Three-phase Flow Research Articles

Classification of Oil-Gas-Water Three-Phase Flow in a Pipeline Based on BP Neural Network Analysis

The flow pattern in a pipeline is a very important topic in petroleum exploitation. This paper is to classify the flow pattern of oil-gas-water flow in a pipeline by using BP neural network. The effects of different parameter combinations are investigated to find the most important ones. It is shown that BP neural network can be used in the analysis of the flow pattern of three-phase flow in pipelines. In most cases, the mean square error is large for the horizontal pipes. The optimized neuron number of the middle layer changes with conditions. So we must changes the neuron number of the middle layer in simulation for any conditions to seek the best results. These conclusions can be taken as references for further study of the flow pattern of oil-gas-water in a pipeline.

Visualization of Vertical Oil–Water–Gas Flows Using Conductance Compensated Wire-Mesh Sensor

Oil–water–gas three-phase flows are frequently encountered in the chemical, nuclear, and petroleum industries. Due to the significant differences in physical properties of the three phases, the oil–water–gas flow structures are more complex compared with two-phase flows, which brings a great challenge to the flow parameter measurement of three-phase flows. In this study, a measurement system consisting of a conductance wire-mesh sensor (WMS) and distributed coaxial conductance sensors (CCSs) is designed to visualize the oil–water-gas flow structures. The distributed CCSs are used to monitor the conductance changes of the liquid phase and to realize the real-time correction of the gas-phase distribution obtained from the WMS. The measurement system can effectively avoid the influence of the nonconductive oil phase on the gas-phase visualization, and thus improve the accuracy of gas volume fraction measurement in oil-water-gas flows. The oil-water-gas flow structure and its evolution characteristics are studied according to the flow visualization and the probability density function (PDF) of the gas volume fraction. Notably, the effect of the dispersed oil phase on the Taylor bubble and the liquid slug is uncovered by investigating the local aerated characteristics of slug flows.

ДИНАМИКА ТРЁХФАЗНОГО ПОТОКА ГАЗ-ЖИДКОСТЬ-ТВЁРДЫЕ ЧАСТИЦЫ В УСТАНОВКЕ ПОГРУЖНОГО ГОРЕНИЯ

The necessity of study of the flow structure in submerged combustion apparatuses was substantiated. A three-phase flow in a laboratory plant with a submerged burner was considered. Modeling thermal mode of operation without vapor phase formation was analyzed. The conclusion was made about the dominance of laminar motion in most of the workspace and the determining significance of the gas phase influence on the structure and time behavior of hydrodynamic flows. The conclusion was made about the suitability of the developed physical and mathematical model for the numerical study of full-size devices.

Multi-conductor Line Models for Harmonic Load-flow Calculations in LV Networks with High Penetration of PV Generation

Low-voltage (LV) distribution networks are unbalanced and present loads with nonlinear behavior, which introduce harmonics in the networks. The predictable increase in photovoltaic microgeneration (PV µG) accentuates this unbalanced characteristic, as well as poses new technical problems, namely voltage rise and reverse power flow. To accurately account for the distributed PV and loads in the LV network, unbalanced three-phase power flow algorithms should be utilized, where different approaches may be used to represent lines with various degrees of accuracy. The more accurate algorithm considers the electromagnetic coupling between the line conductors, whereas the simpler algorithm represents each conductor of the line as a single-phase line with pure resistive behavior. This paper aims to analyze the influence of the line model on the load flow in a highly unbalanced LV network with a high penetration of PV production, and considers the impact of the harmonics produced by nonlinear loads. Based on the results obtained, it is possible to identify the most suitable model to be used, depending on the study to be performed. Different scenarios of PV generation and loads are addressed in this paper.

