Displacement Flow Research Articles

Promoting recovery and resilience for internally displaced persons: lessons from Colombia

AbstractThe number of forcibly displaced persons has increased substantially since the early 2000s and has more than doubled in the last decade. Responding to the needs of forcibly displaced persons requires comprehensive legal and policy frameworks and evidence-based programmes that promote durable solutions, including sustainable movements out of poverty and their successful integration into hosting communities. In this paper, we review the dynamics of forced displacement in Colombia, the country with the largest number of internally displaced persons worldwide, and the progression of legal and policy frameworks that have been implemented since the late 1990s. We also review over two decades of research on the economic, social, and psychological consequences of forced displacement following an asset-based poverty trap framework that allows us to understand how forced displacement can alter poverty dynamics across time and generations. Throughout the review, we draw lessons for other contexts and countries affected by forced displacement and refugee flows.

Experimental study on the role of polymer addition in Saffman–Taylor instability in miscible flow displacement

The role of nonlinear rheology of polymeric fluids in finger formation and the ensuing morphology of the patterns in miscible flow displacement is examined experimentally. The poly(ethylene oxide) (PEO) is introduced in either displaced or displacing fluid. The PEO solutions exhibit shear-thinning viscosity as well as normal stresses. As viscous fingering is primarily caused by the viscosity contrast between two miscible fluids, the zero-shear viscosities of the two fluids are controlled mainly by their composition. The contribution of rheological behavior in fingering is studied by varying the molecular weight of the polymer. The development of fingering patterns in PEO solutions is observed to be more complex showing more branches and tip-splitting vis-à-vis Newtonian fluid even for the same value of effective viscosity contrast regardless of polymer addition in either fluids. Particularly, flow displacement with displaced PEO solution exhibits significantly intensified patterns such that a fractal-like growth is observed when PEO solution of either high concentration or high molecular weight is being displaced. The additional nonlinear behavior, sidebranching, tip-splitting, and shielding is attributed to the inhomogeneity in fluid viscosity and normal stresses (or elasticity) due to local flow behavior. While shear-thinning behavior promotes the longitudinal growth of fingers leading to the shielding effect, the presence of normal stresses inhibits longitudinal growth of fingers promoting fingers in the transverse direction that imparts tip-splitting. Overall, the nonlinear rheology of the fluids gives rise to the effects, in addition to the viscosity modifications, and hence, is crucial for determining the morphology of the fingering instability.

Prenatal ultrasonographic characteristics and prognosis of isolated redundant foramen ovale flap

ObjectiveTo analyze the prenatal ultrasonographic characteristics and prognosis of the isolated redundant foramen ovale flap (RFOF). MethodsFrom January 2014 to December 2021, we collected data on fetal echocardiography analyses and perinatal outcomes for fetuses with isolated RFOF in Peking University People's Hospital. ResultsWe found that 0.31% (87/28308) of participants have RFOF. The four-chamber results of the foramen ovale flap (FOF) showed that it was stiff and extended >50% or reached the lateral wall of the left atrium (LA) in diastole. As seen from the foramen ovale(FO) channel and four-chamber views, the hypermobile and redundant flap were observed shrinking and stretching with the fetal cardiac cycle, which is similar to jellyfish. The lateral displacement of flow from LA to the left ventricle (LV) around the FOF on color doppler demonstrated thin linear blood flow from the right to left and a reversal of flow across FO. A uniphasic, but not biphasic, pattern of FOF displacement was observed on M-mode. Stages I (23/87) and II (51/87) had a higher ratio of ventricular disproportion than Stage 0 (11/87) and III (2/87). We observed the RA/LA (right/left atrium) ​> ​1.2 in 53 cases (60.9%), RV/LV (right/left ventricle) ​> ​1.2 in 53 cases (60.9%), PA/AO (pulmonary/aortic artery) ​> ​1.2 in 53 cases (60.9%), and moderate or severe tricuspid regurgitation in 10 cases and moderate pericardial effusion in 2 cases (2.2%). Seventy-four RFOF cases had follow-up data. Neonatal death occurred in 2 cases; 72 fetuses survived with normal or minor heart defects. ConclusionRFOF should be considered if the left side of the heart of a fetus is smaller and related to hypermobile FOF. For isolated RFOF cases, a monthly follow-up is recommended to monitor arrhythmia or fetal hydrop status. Prompt treatment is recommended for those with adequate gestational age and lung maturity.

