Phase Two-phase Flow Research Articles

Experimental and EOR Mechanism Study of Water Shutoff Effects on Fractured Tight Sand Gas Reservoirs Using Fuzzy Ball Fluids

In recent years, there has been quite a dispute over the water shutoff effect of fuzzy ball fluids in fractured tight sandstone gas reservoirs. The core issue of this dispute is to try and make fuzzy ball fluid stabilize gas during the water shutoff process for sustainable development. In order to solve this dispute, the Linxing He-2 reservoir matrix core and a core with artificial fractures were used to simulate interlayer water, artificial fractures, and water output channels from the side and bottom. Simulated formation water and nitrogen were used as the two-phase flow phase. The breakthrough pressure of the air and water phases was tested after plugging with fuzzy ball fluid in order to simulate and analyze the water shutoff effect of the fuzzy ball fluid and its ability to achieve air establishment and water control. The results of this study show that for the core matrix, the breakthrough pressure gradient for water and gas varied from 0.200 MPa/cm to 0.210 MPa/cm and 0.015 MPa/cm to 0.025 MPa/cm, and for artificial fractured cores, the breakthrough pressure gradient of water and gas varied from 0.035 MPa/cm to 0.040 MPa/cm and 0.015 MPa/cm to 0.020 MPa/cm. These results prove that fuzzy ball fluid can block small-scale water output channels, such as matrix pores, through the polymer film-forming structure, and plug the artistic cracks and large-scale water output channels of the water flowing into the sides and bottom through the accumulation of a large number of fuzzy balls, which greatly improves the flow resistance of water. The amount of fuzzy ball fluid should be carefully adjusted with consideration of the water output and formation conditions. For large-scale water output channels and side and bottom water shutoff operations, it is recommended that the amount of fuzzy balls be increased along with the number of fuzzy balls in the system in order to increase the breakthrough pressure of water and achieve the stable control of air and water. It is believed that the fuzzy balls would quickly change their shapes to match the sizes of fracture channels to enter into fractured reservoirs and that an active hydrophobic membrane would form on the surface of fractured rocks, with macromolecules and surfactants being dispersed in the fluid system. In addition, the interface between the fuzzy balls is also hydrophobic, which would slow down the flow of water and provide a continuous gas percolating channel after aggregating and entering into the fractures. This increases the persistence of water intruding into the formation and does not affect the percolation of the gas of fractured tight sandstone gas reservoirs. This research is of great significance for the EOR of tight sand gas reservoirs and the sustainable development of oil and gas resources in China.

Local characteristic of horizontal air–water two-phase flow by wire-mesh sensor

Two-phase flow widely exists in many industries. Understanding local characteristics of two-phase flow under different flow conditions in piping systems is important to design and optimize the industrial process for higher productivity and lower cost. Air–water two-phase flow experiments were conducted with a 16×16 conductivity wire-mesh sensor (WMS) in a horizontal pipe of a multiphase flow facility. The cross-sectional void fraction time series was analysed by the probability density function (PDF), which described the void fraction fluctuation at different flow conditions. The changes and causes of PDFs during a flow regime transition were analysed. The local structure and flow behaviour were characterized by the local flow spectrum energy analysis and the local void fraction distribution (horizontal, vertical and radial direction) analysis. Finally, three-dimensional transient flow fluctuation energy evolution and characteristic scale distribution based on wavelet analysis of air–water two-phase flow were presented, which revealed the structural features of each phase in two-phase flow.

Application of Optical Tomography for Monitoring Gas Bubbles Flow Based on Independent Component Analysis Algorithm

This paper presents the monitoring process of gas bubbles flow in water using an optical tomography system. The system is aided by an Independent Component Analysis (ICA) algorithm for distinguishing the gas bubbles in pure water. The optical attenuation model is implemented for studying the light transmissions to different media which is water and air. Several quantities of air are inserted using an air pump which is installed at the bottom of a flow pipe in order to produce the gas bubbles flow upwards. The quantity of air is controlled by using a valve and five types of bubble flow are investigated; a single bubble flow, double bubble’s flow, 25% of air opening, 50% of air opening and 100% of air opening. The concentration profiles of the gas bubble flow are constructed. The concentration profile obtained from the experiments shows that the ICA algorithm can be used as a tool for imaging the two-phase flow phase distribution.

