Variations in fracture system geometry and their implications for fluid flow in fractured hydrocarbon reservoirs

Studies assembling high quality datasets of fracture systems (joints and fa ults) from four reservoir analogues are described. These comprise limestone s (Ireland), sandstones (Norway and Saudi Arabia) and chalk (Denmark). Thes e are used with existing information from the literature to review the majo r controls and scaling behaviour of fracture systems expected in reservoir rocks. Lithological layering was found to be important and two end-member f racture systems have been identified. In 'stratabound' systems, fractures a re confined to single layers, sizes are scale restricted, and spacing is re gular. In 'non-stratabound systems', fractures show a wide range of sizes ( often power-la iv), are spatially clustered and vertically persistent. In n ature, variations between and combinations of these systems exist. These en d-member systems have contrasting implications for fluid flow, including th e scale of fracture that controls flow and the existence of a representativ e elementary volume, and thus on appropriate modelling approaches.