Advanced and Integrated Petrophysical Characterization for CO2 Storage: Application to the Ketzin Site

Reservoir simulations and monitoring of CO2 storage require specific petrophysical data. We show a workflow that can be applied to saline aquifers and caprocks in order to provide the minimum data set for realistic estimations of storage potential and perform pertinent simulations of CO2 injection. The presented series of experiments are fully integrated with quantitative log data analysis to estimate porosity, irreducible saturation, drainage capillary pressure and water relative permeability, residual gas saturation, resistivity-saturation relationships and caprock transport properties (permeability and diffusivity). The case considered is a saline aquifer of the Triassic Stuttgart formation studied in the framework of the CO2SINK onshore research storage, the first in situ testing site of CO2 injection in Germany located near the city of Ketzin. We used petrophysical methods that can provide the required data in a reasonable amount of time while still being representative of the in situ injection process. For two phase transport properties, we used the centrifuge technique. For resistivity measurements, we used the Fast Resistivity Index Measurement (FRIM) method in drainage and imbibition, at ambient and storage conditions. For caprock characterization, we used a fast NMR (Nuclear Magnetic Resonance) deuterium tracer technique to measure diffusivity and a modified steady state innovative technique to determine permeability. Entry pressure has also been evaluated using several methods. Resistivity and NMR logs were analyzed to provide a continuous estimation of irreducible saturation for the entire storage zone and to judge on the representativity of the samples analyzed in the laboratory. For the Ketzin site, the storage zone is a clayey sandstone of fluvial origin locally highly cemented, with porosity around 30% and permeability ranging from 100 to 300 mD. Two zones were identified on the logs characterized by two different irreducible saturation ranging from 15 up to 35%. The measured relative permeability curves show a sharp decrease of the water effective permeability and suggest that a saturation lower than 50% cannot be reached in practice. The exponent of the resistivity index curve is about 1.7, lower than the default value of 2. The caprock has a permeability of 27 nD, a porosity around 15% and a pore diffusivity of 0.8 x 10(-9) m(2)/s.