Residual Co2 Trapping and Enhanced Oil Recovery in Carbonate Reservoirs: Three-Phase Flow Dynamics Examined Via Nmr

Residual Co2 Trapping and Enhanced Oil Recovery in Carbonate Reservoirs: Three-Phase Flow Dynamics Examined Via Nmr

Analytical solutions of critical oil film thickness of negative spreading coefficient in a capillary corner

In this paper, by combining applications of minimum surface free energy with capillary force balance equations, and considering that the total free energy change is zero at thermodynamic equilibrium, an analytical equation of the oil film critical thickness to spread over a water film in a three-dimensional capillary corner is derived. The derivation is based on the analysis proposed by Dong et al. [Journal of Colloid and Interface Science 172 (1995) 21–36]. This analytical solution allows the critical oil film thickness in three-phase systems to be calculated conveniently without lengthy calculation and be readily applied in simulation of three-phase systems in porous media using predictive models. The equation was examined by comparing the analytical solutions with the numerical results by Dong et al. Using the analytical solution, the reason why the oil phase spreads between the gas and water phases in three-phase systems in porous media was analyzed. The spreading of oil phase is controlled by the free energy change, and the spreading of oil phase only occurs in the system when the free energy change during the oil spreading process is negative. Also, there is a critical oil film thickness controlling this process that is a function of interfacial tension, contact angles, and corner angles. This analytical solution of critical oil film thickness can also be utilized to find the correlation of three-phase capillary pressure when the system is in thermodynamic equilibrium for water-wet porous media. This correlation should be useful in pore-scale simulation of three-phase flow of spreading oil.

A difference scheme for a triangular system of conservation laws with discontinuous flux modeling three-phase flows

<abstract><p>A triangular system of conservation laws with discontinuous flux that models the one-dimensional flow of two disperse phases through a continuous one is formulated. The triangularity arises from the distinction between a primary and a secondary disperse phase, where the movement of the primary disperse phase does not depend on the local volume fraction of the secondary one. A particular application is the movement of aggregate bubbles and solid particles in flotation columns under feed and discharge operations. This model is formulated under the assumption of a variable cross-sectional area. A monotone numerical scheme to approximate solutions to this model is presented. The scheme is supported by three partial theoretical arguments. Firstly, it is proved that it satisfies an invariant-region property, i.e., the approximate volume fractions of the three phases, and their sum, stay between zero and one. Secondly, under the assumption of flow in a column with constant cross-sectional area it is shown that the scheme for the primary disperse phase converges to a suitably defined entropy solution. Thirdly, under the additional assumption of absence of flux discontinuities it is further demonstrated, by invoking arguments of compensated compactness, that the scheme for the secondary disperse phase converges to a weak solution of the corresponding conservation law. Numerical examples along with estimations of numerical error and convergence rates are presented for counter-current and co-current flows of the two disperse phases.</p></abstract>

Mass transfer of phases in the flow of oil-water-gas mixture on the core scale

The study of three-phase fluid filtration in the pore space is one of the urgent tasks in the development of oil and gas and gas condensate fields. In the study of three-phase flows, semi-empirical methods for calculating relative phase permeabilities (RPP) are used in practice, which do not consider the structure of the pore space and the fundamental equations of hydrodynamics. The paper proposes and substantiates a physical and mathematical model of mass transfer in the filtration flow of an oil-water-gas mixture in a porous medium. The pore space structure model is based on the distribution of pore diameters obtained from capillary pressure curves (CCP). In the core, clusters are identified, consisting of a large channel through which oil, water and gas move in a “beaded” mode; channels of medium diameter filled with water and gas and channels of small radius in which gas moves. A system of equations is presented and solved that determines the distribution of moving volumes and volumetric flows over channels and phases. When determining pressure losses in the system of pore channels, friction losses, local losses, and also losses due to interfacial interaction are taken into account. For the first time, on the basis of a hydrodynamic model, analytical expressions were obtained to determine the RPP for oil, water and gas. The calculation-experimental method is based on three model experiments, the results of which determine the properties of the cluster channels in relation to the separately filtered phases. It is shown that the developed theory and calculation method, in the particular case of an oil-water mixture, coincide with the previously developed theory of two-phase filtration on the core scale.

