Numerical Simulation of CO2-EOR and Storage Potential in the Morrow Formation, Ochiltree County, Texas

Abstract

Abstract This paper presents a numerical study of CO2 enhanced oil recovery (EOR) and storage in partially depleted reservoirs. A field-scale compositional reservoir flow model was developed for assessing the performance history of a CO2 flood and optimizing oil production and CO2 storage in the Farnsworth Field Unit (FWU), Ochiltree County, Texas. A geocellular model was constructed from geophysical and geological data acquired at the site. The model aided in characterization of heterogeneities in the Pennsylvanian-aged Morrow sandstone reservoir. Seismic attributes illuminated previously unknown faults and structural elements within the field. A laboratory fluid analysis was tuned to an equation of state and subsequently used to predict the thermodynamic minimum miscible pressure (MMP). Datasets including net-to-gRose ratio, volume of shale, permeability, and burial history were used to model initial fault transmissibility based on the Sperivick model. An improved history match of primary and secondary recovery was performed to set the basis for a CO2 flood study. The performance of the current CO2 miscible flood patterns were subsequently calibrated to historical production and injection data. Several prediction models were constructed to study the effect of recycling, addition of wells and/or new patterns, water alternating gas (WAG) cycles and optimum amount of CO2 purchase on incremental oil production and CO2 storage in the FWU. The history matching study successfully validated the presence of the previously-undetected faults within FWU that were seen in the seismic survey. The analysis of the various prediction scenarios showed that recycling a high percentage of produced gas, addition of new wells and a gradual reduction in CO2 purchase after several years of operation would be the best approach to ensure a high percentage of recoverable incremental oil and sequestration of anthropogenic CO2 within the Morrow reservoir.