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 facility will support research on long term trapping mechanisms for CO2 in storage reservoirs. It is therefore relevant for research and demonstration of CO2 storage safety. The porous medium in the pressure vessel can be made to be homogeneous or heterogeneous, e.g. to study the effect of layering in storage reservoirs.
The facility can also be used for research into related fields such as gravity segregation during water flooding of heterogeneous oil reservoirs.
The pressure vessel itself, with supporting infrastructure, is the only installation for the Trapping mechanisms facility. The supporting infrastructure consists of equipment for temperature control, a high precision two-cylinder CO2 pump for pressure stabilisation of the process volume during tests, and a computer that runs the control and logging software. The logged parameters are the pressure and temperature in the interior of the pressure vessel, as well as the pressure and temperature of the pump.
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.
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.
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