Foam stability: The key to inhibiting slug generation in gas–liquid flow

https://doi.org/10.1016/j.petrol.2022.110969Get rights and content

Highlights

  • Mechanisms of using more stable foam to inhibit slug generation were clarified.

  • Effects of MgCl2 on gas-liquid two-phase flow containing SDS foam were elucidated.

  • Gas-liquid flow characteristics of foams with different properties were analyzed.

  • Suitable foams for removing liquid accumulation at varied gas velocities were stated.

Abstract

Surfactant-based foam drainage technology is a favored method of liquid accumulation removal, and it has been demonstrated as an efficient way to improve gas production efficiency. However, foam properties are extremely complex and the same surfactant can produce foam systems with widely varying properties under different environmental conditions. This has a huge impact on the multiphase flow containing foam and thus on the efficiency of fluid removal. To further explore the influences of changing foam properties on the flow characteristics and the liquid-carrying capacity of foam, this study experimentally investigated the gas–liquid multiphase flow containing different foams in a hilly terrain pipeline with different properties in pipelines by adding SDS surfactant and MgCl2. The results show that the foam stability can significantly affect the gas–liquid multiphase flow characteristics. Adding MgCl2 enhances the stability of SDS foam. This narrows the range of intermittent flow conditions and leads to a significant fall in the critical gas velocity corresponding to the transition from intermittent to separated flow. Meanwhile, under the same gas and liquid velocities conditions, the foam with higher stability has a more pronounced suppression effect on the velocity of liquid in the upward inclined section, both the slug velocity and the liquid reflux velocity. The reduction in the holding rate also indicates that a more-stable foam improves the liquid-carrying capacity of gas and the discharge efficiency. In addition, as the gas velocity increases, the enhanced stability promotes the transition of the flow pattern from stratified to annular flow, resulting in a remarkable increase in the pressure drop gradient. This suggests that a more stable foam system is suitable for environments with lower gas velocities.

Introduction

Foams based on surfactants are widely used in the petroleum chemical field (Chen et al., 2018; Gong et al., 2020; Kumar and Mahto, 2017; Rashed Rohani et al., 2014). During the process of natural gas production, surfactant-based foam drainage technology has been proved to be an efficient method for the removal of accumulated liquid in gas wells (Saleh and Al-Jamae'y, 1997; Wang et al., 2018), which can improve the production efficiency, prevent flooding accidents, and reduce the risk of hydrate generation (Li et al., 2010). In addition, using surfactants to generate foam in gas-gathering systems can inhibit the occurrence of severe working conditions such as intermittent flow in pipelines, which is the current research priority of scholars (Van Nimwegen et al., 2013). Moreover, foam performance is one of the most important factors that affect its effectiveness in liquid removal (Govindu et al., 2019; Shojaei et al., 2021).

Inorganic salts are widely present in formation water and have a significant impact on the field application of foaming agents (Angarska et al., 1997; Yang et al., 2021). Existing studies have proven that the foaming performance of surfactants and the stability of the corresponding foam systems are strongly affected by inorganic salts due to the degree of ionization of metal salts and the different valence states of their ions (Jiang et al., 2020; Zhao et al., 2010). Obisesan et al. (2021) experimentally studied the influence of different salts on the drainage performance of aqueous foams. The results indicated that the drainage volume of the foam with added NaCl decreased as the foam mass increased, while that of foams containing CaCl2 showed no obvious trend with the change in foam mass. Based on experimental tests, Wang and Yoon (2006) found that the adsorption capacity of sodium dodecyl sulfate (SDS) could be promoted by adding NaCl at the air-liquid interface and that the hydrophobic force weakened with increasing concentrations of NaCl and SDS. Alonso et al. (2020) investigated the effects of various inorganic salts on the interfacial tension at oil-water interfaces with nonionic surfactants. It was found that inorganic salts, especially NaCl, could significantly reduce the interfacial tension of the system. Combined with previous experiments and the theoretical derivations, Katsiavria and Bontozoglou (2020) found that adding salts significantly increased the foam stability and enabled the adsorption of surfactants at the interface by reducing electrostatic repulsion, thus obviously lowering the surface tension at the gas–liquid interface with low-concentration surfactants. Therefore, the presence of salt ions affects the foam characteristics, and Mg ions can significantly enhance the stabilization properties of foam containing anionic surfactants (Li et al., 2013).

