A 20-year-old concept is receiving increasing attention in the North Sea as operators look for options to develop marginal fields.
The concept is for unmanned production buoys, which could cost-effectively support production from small or marginal fields.
About 60% of newly discovered fields have less than 20MMboe recoverable reserves, according to Guernsey-based investment firm Shore Capital.
Citing IHS data, independent, Manchester-based explorer Enegi, which is a joint venture partner in unmanned production buoy technology firm ABT Oil & Gas, says there are 88 fields in the North Sea containing less than 15MMboe, which it believes no conventional offshore unit can currently develop economically. In addition, it says there are a total 116 fields with < 30MMboe.
Image: ABT Oil & Gas's inamnned buoy concept.
Many are proven discoveries that have remained undeveloped because capital and operating costs are thought to be too high to justify commercialization.
As a result, the licenses in which they sit have been relinquished. Some projects, although fundamentally economic, are stranded due to a lack of nearby infrastructure.
When infrastructure is nearby, projects can also struggle to agree tariffs associated with using third party infrastructure, for oil and gas processing, storage and utility provision. In the North Sea, failure by multiple partners to negotiate satisfactory terms for tie-backs to existing infrastructure has notoriously held back a number of projects.
Unmanned production buoys could also provide an early production solution and or end of field life redevelopment concept. To date, most buoy technology has been limited to control buoys, housing control technology for subsea wells, with remote communications, as well as power, flare, monitoring, metocean data, or offloading buoys. Only half a dozen control or flare buoys have been installed to date, between 1993 and 2000, according to Intecsea. Two of these were conversions, from a CALM buoy and a metocean data buoy.
Last year, production buoy technology started to make the move to the mainstream. Major engineering fi rms AMEC and Wood Group PSN joined the market, by agreeing partnerships with technology development companies Unmanned Production Buoy (UPB) and ABT Oil & Gas, respectively. China Offshore Oil Engineering Company (COOEC) also signed an agreement with UPB for manufacturing.
Here we take a look at the technologies being developed.
Under a former name, Ocean Resource, based in Monmouthshire, UK, patented its first remotely controlled buoy concept in 1979.
Based on experience on the early Condeep platforms, in the 1970s and 1980s, and in civil engineering, the firm has engineered three buoys for offshore production: a three-tether flare buoy for Zafiro, off Equatorial Guinea; a control buoy for Mossgas’ current E-M development off South Africa, in partnership with Mentor Subsea, a division of Dubai-based McDermott subsidiary J Ray McDermott; and the East Spar control buoy offshore Australia.
Ocean Resource also designed a 5MW power buoy for CNR International’s Lyell field, in the North Sea, to provide power generation for up to 16 downhole electrical submersible pumps. The project stalled during final construction. In addition, the firm has designed and seen installed 10 other monitoring buoys over the last 20 years.
Dr. Lewis Lack, commercial director for Ocean Resource, says buoy technology is proven and there is growing demand, be it for control and power buoys, which can be used for local power or control, where space on a facility is limited or to power stranded fields where they can be tied back but do not have local control.
Image: Ocean Resource's buoy concept
“They are a proven entity,” Lack says. “This is why we are seeing now an upturn in offshore activity. There is strong interest in the buoys, not so much in the North Sea, but in many other regions. One area with a lot of interest right now is Perth, Australia, and the areas driven out of Australia, southeast Asia and to some extent West Africa. Buoys are one of the lowest cost structures you can put in to water to do a job, including in deeper waters.”
In total, the firm has five different buoy concepts: SeaCommander, SeaPower, and SeaSentinel, for oil and gas well control, electrical submersible pump power and control, and offshore monitoring, the SeaProducer, for production, and the SeaSequestor, for CO2 injection.
Ocean Resource has an agreement with ABTechnology to license SeaProducer technology for oil production systems. The SeaProducer is the firm’s production buoy concept, aimed at fields able to produce 1-20,000b/d. Its design differs from previous Ocean Resource designs in that, for installation, the buoy would be towed to the location upright, instead of horizontally, to protect production equipment. This means the design is wider than previous designs, and also with fewer decks, better facilitating integration of production equipment. The system is designed to last 25 years, and comprises a semisubmersible buoy, taut-moored with tethers, to a gravity base, with a subsea riser connecting the production facilities to subsea wells.
