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Direct Strain Estimates from Palinspastic Restoration of Compressional Structures: Strengths and Limitations

Brandenburg, John Paul *1; Cardozo, Nestor 2; Naruk, Steve 1; Wolf, David E.1
(1) Shell Int'l E & P, Houston, TX.
(2) Department of Petroleum Technology, University of Stavanger, Stavanger, Norway.

A number of methods used for palinspastic restoration invoke to some extent a process of deformation by which the structure formed. If that method does a reasonable job reproducing the kinematic evolution of the structure, the results can be analyzed to estimate the associated finite strain. The accuracy and physical meaning of such calculations depends both on correct choice and application of methodology, as well as the level of approximation inherent in the method. More physically complete numerical simulations or analog models are needed to calculate stress and fine-scale strain. However, the coarser strain estimate from palinspastic restoration is likely sufficient for a number of applications, and can be used as a proxy for fine-scale reservoir structures such as fractures, small-scale faults and deformation bands provided that the limitations of the approach are understood. This is particularly true in exploration and appraisal where incomplete and uncertain data require that multiple scenarios be entertained. Here, we examine strain calculated from palinspastic restoration as applied to large compressional folds. Finite strain is calculated by multiple methods, then compared to observations from outcrop and wellbores. We find that palinspastic methods provide an adequate strain estimate for a number of smaller structures such as deformation bands, small displacement intra-reservoir faults, and local tectonic thickening, but that the orientations of principal strains can be highly dependent on the details of the restoration.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California