Traditional water based fluids tend to penetrate into shale formations, and interact with clay minerals, which results in clay swelling and wellbore instability. The larger content of clay in some deep water shales compared to regular onshore shales generates more wellbore instability problems. To reduce shale-fluid interaction, we need to reduce water invasion by sealing the pores and micro-fractures in shales. Therefore, the objectives of this study are to conduct pore pressure transmission (PPT) tests with test fluids that contain two new families of nanoparticles and to evaluate the major factors that affect pore pressure transmission.

For the first time, Mancos Shale and Eagle Ford Shale have been investigated with PPT tests using fluids that contain nanoparticles in different sizes (10 nm, 20 nm, 30 nm, 40 nm), types (aluminum oxide, magnesium oxide) and concentrations (3%, 10%). Results show that nanoparticles of 10 nm size can delay the time needed to reach the equilibrium state to 48.2 hours, compared to 27.8 hours needed for Eagle Ford Shale treated with suspensions that contain 40 nm nanoparticles. Based on the test matrix, the better combinations to decrease pore pressure at the equilibrium state are 10% 10 nm Al2O3 for Eagle Ford Shale and 10% 30 nm Al2O3 for Mancos Shale.

This relatively new plugging technique using nanoparticles has great practical potential for successful application in deep water drilling. A decrease in pore pressure transmission and the delay of the time to reach the equilibrium state will reduce problems of hydration and swelling in shale formations. This study can also help to define water based drilling fluid properties for the purpose of improving wellbore stability in deep water drilling.

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