Untitled - Technische Universiteit Eindhoven

1.4. Outline of thesis 5(SNR) [38]) NMR is a non-intrusive technique which can be employed to study (reactive)transport in porous media in situ. NMR imaging and spectroscopy are powerful toolsand are widely used in (bio-)medicine [39] and chemistry [40]. A brief introduction toNMR is given in Appendix A. NMR techniques are based on radio frequency (rf) energyabsorption by and emission from elements whose nuclei have a nonzero nuclear magneticmoment. In an NMR measurement the nuclei exhibit characteristic relaxation times (T 1and T 2 ; see Appendix A) which depend on the chemical and physical conditions [41]. Inmany NMR imaging (MRI) applications the spatial variation in T 1 or T 2 within a sampleis utilized to obtain spatial contrast based on T 1 or T 2 (see for example Figure 1.3). Inour study we focus on the relaxation times T 1 and T 2 in order to monitor the reactivetransport of TMOS in bulk and porous materials.1.4 Outline of thesisThe first part (Chapters 2, 3, 4 and 5) deals with the coupled mass transfer and gelreaction of TMOS in two-phase bulk systems. In the second part (Chapters 6, 7 and 8)the placement of the chemical in porous materials is analyzed. We note that Chapters2, 3, 4, 6 and 7 are based on published articles or articles which are to be published.Therefore, some repetition of content is present in these chapters.In Chapter 2 the experimental technique to monitor the coupled mass transfer andgel reaction in bulk systems is described in detail. The method and results of NMRrelaxation time measurements on bulk model systems are discussed. Further analysisof the experimental results, described in Chapter 2, is presented in Chapter 3. Thisincludes a basic mass transfer model and an interfacial tension analysis of the bulk systems.Chapter 4 deals with the results of a second set of bulk phase experiments in which theeffect of pH on the reactive transfer was determined. It also sets a framework for theNMR response of the fluids and gels which were used (including heavy water) in theexperiments with the porous materials. In Chapter 5 the cross-linking of the silica in thesol-gel is considered and described by a phenomenological model. The experimental studyon the reactive transport of TMOS in sandstone is presented in Chapter 6. The focusis on the coupled mass transfer and gel reaction which were monitored using the NMRtechniques. In Chapter 7 the results obtained from a series of beam bending experimentsare presented, which show the effect of gel treatment on the permeability of sandstone.A numerical model of TMOS placement in porous materials is presented in Chapter 8,together with the simulation results. Finally, the general conclusions and an outlook aregiven in Chapter 9.