Currently, the development of renewable energy has become a trend with the increasing demand for energy. Wind energy, as a renewable source of energy, is also getting more attention. Increasing effort is devoted to developing floating offshore wind turbines in deep water. In this paper, a V-shaped semisubmersible floating wind turbine was adopted to investigate the dynamic response of the system. Numerical simulations are conducted using aero-hydro coupled analysis in a time domain. The performance of the V-shaped semisubmersible floating wind turbine with respect to global platform motion, mooring line tensions and tower base moment is evaluated in this study. It turns out that the V-shaped semisubmersible offshore wind turbine is a promising concept that provides a good practice for the application of wind energy in deep water in the future.
Currently, due to energy deficiency, many countries are devoted to developing renewable energy to meet energy demands. According to the Chinese 13th renewable energy development five year plan, by 2020, total electric from renewable energy will grow to up to 27% of the total electricity generated(NDRC, 2017). Wind energy, one of the promising renewable energies, has attracted more and more attention because of its low environmental pollution. Compared with onshore wind energy, offshore wind energy has better wind condition, unlimited sites and negligible environmental impact. Especially in China, the area with rich onshore wind resource is far from the energy consumption center, which is located near the eastern coastline (Li et al., 2012). A number of studies have been carried out for offshore wind turbine analysis (Jiang et al., 2015; Shi et al., 2016; Shi et al., 2014). The bottom-fixed wind turbine is not suitable for deep water due to increase in cost (Shi, 2015). Therefore, the floating offshore wind turbine (FOWT) is becoming one of the promising solutions.
According to the offshore oil and gas industry, several different foundations are suitable for FOWT: spar buoy, tension leg platform (TLP), semi-submersible platform and barge. In particular, the semisubmersible platform, compared with spar buoy and TLP, has more feasibility in various water depth, seabed conditions and low installation costs due to the simpler installation (it is fully constructed onshore). The semi-submersible platform can also avoid the main energy range of the waves because of its relatively large natural period. The OC4 semi-submersible offshore wind turbine was simulated by Bayati (2014) to focus on the impact of second-order hydrodynamics on semi-submersible platforms. Moreover, the second-order hydrodynamic force can stimulate the oscillation of the platform and further cause fatigue damage to the structure. How the mooring systems influence the motion of the FOWT (Masciola and Robertson, 2013) determined by using coupled and uncoupled model on DeepCwind semi-submersible FOWT. Luan et al. (2016) employed a braceless semi-submersible platform to establish a numerical model and performed extreme sea states analysis on a braceless semi-submersible platform. The results showed that the platform has good stability under extreme sea and is a good design concept. A 5 WM wind turbine was employed by Kim et al. (2017), and WindFloat and OC4 floating platform were carried out to focus on the motion of FOWT and evaluating the mooring system force by using FAST (Jonkman, 2005) code.
This paper aims to numerically simulate the loading process when a moored ship is intruded by an ice ridge. Ice force caused by ice keel is calculated based on suggestions from ISO while the ice force due to consolidated layer is taken as level ice and simulated with circumferential crack method. The equation of motion is solved at each time step. A case study is given to show main features during the moored ship and ice ridge interaction. The result shows that the present numerical simulation is promising to be used in the design for moored structures in ice ridge.
In the Arctic, there exist many different types of features such as pure level ice, brash ice, ice rubble and ridges, ridge fields and icebergs, all with different structural and mechanical properties and behavior. For ships and offshore structures, first year ice ridge is a key consideration due to the extreme ice loads acting on the structures. It is crucial to determine the design load levels for offshore structures in ice-infested waters, can also bring a threat to shipping and navigation activities.
Typically, an ice ridge is formed when ice sheets are compressed against each other due to environmental factors, such as wind, current in the sea, thermal expansion etc. From geometry aspect of ice ridge, it is composed of three parts: sail, consolidated layer and keel. The above water part, called the sail, has pores filled with air and snow. The underwater part, called the keel, has pores filled with water and air pockets can exist. The ridge keel is further separated into an upper refrozen layer called the consolidated layer and a lower unconsolidated part. The consolidated layer grows through the ridge lifetime as a function of the surrounding meteorological and oceanographic conditions, air and water temperature, snow depth and the velocity of the wind, and surrounding currents are of principal importance. There was a wide variation in the shapes of the first-year sea ice ridges (Timco & Burden, 1997).
