Throughout the past decade, the number of horizontal wells drilled in the United States has continued to increase. Several fields currently being developed are only economical with the application of horizontal wells. One such area where this is the case is in the Bakken formation in the Williston Basin. In the Bakken, operators have used a variety of different completion methods ranging from multilateral, openhole wellbores to single lateral cemented liners. Regardless of the completion method, hydraulic fracturing is required for increased oil recovery. In the past two years, most operators have started to converge on running uncemented liners with external packers as the preferred completion method. The purpose of the external packers is to compartmentalize the wellbore for more efficient fracture stimulation, as demonstrated by Miller (2008).

As this type of completion becomes more common, three key questions should be addressed: (1) how does the fracture initiate in an open-annulus wellbore (transverse or longitudinal), (2) what is the affect of the packer type on the stress on the wellbore surrounding the packer, and (3) can any of this be used to help with fracture design, or does it even matter?

Finite-element modeling provides several advantages for modeling the different physical characteristics and responses for a system with very different sensitivities across the scale of the model. In the cases considered in this paper, the edge of the wellbore must be finely modeled to take into account the hoop stresses developed as a result of removing the rock volume from the original stress state. This is further complicated by the effects of orientation of the wellbore relative to the maximum and minimum horizontal stress and of different packers placed in the wellbore for isolation between stages.

Conclusions on fracture-initiation behavior based on typical wellbore geometries, physical-rock properties, in-situ stress scenarios, and common packers are presented in this paper.

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