A method for shallow geothermal exploration and automatic gas extraction device in a hole

Abstract

The present invention belongs to the field of geothermal exploration, and specifically discloses a method for shallow geothermal exploration, which comprises the following steps: step 1, drilling a hole in a selected area and measuring and recording the temperature; step 2, collecting and storing the gas sample in the hole in the selected area in the above step 1; step 3, sampling and pre-treating the soil in the hole in the selected area collected in the above step 2.1; step 4, performing soil geochemical element analysis, pH value analysis, CO 2 analysis and the like on the gas sample collected and stored in the selected area in the above step 2 and the soil sample sampled and pre-treated in step 3. 2 Gas concentration analysis; Step 5: Combine the soil geochemical element analysis, pH value analysis, CO 2 The results of gas concentration analysis are used to draw geochemical maps, which are projected onto the same geological base map, and the composite halos of different indicators are circled to screen out geothermal vision blocks and complete shallow geothermal exploration. The method of the present invention greatly improves the reliability, efficiency and accuracy of shallow geothermal exploration.

Description

Technical Field

[0001] The invention belongs to the field of geothermal exploration, and in particular relates to a method for shallow geothermal exploration. Background Art

[0002] At present, the main shallow exploration methods include geothermal measurement (direct measurement) and geochemical sampling (including B, Hg, AS and other elements in the soil) analysis. These two methods are to infer geothermal anomalies, heat sources and structural distribution connectivity by directly measuring the temperature of shallow formations and sampling and analyzing the content of certain geochemical elements. In addition to the limitations of the methods themselves, these two methods do not belong to the same type of methods and means, and cannot be verified and effectively coordinated with each other in actual application. Other methods include shallow drilling, which has the problems of high cost, long time consumption and low efficiency (relative to geological methods); geophysical measurement belongs to indirect detection methods.

[0003] In the current exploration practice, the above-mentioned shallow geothermal exploration methods are generally used separately and interpreted separately, especially in the sampling, testing, and application links, which are independent of each other. There are problems such as lack of coordination, lack of systematic and standardized sampling and analysis specifications, and inability to correspond to the interpretation of results. Therefore, it is urgent to design a shallow geothermal exploration method to improve efficiency, speed up time, and improve the reliability of shallow exploration. Summary of the invention

[0004] The purpose of the present invention is to provide a method for shallow geothermal exploration, which greatly improves the reliability, efficiency and accuracy of shallow geothermal exploration.

[0005] The technical solution to achieve the purpose of the present invention is as follows: A method for shallow geothermal exploration, the method comprising the following steps:

[0006] Step 1: Drilling a hole in a selected area for geothermal exploration, and measuring and recording the temperature. Step 1 includes the following steps:

[0007] Step 1.1, drilling holes in the selected area of ​​geothermal exploration;

[0008] Step 1.2, measure and record the temperature of the boreholes in the selected area of ​​geothermal exploration;

[0009] Step 2: Collect and store the gas samples in the boreholes in the geothermal exploration selected area in step 1 above, wherein step 2 comprises the following steps:

[0010] Step 2.1, collecting gas samples in the boreholes in the geothermal exploration selected area in step 1 above;

[0011] Step 2.2, storing the borehole gas collected in the above step 2.1;

[0012] Step 3: sampling and pre-treating the soil in the borehole of the geothermal exploration selected area collected in the above step 2.1, wherein the step 3 comprises the following steps:

[0013] Step 3.1, sampling the soil in the borehole of the selected geothermal exploration area collected in the above step 2.1;

[0014] Step 3.2, pre-treating the soil in the borehole of the selected geothermal exploration area collected in the above step 2.1;

[0015] Step 4: Perform soil geochemical element analysis, pH value analysis, and CO2 gas concentration analysis on the gas samples collected and stored in the geothermal exploration selected area in the above step 2 and the soil samples sampled and pretreated in step 3;

[0016] Step 5: Draw geochemical maps of the soil geochemical element analysis, pH value analysis, and CO2 gas concentration analysis results in the above step 4, project them onto the same geological base map, circle the composite halos of different indicators, screen out geothermal prospect blocks, and complete shallow geothermal exploration.

[0017] In the step 1.1, a steel chisel is driven vertically into a hole deep in the stratum with a sledgehammer.