By developing general constitutive laws for ice ridge, Heinonen (2004) and Serré (2011) used finite element software to simulate the ice ridge load. At present, moored ships are often used to oil exploration and exploitation in ice-infested waters. For example, starting in the mid-1970s to the late 1980s, Dome Petroleum deployed floating drill-ships named Canmar during the summer months. In some water, the ice ridge action should be taken into consideration. A sketch of the moored ship in ice ridge is shown in Figure 1.
Shi, Wei (Dalian University of Technology) | Tan, Xiang (Nanyang Technological University) | Zhou, Li (Jiangsu University of Science and Technology) | Ning, Dezhi (Dalian University of Technology) | Karimirad, Madjid (Queen's University)
The ice loading process has a clear stochastic nature due to variations in the ice conditions and in the ice-structure interaction processes of offshore wind turbine. In this paper, a numerical method was applied to simulate a monopile fixed-bottom and a spar-type floating wind turbine in either uniform or randomly varying ice conditions, where the thickness of the ice encountered by the spar were assumed to be constant or randomly generated. A theoretical distribution of the ice thickness based on the existing measurements reported in various literatures was formulated to investigate the response characteristics of the monopile wind turbine and spar wind turbine in such ice conditions. The effect of the coupling between the ice-induced and aerodynamic loads and responses for both operational and parked conditions of the rotor was studied. Moreover, the dynamic response of wind turbine in randomly varying ice was compared and verified with that of the wind turbine in constant ice.
So far, more than 80% of the energy all over the world comes from fossil fuels. Excessive and improper use of fossil fuels has caused climate change and threatened human security and development. The Paris Agreement, which entered into force on 4 November, 2016, is a major step forward in the fight against global warming. Due to severe smog, forty Chinese cities reel under heavy air pollution. Air pollution becomes one of the key words in China in 2016 (PTI, 2016). Renewable energies play an important role for reducing greenhouse gas emissions, and thus in mitigating climate change. Offshore wind energy is recognized as one of the world's fastest growing renewable energy resources. By the end of 2015, totally 12,107 MW of offshore wind energy was installed around the world according to Global Wind Energy Council (GWEC) report (Fried, 2016). In Europe, 3230 turbines are now installed and grid-connected, making a cumulative total of 11,027 MW (Ho, 2016). However, governments outside of Europe have set ambitious targets for offshore wind and development is starting to take off in China, Japan, South Korea and the US. The 1.2 GW of capacity installed in Asia as of the end of 2015 was located China and mainly in Japan.
The development of oil and gas reservoirs in the deep water environment is playing an increasingly significant role in supporting the global energy demand. Oil field scale is an important aspect of flow assurance that determines continuous production from reservoirs, because improper scale management could result in astronomical losses. Currently most commercial software packages for scale prediction and risk assessment use stand-alone thermodynamic models that rely on water composition data as input parameters. As seawater injection has become an integral part of deepwater development, the coupling of scale modeling with reservoir simulation becomes necessary to not only track scale reactions and precipitation in the reservoir, but also to assess scaling risks in production wells and surface facilities as a result of the these reactions. Appropriate treatment strategies can thus be recommended based upon simulation results. The scale reaction for barium sulfate (BaSO4) has currently been implemented as a coupled option in our in-house reservoir simulator, CHEARS. Besides conventional reservoir simulation results, the model also outputs scale related information, such as barium and sulfate scaling ion concentrations, the amount of barium sulfate precipitation, scaling tendency of barium sulfate, as well as the time and extent of injection water breakthrough over years.
