Straightforward Assessment of Wettability Changes by Washburn Capillary Rise: Toward a Screening Tool for Selecting Water Compositions for Improved Oil Recovery

Abstract

Evaluating the wettability state of reservoir rocks is key for understanding and optimizing waterflooding and improved oil recovery techniques that imply the use of low-salinity water. Aside from established petrophysical techniques, such as Amott imbibition tests, we evaluated the Washburn capillary rise method as a low-cost, easy-to-implement, and rapid screening tool for probing the wettability state of rock samples. The well-known limitations of this method are discussed and circumvented. We show that measuring the capillary rise of two liquids ─brine and n-octane─is required to assess the evolution of the wettability state of a material induced by various treatments. The wettability state is quantified by the adhesion tension of brine to the solid. The higher the adhesion tension of brine, the more water-wet the sample. An increase in oil-wetness is observed when the sample is contacted with a crude oil or its released waters; an increase in water-wetness is obtained by postcontacting the oil-wet sample with low-salinity brine or surfactant solutions. The Washburn capillary rise is revealed to be a robust method for screening wettability alteration. With a typical duration of 1-10 min, it allows reproducibility check and screening of a wide range of brine compositions in a reasonable time frame. Therefore, it is a relevant tool to identify the most favorable brine compositions to be tested afterward with more time-consuming techniques, such as Amott tests and corefloods.