Modified Laponite synthesized with special wettability as a multifunctional additive in oil-based drilling fluids

In this study, Modified Laponite with lyophobic wettability was synthesized as a multi-functional additive to solve instability of emulsions, rheological deterioration, and wellbore instability of oil-based drilling fluid. Properties and its influence on emulsion stability, rheological behavior and plugging property were investigated. The results showed that Modified Laponite was in a shape of sheet layer and had micro-meter length and nano-meter thickness which was in match with the diameter of shale pores. And it was proved to be resistant to approximately 450 °C by thermogravimetric analysis measurement. Mechanism analysis revealed that Modified Laponite could stable the oil-based drilling fluid through four sections. Firstly, Modified Laponite with lyophobic wettability could promote its existence in the interface of brine/mineral oil. Secondly, Modified Laponite could decrease the interfacial tension from 32.8 to 13.5 mN/m to maintain the emulsion particles in a small size for a long time then to ensure the emulsion stability. Thirdly, Modified Laponite could enhance the shear-thinning rheological behavior which could maintain the rheological stability and enhance the sedimentation stability in ultra-deep reservoirs with high temperature and high pressure conditions. Fourthly, Modified Laponite could plug the shale pores effectively by preventing pressure transmission and enhancing shale compressive strength, and decrease the filtration volume of oil-based drilling fluid from 7.4 mL to 2.6 mL after aging at 180 °C for 16 h to stable the wellbore. Therefore, Modified Laponite was a multifunctional additive to stable the emulsion, enhance the rheological stability and strength the wellbore stability, which could ensure the application of oil-based drilling fluid in drilling process of ultra-deep reservoirs.