Abstract

It is well known that a, hydraulic fracture preferentially extends in a plane perpendicular to the least principal in-situ formation stress. However, it is not generally recognized that in an openhole completion, the hydraulic fracture will only initiate perpendicular to the least principal formation stress if the well's axis is aligned with the preferred fracture plane throughout the treatment interval, If the well intersects the preferred fracture plane, a hydraulic fracture initiated in an openhole section will intersect both the borehole and the preferred fracture plane.

As the fracture extends away from the well, it turns, realigning itself with the preferred fracture plane. In the immediate vicinity of the wellbore, this turning results in tortuosity and a reduced fracture width, which can lead to premature screenouts or a choke effect during production. The most severe case of this occurrence is in an openhole completion in a well drilled perpendicular to the preferred fracture plane, where a hydraulic fracture initiates longitudinally but rapidly realigns itself with the preferred fracture plane normal to the borehole. Once realigned, the fracture grows back toward the well. As a result, both longitudinal and transverse fractures are present at the wellbore.

Extensive calculations detailing the orientation of the initial fracture relative to the wellbore and the preferred fracture plane are presented for all borehole deviations relative to the preferred fracture plane and the maximum formation-stress direction. Results of laboratory investigations of fracture initiation and propagation from openhole, deviated wellbores are summarized and compared to analytical predictions. The effects of wellbore diameter on fracture orientation and the potential for link-up of multiple fractures are also discussed.

P. 391

This content is only available via PDF.
You can access this article if you purchase or spend a download.