Single buoy mooring

Last updated
Single point mooring at Whiddy Island, Ireland Whiddy Spim.jpeg
Single point mooring at Whiddy Island, Ireland
Single-point mooring facility off Puthuvype, Kochi, India SBM01.jpg
Single-point mooring facility off Puthuvype, Kochi, India
SBM02.jpg
SBM03.jpg

A Single buoy mooring (SrM) (also known as single-point mooring or SPM) is a loading buoy anchored offshore, that serves as a mooring point and interconnect for tankers loading or offloading gas or liquid products. SPMs are the link between geostatic subsea manifold connections and weathervaning tankers. They are capable of handling any tonnage ship, even very large crude carriers (VLCC) where no alternative facility is available.

Contents

In shallow water SPMs are used to load and unload crude oil and refined products from inshore and offshore oilfields or refineries, usually through some form of storage system. These buoys are usually suitable for use by all types of oil tanker. In deep water oil fields, SPMs are usually used to load crude oil direct from the production platforms, where there are economic reasons not to run a pipeline to the shore. These moorings usually supply to dedicated tankers which can moor without assistance. [1] Several types of single point mooring are in use. [1]


Parts

There are four groups of parts in the total mooring system: the body of the buoy, mooring and anchoring elements, product transfer system and other components.

Buoy body

The buoy body may be supported on static legs attached to the seabed, with a rotating part above water level connected to the (off)loading tanker. The two sections are linked by a roller bearing, referred to as the "main bearing". Alternatively the buoy body may be held in place by multiple radiating anchor chains. The moored tanker can freely weather vane around the buoy and find a stable position due to this arrangement.

Mooring and anchoring parts

Moorings fix the buoy to the sea bed. Buoy design must account for the behaviour of the buoy given applicable wind, wave and current conditions and tanker tonnages. This determines the optimum mooring arrangement and size of the various mooring leg components. Anchoring points are greatly dependent on local soil condition. [2]

Mooring components

  • Anchors or piles - To connect the mooring to the seabed [2]
  • Sinker or anchor chain joint to buoy (SPM) [2]
  • Anchor chain [2]
  • Chain stoppers - To connect the chains to the buoy [2]

Hawser arrangement

A tanker is moored to a buoy by means of a hawser arrangement. Oil Companies International Marine Forum (OCIMF) standards are available for mooring systems.

The hawser arrangement usually consist of nylon rope, which is shackled to an integrated mooring uni-joint on the buoy deck. At the tanker end of the hawser, a chafe chain is connected to prevent damage from the tanker fairlead. A load pin can be applied to the mooring uni-joint on the buoy deck to measure hawser loads.

Hawser systems use either one or two ropes depending on the largest tonnage of vessel which would be moored to the buoy. The ropes would either be single-leg or grommet leg type ropes. These are usually connected to an OCIMF chafe chain on the export tanker side (either type A or B depending on the maximum tonnage of the tanker and the mooring loads). This chafe chain would then be held in the chain stopper on board the export tanker.

A basic hawser system would consist of the following (working from the buoy outwards):

Buoy-side shackle and bridle assembly for connection to the padeye on the buoy; Mooring hawser shackle; Mooring hawser; Chafe chain assembly; Support buoy; Pick-up / messenger lines; Marker buoy for retrieval from the water.

Under OCIMF recommendations, the hawser arrangement would normally be purchased as a full assembly from a manufacturer.

Product transfer system

The heart of each buoy is the product transfer system. From a geostatic location, e.g. a pipeline end manifold (PLEM) located on the seabed, this system transfers products to the offtake tanker.

The basic product transfer system components are:

Risers

The risers are flexible hoses that connect the subsea piping to the buoy. Configuration of these risers can vary depending on water depth, sea conditions, buoy motions, etc.

Floating hose string

Floating hose string(s) connect the buoy to the offloading tanker. The hose string can be equipped with a breakaway coupling to prevent rupture of hoses/hawser and subsequent oil spills.

Product swivel

The product swivel is the connection between the geostatic and the rotating parts of the buoy. The swivel enables an offloading tanker to rotate with respect to the mooring buoy. Product swivels range in size depending on the capacity of attached piping and risers. Product swivels can provide one or several independent paths for fluids, gases, electrical signals or power. Swivels are equipped with a multiple seal arrangement to minimise the possibility of leakage of product into the environment.

