Impact of Three‐Phase Relative Permeability and Hysteresis Models on Forecasts of Storage Associated With CO₂‐EOR

Geological CO 2 sequestration in conjunction with enhanced oil recovery (CO 2 ‐EOR) includes complex multiphase flow processes compared to CO 2 storage in deep saline aquifers. Two of the most important factors affecting multiphase flow in CO 2 ‐EOR are three‐phase relative permeability and associated hysteresis, both of which are difficult to measure and are usually represented by numerical interpolation models. The purpose of this study is to improve understanding of (1) the relative impacts of different three‐phase relative permeability models and hysteresis models on CO 2 trapping mechanisms, and (2) uncertainty associated with these two factors. Four different three‐phase relative permeability models and three hysteresis models were applied to simulations of an active CO 2 ‐EOR site, the SACROC unit located in western Texas. To eliminate possible bias of deterministic parameters, we utilized a sequential Gaussian simulation technique to generate 50 realizations to describe heterogeneity of porosity and permeability, based on data obtained from well logs and seismic survey. Simulation results of forecasted CO 2 storage suggested that (1) the choice of three‐phase relative permeability model and hysteresis model led to noticeable impacts on forecasted CO 2 sequestration capacity; (2) impacts of three‐phase relative permeability models and hysteresis models on CO 2 trapping are small during the CO 2 ‐EOR injection period, and increase during the post‐EOR CO 2 injection period; (3) the specific choice of hysteresis model is more important relative to the choice of three‐phase relative permeability model; and (4) using the recommended three‐phase WAG (Water‐Alternating‐Gas) hysteresis model may increase the impact of three‐phase relative permeability models and uncertainty due to heterogeneity.