Offshore Platform – at a Glance

Offshore platform has been used in oil and gas industry as early as 1930 in Venezuela. The first offshore platform was made by wood material. The steel type platform was then used in 1947 in a 6 m depth of water in the Gulf of Mexico. Since that period, various types of offshore platform has been developed and used as main offshore facility in oil and gas industry. Offshore platform can be used in many ways. A full offshore oil and gas facility can have many platforms such as quarters platform, wellhead platform, process platform, compressor platform, etc.

Type of structure and the support configuration of offshore platform are in consideration with depth and difficulties in erecting the platform. Therefore, there are many types of offshore platform. Based on the type of structure, offshore platform can be divided as :

• Concrete gravity platform
• Fixed steel platform
• Semi submersible platform
• Tension leg platform
• Guyed tower platform

A ‘Statfjord’ gravity based structure under construction in Norway.

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1, 2) conventional fixed platforms; 3) compliant tower; 4, 5) vertically moored tension leg and mini-tension leg platform; 6) Spar ; 7,8) Semi-submersibles ; 9) Floating production, storage, and offloading facility; 10) sub-sea completion and tie-back to host facility.

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In addition to that classification, depending on the number of legs & jacket type, fixed offshore platform can be divided into :

• Monopod platform
• Bipod platform
• Tripod platform
• 4, 6, or 8 pile platform

A common offshore platform is consisted of platform deck, jacket, and pile. Deck is the place where all production equipments are placed. Jacket is a tubular steel structure that serves as a lateral load support for the platform while pile serves as a vertical load support. For come cases, jacket is not used because the lateral load of platform is neglect able.

In a common Offshore platform, deck, jacket, and pile are fabricated onshore. The first stage of platform erection is transporting the jacket and putting it in the designated place. After the jacket is fixed in the right place, pile is driven via the jacket hollow tube to the sea bed. Finally, the deck part is placed and connected at the top of support structure.

For safety and ergonomic reasons, platform layout should be carefully designed. Platform north should be facing to deeper water. This north part is also used as the area for jack up drilling rig and foundations spud can or mat. The south side platform is used for boat berthing, pipeline riser and subsea pipeline. Layout of platform should also be designed by considering drilling sequence, prevailing wind, and other utility such as helipad.

Load acting on platform is vital in a platform’s design stage. In designing a platform, load can be divided to load at deck structure and load at jacket structure. In general, the working load in an offshore platform consisted of the following load.

Load at Deck structure:

• Topside load : Deck structure, piping, equipment, life load, crane load, helicopter load, drilling work over load.
• Lateral load : Wind and earthquake.

Load at Jacket structure:

• Vertical load : Deck structure and buoyancy
• Lateral load : Wind, wave, current, earthquake, and added hydrodynamic mass.

Some of applicable engineering standards for offshore platform design are:

• API RP2A Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms
• AISC Specifications for Design, Fabrication and Erection of Structural Steel Buildings
• API Spec 2B, Fabricated Structural Pipes
• AWS D 1.1, section 8 and 10
• ISO 19902   Petroleum and Natural Gas Industries – Fixed Steel Offshore Structures
• ISO 19901-2      Petroleum and Natural Gas Industries – Specific requirements for offshore structures Part 2 Seismic Design Procedures and Criteria

Gunanusa Yard Visit

Last month, I was given a chance to visit PT Gunanusa Utama fabrication yard in Serang, Banten. Currently, they are working on three major projects so it was a perfect time to see how they handle their project. I and peoples from engineering team in the company where I worked were invited to the yard as Gunanusa’s routine occasion to strengthen the relation to their industry partner.

What is Gunanusa actually? Peoples with background in Oil & Gas industry must have known it. Gunanusa is a heavy engineering and steel fabrication company based in Indonesia. Established in 1983, its main activity is the fabrication of offshore oil and gas platforms, though, the company also has successfully delivered a number of onshore plants on a turn-key basis. Occupying an area of 18 ha with two load out jetty, working hours up to 24 hours a day, and thousands of personnel working on shift basis, the company really amazed me as they demonstrated their capability of working many projects from all over the world.

It took 2 hours drive from Jakarta to their fabrication yard in Serang. The yard is located near the shore in since water transportation is used to transport the fabricated platform to all over the world. Right after we arrived at the site, their representative greeted and took us to their meeting room for a brief presentation about the company. They informed us their profile, activity, and current project.

After the presentation finished, we headed to the fabrication yard and saw three major offshore platforms they are working on. Currently, the major projects they are working on are :

1. ONGC – ICP-R PLATFORM

Oil and Natural Gas Corporation Limited (ONGC), India largest oil and gas company, awarded Gunanusa-AFCON Joint Venture to execute the ICP-R Process Platform Project in Mumbai High North, India.

2. PTTEP- Quarter Platform South (QPS) and Flare Platform South (FPS)

PTT Exploration and Production Plc (PTTEP) operates the Greater Bongkot South (GBS) gas field in the Gulf of Thailand. For the Development Phase 4a of GBS, Gunanusa has been awarded the contract for Supply and Installation of Quarter Platform South (QPS) and Flare Platform South (FPS), with the scope of work to perform Engineering, Procurement, Construction, Installation, Hook Up and Commissioning.

3. HESS – Ujung Pangkah Central Processing Platform (CPP) and Auxiliary & Utility Platform (AUP)

Hess operates the Ujung Pangkah area at East Java in shallow water at 10 m depth. Gunanusa has been awarded to perform Engineering, Construction, Hook Up and Commissioning of Central Processing Platform (CPP) and Auxiliary & Utility Platform (AUP).

Below are some snapshots of the yard. Thank you pak Icang for providing these awesome pictures.

After we finished circling their fabrication yard, we went back to the meeting room and had another discussion about their current project. The discussion concluded our visit. Then, after 4 hours of drive, we arrived back at Jakarta. The visit really improves my knowledge of steel structure which I will mostly deal with.