Research On Microscopic Occurrence State And Numerical Simulation Of Natural Gas Hydrate

Natural gas hydrate is an ice-like crystalline compound formed by water molecules trapping natural gas molecules(mainly methane)under high pressure and low temperature.As a new type of clean and efficient natural gas resource,it has the characteristics of wide distribution,large reserves and high mining difficulty.Its safe and controllable mining still faces many scientific and engineering problems.The microscopic occurrence state of natural gas hydrate,that is,the configuration relationship between hydrate crystals and intergranular pores in the sediment,affects the mechanical strength,decomposition rate of hydrate sediments and the seepage characteristics of fluids such as gas and water in the porous medium.Affect the calculation of natural gas hydrate reservoir geological reserves and optimization of development methods.In this paper,laser Raman spectroscopy and scanning electron microscopy are used to study the effect of sediment particle size on the occurrence of tetrahydrofuran hydrate and methane hydrate,and numerical simulation methods are used to study the effects of different occurrences of hydrate on the porosity and permeability of fluids in porous media.Rate and flow rate and other aspects of the flow characteristics.Through experimental research,it is found that when the particle size of tetrahydrofuran hydrate is 10μm,its occurrence state is cemented,and as the particle size increases to 100μm,its occurrence state changes to suspension type.For methane hydrate,the distribution law is the same in 500μm and 300μm quartz sand,mainly contact type growth.When the particle size is100μm,the hydrate occurrence state at the top of the quartz sand is contact type,and the center and bottom are mainly suspended type.In a particle size of 10μm,hydrates are mainly distributed in contact type at the top and middle of quartz sand,and hydrates are mainly distributed in cemented type at the bottom of quartz sand.Using numerical simulation methods to study the fluid flow characteristics in porous media under different hydrate occurrence states,Regarding porosity,as the hydrate saturation increases,the porosity of the porous media decreases under the three different occurrence states.The cemented type has the greatest impact on the porosity.The suspension type has a lower porosity than the contact type hydrate at low saturation.For permeability,in the process of increasing hydrate saturation from 0 to 0.2,the permeability of porous media in the three occurrence states of hydrates all decrease sharply,and then the rate of decline slows down.Porous media has the lowest permeability,and when S_h<0.6,the permeability of contact hydrates is greater than that of suspended hydrates,and when S_h>0.6,the permeability of suspended hydrates exceeds the permeability of contact hydrates.The study found that under the same conditions,the flow rate of the porous medium containing cemented hydrate is the smallest.When S_h<0.7,the flow rate of the porous medium containing contact hydrate is higher than that of the suspension type.When S_h>0.7,the flow rate of the suspension type exceeds that of the contact type.At the same time,it is found that under the same hydrate occurrence state,the influence of hydrate saturation on fluid flow is greater than that of pressure.