Cyclopentane Hydrate Particles Research Articles

Experimental investigation to elucidate the hydrate Anti-Agglomerating characteristics of 2-Butoxyethanol

To alleviate the severity of hydrate formation in subsea oil and gas pipelines, the injection of anti-agglomerants (AAs) is one of the promising approaches. In this work, we investigate the hydrate anti-agglomerating characteristics of 2-butoxyethanol, also called butyl glycol ether (BGE), which has been reported in the literature as an effective synergist for kinetic hydrate inhibitors (KHIs), and a solvent for low dosage hydrate inhibitors (LDHIs). In view of its hydrophobic and hydrophilic moieties, we evaluate the adsorption affinity of BGE for the oil–water interface employing the interfacial tensiometer (IFT) apparatus. Moreover, a micromechanical force (MMF) apparatus was used to probe the interfacial behavior of hydrate particles, wherein we measured the cohesive forces between cyclopentane hydrate particles in the presence of BGE at atmospheric pressure and 274.2 K. The kinetics of methane hydrate formation and resistance-to-flow were assessed while measuring the dynamic pressure–temperature data and motor torque signals alongside with visual observations, respectively, employing a high-pressure visual autoclave (HPVA). IFT results reveal the strong surface active properties of BGE with a substantial reduction in oil–water interfacial tension at ambient conditions. However, no considerable change in the cohesive forces between cyclopentane hydrate particles was observed through MMF measurements. In contrast, HPVA results reveal that the addition of BGE enhanced the kinetics of methane hydrate formation; however, the corresponding torque pattern/visual interpretations indicated an anti-agglomerating action of BGE. While synergistically combining the BGE with under-inhibited dosages of mono-ethylene glycol, we further demonstrated a significant improvement in the hydrate transportability, wherein this synergism led to a non-plugging scenario (flowable hydrate slurry). Our findings will offer new insights into the development of new anti-agglomerant chemistries.

Hydrate growth and agglomeration in the presence of wax and anti-agglomerant: A morphology study and cohesive force measurement

During deep-sea and ultra-deep-sea oil and gas exploitation, multiphase transmission lines are prone to be clogged by sediments produced by the various components in crude oils under extreme subsea conditions, such as hydrates, wax, resins, and asphaltenes. The pipelines face higher plugging risks when these deposits exist simultaneously. In order to elucidate the effects of wax and anti-agglomerants (AA) on hydrate growth and aggregation, microscopic morphology observation and cohesive force measurement of cyclopentane hydrate particles were conducted through a piece of equipment similar to the micromechanical force (MMF) apparatus. Results showed that in the low concentration of AA (0.05 wt%), hydrate particles experienced an approximately 10 % reduction in the profile area after converting water droplets to hydrate particles. Furthermore, the cohesive force between hydrate particles decreased from 8.57 ± 0.90 mN/m to 3.51 ± 0.43 mN/m as the AA concentration increased from 0.05 to 0.2 wt%. On the other hand, the presence of wax significantly altered the morphologies of hydrate particles. When wax coexisted with AA, the hydrate cohesive force was reduced by wax under low AA concentration (0.05 wt%) but increased under higher AA concentration. For a given concentration of AA, the hydrate cohesive force increased with the increasing wax content (from 0.1 to 0.3 wt%), indicating that wax crystals weakened the efficiency of AA, such as Span 80. Additionally, the effect of surface wetness of waxy hydrate particles on their cohesion was also investigated. The liquid bridge appeared between wet waxy hydrate particles, while the solid–solid contact existed between dry waxy hydrate particles. The cohesive force between dry waxy hydrate particles was smaller. Either liquid bridge or solid–solid contact that dominated hydrate cohesive force was affected by wax.

Application of a biomimetic wellbore stabilizer with strong adhesion performance for hydrate reservoir exploitation

