Hydraulic permeability determined directly from logging-while-drilling Induced Polarization data
DC and full-decay IP data were inverted in 1D in terms of Cole-Cole parameters and the permeability values were computed from the DC conductivity σ0 and the maximum imaginary conductivity σ’’, using the formulas retrieved in the laboratory for unconsolidated samples [Weller, A., Slater, L., Binley, A., Nordsiek, S., and Xu, S., 2015, Permeability prediction based on induced polarization: Insights from measurements on sandstone and unconsolidated samples spanning a wide permeability range. Geophysics, 80 (2), D161-D173].
The IP-derived k estimates were compared to the GSA-derived estimates on 58 samples (19, 25 and 14 samples from the 3 boreholes) and to the ST-derived estimates (2, 6 and 1 slug tests, respectively). Furthermore, the surface area per unit volume Sporwas measured on 25 samples with the methylene blue method and compared to the σ’’ IP estimates.
A very good correlation was found between the k estimates over four orders of magnitude, with similar depth-trends. On average, the IP-derived k estimates are in agreement with the GSA and ST estimates within one order of magnitude. Analogous results were found for the Spor-σ’’ correlation.
In conclusion, IP can be reliably used for estimating hydraulic permeability on unconsolidated formations at the field scale, using the relations found in the laboratory without any further calibration. Furthermore, the effect of water conductivity appears to be negligible for the k estimates, because the influence on σ0 and σ’’ almost cancels out in the laboratory-derived formula. These new findings pave the way for detailed and inexpensive mapping of permeability at the field scale.