Yang Xudong Cao Fuxiang
(Institute of Hydrogeological Engineering Geological Technology Methods, China Geological Survey)
Abstract: The earth is a huge energy treasure house, which is produced by the earth every day The heat transferred from the interior to the surface is equivalent to 2.45 times the energy used by all humans in a day. Especially in today's situation where people are increasingly paying attention to global climate change, environmental pollution issues and the sustainable development of society, as ground source heat pump technology becomes increasingly mature, low-temperature and low-enthalpy shallow geothermal energy has attracted much attention as a renewable and clean energy. focus on. As the technical support for its development and utilization, exploration technology needs to be solved urgently. This article only discusses relevant issues and experiences.
1 Current status of shallow geothermal energy development
The earth is a huge energy reservoir. The deeper you enter the interior of the earth, the higher the temperature. The heat transferred from the interior of the earth to the surface every day is equivalent to 2.45 times the energy used by all humans in a day. This kind of energy stored in the earth's interior is actually more abundant than fossil fuels. Especially in today's situation where people are increasingly concerned about global climate change, environmental pollution issues and the sustainable development of society, geothermal energy has attracted much attention as a renewable and clean energy. focus on.
Shallow geothermal energy is a part of geothermal energy. It is a geothermal energy with development and utilization value in the constant temperature zone of the formation within 200m below the surface. The general temperature is around 15℃. Its development and utilization are inseparable from the development of ground source heat pump technology.
1.1 Current application status abroad
In 1912, Zoelly of Switzerland first proposed the concept of using shallow geothermal energy as a low-temperature heat source for a heat pump system and applied for a patent, marking the advent of the ground source heat pump system. . It was not until 1948 that Zoelly's patented technology really attracted widespread attention, especially in the United States and European countries, which began to pay attention to the theoretical research of this technology. Since 1974, as the energy crisis and environmental problems have become increasingly serious, people have paid more attention to the research on geothermal pump systems that use low-temperature geothermal energy as energy.
The application of ground source heat pumps is the largest in the United States. Among the direct utilization of geothermal energy in 1990, 1995 and 2000, ground source heat pumps accounted for a large proportion, about 59%, and the development was very stable, with an average annual growth of 7.7%. about. In 1997, 40,000 12kW ground source heat pumps were installed, and the number reached about 400,000 in 2000. It is expected that the total installed capacity will reach 1.5 million in 2010. At present, ground source heat pumps are most commonly used in schools and office buildings in the United States. About 600 schools have installed ground source heat pumps, mainly in the Midwest and South.
Ground source heat pump applications in Europe are mainly concentrated in central and northern European countries, such as Sweden, Austria, Switzerland, Germany, etc. There was a climax in the use of ground source heat pumps in the 1950s, but due to high prices, there was no further development. After the oil crisis, some European countries organized five large-scale international academic conferences on ground source heat pumps and conducted research on more than 30 ground source heat pump projects. Different from the situation in the United States, Europe mainly uses shallow geothermal resources and uses ground source heat pumps with coils buried in the underground soil (the burial depth is less than 400m). It is mainly used for indoor floor radiant heating and providing domestic hot water. According to statistics in 1999, among household heating equipment, the proportion of ground source heat pumps in Switzerland was 96, Austria was 38, and Denmark was 27, which was significantly higher than before 1996.
1.2 Domestic application status
my country has good scientific research results and application foundation of heat pumps. As early as the 1950s, Tianjin University carried out research on heat pumps in my country. After the late 1980s, major domestic universities began to study ground source heat pumps. At the National Heat Pump and Air Conditioning Technology Exchange Conference held in Ningbo in 2001 and the International Heat Pump Conference held in Beijing in 2002, relevant people at home and abroad Start paying attention to China, a large market with great development potential. In recent years, domestic research on the application of ground source heat pumps has been strengthened, and there have been more than a dozen manufacturers that have independently researched and produced ground source heat pump units, such as Shandong's Fulda, Beijing's Zhongkeneng, and Shenyang's Dongyu.
