Using subsea test trees in well operations includes improved control and safety, increased economic limit, and lower costs. First, let’s examine some of these benefits. Depending on the reservoir type, the productivity gains can be as high as 30%. But what exactly is a test tree? It can be a single spool or a complex system of multiple spools.

Provides surface well control

A subsea test tree is a component of a completion system. The test tree connects to the landing string and provides surface isolation during well completion and intervention operations. A subsea test tree also provides the capability to disconnect and reconnect a well. It is often designed to meet API 17G and ISO13628-7 requirements. 

The testing string is attached to the testing tree apparatus 18 and hangs from a spiral tooth. The hang-off point varies from well to well. An adapter may be provided to allow for a certain amount of space between the actual hang-off point and the test tree apparatus. In this way, the test string will not rotate while drilling. It can be adjusted to suit specific conditions and avoid compromising surface well control.

Reduces costs

Subsea test trees are critical for hydrocarbon production. They are complex assemblies of valves, pipes, and pumps installed by PRT Offshore at the wellhead to monitor production flow and control fluid and gas injection. They can be horizontal or vertical, and the materials and design depend on the well’s physical environment and operating conditions. For example, one North Sea operator used a hybrid subsea tree design that combines physical MPFM and water-cut meters with a VFM model. This system allows for more accurate, more reliable data to be collected and requires less capital and OpEx to run.

Landing strings interface with the subsea wellhead on the seabed to facilitate completion activities from a floating vessel. A subsea test tree located in the blowout preventer contains large hydraulically-controlled valves for enhanced well control, cutting, and sealing capabilities. Landing strings also allow the operator to quickly shut in the well and disconnect the vessel if needed. A subsea test tree control system also reduces costs and personnel on board.

Improves safety

The downhole safety valve is the operator’s most important consideration during subsea well operations. A subsea test tree, located in the BOP stack on the ocean floor, provides an easy means of shutting in the well and unlatching the test string. It’s designed to reduce the risk of well failure by providing reliable access to the production tubing. This tree is capable of both horizontal and vertical installation. Its design is determined by each well’s operating conditions and physical environment. The subsea test tree is part of the subsea landing string used for well intervention and testing. 

Increases economic limit

Subsea test trees are essential for controlling the flow of hydrocarbons and managing gas and fluid injection. The test trees are complex assemblies of valves installed at the wellhead. They can be horizontal or vertical, depending on the physical environment of each well. A well’s design, materials, and installation depend on the operating conditions of the oilfield. Typically, the wellhead and production casing must be tied back to a single master valve, reducing the risks associated with a leak.