Primary cementing of vertical wells: displacement and dispersion effects in narrow eccentric annuli

Laminar miscible displacement flows in narrow, vertical, eccentric annuli show a wide range of interesting physical phenomena, e.g. static layers and channels, dispersive spikes/fronts and various instabilities. These are of relevance to the primary cementing of wells, where gas leakage and greenhouse gas emissions can result from ineffective cementing. The current popular way to model this process is via a Hele-Shaw approach, reducing the Navier–Stokes equations via scaling arguments and then averaging across the annular gap: the two-dimensional (2-D) gap averaged (2DGA) model. This leads to a reduced model that is computationally efficient and represents some important features of cementing flows, but is also deficient in capturing the effects of dispersion. While three-dimensional (3-D) simulations are able to capture dispersion and most other physical phenomena, they suffer from excessive computational times due to the extreme aspect ratios of cementing geometries and non-Newtonian properties of the fluids. Here we extend the 2DGA approach by modelling the high Péclet number limit of miscible duct displacement flows, to take into account the leading-order effects of dispersion. Our modified dispersive 2DGA model is well able to approximate dispersive effects that are observed by gap-averaging the results of 3-D computations, including geometric effects of eccentricity and instabilities. This represents a marked improvement over the 2DGA approach, while keeping the computational advantages of a 2-D model.

Linking of pedestrian spaces to optimize outdoor air ventilation and quality in tropical high-density urban areas

Pedestrian spaces in cities allow a large number of outdoor activities. However, they are vulnerable to vehicular pollutants. This study aims to investigate how pedestrian spaces should be linked to optimize wind conditions and air quality in tropical cities. Numerical simulations are conducted to evaluate various upwind-to-downwind linking patterns in urban areas with three levels of high-density. The results suggest that wind velocity and pollutant concentration can be effectively optimized by adjusting their linking patterns even without compromising building density. However, wind velocity and pollutant concentration are not always inversely related. Key findings are achieved: 1) expanding pedestrian spaces particularly those at the upwind of a vehicle road introduces more prevailing wind which improves both air ventilation and quality in most scenarios; 2) offsetting pedestrian spaces at the upwind/downwind of a vehicle road generates more displacement (i.e., span-wise and vertical) flow which enhances pollutant dispersion; 3) diverging pedestrian spaces from the upwind to downwind restricts transmitting pollutants to the downwind; and 4) diversifying urban block configurations with more non-uniform linking patterns improves air quality but is less useful to wind conditions. A better-ventilated pedestrian environment is expected to encourage outdoor activities, promoting sustainable living styles and vibrant mixed-use urban developments.

Experimental investigation of internal and external flow fields of jetting nozzles with different structures

Jetting has been widely used in the petroleum fields, the nozzle has been investigated for a long time and the structure has been optimized for different applications as the key part of jetting. However, most of these researches are focused on the outer flow with simulations, the real flow characteristics are not been revealed clearly. A visual experimental platform was built with Particle Image Velocimetry (PIV) and a high-pressure pump. 40 nozzles of different profiles were machined and measured. The internal and outer flow fields were captured by PIV under low velocity, and the pressure drop and flow displacement were measured under high-pressure conditions in this paper. The jetting performance such as discharge coefficient, flow core length, jet angle, and velocity distributions were analyzed. The internal flow characteristics including the flow field near the nozzle wall were captured by PIV. The converging angle and the throat section length play an important role in the jetting performance and are suggested to be set to 15° and 3 times the nozzle diameter when designed. The throat length has little effect on the flow field of the streamlined nozzle compared to the cone-straight nozzle, especially the concave curve nozzle. The vortex generated at the corner and the entrance of the throat section can indicate the boundary layer separation and transition, which agrees with our previous simulation work. All work will provide theoretical support for the design of the nozzle on-site application.

Numerical study on rotor tip flow loss in a boundary layer ingesting fan under different operating conditions

As a key component of boundary layer ingesting (BLI) propulsion system, the BLI fan operates permanently at an inflow distortion condition and the distortion-induced aerodynamic loss in the fan would seriously in turn discount the aerodynamic benefit achievements of BLI propulsion system. Moreover, as the fan rotor rotates along the annulus, the blade tip region will encounter the greatest distortion intensity and operating condition variation, thus contributing to major loss source in the BLI fan rotor. To explore the loss mechanisms in rotor blade tip region of a BLI fan, numerical investigations are conducted to study the influences of BLI inflow distortion on the flow loss in the fan rotor blade tip region at different mass flow working conditions. The results indicate that the flow loss in blade tip region increases notably from near choke to near stall condition, accounting for about 38%–51% of total aerodynamic loss in the BLI fan rotor. The loss in the tip region reaches the maximum at 240° circumferential location where the rotor blade is leaving the distortion region along the annulus because high local blade load and maximum relative Mach number are presented. In the meanwhile, as the rotor blade load increases from near choke to near stall condition, the shock structure in the blade passage varies and the interaction between shock and tip leakage flow is also intensified because of enhanced local leakage flow and forward displacement of shock. At near peak efficiency and near stall conditions, the interaction between the leakage vortex and shock in the tip region is notably intensified at 240° circumferential location and the local leakage vortex expands rapidly after the shock, leading to a vortex breakdown. The resultant flow blockage at 240° circumferential location is much higher than those at other annulus locations and the maximum blockage has increased from 18% to 42% from near choke to near stall condition, contributing fundamentally to the additional loss in the BLI fan. At the same time, by further quantifying local aerodynamic loss, it is also found that the leakage flow loss due to interaction between leakage flow and shock is the major source of loss in the BLI fan rotor, and the vortex breakdown at high blade load condition (from peak efficiency to near stall condition) could even lead to an increment of loss with a slop about three times of that at low blade load condition (near choke condition).

Displacement flows in rotating pipes

<h2>Abstract</h2> Displacement flows frequently occur in natural phenomena and industrial applications, e.g., in lung airways, oil well cementing, coating and cleaning of processing machinery. We study experimentally and numerically the effects of a pipe axial rotation on buoyant miscible flows in inclined pipes, while considering three cases of progressively increasing complexity: (i) Newtonian exchange flows (Lyu et al., 2020), (ii) Newtonian displacement flows (Lyu & Taghavi, 2018), and (iii) viscoplastic displacement flows (Lyu & Taghavi, 2020). We show how the flow dynamics is governed by an elegant balance among the characteristic velocities of the flow. We demonstrate that increasing the pipe rotation speed induces transverse mixing and results in a complete removal of the displaced fluid by the displacing fluid, above a critical rotation speed. Our findings offer insights on how to improve displacement efficiency using rotational motion.

A New Method to Calculate the Relative Permeability of Oil and Water in Tight Oil Reservoirs by Considering the Nonlinear Flow