[0018] The temperature measurement steps in step 1.2 are as follows: insert a thin metal rod of a digital thermometer into the bottom of the drilled hole, read the temperature, and measure it three times in sequence to ensure that the error between the three measured values ​​is better than ±0.1°C, record the three measured values, and take the average value as the temperature measurement value.

[0019] The steps for collecting gas samples in the borehole in step 2.1 are as follows: open all the clamps on rubber tube I and rubber tube II, turn on the peristaltic pump to extract air, and the gas sample in the borehole enters the gas sampling bag through the exhaust pipe, the orifice filler, rubber tube I, the glass tube, and rubber tube II under the action of the peristaltic pump. When the gas sampling bag is full and expanded, clamp all the clamps on rubber tube I and rubber tube II, stop the peristaltic pump, and take the gas sampling bag connected to rubber tube II from the glass tube. The collected gas sample in the gas sampling bag is the gas in the borehole.

[0020] In step 2.1, before collecting the sample, if the silica gel resin should appear blue, if it changes color, bake it in an oven at 105°C until it turns blue.

[0021] In the step 2.2, the collected gas in the borehole is stored in a wide-mouth brown bottle.

[0022] The soil sample collection in step 3.1 is carried out by using a Luoyang shovel to take out the soil sample in the borehole and then put it into a double-layer plastic bag. The soil sampling amount is not less than 500g.

[0023] The soil sample pretreatment in step 3.2 includes soil geochemical element analysis pretreatment and soil pH measurement pretreatment.

[0024] The soil geochemical element analysis pretreatment in step 3.2 is to grind the soil sample and pass it through a 20-100 mesh sieve, and take 100g of the soil sample and put it into a plastic sample bag.

[0025] The soil pH measurement pretreatment in step 3.2 adopts the potentiometric method. The soil sample is dried in the shade and ground, then passed through a 20-mesh sieve. 20 g of the soil sample is put into a plastic sample bag and sealed to avoid light.

[0026] The soil sample analysis in step 4 includes soil geochemical element analysis, soil pH value analysis and CO2 gas concentration analysis.

[0027] The soil geochemical element analysis in step 4 adopts the ICP-MS analysis and measurement method, and the soil pH value analysis adopts the potentiometric measurement method; the CO2 concentration gas analysis adopts the non-dispersive infrared method or gas chromatography measurement method, or adopts the CO2 test tube or test paper measurement.

[0028] The specific steps of drawing the geochemical map in step 5.1 are as follows: the ground temperature measurement results are taken as the average value plus 3 times the standard deviation as the abnormal lower limit, and the sampling Kriging interpolation method is used to draw the contour map; the soil pH value is taken as a certain value as a step, and the contour map is drawn; each soil geochemical element is taken as the average value plus several times the standard deviation as the abnormal lower limit, and the contour map of different elements is drawn; the atmospheric CO2 concentration in the area where the measurement point is located is taken as the background value, and the value plus several standard deviations is taken as the abnormal lower limit, and the contour map of CO2 concentration in the gas is drawn.

[0029] The geological base map in step 5.2 is a geological map, a hydrogeological map or a geothermal geological map.

[0030] The invention discloses an automatic in-hole air extraction device for shallow geothermal exploration, comprising an air extraction pipe, a rubber tube I, a clamp, a glass tube, a peristaltic pump, a rubber tube II and an air extraction bag. The bottom of the air extraction pipe is inserted into a borehole, an outlet on one side of the top of the air extraction pipe is connected to one end of the glass tube through the rubber tube I, a clamp is provided in the middle of the rubber tube I, the other end of the glass tube is connected to the opening of the air extraction bag through the rubber tube II, the two ends of the rubber tube II are respectively clamped with clamps, and the middle of the rubber tube II is connected to the peristaltic pump.

[0031] The automatic air extraction device in the hole further comprises a hole filler, which is located between the air pipe and the drill hole.

[0032] The automatic air extraction device in the hole further comprises silica gel, which is located in the outlet of the air extraction pipe.

[0033] The automatic air extraction device in the hole further comprises cotton and a filter screen, and the cotton and the filter screen are located between the outlet of the peristaltic pump and the rubber tube II.

