| With the increase in the demand for resources and space in our country,the exploitation and utilization of earth resources has gradually developed to a deeper level.In the deep energy development and engineering construction,the rock mass is in a complex geomechanical environment of high in-situ stress,high temperature and high osmotic pressure.The study of the mechanical and transport properties of rocks under the coupling of hydro-thermal-mechanics is significant for both the exploitation of geothermal energy and deep oil and gas reservoirs or the safety and stability of deep rock engineering.To focus on this problem,the yellow sandstone is used as the test material to carry out laboratory triaxial tests under different confining pressures,osmotic pressures and temperatures,combined with acoustic detection technology to conduct real-time monitoring of the entire process of loading.In addition,the particle flow numerical software is used to simulate the experiment.From the aspects of mechanical properties,failure properties and permeability properties,the effects and mechanisms of the interaction of stress,osmotic pressure and temperature are further explored.The research aims to provide a theoretical basis for deep energy mining and deep engineering construction.The main research contents and conclusions are as follows:(1)The basic physical and mechanical properties of yellow sandstone is test to provide a basis for subsequent research.Through XRD phase analysis,it is found that the yellow sandstone is mainly composed of two clay minerals,of which illite accounts for 72%,and the illite-montmorillonite mixed layer accounts for 28%.Through SEM scanning electron microscopy technology,it can be observed that the yellow sandstone has a uniform texture and is a sedimentary rock with a transitional support clastic structure.It also has obvious pore structure and has the basis for seepage experiments.(2)The yellow sandstone is subjected to laboratory triaxial tests under different confining pressures,osmotic pressure and temperatures.The rock ultrasonic tomography observation system and the multi-channel acoustic emission system are used to simultaneously record the wave velocity and acoustic emission characteristics during the loading process,which can invert the failure process.The changes of sandstone mechanical properties,damage and permeability properties under different coupling conditions are studied.The results show that the damage mode is dominated by shear failure;the wave speed of increases first and then decreases during the loading process.The increase of the confining pressure will increase the strength of the sample and decrease its permeability.Osmotic pressure and temperature have little influence on rock structure,so the influence on strength and permeability of rock is not significant,and influence degree is less than the difference of the sample itself.(3)The particle flow numerical simulation software was used to carry out the biaxial temperature seepage simulation.The coupling algorithm is improved: the particle temperature is detected to assign fluid parameters;a cracking coefficient is added to accelerate seepage after rupture;a monitoring algorithm for permeability is added.The moment tensor acoustic emission algorithm is used to record and classify the acoustic emission events.The simulation results is processed to obtain figures such as stress and porosity cloud diagram,acoustic emission source type distribution diagram.The results show that the strength increases with the increase of confining pressure,and decreases with the increase of osmotic pressure and temperature,while the poisson’s ratio is just the opposite.The sample shows macroscopic shear failure,and different conditions will affect crack numbers and the rupture direction.The permeability decreases with the increase of confining pressure,and increases with the increase of osmotic pressure.Temperature affects the permeability by affecting the direction of the fracture shear zone,but has almost no effect on the initial permeability.(4)The mechanism of hydro-thermal-mechanical coupling is analyzed.The effects of seepage water,temperature and pressure on sandstone are multi-directional,and can be divided into "mechanical coupling" and "parametric coupling" according to the way the coupling is realized.The internal structure of the rock changes under the action of stress,which affects the seepage;the seepage reacts on the rock and affects its internal stress distribution,which ultimately affects the stability of the rock mass.In addition,the temperature will also affect the fluid viscosity and pore deformation inside the rock,thereby affecting rock deformation and fluid seepage. |
