Rapid Estimation of Carbon Dioxide Stored in CO₂ EOR Operations for Screening Purposes

We describe the development, testing, and first application of a rapid method for estimating the CO₂ storage potential associated with CO₂ enhanced oil recovery in both secondary and tertiary modes. The new method builds on various published empirical models for predicting incremental oil recovery (and hence CO₂ storage) in solvent floods. It improves the representation of reservoir heterogeneity caused by depositional layering and fracturing. This is then combined with material balance to make site-specific estimates of the CO₂ storage potential.

We cross-checked predictions from the new method against historical field data for major onshore CO₂ floods with satisfactory results considering the very approximate nature of the estimation. We then applied the method to a selection of offshore oil reservoirs and found that, generally, the larger the remaining oil, which is a function of initial size and current recovery factor, the greater the CO₂ storage potential. We also modelled the case of continued injection after ceasing oil production at, or after, CO₂ breakthrough and observed that, as expected, the amount of CO₂ stored at breakthrough depends on how early this occurs, which is affected by reservoir heterogeneity, whereas continued injection is limited by the headroom between current reservoir pressure and fracture pressure. The overall storage is the result of the interplay between these two mechanisms. In the studied fields/reservoirs, we demonstrated that large amounts of CO₂ can be stored in terms of absolute mass and that storage of these quantities would represent significant abatement of the emissions generated by burning the incremental oil.

The new method can be used as a screening tool to identify and rank candidate oil fields for combined CO₂ enhanced oil recovery and storage in regional, national, or corporate portfolios.