[0034] The beneficial technical effects of the present invention are:

[0035] (1) The present invention establishes a technical method standard for multi-method integration for shallow geothermal exploration, which can be used as an effective means to find geothermal anomaly points (zones) with high reliability;

[0036] (2) The present invention establishes a multi-method integrated method standard for shallow geothermal exploration, which is standardized, procedural, and highly cost-effective, and is conducive to the horizontal comparison of measurement results under different regions, geological, geomorphological, climatic and other conditions, and has wide adaptability;

[0037] (3) The present invention establishes a multi-method integrated method standard for shallow geothermal exploration, which greatly improves the shortcomings of the previous single method, such as multiple solutions and low reliability, and significantly improves the efficiency and accuracy of geothermal exploration.

[0038] The present invention has been used in a geothermal field abroad to make a beneficial attempt, and has achieved a more rapid, effective and reliable exploration method than a single method. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A flow chart of a method for shallow geothermal exploration provided by the present invention;

[0040] Figure 2 A schematic diagram of the automatic air extraction device in a hole provided by the present invention;

[0041] Figure 3 This is a schematic diagram of the distribution of geothermal prospecting areas delineated from an actual geothermal field exploration example provided by the present invention.

[0042] In the figure: 1—exhaust pipe; 2—hole filling material; 3—drilling hole; 4—silicone gel; 5—rubber tube I; 6—clamp; 7—glass tube; 8—peristaltic pump; 9—cotton and filter; 10—rubber tube II; 11—gas collection bag. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0044] The present invention firstly drills a 1m deep borehole in a selected area according to a certain grid or spacing, and simultaneously carries out geothermal measurement, soil sample and gas sample collection in the same hole, and pre-processes the samples. The sample analysis results, temperature measurement values, etc. are respectively drawn into geochemical diagrams, which are projected onto the same geological base map, and the composite halos of different indicators are circled. The geological significance they represent is comprehensively analyzed to provide indicator information related to geothermal exploration.

[0045] like Figure 1 and Figure 2 As shown, the present invention provides a method for shallow geothermal exploration, which comprises the following steps:

[0046] Step 1: Drill a 1 m borehole 3 in the selected area for geothermal exploration, and measure and record the temperature. Step 1 includes the following steps:

[0047] Step 1.1: Drill a 1m borehole in the selected area for geothermal exploration

[0048] Use a 12-pound sledgehammer to hammer the steel chisel vertically into the ground 1m deep and drill a 1m borehole. Then quickly pull out the steel chisel. Be careful to avoid hole collapse and foreign matter being introduced into the hole when pulling out the steel chisel.

[0049] Step 1.2: Measure and record the temperature of borehole 3 in the selected area of ​​geothermal exploration

[0050] Quickly insert the thin metal rod of the digital thermometer into the bottom of the 1m borehole 3, preferably when the thin metal rod just touches the soil layer at the bottom of the hole. Quickly read the temperature and measure it three times in sequence, ensuring that the error between the three measured values ​​is better than ±0.1℃. Record the three measured values ​​and take the average value as the temperature measurement value of this point;

[0051] Record the point number, coordinate position, temperature value, buried characteristics, rock type, etc. in the log book, and record the re-survey or re-survey results for abnormal points.

[0052] Step 2: Collect and store the gas samples in the borehole 3 in the geothermal exploration selected area in step 1 above, wherein step 2 comprises the following steps:

[0053] Step 2.1: Collect gas samples from the borehole 3 in the geothermal exploration selected area in step 1 above.

