Restoration of interpreted cross sections in 2-D and volumes in 3-D is increasingly used to validate interpretations in structurally complex areas or areas where seismic is of poor quality thus reducing exploration risk. Restoration provides sequential geological models of structures that include hydrocarbon generation, migration and trapping thus providing a full understanding of structuring and its controls on the petroleum system.

Restoration based on simple shear constructions use either vertical or inclined shear geometrical techniques. For inclined shear in 3-D restoration the main components are the horizontal displacement vector, the deformation plane that contains the principal strain axes and the vertical/inclined shear angle parallel to which the hangingwall deforms during translation. It is possible to vary the orientation of the displacement vector and shear angle in both azimuth and plunge. Restorations are very sensitive to both shear angle and to the movement direction. Using map view visualisation of faulted hangingwall and footwall cut offs it is possible to obtain a good estimate of the original slip vector thus minimising errors in restoration.

The flexural flattening technique involves the restoration of complexly folded surfaces to a horizontal plane while conserving surface area and minimising finite strain. Multiple surfaces showing complex folding are restored using the flexural flattening method applied sequentially to pregressively deep surfaces. Volumes between the uppermost flattened surface and underlying surfaces are preserved giving volumetric balance. The jigsaw fit of footwall and hangingwall cut-offs of flattened surfaces in map view, provides a unique restoration solution based on translation and/or rotation of the hangingwall block. Sequential restoration of progressively deep surfaces may incorporate three-dimensional decompaction at each restoration step.

The new flexural flow restoration algorithm involves the movement of particles in a fault hangingwall parallel to the underlying fault. The technique is loosely based around the geometrical constructions of classical inviscid fluid mechanics and means that hangingwall fold geometry is determined primarily by the shape of the underlying fault, without the requirement for predetermination of hangingwall fold geometry prior to restoration, or establishment of a direct relationship between fault shape and fold axial surface geometries prior to forward modelling. Line length and area balance is achieved via the application of a heterogeneous fault parallel shear to the hangingwall during forward deformation and/or restoration. The technique uses a laminar, fault parallel flow field to define the movement of the sedimentary layers in the hangingwall of the fault (Fig. 1). The technique can be applied to complex, curvilinear fault geometries in 2D and is more readily extendible to 3D than current techniques which rely on cumbersome geometrical analysis of hangingwall fold shape prior to restoration or forward modelling of fault bend fold development.

Three dimensional flexural isostatic modelling is available in the modelling procedure. Variables used in 3-D flexural isostatic modelling include structural geometries, sediment versus water fill, thermal structure of the lithosphere and effective elastic thicknesses Te. This enables predictions of accommodation space as a result of structuring plus isostatic adjustments and palaeobathymetries may be calculated through the forward models.

The application of variable angular shear to the hangingwall units permits surface area and volume balance on hangingwalls moved over complex 3-D fault surfaces. In a forward model or structural restoration it is possible to perform adjustments to volumes as a result of compaction or decompaction. Using an exponential decay of porosity with depth (Sclater and Christie 1980), the effects of compaction/decompaction of layers of varying lithologies and with laterally varying lithologies can be modelled.

Computer models using ray tracing techniques are used to forward model hydrocarbon migration from source kitchens to traps. The forward models allow sequential stages of deformation, sediment accumulation and compaction, source rock maturation and fluid flow.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah