Minimizing Water Invasion in Shale Using Nanoparticles

TLDR

Water‑based drilling muds can penetrate shale, causing swelling and wellbore instability, but shales’ nanometer pore throats are too small for conventional particles to invade and form a mud cake. The study evaluates the effect of adding appropriately sized nanoparticles to water‑based drilling muds on fluid penetration into hard and soft shale. Field tests on Atoka and Gulf of Mexico shales compared muds with and without nanoparticles, and SEM imaging confirmed that the nanoparticles penetrate and plug the shale pores and throats. Nanoparticles dramatically reduced shale permeability—by 5 to 50 times for Atoka, similarly for GOM—and cut water penetration into Atoka shale by 98%, providing an economically viable solution for wellbore stability.

Abstract

Abstract This paper presents data showing the positive impact of adding nanoparticles to water-based drilling muds and their effect on fluid penetration into hard and soft shale. Use of present-day water-based muds during drilling can produce fluid penetration from the mud into shale formations resulting in swelling and wellbore instability. The nanometer sized pore throat diameters of shales are too small for conventional drilling fluid particles to invade and build an internal or external mud cake. Four field muds in contact with Atoka and Gulf of Mexico (GOM) shales were studied with and without the addition of nanoparticles. Penetration of fluids into the shales was shown to decrease dramatically when nanoparticles were properly sized and applied. Results show that nanoparticles reduce the permeability of the Atoka shale by a factor of 5 to 50. Similar results are obtained for the GOM shale. When nanoparticles were used, water penetration into Atoka shale was reduced by 98% as compared to sea water. Measurement of shale pore sizes and scanning electron micrographs of the Atoka shale taken after exposure to nanoparticle dispersions, show that the nanoparticles are indeed small enough to penetrate and plug the shale pores and pore throats. This plugging of pore throats by the use of nanoparticles offers a powerful and economically viable new solution for controlling wellbore stability problems in troublesome shales.