Geothermal resource exploration method for weak water-containing bedrock region

Abstract

The invention relates to a geothermal resource exploration method for a weak water-containing bedrock region, and belongs to the field of geothermal resource exploration. The method comprises the following steps: firstly, acquiring geological data, pre-judging whether a fracture attribute belongs to a water guide type or a water blocking type, performing geophysical exploration verification, and finding a feasible fracture through verification; for the fractures with feasibility, the occurrence of the fractures with feasibility is researched by arranging a controllable source audio magnetotelluric sounding method, target fractures are searched according to occurrence results, and drilling well positions are recommended on the basis of the target fractures; and drilling in the recommended drilling well location area by adopting an air down-the-hole hammer drilling process. Through drilling verification and early-stage geological research, an inversion result of the CSAMT method is well matched with actual drilling data, a high-quality geothermal well is successfully drilled finally, the well completion depth is 1820 m, the water yield is 463 m < 3 > / d, and the water outlet temperature is 49 DEG C. The method has obvious feasibility and effectiveness in the aspect of finding out heat and water control structures.

Description

Technical Field

[0001] The invention relates to the technical field of geothermal resource exploration, in particular to a method for geothermal resource exploration in a weakly water-bearing bedrock area. Background Art

[0002] Geothermal water resources are a green, low-carbon, recyclable renewable energy source with multiple attributes such as heating, physical therapy, health care, and leisure. They can be well integrated with many industries and can easily create marketing concept highlights in various industries.

[0003] Geothermal water resources in many areas of my country have obvious uneven distribution characteristics, especially in the southern bedrock areas. Unlike the conductive layered heat reservoirs in sedimentary basins, most of them are convection-type belt-shaped heat reservoirs controlled by fault structures. Whether it is possible to accurately find favorable heat and water control structures is the key. In bedrock areas with relatively weak stratum water richness within a certain area, the accuracy of exploration and research on hidden faults is required to be higher, which is also the focus of this invention. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for geothermal resource exploration in weakly water-bearing bedrock areas, and its technical solution is as follows:

[0005] A method for geothermal resource exploration in a weakly water-bearing bedrock area comprises the following steps:

[0006] Step 1: Obtain geological data, pre-judge whether the fracture attribute belongs to water-conducting or water-blocking type, and then verify through geophysical exploration to find a feasible fracture;

[0007] Step 2: For the above-mentioned feasible faults, the occurrence of the feasible faults is studied by deploying the controlled source audio frequency magnetotelluric sounding method, the target fault is found according to the occurrence result, and the drilling location is recommended based on the target fault;

[0008] Step 3: Drill in the recommended drilling location area using the air down-the-hole hammer drilling process.

[0009] As a further solution of the present invention, in the controlled source audio frequency magnetotelluric sounding method of step 2, the electrode pit at the transmitting end is deepened to 2-3 m, and the transmitting low frequency power supply current is increased to 26±1 A;

[0010] The electrodes at the receiving end use non-polarized electrode tanks, the range difference between the non-polarized electrode tanks is less than 1mV, and the grounding resistance of the two electrodes is less than 1kΩ.

[0011] As a further solution of the present invention, the electrode arrangement pit at the receiving end is deeply buried, cleaned, and fully stirred and mixed with saturated salt water to ensure that the non-polarized electrode tank is in close contact with the soil.

[0012] As a further solution of the present invention, at least 5 survey lines are arranged perpendicular to feasible faults, with a point spacing of 50 m; all survey lines are analyzed to find the target fault.

[0013] As a further solution of the present invention, in step 2, the method of increasing the transmitted low-frequency power supply current includes one or more of increasing the area of ​​aluminum foil electrodes laid at the bottom of the pit, increasing the number of laid tunnels, and pouring saturated salt water or soapy water at the bottom of the pit.

