Effects of crustal stresses on fluid transport in fractured rock: case studies from northeastern and southwestern USA |
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Authors: | Roger?H?Morin Email author" target="_blank">William?Z?SavageEmail author |
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Institution: | (1) , US Geological Survey, Denver, Colorado 80225, USA, |
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Abstract: | The link between stress and hydrologic properties was examined at two sites that are distinguished by different rock types
and different stress states. This investigation is based upon the analysis and interpretation of geophysical logs obtained
in water wells at the two locations. At the northeast site (Newark Basin), the hydrologic characteristics of sedimentary rocks
are dependent upon the relationship to the current regional stress field of two primary types of orthogonal features that
serve as preferential pathways for fluid flow. Subhorizontal bedding-plane partings are highly transmissive near the surface
and delineate transversely isotropic fluid flow at shallow depths. With increasing depth, the subhorizontal planes become
less dominant and steeply dipping fractures become more influential hydrologically. These high-angle features define anisotropic
flow pathways that are preferentially oriented along strike. At the southwest site (west Texas), extrusive rocks are subjected
to topographically modified tectonic and gravitational stresses that vary spatially within a valley setting. The attendant
changes in stress invariants cause fracture connectivity within the rock mass to systematically increase with depth along
the valley flanks, but to remain relatively low in the central valley. The degree of fracture connectivity predicted within
this valley configuration is consistent with variations in transmissivity determined at several well locations. In each of
these cases, the idealized understanding of the hydrologic system is enhanced by considering the effects of regional and local
stresses that act upon the fractured-rock aquifer.
Electronic Publication |
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Keywords: | Crustal stresses Fluid transport Fractured rock USA |
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