Countercurrent imbibition in low-permeability porous media: Nondiffusive behavior and implications in tight oil recovery

Countercurrent imbibition is an important mechanism for tight oil recovery,that is,water imbibes spontaneously from the fracture into the porous matrix while oil flows reversely into the fracture.Its significance over cocurrent imbibition and forced imbibition is highlighted when permeability reduces.We used the computed tomography(CT)scanning to measure the one-dimensional evolution of water saturation profile and countercurrent imbibition distance(CID)at different fluid pressures,initial water saturations,and permeability.Surprisingly,experiments show that CID evolution for tight reservoir cores dramatically deviates from the classical diffusive rule(i.e.,evolutes proportional to square root of time,t^(0.5)).At early stage,CID extends faster than t^(0.5)(super-diffusive);while at late stage,CID extends much slower than t^(0.5)(sub-diffusive).After tens of hours,the CID change becomes too slow to be practically efficient for tight oil recovery.This research demonstrates that this deviation from classic theory is a result of(1)a much longer characteristic capillary length than effective invasion depth,which eliminates full development of a classical displacement front;and(2)non-zero flow at low water saturation,which was always neglected for conventional reservoir and is amplified in sub-mili-Darcy rocks.To well depict the details of the imbibition front in this situation,we introduce non-zero wetting phase fluidity at low saturation into classical countercurrent imbibition model and conduct numerical simulations,which successfully rationalizes the non-diffusive behavior and fits experimental data.Our data and theory imply an optimum soaking time in tight oil recovery by countercurrent imbibition,beyond which increasing exposed fracture surface area becomes a more efficient enhanced oil recovery(EOR)strategy than soaking for longer time.

Component Content Soft-sensor Based on Neural Networks in Rare-earth Countercurrent Extraction Process

Throught fusion of the mechanism modeling and the neural networks modeling,a compo- nent content soft-sensor,which is composed of the equilibrium calculation model for multi-component rare earth extraction and the error compensation model of fuzzy system,is proposed to solve the prob- lem that the component content in countercurrent rare-earth extraction process is hardly measured on-line.An industry experiment in the extraction Y process by HAB using this hybrid soft-sensor proves its effectiveness.

CFD Simulation of Film Flow and Gas/Liquid Countercurrent Flow on Structured Packing

A mathematic model of two-phase flow and a physical model of two-dimensional (2D) vertical section for the plate-type structured packing Mellapak 250.Y were set up and verified. The models were used to study the influence of packing’s surface microstructure on the continuity of liquid film and the amount of liquid holdup. Simulation results show that the round corner shape and micro wavy structure are favorable in remaining the continuity of liquid film and increasing the amount of liquid holdup. The appropriate liquid flow rate was determined by investigating different liquid loadings to obtain an unbroken liquid film on the packing surface. The pressure difference between inlet and outlet for gas phase allowed gas and liquid to flow countercurrently in a 2D computational domain. The direction change of gas flow occurred near the phase interface area.

Research and Application Progress in Countercurrent Solvent Extraction

In this article, the recent progress made by Peking University is briefly introduced. Based on Theory of Countercurrent Extraction established by Prof. Guangxian Xu, the static equilibrium and dynamic process for two- and three-outlet countercurrent extractions, and designed the optimized parameters for the real cascades to separate different rare earth minerals, which can be scaled-up to the industrial process without any further experimental verification were systematically investigated. In order to stabilize the quality of products and improve the capability of automation for extraction process, we have also established an (()^(241)Am) stimulated X-ray fluorescent energy dispersive method to detect the elemental composition in both organic and aqueous phases, which can be used as an on-line analysis method in practice. Furthermore, the expert system and the control software with open- and close-loop models have been set up. Combined with the detected data from on-line analysis, the flow-rates of extracting, feeding, scrubbing and stripping solutions can be (controlled) in an optimum status for the industrial cascades. In addition, we have developed a new multi-input and multi-output countercurrent extraction process for separating multi-component rare earth mixture with lower chemical cost and pollution.