[0014] Conventional mud drilling technology is a type of overbalanced drilling technology. Its principle is that while the drilling rig drives the drill bit to rotate and drill, the mud pump is used to transport mud to the bottom of the hole through the tap and the inner hole of the drill pipe to flush the bottom of the hole. Then the mud will carry the cuttings along the outer annular space between the drill pipe and the hole wall, flow from the wellhead to the sedimentation tank, and then be pumped into the well by the mud pump to form a circulation loop. The liquid column pressure is less than the formation pressure, and the drilling fluid in the wellbore enters the formation.

[0015] This technology is currently widely used in oil drilling, shale gas and other oil and gas reservoirs. In recent decades, with the need for geothermal resource drilling, this technology has also been introduced into the field of geothermal wells. However, geothermal resources are different from other oil and gas extraction. Its main purpose is to obtain water resources in thermal reservoirs. In areas with abundant groundwater, the use of mud drilling technology is not a big problem. However, in bedrock areas with scarce groundwater, the shortcomings of mud drilling technology are more obvious, mainly polluting the thermal reservoir, which in turn affects the water output of geothermal wells. Mud is the key factor here. Mud is a special mixture of water, bentonite, saturated salt solution and various additives. It is generally greater than the density of water, resulting in the circulating fluid pressure in the well being higher than the formation (water-containing pore) pressure.

[0016] Compared with oil and gas reservoirs, bedrock thermal reservoirs have developed fissures, high permeability, and low formation pressure, mostly normal pressure or low pressure (the formation pressure of thermal reservoirs is usually less than 1). During the drilling process, clay particles and drill cuttings in the denser mud fluid will inevitably enter the thermal reservoir formation, which may block cracks or pores, reduce the thermal reservoir permeability, pollute the thermal reservoir, and reduce production.

[0017] The present invention adopts the air down-the-hole hammer drilling process, which belongs to one of the underbalanced drilling processes. The principle is to use air as the cuttings carrying medium and rock crushing power, and use the air compressor to transfer high-pressure gas to the air down-the-hole hammer (commonly known as pneumatic impactor) through the drill bit. The air down-the-hole hammer converts the high-pressure gas energy into intermittent pulse force, driving the drill bit to perform high-frequency impact rotation rock breaking on the rock. The crushed cuttings are carried to the surface with the exhaust gas discharged after the down-the-hole hammer works, forming a circulation loop, realizing "spraying while drilling". Its liquid column pressure is greater than the formation pressure, and the formation fluid enters the wellbore.

[0018] Since gas is used as the drilling circulation medium instead of water as the medium, the fluid pressure in the wellbore is kept lower than the fluid pressure of the formation being drilled during the drilling process, and the wellbore is always kept in a negative pressure state, which can reduce the damage to the aquifer fissures, which is equivalent to drilling and washing the well at the same time, so it can protect the geothermal reservoir very well. This feature is more effective in water-rich and poor bedrock formations. In addition, the process also has impact and rotary rock crushing mechanisms, especially in extremely hard and medium-hard formations, and the greater the formation hardness, the more obvious the drilling efficiency advantage compared with conventional mud drilling technology.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. Through geological research, the present invention analyzes that the F2 hidden fault is the main heat and water conduction channel in the work area. After determining the target fault, the reliability of the original data is guaranteed by optimizing the CSAMT technical methods and measures in view of the complex strong interference electromagnetic environment, and the survey line is scientifically arranged. Finally, the spatial distribution morphology and water-rich favorable positions of the F2 hidden fault are found, and a geothermal well location is recommended.

[0021] 2. Through drilling verification, the results of the previous geological research and CSAMT inversion method were well consistent with the actual drilling data. Finally, a high-quality geothermal well was successfully drilled with a well depth of 1820m and a water output of 463m 3 / d, outlet water temperature 49℃.

