Multiphase Pipeline Research Articles

Molecular dynamics simulation of wax micro-structure characteristics in the oil-water emulsion

As a key issue in the flow assurance of wax-containing crude oils, the microscopic mechanism of wax deposition in multiphase pipelines is still unclear. Based on macroscopic experimental data, two forms of crystallized wax have been found under an oil-water emulsion, including adsorbed wax on the interface of water droplets and suspended wax in the bulk oil phase, which are the important factors influencing wax deposition. However, the micro-formation mechanism of the adsorbed & suspended wax is not elucidated. In this work, molecular dynamics simulations are used to investigate the micro-structure characteristics of the adsorbed & suspended wax in the oil-water emulsion containing surfactant Span60. A method is proposed to quantitatively calculate the distributions of the adsorbed & suspended wax and the percentage of wax adsorption area at the oil-water interface. The results indicate that surfactant with the hydrophilic end will insert into the water phase and the trailing hydrophobic end stretching will point to the oil phase during co-crystallizing with wax molecules. Meanwhile, the interface tension is further reduced by tilting the adsorbed wax tail chain to enhance the adsorption stability. Based on the complicated influence of surfactants on wax adsorption, the quantitative distribution characteristics of the adsorbed & suspended wax in the oil-water emulsion are complex under different wax carbon numbers and surfactant/wax contents. This microscopic investigation of wax distribution in oil-water emulsion can support the establishment of better strategies for solving the wax deposition problem in multiphase flow.

Assessing the safe transportation of multiphase pipeline by integrating mechanism and Machine learning models

Developing a safe Multiphase Transport Boundary (MTB) is crucial due to the complex flow and heat transfer laws of multiphase transportation of fluids in pipelines. However, there is no efficient, accurate, and widely adaptable method for MTB formulation. This paper proposes a hybrid method based on traditional multiphase flow mechanisms and machine learning models to determine the safe operational MTB for multiphase pipeline transportation processes. The interactive logic enables the efficient and accurate calculation of MTB under real-time measurement data-driven for the proposed new hybrid model. Using a northwest oil field in China as an example, the results indicate that the hybrid model has an average relative error of less than 4.7% compared with simulated data, showing high accuracy. The calculation of a million operating conditions only takes 232 s. The research results can guide promoting the design, operation, and modification of pipeline transportation systems to ensure safety.

Formation behaviors of gas hydrates in water-in-oil emulsions with the coexistence of asphaltenes and resins

Hydrate formation is one of the major flow assurance issues for the subsea multiphase pipelines. The effects of the interaction between heavy fractions of crude oil components on hydrate behaviors are still not well understood. In this study, the effects of resins on hydrate formation behaviors in asphaltene-containing emulsions were investigated using a high-pressure reactor apparatus. The results indicated that both resins and asphaltenes inhibited hydrate nucleation and increased the induction time. Furthermore, considerable synergistic effects of asphaltenes and resins on the hydrate formation behaviors were discovered in the water-in-oil emulsions, depending on the aggregation state of asphaltenes. The addition of resins was observed to disperse the asphaltene aggregates significantly and enhance the inhibitory effect of asphaltenes on hydrate nucleation. Additionally, the calculated results of gas consumption showed that the presence of resins can decrease the growth rate of hydrates in the asphaltene-containing emulsions. A potential mechanism was presented to illustrate how resins affect hydrate formation in an emulsion with varying asphaltene aggregation states. These findings offer a better knowledge of the synergistic effects between the heavy components of resins and asphaltenes and have potential application in the hydrate management of crude oil pipelines.

Digital twinning of temperature fields for modular multilayer multiphase pipeline structures

The temperature field of oil and gas wells in the field of petroleum engineering presents a core problem and challenge in the digital twin framework due to its ultra-long-distance and highly variable structural characteristics. The varying wellbore cross-sectional structures with depth make it difficult to establish an effective and generalized analytical model for heat transfer. In this study, we propose, for the first time, a method to automate the construction of multi-layered and multi-component heat transfer models by using a general computational model based on non-steady-state single-phase structural modules. This method enables the automated generation of complex multi-layered and multi-component heat transfer models, thereby achieving the construction of a generalized model for temperature field characterization with varying wellbore cross-sectional structures over ultra-long distances. Utilizing this modeling approach, we validate the proposed method through case studies using actual wellbore temperature field data. The results demonstrate the lightweight and efficient computational analysis of temperature field information under non-steady-state conditions.

