The purpose of this work is to perform an improved method to optimize different CO2 Enhanced Oil Recovery (EOR) processes in unconventional liquid reservoirs, particularly in the volatile oil region of the Eagle Ford shale. The dual-porosity, structured grid model in this research will be history matched with actual data collected from the field to ensure the results of CO2 EOR study to be meaningful. Previous simulation studies of CO2 EOR in the unconventional liquid reservoirs were not done in full field-scale and were not history matched before applying CO2 EOR to the model. Without history matching step, the simulation might generate misleading results in CO2 EOR studies. In addition, we are implementing the simulation in the dual-porosity mode to account for the presence of natural fractures which have been observed on Eagle Ford outcrop.
This research provides comprehensive sensitivity analyses of important parameters in both matrix and natural fracture systems of the dual-porosity model. The history matched model suggests that matrix porosity in the volatile oil region of Eagle Ford shale might be overestimated in many previous investigations. Also, sensitivity analysis shows that the natural fracture permeability perpendicular to the direction of the horizontal well has a significant impact on oil rates in numerical simulation.
Different injection schemes were considered as performed in CO2 EOR in conventional floods. WAG (water alternating gas) and continuous injection were both tested to provide the basic output performance in order to calibrate economic models. Among different CO2 EOR methods tested in this research, huff-n-puff yields the most promising outcome as compared to continuous injection in both oil production and economic performance in the volatile oil region of the Eagle Ford shale.