Author: Stephen Auld – Global Business Manager – Subsea Asset Monitoring

It was pleasing and reassuring to hear at the recent Underwater Intervention (UI) conference in New Orleans that environmental awareness and ensuring hydrocarbon containment are on major operators’ 2025 roadmaps.

Alongside moves towards autonomy, reducing offshore personnel and vessels to drive cost efficiency, subsea leak detection and early identification of loss of integrity or flow control featured highly on each of their wish lists.

Much like other areas in the offshore domain, technology – automated and unmanned technology specifically – will play an important role in realising these visions. This blog aims to outline some of the drivers, challenges and solutions that will help to ensure these visions become reality.

Who is in the Driving Seat?

High profile losses of flow control reach the public domain with the understandable and expected negative response, with the resulting financial consequences imposed on the companies involved. However, there are the more regular events that, while documented or attended to by the oil spill response companies, go largely unreported to the public. The offshore industry has gold-standard levels of safety and these have been maintained even during the recent focus on driving down operating costs. But, drivers or legislation for subsea leak detection and monitoring, in certain areas around the world, were formed with historic operating environments in mind. This means that they have failed to keep up with moves into deeper waters and towards higher pressure and temperature developments. Self-policing is good and does occur, but without a driving force of a regulatory body in these price-sensitive days, leak monitoring can fall off the agenda; making the vision of the UI panel all the more impressive.

What and Where are Operators trying to Monitor?  

Subsea developments offer a very wide spectrum of entities that need monitoring, from manmade structures, like pipelines, termination assemblies and wellheads (to name but a few) to seabed locations where seepage can occur during the production phase when close to natural fractures or  fault lines.

For containment monitoring purposes, manmade structures can be sub-divided into near wellhead locations and longer export or trunk pipelines. Near wellhead locations are contained within relatively smaller areas, making the boundaries for leak detection monitoring more defined. For longer dispersed pipeline monitoring, potentially stretching over hundreds of kilometres, the distances involved dictate a different approach.

For these two types of asset, two different strategies exist. One is more static in nature, in order to continuously monitor the area in and around the wellhead and associated structures, while the other is more mobile in nature, and likely to be performed during regular pipeline inspection campaigns.

For monitoring of seabed areas, where hydrocarbon seepage can occur, either naturally or from an inability to control the reservoir integrity or overburden pressure, either a static or mobile seepage monitoring approach can be taken. Where seepage occurs in a known location, due to variations in reservoir pressures, static monitoring can alert the operator to changes in seabed seepage rates. In other instances, where natural seepage is occurring, but the exact location remains unknown, monitoring from a mobile platform is the preferred solution.

We supply solutions and sensors for both static and mobile automatic leak and seep detection. This blog, however, has static monitoring as its primary focus. Mobile leak detection using our Solstice multi-aperture sonar and patented automatic target recognition algorithms will be discussed in more detail in a future blog.

Static Monitoring using Sentry IMS

Although near wellhead areas are more defined, an operator can point to many different locations around the wellhead that merit monitoring in order to ensure hydrocarbon containment. One approach would be to attempt to install many smaller devices for localised leak detection. This is difficult and challenging to integrate into a centralised solution, especially if they are being retrofitted to existing assets.

Our alternative approach is the Sentry IMS (integrity monitoring sonar) which is an automatic subsea leak detection system that covers a wide area and is able to localise leak detections for the operator. An area covering 2.5 square kilometres is continuously monitored by a single 360° field of view Sentry sonar head. Several Sentry IMS systems can be networked and monitored from a central command and control system, should larger areas need to be monitored simultaneously. To put this in to perspective, one Sentry IMS will monitor over 28 million cubic metres of water, making it an efficient system to monitor many assets at once.

Sentry IMS is tried and tested, having been deployed in several deepwater locations around the world, where it has proven to accurately and automatically determine the location of both simulated gas and simulated oil leaks to a radius of around 700m (in the case of the simulated gas leak). Simulated tests on oil leaks for ‘dead’ oil (meaning oil that contains little to no gas content) to the more commonly found ‘live’ oil, i.e. containing larger percentages of gas, has shown that the detection of live oil at typical deep water gas to oil ratios resulted in outstanding detectability.

Brownfield and New Development Sites

For static wide-area leak monitoring, the deployed Sentry IMS system may differ depending on whether the site is an existing brownfield location or a modern field development. Older brownfield sites may not have the power and communication infrastructure needed to easily support a Sentry IMS. Equally, an operator may wish to monitor an area with no infrastructure installed at all (see Baseline, issue 20, article on Sentry IMS monitoring offshore Papua New Guinea).

For these situations, a self-contained and battery operated system, called Sentry-B, can be deployed. Alongside the Sentry sonar head, a battery bank is integrated into the Sentry-B subsea lander to provide power for the duration required. To avoid transmitting raw data to the surface, signal processing plus automatic detection and tracking of the returning sonar signal is performed subsea. Then, periodically, or whenever an alert event is detected, a lander-mounted acoustic modem transmits summary data to a surface located transceiver, which could be mounted from a buoy, a USV, ROV or over-the-side deployed from a permanent facility or vessel.

Where sufficient power and communication bandwidth exist, the Sentry-W (i.e. wired), version can be deployed and operated either remotely from the shore or from a production facility. This has been successfully achieved for a recent deployment for a major operator at a deepwater development in the Gulf of Mexico.

Integrity Monitoring Now and Towards 2025

Oil majors’ have environmental awareness and hydrocarbon containment firmly in their sights for 2025, which can only be welcomed. However, their vision could be realised today – the automated monitoring technologies are already here, proven and available.