluid chemically interacted with the clay surface and reduced the hydrophilicity of clay, which restricts the exchange of water onto the clay surface.