| Description |
A critical aspect in the risk assessment of geologic carbon storage, a carbon-emissions reduction method under extensive review and testing, is effective multiphase CO2 flow and transport simulation. Relative permeability and capillary pressure are flow parameters particularly critical for accurate forecasting of multiphase behavior of CO2 in the subsurface. The relative permeability relationship assumed and especially the residual saturation of the gas phase greatly impacts predicted CO2 trapping mechanisms and long-term plume migration behavior. The capillary pressure relationship assumed will impact the long-term CO2 plume movement in the reservoir and the sealing behavior of the cap rock. A primary goal of this study is to evaluate the impact the selection of relative permeability and capillary pressure relationships has on the efficacy of regional-scale CO2 sequestration models. To accomplish this, we selected the San Rafael Swell area of East-central Utah as a case study to evaluate the impact of two-phase relative permeability formulations on CO2 plume movement and behavior. We evaluated five different relative permeability relationships to quantify their relative impacts on forecasted flow results of the model, with all other parameters maintained uniform and constant. A second study site, the Farnsworth Unit (FWU) in North Texas, was used to evaluate the impact of relative permeability and capillary pressure relationships in a three-phase environment (gas, oil, water). We applied a novel approach to assigning relative permeability and capillary pressure relationships in the FWU numerical model. Ongoing work by the SWP has identified distinct regions of porosity and permeability coloration that are believed to exhibit similar flow characteristics called hydrostratigraphic units. We assign and calibrate relative permeability and capillary pressure by hydrostratigraphic units (heterogeneous parameter assignment). Petrophysical and mercury intrusion capillary pressure measurements for each of the hydrostratigraphic units were used to calibrate and parameterize relative permeability relationship and capillary pressure relationships. Results of forward simulations with the newly-calibrated models were compared to models that assigned relative permeability and capillary pressure by geologic formation or lithology alone (homogenous parameter assignment). |