Analytical investigation of an inductive flow sensor with arc-shaped electrodes for water velocity measurement in two-phase flows

An inductive flow sensor with spot-shaped electrodes (IFS-SE) is sensitive to the shape of the flow profile and is restricted to be used to measure the flow rate of axisymmetric single-phase flows in a circular pipe. In many cases of application, it is not possible to provide a fully developed flow profile. Therefore, the inductive flow sensor has to cope with flow profiles that are not fully developed. To improve the accuracy, an inductive flow sensor with a pair of arc-shaped electrodes flush-mounted on the internal surface of an insulating section of a pipe is proposed in this article to investigate the characteristics of vertical gas-water two-phase flows. The effect of the flow profile on the inductive flow sensor is analyzed. A key contribution of the present work is to estimate the relationship between the induced voltage and the velocity of the conductive phase in two-phase flows. The estimation is achieved by the analytical calculation of magnetic-inductive equations through the method of variables separation. The analytical solution is compared with the results from an ideal model and from numerical simulation. Experiments are conducted to calibrate the inductive flow sensor with arc-shaped electrodes (IFS-AE). It is noted that the proposed IFS-AE can be adopted to obtain the velocity of the conductive phase in two-phase flows by measuring the voltage induced on the arc-shaped electrodes.

Study on Interphase Force Quantitative Detection Device of Horizontal Pipe Gas-Liquid Two-Phase Flow

The paper focuses on the interphase force of the gas-liquid two-phase flow in the horizontal pipe design and designs a new interpahse force quantitative detection devices. On the basis of analyzing the physical models and the mathematical models, the devices got the more accurate differential pressure and the two-phase flow phase holdup, avoiding many factors by using the capacitance sensor which is made up of the complete closure outer electrode and flow media as the inner electrode. Finally, the devices achieved the quantitative detection of the interphase force through the differential pressure and the phase holdup. The experiments proved that the devices can better reflect the interphase force changes of the gas-liquid two-phase flow in the horizontal tube and reached the design goal very well.

Relationship between velocity profile and distribution of induced potential for an electromagnetic flow meter

This paper investigates the relationship between the induced electric potential and the velocity distribution of the conductive continuous phase in two-phase flows in pipes to which an electromagnetic field is applied, with a view to measuring the continuous phase velocity profile. In order to investigate the characteristics of an electromagnetic flow meter in multiphase flow, an alternating current electromagnetic flow meter was modelled using FEMLAB software. Using the model, electrodes could be placed at any position on the insulating internal surface of the flow meter to satisfy the requirement of measuring the induced potentials at specific locations at the boundary of the flow. The induced electric potential or potential differences from the electrodes were analysed for various simulated flow conditions. The numerical simulation results suggest that electromagnetic flow metering may be an effective novel method for measuring the axial velocity profile of the conducting continuous phase. Furthermore, when combined with the local volume fraction distribution of the continuous phase (obtained, for example, using Electrical Resistance Tomography, also known as ERT), it is expected that the measured continuous phase velocity profile would enable the volumetric flow rate of the continuous phase to be obtained.

Three-dimensional fluid mechanics of particulate two-phase flows in U-bend and helical conduits

The results of numerous studies performed to date have shown that the performance of various hydraulic systems can be significantly improved by using curved conduit geometries instead of straight tubes. In particular, the formation of Dean vortices, which enhance the development of centrifugal instabilities, has been identified as a factor behind reducing the near-wall concentration buildup in particulate flow devices (e.g., in membrane filtration modules). Still, several issues regarding the effect of conduit curvature on local multidimensional phenomena governing fluid flow still remain open. A related issue is concerned with the impact that conduit geometry makes on the concentration distribution of a dispersed phase in two-phase flows in general, and in particulate flows (solid/liquid or solid/gas suspensions) in particular. It turns out that only very limited efforts have been made in the past to understand the fluid mechanics of such flows via advanced computer simulations. The purpose of this paper is to present the results of full three-dimensional (3D) theoretical and numerical analyses of single- and two-phase dilute particle/liquid flows in U-bend and helical curved conduits. The numerical analysis is based on computational fluid dynamics (CFD) simulations performed using a state-of-the-art multiphase flow computer code, NPHASE. The major issues discussed in the first part of the paper are concerned with the effect of curved/coiled geometry on the evolution of flow field and the associated wall shear. It has been demonstrated that the primary curvature (a common factor for both the U-bend and helix geometries) may cause a substantial asymmetry in the radial distribution of the main flow velocity. This, in turn, leads to a significant, albeit highly nonuniform, increase in the wall shear stress. Specifically, the wall shear around the outer half of tube circumference may become twice the corresponding value for a straight tube, and gradually decrease to the straight tube level when approaching the inner bend location. Another important issue is concerned with the effect of the length of the curved section and of the straight tube just upstream of the bend. Specifically, the discontinuity in curvature at the straight-to-curved transition location results in a localized change in the wall shear distribution around the tube circumference. On the other hand, if the curved tube is sufficiently long, such as in the case of a helix, the asymmetric velocity profile eventually reaches a fully developed pattern. The effect of nondimensional flow parameters, the Reynolds and Dean numbers, on the entry length along the curved helix geometry is also investigated in this paper. It is shown that the predicted developing length agrees well with the existing experimental data. The objective of the second part of the paper is to investigate the mutual interactions between the liquid flow and solid particles in particulate two-phase flows in both the U-bend and helical geometries. It is shown that particle inertia causes an increase in the wall shear. At the same time, two interesting aspects are shown of Dean vortices on particle concentration under the effect of gravity. One of them is the shift in the particle settling zone from the bottom of the horizontal (or nearly horizontal) tube toward the inner bend of the tube. The other, even more important, is a dramatic reduction in peak concentration with increasing Dean number. Both effects are important for equipment design and optimization in biotechnology and process industries.

