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Journal of Applied Sciences

Year: 2014  |  Volume: 14  |  Issue: 23  |  Page No.: 3349 - 3353

Measurement of Isoelectric Point of Sandstone and Carbonate Rock for Monitoring Water Encroachment

M.Z. Jaafar, A. Mohd Nasir and M.F. Hamid

Abstract

Excessive water production is one of the main problems in oilfields. Isoelectric point (IEP) is defined as the point of pH at which a solid surface, such as sandstone or carbonate rock, submerged in an electrolyte, exhibits zero net charge. Previous studies reported different values of IEP for carbonate and sandstone rocks, mostly utilizing the electrophoresis technique. Precise values of IEP for both types of reservoir rocks need to be investigated in order to interpret the streaming potential signal. Recently, streaming potential measurement has been proposed to be applied in managing oilfields. By combination of intelligent well technology and streaming potential measurement, water encroachment will be able to be detected proactively. The IEP measurement will start in low salinity (1x10-3 M), seawater salinity (0.6 M) and high salinity (5.5 M) brine solutions. The voltage measurements will be recorded continuously by National Instrument Data Acquisition System using Labview software. Values of IEP were determined from a plot of voltage against pH for every run. Measured values of IEP for both carbonate and sandstone rocks were lied in range of 9.40-9.60 and 2.2-2.8, respectively. As the pH of the flowing fluid get closer to the IEP, the surface charge becomes smaller and so does the magnitude of the streaming potential. The knowledge of the IEP values for both types of reservoir rocks plays a crucial role in understanding the ion-sorption processes at the mineral and solution interface. Having the understanding will enable the streaming potential signal to be interpreted accurately. As a result, water encroachment issue will be overcome efficiently.

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