Fundamental Analysis of Relative Permeability and Heterogeneity on CO2 Storage and Plume Migration

Nathan Moodie
University of Utah

Relative permeability is a critical flow parameter for accurate forecasting of long-term behavior of CO2 in the subsurface. In particular, for clastic formations, small-scale (cm) bedding planes can have a significant impact on multiphase CO2-brine fluid flow, depending on the relative permeability relationship assumed. Such small-scale differences in permeability attributable to individual bedding planes may also have a substantial impact on predicted CO2 storage capacity and long-term plume migration behavior. Relative permeability model calibration in this study was accomplished by analyzing previously-published laboratory-scale measurements of relative permeability of Berea sandstone. A core-scale model of the flow test was created in TOUGHREACT to elucidate the best-fit relative permeability formulation that matched experimental data. Among several functions evaluated, best-fit matches between TOUGHREACT flow results and experimental observations were achieved with a calibrated van Genuchten-Mualem function. Using best-fit relative permeability formulations, a model of a small-scale Navajo Sandstone reservoir was developed, implemented in TOUGHREACT with the ECO2h module. The model was one cubic meter in size, with eight individual lithofacies of differing permeability, instigated to mimic small-scale bedding planes. The model assumes that each lithofacies has a random permeability field, resulting in a model with heterogeneous lithofacies. Three different relative permeability functions were then evaluated for their impact on flow results for each model, with all other parameters maintained constant. Results of this analysis suggest that CO2 plume movement and behavior are directly dependent on the specific relative permeability formulation assigned, including the assumed irreducible saturation values of CO2 and brine. Model results also illustrate that, all other aspects held constant, different relative permeability formulations translate to significant contrasts in CO2 plume behavior.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62^nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013