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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 19769, “Modeling Liquid Holdups in Pseudoslugs,” by Yilin Fan, SPE, Colorado School of Mines; Eissa Al-Safran, SPE, Kuwait University; and Eduardo Pereyra, SPE, The University of Tulsa, et al., prepared for the 2020 International Petroleum Technology Conference, Dhahran, Saudi Arabia, 13-15 January. The paper has not been peer reviewed. Copyright 2020 International Petroleum Technology Conference. Reproduced by permission. Pseudoslug flow does not comply with the basic characteristics of conventional unit-cell slug flow. The liquid in the pseudoslug body is insufficient to reach the upper part of the pipe wall, resulting in only a large wave with entrained gas bubbles at the bottom part of the pseudoslug body. The pseudoslug body can be divided into two regions, liquid film (wave) with entrained gas bubbles at the bottom and gas core with entrained liquid droplets. The complete paper develops a plausible physical model of the experimentally observed pseudoslug liquid-holdup phenomenon and models physical and hydrodynamic behavior using a dimensional regression modeling approach.
Pseudoslug flow does not comply with the basic characteristics of conventional unit-cell slug flow. The liquid in the pseudoslug body is insufficient to reach the upper part of the pipe wall, resulting in only a large wave with entrained gas bubbles at the bottom part of the pseudoslug body. The pseudoslug body can be divided into two regions, liquid film (wave) with entrained gas bubbles at the bottom and gas core with entrained liquid droplets. The complete paper develops a plausible physical model of the experimentally observed pseudoslug liquid-holdup phenomenon and models physical and hydrodynamic behavior using a dimensional regression modeling approach. Pseudoslug flow has been named differently in early studies because of its ambiguous flow behavior, while the term "pseudoslug" has been adopted widely in recent studies.
Soedarmo, Auzan A. (The University of Tulsa / Schlumberger Norway Technology Center) | Rodrigues, Hendy T. (The University of Tulsa / Petrobras R&D Center) | Pereyra, Eduardo (The University of Tulsa) | Sarica, Cem (The University of Tulsa)
Pseudo-slug flow is widely encountered in gas wells or pipelines with liquid-loading issues. Pseudo-slug characteristics data, such as length, body holdup, frequency, and structure velocity, are very limited in literature despite their importance in modelling and facilities design. Moreover, there are no prior measurements for these variables at large diameter and high pressure conditions. In this study, experiments were performed in a 2° upward 0.1557 m ID flow loop for a pressure range of 1.48 to 2.86 MPa, using mineral oil and nitrogen as testing fluids. Pseudo-slug is characterized based on time-trace signals from Wire-Mesh-Sensors (WMS). The measured length, body holdup, film holdup, frequency, and structure velocity are reported. New pseudo-slug closure relationships are proposed, resulting in noticeable improvements in available model’s performance.
Pseudo-slug flow is commonly present in wet gas or gas-condensate production wells or pipelines with liquid-loading issues [1-3]. Pseudo-slug is physically similar to churn flow observed in near vertical pipes [4, 5]. In horizontal flow, this flow pattern may also exist at high gas flow rates [6, 7]. Additionally, it has been reported that as system pressure increases, slugs may gradually evolve into smaller slugs or pseudo-slugs [8, 9], and the transition from slugs to pseudo-slugs may occur at lower vSG [10, 11], suggesting the importance of pseudo-slugs in high pressures.
Abstract This paper studies the effects of system pressure in oil-gas low-liquid loading flow in a slightly upward inclined pipe configuration using new experimental data acquired in a high-pressure flow loop. Flow rates are representative of the flow in wet gas transport pipelines. Results for flow pattern observations, pressure gradient, liquid holdup and interfacial roughness measurements are presented and compared to available predictive models. The experiments were carried out at three system pressures (1.48, 2.17 and 2.86 MPa) in a 0.155 m ID pipe inclined at 2° with the horizontal. Isopar-L oil and nitrogen gas were the working fluids. Liquid superficial velocities ranged from 0.01 to 0.05 m/s while gas superficial velocities ranged from 1.5 to 16 m/s. Measurements included pressure gradient and liquid holdup. Flow visualization and Wire-Mesh Sensor (WMS) data were used to identify the flow patterns. Interfacial roughness was obtained from the WMS data. Three flow patterns were observed: pseudo-slug, stratified and annular. Pseudo-slug is characterized as an intermittent flow where the liquid does not occupy the whole pipe cross-section as the traditional slug flow does. In the annular flow pattern, the bulk of the liquid was observed to flow at the pipe bottom in a stratified configuration, however, a thin liquid film covered the whole pipe circumference. In both stratified and annular flow patterns, the interface between the gas core and the bottom liquid film presented a flat shape. The superficial gas Froude number, FrSg, was found to be an important dimensionless parameter to scale the pressure effects on the measured parameters. In the pseudo-slug flow pattern, the flow is gravity-dominated. Pressure gradient is a function of FrSg and vSL. Liquid holdup is independent of vSL and a function of FrSg. In the stratified and annular flow patterns the flow is friction-dominated. Both pressure gradient and liquid holdup are functions of FrSg and vSL. Interfacial roughness measurements show a small variation in the stratified and annular flow patterns. Model comparison gives mixed results, depending on the specific flow conditions. A relation between the measured interfacial roughness and the interfacial friction factor is proposed, and the results agree with existing measurements.
Abstract This paper presents a unique gas-liquid experimental dataset acquired at large-diameter laboratory multiphase loop under elevated pressures. The dataset and corresponding model validations are useful to upscale available multiphase flow knowledge into large-diameter-high-pressure conditions commonly encountered in offshore facilities. Intermittent (slug and pseudo-slug) and segregated (stratified and annular) flow patterns were observed in the experiments. For given superficial liquid Froude number (FrSL), all flow pattern transitions scale with superficial gas Froude number (FrSG) within the experimental range, capturing the effects of pressure (gas density). The change in pressure gradient and liquid holdup across the intermittent to segregated transition is more pronounced at low vSL. In segregated flow, the pressure gradient (-dp/dL) increases with pressure and vSL. However, these effects are less noticeable in intermittent flow. In intermittent flow, -dp/dL is generally gravity dominated but may become friction dominated as vSL increases, owing to absence of film reversal. For given vSL, -dp/dL scales with FrSG. The relationship between dimensionless -dp/dL (P*) and Lockhart-Martinelli parameter (X*) scales the effects of pressure and vSL for segregated flow. Liquid holdup was observed to decrease with pressure and increase with vSL. As pressure increases, density difference between phases decreases and interfacial friction increases, thereby reducing slippage and holdup (HL). Two state-of-the-art models exhibit similar bias tendency. In the intermittent region the inaccuracy of -dp/dL and HL predictions increase with vSG, i.e.: deeper into pseudo-slug region. This error is larger at low vSL. For segregated flow, the models tend to underpredict -dp/dL as vSG increases. The magnitude of this error is larger at high vSL. This paper addresses the limitation of large-diameter-high-pressure data in multiphase flow literature. The presented data, scaling approaches, and model validation results are critical for model improvement. For practicing engineers, they can be used as an upscaled benchmark/practical guidance to design multiphase flow pipelines.