Numerical simulation on oil-water-particle flows in complex fractures of fractured-vuggy carbonate reservoirs

The reservoir spaces of the carbonate reservoirs in the Tahe oilfield consist of fractures and vuggies. The injection of particle plugging agents to control the dominant channel of water flooding is an important measure in enhancing oil recovery. In this paper, a simplified parallel fracture is used to represent the complex fracture structure, and an oil-water-particle three-phase flows computational fluid dynamics model based on the volume of fluid-discrete element method (VOF-DEM) model is established to study the particle transport and accumulation behaviors after water flooding in the fractures. The results show that the injected particles are transported and accumulate along the water phase channel in the main fracture after water flooding but barely flow directly into the secondary fracture. The particle accumulation in the main fracture reduces the cross-section of the water phase flow channel, which leads to an increase in the pressure loss in the main fracture and the flow ability in the secondary fracture. The oil-water interface at the top of the accumulation changes during the process of particle injection, which is beneficial in enhancing oil recovery. The simulation results of different parameters show that the injection velocity, particle volume fraction, and particle diameter affect the position, length, and height of the particle accumulation in the main fracture, which exhibits an important influence on the oil-water interface in the main fracture and the flow ability in the secondary fracture.

Two three-phase linear power flow models for distribution power system under polar coordinates

PurposeThe purpose of this study is to provide a non-iterative linear method to solve the power flow equations of alternating current (AC) power grid. Traditional iterative power flow calculation is limited in speed and reliability, and it is unsuitable for the real-time and online applications of the modern distribution power system (DPS). Thus, it would be of great significance if a fast and flexible linear power flow (LPF) solution could be introduced particularly necessary for the robust and fast control of DPS, especially when the system consists of star and delta connections ZIP load (a constant impedance, Z, load, a constant current, I, load and a constant power, P, load) and the high penetration of distributed solar and wind power generators.Design/methodology/approachBased on the features of DPS and considering the approximate balance of three-phase DPS, several approximations corresponding to the three-phase power flow equations have been discussed and analyzed. Then, based on those approximations, two three-phase LPF models have been developed under the polar coordinates. One model has been formulated with the voltage magnitudes [referred to the voltage magniudes based linear power flow method (VMLPF)], and another model has been formulated with the logarithmic transform of voltage magnitudes [referred to the logarithmic transform of voltage based linear power flow method LGLPF)].FindingsThe institute of electrical and electronic engineers (IEEE) 13-bus, 37-bus, 123-bus and an improved 615-bus unbalanced DPSs are used to test the performances of the methods considering star and delta connections ZIP load and PV buses (voltage-controlled buses). The test results validate the effectiveness and accuracy of the proposed two models. Especially when considering the PV buses and delta connection ZIP load, the proposed two models perform much well. Moreover, the results show that VMLPF performs a bit better than LGLPF.Research limitations/implicationsExcept for the transformer with Yg–Yg connection winding can be dealt with directly, the transformers with other connections are not discussed in this proposed paper and need to be further studied.Originality/valueThese proposed two models can deal with ZIP load with star and delta connections as well as multi slack buses and PV buses. The single-phase, two-phase and three-phase hybrid networks can be directly included too. The proposed two models are capable of offering enough accuracy level, and they are therefore suitable for online applications that require a large number of repeated power flow calculations.

