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Offshore production operations can be either very similar to or radically different from land-based installations. Except for a few innovative installations, wellheads and Christmas trees on platforms are basically the same as for land wells (see Fig 1). Control valves, safety valves, and piping outlets are configured the same and use the same or similar components. Some of the valves probably will have pneumatic or hydraulic actuators to facilitate remote and rapid closure in an emergency. Also, some Christmas trees may have composite block valves instead of individual valves flanged together.
Production operations in the offshore artic regions are within the reach of existing technology. Procedures used onshore and offshore in less hostile regions, however, must be modified to meet the challenges of the harsh climatic conditions in the remote locations. In the last decade, the major area of industry interest has been the offshore region of Alaska and Canada. The environmental conditions vary significantly in each of these regions. The specific production system that is selected must be tailored to each unique combination of these factors to ensure safe oilfield development.
From a historic point of view, as jackup drilling vessels drilled in deeper water, the need to transfer the weight of the well to the seabed and provide a disconnect-and-reconnect capability became clearly beneficial. This series of hangers, called mudline suspension equipment, provides landing rings and shoulders to transfer the weight of each casing string to the conductor and the sea bed. Each mudline hanger landing shoulder and landing ring centralizes the hanger body, and establishes concentricity around the center line of the well. Concentricity is important when tying the well back to the surface. In addition, each hanger body stacks down relative to the previously installed hanger for washout efficiency.
Flow assurance in subsea oil and gas fields often presents significant challenges. Every field has its own combination of difficulties, and no universal process or system can be used to mitigate these. Detailed knowledge across a broad range of competencies, therefore, is required to find solutions that can minimize the risk of not getting the hydrocarbons safely to the process facilities. Many subsea fields that are being developed today are long tiebacks, taking advantage of existing offshore infrastructure or producing directly to shore. These developments must deal with the long-distance transport of hydrocarbons in deep cold water, commonly increasing the risk of hydrate formation and wax deposition, for example.
Just as there are shortcomings of deterministic models that can be avoided with probabilistic models, the latter have their associated pitfalls as well. Adding uncertainty, by replacing single estimate inputs with probability distributions, requires the user to exercise caution on several fronts. Without going into exhaustive detail we offer a couple of illustrations. First, the probabilistic model is more complicated. It demands more documentation and more attention to logical structure.
Subsea 7 is expanding its offshore wind construction business with a deal that puts it in control of a company that effectively doubles its fleets of vessels to transport and install offshore turbines. It will combine its current offshore wind business with another Norwegian company, OHT, known for transporting massive components. Combining these companies with roots in the oil business is expected to create a stronger, more diversified provider of installation services called Seaway 7. Both companies are drawing on their experience in deepwater oil developments to rapidly expand into renewable power. In its first quarter report, the UK-headquarted Subsea 7 reported that 30% of $1.8-billion worth of its order backlog is now from its renewables business and nearly one-quarter of its revenues.
Subsea processing using subsea separation and pumping technologies has the potential to revolutionize offshore oil and gas production. When combined with relatively mature subsea production technologies (see subsea chapter on well systems, manifold, pipeline, power and control umbilical, and so on), it can reduce development cost, enhance reservoir productivity, and improve subsea system reliability and operability. Over the period from 1970 to 2000, millions of dollars have been spent to develop subsea separation and pumping systems. But because of unresolved technical issues, along with a lack of confidence and clear understanding of the costs and benefits, industry has not rushed to deploy the technology on a commercial basis. However, as the industry moves into remote deep and ultradeep water, various degrees of subsea processing are becoming more common. In deep water, the technology can enable hydrocarbon recovery from small reservoirs that are subeconomic by conventional means, making small fields economically viable and large fields even more profitable. Subsea processing refers to the separation of produced fluids into gas and liquid--or gas, oil, and water--for individual phase transport and disposal (in the case of water). The liquid stream can be pumped to a central facility for final processing.
Figure 1.6--The Baldpate Compliant Tower is one of the tallest free-standing structures in the world – Empire State Building (right) for comparison (Web Photograph, Amerada Hess Corp., New York City). Figure 1.9a--Worldwide fleet of installed and sanctioned semisubmersible FPS (courtesy of BP). Figure 1.9c--Worldwide fleet of installed and sanctioned spars (courtesy of BP). Figure 1.10--Semisubmersible FPS planned for the Thunder Horse field (courtesy of BP). Figure 1.11--Alternative proven technology field development options (courtesy of BP). Figure 1.12--Subsea production trees used in conjunction with a fixed jacket structure (Intec Engineering, Houston).
Equinor, along with partners ExxonMobil, Petrogal Brasil, and Pré-Sal Petróleo SA, will move forward with a planned $8-billion Phase 1 development of the Bacalhau field in the Brazilian pre-salt Santos area. The Bacalhau field is situated across two licenses, BM-S-8 and Norte de Carcará. The target resource is a high-quality carbonate reservoir containing light oil. The development will consist of 19 subsea wells tied back to a floating production, storage, and offloading unit (FPSO) located at the field. The vessel will be one of the largest FPSOs in Brazil with a production capacity of 220,000 B/D of oil and 2 million bbl of storage capacity.
Baker Hughes has been tapped by Petrobras to supply flexible pipe under two separate contracts covering four field developments off Brazil. The first contract covers up to 96 km of flexible pipe for the Sapinhoá and Tupi fields, and the second contract covers up to 226 km of flexible pipe for the Marlim 2 and Itapu fields. Including two earlier flexible pipe contracts Petrobras awarded to Baker Hughes for the Buzios field, Petrobras has contracted Baker Hughes during the first half of 2021 to provide up to 370 km of flexible pipe for its subsea projects. This is larger than the amount of flexible pipe awarded by Petrobras to Baker Hughes in 2019 and 2020 combined. "These back-to-back contract wins reflect our strong capabilities and the relationship we have developed with Petrobras as a trusted partner," said Adyr Tourinho, vice president of Brazil and oilfield equipment for Latin America at Baker Hughes.