Evaluation of CO 2 Storage Mechanisms in CO 2 Enhanced Oil Recovery Sites: Application to Morrow Sandstone Reservoir

This article presents numerical simulations of CO 2 storage mechanisms in the Pennsylvanian Upper Morrow sandstone reservoir, locally termed the Morrow B sandstone in the Farnsworth Unit (FWU) of Ochiltree County, Texas. The CO 2 storage mechanisms considered in the study under a CO 2 enhanced oil recovery (EOR) mode include structural-stratigraphic trapping, CO 2 dissolution in formation water and oil, and residual trapping. The reservoir simulation model was constructed on the basis of field geophysical, geological, and engineering data such as three-dimensional surface seismic data, well logs, and fluid analysis. A representative fluid sampled from the reservoir was analyzed and used to tune the equation of state. A thermodynamic minimum miscible pressure was subsequently computed and compared to the experimental outcome. A history-matched model was constructed and used as a baseline to determine the effects of different hypothetical injection strategies (that consider CO 2 purchase, gas recycling, and infill drilling), water-alternating-gas (WAG) schemes, and variable salinity on CO 2 storage. The simulation results showed that a significant amount of stored CO 2 was dissolved in residual oil, contributing to enhanced oil recovery from the tertiary stage of the field operations. Supercritical-phase CO 2 mass within the reservoir compared to CO 2 dissolved in formation water was found to be dependent on the CO 2 injection strategy. The residual trapping contribution was significant when hysteresis was considered. Pressure, volume of reservoir fluid present, caprock integrity, and optimized WAG injection strategies were significant parameters determining the long-term CO 2 storage capacity within the FWU. Caprock integrity analyses showed that sealing units have excellent storage capacity with the potential to support column heights of up to 10000 ft. This work shows an improved strategy of maximizing CO 2 storage within a depleted oil reservoir. The results from this study show that pressure changes within the reservoir should be continuously monitored to enhance CO 2 storage. This study serves as a benchmark for future CO 2 -EOR projects in the Anadarko basin or geologically similar basins throughout the world.