PE GATE: Production: Well equipments : X mas tree

Subsea Xmas tree

After completion and testing of production well, what will we require ?

A controlled oil flow rate, that is what we require. And for control rate, we have to control drawdown pressure. ( Drawdown pressure is pressure difference between average reservoir pressure and flowing bottom hole pressure. )

In drawdown term, we can not control average reservoir pressure from surface equipments, so we have to control flowing bottom hole pressure everytime after production starts.

And second thing, after completion of well, we will not encounter new horizon or new pressure conditions which can lead to kick or blowout. So we will not required Blow out preventer any more (mostly).

So,

We uninstall BOPs and make well flow with equipment which can control flow rate by controlling flowing bottom hole pressure along with providing conduit path for fluid to flow from tubing bottom to surface.

Sometimes, we convert production well into injection well or we have to inject gas or other fluids (kill fluids) to reservoir, so we will require additional feature in our equipment, to provide circulation or injection And to repair tubing problems also we will require conduit path.

So, our requirements for tool to install instead of BOP is,

1) controlled flowing bottom hole pressure

2) Provides conduit path for fluid to flow from tubing bottom to surface.

3) Path for injection or remedial things in tubing.

Lets try to solve each problem.

It will be good if we have any small mechanism which we can use as pressure controlling mechanism like installed choke.

Lets guess a strong steel pipe which can manage high well pressure and provides conduit for fluid flow from one side to another.(strong hollow pipe).

To make our equipment, we install choke on one side of that strong pipe. So, it will control bottom hole flowing pressure. (Choke)

So, we have one side for producing fluid. (Production valve)

We can have another side for injection. This option will be utilised only for injection or recirculation. (Kill valve)

What if, in certain conditions, well pressure or flow become uncontrolled ? How to manage to shut well from surface in that time ?

For that, we can install one or two (one for use, one as a backup) valves, which can shut off well from surface. (Master valves).

For all well intervention and other tubing related operations, we can have another valve which can opened or closed during operation only. (Swab valve).

Combine all these equipment and accessories, it will be known as X-mas tree or christmas tree.

We install Christmas tree on top of production wells.

Just for Fun

So, by definition,

Christmas tree, or "tree", is an assembly of valves, spools, and fittings used to regulate the flow of pipes in an oil well, gas well, water injection well, water disposal well, gas injection well, condensate well and other types of wells. (Wikipedia).