Wellhead Christmas Tree

A wellhead christmas tree is the general term used to describe the surface of an oil and gas well. A wellhead Christmas tree provides the structural and pressure-containing interface for oil and gas drilling of production equipment.

The primary function of a well head Christmas tree is to control the flow, usually oil or gas out of the well. A tree can also be used to control the injection of gas or water into a non-producing well in order to enhance production rates of oil from other wells. When the well and facilities are ready to produce or receive oil or gas the tree valves are opened and the formation fluids are allowed to go through a flow line. This leads to a processing facility, storage depot and/or other pipeline eventually leading to a refinery or a distribution centre for gas. Flow lines on subsea wells usually lead to a fixed or floating production platform or to a storage ship or barge, known as a floating storage offloading vessel (FSO) or a floating processing unit (FPU), or floating production and offloading vessel or FPSO.

A tree often provides numerous additional functions including chemical injection points, well intervention means, pressure relief means, monitoring points and connection points for devices such as down hole pressure and temperature transducers.

Tree complexity has increased over the past few decades. They mainly manufactured from blocks of steel containing multiple valves rather than being assembled from individual flanged components. This is especially true in subsea applications where the resemblance to Christmas trees no longer exist given the frame and support systems into which the main value block is integrated.

It's important to remember that a tree and wellhead are separate pieces of equipment which shouldn’t be mistaken as the same piece. The Christmas tree is installed at the top of the wellhead. A wellhead is used without a Christmas tree during drilling operations.

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