Hydraulic and electrical functions need to controlled and monitored from the host facility control station.
The control station master control station or MCS for the production control system can be located on a platform or on a floating facility such as an FPSO.
Selecting the correct type of control system is critical to ensuring safe, efficient and long term reliability of the system. Critical components of the system can be retrieved to surface for maintenance and replacement as required and the graphic below shows the major components of the subsea control system. In a subsea system control system, typically hydraulic and electrical controls umbilicals will be connected between subsea components using relatively short lengths of umbilical.
For this requirement Hydraulic and Electric Jumper Umbilicals are used. These can be located on subsea distribution modules located on the seabed positioned close to the subsea components e. Christmas tree or manifold. Traditional developments have instruments for pressure and temperature monitoring of the produced fluids located on the tree.
The integrity of the production tubing is evaluated by monitoring the pressure between the production tubing and production casing through sensors located in the XT. For the production path, instruments are normally located down-stream the production master valve.
The condition of the electrical supply through the umbilical is monitored from the topside Electrical Power Unit. Today the subsea trees and manifolds are getting more instruments and are also often equipped with a multiphase meter which is getting more popular as they have become more accurate and reliable in operation.
The multiphase meters have been installed for better production optimization and to some extent for production allocation when different Operators are producing through same infrastructure to the processing unit. With the introduction of subsea processing facilities, there will also be an increased need for electric power to operate electric motors and separator systems and their control systems.
For signal transmission the industry is moving from communication using copper wire to fibre optic cables due to the massive increase in transmission capacity and speed. The development of subsea production systems requires specialized subsea equipment.
The deployment of such equipment requires specialized and expensive vessels, which need to be equipped with diving equipment for relatively shallow equipment work, and robotic equipment for deeper water depths. Subsea installation refers to the installation of subsea equipment and structures in an offshore enviromnent for the subsea production system.
Installation in an offshore environment is a dangerous activity, and heavy lifting is avoided as much as possible. This is achieved fully by subsea equipment and structures that are transmitted to the installation site by installation vessels. Special vessels can run the trees and rigless installation and subsea equipment to be installed is categorized based on weight, shapes volume versus line type , dimensions, and water depth deep versus shallow.
The buildup of wax, scale and hydrate deposits in wells, subsea flowlines, wellheads, risers and surface equipment is a special problem for subsea production where temperatures are quite low and the pressurized fluids are an un-processed wellstream. Flow assurance is the new term referred to the study of the complex phenomena involved with steam of produced fluids in order to guarantee the maximum flow. For an effective subsea production, it is necessary to identify the potential for and quantify the magnitude of all of these solid depositions in the production system.
Changing pressures, temperatures and production flow profiles over the field life also complicates the posed difficulties. It is also necessary to control and predict potential problems during transient flow regime , which means that the system should be able to shutdown and restart in a controlled manner. There are many considerations that go into designing an effective flow assurance program for a field and these include considering the requirements for all parts of the system for the entire production life.
Some of the considerations for an effective flow assurance program are listed below:. The petroleum industry are developing distributed sensors and other devices that can warn the operators of impending flow blockages. Thermal insulation and protective coating can be applied to components subjected to deepwater immersion.
Subsea Thermal Insulation with materials of superior thermal properties helps delay the onset of hydrate formation and wax deposition or DEH Direct electric heating is also an alternative mature and growing technology which can keep fluid temperatures above the hydrate formation temperature and above the wax appearance temperature. These developments are often characterized by utilizing conventional and cost effective solutions and may therefore not be regarded as technology drivers, and due to known production regime, these developments may be developed efficiently and with little effort spend on tailored design The Norwegian Continental Platform NCS is a region where subsea development have been adopted and represents an area of pioneering subsea technology application.
Left :Offshore rigs and structure and subsea production systems Right: Subsea Drilling System can be provided in different wellhead systems, for example FMC Technologies provides: Standard, Rigid Lock, and Large Bore as shown in the figure below, each of the system has different characteristics and finds diverse application. Subsea wells, and processing and flow—line systems must be installed at the seabed at depths well beyond the capability of any diver. They need to be operated reliably and safely over periods of up to twenty years.
The requirement is thus for remotely operated and smart systems for both the installation and operation of these equipments. In many locations, in particular in very deep waters, where there are no pipelines taking the product ashore, reliance is placed on floating production, storage and offloading FPSO vessels.
These vessels process the oil from the wells and tranship it to a shuttle tanker or export pipeline to take ashore.
Other work for offshore engineers includes the harnessing of wave, current and wind energy, and, the recovery of minerals from the seabed in shallow or deep water. Whatever the work, equipment must be designed, built, installed and operated so that it can work reliably, safely and efficiently for perhaps long periods of time without maintenance, and with limited supervision.
