Geothermal resources refer to the renewable thermal energy stored in the interior of the earth, generally concentrated in the edge of tectonic plates, originating from the decay of molten magma and radioactive substances of the earth.
The geothermal resource is a very valuable comprehensive mineral resource. It has multiple functions and wide uses. It is not only a clean energy resource for power generation and heating, but also is also a hot brine water resource and natural fertilizer water resource that can be used to extract industrial raw materials such as bromine, iodine, borax, potassium salt, an ammonium salt, but also valuable medical hot mineral water and drinking mineral water resources and domestic water supply.
Years of practice have shown that the comprehensive development and utilization of geothermal resources has significant social, economic and environmental benefits, and has played an increasingly important role in the development of the national economy.
There are various hypotheses about the origin of geothermal heat. It is generally believed that geothermal energy mainly comes from the disintegration and exothermic energy of radioactive elements in the earth, followed by the rotational energy generated by the earth’s rotation, as well as the heat energy released by gravity differentiation, chemical reactions, and rock and mineral crystallization. During the formation of the earth, the total amount of these heat energy exceeded the heat energy dissipated by the earth, forming a huge heat reserve, causing partial melting of the crust to form magmatism and metamorphism.
It has been basically calculated that the temperature of the earth’s core reaches 6000 °C, the temperature of the bottom crust reaches 900-1000 °C, and within a range of about 15 kilometers below the surface normal temperature layer (about 15 meters from the ground), the ground temperature increases with depth. The average geothermal temperature increase rate is about 3°C/100m. There are differences in the geothermal warming rate in different regions. The area close to the average warming rate is called the normal temperature area, and the area higher than the average warming rate is called the geothermal anomaly area. The geothermal anomaly area is the main object of research and development of geothermal resources. The edges of the crustal plates, deep and large faults and volcanic distribution belts are obvious geothermal anomalies.
General survey and exploration of geothermal resources generally use surface geothermal surveys, drilling and various geophysical methods. Infrared remote sensing technology has achieved remarkable results in exploration.
Geothermal resource is one of the oldest energy sources in the world. According to estimates, the total thermal energy inside the earth is about 170 million times the global coal reserves. The amount of heat lost from the interior of the earth through the surface every year is equivalent to the heat produced by burning 100 billion barrels of oil.
The earth itself is like a big boiler, and there is a huge amount of heat energy deep inside. Under the control of geological factors, these thermal energy will accumulate in a certain range of the crust in the form of hot steam, hot water, hot dry rock, etc. If the conditions for development and utilization are reached, it will become a geothermal resource with development significance.
Geothermal resources can be divided into three categories according to temperature: high temperature, medium temperature and low temperature. Geothermal with a temperature greater than 150°C exists in the form of steam, which is called high-temperature geothermal; geothermal with a temperature of 90-150°C exists in the form of a mixture of water and steam, which is called medium-temperature geothermal; Geothermal with a temperature of 25-90°C exists in the form of Warm water（25 ℃-40℃), warm hot water (40℃-60℃), hot water (60℃-90℃) and other forms, which is called low temperature geothermal. High-temperature geothermal generally exists on the boundaries of global plates with strong geological activity, that is, areas with frequent volcanoes, earthquakes, and magma intrusions. Datun geothermal fields in Taiwan belong to high-temperature geothermal fields. The medium and low temperature geothermal fields are widely distributed in the interior of the plate, and most of the geothermal fields in North China and Beijing-Tianjin regions belong to the medium and low temperature geothermal fields.
Geothermal wellhead equipment is the most basic work and safety equipment in the development of geothermal wells. It is mainly used to extract geothermal resources and maintain the normal operation of geothermal well production. In order to reduce the heat loss of geothermal energy during the production process, the existing geothermal wellhead device usually adopts thermal insulation pipe (VIT) to achieve the thermal insulation effect, which has high production cost and complex manufacturing process. Moreover, the current geothermal wellhead device only has a production function without a test function, and cannot detect the utilization efficiency of geothermal energy.
Therefore, Sanjack Company has developed a concentric double-pipe geothermal wellhead device with test function, which realizes the concentric hanger of the double pipes, and uses the method of injecting insulation medium into the pipe string annulus to replace the insulated pipe(VIT), reducing the production cost; A test channel is designed, and the test pipeline carries test instruments from the test channel into the well to perform real-time detection of bottom hole temperature and pressure.
The structure consists of bottom flange (1), tubing head spool (2), hanger (3), valve (4), test pipeline lower seal (5), adapter flange gland (6), adapter flange body (7), test channel (8), test pipeline upper seal (9), tee (10), clamp connector (11), nipple(12), injection channel (13), injection channel connecting pipe (14) ), pipe string annulus (15), test pipeline (16), outer tube (17), inner tube (18), etc.
Working principle: It includes a bottom flange, tubing head spool, hanger, valve, adapter flange gland, adapter flange body, nipple, tee, clamp connector, and the hanger consists of the outer pipe hanger, the inner pipe hanger, the hanger connecting pipe and the protective wire. The outer pipe and the inner pipe are concentric. The adapter flange body and the outer pipe hanger both are provided with injection channels and test channels.
The double-pipe concentric hanger is realized, and the method of injecting insulation medium into the annulus of the pipe string is used to replace the insulation pipe (VIT), which reduces the production cost; the test channel is designed, and the test pipeline carries the test instrument from the test channel into the well, to perform Real-time detection of bottom temperature and stress.
The test channel is designed. The test pipeline carries the test instrument into the well from the test channel to detect the bottom hole temperature and pressure in real-time, and the method of injecting the insulating medium into the annulus of the double concentric pipe replaces the insulating pipe.