Organophilic Clay-Based Drilling Fluids for Mitigation of Unconventional Shale Reservoirs Instability and Formation Damage

High-performance drilling fluid was designed for unconventional reservoirs to minimize the formation damage and borehole instability using organophilic clay treated with trimethyloctylammonium bromide, novel in-house synthesized gemini surfactant, and a high-molecular weight polymer. This gemini surfactant has not been reported in the literature for drilling fluid applications. The performance of designed drilling fluid was evaluated and compared with the base drilling fluid (4 w/v.% bentonite dispersion water). Shale dispersion, linear swelling, filtration, and rheological experiments were performed to investigate the effect of drilling fluids on borehole stability and formation damage. The combined use of organophilic clay and surfactant in the drilling fluid formulation reduced the shale dispersion up to 89%. The linear swelling experiment of shale sample shows 10% swelling of the core in the modified drilling fluid while in base fluid 13% swelling of shale was observed. It was found that modified drilling fluid interactions with shale were greatly reduced using a surfactant and associative polymer in the drilling fluid formulation. Rheological properties of drilling fluids were stable, and filtration characteristics showed that the filtrate volume was within the acceptable limit. The designed drilling fluid made a thin and impermeable filter cake that prevents the invasion of drilling fluid into the formation. This study opens a new direction to reduce the formation damage and borehole instability using organophilic clay, surfactant and high-molecular weight additive in water-based drilling fluid.