Since the holidays are quickly approaching I thought I’d include a short article on Christmas trees. Normally, you’d think Christmas trees and Israel wouldn’t go together. But there’s a Christmas tree already up at Zion Oil’s Ma’anit-Rehoboth #2 site. It’s not green (it’s kind of a dirty gray) and it doesn’t have needles, but there are a good many valves.
The Ma’anit-Rehoboth #2 Christmas tree is installed on the wellhead. I’ll leave it to Wikipedia to explain why it’s there and what it does.
Note that a tree and wellhead are separate pieces of equipment not to be mistaken as the same piece. For clarity, a wellhead must be present in order to utilize a Christmas Tree and a wellhead is used WITHOUT a Christmas Tree during drilling operations, and also for riser tie-back situations which would then have a tree included at riser top. 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 (eg 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), etc.
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. The pipeline then leads to a processing facility, storage depot and or other pipeline eventually leading to a refinery or distribution center (for gas).
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 oil from other well(s) in the area (field).
On producing wells, injection of chemicals or alcohols or oil distillates to prevent and or solve production problems (such as blockages) may be used.
A typical sophisticated surface tree will have at least four or five valves, normally arranged in a crucifix type pattern (hence the endurance of the term “Christmas tree”). 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, allowing it to be a means of well control while an actuated wing valve is normally the primary well remotely (from control room or control panel) controlled valve. Hydraulic tree wing valves are usually built to be fail safe closed, meaning they require active hydraulic pressure to stay open.
If you’re lucky enough to visit Zion’s well site one day, you’ll know why that complicated combination of valves and gauges is there and what it’s called – a Christmas tree!