Abstract
This thesis forms part of a continuing programme of research to investigate the application of NMR to fluid saturated rock. The work falls into four sections; (i) The development of a novel broad line NMR imaging technique for the study of short T2 fluid components in reservoir rock The technique is a repetitive pulse variant of an established gradient echo method which employs oscillating magnetic field gradients. The variant uses low flip angle r.f. pulses to reduce image rounding artefacts and provide naturally T1 weighted data. (ii) The selective imaging of fluids within preserved reservoir rock and the first broad line NMR imaging study of immiscible fluid flow. The selective imaging of reservoir fluids within preserved rock core samples has been achieved using T1 weighted MRI methods. To account for the natural heterogeneity of the rock and the observed mixed wettability, T1 suppression has been enhanced by lowering the temperature of the rock cores, thus exploiting the difference in dominant relaxation mechanisms of the two core fluids. A model has been developed to explain this temperature dependence in terms of pore surface relaxation theory. Fluid flow processes within reservoir rock have been investigated using chemical substitution and T1 weighted imaging. Due to the short transverse relaxation times expected at irreducible saturation, short T2 imaging protocols have been adopted and represent the first such study. This has provided quantitative data from which the individual phase saturations can be directly obtained. (iii) The first broad line NMR imaging study of liquid and vapour phase diffusion processes in partially saturated rock. Excellent agreement is found between the NMR diffusion profiles of partially saturated rock and a model based on a combination of vapour and liquid phase transport. Estimates of the surface water diffusion coefficient and vapour percolation threshold have thus been obtained. (iv) A detailed study of proton relaxation times of water-saturated rock as a function of saturation. The saturation levels range from 0.06%, equivalent to monolayer water coverage, to 100%. The results have been used to test fast diffusion relaxation theory in rock over the full saturation range for the first time. The relaxation measurements at monolayer coverage have led to the first unambiguous estimates of rock plug pore surface relaxivity. Evidence has been obtained for the effect of pore throats on the relaxation times and pore throat size estimates have been made.