Hou, Qingfeng (Key Laboratory of Oilfield Chemistry, Research Institute of Petroleum Exploration and Development, CNPC) | Zheng, Xiaobo (Key Laboratory of Oilfield Chemistry, Research Institute of Petroleum Exploration and Development, CNPC) | Guo, Donghong (Key Laboratory of Oilfield Chemistry, Research Institute of Petroleum Exploration and Development, CNPC) | Zhu, Youyi (Key Laboratory of EOR, Research Institute of Petroleum Exploration and Development, CNPC) | Yang, Hui (Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences) | Xu, Xingguang (Energy Business Unit, Commonwealth Scientific Industrial Research Organization) | Wang, Yuanyuan (Key Laboratory of Oilfield Chemistry, Research Institute of Petroleum Exploration and Development, CNPC) | Chen, Gang (Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences) | Hu, Guangxin (Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences) | Wang, Jinben (Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences)
Stimuli-responsive emulsions have attracted much attention in diverse fields. However, research on the rapid and effective demulsification based on pH-responsive emulsions has barely been reported, although they are viewed as promising canditates for oil-water separation processes after oil recovery. In the present work, we have successfully synthesized a series of pH-responsive emulsions on the basis of a novel polymer containing amphiphilic and protonated moieties. The properties of these pH-responsive emulsions including stability, morphology microscopy, Zeta potential, and interfacial tension have been extensively investigated. We observed that the prepared oil-in-water emulsion could stay stable for more than 24 h within the pH range of 8-10, while it lost 80-90% of the water in 10-20 min if the pH was adjusted to 2-4. The variation in emulsion stability can be attributed to the protonation of poly [2-(N, N-diethylamino) ethyl methacrylate] (PDEA) residues at low pH values. Accordingly the polymers intend to become more hydrophilic and depart from the oil-water interface, leading to an increased interfacial tension. Furthermore, it was found that the applied polymers aggregated at the oil-water interface and that the morphology of aggregations was strongly affected by the pH values. These proposed polymers enabled the formation of emulsion with a controllable response to the pH stimuli. This work is expected to shed light on the development of stimuli-responsive emulsions and may have significant implications in the fields of oil recovery, waste water treatment, and so forth. For example, due to the high w/o interface activity of surfactants such as heavy alkyl benzene sulfonate (HABS) and petroleum sulfonate, severe emulsion has also been found with the alkali-surfactant-polymer (ASP) produced fluid. Currently, rapid breaking of these emulsion fluid is still a big challenge.
Chen, Xin (BGP) | Wang, Guihai (CNODC) | Wang, Zhaofeng (CNODC) | Liu, Zundou (CNODC) | Liu, Zhaowei (CNODC) | Cui, Yi (CNODC) | Tian, Wenyuan (CNODC) | Wei, Xiaodong (BGP) | Hou, Liugen (BGP) | Yang, Ke (BGP) | Chen, Gang (BGP) | Xia, Yaliang (BGP) | Yan, Xiaohuan (BGP) | Zhang, Zeren (BGP) | Liu, Jingluan (BGP)
To improve the accuracy of permeability prediction, seismic constraint and sedimentary facies has often been adopted in conventional methods. However, it is porosity that both of them constrain, rather than permeability, and different pore structure with different permeability, the accuracy of permeability prediction cannot be radically improved. To address the problem of permeability prediction in carbonate reservoir, new permeability prediction technique workflow were summarized based on pore structure analysis and multi-parameters seismic inversion: division reservoir types based on the pore structure, construction of the rock types identification curve, carry out a rock type inversion and a porosity inversion constrained by seismic impedance respectively, and then get a final permeability prediction volume according to the porosity-permeability relationship and pore structure of core samples. It breaks the bottleneck that is difficult for seismic impedance (continuous variable) to constrain rock type (discrete variable), then constrains pore structure (continuous variable) related to rock type instead, and converts it into rock type using multi-parameters seismic inversion. According to the certification of new wells, this workflow have been applied successfully in carbonate reservoir of H oilfield in Middle East, it not only improves the prediction of rock type in space, but also permeability prediction accuracy.