[0054] like Figure 2As shown, the present invention provides an automatic air extraction device in a hole, which includes an air extraction pipe 1, an orifice plugging material 2, silica gel 4, a rubber tube I5, a clamp 6, a glass tube 7, a peristaltic pump 8, cotton and a filter screen 9, a rubber tube II10 and an air sampling bag 11. The borehole 3 in the Quaternary soil has a depth of 1m and a hole diameter that can just be inserted into the bottom of the front end of the air extraction; the air extraction pipe 1 is connected to a 1m long tube at one end and a rubber air extraction tube at the other end. The front end of the air extraction is made of iron or PVC to ensure smooth air extraction and no air leakage, and easy to carry; the orifice plugging material 2 can be filled with dead branches and leaves in the field to fill the air extraction end and the orifice and compact them; the silica gel 4 is spherical silica gel particles for drying, which are blue when dry and turn pink when containing water; the rubber tube I5 and the rubber tube II10 are for medical or Commonly used connecting tubes in laboratories; clamp 6, which is a daily water pipe clamp; glass tube 7, a connecting component for laboratories; peristaltic pump 8, which is a commercial small-scale vacuum pump driven by lithium battery or dry battery, easy to carry and durable; cotton and filter 9, commonly used items in laboratories, placed before the air inlet end of peristaltic pump 8 to prevent foreign matter and water from entering the pump body; air sampling bag 11, which is an aluminum foil composite film under standard conditions, and can be replaced by ordinary rubber, plastic, or glass containers for low-precision measurements in the field, as long as it is airtight, clean and dry.

[0055] Before the test, a plastic aluminum foil composite film gas sampling bag 11 with a volume of 0.5 to 1 L is prepared, and the front end of the gas sampling bag 11 is fixedly connected to one end of the rubber tube II 10 through a clamp 6.

[0056] The bottom of the air extraction pipe 1 is inserted into the borehole 3, and the hole filling material 2 is filled between the top of the borehole 3 and the air pipe 1. The outlet on one side of the top of the air extraction pipe 1 is connected to one end of the rubber tube Ⅰ5, and the outlet of the air extraction pipe 1 is plugged with silica gel 4, and a clip 6 is sandwiched in the middle of the rubber tube Ⅰ5; the other end of the rubber tube Ⅰ5 is connected to one end of the glass tube 7; the other end of the glass tube 7 is connected to one end of the rubber tube Ⅱ10, and a clip 6 is sandwiched at both ends of the rubber tube Ⅱ10; the other end of the rubber tube Ⅱ10 is connected to one end of the gas collection bag 11. The middle of the rubber tube Ⅱ10 is connected to the peristaltic pump 8, and cotton and a filter 9 are provided between the outlet of the peristaltic pump 8 and the rubber tube Ⅱ10. Note the closed state of the connection of the entire device.

[0057] The steps for collecting gas samples in the borehole of the selected area of ​​geothermal exploration in step 2.1 are as follows: open all the clamps 6 on the rubber tube I5 and the rubber tube II10, turn on the peristaltic pump 8 to extract air, and the gas sample in the borehole 3 enters the gas bag 11 through the exhaust pipe 1, the orifice filler 2, the rubber tube I5, the glass tube 7, and the rubber tube II10 under the action of the peristaltic pump 8. When the gas bag 11 is filled and expanded to more than 80% of its volume, clamp all the clamps 6 on the rubber tube I5 and the rubber tube II10, stop the peristaltic pump 8, and take the gas bag 11 connected to the rubber tube II10 out of the glass tube 7. The collected gas sample in the gas bag 11 is the gas in the borehole 3. According to the above-mentioned step 2.1 of collecting gas samples in the borehole of the selected area of ​​geothermal exploration, open all clamps 6, use the peristaltic pump 8 to extract gas from the depth of 1m borehole 3 on site, flush the gas bag 113 times, each time for 1 to 5 minutes, extract 0.5 to 1L of gas sample from the gas bag 11, seal the bag mouth of the gas bag 11 and take it back to the laboratory or directly measure on site.

[0058] Before vacuuming, the silica gel 4 resin connected to the front end of the vacuum pipe 1 should appear blue. If it changes color, it can be baked in an oven at 105°C until it turns blue for use; the filter screen and cotton 9 connected to the peristaltic pump 8 should be kept dry.

[0059] The peristaltic pump 8 has an air intake speed of 0.1 to 1 L / min, a sampling time of 1 to 10 min, and the gas is directly pumped into the gas collection bag 11 and the port is sealed. Step 2.2: Storing the gas in the borehole 3 collected in step 2.1 above

[0060] The gas sampling bag 11 is placed in a wide-mouth brown bottle to store the gas in the borehole, sealed and stored at low temperature, and then transported back to the laboratory for analysis.

[0061] Note that CO2-containing gas samples should be analyzed and tested within 7 days or measured using direct measurement methods.

[0062] Step 3: sampling and pre-treating the soil in the borehole 3 in the selected geothermal exploration area collected in the above step 2.1, wherein step 3 comprises the following steps:

[0063] Step 3.1: Collect soil samples from the borehole 3 in the geothermal exploration selected area collected in step 2.1 above.

[0064] Use a Luoyang shovel to take out the soil sample in borehole 3 and put it into a double-layer plastic bag. Be careful to pick out debris such as gravel and plant roots. Determine the sampling volume according to the requirements of the analysis project. The soil sampling volume is generally not less than 500g.

[0065] Step 3.2: Pre-treat the soil sample in the borehole 3 in the geothermal exploration selected area collected in step 2.1 above.

[0066] The soil samples collected in the borehole 3 in the field are brought back to the room and processed according to different test requirements. The pretreatment includes soil geochemical element analysis pretreatment and soil pH measurement pretreatment. The soil thermal release Hg test analysis pretreatment in the soil geochemical element analysis pretreatment is to directly put the soil sample into a 20g plastic vial outdoors and bring it back to the room for analysis; soil geochemical element analysis pretreatment B, Be, Hg and other elements can grind the soil sample and pass it through a 20-100 mesh sieve, which is equivalent to a pore size of 0.85mm-0.15mm. Take about 100g of soil sample and put it into a plastic sample bag for laboratory analysis. The soil pH measurement pretreatment adopts the potentiometric method. The soil sample is dried in the shade and ground, then passed through a 20-mesh sieve. Take about 20g of soil sample and put it into a plastic sample bag, seal it in the dark, and bring it back to the room for testing.

[0067] Step 4: Perform soil geochemical element analysis, pH value analysis, and CO2 gas concentration analysis on the gas samples collected and stored in the geothermal exploration selected area in step 2 and the soil samples sampled and pretreated in step 3.

[0068] The temperature in borehole 3 was measured on site and the results were recorded, while the other items were analyzed and tested indoors.

[0069] After step 2 and step 3 are completed, the gas sample collected and stored in step 2 and the soil sample sampled and pretreated in step 3 are brought back to the laboratory for analysis and testing.

[0070] Soil sample analysis includes soil geochemical element analysis, soil pH value analysis and CO2 gas concentration analysis.

[0071] The soil geochemical element analysis adopts ICP-MS analysis and measurement method to analyze soil geochemical elements B, Be, Hg, AS. The soil mercury analysis can be determined by thermal mercury method.

[0072] The soil pH value analysis adopts the potentiometric measurement method. The soil B analysis, soil Be analysis, and soil AS analysis adopt the soil geochemical measurement procedures, DZ / T 0145-2017 for analysis and testing.

[0073] The CO2 concentration in the gas can be analyzed by non-dispersive infrared method or gas chromatography, or by direct on-site measurement using a dedicated CO2 test tube or test paper.

[0074] When measuring the gas temperature, the relative error of two measurements at the same point is less than ±10%. Since the temperature measurement in hole 3 is carried out outdoors in real time, when an abnormal point is found, the operation of step 1.2 is repeated at the abnormal point until the required data is obtained. Other analytical tests are laboratory analytical tests, and abnormal results are not re-tested. The cause of the abnormality needs to be analyzed and the abnormal results need to be screened.

[0075] Step 5: Draw geochemical maps of the soil geochemical element analysis, pH value analysis, and CO2 gas concentration analysis results in step 4 above, project them onto the same geological base map, circle out the composite halos of different indicators, screen out the geothermal prospect blocks, and complete the shallow geothermal exploration.

[0076] Step 5.1: Draw geochemical maps based on the soil geochemical element analysis, pH value analysis, and CO2 gas concentration analysis results in step 4 above. The specific steps are as follows:

[0077] (1) The ground temperature measurement results are taken as the average value plus 3 times the standard deviation as the lower limit of abnormality, and the sampling Kriging interpolation method is used to draw the contour map;

[0078] (2) The soil pH value is set at a step of 0.02, and the contour map is directly drawn;

[0079] (3) For each soil geochemical element, the average value plus three times the standard deviation is used as the lower limit of the anomaly, and the contour maps of different elements are drawn using the sampling Kriging interpolation method;

[0080] (4) Taking the atmospheric CO2 concentration in the area where the measurement point is located as the background value and this value plus three times the standard deviation as the lower limit of the abnormality, the Kriging difference method is used to draw a contour map of CO2 concentration in the gas.

