CO2 Injection in a Saline Formation: Pre-Injection Reservoir Modeling and Uncertainty Analysis for Illinois Basin – Decatur Project.

Abstract: The Illinois Basin – Decatur Project (IBDP), funded by the United States Department of Energy National Energy Technology Laboratory, aims to inject one million tonnes of carbon dioxide (CO₂) into the Mount Simon Sandstone. The injection of CO₂ started in November 2011 and will extend over three years. Pre-injection reservoir modeling and uncertainty analysis has been carried out to obtain probabilistic predictions of storage performance indicators. Key characteristics of the storage site such as capacity, injectivity and containment are often evaluated based on the modeling results. Simulation studies for IBDP started in 2007 using general regional knowledge. Over time, simulations have increased in complexity and have become more representative of the Mount Simon Sandstone as more data have been acquired. In this study, a high resolution reservoir model consistent with all available data was developed. Water injection/fall-off tests were used to history match and calibrate the petrophysical properties of the injection zone. Using a high-resolution grid around the wellbore in the injection zone allowed us to quantify uncertainties in plume shape and size. Lateral and vertical extent of the model was sufficient to account for the injection induced differential pressure front defined by regulatory requirements. Using two hundred realizations, a detailed uncertainty analysis was performed to provide probabilistic evaluation of the storage site performance. Irreducible water (H₂O) saturation, residual CO₂ saturation, CO₂ relative permeability at the residual H₂O saturation, and horizontal-vertical permeability ratio were among the parameters considered uncertain. These parameters were studied to quantify the uncertainties of performance factors including containment of CO₂, injectivity, and dynamic mass partitioning (mobile, residually trapped, and dissolved). On the reservoir scale, we analyze uncertainty in CO₂ saturation and pressure profiles, and its potential implications for regulatory requirements for Area of Review (AoR) evolution during the life of the project. [Copyright &y& Elsevier]