Adhesion Effects And Agglomeration Mechanism Of Hydrate Particles In The Presence Of Low Dosage Hydrate Inhibitors

Hydrate formation would block pipelines in the process of oil and gas transportation, resulting in great harms. One of the reasons which lead to the hydrate blockage is the aggregation of hydrate particles due to the particle-particle adhesion forces. Some studies and experiments have been done on the adhesion effects of hydrate particles; however, it is still unclear. The study on hydrate prevention based on reliable mechanism is becoming more and more important. Low dosage hydrate inhibitors (LDHIs) is a newly developing method to resolve hydrate problem. Some types of LDHIs have been developed, but the working mechanism is under debated. This work aims to weaken the adhesion force of hydrate particles on the basis of understanding the particles aggregation mechanism, and study the mechanisms of LDHIs on preventing the hydrate agglomeration.Experimantal equipment on measureing the adhesion force of hydrate particles was setup, and the reliability of the experimental system was verified. The micro-manipulation and observation method for studying the aggregation effects of hydrates were determined.The adhesion forces of tetrahydrofuran (THF) hydrate particles in n-decane under different temperature, contact force and in the presence of some LDHIs were measured. The LDHIs used in the experiment include polyvinyl alcohol (PVA), non-ionic surfactants with different hydrophilic-lipophilic balance values (HLB value), poly(vinylpyrrolidone) (PVP) and inhibitor ISP501, and synthesized inhibitors HGs. Results show that temperature and contact force are the important factors which affect the adhesion forces. The measured adhesion forces increase with the increasing temperature and contact force. At the temperature in the range of -2.5~-3 oC and the contact force at 0.5μN, in the presence of PVA, Span20, Span80 , Span85 which have low HLB, the adhesion forces decrease with the increasing concentration of the additives. In the presence of Span surfactants with high HLB, PVP and ISP501, the adhesion forces increase with the increasing concentration of the additives. Six kinds of HGs inhibitors reduced the adhesion forces. Therefore, PVA, Span20, Span80 , Span85 and HGs show anti-agglomeranting effects on hydrate particles, and can be used as hydrate antiagglomerants (AAs); whereas, PVP and ISP501 show enhancing effects on hydrate particles aggregation.The micro-morphologies of THF hydrate particles in the presence of different LDHIs were observed, the initial affecting regulars of morphology on the adhesion force were explored. The influences of the LDHIs on the wettability of hydrate particles were analysed. The results show that PVA, Span20, Span80 and Span85 can induce surface roughness on the THF hydrate particles and weaken the hydrophilibity of the particles. The Span class surfactants with high HLB, PVP and ISP501 can make smooth hydropholic hydrate particles. Both the surface roughness and weakened hydrophility reduce the adhesion forces. According to the surface roughness and the surface wettability, the equation was established which associating the adhesion force with the surface properties of the hydrate particles.The different contacting interactions among liquid droplets and hydrate particles in n-decane were obsersed in the presence of PVA, Span20, Span80, Span85 and PVP. The results of liquids droplets observation show that Span20, Span80 and Span85 can form interfacial film by adsorbing onto the the surface of the liquid droplets. The films formed by Span80 and Span85 exhibit strength which can prevent the liquid droplets aggregating into large droplet. The observation of liquid droplet-hydrate contacting interaction show that PVA, Span20, Span80, Span85 can alter the liquid droplet/n-decane, liquid droplet/hydrate particle and hydrate particle/n-decane interfacial tensions on the liquid droplet/hydrate particle/n-decane three phase contacting point, which results in the enhancement of the particles hydrophobicity, thus weaked the wetting of the liquid droplets on the hydrate particles. The interfacial films of Span 80 and Span85 can prevent the liquid droplets wetting the hydrate particles, thus avoid the hydrate growing into the liquid droplets. The analysis of the interaction between hydrate particles show reveals that LDHIs can either perform on medium modification to reduce the medium/liquid interfacial tension, or perform on hydrate particle modification to alter the morphology and wettability of hydrate particles, and consequently, weaken the hydrates agglomeranting tendency.Finally, in the view of the interactions among liquid droplets and hydrate particles, the mechanism of LDHIs on hydrate antiagglomeration was analysed according to the hydrate development process: nucleation, growth and agglomeration. The expressing equation of hydrate particle adhesion force was established, which associates the factors including environment, surface properties and interacting methods of hydrate particles.