Abstract

In trying to understand the affect of electrokinetics on the spontaneous potential (SP) log, the focus has generally been on the solid-brine streaming potential. Within the accuracy of the measurements, the streaming-potential coupling coefficient is shown to be independent of the permeability of the rock. The solid-brine streaming potential is of much smaller magnitude than the electrostatic potentials from gas-liquid and liquid-liquid flow. Air bubbles were found to increase the streaming potential coupling coefficient by more than two orders of magnitude over the value for single-phase brine flow. Thus, two-phase gas-liquid flow is more likely to have a significant impact on the SP log than is single phase liquid flow.Two-phase oil-brine flow may also produce a larger electrokinetic potential than single-phase flow. The magnitude of the electrokinetic potential caused by oil-brine flow will depend on the composition of the oil and the brine. Trace materials can have a major impact on the electrokinetic potential of hydrocarbons. In a system with multiphase flow, the solid-liquid interaction is probably the smallest component of the electrokinetic potential.

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