AUVs for underwater oil and gas pipeline inspections
One of the most important strategic topics in deep-offshore oil & gas sector is the success of subsea pipeline installations. Hydrocarbon or chemical leaks, along with other operational failures are common occurrences that can harm the environment. The repairs required against these faults are quite expensive and the only conventional mechanism designed to anticipate and mitigate these failures is with Remotely Operated Vehicles (ROVs) that are sent to the sea bed. However, the method itself is costly due to lack of ROV resources and the need for them to be connected by cables to ships or boats and controlled remotely.
In this respect, a vital new-generation development has been the development of Autonomous Underwater Vehicles (AUVs) that are not required to be connected to deploying vessels and is equipped with acoustic sonars and visual detectors to inspect subsea pipelines and associated sea floor deteriorations. From initial analysis, it is expected that AUVs will be able to carry out inspections four times faster than ROVs and with fewer logistical resources.
A pipeline inspection AUV can be piloted to execute a 24-hour dive from any vessel or base. It travels without any assistance from the surface, detecting and avoiding obstacles with a sonar system that has a range of up to 300m. A multi-beam echo sounder is also attached to the AUV to provide 3D imagery of the pipeline and sea floor. With an underwater laser scanner, the AUV is able to detect deformations or cracks in the pipelines and produce high resolution digital photos.
As AUVs become successfully integrated into the oil and gas operations for geophysical and environmental inspections, there has been identified a need to rapidly enhance technology growth in pipeline inspections. In this respect, an important research-based collaboration was initiated between Total and Chevron to understand, influence and adopt technological advances to enable sonar and visual pipeline inspections using AUVs. According to the deliverables for this collaboration, improvements are required in sensors, data processing, management and autonomy software, along with 3D mapping, feature recognition and communications between the AUV and its sensors.
Total and Chevron have also combined resources to develop specifications for AUV pipeline inspection surveys to guide AUV suppliers and operators to enhance their current capabilities. Their goal is to develop a global alignment in requirements for pipeline inspections and specify these requirements in an AUV pipeline specification document. This document considers the potential limitations of AUVs compared to conventional ROVs and towed platforms, and aims to minimize the compromise in key requirements to assess the integrity of offshore pipeline assets. The specification document also provides a basis to introduce AUV pipeline inspections to various businesses while fully complying with existing regulatory standards and industry best practices.
Another technique in AUV pipeline inspections is the integration of automated cloud-based data processing. Fugro offers such an automated digital solution that delivers vital information on the condition of subsea pipelines. This speeds up the processing of vast amounts of data generated from inspections, that enables shorter timeframes and reporting schedules. The solution creates a digital model of the pipeline within hours after acquisition and uses cloud-based processing to manage inspections. A designated software acquires high-definition imagery and laser profiles from the AUV and transfers substantial amount of data to be processed back to the operation centers. The innovative digital approach also eliminates human error and subjectivity from the process while ensuring greater flexibility to meet a variety of customer needs.
In the deep offshore fields in West Africa, an expansive set of tools for baseline surveys, field monitoring and inspections are being utilized. This approach aims to integrate data obtained from AUV sensors to a Geographical Information System (GIS), which is a decision-making tool for life-of-field integrity. GIS allows the operator to make a high-resolution baseline of the pipeline installation to identify particular points of interests that potentially require further assessments. The reported results exceed that of previously used methods and aids in carrying out detailed investigations. The final datasets could also be utilized as reference to conduct repeated AUV acquisitions and in monitoring changes over time.
In a similar project, the ECA Group has designed and produced a comprehensive autonomous unmanned underwater system that is able to carry out both deep and shallow water pipeline inspections in up to 3000 m water depth. The solution integrates data management and processing tools with an autonomous underwater recovery system that is compliant with the Oil and Gas industry standards.
With continued great developments being made in the AUV technology area, AUVs are also being integrated with various other technologies. In 2020, Kawasaki Heavy Industries, Ltd. announced the successful completion of verification tests for their robotic AUV, called SPICE (Subsea Precise Inspector with Close Eyes). It is the world’s first AUV equipped with a robot arm for performing subsea pipeline inspections. Kawasaki reported that SPICE was able to execute a close-range inspection process including deployment at sea and tracking operations, after which it was able to return to the docking station. The tests were regarded successful in using an autonomous robot arm control and sensor-equipped AUV together to carry out a close-range inspection and represent a major path forward for fusing industrial robot technology with subsea automation.
The AUV-specific approach to replace conventional ROVs to carry out pipeline inspections provides better data quality and results to enhance integrity management of subsea pipeline assets. These highly equipped AUVs not only conduct detailed inspections and surveys of underwater pipelines, but also help save engineering time and budgets to maintain schedules and manage projects better. AUVs are consistently being integrated with various other technologies, like GIS and advanced robotics, which only enhances its prospect to be adopted worldwide to carry out underwater inspections.
The ability of AUVs to successfully perform pipeline inspections will also provide a stepping stone towards acceptance of AUVs as capable tools for additional inspection and light intervention programs, and will eventually lead to the development of field resident AUV systems.