In addition, some well-known foreign companies have also set up sales departments in China and established projects in Beijing, Tianjin, Guangzhou, Chongqing, Shandong, Henan, Hunan, Liaoning, Xi'an, Heilongjiang and Hebei. At present, there are more than 100 ground source heat pump projects in my country, with a heating/air conditioning area of ??1 million m2. Almost all of these projects are water source heat pump systems that use groundwater as the heat source. The ground source heat pump system with underground pipes only has demonstration projects in Shandong, Tianjin, Hunan, Hebei and Jilin, and has achieved preliminary results.
2 Hydrogeological classification of shallow geothermal energy development
Category of shallow geothermal energy hydrogeological types based on the type, characteristics and burial distribution of shallow geothermal energy utilization aquifer media . Combined with the existing relevant exploration specifications, the hydrogeological types of geothermal energy development can be basically divided into 4 categories and 16 types. The 4 categories are pore water, karst water, fissure water and special water. The various classifications and hydrogeological issues that need to be identified are detailed in Table 1.
Table 1 Types of hydrogeological exploration of water sources and main hydrogeological issues that should be identified
Continued table
3 Shallow geothermal energy exploration technology
In the process of shallow geothermal energy exploration, on the one hand, traditional hydrogeological exploration methods are inherited and developed, and at the same time, new theories, new technologies and new methods are constantly applied to shallow geothermal energy exploration in a timely manner. From aerial surveys of satellite images and aerial photos to geochemical and geophysical surveys, and then to geological drilling, an all-round three-dimensional survey system from the sky to the surface to the underground has been formed, meeting the strategic requirements of economic development and geology first. Shallow geothermal energy exploration should follow the following optimization principles: data collection - geological survey - geophysics - geochemistry - geological drilling - resource evaluation - development and utilization - recharge protection - measurement and monitoring.
3.1 Data collection
Before any exploration is carried out, it is first necessary to collect, organize and analyze the geological, hydrogeological, geophysical and geochemical exploration data of the area as much as possible. When collecting data, pay attention to the following four points:
(1) The scope of the review should be as large as possible, including a complete geological structural unit and its adjacent areas;
(2) It is necessary to Pay attention to the collection of rock mass and geological structure data;
(3) For geothermal fields where low-temperature conduction dominates, the important thing is the protrusions in the depressions, and attention should be paid to the collection of geophysical and geochemical exploration data;
(4) Attention should be paid to the collection of temperature data, and data such as the location, temperature, and water volume of hot springs should be collected as much as possible. In the covered area, we mainly look for the measured temperature data when drilling water is pumped.
3.2 Geological and hydrogeological survey
The purpose of the geological survey is to understand the geological background of shallow geothermal energy, and to identify the stratigraphic age, lithological characteristics, and age of the magma rock of the geothermal field. , distribution range, geological structural characteristics, and groundwater supply, runoff and discharge conditions, etc., in order to provide a basis for the next step of shallow geothermal energy exploration work. The following issues should be noted during geological surveys.
(1) Structural control of shallow geothermal energy development zones. Judging from the investigation of known wells and springs, most of their exposed locations are at tectonic composite locations that have had strong activity in modern times; or where large faults intersect with secondary faults caused by them; or In tensional and tensile-torsional fractures and joints, because the rocks in these places are relatively broken, they are often favorable places for groundwater to move and for deep water to rise.
(2) When investigating regional fault profiles, focus on describing the pore aquitards and impermeable layers, as well as the occurrence and age of all volcanic rocks, while paying attention to the chemical composition, hydrothermal alteration and minerals of the rock formations Character and extent of sedimentation. By analyzing the phenomena of surrounding rock alteration and mineral deposition in fissures, we can help find those thermal anomaly areas buried deep with no geothermal display on the surface, and can also point out the direction for further exploration.
