Alteration of Wettability and Hydration Properties of Shale using Ionic Liquids in Water-Based Drilling Fluids

Hydration of shale formations during drilling operations have adverse effects on wellbore stability. The shale hydration resulted from the interactions between drilling fluid and swelling clay contents in the shale formations. This paper addresses the improvement of wettability and hydration properties of shale to enhance the wellbore stability during the drilling operations. The novel ionic liquid-based drilling fluids were used to alter the wettability and hydration properties of shale. The novel ionic liquid based drilling fluid was developed by blending various ionic liquids and drilling fluid additives such as filtration control agent and rheological modifier. The rheology and filtration related properties of the base drilling fluid and its modified version with ionic liquids were determined. Shale inhibition characteristics of modified drilling fluids were evaluated by using real field shale sample and analyzing it with linear shale swelling test and hot rolling dispersion test. Two different ionic liquids (IL-1, IL-2) were deployed in the formulation of drilling fluids with a concentration of 0.05%. The conventionally used shale inhibitor KCl was also used in the formulation of drilling fluid with the concentration of up to 2%. The results of modified drilling fluids were then compared with the base drilling fluids prepared by mixing bentonite and cationic polymer (polydadmac). The rheological experiments showed that the addition of KCl and ionic liquids in the base drilling fluid resulted in a decrease in rheological properties. The filtration experiments also showed that filtrate volume has increased with the addition of KCl and ionic liquids in the drilling fluids. The hot rolling shale recovery experiment was performed at 65°C and superior shale recovery was observed with the synergistic effect of B/IL-2/K drilling fluid. Linear swelling of shale was assessed over a time period of 10 hours and minimum linear swelling of shale was observed with B/IL-2/K drilling fluid which indicated that the ionic liquid in the drilling fluid chemically interacts with the shale surface and makes it hydrophobic in nature which limits the interactions of water with shale. This use of novel ionic liquid-based drilling fluid enhances the borehole stability by modifying the shale surface and resulted in improved wellbore stability. The novel drilling fluid also has superior rheological, filtration properties and salt tolerance.