Oil-gas Two-phase Flow Research Articles

Modelling pressure dynamics of oil–gas two-phase flow in double-porosity media formation with permeability-stress sensitivity

Pressure dynamics can reflect the basic characteristics of fluid flow through underground porous formation. In this research, the oil–gas two-phase flow model for a double-porosity media formation with permeability-stress sensitivity was first established for three kinds of outer boundaries. The unified governing equation was deduced by utilizing the H function. The nonlinear mathematical model in consideration of permeability-stress sensitivity was linearized by implementing the canonical perturbation transformation and then solved by using the Laplace transformation. After that, a sequence of typical log–log curves of pressure dynamics influenced by various model parameters were plotted and analyzed. These curves reflect the typical characteristic of a V shape caused by the inter-porosity fluid flow from matrix toward natural fractures. Oil saturation and permeability-stress sensitivity coefficient have much influence on the pressure dynamics. Ultimately, the established model of oil–gas two-phase flow was validated through a well-test fitting interpretation for a real condensate gas well in a sandstone formation. This research can offer insights into the pressure dynamics dominated by the oil–gas two-phase flow in naturally fractured formations and the permeability-stress sensitivity effect.

Pore-Scale Modeling of Gas–Oil Two-Phase Flow Based on the Phase-Field Method—A Case Study of Glutenite Reservoirs in China

Pore-Scale Modeling of Gas–Oil Two-Phase Flow Based on the Phase-Field Method—A Case Study of Glutenite Reservoirs in China

Numerical Simulation of Inlet Void Fraction Affecting Oil-gas Two-phase Flow Characteristics in 90° Elbows

Numerical Simulation of Inlet Void Fraction Affecting Oil-gas Two-phase Flow Characteristics in 90° Elbows

Experimental research on the transformation of gas-oil two-phase flow pattern in large vertical annulus

Criteria for gas-oil two-phase flow transformation are essential guidelines that are used as auxiliary equations for the calculation of two-phase flows in gas-oil based drilling fluids within wellbores. The currently used flow pattern transformation criteria, which are based on gas-water two-phase flow experiments in circular pipes or small annuli, have limited applicability when calculating the gas-liquid two-phase flows in oil-based drilling fluids. In this study, experiments were carried out on the transformation of gas-oil two-phase flow patterns in a large annulus (φ100 mm × φ60 mm × 12 m) under different viscosities (16–39 mPa s). The flow characteristics of gas-liquid two-phase flows were measured using electrical capacitance volume tomography (ECVT) at different superficial gas-liquid velocities. It was found that as the liquid phase viscosity increased, the slug flow area gradually expanded, and the superficial gas velocity at which the annular mist flow appeared decreased. When the superficial Reynolds number of the liquid phase exceeded the critical value (approximately 135), the slug flow no longer appeared in the wellbore, and the bubble flow was directly transformed into the churn flow. Based on the results of the dimensionless analysis in the experiments, the criteria for flow-type transitions among different flow patterns were established by considering the influence of the liquid-phase viscosity. Both the average relative errors between the predicted and experimental values of the superficial gas velocity during the bubble-slug, bubble-churn, slug-churn, and churn-annular transitions, at the same superficial liquid velocities, were less than 3.5, 4.5, 3, and 7%, respectively.

Research on flow pattern identification model of oil–gas two-phase flow in scavenge pipe

Research on flow pattern identification model of oil–gas two-phase flow in scavenge pipe

A transient production prediction method for tight condensate gas wells with multiphase flow

