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PANORAMA: 1996

At the Front of Subsea Technology
by Edward Crowley
Specialist writer on maritime topics

Many projects involving British companies are at the forefront of underwater technology in the fields of survey work, maintenance and inspection, surveillance and remote control.

One current project being done by GEC-Marconi and assisted by subsea consultants Kordale Engineering is the development of autonomous (free swimming) Underwater Vehicle (AUV) . This vehicle is being developed to undertake autonomous oilfield pipe line survey missions, with minimal weather dependence and without the indeed for surface support vessels. A substantial reduction in operating costs would be achieved.

Built and Tested
The base vehicle has already been built and tested by GEC -Marconi Naval Systems and is being made available for the project. Development work will centre on the attainable and specifically defined goals of optimising offshore launch and recovery, and navigation techniques and selecting suitable data gathering instrumentation.

Important factors influencing the viability of a practical AUV system include:

Energy sources - how is the AUV powered?
It has been designed to accept either lead/acid batteries or high-energy sodium sulphur cells designed for road vehicles.

Communications - how are commands given and data received?
It will be programmed to follow the pipeline, carry out the desired survey and return to the launch point. As there is no strict requirement for "real-time" monitoring of the mission, survey data will be collected and stored on board for subsequent downloading following vehicle recovery.

Navigation how does it find out its position and course?
The output from the development work on the navigation system will be a fully integrated navigation suite using Kalman filter techniques to optimally select from various sensor signals. The resulting system will be mathematically modelled using GEC-Marconi's existing AUV real-time simulator.

Sensor systems how is data obtained?
A suite of instruments will be selected from sensors which may include: high resolution side-scan sonar, sub-bottom profilers, magnetometers , low-light cameras and multibeam echo sounders. The unprocessed data will require temporary on-board storage and the options of digital tape high-capacity hard disk and optical disk will be assessed to determine the most suitable medium.

Launch and recovery - how is this achieved safely?
The project will develop the design of a launch system selecting from the "garage" cradle or simple release sling options. In all cases it is envisaged that either a small "HIAB''-type arm or platform crane will be used to lift, lower and position the AUV and associated launch mechanism. For recovery the AUV will return to the launch point. The capture may be by "soft" entrapment easel the release of a pick-up line and buoy or the reparking of the AUV in the launch ''garage''. Control will be by radio, acoustic mediated commands or via a pre-programmed recovery manoeuvre sequence in the vehicle's software.

Robot Manipulator
The ARM (Automated Remote Manipulation) Project aims to produce a new kind of subsea inspection system, capable of doing advanced cleaning and inspection tasks in areas beyond the reach of divers, It will also be able to work at the same operating depths as divers but at lower cost and with greater safety and reliability. In particular, it was a requirement to be able to clean and inspect complicated node welds on subsea structures - these nodes generally consisting of a number of intersecting tubulars and the welds therefore being of a very complex shape.

Special Toolskid
The ARM consists of an advanced robotic manipulator mounted on an extend/roll mechanism. This is part of a special toolskid carried by a standard workclass Remote Operated Vehicle (ROV). The manipulator was developed specially for inspection by Slingsby Engineering Ltd. It is controlled by a unique, PC-based robot system developed by Technical Software Consultants with sponsorship from Mobil North Sea and the Offshore Supplies Office.

The robot system provides a full 3D graphical model of the ROV, toolskid, manipulator and workpiece node. It provides full manual, semi-automatic and robotic control of the manipulator (with collision detection).

The complete ARM inspection toolskid has undergone dry and wet factory inspection tests and it is planned for the system to be mounted on a workclass ROV at the end of 1995 for major wet-tank trials. It will then be used to inspect Mobil's Beryl Bravo platform in 1996.

There are many production challenges in deep water oilfield developments. Typically, reservoirs are produced using subsea completions where subsea wells are concentrated in clusters. Flowlines from individual wells are combined in a manifold at the subsea production control centres.

Multiphase pipelines connect the production control centre to the nearest platform which can be some distance away - where separators process the fluids. Sometimes the produced fluid is handled by a floating production system or by a tanker loading terminal.

Integrated Surveillance
SensorDynamics has developed a unique sensor deployment system that will deal with the integrated surveillance of subsea oil and gas production. The system together with fibre-optic temperature, pressure, acoustic and seismic sensors - will offer solutions to many of the challenges associated with subsea production, even in deep waters. These challenges include leak detection and location, wellhead pressure, multiphase flow, valve and choke, hydrate and wax drop-out, sand production, gas lift and ESP monitoring.

This innovation from Ocean Technical Systems enables a subsea wellhead to be controlled from the surface using a unique design of tethered buoy, it offers a cost-effective solution for the economic development of marginal oil and gas fields.

The system was developed as a result of studying the needs of the Subsea Production Systems Market and it addresses the steadily growing requirements for the use of subsea well completions, It allows offshore operators and engineering contractors to optimise subsea developments and is particularly appropriate when a new development can be tied back to an existing offshore facility.

Using proven technology already installed by Ocean Technical in over 60 locations worldwide, it is possible to eliminate the conventional seabed umbilical and provide an inherently safe and redeployable system while saving about 50% in capital expenditure.

As an unmanned facility, it requires far less equipment that traditional solutions and offers the great advantage of modular repair. The total installation cost is extremely low and, as a very flexible solution it can be moved and re-used very cost effectively.

  

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