HR: 1330h
AN: H42F-1132    [PDF]
TI: Forms and Analysis of Hydraulic Fractures at Shallow Depth
AU: * Tan, Q
EM: tqingfe@clemson.edu
AF: Clemson University, 340 Brackett Hall, Clemson, SC 29634 United States
AU: Richardson, J R
AF: Clemson University, 340 Brackett Hall, Clemson, SC 29634 United States
AU: Murdoch, L C
AF: Clemson University, 340 Brackett Hall, Clemson, SC 29634 United States
AB: The form of a hydraulic fracture plays a key role in the performance of the fracture during environmental remediation projects. Fractures that are relatively thick and flat lying are suited to improve the performance of remediation wells, whereas fractures that are steeply dipping may be suited to the creation of reactive barriers. To sharpen the resolution of the details of fracture form at shallow depth in Piedmont soil, the vicinity of four hydraulic fractures initiated at 1.5 m depth was excavated and mapped on trench exposures. The data from these maps were used to characterize fracture form, including geometry, sand thickness, distribution of sand within the fracture, and ground surface deformation during fracturing. The fractures were roughly elliptical in plain view, and the centers of the fractures were offset from the injection casing. In general, they were shaped like gentle bowls whose sides dip from 12 to 16 degrees. A peculiar aspect of the fracture form occurred in the vicinity of the injection casings, where three of the fractures curved downward and then back up to produce gentle trough-like structures around the casings. The finite element code FRANC2D was modified to simulate fluid flow in a propagating fracture. The modified code predicts curved fracture traces that are gentle bowl-like forms, where the enveloping medium is uniform and characterized by material properties similar to field conditions, and ambient stresses result from body forces. Another model was created using two layers, where the elastic modulus of the upper layer was greater than that of the lower layer. Fractures simulated using this model curve downward toward the softer layer, and then curve upward as they become longer to produce a trough-like form similar to the field. The fractures were created in a layer of relatively stiff clayey silt that was underlain by softer saprolite, and this layering may be able to explain the downward propagation observed in the field. Additional simulations have been conducted to evaluate the effects of fracture toughness and in situ state of stress on fracture form, and preliminary results suggest that these parameters can explain field observations from a variety of sites.
DE: 1719 Hydrology
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 4842 Modeling
DE: 5104 Fracture and flow
SC: Hydrology [H]
MN: 2003 Fall Meeting