A strong inhibition of polyethyleneimine as shale inhibitor in drilling fluid

In this paper, the inhibition property of polyethyleneimine (PEI) in montmorillonite solution was studied. The inhibition property was evaluated by linear swelling test and rolling recovery test. Compared with other inhibitors, the addition of PEI resulted in the lowest swelling height in drilling fluid. In rolling recovery rate study, the addition of PEI resulted in the highest recovery rate after rolled at 120 degrees C. More importantly, PEI was environmental friendly inhibitor. The inhibition mechanism was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, Transmission electron microscope, Scanning electron microscopy, Atomic force microscope, Zeta potential and Particle-size analyzer. The spectrums and images showed that the negative charge in the surface of montmorillonite (MMT) was neutralized by the positive charge in amino group of PEI. PEI was adsorbed in the surface and intercalated into interlayer of MMT, which reduced the hydration repulsion of diffuse electric double layer and prevented the invasion of water. Hydrogen bonding between hydroxyl in the surface of clay and amino groups in the backbone and side chain of PEI can be formed in the process. The adsorption and intercalation of PEI in the surface and interlayer of MMT was the major factor to prevent water molecules from invading into the gallery of clay. There were a quantity of positive ions in solution because of the protonation of nitrogen in water. More positive ions resulted in the stronger force between inhibitor and clay.