OFFSHORE ENGIEERING_Monday

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OFFSHORE ENGIEERING - Introduction




The first steel platform in open water, completely out of sight of land, was installed in 1947 after World War II in the Gulf of Mexico. The platform was installed off the coast of Louisiana in 6 m of water. This was followed closely by another installation in 15 m of water. Oil activities in the Persian Gulf and North Sea saw the rapid development of offshore structures in the 1970’s, and the advances into deeper water depth of the oceans. 4
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OFFSHORE ENGIEERING - Introduction



Drilling in the early days took place near beaches, inland lakes and swamplands. In 1869, T.F. Rowland installed a four legged tower structure resembling modern offshore rigs in very shallow water. In the early 1900’s, drilling was also carried out on piers that extended from the beach along the coastline of California. The early structures were mainly made of timber. By the 1930’s, more and more ‘over-water’ drilling activity took place in marsh and swamplands of South Louisiana.


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OFFSHORE ENGIEERING - Offshore Structures
– 1. Fixed steel structures

These multi-jacket installations tend to be restricted to shallow water developments where the construction costs are considerably less than their deep water counterparts. Whilst the fixed steel structure is likely to remain as the industry’s first choice of installation design based on operational requirements, its future use may well be restricted to the development of large fields located in intermediate water depths where a substantial return on the capital sums invested can be guaranteed. The ever changing demand of the offshore industry has spawned a number of competitors more ideally suited to specific applications.
OFFSHORE ENGIEERING - Offshore Structures – 1. Fixed steel structures

The traditional offshore installation shown utilizes a welded steel, tubular framework or jacket to support the topside facilities and this arrangement is referred to as a fixed steel structure. The topside facilities will vary slightly depending on whether it is an oil or gas producing installation but they will include hydrocarbon process equipment, power generation, a heli-deck, and accommodation and hotel services designed to cater to the need of the personnel employed in the operation and maintenance of the installation.


OFFSHORE ENGIEERING - Offshore Structures
– 2. Concrete gravity base structure

This type of installation was pioneered by the Norwegians who had experienced difficulties in producing the enormous quantities of high quality steel products and the large skilled workforce that are essential ingredients to the success of steel fabrication projects. Also, the presence of the Norwegian Trough, a large undersea valley, made the laying of the sub-sea pipelines an expensive and challenging operation so the void spaces which feature so prominently in the design of a GBS provide valuable storage space for the crude oil prior to discharge into oil tankers via a single buoy mooring (SMB).
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OFFSHORE ENGIEERING - Offshore Structures
– 2. Concrete gravity base structure

The concrete structure has emerged as a viable alternative to the steel jacket but they both tend to suffer from the same inherent disadvantages when used to develop deep water reserves. The scantling requirements of structures that are capable of withstanding the extremes of whether conditions associated with the North Sea are considerable and this is reflected in the construction costs. Whilst the vast majority of fixed offshore platforms employ a tubular steel jacket to support the topside facilities, a number of installations have been constructed using a base manufactured from reinforced 11 concrete.
Development of offshore platforms with increasing water depth
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OFFSHORE ENGIEERING - Offshore Structures


The structure shown opposite is instantly recognizable as an offshore rig. This type of structure, more correctly described as a fixed steel offshore installation or platform forms the backbone of the offshore industry and there are in excess of 7,000 such structures dotted about the oceans of the world.
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OFFSHORE ENGIEERING - Offshore Structures
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Fixed steel structures Concrete gravity base structure Tension leg platform Semisubmersible vessel Floating production systems Self-elevating jack-up Single point mooring Spar Platform 7