Production • Processing • Handling
Despite these difficulties, interest in the Arctic is on the up – especially at a time when oil and natural gas fields in other areas are depleting. Te combination of environmental conditions experienced in this region is unlike those in existing fields therefore, companies must ensure they have a deep understanding of their influence on oil and gas exploration. Tis will allow for the design of their marine operations to be optimised and the associated risks when operating within such harsh and remote environments, to be mitigated. Planning marine operations in these demanding environments is no mean feat. Each stage has its own associated risks which must be managed effectively. Te number of FPSOs being put into service is continuing to increase. FPSOs are known to be a particularly attractive and flexible option in remote or deepwater locations as they eliminate the need to lay expensive long-distance pipelines from the processing facility to an onshore terminal. Tis can provide an economically attractive solution for smaller oil fields which can be exhausted in a few years and do not justify the expense of major investments in fixed infrastructure including pipelines. Furthermore, once the field is depleted, the FPSO can be moved to a new location. However environmental conditions can significantly impact the operation of FPSOs and in turn production, therefore the risks must be managed. Te Arctic for example, presents challenges in the prediction of weather
and ice flow patterns for the design of FPSOs and transport systems, as well as the evaluation of ice-induced loads on vessels during exploration operations. By overcoming these challenges, companies can minimise downtime. In order to stay in place, FPSOs are either moored to the seabed, or utilise Dynamic Positioning (DP), a computer- controlled system which automatically maintains the FPSOs position by using its own propellers and thrusters. Regardless of the option used, severe metocean (wind, wave and currents) conditions cause motion of the FPSO and loads in the mooring system, if used. Terefore, companies must analyse these conditions and responses early in the design stage so that the optimal choices can be made between DP and mooring - and the type of mooring, if this is the preferred option. Further, the system for mooring shuttle tankers to the FPSO has to be considered carefully. Tis can be done either with tandem mooring (generally easier both to remain attached and for arrival and departure) or using side by side mooring (generally required because of restrictions in the ability to transfer the product through long or flexible hoses). An unsuitable mooring solution can result in unnecessarily frequent disconnection of the shuttle tanker from the FPSO and subsequently a suspension in production. Badly designed mooring systems are also a safety issue and could result in a fatal accident, so this aspect obviously deserves attention early in the design process.
Radar positioning sensors M
aintaining tanker and supply vessel position relative to FPSOs is critical to safe loading
operations and is particularly challenging in harsh environments and high latitudes poorly served by GNSS. In response to laser targets suffering from
ice riming and snow accumulation Guidance developed its RadaScan range of radar positioning sensors. Both the RadaScan (good to 1000m+) and miniRadaScan (600m) have XT (Extreme Temperature) versions capable of working to -40˚C. In 2014 these will be joined by a 10km version of Artemis for shuttle tanker operations.
BMT ARGOSS offers metocean consultancy, weather forecasting, and state-of-the- art systems for emergency response, vessel simulation and performance monitoring.
Following problems in the Kara Sea with
heavy sea fogs and early laser solutions, Guidance developed its CyScan sensor instead to operate in the near-infrared, thereby mitigating the effect of sea fog. In tests for a paper to be presented at the Houston DP conference in September, the sensor was shown to work perfectly with prism targets 130m away where visibility was below 40m. Recognising the importance of vessels being
able to work in all weathers, independent of the FPSO, Guidance has developed a target-less solution for close range work. Two Guidance range finders triangulate the
measurements from two microwave cones to provide a range and bearing into the DP system offering a year-round, all weather ‘lock down’ capability. This is particularly useful when supply vessel mobility is restricted when connected to the FPSO with hoses and provides users with a completely independent, additional level of safety, critical in regions where weather and currents can be harsh and erratic. l
For more information ✔ at
www.engineerlive.com/iog Guidance Navigation is based in
Leicester, UK.
www.guidance.eu.com www.engineerlive.com 67
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