Single-Phase, Two-Phase, and Multiphase Flows, and Methods to Model These Flows

Strong heterogeneity, low matrix permeability, and complex oil–water interaction make the fluid flow in carbonate rocks extremely complicated. In this study, we quantitatively characterize and simulate single-phase and multiphase flows with multiscale pore–vug–fracture structures involved in the carbonate reservoir developments. The main studies and conclusions include: (i) The CT technology is utilized to characterize the pores, fractures, and vugs of carbonate cores at multiple scales. It is found that even if the CT resolution reaches 0.5 μm, the pores of the core are still unconnected as a network, indicating that the carbonate matrix is particularly tight. The existence of fractures can increase the effective permeability, and even poorly connected fractures can significantly increase the permeability because it reduces the flow distance through the less permeable matrix. (ii) A numerical model of low-porosity strongly heterogeneous carbonate rocks was constructed based on digital image processing. Simulations of single-phase fluid flow under reservoir conditions were conducted, and the effects of surrounding pressure, pore pressure, and core size on the single-phase flow were investigated. Due to the strong heterogeneity of carbonate rocks, the pores, vugs, and fractures cause local preferential flow and disturbance within the core, which significantly affects the fluid flow path and the pressure distribution in the core. The overall permeability is a composite representation of the permeability of numerous microelements in the specimen. Permeability increases with an increasing pore pressure, and it decreases with increasing circumferential pressure. (iii) The gas–water two-phase flow model of a low-porosity strongly heterogeneous carbonate rock was established based on digital image processing. The variation law of the two-phase outlet flow velocity with the inlet gas pressure and the movement law of the two-phase interface of carbonate rock samples were obtained. Under certain surrounding pressure, the outlet gas velocity is larger than the outlet water velocity; with the increase of the inlet gas pressure, the pore space occupied by the gas phase in the rock becomes larger. With the increase of the surrounding pressure, the velocities of both outlet gas and water decrease. As the sample size decreases, the velocities of both outlet gas and water increase.

Continuous delivery of segmented reagents using pressure-driven multiphase flow in microchannels is a promising technology for high throughput microfluidic bioassays. Separation and encapsulation of the target reagents with another inert fluid provide many advantages over single phase flow in microfluidic applications of biotechnology. In order to achieve these advantages and control these multiphase flows, it is necessary to understand their generation and transport characteristics as influenced by geometrical miniaturization, channel wall properties, the effects of surfactants and operating conditions. For gas-liquid two-phase flow, dry air and deionized water were driven into hot embossed PMMA microchannels with 200 μm square test microchannels. Flow regimes, flow maps and the lengths of the gas bubbles and liquid plugs in terms of the liquid volumetric flow ratio (βL) were determined. Continuous generation of regular segmented flow was also discussed. Three sub-regimes of the Segmented flow were identified based on the statistical phase length scales observed over a substantial test channel length. For the liquid-liquid segmented flow, deionized water and perfluorocarbon with a surfactant were used as test fluids in the hot embossed polycarbonate microchannels. The effects of three expansion ratios from the injection to the test channels of 2, 4, and 16 were investigated comparing the flow regimes, transitions and maps in terms of a fixed carrier fluid volumetric flow ratio. The length of the dispersed fluids and the distance between consecutive droplets or plugs in terms of the carrier fluid volumetric flow ratio (βC) were determined. Velocities of the dispersed droplets and plugs were measured using double-pulsed laser illumination and were found to be 1.46 ± 0.08 and 1.25 ± 0.05 times faster than the superficial velocity of the segmented flow, respectively. The multiphase flow pressure drops were measured for all of the flow regimes in gas-liquid two-phase and liquid-liquid segmented flows. Each flow regime identified on the basis of topological observations, including the length scale of each fluid phase and the number of the gas bubbles or dispersed droplets in unit length with respect to the volumetric flow ratio, was associated with different trends in the pressure drop variation.

When sand, water, and COZ gas are produced along with other production fluids, erosion-corrosion can occur in carbon steel piping and fittings, Metal loss rates in erosion-corrosion can be extremely high. The term 'threshold velocity' is sometimes used to define a limiting flowstream velocity above which erosion-corrosion takes place. Threshold velocities depend on a number of factors such as temperature, solution composition (including PI-I), sand size, and pipe size. Sometimes desired production velocities are above threshold velocities and costly erosion-corrosion is a risk. But, in some cases, using a corrosion inhibitor can prevent erosion-corrosion damage by shifting threshold velocities to above production velocities. This paper describes how a laboratory flow loop and an erosion prediction model have been used to quantify the effect that using a corrosion inhibitor can have on the threshold velocity. Several examples of how the results of this research can be applied to oilfield problems are provided. Introduction The process termed 'erosion-corrosion' involves both erosion and corrosion mechanisms. In this paper, the term is applied to a process in an environment/metal system in which a protective corrosion product scale can form on the surface of the metal. At locations where the protective scale is prevented or removed by the erosive effects of the flowing medium, corrosion is again enabled at bare metal loss rates. Ellison and Wen argued that erosion-corrosion is generally most severe in two-phase (gas-liquid, or liquid-solid) flows or multiphase flows. In single-phase flows, only shear stresses of rather small magnitude can be impressed on the wale covering the pipe wall. By contrast, in two-phase flows, stresses on the scale can be quite high when a solid particle or slug of liquid (in gas-liquid flows) impinges the wall. According to Levy2 in elevated temperature air streams, such as those occurring in fossil fuel combustion chambers, the morphology of the corrosion product scale that forms on carbon steel surfaces has a major effect on the loss rate of the material. Removal of scale can take place under both ductile and brittle erosion mechanisms depending on the characteristics of thescale and of the particles. For two-phase liquid/particle flow, Lot recognized that sand may cause severe erosion and erosion-corrosion attack in the production of oil and gas, and suggested an erosion rate, of the form: R= Constant .Vn. .. .. .. .. ... .(1) where V is the flow velocity, and the power n is in the range of 1 to 3 depending on whether corrosion (closer to 1) or erosion (closer to 3) is the rate controlling process. In erosion-corrosion where the erosion component is provided by the presence of solid particles in the flow, the efficiency of the particles in removing the protective corrosion product scale plays an important role in determining the metal loss rate. Shirazi, et al, developed a procedure for predicting erosion rates in piping systems.

Influence of fractal surface roughness on multiphase flow behavior: Lattice Boltzmann simulation

One of the fundamental problems in simulating the motion of sharp interfaces between immiscible fluids is a description of the transition that occurs when the interfaces merge and reconnect. It is well known that classical methods involving sharp interfaces fail to describe this type of phenomena. Following some previous work in this area, we suggest a physically motivated regularization of the Euler equations which allows topological transitions to occur smoothly. In this model, the sharp interface is replaced by a narrow transition layer across which the fluids may mix. The model describes a flow of a binary mixture, and the internal structure of the interface is determined by both diffusion and motion. An advantage of our regularization is that it automatically yields a continuous description of surface tension, which can play an important role in topological transitions. An additional scalar field is introduced to describe the concentration of one of the fluid components and the resulting system of equations couples the Euler (or Navier–Stokes) and the Cahn–Hilliard equations. The model takes into account weak non–locality (dispersion) associated with an internal length scale and localized dissipation due to mixing. The non–locality introduces a dimensional surface energy; dissipation is added to handle the loss of regularity of solutions to the sharp interface equations and to provide a mechanism for topological changes. In particular, we study a non–trivial limit when both components are incompressible, the pressure is kinematic but the velocity field is non–solenoidal (quasi–incompressibility). To demonstrate the effects of quasi–incompressibility, we analyse the linear stage of spinodal decomposition in one dimension. We show that when the densities of the fluids are not perfectly matched, the evolution of the concentration field causes fluid motion even if the fluids are inviscid. In the limit of infinitely thin and well–separated interfacial layers, an appropriately scaled quasi–incompressible Euler–Cahn–Hilliard system converges to the classical sharp interface model. In order to investigate the behaviour of the model outside the range of parameters where the sharp interface approximation is sufficient, we consider a simple example of a change of topology and show that the model permits the transition to occur without an associated singularity.

