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A Publication Presenting the Restoration-Forward Simulation Workflow in ParaGeo

Forward geomechanical modelling over geological time scales is a special type of basin modelling technique that:

  1. Predicts the structural development in the basin during its history as opposed to prescribing a given geometry

  2. Accounts for the evolution of the full 3D stress and strain tensors thus enabling to appropriately capture the effects of tectonic compaction on sediment properties and overpressure development

  3. Captures the evolution of sediment properties since their deposition to a consolidated state after burial

However there is an inherent high uncertainty in basin history as only present day may be observed/measured to a given extent. It is useful therefore to use information from geological structural restoration (which consist in the simulation of the evolving structure backwards in time from present day to a paleo time of interest) to gain insights in basin history.

In our paper “Towards an integrated restoration/forward geomechanical modelling workflow for basin evolution prediction” we discuss the integrated restoration – forward modelling workflow in ParaGeo that enables to constrain the forward models using restoration. We first present our restoration and forward simulation methodologies as well as the main relevant functionality in the code. Then we discuss how we use restoration results and process them in order to automatically generate input data for the forward model:

  1. The initial geometry for the forward model is built from the restored geometry at the selected paleo time (it may be the final restored geometry or there may be a few formations already present in the model)

  2. The boundary displacements in the forward model are prescribed using the reversal of the boundary displacements calculated from restoration

  3. Fault propagation pathways used to extend contact surfaces to newly deposited units in the forward model are derived from fault geometries at each restoration stage

We demonstrate the capabilities of the workflow using an extensional sandbox scale synthetic benchmark and a published geometry for an isolated thrust from the Niger Delta.

However, even with the advantage of the integrated workflow to derive constrains for the forward model and automatically generate the corresponding boundary conditions from restoration, there may be discrepancies between the predicted geometry by the forward model and the observed target geometry. Those may arise because of the different assumptions between restoration and forward modelling, i.e:

  • Elastic materials in restoration as opposed to more sophisticated poro-elasto-plastic materials in forward simulation

  • In restoration the deformation recovered is mostly brittle whereas ductile deformation that may be required to generate the target observed structure is often underestimated

  • The non-physically based yet convenient back-strip boundary condition applied in restoration to underform the formations to their depositional state vs the deposition and posterior gravity-driven and tectonically driven deformation

In this case presented in the paper a synthetic benchmark was run to provide the target present day geometry. Then we applied our integrated restoration/forward simulation workflow to that geometry. Overall the workflow facilitated to achieve a present day geometry close to the target but small discrepancies were observed due to the different assumptions between restoration and forward simulation
Forward simulation from restoration results

Thus if we require to improve our predicted geometry we can use the integrated workflow in ParaGeo and adopt an iterative approach to perform corrections in either, restoration or forward simulation assumptions until we achieve a prediction with a desired degree of accuracy.

Iterative approach using the integrated restoration - forward simulation workflow

It should be noted that since the publication of the paper we have added a lot of functionality relative to the integrated workflow enabling to simulate a wider range of cases; for example:

  • Improvements in the boundary conditions applied to the forward model from restoration by increasing the frequency of outputs from restoration taken into account for interpolation

  • More control in fault propagation for multiple faults

  • Incorporation of sophisticated boundary conditions for cases with multiple faults

  • Tools to smooth fault geometries based on curvature

We applied our workflow to a published section from the Orange basin encompasing several extensional and compressional structures. Such case required specialized boundary conditions to ensure that the right amount of displacement is prescribed in each fault
Boundary conditions for the Orange basin model

Some of this tools are demonstrated in one of our tutorial examples in which the integrated workflow is applied to a published interpreted section from the Orange basin.

Comparison of predicted and target geometries for the Orange basin model


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