Simultaneous Flow Of Gas Research Articles

Flow regime transition maps and pressure loss prediction of gas, oil and water three-phase flow in the vertical riser downstream 90° bend using data driven approach

The simultaneous flow of gas, oil & water is frequently encountered in pipelines during upstream petroleum operations. The multiphase flow results in different types of flow patterns based on the flow rates of fluids, physical properties and geometry of the flow domain. The flow behavior is characterized based on the governing flow patterns. Hence, the information about the flow patterns, regime maps and resulting pressure loss are important for multiphase flow system design and optimization. The current work is focused on construction of gas, oil and water, three-phase flow regime maps and developing pressure loss prediction correlations for the flow through vertical riser downstream 90° bend. The pipe internal diameter (ID) is 6 inch and the bending radius to pipe diameter ratio is 1. The observed gas-liquid flow patterns are slug, churn, and semi-annular churn flow at the given range of superficial velocities of fluids. The flow pattern data has been used to construct flow regime maps to analyze the variation in flow patterns with flow rates of fluids and compared with the available works in the literature. In addition, the change in pressure loss with respect to flow patterns has been analyzed. Previous models are used for the prediction of pressure loss. However, according to the assessment, the models underpredicted the pressure loss. Based on three-phase pressure loss data, multiple linear regression analysis has been carried out to propose new correlations for pressure loss prediction. Comparison of the calculated and experimental data showed good agreement between the results. The knowledge of flow regime variation and pressure loss correlations can help flow assurance engineers in designing and optimization of multiphase flow systems.

Detachment of particulate structures from a fiber array due to stretching and simultaneous gas flow

The main cause of high pressure drop and increased energy consumption in a filtration process is the clogging of particulate material in the upstream layers of a depth filter. To alleviate this issue, stress can be introduced into the particulate structure through stretching, which promotes rearrangement and detachment of particle structures, allowing for transfer of some of the clogged particulate material from the upstream layers to downstream void regions. This study aims to extend previous findings from experiments with single fibers to the level of an array. The goal is to analyze the introduction of a multiple stress state by performing stretching experiments with a particle-structure on a fiber array.The stretching tests investigate the influence of different process parameters such as stretching velocity and air flow velocity during stretching on the rearrangement and detachment behavior of a separated particle structures from the fiber array. Rearrangement and detachment of the particle structure are a direct consequences of the stress induced by stretching. The experiments showed a significant increase in relative free projection area of fiber interspaces (RFPI) of up to 160% and thus a large-scale removal of particle material from the fiber interspaces when the flow velocity was increased from 0.05 m/s to 0.8 m/s. Surprisingly, the radial rearrangement of the compact particle structures during stretching resulted in a clogging and blockage of the interfiber spaces (negative RFPI in the range of minimum −54% after the first stretching cycle) and not in a total release of the interfiber spaces. The size of the particle structures in the experiments decreased by about 331 μm with the number of stretching cycles, indirectly confirming the presence of residual structures. Preliminary experiments also confirmed an increased influence on the rearrangement and detachment (removed pariticulater material of about 30%) of particle structures by further increasing the fiber distance of 27 μm and thus introducing a biaxial stretching into the particle structure.

An Integrated Modeling Approach for Vertical Gas Migration Along Leaking Wells Using a Compressible Two-Fluid Flow Model

Gas migration behind casings can occur in wells where the annular cement barrier fails to provide adequate zonal isolation. A direct consequence of gas migration is annular pressure build-up at wellhead, referred to as sustained casing pressure (SCP). Current mathematical models for analyzing SCP normally assume gas migration along the cemented interval to be single-phase steady-state Darcy flow in the absence of gravity and use a drift-flux model for two-phase transport through the mud column above the cement. By design, such models do not account for the possible simultaneous flow of gas and liquid along the annulus cement or the impact of liquid saturation within the cemented intervals on the surface pressure build-up. We introduce a general compressible two-fluid model which is solved over the entire well using a newly developed numerical scheme. The model is first validated against field observations and used for a parametric study. Next, detailed studies are performed, and the results demonstrate that the surface pressure build-up depends on the location of cement intervals with low permeability, and the significance of two-phase co-current or counter-current flow of liquid and gas occurs along cement barriers that have an initial liquid saturation. As the magnitude of the frictional pressure gradient associated with counter-current of liquid and gas can be comparable to the relevant hydrostatic pressure gradient, two-phase flow effects can significantly impact the interpretation of the wellhead pressure build-up.

Flow pattern identification and measurement techniques in gas-liquid-liquid three-phase flow: A review

The simultaneous flow of gas, oil, and water forms various flow patterns due to the complex interfacial relationships. Three-phase flow patterns are classified as the gas-liquid and liquid-liquid flow patterns. Pressure drop, void fraction, liquid holdup, and phase distribution are important characteristics of the three-phase flow. These characteristics are generally associated with the three-phase flow patterns. Hence, the knowledge about flow patterns can help to predict the overall behavior of the three-phase flow. Studies have been conducted to identify three-phase flow pattern and their characteristics at various superficial velocities of gas, oil, and water. The major purpose of the studies is to gather information about the three-phase co-current flow and use it for improvement of the efficiency of the flow systems. Therefore, the accuracy of the measurement technique is critical. Several types of flow pattern identification and measurement techniques have been developed to improve accuracy and provide high-quality results. In this article, classical and advanced techniques used for the three-phase flow identification and measurement have been reviewed. The survey will help the researchers working in the area of multiphase flow to choose the right technique based on the objectives of the studies.

Foam Generation by Capillary Snap-Off in Flow Across a Sharp Permeability Transition

Summary Foam reduces gas mobility and can improve sweep efficiency in an enhanced-oil-recovery (EOR) process. Previous studies show that foam can be generated in porous media by exceeding a critical velocity or pressure gradient. This requirement is typically met only near the wellbore, and it is uncertain whether foam can propagate several tens of meters away from wells as the local pressure gradient and superficial velocity decreases. Theoretical studies show that foam can be generated, independent of pressure gradient, during flow across an abrupt increase in permeability. In this study, we validate theoretical predictions through a variety of experimental evidence. Coreflood experiments involving simultaneous injection of gas and surfactant solution at field-like velocities are presented. We use model consolidated porous media made out of sintered glass, with a well-characterized permeability transition in each core. The change in permeability in these artificial cores is analogous to sharp, small-scale heterogeneities, such as laminations and cross laminations. Pressure gradient is measured across several sections of the core to identify foam-generation events and the subsequent propagation of foam. X-ray computed tomography (CT) provides dynamic images of the coreflood with an indication of foam presence through phase saturations. We investigate the effects of the magnitude of permeability contrast on foam generation and mobilization. Experiments demonstrate foam generation during simultaneous flow of gas and surfactant solution across a sharp increase in permeability, at field-like velocities. The experimental observations also validate theoretical predictions of the permeability contrast required for foam generation by “snap-off” to occur at a certain gas fractional flow. Pressure-gradient measurements across different sections of the core indicate the presence or absence of foam and the onset of foam generation at the permeability change. There is no foam present in the system before generation at the boundary. CT measurements help visualize foam generation and propagation in terms of a region of high gas saturation developing at the permeability transition and moving downstream. If coarse foam is formed upstream, then it is transformed into stronger foam at the transition. Significant fluctuations are observed in the pressure gradient across the permeability transition, suggesting intermittent plugging and mobilization of flow there. This is the first CT-assisted experimental study of foam generation by snap-off only, at a sharp permeability increase in a consolidated medium. The results of experiments reported in this paper have important consequences for a foam application in highly heterogeneous or layered formations. Not including the effect of heterogeneities on gas mobility reduction in the presence of surfactant could underestimate the efficiency of the displacement process.