(3) In terms of hydrogeology, the temperature, water volume and pH value of cold spring water or cold water wells exposed on the surface should be measured one by one in the field, the geological and structural conditions of the cold spring exposure should be described, and water samples should be selected for chemical analysis and isotopes (tritium) and other determinations.
The flow and water temperature of the rivers and streams passing through the area should also be measured. Some major rivers should be measured in sections. The water temperatures before, in the middle and after the thermal area should be measured and water samples should be taken to determine the relationship between surface water bodies and The supply and discharge relationship between geothermal water. In areas where alluvial fans develop, the boundaries between the top recharge area, the middle runoff area and the lower discharge area should be divided.
3.3 Ground geophysical prospecting technology
The specific tasks of ground geophysical prospecting are: to determine the thickness of the overlying layer on the aquifer, the interface and shape of the stratum and lithology; to determine the location and location of the fault. Occurrence; understand the location, scale and morphological characteristics of karst development; identify groundwater occurrence space and connectivity of runoff channels; identify groundwater burial depth, flow velocity, flow direction, aquifer depth, water content, etc. Commonly used methods for groundwater exploration are mainly direct current method and electromagnetic method, including: natural electric field method, charging method, DC resistivity method, stimulated polarization method, audio telluric field method, high density resistivity method, geological radar, frequency domain Various methods such as electromagnetic sounding method (EH-4 conductivity imaging system), transient electromagnetic method and nuclear magnetic resonance method have their own technical characteristics and therefore have different scopes of application.
Natural electric field method and charging method are often used to determine the direction and flow rate of groundwater. Nuclear magnetic resonance technology can directly detect the location, water volume and permeability of aquifers. This is a geophysical exploration technology for shallow geothermal energy groundwater exploration. A fundamental problem to be solved. According to the occurrence conditions of different types of groundwater and the technical characteristics of geophysical prospecting methods, how to establish reasonable and effective geophysical prospecting technology is the primary issue to be solved in ground geophysical prospecting.
3.3.1 Loose layer pore water
The main purpose of geophysical exploration is to understand the aquifer structure and its water richness, groundwater table depth and groundwater salinity. Shallow pore water exploration technology is relatively mature at home and abroad. In general, direct current sounding method or induced electric sounding method is more suitable. It is low cost, simple and popular. The apparent resistivity parameter can determine the aquifer structure and groundwater minerals. Degree of chemicalization, electrostatic parameters are used to understand water richness. However, the conventional resistivity method is more difficult to work in some areas. For example, in desert areas, the surface is extremely dry, the electrode ground resistance is large, and power supply is difficult; for shallow areas with high salinity, the resistivity is low, resulting in excessive power supply current, which requires High-power power supply equipment and small measurement voltage signal affect the observation accuracy; the terrain conditions in some areas are unfavorable and it is difficult to carry out work. At this time, electromagnetic sounding methods can be selected, such as frequency domain electromagnetic sounding method (EH-4 conductivity imaging system). The input impedance of the observation system is high, easy to carry out work, and high efficiency; the transient electromagnetic method can use magnetic source excitation Return line, no grounding issues involved. For areas with complex hydrogeological conditions, on the basis of other geophysical prospecting work, we select key areas and use Numis nuclear magnetic resonance technology to determine the depth, thickness, water supply and water volume of the aquifer and other parameters. The application effect in the northwest loess plateau area Obviously, this method is costly and less efficient.
3.3.2 Clastic rock fissure water
The medium in which it occurs is mainly a set of extremely thick Jurassic and Cretaceous fluvial and lacustrine sand and mudstones deposited in Mesozoic basins. Groundwater types include network fissure water in weathered zones and shallow pressure-bearing fissure water.