The theoretical research on the percolation mechanism and oil-water relative permeability of low-permeability oil reservoirs is the focus and hotspot of international researchers. Oil-water relative permeability is an important parameter that describes the characteristics of oil-water two-phase flow and is widely used in the dynamic analysis of development and numerical simulation technology in the reservoir. The traditional calculation method of oil-water relative permeability (i.e., the JBN method) is based on the Darcy flow law. When the velocity and the displacement pressure gradient do not follow the linear flow law, there are some errors in the results of oil-water relative permeability calculated by the JBN method. In this paper, the traditional JBN method is improved, and we establish a new processing method of experimental data for oil-water relative permeability considering the effects of nonlinear flow, capillary pressure, and gravity in tight oil reservoirs. The experiments on the flow characteristics of single-phase oil and oil-water relative permeability under nonsteady-state conditions were carried out. The flow velocity and displacement pressure gradient show nonlinear characteristics when single-phase oil is passed through a tight core. At the same time, when the air permeability decreases from 1.92 × 10 − 3 μ m 2 to 0.1 × 10 − 3 μ m 2 , the nonlinear characteristics are becoming more and more obvious. Compared with the traditional JBN method, when the nonlinear flow characteristics are considered, the oil phase relative permeability increases, and the water phase relative permeability is slightly lower. If nonlinear flow characteristics are considered, when the water saturation increases from 0.605 to 0.699, the difference of oil phase relative permeability calculated by the JBN method and this method is gradually decreasing and, with the increase of water saturation, decreases from 0.0029 to 0.0001. In addition, the effects of capillary pressure, gravity, and the nonlinear flow coefficient on the oil-water relative permeability in tight oil reservoirs are studied. The capillary pressure also has a great influence on the relative permeability of the oil phase, and the relative permeability of the oil phase increases with the increase in capillary pressure. In the development process of the low-permeability reservoir, the seepage characteristics of each flow area are different, and the oil-water relative permeability is also different. Therefore, the research results play an important role in guiding the understanding of seepage characteristics of low permeability of tight oil reservoirs.

Role of viscoelastic fluid rheology in miscible viscous fingering

Classical viscous fingering patterns in flow displacement can be modulated by incorporating polymers into either of the two fluids. The polymeric solutions are viscoelastic fluids exhibiting both shear-thinning as well as elastic behavior. The present numerical study examines the dynamics of viscous fingering in miscible flow displacement with either displacing or displaced fluid being treated as polymeric fluid. The nonlinear rheology of the polymeric fluid is described using the White–Metzner model. The role of fluid rheology in the transient evolution of concentration field and fingering patterns defined using quantities such as mixing length, relative contact area, finger width, and the number of fingers, is investigated by performing numerical simulations. The correlation between fingering structure and rheological properties is established. The study shows that incorporation of polymer into the fluid alters the viscous fingering attributed to the three main factors: viscosity modification, shear-thinning behavior, and fluid elasticity. Primarily, incorporating polymers into the displaced (displacing) fluid leads to suppressed (enhanced) fingering patterns, attributed to modification of the viscosity contrast between two fluids, the governing parameter for viscous fingering. Interestingly, when the viscosity contrast at a gap-averaged shear-rate is held fixed, the shear-thinning behavior promotes the longitudinal growth of fingers irrespective of the fluid to which polymers are added. Moreover, the fluid elasticity ends to inhibit the growth of fingers leading to a more efficient flow displacement regardless of the flow arrangement. Thus, the study suggests that in addition to the viscosity at the gap-averaged shear-rate, the nature of the entire flow curve representing nonlinear rheology plays an important role in fingering dynamics. The mechanism for the destabilization due to shear-thinning behavior is explained by analyzing the vorticity structures, local shear-rate, and local viscosity distribution in the flow domain. The normal stress distribution is analyzed to comprehend the stabilization attributed to the fluid elasticity. Overall, the interplay between the viscosity contrast and the complete rheological description of the fluid governs the fingering dynamics.

Study on the Plugging Limit and Combination of CO2 Displacement Flow Control System Based on Nuclear Magnetic Resonance (NMR)

