Adhesion and Cohesion of Silica Surfaces with Quartz Cement: A Molecular Simulations Study.

This study focuses on developing an adhesive and cohesive molecular modeling approach to study the properties of silica surfaces and quartz cement interfaces. Atomic models were created based on reported silica surface configurations and quartz cement. For the first time, molecular dynamics (MD) simulations were conducted to investigate the cohesion and adhesion properties by predicting the interaction energy and the adhesion pressure at the cement and silica surface interface. Results show that the adhesion pressure depends on the area density (per nm) and degree of ionization, and van der Waals forces are the major contributor to the interactions between the cement and silica surfaces. Moreover, it is shown that adhesion pressure could be the actual rock failure mechanism in contrast to the reported literature which considers cohesion as the failure mechanism. The bonding energy factors for both "dry" and "wet" conditions were used to predict the water effect on the adhesion pressure at the cement-surface interface, revealing that HO can cause a significant reduction in adhesion pressure. In addition, relating the adhesion pressure to the dimensionless area ratio of the cement to silica surfaces resulted in a good correlation that could be used to distribute the adhesion pressure in a rock system based on the area of interactions between the cement and the surface. This study shows that MD simulations can be used to understand the chemomechanics relationship fundamental of cement-surfaces of a reservoir rock at a molecular/atomic level and to predict the rock mechanical failure for sandstones, limestones, and shales.