Other components

Other possible components of SPMs are:

Configurations

Single anchor leg mooring (SALM) Thistle SALM.png
Single anchor leg mooring (SALM)

Catenary anchor leg mooring

A commonly used configuration is the catenary anchor leg mooring (CALM), which can be capable of handling very large crude carriers. This configuration uses six or eight heavy anchor chains placed radially around the buoy, of a tonnage to suit the designed load, each about 350 metres (1,150 ft) long, and attached to an anchor or pile to provide the required holding power. The anchor chains are pre-tensioned to ensure that the buoy is held in position above the PLEM. As the load from the tanker is applied, the heavy chains on the far side straighten and lift off the seabed to apply the balancing load. Under full design load there is still some 27 metres (89 ft) of chain lying on the bottom. The flexible hose riser may be in one of three basic configurations, all designed to accommodate tidal depth variation and lateral displacement due to mooring loads. In all cases the hose curvature changes to accommodate lateral and vertical movement of the buoy, and the hoses are supported at near neutral buoyancy by floats along the length. These are: [1]

Other configurations

Less commonly used configurations include:

  • Jacket type, which has a jacket piled to the seabed with a turntable on top which carries the mooring gear and pipework [1]
  • Spring pile type, which has steel pipe risers in the structure [1]

See also

Related Research Articles

<span class="mw-page-title-main">Anchor</span> Device used to secure a vessel to the bed of a body of water to prevent the craft from drifting

An anchor is a device, normally made of metal, used to secure a vessel to the bed of a body of water to prevent the craft from drifting due to wind or current. The word derives from Latin ancora, which itself comes from the Greek ἄγκυρα.

<span class="mw-page-title-main">Oil platform</span> Large offshore structure with oil drilling and related facilities

An oil platform is a large structure with facilities to extract and process petroleum and natural gas that lie in rock formations beneath the seabed. Many oil platforms will also have facilities to accommodate the workers, although it is also common to have a separate accommodation platform bridge linked to the production platform. Most commonly, oil platforms engage in activities on the continental shelf, though they can also be used in lakes, inshore waters, and inland seas. Depending on the circumstances, the platform may be fixed to the ocean floor, consist of an artificial island, or float. In some arrangements the main facility may have storage facilities for the processed oil. Remote subsea wells may also be connected to a platform by flow lines and by umbilical connections. These sub-sea facilities may include one or more subsea wells or manifold centres for multiple wells.

<span class="mw-page-title-main">Mooring</span> Structure for securing floating vessels

A mooring is any permanent structure to which a seaborne vessel may be secured. Examples include quays, wharfs, jetties, piers, anchor buoys, and mooring buoys. A ship is secured to a mooring to forestall free movement of the ship on the water. An anchor mooring fixes a vessel's position relative to a point on the bottom of a waterway without connecting the vessel to shore. As a verb, mooring refers to the act of attaching a vessel to a mooring.

<span class="mw-page-title-main">Floating production storage and offloading</span> Vessel used by offshore oil and gas industry

A floating production storage and offloading (FPSO) unit is a floating vessel used by the offshore oil and gas industry for the production and processing of hydrocarbons, and for the storage of oil. An FPSO vessel is designed to receive hydrocarbons produced by itself or from nearby platforms or subsea template, process them, and store oil until it can be offloaded onto a tanker or, less frequently, transported through a pipeline. FPSOs are preferred in frontier offshore regions as they are easy to install, and do not require a local pipeline infrastructure to export oil. FPSOs can be a conversion of an oil tanker or can be a vessel built specially for the application. A vessel used only to store oil is referred to as a floating storage and offloading (FSO) vessel.

<span class="mw-page-title-main">Louisiana Offshore Oil Port</span>

The Louisiana Offshore Oil Port (LOOP) is a deepwater port in the Gulf of Mexico 29 kilometers off the coast of Louisiana near the town of Port Fourchon. LOOP provides tanker offloading and temporary storage services for crude oil transported on some of the largest tankers in the world. Most tankers offloading at LOOP are too large for U.S. inland ports. LOOP handles 13 percent of the nation's foreign oil, about 1.2 million barrels (190,000 m3) a day, and connects by pipeline to 50 percent of the U.S. refining capability.

USNS <i>Grapple</i> Rescue and salvage ship

USS Grapple (ARS-53) is a Safeguard-class rescue and salvage ship in the United States Navy. Her home port is Norfolk, Virginia. On 13 July 2006 Grapple was decommissioned from US Navy service and converted to civilian operation by Military Sealift Command. She was redesignated as USNS Grapple.

<span class="mw-page-title-main">Spar (platform)</span> Marine structure used for floating oil/gas platforms

A spar is a marine structure, used for floating oil/gas platforms. Named after navigation channel Spar buoys, spar platforms were developed as an extreme deepwater alternative to conventional platforms. The deep draft design of spars makes them less affected by wind, wave, and currents and allows for both dry tree and subsea production.

Oil tanker Ship that carries oil

An oil tanker, also known as a petroleum tanker, is a ship designed for the bulk transport of oil or its products. There are two basic types of oil tankers: crude tankers and product tankers. Crude tankers move large quantities of unrefined crude oil from its point of extraction to refineries. Product tankers, generally much smaller, are designed to move refined products from refineries to points near consuming markets.

