Christmas Tree (in oil industry)

CHRISTMAS TREE (IN OIL INDUSTRY):
The energy sources of the world are either renewable or non-renewable energy sources. Petroleum is a non-renewable energy source and during extraction, crude oil found underground is usually mixed with water, sand, salt and natural gas. As it is extracted, the pressure of these different substances must be kept at just the right levels.  This is done by turning valves on and off at the surface level. These valves are often green in colour and the small dials are red, much like the pine trees decorated at Christmas time, this assembly is often referred to as a Christmas tree.

A Christmas Tree can be defined as a kind of wellhead assembly consisting of triple valves, four way valves, which can be used for the fluid control of oil and gas well, and providing the inlet for production flow columns. It can also be defined as an assembly of valves, spools, and fittings used for an oil well, gas well, water injection well, water disposal well, gas injection well, condensate well, and other types of wells. It is named for its resemblance to a decorate tree at Christmas. 

The words ‘Christmas Tree’ and ‘Wellhead’ are used interchangeably at times; however, a wellhead and Christmas tree are entirely seperate pieces of equipment. A wellhead must be present in order to utilize a Christmas tree and is used without a Christmas tree during drilling operations. Producing surface wells that require pumps (pump jacks, nodding donkeys, etc.) frequently do not utilize any tree due to no pressure containment requirement.


Tree complexity has increased over the last few decades. They are frequently manufactured from blocks of steel containing multiple valves rather than made from multiple flanged valves.


The primary function of a tree is to control the flow into or out of the well, usually oil or gas. A tree often provides numerous additional functions including chemical injection points, well intervention means, pressure relief means (such as annulus vent), tree and well monitoring points (such as pressure, temperature, corrosion, erosion, sand detection, flow rate, flow composition, valve and choke position feedback, connection points for devices such as Down Hole Pressure And Temperature Transducer (DHPT). 

In oil and gas extraction, a Christmas tree, or ‘tree’ (not ‘wellhead’ as sometimes incorrectly mentioned), is an assembly of valves, spools and fittings used for oil wells, gas wells, water disposal wells, water injection wells, gas injection wells, condensate wells and other types of wells. It was named as Christmas tree due to its crude resemblance to this decorated tree.

Christmas trees are used in both subsea and surface wells. Commonly, there are two types of tree – subsea tree, and surface tree. 

Note that a Christmas tree isn’t the same equipment as wellhead. They are different separate pieces of equipment. The Christmas tree is installed on top of wellhead. A well head can be used without a Christmas tree during drilling operations. Wells being produced with the rod pumps (nodding donkeys, pump jacks, etc.) frequently don’t utilize any tree due to no pressure-containment requirement.

THE STRUCTURE OF A CHRISTMAS TREE:

Two lower valves are called master valves (upper and lower respectively) as they lie in the flow path that well fluids must take to come to surface. Lower master valve is often manually operated, while the upper master valve is normally hydraulically actuated. 

• Hydraulic tree wing valves require active hydraulic pressure to stay open. 

• The right hand valve is often known as production wing valve or flow wing valve, because it is in the flow path that the hydrocarbons take to production facilities. 

• The left hand valve is called the kill wing valve. It is mainly used for injection of fluids like corrosion inhibitors or methanol to avert hydrate formation. 

• The valve at the top is known as the swab valve and lies in the path used for well interventions such as wireline and coiled tubing. 

• A choke is a device either stationary or adjustable. It is used to control the gas flow (also, volume), or create downstream pressure (also, back pressure). 

Shown already on this Christmas Tree Diagram, there are five valves. The Kill Wing valve, the Swab valve, the production wing valve, the upper master valve and lower master valve. When the operator, well, and facilities are ready to produce and receive oil or gas, valves are opened and the release of the formation fluids is allowed to flow into and through a pipeline. It is important to understand where these valves are located and what role they play in getting gas from the well bore to the customer.

RECOMMENDED STANDARDS FOR CHRISTMAS TREE:

API 6A: Specification for Wellhead and Christmas Tree Equipment .

ISO 10423:2009(en): Petroleum and natural gas industries — Drilling and production equipment — Wellhead and christmas tree equipment

ISO 13628-4:2010(en): Petroleum and natural gas industries — Design and operation of subsea production systems — Part 4: Subsea wellhead and tree equipment

(You can contact me on how to get a copy if you need it.)

CHRISTMAS TREE PARTS DEFINED:

•The two lower valves are called the master valves (upper and lower respectively) because they lie in the flow path, which well fluids must take to get to surface.

•The lower master valve will normally be manually operated, while the upper master valve is often hydraulically actuated.

•Hydraulic tree wing valves are usually built to be fail safe closed, meaning they require active hydraulic pressure to stay open.

•The right hand valve is often called the flow wing valve or the production wing valve, because it is in the flow path the hydrocarbons take to production facilities.

•The left hand valve is often called the kill wing valve. It is primarily used for injection of fluids such as corrosion inhibitors or methanol to prevent hydrate formation.

•The valve at the top is called the swab valve and lies in the path used for well interventions like wireline and coiled tubing.

