Streaming-potential coefficient of reservoir rock: A theoretical model

Abstract

The streaming potential is that electrical potential which develops when an ionic fluid flows through the pores of a rock. It is an old concept that is recently being applied in many fields from monitoring water fronts in oil reservoirs to understanding the mechanisms behind synthetic earthquakes. We have carried out fundamental theoretical modeling of the streaming-potential coefficient as a function of pore fluid salinity, pH, and temperature by modifying the HS equation for use with porous rocks and using input parameters from established fundamental theory (the Debye screening length, the Stern-plane potential, the zeta potential, and the surface conductance). The model also requires the density, electrical conductivity, relative electric permittivity and dynamic viscosity of the bulk fluid, for which empirical models are used so that the temperature of the model may be varied. These parameters are then combined with parameters that describe the rock microstructure. The resulting theoretical values have been compared with a compilation of data for siliceous materials comprising 290 streaming-potential coefficient measurements and 269 zeta-potential measurements obtained experimentally for 17 matrix-fluid combinations (e.g., sandstone saturated with KCl), using data from 29 publications. The theoretical model was found to ably describe the main features of the data, whether taken together or on a sample by sample basis. The low-salinity regime was found to be controlled by surface conduction and rock microstructure, and was sensitive to changes in porosity, cementation exponent, formation factor, grain size, pore size and pore throat size as well as specific surface conductivity. The high-salinity regime was found to be subject to a zeta-potential offset that allows the streaming-potential coefficient to remain significant even as the saturation limit is approached.

Measurements of the Relationship Between Microstructure, pH, and the Streaming and Zeta Potentials of Sandstones

“…4c for comparison with the new determinations, showing that the two data sets are mutually consistent. Figure 5 shows a comparison of the new measurements with the database of 266 streaming potential coefficient measurements that were collated by Glover et al (2012b) and which represent the majority of previously available measurements.…”

“…At low salinities there is a flattening of the curves that has been ascribed to the microstructural properties of the rocks (Glover et al 2012b). The flattening is more pronounced for the samples where there has been authigenic quartz overgrowth for both the Fontainebleau and Lochaline sandstones.…”

“…Second, the spread of C sp at low salinities is also due to the effect of the rock microstructure (Jouniaux and Pozzi 1995b;Glover and Déry 2010;Glover et al 2012b).…”

“…[11] mica with NaCl (Will and Nover 1986);[12] sandstone with NaCl (Alkafeef and Alajmi 2007) These high-quality measurements would then allow us answer the questions posed above as well as to provide high-quality experimental data against which the theoretical model of Glover and Déry (2010) and Glover et al (2012b) could be rigorously tested. This paper addresses the questions posed above and reserves the modelling to a forthcoming paper.…”

Nanoparticle-Assisted Water-Flooding in Berea Sandstones

“…It is known that the mobility of particles is affected by four main mechanisms; (i) blockage, (ii) adsorption, (iii) straining, and (iv) gravity sedimentation. The adsorption effect would be small in this study because our nanoparticles are negatively charged, and the zeta potential of Berea sandstone is negative at high ionic strength 57 and in the range of pHs encountered in these experiments and in hydrocarbon reservoirs 28,58,59 . The gravity sedimentation effect is also expected to be small due to short residence time of particles in the core and the effect of Brownian motion.…”