| Based on the deep geological conditions of Qiabuqia area in Gonghe basin,TOUGH2is used to establish a numerical model,which research the temporal and spatial distribution of the reservoir temperature field,the pressure field and the density field of fluid in the reservoir,and further simulate and study the influence of different factors on EGS performance.Finally,different models of well arrangements are established to contrast and analyze the production efficiency of EGS.The main conclusions are as follows:In the early stage of production,a low temperature area of 60?is rapidly formed near the injection well,and the density of fluid near the injection well reach 1003 kg/m~3,while the density of fluid far away from the injection well preserve around 906 kg/m~3.Because of the difference of density,a high pressure area of about 32.5 MPa will be formed near the injection well in the initial stage.With the operation of the EGS,the thermal energy of the reservoir near the injection well is gradually extracted.The range of the low temperature zone continue to expand,and the temperature near the injection well decrease until it approach 50?.The EGS can operate stably for 19 years,in the course of which the overall density of the fluid increase continuously.And the pressure near the injection well continues to rise,reaching 36 MPa by 30 years.In contrast,the pressure of reservoir near the production well barely rise by 1 MPa.Increasing the injection flow rate can obtain a larger heat extraction rate,at the same time,the reservoir flow impedance is increased and the reservoir life is reduced.The lower the temperature of injected fluid,the larger the cumulative heat extraction amount of the EGS,but the fluid temperature has no significant effect on the reservoir life.Under the condition of this paper,the optimal injection flow rate and injection temperature are 30 kg/s and 40?respectively.The smaller the fracture permeability of the reservoir,the greater the reservoir life and the flow impedance,but it has little effect on the heat extraction rate of the system.Subsequently,the larger the spacing between wells is,the longer the life of the reservoir is and the greater the flow impedance is.Under the optimum condition of production parameters,the deeper the mining depth of reservoir,the more power generation from the system generated.And the electricity produced from the 4,000m reservoir can generate 443 million degrees more than the 3,000 m reservoir.The profit is apparent,nevertheless,the cost of drilling and reservoir fracturing should be taken into account in the actual project.The thicker the reservoir is,the greater the cumulative heat extraction and the total power generation of the system will be.Also there is a linear relationship between them.When the reservoir thickness is 100 m,the overall heat recovery rate of the reservoir is the largest,reaching 68.09%.In addition,the larger the length-width ratio(consistent volume and thickness)of the mining reservoir,the greater the total generation capacity of EGS and the overall thermal recovery rate of the reservoir,but also the flow impedance of the fluid will increase.Under the optimum conditions of production parameters,the total power generation capacity of the triangular well arrangement reach 32.6 MW·a and the overall heat recovery rate is also the highest,reaching 70.55%.The geothermal energy can be fully exploited under the triangular well arrangement.Compared with the triangle well arrangement,the total power generation and overall heat recovery rate of the five-spot well arrangement are smaller,additionally,taking the drilling cost into consideration,it isn't suitable to adopt.Therefore,we should combine the economic cost to select the best well arrangement from the opposite well arrangement and triangular well arrangement in practical engineering. |
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