Study On Deformation And Seepage Of Reservoir During Re-injection Of Tail Water In Sandstone Geothermal Engineering

In recent years,in the process of sandstone-type geothermal resources mining,the problem of difficulty in recharging geothermal tail water and low recharging rate has been faced.This has led to the direct discharge of most of the geothermal tail water.Causes heat storage pressure drop,heat loss,and geothermal tail water pollutes surface water,farmland,etc.Studying the stability and seepage characteristics of thermal reservoirs and the influence of geothermal tail water on thermal reservoirs is of great significance to the sustainable development of sandstone-type geothermal.Based on the background of sandstone-type geothermal tail water recharge,this thesis conducted some research on the mechanical seepage characteristics of sandstone in the Key Laboratory of In-situ Modified Mining of the Ministry of Education of Taiyuan University of Technology.The deformation and failure laws of sandstone under different fluid pore pressures,and the effects of suspended solids and reverberation on the seepage characteristics of sandstone and sandstone fractures are analyzed.And came to the following conclusions:(1)Pore pressure has a weakening effect on the peak compressive strength,peak axial strain and elastic modulus of sandstone.This weakening effect is greatly affected by the confining pressure.The greater the confining pressure,the smaller the weakening ability.In terms of peak strength and elastic modulus,the weakening degree of pore water pressure is stronger than that of pore gas pressure.Under the conditions of 5 MPa pore gas pressure and pore water pressure,sandstone cohesion is reduced by 35.04% and 48.34%,respectively,and the internal friction angle is slightly increased.(2)With the increase of temperature and hydrostatic pressure,the permeability of sandstone gradually decreases.Temperature and permeability are in accordance with the relationship of the one-dimensional quadratic equation.As the osmotic pressure increases,the permeability first decreases and then increases.The turning point is the osmotic pressure of 15 MPa.(3)The suspended solids have an inhibitory effect on the flow velocity and permeability of sandstone.The blockage rate is found to be basically below 50%.After the backwashing test,the recovery rate is higher.Under most test conditions,the recovery rate is above 50%,that is,for sandstone thermal reservoirs,backwashing is an effective measure to increase recharge rate.The increase of the recharge pressure and the temperature of the recharge fluid can improve the recharge ability.As the buried depth of the sandstone reservoir increases,the difficulty of recharge increases.(4)The permeability of sandstone fissures is much greater than that of sandstone pores,and the fissures in sandstone become the main channels for fluids.The increase in temperature and hydrostatic pressure have an inhibitory effect on the opening and permeability of sandstone fractures,and the osmotic pressure has little effect on the opening and permeability of the fractures.The suspended solids block the sandstone fissures to a greater degree,and the recovery rate after rebound is lower.(5)The permeability of suspended solids to sandstone fractures is much lower than that of intact sandstone,and the increase in permeability of suspended solids is also smaller than that of intact sandstone.Fissures can greatly promote the permeability of sandstone reservoirs,but suspended solids are more likely to cause blockages,and the recovery of the permeability is poor.