Flow zone, rock deformation

The long time scales (104 to 10s m.y.) involved in deformation and synkinematic isotope exchange in white mica provide a robust, long-term average of meteoric water-rock interaction, characteristic for the time scales of major readjustments in surface elevation. Thus the hydrogen isotope record in recrystallized muscovite provides a direct link between the tectonic and fluid flow history in the shear zone and temporal variations in meteoric water composition due to changing surface elevation. 

The above evidence establishes that fracturing and seismic behavior can extend well into the zone of mid to lower crustal metamorphism at rock pressures of —0.5-1 GPa. Veins preserve a valuable record of this brittle deformation they are fractures in which mineral mass has been deposited. The most common vein-forming minerals are quartz, calcite, and the feldspars, but a huge variety of other minerals are also observed. Fractures tend to focus flow, because they are zones of elevated permeability. Fracture flow is commonly approximated using the well-known expression from fluid mechanics for laminar flow between two parallel plates (e.g., White, 1979). For a set of parallel fractures, the flux is approximated by (e.g., Norton and Knapp, 1977) ... 

Austrheim H. and Engvik A. (1997) Fluid transport, deformation and metamorphism at depth in a collision zone. In Fluid Flow and Transport in Rocks (eds. B. Jamtveit and B. W. D. Yardley). Chapman and Hall, London, pp. 123-135. 

The critical elements of fault damage zones which are needed for fault seal evaluation and for input into reservoir behaviour simulation include (i) the dimensions of the damage zone (ii) the fault clustering characteristics (iii) the fault offset populations, which can control the distribution of fault rocks and juxtapositions (iv) the orientation distributions of deformation features present within damage zones and (v) the total thickness of fault-rocks. Each of these aspects are reviewed below, where the data presented are part of a large database collected from the structural analysis of -90 wells, (-25 km of core) from the North Sea area (see example in Fig. 7). The final part of this section presents a simple model which demonstrates the impact of damage zone structures on flow. 

Two variables are fundamental to assessing the flow across complex fault zones. The first variable is the cumulative fault-rock thickness across the fault zone, i.e., the total thickness of fault-rock from all faults along the flow path. This depends upon the fault frequency along the flow path and is not equivalent to the fault damage zone thickness (cf. Knott, 1993) unless the fault zone is invaded by cements. The second variable is the connectivity of the faults or deformation features with low permeabilities in the fault zone. In the case of a completely connected array with no windows of undeformed material along possible flow paths, the flow is controlled by the permeability of the fault rocks. Where a more open network of faults is present then the flow will depend upon the tortuosity associated with flow around the low permeability zones and the ratio of matrix to fault-rock permeability. The interaction of these two factors will control the effective transmissivity of the zone. We have constructed a database on... 

Occurrence of deformed and crushed rock mass along tunnel route poses several hindrances during excavation like formation of cavities, collapses, debris flow etc. Encountering such zones during excavation is common. 

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