Coupling enhanced gas (EGR) and condensate (ECR) recoveries with CO₂ storage could potentially maintain fossil fuel supply and reduce CO₂ emissions to the atmosphere. This paper evaluates the techno-economic potential of simultaneous EGR, ECR and CO₂ storage in gas condensate reservoirs. We demonstrate that, for a closed gas condensate reservoir, injecting CO₂ later in production life is more profitable than early injection. This is because it delays CO₂ breakthrough at the production wells while enhancing gas and condensate production. In contrast, for a bottom-water drive gas condensate reservoir, we find that early CO₂ injection minimises water influx from the underlying aquifer. This maximises incremental gas and condensate production and CO₂ storage in the reservoir.

Successful completion of the first stage of the CO2CRC Otway Project demonstrated safe and effective CO2 storage in the Naylor depleted gas field and confirmed our ability to model and monitor subsurface behaviour of CO2. It also provided information of potential relevance to CO2 enhanced gas recovery (EGR) and to opportunities for CO2 storage in depleted gas fields. Given the high CO2 concentration of many gas fields in the region, it is important to consider opportunities for integrating gas production, CO2 storage in depleted gas fields, and CO2-EGR optimisation within a production schedule. The use of CO2-EGR may provide benefits through the recovery of additional gas resources and a financial offset to the cost of geological storage of CO2 from gas processing or other anthropogenic sources, given a future price on carbon. Globally, proven conventional gas reserves are 185 trillion m3 (BP Statistical Review, 2009). Using these figures and Otway results, a replacement efficiency of 60 % (% of pore space available for CO2 storage following gas production) indicates a global potential storage capacity—in already depleted plus reserves—of approximately 750 Gigatonnes of CO2. While much of this may not be accessible for technical or economic reasons, it is equivalent to more than 60 years of total global stationary emissions. This suggests that not only gas—as a lower carbon fuel—but also depleted gas fields, have a major role to play in decreasing CO2 emissions worldwide.

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