The purpose of water physical exploration in network-shaped fissures in clastic rock weathering zones is first to determine the burial depth of the bottom boundary of the weathering crust, and secondly to understand the development degree of weathering fissures and their water richness. Since the exploration depth is less than 50m, it is more appropriate to choose the high-density resistivity method with high resolution.
Shallow fissure confined water refers to the interlayer fissure water of a certain thickness of sandstone layer sandwiched by large pieces of clastic rock mudstone. Due to the very low pore penetration of sandstone bodies with different types of cementation methods, the sandstone layer is characterized by fissures. Mainly containing water. The purpose of geophysical exploration is to understand the thickness of the sand layer. Although the model is relatively simple, geophysical exploration is difficult due to the limitation of the thickness of the water-bearing sandstone layer. At present, frequency domain electromagnetic sounding method is a more feasible method.
3.3.3 Carbonate rock karst water
According to different occurrence media, groundwater in karst areas is divided into surface zone karst water, karst cave water, karst pipe water, and structural fissure karst. water and buried karst water. They exist independently and intersect with each other, forming a complex karst groundwater system.
(1) Karst water in the surface layer.
The main purpose of geophysical exploration is to understand the thickness of the overburden, the undulating shape of the bedrock, and the development of caves and troughs. The geophysical characteristics of the detection object are reflected in low resistance, and there is a certain difference in wave impedance on both sides of the contact interface with the surrounding rock. Since the detection depth is generally less than 30m and the scale of anomalies is small, geophysical exploration methods are required to have high resolution capabilities. Therefore, the available methods include high-density resistivity method and ground-penetrating radar.
(2) Karst cave water. Karst cave water develops in pure and thick limestone and dolomite, and is distributed in a planar or layer-like pattern. Since caves, pores, and gaps contain water, they exhibit low resistance characteristics. Geophysical prospecting to find water first uses profile methods such as joint profile method and audio-frequency telluric field method to determine the plane position of karst caves and karst development zones, and then uses electromagnetic sounding methods to understand the spatial distribution characteristics of karst development zones, especially transient electromagnetic surveying. The abnormality reflected by the deep method is more obvious.
(3) Karst pipe water. Karst pipe water, also known as underground river, is the most typical type of groundwater in southwestern carbonate rock areas. Due to the frequent transformation between surface water and groundwater in karst areas, the spatial distribution of groundwater is extremely uneven and has a double- or multi-layered structure vertically. At the same time, controlled by strata, structures and karst landforms, the karst hydrogeological system is small and dispersed. The geological-geophysical models of karst pipeline water are relatively simple. Compared with the surrounding rock, its electrical and elastic parameter characteristics change significantly. However, due to its scale and burial depth conditions, it is difficult to geophysically prospect for water. Currently, there is no practical method to find water. Effective technical methods. For karst pipe water buried deep less than 100m, geophysical exploration methods can include ground penetrating radar, EH-4 conductivity imaging system, and transient electromagnetic method. Ground-penetrating radar can intuitively reflect the distribution pattern of abnormal bodies within its effective exploration range; the EH 4 system can reflect the development of underground fissures and karsts, but when the surface is uneven, it is prone to static effects and cannot even make a reasonable explanation; transient The electromagnetic method observes pure secondary fields and is effective in detecting low-resistance anomalies in high-resistance surrounding rocks. Various methods can reflect the morphological characteristics of abnormal bodies from different sides, thereby identifying the distribution of underground karst pipes. When the water burial depth of karst pipelines is greater than 100m, it is difficult to find water. Currently available methods include transient electromagnetic methods, but their application is not yet mature and further testing and research are needed.
