  In a uniform stress field, a tensile hydraulic fracture will favor
propagation in the plane formed by the maximum (most compressive) and
intermediate principal stresses. For the propagation of hydraulic fractures in
non-uniform stress fields, especially those where the principal stress
directions change spatially, things become much more complex, are less well
understood, and therefore are more difficult to predict. Such is often the case
when a hydraulic fracture is initiated from a borehole drilled in the direction
of the minimum principal stress. This is a well-known problem that has been the
subject of several numerical and experimental studies. The purpose of this
paper is to offer new insights from a series of hydraulic fracture tests
conducted in sub-horizontal boreholes drilled in the Sanford Underground
Research Facility. This project, called the Enhanced Geothermal Systems (EGS)
Collab project, has developed a test bed at a depth of approximately 1478
meters underground consisting of sub-horizontal injection, production, and
monitoring wells. This paper presents stimulation test data, and supporting
geologic/geophysical characterization data. The test data are compared to
previous numerical and experimental studies to determine how well this new
experimental data compares with previous modeling, laboratory, and field tests.
