Determination of the Effect of Geological Reservoir Variability on Carbon Dioxide Storage Using Numerical Experiments Détermination de la variabilité des réservoirs géologiques sur le stockage du CO2 par la méthodologie des plans d’expériences

The simulations of carbon dioxide storage in sedimentary reservoirs model the fluid and gas flow and the chemical reactions which occur between the minerals (calcite and dolomite) and the injected CO2 [André et al. (2007) Energy Convers. Manage. 48, 17821797; Gunter et al. (1999) Appl. Geochem. 4, 1-111. However because of the lack of data, these reservoirs are always partially known and the fitted variograms of petrophysical and mineralogical quantities are approximate. The aim is to quantify the impact of uncertainties on reservoir characteristics on the storage predictions. We focus on two operational parameters: the quantity of the stored carbon dioxide and the mean variation of the porosity. Two sources of uncertainties are examined: the draw dispersion and the approximation on the variogram parameters. To study the influence of the draw dispersion, variogram parameters are kept fixed and different simulations are run; the associated variance on the operational parameters then has the meaning of a repeatability error. In the second case, a sensibility analysis is carried out to study the influence of variogram parameters variations (sill, range, nugget effect) on the CO2 storage. The chosen methodology is the designs of experiments. The simulations are carried out using reactive transport software. The studied carbonated reservoir is built in reference to the Dogger formation of Paris Basin (France) [Diedro (2009) Thèse, école Nationale Supérieure des Mines de St- étienne). This reservoir is composed of several minerals, some of them being disposed in spots. The results show that the impact of the draw dispersion remains lower than the impact of the variogram parameters. The effect of the size of the dolomite spots within the rock on the stored carbon dioxide is to be noticed. Larger spots of the dolomite field with low concentration lead to a greater precipitation of carbonate and reduction of porosity than little ,spots with higher concentrations. The interaction between the sill and the range of the variogram of the initial dolomite concentration is also important. The initial calcite concentration has a slight influence only on the average porosity in the reservoir. Except for the variations of the size of the dolomite spots within the rock, small variations on the variogram parameters of the mineralogical concentration do not involve important modification of stored carbon nor of the final porosity. Dans le contexte de l’étude du stockage géologique du dioxyde de carbone dans les réservoirs sédimentaires, les simulations tentent de reproduire l