[0081] Step 5.2: Project the geochemical maps drawn in step 5.1 above onto a geological base map with a scale of no less than 1:50,000 that includes the survey area, circle the composite halos of different indicators, comprehensively analyze their geological significance, provide indicator information related to geothermal exploration, screen out geothermal prospect blocks, and complete shallow geothermal exploration.

[0082] The geological base map is a geological map, a hydrogeological map or a geothermal geological map.

[0083] The temperature measurement results are analyzed based on the geological, geomorphological, hydrological and climatic conditions of the measuring points. Generally, high anomaly points and halo overlapping areas are geothermal channels connected by faults, which are favorable sections for further deep exploration.

[0084] Soil pH is mainly affected by the H + Control, here it can reflect the acidity and alkalinity of groundwater in the soil. Although geothermal water is mostly alkaline, it is found in actual applications that when the soil pH value is weakly acidic, it can reflect the activity or mixing of groundwater.

[0085] CO2 in shallow underground gas can reflect plant respiration and is also affected by deep sources such as magma and mantle gas release. It can also reflect the connectivity of faults and can be an indirect indicator of underground heat sources and the degree of structural development. It needs to be analyzed specifically based on actual conditions.

[0086] If it is found that the abnormal halos of different items are distributed linearly, it is inferred that they are affected by the fault structure. When the abnormal halos are combined with the pH high value contour line, it can reflect the structural connectivity and the possible existence of underground hot water. The present invention collects gas samples in a small underground space, collects and pre-treats soil samples, including the temperature in the hole, the content of soil elements and pH value, and the CO2 content in the gas. The present invention mainly involves collecting soil samples and air samples at the same point or layer of the shallow cover layer while measuring the ground temperature on site. After the sample pre-treatment, it is taken back to the laboratory to analyze the soil geochemical elements (B, Be, Hg, AS, etc.), pH value, and air CO2 concentration. When conditions permit, the deep magma source temperature is calculated by analyzing the carbon isotope fractionation value in CO2 and CH4, and the geothermal prospect area is predicted and divided based on the comprehensive analysis of these results.

[0087] Figure 3 For the actual exploration and application of the present invention in a geothermal field in Southeast Asia, shallow soil B, Hg, pH value sampling and analysis, gas CO2 analysis, temperature measurement and other work were carried out in a key geothermal block in the geothermal field. The analysis and measurement results were projected on a 1:20,000 geothermal geological map, and geothermal anomaly blocks were demarcated. The blocks were compared with the geophysical measurement results, and satisfactory exploration results were obtained, providing a reliable basis for geothermal development.

[0088] An example of geothermal exploration in a geothermal field in a Southeast Asian country is as follows:

[0089] The present invention provides a method for shallow geothermal exploration, which comprises the following steps:

[0090] Step 1: Drilling and Temperature Measurement

[0091] Step 1.1: Drilling

[0092] Use a portable drill or steel chisel to drill holes with a depth of 1m and a diameter of about 2 to 3cm.

[0093] Step 1.2: Ground temperature measurement

[0094] Use a sampling digital thermometer to measure the bottom temperature of the hole. When the error between the three temperature measurements is no more than 0.1°C, record the temperature value. At the same time, record the point number, coordinates, geographical and geological features, etc.

[0095] Step 2: Soil sample collection and determination of CO2 concentration in the borehole

[0096] Step 2.1: Use a thin round bucket shovel to pull up the soil sample in the hole. The sampling weight is about 500g.

[0097] Step 2.2: Determination of CO2 in the pore gas

[0098] On-site use Figure 2The automatic exhaust device shown is connected to a glass tube 7, in which a CO2 test paper is built. The concentration value (volume ratio) is directly read by exhausting air to the test paper in the glass tube 7, and the CO2 concentration value in the outside atmosphere is measured at the same time. Each point is measured twice, and the measurement error between the two times is no more than 10%.

