Evaluating the Efficacy of Restoration Based Fracture Prediction Methods in Structurally Deformed Reservoirs

Shackleton, Ryan; Cooke, Michelle; Johnson, Gareth; Muir, Roddy

We use 3-D restorations of Sant Corneli anticline in the Spanish Pyrenees to test the fracture prediction capability of several structural restoration algorithms in fold and thrust belts. Prediction of deformation related fractures is of particular significance to shale plays where the reservoir has undergone significant folding or faulting, e.g. the Niobara shale in the Teapot Dome region.

Sant Corneli anticline is a plunging thrust-related anticline, cored by fractured carbonates and overlain by a sequence of syn-tectonic sediments. Reconstruction of the 3-D architecture of the syn-tectonic strata provides a template for incrementally unfolding the anticline using different geometrical and geomechanical restoration techniques. We use several techniques to unfold the anticline, including a simple shear, flexural slip, and a geomechanical algorithm.

To evaluate the strain predictions produced by the restoration, we utilize the strain history recorded by faults and joints exposes in the field at Sant Corneli anticline. Structural restoration provides a link between fold evolution and fracturing because unfolding and forward modeling of unfolded strata can be used to predict the orientation of faults and fractures. The goal of the restoration is to predict the generalized strain patterns associated with fault-related folding within Sant Corneli anticline at different stages of deformation. Orientations and cross cutting relationships of joints, relationships of fractures to growth strata, and identification of sub-aerial exposure allow the sequence of fractures associated with folding to be determined.

Sant Corneli anticline offers a unique opportunity to evaluate the efficacy of structural restoration in predicting sub-seismic scale fractures and faults because each fracturing event is temporally constrained by relationships to growth strata that constrain fold evolution. Where exposure is limited or non-existent the validation of restoration approaches to fracture prediction is critical. Thus, the strains predicted by the restorations are compared to the fracture sets that formed over the corresponding time intervals. In this manner, we can directly evaluate the efficacy of the restoration in predicting fracture patterns, although the time intervals identified by the growth strata are typically much larger than the time scales we expect individual fracturing events to occur.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013