OIL LAYER FLOW AROUND SKIMMING VESSELS

The main pay of Guantao Formation in Gudao Field is a large-scale thick positive-rhythm channel sand oil layer. At the extra high water-cut stage, the thick oil layer is waterflooded seriously, but the top remaining oil is still enrichment due to influence of reservoir heterogeneity. The research shows that the development effectiveness of tapping the potential with vertical well is bad and the economic benefit is low [1]. If horizontal well is used, the producing degree and the recovery of the remaining reserve can be improved effectively. Among various factors of affecting development effectiveness of horizontal well, the influence of intraformational bed development is much more important. The development of intraformational bed and its control on remaining oil distribution should be understood first, then the technology policy research of tapping the potential with horizontal well was conducted in order to ensure the good development effectiveness with horizontal well. In this paper, the remaining oil distribution features under the different developmental conditions of intraformational bed are expounded in detail, the intraformational bed was divided into two kinds, developed and undeveloped; according to its developmental conditions, the technology policies of horizontal well were studied respectively, and the commensurate design criteria of horizontal well was proposed. The application of the achievements in tapping the potential of remaining oil in thick positive-rhythm oil layer during the extra-high water cut period has achieved preferable effectiveness, which provides reference for that in the same type of reservoir.

An air–oil and oil–water interface detector composed of bent plastic optical fiber, photodiode, light emitting diode (LED) and five analog electric circuits was developed and the sensor system was applied to measurement of the oil layer thickness of kitchen wastewater in a grease trap (oil separator for industrial kitchen wastewater). The raw output voltage of the developed sensor system depends on the refractive indexes of the air, soybean oil and tap water. When the sensitive part of the sensor passes through the oil layer, the air–oil and oil–water interfaces can be detected by the peak of the first derivative data calculated from the output voltage of the sensor system. The optimal sampling interval of the output voltage and the optimal movement speed of the sensor are between 100 and 400 ms and over 2.56 mm/s, respectively. The detection limit of oil layer thickness is approximately 3 mm at a 100 ms sampling interval and 2.56 mm/s movement speed. To evaluate the developed sensor system, the thickness of the oil layer in the actual wastewater was measured. Good agreement between the conventional analysis value obtained by a hexane extraction method and the calculated value obtained by the developed sensor was observed. The developed plastic optical fiber sensor system is useful to measure the amount of the floating oil (oil layer thickness) in a grease trap installed in the stream of the wastewater discharged from an industrial kitchen, and the sensor materials are very cheap. A sensing system for detecting the interface of the various materials can be constructed because the refractive index of the materials may be detectable by the developed sensor.

The identification of oil and water layers is an important process on oil production. For this reason, it is necessary a sensor capable of detect water and oil layers. Since crude oil tanks present high inflammable gases that can cause explosions, a technique for determining liquids interface level that is intrinsically safe is desired. This paper presents the development and characterization of an interface level sensor based on a FBG-embedded multi-diaphragm sensors system for the detection of water and oil layers. The responses of the two diaphragms with respect to water and oil layers were characterized and a reduction of the sensitivity of the diaphragms when the water is substituted by oil was obtained due to the lower density of the oil when compared with water. Tests varying the interface of both water and oil are also presented and the sensors show a variation of its responses when the water and oil layers are changed, which proves the feasibility of the optical sensor system proposed to measure water-oil interface.

Space–time variation of the free-surface roughness pattern, due to sub-surface turbulence, is one of the most important features of turbulent open-channel flows. Despite its importance, the free-surface dynamics is not fully understood, especially regarding the advection and propagation features of surface variations. In this study, a direct numerical simulation of a smooth-wall turbulent open-channel flow allowing free-surface deformation was performed to investigate the dependence of the free-surface features on Reynolds and Froude numbers. The results show that the key features of the free surface are due to surface waves and turbulence, and one or another may prevail depending on the Froude number. While the turbulence is dominant in subcritical flow at low Froude number, the surface waves propagating upstream become more dominant at high Froude number when flow becomes supercritical. Furthermore, it was found that the advection velocity of the roughness patterns becomes slower than the mean surface velocity in the flow where the surface waves become dominant.