An example of a configuration, the firm says the floating buoyant structure, could be 57m-high, weighing 650-tonne (dry), with a 20m hull diameter, moored to a self-installing, 4000-tonne, concrete gravity base. The production facilities, which could be stored across three or more decks, will house first and second stage separation facilities, heat generation and process control systems.
“The production process used will depend on the clients’ preferences and also the produced fluid, plus availability and reliability requirements, Lack says.
“As well as temperature, vacuum separation has been considered.” Up to 4.1MW of power could be generated through six 820kW on board diesel generators, using one generator as a standby, to power, via a subsea riser and seabed umbilicals, up to eight electrical submersible pumps (ESPs), or other functions requiring power. Associated gas could also be used to provide power, as well as heat for separation. ESP control will be through eight onboard variable speed units, with a ninth installed as backup. The number of wells produced will depend on the tie-in system used, and will be driven, in most cases, by the selection of subsea system, Lack says.
Image: An Ocean Resource unit in construction.
The unit would include a 3m diameter access shaft for maintenance. The buoy could support a helideck. Produced liquids would be stored in subsea storage tank, positioned up to 500m away, or exported to a host facility. The storage tank size will depend on production rate and offtake frequency. Typically, Ocean Resource says it will be a 200,000 bbl concrete storage tank, weighing 13,000-tonne, using an oil water interface designed to avoid high hydrostatic loading, instead using the hydrostatic pressure differential to minimize additional energy requirements to pump out the oil.
Control and monitoring could be from a remote host platform or a land-based station through UHF, VHF and satellite communications. Ocean Resource has also been investigating use of a buoy for carbon sequestration for enhanced oil recovery.
SeaSequestor would be able to store 45,000-tonne of liquid CO2 in a subsea tank and then pump it into the seabed to support EOR. The buoy would provide power for the pumps and conditions the CO2 so it is ready for the subsea well and condition the CO2 to meet subsea well operating parameters.
ABT Oil & Gas
ABTechnology is part of a joint venture (JV) called ABT Oil & Gas, with Manchester-based exploration firm Enegi Oil. The ABT JV has partnerships with Wood Group PSN for engineering on its unmanned production buoy design, which it has said would typically cost US$140 million to construct and install, and oil and gas consultancy RMRI.
The JV also has an agreement with GMC to look at unmanned self-installing buoyant platform designs for use in the North Sea (OE: December 2013), agreed in 2013. The company also has an agreement with Ocean Resource, which could see it use the firm’s SeaProducer technology.
The company’s most advanced project is the Antrim Energy-operated 9MMbbl Fyne oil field, in blocks 21/28a in the central North Sea. Early April, ABT Oil & Gas submitted an environmental statement, for Fyne, which revealed the firm is planning to use a GMC self-installing tower design on the field. Following approval for the three-well development (two producers and one water injection well) from the UK Department of Energy and Climate Change (DECC), it will in late summer submit a field development plan, earning
Enegi and ABT 50% interest in the field, as part of an agreement made with Antrim last year. First production is anticipated prior to 25 Nov 2016, a date agreed with agreed with DECC. Late last year, ABT agreed a farm in deal with Providence Resources and its partners on the Helvick and Dunmore oil discoveries, in the North Celtic Sea basin, offshore Ireland.
The terms were for ABT to carry out an assessment of the commerciality of using its buoy technology on the fields, and to then to provide a field development plan for the scheme.
ABT’s own unmanned production buoy technology is aimed at fields containing 3-30MMboe recoverable, in 60-600m water depth, with a capacity for up to 20,000b/d total fluids and 20,000b/d water injection, with any suitable number of production and injection wells tied in via subsea manifolds.
Image: ABT's buoy concept.
The production buoy, which is over 60m-high and up to 30m-wide, consists of a semi-submerged hull and topsides structure, with a 4500-tonne dry weight, which is taut-moored to the seabed.
