1 Introduction
2 Blocking process of hydrates in oil and gas pipelines
2.1 Mechanism of hydrate aggregation
2.2 Mechanism of hydrate deposit
Tab.1 Three major mechanisms of hydrate deposition |
Deposition mechanism | Implantation deposition | Tube wall film growth | Tube wall adhesion |
---|---|---|---|
Macro characteristics | A process in which numerous hydrate particles settled to the bottom or top of the pipe under the action of gravity to form a fixed bed of hydrates | After the medium in the pipe contacts the pipe wall, the hydrates are formed on the pipe wall and grew into a film | After the hydrate is generated inside the flow field and contacts with the pipe wall, hydrate particles stay on the pipe wall through the adhesion force with the pipe wall |
Main reasons for formation | High concentration of hydrate particles, large particle size, and low fluid flow rate | There is a temperature gradient between the fluid in the pipe and the pipe wall, which causes the medium to diffuse from the center of the pipe to the pipe wall | Capillary liquid bridge force and van der Waals force |
2.2.1 Hydrate bedding
2.2.2 Wall film growth of hydrate
2.2.3 Wall adhesion of hydrate
3 Mechanism of hydrates blockage in rich-liquid systems
3.1 Mechanisms of hydrate blockage in oil-based systems
3.2 Mechanisms of hydrate blockage in water-based systems
3.3 Clogging mechanism in PD system
4 Factors affecting the blockage under the liquid-rich system in the pipeline
Tab.2 Summary of the investigation of the loop experimental of hydrate |
Ref. | Time | Experimental device or method | Hydrate guest molecule type | Main research content | Research result |
---|---|---|---|---|---|
[63] | 1995 | High-pressure wheel loop | Methane, ethane, propane hydrate | Inhibition performance of chemical additives on gas hydrate | Most kinetic inhibitors can increase the degree of supercooling required for the formation of hydrates, thereby inhibiting the formation of hydrates |
[64] | 1999 | NTNU (Norwegian University of Science and Technology) loop experiment | Methane or a mixture of methane, ethane, and propane | Flow characteristics of hydrate slurry under different hydrate concentrations | The apparent viscosity of the hydrate slurry increased with the increase of the hydrate concentration; in the turbulent state, the frictional pressure drop of the hydrate slurry was only determined by the nature of the water-carrying phase |
[33] | 2002 | Archimede Loop | Methane hydrate | Influence of dispersant and kinetic inhibitor (PVP) on the formation and fluidity of methane hydrate slurry | The concentration of additives had a significant impact on the flow characteristics of water-in-oil emulsions and hydrate slurries, and additives can effectively alleviate pipe blockage |
[65] | 2012 | ExxonMobil loop | He, N2, CO2, etc. | Main factors affecting the formation of hydrate slurry | Determination of the main parameters affected the transportation of hydrate slurry |
[25] | 2013 | ExxonMobil loop | CH4 | Mechanism of hydrate formation and blocking in the high water content system | The mechanism was the increase of interaction and agglomeration between particles, which ultimately led to the formation of hydrate beds and wall deposits |
[66] | 2014 | Small flow loop experiment | CH4+C3H8/CH4+i−C4H10 two-component gas hydrate | Effect of dual kinetic inhibition of PVP and L-Tyrosine on the induction period of binary component gas hydrate formation | The simultaneous addition of PVP and L-Tyrosine increased the induction time of gas hydrate formation several times, which was more effective than adding PVP alone as a kinetic inhibitor |
[58] | 2014 | High-pressure hydrate experimental circuit | Natural gas hydrate | Influence of subcooling, supersaturation, flow rate, water content, and polymerization inhibitor concentration on the induction period of natural gas hydrate formation | Induction time was inversely proportional to the degree of subcooling; as flow rate and supersaturation increase, the induction time presented a V-shaped curve or gradually increased; the induction time decreased first and then increased with the increase of water content |
[67] | 2014 | IFP-Lyre (Institut Francais Du Petrole) loop experiment | CH4 | Influence of factors such as moisture content, liquid phase flow rate, and polymerization inhibitors on the flow characteristics of hydrate slurry in the case of high water content | The higher the water content, the more difficult it was to crystallize the hydrate; addition of AA-LDHI (Anti-Agglomerates and Low Dosage Hydrate Inhibitor) could effectively maintain the fluidity of the pipeline |
[68] | 2014 | University of Tulsa loop | Natural gas hydrate | Mechanism of hydrate formation and blocking in the PD system | The growth of hydrate/sediment on the tube wall seemed to be the dominant phenomenon of hydrate growth in PD systems |
[69] | 2017 | CUPB (China University of Petroleum, Beijing) storage and transportation experimental loop | Natural gas hydrate | Mechanism of hydrate formation and blockage under different gas-liquid flow patterns | The blocking mechanism and pipe blocking tendency of hydrates were different under different flow patterns. (mentioned later) |