What sets this oil well apart from other offshore wells is that it does not use a pipeline to pump its oil to the mainland. Rather, the oil produced by the well has been flowing to the FSO unit “Queensway” since 25 November 2008 via a Central Processing Platform (CPP). “Queensway” arrived at her moorings in the oilfield in late October and soon began loading oil. The oil will be offloaded onto the shuttle tanker at regular intervals.
By the time the first shuttle came alongside, “Queensway” had already stored roughly 350,000 bbl, about one third of her capacity. FSO, or Floating Storage and Offloading units such as “Queensway”, are essentially huge floating oil tanks. They store the oil produced before exporting it via shuttle tankers for further processing on land. The shuttles arrive at scheduled intervals that depend on the production rate of the well and the FSO’s storage capacity.
Floating All-Rounders
FPSO ships – with an added “P” for “production” – can do even more. They not only receive crude oil from a nearby production platform but also process oil, gas and water using their own, on-board production plants. After all, what comes out of the ground is by no means pure oil. Rather, it is a mixture of oil, gas and water. FPSO units separate oil, gas and water. The water is cleaned and dumped back into the sea. The gas is dried, compressed and exported to share via a pipeline pumped through a pipeline, while the oil is stored on board the vessel. An FPSO or FSO can usually store the production of two weeks. The pipeline running to the mainland is used exclusively for gas.
“FSOs and FPSOs are an excellent option for remote or deep-sea oilfields. Installing pipelines to connect wells to the mainland increases costs immensely, mainly because of the large quantities of steel required. This is why an FSO or FPSO is an ideal solution,” explains GL Noble Denton's Raza Amin. But cost efficiency is not the only benefit of using stationary storage vessels, says Amin: “FSOs or FPSOs are also an ideal choice for fields with limited oil reserves. It does not make sense to invest huge sums of money to extract oil out of these fields. An FPSO is more economical than installing a pipeline. For smaller oil companies and for newly industrialising or developing countries, FPSOs are a natural choice.”
Manageable Risk
Both the equipment installed on the “floaters“ and the operational procedures used must be designed for both economic feasibility and safety. “The FPSO business is full of challenges," says Amin. “To give an example, it is extremely weather-dependent.”
Rough weather conditions make loading a very complicated process because the shuttle tanker must manoeuvre very close to the FPSO. "While there are sophisticated rules for these offshore operations, implementing them is nearly impossible without expert advice," Amin adds. “So our job is to analyse technical risks and do our best to minimise them. To accomplish this we cooperate closely with government and private-sector supervisory bodies. We try to lower risks as much as reasonably possible.”
A Cost-Effective Alternative
The most important component of an FPSO system is the ship itself. "To find the best solution for a given application, you need to consider the size of the oil reservoir," says Amin. “If the reservoir is substantial, it may make sense to custom-build an FPSO vessel, or floater, including a double hull and special features to suit the operating environment. That is the expensive option. And apart from the cost, shipyards around the world have long waiting lists. Time is a big factor in this business.” In the West African Bonga Field, for example, Shell deployed large, custom-built floaters. Another field in Indonesia was likewise exploited using newly-built floaters several years ago. But those are exceptions to the rule. “Most FPSO solutions are converted tankers. After their decks have been cleared of all redundant parts, the required equipment is installed.”
The second most important feature for trouble-free, safe operation is the mooring system. An FSO or FPSO unit must be anchored in place reliably so its movements in the water remain predictable. The technology preferred today is a single-point mooring (SPM) system. Maritime engineers categorise this technology as a “dual system” because it consists of both anchoring and loading/unloading equipment. Advanced FPSO vessels feature an internal turret mooring system and an integrated anchoring system. The anchor cables are attached to the revolving turret located in the centre or bow of the ship. The FPSO is loaded through a riser from the wellhead that attaches to the underside of the turret.
The third main component is the production plant, which consists primarily of separators for separating oil, water and gas, treating the produced water, and separating the gas from the oil. But the work of GL Noble Denton is by no means limited to offshore equipment and maritime manoeuvrability of FPSOs. The production facilities themselves, which represent a substantial capital investment, are subject to risk management as well. “We also advise our customers on technical equipment they need to maintain the production plants and keep them in good operating condition,” says Amin. An effect offshore operators dread is the so-called water hammer. It occurs when a flowing liquid is stopped abruptly by a rapidly closing valve. “Our customers want to understand it, control it, and be assured that their equipment can cope with these dynamic effects.”
Integrated Drilling Equipment
FSO and FPSO units offer many benefits in the current volatile situation on the energy markets. Oil prices have been fluctuating wildly in recent months, but will inevitably rise in the long term. Even in remote oil fields and challenging environments, mobile crude oil storage systems can make oil production economically feasible. Perhaps their most important advantage, says FPSO expert Amin, is their flexibility. Once an oil field has been exhausted, the oil company can relocate the FPSO system to another field with relative ease. It is this benefit in particular that is causing the number of FSO and FPSO deployments to rise globally.
Not only do these vessels offer volume storage; there are also technical innovations adding value to this concept. The first-ever FDPSO units have already left their shipyards. “D” is for “drilling”: carrying drilling equipment on board, these innovative floaters can operate more or less independently in offshore oil fields. A yard in Singapore delivered one of the world’s first FDPSO ships for deployment in an oilfield off the West African coast in waters 1,500 m deep a few years ago, says Amin, with GL Noble playing a strong part in developing a comprehensive risk management concept for the project.
This article first appeared in nonstop magazine edition 2/2009. Click here to read additional articles from this issue or other issues.
