Some mechanisms for the genesis of fractures in sedimentary rocks

Understanding the spatial and temporal distribution of fluid flow in the subsurface is of fundamental importance to the successful management of groundwater and hydrocarbon resources. The analysis is restricted to open mode fracture sets, usually recognized for important contributors to permeability in the case of low porosity reservoirs. We investigated, on a mechanical basis, several field representations likely to occur when jointing and fracture clustering take place. Clustering cannot be explained by effective horizontal tensional conditions resulting in fluid driven fractures, in view of the screening effect between very closely spaced fracture planes, even if we assume sub-critical propagating conditions. Systematic joints form at depth, as a result of tectonic compression in combination with high pore pressure. Unconfined effective conditions arise to produce low rock strength and brittle deformation and load parallel extension fractures are the rule.