Response of Mode Water and Subtropical Countercurrent to Greenhouse Gas and Aerosol Forcing in the North Pacific

The response of the North Pacific Subtropical Mode Water and Subtropical Countercurrent (STCC) to changes in greenhouse gas (GHG) and aerosol is investigated based on the 20th-century historical and single-forcing simulations with the Geo-physical Fluid Dynamics Laboratory Climate Model version 3 (GFDL CM3). The aerosol effect causes sea surface temperature (SST) to decrease in the mid-latitude North Pacific, especially in the Kuroshio Extension region, during the past five decades (1950-2005), and this cooling effect exceeds the warming effect by the GHG increase. The STCC response to the GHG and aerosol forcing are opposite. In the GHG (aerosol) forcing run, the STCC decelerates (accelerates) due to the decreased (increased) mode waters in the North Pacific, resulting from a weaker (stronger) front in the mixed layer depth and decreased (increased) subduction in the mode water formation region. The aerosol effect on the SST, mode waters and STCC more than offsets the GHG effect. The response of SST in a zonal band around 40?N and the STCC to the combined forcing in the historical simulation is similar to the response to the aerosol forcing.

Component Content Soft-Sensor Based on Hybrid Models in Countercurrent Rare Earth Extraction Process

In consideration of the online measurement of the component content in rare earth countercurrent extraction separation process, the soft sensor method based on hybrid modeling was proposed to measure the rare earth component content. The hybrid models were composed of the extraction equilibrium calculation model and the Radial Basis Function (RBF) Neural Network (NN) error compensation model; the parameters of compensation model were optimized by the hierarchical genetic algorithms (HGA). In addition, application experiment research of this proposed method was carried out in the rare earth separation production process of a corporation. The result shows that this method is effective and can realize online measurement for the component content of rare earth in the countercurrent extraction.

Enantioseparation of Aminoglutethimide by High-speed Countercurrent Chromatography Using Carboxymethly-β-cyclodextrin as Chiral Selector

Enantioseparation of aminoglutethimide was performed by high-speed counter-current chromatography with a two-phase system composed of ethyl acetate： methanol： water = 10： 1： 9. The lower phase contained 20 mmol/L of carboxymethly-β-cyclodextrin as chiral selector. The enantiomers were separated in 1.2 h and identified by chiral HPLC. This method was very efficient for the chiral preparative separation.

Neural Networks Based Component Content Soft-Sensor in Countercurrent Rare-Earth Extraction

The equilibrium model for multicomponent rare earth extraction is developed using neural networks, which combined with the material balance model could give online prediction of component content in countercurrent rare earth (extraction) production. Simulation experiments with industrial operation data prove the effectiveness of the hybrid soft-(sensor).

High-speed countercurrent chromatography for purification of single-walled carbon nanotubes

A new chromatographic purification of single-walled carbon nanotubes using high-speed countercurrent chromatography is reported. The purification was accomplished on the basis of experiment that dispersed the single-walled carbon nanotubes with sodium dodecyl sulfate, and the result mixture was separated using the two phase system composed of n-butanol/water = 1/1 （v/v）. The sizes of SWNTs separated were observed by scanning electron microscopy. The results demonstrated that the high-speed countercurrent chromatography possessed a good efficency for purification of single-walled carbon nanotubes.

Situation and Developing Trend of Rare-Earth Countercurrent Extraction Processes Control

On the basis of the description of the rare-earth countercurrent extraction process, the on-line detecting method and equipments of rare-earth elements and the application in the process of the rare-earth countercurrent extraction are summarized. The procedure simulation of the computer, the automation control method and its current application are also mentioned in the process of rare-earth countercurrent extraction. The method of soft sensor is proposed. Optimal control method based on object-oriented rare-earth countercurrent extraction process and integrated automation system composed of process management system and process control system are presented, which are the developing direction of the automation of rare-earth countercurrent extraction process.

Relationship of Purity Gradient and Accumulation with Feed Composition in Two-Component Countercurrent Extraction System

The formulations of the purity gradient and accumulation were proposed, and their relationships with purity distribution were studied in twocomponent countercurrent extraction system. By the static and dynamic simulation, the purity distribution curves with various feed composition and separation factor were interrelated, and the related purity gradient and accumulation were calculated. The results show that there are purity gradient maxima in extraction and scrubbing sections for each component in both aqueous and organic phases. The accumulation of each component in both phases increases with its content in the feed. Meanwhile, its absolute value of purity gradient decreases in extraction section and increases in scrubbing section. Furthermore, the purity gradient and accumulation as the monitoring parameters for automation were evaluated. The precision of the online analysis in the sensitive point and the range of accumulation were also estimated.

