New insights into the nonmonotonic wetting effect: The principle of minimum operating power during two-phase displacement

Abstract

In this study, based on the minimum operating power principle, the potential control mechanism of nonmonotonic wetting effects in porous media is analyzed. When different wetting conditions are applied to the system, the contribution weights of different energy contribution terms are different during the process when the system approaches the minimum operating power state. For weak drainage or weak imbibition wetting systems, the contribution weights of the solid‒liquid and liquid‒liquid surface energy change rates are comparable. The system may have a series of stages in which the solid‒liquid and liquid‒liquid surface energy change rates alternate in dominance, which lays a foundation for the existence of a capillary energy barrier regulatory mechanism. In addition, during interfacial reconstruction, the solid‒liquid surface energy change rate in high specific surface area regions plays a dominant role, resulting in a cooperative mechanism (Haines jump events) and noncooperative mechanisms (contact, overlap events), which also establishes a basis for the formation of preferential flow paths and compact displacement states. However, for strong imbibition wetting systems, the contribution weight of the solid‒liquid surface energy change rate begins to dominate, and the capillary energy barrier regulatory mechanism disappears. The system maximizes the solid‒liquid surface energy change rate to approach the minimum operating power state, resulting in an arc meniscus at surface grooves or pore corners with a much higher advancing speed than that of the terminal meniscus. The preferential flow path state dominated by the arc meniscus reappears.