Subsea Production: Diving and Cable Laying Advances

Presented by:

Editor's note: This article appears in the new E&P newsletter. Subscribe to the E&P newsletter here. 

Despite the progress in exploring alternative energy sources, the increasing global energy demand means that fossil fuels will continue to supply a significant part of the energy landscape in years to come. However, with depleting oil prices, tighter project budgets and other impacts, including the effects of the COVID-19 pandemic, efficiency and reliability must play a vital role when choosing an appropriate solution for any project within the oil and gas sector, including E&P. 

Unique Group supplies turnkey equipment and service packages for diving, buoyancy and load testing requirements in the offshore industry, in addition to a wide range of survey equipment and autonomous survey vessels, for pre-construction survey as well as asset integrity inspection. In the following sections, Unique Group details two subsea production case studies that involve its dive system and cable laying system. 

Case study: diving 

Unique Group’s Diving & Life Support division is a manufacturer and supplier of deepsea marine, commercial diving and life support equipment to the oil and gas sector. With its team of experts, the company offers a portfolio of diving products and services, including design and manufacture of air, mixed gas and saturation diving equipment, mono and multiplace decompressions chamber, marine winches, certified man-rider winches, and specialized subsea rigging equipment. 

Unique Group’s expertise was called upon to manufacture and deliver double utility Nitrox Air Dive Systems to Nigerian-based African Diving Services. The scope of work included developing a compact, low-cost surface dive system, compatible for both Air and Nitrox diving operations, with an integrated inspection ROV control station. The system was also required to meet the specific criteria of International Marine Contractors Association (IMCA) and the International Association of Oil & Gas Producers (IOGP) as well as the end clients, Shell and Exxon Mobil. 

Working closely with African Diving Services, Unique Group’s Diving & Life Support division developed a distinctive system specifically designed to meet the requirements of the client’s particular diving operations. The Group’s team of experts also liaised with both Shell and Exxon Mobil’s diving authorities, assuring compliance with their specifications. 

Following stringent guidelines to comply with the latest IMCA, IOGP, Shell and Exxon Mobil requirements, Unique Group developed two customized ABS Nitrox Surface Dive-ROV systems that comprised:

• A combined Dive & ROV control space and chamber container;
• A machinery container;
• Air and Nitrox 10-ft HP gas storage containers;
• Two single-basket launch and recovery systems; and
• A Rhino Marine SRP boat.

The bespoke and flexible design of the system allows easy and quick modification from Air to Nitrox diving, offering the ability to apply this compact system in two different diving functions, thus saving preparation time and, subsequently, improving efficiency and reducing costs. 

The technically and ergonomically designed control center with an integrated ROV control station offers effective cooperation between diving and ROV operations, revoking the need for dedicated ROV control containers, saving valuable space and improving performance.

With the expertise to fully understand and meet the technical specifications, Unique Group was able to develop a bespoke system that assured compliance with the requirements and mitigated risks of non-conformances and diving job interruptions, thus offering further cost and time savings. 

Case study: cable laying 

With constant advances made in telecommunications and renewable energy sectors, there is a significant increase in cable laying on a global scale. As laying cables in offshore environments can often present a range of challenges, it is vital the operations are carefully planned and managed to achieve project goals and guarantee safety of both the personnel and the operations. 

Unique Group’s Seaflex SeaSerpent is a safe, effective and flexible cable installation buoyancy system, which is ideal for installing cables in shallow water.  

Following technical discussions with the Seaway Offshore Cables team and commercial conversations with Subsea7, Unique Group successfully deployed its SeaSerpent buoyancy system to support a global offshore contractor in May 2019. 

Having supplied more than 5 km of SeaSerpent within the first few weeks, Unique Group’s scope of work also included provision of dedicated launch and recovery pedestals and 4,000 SeaBuckles for ease of attachment to and release from umbilical. 

SeaSerpent allowed operational flexibility during installation, with an easy launching procedure followed by progressive and controlled sinking sequences, which can be started, slowed or reversed by simple surface control without subsea intervention. 

With the support of Unique Group’s U.K.-based Site Support Manager Ben Board and Site Technician Trevor Barton, the company provided initial training on the system and supervisory expertise to the Subsea7 deck crew, ensuring the most effective use of the technology during the landing of the cable. 

Unlike traditional solid floats, Seaflex’s SeaSerpent allows easy parking of the cable on the seabed, even during adverse tide or weather conditions, giving the ability to re-float it when required. Tested and proven to greater than 3:1 over maximum working pressure, the system provides no stress point loads, supporting cable fully and gently, with reduced risk of kinking.

From the initial inquiry through to assistance on the barge as the cable is landed, Unique Group supplied a solution as well as technical support throughout the operation, ensuring maximum efficiency and further cost savings. 

In addition to its operational advantages of speed and control, SeaSerpent's compact design provides cost-effective shipment, storage and deployment, while reducing transport and replacement costs. Not being a subject to the high attrition rate of traditional individual cable floats, the system also significantly minimizes both the required deck space and manpower at the launch point.