Subsea tiebacks are becomingincreasingly prevalent in oil and gas field developments. As the accessibilityof the production from wellheads becomes more difficult, the need for subseacompression and pumping increases. Compression and pumping require significantpower which can be distributed and controlled from a HVSS (High-Voltage SubseaSubstation). The viability of an Arctic field development will be determined bythe reliability of all elements in the tieback and in particular, thecentralized subsea power distribution system.
Hydrocarbon development in arctic regions presents formidable challenges tothe petroleum industry. The Centre for Arctic Resource Development (CARD)serves as focal point for planning, coordinating and conducting research tofill gaps in the knowledge, technology, methodology and training needed toovercome these barriers. CARD research programs have been organized into coreareas of Ice Mechanics, Ice Management and Station-Keeping in Ice, and arerelated through the common activities of Floating System Modelling andLarge-Scale Experiments.
A brief description of proposed research and development (R&D) plans inthe areas of Ice Mechanics, Ice Management, Large-Scale Experiments, FloatingSystem Modelling and Station-keeping in Ice is provided below. Three of theseare core areas, while the activities in Large-Scale Experiments and FloatingSystem Modelling will draw upon expertise from the core areas. Structures andvessels designed for arctic operations must have adequate structural strengthto allow for safe operations under the extreme ice loads expected during theiroperational lifetimes; research in this area is a strong focus of the plannedwork.
The initiatives described in this plan represent the major priorities andrange of activities that CARD will undertake with guidance from the CARDIndustry Advisory Committee (IAC) to overcome challenges associated with arctichydrocarbon development. It is expected that research programmes will befurther developed and refined as Principal Investigators are hired for each ofthe core research areas and they bring the full extent of their knowledge andexpertise into CARD.
The extreme conditions and harsh environment for which FPSO's andhydrocarbon gathering facilities are being considered introduces distinctchallenges to effective and efficient project management and execution. The presentation is based on the experiences gathered during the design phasesof two contemporary harsh environment FPSO's and the associated subsea,flowline, pipeline and riser systems (Chevron Rosebank and GAZPROMShtokman). This presentation will focus on the adjustments that must beconsidered to "standard" project execution and management in order toincorporate the elemental distinctions without sacrificing efficiency, logicalsequencing, safety or project schedule. Specifically, the presentationwill focus on the following:
The paper is intended to inform the audience as to the distinctivecharacteristics of harsh environment design management contrasted with the morefamiliar benign environment design projects.
A Joint Industry Project (JIP) was conducted in 2007 to determine the degreeof consensus of leading ice mechanics experts on the loads exerted bymulti-year ice on offshore platforms. Seven international experts on multi-yearice loads were asked to predict loads for three different ice loading scenariosinvolving multi-year ice floes: isolated floe, a multi-year floe in pack ice,and a multi-year hummock field in a sheet of first-year ice. The Experts wereasked to calculate the loads from these three ice conditions interacting with a150 m wide vertical caisson structure and a 45 degree conical-shapedstructure. There were significant differences in the methodologies usedand the assumptions made to estimate the loads. Load predictions variedconsiderably for each scenario with estimates differing by a factor of 4.6 forthe vertical caisson and 3.5 for the conical structure. In spite of the lowerratio of predicted loads for the conical structure, the Experts were moreconfident with loads on the vertical caisson. The key areas for furtherresearch were identified and these include improved knowledge of the icethickness and its variation for Old Ice, new and innovative techniques forobtaining ice loads, improved knowledge of pack ice driving forces, and betterunderstanding of the failure behavior of multi-year ice. This paper provides anoverview of the loading scenarios, details of the load predictions, andoutlines the areas identified for future research to help to provide morereliable load predictions.
Gadd, Peter E. (Coastal Frontiers Corporation) | Leidersdorf, Craig B. (Coastal Frontiers Corporation) | Hearon, Greg E. (Coastal Frontiers Corporation) | McDougal, William G. (Oregan State University)
Eighteen artificial (man-made) islands have been constructed in the AlaskanBeaufort Sea to support oil exploration and production. The first islands,constructed in the late 1970s, were in shallow nearshore waters where wave andice conditions are relatively benign. By the early 1980s, island constructionhad ventured to more exposed sites with water depths approaching 15 m.Innovative slope protection systems and construction methods were developed toaddress the remote Arctic locations, short construction seasons, scarce localresources, and the challenging, yet poorly defined, offshore wave and iceclimate. This paper provides an overview of the history of island developmentin the Alaskan Arctic and discusses design evolution, construction, andperformance.
In iceberg prone regions, subsea substructures placed on the seabed are atrisk of impacts from free-floating and scouring iceberg keels. Here themethodology for assessing iceberg loads and two mitigation strategies aredescribed. The iceberg load model was an extension of previous work forestimating iceberg impact loads on offshore surface-piercing structures.Components of the algorithms were modified such that global design loads fromkeel contacts account for the change in contact location (i.e., longer leverarm in the vertical direction resulting in greater rotation effects). Theiceberg eccentricity model and the relationship between contact area andpenetration distance were also modified to account for iceberg keel contactswith a generic low profile structure on the seabed. One concept considered wasa single wellhead structure fitted with a special weak shear link incorporatedinto the design at the expected scour level. The shear link, or failure joint,would act as a mechanical fuse designed to fail in a combination of shear,tension and buckling during keel loading. The failure joint minimizes downholestructural response during iceberg keel loading on the production tree. Thedesigned failure mechanism would allow the well to be re-entered by protectingthe well casing from damage. Another concept considered was a steel truncatedcone structure installed over the well installation and fixed to the seabed byone of several identified foundation concepts. The protection structure absorbsenergy through crushing of the ice keel and encourages the iceberg to deflectaround and over the structure. The steel structure would be designed accordingto ultimate limit states accounting for energy absorption through elastic andplastic deformation of the structure. Design loads would correspond to anAbnormal Level Ice Event (ALIE) with an annual exceedance probability of 10-4.The size of the frame is governed by the size of the wellhead and tree system,Remotely Operated Vehicle (ROV) access requirements, and slope to encourageiceberg keel deflection. Piles may be the best option for securing a protectionstructure to the seabed, especially if a local vessel can be sourced to performthe installation. As an alternative to piles, using a drill rig to install wellcasings may be an option; however, market conditions for drilling rigs maydictate economic feasibility.