AN EXPERIMENTAL STUDY ON THE COHERENT STRUCTURES AND CHAOTIC PHENOMENA IN THE AXISYMMETRIC COUNTERCURRENT SHEAR FLOW

The coherent structures and the chaotic phenomena in the transition of the axisymmetric countercurrent mixing shear flow were investigated experimentally. Two kinds of self-excited oscillation modes could exist in the axisymmetric countercurrent mixing shear flow. One is the shear layer self-excited oscillation mode corresponding to the high Reynolds number regime and the other is the jet column self-excited oscillation mode corresponding to the low Reynolds number regime in the case of the velocity ratio ranging from I to 1.5. Analyzing the auto-power spectrum, self-correlation-function and three dimensional reconstructed phase trajectory, the route to chaos through three Hopf bifurcations intercepted by an intermittence of the dynamical system corresponding to the axisymmetric countercurrent mixing shear flow was discovered when the velocity ratio is equal to 1.32.

Integrated Automation System for Rare Earth Countercurrent Extraction Process

Lower automation level in industrial rare-earth extraction processes results in high production cost, inconsistent product quality and great consumption of resources in China. An integrated automation system for extraction process of rare earth is proposed to realize optimal product indices, such as product purity,recycle rate and output. The optimal control strategy for output component, structure and function of the two-gradcd integrated automation system composed of the process management grade and the process control grade were discussed. This system is successfully applied to a HAB yttrium extraction production process and was found to provide optimal control, optimal operation, optimal management and remarkable benefits.

Seasonal variation of atmospheric coupling with oceanic mesoscale eddies in the North Pacific Subtropical Countercurrent

This study investigated the seasonal variation in the atmospheric response to oceanic mesoscale eddies in the North Pacific Subtropical Countercurrent(STCC)and its mechanism,based on satellite altimetric and reanalysis datasets.Although mesoscale eddy in the study area is more active in summer,the sea surface temperature(SST)anomaly associated with mesoscale eddies is more intense and dipolar in winter,which is largely due to the larger background SST gradient.Similarly,the impact of the oceanic eddy on sea surface wind speed and heat flux is strongest in winter,whereas its effect on precipitation rate is more significant in summer.The study revealed that the SST gradient in STCC could impact the atmosphere layer by up to 800 h Pa(900 h Pa)in boreal winter(summer)through the dominant vertical mixing mechanism.Moreover,the intensity of the SST gradient causes such seasonal variation in mesoscale air-sea coupling in the study region.In brief,a stronger(weaker)background SST gradient field in wintertime(summertime)leads to a larger(smaller)eddy-induced SST anomaly,thus differently impacting atmosphere instability and transitional kinetic energy flux over oceanic eddies,leading to seasonal variation in mesoscale air-sea coupling intensity.

Seasonal variation of the surface North Equatorial Countercurrent (NECC) in the western Pacific Ocean

The North Equatorial Countercurrent(NECC) is an important zonal fl ow in the upper circulation of the tropical Pacifi c Ocean, which plays a vital role in the heat budget of the western Pacifi c warm pool. Using satellite-derived data of ocean surface currents and sea surface heights(SSHs) from 1992 to 2011, the seasonal variation of the surface NECC in the western tropical Pacifi c Ocean was investigated. It was found that the intensity(INT) and axis position(Y_(CM)) of the surface NECC exhibit strikingly different seasonal fl uctuations in the upstream(128°–136°E) and downstream(145°–160°E) regions. Of the two regions, the seasonal cycle of the upstream NECC shows the greater interannual variability. Its INT and Y CM are greatly infl uenced by variations of the Mindanao Eddy, Mindanao Dome(MD), and equatorial Rossby waves to its south. Both INT and YC M also show semiannual signals induced by the combined effects of equatorial Rossby waves from the Central Pacifi c and local wind forcing in the western Pacifi c Ocean. In the downstream region, the variability of the NECC is affected by SSH anomalies in the MD and the central equatorial Pacifi c Ocean. Those in the MD region are especially important in modulating the Y CM of the downstream NECC. In addition to the SSH-related geostrophic fl ow, zonal Ekman fl ow driven by meridional wind stress also plays a role, having considerable impact on INT variability of the surface NECC. The contrasting features of the variability of the NECC in the upstream and downstream regions refl ect the high complexity of regional ocean dynamics.

