Assessment Of Geothermal Reservoirs And Enhanced Geothermal System Potential Research In Wujiatun District,Northern Yitong Basin

With the development of science and technology,mankind's demand for energy has been increasing year by year,and traditional fossil fuel-based energy structure has brought tremendous pressure on the environment.The greenhouse effect,air pollution and haze have become increasingly prominent.In order to solve the above problems,the search for a clean and renewable alternative energy source is the only way to go.Geothermal energy is gradually being valued by all countries in the world for its characteristics of wide distribution,huge reserves,clean and environmental protection.The amount of high-temperature geothermal resources within the range of 3¹0km in mainland China is 2.5×10⁵J?a total of 857 trillion tons of standard coal?.The use of deep high-temperature geothermal resources needs to be realized through Enhanced Geothermal Systems?EGS?.Reservoir stimulation and stable exploration of thermal energy are the two key issues of EGS.This paper study the problem about heat extraction of EGS based on the geothermal data of the Wanchang structural belt in the north of Yitong Basin.Yitong Basin is located on the northern section of the Tanlu fault zone and is a Cenozoic mantle type basin.The deep and large active faults in the basin constitute the thermal channels of the deep mantle heat source and the upper thermal reservoir;The distribution area of granite intrusions in the basement of the basin is large?super80%?.The high thermal conductivity of the acid rock mass and the radioactive elements contained therein could transports the deep heat to the upper reservoir effectively;The thickness of the sedimentary layer in the basin of the Cenozoic Basin ranges from 2000 to 6000 m,which is a good barrier to the loss of geothermal energy in the reservoir.These conditions make the geothermal flow values and geothermal gradients of the Yitong Basin higher than those of the global sedimentary basins.The basins are geothermal anomalies in mantle basins.In order to understand the thermal properties and basic physico-mechanical properties of basement reservoir granites and shallow metamorphic conglomerates,this paper carried out laboratory experiments on the outcrop samples of granite and shallow metamorphic conglomerate taken from the site.The granite density?2.659².679g/cm³?andshallowmetamorphicconglomeratedensity?2.758².792g/cm³?are relatively high,and the weathering degree of the rock is relatively low,indicating that the mechanical properties and other test results have certain properties for the understanding of deep reservoirs'properties.The mechanical strength of the shallow metamorphic conglomerate is higher than that of the granite;the porosity of the two rocks?2.02%for granite,less than 1%for shallow metamorphic conglomerate?and permeability(0.2243⁰.2972×10^-15m²)are all lower,but the frequency of fractures in granite is higher than the frequency of fracture in shallow metamorphic conglomerate;The thermal properties of the two types of rock are similar.Under the same geological conditions,granite has more natural fractures and its mechanical strength is lower than that of shallow metamorphic conglomerates.Granite reservoirs are easier to fracturing and stimulation.Based on the above studies,combined with the drilling data of the Wuchangtun area in the northern Wanchuan tectonic belt of the Yitong Basin,a single fracture and equivalent homogeneous hydrothermal coupled numerical model for the granite and fractured granite reservoirs was established using the TOUGH2-EOS1 software.The hydrothermal output capacity of 20a reservoir models was simulated and analyzed.Based on the single fracture model of granite,the sensitivity of the four parameters of well spacing,water injection temperature,injection rate and fracture permeability was analyzed.The analysis results show that the fracture permeability and water injection temperature have a great influence on the flow impedance of the system,and the well spacing and injection rate have little effect on the flow impedance of the system,but the injection rate has a greater impact on the pore pressure at the injection well;Crack permeability,well spacing and injection rate have a great influence on the production well water temperature.Only the water injection temperature has little effect on the system temperature field.The simulation results of the two models show that:with the single fracture EGS model of the reservoir,when the production flow rate of the system is 10 kg/s,the flow impedance reaches 1.203 MPa/?kg/s?after the system operates for 20 years,and the average heat production power between 20a is 4209.6.kJ/s;with the fragmented granite equivalent homogeneous model with more natural fractures,when the reservoir permeability is 2×10^-13 m²,water of about 25°C is circulated at an injection rate of 40kg/s.The system is operated after 20 years.The flow impedance is 0.094MPa/?kg/s?,the production temperature is reduced by 9.75%,and the average heat production power of the 20a system is 21390.84kJ/s,which is more economical.According to the numerical simulation results of the hydrothermal output capacity of different reservoirs and different reconstruction methods,It is found that the area has high potential for EGS development according to the numerical simulation results of the hydrothermal output capacity of different reservoirs and different reconstruction methods.