The production tree represents the top of the topside production equipment. The tree is typically comprised of a series of valves, junctions and tubing so as to be able to control both the pressure and flow into and out of the well and subsequently the reservoir.
Typically the tree attaches to the top of the wellhead be it the upper most casing spool or the tubing spool. Typically the tree attaches to the top of the tubing spool, with the fluid flow from the tubing leading to tree and being directed through the tree.
At the lowest point of the tree, where it attaches to the tubing spool, there is a valve, the lower master valve. This valve represents the first line of control for the fluid flow. This master valve is capable of shutting of the flow from the well and to the tree. In the closed position this lower master valve faces the brunt of the the fluid flow and pressure from the wellbore. The valve is thus critcal to flow and pressure control.
The upper master control valve serves to ensure or secure the integrity or at the very least safe guard the operation of the tree in the event to the failure of the lower valve. These two valves are the primary line of fluid and flow control. Above these two valves sits either a cross or “T” junction depending on the number of “wings” the tree has. Typically at this point off this junction we will have a valve so as to isolate the flow coming off this junction.
Toward the top of the junction you have a valve that allows for vertical access to the tubing and above this a tree cap, which is a blank. This has to port or access to the flow path, it ends it. If one wanted access to the path this cap would be removed and the valve opened thus allowing access to the tubing string. This upper valve is sometimes known as a swab valve, as this valve facilitates swabbing workover operations typically through tubing.
On either side of the junction we have the “wings”, now these “wings” usually bear the brunt of the load when it comes to allowing fluid flow to and from the wellbore. One wing may be a dedicated injection wing where fluid can be injected into the wellbore for specific purposes, and the other wing the production wing where fluids are allowed to flow out of the wellbore.
For most wings we have 2 valves in succession, an inboard, closest to the junction and an outboard, just after the inboard, furthest from the junction. These 2 valve control fluid flow across the wing, but more importantly they serve each other, with each one allowing the safe operation of the tree, similar to that of the upper and lower master valves.
The difference between these two “wings” is what comes after the valves, on the injection end you may have either a flanged end, that is capped when not in use, or a ported connection for connection to an external source for injection purposes. On the production wing you typically have either flanged or ported connection to attached to a flowline or a production choke that has a flage for attachment to a flowline to a gathering station, production facility, tank or some such facility.
Production trees are there to give the operators of a well the first line when it comes to wellbore intervention after the well has been drilled. It facilitates work done to the well as well as allowing the well to be produced to its maximum capacity and will probably serve throughout the well’s lifetime.