This is the challenge of offshore engineering! Offshore engineers often have a broad—based knowledge across a range of subjects including structural design, dynamic loading and motion response, construction and quality assurance, materials technology, control engineering, fluid dynamics and reliability, combined with project management skills.
A number of water-depth records were set for steel-jacket structures. In , the Hondo platform was installed as a two-piece jacket in ft of water off the coast of California. Two years later, the Cognac platform was installed in three pieces in 1, ft of water in the Gulf of Mexico. As fabrication, transportation, and installation technology advanced, it became possible to install single-piece structures in deep water.
In the early s, the Harmony and Heritage platforms were installed single-piece in 1, ft of water off the coast of California. However, the record for the largest single-piece jacket ever installed rests with the Bullwinkle platform, installed in 1, ft of water in The platform deck gives little clue as to the size of the substructure below see Fig.
In the Gulf of Mexico, a large number of minimum facility platform designs were adopted in the s and s to exploit marginal fields. As the North Sea industry matured in the s, minimum facility platforms gained favor as flow assurance improved and as the need to minimize capital expense CAPEX for marginal fields was acknowledged.
It became clear in the s that the water depth limit for fixed platforms, from a functional and an economic perspective, was restricted to 1, ft. Exploration drilling was progressing in water depths beyond this limit, and offshore engineers began developing platform designs that circumvented the problems associated with fixed platforms beyond 1, ft. The Lena compliant guyed tower was developed and was installed in 1, ft of water in the Gulf of Mexico in The guys provided vertical and lateral stability for the structure.
In , the Baldpate and Petronius compliant towers were installed in 1, and 1, ft of water, respectively, in the Gulf of Mexico; Baldpate is illustrated in Fig.
In the s and s, for discoveries remote from existing infrastructure, ship-shaped floating production, storage, and offloading systems FPSOs provided a solution to economic development as they offered oil-storage capability. In , off the coast of Spain, oil was drawn from a subsea well in ft of water into a tanker moored to an oscillating mooring tower. Other similar developments followed e. Because of the motions of the FPSO vessel, the concept required that the wellheads be located on the seabed, known as wet or subsea wellheads.
A variant to this approach was the use of dry wellheads, located on a fixed steel platform, in combination with an FPSO [e. SBM , Marly, Switzerland]. Up to , FPSOs were based on conversion of existing tankers. In , Golar Nor demonstrated that a purpose-built FPSO, with oil, gas, and water separation, was economically feasible for production in the harsh North Sea environment. An alternative concept in regions with an economically accessible infrastructure was the semisubmersible floating production system FPS.
This system consists of a buoyant floating facility moored to the seabed. The system offers reduced motions compared to an FPSO. In , a production semi-submersible was used in the Argyll field in the North Sea in ft of water.
Two years later, the first production semisubmersible was placed offshore Brazil in the Enchova field. From that time, the use of production semisubmersibles gained increasing popularity, particularly offshore Brazil in water depths up to 6, ft.
In the Gulf of Mexico, the pioneering application of a semisubmersible was at a Green Canyon field for extended well testing in 1, ft of water from to However, initial deepwater production from floating systems in the Gulf of Mexico was dominated by an alternative concept known as the tension leg platform TLP. A TLP is a vertically moored, buoyant structure anchored to the seabed with vertical taut steel tendons.
The system relies on the tension in the tendons for its stability. The reduced motions permit the use of dry wellheads. As with an FPS, a TLP has no storage capacity and, therefore, requires a separate storage tanker or a pipeline or shuttle tanker for export.
Following large-scale TLP model testing offshore California in and , the concept was adopted for the first time in the Hutton field in the North Sea in Located in ft of water, the Hutton field could have been developed using a conventional steel-jacket structure, but the harsh North Sea environment was judged to provide the ideal test bed for the TLP design prior to venturing into deeper waters.
Since , a number of TLPs have been installed in deep water in the North Sea, Gulf of Mexico, and offshore Indonesia in water depths ranging from 1, to almost 4, ft. With the focus in the late s and throughout the s firmly on the development of deepwater production technology, a number of new concepts, or variants of established concepts, have emerged.
Of these, the most widely used has been the deep draught caisson vessel DDCV or spar concept. The spar is a floating system comprising a deep draught cylindrical hull caisson , which supports a topsides structure, and is moored using a system of mooring lines from the hull that are anchored to the seabed.
Spars have proved a popular development choice in the Gulf of Mexico, where three classic spars and six truss-spars have been installed or sanctioned for installation as of in water depths up to 5, ft; see Fig. Other recent technology development efforts have focused on a variant of the semisubmersible FPS concept.
0コメント