Ovadia Shoham

A Comprehensive Mechanistic Model for Upward Two-Phase Flow in Wellbores

A comprehensive model is formulated to predict the flow behavior for upward two-phase flow. This model is composed of a model for flow-pattern prediction and a set of independent mechanistic models for predicting such flow characteristics as holdup and pressure drop in bubble, slug, and annular flow. The comprehensive model is evaluated by using a well data bank made up of 1,712 well cases covering a wide variety of field data. Model performance is also compared with six commonly used empirical correlations and the Hasan-Kabir mechanistic model. Overall model performance is in good agreement with the data. In comparison with other methods, the comprehensive model performed the best.

A Unified Model for Predicting Flowing Temperature Distribution in Wellbores and Pipelines

This paper presents a general and unified equation for flowing temperature prediction that is applicable for the entire range of inclination angles. The equation degenerates into Rameys equations for ideal gas or incompressible liquid and into the Coulter and Bardon equation, with the appropriate assumptions. This work also proposes an approximate method for calculating the Joule- Thomson coefficient for black-oil models

Two-phase flow splitting in a tee junction—experiment and modelling

Abstract A model is presented for the prediction of two-phase flow splitting in a horizontal pipe tee for the stratified wavy and annular flow patterns. The model is based on a splitting mechanism which suggests that the preferential liquid flow is controlled by competing inertial and centripetal forces acting on the liquid phase at the tee junction. The model is compared with experimental data and gives reasoanble agreement.

The elimination of severe slugging—experiments and modeling

Severe slugging can occur in a pipeline-riser system operating at low liquid and gas rates. The flow of gas into the riser can be blocked by liquid accumulation at the base of the riser. This can cause formation of liquid slugs of a length equal to or longer than the height of the riser. A cyclic process results in which a period of no liquid production into the separator occurs, followed by a period of very high liquid production. This study is an experimental and theoretical investigation of two methods for eliminating this undesirable phenomenon, using choking and gas lift. Choking was found to effectively eliminate or reduce the severity of the slugging. However, the system pressure might increase to some extent. Gas lift can also eliminate severe slugging. While choking reduces the velocities in the riser, gas lift increases the velocities, approaching annular flow. It was found that a relatively large amount of gas was needed before gas injection would completely stabilize the flow through the riser. However, gas injection reduces the slug length and cycle time, causing a more continuous production and a lower system pressure. Theoretical models for the elimination of severe slugging by gas lift and choking have been developed. The models enable the prediction of the flow behavior in the riser. One model is capable of predicting the unstable flow conditions for severe slugging based on a static force balance. The second method is a simplified transient model based on the assumption of a quasi-equilibrium force balance. This model can be used to estimate the characteristics of the flow, such as slug length and cycle time. The models were tested against new severe slugging data acquired in this study. An excellent agreement between the experimental data and the theoretical models was found.

Simplified transient solution and simulation of two-phase flow in pipelines

A simplified transient formulation for calculating transient behavior of two-phase flow in a pipelines system is proposed. The formulation assumes a quassi-steady-stage gas flow and a local equilibrium momentum balance. The applicability of this method is demonstrated for the case of a pipeline system with horizontal, upward and downward inclined sections.

Severe slugging in a riser system: experiments and modeling

Abstract Previous analysis showed that “severe” slugging would exist in a pipeline—riser system when the liquid in the riser is unstable and gas penetrates into the riser. This would then result in an unstable blowout and a cyclic process. When the liquid column is stable, a steady state is assumed to exist. However, observations made on a small-scale test facility have demonstrated that when the liquid column is stable there is still a tendency for a cyclic process to occur. This cyclic process can be damped and become a steady flow or it can continue indefinitely. From these observations a new theory is developed for predicting the behavior in the stable region and is verified with experimental results. It is also shown that in the region predicted by the Boe criterion to be a steady flow, the flow can be unstable and lead to a severe slugging type of behavior.

The effects of geometry, fluid properties and pressure on the hydrodynamics of gas–liquid cylindrical cyclone separators

Abstract The hydrodynamic flow behavior in a Gas–Liquid Cylindrical Cyclone (GLCC) compact separator is studied experimentally and theoretically. New experimental data are acquired utilizing a 7.62 cm I.D, 2.18 m high, GLCC separator for a wide range of operating conditions. Investigated parameters include three different inlet geometries (5.08 cm I.D single, 7.62 cm I.D single and 7.62 cm I.D dual inlets), four different liquid viscosities (1, 2.5, 5 and 10 cps), three system pressures (101.3, 273.6 and 487.2 kPa), and the effect of surfactant. The measured data comprise of equilibrium liquid level, zero-net liquid flow holdup and the operational envelope for liquid carry-over. The data are utilized to verify and refine an existing GLCC mechanistic model. Comparison between the modified model predictions and the experimental data show a very good agreement.

Hydrodynamics of Two-Phase Flow in Gas-Liquid Cylindrical Cyclone Separators

This paper presents new experimental data and an improved mechanistic model for the Gas-Liquid Cylindrical Cyclone (GLCC) separator. The data were acquired utilizing a 3” ID laboratory-scale GLCC, and are presented along with a limited number of field data. The data include measurements of several parameters of the flow behavior and the operational envelope of the GLCC. The operational envelope defines the conditions for which there will be no liquid carry-over or gas carry-under. The developed model enables the prediction of the hydrodynamic flow behavior in the GLCC, including the operational envelope, equilibrium liquid level, vortex shape, velocity and holdup distributions and pressure drop across the GLCC. The predictions of the model are compared with the experimental data. These provide the state-of-the-art for the design of GLCC’s for the industry.

Drift velocity of elongated bubbles in inclined pipes

Abstract The drift velocity, which is defined as the velocity of long bubbles propagating into a stagnant liquid column, has been treated successfully in the past using inviscid flow theory. However, different approaches were used for the horizontal and the vertical cases. In this work, Benjamins simple approach, which was originally applied for the horizontal case only, is extended to the inclined and the vertical cases, taking into consideration surface tension effects. Good agreement with experimental data is obtained.

A unified model for stratified-wavy two-phase flow splitting at a reduced T-junction with an inclined branch arm

Abstract Stratified-wavy two-phase flow splitting at a reduced T -junction with an inclined branch arm has been investigated experimentally and theoretically. Experimental data have been acquired with the reduced branch arm inclined at horizontal, downward inclination angles of −5°, −10°, −25°, −40° and −60° and upward inclination angles of 1°, 5°, 10°, 20°. The data reveal that for the case of a downward branch arm configuration the high gas velocity in the reduced branch arm and the gravity effects tend to increase the liquid flowing into the branch, as compared to the horizontal case. For upward inclinations of the branch arm, gravity forces tend to reduce the liquid flow into the branch. Comparison between published experimental data for a regular tee and the present data for a reduced tee for the different inclination angles is also presented. A unified model has been developed for the prediction of the splitting phenomenon for the horizontal, upward and downward orientations of the reduced branch arm. The model is based on the momentum balance equations applied for the separation streamlines of the gas phase and liquid phase. Comparison between the model predictions and experimental data shows good agreement with respect to the general trend and shape of the splitting curves and reasonable agreement with respect to the absolute values.