Seeing a new dimension - The past decade's developments On electrical impedance tomography

Abstract Multi-component and multiphase fluid flows exist in many industrial processes. The phase distribution and interfaces in an aqueous-based process or multiphase flow carries significant information about the processes. Due to the correlation of the multiphase and independency of each phase, the correct measuring of multiphase flow, in the terms of concentration, disperse interface, local velocity and mass flow rate, are of extremely challenged tasks. In 1990s, electrical capacitance tomography was originally developed for oil-water two-phase flow, then electrical resistance tomography was introduced from medical research to process engineering. Significant progress has been made during the past decade and now the technology has been proved as a powerful tool for mapping the concentration and velocity distributions of the second phase in two-phase flows, where electrical impedance differences between the two-phase fluids exist. Previous and current work on electrical resistance tomography by the author and his colleagues are reviewed. Developments on sensor, measurement, image reconstruction and application are also briefly introduced. At the end of the paper, existing challenges and prospect of new dimensions in process tomography are discussed.

Wettability Alteration to Intermediate Gas-Wetting in Porous Media at Elevated Temperatures

Wettability alteration to intermediate gas-wetting in porous media by treatment with FC-759, a fluorochemical polymer has been studied experimentally. Berea sandstone was used as the main rock sample in our work, and its wettability before and after chemical treatment was studied at various temperatures from 25 to 93°C. We also studied recovery performance for both gas/oil and oil/water systems for Berea sandstone before and after wettability alteration by chemical treatment. Our experiment shows that chemical treatment with FC-759 can result in: (1) wettability alteration from strong liquid-wetting to stable intermediate gas-wetting at room temperature and at elevated temperatures; (2) neutral wetting for gas, oil, and water phases in two-phase flow; (3) significant increase in oil mobility for gas/oil system; and (4) improved recovery behavior for both gas/oil and oil/water systems. This work reveals a potential for field application for improved gas-well deliverability and well injectivity by altering the rock wettability around wellbore in gas condensate reservoirs from strong liquid-wetting to intermediate gas-wetting.

Damping Ratio and Excitation Force of a Vibrating Tube in Two-Phase Flow.

This paper deals with the mechanism of damping and excitation force acting on a vibrating tube in two-phase flow. The gas phase flows faster than the liquid phase in two-phase flow. This relative velocity can cause turbulence and momentum diffusivity which induce pressure fluctuation and additional viscosity. The investigation of the relationship between tube vibration and two-phase flow showed that damping ratio and excitation force are closely related to the drift flux of the gas phase. From these results it was found that damping ratio ζ is given by ζ∝ρL(1-α)√jGL, and excitation force √Φeq is by √Φeq∝ρL(1-α)jGL, where, ρL is liquid density, α is void fraction, jGL is drift flux.

A Theoretical and Experimental Study to Measure the Concentration and Particle Size Distribution in Two-Phase Flows

Based on light scattering theory, an optical method is presented for measuring the concentration and particle size distribution of the dispersed phase in two-phase flows. A prototype was also constructed. Comprehensive computer simulation and numerical calculations were carried out to calibrate the correctness of this method. An experimental study was also performed in gas–solid and gas–liquid two-phase flows. The results of the measurements are given and discussed in detail.

Simulation of particle-fluid turbulence interaction in sudden-expansion flows

Turbulence interaction between gas and particle phases has been studied by numerical simulation in axisymmetric sudden-expansion chambers in this paper. A two-fluid model coupled with a k− ϵ− k p two-phase turbulence model proposed by the present authors was used in the computations. The predicted axial mean velocity, the turbulence intensity of the single phase (flow without particles) and the particle phase in two-phase flows are in agreement with the experimental data reported by Shahnam and Morris in 1989. Furthermore, predictions show that the particle mass loading strongly modifies gas-phase turbulence but has only a slight effect on particle turbulence. Comparison of the numerical results calculated by different of the k− ϵ− k p models with the experimental data indicates that the k− ϵ− k p model is inadequate and that the k− ϵ− k p model can properly predict the gas-particle turbulence in recirculating flows.

