Introduction to Fixed Offshore Platform
Offshore Platform is a comprehensive structure that has no permanent access to the shore or dry land for oil and gas purposes. Generally, fixed and floating platform are two options which could be selected after considering particular requirements criteria. In order to install its structure permanently to the sea-bad, fixed offshore platform use some piles as foundation. Approximately 500 meter is the maximum of sea level that is still acceptable in using this type of platform for oil and gas facilities.
As shallow water platform, fixed structure may be grouped into several type based on the quantity of its leg/pile. Those structures are supposed to withstand certain load during fabrication, construction, installation, and operation. Gravity, environmental, earthquake, and fatigue should be concentrated for operation intention. Self weight, live load, piping weight, electrical and instrument weight, and mechanical weight should be considered as gravity load. Wind, wave, and current are the main interests for environmental load concern. Ice load may also be calculated as environmental consideration in some offshore area. Time history or response spectra method could be selected for earthquake judgment. Fatigue damage would be occurred due to cyclic load on the joint intersections.
Normally, platform is divided into three major components which are topside/deck, sub-structure/jacket, and foundation. Wellhead platform and living quarter platform could be distinguished from different category of deck. Piping, electrical, instrument, and mechanical equipment are placed on the appropriate deck in wellhead platform. At least two level of deck can be found for accommodating those devices which are main deck and cellar deck. Small wellhead access deck is also supposed to set up for Christmas tree access. Its equipment is used for drilling and production accordingly. On the other hand, living quarter platform should be built for office representative. Sport facilities could also be enjoyed as entertainment for offshore crews. Helideck can also be found in some platform for transportation by chopper.
Sub-structure has the important function for transferring load to the foundation. Deck and sub-structure is connected by stubbing guide in the working point elevation. Jacket walkway and boatlanding are the primary part of the sub-structure. On mudline elevation, mudmet should be designed for on bottom stability purpose before piling, as well. Mostly, pile is the best option for offshore fixed platform foundation. There are some concepts of connection between sub-structure and pile. Pile can also be sub-structure section in monopod platform while it is wrapped by leg in jacket type. Grouted and un-grouted pile would be the alternative decision in designing jacket platform type.