Kansas Geological Survey, Open-file Report 2017-6
KGS Open File Report 2017-6
July 22, 2015
Relative permeability curves play major roles in simulation for the following reasons: 1) Distribution and residual trapping of CO2 are dependent on drainage relative permeability curves and, in addition, imbibition curves and hysteresis play important roles in calculating the residual CO2 that can be permanently immobilized in the subsurface (Krevor et al., 2012). 2) Accurate characterization of relative permeability is important to determine the correct injectivity and, therefore, to minimize the number of injectors for more efficient injection rates and injection volume (Krevor et al., 2012).
There have been some studies, including laboratory experiments, of relative permeability in CO2-brine systems for different samples in carbonate and sandstone reservoirs (e.g., Bennion and Bachu, 2008; Krevor et al., 2012). However, most and very likely all of the experimental studies do not represent the actual maximum CO2 relative permeability (KrCO2max) and the maximum CO2 saturation (SCO2max) correctly. In Bennion and Bachu (2005, 2008) studies, maximum measured relative permeability (KrCO2max) is 0.54 and more often samples with higher absolute permeability have lower KrCO2max than samples with lower absolute permeability. Often there is no consistency in KrCO2max measurements achieved in the laboratory experiments and inconsistency in maximum CO2 saturation (SCO2max) and Corey exponents can be seen. Krevor et al. (2012) and Benson et al. (2015) showed that maximum experimental CO2 saturations (SCO2max) and KrCO2max are limited by the capillary pressure (CO2 pressures) that can be achieved in the experiment and therefore their values are always lower than the actual. Because of the unattainable high capillary pressure during the experiments when 100% CO2 is injected, irreducible water saturation cannot be achieved and, therefore, measured KrCO2max, CO2 Corey exponents are inferior.
Another issue is that CO2-brine relative permeability lab measurements are expensive to run and limited to few samples. Moreover, relative permeability curves vary with different samples and so one set of relative permeability curves cannot represent relative permeability for all rock types in a reservoir. Different sets of relative permeability curves are needed for different samples. In this work, different relative permeabilities were calculated for different Reservoir Quality Index (RQI) ranges, which are more representative and realistic and specific to the Arbuckle reservoir. Drainage and imbibition relative permeability curves were calculated for a CO2-brine system based on a water-wet system in the Arbuckle. Nine drainage and nine imbibition curves were calculated for nine rock types based on RQI.
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Kansas Geological Survey
Placed online March 27, 2017
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