Characterisation of surface electrical charge and wettability in carbonates with application to controlled salinity waterflooding

It is well known that the wetting behavior of carbonate mineral surfaces is affected by their surface electrical charge (Strand et. al., 2006; Hiorth et. al., 2010) and that the surface charge in saturated porous media can be characterized using measurements of streaming potential (Jouniaux and Pozzi (1995); Delgado et. al., 2007). Streaming potentials in porous media arise from the charge separation that occurs in the electrical double layer at mineral-fluid interfaces (Hunter, 1981). If the fluid is induced to flow by an external potential (pressure) gradient, then some of the excess charge within the double layer is transported with the flow, giving rise to a streaming current. Divergence of the
streaming current density establishes an electrical potential, termed the streaming potential. The closest plane to the mineral surface at which flow occurs in the double layer is termed the shear plane; the electrical potential at this plane is termed the zeta potential. The relationships between streaming potential and surface electrical charge, and between surface electrical charge and wettability, suggest that measurements of streaming potential may be used to probe the wetting state of mineral surfaces in intact core samples. Previous studies have measured streaming potential in core samples saturated with oil, and with oil and brine, but the samples had not been aged to alter their wetting behavior (Alkafeef et. al., (2001); Alkafeef and Alajmi (2006); Vinogradov and Jackson (2001). Consequently, the relationship between streaming potential and wettability has not been investigated. Yet if streaming potential measurements, and the electrical properties interpreted from these measurements such as zeta potential and surface electrical charge, are affected by wettability in a direct and
quantifiable manner, then streaming potential measurements may be of great utility in characterizing wettability and processes that affect wettability. The aim of this paper is to determine whether wettability alteration in carbonate core samples leads to measurable changes in streaming potential.