The Production string is a string which is installed to separate productive zones from other reservoir formations or for testing purposes.
- The string through which the well will be completed, produced and controlled
- Used with or without a packer or flow tubing and inside which product flows.
- In most cases, the production casing will serve to isolate the productive intervals, to facilitate proper reservoir control and to prevent the influx of undesired fluids.
- In some conditions the well can be left with an open-hole completion below the production string.
- The casing itself can be used as a conduit for maximising well deliverability, for minimising pressure losses during a frac job, for injecting inhibitor or for lift gas. This may require Annular Safety Valves, which impose severe loads on the uncemented casing.
- Remember that production operations will affect the temperature of the production casing and impose additional thermal stresses.
- The production loads are quite different from those imposed during drilling.
- Special care to be taken in the selection of the steel type and the connections
- Special consideration is required where drilling below the production casing since it may suffer some damage, e.g. in barefoot completions, open-hole gravel packs, liner completions and deep-zone appraisal.
- In a liner completion both the liner and casing form the production string and must be designed accordingly.
- Quality of the primary cement job is of paramount importance for the production casing, especially where zonal isolation is critical. It is recommended that the production casing should be rotated and/or reciprocated during cementing. This imposes additional design requirements.