CO2 displacement is an important technology to reduce emissions and improve crude oil recovery, as well as prevent CO2 escape. Effective storage is key to the successful implementation of this technology, especially for medium and high permeability reservoirs. The current flow control systems that are applied to seal gas escape are mainly gas/water alternation, CO2 foam, and CO2 foam gel, but there is no clear understanding of the plugging limits of various flow control systems and the mechanism of their combined use of residual oil. Therefore, in this paper, a series of core replacement experiments are conducted for different flow control systems and their combinations. The quantitative characterization of the core pore size distribution before and after the replacement is carried out using the NMR technique to try and determine the plugging limits of different plugging systems, and to investigate the residual oil utilization patterns of self-designed flow control system combinations and common flow control system combinations under two reservoir conditions with and without large pores. The results show that the plugging limits of water/gas alternation, CO2 foam, and CO2 foam gel systems are 0.86–21.35 μm, 0.07–28.23 μm, and 7–100 μm, respectively, as inferred from the T2 (lateral relaxation time) distribution and pore size distribution. When different combinations of flow control systems are used for repelling, for reservoirs without large pore channels, the combination of flow control systems using higher strength CO2 foam first can effectively improve the degree of crude oil mobilization in small pore throats, compared to using gas/water alternation directly. For reservoirs containing large pore channels, using high-strength CO2 foam gel first to seal the large pore channels increases the degree of utilization of the large pore channels; using water/gas alternation first causes damage to the middle pore channels; High-strength CO2 foam gel seals the large pore channels when the plugging strength is not enough; and using water/gas alternation can effectively improve the degree of utilization of small and medium pore channels. The results of this paper can provide theoretical guidance for the multi-stage flow control of CO2 displacement in the field.

Flow instabilities in fluid displacement through enlarged regions in annular ducts

This work presents numerical results of flow displacement and the instabilities that appear when a viscoplastic fluid is displaced by a Newtonian one in a vertical annular duct with an enlarged region. Hydrodynamic instabilities in displacement flows may be due to viscosity and density differences, inertia effects and geometry irregularities like eccentricity and variable cross sections. If one of the fluids is non-Newtonian, the situation can be more challenging due to the dependence of the rheology on the flow kinematics. The geometry analyzed is found in the well cementation process in the oil industry, where the drilling fluid (viscoplastic behavior) is displaced by a spacer fluid (Newtonian). The drilling fluid wash out must be perfect in order to guarantee the success of the cementation operation, thus preventing the collapse of the oil well. Situations with excessive wellbore enlargement can occur, hampering the removal of the drilling fluid and the establishment of a perfect zonal isolation. The numerical solution of the problem is obtained using the finite volume technique to solve the governing conservation equations of mass and momentum. The volume of fluid method is employed to deal with the multiphase problem. The aim of this study is to look at how the governing parameters affect the flow displacement pattern and efficiency inside the enlarged region, with the goal to optimize the displacement process. The results focus on real case scenario for unstable situations, and present new findings that helps understanding the role of viscous, inertia and buoyancy effects. • Instabilities in flow displacement in enlarged annular tubes. • Well cementation process in oil industry. • Viscous, inertia and buoyancy effects on the displacement efficiency. • Displacement of a yield stress fluid by a Newtonian one.

Viscoelastic effects of immiscible liquid–liquid displacement in microchannels with bends

The displacement flow of an organic Newtonian fluid by a pure viscoelastic aqueous solution is experimentally investigated inside a circular microchannel of 200 μm. Displacement is commonly encountered in many industrial applications, from cleaning and decontamination to enhanced oil recovery. In this study, a pure viscoelastic fluid with no shear-thinning properties (known as Boger fluid) made up of polyethylene oxide, polyethylene glycol, and zinc chloride is used to displace an immiscible organic liquid (silicone oil). The results were compared against those from displacement with a Newtonian fluid of similar density and viscosity as the viscoelastic one. High-speed imaging is used to track both the residual film thickness of the organic phase and the interface deformations during displacement. It is found that the Boger fluid displacing phase produces a thinner displaced phase film compared to the Newtonian fluid, particularly at high capillary numbers. A correlation is proposed for the film thickness, which includes the Weissenberg number for the viscoelastic case. After the displacement front, the interface becomes unstable with two modes of instability identified. In the case of the Boger fluid, the two modes of instability are core shifting, which is also present in the Newtonian case, and a periodic instability from the elastic stresses during displacement. Additionally, the shape of the interfacial instabilities switches freely from asymmetric to axisymmetric ones throughout the flow. The frequency of the periodic instabilities increases with the displacing phase flow rate. It was also found that microchannel bends downstream of the observation point affect the shape and frequency of the instabilities.