Influence and optimization of swirler parameters on elbow wear of deep coal fluidization pipeline transportation system

Elbow wear is a major threat to the multiphase pipeline transportation industry, which has a negative impact on the stable operation of the transportation system. In order to find the wear reduction methods of elbows in the fluidization pipeline transportation system for 2000-meter-deep coal resources, the swirler was installed upstream of the elbows, and wear simulations and tests of three kinds of elbows were carried out. The results showed that the maximum wear rate (MWR) of elbows increased and then decreased along the elbow angle. Due to the different directions of gravity, the heavy wear position (HWP) of the horizontal-vertical (H-V) elbow was in front of the vertical-horizontal (V-H) elbow. Because the downstream portion of the horizontal-horizontal (H-H) elbow was still a horizontal pipe, the HWP of the H-H elbow almost covered the whole elbow. The swirler placed upstream of the elbows could make the particles at the elbow move to the intrados of the elbows, resulting in less collision between the particles and the extrados of the elbows, thus reducing the wear of the elbows. The wear reduction effects of swirlers on three different elbows were favorably connected with the guide vane angle (GVA) and negatively correlated with the guide vane length (GVL), decreased first and then increased as the guide vane height (GVH) increased, and were little affected by the guide vane number (GVN) and the guide vane thickness (GVT). The mathematical models between the MWR of the elbows and guide vane parameters were established. By bench tests, the wear reduction effect of three kinds of elbows under the optimal guide vane parameters was 58.4%, 76.9%, and 78.6%, respectively. The errors between the bench test results and the simulation results were around 10%.

Hydraulic hammer and dynamic loads in multiphase pipelines

In oil and gas production and from the practice of transporting hydrocarbons, it is well known that, when a mono- or multiphase flow is instantly pumped, a sharp change in pressure occurs in the pipeline. As a result of hydraulic hammer, i.e., when pressure waves form and are distributed in the pipeline, compression of the pumped system and elastic deformation of the pipeline occur. Increasing the efficiency of pipeline operation requires the necessary diagnostics and consideration of the influence of such factors. The article discusses the issues of analyzing various dynamic loads in pipelines, taking into account the influence of structural forms and phase features of pumped multiphase systems.

World’s largest natural gas leak from nord stream pipeline estimated at 478,000 tonnes

Methane is a potent heat trapping gas believed to account for 30% of the observed global warming to-date. At a capacity of 110 bcm/year, the Nord Stream (NS) pipeline corridor measuring 1,153mm in internal diameter and stretching 1,224km from Russia to Germany is the biggest in the world. The explosions that NS sustained in September, 2022, in the Baltic Sea, have unleashed the largest single methane gas source in recent memory. Over the course of 7days, our transient multiphase pipeline model has estimated that the gas leaks from 3 lines pumped 478,000 tonnes of methane into the atmosphere. A range of pipeline shut-in pressures as a function of leakage time deduced an envelope of gas volume that matched the timeline of observed outflows. Interestingly, the methane gas that escaped from the damaged threads amounted to the CO2 equivalent emitted by concrete sufficient to build about 27 Burj Khalifa towers.

Numerical analysis of dispersion characteristics of underwater gas-oil two-phase leakage process

Fatigue failure, third-party destruction and internal corrosion may easily trigger gas and oil leakage during the operation of submarine multiphase pipelines. In order to analyze the underwater gas-oil plume development and migration law, a 3D model based on coupled Eulerian-Lagrangian numerical approach is proposed. The model is validated by laboratory experiment and the dynamic dispersion process of gas-oil plume in a large scale shallow sea environmental is further explored. Influencing factors such as leak location, leak size and water depth, flow pattern are investigated. The simulated results show that leak location affects the gas-oil plume migration behaviors by influencing the leakage amount. Water depth significantly affects gas-oil migration and the separation of gas plume and oil plume is gradually apparent as water depth increases. This study fills in the gap of ignoring the influence of flow pattern previously and is expected to help build more accurate emergency response guidelines.