Production will be based on a conventional thermal stabilization approach, says the firm. Control and process equipment, will typically consist of a two stage separation system, to remove water and gas, located on decks within the buoy, which has an access tower for maintenance.
Internal power systems will be fieldspecific, ABT says, and will be fuelled by associated gas, with excess gas flared. The production buoy will be linked by flow lines and flexible risers to the subsea production wells. An autonomous shutdown control system is housed inside the buoy and remote intervention is possible using radio, microwave or satellite communications, ABT says. Crude oil is transferred and stored in a 100,000-300,000 bbl seabed storage system, made from steel, which is secured by piles driven into seabed, and from where the oil will be offloaded to a shuttle tanker.
In a recent statement, the JV partners said: “In order to maximize the opportunities to develop marginal fields, Enegi and ABT are reviewing the structure of its JV, ABT Oil and Gas, and expect to make an announcement on this in due course.” The firm added: “We are in discussions with a number of players about utilizing both our buoyant technologies on their assets. We also announced that we have farmed into the Helvick oil field and Dunmore discovery last November and work has started on evaluating the feasibility of implementing buoyant solutions to develop both.” The firm is also planning to apply for further licenses in the 28th licensing round.
Unmanned Production Buoy
Founded eight years ago, Aberdeenshire-based Unmanned Production Buoy (UPB) says it has a £756 million European field development program using unmanned buoy technology.
The plan involves three units, to develop six oil fields across the UK (UPB-1), Ireland (UPB-2), and Denmark (UPB-3). UPB’s foci are producing fields which are reaching the end of their economic life using a floating production vessel (FPSO), or small deposits (3- 5MMbbl) that are uneconomic using manned methods (FPSO or platform).
UBP has announced a 10-year hull and shell-manufacturing deal with China Offshore Oil Engineering Co. (COOEC) and says it is close to agreeing a UK assembly site for fit-out and detailed fabrication. The first commercial units are planned to be on stream in late 2016-2017. UPB has a memorandum of understanding with AMEC for support on engineering, procurement, construction management, and asset support services.
The first fields UPB plans to develop are Angus, with a single well, and Fife, both in the UK North Sea, and awarded to UPB in the 27th offshore licensing round, in which the company was also awarded licenses containing the Fergus and Flora fields. Angus and Fife are former producers, decommissioned by Amerada Hess, after becoming uneconomic. An independent testing and verification program is about to start, UPB founder and chairman Richard Selwa says, as well as site survey work, for an environmental impact assessment, required for a field development plan to be approved.
The UPB system
The firm says its reusable design is based on mass-manufacturing principles, using standardized components, based on learnings from tank farms in Canada, and the principles of onshore “nodding donkeys”.
UPB’s design comprises three main parts, a 1800-tonne dry-weight semi-submerged buoy, a 500-tonne subsea, steel, sealed tank system, and a combined, service riser bundle. The riser bundle will connect to up to three subsea production wells and two water injection wells, via infield flowlines, and be expected to produce 600-15,000 bo/d over a 20-year life span.
Selwa says the maximum 28m-diameter buoy and 200,000 bbl-capacity gravity-based storage tanks, both fabricated from steel, are standard designs. Depending on depth, the buoy will either be moored with a spread mooring system (60-90m) or tension leg configuration (90m+), with a standard offloading system.
The production system will be a standardized, temperature-stabilized, “nodding donkey,” system, typically deploying electric submersible pumps. The electric submersible pumps will be powered using 10MW onboard generated electricity, created using flue gas for power and heating. It will also carry its own diesel supply, where there is not enough produced gas, on which it could operate for up to four months.
Process equipment, controlled via satellite, will be in an enclosed environment, so access for maintenance will be via a walk-to-work system, using a supply vessel. As a result, system availability, Selwa says, will be 60-70%, with process up time at 90%, due to not being able to get access in bad weather. The units will be self-installing, by floating out the unit, using 2-3 tugs, and then ballasting at sea. Selwa says while the North Sea will be the first basin to use the system, Asian countries are showing great interest in its potential, for smaller fields they would like developed quickly, or larger fields they would like production to start on early, to bring in revenues.