Undulating wells are one of the alternatives to horizontal wells in field developments for extremely low vertical permeability formations. Undulating wells offer higher reservoir exposure and they do not depend on vertical permeability as much as horizontal wells do. This makes undulating well trajectory sometimes more attractive than horizontal wells.
Although undulating wells have been used in the field, predicting and understanding well performance is still a challenge. In the past, we have presented an analytical model that uses a segmented vertical well model with a slanted skin factor to estimate undulating well performance. The analytical model works well under certain formation and well structure conditions. In this paper, we will present a more comprehensive model for undulating well performance. The model evaluates undulating well performance in a parallelepiped reservoir based on a line source solution. The well can be located anywhere in the reservoir. The result is also compared with the previously developed analytical model to identify the conditions that the analytical model can be applied.
Field examples are used in the paper to illustrate optimizing undulating well performance by the model. The Cosmopolitan Field, Cook Inlet Alaska, and the Oooguruk Field, North Slope Alaska, are planned for development with undulating horizontal wells. Both reservoirs are challenged with relatively low permeability, low kv/kh ratios and moderate viscosity oil. Undulating horizontal wells are needed to overcome these issues and deliver commercial production rates. The performance model developed in this study demonstrated the additional value of an undulating well over a conventional horizontal well, which provided a key support in well design and field development plan.