Measurements of Streaming Potential for Downhole Monitoring in Intelligent Wells

Abstract

Downhole monitoring of streaming potential, using electrodes mounted on the outside of insulated casing, is a promising new technology for monitoring water encroachment towards an intelligent well. However, there are still significant uncertainties associated with the interpretation of the measurements, particularly concerning the streaming potential coupling coefficient. This is a key petrophysical property which dictates the magnitude of the streaming potential for a given fluid potential. The coupling coefficient can be measured experimentally, but previous studies have obtained data for sandstone cores saturated with relatively low salinity brine (less than seawater). Formation and injected brine in hydrocarbon reservoirs is typically more saline than this. Extrapolating data obtained at low salinity into the high salinity domain suggests that the coupling coefficient falls to zero at approximately seawater salinity. If this is the case, then streaming potential signals will be very small in most hydrocarbon reservoirs.We present the first measured values of streaming potential coupling coefficient in sandstone cores saturated with brine at higher than seawater salinity. We find that the coupling coefficient is small, but still measureable, even when the brine salinity approaches the saturated concentration limit. Consistent results are obtained from two independent experimental setups, using specially designed electrodes and paired pumping experiments to eliminate spurious electrical potentials. We apply the new experimental data in a numerical model to predict the streaming potential signal which would be measured at a well during production. The results suggest that measured signals should be resolvable above background noise in most hydrocarbon reservoirs, and that water encroaching on a well could be monitored while it is several tens to hundreds of metres away.

Frequency-dependent streaming potential of Ottawa sand

“…Physical modeling of the zeta potential and the streaming potential coupling coefficient of the Ottawa sand using the approach of Glover and Déry [2010] gives values of ζ = −15.9 mV and C so = 1.04 V/MPa for Γ o = 5 sites/nm 2 , F = 4.67, m = 1.37, r grain = 2.51 × 10 −4 m, pH = 6, pK me = 7.5, pK ‐ = 8. The measured value for the streaming potential coupling coefficient is consistent with the data compilation for silica‐based earth materials made by Jaafar [2009] and subsequently used by Jaafar et al [2009] and Vinogradov et al [2010], as can be seen in Figure 6.…”

“…The steady state streaming potential coupling coefficient measured in this work (gray triangle) shown with a compilation of silica‐based earth materials measured by (open symbols) or compiled by (solid symbols) [ Jaafar , 2009]. The line represents the theoretically modeled streaming potential coupling coefficient using the method of Glover and Déry [2010] with the parameters Γ o = 5 sites/nm 2 , F = 4.67, m = 1.37, r grain = 2.51 × 10 −4 m, pH = 6, pK me = 7.5, pK ‐ = 8, and T = 24.0°C.…”

Self-potential anomalies induced by water injection into hydrocarbon reservoirs

“…The EK potential is maximized in thick reservoirs with a low shale content because the high electrical conductivity of water-saturated shales bounding the reservoir and=or within the reservoir interval suppresses the signal. Jaafar et al (2009b) find that the measured potentials at the well are large enough to be resolved above the backgroundnoise-level $ 0:1 mV ð Þin most reservoir and production scenarios. They conclude that the flow of brine toward a production well can be monitored by measuring the EK component of the SP at the well, using electrodes permanently installed downhole, even when the encroaching water front is some distance away (>100 m) from the well.…”

“…Saunders et al (2006Saunders et al ( , 2008 and Jaafar et al (2009b) investigate the behavior of the EK component of the SP generated during oil production in a range of reservoir models. These workers use a 3D finite-element scheme to model multiphase flow and the resulting EK potential in a sandstone reservoir bounded by impermeable conductive shales.…”

“…However, gradients in the brine-phase salinity and temperature may also generate EC and TE potentials. These potentials will contribute to the SP signal measured downhole but are neglected by Saunders et al (2006Saunders et al ( , 2008 and Jaafar et al (2009b).…”