Mechanism of Synergistic Inhibition of Water Base Drilling Fluids on South Edge of the Dzungaria Basin

Drilling fluids containing inorganic and organic compounds are used in the south edge of the Dzungaria Basin, to drill formation rocks that are sensitive to water invasion and are easy to hydrate, swell, disperse and slough. Different kinds of shale inhibitors were tested in laboratory for their ability in inhibiting shale dispersion and swelling, both used as a single additive and used in combination. The testing results are used to formulate an inhibitive drilling fluid, and its performances were again tested. In these tests, the c-spacing, zeta potential, distribution of particle sizes, water activity and adsorptive capacity of clays were measured in an effort to reveal the working mechanism of shale inhibitors used in water base drilling fluids in the south edge of the Dzungaria Basin. It shows that KCl functions remarkably in crystal lattice fixation, electric double layer compression and enhancement of polymer adsorption. Compound organic salts, to some extent, can fix crystal lattice, remarkably compress the thickness of electric double layer, and adjust the water activity. Modified poly glycol has the ability of adsorption on to the surface of clay particles and therefore encapsulation of the clay particles. Poly glycol also synergistically functions with KCl. A combination of multiple shale inhibitors in water base drilling fluids therefore has these functions such as crystal lattice fixation, electric double layer compression, water activity adjustment, adsorption on the surface of clay particle and encapsulation, which are working synergistically.