Chen, Xin (BGP) | Zhang, Suhong (BGP) | Ou, Jin (CNODC) | Ye, Yufeng (CNODC) | Xu, Lei (CNODC) | Ma, Yingze (CNODC) | Wei, Xiaodong (BGP) | Yang, Ke (BGP) | Chen, Gang (BGP) | Zhou, Guofeng (BGP) | Xia, Yaliang (BGP) | Yan, Xiaohuan (BGP) | Zhang, Zeren (BGP) | Liu, Jingluan (BGP) | Zhou, Xiaoming (BGP)
In order to improve the accuracy of reservoir prediction results, the conventional method usually include seismic inversion, and seismic attribute analysis. Due to the limitation of the vertical resolution of seismic data, it is hard to identify the thin reservoir by seismic attributes directly. In order to improve the prediction accuracy of reservoir, this paper show a new reservoir characterization technique based on geological seismic conditioning. The new method mainly includes five steps. The first step is sedimentary facies classification based on the geological seismic analysis, such as core data, thin section analysis, FMI logging, NMR logging and conventional logging. The second step is modern sedimentary model optimization and forward modelling. In order to establish a reasonable sedimentary facies model, a similar barrier island modern sedimentary model was chosen. To understand the geological significance of seismic data, two different dominant frequency were designed for forward modelling based on the sedimentary facies model and petrophysical analysis. The third step is seismic conditioning under the guide of sedimentary facies model forward modelling. The next step is seismic constraint stochastic inversion, and the last step is reservoir characterization and new well confirm. The application of this method in A oilfield shows that the techniques not only improved the identification ability of the reprocessing seismic data, but also improved the prediction accuracy of the reservoir characterization results. This new reservoir characterization technique can integrated multidisplinary information, such as modern sedimentary model, well data and seismic data, to establish a reasonable sedimentary model, to enhance the resolution of seismic data by conditioning, and get an reasonable reservoir characterization results based on the seismic inversion.
Tong, Fangchao (Yanchang Petroleum) | Tang, Mingming (Yanchang Petroleum) | Chen, Gang (Yanchang Petroleum) | Wang, Ningbo (Yanchang Petroleum) | Liu, Peng (Schlumberger) | Yan, Gongrui (Schlumberger) | Lin, Wei (Schlumberger)
Drilling horizontal wells in YB gas field in Ordos Basin presents significant challenges due to severe wellbore instabilities problems in drilling through Permian Lower Shihezi and Upper Shanxi formations, where laminated shales overlies with sand and coal seam. In first phase of horizontal wells drilling, most wells encountered severe wellbore instabilities including pack-off, stuck-pipe, over-pull, drilling pipe lost in hole and even side track. Post-well analysis showed that these horizontal wells instabilities mainly occurred in Permian Lower Shihezi and Upper Shanxi formation where most cavings and drilling events (stuck-pipe, over-pull) were observed. In contrast, vertical exploration wells have no such instability issues in same interval. To analyze and understand the mechanism of wellbore instability issue and provide optimal mud weight and better drilling practice to reduce the risk of wellbore instabilities, an anisotropic wellbore stability modeling using Plane-of-Weakness (PoW) failure criterion was carried out in this study. The PoW failure criterion is adopted to compute the onset of rock shear sliding and/or fracture along a weak plane (bedding or fracture) and identify the potential wellbore instability risk in drilling through anisotropic rock formations. The influence of bedding orientation, rock anisotropic elastic and strength properties, and wellbore trajectory on the wellbore stability are all included in the model.
