Rock Fractures and Fluid Flow Contemporary Understanding and Applications (1996) / Chapter Skim
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1 Rock Fractures and Fluid Flow: Practical Problems
1 Rock Fractures and Fluid Flow: Practical Problems
Pages 11-28
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From page 11... ...
Many economically significant petroleum, geothermal, and water supply reservoirs form in fractured rocks. Fracture systems control the dispersion of chemical contaminants into and through the subsurface.
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From page 12... ...
The geometry of the void space affects both the flow properties and the physical properties of the rock mass, such as the elastic and electric properties. An understanding of how the void space geometry controls the fluid flow and geophysical properties of rock forms the foundation of geophysical methods used to detect fractures in the subsurface.
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From page 13... ...
Indeed, most of the errors involved in predicting flow behavior with numerical models usually reflect deficiencies in the underlying conceptual models. A numerical model provides quantitative estimates of the flow and transport behavior of the system described by the conceptual model.
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This iterative process must be designed to test improvements in the predictive capabilities of a numerical model. If the predictions improve with each iteration, confidence in the conceptual model as an accurate representation of the flow and transport system is enhanced.
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Many petroleum reservoirs form in highly fractured rocks, where fracture properties such as density and orientation are crucial to reservoir economics. In these cases the fractures are usually important because of permeability rather than porosity.
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Consequently, it is important to control and monitor hydrofracturing operations. Geothermal Reservoirs and Hot Dry Rock Most hydrothermal-geothermal systems are found in fractured rock masses.
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Improperly designed land disposal facilities can release contaminants into the subsurface through fractured rocks. Fracture networks control the dispersion of these contaminants
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In a relatively homogeneous porous medium, capture zone boundaries can be estimated by using numerical fluid flow models. In fractured systems the shape of the capture zone depends on the geometry of the fracture network.
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At these facilities, it has been observed that a relatively small number of fracture zones or faults account for the majority of fluid flow. Consequently, the general concept for waste storage is to develop repositories in relatively unfractured rock in order to isolate the waste from conductive fracture zones.
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Prediction of the behavior of the flow system around a repository requires conceptual models for flow in variably saturated, fractured rocks. Such understanding is as yet incomplete.
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It is expected that low rates of groundwater flow and geochemical retardation in a sparsely fractured repository will contribute to the overall containment design as required by existing regulatory standards. Fractures provide the most probable pathway to the biosphere for nuclear waste buried at depth.
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From page 22... ...
can seriously impede mining operations. Mining activities most influenced by fracture flow include in situ leaching, mine waste disposal, underground mine dewatering, and structural stability.
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From page 23... ...
Hydraulic reservoir pressures exert significant loads parallel to the ground surface that can lead to opening of fractures upstream of the dam and closure of fractures downstream. This response produces shorter seepage pathways and higher water pressures near the ground surface downstream of the dam.
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From page 24... ...
Elevated water pressures reduce effective stresses around underground excavations, which can lead to rock deformation and instability. Particularly problematical are rock masses composed of alternating impermeable and permeable (fractured)
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PRACTICAL PROBLEMS 25 underground structure is near a slope at the surface, such conditions may destabilize the slope. Problems with fluid loss, lining, and slope stability can be largely avoided if positive pressure gradients are maintained from the groundwater outside these underground facilities.
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From page 26... ...
Lost circulation complicates and delays the drilling operation. The materials used to plug these low-pressure zones can damage the productivity of other feed zones.
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The greatest difficulty in the investigation was characterization of large-scale features such as major fractures, local faults, and caverns that are known to influence flow patterns, and ultimately contaminant transport, at the site. Several actions were taken to clean up the contamination at this site (U.S.
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From page 28... ...
Geothermal Resources Council Transactions, 12:37-40. Everitt, R
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