Case study of CO₂-IGR and storage in a nearly depleted gas- condensate reservoir in Taiwan

The purpose of this modelling study is to investigate the combined contributions of CO₂-IGR and CO₂ storage in a nearly depleted gas-condensate reservoir, Taiwan. The estimation of the storage potential of a depleted gas condensate reservoir, the evaluation of the economic benefits from the CO₂-improved gas recover (IGR), and the determination of the best operating strategy for maximizing economic benefits were studied. After the CO₂ mixed with the natural gas, the two-phase envelope shrinkage was noticed in the Pressure-Temperature (P-T) diagram for CO₂-IGR phase in the reservoir. The mechanisms of CO₂ displacement and condensate revaporization contributed to the gas recovery. Due to the gravity, the stored CO₂ sank to the bottom of the gas cap; consequently, and the injected CO₂ can be stored permanently. The best economic scenario for this case study, which had the highest net present value (NPV) of US $18.7 million, was to use one down-dip injection well with an injection rate of 30,000 standard cubic meters (SCM)/day and a discount rate of 10%. The analysis of the principal components of the economic assessment showed that the benefit of CO₂-IGR was highly sensitive to the cost of CO₂ capture, and that the carbon tax incentive had a positive effect on the economic benefit of the Carbon Capture, Utilization, and Storage (CCUS) method.