OFFSHORE PLATFORM

Offshore platforms are used for exploration of Oil and Gas from under Seabed and processing. The First Offshore platform was installed in 1947 off the coast of Louisiana in 6M depth of

water. Today there are over 7,000 Offshore platforms around the world in water depths up to 1,850M Platform size depends on facilities to be installed on top side eg. Oil rig, living quarters, Helipad etc. Fixed structures that extend to the Seabed: Steel Jacket, Concrete gravity Structure, Compliant Tower Structures that float near the water surface: Tension Leg platforms, Semi Submersible, Spar and Ship shaped vessel (FPSO) .

Offshore structure shall be designed for following types of loads: 1. Permanent (dead) loads. 2. Operating (live) loads. 3. Environmental loads a) Wind load b) Wave load c) Earthquake load 4. Construction - installation loads. 5. Accidental loads.

PLATFORM PARTS • Facilities are tailored to achieve weight and space saving • Incorporates process and utility equipment 1. Drilling Rig 2. Injection Compressors 3. Gas Compressors 4. Gas Turbine Generators 5. Piping 6. HVAC 7. Instrumentation • Accommodation for operating personnel. • Crane for equipment handling • Helipad

Different types of Offshore Structures:An offshore platform, often referred to as an oil platform or an oil rig, is a large structureused to house workers and machinery needed to drill wells in the ocean bed, extract oil and/ornatural gas, process the produced fluids, and ship or pipe them to shore. Depending on thecircumstances, the platform may be fixed to the ocean floor, may consist of an artificial island,or may float.Most offshore platforms are located on the continental shelf, though with advances in

technology and increasing crude oil prices, drilling and production in deeper waters has becomeboth feasible and economically viable. A typical platform may have around thirty wellheadslocated on the platform and directional drilling allows reservoirs to be accessed at bothdifferent depths and at remote positions up to 5 miles (8 kilometers) from the platform.

A fixed platform is a type of offshore platform used for the production of oil or gas. Theseplatforms are built on concrete and/or steel legs anchored directly onto the seabed, supporting adeck with space for drilling rigs, production facilities and crew quarters. Such platforms are, byvirtue of their immobility, designed for very long term use. Various types of structure are used,steel jacket, concrete caisson, floating steel and even floating concrete. Steel jackets are verticalsections made of tubular steel members, and are usually piled into the seabed. Concrete caissonstructures, pioneered by the Condeep concept, often have in-built oil storage in tanks below thesea surface and these tanks were often used as a flotation capability, allowing them to be builtclose to shore and then floated to their final position where they are sunk to the seabed. Fixedplatforms are economically feasible for installation in water depths up to about 1,700 feet (520m).

Gravity PlatformPractically, this type of structures are being used in the harsh environments such as North Sea.Also known as Gravity Base Structure (GBS) platform, it is design to withstand the loads(environment + iceberg) and also for the storage of its base support. Normally GBS isapplicable for water depths up to 300 meters. When completed, a GBS is towed to its intendedlocation and sunk. GBS = TOPSIDE + CONCRETE BASE.

A compliant tower (CT) is a fixed rig structure normally used for the offshore production ofoil or gas. The rig consist of narrow, flexible (compliant) towers and a piled foundationsupporting a conventional deck for drilling and production operations. Compliant towers aredesigned to sustain significant lateral deflections and forces, and are typically used in waterdepths ranging from 1,500 and 3,000 feet (450 and 900 m). At present the deepest is Baldpatein 580 m of water.With the use of flex elements such as flex legs or axial tubes, resonance is reduced and wave

forces are de-amplified. This type of rig structure can be configured to adapt to existingfabrication and installation equipment. Compared with floating systems, such as Tension-legplatforms and SPARs, the production risers are conventional and are subjected to less structuraldemands and flexing. This flexibility allows it to operate in much deeper water, as it can'absorb' much of the pressure exerted on it by the wind and sea. Despite its flexibility, thecompliant tower system is strong enough to withstand hurricane conditions.

