The main objective of this study was to investigate wellbore stability in shales after and before adding the conventional LCM particles in combination with a novel nanocomposite to a weighted water based drilling mud. A unique Pore Pressure Transmission (PPT) apparatus was used to evaluate the plugging capabilities of the mixtures. Results showed that the presence of nanocomposite was conductive to forming a thinner impermeable mud-cake to effectively reduce water invasion and prevent pore pressure transmission into the water-sensitive shales formation at an earlier stage of the shale-fluid interactions. However, the pore pressure would gradually increase over time if only LCM materials were in the existence of the drilling mud. When the test time went on for 8 hours, the downstream pressure increased to 80% of the upstream pressure. Results also showed that the combination of nanocomposites and the conventional LCM materials in appropriate proportion could create a lasting and effective sealing during drilling in shales, but the combinational material was incapable of sealing the fracture seen by the naked eye. Hence, the fast sealing developed through the combinational method was essential to resolve the problems of wellbore instability in Shales.

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