This paper describes the process and workflow of conducting PoW wellbore stability modeling for YB field wellbore drilling. The proposed drilling parameters (stable mud weight) from the modeling and its application and improvement for next wells drilling, are also included. The analysis showed that the laminated shale and coal intervals were very prone to fail when well drilled with deviation between 600 to 850. The stable mud weight computed from PoW for drilling through these intervals is 1.40-1.45 g/cc, where as it is 1.20-1.25 g/cc from conventional isotropy wellbore stability model, which was not enough to keep wellbore stable. Based on results from PoW modeling, drilling mud weight scheme was updated and applied to another 3 horizontal wells planned at nearby location. All these three wells were drilled and completed safely without severe wellbore instability issue. In these wells’ 216mm (8.5 in) section, wellbore instability related non-productive time (NPT) was reduced about 11.5 days per well and section time was reduced about 26 days per well.
This PoW modeling was first time applied in wellbore stability analysis for horizontal well drilling at Ordos Basin and the results are satisfied and encouraged. The insights provided in this paper suggests that, for drilling in other locations with similar instability challenges, PoW modeling will be a better choice to provide solution and recommendation to ensure drilling safely, improve drilling efficiency and reduce drilling costs.
Vortex shedding of multi-column floating structures is complex due to the wake interaction between front and rear columns. The vortex shed from upstream columns will impinge upon the downstream columns and change their pressure distributions on the surface, which sequentially affects the dynamic response of vortex-induced motions (VIM). This paper tries to reveal the mechanisms of the vortex shedding, wake interference, and their impacts on the VIM of a paired-column semi-submersible by means of computational fluid dynamics (CFD). In the present work, a scaled model (1:54) of paired-column semi-submersible (PC-Semi) is studied. The CFD solver used in this paper is an in-house CFD code naoe-FOAM-SJTU, which is developed on top of the OpenFOAM framework. Turbulent flows around the geometry are modeled by delayed detached-eddy simulation (DDES). Meanwhile, the motions of the model are constrained in the horizontal plane and obtained by solving six-degrees-of-freedom motions equations. Numerical simulations at different current headings and reduced velocities are performed. The overall motion responses of the structures are evaluated. Vortex shedding process and wake impingement on downstream columns are also discussed. These preliminary results show how the vortex shedding process and wake impingement influence the VIM characteristics of a multi-column floating structures.
Vortex shedding is a common physical phenomenon on flow past bluff body. It is a consequence of boundary layer separation, which is caused by the reduction of velocity in the boundary layer, combined with a positive pressure gradient. The vortex shedding will generate periodic pressure fluctuation on alternate sides of the bluff body. For long and thin cylindrical structures, the pressure fluctuation should lead to vortex-induced vibrations (VIV). In ocean engineering, the vertical columnar shaped floating structures will suffer similar excitations, which is called vortex-induced motions (VIM). VIM is very complicated due to the involvement of flow separation, rigid body motion, mooring stiffness and other physical properties of the system. Understanding the physical principle of VIM is vital to engineers to avoid mooring line fatigue failure.
In the present work, the development of sheet cavitation and the shedding of cloud cavitation around hydrofoil NACA0015 are simulated in RANS and LES method. Three kinds of turbulence models -- SST k-omega, modified SST k-omega and Smagorinsky model are used in this paper. The simulating abilities of sheet and cloud cavitation with those three turbulence models are compared in cavitation shape, shedding frequency and so on. It is found that when simulating at the cavitation number σ = 1, Smagorinsky and modified SST k-omega turbulence models perform better at the aspects of cavitation shape and shedding frequency. The numerical results also show that the vortex near the wake of sheet cavitation on the suction side is the primary reason for the pinch-off and shedding of sheet cavitation.
Cavitation is a dynamic phase-change phenomenon that often occurs in the flow over rudders, propellers, pumps and other fluid machinery. It is recognized that cavitation occurs when the local pressure drops below the saturated vapor pressure, and collapses in the area where the pressure recovers to large enough, which may lead to several problems such as vibration, erosion and noise on the surface of fluid machinery. Therefore, accurate simulation of cavitation flow becomes more and more significant in the section of propeller design.
