Abstract
Wettability, defined as a tendency of one fluid to adhere to or spread on a solid surface in the presence of another immiscible fluid, has a crucial effect on multiphase flow in porous media. Among other things, wettability governs capillary pressure and relative permeability, concepts widely applied in the energy industry. Several methods are available to measure wettability. However, they have drawbacks, such as oversimplification of geometry, timeand cost-intensive nature, or the need for specialized equipment. Therefore, in this Ph.D. thesis, the zeta potential derived from streaming potential measurements is investigated as an alternative method for wettability characterization. Streaming potential measurements are rapid, cost-effective, do not require additional expensive equipment beyond the flooding setup, and can be performed on core samples during water flooding or permeability experiments.
Through the compilation of 3 articles, we systematically address the research question of whether zeta potential can be used as a proxy for wettability characterization, while addressing identified gaps in the existing literature, such as a lack of tunable wettability systems and insufficient documentation on the validation of streaming potential apparatuses. Each article represents a separate work package: the establishment of a wettability alteration procedure and its measurement using a conventional method; the construction of an
in-house streaming potential apparatus and benchmarking/validation; and the correlation between the traditional wettability characterization method and the streaming potential method.
Summarizing the findings, one can conclude that the streaming potential method presents several challenges that prevent straightforward interpretation of the results. The main challenge experienced in this research was the reactivity of soda-lime glass beads. Reactivity of the beads increases the pH and conductivity of the brine as a function of the bead surface area to brine volume ratio, effectively preventing comparisons across different setups and bead sizes.
Furthermore, in cases where the system’s experimental conditions (pH, conductivity) were stable due to prior equilibration, a non-unique correlation between zeta potential and contact angle was observed. The system had a critical treatment volume ratio at which the contact angle plateaued, but surface changes still affected zeta potential measurements. Below the critical volume ratio, a clear relationship was observed.
In summary, streaming potential is currently not a reliable method for wettability characterization without extensive preparation work.