The spatial heterogeneity of structures in high porosity sandstones: Variations and granularity effects in orientation data

Despite many studies on the scaling and geometrical properties of fracture systems, much less attention has been paid to analysing their spatial characteristics. At a well exposed section at George Gill, Appleby, we investigated the spatial heterogeneity in deformation band orientations in a high porosity sandstone using bootstrap, variogram and hierarchical analysis methods. At metre-scales the structures displayed multimodal orientation patterns with orthorhombic symmetry whereas at 20 m scales they appeared bimodal. Our analysis shows that this situation arises due to a combination of small-scale noise superimposed on a regional trend related to the presence of a nearby major fault structure. We suggest that this type of geospatial analysis can be used as a general tool to investigate spatial heterogeneity in structural systems. We also suggest that these types of granularity and aliasing effect impact the prediction and modelling of rock properties and they therefore warrant further investigation.