On the 23rd of March 2021, Melchior will defend his work entitled: "Using Stokes flow equations for the geomechanical restoration of geological structural models".
The defense will be streamed online using Microsoft Teams. Save the date!
Abstract: In order to study the subsurface, one must first understand its deformation through time. As the available data coverage is not sufficient to determine these deformations precisely, geologists make hypotheses to link them depending on their knowledge. This allows them to create structural models, which can be seen as the sum of all the data and knowledge on a specific area. Structural restoration was developped to try and make a model go back in time. The advantages are dual: first, it allows the validation
of the structural model by checking if the restored model has a reasonable geometry. Second, the history and retrodeformation
of the rock layers can be studied from the path they take during the restoration process (which also allows checking the hypotheses that were made on the history of the area). In the context of faulted and folded sedimentary basins, mechanics have been incorporated in the restoration process to compute the deformation of the rock layers inside the models, but the time reversal is still driven mainly by geometric conditions. In the context of basins incorporating salt tectonics, creeping flow restoration was developped by considering the rocks as highly viscous fluids, but neglects faults and non-flat topography.
of the structural model by checking if the restored model has a reasonable geometry. Second, the history and retrodeformation
of the rock layers can be studied from the path they take during the restoration process (which also allows checking the hypotheses that were made on the history of the area). In the context of faulted and folded sedimentary basins, mechanics have been incorporated in the restoration process to compute the deformation of the rock layers inside the models, but the time reversal is still driven mainly by geometric conditions. In the context of basins incorporating salt tectonics, creeping flow restoration was developped by considering the rocks as highly viscous fluids, but neglects faults and non-flat topography.
The main contribution of this thesis is to provide an approach to add more physical conditions to the restoration of faulted sedimentary basins. This approach relies on mechanical simulations of the subsurface. The rock layers are treated as highly viscous fluids, and the restoration is driven by a negative time-step advection. The faults are considered as shear zones with an effective viscosity lower than the surrounding sediments. This methods allowed the restoration of several simplified models of the subsurface.
The second contribution of this thesis is an assessment of the choice of the parameters for the restoration simulations. This assessment is based on the restoration of a laboratory analogue model. The boundary conditions are first studied, to determine how to provide an adequate choice of conditions that still allow the restoration of the model. The material properties and their influence are then looked upon, to determine the effective parameters that are closest to those of the rocks inside the model.
These contributions offer a new perspective on how to add more physical conditions to the geomechanical restoration of structural models of the subsurface.
Keywords: structural model, structural restoration, geomechanical restoration, boundary conditions, sedimentary basins
Many thanks to the external PhD Committee members Prof. Susanne Buiter (RWTH Aachen), Dr. Fanny Garel (U. Montpellier), Prof. Laetititia Le Pourhiet (ISTEP, Sorbonne Univ), Prof. John Shaw (Harvard U.). Melchior collaborated with Dr. Cedric Thieulot (Utrecht University) and the PhD was advised by Guillaume Caumon and Paul Cupillard.