The interfacial phenomenon of spreading and adhesion of fluid on the rock surfaces, known as wettability, has serious implication because of their impact on multi phase flow in the rock hence the recovery efficiency of petroleum reservoirs. However, the prediction of wetting properties and its alteration during the production or any chemical treatment processes is difficult because of the complex chemical composition of the crude oil and the formation brine as well as the interaction with the minerals very close to the rock surface. Many practical techniques to assess the wettability of mineral surfaces are available, but these measurements cannot capture the micro mechanism of wetting and the mechanisms of wettability changes. To understand these mechanisms one needs to investigate the interactions that take place between crude oil, brine and rock surfaces close to the solid-fluids boundary. The objective of this work is to present the results of developed software based on the rock-fluids interactions for the prediction of the wettability state in a solid-liquid-liquid system. In this model, macroscopic contact angle and surface wettability are related to the film stability through disjoining pressure isotherm of the wetting phase film separating the solid and non-wetting phase. Besides, the mechanism of wetting changes and predominant surface forces is diagnosed through disjoining pressure. The contribution of van der Waals, electrostatic and structural forces is identified as the main forces to affect the status of the wetting film through disjoining pressure calculation. In this model some efficient parameters such as pH, brine composition, zeta potential, crude oil composition especially its polarity and acid-base number and crude oil refractive index are considered. This model is especially designed to predict the wettability and its alteration for the tight rocks, which is seldom to be done through the laboratory measurements.

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