Modeling synrift sediment infill patterns of synthetic normal faults

Abstract

Previous studies of normal faulting and their control on sedimentation have largely focussed on geometrical infill patterns from a two dimensional perspective. In order to overcome this a series of 3D models have been generated which allow 3D infill patterns to be examined in detail. This study uses a series of synthetic 3D experiments to highlight the effect of changing fault displacement parameters on synrift sedimentation patterns. Several experiments have been run using new functionalities in Roxar’s RMS 2013 software (part of their uncertainty module), in particular the ability to change displacements within a structural model. A new workflow has been established which combines the different RMS functionalities to sequentially displace surface models and infill the resulting hanging wall depressions. This workflow enables the user to manipulate various fault parameters, including length, displacement field and reverse drag, plus the option to manipulate the number of faults and their evolutionary geometry. The modifications to the structural models make it possible to generate topographic surfaces and displace them in a similar manner to faults cutting the earth’s surface. The resulting hanging wall basins can then be infilled using flat surfaces. The displacement-infill sequence forms a series of evolutionary models where the relative impact of the rate of the displacement and sedimentation can be observed (these rates are user controlled). In RMS, semi-automated modeling techniques were developed to accomplish various scenarios, which allowed specific parameters to be altered and their impact assessed. The structural models have been converted to 3D grids in order to utilise RMS’s visualization of layered/segmented models and optimize the presentation of the results (successive time steps, layer geometries, fault displacement view, map view and multi cross-section view). Initial models concentrated on using a single fault model in order to test the RMS functionalities. These models have been used to develop the RMS workflow and check the resulting models produced the expected results. The initial experiments have been developed to generate more complex structural situations in order to demonstrate how these techniques can be applied to more real world scenarios. The more complex experiments include asymmetric faults (where the point of maximum displacement is not in the center of the fault), multiple faults with similar displacement rates and relay ramps. Finally, further modeling techniques were developed in order to model the formation of sedimentary lobes such as those in a Gilbert delta environment. These techniques include the use of cone-shaped infill surfaces to mimic the radial sedimentation patterns associated with Gilbert type fan deltas. These visualizations attempt to replicate field examples of synrift sedimentation from the Corinth Rift in Greece (especially the Vouraikos Delta).