Investigating the Occurrence of Membrane Polarization during the Precipitation of Carbonate Minerals.

Abstract:

Changes in the complex electrical conductivity due to the precipitation of carbonates are not well understood. Prior research by our group has shown little to no effect from the precipitation of calcite crystals in isolation which may indicate that the primary driver of observed Spectral Induced Polarization (SIP) signals in porous media is not the polarization of the electrical double layer (EDL) around isolated grains but rather a membrane polarization effect. This effect is observed in lithified samples and is attributed to polarization of dissolved ions across tight pore constrictions and/or pore throats. The precipitation of carbonates may produce similar constrictions by cementing loose grains together and filling in pore spaces. This membrane polarization effect may be relevant to the monitoring of field scale carbonate precipitation. We present the results of SIP measurements on sand and crushed peridotite samples to better understand changes in the capacitive properties of sediment during carbonate cementation. We utilize a novel double diffusion experimental design whereby precipitation is driven by the passive diffusion of reactants into an agarose gel saturated sample. This method produces controlled homogeneously distributed precipitation of crystals within the pore space. Our results show that signals only related to the precipitation of calcite are subdued and that strong signals in contemporary studies may be the result of experimental error.