North-Central Section - 50th Annual Meeting - 2016

Paper No. 22-8
Presentation Time: 10:35 AM


MEHNERT, Edward1, CHEN, Yu2, GERSHENZON, Naum I.3, KOHANPUR, Amir H.2, VALOCCHI, Albert J.4, OKWEN, Roland T.1, PATTERSON, Christopher1 and RITZI Jr., Robert W.3, (1)Illinois State Geological Survey - Prairie Research Institute, University of Illinois at Urbana-Champaign, 615 E. Peabody Dr, Champaign, IL 61820, (2)Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Ave., Urbana, IL 61801, (3)Earth and Environmental Sciences, Wright State University, 3640 Colonel Glenn Hwy, Dayton, OH 45435, (4)Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801,

When modeling geologic carbon sequestration, predicting the saturation of carbon dioxide (CO2) over space and time, the distribution of CO2 mass over time, and pressure changes over time are primary concerns. Modeling may be done to address short-term concerns such as determining the saturation of CO2 at the end of the injection period or long-term concerns such as estimating the mass of dissolved CO2 decades or centuries after injection ceases. Model complexity describes the physics included in the model and encompasses how simply key input data can be described-- homogeneous or heterogeneous permeability, homogeneous or heterogeneous capillary pressure and simple or hysteretic relative permeability. Studies have shown that the relative permeability function can significantly control long-term CO2 distribution. The petrophysical and geological parameters of any specific reservoir are typically uncertain, which motivates studies of parameter sensitivity. Permeability contrast, irreducible gas and water saturation, trapping saturation, and capillary entry pressure will be included in this sensitivity analysis. We assess the impact of changes in model complexity and these basic parameters have on CO2 mass distribution and injection pressure.

The vertical transport of CO2, as measured by the mass of CO2 moving into a caprock or baffle, was significantly reduced as the model became more complex by introducing permeability anisotropy (36.8% to 11.3% of total CO2 mass) and by introducing capillary pressure to the caprock (36.8% to 4.8% of total CO2 mass). While both are significant, the modeling results indicate that adding capillary pressure to the caprock was the dominant factor. At the end of the simulation period (150 years), CO2 was present as a supercritical fluid or dissolved in the brine. The amount of CO2 dissolved in the brine was significantly lower after adding capillary pressure (23.1% to 14.2%) or increasing the residual gas saturation (23.1% to 16.3%). The amount of CO2 dissolved in the brine was slightly higher after converting from homogeneous to heterogeneous geology (23.1% to 28.2%). Changes in injection pressure were observed when the permeability was reduced by adding permeability anisotropy but was increased by introducing heterogeneous geology or by changes in relative permeability.