Molecular simulation on the inhibition mechanism of organic amine to montmorillonite hydration

Wellbore instability has always been the major diffculty in the process of well drilling, and mud shale hydration is one of the most important factors leading to wellbore instability. Montmorillonite, as the composition with the highest water absorption and the main component in mud shale, is the radical factor of wellbore instability. In this paper, the molecular structure model for the reaction between organic amine inhibitors and Na-montmorillonite was established by means of molecular simulation to study the inhibition mechanisms of small-molecule organic amine inhibitors (e.g. formamide and urea) to montmorillonite hydration. It is shown that the inhibition capacity of small-molecule organic amine mainly depends on its molecular structure and functional group. Formamide andurea can form hydrogen bond with the interlayer hydrone and the oxygen on the surface of montmorillonite to inhibit the hydration of interlayer sodion and limit the self-diffusion of interlayer hydrone and sodion. When the concentrations of formamide and urea change, their effects on the density and mechanical performance of Na-montmorillonite are different, but they follow the same change laws.There is a certain critical concentration, below which the addition of amine can increase the density of montmorillonite, increasing the mechanical performance of this system, and vice versa. And at low concentration, they both can present good inhibition and increase the stability of montmorillonite. Based on the parameter analysis and comparison, formamide is, on the whole more effective than urea.