Mechanism of shales stabilization by hydrophobized poly(ethylene glycol)/K+ in water-base drilling fluids

The mechanism of the hydrophobized poly(ethylene glycol) (PEG)/K+ system inhibiting shale hydration was studied by laboratory experiment. The inhibition performance was evaluated through cuttings hot-rolling dispersion, bentonite inhibition and contact angle tests. The inhibition became stronger as contact angle and PEG concentration increased. A modified cuttings hot-rolling dispersion experiment suggested that these molecular systems did not act through the thermally activated mud emulsion (TAME) mechanism. The interaction of the PEG/K+ with clay samples was investigated through adsorption studies and by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The adsorption isotherms showed that the presence of K+ increased the PEG affinity for the clay surface. This inhibition effect was accompanied by a reduction of the bentonite hydration with PEG adsorption, evidenced by FT-IR, TGA and differential thermogravimetric (DTG) curves. XRD patterns were conclusive in showing that the presence of K+ ions limited the expansion of the clay interlamellar region to only one PEG layer, and the terminal hydrophobic segments of the PEG chains turned out to be determinant in enhancement of the inhibitory efficiency. The cuttings hot-rolling dispersion was carried out on water-base drilling fluid with PEG/K+, which proved the inhibition performance of PEG/K+ in oil field drilling.