Synergistic stabilization of shale by a mixture of polyamidoamine dendrimers modified bentonite with various generations in water-based drilling fluid

•Polyamidoamine dendrimers as shale hydration and dispersion inhibitors•Polyamidoamine dendrimers intercalated into the clay gallery with different conformations•Internal and external inhibition was obtained by synergetic use of various dendrimers

The amine terminated polyamidoamine (PAMAM) dendrimers were investigated as potential shale stabilizers for the first time. Its inhibitive properties were characterized by a bentonite inhibition test and a shale cuttings dispersion test. The interaction between PAMAM dendrimers of various generations and sodium bentonite was examined by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The hydration and dispersion of shale can be effectively inhibited with PAMAM dendrimers. The decrease of pH value in the dendrimer aqueous solution improved the inhibitive performance. For lower generations of dendrimer growth (G0 to G3), the inhibitive level decreased with the increase of generation. For higher generations (G4, G5), the inhibitive level increased with the increase of generation. Low generation PAMAM dendrimers could penetrate into the clay interlayer space, but exhibited highly oblate intercalation behaviors. G0 intercalated into the interlayer space with a monolayer conformation as concentration increased, while G1, G2, G3 and G4 intercalated into the interlayer space with monolayer arrangement at low concentrations, and mixed phase orientation at high concentrations. G5 could not fully intercalate into the interlayer space due to the steric hindrance. According to the interaction between PAMAM and clay, effective internal and external inhibition on shale hydration and dispersion could be obtained with the combination of low generation G0 and high generation G5. A new water-based drilling fluid including G0 as shale swelling inhibitor and G5 as shale dispersion inhibitor was established and exhibited excellent inhibitive properties.