[0022] 3. The results obtained through the invention further illustrate that the combination of comprehensive geological research and targeted optimization of CSAMT technical means and measures has obvious feasibility and effectiveness in identifying heat and water control structures, especially in weakly water-bearing bedrock areas, which can accurately identify favorable locations for geothermal water storage, and also provide reference for relevant units to carry out geothermal water resource exploration in other similar areas in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 For regional geological maps;

[0024] Figure 2 This is the result of the interpretation of the geophysical exploration section in the northeast;

[0025] Figure 3 This is the result of the interpretation of the geophysical profile in the work area. DETAILED DESCRIPTION

[0026] The present invention is described in detail below in conjunction with specific embodiments. The embodiments described below are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0027] Example 1

[0028] Taking the Fenghuang DR02 geothermal well in western Hunan as an example, this paper introduces a landmark exploration idea for successfully finding high-quality geothermal hot spring water in a water-rich bedrock area by conducting geological surveys and research, geophysical exploration, and targeted optimization of the CSAMT method and other technical measures.

[0029] 1. Regional geological overview

[0030] 1.1 Hydrogeology

[0031] According to the rock type, hydraulic characteristics and water richness of the groundwater, the groundwater in the work area is divided into four categories, namely, pore and fissure water in clastic rocks, fissure water in shallowly metamorphosed clastic rocks, karst fissure water in clastic rocks intercalated with carbonate rocks, and fissure water in carbonate rocks intercalated with clastic rocks.

[0032] The pore and fissure water of clastic rocks is composed of Cretaceous siltstone, and the underground runoff modulus is 0.054~0.149L / (s·km 2 ), weak water-richness.

[0033] The shallow metamorphic clastic rock fissure water is composed of sandstone and slate of the Nantuo Formation-Jiangkou Formation and Banxi Group of the Lower Sinian System. Although the rock fissures are well developed, most of them are closed or filled with clay. The surface fissure rate is only 0.1-1.0%, and the permeability is weak. The vertical runoff and drainage conditions are poor, and the groundwater runoff modulus is less than 0.1L / (s·km 2 ), the water-richness is extremely weak, and the surface spring flow is also very small, generally less than 0.2L / s.

[0034] The karst fissure water in clastic rock and carbonate rock is composed of shale, siliceous rock and marl of the Dengying Formation-Doushanduo Formation of the Upper Sinian System. Most of the fissures are filled with debris, with a surface fissure rate of only 0.86%. The groundwater runoff modulus is 0.13-0.404L / (s·km2), and the water-richness is weak.

[0035] The carbonate intercalated clastic rock fissure water is composed of Cambrian dolomite, limestone, and shale, with relatively developed pores and cracks, and the groundwater runoff modulus is less than 0.13-2.4 L / (s·km 2 ), with medium to strong water-richness, distributed in the west and northwest far away from the work area.

[0036] Combined with the regional geology and work area location analysis, the deep target geological body of the present invention is closely related to the shallow metamorphic clastic rock fissure water type, belonging to the bedrock area with extremely weak water richness, and has a low correlation with the other three types of groundwater.

[0037] 2. Geothermal geological survey and research

[0038] 2.1. Groundwater circulation system

[0039] The entire geothermal system consists of an upper cap layer, a lower heat reservoir, heat and water channels, and a heat source. First, atmospheric precipitation moves underground along fault zones, fissures, depressions, and other channels over a large area, and circulates deeply under the control of water-rich faults. The heated fluid generates buoyancy due to volume expansion and moves upward; at the same time, the upper, denser, low-temperature fluid continues to move downward under the action of gravity, thus forming an underground hot water circulation system.

[0040] 2.2. Heat storage type

[0041] From the regional geology and hydrogeology, it can be known that the upper Cretaceous and Sinian siltstones and mudstones have low rock fissure rates, poor groundwater permeability, and low thermal conductivity when faults are not developed. They have good heat and water insulation characteristics and can serve as the cap rock in the area. Heat flows up from the deep crust and heats the cold water that seeps down from the surface and exists in the rock formations. Hot water is stored in the form of shallow metamorphic clastic rock fissure water in the rocks near the water-rich faults, forming the target heat storage space for the development of geothermal water resources in this area. The heat storage type is "banded heat storage".

[0042] 2.3 Study on heat and water conduction channels

[0043] The control effect of fault structure on groundwater is generally manifested in two aspects: one is to communicate and guide groundwater, and the other is to gather and block groundwater. The F1 fault is a large regional compressive fault formed by extrusion geological action. The pressure on the fault surface is the greatest. The fault zone is often filled with fault mud, mylonite, fault breccia, etc. The rock has recrystallization, dense structure, extremely low porosity, and strong water-isolating effect. According to relevant fracture mechanism research, when the fracture is subjected to stress, it will continue to expand along its two ends and form a secondary fault in the stress concentration area. When the tectonic stress of different periods is superimposed, the rock in the secondary fault (such as the F2 fault) will be further broken. At this time, the water-blocking fillings of the rock fissures such as sandstone and slate in the Banxi Group will be destroyed and dispersed, thereby increasing the fissure rate of the rock body, improving the connectivity of the rock fissures, and increasing the water content and water-rich space of the rock formation.

[0044] In addition, from the distribution pattern of springs in field geological surveys, more than 80% of the surface springs are distributed near the intersection of two or more groups of faults and the secondary faults next to the main faults, while there are fewer springs near the large faults dominated by compression and the flow rate is small. It is further explained that the F1 fault is a structure that mainly blocks water and conducts water, while the F2 fault is a secondary structure that mainly conducts water and blocks water. At the same time, the F2 fault is close to the F1 main fault and belongs to the same structural unit. It inherits some characteristics of deep large faults and provides a good channel for communicating deep upper mantle heat sources and groundwater seepage to the deep. Therefore, the F2 fault can be used as the main heat and water conduction channel in this area.

[0045] Comprehensive geological analysis shows that the purpose of this geophysical survey should be to study the spatial distribution of the F2 hidden fault, and to study the occurrence of the F2 fault by deploying the controlled source audio frequency magnetotelluric sounding method (referred to as the "CSAMT method").

[0046] 3. Geophysical exploration research

[0047] 3.1. Overall geophysical detection line layout

[0048] The present invention uses the SEP system for field data collection, including a TRU high-power electromagnetic transmitter, a DRU wide-band electromagnetic receiver, an IMC inductive magnetic field sensor and corresponding data processing and interpretation software. The layout of the geophysical detection line follows the principle of "from known to unknown", and a total of 9 survey lines are arranged, with an operating frequency of f = 0.35 ~ 9600Hz, a receiving pole distance MN = 50m, and a point distance of 50m. First, in order to verify the occurrence of the F1 fault determined by the geological survey and its control properties on geothermal water, 4 survey lines were arranged at a location far away from the northeast of the work area, with a transmitting dipole AB = 1350m and a transmitting and receiving distance r = 9.0 ~ 13.0km; then 5 more survey lines were arranged around the F2 fault in the work area, with a transmitting dipole AB = 1300m and a transmitting and receiving distance r = 12.0 ~ 13.0km. The data inversion adopts the one-dimensional smooth model inversion interpretation method. See the layout of the geophysical detection line. Figure 1 .

[0049] 3.2. Geophysical exploration results and geological interpretation in the northeast

[0050] From the resistivity inversion profiles of the K2, K4, K6, and K10 survey lines in the northeast, the resistivity is generally high, with only a layered low-resistance area in the shallow 300-500m and deep 1400-1700m intervals. The electrical distribution is highly non-uniform in the lateral direction, and there is no obvious stratification. From the analysis of the lateral resistivity variation characteristics, there is a steeply inclined low-resistance anomaly near the K2 line pile number 1200, the K4 line pile number 1100, the K6 line pile number 1400, and the K10 line pile number 1200. Analysis shows that it is caused by the influence of the F1 fault and water content. The anomaly is locally "steeply rising or falling" along the resistivity contour lines of the above pile numbers in the vertical direction, and has a trend of continuous extension to the deep strata, with an overall flat arc distribution of "steep on top and gentle on the bottom". Combining geological data and spatial distribution, it is basically determined that the above anomaly is a reflection of the F1 fault. The fault strikes NE and dips NW. The shallow part has a dip angle of more than 70°, while the deep part has a gentle dip angle.

