Offshore enhanced gas recovery (EGR) by CO2 injection is a potential solution to reduce greenhouse gas emissions and increase recoverable reserves on mature gas assets.

The main objective of the paper is to determine if an Extended Black Oil simulator could be used for EGR simulation on dry gas reservoir to quantify the incremental recoveries that could be achieved on a typical Southern North Sea mature gas field.

Technical and geological criteria governing a successful CO2 EGR programs have been assessed on simplified shoebox reservoir simulations in order to better understand EGR in preparation for full field model upscaling. Results have been compared with a full compositional model to validate the use of a CO2 solvent module as simulation simplification.

Shoebox simulations using an extended black oil model suggest that EGR is achievable on relatively homogeneous reservoirs with an incremental technical recovery factor ranging from 1 to 10%. Use of both vertical and horizontal shoebox models allowed assessment of sweeping efficiency in both dimensions and oriented completion and selectivity strategies. Sensitivity studies confirmed the link between recoverable reserves and CO2 injection flowrates and the risk of preferential paths when the reservoir is fractured or highly heterogeneous.

Upscaling from a simplified shoebox to a full field model has been realized on a depleted Southern North Sea field with sensitivities on injection flowrate, well conversion sequence and CO2 production cut off.

Using Extended Black Oil models for EGR project assessment has been demonstrated as a valid fast-track alternative for dry gas field EGR versus using full Compositional models, which requires more technical data, modelling workforce and computing time.

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