The sub-surface design of wellbores and associated well completions to be used in thermal oil sand operations must take into account a significant number of criteria and factors to ensure the delivered wells can provide the required long-term operating life and reliability required of them, especially when it comes to operating safety.

These considerations cover a wide range of primarily technical aspects, including the location and layout of the wells at surface and sub-surface; type of service the wellbore will be used for, therefore, the construction materials to be used and their properties; recovery process impact on the wellbore design including the geology and reservoir behaviour; tubing size, perforation and sand control considerations; artificial lift requirements; downhole operation selectivity; produced fluid compositions and conditions, and well operability requirements.

The level of detail that needs to be considered for each of these depends on the stage of project development. As work progresses, the level of detail increases in order to be able to arrive at an appropriate and balanced technical and safety design, as well as associated cost, once the final concept selection is made. The subsequent "Detailed Engineering" phase should be used only to fine-tune any remaining questions or issues that may arise in preparation for final project approval, and to provide the required definition of each element in order to be able to build / purchase / install / operate it. It is not discussed in this paper.

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