Investigation and prediction of slug flow characteristics in highly viscous liquid and gas flows in horizontal pipes

Slug flow characteristics in highly viscous liquid and gas flow are studied experimentally in a horizontal pipe with 0.074 m ID and 17 m length. Results of flow regime map, liquid holdup and pressure gradient are discussed and liquid viscosity effects are investigated. Applicable correlations which are developed to predict liquid holdup in slug body for low viscosity flow are assessed with high viscosity liquids. Furthermore, a mechanistic model is developed for predicting the characteristics of slug flows of highly viscous liquid in horizontal pipes. A control volume is drawn around the slug body and slug film in a slug unit. Momentum equations with a momentum source term representing the significant momentum exchange between film zone and slug body are applied. Liquid viscosity effects are considered in closure relations. The mechanistic model is validated by comparing available pressure gradient and mean slug liquid holdup data produced in the present study and those obtained from literature, showing satisfactory capabilities over a large range of liquid viscosity

Restart time correlation for core annular flow in pipeline lubrication of high-viscous oil

One of the fundamental questions that must be addressed in the effective design and operation of pipeline lubrication of heavy oil is; “how much time will be needed to restart a blocked core annular flow (CAF) line after shutdown due to fouling or pump failures”, if the pipe is to be cleaned using water only. In this work, laboratory results of shutdown and restart experiments of high-viscous oil conducted in a 5.5-m-long PVC horizontal pipe with internal diameter of 26 mm are first presented. A new correlation for the prediction of the restart time of a shutdown core annular flow line is then formulated. The predictive capabilities of the correlation are checked against measured restart time and pressure drop evolution data. Somewhat high but still reasonable predictions are obtained. The restart time correlation, together with the associated correlations formulated as well, can be of practical importance during the engineering design of high-viscous oil pipeline transportation facility for predicting restart process

Minimum sand transportation conditions in multiphase pipelines: an assessment exercise

In offshore multiphase gas and oil pipelines, sand management is a vital task to prevent sand accumulative blockage and maintain pipeline mechanical integrity. This paper reports a study on the minimum transport condition (MTC) issue for typical subsea gas and liquid pipelines as a part of sand management strategy. A literature review was conducted on published prediction methods wrt sand transportation. A selective set of these models were benchmarked against the published experimental data and evaluation of model performances has been reported. The exercise started with the models of MTC in single phase liquid flows and followed by the models in gas/liquid flows. An Excel-based prediction tool was developed aiming to provide a straightforward method to obtain “sand -deposit-free” operating envelope for a multiphase flow pipeline during initial screening. Two methods were incorporated in this Excel based tool to assess MTCs in gas-liquid multiphase flow, including (i) modified King’s correlation (2016) and (ii) Danielson’s correlation (2007). The modified King’s model is found to be more flexible to account for the uncertainty in terms of definitions on “sand transport conditions” in multiphase flow

Physical properties of water-oil mixtures involving waxing

Non-Newtonian fluids exist extensively in the oil and gas industry and possess distinct physical properties that differ from those of Newtonian fluids. The multiphase flow involving non-Newtonian fluids have posed a serious challenge to the industry; however, comprehensive information expressing a wider knowledge of the mixture properties have not been well acquired. The focus of this paper is on water-oil mixtures involving petroleum wax, and seeks to highlight the waxing issue which is frequently encountered in offshore oil and gas transport pipelines. Experimental tests are carried out to investigate the behaviour of the water-oil mixture (with wax composition) and examine their fundamental physical and rheological properties. Furthermore, the effect of changes in temperature and varying water volume fraction on the shear rate – shear stress characteristics of the mixture are also considered. Results from this study show that the mixture properties depend significantly on temperature changes, fluid composition and the water content. Investigations also suggest that the phase inversion phenomenon has a significant impact on the shear rate-shear stress characteristics of the non-Newtonian oil/water mixture

Gas/liquid flow behaviours in a downward section of large diameter vertical serpentine pipes

An experimental study on air/water flow behaviours in a 101.6 mm i.d. vertical pipe with a serpentine configuration is presented. The experiments are conducted for superficial gas and liquid velocities ranging from 0.15 to 30 m/s and 0.07 to 1.5 m/s, respectively. The bend effects on the flow behaviours are significantly reduced when the flow reaches an axial distance of 30 pipe diameters or more from the upstream bend. The mean film thickness data from this study has been used to compare with the predicted data using several falling film correlations and theoretical models. It was observed that the large pipe data exhibits different tendencies and this manifests in the difference in slope when the dimensionless film thickness is plotted as a power law function of the liquid film Reynolds number

Interfacial shear in adiabatic downward gas/liquid co-current annular flow in pipes

Interfacial friction is one of the key variables for predicting annular two-phase flow behaviours in vertical pipes. In order to develop an improved correlation for interfacial friction factor in downward co-current annular flow, the pressure gradient, film thickness and film velocity data were generated from experiments carried out on Cranfield University’s Serpent Rig, an air/water two-phase vertical flow loop of 101.6 mm internal diameter. The air and water superficial velocity ranges used are 1.42–28.87 and 0.1–1.0 m/s respectively. These correspond to Reynolds number values of 8400–187,000 and 11,000–113,000 respectively. The correlation takes into account the effect of pipe diameter by using the interfacial shear data together with dimensionless liquid film thicknesses related to different pipe sizes ranging from 10 to 101.6 mm, including those from published sources by numerous investigators. It is shown that the predictions of this new correlation outperform those from previously reported studies

On-line mixing and emission characteristics of diesel engine with DME injected into fuel pipeline

