Investigation of Hydrate Agglomeration and Plugging Mechanism in Low-Wax-Content Water-in-Oil Emulsion Systems

Abstract

Pipeline blockage caused by hydrates and wax in subsea pipelines is a major hazard for flow assurance in the petroleum industry. When hydrates and wax coexist in a flow system, the plugging risk is more severe. The effects of wax on hydrate formation, agglomeration process, flow properties, and plugging mechanisms were studied in a high-pressure flow loop using water-in-oil (w/o) emulsion systems. The flow properties of the system with the presence of wax were entirely different from those of the system without wax under the same experimental conditions. Three types of plugging were observed in the flow loop: rapid plugging, transition plugging, and gradual plugging. The interaction relationships between wax crystals, water droplets, and hydrate particles and the formation of wax−hydrate aggregates were proposed based on the particle video measurement (PVM) probe observation and the analysis of the fluid viscosity. The mechanisms of different plugging scenarios were presented, which were highly correlated with the temperature and initial flow rate. The presence of wax would impact on the agglomeration process of hydrate particles leading to a catastrophic decrease in the transportation ability and an extremely high plugging risk after hydrate formation in the pipeline.

Evolution of morphology and cohesive force of hydrate particles in the presence/absence of wax

“…This experimental phenomenon is similar to that of Liu et al who have conducted experiments in a flow loop. 22 The reason is that wax crystal will destroy the shell structure of hydrate particles, changing the surface properties and liquid bridge formation process of hydrate particles, and making the cohesive force between hydrate particles increases steeply and sharply. Fig.…”

“…After the contact of hydrate particles that formed in the presence of wax crystals, it is suggested that the structure of wax-containing hydrate shell is destroyed due to the compatibility of wax crystals at the interface. 22 The untransformed water inside the particles is rapidly flushed out, and a huge liquid bridge is rapidly formed between the two particles (see Fig. 8b ), which greatly increases the cohesion between the wax-containing hydrate particles.…”

“…Some studies have been conducted on the risk and the potential safety hazard of pipeline blockage in the coexistence system of wax and hydrate. Liu et al 22 studied the effect of wax on the formation, agglomeration, flow characteristics and plugging mechanism of hydrates in w/o emulsion systems. They suggested that the presence of wax would affect the agglomeration process of hydrate and greatly increase the risk of pipeline blockage.…”

Investigation on Hydrate Growth at the Oil–Water Interface: In the Presence of Wax and Kinetic Hydrate Inhibitor

“…Up to now, many studies have been conducted to investigate the interaction between hydrate and wax in terms of nucleation, 15−21 formation, 22−27 agglomeration, 12,28−30 deposition, 15,31 and plugging. 29 The details and main conclusions of these studies have been discussed in our previous study 32 and will not be repeated here. According to these literatures, it can be concluded that the presence of wax do have profound effects on pipeline hydrate issues.…”

Study on the Decomposition Mechanism of Natural Gas Hydrate Particles and Its Microscopic Agglomeration Characteristics

“…As exploration and production is going into deeper water, the focus of flow-assurance strategies are shifting from traditional methods to risk-control techniques [2]. Hydrate slurry flow has gradually gained the attention of researchers [13][14][15][16][17][18][19][20], who have referred to it as a form of hydrate risk control. However, studies on hydrate slurry are still in the period of experimental investigation with preliminary theoretical development [21].…”