The researches on cavitation have been conducted in the last half century. In the early study, experiment was the most effective method which often used stroboscope, pressure sensor and high-speed camera to carry out the prediction in the model scale. Rouse and Mcnown (1948) investigated the cavitation on the cylinders with different head shapes including hemispherical shape, blunt shape, ellipsoidal shape and so on at 0 degree angle of attack. Their cases were introduced as soundness check for cavitation flows by Kunz et al. (2000) and repeated by several authors in the next decades, e.g. Senocak and Shyy (2004), Ahuja et al. (2001) and so on. Kjeldsen et al. (2000) observed the flow around an hydrofoil NACA0015 in a cavitation tube. The results showed that the characteristics of the cavitation are influenced by the angle of attack (AoA) and the cavitation number. Besides, they found that the lift force of the hydrofoil fluctuated violently in a small cavitation number. The case of this hydrofoil at 6 degree angle of attack has been often used as a test case. Amromin et al. (2006) obtained a new hydrofoil OK-2003 by modifying the suction surface of NACA0015 and compared them in experiments. It was found that the cavitation on the suction surface of OK-2003 can effectively reduce the resistance of the hydrofoil, and the amplitude of lift and drag force.
Accurate prediction of hydrodynamic loads on offshore structures is of great importance for the safety design of offshore platforms in severe environment. In this work, the generation of breaking focusing wave is carried out and the wave loads on a truncated circular cylinder is investigated using the in-house CFD solver naoe-FOAM-SJTU. The time history of wave elevation at focusing location is compared with experimental data provided by KRISO. The numerical forces, pressures and the scattered wave surface elevations around the cylinder are presented. The results show that the present CFD solver can be an effective tool to deal with breaking wave-structure interactions.
Wave breaking is one of the most common sea conditions and plays an important role in many engineering problems. The forces from breaking waves have been a major concern in coastal and offshore engineering. Evaluation of breaking wave impact on fixed or floating structures is of great significance. Theoretical approaches for studying breaking wave forces are generally based on the Morison formula (Morison et al., 1950). Due to the high impact forces during a breaking wave process, an impact force term must be added to Morison formula to describe the total force from breaking waves. However, theoretical approaches are still inadequate in evaluating wave breaking force. So numerous researchers have done experimental and numerical studies on breaking wave forces on cylinders.
Previous investigations of wave forces on cylinders were mainly carried out by model tests performed in a marine basin. Wienke and Oumeraci (2005) examined the plunging breaking waves acting on a slender cylindrical pile. The time history and the intensity of slamming force were analyzed. They found that the impact force was strongly depended on the distance between breaking location and cylinder. Zang et al. (2010) carried out physical experiments on the interaction of breaking and nonbreaking steep waves with a fixed vertical cylinder. The free surface deformation around the cylinder and the horizontal forces for different wave conditions were investigated. Arntsen et al. (2011) conducted small scale experimental tests and presented the results of plunging breaking wave impact forces on a single fixed vertical cylinder. They found that the slamming force intensity along a vertical pile is triangularly distributed. Mo et al. (2013) performed laboratory experiments for solitary waves breaking on a constant slope and investigated the impact of a shoaling solitary wave on a vertical cylinder. Kim and Kim (2001) used the diffraction and the Morison method with a universal nonlinear input output model to simulate the impact forces and wave kinematics of a Draupner freak wave on a vertical cylinder.
