Impact of Relative Permeability Uncertainty on CO2 Trapping Mechanisms in a CO2-EOR Process: A Case Study in the U.S. Gulf Coast Cranfield

Abstract

Abstract Relative permeability is an essential petrophysical property to describe the multi-phase flow in porous media. However, relative permeability data is scarce for many geological regions and often cited as a major source of uncertainty. In this study, we investigated the effect of relative permeability on the CO2 trapping mechanisms (i.e. structural trapping, dissolution trapping, residual trapping, and mineral trapping) during and after a CO2-EOR process. We reported and used a set of relative permeability data that has been measured in a commercial laboratory using steady state method for Cranfield oil field. We used the relative permeability data to calculate the trapping mechanisms contribution and compare it with our previous study which was based on estimated relative permeability curves. We use Fractional Flow theory to explain the significant difference in the results. First, we used a high resolution geocellular model, which was designed based on wireline logs, seismic surveys, core data, and stratigraphic interpretation. After finishing a comprehensive history matching of pressure and production data, we designed four CO2 injection scenarios: Continuous Gas Injection (CGI), Water Alternating Gas (WAG), Water Curtain Injection (WCI), and hybrid WAG and WCI. We calculated the trapping mechanism contribution for 50 years of post-injection for all of the four scenarios with two sets of relative permeability data. The first set was borrowed from literature and the second set was the actual Cranfield measured data. We found the amount of CO2 dissolved in water, CO2 dissolved in oil, and mobile CO2 by writing the fractional flow for first contact miscible displacement in the presence of aquifer. We used the Cranfield initial and injection conditions as well as the two sets of relative permeability data. The simulation results show a significant difference not only in the trapping mechanisms contribution, but also in the total CO2 trappment and incremental oil recovery. The results show 5% difference in incremental oil recovery. However, for both of the relative permeability data sets, WAG seems be a promising operational approach to balance both storage and oil production. Applying fractional flow theory, we found that relative permeability changes the CO2/water and CO2/oil fractional flow curves and hence the velocity of the front. A change in the front velocity leads to a significant difference in flood efficiency. A change in flood efficiency means a change in the amount of residual CO2, the amount of CO2 miscible in oil, and the amount of CO2 dissolved in water. Therefore, the contribution of trapping mechanisms could be changed by the relative permeability. The present work provides valuable insights for evaluating the uncertainties induced by relative permeability using both analytical and numerical methods. In addition, this work helps decision makers to decide for the best operating strategy to optimize both the oil recovery and storage goals.