Natural gas hydrate (NGH) in marine is usually reserved in the pores or cracks of weakly cemented argillaceous siltstones. Moreover, the hydrates are susceptible to variations in temperature and pressure conditions when water-based drilling fluids (WBDFs) are drilled into hydrate reservoirs, leading to the hydrate in-situ decomposition and severe sand production. In this work, an inexpensive and facilely prepared biomimetic wellbore stabilizer with strong adsorption of multiple hydrogen bonds was prepared by fusing catechol-rich tannic acid (TA) and polyvinyl alcohol (PVA) with polyol hydroxyl adsorption function, referred to as TA-PVA complex (TA-PVA). TA-PVA was added to WBDFs to strengthen the NGH reservoir wellbore for ensuring the safety of drilling process in a wide temperature range (2-60℃). The microscopic characterization of TA-PVA and its cohesion mechanism with argillaceous siltstone was investigated by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The mechanical properties of skeleton of the artificial hydrate cores were evaluated by compressive strength test, with maximum compressive strength reaching 0.45 MPa. And the adhesion force of TA-PVA to the probe modified by silica microsphere (PSM) was further studied by AFM. Meanwhile, the adhesion forces between TA-PVA and cyclopentane hydrate particles were measured at 1.5℃. Adhesion test results demonstrate that TA-PVA can bond clay particles, quartz sand and hydrate particles together. In detail, the adhesion force between TA-PVA and PSM reaches more than 164.46 mN/m, the adhesion force between TA-PVA droplet and cyclopentane hydrate particle reaches 43.19 mN/m. The differential scanning calorimetry (DSC)curves demonstrate that TA-PVA releases no heat between 0 and 60 °C, indicating that TA-PVA has no impact on the decomposition of NGH, showing the potential to maintain the integrity of NGH reservoir.

Effect of Surfactants with Different Hydrophilic–Lipophilic Balance on the Cohesive Force between Cyclopentane Hydrate Particles

Effective control of the cohesive force between hydrate particles is the key to prevent their aggregation, which then causes pipeline blockage. The hydrophilic–lipophilic balance (HLB) value of surfactants was proposed as an important parameter for the evaluation and design of hydrate anti-agglomerants. A microscopic manipulation method was used to measure the cohesive forces between cyclopentane hydrate particles in the presence of Tween and Span series surfactants with different HLB values; moreover, the measured cohesive force was compared with the results of calculations based on the liquid bridge force model. Combined with the surface morphology and wettability of the hydrate particles, we analyzed the mechanism by which surfactants with different HLB values influence the cohesion between hydrate particles. The results show that for both Tween (hydrophilic, HLB > 10) and Span (hydrophobic, HLB < 10) surfactants, the cohesive force between cyclopentane hydrate particles decreased with decreasing HLB. The experimental results were in good agreement with the results of calculations based on the liquid bridge force model. The cohesive force between hydrate particles increased with increasing concentration of Tween surfactants, while in the case of the Span series, the cohesive force decreased with increasing surfactant concentration. In the formation process of cyclopentane hydrate particles, the aggregation of low-HLB surfactant molecules at the oil–water or gas–water interface increases the surface roughness and hydrophobicity of the hydrate particles and inhibits the formation of liquid bridges between particles, thus reducing the cohesion between particles. Therefore, the hydrate aggregation and the associated blockage risks can be reduced.

Study on the Adhesion Force between Wax Crystal Particles and Hydrate Particles.

In this work, to solve the problem of pipeline blockage caused by the accumulation of hydrate particles and wax particles and to explore the interaction characteristics of adhesive force between gas hydrate particles and wax particles as well as droplets, a high-pressure triaxial mobile device was used to measure the adhesion strength between cyclopentane hydrate particles and different commonly seen phases in the pipeline, including cyclopentane hydrate particles themselves, liquid droplets, and wax crystal particles. These experiments were conducted at different temperatures. The results showed that the adhesion between hydrate and wax particles was decreased with the increase in temperature; this is because the wax is amorphous, the heat absorbed when the temperature rises only increases its average kinetic energy, and the stronger the kinetic energy, the lower its viscosity, resulting in reduced adhesion between particles. Meanwhile, this adhesion was also affected by the concentration of wax. As the wax concentration increased from 1 to 5.32 wt % and then to 8.14 wt %, the adhesion between hydrate and wax particles was first decreased and then increased. This was because when the wax crystal concentration was below 5 wt %, a higher wax molecule concentration meant a more hydrophobic surface, which restricted the formation of a capillary liquid bridge between particles and thus reduced the interforce between wax crystal particles and hydrate particles. When the wax crystal concentration was between 5 and 8 wt %, the change of hydrophobicity was no longer the dominating factor, the increase in wax concentration blocked the hydrate molecular diffusion path, which caused a higher hydrate viscosity, therefore leading to a decreased hydrate molecular diffusion rate and a reduced conversion rate of the liquid bridge in hydrates, the lower conversion rate could subsequently lead to the increasing size of micropores in the hydrate shell, and adhesion between particles was increased.

