Numerical Simulation Of Well Pattern Optimization For Hot Dry Rock Geothermal Resources Exploitation

Global fossil fuels such as petroleum and coal are reducing day by day,bringing environmental problems which are more and more serious.Fortunately,we still have geothermal energy,which is clean,non-polluting and renewable.According to its characteristics,geothermal energy can be divided into hydro-thermal type and dry-hot-rock type(HDR).The hydro-thermal now is widely used for its low temperature and low development depth,but not the HDR.At present,the method of HDR exploitation is the Enhanced Geothermal System(EGS).The production parameters(such as injection flow rate and temperature,mining pressure,etc.)are the key engineering problems of the actual EGS construction,as well as the design optimization of injection-well distribution(well number,well type,well spacing and so on).Combined with the geological background of HDR,especially the Tengchong Rehai Geothermal Field,this paper studies the production parameters and the injection-well distribution,which will affect the heat extraction performance of the EGS.The numerical simulation experiment is carried out by using the orthogonal design method.The influence of the wells spacing,the temperature and the flow rate of the injected fluid and the permeability of the reservoir on the heart extraction performance of EGS is analyzed.The well spacing plays the most important role in the heat extraction performance of the EGS.The injected water's temperature plays a second important role.When the well spacing is small,the higher the injection temperature,the longer the running time of the system;when the well spacing is large enough,the injection temperature has little influence on the running time.The injection temperature should be determined according to the spacing of the wells.When the spacing of wells is small,the permeability of artificial fractured reservoirs can be lower;when the spacing of wells is large,the permeability of artificial reservoirs also needs to be higher.When the well spacing increases to a certain range,the change of permeability has little influence on the extracted water.The key factors to determine permeability are well spacing and economic feasibility.In the vertical-well EGS,the number of producing wells has an influence on the uniformity of water seepage--the non-uniformity of seepage will lead to the failure of the reservoir heat to be fully exploited,and the thermal exploitation temperature will decrease rapidly;the number of injecting wells affects the water's seepage area and flow--the system with smaller seepage area and flow will be the first to reduce the heating temperature after running a period of time.In the horizontal-well EGS,the hot water will not change after increase the number of producing wells,but will increase the water seepage area,so as to increase the recoverable heat and make the system thermal recovery temperature decreasing slowly;the increase of the injection wells leads to the decrease of the producing well's seepage flow and the loss of the regional recoverable heat,and so does the thermal mining temperature.