Predicting subseismic fracture density and orientation in the Gorm Field, Danish North Sea

Abstract

The chalk reservoir of the Gorm Field, southern North Sea is dome-shaped and faulted owing to a combination of salt diapirism and regional east–west extension. Fractures developed in the structure considerably enhance permeability. The dataset discussed here records fractures in horizontal wells from more than 10 km 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°; 75% are less than 45°. 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.

Subseismic pathway prediction by three-dimensional structural restoration and strain analysis based on seismic interpretation

“…From 3-D retrodeformation analysis, it is possible to infer paleogeomorphology, elongation rate, and subseismic scale strain that occurred within the faulted blocks of geologic formations. Comparative studies are rare (e.g., Mohr et al, 2005;Lohr et al, 2008;Freeman et al, 2015). Most case studies analyzed the structural style, fault growth, and fault population of seismic-scale faults (e.g., Needham et al, 1996;Mansfield and Cartwright, 2001;Nicol et al, 2005;Tvedt et al, 2013), but subseismic scale faults and fractures are commonly not considered.…”

Industrial structural geology: principles, techniques and integration: an introduction

“…Freeman et al (2015) illustrate this by way of the novel application of geomechnical modelling techniques to the Gorm Field in the Danish sector of the southern North Sea. They have developed an elastic dislocation model in which strains are calculated using the observed geometry of seismically interpreted surfaces, and constrained by image log data from well penetrations, in order to forward model the location, density and orientation of fractures within the reservoir.…”

Impact of seismic image quality on fault interpretation uncertainty

“…Fault interpretations are important components in the prediction of hydrocarbon reservoir volumes in structural traps, and in forecasting the integrity and performance for structurally complex reservoirs (e.g. Richards et al, 2015;Yielding, 2015;Wood et al, 2015;Freeman et al, 2015). However, in publications, faults are commonly shown as single, deterministic interpretations -even though there are uncertainties in these seismic interpretations that will impact on the application of the interpretation.…”