Algorithms
ezValidator algorithms: unfaulting, unfolding and unconformities
Unfaulting
Fault displacement model of Fault Analysis Group
Drawing Barnett et al. (1987)
In unfaulting, the seismic is moved along interpreted faults to remove the throw so that seismic character and stratigraphy are continuous across these faults. The amount of throw is specified by the user in the form of a tip point, a seismic correlation and/or a horizon correlation. Throw can vary along the fault. Tip points and horizons correlations are inserted automatically. Seismic correlations are placed by dragging the seismic until the seismic character matches across the fault. In good seismic, ezValidator can determine throw automatically.
The unfaulting algorithm is based on elastic deformation following the model of the Liverpool Fault Analysis Group (now in Dublin). See Barnett, J.A.M, Mortimer J., Rippon, J.H., Walsh, J.J. & Watterson, J. (1987): Displacement Geometry in the Volume Containing a Single Normal Fault. AAPG Bulletin 71 p. 925-937.
Unfolding
Busk (1929) fold construction method.
Drawing Steven Dutch
The software removes folds in one or more interpreted horizons to approximate the original flat-lying sediments. The unfolding retains bed thickness and fault/horizon intersection angles around the unfolded horizon. Further away from the horizon the section can get deformed to accommodate rotational movements.
The unfolding algorithm is based on Busk, H.G. (1929): Earth flexures; their geometry and their representation and analysis in geological section with special reference to the problem of oil finding. Cambridge University Press 7+106 pp. The Busk unfolding construction verticalizes lines that are orthogonal to the horizon. It is followed by vertical shear to adjust remaining deviations and differences between horizons. In case the horizons show rotation only, the unfolding applies rigid-body rotation.
Unconformities
Unconformity gap determined by sequence above and below.
Drawing Kees Rutten
Unconformities (time gaps or breaks in sedimentation) are converted to gaps in the section if such breaks would lead to overlap in the reconstructed section. The gaps depend for example on which horizons are unfolded above and below.
And more...
You do not have to specify a fault hierarchy. Fault branching and fault crossing is handled automatically.
Fault/horizon intersections are automatically processed to obtain the throw implied by horizon correlations across faults.
You can insert correlations across faults by dragging and dropping the seismic on either side. When the strain implied by conflicting correlations gets too high then earlier correlations are optionally broken in favour of later correlations.
Throw is allowed to vary along a fault: growth faults are no problem.
When good seismic is available, throw is calculated automatically.
Horizons can be interpreted on the unfaulted/unfolded seismic backdrop. ezValidator converts the horizon picks back to the original coordinates and stores these in the OpenWorks database.
You can apply ezValidator on seismic sections displayed in two-way seismic-reflection time or in depth. The strain calculation may, of course, be inaccurate in time seismic.
Implementation...
The unfaulting, unfolding and unconformity algorithms are implemented in the ezValidator™ software. This forms part of Landmark’s DecisionSpace® Geosciences software environment. An early version is included in Landmark’s GeoGraphix® system.
For further information, contact your local Landmark representative.
The software is protected by US patent 7,480,205 and 14/236,601 (pending).