Measurement of streaming potential coupling coefficient on carbonate rocks for downhole monitoring in smart wells

Abstract

Smart wells refer to wells containing downhole sensors and inflow control valves (ICV) mounted on the production tubing. These wells allow the operator to record fluid flow rates, temperature and pressure incessantly. Recently, streaming potential measurement in smart wells has been proposed to monitor water encroachment. 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 that dictates the magnitude of the streaming potential for a given fluid potential. Streaming potential magnitude is basically related to the fluid flow rate, fluid properties (particularly salinity), and the rock matrix properties. The coupling coefficient has been measured experimentally in sandstone cores saturated with different brine salinities, but very little works have been published on carbonate rocks. The huge number of carbonate reservoirs around the world suggests that measurement of streaming potential in carbonate rocks is also important. In this study, we present value of streaming potential coupling coefficient in a carbonate rock saturated with various salinities of brine. As we expected, streaming potential in such core is small but measurable and higher salinity gives smaller streaming potential coupling coefficient. Consistent results are obtained using specially designed electrodes and paired pumping experiments to eliminate spurious electrical potentials. We noticed that streaming potential coupling coefficient in carbonate rock is lower compared to the one in sandstone cores saturated with the same salinity of brine. This observation could be explained by comparing the difference in point of zero charges (pzc) between those two types of rock. Qualitatively, the result suggests that measurements of streaming potential could be applied for monitoring water encroachment in carbonate reservoirs, in the same manner it is applied for sandstones reservoirs. © Penerbit UTM Press, Universiti Teknologi Malaysia.