In the recent years, the increased consumption of hydrocarbon resources and the decline in discoveries of low viscosity oils increased the importance of high viscosity oils. Significant changes in flow behavior were observed with increasing oil viscosity. Determination of the liquid holdup in the slug body is essential to calculate pressure drop for multiphase flow systems.An experimental study was performed to investigate the effect of high oil viscosity on slug liquid holdup and liquid film height. 144 tests were carried out in 50.8-mm ID horizontal pipe for different oil viscosities and superficial liquid and gas velocities. Tests were conducted at oil viscosities of 0.587, 0.378, 0.257 and 0.181 Pa·s. Superficial liquid and gas velocities varied from 0.1 to 0.8 m/s and 0.1 to 3.5 m/s, respectively. The experimental measurements were compared with the existing slug liquid holdup model predictions to investigate the performances of these models for high viscosity oil. mechanistic model were compared with high viscosity data. It was concluded that the slug liquid holdup predictions of these empirical and mechanistic models disagree with measurements especially above a 2 m/s mixture velocity. New slug liquid holdup correlations were developed in this study. The new correlations are expected to improve predictions of slug liquid holdup for high viscosity oil especially at high mixture velocities. No significant effect of high oil viscosity on liquid film holdup was observed within the selected oil viscosity range of this study.

Taylor bubble velocity in slug flow is a closure relation which significantly affects the prediction of liquid holdup (or void fraction) and pressure gradient in mechanistic models of slug flow for oil and gas pipe applications. In this work, we use a validated Computational Fluid Dynamics (CFD) approach to simulate the motion of Taylor bubbles in pipes; the interface is tracked with a Level-Set method implemented in a commercial code. A large numerical database is generated covering the most ample range of fluid properties and pipe inclination angles explored to date (Eo ∈ [10, 700], M o ∈ [1•10 −6 , 5•10 3 ], and θ ∈ [0 • , 90 • ]). A unified Taylor bubble rise velocity correlation is extracted from that database. The new correlation predicts the numerical database with 8.6% absolute average relative error and a coefficient of determination R 2 = 0.97, and other available experimental data with 13.0% absolute average relative error and R 2 = 0.84 outperforming existing correlations and models.

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Summary Understanding the behavior of two-phase flow is a key parameter for a proper oil/gas-production-system design. Mechanistic models have been developed and tuned to model the entire production system. Most existing two-phase-flow models are derived from experimental data with low-viscosity liquids (μL < 20 mPa·s). However, behavior of two-phase flow is expected to be significantly different for high-viscosity oil. The effect of high liquid viscosity on two-phase flow is still not well-studied in vertical pipes. In this study, the effect of high oil viscosity on upward two-phase gas/oil-flow behavior in vertical pipes was studied experimentally and theoretically. A total of 149 air/high-viscosity-oil and 21 air/water experiments were conducted in a vertical pipe with an inner diameter (ID) of 50.8 mm. Six different oil viscosities—586, 401, 287, 213, 162, and 127 mPa·s—were considered. The superficial-liquid and -gas velocities were varied from 0.05 to 0.7 m/s and from 0.5 to 5 m/s, respectively. Flow pattern, pressure gradient, and average liquid holdup were measured and analyzed in this study. The experimental results were used to evaluate different flow-pattern maps, mechanistic models, and correlations for two-phase flow. Significant discrepancies between experimental and predicted results for pressure gradient were observed.

Summary Slug frequency is defined as the number of slugs passing at a specific point along a pipeline over a certain period of time. Most experimental studies related to slug frequency in the literature were conducted using air and water. Data with a viscous liquid phase are scarce. Knowledge of the effect of liquid viscosity on slug flow is crucial to size pipelines and design preprocess equipment. In this study, the effects of high oil viscosity on slug frequency for horizontal pipes are investigated experimentally. The experiments are performed at oil viscosities between 0.181 and 0.589 Pa·s in a horizontal pipe. Experimental results are compared with the existing slug-frequency correlations. Experimental observations reveal that slug frequency appears to be a strong function of liquid viscosity. However, existing slug-frequency closure models do not show any explicit dependency on liquid viscosity. A closure model taking into account viscosity effects for horizontal pipes on slug frequency is proposed. The proposed slug-frequency model is compared against published data. The comparison between the proposed closure model and the limited published data shows that the former is a better alternative than existing correlations for high-viscosity oils. The proposed slug-frequency closure model can improve the performance of the existing mechanistic models for high-viscosity-oil applications.

Summary Slug-liquid holdup is a critical slug-flow parameter, which affects average liquid holdup and pressure gradient in pipes. Most experimental slug-liquid-holdup studies in the literature were conducted either by use of low-viscosity liquid for all inclination angles or high-viscosity liquid for horizontal and slightly inclined pipes, indicating a lack of experimental data for vertical flow of high-viscosity liquid. Therefore, the objective of this study is to experimentally and theoretically investigate the effect of oil viscosity on slug-liquid holdup in gas/liquid upward vertical flow, and to develop a new closure model to predict slug-liquid holdup in vertical pipes. In this study, experiments were conducted in a 50.8-mm inner-diameter (ID) vertical pipe for six oil viscosities: 586, 401, 287, 213, 162, and 127 mPa·s. A new slug-liquid-holdup closure model derived from Froude and inverse viscosity numbers was developed in this study for high-viscosity-liquid two-phase upward vertical flow. The proposed model was validated against independent experimental data and showed excellent prediction for high-viscosity data. Furthermore, the proposed model was compared with existing models that take into account the viscosity effects showing better performance. The new model was incorporated in the Tulsa University Fluid Flow Projects (TUFFP) unified model (all versions; Zhang et al. 2003b), improving the prediction of pressure gradient and average liquid holdup for high-viscosity upward vertical flow.