Papanastasiou, P. and Zervos, A.
Stability of perforations near hydraulic fractures
International Journal of Rock Mechanics and Mining Sciences, 35, (4), . (doi:10.1016/S0148-9062(98)00107-7).
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This paper presents results of large scale stress analysis of a wellbore with perforations. Both vertical and horizontal wellbores with perforations at different orientations were considered. The change of stresses in the unfractured perforations induced by a propped fracture is also examined. The computations were carried out using boundary element analysis with the fracturing code FRANC3D.
The results are discussed in relation to the problem of perforation failure, and possible risk of sand production, due to high compressive stresses.The results show that in a vertical wellbore all perforations, independent of orientation, suffer locally in the lateral faces by high compressive stresses, primarily caused by the vertical in-situ stress. In addition, the perforations parallel to the minimum far-field stress suffer from high compressive stresses all-around them. The highest compressive stresses were encountered in the lateral faces of horizontal perforations of a horizontal wellbore. In this case the calculated stresses were more than double the stresses of a corresponding vertical wellbore.
In both vertical and horizontal wellbores, high stress concentration was observed near the base of perforations. The near-wellbore area of stress concentration is approximately equal with one wellbore radius.A propped fracture results in increase of the compressive stress around the perforations. The stress increase is higher in the perforations closer to the fracture and increases with propped width. The increase of compressive stress is much higher at the top/lower faces of perforations which is already less than the existing compressive stress at the lateral faces of the perforations. Nevertheless, the compressive stress in the lateral faces may increase by more than 30% leading to an extra risk of perforation failure and sand production.
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