The reduction of Greenhouse Gases emission is a growing concern of many industries. Following the mitigation solutions recommended by the Kyoto Protocol, underground sequestration of CO2 is a way to meet this goal, as oil and gas fields offer huge CO2 storage capacities, while preserving the environment.

The oil and gas industry has a long commercial practice of gas injection: EOR, natural gas storage. Using a depleted oil or gas reservoir for CO2 storage has several interesting advantages among which the relatively large pressure range available for injection, allowing the storage of significant gas quantities for a low compression power, without altering the cap-rock integrity. Besides, the availability of reservoir dynamical and geological characterization and existing production/injection wells contributes to the optimization of the project, both technically and economically.

This CO2 storage can be permanent in the case of mineral trapping or very long term (several thousand years) in the case of hydrodynamic trapping. The long-term risk analysis of the CO2 behavior and its impact on the environment is a key objective of the project. That is why the selection of an appropriate reservoir is crucial to the success of the sequestration.

Two major steps have been identified while sequestering CO2. The injected CO2 dissolves and diffuses in oil and water and follows the pressure gradient (hydrodynamic trapping). Then, the dissolved CO2 reacts with the minerals within the formation and induces dissolution/precipitation reactions (mineral trapping), that may impair the well injectivity and/or the cap-rock sealing properties.

For the first time, this study investigates both sides using reservoir simulator with improved CO2 thermodynamics (ATHOS) and reactive transport simulator (DIAPHORE) to evaluate the extend of mineral trapping (kinetically controlled reaction) and long term behavior of CO2 within the reservoir and its neighboring geological formations (cap rock, aquifer).

This work is funded by Institut Français du Pétrole (IFP), Geostock, TotalFinaElf and sponsored by the French Ministry of Industry (FSH).

You can access this article if you purchase or spend a download.