[0099] Step 3: Geochemical element and pH determination of soil samples

[0100] Determination of B, Hg content and pH value in soil samples: soil samples collected outdoors were brought back indoors; according to the requirements of B and Hg element analysis, the soil was dried in the shade and ground, passed through an 80-mesh sieve, and about 50 g of the sieved sample was taken. 5 g of the sample was weighed for 3 minutes, and the B, Hg element content and pH value were determined respectively. The element measurement was carried out in accordance with the ICP-MS analysis method, and the pH measurement was performed by electrode measurement of distilled water infusion.

[0101] Step 4: Temperature, CO2 concentration, B, Hg content and pH value projection analysis

[0102] The measurement and analysis results are projected onto the geological map and their geological significance is comprehensively analyzed.

[0103] (1) For all measurement results except pH, three times the standard deviation plus the mean value were used as the lower limit of abnormality, and Kriging difference was used to draw contour maps;

[0104] (2) The pH value is directly plotted in 0.02 steps;

[0105] (3) All contour maps were projected onto a 1:20,000 geological map. A comprehensive analysis of the different measured value anomalies and halo composite locations was performed. Based on the hydrogeological and structural distribution conditions of the work area, the existing geothermal hotspots, and the comparison with the geophysical survey results, three geothermal prospecting blocks were identified (see Figure 3 ).

[0106] The geothermal prospecting blocks delineated by the present invention are compared with the geophysical exploration results, geothermal display distribution, and geothermal exploration results in adjacent areas, and have high reliability, providing a decision-making basis for the next step of geothermal development.

[0107] The present invention has been described in detail above in conjunction with the accompanying drawings and embodiments. The above implementation modes are only the best embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for shallow geothermal exploration, It is characterized in that The method comprises the following steps: Step 1: Drill a hole (3) in a selected area for geothermal exploration, and measure and record the temperature. Step 1 includes the following steps: Step 1.1, drilling a hole in the selected area for geothermal exploration (3); Step 1.2, measuring and recording the temperature of the borehole (3) in the selected area for geothermal exploration; Step 2: using an automatic gas extraction device in the hole to collect and store the gas sample in the borehole (3) in the selected area of ​​geothermal exploration in step 1 above, said step 2 comprises the following steps: Step 2.1, using an automatic gas extraction device in the hole to collect gas samples in the borehole (3) in the geothermal exploration selected area in the above step 1; The device comprises an air extraction pipe (1), an orifice plugging material (2), silica gel (4), a rubber tube I (5), a clamp (6), a glass tube (7), a peristaltic pump (8), cotton and a filter (9), a rubber tube II (10) and an air collection bag (11), wherein the silica gel (4) is located in the outlet of the air extraction pipe (1), the bottom of the air extraction pipe (1) is inserted in the drill hole (3), and the orifice plugging material (2) is located between the air extraction pipe (1) and the drill hole (3); an outlet on one side of the top of the air extraction pipe (1) is connected to one end of the glass tube (7) through the rubber tube I (5), a clamp is provided in the middle of the rubber tube I (5), the other end of the glass tube (7) is connected to the opening of the air collection bag (11) through the rubber tube II (10), the two ends of the rubber tube II (10) are respectively clamped with clamps, the middle of the rubber tube II (10) is connected to the peristaltic pump (8), and the cotton and the filter (9) are located between the outlet of the peristaltic pump (8) and the rubber tube II (10); The steps for collecting the gas sample in the borehole (3) in step 2.1 are as follows: open all the clamps (6) on the rubber tube I (5) and the rubber tube II (10), turn on the peristaltic pump (8) to extract gas, and the gas sample in the borehole (3) enters the gas sampling bag (11) through the gas extraction pipe (1), the orifice filler (2), the rubber tube I (5), the glass tube (7), and the rubber tube II (10) under the action of the peristaltic pump (8). When the gas sampling bag (11) is full and expanded, clamp all the clamps (6) on the rubber tube I (5) and the rubber tube II (10), stop the peristaltic pump (8), and remove the gas sampling bag (11) connected to the rubber tube II (10) from the glass tube (7). The gas sample collected in the gas sampling bag (11) is the gas in the borehole (3); Step 2.2, storing the gas in the borehole (3) collected in the above step 2.1; Step 3, sampling and pre-processing the soil in the borehole (3) in the selected geothermal exploration area collected in the above step 2.1, said step 3 comprises the following steps: Step 3.1, sampling the soil in the borehole (3) of the selected geothermal exploration area collected in the above step 2.1; Step 3.2: pre-treat the soil in the borehole (3) in the selected geothermal exploration area collected in the above step 2.1; the specific steps of step 3.2 are as follows: The soil samples collected from the borehole (3) in the field are brought back to the laboratory and processed according to different test requirements; the pretreatment includes soil geochemical element analysis pretreatment and soil pH measurement pretreatment; the soil thermal release Hg test analysis pretreatment in the soil geochemical element analysis pretreatment is to directly put the soil sample into a 20g plastic vial outdoors and bring it back to the laboratory for analysis; the soil geochemical element analysis pretreatment for B, Be, and Hg elements can be ground and then passed through a 20-100 mesh sieve, which is equivalent to a pore size of 0.85mm-0.15mm, and about 100g of soil sample is put into a plastic sample bag and sent to the laboratory for analysis; the soil pH measurement pretreatment adopts the potentiometric method, and the soil sample is dried in the shade, ground and passed through a 20-mesh sieve, and about 20g of soil sample is put into a plastic sample bag, sealed in a light-proof manner, and brought back to the laboratory for testing; Step 4: Perform soil geochemical element analysis, pH value analysis, and CO analysis on the gas samples collected and stored in the geothermal exploration selected area in step 2 and the soil samples sampled and pretreated in step 3. 2 Gas concentration analysis; Step 5: Combine the soil geochemical element analysis, pH value analysis, CO 2 The results of gas concentration analysis are used to draw geochemical maps, project them onto the same geological base map, circle out composite halos of different indicators, screen out geothermal prospect blocks, and complete shallow geothermal exploration; The specific steps of drawing the geochemical map in step 5.1 are as follows: the ground temperature measurement results are taken as the average value plus 3 times the standard deviation as the abnormal lower limit, and the sampling Kriging interpolation method is used to draw the contour map; the soil pH value is taken as a certain value as a step, and the contour map is drawn; each soil geochemical element is taken as the average value plus several times the standard deviation as the abnormal lower limit, and the contour map of different elements is drawn; the atmospheric CO in the area where the measurement point is located is taken as the abnormal lower limit. 2 The concentration is the background value, and the value plus a certain standard deviation is taken as the abnormal lower limit. 2 Concentration contour plots; Step 5.2: Project the geochemical maps drawn in the above step 5.1 onto a geological base map with a scale of not less than 1:50,000 that includes the survey area, circle the composite halos of different indicators, comprehensively analyze the geological significance they represent, give indicator information related to geothermal exploration, screen out geothermal vision blocks, and complete shallow geothermal exploration; the geological base map in the step 5.2 is a geological map, a hydrogeological map, or a geothermal geological map.