(4) Structural fissure karst water. This type of groundwater is controlled by structural fissure zones. The main purpose of geophysical prospecting for water is to identify the distribution characteristics and water richness of structural fissure zones. The technology for water geophysical exploration in fissures in fault zones has matured in the 1980s. The most economical and effective method combination is the audio-frequency telluric field method and induced electric sounding method. The audio telluric field method can quickly determine the plane position of the structural zone, while the comprehensive parameters such as apparent resistivity, polarizability and half-life time of the induced electric sounding method can understand the fracture of faults and water-rich sections with developed fissures. When limited by terrain conditions, it is difficult to carry out induced electric sounding method. The EH-4 conductivity imaging system can be used to understand the spatial distribution characteristics and water richness of structural fracture zones. When the thickness of the covering layer is greater than 30m, the abnormal strength of the audio-frequency telluric field method is weak, and the joint section method should be selected to determine the plane position of the structural zone.
(5) Buried karst water. The purpose of geophysical exploration of deep buried karst water is to understand the burial depth of the limestone interface and the development of karst. There are large differences in electrical characteristics and elastic parameters between the limestone and the overlying strata. The development of karst is controlled by deep structures, showing low resistance and discontinuous elastic parameters. Seismic technology can more accurately understand the burial depth of the limestone interface and the spatial distribution characteristics of faults; electromagnetic sounding method mainly reflects the stratigraphic structure and karst development degree; DC sounding is mainly used in the survey stage. At present, the effective combination of several methods has made new progress in the exploration of deep karst water in southern Ningxia.
Several problems faced by deep buried karst water geophysical exploration technology are: the groundwater level is deeply buried and changes greatly, and it is still difficult to determine the depth of the water level; deeply buried Paleozoic carbonate karst Groundwater is controlled by structure and is distributed unevenly, making it difficult to determine the salinity of groundwater. In fact, similar problems exist in shallow structural fissure water exploration; when limestone is overlain by clastic rock, it is difficult to understand the degree of karst development.
Several problems faced by deep buried karst water geophysical exploration technology are: the groundwater level is deeply buried and changes greatly, and it is still difficult to determine the depth of the water level; deeply buried Paleozoic carbonate karst Groundwater is controlled by structure and is distributed unevenly, making it difficult to determine the salinity of groundwater. In fact, similar problems exist in shallow structural fissure water exploration; when limestone is overlying clastic rock, it is difficult to understand the degree of karst development.
3.3.4 Bedrock structural fissure water
The occurrence medium of this type of groundwater is igneous rock or pre-Sinian metamorphic rock. The bedrock is exposed or the caprock is thin, and the rock weathering fissures are not developed. , lack of groundwater resources. Groundwater mainly exists in structural fracture zones.
The geophysical exploration technology is similar to that of carbonate rock structural fissure karst water. For areas where exploration is more difficult, nuclear magnetic resonance technology can be used to distinguish fault mud or water richness.
3.4 Drilling method
Drilling method is a kind of high investment and high risk, but it is an indispensable and important method in the exploration and evaluation of shallow geothermal energy. It is also an important method to identify the shallow geothermal energy. The basic means of thermal energy distribution and storage conditions are important links in shallow geothermal energy exploration. Drilling is mainly used in the detailed investigation and exploration stage of shallow geothermal energy. The purpose is to verify whether the scope delineated by past work is correct and to find out the burial conditions, movement patterns, water temperature, water volume, water level and quality of groundwater and other hydrogeological conditions. At present, my country's drilling construction technology is becoming increasingly mature.
4 Well Development Technology for Shallow Geothermal Energy
In shallow geothermal energy drilling construction, drilling is the foundation and completion is the key, both of which are unified in the entire construction process. Drilling to reach the target layer does not mean the completion of the heat source well. The quality of the completion process determines the quality of the geothermal well.
4.1 Completion process selection
According to the different well structure, the level of the target layer determines the completion construction process. According to the current construction of the heat source well, it is basically divided into two types: There are two major types: one is loose strata, that is, Quaternary strata, weathered layers and fault fracture zones; the other is heat source wells in bedrock target layers, such as the mist of the Ordovician, Cambrian, Qingbaikou, and Jixian systems. Mountain group. Because the target layer is different, the completion technology is also different.
4.1.1 Well Completion Technology in Loose Formation
Filters are required for well completion in loose formation, so the completion process is more complicated. The basic process is as follows:
Drilling is completed → slurry change → physical detection well → well opening → wall breaking → slurry change → running pipe → water stop → gravel filling → well cleaning → pumping test (obtaining hydrogeological data) → handover of the well.
After drilling, in order to ensure the smooth completion of the logging work, it is necessary to change the slurry and adjust the performance of the downhole mud (but the stability of the well wall must be ensured). The adjustment items are mainly viscosity and density. , sand content and other indicators, the purpose is to ensure the smooth completion of the logging work. The well logging work must be tested one by one according to the technical requirements of the geological design. Based on the well logging interpretation data and the actual well logging data, the depth of the water filter pipe, the spacing between the wires and the position of the water stop are determined. After the well logging work is completed, the well should be drilled again and the breaker should be lowered at the same time to break the wall. After the well is broken and the wall is broken, the filter should be lowered.
Carry out cement cementing at the top 20 to 30m of the water filter pipe, and seal all the upper strata of the water filter pipe with cement. The sealing length should be no less than 300m. Cementing is required at the overlapping area between the pump chamber and the well pipe, and the annulus is sealed with cement to ensure that the sealing quality of the annulus can be guaranteed only after the pressure test is stable at 3 to 4 MPa for 20 minutes. Install 5mm thick rubber bags at the parts of each layer of water filter pipes that need to be water-stopped to stop water. The number of rubber bags per layer should be no less than 2.
After the pipe running work is completed, run the drilling tool with a nozzle and flush the water filter pipe up and down. The flushing pressure should be 5MPa and the flushing time should not be less than 4 hours. Then the nozzle is raised, the drilling tool is lowered and connected to the compressor to wash the well with air and water. After the water and sand are removed, the drilling tool is lifted into the pump chamber and the well is washed with air and water again. Finally, according to the water level drawdown of the well cleaning well, a submersible pump is used for formal pumping, and the actual water output, dynamic and static water levels and drawdown of the well are measured. Conduct a pumping test according to the geological design requirements. After acceptance by the builder, construction party, and supervisor, the well will be handed over to complete all construction of the geothermal well.
4.1.2 Completion technology of bedrock heat source wells
Completion of bedrock heat source wells is basically open hole completion, and the completion technology is relatively simple. After completing the well according to the designed well depth structure and depth, perform mud replacement work and stop the mud in the well for less than 20 seconds before logging can be carried out. After the well logging work is completed, the drilling tool is lowered to the bottom of the target layer to wash the well with gas and water. After the water is cleaned and the sand is removed, the deep well pump is lowered to pump water. After measuring the actual water output and water level of the well and the unit water inflow, Carry out well work.
4.2 Exploration after well completion
No matter what type of heat source well it is, exploration work must be carried out after all work is completed. After exploring the loose layer heat source well, the sand in the settling pipe cannot exceed 1/3 of the settling pipe. If it exceeds 1/3, the sand in the settling pipe should be fished out. The sedimentation pipe at the bottom of the loose layer heat source well should not be less than 20m.
Requirements for post-completion exploration of bedrock heat source wells: The sediment at the bottom of the well must not exceed 1 of the length of the aquifer (target layer). If the above standards are not met, sand discharge work should be carried out again until it meets the requirements. The well will be handed over upon request.
4.3 Acidizing well cleaning
During the construction of bedrock heat source wells, if the cracks in the target layer are small or the cuttings block the water channel, acidizing fracturing should be used.
In the construction of the heat source well, the concentration of hydrochloric acid used for acidification and the rock cuttings of the formation were sampled for indoor testing to determine the concentration of hydrochloric acid for acidification. Generally, the concentration that should be used is 15 to 18.
