HR: 11:35h
AN: H51H-06    [PDF]
TI: Using Changes in Fracture Aperture During the Interpretation of Hydraulic Well Tests
AU: * Murdoch, L
EM: lmurdoc@clemson.edu
AF: Clemson University, 340 Brackett Hall, Clemson, SC 29634 United States
AU: Schweisinger, T
EM: tschwei@clemson.edu
AF: Clemson University, 340 Brackett Hall, Clemson, SC 29634 United States
AU: Svenson, E
EM: eriksvenson409@hotmail.com
AF: Clemson University, 340 Brackett Hall, Clemson, SC 29634 United States
AU: Germanovich, L
AF: Georgia Tech, 790 Atlantic Dr, Atlanta, GA 30332 United States
AB: Fractures either dilate or contract in response to head changes during hydraulic well tests. We are measuring those changes in aperture in an effort to increase the information obtained from well tests. The measurements are made with a borehole extensometer temporarily anchored to the walls of an open borehole at two locations. An LVDT measures axial displacement between the anchors and those measurements are recorded along with pressure and temperature during a well test. Current investigations have focused on isolated flat-lying fractures, so axial displacements are assumed to equal changes in aperture. The current design of the extensometer can resolve displacements on the order of several tenths of a micron. Limiting sensitivity of the device to changes in temperature has been an important aspect of ensuring accuracy. Field tests are conducted on fractures identified using caliper and camera logs, and intact borehole intervals are tested for control. Preliminary tests have made use of a borehole cutting flat-lying fractures in biotite gneiss, where the fracture spacing and degree of weathering decreases with depth. Results show that the characteristics of the fractures change with depth: average normal compliance decreases from 0.5 micron/kPa to less than 0.05 micron/kPa, and the effective transmissivity decreases as depth increases from 23 m to 29 m. Normal compliance can be used to determine specific storage, suggesting that the displacement measurements can be used to determine aquifer storativity using a test conducted at a single well. Moreover, fracture compliance of the observed magnitudes implies that the fracture aperture, and thus the transmissivity, may change markedly during well tests where changes in head are significant. More detailed interpretations of the results are being made using a model that considers fluid flow along a deformable fracture embedded in porous material. Inverting the model using transient displacement data provides an approach for deriving information about the in situ dimensions and deformation characteristics of fractures that go beyond what can be determined from hydraulic measurements alone.
DE: 1829 Groundwater hydrology
DE: 8010 Fractures and faults
DE: 8045 Role of fluids
SC: Hydrology [H]
MN: 2003 Fall Meeting