Offshore Vessels

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Introduction

The Offshore Industry is a varied sector within which many vessel types operate, performing numerous different tasks with often unique systems and equipment in order to fulfill the specific tasks or a more general ones. Due to the development of oil and gas fields heads in to ever deeper water and more hostile environments, there has been a dramatic demand for new vessels, capable of operating in this dramatic area. Moreover the new developments in the wind power industry in which the oil and gas major players are more and more involved taking into advantage their knowledge and skilled personal, have led to the development or new types of vessels in order to maintain the wind farms.

The ever-growing need to explore and suitably harness the potentialities that the high seas offer has led to a huge growth in the need and demand for offshore ships. Coupled with the advantages of technological researching and suitably resulting developments, the present-day fleet of offshore vessels across the world is one that portrays the huge strides taken in the maritime sector.

The present work try to summarize what means the offshore vessels fleet, their types and roles in the oil industry.

Definition of Offshore vessels

Offshore Vessels or Cargo vessels are specially designed ships that regularly transport goods and personnel to and from offshore oil platform that operate deep in oceans. Usually the size of these vessels ranges between 20-100 meters. There are a variety of offshore vessels, which not only help in the exploration and drilling for the oil and gas pools, but also provide the necessary supplies to the excavation and construction units located at the high seas. In some particular cases the offshore vessels are used to transport the crude from the production platform. The denotation of offshore vessels is a collective reference and as such includes a wide array of vessels employed in the high seas sector. They can be classified into the fallowing main groups:

Oil Exploration and Drilling Vessels, this vessels help in exploration and drilling of oil at high seas.

Offshore Support Vessels provide the necessary manpower and technical reinforcement required so that the operational processes in the high seas continue smoothly and without any undesired interruptions. The technical reinforcement includes: bop (blow out preventor) drilling pipes, drilling bits, drilling mud, casing, cement and other chemicals and specific materials for drilling operation. Offshore supply vessels operate in the harshest working conditions known to man and their reliability is of paramount importance to protect their crews, the environment and the infrastructure of the fields where they operate. Offshore Support Vessels transport the required structural components to the designated high seas sector along with providing assistance to supply freight as well. The constructional aspect of these vessels can be purpose-built to suit the operational demands.

Offshore Production Vessels refer to those vessels that help in the production processes in the drilling units in the high seas, such as floating, production, storage and offloading etc.

Construction/Special Purpose Vessels are the ships that primarily aid in the construction of various high seas structures are known as offshore construction vessels. Other offshore vessels of these type also include those that provide anchorage and tugging assistance and those kinds of ships that help in the positioning of deep sub-water cable and piping lines.

Each of this category comprise of a variety of vessels which will be described in the following chapters.

In addition to these, those variances of ships that provide aid in case of any emergencies occurring in the high seas and those types of vessels that undertake researching and analyzing activities in the high seas are also included under the offshore vessels classification.

Types of Offshore vessels

Based on the above classification, in the following lines I will detail the types of Offshore vessels.

Oil Exploration and Drilling Vessels are classified in: Drill ship, Jack Up Vessels, Semi-submersible vessels, Offshore barge and Floating Platforms.

Drill ships are special ships which are used for drilling on the ocean beds at deep seas. This ships are designed to provide optimum viability while on water, thus making it easy for the conglomerates to engage their services for better qualitative results in the overall scheme of drilling viability and functionality.

Figure 1. Drill ship (http://www.marineinsight.com/types-of-ships/what-is-a-drill-ship/)

Drilling ships can also be used as analytical vessel to carry out sub-water researching operations in the high seas. The drilling equipment aboard these vessels can penetrate to really greater depths, maybe between 600 – 3000 meters, and can be relocated in the high seas as the requirement necessitates. To keep them firmly positioned in the drilling area these vessels utilize equipment’s like GP systems, strong support cables and ground tackles.

Semi-submersible rigs are specialized marine vessels used mainly into the drilling activities in the deep water settings where jack-up rigs cannot operate (more than 520 m water depth) and requires a floating platform to perform the task (in a similar way with the drilling ship). The advantage of drilling rig in from of the ships is the available space for storage and more powerful lifting capacity for the tower. The disadvantage is that

Figure 2. Ocean Endeavor drilling rig. http://www.diamondoffshore.com/video-the-ocean-endeavor-journey. This rig was used by Exxon and their partner OMV-Petrom for drilling campaign in the Romanian Black Sea.

A semi-submersible obtains most of its buoyancy from ballasted, watertight pontoons located below the ocean surface and wave action. Structural columns connect the pontoons and operating deck. The operating deck can be located high above the sea level owing to the good stability of the design, and therefore is kept well away from the waves.

Figure 3. Comparison of drilling rig vs drilling ship (www.wikipedia.org)

Jack Up Vessels is a mobile platform that consists of a buoyant hull fitted with a number of movable legs which are capable of raising its hull over the surface of the sea. The legs of such units may be designed to penetrate the sea bed, may be fitted with enlarged sections or footings, or may be attached to a bottom mat. Jack Up vessels are used as exploratory drilling platforms and offshore and wind farm service platforms.

