Types of permeable fractures in granite
This study presents a multidisciplinary approach to understanding and describing types of fracture permeability in the Soultz-sous-Forêts granite, Upper Rhine Graben. At Soultz, during the 1993 stimulation tests in the GPK1 well, it was shown that only a limited number of natural fractures contributed to flow, whereas there are thousands of fractures embedded within the massive granite. In order to understand the flow hierarchy, a detailed comparison between static (fracture apertures based on ARI raw curves) and dynamic data (hydraulic tests) was carried out. We propose that two scales of fracture networks are present: a highly connected network consisting of fractures with small apertures that may represent the far-field reservoir, and another network that contains isolated and wide permeable fractures (that produce an anisotropic permeability in the rock) and allows a hydraulic connection between the injection and production wells.