Klaus Bitzer

SIMSAFADIM-CLASTIC: A new approach to mathematical 3D forward simulation modelling for terrigenous and carbonate marine sedimentation

Most sedimentary modelling programs developed in recent years focus on either terrigenous or carbonate marine sedimentation. Nevertheless, only a few programs have attempted to consider mixed terrigenous-carbonate sedimentation, and most of these are two-dimensional, which is a major restriction since geological processes take place in 3D. This paper presents the basic concepts of a new 3D mathematical forward simulation model for clastic sediments, which was developed from SIMSAFADIM, a previous 3D carbonate sedimentation model. The new extended model, SIMSAFADIM-CLASTIC, simulates processes of autochthonous marine carbonate production and accumulation, together with clastic transport and sedimentation in three dimensions of both carbonate and terrigenous sediments. Other models and modelling strategies may also provide realistic and efficient tools for prediction of stratigraphic architecture and facies distribution of sedimentary deposits. However, SIMSAFADIM-CLASTIC becomes an innovative model that attempts to simulate different sediment types using a process-based approach, therefore being a useful tool for 3D prediction of stratigraphic architecture and facies distribution in sedimentary basins. This model is applied to the neogene Valles-Penedes half-graben (western Mediterranean, NE Spain) to show the capacity of the program when applied to a realistic geologic situation involving interactions between terrigenous clastics and carbonate sediments.

Hydrogeochemistry and diagenesis of Miocene sandstones at Montjuı̈c, Barcelona (Spain)

Abstract Massive silicification of Miocene sandstones cropping out at the Montjuic mountain in Barcelona has been analyzed in order to constrain paleoflow systems, which may have contributed to the diagenetic reactions. The section consists of five units with alternating sandstone–marl units. The principal diagenetic features are observed in strongly silicified sandstone units. Alunite mineral precipitation indicates presence of saline fluids and low pH. Salinity is most probably derived from marine seawater and low pH may be due to oxidation of pyrite. A quantitative thermodynamic modeling is applied to characterize the percolating fluids and to constrain the hydrodynamic system.

Fluid pressure, flow velocities and transport processes in a consolidating sedimentary column with transient hydraulic properties

Abstract Consolidation is the principal process in generating fluid overpressures and fluid expulsion in a sedimentary column. While low sedimentation rates and permeable sediments with low compressibilities create low fluid overpressures and rapid compaction equilibrium, high sedimentation rates and low permeable sediments with high compressibilities such as shales inhibit fluid expulsion and contribute to elevated fluid pressures. Predictions of fluid overpressures based on solutions of the consolidation equation need to take into account that hydraulic conductivity and compressibility in the sedimentary column are varying with time and that the sediment column itself is subject to deformation. Although flow velocities are low, the effect of advection on the vertical displacement of solutes within the consolidating column is important. This contribution presents numerical solutions of the equations for consolidation and solute transport in one dimension in space, taking into account the changing hydraulic properties of sediment during compaction and the deformational shortening of the column.

Origin and genesis of the Oklo uranium ore deposits (Gabon): results from a basin scale fluid flow modelling

Abstract Hydrologic processes that have contributed to the mineralogenesis of uranium ore deposits in the Franceville basin at Oklo (Gabon) are still uncertain. Based on stratigraphic, sedimentological and petrophysical data available from the outcrops at the Oklo area, we have performed a series of simulation experiments in order to constrain hypothetical paleoflow systems at the basin scale. Two-dimensional (2D) models have been applied to test hypotheses concerning convective flow systems in the Franceville basin and its transport capacity, the possible location of recharge and discharge areas and the existence of tectonosedimentary drains. Modelling results show that 2D flow models are insufficient to describe a system flux that is compatible with the location and distribution of the uraninite bodies in the Franceville basin. A 3D model has therefore been developed that successfully represents possible paleoflow systems with sufficient system flux in those parts of the basin, where the mineralisation is observed.

Modeling episodic dewatering and evolution of fluid pressure/total load ratio (λ) in a sedimentary basin

Abstract This contribution presents a two-dimensional modeling study of fluid release from an overpressured compartment at depth towards a shallower aquifer. A transient fluid flow model is applied to simulate the evolution of fluid flow taking into account the effects of synchronous consolidation created by the fluid pressure release. The evolution of the ratio between fluid pressure and total load, denoted as λ, is calculated during the dewatering of a sediment pile. Results show that the fluids are drained from the overpressured compartment and flow into shallower aquifers, thereby creating elevated values of λ in shallower zones, indicating favorable conditions for hydrofracturing. Simulation results suggest a zipper-like propagation of hydrofracturing conditions towards shallower depths.