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A Hover-Capable Autonomous Inspection Vehicle
New Class of Vehicle Will Allow Subsea Inspections Without a Dedicated Infield Support Vessel, Reducing Costs

John Mair
Technology Development Director
Subsea 7
Aberdeen, Scotland

Ioseba Tena
Sales Manager
SeeByte Ltd.
Edinburgh, Scotland

The offshore oil and gas exploration and production industry is installing a growing amount of infrastructure of increasing complexity on the seabed, in deeper waters and with increased criticality to successful operations. Installation, support and maintenance of this equipment is currently carried out using specialized vessel-based remotely operated vehicles (ROVs) and/or diving operations.

Subsea 7 and SeeByte intend to provide these same services with a hover-capable inspection autonomous underwater vehicle (AUV) operating from a host facility, such as a floating production platform.

This vehicle, named the autonomous inspection vehicle (AIV), will have the ability to be launched directly from the host facility with existing infrastructure used to lower equipment to the seabed, providing significant advantages, as routine or unplanned inspections can be easily and frequently carried out without a dedicated infield support vessel.

The AIV, which is now in the preproduction phase, will be going in the water soon. It is planned to go through de-risking trials in 2011 and to be ready for operations in 2012.

CAD drawing of the AIV.

Initial PAIV Development
Subsea 7 and SeeByte have developed a de-risking plan to demonstrate operating methods and qualify the technology for use. To achieve this, a prototype AIV (PAIV) was developed as a test bed and went through in-water testing.

Initial development on the PAIV was based on a torpedo-shaped AUV to help develop intelligent payload systems, such as SeeByte's SeeTrack AutoTracker, which analyze side scan sonar and multibeam data in real time to detect and track pipelines. The output from the tracker is fused with the legacy data and is used to plan an optimal route for the AUV to survey the pipeline.

The PAIV is based on a converted inspection-class ROV and, as such, does not have the hydrodynamic form that might be expected of a self-powered vehicle. As a prototype, the PAIV's primary function is to provide a stable and robust platform to carry the sensors and systems required by the SeeByte software during the de-risking phase of the development. Its shape and form ensure it is more efficient for in-field work than a torpedo-shaped vehicle that is unable to match its hovering or maneuvering capabilities. The production AIV will be of a shape and form that will be more efficient for the task.

PAIV Sensor and Control Systems
The PAIV is fitted with an array of sensors that provide the vehicle control system and inspection system with information. Sensors in this array include those for video and acoustic imaging, heading, depth and position, communication and navigation.

The control system for PAIV has been developed by SeeByte. The system is constructed using a modular software architecture that has at its core a series of modules that dynamically control the vehicle's position, allowing it to be navigated around a world model, which is a model that represents the information needed by the vehicle to understand its operating environment. These modules are linked to the vehicle's actuators and sensors, closing the loop between the real world and the world model. It can also be interfaced to the geographic information system of a client's integrity management systems. Updates from the model have the potential to highlight changes symptomatic of anomalies.

This control architecture has allowed for the testing of the vehicle control system to be accelerated, as all functions can be fully exercised in virtual and hardware-in-the-loop environments. These can then be followed by in-water testing of the vehicle for final qualification.

Field Testing
The last phase of the technology development was focused on de-risking and demonstrating the world model. After development, simulation testing and hardware-in-the-loop testing, a final set of underwater tests and demonstrations were carried out in November 2009 in Loch Earn in Perthshire, Scotland. This stretch of open water provided the ideal trials area.

A series of four artificial risers installed in the loch provided the targets to be inspected, one of which would be inspected using the world model.

The key points demonstrated were the creation of a 3D model that represented the installed structures and the continual navigation correction, as the world model information controlled the vehicle position by fusing computed position with sensor data to minimize drift. Decision making was also demonstrated by identifying the correct riser to inspect by fusing sensor data with the model, as well as 3D inspection of the riser and safe transit back to the recovery point.

The PAIV de-risking vehicle performing tank trials.

Typical AIV Mission Elements
During a field development, there are some basic tasks that the AIV will have to carry out during every mission and others that will be mission specific. It is important to note that, unlike a seabed survey, where an AUV's task is to find out what is on the seabed, the AIV will be deployed into a field development where the seabed infrastructure is relatively well understood.

Some typical mission elements, and the advantages of an AIV as compared to other systems, are described below:

Launch and Recovery. The launch and recovery of AUV systems is currently recognized as being one of the major difficulties in operations. The AIV solution adopted in this instance is both simple and robust. It taps into the techniques developed during many years of ROV operations utilizing a deck winch or vessel crane.