2. A method for shallow geothermal exploration according to claim 1, Features: In step 1.1, a steel chisel is driven vertically into a borehole (3) deep in the ground using a sledgehammer.

3. A method for shallow geothermal exploration according to claim 2, Features: The temperature measurement steps in step 1.2 are as follows: insert a thin metal rod of a digital thermometer into the bottom of the borehole (3), read the temperature, and measure it three times in sequence, ensuring that the error between the three measured values ​​is better than ±0.1°C, record the three measured values, and take the average value as the temperature measurement value.

4. A method for shallow geothermal exploration according to claim 3, Features: In step 2.1, the resin of silica gel (4) should appear blue before collecting the sample. If it changes color, it should be baked in an oven at 105°C until it turns blue.

5. A method for shallow geothermal exploration according to claim 4, Features: In step 2.2, the gas collected from the borehole (3) is stored in a wide-mouth brown bottle.

6. A method for shallow geothermal exploration according to claim 5, Features: In the step 3.1, the soil sample is collected by using a Luoyang shovel to take out the soil sample in the borehole (3) and then put it into a double-layer plastic bag. The soil sampling amount is not less than 500g.

7. A method for shallow geothermal exploration according to claim 6, Features: The soil geochemical element analysis in step 4 adopts the ICP-MS analysis and measurement method, and the soil pH value analysis adopts the potentiometric measurement method; CO 2 The concentration gas analysis adopts the non-spectral infrared method or gas chromatography measurement method, or uses CO 2 Test tube or test strip measurement.

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