Transport efficiency and dynamics of hydraulic fracture networks

Abstract

Intermittent fluid pulses in the Earth's crust can explain a variety of geological phenomena, for instance the occurrence of hydraulic breccia. Fluid transport in the crust is usually modeled as continuous Darcian flow, ignoring that sufficient fluid overpressure can cause hydraulic fractures as fluid pathways with very dynamic behavior. Resulting hydraulic fracture networks are largely self-organized: opening and healing of hydraulic fractures depends on local fluid pressure, which is, in turn, largely controlled by the fracture network. We develop a crustal-scale 2D computer model designed to simulate this process. To focus on the dynamics of the process we chose a setup as simple as possible. Control factors are constant overpressure at a basal fluid source and a constant "viscous" parameter controlling fracture-healing. Our results indicate that at large healing rates hydraulic fractures are mobile, transporting fluid in intermittent pulses to the surface and displaying a 1/f α behavior. Low healing rates result in stable networks and constant flow. The efficiency of the fluid transport is independent from the closure dynamics of veins or fractures. More important than preexisting fracture networks is the distribution of fluid pressure. A key requirement for dynamic fracture networks is the presence of a fluid pressure gradient.

Activation of stylolites as conduits for overpressured fluid flow in dolomitized platform carbonates

“…The rapid flow quickly dissipates the overpressure and, therefore any drive for further fast flow and hydrofracturing. Fast flow thus occurs in short pulses (Sachau et al 2015).…”

“…This "excess volume" of fluid can flow upwards along mobile hydrofractures in quick and localized fluid flow pulses (e.g. Bons 2001;Sachau et al 2015). This mechanism has been used to explain the formation of ore deposits ) and the development of massive hydraulic breccias (Weisheit et al 2013).…”

Seismic geomorphology and origin of diagenetic geobodies in the Upper Cretaceous Chalk of the North Sea Basin (Danish Central Graben)

“…Jensenius & Munksgaard, 1989;Egeberg & Saigal, 1991) (Figure 20, Step 6). The fluids ascended into the chalk following existing structural weaknesses and/or induced hydraulic fracturing (Sachau, Bons, & Gomez-Rivas, 2015;Figures 10 and 12). The strong correlation between the orientation of the faults and the SCRs (Figure 17) suggests that highly permeable zones were established where the N-S-and NW-SE-oriented faults crossed.…”

Fenites associated with carbonatite complexes: A review

“…Fenitizing fluids may exploit pre-existing structural weaknesses in the host rock or cause the propagation of new fractures by fluid overpressure or volume changes related to metasomatic mineral reactions (Skelton et al, 2007;Sachau et al, 2015). During fracture-hosted flow, only a small fraction of the fenitizing fluids can metasomatize the country rock adjacent to the host fractures (see Figs.…”