Experimental study of induced polarization relaxation time spectra of shaly sands

Abstract

The induced polarization decay curve contains much more information than chargeability which is often used in traditional induced polarization logging tool. The singular value decomposition algorithm makes it possible to transform induced polarization decay data into relaxation time spectrum. The spectrum logging tool can be used as an in-situ method to estimate pore structure, permeability, formation water resistivity and shaliness of reservoir with deep investigation depth and high signal-to-noise ratio. In order to use this new logging method in practice, effect of some factors on the relaxation time spectrum should be investigated. The induced polarization decay curve measurements have been performed on seven samples from Daqing Oil Field using a four-electrode technique. The effects of temperature, overburden pressure, electrolyte and salinity on the relaxation spectra of the core samples were analyzed qualitatively. When we discussed the effect of one parameter on the spectra, the others were fixed. The results show that the spectra shift to low time constants with temperature increasing, but the shape is almost the same. The temperature dependence of the spectrum can be corrected. When the overburden pressure increases, the relative amplitudes of low relaxation time constants are the same, and those of high constants decrease. When pressure is diminished again, the amplitudes of high time constants do not recover to the original distribution. The salinity has small influence on the spectra. The electrolyte has the influence on the spectra because of the diffusion coefficient different. This influence of electrolyte can also be corrected.