Shale inhibitive properties of polyether diamine in water-based drilling fluid

In this paper, the shale hydration inhibitive properties of polyether diamine (PEDA) in drilling fluid system were studied. The inhibition was evaluated by bentonite inhibition test and bulk hardness test. The results indicate that the inhibition properties of PEDA are superior to potassium chloride which is a kind of conventional inhibitor, and can be improved with decrease of pH value. The inhibition mechanism of PEDA was investigated via Fourier transform infrared spectroscopy, X-ray diffraction, zeta potential measurement and surface tension analysis. After being added into the drilling fluid system, the low-molecular-weight PEDA can intercalate into the lattice of clay. The protonated diammonium ions exchange sodium ions and neutralize the negative charges of clay interlayer, which reduces hydration repulsion of diffuse electric double layer. Moreover, hydrogen bonding between PEDA and silica of clay surface can form in the process. The coordination of electrostatic interaction and hydrogen bonding expels water molecules out of the clay gallery and binds the plates together, which leads to the dehydration of clay. Otherwise, monolayer adsorption of PEDA on the interlayer of clay weakens the hydrophilicity of clay particles which further inhibits water ingress.