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Storage change in a flat‐lying fracture during well tests
Author(s) -
Murdoch Lawrence C.,
Germanovich Leonid N.
Publication year - 2012
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2011wr011571
Subject(s) - fracture (geology) , groundwater , geology , extensometer , geotechnical engineering , borehole , volume (thermodynamics) , mechanics , hydrology (agriculture) , environmental science , soil science , materials science , physics , quantum mechanics , composite material
The volume of water released from storage per unit head drop per volume of an REV is a basic quantity in groundwater hydrology, but the details of the process of storage change in the vicinity of a well are commonly overlooked. We characterize storage change in a flat‐lying fracture or thin sedimentary bed through the apparent hydraulic compliance, C f , the change in aperture of the fracture or thickness of the layer per unit change in pressure. The results of theoretical analyses and field measurements show that C f increases with time near the well during pumping, but it drops suddenly and may become negative at the beginning of recovery during a well test. Profiles of C f increase with radial distance from a well, but they are marked by a sharp increase and a sharp decrease at the edge of the region affected by the wellbore pressure transient. The conventional view in groundwater hydrology is that storage change at a point is proportional to the local change in pressure, which requires that the hydraulic compliance is uniform and constant. It appears that this conventional view is a simplification of a process that varies in both space and time and can even take on negative values. This simplification may be a source of uncertainty when interpreting well tests and extensometer records or predicting long‐term well performance.