Optimization of a Mature CO2 Flood — From Continuous Injection to WAG

Abstract

Abstract Although CO2 EOR is a well-accepted technology with 30+ years' field history, the optimization in its design and operation is historically constrained by the oil price – trying to minimize the cost especially when oil price is low. When we enter a high oil price regime, CO2 becomes a valuable commodity and its supply starts to limit the flood operation and design. This paper will first review the industrial practice of CO2 design and optimization and the current status of CO2 projects within Chevron. We then focus on a case study to demonstrate the impact of reservoir heterogeneity on flood design. The field was originally designed as crestal gravity stable CO2 injection based on the excellent water flood performance. Good initial oil response was observed but followed by high gas recycling and complicated operational issues. The simulation study suggests that the existence of high permeability, vertical conduits causes the CO2 flow rates in the reservoir significantly higher than the critical gravity-stable flow rate resulting in high gas recycling. Therefore balancing recovery efficiency and project economics is a challenge for gravity stable injection design. A tapered WAG design is proposed to improve operational flexibility and recovery efficiency in this mature field. The case study also demonstrates that it is critical to include proper characterization of flow barriers and channels for a successful CO2 flood design.