Experimental Study On Hydrate Decomposition In Water-based Sand-bearing Flow System

In the solid-state fluidized exploitation of marine non-diagenetic gas hydrate,the hydrate slurry after mechanical crushing will carry micron-sized sand.In the process of solid-state fluidized mining,the research on the decomposition law of hydrates in micron-sized sand slurry is the key research basis for obtaining high-efficiency gas production rate and gas production.In this paper,a series of experiments are carried out through the hydrate high-pressure loop,focusing on the study of the non-equilibrium decomposition law of hydrate in the sand-bearing brine system;in order to study its non-equilibrium decomposition process,the hydrate slurry of the sand-bearing brine system is configured.System hydrate formation law.First,in this study,hydrate formation and flow experiments in a sandy brine system were carried out.Based on the analysis method of the induction period of the hydrate flow loop,the evolution law of the induction period of the hydrate formation in the system with the initial pressure,water bath temperature,flow rate and sand content of the experimental conditions was explored.Based on the macroscopic temperature in the hydrate formation process,The pressure data was used to calculate the hydrate formation volume fraction and the average gas consumption,and the influence of the initial pressure,water bath temperature,flow rate and sand content on the hydrate formation kinetics in the experimental conditions was explored.Based on the online particle size monitored during the experiment The microscopic observation data of the instrument and video recorder（FBRM and PVM）were used to analyze the change rule of the microscopic particle size in the system during the hydrate formation process,and to analyze the microscopic evolution process of hydrate nucleation,growth and aggregation.Secondly,based on the gas release data calculated by the system pressure and temperature during the decomposition of sand-brine hydrate slurry,this study proposes that the non-equilibrium process of hydrate slurry decomposition of sand-brine system can be divided into three stages,and explores The effects of initial pressure,flow rate and sand content on the hydrate decomposition characteristics of the system were investigated.Based on the macroscopic decomposition process of hydrate shedding,fragmentation and coalescence from the sedimentary layer observed in the visible transparent window,coupled with the pressure drop change data in the non-equilibrium dynamic decomposition process,combined with the Hangen-Poiseuille law to inversely calculate the system The viscosity of the hydrate in the process of decomposition,and the influence of the key parameters of the experiment on the apparent viscosity of the decomposition process was found out.Finally,on the basis of the above experimental qualitative analysis,considering the influence of mass transfer and heat transfer in the process of hydrate decomposition in the flowing system of sand-bearing brine,on the basis of the Kim-Bishinoi kinetic model improved by the research group,the coupling effect of sand and salt is introduced.The non-equilibrium mass transfer and heat transfer coefficientαis used to establish a kinetic model for the decomposition of hydrate slurry in a sandy brine flow system.After verifying the regression with the experimental data,the values of the equivalent rate constant K_s0 of hydrate decomposition,the activation energy of hydrate decomposition and the coefficientγin the model were determined,and the influence of different initial pressure,flow rate and sand content on the key parameters of the model was discussed.The absolute deviation between the experimental results and the model calculated values is within the range of 24.56%,which provides a theoretical support for quantitatively predicting the non-equilibrium decomposition rate in the solid-state fluidization process.