Experimental determination of wetting behavior under non-atmospheric conditions relevant to reservoirs: a practical guide

Abstract

The wetting behavior in subsurface reservoirs plays a crucial role in storage, migration and liberation of fluid phases that are especially relevant to the energy sector. Further, the three-phase contact angle is important for implementing safe and successful subsurface storage of hydrogen and carbon dioxide. For reliable statements on the in situ wetting, it is important to be aware of the decisive factors of influence in order to design and perform the respective experiments in an appropriate way. This paper discusses the most important effects that shall be considered when determining contact angles experimentally, like drop size, surface roughness, aging process, dynamic behavior, and the pH, giving some valuable guidance to guarantee significant results. A drop base diameter of no less than 5 mm is found to be appropriate to minimize the impact of gravity on the contact angle under reservoir conditions. It is further confirmed that surface roughness contributes to better water wetting when the contact angles are below 90°. The versatility of contact angle measurements is shown through the dual-drop dual-crystal method that can be applied to estimate the adhesion forces present at the rock-brine interface and that need to be overcome by the flooding liquid to effectively displace hydrocarbons from the pores.

Influence of Surface Cleaning on the Wettability of Quartz/Oil/Brine Systems

“…It provides a direct and quantitative means of wettability estimation; it is one of the most used techniques. However, contact angle measurement is sensitive to many factors such as the surface roughness, droplet size, cleaning process, fluid dynamic behavior, diffusing band (water foot/precursor film), and resolution of measurement scale, among others. ,− This sensitivity has made it difficult to find an accepted collection of contact angle data for common surfaces to serve as a reference source. Despite its presumed simplicity, the contact angle observed for a fluid/fluid/rock system is not necessarily a unique value .…”