3D pore network modeling and simulation for dynamic displacement of gas and condensate in wellbore region

Condensate dropout in near a wellbore region in gas condensate reservoir is the main reason of low well deliverability. Many researchers have studied gas and condensate relative permeabilities (RPs) in this region to find the condition for better deliverability. It is known that RP is a function of capillary number in low interfacial tension (IFT) systems such as gas-condensate. The positive dependency of RPs to velocity which is referred to as "positive coupling effect" is related to the simultaneous flow of gas and condensate associated with intermittent opening and closure of channels in porous media. The negative dependency of RPs to velocity named "negative inertia" is due to non-Darcy high-velocity flow. In this study, a 3D pore network modeling is developed to investigate fluids distribution in a gas-condense system at a pore scale to find out the effects of IFT and velocity on RPs. A new method is developed that applies a flash calculation in all throats in the network to estimate the amount of accumulated condensate in throats' corners at different time steps. A modified form of Poiseuille's law for polygonal cross-sectional throats is used to find and update pressure field and fluids distribution in the network and to determine the quantity of pushed out condensate from closed throats to neighboring throats. The displacement mechanism is considered to be determined by the volume of displaced phases in throats without applying any correlation. Simulation results indicate that gas and condensate RPs are increased by an increase in velocity. However, RPs sensitivity to velocity is reduced by increasing IFT which is in agreement with previous studies.

Modeling Two-Phase Flowback of Multifractured Horizontal Wells Completed in Shale

Summary Early fluid production and flowing pressure data gathered immediately after fracture stimulation of multifractured horizontal wells may provide an early opportunity to generate long-term forecasts in shale-gas (and other hydraulically fractured) reservoirs. These early data, which often consist of hourly (if not more frequent) monitoring of fracture/formation fluid rates, volumes, and flowing pressures, are gathered on nearly every well that is completed. Additionally, fluid compositions may be monitored to determine the extent of load fluid recovery, and chemical tracers added during stage treatments to evaluate inflow from each of the stages. There is currently debate within the industry of the usefulness of these data for determining the long-term production performance of the wells. “Rules of thumb” derived from the percentage of load-fluid recovery are often used by the industry to provide a directional indication of well performance. More-quantitative analysis of the data is rarely performed; it is likely that the multiphase-flow nature of flowback and the possibility of early data being dominated by wellbore-storage effects have deterred many analysts. In this work, the use of short-term flowback data for quantitative analysis of induced-hydraulic-fracture properties is critically evaluated. For the first time, a method for analyzing water and gas production and flowing pressures associated with the flowback of shale-gas wells, to obtain hydraulic-fracture properties, is presented. Previous attempts have focused on single-phase analysis. Examples from the Marcellus shale are analyzed. The short (less than 48 hours) flowback periods were followed by long-term pressure buildups (approximately 1 month). Gas + water production data were analyzed with analytical simulation and rate-transient analysis methods designed for analyzing multiphase coalbed-methane (CBM) data. This analogy is used because two-phase flowback is assumed to be similar to simultaneous flow of gas and water during long-term production through the fracture system of coal. One interpretation is that the early flowback data correspond to wellbore + fracture volume depletion (storage). It is assumed that fracture-storage volume is much greater than wellbore storage. This flow regime appears consistent with what is interpreted from the long-term pressure-buildup data, and from the rate-transient analysis of flowback data. Assuming further that the complex fracture network created during stimulation is confined to a region around perforation clusters in each stage, one can see that fluid-production data can be analyzed with a two-phase tank-model simulator to determine fracture permeability and drainage area, the latter being interpreted to obtain an effective (producing) fracture half-length given geometrical considerations. Total fracture half-length, derived from rate-transient analysis of online (post-cleanup) data, verifies the flowback estimates. An analytical forecasting tool that accounts for multiple sequences of post-storage linear flow, followed by late-stage boundary flow, was developed to forecast production with flowback-derived parameters, volumetric inputs, matrix permeability, completion data, and operating constraints. The preliminary forecasts are in very good agreement with online production data after several months of production. The use of flowback data to generate early production forecasts is therefore encouraging, but needs to be tested for a greater data set for this shale play and for other plays, and should not be used for reserves forecasting.