The method of acid fracturing: first inject hydrochloric acid of the volume of the open hole section into the well, and then lower the packer (the size of the packer must be able to seal the upper casing) for fracturing. Different pressures are used depending on the well depth. The minimum pressure should not be less than 15MPa, so that the acidification effect can be better achieved under such pressure.
5 Problems with the development of shallow geothermal energy
Shallow geothermal energy (including groundwater, soil or surface water) can provide both heating and cooling with the help of ground source heat pump technology, which is highly efficient and energy-saving. Air conditioning systems, with their unique advantages, have developed rapidly in China in recent years. With the adjustment of my country's energy structure policy, my country's traditional forms of coal-fired boiler heating and air source heat pump cooling will be replaced by more efficient ground source heat pumps. With the research and development of ground source heat pump technology, as an air conditioning system that utilizes renewable energy, it has the dual benefits of energy saving and environmental protection. It will surely become the most common and effective heating and cooling technology in the 21st century.
However, overall, the development of ground source heat pumps in China is not standardized enough. Basic research needs to be further improved, relevant professional standards need to be formulated, and there is a lack of necessary cooperation and exchanges between industries. These factors may More or less affects the promotion of this technology.
The main problems in the exploration and development of shallow geothermal energy in my country include the weak national unified management of shallow geothermal energy; the low level of geothermal resource exploration and evaluation nationwide; the low level of development and utilization of geothermal resources; Research on resource exploration and development technology needs to be strengthened; heat source wells in some areas are too concentrated and over-exploited. In addition, environmental problems caused by geothermal energy development have also emerged one after another. The main manifestation is that except for a very small amount of recharge, most of the heat source tailwater flows into nearby rivers and wetlands through the urban drainage system. For heat source tailwater discharged on-site, the water quality and temperature must be ensured that the surrounding water and soil will not be polluted or cause thermal pollution during discharge. Therefore, it is necessary to pay close attention to the dynamic trends of water chemistry and conduct follow-up research so that problems can be discovered and solved in a timely manner.
There are still the following problems in using tube wells to irrigate and extract groundwater: ① The well structure of the extraction and irrigation wells is unreasonable. Most of the extraction and irrigation wells still use the single filter pipe structure of the extraction wells, and some well tubes are made of Cement pipes affect the life of the well. ② The surface installation of the mining and irrigation wells is unscientific, and the wellhead and pump pipe system are not sealed. The recharge process can easily cause gas phase blockage, and the tube well will be scrapped over time. ③ In most areas, the extraction and irrigation wells have only one function, either extraction or irrigation. This situation for a long time in winter and summer will cause physical and biochemical blockage of simple recharge wells, leading to the scrapping of recharge wells. ④ Make rational use of groundwater resources. To use suitable groundwater, it must be recharged into the ground, and the quality of the recharged water must be strictly controlled to prevent waste or pollution of water resources.
⑤ Reasonable design and selection of underground water source heat pump hot and cold water units to improve energy efficiency.
6 Suggestions and Countermeasures
The technical and resource conditions for using ground source heat pumps to develop shallow geothermal energy are basically available. The highest efficiency and high environmental protection of heat pumps have won the favor of the world. Therefore, heat pump technology and industry are developing rapidly around the world. Our country also has the corresponding development conditions and the development prospects are very promising.
(1) Pay attention to the exploration and development of geothermal resources in non-geothermal anomaly areas, which broadens the scope of geothermal resource development and utilization. Geothermal resources are widely distributed. Under the condition of strong permeability reservoir distribution in deep areas, it is possible to obtain the desired geothermal resources within a certain depth based on the geothermal heating rate. With the advancement of exploration technology, currently 3,000 to 4000m deep geothermal wells are no longer a problem. This has given rise to new ideas for the development of geothermal resources, which are not limited to geothermal anomaly areas or distributed in shallow locations, especially in some large sedimentary basin areas and towns with economic foundations. The exploration of geothermal resource development has begun, and some have achieved success, such as Shijiazhuang, Hebi and other places.