Considering the phase behaviors in condensate gas reservoirs and the oil-gas two-phase linear flow and boundary-dominated flow in the reservoir, a method for predicting the relationship between oil saturation and pressure in the full-path of tight condensate gas well is proposed, and a model for predicting the transient production from tight condensate gas wells with multiphase flow is established. The research indicates that the relationship curve between condensate oil saturation and pressure is crucial for calculating the pseudo-pressure. In the early stage of production or in areas far from the wellbore with high reservoir pressure, the condensate oil saturation can be calculated using early-stage production dynamic data through material balance models. In the late stage of production or in areas close to the wellbore with low reservoir pressure, the condensate oil saturation can be calculated using the data of constant composition expansion test. In the middle stages of production or when reservoir pressure is at an intermediate level, the data obtained from the previous two stages can be interpolated to form a complete full-path relationship curve between oil saturation and pressure. Through simulation and field application, the new method is verified to be reliable and practical. It can be applied for prediction of middle-stage and late-stage production of tight condensate gas wells and assessment of single-well recoverable reserves.

An optimised and novel capacitance-based sensor design for measuring void fraction in gas–oil two-phase flow systems

ABSTRACT This study explores a new electrode configuration for measuring the void fraction of two-phase flows using capacitance-based sensors. The proposed method is considered ‘skewed’ because of its unique geometric shape, and the performance of the proposed sensor was evaluated and improved via multiple simulations using the COMSOL Multiphysics software. The simulations encompass three different flow patterns, stratified, annular and homogeneous, whose performance themselves were verified in a previous study. The influences of geometric properties and parameters on the sensitivity of the proposed sensor were evaluated to determine an optimal configuration. Furthermore, the sensitivity distribution on different void fractions of the sensor was analysed for various void fractions in different flow patterns. Additionally, the proposed configuration was also compared alongside double-ring and concave sensors to determine the overall sensitivity. At 2.11 pF, the overall sensitivity of the proposed sensor was significantly higher than that of the other sensors. It is worth mentioning that the measurement precision of multiphase flow meters is of high importance, particularly in petroleum industry because of the oil price and also the high amount of transported products.

Experimental Study on Friction Coefficient of Gas–Oil Two-Phase Flow in a Large Annulus

Summary The friction coefficient is an important factor that affects the accurate calculation of wellbore annular pressure distribution and is of great significance for the safety of drilling operations. To date, investigations of the friction coefficient mainly focused on low-viscosity liquids (such as water and kerosene). Thus, the obtained friction coefficients have poor applicability in the calculation of gas–oil-based mud two-phase flow. This study reports gas–oil two-phase flow experiments for different viscosities (16–39 mPa·s) in the annulus of a large wellbore, performed using an experimental wellbore (Φ100×Φ60×12 000 mm). The gas–liquid mixture Reynolds number ranges from 500 to 10,000. The results reveal a consistent trend for the variation of the friction coefficient under different flow patterns. For the same mixture Reynolds number, a larger liquid viscosity corresponds to a smaller variation of the friction coefficient among different flow patterns. The larger the superficial liquid velocity, the greater the friction coefficient. Based on the dimensionless analysis of the experimental data, a model for the calculation of the friction coefficient of gas–oil two-phase flow in a large annulus is established, and its prediction error relative to the experimental data is found to be less than 30%. This study can provide a basis for accurate calculations of gas–oil-based mud two-phase flow in drilling wellbores.

Research on gas–liquid separation characteristics in the helico-axial multiphase pump

Due to the fact that it serves as both a pump and a compressor, the helico-axial multiphase pump is better suited for mixed-transport oil-gas two-phase flow and is frequently used for deep-sea oil extraction. The gas–liquid separation caused by the asynchrony of the gas–liquid two-phase medium is the primary cause of the damage or failure of the helico-axial multiphase pump in the project, resulting in the pump's damage or inability to operate. To investigate the variation of phase separation in the helico-axial multiphase pump under diverse operating conditions, a test system was designed and the theory of fluid flow mechanics was applied. The effects of different flow fields on the energy conversion characteristics of the pump were investigated. The results indicate that the gas–liquid separation position in the impeller occurs near the 2/3 of the airfoil bone line. After the gas–liquid separation, gas mass will be formed, pocket flow will be readily induced, and the gas block-up phenomenon will result in energy loss in the compression unit. Simulations indicate that the static pressure recovery and total pressure loss in a diffuser fluctuate over time. The static pressure recovery efficacy of the diffuser is highest when the imported gas volume fraction is 10% and lowest when the imported gas volume fraction is 60%. On the surface of the impeller blade, perpendicular to the flow direction, the separation phenomenon near the hub side is more severe than that near the rim. Along the flow direction, the pattern of phase separation is comparable.