Linear non-modal analyses are performed to study the mechanism of how deformable free surfaces influence very-large-scale motions (VLSMs) in turbulent open channel flows. The mean velocity and eddy viscosity profiles obtained from direct numerical simulations are used in the generalised Orr–Sommerfeld and Squire equations to represent background turbulence effects. Solutions of surface-wave eigenmodes and shear eigenmodes are obtained. The results indicate that at high Froude numbers, free surfaces enhance the maximum transient growth rate of VLSMs through surface-wave eigenmodes. We then analyse the energy budget equation to reveal the underlying mechanism. For streamwise-uniform motions, the energy growth rate is enhanced by an energy production term associated with the correlation between the streamwise velocity, which is generated by the lifting-up effect of streamwise vortices composed of shear eigenmodes, and the vertical velocity, which is induced by a spanwise standing wave composed of surface-wave eigenmodes. For streamwise-varying motions, the energy growth rate is enhanced by a standing wave moving with a pair of vortices that travel at a speed approximately equal to the projection of the mean surface velocity along the wavenumber vector direction. Finally, an analytical expression of the energy production term is derived to provide the initial conditions for the maximum transient growth and explain the weak free-surface effect observed at large spanwise wavenumbers and low Froude numbers. The results demonstrate a linear non-modal mechanism in interactions between free surfaces and VLSMs in open channel flows.

We have investigated the effect of buckling of particle-stabilized water droplets on the drying kinetics. Particle-stabilized water droplets in an oil phase were prepared and the shrinking modes of the droplets during drying were controlled by the wettability of the particles. We obtained water droplets with and without buckling and used them in drying experiments. The drying times were comparable when the droplets were fully immersed in a thick oil layer. However, when the thickness of the oil layer was smaller than the droplet diameter, the buckled droplets showed faster drying. Observation of the reflection images around the droplets suggested that the buckled droplets preferentially shrank in the height direction, while the droplets without buckling isotropically shrank. Mathematical models that assumed diffusion of dissolved water molecules in the oil layer showed good agreement with the experimental data. The effective water-oil interfacial area was constant in the buckled droplets, whereas it shrank in the droplets without buckling. This would be a reason for the faster drying of the partially immersed buckled droplets. Particulate shells on liquid droplets could be used to enhance droplet drying.

The establishment of an upstream intrusion of a buoyant fluid discharged into an open-channel flow of uniform density and finite depth is studied numerically using the full Navier-Stokes and diffusion equations. The problem is posed as an initial-boundary-value problem for the laminar motions of a Boussinesq fluid. The equations are integrated numerically by finite-difference methods. The flow patterns produced are controlled by the influx of buoyancy; therefore they are characterized by an inflow densimetric Froude number. A comparison with available experimental data provides favourable support to the theoretical predictions. The critical value of densimetric Froude number of the source of a vertically downward inflow at the free surface of a channel is determined. For densimetric Froude number less than critical, an intrusion is established on the upstream side of the source. Because dissipative mechanisms associated with viscosity take a finite time to intervene, the intrusion starts as an inviscid gravity current with a propagation speed greater than the surface velocity of the stream. The front speed is proportional to the phase velocity of long internal waves. Subsequently, the front decelerates as the interfacial friction, and, if applicable, the boundary frictional forces increase simultaneously with mass entrainment across the interface. The current slows down towards a two-zone equilibrium: (1) the zone encompassing the current behind the frontal zone, where a steady state is approached with respect to the inertial frame of reference; (2) the frontal zone, where the upstream speed approaches a steady speed of frontal advance, albeit small. The upstream intrusion alters the flow pattern of the ambient stream dramatically. A significant feature of both the upstream and downstream currents is the presence of surface convergence with concomitant downwelling near the fronts. As the upstream front decelerates, wavelike disturbances are excited just behind the front at frequencies characteristic of internal waves. As the front approaches steady state, these disturbances appear to be damped. This problem has practical implications in the design of once-through cooling-water systems for power plants taking their cooling water from rivers.