The scale model in reservoir simulation has been validated using both literature data (
Deepwater oil and gas production plays a more important role in global energy support today in which high temperature and high pressure (HTHP) conditions usually occur. Mineral solubility predictions at HTHP with mixed electrolytes is thus getting more attention since it is critical for getting rid of scaling risks under such extreme conditions. In this study, Pitzer theory was applied to predict the solubility of gypsum, anhydrite and calcite over wide ranges of temperature, pressure, and ionic strength with mixed electrolytes. Solubility of gypsum was measured from 0 to 40 °C, from 14.7 to 20,000 psi, with 0 to 4 mol NaCl/kg H2O. Anhydrite solubility reported in literature was confirmed and adopted in this study. The equilibrium constants of gypsum and anhydrite are incorporated by the temperature dependent part reported in SOLMINEQ.88, and Atkinson and Mecik’s pressure dependent part. Based on these solubility data, equilibrium constants, and other virial coefficients, virial coefficients for Ca2+ and SO42- interactions with pressure dependence (i.e.
Deep water oil and gas production has been challenged due to limited knowledge of thermodynamic properties of minerals under high temperature (150 to 200oC), high pressure (1000 to 1500 bar), and high total dissolved solids (more than 300,000 mg/L). Scale prediction models are limited by lack of experimental data and inadequate understanding of modeling parameters. With a new apparatus, solubilities of barite and calcite were measured at temperatures up to 250oC, pressures up to 22000 psi, and ionic strength up to 6 m NaCl and in the presence of elevated concentrations of mixed electrolytes representing the nealy maximum range of interferences expected in brine. Preliminary measurement of gypsum solubility under high pressures were also conducted. Based on solubility measurements, the temperature and pressure dependence of stability constants and Pitzer coefficients were validated and adjusted. In addition, specific ion interactions are validated and constructed through solubility measurement in synthetic brine with mixed electrolytes. On these bases, our thermodynamic model was improved and can be applied to scale prediction for barite and calcite under extreme conditions usually encountered in the oil field.
Kan, Amy T. (Rice University) | Zhang, Nan (Rice University) | Shi, Wei (Rice University) | Wang, Kevin (Rice University) | Wang, Lu (Rice University) | Yan, Chao (Rice University) | Yan, Fei (Rice University) | Tomson, Mason B. (Rice University) | Tomson, Ross C. (Shale water research center) | Zhu, Huiguang (Shale water research center) | Razavi, Syed M. A. (Shale water research center)
pH is one of the most important parameters for evaluating the scale and corrosion potential of the water during oil and gas production. The effectiveness of chemical treatment can also be influenced by pH in the production tubing and reservoir. Unfortunately, pH is not a conservative parameter that can be determined independently. pH changes from reservoir to surface facilities due to changes in temperature and pressure of the production system and the corresponding G/O/W phase changes. Measured pH value of a produced water sample is often unreliable and influenced by temperature and ionic strength of the solution, degree of degassing and sample preservation. Measuring pH in line or with downhole probe at real field condition can be expensive and difficult. pH can be predicted theoretically from charge balance equations more economically and reliably by assuming a good knowledge of thermodynamic equilibrium constants, activity coefficients, G/O/W flow rates, temperature, pressure, and reliable produced water composition. The author's research group recently developed a new automatic titration method to simultaneously measure total alkalinity and weak organic acids concentrations of brine. The carbonate thermodynamics were evaluated with calcite solubility studies at ultra-high temperature and pressure. The newly developed thermodynamic data and method enable accurate prediction of produced water pH at temperature and pressure typically encountered in deep water production. In this paper, the influences of water chemistry parameters on pH are reviewed. The newly developed automatic alkalinity titration method is discussed. pH calculated by the recently validated thermodynamic constants and activity coefficients are compared with live water pH measurements.
pH is an important variable in problems related to scale formation, corrosion, and inhibitor action. Scale and corrosion control is a vital part of not only production process but also development planning phase. Corrosion potential of the water is important for material selection for tubing, pipeline, and process equipment, and scaling potential is critical for the selection of an optimal scale formation strategy by choice of operation conditions and treatment technologies.
