Accurate well placement and spacing, especially when using horizontal wells, is essential for optimizing reservoir development and production. In order to develop such a plan, the production mechanisms governing the reservoir must first be fully determined. Several approaches and techniques have been used to achieve this objective. The capacity of the reservoir to deliver hydrocarbons to the horizontal well bore must be understood and defined by a technique that will enable intelligent construction of a reservoir management philosophy. A variation of as little as a 30 degrees from the optimum well bore direction can result in reductions of reservoir efficiency as much as 14%.

Fracture propagation achieves greater length and height when a borehole is oriented in the direction of the minimum stress. The orientation of the in-situ stress field is the critical information needed to achieve optimal placement of horizontal wells. Crossed-dipole sonic logs with directional information enable the magnitude and orientation of acoustic anisotropy to be determined, which provide representations of the in-situ stress field (Fogal 2002). After the direction of maximum horizontal stress is known, the well can be placed and the direction of the horizontal wellbore oriented to attain maximum reservoir exposure after fracture treatment. Compressional- and shear-wave slowness provided by the dipole sonic tool also enable the direct calculation of the rock mechanical properties that define fracture treatment initiation and propagation (Cipolla 1994).

Because the cost of acquiring of crossed-dipole sonic data can be prohibitive, an alternative, cost-effective method for acquiring the necessary data about the in-situ stress field orientation was evaluated. Wellbore elongation is an indicator of stress anisotropy. A directional package was added to an openhole multiarm caliper and the observed borehole deformation was evaluated to determine the implied direction of the horizontal stresses. This defined regional horizontal stress information was then used to orient the horizontal component of each well. This paper compares the results derived from the examination of borehole elongation with the more precise data derived from the dipole sonic logs. This technique provides a cost-effective alternative for determining the orientation of the stress anisotropy in unconventional reservoirs.

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