Zigzag maneuver is one of the typical tests to estimate the ship maneuverability. Most current studies of zigzag maneuver use the simplified model, which cannot resolve the detailed flows around the maneuvering ship. Therefore, simulations of free running ship model with direct rotating propellers and turning rudders are necessary in order to reappear the realistic operational scenario. In the present work, a RANS-overset grid method is used to numerically investigate standard zigzag maneuver in waves of twin-screw ONR Tumblehome ship. Overset grids are used to deal with the complex motions of the ship hull-propeller-rudder system. Standard 10/10 zigzag maneuver in three incident waves with different wave-lengths are simulated at Fr=0.20. The open source toolbox waves2Foam is utilized to generate desired waves for the moving computational domain. Numerical computations are carried out by the in-house CFD solver naoe-FOAM-SJTU. The main parameters of the zigzag maneuver, ship motions, hydrodynamic forces and moments are presented for further analysis. Detailed flow visualizations of wave elevations and vortical structures are also illustrated. The predicted results for the zigzag maneuver in waves are compared with the available experimental measurements and overall agreement is achieved. It is found that the wavelengths can significantly affect the ship motions while the influences on overshoot angles are relatively small. Furthermore, strong nonlinear effects due to the waves can be observed through the FFT analysis of the ship motions and hydrodynamic forces.
Steering operation during ship maneuvering motion is closely related to the navigational safety. When considering ship maneuver in waves, it will further associate with the seakeeping performance, thus making the evaluation of ship maneuverability more complicated and difficult. Recently, the research of maneuvering in waves is becoming increasingly popular, consequently, a specialist committee which is responsible for maneuvering in waves is established by the 28th International Towing Tank Conference (ITTC, 2017). In general, ship maneuver in waves will experience large low-frequency maneuvering motions and high-frequency wave induced motions. Free-running ship maneuvering test in most cases is conducted by executing rudders along with rotating propellers, thus making it very complicated when evaluating the performance of fully appended ship in waves. So far, it is one of the most difficult problems in the research of ship hydrodynamics, the accurate prediction of ship maneuvering performance during free-running motion through either experimental or numerical way is still challenging.
The aim of this paper is the investigation of the two-layer-liquid sloshing phenomena inside a rigid tank using a new multiphase method developed based on the meshless MPS method. The MPS method is particularly suitable for simulating the deformations of two-phase interface in multiphase flows. To extend the MPS method to a multiphase system, special interface treatments are applied for the interface particles, including density smoothing technique, interparticle viscosity model and surface tension model. The capabilities of present multi-phase MPS method to treat this two-layer sloshing problem are assessed through comparisons with experimental data in literature, and the results show that the present method is able to capture the deformations of two-phase interface at different locations. The pressure field obtained by present method is smooth and the impact pressure at the inner walls of liquid tank shows a reasonable agreement with experiment.
On offshore structures, such as FPSOs and oil production platforms, oil-water separators are necessary for the initial processing of crude oil. However, violent multi-layer-liquid sloshing phenomena may occur when the separators are excited by the large oscillations of offshore structures. On the one hand, the multi-layer-liquid sloshing induces the undesirable motion of the two-phase interface and reduces the processing efficiency of the oil-water separators. On the other hand, the sloshing induced impact pressure can bring about critical damages to the oil-water separators. To figure out potential hazards and provide guidance for designing more efficient separators, accurate prediction method of the motion of interfaces and impact pressure is necessary to check that no undesirable resonances take place at the design stage.
In general, sloshing with only a single layer fluid has been the main focus of most studies reported, while the multi-layer-liquid sloshing phenomena have rarely been concerned. Xue et al. (2013) developed a liquid sloshing experimental rig, to study the layered liquid sloshing in a rectangular tank partially filled with water and oil. In their work, the pressure distribution on the tank walls and the interfacial wave displacement are estimated by changing external excitation frequency of the shaking table. La Rocca et al. (2005) performed a theoretical and experimental investigation on the sloshing of a two-liquid system with both two-phase interface and free surface. Sciortino et al. (2009) investigated the sloshing of a layered fluid system using both a new Hamiltonian mathematical model and new laboratory experiments, and good agreements between mathematical predictions and laboratory measurements were found in all the analyzed cases. Molin et al. (2012) reported sloshing experiments with a rectangular tank filled with three fluids of different densities, then an analytical model is proposed based on linearized potential flow theory and compared with a fully nonlinear CFD code with VOF tracking of the interfaces. However, the potential flow theory and VOF method employed in the above mentioned studies become less effective with the increase of the sloshing intensity. To overcome this limitation, a multiphase method is developed based on the meshless MPS method and applied to the numerical simulation of the two-layer-liquid sloshing phenomena in oil-water Separators.