A semi-discrete Lagrangian–Eulerian scheme for hyperbolic-transport models

In this work, we introduce a new semi-discrete scheme based on the so-called no-flow curves and its numerical analysis for solving initial value problems that involve one-dimensional (1D) scalar hyperbolic conservation laws and of the form, ut+H(u)x=0, x∈R,t>0, u(x,0)=u0(x). In addition, we present a two-dimensional (2D) version of the semi-discrete Lagrangian–Eulerian scheme to show that the proposed method can be applied to multidimensional problems. From an improved 1D weak numerical asymptotic analysis, we found that the solutions provided by the novel semi-discrete scheme satisfy a maximum principle property and a Kruzhkov entropy condition. We also highlight the possibility of using the no-flow curves as a new desingularization analysis technique for the construction of computationally stable numerical fluxes in the locally conservative form for nonlinear hyperbolic problems. We provide nontrivial 1D and 2D numerical examples with nonlinear wave interaction to illustrate the effectiveness and capabilities of the proposed approach and verify the theory. According to the results, the scheme handles discontinuous solutions (shocks) with low numerical dissipation quite well and shows a very good resolution of rarefaction waves with no spurious glitch effect in the vicinity of the sonic points. We also consider a test case for nonstrictly hyperbolic conservation laws with a resonance point (coincidence of eigenvalues) modeling three-phase flow in a porous media transport problem.

Stochastic multi-objective optimal energy management of grid-connected unbalanced microgrids with renewable energy generation and plug-in electric vehicles

Microgrids (MGs) contribute to the integration of renewable energy-based distributed generation (DG) units and electric vehicles (EVs) in a smart, secure, sustainable, and economic fashion. However, the unbalanced nature of MGs along with the probabilistic nature of renewable energy, electricity prices, and EV demand complicate the energy management process. To overcome that challenge, a stochastic multi-objective optimization model for grid-connected unbalanced MGs is proposed here to minimize the total operational cost and the voltage deviation. The epsilon-constraint method and fuzzy satisfying approach are used to solve the multi-objective optimization problem and to obtain compromise solutions. Uncertainties are considered by employing the roulette wheel mechanism for generating scenarios regarding renewable energy generations, EV charging demands, electric loads, and electricity prices. In addition, to avoid adopting infeasible and impractical solutions, a three-phase power flow is integrated in the proposed model. The proposed method is assessed in a modified IEEE 34-bus test system consisting of EVs, battery systems, wind turbine units, photovoltaic units, and diesel generators. The results show the effectiveness and benefits of the proposed model for handling uncertainties while minimizing both operational cost and voltage deviation index and providing more realistic and reliable solutions that can be applied by MG operators.

Pore-scale study on interfacial force-induced residue mobilization under immiscible ternary fluids flow

Immiscible three-phase flow and the trapping/mobilizing mechanism are significant to many water and energy applications such as water infiltration, oily wastewater treatment, CO2 sequestration, and water-alternating-gas (WAG) for oil recovery enhancement. This work targets the ternary fluid system, namely water, gas, and oil, to uncover the significant role of interfacial forces in the transient flow behavior and trapped-phase mobilization. From both the lattice Boltzmann method (LBM) modeling and experimental observations, we firstly showed the deformation and mobilization process of the oil droplet when interacting with water droplet in air. The re-distribution of oil phase reveals the strong interfacial interactions at the water-gas-oil three-phase contact point (fluid-TPCP). For the more complicated three-phase flow in porous media, our visualization results also showed that the trapped oil phase, which initially adhered to rough surfaces or inside dead-end pores, was extracted by the pulling effect at fluid-TPCP during WAG injection. The influence of surface wettability conditions residue extraction efficiency was also discussed. This work provides insightful understandings of the interfacial forces in mobilizing the residues under immiscible three-phase flow in porous media.

Universality of Riemann solutions in porous media

Universality, a desirable feature in any system. For decades, elusive measurements of three-phase flows have yielded countless permeability models that describe them. However, the equations governing the solution of water and gas co-injection has a robust structure. This universal structure stands for Riemann problems in green oil reservoirs. In the past we established a large class of three phase flow models including convex Corey permeability, Stone I and Brooks–Corey models. These models share the property that characteristic speeds become equal at a state somewhere in the interior of the saturation triangle. Here we construct a three-phase flow model with unequal characteristic speeds in the interior of the saturation triangle, equality occurring only at a point of the boundary of the saturation triangle. Yet the solution for this model still displays the same universal structure, which favors the two possible embedded two-phase flows of water-oil or gas-oil. We focus on showing this structure under the minimum conditions that a permeability model must meet. This finding is a guide to seeking a purely three-phase flow solution maximizing oil recovery.