Navigation. Once the AIV is on the seabed, it will have a position error limited to a few tens of meters. This accuracy is sufficient to seed the initial frame of reference for the vehicle to start navigating. As it departs to locate the start point of its first task, it uses real-time data from the vehicle sensors to identify known features, then uses this information to refine its position estimate. Even though the intelligence in the onboard software to achieve this is very advanced, the process adopted is well understood. This method of navigating is different from the prescriptive script-based navigation of survey AUVs, which have no real knowledge of the outside world other than depth, heading and distance from a known start point.

Inspection. As the AIV navigates closer to the start point of the first task, the position estimate and sensor data interpolation reaches a confidence level that positively identifies the start point of the task. When this occurs, the vehicle will navigate relative to the object to be inspected using sensor data as a position input to the control system. In the case of a riser inspection, for example, the riser will be tracked in three dimensions and the vehicle positioned to optimize the inspection data capture. This information is stored digitally on board the vehicle. This technique of sensor-enhanced navigation, positive identification of the task start point and relative sensor-based positioning of the vehicle while on task provides the vehicle with an accurate navigation system capable of removing accumulated dead-reckoned errors.

Intervention. All indicators point to an AIV development following the same path ROV evolution has taken, beginning with observation tasks, moving to simple manipulation then to intervention (look, touch and act). The intelligent navigation and accurate positioning control of the vehicle provides a suitable platform for deploying subsea intervention tools. Development of docking techniques is already well advanced. Several publicized research projects have already demonstrated the final maneuvers needed to successfully dock tools into subsea structures. This work has also been added to by intervention tooling Subsea 7 engineers, who have applied their operational experience to the solution, including docking into American Petroleum Institute interfaces.

Communications. When the vehicle is subsurface, communication is limited to acoustic or short-range electromagnetic modems. The acoustic systems are to be used for long-range communication in support of specific tasks. The retrieval of large volumes of data from a remote sensor in areas where direct communications (i.e., plug-in) is not possible requires the vehicle to be close enough to the sensor to use high-data-rate acoustic or electromagnetic data modems. This type of mission, to pick up data from a sensor or to monitor for changes in a seabed asset over a long period of time, is ideally suited to an AIV.

Technology Integration
As offshore production moves into increasingly deeper water, often with added production challenges, the condition of the subsea infrastructure and its operating performance is being addressed under an increased focus. The technical challenges, remote locations and drive for cost efficiency have seen some novel techniques being adopted. Integrity management systems are becoming more sophisticated and are expanding to acquire data from sensors distributed all over the subsea infrastructure.

The ability to deploy unplanned or use new sensor technology not available before project implementation is a gathering trend and therefore a desirable capability to have throughout the life of the field. Another role of the AIV may be to provide this service and perform the sensor installation, communication and maintenance.

Multiple AIV Systems
Maximizing the efficiency of operations is a key driver. Operating multiple AIV systems from a single platform in support of a field-wide campaign is one attractive scenario being developed. In this case, multiple AIVs would be deployed at a variety of work sites, often to carry out specific tasks, while the support vessel moves between sites in support. This echoes the latest thinking for ROV operations where multiple systems are deployed from a dedicated vessel.

The introduction of AIVs is more than a little similar to the path followed by ROV systems. There have been some significant steps in the evolution of the ROV from their introduction in the late 1970s to the present day, and there have been two main factors pushing development forward.

The first factor was the ability to develop and deliver the required technology. The second factor was the existence of a viable and robust business case. All through the development, milestone decisions, both commercial and technical, have constantly moved the business forward. The decision by a major operator, for example, in the early 80s to replace divers with ROVs on North Sea drilling rigs and the commitment by another major operator to develop a deepwater field with only ROV support are two such milestones.

Today, the ROV plays a key role supporting offshore subsea oil and gas infrastructure. Tomorrow may be the time for the AIV.

Special thanks goes to the technology teams at BP and Chevron, which have recognized the potential of this technology and supported its development.

John Mair has 30 years of experience in subsea engineering. His position as Subsea 7's technology development director enables him to bring to the table a view on the global subsea market, technology issues and promotion.

Ioseba Tena is responsible for the development of SeeByte's commercial strategies and managing the marketing sales process within the company. He has been involved in developing solutions for the underwater vehicle industry for more than 10 years.

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