The paper will present the design of a floating platform incorporating the following systems: Conventional Wind Turbine Long and Short Period Wave Energy Capture Ocean Thermal Energy Conversion (OTEC) Open Flow Current Turbines Energy Storage The focus will be integration of the systems from a structural standpoint; effects on the cost of each system and the resulting LCOE and overnight cost; and the nameplate and peak power for given conditions. Energy mechanisms in the marine environment are the wind, waves, water currents, and seawater temperature differences. An assessment and rating of the energy resource potential of a given development site is used to inform the renewable energy technology system selection process. Offshore Renewable Energy (ORE) technologies can be summarized into the following groups: Offshore Wind Turbines are the prevalent ORE technology exploiting the present market, similar to onshore wind turbines, but mounted upon a fixed or floating offshore platform. Ocean Thermal Energy Conversion (OTEC) uses the temperature differential between surface water and seabed water to drive heat engines. Marine Hydro-Kinetic (MHK) devices convert energy from waves or fluid flow. Wave Energy Converters (WEC) are oscillating/reciprocal/pressure driven systems operating at or near the ocean surface or bottom mounted in shallow waters. Flow Energy Converters (FEC) are used in areas where velocity and direction of water flow is relatively constant or highly predictable if intermittent (tidal). Unlike an onshore wind energy site, offshore wind energy systems (especially floating ones) are surrounded by these other energy sources; the integrated renewable energy facility design process addresses selecting systems that will complement each other while capturing the energy resident in the operating environment, as well as leveraging the wind turbine supporting structure and infrastructure to reduce the costs of the WEC, FEC and OTEC systems. The amount of CAPEX spent on non-power generating equipment can be optimized by leveraging the floating system structure cost to host various ORE technologies. Between 50% and 70% of the overnight cost of a typical MHK or OTEC facility will consist of equipment and activities that do not generate power. This is one of the key differences with offshore wind which has an overnight capital cost overhead of roughly 30%. By combining multiple technologies into a single platform, it is possible to reduce the MHK overhead costs to 18 to 36%, with little or no effect on the offshore wind overhead costs. The resulting design is novel in configuration which takes the form of a Multi-source Articulated Spar Leg (MASL) platform and can reduce the Levelized Cost of Energy (LCOE – the economic measure used to compare energy systems) by at least 25%; can be fabricated and pre-commissioned in port; is fully configurable to the local conditions; is more stable than the current floating wind designs in use; and can be scaled up to carry any sized wind turbine. Both cost savings and an increase in revenue can be realized using integrated ORE facilities given the higher average availability factor offered by blended ORE systems and reduction of individual system OPEX relative to stand-alone ORE systems, and example of which is shown in Illustration of Results A single MASL platform prototype is expected to produce power as cost effectively as the only commercial floating wind farm consisting of 5 spar-type platforms that comprise the Hywind Project. Using published information, the internal rate of return (IRR) of Hywind is between 8% and 10%. The estimated return for the MASL prototype is 8.7%. Both based on a realized electricity price of $0.25/kWh and design life of 25 years.
