| Since 1950s, time-domain 1H NMR have been extensively studied to assist rock characterization. Geological properties such as pore-size distribution and tortuosity, petrophysical properties, i.e. porosity and permeability, can be estimated via diffusion coefficient or transverse relaxation (T2) time measurements. Recently, the determination of pore-scale transport properties of diffusive water molecules by pulsed field gradient (PFG) NMR method have been widely used to probe pore structures in porous systems. However, time-dependent restricted diffusion coefficient is not only a function of pore structure, but also affected by composition and ionic strength of the saturating brine, which varies with depth and locations. In this dissertation, the effect of ionic strength and pore size on the self- and effective-diffusion coefficient distributions (DCD) for beadpacks with different glass bead sizes were analyzed. On the other hand, NMR T2 relaxation time represents the pore size distribution (PSD) of porous media with an unknown parameter--surface relaxivity, which is the key parameter to transform NMR T2distribution (time domain) to PSD (size domain).;Injection of supercritical carbon dioxide (scCO2) into deep saline aquifers is the most promising way for the geological storage. With large amount of CO2 injected, geochemical reactions between rock and CO2 saturated brine occur and mineral dissolution and re-precipitation take place, which affect the rock wettability, porosity, permeability, relative permeability and capillary pressure. As these rock properties change during CO2 injection (short-term) or after CO2 injection (long-term), CO2 injectivity, saturation distribution, reservoir CO2 storage capacity and plume stability will be affected. The changes in porosity, permeability, and pore structure caused by CO2 saturated brine-rock reactions were investigated. As all macroscopic changes in pore structure and mineralogy are critically dependent on reactions, water analysis before and after aging was also performed to provide geochemical explanation. |