To study the requested blind test, our in-house two-phase flow solver naoe-FOAM-SJTU is applied to simulate the wave-structure interaction problem between focused waves and the FPSO benchmark model. According to the experimental requirements, a series of focused waves with different wave steepness (kA=0.13, 0.18 and 0.21) are generated using underlying JONSWAP Spectrum. The validation work shows a good correlation when comparing the numerical wave elevation results of focused waves with the corresponding experimental results. On the basis of effective wave environments, the pressures on the FPSO bow are calculated. The diffraction effect and the wave run-up phenomenon around the FPSO hull in different wave steepness are discussed to explain the blind calculation results.
Dangerous extreme waves like focused waves are more possibly impact on the marine architectures which are dispatched to a particular place for a long-term production operation. Due to the potential method cannot solve the extreme sea states with strong non-linear phenomenon, the advantages of CFD method arouse the widespread concern in shipbuilding engineering. However, the range of model fidelity still remains considerable uncertainty when simulating the interaction of waves with offshore structures when using numerical methods. To deeply understand these issues, the wave-structure interaction and the wave evolution of the focused waves are studied in this paper.
It is known that the focused wave has significant characteristics of randomness. Thus the real sea state statistics can be hardly recorded. One striking case is the “New Year Wave” which happened in the central North Sea at Statoil Draupner Platform on Jan 1st, 1995. The peak crest elevation reached 18.5m, while the significant wave height there is 12m. (Bihs et al., 2017) Currently, as the rare appearance of focused waves in nature, the main approaches to study its generation and hydrodynamic properties are experimental and numerical methods.
Experiments are usually carried out in water flumes using wave paddles to generate focused waves. By adopting a focused wave group, many irregular wave components in a spectrum will focus at the designated time and place simultaneously. Previous method included frequency focusing method (Chaplin, 1996) and modified phase and amplitude wave maker control signal to make optimized focused waves (Schmittner et al., 2009). Nevertheless, the effectiveness of their linear wave theory decreases when solving wave groups with high non-linearity. Buldacov, Simons and Stagonas (2014) implement an empirical iterative methodology which can generate focused waves at designated time and space with any height. By controlling the frequency spectrum and phase of the wave components, the extreme wave profile can be formed in a short time and focused at the designated time and location, this make the physical experiments and numerical simulation more efficient. Several experiments are done to investigate the focus waves and the interaction between wave and structure. Liu, Zang and Ning (2009) conducted experimental and numerical studies about a series of steep focused wave groups in a water flume. By using high order boundary element method, their calculation results fitted the experimental results well, even for the waves near to breaking. As for high-order boundary element method, a domain decomposition technique is implemented by Bai and Taylor (2007) to make this method more efficient. To investigate the wave-structure interaction, a simplified FPSO model was set in the Ocean Basin at Plymouth University's COAST Laboratory (Mai, et al., 2016). This experiment took the model length, focused wave steepness and incident wave angles into account. Results were given and analyzed with a general phase-based harmonic separation method. Besides, based on the experiment of COAST laboratory, several numerical methods are used for further researches. Based on the fully nonlinear potential theory (FNPT), Greaves, Ma and Yan (2015) used the Quasi Arbitrary Lagrangian Eulerian Finite Element Method (QALE-FEM) combined with modified time domain self-correction technique. The results are in good agreement with the experimental results. Greaves, Hu, Mai and Raby (2016) then took the advantage of the computational fluid dynamics to do corresponding numerical simulations using open source code OpenFOAM. The comparison of calculation results shows OpenFOAM is reliable to solve the hydrodynamic problems of wavestructure interaction.