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The Lower Triassic Buntsandstein is a candidate reservoir for direct heating usage and carbon dioxide storage in Luxembourg. In this thesis, the Buntsandstein section of the Mersch core is studied as a worst-case scenario of a tight reservoir in the Trier-Luxembourg basin. This study aims to identify the depositional and mainly the diagenetic factors responsible for such a reduced reservoir quality. The study approach was primarily based on combining literature, petrography, XRD, and stable isotope analysis to refine the paragenetic sequence and the authigenic phases that affected the Buntsandstein reservoir in the Trier-Luxembourg basin. This study showed that the Buntsandstein section of the Mersch core experienced diagenetic alterations started nearly immediately after deposition till later stages of burial and subsequent possible telogenesis. The paragenetic sequence, as well as the dominant primary sedimentary facies of floodplain, were critical in destroying the reservoir quality. The clay-rich sediments at the location of the Mersch core, as well as early alteration of detrital grains, made the lithology vulnerable to compaction and the loss of primary porosity. Early eogenetic carbonates were dolomitized during later burial in a closed fluid circulating system that prevented the formation of secondary porosity. Smectite to illite transformation contributed to further permeability reduction. Possible development of late-stage secondary dissolution porosity was interpreted. However, the later authigenic gypsum completely blocked any open porosity.

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The study of rocks to determine their potential as reservoir rock is very important. Reservoirs can be studied for a variety of different purposes, for the classical oil and gas industry, but also for groundwater, environmental and geothermal studies. In this thesis, the focus was put on two important reservoir properties; the porosity and permeability. Based on these properties we get information on if fluids can be found or stored inside a reservoir as well as information on how these fluids can move. These properties will be studied using nuclear magnetic resonance (NMR). A range of different rock types are studied to discover the potential of NMR as analysis technique for reservoir characterisation. Research is done on both carbonates (chalk, limestone and travertine) and sandstones (Neeroeteren and Buntsandstein Formations). The goal of this thesis is to get a good understanding of NMR as analysis technique with its advantages and disadvantages and to be able to formulate its limitations. In the first phase of this study, mainly attention was given to the fundamental processes influencing NMR and the physics behind the phenomenon. Afterwards, NMR experiments are carried out on the different rock types. It is important to first saturate the studied samples, as NMR measures the water inside of a sample. Based on the obtained information, under the form of relaxation times, the porosity could be determined. Also, information on the pore size distribution and amounts of fluids which are bound and freely available in the sample can be estimated. The permeability is determined with two models which make use of the porosity but also other characteristics such as the amounts of bound and free fluids. When these estimated values for the porosity and permeability are compared with values obtained with standardised analysis techniques, a good match between values occurs. Based on the differences between rock types and their NMR-result, several effects could be observed. The travertines show very large pores which make good measurements difficult to obtain information on the pore dimensions. Pores and fractures along the side of a plug cannot contain any water and thus cannot be measured with NMR. The presence of iron-bearing minerals will affect the NMR-results as the iron inside of these samples will influence the magnetic field in which the measurements are carried out. This will cause an underestimation of the porosity and permeability. Clays can be recognised by measuring samples dry as clays also contain water. This research shows NMR is a good complementary analysis technique to determine the potential of reservoir rocks.