Experimental investigation on hydrate anti-agglomerant for oil-free systems in the production pipe of marine natural gas hydrates

During the production of marine natural gas hydrates, as gas hydrates are easily formed, they tend to agglomerate, deposit on the pipe walls, and eventually block the pipe. In this study, high-pressure autoclave and micromechanical force apparatus were used to investigate the effects of anti-agglomerants and kinetic inhibitors on the hydrate agglomeration in the oil-free gas–water system, and the anti-agglomeration mechanism was analyzed. The results indicate that when the hydrate conversion rate reached about 27%, a complete blockage occurred. In the oil-free system, conventional anti-agglomerants did not exhibit any anti-agglomeration performance; while kinetic inhibitors slowed down the hydrate formation, but could not inhibit their agglomeration. An amphiphilic amide compound, namely DCA, effectively prevented hydrate agglomeration and blockage under the simulated hydrate production conditions of 8-h stirring and subsequent 8-h shut-in. From the perspective of interparticle interaction, 1.0 wt% DCA reduced the cohesion force between cyclopentane hydrate particles by 62% and 70% in liquid cyclopentane and air, respectively. These effects were attributed to the adsorption of DCA on the surface of hydrate particles, which converted the surface characteristic from hydrophilic to hydrophobic; thus, no liquid bridge could be formed between particles. Moreover, DCA formed an isolating layer and offered steric hindrance, thus preventing the adhesion and agglomeration of hydrates.

Effects of sorbitan monooleate on the interactions between cyclopentane hydrate particles and water droplets

ABSTRACTThe effects of a typical anti-agglomerant, sorbitan monooleate (Span80), on the interactions between cyclopentane (CyC5) hydrate particles and water droplets were investigated using a micromechanical force (MMF) apparatus. The concentration of Span80 in CyC5 was ranged from 0.01 wt% to 1 wt%, and the experimental temperature was set at 1.5°C and 7°C, respectively. The results indicate that the absorption of Span80 on the droplet surface can render the interfaces more stable, preventing hydrate agglomeration. When the preload/contact force exceeds the strength of the interface (< ∼ 10 µN), the droplet ruptures, and the subcooling influences the interaction behavior significantly. At the lower temperature (1.5°C), the water droplet can spontaneously spread over the whole hydrate particle due to the significant reduction in water–CyC5 interfacial tension, and the water converts into hydrate rapidly. In this case, Span80 actually accelerates the agglomeration process and grants much shorter time to allow the external force to separate the water droplet and hydrate particle. At the higher temperature (7°C), the capillary bridge dominates the interaction behavior. The addition of Span80 reduced the capillary force through reducing the water–CyC5 interfacial tension. The measurements and observations in the present work can provide new insights into the mechanism of Span80 on inhibiting hydrate agglomeration.

Experimental Investigation on the Interaction Forces between Clathrate Hydrate Particles in the Presence of a Water Bridge

The agglomeration of hydrate particles is one of the main causes of hydrate accumulation or bedding in oil and gas pipelines. The unconverted water droplets in the system play a crucial role in hydrate particle agglomeration. In this study, a novel technique was developed to directly measure the interaction forces between cyclopentane hydrate particles with a water bridge between them using a micromechanical force apparatus. On the basis of the developed method, the interaction forces at different temperatures and water bridge volumes and the effects of mineral oil were experimentally studied. At a low subcooling level of 1.7 °C, the contact areas and adhesion forces between the hydrate particles and water droplets increased with the increase in the water droplet volume. For the case of a higher subcooling level of 6.2 °C, rapid hydrate formation between the bridging water droplets prevented the hydrate particles from being effectively wetted, resulting in a small contact area. There was no clear relation...

Micromechanical Interactions between Clathrate Hydrate Particles and Water Droplets: Experiment and Modeling

The micromechanical interactions between hydrate particles and unconverted water droplets play an important role in determining hydrate agglomeration, which is a key cause of hydrate blockages. In this study, the interaction behaviors between cyclopentane hydrate particles and water droplets in different conditions were directly investigated using a micromechanical force apparatus. For a smaller extent of subcooling, no hydrate was visibly converted from the water droplet during the measurement. A modified theoretical model was proposed to predict the corresponding interaction behavior. A parabolic approximation was found to be adequate for describing the liquid bridge shape. The insignificant change in the interfacial area between the liquid and the hydrate as the separation distance varied suggests the presence of a strong wetting hysteresis between liquid bridges and hydrate particles. The capillary force model can predict the interaction force with satisfactory accuracy. At a higher level of subcoolin...

Micromechanical cohesion force between gas hydrate particles measured under high pressure and low temperature conditions.