Operational Processing of Big Satellite Data for Monitoring Glacier Dynamics: Case Study of Muldrow Glacier

Frequent acquisition of Synthetic Aperture Radar (SAR) data by the European Sentinel-1 satellites provides an opportunity for monitoring the dynamics of worldwide glaciers. We present a fully-automated processing system for producing multi-dimensional time series of glacier flow. We then use this fully-automated processing system to investigate the dynamics of Muldrow Glacier, located in the Denali National Park and Preserve (Alaska, AK, USA) during the October 2014—November 2021 period. We compute north, east, and vertical Surface-Parallel-Flow (SPF) and non-Surface-Parallel-Flow (nSPF) components of flow velocity and displacement with an average temporal resolution of 9 days and grid spacing of 100 m. During this period, we observe a glacier surge, a manifold increase in glacier flow velocity, that started as early as 2017 and continues until the present; however, the near completion of this surge is apparent. This glacier previously surged in 1906–1912 (the exact date is unknown) and in 1956–1957. We present our results in different ways to emphasize various aspects of the observed surge and demonstrate the full capability of our processing system. As the availability of SAR data improves, we expect that the fully-automated processing systems, similar to the one presented here, will play an increasingly dominant role and soon entirely replace manual processing.

Numerical Simulation of Robustness to Large Displacement of Optical Flow Based on Deep Learning

Traditional optical flow algorithm based on prior is sensitive to large displacement, in order to solve the problems, one optical flow algorithm based on deep learning is introduced to measure the global velocity of fluorescent oil film. The test results of numerical simulation show that the Average Endpoint Error (AEE) of HS, LK and Flownet2 are 2.4604 pixels, 2.3898 pixels and 0.9916 pixels in terms of warping 0.1s respectively, and the error of FlowNet2 is always the lowest under the conditions of large displacement. Therefore, the algorithm is more robust to large displacement than the others that is currently being used, which has certain exploration significance and engineering reference value.

Time-frequency analysis of venous pulsatile flow and sigmoid sinus vascular wall displacement causing pulsatile tinnitus using time series and magnitude squared coherence methods

Displacement of the sigmoid sinus vascular wall and intrasinus blood flow motion is known to cause pulsatile tinnitus (PT) in patients with sigmoid plate dehiscence. To investigate the source of sound that causes PT, this study sought to determine the correlation between in vivo displacement of the vascular wall and intrasinus flow hemodynamics. A confocal laser displacement sensor and color-coded Doppler ultrasound system were implemented on a participant diagnosed with venous PT. The displacement and Doppler velocity data were analyzed using time series and magnitude squared coherence methods. The median and peak displacement values of the vascular wall were 6.7 [Formula: see text]m and 11.7 [Formula: see text]m, respectively. The major frequency range of vascular displacement was below 4 Hz. The portmanteau test was rejected for different values of m. The cross-correlation of the two processes was not zero, indicating the existence of cross-correlation. The peak magnitude squared coherence of the two gauged signals was 0.3 at 7.143 Hz. The displacement of the sigmoid sinus vascular wall was temporally correlated with the intrasinus flow, although the major frequency range of the induced vascular displacement fell below the human hearing threshold. Therefore, the hydroacoustic and vibroacoustic sounds induced by the fluid–structure interaction between the vascular and osseous structures overweighed the displacement of the vascular wall at the focal dehiscence area in PT production.

Analytical Analysis on the Capillary Pressure of Underfill Flow Meniscus During the Flip-Chip Encapsulation Process

In the conventional flip-chip underfill encapsulation process, the underfill fluid is driven into the gap beneath the chip and substrate through capillary action. Particularly, the capillary pressure of the flow front determined the strength of overall capillary flow advancement through the bump array, hence the filling time and subsequently the manufacturing productivity. This paper analytically studied the capillary pressure of the flow front. Accordingly, the variation effects of bump contact angle and bump pitch on the flow front capillary pressure were presented. It was found that the variation trend of capillary pressure along the flow displacement between the region confined by two adjacent bumps is sinusoidal. The magnitude of capillary pressure is positive near bump entrant and acting along the flow direction before the capillary pressure gradually decreasing to oppose the flow advancement. The increasing of contact angle shifted the capillary pressure trend leftward with the peak being lowered, whereas the magnitude of capillary pressure decreases with the increases in bump pitch. Additionally, by studying the capillary pressure of flow meniscus, a new dynamic-based contact line jump criterion was proposed by considered the peak capillary pressure along the underfill advancement. These findings are practically useful for the design optimization of flip-chip package to promote the longevity of electronic package and reduce electronic wastes.