Figure 4. Jack Up Vessels (http://www.ship-technology.com/projects/pacific-orca-wind-farm-installation- Semi-submersible vessels vessel/)

Semi-submersible vessels are used in marine operations carried out in the high seas like oil drilling and production platforms for oil. Also the semi-submersible ships are used as heavy duty cranes. This kind of vessels was developed because of the need for vessels that could stay afloat and carry out their required functions in the high seas amidst the constant movement of the waves. The most important advantages of a semi-submersible ship is that it helps to haul seemingly large cargo, also a lot of marine operations are carried out with the least amount of problems due to the semi-submersible vessel, and this is the most important factor that makes these vessels indispensable in important marine operations.

Figure 5. Semi-submersible vessels (http://gcaptain.com/dockwise-vanguard-to-lift-costa-concordia-from-giglio/)

Offshore barge is a flat-bottomed boat, especially built for river and canal transport of heavy goods. Usually these measures 195 by 35 feet and can carry up to 1,500 tons of cargo.

Figure 6. Offshore barge (http://www.marineinsight.com/types-of-ships/what-is-an-offshore-barge%C2%A0/)

Floating Platforms or mobile offshore platform means an offshore platform that is designed to operate in a floating mode or which can be moved from a place to another without major dismantling, also its own motive power.

Figure 7. Floating platform (http://theogm.com/2015/03/05/7-technologically-advanced-oil-rigs/)

Offshore Support Vessels are classified in: Anchor Handling Tug Vessel (AHTV), Seismic Vessel, Platform Supply Vessels (PSVs), Well Intervention Vessel and Accommodation Ships.

Anchor Handling Tug Vessel (AHTV) is a naval vessel which has the ojective of either tugging or towing an oil-rig or a ship. Without their help, it would be impossible to place oil rigs in the required sea and oceanic areas. AHTV have a crane like equipment that can be attached to the oil rigs and then propelled forth in the water. AHTSV supply also the cargo-carrying barges. Technically an AHTSV is a very huge naval, mainly because of the equipment’s that it carries, tugs and anchors along with the winches. Also such kind of vessels act as rescue vessels for other ships in times of some emergency. Due to their multy-utility facility’s they are demanded in a higher coverage area.

Figure 8. Anchor Handling Tug Vessel (AHTV) (http://www.marineinsight.com/types-of-ships/what-are-anchor-handling-tug-vessels-aths/)

Seismic Vessel this vessels are used for seismic survey in the high seas and oceans. A seismic vessel is used as a survey vessel for the purpose of pinpointing and locating the best possible area for the oil drilling in the middle of the oceans. This vessels are also important because the usage of them prevents dangerous accidents for the marine eco-system, when it is not fond the best subsea location to drill the oil and gas. Seismic waves are the main components which are analyzed in the seismic survey, this vessels are equipped with a seismic detector that shoots such seismic waves to a selected underwater point. The time taken for the waves to refract back to their origin point determines whether that particular subsea area is feasible for the oil drilling purpose. The most important thing of this vessels is the technological gadgets like GPS computer, nautical charts and other equipment that would enhance the process of seismic survey. Due to this very important equipment the seismic vessels are built carefully and only in selected locations across the world.

Figure 9. Seismic Vessel (http://www.marineinsight.com/types-of-ships/what-are-seismic-vessels/)

Platform Supply Vessels (PSVs) is used for transiting essential equipment and additional manpower to reinforce the high seas operations. Usually Platform Supply Vessels help to sustain the demands of the constructional and maintenance projects thus fulfilling a vital necessity in the nature of operations at the high seas. This ships can measure between 65 meters to over 300 meters.

Figure 10. Platform Supply Vessel (http://www.offshoreenergytoday.com/norway-stx-confirms-two-platform-supply-vessels-contracts-from-island-offshore/)

Well Intervention Vessel is a well intervention performed on an oil or gas well to increase production by improving the flow of hydrocarbons form the drainage area into the well bore.

Figure 11. Well Intervention Vessel (https://en.wikipedia.org/wiki/Well_intervention)

Accommodation Ships are used wherever there is a need for additional accommodation, engineering, construction or storage capacity offshore. Usually the Accommodation Ships have a capacity for 306-780 people and offer high quality welfare and catering facilities, storage, workshops, offices, medical services, lifesaving and firefighting equipment. The vessels are positioned alongside the host installation and are connected by means of a telescopic gangway so that personnel can walk to work.

Figure 12. Accommodation Vessel (http://www.abcmaritime.ch/vessel/elisa/)

Offshore Production Vessels are classified in: Floating Production Storage and Offloading (FPSO), Single Point Anchor Reservoir (SPAR) platform, Shuttle Tankers and Tension Leg Platform (TLP).

Floating Production Storage and Offloading (FPSO) is a system used only by oil companies for the purpose of storing oil from the oil rigs in the middle of the ocean and in the high seas. This is a floating contraption that allows oil rigs the freedom to store oil and to produce or refine it before finally offloading it to the desired industrial sector.