Interaction Force between Solid and Liquid Phases in Two-Phase Flow

It's necessary to consider the interaction force between solid-and liquid-phase in two-phase flows. In this paper, the governing equations of solid-liquid flows are established by space average and Reynolds average mothers. The drag force of particles is evaluated on the basis of experiments of solid-liquid flow in vertical tube. The results show that the accumulation effect of particles on drag force is closely to the particles concentration and relative density of two-phase flow.

Analysis of extractor performance. II. Longitudinal mixing of the continuous liquid in a two-phase system

Longitudinal mixing characteristics have been determined in an asymmetric rotating disc contactor for the continuous phase in two-phase flow. Comparison with longitudinal mixing in single-phase flow does not reflect adequately the actual hydrodynamic regime in the type of extractor under consideration, where longitudinal mixing in the continuous phase is substantially more extensive. This is attributed to the countercurrent flow of the dispersed phase, observed mainly at high dispersed-phase flow rates. A simple model is suggested, based on the idea of entrainment, in the wake of monodisperse drops, of a certain quantity of the continuous phase, in proportion to the surface area of the drops. The description of this phenomenon has enabled us to broaden the applicability of the expression for back flow in the existing correlation, derived for single-phase flow Processing of the experimental data proved that both the method of injection into the stationary continuous phase, and the relation proposed for evaluating the extent of longitudinal mixing were suitable for investigating two-phase systems.

Two-phase flow of a shear thinning fluid in reservoir rock

The flow of a purely viscous rheologically complex fluid as the aqueous phase in two-phase flow in a porous medium is developed. The relationship relative permeability vs. saturation is related to the pore-size distribution of the medium using a “bundle of capillaries”, generalized to allow for flow paths of various diameters and lengths. The pore size distribution is determined by a capillary pressure vs. saturation curve. A weighted shear rate and saturation-dependent viscosity function is used to calculate the aqueous phase flow rate from the multiphase Darcy equation using conventional water relative permeability values. A similar approach can be applied to the hydrocarbon phase if one suspects the displaced phase is rheologically complex. The viscosity function is represented by the empirical power law model. However, the viscosity function may also be represented by a variation of the generalized scale-up method for single-phase non-Newtonian flow in porous media. The analysis predicts interactions between advance rate, rheology, shear rate, reservoir rock morphology, and the displacing phase saturation. Some predicted interactions are absent in the case of a Newtonian/Newtonian fluid pair. The analysis is extended to a consideration of the mobility ratio referenced with respect to the displacement front between the aqueous and hydrocarbon phases. The predicted relationship between the apparent viscosity of the aqueous phase and the saturation level suggests sharp changes in polymer phase mobility can occur over rather small intervals of saturation. These results are used to develop a modified fractional flow expression for non-Newtonian two-phase flow. Fractional flow for a non-Newtonian/Newtonian fluid pair is illustrated for a shear thinning aqueous phase using the properties of a xanthan gum solution.

Equations of motion for two-phase flow in a pin bundle of a nuclear reactor

By performing Eulerian area averaging over a channel area of the local continuity, momentum and energy equations for single phase turbulent flow, assuming each phase in two-phase flows to be continuum but coupled by the appropriate “jump” conditions at the interface, the corresponding axial macroscopic balances for two-fluid model in a pin bundle are obtained. To determine the crossflow, a momentum equation in transverse (to the gap between the pins) direction is obtained for each phase by carrying out Eulerian segment averaging of the local momentum equation, where the segment is taken parallel to the gap. By considering the mixture as a whole, a diffusion model based on drift-flux velocity is formulated. In axial direction it is expressed in terms of three mixture conservation equations of mass, momentum and energy with one additional continuity equation for the vapor phase. For the determination of crossflow, transverse momentum equation for a mixture is obtained. It is discussed that the previous formulation of the two-phase flow based on the “slip” flow model and integral subchannel balances using finite control volumes is inadequate in the following respects: (a) The model is heuristic and a priori assumes the order of magnitude of the terms. An excellent example of this provided by the manner in which the form of transverse momentum equation has evolved since its first crude form. (b) The model is incomplete and incorrect when applied to two-phase mixtures in thermal non-equilibrium such as during accidental depressurization of a water cooled reactor. It is demonstrated that the governing equations presented here are based on very formal and sound physical basis and are indispensable if physically correct methods are desired for analyzing two-phase flows in a pin bundle.