[0051] From the comprehensive situation on the profile, although the F1 fault has some abnormal display, it is not strong, and even not obvious on some profiles, which may indicate that the water content of the F1 fault is not very ideal. It is a fault that mainly blocks water and conducts water as a supplement, which verifies the water control characteristics of the geological F1 fault. Figure 2 .

[0052] 3.3 Geophysical exploration results and geological interpretation in the work area

[0053] (1) Method optimization

[0054] The electromagnetic working environment in the work area is not good. If effective suppression measures are not taken, it is difficult to ensure the accuracy of the original data of the CSAMT method. In view of the strong interference in the work area, in order to reduce the grounding resistance (generally the grounding resistance is more than tens of ohms) and increase the power supply current (generally the power supply current is 10-20A), the electrode pit is deepened to 2-3m at the transmitting end, the aluminum foil electrode laying area at the bottom of the pit is increased (increased to 7.5-10 square meters) and the number of laying tunnels (5-6 tunnels are laid at each electrode), and multiple optimization technologies such as pouring saturated salt water and soap water are adopted. After processing, the low-frequency power supply current of the transmitter reaches about 26A. At the receiving end, the electrode uses a non-polarized electrode tank. Before the measurement, the electrode is paired. The range between the non-polarized electrode tanks is less than 1mV; the electrode layout pit is deeply buried, cleaned, and the saturated salt water is fully stirred to ensure that the tank bottom is in close contact with the soil. After testing, the grounding resistance between the two electrodes is less than 1kΩ.

[0055] After optimizing the CSAMT method in a targeted manner, five survey lines, K5, K7, K9, K11, and K13, were arranged perpendicular to the F2 fault, with a point spacing of 50m.

[0056] (2) Geophysical exploration results and geological interpretation

[0057] 1) From the K5 line profile, the low resistance is mainly distributed in the shallow part within -1000m above sea level, the middle part is a relatively uniform medium resistance area, and there is a slightly larger low resistance area in the deep part, which may be caused by water-bearing strata. A fault F2 was interpreted near pile number 750, with a NE trend, NW dip, an angle of about 80°, and a cutting depth of about 2000m.

[0058] 2) The profile of K7 line is basically similar to that of K5 line, except that there are continuous high-resistance areas within -300m above sea level in the shallow part, which may be composed of sedimentary rocks with poor water content in the shallow part; the deep part is a relatively uniform medium-resistance area, and there are local low-resistance anomalies toward the large end. The above situation shows that the water content of the strata in the middle and upper parts from -300m to -1000m above sea level may be good, the water content of the strata at the deep small end is not very good, and there may be a water-bearing broken area in the deep large end. A fault F2 was interpreted near pile number 750, and its occurrence is basically the same as that of K5 line.

[0059] 3) The profiles of lines K9, K11 and K13 are similar. The shallow, near-surface, water-bearing, low-resistivity layer composed of the Quaternary system and the bedrock weathering zone is very obvious, with a thickness of about 50 to 100 m. Below it is a relatively high-resistivity layer, with a thickness of about 600 m. Except for a few local low-resistivity anomalies, most of the strata in this section have poor water content. Going down vertically, from an altitude of about -300 m to a depth of -1200 m, there are several strong low-resistivity anomaly closures. It is speculated that this section of the strata is affected by the fault structure and the rocks are broken, making it a locally water-rich section. A fault F2 was interpreted near stake number 800 of line K9, stake number 850 of line K11, and stake number 900 of line K13, and its occurrence is the same as above. The interpretation of the 5 profiles is as follows. Figure 3 .