Effects of wax on the formation of methane hydrate in oil-dominate systems: Experiments and molecular dynamics simulations

Hydrate formation and wax deposition in underwater multiphase pipelines have become two vital problems affecting the flow assurance safety. Experiments and molecular dynamics (MD) simulations were performed to investigate the effect of wax crystals on hydrate nucleation and growth. Our experimental results showed that wax crystals had an inhibitory effect on hydrate growth, but played a dual role in methane hydrate nucleation (promotion and inhibition). The addition of wax could decrease mass transfer coefficient of methane by increasing viscosity of oil phase, which lower methane supply from the oil bulk phase to the oil–water interface. The simulation results revealed that the wax crystals at the interface influenced the mass transfer of methane molecules instead of providing heterogeneous nucleation sites. Small wax crystal adjacent to the oil–water interface accelerated methane supersaturation dissolution and restricted gas diffusion in the aqueous phase because of adsorption to methane, which promoted hydrate nucleation and shifted the nucleation position toward the oil–water interface. While the large wax crystal could effectively block the methane mass transfer from oil phase to aqueous phase by covering the oil–water surface, which reduced the concentration of methane in the aqueous phase and prolonged the induction time of hydrate formation. These results of this work would provide a better understanding of the interaction mechanism between hydrate and wax.

Influence of solid-liquid two-phase flow conveying parameters on the elbow wear with and without the swirler

Elbow wear is a considerable threat to the multiphase pipeline transportation industry. The swirler placed upstream of elbows could reduce wear. The dense discrete phase model (DDPM) was used to study the effects of different concentrations, particle sizes, and flow velocities on the wear of elbows with and without the swirler, and the formation mechanism of different wear morphologies was revealed. The mathematical models between conveying parameters and the MWR (maximum wear rate) were established, and the conveying parameters that were most suitable for using the swirler to reduce elbow wear were obtained. The bench test proved that the MWR of the horizontal-horizontal (H-H) elbow, horizontal-vertical (H-V) elbow, and vertical-horizontal (V-H) elbow could be reduced by 51.9%, 35.5%, and 23.2%.

Application and prospects of multi-phase pipeline simulation technology in empowering the intelligent oil and gas fields

This paper reviews the application of multiphase flow simulation technology for constructing intelligent oil and gas fields. By utilizing the theoretical multiphase flow simulation model and solution algorithm, the practical engineering application of this technology in various oil and gas gathering and transportation system scenarios, including subsea production systems in offshore oil and gas fields, well site gathering and transportation production systems in onshore gas fields, and platform gathering and transportation production systems, was assessed and described. In addition, the role of multiphase flow simulation technology in intelligent oilfield surface production was discussed from the perspective of surface oil and gas pipeline networks and intelligent oilfield operations. Moreover, the future development prospects of multiphase pipeline transport simulation technology were proposed, providing a reference for improving related research and constructing intelligent oilfields.

Predictive Analytical Model for Hydrate Growth Initiation Point in Multiphase Pipeline System

Gas hydrates account for a huge flow assurance encounter in the passage of natural gas through pipelines. Its undesirability stems from the fact that these solids reduce pipe diameter open to gas flow, and challenge pipeline integrity, therefore leading to bursting pipes and increasing costs. Hydrates undergo four phases of development: entrainment, growth, agglomeration and plugging – and do not usually constitute a flow assurance challenge until agglomeration. These challenges are even more pronounced in the presence of condensate in the pipeline. This study was therefore designed by developing a predictive model of the hydrate growth initiation point along the pipeline where hydrates start to form in the presence of gas, condensate, and water. The developed predictive analytical model at which quasi liquid layer starts to form on the hydrate seed relates the quasi-liquid layer temperature to the gas hydrate mass, pipeline length, induction time, hydrate percentage in the fluid composition, hydrate density, change in enthalpy and the flowing hydrate velocity in the pipe system. The developed predictive model will assist in identifying when heating of pipelines can be done to control hydrate formation by keeping the temperature above the quasi-liquid layer temperature. This predictive model was in concordance with field observation.

