| Summary: | 碩士 === 國立中正大學 === 應用地球物理研究所 === 103 === Carbon capture and sequestration (CCS) is believed to be an economically feasible technology to mitigate global warming by capturing carbon dioxide (CO2), the major component of greenhouse gases, from the atmosphere and injecting it into deep geological formations. Injecting CO2 into deep aquifers needs to be careful not to exceed the maximum pressure threshold that would otherwise fracture the cap rock. Mechanically compromised cap rock will not only form an artificial leakage pathway but also cause groundwater acidification in shallow aquifers. If injecting a great amount of CO2 at a constant rate, excessive pressure buildup will be induced in the vicinity of the injection borehole. However, such pressure buildup can be significantly reduced and safely controlled by maintaining a constant pressure in the injection borehole. Therefore, the objective of this research was to develop a new semi-analytical solution for the pressure distribution in the storage formation when CO2 is injected under a constant pressure condition. Under the assumptions of immisicibility, zero capillary pressure and compressibility, vertical equilibrium in pressure, fully penetrating borehole, and the validilty of the Darcy’s Law, a sharp interface between CO2 and brine will be formed in the formation, which is closely related to the fluid pressure. Solving the mass balance equations of brine and CO2 was facilitated by applying a similiarity transformation to these equations. The CO2-water interface height was first solved, which was then used to solve the pressure distribution. Simulation results indicate that the radial extent of the interface is increased whenthe quotient of the water to CO2 mobility ratio (increases, especially at the top of the aquifer. Whenthe ratio of gravity to pressure driving force (is increased, the CO2 front at the bottom of the aquifer migrates less than that at the top of the aquifer, manifesting that gravity segregation dominates the migration of CO2.
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