Study On In-situ Detonation Characteristics Of Shale Gas In Reservoir Microchannels

Shale gas in-situ combustion and explosion mining technology enables shale gas combustion to reach deflagration or detonation state by igniting shale gas in the reservoir microcracks,generating high temperature and high pressure gas shock waves,thus cracking the shale reservoir,building more self-supporting threedimensional fracture networks,so as to achieve the purpose of shale gas production increase.Based on the microchannel combustion theory,this thesis establishes the physical model and mathematical model of shale gas and air premixed gas combustion and explosion in the reservoir microchannel,uses the ANSYS Fluent simulation software to numerically simulate the combustion and explosion process of shale gas in the shale reservoir microchannel,and analyzes the flame propagation law and pressure wave propagation law of shale gas combustion in the reservoir microchannel,The relationship between flame propagation and pressure waves in microchannels was identified and compared with experimental results for verification.Firstly,the influencing factors of combustion and explosion characteristics of shale gas in reservoir microchannels are studied.Using the ANSYS Fluent simulation software,by changing the initial pressure,initial temperature and opening of the reservoir microchannel,the flame propagation law of shale gas during combustion and explosion in the shale reservoir microchannel and the pressure distribution law in the microchannel were simulated,and the influence of the change of initial conditions on the combustion and explosion flame and pressure wave propagation law was analyzed.In addition,considering that the actual reservoir microchannel wall is a heat dissipation wall,the effects of the heat dissipation wall and the adiabatic wall on the flame and pressure wave propagation are simulated and compared.The results show that the heat dissipation wall only affects the total combustion time of shale gas in the reservoir microchannel,and its flame propagation law and pressure wave propagation law have little influence.The change of initial pressure will not affect the detonation pressure of shale gas in the shale reservoir microchannel,but the increase of initial temperature will reduce the detonation pressure in the shale gas reservoir microchannel.The change of reservoir microchannel opening will affect the pressure required for shale gas to reach detonation in the shale reservoir microchannel.Then,the combustion and explosion characteristics of shale gas in the complex micro channel of reservoir are studied.The branch microchannel model and the cross scale microchannel model of the reservoir are established,and the flame and pressure wave propagation laws in the branch microchannel and the cross scale microchannel are numerically simulated.The results show that the branch microchannel of shale reservoir can prolong the combustion time of shale gas in the shale reservoir microchannel and increase the pressure of shale gas during detonation;The angle between the branch channel and the main channel will affect the combustion time of shale gas in the branch channel of shale reservoir,and the flame propagation law will also change;The change of branch channel opening affects the deflagration time and peak pressure of shale gas in the branch channel of shale reservoir;The combustion and explosion time of shale gas in the cross scale micro channel of shale reservoir is longer than that of shale gas in the simple micro channel of shale reservoir.When the flame surface reaches the point where the opening changes,combustion is in different states,and the detonation pressure changes during detonation.Finally,the combustion and explosion process of shale gas in microchannels was experimentally studied using the shale gas ultra-high pressure combustion and explosion experimental system.The results indicate that an increase in initial pressure can promote the flame to enter the microchannel,and the flame enters the microchannel.The combustion state is in the detonation stage,indicating that the flame propagation speed is insufficient to enter the microchannel and will be blown out by high-temperature and high-pressure gas.The peak combustion pressure and temperature at the flame surface in the microchannel are significantly lower than those in the conventional channel.The experimental results are basically consistent with the numerical simulation results.