Use of Nanoparticles for Maintaining Shale Stability

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Date

2009-05

Authors

Sensoy, Taner

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Abstract

This experimental study presents the effect of adding nanoparticles to water-based drilling muds and their effect on fluid penetration into hard and soft shale. Use of water-based muds during drilling can cause fluid penetration from the mud into shale formations resulting in swelling and wellbore instability. The nanometer sized pore throat diameters in shales are too small for conventional drilling fluid particles to invade and build a mud cake. Nanoparticles in the shale pore size range were added to lab and field muds to effectively reduce fluid invasion. The sensitivity of nanoparticle dispersions to temperature and salt concentration in the mud was also determined. Four different field muds were studied with and without the addition of nanoparticles using Atoka and Gulf of Mexico shales. 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. Using a nanoparticle dispersion, water penetration into Atoka shale was reduced by 98% as compared to sea water. The membrane efficiency of the shale (a measure of the osmotic pressure contribution) was found to increase by an order of magnitude. Scanning electron micrographs of the Atoka shale taken after exposure to nanoparticle dispersions show that the nanoparticles do indeed penetrate and plug the shale pore throats. These results suggest that nanoparticles could significantly reduce wellbore instability problems in reactive shales. This plugging of pore throats by the use of nanoparticles is a new approach for controlling fluid invasion into shales, and could have a major impact on solving the chronic problem of wellbore instability.

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