Figure 13. Floating Production Storage and Offloading (FPSO) (http://www.marineinsight.com/types-of-ships/what-is-fpso-floating-production-storage-and-offloading-system/)

Single Point Anchor Reservoir (SPAR) platform refer to a certain type of offshore oil platform that provides a base to extract and process oil in ultra-deep water regions and it is an alternative to the conventional oil extraction platforms constructed on the sea/ocean beds. Provides strong resistance to wind and waves and have an additional advantages which include an enclosed cylinder that can act as a protective barrier for risers and equipment.

Figure 14. Single Point Anchor Reservoir (SPAR) platform (http://www.marineinsight.com/types-of-ships/what-is-fpso-floating-production-storage-and-offloading-system/)

Shuttle Tankers is a type of tanker ship, which provides invaluable contribution in the high seas oil exploratory areas, thereby helping to maintain a steady constancy in the oil and gases supply chain. This type of tanker vessels can be used in any kind of oceanic exploratory condition. An advantage of this Shuttle Tankers is that they are equipped with capable ancillaty tehnical systems, which ensure that there are no unwanted stoppages in the extraction and transference processes.

Figure 15. Shuttle Tankers (http://www.marineinsight.com/types-of-ships/what-are-shuttle-tankers/)

Tension Leg Platform (TLP) is an offshore floating platform which is used for oil and gas exploration. The offshore platform consists of steeled sinewy pillars that are tautened on purpoe and supported with cable-lines to provide weightlessness to the floating operational platform structure above the surface of the water.

Figure 16. Tension Leg Platform (http://www.marineinsight.com/types-of-ships/what-is-tension-leg-platform-tlp/)

Construction/Special Purpose Vessels are classified in: Diving Support Vessel, Crane Vessel and Pipe Laying Vessel.

Diving Support Vessel is a vessel that is used for the objective of diving into oceans. This ships are important to the field of commercial diving which forms a vital part of professional diving. Usually professional diving means diving for the prospect of construction, repairing and maintenance of oil-rigs and other important offshore naval constructions.

Figure 17. Diving Support Vessel (http://www.marineinsight.com/types-of-ships/what-is-a-diving-support-vessel/)

Crane Vessel is a vessel which has a crane attached to it. A crane vessel is very important when it comes to the aspect of constructing structures in the high seas. It is only beacause of such vessels that many important constructions are carried out in trickier parts of the seas and oceans. All suc crane vessels are capable of lifting heavy tonnage, usually this cranes can be used to haul and lift around 2500 tons. Another type of cranes are the semi-submersible ones, which submerge partially into the water to give the weight placed on top of them the balance required. The heaviest limit that such semi-submersibles can carry extends to around 14.000 tonnes.

Figure 18. Crane Vessel (http://www.marineinsight.com/types-of-ships/what-is-crane-vessel/)

Pipe Laying Vessel is a maritime vessel used in the construction of subsea infrastructure. The term Pipe Laying Vessel refer to all vessels capable of laying on the ocean floor. It serves to connect oil production platform with refineries on shore. The procees consist that a pipelaying vessel carries a heavy lift crane, used to install pumps, valves and equipment to lay pipe between subsea structures.

Figure 19. Pipe Laying Vessel (https://www.flickr.com/photos/nachtdienst/6181491708)

Mission of Offshore vessels

The general mission of Offshore vessels is to provide support to offshore oil and gas exploration and production, which can be sub-divided according to specific mission requirements. Also vessels may involve in more than one kind of such specific missions. Like every other design criteria, optimizing based on the priority is done in the design process, and also meeting the safety requirements.

These specific missions of Offshore vessel include:

seismic survey to locate oil and gas bearing areas

towing of rigs and platforms to their location, positioning them, and laying anchoring & mooring equipments

supplying rigs and platforms with necessary personnel, equipment, stores, provisions, etc.

Subsea operations like ROV operation, diving support, inspection, and maintenance

safety standby

Conclusions

As a general conclusion we can retain that there are four general categories of Offshore Vessels: Oil Exploration and Drilling Vessels, Offshore Support Vessels, Offshore Production Vessels and Construction/Special Purpose Vessel, each of them having sub-categories of ships, properly specialized to fulfill their missions.

Due to ever rising demand for oil and gas in the world today, the global offshore oil and gas industry, which involves automatically the offshore vessels industry, is requested a permanent improvement of these. The rising cost of oil and gas prices holds great promises for the offshore vessels industry in coming years and the large manufacturing companies of offshore vessels will face new challenges.

Although they are technically highly sophisticated and extremely expensive, without these specialized offshore vessels, would not be possible to develop the oil industry and because of this reason we should offer more attention to them in the future.

References

http://www.marineinsight.com/types-of-ships/what-are-offshore-vessels/

http://maritime-connector.com/wiki/offshore-vessels/

http://www.wartsila.com/products/marine-oil-gas/ship-design/offshore-special

http://marinewiki.org/index.php/Offshore_Supply_Vessels

https://boskalis.com/about-us/fleet-and-equipment/offshore-vessels.html

http://products.damen.com/en