Co-optimising CO2 storage and enhanced recovery in gas and gas condensate reservoirs

摘要

Burning fossil fuels supply energy and releases carbon dioxide (CO2). Carbon capture and storage (CCS) can reduce CO2 emissions. However, CCS is an expensive process. Integrating CCS with a producing gas reservoir potentially offsets the incremental costs by enhancing gas recovery. This thesis looks at the techno-economics potential of co-optimising enhanced gas recovery (EGR), enhanced gas condensate recovery (EGCR) and CO2 storage in gas and gas condensate reservoirs. This thesis aims to demonstrate when it is best to inject CO2 for simultaneous EGR, EGCR and CO2 storage developments.This co-optimisation evaluation examines hypothetical, homogeneous, isotropic and non-dipping gas and gas condensate reservoirs. The economics model estimates field development net cash flow with a simple taxation regime. Field development strategy is a combination of field development parameters. The optimal field development strategy is to maximise the field development net present value (NPV).The gas condensate reservoirs co-optimisation analyses show that it is best to inject CO2 during production. This is because it maximises the NPV. However the optimal injection time depends on reservoir characteristics. The difference is caused by different fluid behaviour. In closed gas condensate reservoirs, production declines because of condensate blockage around production wells. Injection during production avoids condensate blockage by maintaining reservoir pressure above the dew point. Furthermore, delayed CO2 injection delays CO2 breakthrough. Therefore, production is continuous. Bottom-water drive gas condensate reservoirs experience production decline when water breaks through at production wells. Injecting CO2 earlier for a bottom-water drive gas condensate reservoir minimises water influx from the underlying aquifer and delays CO2 and water breakthrough.Bottom-water drive gas reservoir co-optimisation analyses also suggest that it is most profitable to inject CO2 during production. This is because it minimises water influx and delays CO2 breakthrough. Literature suggests that a depleted gas reservoir has maximum EGR, EGCR or CO2 storage capacities. However, literature concentrates on optimising incremental recoveries or CO2 storage capacity. This research has provided operators with the potential to co-optimise simultaneous EGR, EGCR and CO2 storage in gas reservoirs. This allows us to continue utilising methane and condensate as a fuel while minimising CO2 emission.