This article presents a new on-line dimethyl ether (DME)/diesel mixing method, researches its blend characteristics, and also validates combustion and emission effects on a light-duty direct injection engine. This new blend concept is that DME is injected into the fuel pipeline to mix with local diesel as the injector stops injection, and this mixing method has some advantages, such as utilization of the original fuel system to mix DME with diesel intensively, flexibility on adjustable mixing ratio varying with the engine operating condition, and so on. A device was designed to separate DME from the blends, and its mixing ratios and injection quantity per cycle were also measured on a fuel pump bench. The results show that compared with the injected diesel, the percentages of DME injected into fuel pipeline are 13.04%, 9.74%, 8.55% and 7.82% by mass as the fuel pump speeds increase, while DME injected into fuel pipeline are 45.46%, 35.53%, 31.45% and 28.29% of wasting DME. The power outputs of engine fuelled with the blends are slight higher than those of neat diesel at low speeds, while at high speeds, its power outputs are a little lower. Smoke emissions of the blends are lower about 30% than that of neat diesel fuel at medium and high loads with hardly any penalty on smoke and nitrogen oxides (NOx) emissions at light loads. NOx and hydrocarbons (HC) emissions of the blends are slight lower than that of neat diesel fuel at all loads

Venturi multiphase flow measurement based active slug control

Riser slug flow poses a significant challenge to offshore oil production systems, most especially for oil fields in their later life. Active control of slugging through choking has been proven a practical approach in eliminating riser slug flow in oil production pipeline-riser systems. However, existing conventional active slug control systems may reduce oil production significantly due to excessive over choking. Again, some of the existing active slug flow control systems rely on seabed measurements, which are difficult to maintain, costly to install, unreliable, and seldom readily available. This study is an experimental investigation of the feasibility of active riser slug control by taking topside differential pressure measurement from the inlet of the venturi flow meter to the throat. Experimental results indicate that under active slug flow control, the system was able to eliminate slug flow at a higher valve opening when compared to manual choking. A valve opening of 24% with riser base pressure at 2.85 bar from open loop unstable of 23% was recorded, which is superior to manual choking which maintained flow stability up to 21% valve opening with riser base pressure of 3.8 bar

Forecasting of Two-Phase Flow Patterns in Upward Inclined Pipes via Deep Learning

Conventionally, the boundaries of gas-liquid flow regime transition are extremely sensitive to the inclination of flow channels. However, traditional two-dimensional flow regime maps have difficulties to reflect this fact as it can only accommodate two independent variables, which are often the gas and liquid superficial velocities. Few investigators have been able to propose a single model with accessible inputs under the considerations of the whole range of upward inclined angels. In this paper, we developed a novel approach by applying a typical machine learning (ML) method, artificial neural network (ANN), to predict flow pattern along upward inclined pipe (0 ~ 90°) using easily accessible parameters as inputs, namely, superficial velocities of individual phase and inclination angles. TensorFlow, a new generation and popular open-source foundation for ML programming, was used for building the ANN model, which was trained and tested by experimental data (1952 data points) that were reported in the literature. The predicting results show that ANN identifications have a satisfying agreement with experimental observations. The predicting accuracies of stratified smooth, stratified wavy, annular, intermittent, bubble flow are all above 90%, with the only exception of dispersed bubble flow (73%). In addition, the validation of the model was extended by comparing the ANN’s performance with well-established two-phase transition boundary models among different flow regimes. Comparing against conventional methods based on either correlation or flow regime map, the developed ANN model is expected to be a more efficient tool in flow pattern prediction. Furthermore, the impact of inclination angles on final ANN outputs was evaluated quantitatively. Results showed, given flow conditions fixed, variations of inclination angles have a significant influence on gas- liquid flow patterns in channels of conventional sizes

A microwave cavity resonator sensor for water-in-oil measurements

Online monitoring of Water-Liquid Ratio (WLR) in multiphase flow is key in petroleum production, processing and transportation. The usual practice in the field is to manually collect offline samples for laboratory analysis, which delays data availability and prevents real time intervention and optimization. A highly accurate and robust sensing method is needed for online measurements in the lower end of WLR range (0%–5%), especially for fiscal metering and custody transfer of crude oil, as well as to ensure adequate flow assurance prevention and remedial solutions. This requires a highly sensitive sensing principle along with a highly precise measurement instrument, packaged together in a sufficiently robust manner for use in the field. In this paper, a new sensing principle is proposed, based on the open-ended microwave cavity resonator and near wall surface perturbation, for non-intrusive measurement of WLR. In the proposed concept, the electromagnetic fringe field of a cylindrical cavity resonator is used to probe the liquid near the pipe wall. Two of the cylindrical cavity resonance modes, TM010 and TM011 are energized for measurements and the shift in the resonance frequency is used to estimate liquid permittivity and the WLR. Electromagnetic simulations in the microwave frequency range of 4 GHz to 7 GHz are used for proof-of-concept and sensitivity studies. A sensor prototype is fabricated and its functionality demonstrated with flowing oil-water mixtures in the WLR range of 0–5%. The frequency range of the proposed sensors is 4.4–4.6 GHz and 6.1–6.6 GHz for modes TM010 and TM011, respectively. The TM011 mode shows much higher sensitivity (41.6 MHz/WLR) than the TM010 mode (3.8 MHz/WLR). The proposed sensor consists of a 20 mm high cylinder, with a diameter of 30 mm and Poly-Ether-Ether-Ketone (PEEK) filler. The non-intrusiveness of the sensor, along with the high sensitivity in the resonance shift, makes it attractive for practical applications