(2) The development of geothermal resources in oil field areas has received widespread attention. Oilfield areas in sedimentary basins are actually areas where geothermal resources are widely distributed. A considerable number of oil exploration wells with water but no oil can be transformed into geothermal production wells. In the later stages of oil field exploitation, there is more water and less oil and gas, and the main focus is to exploit geothermal resources. The simultaneous development of geothermal and remaining oil and gas resources is very beneficial to the economic development and industrial adjustment of oilfield areas. This has attracted widespread attention from peers in the petroleum industry, and has been piloted in North China, East China, Daqing and other places, and achieved good results. Effect.
(3) Pay attention to the comprehensive utilization and cascade utilization of geothermal resources, and improve the utilization rate and economic benefits of geothermal resources. The development and utilization of geothermal resources has been transformed from the initial one-time utilization to the direction of comprehensive and cascade utilization. The geothermal water used for heating is often used for heating first and then heating and environmental water or according to the different temperature requirements of the building. Cascade heating, or the use of heat pump technology to convert the tail water after primary heating into heat energy for secondary use, has improved the utilization rate and technical content of geothermal resources. When using geothermal resources for agricultural greenhouse cultivation, we are also considering taking advantage of the different temperature requirements of different crops and implementing a reasonable cascade configuration of temperatures, such as the modern agricultural park in Xiaotangshan area of ??Beijing.
(4) Pay attention to the combination of harvesting and irrigation to maintain the sustainable use of geothermal resources. In some areas where geothermal was developed early, such as Beijing, Tianjin, Fuzhou, Xi'an and other places, the head of geothermal water has dropped significantly, which has affected the further development and sustainable utilization of resources to a certain extent. Contact the domestic and foreign development of geothermal Experience, geothermal recharge has become the most common knowledge to maintain the sustainable utilization of geothermal resources and improve the utilization rate of geothermal resources in hot fields. In these areas where geothermal resources were developed early, in addition to experimental research on mining recharge, a combination of mining and irrigation has been included. Important management content for further exploitation of hot fields has been included.
(5) Promote large-scale development to rationalize the allocation of geothermal resources and improve the overall economic benefits of development and utilization. This is inseparable from the characteristics of geothermal resources, the need for combined mining and irrigation, and the development situation of economic scale and large-scale development. With the emergence of large-scale enterprises in economic development and the implementation of the combination of geothermal mining and irrigation, the development of geothermal resources by small units that only mine without irrigation will actually be restricted, while large-scale mining with good resource conditions and economic conditions will be encouraged and feasible. It will be an inevitable trend to develop geothermal resources by units combining irrigation and irrigation.
(6) Formulate a unified development plan and implement unified development. The development of geothermal is to develop geothermal fluid resources or geothermal water resources with water as the carrier. Due to its flow characteristics, when geothermal water resources are exploited in the same thermal field or in the same widely distributed thermal reservoir, there will be a gap between the extraction wells. Mutual interference is inevitable. In order to rationally develop and protect geothermal resources and reduce or even avoid blind mining problems, a unified development plan should be formulated and unified development and management should be implemented under the conditions of identifying the recoverable geothermal resources.
In this regard, Beijing, Tianjin, Fuzhou and other places that early developed geothermal resources have noticed this problem and formulated regional geothermal resource development plans early to promote the orderly development of geothermal resources.
(7) Application of control technology in geothermal ground utilization. Mainly, the output of geothermal extraction wells, water volume allocation, and the discharge temperature of geothermal tail water are controlled according to the actual needs of supply and demand; the output of geothermal water wells, changes in water level (head) in the well, water temperature, etc. are automatically monitored and transmitted. The application of automatic control technology has become more common in units newly developing geothermal resources in Beijing, Tianjin and other places.
(8) Strengthen management. Strengthen administrative legislation, formulate relevant technical standards, and implement standardized management and legal management of the development and utilization of geothermal energy.