Approximation of electrical double-layer thickness in hydrocarbon systems flowing through the pores of reservoir...

In porous systems, such as in oil reservoir rock formations, the double layers from opposite sides of the pores may overlap if the pore size is narrow. This overlap is relatively likely to occur under low-electrolyte concentrations, such as those in crude oil, thus markedly affecting the electrokinetic measurements. This article evaluates the effects of overlap of the diffuse layers in the narrow capillaries of the reservoir rock cores in oils. Methods were developed to estimate the double-layer thickness in hydrocarbon systems, and to predict the effects of double-layer overlap on the streaming current and hence on the calculation of surface potentials for flat-sided capillaries. These methods are used to interpret results from sandstone cores in crude oil and hydrocarbon solvents. The estimation of double-layer thickness in non-aqueous solvents on the basis of 1:1 charge carriers by analogy to water systems, with correction for viscosity and permittivity differences provides good results with respect to those from streaming current measurements.