In view of the widespread use of foam drainage technology in gas wells containing liquid, a large number of studies have already been conducted on the gas–liquid multiphase flow with or without foam in vertical pipelines (Duangprasert et al., 2008; Gao et al., 2021). Liu et al. (2014) investigated the effects of surfactants on the flow pattern and void fraction of gas–liquid flow in a vertical pipeline. The results indicated that the liquid holdup could be reduced dramatically by adding the right amount of surfactants in the pipeline. In addition, Rozenblit et al. (2006) investigated the effects of surfactants on the liquid holdup in a vertical pipe with a diameter of 24.2 mm. Several flow patterns containing foam were visually observed, and the foam flow patterns were redrawn. As gas velocity increased, the flow regimes were classified as bubble flow, slug flow, churn flow, and annular flow, which were similar to gas–water two-phase flow (Dziubinski et al., 2004; Wu et al., 2017). Ajani et al., 2016a, Ajani et al., 2016b studied the influences of surfactants on the pressure drop and void fraction in risers and established closed relationships for liquid accumulation, foam accumulation, gas content in foam, and friction coefficient at the gas-foam phase interface. In addition, van Nimwegen et al., 2015a, van Nimwegen et al., 2015b studied the influences of surfactants on the void fraction and pressure drop gradient in stirred and annular flow in a vertical pipe. This result indicated that surfactants in the annular flow state increased the pressure drop gradient because of the increase in friction, while the addition of surfactant could significantly reduce the pressure drop gradient for the stirred flow state. The corresponding prediction models for liquid holdup and pressure drop were also proposed (van Nimwegen et al., 2018). Zhang et al. (2019) researched the effects of SDBS foam on gas and liquid distributions in stirred and annular flows and stated that the presence of foam increased the momentum transfer between gas–liquid phases, contributing to a remarkable increase in the pressure gradient.

Owing to the progress of horizontal gas wells and the accumulation of liquids in undulating natural gas pipelines, studies on multiphase flow with foam in horizontal and slightly upward pipes have been booming in recent years. Wilkens et al. (2006; 2007) performed gas–water flow experiments in a 52.0 mm horizontal pipeline containing surfactants and summarized patterns of gas–liquid flow with or without foam. In addition, the addition of surfactants narrowed the occurrence range of slug flow. Colombo et al. (2018) showed experimentally that the addition of surfactants was able to improve the void fraction in the horizontal pipe and increase the pressure drop along the flow direction. In inclined pipelines, van Nimwegen et al. (2016) conducted experiments on multiphase flow containing foam in pipes with upward flow at different inclined angles and found that the addition of surfactant in inclined pipelines was less effective in promoting the transformation of intermittent flow patterns to separated flow patterns than in vertical pipelines. Yin et al., 2022, Zhang et al., 2021b experimentally studied the effects of different concentrations of SDS and SDBS on gas–liquid multiphase flow in slightly upward pipes. The addition of surfactants was led to marked changes in the slug structure, and the flow patterns of multiphase flow with foam were plotted. For gas–liquid multiphase flow containing foam, many variables affect foam formation and transport, such as the inclination angle (Govindu et al., 2020), pipe diameter (van Nimwegen et al., 2017), and medium (Besagni et al., 2017; Mahmoud et al., 2020). Meanwhile, various factors cause large differences in foam properties, such as the type and concentration of surfactants (Lioumbas et al., 2015; Wang et al., 2019), ambient temperature (Bashir et al., 2022; Kawai et al., 2005), ion concentration (Alonso et al., 2020), etc. Therefore, research in this field has mainly focused on the description of the phenomena by which foam affects the flow characteristics.

As mentioned above, the influences of the presence of foam on gas–liquid multiphase flow characteristics in pipelines have been widely studied. However, due to the diversity of foams, studies on the differences in the above effects caused by changes in foam properties have not been carried out. Our previous studies have shown that the addition of MgCl2 can enhance the stability of the foam system (Zhang et al., 2021a). Therefore, to further clarify the effects of foam stability on the gas–liquid two-phase flow characteristics by changing the foam properties, this paper reports the integration of a variety of test methods followed by experimental investigations on gas–liquid two-phase flow containing SDS foam and MgCl2. The mechanism of the effect of foam performance on the flow characteristics was clarified, and the reasons why MgCl2 influenced the flow characteristics in gas–liquid–foam flow were systematically analyzed. In addition, the flow parameters and pressure and differential pressure characteristics of different flow states of gas–liquid flow containing foam are obtained. These provide both valuable guidance the overall production of the natural gas industry and references for the promotion of foam drainage technology in gathering pipelines and horizontal wells.

Section snippets

Experimental loop

The multiphase flow loop is schematically shown in Fig. 1. It consists of a flow control system, a circulation system, and a measurement system. The circulation system includes a water tank, a pump, a compressor, a cyclone separator, and pipelines. Among them, the pipeline section includes the development part, the stabilization part, and the test part. The control system consists of flow control valves, gas and liquid flow meters, and pressure gauges. In addition, the measurement system

Flow pattern

To analyze the effects of the presence of foam and MgCl2 on the multiphase flow containing foam, the mechanisms of different foam performance characteristics on the flow pattern distribution are discussed in conjunction with flow photographs with distinct structural features captured by the visualization system. The arrangement of the high-speed camera system is shown in Fig. 5. All the examples presented below were carried out with a superficial liquid velocity of 0.01 m/s.