Research on Oil–Gas Two-Phase Flow Characteristics and Improvement of Aero-Engine Bearing Chamber

In order to study the oil–gas two-phase flow characteristics of an aero-engine bearing chamber and improve the scavenge effect of lubricating oil, the two-phase flow solution model of a bearing chamber based on the Euler–Euler method was established. Three improvement schemes were proposed for the ventilation structure and scavenge structure of the bearing chamber. The flow characteristics and scavenge characteristics of a conventional bearing chamber and three improvement schemes under different working conditions were analyzed in depth. The results show that after the conventional bearing chamber ventilation structure is embedded (Embed) and improved, with the increase in the embedding depth, the oil in the cavity is further blocked in the cavity, the amount of oil flowing out from the vent is further reduced, and the scavenge efficiency is further improved. After the slope improvement of the scavenge structure of the conventional bearing chamber, due to the increase in the depth of the oil return groove, the drag effect of the air shear force in the cavity on the oil in the oil return groove is further weakened, and the oil accumulation area on the right side of the scavenge port is further suppressed. The volume fraction of the oil in the cavity is further reduced, and the scavenge efficiency is further improved. The combined improvement scheme (ES) can take into account the advantages of embedding and slope improvement schemes, and further improve the scavenge efficiency. Compared to the conventional bearing chamber, when the oil flow rate is 200 L/h and the speed is 15,000 r/min, the oil return efficiency of the embedded (h = 12 mm), slope (l = 56 mm) and combined improvement schemes are increased by 20.19%, 13.43%, and 37.94%, respectively.

Research on the calculation method of windage power loss of aviation spiral bevel gear and experiment verification

This paper proposes a method for calculating windage power losses of spiral bevel gears by dividing the losses into the sum of windage effects on tooth surface, toe/heel, conical surface, and circumferential surface, according to the gear structure. A calculation model for each component of windage losses is established based on the basic equation of fluid dynamics. Subsequently, a windage loss measurement test bench is developed, and a windage moment measurement method is proposed for experimental spiral bevel gears. The individual contributions of each windage loss component are calculated. The results of the calculations indicate that the gear speed is the primary factor that impacts windage losses, with the windage power loss being proportional to the 2.96th power of gear speed. Gear geometry parameters and the jet flow impacting the tooth surface are also significant factors, followed by the hub and spoke values in the wheel body parameters. The findings also show that an increase in lubricating oil content in oil-gas two-phase flow can significantly increase windage losses. Finally, a comparison between the dimensionless windage calculation values and the experimental measurement values demonstrates good agreement. This paper provides theoretical guidance for future research aimed at reducing windage power loss and improving the efficiency of aviation gear transmission.

Flow pattern identification for gas-oil two-phase flow based on a virtual capacitance tomography sensor and numerical simulation

