Frangeul, Johann¹, Long Nghiem², Emmanuel Caroli³, Sylvain Thibeau³
(1) Total E&P Norge, Stavanger, Norway
(2) Computer Modelling Group Ltd, Calgary
(3) Total, Pau, France

ABSTRACT: Sleipner/Utsira CO2 Geological Storage Full Field Flow and Geochemical Coupling to Assess the Long Term Fate of the CO2

Underground storage of CO₂ is an important option for tackling greenhouse gases emissions. The world first industrial scale application is ongoing in the North Sea (Sleipner area). One million tonnes of CO₂ per year, produced from the Sleipner Hydrocarbon gas field is captured, reinjected and stored in an underground saline aquifer (Utsira formation) since September 1996.
For storage safety issues, it is crucial to predict the long-term fate of the CO₂, including its migration within the aquifer and its reactivity with the sand minerals. This paper presents a novel approach coupling these two issues at the Utsira reservoir scale, using a dedicated simulator.

The key issues developed in this paper are:
- How to calibrate a coupled flow-geochemical model using batch, geochemical models as input;
- The CPU time contribution of the geochemical module to the total simulation time using a 48 000 cell geomodel;
- The quantification of the CO₂ mineral trapping compared to the quantity of CO2 injected, which is the safest long-term mechanism for CO₂ storage.

The main results obtained are the following:
- The software we used is perfectly suited to long term simulations of CO₂ disposal in saline aquifers, with both transport and reaction effects taken into account;
- CO₂ injection leads to significant changes in the reservoir mineralogy but has a minor effect on porosity and permeability changes;
- These changes could not be derived directly from batch experiments, as the conditions where not fully representative to the reservoir ones.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.