Structural Evolution, Temperature, and Maturity of Sedimentary Basins in the Netherlands: Results of Combined Structural and Thermal Two-Dimensional Modeling
Susanne Nelskamp, Jan D. van Wees, Ralf Littke, 2012. "Structural Evolution, Temperature, and Maturity of Sedimentary Basins in the Netherlands: Results of Combined Structural and Thermal Two-Dimensional Modeling", Basin Modeling: New Horizons in Research and Applications, Kenneth E. Peters, David J. Curry, Marek Kacewicz
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Structural modeling combined with basin modeling was used to demonstrate the influence of the structural history on hydrocarbon generation. For this purpose, a tectonic setting in the Netherlands was selected that shows large-scale tectonic inversion, associated erosion, and later subsidence. On the basis of a 300-km (186-mi) two-dimensional section that crosses the main tectonic features of this setting, a structural model consisting of 21 paleosections was created. The results generated by the structural model show that the Late Cretaceous inversion affected the basins the most, whereas the erosion in the Jurassic had the strongest influence on the structural highs. This can be seen from the amount of erosion associated with these erosion phases. Using the structural model as input for the basin model allowed the temperature and maturity of the sediments to be calculated. A temperature profile at 2000-m (6562-ft) depth along the section shows that the present-day temperature distribution is also strongly influenced by the inversion. In the inverted basins, highly conductive layers, such as overcompacted sediments or salt, are closer to the surface, which results in higher temperatures than in the noninverted. Finally, the timing of hydrocarbon generation from the Posidonia Shale source rock was found to be related to the structural history within the basin. In strongly inverted parts of the basin, present-day burial is insufficient to restart hydrocarbon generation, but in less inverted parts, hydrocarbon generation resumed during the Tertiary.
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Temperature-time–based first-order kinetic models are currently used to predict hydrocarbon generation and maturation in basin modeling. Physical chemical theory, however, indicates that water pressure should exert significant control on the extent of these hydrocarbon generation and maturation reactions. We previously heated type II Kimmeridge Clay source rock in the range of 310 to 350°C at a water pressure of 500 bar to show that pressure retarded hydrocarbon generation. This study extended a previous study on hydrocarbon generation from the Kimmeridge Clay that investigated the effects of temperature in the range of 350 to 420°C at water pressures as much as 500 bar and for periods of 6, 12, and 24 hr. Although hydrocarbon generation reactions at temperatures of 420°C are controlled mostly by the high temperature, pressure is found to have a significant effect on the phase and the amounts of hydrocarbons generated.
In addition to hydrocarbon yields, this study also includes the effect of temperature, time, and pressure on maturation. Water pressure of 390 bar or higher retards the vitrinite reflectance by an average of ca. 0.3% Ro compared with the values obtained under low pressure hydrous conditions across the temperature range investigated. Temperature, pressure, and time all control the vitrinite reflectance. Therefore, models to predict hydrocarbon generation and maturation in geological basins must include pressure in the kinetic models used to predict the extent of these reactions.