Study of the influence of hydrate-like particles on the stratified gas-liquid flow pattern

Abstract

Gas hydrates are solid, crystalline compounds formed at high pressures and low temperatures. Hydrates pose a significant threat to oil and gas operations because of their potential to agglomerate and cause pipe blockages. There are two main strategies for managing hydrates: the traditional hydrate avoidance approach, which prevents the conditions leading to hydrate formation, and hydrate management, which is the focus of the present work. Hydrate management allows hydrates to form while using anti-agglomerants that prevent their agglomeration. In this scenario, the hydrate particles are carried by the liquid phase, resulting in a hydrate slurry flow. Despite the importance of this topic, there is scarce literature on the impact of these particles on key flow parameters, including pressure drop, liquid holdup and overall flow topology. This study is meant to address these gaps, with a special focus on the stratified flow pattern. To achieve these goals, two experimental scenarios were explored: airwater-particle flow and air-oil-particle flow. These experiments used model polyethylene particles with a density similar to that of hydrates, in a 50-mm ID, 34-m-long test section flow loop. Four different particle concentrations were investigated: 0, 5, 10 and 20% v/v in the liquid phase. Key flow parameters such as the phase fraction in the pipeline and solid distribution within the liquid layer were obtained through image processing techniques. The pressure drop was measured with the use of differential pressure transducers. The results showed that, especially at low gas superficial velocities, the liquid layer velocities were often insufficient to guarantee a homogeneous particle distribution, leading to the formation of solid beds. The cross-sectional restriction caused by the accumulation of solids increased the velocity of the flowing layers, destabilizing the stratified configuration and triggering an early transition to intermittent flow. These changes in flow pattern significantly impacted the pressure drop of the system and phase fraction characteristics. In general, pressure losses increased considerably compared to the original system without particles, where stratified flow remained stable. Besides evaluating the effect of particles on flow topology and linking the behavior of key flow parameters to the hydrodynamics observed in the experiments, this work also proposes theoretical and empirical modeling. The theoretical modeling focused on the stratified flow configuration and demonstrated that, as long as the particle distribution within the liquid becomes more homogeneous, the effect of the particles on the modeling can be satisfactorily predicted by using mixture properties. In addition, the proposed empirical correlationsaccurately predicted the experimental data under stratified flow and in the intermittent flow regime induced by cross-section restrictions due to particle accumulation.