The oil-water transition zone in the eastern part of the Sazhong Development Zone is located on the eastern flank of the anticline in the Sartu Oilfield, among them, three to four Sartu oil layers are sand-mudstone interbeds deposited by rivers and deltas in large inland lake basins, and the oil layer heterogeneity is more serious. To tap the remaining oil in the submerged area, our plant has deployed 24 horizontal wells in the SII1 and SII2 formations The predicted thickness of the target oil layer is generally about 1.0–2.0 m, thinly developed, It is difficult to control the trajectory to extend in the reservoir, our factory through exploration and practice in the process of tracking while drilling, developed a practical approach to design and tracking of horizontal wells. Application and cooperation of various technologies on-site have increased the oil layer drilling rate of horizontal wells to more than 80%, the success rate is over 90%, and it provides technical support for guiding the potential tapping of horizontal wells in the future.

Using core, well logging, geological analysis, production, and test data, this study characterizes a method of well logging for identifying lithology, oil or water layers, and thickness of oil layers of tight sandstone reservoir in the Chang 7 member of the Upper Triassic Yanchang Formation, southwestern Ordos Basin, China. This reservoir consists of two rock types: fine sandstone and siltstone. The fine sandstone has distinct oil traces and flecks, which strongly indicate the presence of oil, and this rock is therefore the superior reservoir. The siltstone exhibits essentially no oil shows and thus is an unproductive layer. A method of density and neutron curve normalization and overlay was used to identify the tight fine sandstone, tight siltstone, mudstone, and shale. The criteria for identifying the tight fine sandstone are a natural gamma value of less than 93 API (American Petroleum Institute units) and a difference between the normalized curves exceeding 0.05. A resistivity-porosity plot was used to identify oil or water layers relatively effectively. The criteria for identifying the tight oil layers are (1) a resistivity exceeding 28 Ω·m and a porosity exceeding 9.5% or (2) a resistivity between 20 and 28 Ω·m, a porosity exceeding 9.5%, and an oil saturation exceeding 65%. Based on the lithologic identification via normalization and overlay of the density and neutron curves and the criteria for distinguishing the tight oil layers, the thickness of the tight fine sandstone oil reservoir was accurately determined by overlaying the normalized difference curve on the resistivity curve.

Introduction: Side weir structures are extensively used in hydraulic engineering, irrigation and environmental engineering, and it usually consists of a main weir and a lateral channel. Side weirs are also used as an emergency structure. This structure is installed on one side or both sides of the main channel to divert the flow from the main channel to the side channel. Lateral outflow takes place when the water surface in the main channel rises above the weir sill. Flow over a side weir is a typical case of spatially varied flow with decreasing discharge. There have been extensive studies on side weir overflows. Most of the previous theoretical analysis and experimental research works are related to the flow over rectangular side weirs in rectangular main channels. In the current study, the flow conditions over a trapezoidal side weir located in a rectangular main channel in subcritical flow regime is considered. Materials and Methods: The experiments were performed in a rectangular open channel having provisions for a side weir at one side of the channel. The main channel was horizontal with 12 m length, 0.25 m width, and 0.5 m height, and it was installed on a frame; lateral channel that has a length of 6 m, width of 0.25 m, and height of 1 m. It was set up parallel to the main channel; walls and its bed were made up of Plexiglas plates. The side weir was positioned at a distance of 6 m from the channel’s entrance. A total of 121 experiments on trapezoidal side weirs were carried out. Results and Discussion: For trapezoidal side weir, effective non-dimensionnal parameters were identified using dimensional analysis and Buckingham's Pi-Theorem. Finally, the following non-dimensional parameters were considered as the most effective ones on the discharge coefficient of the trapezoidal side weir flow. in which Fr1= upstream Froude number, P= hight of the trapezoidal side weir, y1= upstream water depth, z=side slope of the trapezoidal side weir and T=top flow width of the trapezoidal side weir. Water surface profiles were measured along the weir crest, the main channel centerline, and far from the weir section. Different elevations in water surface profile depend on the upstream Froude number in the main channel; depth differences in low Froude numbers are at minimum values, and in high Froude numbers are at maximum amounts. The water surface level along the crest drops at the entrance of the side weir to the first half of the side weir; and it has been attributed to the side weir entrance effect at the upstream. Afterwards, the water level rises towards the downstream of the weir. According to the experimental results, measurements of the water in the centerline of the main channel are reliable and water surface drop is negligible. According to the parameters affecting the discharge coefficient for each value of z, discharge coefficient equations were developed with acceptable accuracy such that the effects of this parameter were shown separately. Finally, the general equation was proposed. The general functional form for discharge coefficient is presented as follows where the effect of the side slope parameter, z, is also considered. The mean and maximum percentage errors of the discharge coefficient computed using the proposed equation are as 2.6% and 11.5% , respectively. Conclusion: In this study, the characteristics of trapezoidal side weir overflows in subcritical flow regime were discussed. For this purpose, experimental data related to the water surface profile of the side weir and discharge coefficient were collected and analyzed. The results showed that the most efficient section for measuring water surface profile is located at the center line of the main channel. It was found that for trapezoidal side weir, the discharge coefficient depends on the Froude number, the ratio of crest height to initial depth, the overflow length to initial depth, and the side slope of the weir. In this study, conventional trapezoidal weir theory has been used in order to evaluate the discharge coefficient and provide side weir discharge equation. For this purpose, three reference depths were considered for conventional weir, and for each depth an equation was developed for the discharge coefficient. Comparison between predicted values and experimental data showed that average flow depth results in accurate outcomes for assessing the discharge coefficient. The average value of error for discharge coefficient estimation by the proposed equation is 2.6%. Thus this equation is proposed for use in practice by water engineers. Keywords: Control structure, Conventional weir, Discharge coefficient, Spatially varied flow, Trapezoidal side weir, Water surface profile