A semi-submersible is a specialised marine vessel with good stability and seakeepingcharacteristics. The semi-submersible vessel design is commonly used in a number of specificoffshore roles such as for offshore drilling rigs, safety vessels, oil production platforms andheavy lift cranes.These platforms have hulls (columns and pontoons) of sufficient buoyancy to cause thestructure to float, but of weight sufficient to keep the structure upright. Semi-submersibleplatforms can be moved from place to place; can be ballasted up or down by altering theamount of flooding in buoyancy tanks; they are generally anchored by combinations of chain,wire rope and/or polyester rope during drilling and/or production operations, though they canalso be kept in place by the use of dynamic positioning. Semi-submersibles can be used inwater depths from 200 to 10,000 feet (60 to 3,050 m).Jack-up platforms (or jack-ups), as the name suggests, are platforms that can be jacked upabove the sea using legs that can be lowered, much like jacks. These platforms are typicallyused in water depths up to 400 feet (120 m), although some designs can go to 550 feet (170 m)depth. They are designed to move from place to place, and then anchor themselves bydeploying the legs to the ocean bottom using a rack and pinion gear system on each leg.

A drillship is a maritime vessel that has been fitted with drilling apparatus. It is most oftenused for exploratory offshore drilling of new oil or gas wells in deep water or for scientificdrilling. The drillship can also be used as a platform to carry out well maintenance orcompletion work such as casing and tubing installation or subsea tree installations. It is oftenbuilt to the design specification of the oil production company and/or investors, but can also bea modified tanker hull outfitted with a dynamic positioning system to maintain its position overthe well.

The greatest advantages these modern drillships have is their ability to drill in water depths ofmore than 2500 meters and the time saved sailing between oilfields worldwide. Drillships arecompletely independent, in contrast to semi-submersibles and jackup barges. In order to drill, amarine riser is lowered from the drillship to the seabed with a blowout preventer (BOP) at thebottom that connects to the wellhead. Drillships are just one way to perform exploratorydrilling. This function can also be performed by Semi-submersibles, jackup barges, barges, orplatform rigs.

A Floating Production, Storage and Offloading (FPSO) unit is a floating vessel used by theoffshore industry for the processing and storage of oil and gas. The FPSO vessel is designed toreceive oil or gas produced from nearby platforms or subsea template, process it, and store ituntil the oil or gas can be offloaded onto a tanker or transported through a pipeline. FPSO's canbe a conversion of an oil tanker or can be a vessel built specially for the application. A vesselthat is used for oil storage purposes only is designated a Floating Storage Unit (FSU). FPSOsare preferred in frontier offshore regions as they are easy to install, and do not require a localpipeline infrastructure for exporting the oil and gas.

A Tension-leg platform or Extended Tension Leg Platform (ETLP) is a vertically mooredfloating structure normally used for the offshore production of oil or gas, and is particularlysuited for water depths greater than 300 metres (about 1000 ft) and less than 1500 meters(about 4900 ft). Use of tension-leg platforms has also been proposed for wind turbines.The platform is permanently moored by means of tethers or tendons grouped at each of thestructure's corners. A group of tethers is called a tension leg. A feature of the design of thetethers is that they have relatively high axial stiffness (low elasticity), such that virtually allvertical motion of the platform is eliminated. This allows the platform to have the productionwellheads on deck (connected directly to the subsea wells by rigid risers), instead of on theseafloor. This allows a simpler well completion and gives better control over the productionfrom the oil or gas reservoir, and easier access for down hole intervention operations.

Spars are moored to the seabed like TLPs, but whereas a TLP has vertical tension tethers, aspar has more conventional catenary mooring lines. Spars have to-date been designed in threeconfigurations: the "conventional" one-piece cylindrical hull, the "truss spar" where themidsection is composed of truss elements connecting the upper buoyant hull (called a hardtank) with the bottom soft tank containing permanent ballast, and the "cell spar" which is builtfrom multiple vertical cylinders. The spar has more inherent stability than a TLP since it has alarge counterweight at the bottom and does not depend on the mooring to hold it upright. It alsohas the ability, by adjusting the mooring line tensions (using chain-jacks attached to the

mooring lines), to move horizontally and to position itself over wells at some distance from themain platform location. The first production spar was Kerr-McGee's Neptune, anchored in1,930 feet (588 m) in the Gulf of Mexico; however, spars (such as Brent Spar) were previouslyused as FSOs. Eni's Devil's Tower is located in 5,610 feet (1,710 m) of water, in the Gulf ofMexico, and is currently the world's deepest spar; however, when Shell's Perdido spar isinstalled, it will be the deepest at almost 8,000 feet (2,438 m).