Gas-oil two-phase flow is widely encountered in oil exploitation and transportation pipelines. It's complex and transient changes of flow regimes present a great challenge for accurate and real-time measurement. As a non-invasion and real-time measuring method, electrical capacitance tomography (ECT) is suitable for the transient measurement of non-conductive gas-oil flow. However, the highly random and nonlinear nature of multiphase flow make it difficult and limited to investigate the flow parameters based on either static or dynamic measurement. In this research, the whole process of dynamic measurement of ECT applying in gas-oil two-phase flow is thoroughly studied, including simulation calculation, experimental validation and comprehensive data analysis. A simulation approach by coupling the flow and electrostatic field is proposed based on a virtual ECT sensor, in order to monitor the gas-oil two-phase flow characteristics. Based on FLUENT and COMSOL platform, the numerical simulation under six typical flow patterns in a horizontal pipe is carried out. Combining the visualized image generated by ECT measurement and the theory of flow pattern transition, the formation mechanism and structural characteristics of different gas-oil flow patterns are analyzed in detail. Furthermore, this research attempts to analyze the signal fluctuation characteristics caused by flow pattern change, in order to access more in-depth flow information implied in the original capacitance data, via time-series analysis as well as frequency domain analysis based on Flourier Transform. At last, a series of dynamic experiment is conducted to verify the feasibility of the simulation and data analysis approach. The experiment focuses on the flow pattern transition, gas-liquid dynamic characteristics and noise influence in the actual process. It can be concluded from the results of simulation and experiment tests, combining the visualized images and the dynamic characteristics of capacitance signals can make it more effective and intuitive for flow pattern identification, which might be used for the online measurement in real-industry process.

Identification of Oil and Gas Two-Phase Flow Patterns in Aero-Engine Bearing Chambers Based on Kriging Method

The identification of the flow pattern within the bearing chamber's oil and gas two-phase flow is crucial for its lubrication design. Aiming at the lack of accuracy and universality of the current bearing chamber oil and gas two-phase flow pattern recognition, this paper introduces a new method for recognising oil and gas two-phase flow patterns based on the Kriging model. In this paper, the oil-gas two-phase flow field in the bearing chamber is modelled in Comsol simulation software using the level set-k- ε model. Subsequently, the finite element analysis results were used as samples to fit the Kriging model, and the effects of different variables on the flow pattern were analysed and compared with the actual results. The results demonstrate that the flow pattern discrimination results fitted by the Kriging model exhibit higher accuracy and greater generalisability. This holds significant implications for future lubrication and structural design of bearing chambers.

Flow-Induced Vibration of a Reversed U-Shaped Jumper Conveying Oil-Gas Two-Phase Flow

Subsea jumpers connecting the underwater wellhead and nearby manifold commonly undergo flow-induced vibration (FIV) due to the spatially frequent alteration in the flow direction, velocity, pressure and phase volume fraction of the oil–gas two-phase flow, potentially leading to fatigue damage. This paper reports the numerical results of the FIV of a reversed U-shaped jumper excited by gas–liquid two-phase flow, which evolves from the initial slug flow with a fixed gas–liquid ratio of 1:2 when transporting through the jumper. The FIV response and flow pattern evolution are examined with a gas flow rate of Qg = 4–12 kg/s and a liquid flow rate of QL = 96–288 kg/s. When the gas–liquid flow passes through the jumper, the flow regime subsequently presents the slug flow, bubble flow, churn flow and imperfect annular flow. The out-of-plane response frequency coincides with the pressure fluctuation frequency for the four connecting bends, suggesting the fluid–structure interaction (FSI). Nevertheless, the vibration displacement is limited with the maximum value less than 0.0014D (where D is the jumper diameter) in the present considered flow rate range.

Investigation in Gas-Oil Two-Phase Flow using a Differential Pressure Transducer and Wire Mesh Sensor in Vertical Pipes

The current study is performed to identify the flow regimes of oil-gas two-phase flow experimentally in a vertical pipe has an internal diameter of 6.7 cm. It also aims to provide more details about the possibility of using Differential Pressure Transducers (DPT) for indicating flow patterns. A flow development of oil and gas has been investigated in a vertical pipe of 6 m in length and operated at atmospheric pressure. A series of experiments have been run to cover a range of inlet oil superficial velocities from 0.262 to 0.419 m/s, and inlet gas superficial velocities from 0.05 to 4.7 m/s. Wire Mesh Sensors (WMS) have been used to collect the obtained void fraction values of the flow. The Differential Pressure Transducer (DPT) is utilized to measure the pressure drop values of a one-meter along the pipe. The flow patterns are classified according to the analysis of void fractions, pressure gradients regarding time series, tomographic images, probability density functions of the void fractions, and pressure gradients. A bubbly flow is observed at low superficial velocities of gas and liquid, slug flow is observed at the lower flow rate of liquid and moderate flow rates of gas, while the churn flow pattern is recognized at the higher rates of liquid and gas. Also, the result has revealed the possibility of using Differential Pressure Transducers (DPT) to classify the gas-oil flow patterns in vertical pipes.

