Ionic liquids as completion fluids to mitigate formation damage

Abstract

Formation damage can occur in any phase of oil and gas operation from drilling, completion, or stimulation. Fluids used to drill, complete, and fracture the formation may invade and damage the formation. These fluids may interact with clays present in the formation and adversely affect the flow performance. The change in flow performance could occur due to flow restriction or decrease in permeability, change in relative permeability, or unintended flow restriction during the specific operation. In this work, ionic liquids are proposed as clay swelling additives in completion fluid to overcome the formation damage problem. Imidazolium-based ionic liquids and three different salts are tested with 0.5 wt % and 3 wt % concentration, respectively, on tight sandstone formation containing high clay contents. Completion fluids prepared using ionic liquids resulted in complete stabilization of clays and therefore nearly maintain the in-situ permeability of tight sandstone. The completion fluids are prepared in deionized water for experimental consistency. Coreflooding experiments were performed on Scioto sandstone core samples containing an average porosity and permeability of 16.9% and 0.72 mD., respectively. Cores were saturated with completion fluids based on salts such as calcium chloride (CaCl2), magnesium chloride (MgCl2), and ammonium chloride (NH4Cl) and with Imidazolium-based ionic liquids before the coreflooding experiments. These coreflood experiments involve a preflush with the prepared completion fluid and post-flood with deionized water. Moreover, Nuclear Magnetic Resonance (NMR) tests were performed on all samples before and after coreflood to estimate the change in porosity and pore size distributions of the rock samples. Results showed that the porosity and permeability loss were significantly large in cores flooded with CaCl2 and NH4Cl salts solution when flooded with water. MgCl2 salt solution showed exceptionally stable porosity and permeability compared to other completion fluids. Furthermore, the results of ionic liquid-based completion fluids showed no significant loss in porosity and permeability when flooded with water. Therefore, the proposed ionic liquid-based completion fluids can be used for well-completion operation without any formation damage.