Puerto José is a sea port in northeastern Venezuela, on the Caribbean Sea, in the state of Anzoátegui, about 10 km west of Barcelona. It is home to an important oil tanker loading complex, the Complejo criogenico de Oriente José, created in 1985 and now more often referred to by its original name, the Cryogenic Complex of Oriente, San Joaquin Plant. The complex is used to load several of Venezuela's petroleum products onto oil tankers, including Ameriven-Hamaca, Cerro Negro, Sincor, and Zuata Sweet.

A loading arm permits the transfer of liquid or liquefied gas from one tank to another through an articulated pipe system consisting of rigid piping and swivel joints to obtain flexibility.

<span class="mw-page-title-main">Evopod</span> Tidal energy device

Evopod is a unique tidal energy device being developed by a UK-based company Oceanflow Energy Ltd for generating electricity from tidal streams and ocean currents. It can operate in exposed deep water sites where severe wind and waves also make up the environment.

USNS <i>Grasp</i> Safeguard-class rescue and salvage ship

USNS Grasp (T-ARS-51) is a Safeguard-class rescue and salvage ship, the second United States Navy ship of that name.

<span class="mw-page-title-main">Al Başrah Oil Terminal</span> Iraqi oil terminal

Al Başrah Oil Terminal, commonly referred to as ABOT, is a strategically critical Iraqi offshore, deep sea crude oil marine loading terminal that lies approximately 50 km (31 mi) southeast of the Al-Faw Peninsula in the Persian Gulf. Along with its sister terminal, the Khawr al ‘Amīyah Oil Terminal, the terminals provide the principal point of export for more than eighty percent of Iraq's gross domestic product as of 2009, and all of the oil from the southern Başrah refinery.

A steel catenary riser (SCR) is a common method of connecting a subsea pipeline to a deepwater floating or fixed oil production platform. SCRs are used to transfer fluids like oil, gas, injection water, etc. between the platforms and the pipelines.

<span class="mw-page-title-main">Commercial offshore diving</span> Professional diving in support of the oil and gas industry

Commercial offshore diving, sometimes shortened to just offshore diving, generally refers to the branch of commercial diving, with divers working in support of the exploration and production sector of the oil and gas industry in places such as the Gulf of Mexico in the United States, the North Sea in the United Kingdom and Norway, and along the coast of Brazil. The work in this area of the industry includes maintenance of oil platforms and the building of underwater structures. In this context "offshore" implies that the diving work is done outside of national boundaries. Technically it also refers to any diving done in the international offshore waters outside of the territorial waters of a state, where national legislation does not apply. Most commercial offshore diving is in the Exclusive Economic Zone of a state, and much of it is outside the territorial waters. Offshore diving beyond the EEZ does also occur, and is often for scientific purposes.

The Aasta Hansteen spar is a floating production storage and offloading (FPSO) unit for natural gas operated by Equinor located 186 miles offshore in the Norwegian Sea. It is the first spar platform to be located on the Norwegian Continental Shelf (NCS). The Aasta Hansteen is named after Norwegian painter, writer and early feminist.

<span class="mw-page-title-main">Submarine pipeline</span> Pipeline that is laid on the seabed or below it inside a trench

A submarine pipeline is a pipeline that is laid on the seabed or below it inside a trench. In some cases, the pipeline is mostly on-land but in places it crosses water expanses, such as small seas, straits and rivers. Submarine pipelines are used primarily to carry oil or gas, but transportation of water is also important. A distinction is sometimes made between a flowline and a pipeline. The former is an intrafield pipeline, in the sense that it is used to connect subsea wellheads, manifolds and the platform within a particular development field. The latter, sometimes referred to as an export pipeline, is used to bring the resource to shore. Sizeable pipeline construction projects need to take into account many factors, such as the offshore ecology, geohazards and environmental loading – they are often undertaken by multidisciplinary, international teams.

The Thistle SALM was a tanker loading facility that allowed oil from the Thistle oilfield to be transported to land where a submarine export pipeline did not yet exist. It was also the site of the August 8, 1979 Wildrake diving accident that killed two divers. and the January 21, 1981 Stena Seaspread diving accident (non-fatal).

<span class="mw-page-title-main">Offshore embedded anchors</span> Type of marine mooring component

Offshore embedded anchors are anchors intended for offshore use that derive their holding capacity from the frictional, or bearing, resistance of the surrounding soil, as opposed to gravity anchors, which derive their holding capacity largely from their weight. As offshore developments move into deeper waters, gravity-based structures become less economical due to the large size needed and the consequent cost of transportation.

<i>Safeguard</i>-class rescue and salvage ship United States Navy salvage and rescue ships

The Safeguard class is a class of Towing, Salvage and Rescue Ship under the United States Navy.

References

  1. 1 2 3 4 5 6 7 8 9 Bevan, John, ed. (2005). "Section 1.10". The Professional Divers's Handbook (second ed.). Alverstoke, GOSPORT, Hampshire: Submex Ltd. p. 41. ISBN   978-0950824260.
  2. 1 2 3 4 5 IALA Guideline 1066 - The Design of FLoating Aid to Navigation Moorings - May 2009 - Revised June 2010