Popko, Wojciech (Fraunhofer Institute for Wind Energy and Energy System Technology IWES) | Vorpahl, Fabian (Fraunhofer Institute for Wind Energy and Energy System Technology IWES) | Zuga, Adam (Fraunhofer Institute for Wind Energy and Energy System Technology IWES) | Kohlmeier, Martin (Fraunhofer Institute for Wind Energy and Energy System Technology IWES) | Jonkman, Jason (National Renewable Energy Laboratory) | Robertson, Amy (National Renewable Energy Laboratory) | Larsen, Torben J. (Technical University of Denmark, Department of Wind Energy) | Yde, Anders (Technical University of Denmark, Department of Wind Energy) | Sætertrø, Kristian (Fedem Technology AS, Trondheim) | Okstad, Knut M. (Fedem Technology AS, Trondheim) | Nichols, James (Garrad Hassan & Partners Ltd.) | Nygaard, Tor A. (Institute for Energy Technology) | Gao, Zhen (Centre for Ships and Ocean Structures at the Norwegian University of Science and Technology) | Manolas, Dimitris (National Technical University of Athens) | Kim, Kunho (American Bureau of Shipping) | Yu, Qing (American Bureau of Shipping) | Shi, Wei (Hyunchul Park, Pohang University of Science and Technology) | Vásquez-Rojas, Andrés (Institute of Steel Construction at the Leibniz Universität Hannover) | Dubois, Jan (Institute of Steel Construction at the Leibniz Universität Hannover) | Kaufer, Daniel (Endowed Chair of Wind Energy at the Institute of Aircraft Design at Universität Stuttgart) | Thomassen, Paul (Norwegian University of Science and Technology) | de Ruiter, Marten J. (Knowledge Centre WMC) | Peeringa, Johan M. (Energy Research Centre of the Netherlands) | Huang, Zhiwen (China General Certification) | von Waaden, Heike (REpower Systems SE, Osnabrück)
In order to assess scaling risk in pipes, a better understanding of scale deposition kinetics on steel surface under realistic and complex oil field condition is needed. In this paper, we introduce the development of a novel CaCO3 pre-coated steel tubing for studies of CaCO3 crystal growth kinetics and inhibition kinetics at oilfield conditions. This approach provides a relatively stable surface area and eliminates the limits of laboratory batch experiments. Initially, the heterogeneous precipitation rate of CaCO3 from a supersaturated solution (Calcite SI=0.3-0.7) was evaluated at specific temperatures (60-80???C), linear velocities (0.01-0.75 cm/sec), and ionic strengths (0.1-1M). The curve fitted heterogeneous precipitation rate constant, kppt, ranged from 10 -5 to10 -4 cm/sec. The results are comparable to that calculated from the Sieder and Tate equation, which indicates that the crystal growth was dominated by mass transfer rate. With the injection of scale inhibitors for one hour through the pre-coated tubing, the calcium carbonate precipitation can be prevented for days, and the crystal growth rate can be significantly slowed down. Not only does this study contribute to the limited data base of scaling kinetics in actual flowing pipes, but also provides a new approach to better understand the inhibitor reaction with the subsurface. The approach and results will assist in the prediction of scaling risk as a function of brine composition, well conditions and scale inhibitor composition, which will improve our ability to predict the severity of scale risk, including the rate of scaling, minimum blockage time, and thus the minimum inhibitory concentration needed in actual flowing pipes.
The ultra-high temperature (150-250oC), pressure (1,000-2,000 bar, 15,000 to 30,000 psi) and TDS (>300,000 mg/L) in deepwater oil and gas production pose significant challenges to scaling control due to limited knowledge of mineral solubility, kinetics and inhibitor efficiency at these extreme conditions. Prediction of thermodynamic properties of common minerals is currently limited by lack of experimental data and inadequate understanding of modeling parameters. In this study, a new apparatus was built to test scale formation and inhibition at high temperatures and pressures. Solubilities of two common minerals, barite and calcite, were tested at temperature up to 250oC, pressure up to 1,500 bar (22,000 psi) and ionic strength up to 6m in solutions with elevated concentrations of mixed electrolytes (e.g., calcium, magnesium, sulfate and carbonate) representing the maximum range of interferences expected (95%CI) in oil and gas wells. As an attempt towards experimentally determining mineral solubility at high temperature, pressure and salinity, not only does this study contribute to the extremely limited data base, but it also provides a reliable approach for evaluating and adjusting model predictions at extreme conditions. Predictions by a thermodynamic model based on Pitzer's ion interaction theory were evaluated using experimental data. The dependence of Pitzer's coefficients for ion activity coefficients on temperature and pressure was examined and incorporated into the scale prediction model, whose prediction is consistent with both experimental and literature data at all conditions tested.