Mathematical modelling and numerical simulation of carbonated water injection for enhanced oil recovery and CO2 storage
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Numerical simulation of carbonated water injection (CWI) as an EOR and CO2 storage technique is studied in this thesis. When carbonated water (CO2 saturated water) contacts oil during injection into oil reservoirs, because of higher solubility of CO2 in hydrocarbons compared to water, CO2 will migrate from water into oil phase. Therefore, oil mobility, and in turn oil recovery, will increase. In addition, CO2 can also be stored securely in reservoir during CWI. The compositional simulation approach should be used for simulation of CWI in order to capture the mechanisms and the changes of composition happening during CWI process. However, the conventional compositional approach is based on the assumption of instantaneous thermodynamic equilibrium. That is, it assumes that the CO2 is transferred and distributed between oil and water phases very fast such that the thermodynamic equilibrium state is reached instantaneously. However, the CWI coreflood experiments presented in the literature show that during CWI, the CO2 transfer between water and oil phases happens slowly and therefore, the assumption of instantaneous equilibrium is not valid during the simulation of CWI coreflood experiments. As a result, the available compositional simulators cannot simulate CWI coreflood experiments correctly. Hence, in this thesis, a new compositional simulator is developed, in which the assumption of instantaneous equilibrium is relaxed by including the kinetics of mass transfer. To evaluate the performance of the developed simulator and to explore its generic capability, two different sets of CWI coreflood experiments performed in a water-wet and a mixed-wet (aged) sandstone core are selected from the literature. These coreflood experiments are simulated and studied in detail including the role of oil swelling and wettability alteration during CWI process. The simulator can predict the production profiles of oil, water and CO2; the CO2 storage profile; the differential pressure across the core and the CO2 concentration in oil and water phases. The impacts of dispersion, injection rate and carbonation level on the performance of CWI process are investigated using the developed simulator. The simulator shows that the dispersion effect on oil production is minimal here during the coreflood experiments. It is also shown that at low injection rates and high carbonation levels, higher oil recovery will be obtained by CWI. In addition, at low injection rates, more CO2 can be stored in core during the coreflood experiments with a lower and delayed CO2 production at the core outlet. Moreover, the compositional simulator of ECLIPSE300 (E300) is used to simulate the CWI coreflood experiments and its capability is compared to the capability of the developed simulator. E300 over predicts the oil recovery of CWI coreflood experiments due to the assumption of instantaneous equilibrium made by ECLIPSE 300. A dimensionless number so-called equilibrium number (Ne) is introduced and it is shown that at a specific range of Ne values, the assumption of instantaneous equilibrium made by E300 is acceptable. Accordingly, it is shown that at reservoir-scale, the system will reach the equilibrium state and therefore E300 can be used to simulate the CWI process at reservoir-scale. Based on this, finally, the reservoir-scale simulation of CWI is studied employing the ECLIPSE300 simulator. The impacts of some influential parameters on CWI performance are investigated using the results of reservoir-scale simulation.