The purpose of this paper is to introduce various offshore platform conceptsthat can be employed in ice infested waters, particularly shallow waters,depths varying from 65 ft to 500 ft. The paper illustrates five innovativeplatform concepts that for arctic drilling. The proposed platform conceptswould have ability to withstand extreme ice, wind, wave and temperatureconditions to extend the drilling seasons either near to winter sever storm orfor round the year operation. The platforms are designed to operate indifferent water depths in different part of the arctic by accommodating thedrilling structures and equipment on the deck. The emphasis is on theefficient of breaking, moving ice sheets around the structure and withholdingthe topside loads. Some of the platform concepts are fixed and others aredeveloped from the floating solution and the technical details are presented inthis paper.
This paper describes the results of the feasibility study of an arcticoffshore platform concept sponsored by ConocoPhillips. This concept consists ofa Conical Piled Monopod (CPM) platform, shown in Figure 1, assisted by an IceWorthy Jack-up rig, Gemini, to drill development wells in Multi Year iceconditions as illustrated in Figures 2 and 3. The Gemini design is beingjointly developed by ConocoPhillips and Keppel Offshore and Marine TechnologyCentre Pte Ltd based in Houston. Gemini is equipped with two drill rigsthat can simultaneously or individually cantilever above the well slots locatedon the deck of the CPM. The key benefit of Gemini lies in extending thedrilling season from a few months during ice free season to several monthsbeyond the ice free period.
The study was carried out at Granherne Limited under ConocoPhillips'supervision between March 2010 and February 2011. A topsides operatingload of 5,000 tonnes was assumed, instead of 70,000 tonnes (or more)corresponding to a two drill rig stand alone drilling and production CPM. Thefeasibility of a stand alone drilling and production CPM was presented inanother paper at Icetech12 in September 2012.
The study concludes that a Gemini assisted CPM is feasible for iceconditions in the Canadian Beaufort Sea. The ice loads were calculated,in consultation with Ken Croasdale, a well known specialist in this discipline.Ice conditions assumed in this study were in accordance with ISO-19906, namely,12m thick level ice and a very rare 25m thick ice island event. No icemanagement was assumed. A Gemini assisted CPM offers a much lighter platformcompared to a standalone CPM or Gravity Based Structure.
ConocoPhillips has a patent pending on the CPM. ConocoPhillips andKeppel Offshore have patent(s) pending on the Ice Worthy Jack Up drilling rig,Gemini.
In light of the recent increasing interest in the oil and gas developmentsin the arctic region, Huisman Equipment B.V. has developed a Mobile OffshoreDrilling Unit (MODU) named JBF Arctic suited for arctic condition. The stationkeeping in ice is one of the crucial factors determining the feasibility of thedesign. As one of the first steps of the design process ice model tests wereperformed at the Krylov Shipbuilding Research Institute (KSRI) to gain insightin the ice forces acting on the unit. During the model tests the model of theJBF Arctic was retained in a fixed position while being towed through the ice.In reality the station keeping of the unit will be ensured by a mooring system,which has certain flexibility compared to the rigid constrains in the modeltests. This paper elaborates on the creation of a numerical model that canperform time-domain simulations of the dynamic interaction between the vesseland the ice-loads. Using these simulations the mooring system is optimized inorder to cope with the ice loads corresponding to unbroken level ice withthickness up to 3.1m. Several important conclusions were drawn. One is the factthat no dominating frequencies of the ice failing could be identified from themodel tests. This can be explained by a large ratio between the diameter of theunit and the ice thickness. So the ice failure mechanism has a chaoticcharacter. Another conclusion is that the unit does not exhibit significantdynamic behavior. This means that a quasi-static approach can be generally usedfor initial design of the mooring system.
Keywords: ice model test, dynamic ice-structure interaction, ice loadingmodel, mooring system optimization, Arctic MODU.
A growing number of projects are employing some form of subsea processing.Integrated system approaches to subsea processing, commonly known as SubseaActive Processing Technologies (SAPT), can require a great deal of power.Subsea boosting and/or separation pumps can easily reach 3 MW each; withmultiple pump installations quickly adding up to a substantial demand on a hostfacility. When the power transmission distances approach 100 km or more, ACpower distribution becomes less and less practical. For this reason, powerindustry leaders envision the future installation of offshore electricalutility infrastructures based on High Voltage DC (HVDC) TransmissionTechnology, just as they are presently employed for land based utilities.Taking advantage of these large HVDC offshore power grids for small, isolatedsubsea installations requiring only moderate power levels calls for adaptingHVDC technology to a scale sized to the power requirements of theseinstallations. The HVDC Power Buoy concept, proposed for isolated SAPTinstallations requiring subsea power in the range of 10 to 20 MW, is one suchadaptation. This paper will present the HVDC Power Buoy concept and its keycomponents; the benefits and drivers for its development; the perceivedqualification challenges as well as the target applications for thetechnology.