Conclusions

In this study, foam drainage for removing liquid accumulation in natural gas pipelines and horizontal wells was explored by studying gas–liquid multiphase flow containing different foam properties, and a variety of flow characteristic parameters were analyzed. The main conclusions are as follows.

  • (1)

    Foams with different performances have different effects on the flow characteristics of gas–liquid multiphase flow containing foam. Adding MgCl2 contributes to the enhancement of foam stability. More

Credit author statement

Pan Zhang: Conceptualization, Experiments, Methodology, Investigation and Writing – original draft. Dan Guo: Experiments, Writing – review & editing. Xiang Li: Experiments, Data curation. Wenzhu Xia: Software, Data curation. Wenshan Peng: Reviewing. Jiang Bian: Revising. Xuewen Cao: Conceptualization, Funding acquisition, Investigation and Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grants No. 51874340 and No. 52074341 and No. 52104071).

References (61)

  • Y. Fan et al.

    Modeling pseudo-slugs liquid holdup in slightly upward inclined pipes

    J. Pet. Sci. Eng.

    (2020)
  • Y. Fan et al.

    Analysis of flow pattern transition from segregated to slug flow in upward inclined pipes

    Int. J. Multiphas. Flow

    (2019)
  • A. Govindu et al.

    Stability of foams in pipe and annulus

    J. Pet. Sci. Eng.

    (2019)
  • M. Hammoudi et al.

    Dispersed two-phase flow analysis by pulsed ultrasonic velocimetry in SMX static mixer

    Chem. Eng. J.

    (2012)
  • N. Jiang et al.

    Role of salts in performance of foam stabilized with sodium dodecyl sulfate

    Chem. Eng. Sci.

    (2020)
  • J.S. Lioumbas et al.

    Foam free drainage and bubbles size for surfactant concentrations below the CMC

    Colloids Surfaces A Physicochem. Eng. Asp.

    (2015)
  • D. Liu et al.

    Polarity effects of asphaltene subfractions on the stability and interfacial properties of water-in-model oil emulsions

    Fuel

    (2020)
  • L. Liu et al.

    Effect of surfactant additive on vertical two-phase flow

    J. Pet. Sci. Eng.

    (2014)
  • H. Mahmoud et al.

    Hole cleaning and drilling fluid sweeps in horizontal and deviated wells: comprehensive review

    J. Pet. Sci. Eng.

    (2020)
  • R. Rozenblit et al.

    Flow patterns and heat transfer in vertical upward air-water flow with surfactant

    Int. J. Multiphas. Flow

    (2006)
  • S. Sharaf et al.

    Global and local hydrodynamics of bubble columns - effect of gas distributor

    Chem. Eng. J.

    (2016)
  • M.J. Shojaei et al.

    Combined effects of nanoparticles and surfactants upon foam stability

    Chem. Eng. Sci.

    (2021)
  • L. Szalinski et al.

    Comparative study of gas-oil and gas-water two-phase flow in a vertical pipe

    Chem. Eng. Sci.

    (2010)
  • A.T. van Nimwegen et al.

    Modelling of upwards gas-liquid annular and churn flow with surfactants in vertical pipes

    Int. J. Multiphas. Flow

    (2018)
  • A.T. van Nimwegen et al.

    The effect of the diameter on air-water annular and churn flow in vertical pipes with and without surfactants

    Int. J. Multiphas. Flow

    (2017)
  • A.T. van Nimwegen et al.

    The effect of surfactants on upward air-water pipe flow at various inclinations

    Int. J. Multiphas. Flow

    (2016)
  • A.T. van Nimwegen et al.

    The effect of surfactants on air-water annular and churn flow in vertical pipes: Part 2: liquid holdup and pressure gradient dynamics

    Int. J. Multiphas. Flow

    (2015)
  • A.T. van Nimwegen et al.

    The effect of surfactants on air-water annular and churn flow in vertical pipes. Part 1: morphology of the air-water interface

    Int. J. Multiphas. Flow

    (2015)
  • L. Wang et al.

    Stability of foams and froths in the presence of ionic and non-ionic surfactants

    Miner. Eng.

    (2006)
  • T. Wang et al.

    Application of Dopper ultrasound velocimetry in multiphase flow

    Chem. Eng. J.

    (2003)
  • Cited by (0)

    View full text