Effect of Oil Viscosity on Flow Pattern Transition of Upward Gas-Oil Two-Phase Flow in Vertical Concentric Annulus

Summary Gas-oil two-phase flow usually occurs during gas influx into the wellbore annulus of deepwater drilling with oil-based drilling fluid or gas-oil production from the wellbore annulus. A flow pattern transition often is used in well control or in production parameter design. Related studies primarily have focused on gas-water two-phase flow, which is significantly different from gas-viscosity oil two-phase flow. We conducted experiments on a facility that included a flow section that was 13 000 mm long, with a 60-mm inner pipe and a 100-mm outer pipe in the annulus. A range of oil viscosities from 16 to 39 mPa∙s has been studied. The superficial gas and oil velocities varied from 0.55 to 17.077 m/s and from 0 to 0.414 m/s, respectively. A flow pattern was identified based on visualized analysis using electrical capacitance volume tomography (ECVT) and void faction wave analysis. Flow pattern maps of different viscosities were plotted based on measured data. Transition criteria based on Froude number and Archimedes number were established. The new model was compared with gas-water two-phase flow transition models and validated with experimental data. The effect of viscosity on flow pattern transition was revealed. The transition boundary of the bubble to slug flow and slug to churn flow both moved in the direction of smaller superficial gas velocity with an increase in oil viscosity. There may exist a critical viscosity value when churn flow transited to annular flow. When the viscosity was lower than this critical point, the above result was the same for churn to annular flow when the superficial oil velocity was low. With an increase in the superficial oil velocity, however, the boundary gradually changed to high superficial gas velocity as the oil viscosity increased. When the viscosity was larger than the critical point, the oil viscosity had a slight influence on the transition.

Effects of Oil Viscosity and the Solution Gas-Oil Ratio on Foamy Oil Flow in Solution Gas Drive.

The anomalously high recovery of solution gas drive in some heavy oil reservoirs has been associated with foamy oil. The effects of external factors such as temperature, permeability, and the pressure depletion rate on foamy oil flow have been studied sufficiently, but few studies are available on the effect of heavy oil itself. In order to investigate the effect of oil viscosity and the solution gas–oil ratio on foamy oil, 11 tests of solution gas drive through a sandpack were carried out in this work. The results show that a typical foamy oil solution gas drive exists in three stages, which are the oil phase expansion stage, the foamy oil flow stage, and the oil–gas two-phase flow stage. As the oil viscosity decreases, the foamy oil flow stage shortens, resulting in reduced recovery of this stage significantly. In the experiment with an oil viscosity of 200 mPa·s, foamy oil flow was not observed. A lower limit of oil viscosity should exist for steady flow of foamy oil, which is considered to be approximately 600 mPa·s according to the experimental results. As the solution gas–oil ratio increases, the oil recovery first increases and then decreases. Foamy oil flow could be observed clearly when the solution gas–oil ratio was between 10 and 26 Sm3/m3, which indicates that there is an optimal range of solution gas–oil ratios for foamy oil solution gas drive. The test with a solution gas–oil ratio of 35 Sm3/m3 showed that oil–gas two-phase flow followed the oil phase expansion stage as a result of the production of a quantity of gas, which illustrates that excess solution gas is unbeneficial to foamy oil flow on the contrary. The investigation revealed that oil viscosity and the solution gas–oil ratio are essential for foamy oil flow, which provides theoretical support for foamy oil production.

