Born Dec. 24th 1980, Oostende, Belgium
since 2006: Post-Doc at Geologie-Endogene Dynamik, RWTH Aachen (ExxonMobil Unrestricted Research Grant)
2002-2005: PhD at Geologie-Endogene Dynamik, RWTH Aachen (defensed on 18.11.2005, magna cum laude)
This thesis presents an analysis of fracture sealing processes, studied on microstructural and sedimentary basin scale. The aim is to get more detailed insights in these processes and to understand the influence of fluids and precipitation of minerals with respect to the evolution of sedimentary basins.
Numerical simulations of the evolution of vein microstructures are used to investigate the parameters which control the final microstructures. In the simulation code, the main input parameters are crystal growth anisotropy, amount of seed crystals, fracture morphology and opening vector. By simulating anisotropic crystal growth, we focus on the effects of growth competition when crystals are growing in an open space. When crack-seal growth is simulated, the width of the individual crack-seal increments in relation to the fracture morphology influences the final microstructure. The evolution of an elongate-blocky to a fibrous microstructure is illustrated in a series of simulations with different opening increments. Finally, the limitations of the current simulation algorithm are discussed and suggestions are made to improve the program with respect to the simulation of crystal facets and crack-seal growth.
In the next part of this work, polycrystal growth experiments are presented in an accurately controlled flow system. The main focus of these experiments is a detailed analysis of the growth rate evolution of crystals over time. The average growth rate of the crystals is influenced by growth competition and depletion of the fluid along fracture length. In addition, the growth rate of individual crystals depends on the facet type, facet length and facet orientation. Variations in the growth rate over time are observed in some facets and can be explained by a dislocation flux between different crystal sectors. At high supersaturation (>0.176), regularly spaced fluid inclusion bands are generated in the crystals. In natural veins, the presence of such inclusions could probably be an indicator for high paleo-supersaturation. Asymmetric elements, which could be related to the paleo-flow direction are not observed in the final microstructures of the experiments.
The analysis of boreholes in the Lower Saxony Basin (NW Germany) resulted in identification of at least two different vein generations in the Triassic sandstones. The first generation is filled with calcite and has in most cases a fibrous microstructure. Stable isotopes and strontium isotopes indicate that the fluids were mainly locally derived and precipitation took place at low temperatures (<120°C), when the rocks were only slightly consolidated. The second generation is filled with anhydrite and the microstructures are elongate-blocky to blocky. Sometimes, rosette structures with platy anhydrite crystals are observed, indicating growth in an open space. Fluid inclusions in anhydrite indicate that precipitation took place around 150°C, corresponding to burial depths of 3-5 km, and that the fluids had a NaCl-CaCl2-H2O composition. Sulphur and strontium isotopes indicate that fluids were at least partly derived from the underlying Zechstein evaporites. The generation of these veins is explained by overpressures, which significantly reduced the effective stresses. A possible mechanism for overpressure generation in the basin at these depths is a sudden influx of fluids, escaping from the underlying Zechstein evaporites. The supersaturation of the fluid with respect to anhydrite can be caused by a pressure drop during fracturing.
Based on the results of the different parts of this work, some new aspects of crystal growth in fractures are discovered. The comparison of processes on microstructural scale with basin scale improves the understanding on the role of supersaturation of fluids in sedimentary basins.
Nollet, S., Koerner, T., Kramm, U., Hilgers, C. (subm.) Geochemical constraints on the precipitation of veins and cements in the Buntsandstein (NW Germany). Geofluids
Hilgers, C., Nollet, S., Schönherr, J., Urai, J.L., 2006. Paleo-overpressure formation and dissipation in reservoir rocks. Oil Gas European magazine 2, 68-73.Nollet, S., Hilgers, C., Urai, J.L. 2006. Experimental study of polycrystal growth from an advecting supersaturated fluid in a model fracture. Geofluids 6, 185-200.
Nollet, S., Hilgers, C., Urai, J.L. 2005. Sealing of fluid pathways in overpressure cells - a case study from the Buntsandstein in the Lower Saxony Basin (NW Germany). International Journal of Earth Sciences 94, 1039 - 1055.