[0060] 4) From the overall morphology of the above five profiles, the consistency of each profile is relatively good, indicating that there is a good heat and water conduction channel that promotes the circulation of groundwater, namely the F2 hidden secondary fault. This geophysical exploration work basically studied the specific occurrence and spatial distribution of the F2 fault extending in the direction of the work area.

[0061] 3.4 Comprehensive geophysical analysis and recommended well locations

[0062] In summary, it is believed that the F2 fault is a fault that mainly conducts water. The rocks in its influence zone are relatively broken, which can provide a certain amount of water-rich space, which is conducive to the enrichment of underground hot water. It is the target fault for hot water resource exploration in the work area. On this basis, a geothermal well site is recommended, numbered DR02, located at 740m of the K11 line pile number.

[0063] 4. Drilling verification

[0064] 4.1 Drilling technology and geological logging

[0065] The study found that: due to the overall weak water-richness of the geological body in the work area, if conventional overbalanced drilling technology (such as mud drilling technology) is used, it will inevitably cause certain damage to the aquifer. In order to minimize the construction risks caused by the drilling technology, this drilling adopts underbalanced drilling technology, that is, air down-the-hole hammer drilling technology. This technology can capture the location, scale and water-richness of different aquifers (fracture zones) more intuitively.

[0066] Well DR02 was drilled to the final hole at 1820.0m. According to the rock cuttings logging and hydrological observation, the strata from top to bottom are: 0-15.0m is the Cretaceous purple-red siltstone; 15.0-430.0m is the Sinian Jiangkou Formation gray-green sandstone and sericite slate, with quartz veins and pyrite in some places. Among them, 351.3-355.4m encountered a broken zone, and the water output reached 120m 3 / h (cementing and sealing); 430.0-905.0m is gray-green and gray-black banded slate and sandy slate interlayers in the second section of Wuqiangxi Formation of Banxi Group, containing a small amount of pyrite mineralization; 905.0-1090.3m is purple-red sandy slate and slate interlayers in the first section of Wuqiangxi Formation; 1090.0-1820.0m is purple-red sandy slate intercalated with calcareous slate and gray-green banded sandy slate in the second section of Madiyi Formation of Banxi Group. A total of 3 aquifers were encountered in this group of strata, with a cumulative water output of 19-25m 3 / h.

[0067] 4.2 Geophysical logging

[0068] After drilling, geophysical logging was carried out on Well DR02. The logging items included well temperature, well inclination, well diameter, azimuth, dual lateral, natural potential, natural gamma, compensated acoustic wave, and gradient electrode. The logging section 430-1820.0m was all metamorphic rock formations. The natural gamma curve was used to divide the metamorphic rock formation into reservoir and non-reservoir layers, and the resistivity was used as the main basis for the division of various types of fractures. In the process of fracture evaluation, the acoustic time difference and logging were also used to calculate the porosity. A type of fracture layer refers to a well-developed porosity layer with a permeability of more than 10 millidarcy and self-heating capacity. It is the main aquifer section of geothermal water; a type of fracture layer refers to a generally developed porosity layer with a permeability between 1 and 10 millidarcy, a certain seepage capacity, and a certain natural capacity, and can be used as a secondary aquifer section; a type of fracture layer refers to a poorly developed porosity layer with a permeability of less than 1 millidarcy, a low capacity, but a reservoir with certain transformation potential.

[0069] According to statistics, there are 12 first-level fractures from 1000.0m to the bottom of the well, mainly concentrated at 1098.7-1546.0m, with a thickness of 39.1m; 10 second-level fractures are mainly concentrated at 1002.3-1050.2m and 1564.1-1759.5m, with a thickness of 32.1m; 2 third-level fractures are relatively thin. Comprehensive comparison of geophysical exploration, drilling data and logging data has a high degree of consistency.

[0070] 4.3 Pumping test

[0071] After completing the well logging and pipe laying work, two steady flow pumping tests were conducted. Before the test, the static water level was 112.0m, the dynamic water level was 870.0m, and the stable water output was 463m 3 / d, temperature 49℃, stabilization time 19h; small drop dynamic water level 714.0m, stable water output 392m3 / d, temperature 49℃, stabilization time 13h.

