Reactive transport modeling for CO2 storage in a depleted North Sea gas field

The key subsurface selection criteria for a CO2 storage candidate are capacity, injectivity and containment. There are many factors that influence these selection criteria. The factor addressed in this paper is the geochemical interaction between CO2 and the rock minerals. Each of the criteria can be affected by these interactions. For Goldeneye, a depleted gas reservoir in the Central North Sea, we have simulated the potential geochemical interactions with and without coupling to fluid flow. For the standalone interactions we used a standard geochemical modeling package (PHREEQC), using dissolution/precipitation rate formulas. For the coupled interactions we used our in-house reservoir simulator coupled to PHREEQC. The reservoir simulator was run in Equation of State mode so that it takes into account the phase behaviour between the gas (including CO2 - hydrocarbon mixing), oil (thin oil rim) and water. We also considered diffusion models through the caprock. The conclusion is that for Goldeneye the CO2-induced reactions tend to decrease porosity in the caprock as well as in the reservoir. Therefore it is considered unlikely that the geochemical interactions would create leak paths in the caprock. The porosity decrease in the reservoir is not likely to have a significant impact on injectivity