A ‘Choke’ is a device, either stationary or adjustable, used to: 

     •control the gas flow, also known as volume

     •or create downstream pressure, also known as back pressure

FUNCTION OF A CHRISTMS TREE:

The main function of a Christmas tree is to control the oil and gas flow out of the well. It may also be used to control the injection of gas or water into the non-producing well so as to improve production rates of oil from other wells. When the well and facilities are all set to produce and receive oil or gas, the tree valves are opened and the formation fluids are enabled to go through a flow line. Then a processing facility, storage depot and/ or other pipelines lead to a refinery or distribution center for gas. The flow lines on subsea wells often lead to a fixed or floating production platform or to a storage ship, known as floating processing unit (FPU), a floating storage offloading vessel (FSO), a floating production, storage and offloading vessel (FPSO).  

A Christmas tress often provides a number of additional functions, including well intervention means, pressure relief means, chemical injection points, monitoring points (pressure, temperature, erosion, corrosion, sand detection, flow composition, flow rate, valve, choke position feedback, etc.), and connection points for such devices as down hole pressure and temperature transducers (DHPT). 

A tree may also be used to control the injection of gas or water injection application on a producing or non-producing well in order to sustain economic "production" volumes of gas from other well(s) in the area (field); although injection of chemicals or alcohols or oil distillates to prevent and or solve production problems (such as blockages) may be used in producing wells.

The control system attached to the tree controls the downhole safety valve (SCSSV, DHSV, SSSV) while the tree acts as an attachment and conduit means of the control system to the downhole safety valve.

Onshore drilling is used for underground oil reservoirs anywhere on dry land. Drilling on land generally requires relatively low investments and entails fewer risks. Once the crude oil is extracted from the ground, it is taken to gathering centres where the water, sand and salt are removed. 

While there, natural gas is also separated from the crude oil and then sent to a booster station.  The oil is then pumped to storage tanks before being sent to either a refinery for proper processing or to oil tankers for shipment elsewhere.

Offshore drilling is used to extract oil deposits buried under the ocean floor.  Offshore drilling rigs are installed, operated and serviced on large platforms built out in the ocean.  These platforms can either float or sit on tall ‘legs’ that touch the seabed. In this way, the offshore rig is able to remain stable and resist waves, wind and, in colder regions, floating chunks of ice. Due to its difficulty, offshore drilling consumes more than 65% of planned investments even before oil is extracted, increasing the risk of financial losses, especially if wells come up dry!

Exploration activities in finding underground oil reservoirs and drilling wells are risky, complicated and expensive activities.  The cost of drilling an exploratory oil well can be anything from $1 million to $35 million.

Building and developing a well depends on many factors:  the location of the potential oil field (if it is on land or under water), the size of the oil field, the amount of information that is already available and the type of rocks found underground.

Many oil fields are found in hard-to-reach areas on land or below deep ocean water.  New technology is helping oil companies reach these oil fields and increase the amount of oil extracted from the ground.  But in order to pay for new technology, hundreds of millions of dollars in investments are needed. The average amount of time needed to discover, extract and market oil is between 3 to 10 years. But oil explorers also need time to raise the necessary money in order to deal with all the technical challenges.

Much of the time needed depends on the location of the oil field. An offshore oil field in deep water can take much longer to discover and test, especially when the sea bottom is thousands of metres below the surface.

The downstream sector is the part of the oil industry involved with purifying crude oil and refining it into different products. It also involves the transportation and marketing of crude oil and its products.  The process through which crude oil is purified and treated to remove unusable substances is called REFINING. This process is also used to separate oil into different usable petroleum products. All this takes place in an oil refinery. All refineries perform three basic functions: separation, conversion and treatment.

Refining methods are constantly being improved.  A variety of complex operations are now used which have improved their output. Refineries today turn more than half of every barrel of crude oil into gasoline. One barrel is equal to 159 litres (42 US gallons).  This is a big advance from only 70 years ago when only 41 litres (11 gallons) of gasoline were produced from each barrel of crude.

Oil pipelines are made from steel.  They usually have an inner diameter of about 10 to 120 cm (about 4 to 48 inches) and can run for hundreds or thousands of kilometres.  Advances in technology are constantly improving the size and strength of these pipelines. Although pipelines are less flexible than other forms of transportation, they are the safest, most efficient and most economical way to move oil.  All large modern oil fields have direct connections to major pipelines.  Without these pipelines, it would be impossible for oil and oil products to reach consumers.

In conclusion, it is noteworthy that the body that helps to co-ordinate the policies and ensure best practices in the oil industry is Organization of the Petroleum Exporting Countries (OPEC), and it was introduced at Baghdad conference held on September 10–14, 1960. The five Founder Members were: Iran, Iraq, Kuwait, Saudi Arabia and Venezuela. The OPEC logo is the recognizable symbol of the Organization, and was the result of an international design competition held in 1969. An Austrian designer, Gertrude Svoboda, won the competition with her design, which combined the different letters of the Organization’s name in a rounded design.