  Three-dimensional restoration of complex structural models has become a
recognized validation method. Bringing a sedimentary structural model back in
time to various deposition stages may also help understand the geological
history of a study area and follow the evolution of potential hydrocarbon
source rocks, reservoirs and closures.
  Most current restoration methods rely on finite-element codes which require a
mesh that conforms to both horizons and faults, a difficult object to generate
in complex structural settings. Some innovative approaches use implicit horizon
representations to circumvent meshing requirements. In all cases,
finite-element restoration codes depend on elasticity theory which relies on
mechanical parameters to characterize rock behavior during the physical
unfolding process.
  In this paper, we present a geometric restoration method based on the
mathematical theory provided by the GeoChron framework. No assumption is made
on the extent of deformation, nor on the nature of terrains being restored.
Equations derived from the theory developed for the GeoChron model ensure model
consistency at each restored stage.
  As the only essential input is a GeoChron model, this restoration technique
does not require any specialist knowledge and can be included in any existing
structural model-building workflow as a standard validation tool. A model can
quickly be restored to any desired stage without providing input mechanical
parameters for each layer nor defining boundary conditions, enabling geologists
to iterate on the structural model and refine their interpretations until they
are satisfied with both input and restored models.