Modelling bubbly flow and its transitions in vertical annuli using population balance technique

Bubbly flow and its transitions in vertical annuli is studied using population balance technique. Bubble breakup and coalescence is accounted separately to track the evolution of the bubble size during the simultaneous flow of gas and liquid. The conventional two-fluid model is used to simulate the hydrodynamics. The model enables the prediction of voidage profile at any axial location. Presence of peak in the void distribution at the walls of the annulus, center of the annulus and both at walls and centers is observed depending on the phase superficial velocities. Further, transition from bubbly to slug and bubbly to dispersed bubbly is predicted based on the evolved bubble size. The model prediction gives a good match with the experimental data and existing theory. A shift in the transition boundary is noted due to the variation in inlet bubble size and the dimension of the annulus.

Microscopic Mechanisms of Oil Recovery By Near-Miscible Gas Injection

As gas flooding becomes a more viable means of enhanced oil recovery, it is important to identify and understand the pore-scale flow mechanisms, both for the development of improved gas flooding applications and for the predicting phase mobilisation under secondary and tertiary gas flooding. The purpose of this study was to visually investigate the pore-level mechanisms of oil recovery by near-miscible secondary and tertiary gas floods. High-pressure glass micromodels and model fluids representing a near-miscible fluid system were used for the flow experiments. A new pore-scale recovery mechanism was identified which significantly contributed to oil recovery through enhanced flow and cross-flow between the bypassed pores and the injected gas. This mechanism is strongly related to a very low gas/oil interfacial tension (IFT), perfect wetting conditions and simultaneous flow of gas and oil in the same pore, all of which occur as the gas/oil critical point is approached. The results of this study helps us to better understand the pore-scale mechanisms of oil recovery in very low-IFT (near-miscible) systems. In particular we show that in near-miscible gas floods, behind the main gas front, the recovery of the oil continues by cross-flow from the bypassed pores into the main flow stream and as a result almost all of the oil, which has been contacted by the gas, could be recovered. Our observations in high-pressure micromodel experiments have demonstrated that this mechanism can only occur in near-miscible processes (as opposed to immiscible and completely miscible processes), which makes oil displacement by near-miscible gas floods a very effective process.

N doping using N2O and NO sources: From the viewpoint of ZnO

A study of N doping using N2O and NO sources on ZnO, which may prove important for the N doping of oxide materials, was performed by investigating the doping processes of N atoms by each source together with the various properties for the grown N doped ZnO films. N2O was employed as the radio-frequency (rf) plasma source to produce radical N2* species that could effectively incorporate N atoms above 1020 cm−3 into ZnO, which was similar to N doping using N2 as the source. In contrast, it was found that the ZnO films doped with a N concentration above 1020 cm−3 were easily obtained using a gas flow of NO. The N concentration could be controlled systematically by the simultaneous gas flow of NO and O2 sources. The basis of N doping using a NO source could be related to the free radical characteristic of NO molecular. This idea was proposed from the results that the N concentrations doped to ZnO using a gas flow of N2O and N2, which have the characteristics of neutral and nonreactive molecules in air, were in the ranges from 1018 to 1019 cm−3. Further, our investigations clarified that the structural, optical, and electrical properties for the N doped ZnO films were not quite dependent on the N2, N2O and NO sources used as N dopants. This work proposes that NO is a promising source as a N dopant that can be employed without using a rf plasma source in the application of physical vapor deposition techniques that are indispensable for producing radical N2* species through a rf plasma source to achieve the efficient incorporation of N atoms when N2 and N2O sources are used as N dopants.

Simulation of water and gas flow in fractured porous media

Abstract The porous media considered in this paper belong to gas reservoirs characterized by a low-permeability matrix, combined with a high-permeability fracture system. The transient, three-dimensional, two-phase numerical model is presented for simulating the simultaneous flow of gas and water through porous and fractured media. The specific problem to which the numerical simulation is applied assumes a single horizontal fracture perpendicular to the flow direction in a quite small geometry. The equations solved treat both fluids as incompressible and immiscible. Accounted for are the effect of capillary pressure and relative permeability. Technically, the finite volume approach is used to discretize the equations. The set of discretized and linearized equations is solved using the IPSA (inter-phase slip algorithm) method. The results of this study indicate that the multi-layer reservoir provides better estimates of post-fracture performance compared to a more conventional, single-layer reservoir description.

