Resources Evaluation Of Geothermal Field In Reshuizhen Of Chifeng City ,inner Mongolia

Geothermal energy is one of the new energy.It is of great significance for improving energy structure.With oil,coal and natural gas,geothermal resource are cheap,clean and renewable.They can be used directly. China's total geothermal resources are 7.9% around the world, ranking second, fewer than the United States'.High temperature geothermal resources are used for power generation, whereas low-medium geothermal resources mainly for non-electrical utilization. For the correct evaluation of the geothermal fields provide a scientific basis for geothermal resources. Meanwhile, development and utilization of geothermal resources in the development of local economy and improve the level of the living conditions of local people is very important practical significance.Through survering on geological structural of Reshuizhen of Chifeng, The Yinshan faulted structure belonging to one of the oldest tectonic activities with its activities has been extended to the era of the Yanshan orogenic activity, the geological structure of this enormous influence, Bias of Balihan fracture with its main activity period is broken end of the Yanshan orogeny. The fault in the northern part of Balihan is NE - SW direction, south into north and south. Balihan fracture in the area there is about 100m wide fracture zone, and development of a secondary tensile faults and fissures. Balihan occurrence of small earthquakes is still broken, indicating the still active. In addition to the area north-south fracture outside of Balihan fracture, there is also the north west - south east and north east–SW fracture series. Geothermal field is just in the junction of the above fracture structure of north-south direction, west north- east south direction, east north– west north direction, and east- west direction, and the main passageway of hot water in geothermal field consists of these fractures, which are made up of the heat source of local spring with granite formed together with magmatism of the Yanshan orogenic movement in Mesozoic Era and basalt formed together with orogenic movement in Paleocene. And the geothermal field in research faces high and precipitous mountainous area in the west and connects with flat hilly country in the east. The dividing line of the two landforms is Balihan fracture with south- north direction, in the west it is composed of massive rocks, such as crystalline schist, gneiss, and intrusive rock of Precambrian period; while the east sunk part is covered with volcanic rocks of the Jurassic Period and accumulative rocks of the Quaternary period, and in the under part they are Precambrian rocks.The origin of main water of geothermal fluid can be gained through the analysis of the composition of hydrogen and oxygen isotope. Hot spring water samples, water samples nearby geothermal field, and circumjacent earth's surface samples are collected respectively in the research, which are tested and analyzed for chemical composition and isotopic composition, combining the analysis of tritium concentration, you can know that the meteoric water permeating to the underground in high-altitude areas 10～20 km away from geothermal field in the west and north, and we think that this meteoric water has flown to and stayed in this geothermal field through more than eighty years. After the meteoric water permeated to the underground reaches deep part, which is heated to hot water mainly in the way of heat conduction. According to the chemical composition in hot water and data of isotope analysis, the hot-water temperatures in superficial part hot-water layer and deep part reservoir stratum are respectively 100～110℃and 140～150℃, so the hot water in local geothermal field belongs to intermediate and low temperature crevice water originated from meteoric water.In order to detect clearly the basement structure of geothermal field and the location of fault, we should conduct gravitational prospecting in this area. After correcting relevantly the measured gravity data, we get the gravity anomaly distribution in measured area, and the gravity anomaly in this area has the tendency of western high and it becomes lower to the east direction gradually. In the northwest of this researched area also appears partial unusual height. And this is identical to the Precambrian rocks in the west, subsidence in the east, and lithological characters distribution characteristics of Jurassic Period rocks. And at the same time, in order to master the thermo-tectonics and scope of geothermal field and select vantage point, we measure the earth temperature in this area with the depth of 1m and 50cm. After the amendments of the temperature measurement data, the temperature distribution map with the depth of 1m and 50cm has been drawed.The underground hot water flows from the lower part to the higher part, which can be known through ground temperature distribution map, and it leans to the southeast direction.From thermo-tectonics backgrounds, the thermal background of this area has characteristics of thick earth's crust, low terrestrial heat flow, and low temperature within the shell. Under this kind of ground temperature, convective phenomena in the shell are difficult to be seen. Through the analysis and research of volcanic activity in this area, we can know that it is nearly impossible to form large-scale magma pocket of heat source in the geothermal field or concrete to rock mass with high temperature. In this case, we only can imagine that the heat sources of this hot water in the geothermal field are granites of Jurassic Period and tortoise rocks of the Tertiary period. Therefore, the hot-water circulation of this geothermal field is inferred as follows: meteoric water permeating to the underground deep part from the west and north mountainous area of geothermal field, to the under part of geothermal field, and heat sources that consist of granite and basalt intrusive mass become high-temperature hot water in the way of heat conduction, and it rise to the superficial area through the fracture and fissuring of this area, combining with shallow ground water, in this way, the shallow hot-water reservoir stratum is formed. Through the above analysis and research, the thermal structural model of the local geothermal field is given.The terrestrial heat reserves are evaluated with the use of heat release method, volumetric method, and collectable hot water volume method. The given resource amount by different evaluation methods in mainly in the scope of 200～2000 KW. Among these evaluation methods, if the evaluation according to heat release amount method is roughest, then the resource amount with high credibility should be 190～900 KW that is evaluated with the use of volumetric method and collectable hot water volume method. In the evaluation of these resources, the existing reservoir stratum with the highest temperature of 150℃has been considered, therefore, it is nearly impossible to occur that the computative resources amount rise. According to the record of existing data, the actual hot water total gush amount of geothermal field (total extraction amount) is 1400～2100m3/day. If the collectable hot water amount is 1200L/min (1730m3/day) and 1500L/min (2160m3/day) according to reference, then the corresponding generated energy calculation results are 252～720 KW and 315～900 KW respectively.