Inhibiting shale hydration and dispersion with amine-terminated polyamidoamine dendrimers

Dendrimers have been paid increasing attention in the area of drilling fluid recently due to their unique structure and properties. The inhibitive properties of amine terminated polyamidoamine (PAMAM) dendrimers ranging from G0 to G5 were evaluated by relative inhibition rate, shale cuttings hot-rolling dispersion test and particle size distribution measurement respectively. Meanwhile the inhibitive capacity of the polymers under various pH value conditions was studied. The interaction between sodium bentonite and PAMAM dendrimers was characterized by zeta potential measurement and X-ray diffraction (XRD). The results indicated that, G0 and G5 are superior to polyether diamine, while G1, G2, G3 and G4 perform better than KCl. PAMAM dendrimers from G0 to G5 can decrease the zeta potential of clay particles from −39 mV to about −22.6 mV at natural pH values and reverse the charge when the pH value is adjusted to 9. When intercalated into the clay interlayer in aqueous solution, the candidate PAMAM dendrimers can form monolayer arrangement at lower concentrations and reduce the interlayer spacing of hydrated clay from 1.95 nm to 1.38-1.63 nm, which is the direct evidence of inhibiting shale hydration. With the increase of concentration, mixed phase and bilayer orientation are formed in the interlayer. The multi-terminal amine groups of dendrimers can effectively bind the adjacent layers together with electrostatic attraction and hydrogen bonding, and expel the water molecules out of the interlayer, contributing to the suppression of clay swelling and dispersion. The pH value reduction of aqueous solution improves the protonation of terminal-amine group, which can intensify the interaction between the polymers and clay, inducing the decrease of hydrated interlayer spacing and the zeta potential of clay particles, thus enhancing the inhibitive properties.