Development of Middle and Deep Geothermal Energy
1. Introduction
The project is located in the High-tech Campus of Xi’an Research Institute of China Coal Technology & Engineering Group, involving 4 heat exchange boreholes of 3500m in total. Borehole heat exchange (BHE) is a new technology that can realize the development and utilization of middle and deep layers of geothermal energy, with wide applicability and outstanding advantages. However, due to the influence by surrounding rock properties of geothermal reservoir, well type and structure and heat transfer properties of downhole heat exchanger, the heat transfer efficiency is low, and the heat extraction of single well is small.
2. Treatment Solution
Well type and structure of geothermal wells were optimized and slave directional wells were adopted to solve the problem of on-site field shortage. Test method of geothermal geological conditions in geothermal reservoirs was study to obtain accurate thermo physical parameters. A multi-field coupled geothermal heat transfer model was established to analyze the heat exchange properties in borehole. New thermal insulation inner pipe and high thermal conductivity cementing materials were developed to improve heat exchange efficiency and heat extraction from single well. A dynamic monitoring system of geothermal field in geothermal wells was established after optimizing structure and installation process of sensor optical cable. This provides a basis to reasonably formulate the operating plan of the system and to optimize design.
Test of Cementing Materials Numerical Model
3. Construction Situation
Construction is divided into three stages of organization: (1) drill 1 shaft well (test well) with a depth of 3500m, complete testing, testing and analysis, and complete a series of key technology research. (2) drill 1 directional well with a depth of 3500m, and combine with the first test well to meet the heating demand of the main building, test building and apartment building in the high-tech campus in winter. (3) after the engineering test and operation in the first two stages, drill 1~2 directional wells with a depth of 3500m, and complete all the works of study. Finally, the demonstration project of middle and deep geothermal heating energy in the High-tech Campus of CCTEG Xi’an Research Institute was successfully accomplished, which also formed key theory and technical system for the innovation and development of geothermal energy.
Drilling Platform Thermal Insulation Pipe
Test and Monitoring Platform Machine Room
4. Achieved Accomplishment
The first geothermal test well with a depth of 3518m has been completed, and the heat of a single well is 689kW. Geothermal heating has been realized in the office area of the High-tech Campus, and the heating effect is good after a trial operation in a heating season. At the same time, as a scientific and technological innovation project, the main works of study have been basically completed, and major breakthroughs have been made in many key technologies.
5. FAQ
Q1: Will the amount of underground heat energy decrease?
A: The time of heating is in the heating season, and other seasons are taken as the recovery period, so the heat will be replenished around the wells and will not decrease year by year.
Q2: Does this heat extraction method have effect on groundwater at all?
A: The whole well section is cemented with cement to isolate ground water, and completely realize zero emission and zero pollution to the groundwater resources.
Q3: Compared with other companies, what is your biggest advantage in the development and utilization of middle and deep layers of geothermal energy?
A: We independently developed new technologies and equipment such as high thermal conductivity cement-based composite cementing materials, new composite thermal insulation inner pipes, and distributed optical fiber ground temperature monitoring throughout the well, which achieved new breakthroughs in key technologies with obvious advantages, and we formed a complete set of technologies and equipment for the development and utilization of middle and deep layers of geothermal energy.
Q4: What is the cost of developing and utilizing geothermal energy in middle and deep layers? Can it be popularized and applied in a large scale?
A: The project cost depends on many factors such as geothermal geological conditions, load, engineering quantity, etc. Before the project construction, there will be a pre-feasibility study with reference to the estimated cost. Generally speaking, the project cost of geothermal energy is lower than other energy sources such as gas, and it is not limited by region and water, so it has the value of popularization and application.
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