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Sensitivity Analysis of CO2 Injection within Saline Aquifers for Storage Purposes in the Form of Hydrate Using a Reactive Transport Simulator

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journal contribution
posted on 27.09.2016, 14:04 by Khadijeh Qorbani, Bjørn Kvamme, Richard Olsen
One method to mitigate the impact of fossil-fuel-generated CO2 on the climate is to store it in geological structures in the form of CO2 hydrate. Geological sequestration of CO2 involves risks and the capability to predict the response of a geologic system to variations in thermodynamic variables for short- and long-term situations is needed. We have utilized an existing CO2 hydrate reactive transport simulator, which incorporates a full kinetic description of competing hydrate phase transitions through Gibb’s free energy minimization under the constraints of mass and heat flux. Hydrate formation from gas and liquid water and from water and dissolved hydrate formers was considered. Simulations were used to conduct sensitivity studies on some of the main reservoir parameters to understand which characteristics that appeared to have most impact on stability of CO2 storage in the form of hydrate. Hydrate formation was studied for various operational conditions of CO2 injection using a two-dimensional model reservoir. CO2 was injected into a structure consisting of two aquifer zones, one caprock zone, one fracture, and two injection wells. At this stage of the simulator, a fracture is modeled as a zone of very high porosity and permeability. It was found that porosity in the regions of hydrate stability varied linearly with respect to fracture porosity, matrix porosity, injection temperature, injection pressure and water saturation, within the studied ranges. However, porosity followed approximately a second-order polynomial with respect to fracture permeability. Our model was most sensitive to changes in the matrix porosity, whereas changes in temperature, within a realistic range, appeared to have small effects. Variations in either pure calcite or pure quartz only resulted in moderate effects on porosity. A geochemical mineral composition of equal amounts of calcite and quartz, however, appeared to result in substantial reduction in hydrate formation according to the samplings from the model studies.