Modeling of three-phase displacement in three-dimensional irregular geometries using a lattice Boltzmann method

Three-phase displacement process in a porous media is significantly influenced by wettability of the solid surfaces. It remains a research challenge to model and simulate three-phase flows with moving contact lines, especially on arbitrary complex three-dimensional surfaces. We propose a color-gradient lattice Boltzmann model to simulate immiscible three-phase flows with contact-line dynamics. Unlike the previous models in dealing with wettability through assigning virtual mass fractions to the solid surfaces, the present model realizes the prescribed contact angles by correcting the orientation of the color-gradient parameter at the solid surfaces. We first validate this model against analytical solutions by simulating several typical cases, including a Janus droplet deposited on a flat surface and on a spherical surface, and the spontaneous imbibition of ternary fluids in a cylindrical tube. We then use it to study the displacement of residual oil during tertiary gas injection process. To mimic this process, gas is injected into a simple pore-throat connecting structure after water flooding. Results show that in displacement process, an oil spreading layer forms, which changes the oil flow state from adhering to the bottom wall to spreading over the entire interface between gas and water. Therefore, residual oil can be easily recovered in the form of gas-to-oil-to-water double displacement chain, leading to a high oil recovery regardless of the wetting properties of the solid surface. In the cases without the presence of oil spreading layer, increasing capillary number favors the oil recovery under certain wetting conditions only.

Experimental investigation of different simulated formation water salinity in three-phase waxy crude oil-water-gas flow in horizontal pipes

Three-phase oil-water-gas flow experiments have been conducted in a horizontally configured rig made of carbon steel pipe with an ID of 0.041 m and a total length of 24.3 m. The test fluids were Malaysian waxy crude oil from Malay basin and three concentrations of simulated formation water salinity, namely 0 ppm, 15 000 ppm, and 30 000 ppm. The waxy crude oil and simulated formation water are varied at six different superficial liquid velocities ranging from 0.5 to 3.0 m/s while the gas phase is varied at 10 different superficial velocities ranging from 0.01 to 0.61 m/s. Eight flow patterns are observed using observational method; one of which is a newly discovered flow pattern identified as Slug with Oil Film-Oil Continuous (SLOF-OC). Salinity does not give significant effect on oil-gas interface but significantly affects the oil-water interface as lower formation water salinity is dispersed easily in crude oil compared to higher formation water salinity. The highest pressure gradient recorded was 2506.84 Pa/m at the highest superficial gas velocity while the lowest pressure gradient recorded was 89.53 Pa/m at the lowest superficial gas velocity. It is imperative to note that the experimental investigation of Malaysian waxy crude oil with different formation salinity in the three-phase flow study is in an unchartered area, therefore it provides a new platform for furthering more complex research works such as four-phase flow (gas, oil, water, and wax particles) below Wax-Appearing Temperature (WAT).

A fully-discrete decoupled finite element method for the conserved Allen–Cahn type phase-field model of three-phase fluid flow system

In this article, we develop and analyze a novel fully discrete decoupled finite element method to solve a flow-coupled ternary phase-field model for the system consisting of three immiscible fluid components. Based on the L2-gradient flow approach, the conserved Allen–Cahn type dynamics is used to describe the free interface motion, where multiple nonlocal type Lagrange multipliers are used to accurately conserve the volume of each phase. The scheme is also linear, second-order time accurate, and unconditionally energy stable, due to the combination of several effective numerical techniques, including the two-step backward differentiation scheme, finite element discretization, explicit-SAV (scalar auxiliary variable) method for handling the nonlinearity, and projection method of Navier–Stokes equation. At each time step, the non-local splitting technique only requires solving several decoupled constant-coefficient elliptic equations. The implementation issues are discussed in detail. The solvability and the unconditional energy stability of the scheme are rigorously proved. Plenty of 2D and 3D numerical simulations are carried out to numerically demonstrate the accuracy, energy stability, and applicability of the proposed scheme.

