Jeffrey, R.G. (CSIRO Earth Science and Resource Engineering) | Chen, Z.R. (CSIRO Earth Science and Resource Engineering) | Zhang, X. (CSIRO Earth Science and Resource Engineering) | Bunger, A.P. (University of Pittsburgh,) | Mills, K.W. (SCT Operations Pty. Ltd.)
Hydraulic fracture breakdown and reorientation data collected from two test instrumented borehole sites have been analyzed to assess the effect of the initiation type on the treating pressure. Vertical boreholes were drilled and fractures were placed in a conglomerate at depths of 140 to 180 meters into a far-field stress field that favored horizontal fracture growth. Axial initiation resulted in high injection pressures, as a result of near-borehole tortuosity generated as the hydraulic fracture reoriented to align with the far-field stresses. A fracture initiation analysis determined that initiation at the abrasively cut slots should occur before axial initiation. Acoustic scanner logging of the boreholes after fracturing demonstrated that, in many cases, axial initiation occurred and when this was the case, treating pressures were high and consistent with near-borehole tortuous fracture paths. Transverse initiation from the vertical boreholes at pre-cut slots lowered the injection pressures by up to 12 MPa for water injected at approximately 500 liters per minute.