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Analysis of hydromechanical well tests in fractured sedimentary rock at the NAWC site, New Jersey

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Abstract

Hydromechanical well tests involve measuring and interpreting displacements along with hydraulic heads that result when a hydraulic stress is applied to a well. The motivation behind this type of test is that the displacement measurements provide information about the constitutive properties and structure of the aquifer that go beyond what can be derived from pressure signals alone. We used a borehole extensometer to measure transient displacements with a resolution of +/- 25 nm during well tests in fractured mudstone and sandstone at the former Naval Air Warfare Center in West Trenton, New Jersey. One well showed opening displacements on the order of 300nm during slug tests with maximum head changes of 7 m. Inversion of the transient signals suggest that a conductive fracture (aperture = 380 ??m, normal stiffness = 8??10 8 Pa/m) was largely responsible for the pressure signal, but the displacement signal appears to have resulted from both the fracture and deformation of the enveloping sandstone (E = 5 GPa, permeability = 0.6 md). At another well, an anomalous but repeatable signal was characterized by closing displacements during increasing pressure. This displacement signal can be explained by a hydraulically active fracture below the extensometer that became pressurized and compressed the overly sediments. Poroelastic theoretical analyses were inverted to estimate parameters and verify interpretations. Copyright 2009 ARMA, American Rock Mechanics Association.

Additional Publication Details

Publication type:
Conference Paper
Publication Subtype:
Conference Paper
Title:
Analysis of hydromechanical well tests in fractured sedimentary rock at the NAWC site, New Jersey
Year Published:
2009
Language:
English
Larger Work Title:
43rd U.S. Rock Mechanics Symposium and 4th U.S.-Canada Rock Mechanics Symposium
Conference Title:
43rd U.S. Rock Mechanics Symposium and 4th U.S.-Canada Rock Mechanics Symposium
Conference Location:
Asheville, NC
Conference Date:
28 June 2009 through 1 July 2009