State estimation and slug flow control of subsea production systems

The simulation and control of the severe slugging flow in the subsea multiphase pipeline is the focus of research in the production and exploitation of oil companies. Severe slug flow results in severe fluctuations of pressure and flow rate at both the wells end and the receiving host processing facilities, causing safety and shutdown risks. To prevent the severe slugging flow regime in multiphase transport pipelines, an ODE model is established by using the mass conservation law for individual phases in the pipeline and the riser sections. Then, the proposed model is compared to the results from the OLGA simulation. A comparative study of different slugging flow control solutions is conducted. Extended Kalman Filter (EKF), Back Propagation Neural Network (BPNN) and EKF&BPNN are used for state estimation and combined with PI controller. The EKF and BPNN are good nonlinear filters. However, when the nominal choke opening is increased, they work unsatisfying. The EKF&BPNN observer shows slightly better results than EKF and BPNN when the system has high input disturbance.

Kinetic Properties of CO2 Hydrate Formation in the Wax-Containing System at Different Concentrations

Precipitation of wax crystals and hydrate formation during deep-sea multiphase pipeline transportation would limit pipeline transportation flow and even trigger accidents. It is necessary to study the hydrate formation behavior in the wax-containing system. This paper utilized a mixture of number 60 Kunlun paraffin wax and number 2 industrial white oil to simulate the wax-containing system, and the CO2 hydrate was formed in the wax-containing system. The morphology of CO2 hydrate formation was captured by the microscope and the charge-coupled device imaging system. In this study, the influences of the wax crystal concentrations on the induction time and cumulative gas consumption of hydrate formation were investigated, and the effects of wax crystal precipitation on the CO2 hydrate nucleation mechanism were discussed. The experimental results indicated that, for the wax crystal concentrations of 1.50 and 2.50 wt %, the induction time of CO2 hydrate formation in the wax-containing system was reduced by 29.23 and 69.23% compared to that in the pure water system, respectively. However, for the wax crystal concentration of 0.50 wt %, the induction time of CO2 hydrate formation in the wax-containing system was increased by 130.77% compared to that in the pure water system. The reason for this was that the precipitation of wax crystals at high concentrations increased the chance of heterogeneous nucleation and the probability of heterogeneous nucleation increased with the increase of wax crystal concentrations. However, for the wax crystals at low concentrations, it not only lowered the chance of cross nucleation but also increased the mass transfer resistance for gas diffusion, thereby resulting in the increase of the induction time of hydrate formation. It was also found that, with the increase of the wax crystal concentrations, the cumulative gas consumption during hydrate formation decreased gradually. When the wax crystal concentration increased to 2.50 wt %, the cumulative gas consumption was reduced by 32.96% compared to that of the pure water system. The experimental results obtained in this study were helpful for understanding the kinetic characteristics of hydrate formation in the wax-containing system, which is meaningful for the pipeline flow assurance, safety, and economic security of pipeline transportation as well as the development of carbon capture and storage.

A new approach to the estimation of real characteristics of multi-phase flows in gaslift educator

It is known that the multi-phase flows are widespread in the oil-gas production, as well as in the collection and transportation of hydrocarbons from offshore fields. These gravitational upward and downward flows are characteristic for the rising pipes of gaslift and flow wells, as well as for the risers of subsea multi-phase pipelines. A new approach for the estimation of the real parameters of multi-phase flows considering the phase displacement is offered in the paper and the perspectives of their definition based on the microscopic parameters of well operation shown as well. A possibility of the specification of the real density, real gas content and phase displacement of gas-fluid flows in the rising pipes of gas-lift wells based on the actual operation data in the context of the wells of Guneshli (OFP-15) offshore field is shown.

