Novel plugging agent for oil-based drilling fluids to overcome the borehole instability problem in shale formations

Based on borehole instability problems, a new kind of composite plugging agent for oil-based drilling fluids was developed, and the influence of plugging agent on shale stability was evaluated. The results indicated that the oil-based drilling fluids containing composite plugging agent could produce an ultra-thin, tight and relatively impenetrable mud cake, and consequently provided an excellent sealing effect. The core displacement experiment indicated that this plugging agent could reduce the shale permeability by a significant amount, and thus stop fluid invasion and improve wellbore stability. Using this plugging agent to seal the shale is a very powerful and economical approach to address borehole instability problem in troublesome shale formations. This plugging agent is suitable for the drilling of long sections of horizontal laterals. In the future, this plugging agent might hold great promise to resolve shale instability problem.