To prevent hydrate plugging conditions in the transportation of oil/gas in multiphase flowlines, one of the key processes to control is the agglomeration/deposition of hydrate particles, which are determined by the cohesive/adhesive forces. Previous studies reporting measurements of the cohesive/adhesive force between hydrate particles used cyclopentane hydrate particles in a low-pressure micromechanical force apparatus. In this study, we report the cohesive forces of particles measured in a new high-pressure micromechanical force (MMF) apparatus for ice particles, mixed (methane/ethane, 74.7:25.3) hydrate particles (Structure II), and carbon dioxide hydrate particles (Structure I). The cohesive forces are measured as a function of the contact time, contact force, temperature, and pressure, and determined from pull-off measurements. For the measurements performed of the gas hydrate particles in the gas phase, the determined cohesive force is about 30-35 mN/m, about 8 times higher than the cohesive force of CyC5 hydrates in the liquid CyC5, which is about 4.3 mN/m. We show from our results that the hydrate structure (sI with CO2 hydrates and sII with CH4/C2H6 hydrates) has no influence on the cohesive force. These results are important in the deposition of a gas-dominated system, where the hydrate particles formed in the liquid phase can then stick to the hydrate deposited in the wall exposed to the gas phase.

Effect of Kinetic Hydrate Inhibitor Polyvinylcaprolactam on Cyclopentane Hydrate Cohesion Forces and Growth

The effect of Polyvinylcaprolactam (PVCap), a commonly used kinetic hydrate inhibitor (KHI), on the cohesion force between cyclopentane hydrate particles was measured using a micromechanical force apparatus. The presence of PVCap in the aqueous bulk phase reduced the average hydrate cohesive force by 54% (from 1.49 to 0.69 mN/m). However, the cohesion forces did not vary significantly as a function of either the PVCap concentration (0.005–0.5 wt %) or the temperature (from 1.1 to 7.2 °C). When a layer of PVCap solution was applied to the surface of a pure cyclopentane hydrate particle in a bulk liquid cyclopentane phase, the interparticle cohesive force was reduced by 45% (from 4.3 to 2.4 mN/m). Hydrate growth on droplets of PVCap solutions was also studied by contacting a water droplet with a cyclopentane hydrate particle in a bulk cyclopentane phase. In cases where PVCap was absent, complete conversion of the water droplet to hydrate occurred within 30 s. However, when a water droplet of PVCap solution was brought into contact with a hydrate particle, hydrate film growth was significantly slowed, requiring over 2 h for complete conversion.

Measurements of Cohesion Hysteresis between Cyclopentane Hydrates in Liquid Cyclopentane

We measured cohesion hysteresis between cyclopentane hydrate particles in liquid cyclopentane in the temperature range from −8 to 6 °C. Cohesion hysteresis was small within scatter, and no clear temperature dependence was observed in the range studied. Too great of applied loads resulted in damage of the cyclopentane hydrate shells, causing the unconverted water core to leak out of the shell. The leaked out water then converted to irregularly shaped cyclopentane hydrate asperities on the shell after contacting the surrounding liquid cyclopentane. Cohesion hysteresis between the cyclopentane hydrate asperities was also measured and found to be similar to those between particles. The implication of these findings to the friction forces is discussed.

Influence of Model Oil with Surfactants and Amphiphilic Polymers on Cyclopentane Hydrate Adhesion Forces

Adhesion forces between cyclopentane hydrate particles were measured at atmospheric pressure and 3.2 °C using an improved micromechanical force apparatus. Because of the complexity of crude oil systems, a series of model oils was prepared by adding surface-active components to 200 cP mineral oil as analogues to crude oil systems. The addition of 1 wt % sorbitan monooleate (Span80, a commercial anti-agglomerant), 1 wt % polypropylene glycol (an amphiphilic polymer), and 0.6 wt % commercial naphthenic acid mixture, separately, to a mineral oil and cyclopentane continuous phase, reduced the average interparticle hydrate adhesion force by 37, 65, and 80%, respectively, compared to pure mineral oil and cyclopentane. The 95% confidence bounds of the Span80 and mineral oil data points overlap; therefore, we cannot conclude that Span80 was effective at reducing the adhesion force between hydrate particles. These results indicate that model amphiphilic polymers and commercial naphthenic acid mixtures may be surface-active on the hydrate particle, drastically reducing the agglomeration tendency between hydrate particles; naphthenic acids are found to be the most effective at lowering the adhesive force between particles. The structure of the additive plays a role in determining the extent of surface activity and effectiveness. Compounds with small hydrophilic groups can more efficiently adsorb to the hydrate surface, while additives that induce morphological changes to the hydrate surface may cause non-uniform growth and are more effective in preventing hydrate agglomeration.