Experimental Test And Analysis Of Rock Induced Polarization

Electrochemical potential logging, as one distinctive logging method, can be used to determine formation cation exchange capacity and connate water salinity and study other important parameters, such as pore structure. However, there is still no sufficient theoretical and experimental basis for this logging method. In order to provide experimental support for the development of downhole logging tool, this paper, based on electrochemical experiment and the electrochemical and medium polarization theory, emphasizes the effect on the induced polarization potential when there is metal intervention from outside or the measuring electrodes are made of metal.Under different salinities and cation types, the induced polarization potential of the shaly sandstone sample is measured, and also the rules and corresponding characteristics are analyzed. The results show that the shaly sand needs 180 seconds to reach sufficient polarization while the pure shale stone need 50 seconds. Within the allowable scale of the induced current, commonly a relative big measuring current is selected. A longer polarization time can reflect more detailed attenuation property of the formation. With the increasing sample porosity, the amplitude of the polarization ratio decreases gradually.As to the actual requirement for materials of the downhole tool, that is, the ability of withstanding high temperature, high pressure and erosion, different metal materials are selected as experimental electrode in this paper, such as steel, copper, silver and aluminium. And the corresponding induced polarization potentials are measured when these different metals are treated as interventional materials or measuring electrodes. Due to erosion of metal electrodes in the solution, the induced polarization potential can be affected. According to the decay curve of the potential or the polarization curve, the effect is analyzed. Then the feasibility is studied for metal electrodes to be applied in actual formation. It can be concluded for the results that the measuring effect of the silver electrode is the best among the four selected metal electrodes, the copper electrode comes second, and the aluminium and steel electrodes are not suitable to be measuring metal electrodes.