Numerical Simulations on Countercurrent Gas-Liquid Flow in a PWR Hot Leg with Air-Water Flow in a 1/15th Scale-Model

To clarify the countercurrent flow in a PWR hot leg under reflux condensation, numerical simulations of countercurrent air-water flow for a 1/15th scale model of the PWR hot leg were conducted using the two-fluid model implemented in CFD software. In this paper, the effect of expansion of the inclined pipe, which is the actual plant geometry, was evaluated. When increasing the air velocity, CCFL characteristics and the mechanism of flow pattern transition had significant differences between the case with and without expansion of the inclined pipe. CCFL characteristics were mitigated in the case with expansion. The effect of computational grid size was also discussed. When the supplied water velocity was small, the predicted flow pattern transition point agreed well with the measured data by increasing the number of cells. On the other hand, when the air velocity was decreasing, there were no significant differences in each case.

ANALYSIS OF THE COIL CENTRIFUGAL FORCE FIELD IN COUNTERCURRENT CHROMATOGRAPHY

1 INTRODUCTIONCountercurrent chromatography(CCC)is a true liquid-liquid partition chromatographywhich totally eliminates the use of a solid support.Being a support-free system,themethod offers a number of advantages over other chromatographic methods byminimizing problems arising from the use of solid supports such as adsorptive loss andinactivation of samples,tailing of solute peaks,contamination,etc.In practice,CCCprovides its greatest advantage in preparative-scale separations where high-performanceliquid chromatography(HPLC)suffers loss of partition efficiency and high

Numerical Simulation of Liquid–Solid Countercurrent Fluidization inside an Extraction Column Based on Particle Trajectory Model

The liquid–solid countercurrent fluidization process in an extraction column was numerically simulated based on the particle trajectory model of Eulerian–Lagrangian method. The simulation approach was validated by previous experiments. A power function correlation was proposed for dimensionless slip velocity Uslip/Utand hold-up fraction φ, and the operational zone in the countercurrent fluidization was determined. Simultaneous countercurrent fluidization of particles with different diameters was also simulated. The comparison shows that the simulation results are consistent with the calculation values from the multi-particle free sedimentation model based on noninterference assumption, verifying the reliability of the approach in present work.

OPTIMIZATION OF FLOW RATE OF MOBILE PHASE IN COUNTERCURRENT CHROMATOGRAPHY

1 INTRODUCTIONCountercurrent chromatography(CCC)[1,2] is distinguished from other chromatographicmethods by its eliminating the solid support matrix from the separation column.Themethod employs an open tubular column where the partition process takes place be-tween the flowing mobile phase and the stationary phase retained by the effect of

THE EXTRACTION EQUILIBRIUM MODEL AND SIMULATION OF COUNTERCURRENT SOLVENT EXTRACTION OF Gd-Tb-Dy-HCl-HEH(EHP)-KEROSENE SYSTEM

The extraction equilibrium mathematic models for gadolinium,terbium and dysprosium in HCl-1.5 mol/L HEH(EHP)system covering a relatively wide range of lanthanide concentration and acidity,have been developed.There are four independent variables and nine parameters.The average relative error is 4.56%.A computer program for the simulation of the counter current solvent extraetion process has also been written.Thus,the Gd,Tb and Dy concentrations in both aqueous and organic phase in eaeh stage as well as the aqueous acidity may be calculated.Product purities,distribution ratio and extraction factors may also be obtained thereby.The simulation results so obtained may serve as the referenee data for designing solvent ex- traction processes including those processes providing apart from the conventional outgoing organic stream, outgoing raffinate and an extra outgoing third exit stream either organic or aqueous.