With the advent of borehole imaging technology, the ability to analyze naturally fractured reservoirs has improved significantly. Borehole imaging tools provide quantitative information on fracture attributes, such as fracture density, aperture size, porosity, and orientation. The density and orientation characteristics of the fracture system determine the connectivity of the fracture network, whereas the aperture and porosity of the fractures determine their potential transmissibility. Knowledge of these fracture attributes is critical to assess the fractured reservoirs, and it also aids in the exploration and exploitation of many petroleum reservoirs.
In the foothills of western Canada, natural fracture systems are important contributors to reservoir producibility and sometimes porosity in many fractured reservoirs. In general, these natural fracture systems can be classified into four groups: regional fractures, fold-related fractures, fault-related fractures, and random fractures. The different fracture patterns can be reliably identified from borehole images and then used to determine the structures penetrated by the wellbore. Fracture aperture size of each fracture pattern statistically appears to have a log-normal distribution and azimuthally displays a sinusoid-shape; these characteristics are normally associated with specific stress regime.