This paper presents a few hydrodynamics analyses of two corvette hulls with different operational profiles (corvette 1 with maximum maintained speed of 25 knots and corvette 2 with 35 knots), which designs follow some Brazilian Navy high-level system requirements and are based on modern world military vessels. The total resistance coefficient and wave pattern were determined from computational fluid dynamics simulations using free surface models and ITTC procedures, and the form factors of both ships by Prohaska’s method and CFD simulations at low Froude numbers (to neglect the wave resistance). A preliminary numerical analysis of bulbous bow was carried out using CFD, and it was possible to notice that, at high Froude numbers, the ship resistance substantially decreased if compared to the bulbless hull and, with low Froude numbers, the resistance subtly increased. Moreover, the propulsive arrangements of both ships were predimensioned and it was possible to notice the differences due to the operational profiles. Corvette 1 has a combined diesel and diesel propulsion system with two controllable pitch propellers, which optimum pitch was defined using the OpenProp software and the wake field from CFD. Corvette 2, which has a broader range of speed, has a propulsive arrangement of two waterjets and a gas turbine at high speeds, and a CPP with diesel engines when operating at low speeds.

Abstract

We use high-speed imaging to investigate the movement of a floating sphere pulled horizontally along a water surface. The model sphere is 10 cm in diameter and has half of the water density resulting in a half-submerged static sphere. By varying the pulling force, we investigate the flow dynamics in the subcritical Reynolds number range, of Re ≈ 2 × 104 to 2 × 105. We characterize three hydrodynamic regimes with the increase in the pulling force, to which we refer to as: low Froude number, Fr < 0.6, intermediate, 0.6 < Fr < 1.2 and high Froude number, Fr > 1.2 regimes. In the low Fr regime, the sphere moves with little disturbance of the water surface and the drag is close to half of the drag on a fully submerged sphere. In the intermediate Fr regime, a pronounced wave pattern is developed which together with the dipping of the sphere below the water level leads to an increase in the drag force. Based on a potential flow approximation for the downward force on the sphere moving along the surface, we derive a semiempirical relation for the sphere dipping as a function of the Froude number. Finally, in the high Fr regime, the sphere movement switches to a mode of periodic dipping below and surfacing above the water surface. The periodic vertical motion portrays a decrease in the average drag force.

Numerical analysis of the street canyon thermal conductance to improve urban design and climate

The critical velocity for aggregate blow-off from a built-up roof