How Does a Tension Leg Platform (TLP) Work?

A type of floating production system, tension leg platforms (TLPs) are buoyant production facilities vertically moored to the seafloor by tendons.

TLP Design

While a buoyant hull supports the platform's topsides, an intricate mooring system keeps the TLP in place. The buoyancy of the facility's hull offsets the weight of the platform, requiring clusters of tight tendons, or tension legs, to secure the structure to the foundation on the seabed. The foundation is then kept stationary by piles driven into the seabed.

The tension leg mooring system allows for horizontal movement with wave disturbances, but does not permit vertical, or bobbing, movement, which makes TLPs a popular choice for stability, such as in the hurricane-prone Gulf of Mexico.

The basic design of a TLP includes four air-filled columns forming a square. These columns are supported and connected by pontoons, similar to the design of a semisubmersible production platform. Nonetheless, since their inception in the mid 1980s, TLP designs have changed according to development requirements. Now, designs also comprise the E-TLP, which includes a ring pontoon connecting the four air-filled columns; the Moses TLP, which centralizes the four-column hull; and the SeaStar TLP, which includes only one central column for a hull.

Source: A Moses TLP

The platform deck is located atop the hull of the TLP. The topside of a TLP is the same as a typical production platform, consisting of a deck that houses the drilling and production equipment, as well as the power module and the living quarters. Dry tree wells are common on TLPs because of the lessened vertical movement on the platforms.

Most wells producing to TLPs are developed through rigid risers, which lift the hydrocarbons from the seafloor to dry trees located on the TLP deck. Many times, steel catenary risers are also used to tie-in the subsea flowlines and export pipelines.

A SeaStar TLP

TLP Types

The third-most used type of floating production facility in the world, TLPs are ideal for a broad range of water depths. Currently, there are three different types of TLPs: full-size TLPs, mini TLPs and wellhead TLPs.