Novel latex particles and aluminum complexes as potential shale stabilizers in water-based drilling fluids

In this paper, novel latex particles and aluminum complexes as potential shale stabilizers in water-based drilling fluids were successfully synthesized and characterized in detail. The spherical latex particles were prepared by emulsifier-free polymerization of styrene and methyl methacrylate, and it possessed uni-modal distribution from 80 nm to 345 nm with the D90 value of 276 nm. The aluminum complexes were synthesized through the complexation reaction of humic acid with sodium aluminate and it could be completely soluble under alkaline conditions, and aluminum hydroxide and humic acid flocculate would precipitate from the filtrate under neutral or acidic conditions or interacting with magnesium or calcium ion. The synergistic effect on shale stability of latex particles and aluminum complexes was investigated quantitatively through the pressure transmission and membrane efficiency tests. The pore structure of shale cores before and after testing was also characterized via nuclear magnetic resonance core analysis and scanning electron microscope analysis. The results indicated that the latex particles as physical shale stabilizer could be deformable to internally bridge and seal micro-nano scale pore-throats and fractures of shale, and the aluminum complexes as chemical shale stabilizer would precipitate from the filtrate when exposed to pore-fluids and the precipitation could also plug and seal pore-throats and micro-fractures. The latex particles work synergistically with aluminum complexes to impart shale stability due to superior properties of decreasing shale permeability and increasing shale membrane efficiency. Furthermore, the compatible test results confirmed that novel latex particles and aluminum complexes could be alternatives to standard shale stabilizers in water-based drilling fluids.