An object-based modeling and sensitivity analysis study in support of CO2 storage in deep saline aquifers at the Shenhua site, Ordos Basin

The Shenhua Carbon Capture and Storage (CCS) project at the Shenbei Slope injection site in North Yulin is the first 100,000 ton/year scale CCS pilot project in China with an injection operation lasting nearly 3 years. While the project turned into an operational success with 300,000 tons of CO2 being sequestered, several aspects of reservoir dynamic behavior and the role of reservoir heterogeneity are not clearly understood. For example, although there was an initial period of wellhead pressure (WHP) increase at the injection well, WHP incrementally declined for most of the time. The majority of CO2 was received by the topmost sandstone of the Liujiagou formation in the injection interval instead of the lowermost limestone of the Majiagou formation, suggesting strong reservoir heterogeneity. Knowledge of the key reservoir processes and properties that resulted in these observations would help for predicting longterm storage safety and aiding the design of a larger-scale CCS operation at the same site. In this study, we investigate various object-based models and important reservoir parameters to determine aspects of heterogeneity that have the most impact on pressure behavior at the injection well and the observed plume dynamics after injection. Simulation results suggest that the extent of CO2 plume is most sensitive to the geometry of fluvial channels, and specifically, the amount of connected sandbodies that facilitate lateral fluid migration. Along with the injection rate, sandbody permeability plays a significant role in determining pressure near the injection well and in the reservoir. Further work will incorporate the dynamics of CO2 flow down the injection wellbore to derive a more accurate representation of injection rate under the reservoir condition. As drilling and analog data also suggest that fractures may exist in the Liujiagou formation, future work will also construct geomechanical models to investigate the effect of fractures on injection and storage.