CHEMICAL EFFECTS ON OPENING-MODE FRACTURE SIZE AND SPATIAL ARRANGEMENT

Quartz accumulation in opening-mode fractures in sandstones correlates with differences in size distribution, spatial arrangement, strength, porosity, and permeability. Size patterns result from variable resistance to reopening that depends on the completeness and strength of bridges formed during fracture growth. Here we show how fracture pattern reconstructions motivate development of geomechanical models that couple mechanical and diagenetic effects. For testing predictions of fracture size and spatial arrangements, models require validation in outcrops, where fractures have diagnostic features that show they are like those in the subsurface. Localized quartz deposits in otherwise open fractures contain crack-seal textures and fluid inclusion assemblages, allowing fracture temperature histories to be reconstructed and compared with burial histories. Using thermal history as a proxy for time allows inference of duration and rates at which fractures open, and thus comparison of fracture growth models with natural examples. We focus on outcrop and horizontal core data sets, highlighting examples where interaction between cement deposition and fracture widening correlates with differences in many fracture pattern attributes, including length, height, aperture, and clustering.