Fault controlled pressure modelling in sedimentary basins /
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The starting point for this Dr. Ing. thesis was the requirement for models describing basin scale overpressure for use in basin modelling studies. It is necessary to identify, understand and describe both the generating mechanisms and the fluid flow in sedimentary basins in order to meet this requirement. All of the models developed are based upon a study area consisting of fault bounded pressure compartments. A reservoir simulator has applied a lateral cross fault transmissibility model and by defining the overpressure history in some of the pressure compartments it has been possible to model the overpressure through geological time. A simpler model estimating the present day overpressure distribution based upon the same fault transmissibility model is developed. This model is able to provide a snapshot of the main present day pressure trends. This model has further been developed to a full pseudo 3D-pressure simulator including generation and dissipation of pressure through time. Due to the quantification of generation and dissipation of overpressure it is possible to model hydraulic fracturing and leakage through the overlying seals. In addition to the models describing the overpressure, an algorithm that converts the pressure compartments into a quadrangle grid system is developed. The main part of the work in this thesis deals with quantifying basin scale generation and dissipation of overpressure. Different models are developed based upon the available literature and knowledge achieved during this work. All the models used are thoroughly described. The pressure simulator PRESSIM is developed in order to test, improve and reject different models. Several simulations of the overpressure history in the North Viking Graben and the Haltenbanken area offshore Norway are presented. The modelled overpressures are calibrated to the observed pressures revealed by exploration wells. In general, the results are very satisfactory due to relatively small deviations between the modelled and observed overpressures. The simulations provide an increased knowledge of the mechanisms generating and dissipating the overpressure and form a good basis for discussing the nature of the overpressure. In addition, the results suggest which mechanisms are the most important in the different parts of the basin. The pressure simulator PRESSIM can be used to test and verify alternative pressure generation models and flow descriptions in a basin. It is possible to model the position and timing of the hydraulic fracturing because the pressure simulations are based upon a water budget for each pressure compartment.