22.09.15 Floating Production In China

The past few years have been a busy and highly rewarding period for InterMoor’s Asia Pacific team. The company strengthened its presence in the region in 2012 by opening a new equipment servicing facility in Singapore and then completed an important five-month project in Lufeng field in the South China Sea. This centred on the engineering and installation of a mooring system to secure a disconnectable turret for the Nanhai Sheng Kai floating storage and offtake vessel.

The client, China Offshore Oil Engineering Company (COOEC), went on record with its appreciation of InterMoor’s “high level of performance” on the project and said that it was looking forward to working with the group in Singapore again. And it was true to its word. In 2013, COOEC awarded InterMoor two similar projects in the Enping and Panyu fields. Engineering was largely to be done in that year, with both projects mobilising at about the same time: between Q1 and Q2 2014.

“We were delighted at COOEC’s show of confidence in our organisation; our people went the extra mile on Lufeng and this helped to establish a great relationship with the COOEC engineers,” says Martin Kobiela, managing director of InterMoor Pte Ltd. “The Enping field project was awarded first, and, in May 2013, we placed an experienced four-man team in COOEC’s offices in Shekou, China, to help plan the work. Clearly, the guys made a strong impression because, about three months later, COOEC asked us to take on the Panyu field project as well.”

Preparing for a new facility

The Enping project concerned the moorings for a submerged turret production buoy for China National Offshore Oil Corporation’s newly built Hai Yang Shi You 118 floating production, storage and offtake (FPSO) vessel. COOEC tasked InterMoor with project management, installation engineering and procedure development, and then the provision of key offshore personnel for the installation of the moorings and their hook-up. Allied to this work was installing a 12-in.-diameter production hose (made up of a 2.45-km static flowline and a 175-m dynamic riser with buoyancy modules), two power/optical umbilicals, a pipeline end manifold and two power-cable support structures.

The mooring system is set in about 90 m of water and has 12 legs made up of chain and sheathed, spiral-strand wire. The mooring legs are connected to the buoy using Balltec MoorLOK subsea connectors and anchored to the seabed by 84-in. driven piles varying in length from 38 to 49 m. It was these piles, especially the longer ones, that posed the first challenge for the InterMoor engineers, as they had to be installed using a support vessel that was not ideal for the task and only equipped with a 250-t crane of limited hook height.

The engineers developed procedures to get the piles overboard horizontally and to upend them on the seabed before positioning them through a specially designed stab frame. A scheme was also devised to deploy the pile hammer and the follower separately, thus keeping each lift within the capacity of the crane and so minimising downtime. The crane’s capacity was also an issue during the hook-up, when it was planned to add weight to the buoy to pull it down beneath the surface. This was to make it easier to connect it up and to protect it in the event of severe weather during the installation. Taking into account the size of the crane, two clump weights were designed for adding separately to the buoy.

The second challenge facing the engineering team centred on the restricted bend radius of the mooring wires, which meant that the winches on the available anchor-handling vessel needed modifying to increase their diameter. Winch adaptor/separators were also engineered to protect the wire sockets, and measures were devised to protect the wire’s sheath when held in the vessel’s shark jaws. (These same measures to protect the wire sheath were also used aboard the anchor-handling vessel used for the Panyu and Lufeng projects.)

These technical challenges aside, the biggest issue for the project, certainly in the view of the COOEC engineers, was the efficient coordination of the offshore phase of the work, which ran between April and August 2014. This involved three main vessels, the aforementioned installation support vessel, a large anchor handler and a diving support vessel, as well as various tugs and barges. The exact availability of each was unknown until quite a late stage; consequently, much of the scope had to be designed so that given vessel operations could be carried out independently when each of the vessels turned up. Having this flexibility was the key to ensuring that the project stayed on the rails and finished on time, a point COOEC formally recognised at the project closeout.

Extending Production Life

The project in Panyu field, also in the South China Sea, was similar in many ways to the Enping project: it involved the moorings for an FPSO vessel with a submerged production turret buoy, in this case in 105 m of water. However, the vessel, the Hai Yang Shi You 111, was not new and had been in the field for about 15 years. Given this situation, the aim of the project was to extend its production life by replacing the existing mooring system. COOEC asked InterMoor to engineer and install a like-for-like system and to manage the overall project, both on- and offshore.

The mooring system for the Panyu FPSO vessel’s turret buoy has nine chain and sheathed, spiral-strand wire legs, each of the upper chain sections being loaded with 8–16 clump weights. The legs are secured to the seabed by suction piles (7.5 m in diameter, 13 m long and weighing over 130 t) rather than by driven piles, as was the case on the Enping project.

The suction piles provided one of the first challenges for the InterMoor engineering team, as the crane barge COOEC secured to install them was more suited to pipelaying than to pile installation: deck space was limited and there was only one crane block with sufficient lifting capacity that could also go subsea. Following careful analysis of the deck arrangements and detailed planning, InterMoor devised procedures that enabled the deployment of up to five suction piles in a single run offshore. Further, a method was developed whereby each pile could be installed with its lower chain section and the wire section attached, which eliminated the associated subsea connections and saved time and money. InterMoor added a dedicated spooler, a tensioner, an overboarding arch and additional deck winches to the vessel at very short notice to be able to do this.

The pile installation work aside, the biggest challenge the project presented was to install the new mooring system no more than 2.5° from the existing one (a distance apart of about a metre or so), thereby avoiding the need for a new mooring analysis and, more importantly, rotating significantly the lower section of the turret and consequently twisting the riser. Furthermore, COOEC wanted to carry out the replacement without disconnecting the FPSO and so interrupting production.

Given this requirement, InterMoor engineers developed highly detailed installation procedures with comprehensive guidance on simultaneous vessel operations near the FPSO. As well as the crane barge used for pile installation and an anchor handler, there were three positioning tugs involved and the offtake tanker movements to consider. Because of the thorough preparation, the installation was completed safely and on schedule with minimum disruption, despite the last-minute changes required when the lengths of the upper chain sections were found to be different from those specified.

Constructive working relationship

According to Kobiela, that both projects were so successful is a testament to the constructive working relationship between COOEC and InterMoor and the professionalism and positive attitude that characterised the whole team. Wang Jiewen, project manager with COOEC, echoed this when he said, “We were impressed with InterMoor’s innovative approach and attention to detail, which ensured both of these challenging projects were safely completed on time. InterMoor’s project management expertise and their engineers’ ability to work closely with those on the COOEC side enabled us to manage multiple vessels and an international workforce on two complex projects being carried out concurrently.”

Kobiela is proud of the efforts of the team from InterMoor’s Singapore office but is quick to acknowledge the support InterMoor engineers in the UK and the USA provided. “COOEC valued the fact that we could run these projects within the region but call on the resources of a genuinely global organisation when required to respond quickly and strongly to events in the field. With first the Lufeng project and now Enping and Panyu, we have demonstrated the high value that InterMoor can bring to complex mooring projects in Asia Pacific,” he affirms.

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