SummaryCarbonate fractured reservoirs introduce a tremendous challenge to the upscaling of both single- and multiphase flow. The complexity comes from both heterogeneous matrix and fracture systems in which the separation of scales is very difficult. The mathematical upscaling techniques, derived from representative elementary volume (REV), must therefore be replaced by a more realistic geology-based approach. In the case of multiphase flow, an evaluation of the main forces acting during oil recovery must also be performed.A matrix-sector model from a highly heterogeneous carbonate reservoir is linked to different fracture realizations in dual-continuum simulations. An integrated iterative workflow between the geology-based static modeling and the dynamic simulations is used to investigate the effect of fracture heterogeneity on multiphase fluid flow. Heterogeneities at various scales (i.e., diffuse fractures and subseismic faults) are considered. The diffuse-fracture model is built on the basis of facies and porosity from the matrix model together with core data, image-log data, and data from outcrop-analogs. Because of poor seismic data, the subseismic-fault model is mainly conceptual and is based on the analysis of outcrop-analog data. Fluid-flow simulations are run for both single-phase and multiphase flow and gas and water injections.A better understanding of fractured-reservoirs behavior is achieved by incorporating realistic fracture heterogeneity into the geological model and analyzing the dynamic impact of fractures at various scales. In the case of diffuse fractures, the heterogeneity effect can be captured in the upscaled model. The subseismic faults, however, must be explicitly represented, unless the sigma (shape) factor is included in the upscaling process. A local grid-refinement approach is applied to demonstrate explicit fractures in large-scale simulation grids. This study provides guidelines on how to effectively scale up a heterogeneous fracture model and still capture the heterogeneous flow behavior.

The aerodynamic characteristics of droplet-laden flows past a circular cylinder are investigated using a compressible multiphase flow solver based on the six-equation model. The numerical framework is validated against benchmark cases for both multiphase and single-phase flows. Unlike prior studies that have primarily examined compressibility effects in single-phase flows or multiphase interactions at higher Reynolds numbers, this work is the first to systematically analyze the combined influence of compressibility and droplet–gas coupling in the low-Mach, laminar regime. The study explores the effects of droplet size, volume fraction, and Mach number on flow unsteadiness, droplet distribution, and aerodynamic forces. Results reveal that increasing the droplet volume fraction suppresses vortex shedding and promotes a transition to steady flow, primarily through enhanced interphase drag. Droplets preferentially accumulate in the front stagnation region, with minimal penetration into the wake, particularly under high inertial loading. The mean drag increases with droplet concentration, while the lift initially rises and then diminishes as unsteady behavior is suppressed, accompanied by a corresponding decrease in Strouhal number. At higher Mach numbers, smaller droplets contribute more significantly to drag due to stronger coupling with the compressible gas phase. Overall, the study provides new physical insights into the interplay between compressibility and multiphase dynamics in laminar flows, a regime that has remained largely unexplored.

This work experimentally investigates the impact of gas bubbles on the thermal and acoustic energy prorogation within the wellbore, at various water and air flow rates using Distributed Acoustic Sensing (DAS). This is the first study that experimentally investigates the thermal and acoustic propagation at both single and two-phase flow conditions using DAS. Our results will improve the production logging algorithms especially at multiphase flow conditions, benefit the detection of gas leakage in the vertical section of a wellbore, as well as pipeline flow monitoring. Distributed Fiber-Optic Sensing (DFOS) based production logging has drawn much attention in recent years. Comparing to conventional production logging tools, fiber-optic cables can endure much harsher borehole environments and can be deployed at a lower cost. This work presents an experimental study of using DAS to track the thermal slugging in single-phase (liquid) and two-phase (gas and liquid) flow within a vertical wellbore to estimate flow velocity and characterize multiphase flow behavior. A vertical flow loop is constructed for this research, which consists of a 7-m long transparent polyvinyl chloride (PVC) test section with a 1-inch pipe inner diameter. A single-mode optic fiber with thin plastic coating is wrapped evenly around the PVC pipe, with a fiber-to-pipe length ratio of 10.7. Tap water and compressed air are used as the testing fluids. The water and air are injected at the bottom of the test section, similar to field conditions where oil and gas mixture flows into the wellbore from the bottom. The water is directly supplied from the building water system without using an additional pump to minimize the unrelated acoustic noise. Air is supplied from an air tank charged by the building compressor with a maximum pressure of 80 psi. A peristaltic pump is used to inject a small amount of hot water (< 2% of the minimum water volume from the inlet) to generate thermal slugs at the bottom of the test section. For the case of single-phase water flow, the velocity of the thermal slugging signal is similar to the actual water velocity, as expected. For multiphase flow, the thermal signal looks almost identical with that for single-phase, although the bubble velocity is much higher than the water velocity. This observation indicates that gas, with low thermal capacity and in its bubble form, cannot carry enough heat to perturb the thermal slugs in the water severely. However, a detailed analysis of the thermal slugging velocity indicates a small increase with an increase of air flow rate. We interpret that the thermal slugging velocity is associated with the actual water velocity. The existence of the gas bubble decreases the effective water holdup (cross-sectional area occupied by the water phase) in the pipe. We find that, with a constant water volumetric rate, smaller holdup leads to higher in-situ water velocity, thus higher thermal slugging velocity. The decay of the thermal slugging signal is also analyzed. The signal decay is due to the heat exchange between the fluid and the surrounding, as well as between the warmer and cooler fluid within the pipe. We observe a faster signal decay associated with a higher bubble rate, which indicates a faster heat exchange rate with the existence of gas bubbles. Multiple physical processes may cause this correlation. First, as the gas bubbles travel through the water with a higher velocity, they generate local turbulence in the water phase and accelerate the heat exchange within the water. Another possibility is that the gas, although with much smaller thermal capacity, carries heat from the warmer section to the cooler section, therefore accelerating the thermal equilibrium process. The comparison between the single-phase water and two-phase air-water experimental results indicate that the gas bubbles generate acoustic energy as they move through the pipe. Even in the low-frequency DAS data band (<0.5 Hz), it appears that the higher background noise-level is associated with the rising bubbles. Detailed analysis of the DAS data indicates individual bubbles can be traceable if they are separated more than a gauge length.

