ABSTRACT

Petrophysical interpretation of resistivity measurements is often hindered by the dependence of resistivity on the interconnected pore fluids and the interconnected pore surfaces. Induced polarization (IP) measurements yield parameters that are only controlled by the interconnected pore surfaces, thereby offering the opportunity to constrain interpretation of resistivity measurements. Using a database composed of 63 sandstone and unconsolidated sediment samples covering nine independent investigations, we identified a strong linear relationship between the real part of surface conductivity (σsurf) determined from multisalinity (σw) resistivity measurements and the imaginary conductivity (σ) measured with IP at a frequency of about 1 Hz. We found σ/σsurf=l=0.042 with a coefficient of determination (R2) of 0.911 and a standard deviation of l of 0.022. We found a similar relation when the normalized chargeability (from Debye decomposition) of the frequency dependence of the IP response is used instead of σ. By estimating the true formation factor (F) recorded at high salinity, we solved for σsurf(σw) and found that it parallels the salinity dependency of the imaginary conductivity, σ(σw), as reported in recent studies. We also found that the value of the l determined from this experimental study was generally consistent with predictions of the POLARIS model when the mobility of the ions in the Stern layer was assumed to be 1/350 of the mobility of the ions in the diffuse layer (considered equal to the mobility of the ions in the bulk solution). We discovered how the identified relationship can be used to significantly improve (1) the estimation of the true formation factor and (2) the groundwater conductivity, from a single salinity resistivity measurement when an IP measurement is also made. The approach offers an opportunity to improve estimation of porosity, formation factor, and salinity in well logging and hydrogeophysical investigations.

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