The subsea test tree is a large underwater structure used for engineering tests. It comprises many layers of metal, wood, and plastic. It is lowered into the water by waves, which create an interaction force between the tree and the seawater. The interaction force is magnified as the tree enters the water. As a result, its stability will be compromised by the additional forces. If not designed correctly, the subsea tree could overturn and cause damage. In rare cases, it could even cause an engineering accident. This article will walk through the advanced guide to the subsea test tree, rig-based completions, and interventions.

Impact of current on a subsea test tree

The first all-electric subsea test tree is currently being tested on the BP Magnus field. A prominent company envisions a subsea test tree that is entirely electric and will provide the industry with an alternative to hydraulic and electro-hydraulic control systems. Hydraulics are less responsive in deeper water and are inefficient the further away from the host facility.

A large-bore HP/HT subsea test tree will maximize the potential of horizontal tree systems. The tree will not be installed on a production well but rather at the base of a platform, 600 feet below sea level. A hydraulic-actuated choke will close in one minute, while an electric-actuated choke will close in 20 minutes. Ultimately, the test will help determine the most efficient horizontal test tree solution for a given application.

The pressure rating of the subsea test tree

Various types of Christmas trees are used on the surface and subsea wells. There are three main subsea test trees: conventional, dual bore, and through-bore. The conventional ones have a pressure rating of 5,000 to 15,000 psi. Both types feature valves on the lateral side and are manufactured from carbon or low-alloy steel. Horizontal subsea test trees are efficient for tubing recovery and are often installed on wells as part of well intervention.

The SenTREE HP high-pressure completion subsea test tree is an immediate solution for controlling completions in subsea oilfields. The subsea test tree comprises a ball valve module, an integral flapper valve, and a retainer valve with a bleed-off function which provides dual-barrier well control and a reliable method for disconnecting completion landing strings in an emergency.

The temperature rating of subsea test trees also influences their sealing systems. API 6A temperature ratings include K, P, R, S, T, and U. Temperature ratings have little or no effect on the cost of subsea test trees because they vary widely based on reservoir characteristics. Therefore, choosing the material is essential but will not disproportionately affect the test tree's cost.

Workover rigs

Workover rigs are essential to any oil and gas operation. These rigs replace old well completions with new ones, and this work is necessary for several reasons, such as changing reservoir conditions or well deterioration. According to experts like PRT Offshore, a workover also may be required to replace equipment in the well, which may have eroded over time. Sometimes, a well's flow has decreased, and a new tubing installation is necessary to restore the production to previous levels.

Workover rigs are most useful for completions when a completion fails. They are used to replace damaged sections of the casing, which are often damaged and weakened. In addition, rigs are often used to support the tubing, so a rig must be equipped with a snubbing spool. The rig may be loaded with a BOP using this tool.

Challenges with Heavy interventions

For decades, rig-based completions and heavy interventions have been the mainstay of the drilling process. However, their performance has been less than optimal. As an industry, the drilling and completions operations are classified as offshore activities. Most rigs are jack-up or submerge swamp rigs, and the company typically drills 100 wells per year, spending approximately 4 million person-hours on average. The challenges that face the industry include the high level of direct human resource involvement with equipment, high employee turnover, and differing levels of educational background and experience. These challenges have their root causes in inadequate supervision, leadership, and work management.