Numerical Study for Production Performances of a Methane Hydrate Reservoir Stimulated by Inhibitor Injection

This study presents a numerical model for simultaneous flow of gas, water including methanol, and hydrate through methane hydrate reservoirs. The model has been developed to specially investigate the production behavior during injection of methanol with the combination of a depressurization mechanism. The model evaluates the local gas dissociation rate with methanol concentration using the kinetic theory proposed by Kim-Bishinoi and thermodynamics. This kinetic dissociation rate is computed with the aid of the empirical dissociation rate as a function of specific surface area and pressure difference. A number of simulations have been conducted to examine the effect of parameters related to methanol injection on the production behaviors of gas and water, that is, injection rate, time of injection, and methanol content. From the results of numerical studies, it is noted that the effect of methanol injection only appears near the well, rather than whole reservoir, since hydrate reservoirs are extremely low in permeability before dissociation occurs. From the parametric study, it is seen that methanol content is the most sensitive parameter in a sense of time being taken for a well block to be completely dissociated. We also investigated the strategy of injecting methanol in the middle of production. It was found that this strategy is not much expected in the aspect of areal sweeping trend. The results obtained from this model can be used to acquire the relevant reservoir data, to interpret the observed producing behavior, and to design the production scenarios for economical evaluation.

Numerical modeling study for the analysis of transient flow characteristics of gas, oil, water, and hydrate flow through a pipeline

This study presents the development of a four-phase, four-fluid flow pipeline simulator to describe simultaneous flow of gas, oil, water, and hydrate through a pipeline. The model has been equipped with a phase behavior model and hydrate equilibrium model to efficiently estimate thermodynamic and hydrodynamic properties of multicomponent mixtures. The governing equations are formulated for describing the physical phenomena of mass, momentum, and heat transfers between the fluids, and the wall. The equations are solved by utilizing the implicit finite-difference method on the staggered-grid system which can properly describe the boundary conditions as well as phase appearance or disappearance. The developed pipeline simulator has been validated against the field data presented by a previous investigator, and their matches are found to be relatively excellent. The model also has been applied to a multi-component, four-phase flow system in order to examine the transient flow characteristics in pipeline. Also, the potential and the location of hydrate formed in the pipeline have been studied by analyzing the flow characteristics. As a result, it was found that a pipeline system flowing gas, oil, water, and hydrate could be optimized by systematically investigating the hydrodynamic variables for the prevention of hydrate formation.

Phase distribution of gas–liquid mixtures in concentric annuli-inception and termination of asymmetry

A very interesting phenomenon occurs during the simultaneous flow of gas and liquid through a vertical concentric annulus. Although the geometry is axially symmetric, the two phases distribute themselves asymmetrically over a wide range of phase velocities. The present work has attempted to investigate this asymmetric phase distribution across a cross-section through extensive experimentation by using the conductivity probe technique. The probe signals and their probability density function analysis have indicated that this feature is initiated in the bubbly-slug flow regime and persists in the entire range of slug and slug-churn flow patterns. The interfacial configuration is symmetric in bubbly, fully formed churn and the annular flow patterns. Finally, the reason for this asymmetry has been attributed to the formation of cap and Taylor bubbles which are never symmetric with respect to the axis since they always form open annular rings.

A Mechanistic Model of Gas-Condensate Flow in Pores

Recent experimental results reported in the literature indicate that the relative permeability of gas-condensate systems increases with rate (velocity) at some conditions. To gain a better under- standing of the nature of the flow and the prevailing mechanisms resulting in such behaviour flow visualisation experiments have been performed, using high pressure micromodels. The observed flow behaviour at the pore level has been employed to develop a mechanistic model describing the coupled flow of gas and condensate phases. The results of the model simulating the observed simultaneous flow of gas and condensate phases have been compared with reported core experimental results. Most features of the reported rate effect are predictable by the developed single pore model, nevertheless, its extension to include multiple pore interaction is recommended.

