Determination of Archie's Saturation Exponent for CO2 Sequestration in Carbonate Reservoirs

Abstract Accurate evaluation of reservoir fluid in place depends on accurate laboratory measurements of Archie parameters. Sensitivity of resistivity-based saturation models on these parameters, and their determination in non-Archie rocks has been extensively discussed in numerous technical papers. Conventional estimation of saturation exponent involves either steady state or porous plate displacement method whereby a non-wetting phase displaces the wetting phase. When applying this technique in carbon dioxide sequestration projects in order to estimate and monitor carbon dioxide (CO2) accumulation in underground saline carbonate aquifer, it becomes imperative to consider the effect of CO2 – brine – rock interaction (CBRI) since carbonic acid formed from dissolution of CO2 in formation brine will dissolve some soluble carbonate grains and thereby alter rock pore structure and possibly change saturation exponent, ‘n’ as CO2 sequestration last. We hereby present the methodology for determining Archie parameters for CO2 sequestration evaluation projects. The effect of CBRI on change in saturation exponent and pore geometry is also discussed.