An Experimental Study on the Interaction between Hydrate Formation and Wax Precipitation in Waxy Oil-in-Water Emulsions

The coupled formation of wax crystals and hydrates is a critical issue for the safety of deep-sea oil and gas exploration and subsea transport pipeline flow. Therefore, this paper conducts an experimental study on the characteristics of methane hydrate formation in a water-in-oil (W/O) system with different wax crystal contents and explores the influence of different initial experimental pressures on the induction period and maximum rate of hydrate formation. The wavelet function was introduced to process the reaction rate and calculate the maximum speed of hydrate formation. Notably, the higher the pressure, the smaller the maximum rate of hydrate formation. We observed that wax crystal precipitation increases the viscosity of the emulsion, which limits the diffusion of gas in the liquid phase during hydrate nucleation and thus delays the hydrate nucleation. The methane gas precipitation also affects the remaining fraction’s wax content and therefore affects the wax precipitation. Secondary hydrate formation was observed several times during the experiment, increasing the risk of pipeline blockage. Overall, this work provides insights into the effect of wax crystal precipitation on hydrate behaviour that could facilitate flow assurance applications in subsea multiphase pipelines and inform the safe transportation of oil and gas pipelines.

Влияние изменения состава флюида морского многофазного трубопровода на показатели режима эксплуатации при различных диаметрах

The paper investigates the effect of changes in the composition of a multiphase fluid over the time of operation of the field at different diameters of the offshore pipeline on such basic operational parameters as temperature, pressure, and the size of the slugcatcher in front of the platform equipment. The conditions of the pipeline routeare close to the conditions of the Sakhalin shelf. The composition and properties of the extracted fluid were chosen approximately based on the oil fields of the North-East Sakhalin oil and gas region. Modeling of the operating modeof pipelines of various diameters was carried out using the PIPESIM software package and the built-in multiphase flow correlation method «OLGAS 3-Phase HD». The obtained results of the study revealed certain dependencesof the change in the diameter of the pipeline on the parameters of its operation along the profile of pipeline. Based on the results of the study, recommendations for modeling multiphase pipelines for offshore fields were formed.

Construction of a Mathematical Model of the Flow Characteristics of a Multiphase Pipeline with Regard for the Phase Transitions in It

Construction of a Mathematical Model of the Flow Characteristics of a Multiphase Pipeline with Regard for the Phase Transitions in It

A new calculation method and model of hydrate slurry flow of the multiphase pipeline in deep water gas field

The transportation environment of multiphase pipelines in deepwater gas fields is likely to cause the problem of hydrate flow safety. Aiming at the gas-liquid-solid three-phase flow problem containing hydrate, a hydrate slurry flow model for a multiphase pipeline in a deep-water gas field was developed based on the two-fluid model coupled with the population balance equation, and a mesh was carried out for the axial distance of pipeline and size difference of hydrate particles to obtain a transient solution. The multiphase flow characteristics of the pipeline are simulated upon engineering scale, the transient flow characteristics of gas and liquid phases, the aggregation and fragmentation characteristics of hydrate particles, and the coupling interaction between them were studied, which lays the foundation for further research on the characteristics of hydrate particle deposition and blockage based on particle size distribution. This study provides support for the safety of hydrate flow in multiphase pipelines in deepwater gas fields.

Prediction of liquid surge volumes and flow rates for gas wells using machine learning

Liquid surge refers to an excessive liquid inflow to a slug catcher or a separator and is one of the main issues in flow assurance. The wellhead choke valves of gas wells must be adjusted to maintain the target flow rate as the reservoir pressure drops. The wellhead choke opening can be determined by conducting multiphase pipeline transient flow simulations to achieve the target flow rate and avoid liquid surges. However, it is not financially and computationally practical to conduct many multiphase transient pipeline flow simulations simultaneously for hundreds of wells. We found that flow rates and maximum liquid surge volumes for gas wells can be predicted accurately using simple machine learning models when the wellhead choke valve is adjusted. The machine learning models provided accurate predictions (R2 > 0.99) regarding flow rates and maximum liquid surge volumes for different wellhead pressure drop plans, vertical and horizontal well lengths, and current operating conditions in cases involving two real fields, the Horn River Basin (HRB) and Rakhine Basin field. The wellhead operating conditions that are appropriate for achieving the target flow rate and avoiding liquid surges can be efficiently determined using the machine learning models instead of multiphase transient pipeline flow simulators. The proposed approach also accurately estimated downhole pressures that are necessary to evaluate reservoir performances given wellhead pressures and flow rates. Lastly, we presented what features are dominant in predicting liquid surge volumes, flow rates, and downhole pressures in feature importance analyses.