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Predicting Sub-Seismic Fracture Density and Orientation: A Case Study From the Gorm Field, Danish North Sea

Abstract

The chalk reservoir of the Gorm field, southern North Sea is dome shaped and faulted due to a combination of salt diapirism and regional E-W extension. Fractures developed in the structure considerably enhance permeability. The dataset discussed here records fractures in horizontal wells from more than 10km of image logs and provides a special opportunity to test theoretical models of fracture development with quantitative observations. In an effort to forecast fracture density and fracture orientation we have estimated the strains in the structure using an elastic dislocation model that incorporates mechanical boundaries in the form of the tectono-stratigraphic interface with salt and tectonic faults. More than 50% of the angular differences between poles to the planes of simulated and observed fractures are less than 30 degrees, 75% are less than 45 degrees. Relative strain magnitude appears to be a useful indicator of fracture density. At the field scale, small strain magnitudes correspond with small non-zero fracture densities and relatively large strain magnitudes correspond with high fracture densities.