[0072] In order to further study the development characteristics of geothermal reservoirs, the Qiubuyi formula and the Shihart formula were used to analyze and calculate the pumping data to determine the hydrogeological heat reservoir parameters of the geothermal well. The calculation results are shown in Table 1.

[0073] Table 1 Calculation table of hydrogeological heat storage parameters

[0074]

[0075] 5. Conclusion

[0076] (1) This geological study analyzed that the F2 hidden fault is the main heat and water conduction channel in the work area. After determining the target fault, the reliability of the original data was guaranteed by optimizing the CSAMT technical methods and measures in the complex strong interference electromagnetic environment, and the survey line was scientifically arranged. Finally, the spatial distribution morphology and water-rich favorable locations of the F2 hidden fault were identified, and a geothermal well location was recommended.

[0077] (2) Through drilling verification, the results of the previous geological research and CSAMT inversion method were well consistent with the actual drilling data. Finally, a high-quality geothermal well was successfully drilled with a well depth of 1820m and a water output of 463m 3 / d, outlet water temperature 49℃.

[0078] (3) The results obtained through this geothermal water resource exploration and research further demonstrate that the combination of comprehensive geological research and targeted optimization of CSAMT technical means and measures is obviously feasible and effective in identifying heat and water control structures, especially in areas with weak water-bearing bedrock, which can accurately identify favorable locations for geothermal water storage, and also provide a reference for relevant units to carry out geothermal water resource exploration in other similar areas in the future.

[0079] Example 2

[0080] In the Xinquan Township project in Luxi County, Jiangxi Province, the same exploration method as the present invention was used. Through exploration and research on weak water-bearing strata under the background of hidden faults, a high-quality hot spring well was successfully drilled with a depth of 1,680m, a water volume of 600m3 / d, and a temperature of 50°C.

[0081] In addition, it should be understood that those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for geothermal resource exploration in weakly water-bearing bedrock areas, characterized in that: The following steps are involved: Step 1: Obtain geological data, pre-judge whether the fracture attribute belongs to water-conducting or water-blocking type, and then verify through geophysical exploration to find a feasible fracture; Step 2: For the above-mentioned feasible faults, the occurrence of the feasible faults is studied by deploying the controlled source audio frequency magnetotelluric sounding method, the target fault is found according to the occurrence result, and the drilling location is recommended based on the target fault; Step 3: Drill in the recommended drilling location area using the air down-the-hole hammer drilling process.

2. The method for geothermal resource exploration in weakly water-bearing bedrock areas according to claim 1, characterized in that: In the controlled source audio frequency magnetotelluric sounding method of step 2, the electrode pit at the transmitting end is deepened to 2-3 m, and the transmitting low frequency power supply current is increased to 26±1 A; The electrodes at the receiving end use non-polarized electrode tanks, the range difference between the non-polarized electrode tanks is less than 1mV, and the grounding resistance of the two electrodes is less than 1kΩ.

3. A method for geothermal resource exploration in weakly water-bearing bedrock areas according to claim 2, characterized in that: The electrode layout pit at the receiving end is deeply buried, cleaned, and fully stirred and mixed with saturated brine to ensure that the non-polarized electrode tank is in close contact with the soil.

4. The method for geothermal resource exploration in weakly water-bearing bedrock areas according to claim 1, characterized in that: At least five survey lines are arranged perpendicular to feasible faults, with a point spacing of 50m; all survey lines are analyzed to find the target fault.

5. The method for geothermal resource exploration in weakly water-bearing bedrock areas according to claim 2, characterized in that: In step 2, the method of increasing the transmission low-frequency power supply current includes one or more of increasing the area of ​​aluminum foil electrodes laid at the bottom of the pit, increasing the number of laid tunnels, and pouring saturated salt water or soap water at the bottom of the pit.

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