The joint sets on the Lilstock Benches, UK. Observations based on mapping a full resolution UAV-based image

Abstract

Outcrop studies of fracture networks are important to understand fractured reservoirs in the subsurface, but complete maps of all fractures in large outcrops are rare due to limitations of outcrop and image resolution. We manually mapped the first full-resolution UAV-based, Gigapixel dataset and DEM of the wave-cut Lilstock Benches in the southern Bristol Channel basin, a classic outcrop of layer-bound fracture networks in limestones. We present a map of the patterns and age relationships of successive sets of joints in dm-thick limestone layers separated by claystone beds. Using interpretation criteria based on crosscutting relationships, abutting and joint length, up to eight successive sets of joints were mapped. Results show that joint geometry and interrelations are fully resolved in the whole outcrop. Different joint sets have unique characteristics in terms of shape, orientation, spatial distribution and cross-cutting relations. The presence of low-angle crossings and junctions of joints suggest periods of partial joint sealing and reactivation. The dataset and interpretations are proposed as an outline for large scale, complete fracture network mapping to test digital fracture network models.