EXPANDING OFFSHORE NETWORKS

FEATURE

By Greg Otto and Kristian Nielsen

Offshore energy fields are dynamic and evolve over the years - new production platforms come on station, old platforms are decommissioned, new turbines are installed, and older ones are decommissioned. In addition, facilities have ongoing projects and minor expansion. As energy companies look to become more efficient and address climate change, new digital technologies and applications are introduced, and new communication solutions become available, most notably wireless technologies such as 5G.

Together, these factors drive the need to routinely expand and contract offshore energy networks, as well as modify them to address long term issues such as where “mid span” facilities are decommission causing a platform to platform network to fail..

When most of the early offshore oil and gas submarine cable networks were built, the business case was measured in terms of production gain (e.g., boe/day) that could be attributed to improved connectivity and new applications. Focus on fewer offshore personnel did not drive value as those beds would inevitably be replaced with other workers, such as maintenance and project personnel who would work to improve production efficiency (boe/day).

Due to the high capital cost of fiber networks, the payback time exceeded ten years and required a base production of at least 40 or 50 thousand barrels per day per fiber attached facility. As such, the typical offshore facility identified for fiber connections would have at least a 100,000 boe/day production profile and at least a fifteen year expected life before serious decline in production.

Today, these criteria are changing as companies learn more about how technologies such as automation, robotics, artificial intelligence and collaboration are critical to safe and reliable production while optimizing and maximizing efficiency. This is further compounded as the cost to do offshore work in the energy industry increases with higher level standards and scrutiny towards safety and engineering. For example increased frequency and diligence for inspections and protective measures to manage corrosion and have driven higher costs and workloads which in return are driving use of robotics.

Therefore, where older facilities would not have previously qualified for high capital fiber investments in the past, the growing workload has driven an expanding need for improved connectivity and has re-invigorated the desires to expand existing fiber optic systems. Companies like Tampnet in the UK and US have business models directly related to this where they look to expand fiber backbones using fiber and wireless technologies to serve the expanded customer market.

Expansion of a submarine fiber network can take multiple forms and the method chosen is dependent upon several different factors including the original system design, the needs of demanding facilities, local considerations and obviously cost constraints. These considerations will be briefly explored in this paper.

EXISTING SYSTEM

Submarine fiber systems for offshore energy have several different decisions captured in their basis of designs including the choices below:

1. Trunk and Branch versus Platform to Platform ring;

2. Interplatform dependency and criteria for it’s use;

3. One or two cable landing stations;

4. Powered (repeatered) versus Passive (repeaterless); and

5. Fiber only versus a hybrid using fiber, microwave, 4G/5G.

In addition, based on consideration of immediate and future potential needs, there are several additional specific design decisions with respect to:

1. System routing and backbone modification allowances;

2. Fiber count and assignments;

3. Optical wavelength capacity and multiplexing;

4. Branching unit counts including futures and spares;

5. Power Feed sizing for powered systems; and

6. Requirements for fault tolerance to support “in service” modifications.

The decisions identified above have a material impact on the capability to expand a submarine fiber system to additional facilities. Based on distance limitations, capacity, spare fibers, tolerance to outages and many other factors, the ability to expand a system can be heavily limited by engineering. And of course, the cost to expand is always a critical factor. In a trunk and branch system that is powered, branch lines are often limited between 75 and 100 km. With quality engineering, a branch leg might reach 150 km without having to implement costly branch leg repeaters and on facility power feed equipment.

Similarly, a passive, unpowered system may only allow connections up to 400 km between the two ends of the optical pair which can cause issues for longer and farther-reaching offshore energy networks.

Prior to starting any expansion design, a study of the existing system is critical to understand the options and limits available and how this may impact existing operations. This review will help determine the range of capital cost exposure, scope of work and the risks to the integrity of the existing system. Extending a system too far, thereby exceeding initial engineering limits, or creating an inter-facility dependency, may create an unacceptable risk to the existing customer base. Furthermore, the system design will determine if modifications can take place while maintaining some level of service for users or subject them to several days of outage.

INITIAL EVALUATION

Once it has been decided to look at ways to expand the system and an understanding of the current system has been completed, a set of conceptual ideas would be generated. This step should be accomplished in a few days or weeks and would not address, but may capture, any technical or other issues to be explored further. From this, a set of options should be developed based criteria including:

1. Facilities to be connected including location and priority or criticality;

2. Existing work in the basin which can be leveraged (reduce mobilization costs);

3. Service level requirements (availability, bandwidth, tolerance to outage factors);

4. Expected duration of connection (< 5 years, 5-10 years, 10 or more years);

5. Capital availability;

6. Desired “go-live” date;

7. Subsea design and conflict potential; and

8. Impact to existing system design and tolerances.

The conceptual options developed during this initial phase can take on many different structures with some of the more common options being shown in Table 1 with target scenarios or conditions:

You can read the entire article on page 30 of SubTel Forum Magazine Issue 120 linked below.