An experimental study of interfacial dynamics during stratified oil-water draining from storage tank

Oil-water stratification is an inevitable phenomenon in the petroleum industry. The present study describes stratified oil-water draining from a square tank through a 9 mm diameter drain pipe. The purpose of this study is to understand the flow physics of oil as well as air entrainment in drain pipe during drainage of water. In order to observe the influence of the viscosity of oil on the entrainment and flow structure, two different oil-water stratifications are selected. In these two cases, the viscosity ratios of oil to water are 1.64 and 55, respectively. While draining, the flow of single-phase liquid in the drainpipe is transformed to two-phase liquid-liquid flow and then three-phase flow. A pointed tip of oil is formed as the oil-water interface approaches the drainpipe inlet. Different flow patterns, namely bubbly flow, slug flow, churn flow, elongated slug flow, jet flow, and annular flow, are observed as air and oil enter the drain pipe. Reverse flow is observed in the case of a higher viscosity ratio. An empirical correlation based on non-dimensional numbers has been proposed for describing the condition of no air entrainment in the drain pipe. Optical probes are used successfully to detect the presence of several regimes of air-oil-water and oil-water in the drainpipe.

A Phase Generation Shifting Algorithm for Prosumer Surplus Management in Microgrids Using Inverter Automated Control

Four-wire low-voltage microgrids supply one-phase consumers with electricity, responding to a continuously changing demand. For addressing climate change concerns, national governments have implemented incentive schemes for residential consumers, encouraging the installation of home PV panels for covering self-consumption needs. In the absence of adequate storage capacities, the surplus is sold back by these entities, called prosumers, to the grid operator or, in local markets, to other consumers. While these initiatives encourage the proliferation of green energy resources, and ample research is dedicated to local market designs for prosumer–consumer trading, the main concern of distribution network operators is the influence of power flows generated by prosumers’ surplus injection on the operating states of microgrids. The change in power flow amount and direction can greatly influence the economic and technical operating conditions of radial grids. This paper proposes a metaheuristic algorithm for prosumer surplus management that optimizes the power surplus injections using the automated control of three-phase inverters, with the aim of reducing the active power losses over a typical day of operation. A case study was performed on two real distribution networks with distinct layouts and load profiles, and the algorithm resulted efficient in both scenarios. By optimally distributing the prosumer generation surplus on the three phases of the network, significant loss reductions were obtained, with the best results when the generated power was injected in an unbalanced, three-phase flow.

Feasibility Study on Downhole Gas–Liquid Separator Design and Experiment Based on the Phase Isolation Method

As oil exploitation enters its middle and late stages, formation pressure drops, and crude oil degases. In production profile logging, the presence of the gas phase will affect the initial oil–water two-phase flowmeter’s flow measurement results. In order to eliminate gas-phase interference and reduce measurement costs, we designed a downhole gas–liquid separator (DGLS) suitable for low flow, high water holdup, and high gas holdup. We based it on the phase isolation method. Using a combination of numerical simulation and fluid dynamic measurement experiments, we studied DGLS separation efficiency separately in the two cases of gas–water two-phase flow and oil–gas–water three-phase flow. Comparative analysis of the numerical simulation calculation and dynamic test results showed that: the VOF model constructed based on k−ε the equation is nearly identical to the dynamic test, and can be used to analyze DGLS separation efficiency; the numerical simulation results of the gas–water two-phase flow show that when the total flow rate is below 20 m3/d, the separation efficiency surpasses 90%. The oil–gas–water three-phase’s numerical simulation results show that the oil phase influences separation efficiency. When the total flow rate is 20 m3/d–50 m3/d and gas holdup is low, the DGLS’s separation efficiency can exceed 90%. Our experimental study on fluid dynamics measurement shows that the DGLS’s applicable range is when the gas mass is 0 m3/d~15 m3/d, and the water holdup range is 50%~100%. The research presented in this article can provide a theoretical basis for the development and design of DGLSs.