Typically, offset flowlines (both ends located subsea without a surface piercing riser) are installed and tested with the mainline back to the host facility. However, expansion of existing infrastructure in deepwater has created a need for the ability to test flowlines without a surface piercing element. To accommodate subsea expansions of brownfield developments, there exists a need for definition of criteria and design of hardware to provide for the flowline precommissioning function. This paper describes the processes implemented for garnering industry consensus and regulatory approval, as well as the criteria applied to system selection and design. Introduction The first subsea pressure testing of a production flowpath was the Macaroni Manifold testing in June, 1999. The manifold was tested to 10,000 psi in 3700 feet of water. The technology was based on ROV based injection systems, which have been used for pressure testing of subsea connections, such as jumper connectors; and high pressure packages, such as the jetting skid developed for pipeline burial on the Angus project. Einset was the first subsea Gulf of Mexico flowline to perform a regulatory hydrostatic test using an ROV based system. Typically, offset flowlines (both ends located subsea without a surface piercing riser) are installed and tested with the mainline back to the host facility. However, expansion of existing infrastructure in deepwater has created a need for the ability to test flowlines without a surface element. Einset. The SE Tahoe flowlines and wellhead were installed and became operational in 1996. The system included a spare hub on the SE Tahoe sled for future expansion. The Einset prospect is located 5 miles from the SE Tahoe sled, and was tied back to SE Tahoe with a 6-inch flowline in December 2001, as illustrated in Figures 1 and 2. Advantages of a Subsea Hydrotest System. For subsea-bysubsea flowlines, a means of hydrotesting subsea is desirable. The alternative to subsea testing is cleaning the mainline and testing both the existing mainline and new subsea line together. This may require existing production to be deferred while the flowline is displaced with multiple linefills of water to remove all hydrocarbon and residue. The contaminated water must be processed or disposed of appropriately. Alternatively, using a subsea hydrotesting system, the new segment of flowline can be tested without impacting the mainline and then a final pre-tested connection installed without loss of any production. High pressure testing in the congested confines of a production platform creates an undesirable, although manageable, hazard to personnel. However, subsea testing eliminates the exposure by relocating the pressure source to the seabed. As deepwater prospects trend toward higher shutin tubing pressures, the risk is increased. The number of deepwater 15K systems is growing quickly, requiring test pressures exceeding 18,000 psi. In addition to the higher pressures, longer offset lengths (host to well) are being enabled. The longer lengths result in greater flow assurance requirements and better insulation. Traditional hydrotesting typically utilizes surface seawater (70 degrees F).
This paper compares and contrasts key aspects of the Offshore Renewable Energy (ORE) and offshore Oil and Gas (O&G) industries. The objective is to illuminate where synergies exist in the context of technical standards as well as government regulations, policies and practices. The thesis of the work will propose a clear and harmonized approach for utilization of existing proven oil and gas standards, rules, and regulations as a key enabler for the efforts of developers of offshore renewable energy standards. Using process mapping and gap analysis the paper will identify where the standards of oil and gas and ORE overlap. The ORE sector is taking root and producing commercial power in many regions accustomed to hydrocarbon based energy production. The tools, techniques, talents, and disciplines of engineering required to support the offshore renewable energy industry have much in common with those of the O&G industry. Notwithstanding, new systems of international standards are being developed specific to offshore renewable energy and not taking full advantage of the legacy of existing standards already in place and proven by the offshore oil and gas industry. The results of the analysis are presented in the following manner: Process map showing each of the ORE modalities (i.e. MHK, Fixed Offshore Wind, Floating Offshore Wind, and OTEC), highlighting the overlap with O&G activities.Planned and existing IEC and other ORE specific standards are listed for each modalityHighlight coverage of common oil and gas standards and align to each modality of ORE.A proposal to fully leverage the existing standards for use in ORE projects and to unify the ORE standards is presented.The review of Regulations is limited to US waters, and the fractured nature of the US ORE Regulatory environment is addressed and suggested improvements made. Existing comparisons of the two industries’ codes and standards are limited to one or two ORE modalities, and this paper is meant to act as the first step in seeing ORE Standards as a unified system.
Ocean Thermal Energy Conversion, better known as OTEC is a base load power source that runs on the temperature difference between warm surface water and cold depths. Generally, the accepted minimum temperature difference is 18°C, with a minimum surface water temperature of 25°C. The maximum possible thermal efficiency of these systems is 3% to 7% and requires massive flows of seawater. The concept was first developed in the 1890's but has struggled since then, with every commercial scale system to date suffering failures on the cold water riser due to required pipe diameter (up to 14m being considered) and the required water depth to reach the cold waters, usually taken as greater than 1000 meters. This paper presents the thermodynamic analysis of an Enhanced OTEC system that will allow for an order of magnitude reduction in the size of the down risers. This enhancement should both improve the performance of the OTEC system and reduce the cost, bringing the Levelized Cost of Energy on par with Offshore Wind. Using computer modeling the new system is compared to a conventional system's performance. A comparison using a thermodynamics and energy balance, outputs of the models are used to confirm that the increase in power and a reduction required riser size are possible. The new system provides significant improvements in terms of performance, while adding some mechanical complexity, in the form of a second closed fluid loop. The Enhanced OTEC system (E-OTEC) will bring this century old technology into the 21st century as a leading source of clean energy. It is unlike any existing OTEC system.
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