Shackleton, Ryan¹, Michele Cooke¹ 
(1) University of Massachusetts, Amherst, MA

ABSTRACT: 3D Mechanical Modeling of Displacement Trajectories in Fault Related Folds: Insights and Implications for 3D Restoration

Three dimensional fault related folds are commonly modeled and restored by splicing 2D cross sections to generate a 3D surface, assuming that strain and transport only occur in the plane of section. 3D forward models based on continuum mechanics suggest that the assumption of in plane transport is not valid near the plunging noses of fault related folds. Fault related folds were modeled using Boundary Element Method code by prescribing a uni-directional, elliptical slip distribution on a rectangular fault whose center is at 3 km depth in a linear elastic half space. Points in observation planes simulate bed surfaces, and finite deformation of these surfaces is calculated by accumulation of incremental displacements of observation points through a series of infinitesimal strain models. Slip on the fault produces a doubly plunging anticline at the forward fault tip, and a doubly plunging syncline at the trailing fault tip. Analysis of the displacement direction in each bed indicates that pure in plane transport (transport parallel to the direction of fault slip) only occurs near the apex of the fold. Out of plane transport increases with vertical distance from the fault and with proximity to the lateral fault tips. Near lateral fault tips out of plane transport constitutes up to 40% of the total displacement at any given point. These observations have important implications for strain analysis and fracture prediction in folded reservoirs because models that assume in plane transport will over-predict strain magnitude in areas that have significant out of plane transport.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.