Nollet, S., Urai, J.L., Bons, P.D. Hilgers, C. 2005. Numerical simulations of polycrystal growth in veins. Journal of Structural Geology 27, 217-230
Abstracts in conference proceedings
Hilgers, C., Nollet, S. 2005. Fracture sealing processes in the Buntsandstein - comparison of nature and see-through experiments. Terra Nostra 2005/5, 47-50. (DFG-SPP 1135 Meeting Eringerfeld).
Hilgers, C., Nollet, S. 2005. Paleo-overpressures in sedimentary basins: in situ stresses and transport mechanisms. Schriftenreihe der Deutschen GeologischenGesellschaft, Heft 39, 168.
Nollet, S., Hilgers, C., Urai, J.L. 2005. Crystal growth in fractures - results from see-through experiments. Berichte der Deutschen Mineralogischen Gesellschaft, Beih. Z. European Journal of Mineralogy, 17(1), 97.
Hilgers, C., Nollet, S., Urai, J.L. 2005. Fracture sealing processes: microstructural and regional aspects. STOMP meeting, Townsville, 9/2005.
Nollet, S., Hilgers, C., Urai, J.L. 2005. Palaeo-overpressures
in the Lower Saxony Basin (NW Germany) as derived from veins. DRT meeting,
Hilgers, C., Nollet, S., Urai, J.L. 2005. Some constraints on growth conditions drawn from microstructures in veins. DRT meeting, Zurich, 5/2005.
Hilgers, C., Nollet, S., Kirschner, D., Urai, J.L. 2005. Fluid migration und Bildung von versiegelten Klueften in Ueberdruckzonen - Fallstudien von Sandstein- und Kalkstein-Reservoiren. DGMK meeting, Celle, 4/2005.
Nollet, S., Hilgers, C., Urai, J.L. Sealing of fluid pathways in an overpressure cell – A case study in the Buntsandstein (NW Germany). DFG-SPP 1135 Meeting Eringerfeld, Germany (3. Rundgespräch)(1st-3rd Decemer 2004)
Nollet, S., Urai, J.L., Hilgers, C. 2004. Microstructural observations of veins in the Buntsandstein (Lower Saxony Basin). GeoLeipzig, 2004.
Nollet, S., Urai, J.L., Hilgers, C. 2004. Microstructural study of fracture selaing in the Middle Buntsandstein (Lower Saxony Basin, Germany). Poster at Gordon Research Conference on Rock Deformation, 8-13.08.2004.
Nollet, S., Urai, J.L., Hilgers, C. 2004. Experimental study of fracture sealing by advective flow. Geophysical Research Abstracts, Volume 6, 2004.
Nollet, S., Urai, J.L., Hilgers, C. 2004. Simulation of fracture sealing by advective flow using see-through experiments. Terra Nostra 2004/01 (TSK X 10. Symposium Tektonik, Struktur- und Kristallingeologie, Aachen, Germany, 31.03.-02.04.2004).
Nollet, S., Urai, J.L., Hilgers, C. 2003. Fracture sealing processes in the Buntsandstein. Terra Nostra 2003/07. DFG -SPP 1135 (Dynamics of Sedimentary Systems under varying Stress Conditions by Example of the Central European Basin System), pp. 54-57.
Nollet, S., Hilgers, C., Urai, J.L., 2003. Fracture sealing processes in the Buntsandstein - comparison of nature and see-through experiments. SPP 1135 Workshop: Temperaturentwicklung, KW-Systeme, Fluide und Salze, BGR, Hannover, 18.06.2003.
Nollet, S., Hilgers, C., Urai, J.L., 2003. Numerical modelling of microstructures formed by fracture sealing processes. DRT conference, St. Malo, France, 14.-16.04.2003
Nollet, S., Hilgers, C., Urai, J.L., 2002. Fracture sealing processes in the Buntsandstein - project overview and first results. 1. Rundgespraech DFG-Schwerpunktprogramm, Schloss Eringerfeld, Geseke, 28.-29.11.2002
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Fluid migration and associated mineralisations with the emplacement of a limestone nappe on an ofiolitic melange (Northern Isparta Angle, SW Turkey)
Muchez, P., Nollet, S., Sintubin, M., Lens, S., Joachimski, M. 2003. Fluid flow, alteration and mineralisation associated with the emplacement of the Lycian nappes (SW Turkey). Journal of Geochemical Exploration 78-79, 99-103
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