Numerical Simulation of Hydrate Transport in Natural Gas Pipeline

Accurate modeling of hydrate transportation in natural gas pipelines is becoming increasingly important in the design and operation of offshore production facilities. The dynamics involved in the formation of hydrate particles and in its transportation are governed by the multiphase hydrodynamics equations ensuing from the balance of mass, momentum, and energy. In this study, a two-fluid model is solved to characterize particulate transportation. The numerical algorithm employed is stable and robust and it is based on higher-order schemes. This is necessary since the governing equations describing the simultaneous flow of gas and solid particles are hyperbolic and, thus, admit discontinuities. Specialized higher-order schemes provide a viable approach for efficient frontal tracking of continuity waves in particular. Several simulation experiments that can facilitate thorough understanding of the design and maintenance of pipelines susceptible to hydrate formation are presented.

An Experimental Study on Downward Slug Flow in Inclined Pipes

Summary The downward simultaneous flow of gas and liquid is often encountered in hilly terrain pipelines and injection wells. Most of the methods for predicting pressure drop in gas/liquid, two-phase flow in pipes have been developed for either upward vertical or upward inclined pipes. This study experimentally investigates downward co-current slug flow in inclined pipes. A new test facility was designed and built to acquire data for the entire range of pipe inclination angles. A series of slug flow experiments was conducted in a 2-in. diameter, 65-ft long clear PVC pipe installed on an inclinable structure. Liquid holdup and pressure drop measurements were obtained for downward inclination angles from 0° to −30° at different flow conditions. Translational velocity and liquid-slug holdup correlations were investigated based on the acquired data for different inclination angles.

A comparison of MOVPE grown strained and unstrained MQW lasers incorporating continuously graded or single composition confinement layers

Low pressure MOVPE has been used for the growth of 1.58 μm GRIN-SCH strained Ga x In 1- x As ( x = 0.30) MQW laser structures. The GRIN-SCH region is a continuous grade between the quaternary compositions GaInAsP (λ g = 1.07 μm) and GaInAsP (λ g = 1.25 μm), and was achieved by simultaneous gas flow ramping of the group III and group V reagents. For comparison, GRIN-SCH material with 65 Å GaInAs lattice matched ( x = 0.47) quantum wells was grown. The GRIN-SCH is compared to similar structures containing strained and unstrained quantum well material incorporating single step confinement layers of GaInAsP (λ g = 1.25 μm). Device results from broad area, oxide isolated metal-MQW lasers show that higher T 0 values (62 K) are obtained when the material contains a continuous GRIN-SCH, as opposed to a step confinement region. When used in conjunction with strained quantum wells ( x = 0.30) a threshold current density of 650 A/cm 2 is obtained for the GRIN-SCH material, a significantly lower value than is observed for the step confinement material.

Tracer studies of gas circulation in Nuphar: 18O2 and 14CO2 transport

A flow‐through ventilation system operates in the yellow waterlily (Nuphar luteum ssp. macrophylla Beal). The flow of air into the youngest emergent leaves and down their petioles to the rhizome is confirmed by 18O2 and 2H2 tracer experiments conducted in the field, showing that most of the O2 in the rhizome originated in the atmosphere. This flow of air into the rhizome forces a simultaneous gas flow from the rhizome up the petioles of the older emergent leaves to the atmosphere. Radiolabelled CO2 was used to demonstrate that CO2 present in the gas moving up these petioles was fixed before reaching the atmosphere.

Internal Winds in Water Lilies: An Adaptation for Life in Anaerobic Sediments

The network of internal gas spaces in the yellow water lily constitutes a pressurized flow-through system which forces oxygen to the roots and rhizome buried in the anaerobic sediment. By the purely physical processes of thermal transpiration and hygrometric pressure, several liters of air per day enter the young, newly emerged leaves of Nuphar luteum against a small pressure gradient. This air moves en masse down the petioles of the young leaves (at rates up to 50 centimeters per minute) to the rhizome, forcing a simultaneous flow of gas (rich in carbon dioxide) from the rhizome up the petioles of the older emergent leaves to the atmosphere. The ventilation system has important physiological and ecological consequences.