1. Tubular suspension (casings and tubings), focusing on the well.
2. Surface ability to install a flow control device as well:
a) A BOP (Blowout Preventer) drilling
b) A Xmas Tree (Christmas Tree) for the production or injection
3. Hydraulic access to the annulus between casing to allow for displacement during cementing and between the production casing and tubing for the circulation of the well.
The purpose of the Christmas Tree (Xmas Tree) is to provide a control valve produced or injected fluids into the well. The Xmas Tree is usually flanged to the wellhead system after running the production tubing. The design shown is one of the simplest and most common designs, you can see him briefly comprising 2 lateral valves out, usually one for production and one for the injection. Additionally, a third valve outlet tubing provides vertical access through cable tools or concentric coiled tubing tools.
The bottom valve is the master valve and controls all access to mechanical and hydraulic well. In some cases, the importance of this valve to provide security for the well is so high that it is duplicated. All valves are in some cases either manually or hydraulically operated and remotely controlled as in the case of offshore platforms.