Multiphase flow in microfluidics: From droplets and bubbles to the encapsulated structures

Fluid flow monitoring is essential in many industrial processes. However, some flow measurement methods may not be feasible in a few applications such as the ones in potentially explosive atmospheres or under presence of intense electromagnetic fields. In this study, we present the construction and evaluation of an optical fiber transducer, which is suitable for flow monitoring in industrial environments pipes. Besides single-phase flow, which has been already monitored by similar techniques in the past, we also present in this paper the measurement of two-phase gas-liquid flows. Working principle is based on the measurement of the force induced by the streaming fluid into a cantilever whose deformation is indirectly and optically monitored by means of fiber Bragg gratings. Static and dynamic tests were performed for transducer calibration and validation. In static calibration, sensor sensitivity to force corresponded to 2.34 nm/N. The transducer was successfully applied to measure single-phase flow rate in the range of 0 $\text{m}^{{3}}$ /h to 6.68 $\text{m}^{{3}}$ /h, presenting maximal uncertainty of 0.3 $\text{m}^{{3}}$ /h. Finally, the transducer was applied in two-phase gas-liquid flow, being able to correctly identify gaseous and liquid phases since the cantilever is exposed to different forces during the passage of the gas and liquid. In this way, the developed transducer may be well applied to two-phase flow monitoring.

Gas-liquid annular flow at a vertical tee junction—Part I. Flow separation

Computational fluid dynamics (CFD) analysis of single- phase and two-phase flow was performed in a 90 degree horizontal to vertical elbow with 12.7 mm inside diameter. Characteristic flow behavior was investigated at six different upstream and downstream locations of the elbow. To evaluate the effects of different phases, three different air veloci-ties and three different water velocities were used during this study. Commercial CFD code FLUENT was used to perform analysis of both single and multiphase flows. Pressure and velocity profiles at six locations showed an increase in pressure at the elbow geometry with decreasing pressure as fluid leaves from the elbow. Pressure drop behavior observed to be similar for single-phase and multiphase flows. Comparison of CFD results with available empirical models showed reasonably good agreement.

Artificial neural networks (ANNs) are useful for the prediction and control of complex systems in which it is difficult or impossible to do so from first principles. This is particularly true for many thermal systems due to the presence of complex fluid mechanics like turbulence or two-phase flows, lack of knowledge of exact material properties, complex geometries, etc. The applications of ANNs to thermal systems in general has been reviewed before by the present authors (Sen and Yang, 1999). As a continuation of this, there is a growing body of recent work related to multiphase flow and heat transfer which is the subject of this review. There are several areas of applications in multiphase flow and heat transfer to which ANN techniques have been applied. Roughly speaking they may be classified in the following manner: two-phase flow in pipes including flow regime identification in pipes and heat transfer in two-phase flows; multiphase flows and heat transfer in columns, towers, packed beds and other fluid-particle systems; heat transfer in evaporators; boiling heat transfer in liquid mixtures; heat transfer in manufacturing processes; and thermal processing of food. There is a detailed list of references that can be used for further information.Copyright © 2003 by ASME

Challenges and opportunities in modelling of proton exchange membrane fuel cells (PEMFC)

Fines migration and pore clogging induced by single- and two-phase fluid flows in porous media: From the perspectives of particle detachment and particle-level forces