Experimental study on displacement of CH4 by liquid CO2 in coal seam

ABSTRACT Mine gas drainage is an important work in high gas outburst coal mines. How to improve the gas drainage concentration and drainage volume has always been the direction of exploration by coal mine technicians. In this paper, the experiment and field test of displacing CH4 with liquid CO2 were carried out. In the process of low temperature liquid CO2 phase transformation, a low stress and high permeability pressure relief area is formed in the coal and rock mass, so as to accelerate the free state of primary gas in coal and realize the intensified gas extraction of low-permeability coal seams. The results show that CH4 concentration and displacement efficiency in the displacement flow decrease at a greater rate and then stabilize; the cumulative CH4 displacement volume increases rapidly and stabilizes after reaching the critical time; the average concentration of gas drainage from single hole increases from 27.2% to 53.2%, and the gas drainage purity increases 2.3 times from 0.018 m3/min to 0.041 m3/min. The technology is simple to operate, does not produce high temperature and open flame, has the advantages of economy, safety, high efficiency and so on, it can be popularized and applied in gas mines.

Displacement flows in eccentric annuli with a rotating inner cylinder

We experimentally study the effects of inner cylinder rotation on the displacement flow of two Newtonian fluids along a horizontal eccentric annulus, with differing viscosities and densities. With the rotation of the inner cylinder, the flow behavior changes from stratified to helical, as rotation dominates buoyancy, or directly to an azimuthally dispersive regime when rotational velocity dominates axial velocity. Flow separation is observed to occur when eccentricity is high: the displacing fluid is contained in the wide gap of the annulus, and the effective displacement is delayed. Rotation is effective in creating azimuthal flow in the narrow gap, where there is limited flow and bottom-side residual fluid may be present. In most cases, rotation improves the displacement (volumetric efficiency) by shortening the length of the axial elongation of the displacement front, and eventually, steady displacements are seen. The study is motivated by displacement flows occurring during the primary cementing of long horizontal oil and gas wells. Rotating the inner cylinder (casing) is recommended. Our results suggest that this practice increases azimuthal dispersion and can prevent a narrow mud channel from forming if the excess fluid volume is used.

Turbulent displacement flows of viscoplastic fluids in obstructed eccentric annuli: Experiments

We present an experimental study of turbulent displacement flows in eccentric annuli, where the displacing fluids are water, 0.1% and 0.2% xanthan gum solutions, and the in situ fluid is a viscoplastic, 0.15% Carbopol solution. We focus on the effect of a solid obstruction on the narrow side of the annular gap, analogous to a consolidated cuttings bed in well cementing operations. For comparison we include experiments with an unobstructed test section with eccentricity e set at ∼0.5. While the displacement flow is successful without the obstruction regardless of the displacing fluid, we find that the obstruction at e∼0.5 is mostly detrimental to removal of the yield stress fluid stuck downstream of it, and a decrease in Reynolds numbers via formulation of xanthan gum solutions contribute to a less effective displacement in all situations due to the decrease in fluctuating stresses. Upstream of the obstruction, we observe complete removal of the Carbopol, likely due to enhanced vorticity effects. However, at high eccentricity values of e∼0.7, the effect of the obstruction on the displacement of Carbopol appears to be negligible, especially in the less turbulent situations with the xanthan gum solutions where the stationary Carbopol layer covers the entirety of the solid blockage, both upstream and downstream. Thus, in a highly eccentric obstructed annulus, the eccentricity remains the dominant factor to hinder the displacement.