Flow behavior and film thickness of gas-oil two-phase flow in the single screw expander

The objective of this work is to study the flow behavior and oil film thickness in the vertical helical channel to improve the efficient operation of the single screw expander. The volume-of-fluid (VOF) model is adopted to examine various effects, including flow direction, oil viscosity, surface tension, flow rate, and oil inlet width on the liquid film thickness distribution and liquid holdup. An interesting phenomenon is found that the gas axial velocity is accelerated in the flow, and this has a profound influence on the liquid film thickness distribution and liquid holdup. The liquid film thickness exhibits a significant improvement as the downward flow is considered. The liquid film thickness becomes more symmetrical with increasing the oil viscosity, surface tension, oil flow rate, and inlet width, and more liquid are concentrated at the two endpoints of the channel. A higher viscosity oil or larger surface tension coefficient will result in a higher liquid holdup. These results and analysis are crucial for improving the performance of single screw expanders.

Optimal Design of Computational Fluid Dynamics: Numerical Calculation and Simulation Analysis of Windage Power Losses in the Aviation

Based on the theory of computational fluid dynamics (CFD), with the help of the Fluent software and the powerful parallel computing capability of the super cloud computer, the single-phase flow transient simulation calculation of the windage power loss of the engagement spiral bevel gear pair (SBGP) was performed. The two-equation SST k-ω turbulence model based on the assumption of eddy viscosity was adopted, which was improved from the standard k-ε model combined with the Wilcox k-ω model. The SST k-ω turbulence model inherited the respective advantages of the Wilcox k-ω model in the near-wall region and the k-ε model in the free shear layer and could more accurately describe the resistance and separation effect of the gear tooth surface on the airflow. The simulation analyzed the airflow characteristics around SBGP and the mechanism of the windshield to reduce the windage loss of the gear. It also studied the influence of the windshield clearance and opening size on the windage power loss. Then the orthogonal experimental analysis method was adopted to perform numerical simulation analysis. The windage torque was studied under different clearance values between the windshield and the gear tooth surface, as well as the large end and the small end. The variance analysis was performed on the numerical simulation data. The results showed that when the windshield clearance value was 1 mm and the engagement opening was 30°, the windage torque was the smallest, and the effect of reducing the windage power loss was the best. According to the changes in the pressure, velocity, and turbulent kinetic energy cloud diagram of the flow field in the reducer during multi-group simulation tests, the local optimal windshield configuration was obtained, which provided a method for further research on the multi-objective optimization of the windshield and the windage loss of the gear pair under the oil–gas two-phase flow and also provided a reference for the practical engineering application of the windshield.

Experimental Comparison Between Wire Mesh and Electrical Capacitance Tomography Sensors to Predict a Two-Phase Flow Behaviour and Patterns in Inclined Pipe

Two-phase flow behaviour and its flow patterns have a significant effect in many applications in industry. Oil-gas is one of the two-phase flow types that have many applications in petroleum and power stations. An oil-gas two-phase flow behaviour and flow patterns have been investigated in an inclined pipe using two different tomography sensors: Wire Mesh sensor (WMS) and Electrical Capacitance Tomography (ECT). A special experimental facility was designed and built to operate the tow-phase flow application in the inclined pipe with the various angle of inclination. A set of experimental data were collected using operating conditions which covered a two-phase flow range of superficial velocity of gas (Usl) from 0.05 to 0.52 m/s and superficial velocity of liquid (Usg) from 0.05 to 4.7 m/s at atmospheric pressure and room temperature. Three inclined angles to change the pipe’s inclination 45, 60, and 80-degree were applied in the experiments. The Comparison between the Wire Mesh Sensor (WMS) and Electrical Capacitance Tomography (ECT) was completed experimentally. The results revealed that there is a good agreement between the two sensors, however; the WMS had a higher frequency which was calculated 1000 frames per second compared with the ECT which worked at 200 frames per second.