Fold-Thrust Geometries - Is There a Right Model?

Robert Butler¹, Douglas A. Paton², Estelle J. Mortimer², and Clare E. Bond^3
1School of Geosciences, University of Aberdeen, Aberdeen, United Kingdom
²Earth Sciences (SEE), University of Leeds, Leeds, United Kingdom
³Midland Valley, Glasgow, United Kingdom

Fold and thrust structures offer interpretational challenges, even when well-imaged in 3D seismic volumes. There are several end-member kinematic models for folding in compressional belts, including fault-bend, tip-line and detachment structures. On individual 2D profiles, the consequences of particular structural interpretations, either using ideal end-member behaviours or composite styles, can be explored using combinations of graphical restoration and forward models. It is well known that simple 2D restorations can serve to validate structural interpretations and thus begin to reduce interpretation uncertainty. Further tests can include the ability to model the patterns of growth strata. In three dimensions, serial section approaches can be used to test for lateral strain compatibility. Where strain paths and deformation mechanisms are appropriate, 3D forward models and restorations can be applied. While all these strategies can be applied to assess the options for stratal offsets and deformations of surfaces, where input data are restricted to seismic alone, the role of distributed strain on structures below seismic resolution commonly represents uncertainty that is difficult to evaluate. In this presentation, the outcomes of different restoration and modelling strategies are compared for an individual structure imaged on 3D seismic data (from deep water Nigeria). While restoration and modelling can eliminate (or at least risk as being unlikely) geometrically unbalanced options, there remain a range of competing, viable structural interpretations. A key component of assessing this uncertainty lies in capturing a broad range of viable alternatives, best achieved through using different workflows and multiple interpreters with difference experience and backgrounds.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas