TRAPPING MECHANISM (NO3.7b)

The trapping mechanism facility is constructed for the study of the dissolution trapping mechanism in CO₂ storage reservoirs. This trapping mechanism speeds up the transition to safe long-term storage since CO₂-rich water is heavier than CO₂-free water and will therefore sink to the bottom of the storage formation. Density convection currents that will be generated by the density difference will speed up considerably the dissolution of CO₂ into formation water in a storage site, since they will enable continuous exposure of CO₂ in the gas cap to formation water that is not already saturated with CO₂. Initially, however, density differences in brine are smoothened by lateral diffusion of CO₂ in the brine close to the gas cap. A certain period of time therefore elapses until onset of convection. The length of the time period depends on reservoir properties such as permeability. The facility is designed for studies of this process under near reservoir conditions in order to test theoretical and numerical predictions.

The facility is a cylindrical pressure vessel with 60 cm diameter and 60 cm height internal dimensions. It can be pressurised to near storage conditions (65 bar) to increase the solubility of CO₂ in water compared to atmospheric conditions. Wetted materials used are resistant to CO₂/water systems. Specifically, the materials are resistant to the carbonic acid that forms when CO₂ dissolves into water. The pressure vessel is equipped with a removable lid to enable filling of the interior of the pressure vessel with a porous medium to represent the storage formation.

The trapping mechanism facility is integrated into SINTEF's Reservoir laboratory which also host the core flooding (ECCSEL facility NO3.7a) and pVT facilities (ECCSEL facility NO3.7c). This allows a range of auxiliary tests, e.g. of the average permeability of the porous material used in the tank or solubility characteristics of any fluid systems used.

Earlier experiments designed for measuring the dissolution process and the onset of convection-enhanced dissolution have been restricted either to model systems that can be operated at atmospheric conditions, or at a smaller scale (15 cm) (Karimaie & Lindeberg, 2016). Experiments in bulk 3D on this scale has not previously been possible. 

Karimaie, H. and Lindeberg, E. 2016: Experimental verification of CO₂ dissolution rate due to diffusion induced convection. Energy Procedia, vol. 114, pp. 4917-4925.