Study On Seepage Characteristics And Heat Recovery Efficiency Of Water-Gas Injection In Hot Dry Rock

Hot dry rock is high-temperature rock mass with no or little water,which contains huge energy and is a clean renewable energy.Heat recovery of hot dry rock is a process to inject fluid into the reservoir and exchange heat with the rock mass,and then bring out the heat energy for utilization.Therefore,the permeability of injected fluid in high temperature rock mass will greatly affect the heat recovery efficiency of the reservoir.In this paper,experimental and numerical simulation methods were used to carry out the heat recovery experiments of water injection,CO₂ injection and alternate injection of water and gas in high temperature rock mass,and establish the numerical model of water and gas injection.This paper has studied the seepage characteristics and heat recovery efficiency of water and gas in the high temperature rock mass under different conditions and we have achieved the following results:?1?The experiment that injecting CO₂ into high temperature rock mass was carried out to analyze the influence of confining pressures,reservoir temperatures and injection pressures to the seepage characteristics and heat recovery efficiency during the heat recovery process of CO₂ injection.Then,the experiment was carried out to analyze the influence of proppant to the permeability and heat recovery efficiency of rocks after adding proppant into the rock.The results show that the confining pressure and reservoir temperature have a negative effect on the permeability and the injection pressure has a positive effect on the permeability.The proppant improves the rock permeability and reduces the influences of the negative effects which confining pressure and reservoir temperature have to the permeability,and improves the heat recovery efficiency.?2?The experiment that injecting water into high temperature rock mass was carried out to analyze the influence of confining pressures and reservoir temperatures to the seepage characteristics and heat recovery efficiency during the heat recovery process of water injection.Then,the experiment was carried out to analyze the influence of proppant to the permeability and heat recovery efficiency of rocks after adding proppant into the rock.The results show that the confining pressure and reservoir temperature have a negative effect on the permeability.The proppant improves the rock permeability and reduces the influences of the negative effects which confining pressure and reservoir temperature have to the permeability,and improves the heat recovery efficiency.?3?The experiments of water injection and gas injection in the high temperature rock mass under the same conditions were carried out,and the efficiency of water injection and gas injection under the same experimental conditions were compared.The results show that:under the same confining pressure,the water injection heat recovery efficiency is higher;at the same reservoir temperature,the higher the temperature,the higher the CO₂ injection heat recovery efficiency.?4?The experiment that alternately injecting water and CO₂ into high temperature rock mass was carried out to analyze the influence of number of circular injection to the seepage characteristics and heat recovery efficiency during the heat recovery process of water and gas injection.The results show that the rock heat recovery efficiency will decrease as the number of alternate injections increases,and even a negative net heat extraction rate will occur.After the proppant is added,the proppant can obviously improve the heat recovery efficiency,and at the same time,it can increase the number of cycles while ensuring the heat recovery efficiency.?5?A numerical model of heat recovery in high-temperature rocks has been established,and the laws of influence of reservoir temperature and confining pressure changes on heat recovery efficiency have been simulated and analyzed.The numerical simulation results have been compared with the experimental results,and the specific measures to improve the efficiency of rock heat recovery have been given.The paper includes 80 figures,15 tables and 81 references.