A fluid geochemical feature fusion analysis method for geothermal resource evaluation

Abstract

The application discloses a kind of fluid geochemical feature fusion analysis methods for geothermal resource evaluation, it is related to feature fusion technical field, for solving the problem of heat source type discrimination and water supply channel development direction identification result deviation, by monitoring wellhead bubble escape state, when meeting the condition, automatically complete escape gas and radon water sample collection, mass spectrum analysis is carried out to gas sample, calculate helium isotope ratio and discriminate heat source type, while radon concentration is decayed to obtain initial radon concentration, combine wellhead fluid temperature to retrieve fluid circulation depth, automatically identify and remove to the data disturbed by shallow cold water mixing, fusion initial radon concentration and sodium ion content of effective measuring point carry out spatial superposition analysis, identify underground water supply fracture development direction, and combine heat source dominant type to output target area classification result, realize water supply channel independent identification based on geochemical evidence chain.

Description

Technical Field

[0001] This invention relates to the field of feature fusion technology, and more specifically, to a fluid geochemical feature fusion analysis method for geothermal resource assessment. Background Technology

[0002] In the process of geothermal resource exploration and evaluation, the geochemical characteristics of wellhead fluids in fault zones are usually relied upon to comprehensively determine the nature of deep heat sources, fluid circulation paths, and the development of water supply channels. In existing technologies, samples of wellhead escaping gas and groundwater are generally collected and combined with tracer components such as helium and radon, as well as major ion components, to analyze the source composition and circulation characteristics of the geothermal reservoir system, thereby achieving the preliminary delineation of geothermal target areas.

[0003] The existing technology has the following shortcomings: Currently, in complex geological environments where deep high-temperature thermal fluids and shallow cold water systems are strongly mixed and superimposed in actual fault zone intersection areas, and where fluid upwelling channels exhibit multi-branched, unstable, and interconnected structures, there is a lack of continuous state-triggered sampling mechanisms for the wellhead gas-liquid synergistic response process and fusion analysis models with unified constraints on multi-source geochemical parameters. This results in the inability to effectively separate the isotope drift and ion concentration dilution effects caused by the mixing of shallow cold water, leading to deviations in the results of heat source type identification, circulation depth inversion, and water supply channel development direction identification, thus reducing the stability of target area delineation. Therefore, a fluid geochemical characteristic fusion analysis method for geothermal resource evaluation is proposed.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide a fluid geochemical feature fusion analysis method for geothermal resource evaluation, which solves the problems mentioned in the background art by using a wellhead bubble escape state-triggered sampling and multi-source geochemical parameter synergistic fusion analysis mechanism.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a fluid geochemical characteristic fusion analysis method for geothermal resource assessment, comprising the following steps: Step S1: Collect bubble escape data from each wellhead measuring point in the intersection area of ​​the target fault zone and evaluate the fluid escape state. Based on the fluid escape state, determine whether to perform drainage gas collection and sampling treatment and obtain gas samples and radon water samples. Step S2: Perform mass spectrometry analysis on the gas sample and collect isotope ratio data. Calculate the mantle source contribution ratio based on the isotope ratio data and analyze the dominant heat source type. Detect the radon concentration in the radon gas water sample, perform radon decay correction on the radon concentration, and calculate the initial radon concentration. Step S3: Collect the current wellhead fluid temperature at each wellhead measuring point, invert the fluid circulation depth based on the initial radon concentration, screen and mark each wellhead measuring point according to the fluid circulation depth, and detect the sodium ion content at the marked wellhead measuring points; Step S4: Perform spatial overlay analysis on the sodium ion content and initial radon concentration at the wellhead measuring points, assess the water supply development characteristics based on the spatial overlay analysis results, and output the target area classification results of the target fault zone intersection area in combination with the dominant heat source type.

[0007] In a preferred embodiment, in step S1, the target fault zone intersection area refers to the underground structural area formed by the intersection or cutting of two or more regional faults. Wellhead monitoring points refer to fixed monitoring locations set at geothermal wells, hot spring wells, or natural hot springs in the intersection area of ​​the target fault zone for the continuous collection of fluid geochemical parameters. In-situ bubble flow monitoring devices are installed at each wellhead measuring point to continuously count the total volume of bubbles escaping from the wellhead per unit time. Divide the total volume of bubbles detected within the current sampling period by the duration of the sampling period to obtain the bubble escaping flow rate corresponding to the wellhead measuring point.

[0008] In a preferred embodiment, in step S1, the bubble escape flow rate within a continuous sampling period is arithmetically averaged to obtain the average bubble escape flow rate. When the average bubble escape flow rate is greater than or equal to the preset escape judgment threshold, the current wellhead measuring point is determined to be in an effective fluid escape state. Otherwise, the current wellhead measuring point is determined to be in an invalid fluid escape state; Once the wellhead measuring point is determined to be in an effective fluid escape state, the drainage gas collection sampling device is controlled to move to a preset depth below the wellhead liquid surface and the surface water of the wellhead is removed, allowing the escaped air bubbles to enter the sealed gas collection chamber. After gas-liquid separation is completed in the sealed gas collection chamber, the collected escaped gas is introduced into the vacuum gas collection bottle to form a gas sample. At the same time, a vacuum diffusion sampling device was activated to collect radon gas water samples.

[0009] In a preferred embodiment, in step S2, the gas sample is introduced into a rare gas mass spectrometer, and the abundance of He³ in the sample is detected under constant vacuum conditions. Abundance; Calculate the abundance of He³ in a gas sample and The abundance ratio is used to obtain isotope ratio data. The isotope ratio data is then normalized to obtain standardized isotope ratios. Based on standardized isotope ratios, the mantle source contribution ratio was calculated using the two-terminal mixing method. When the proportion of mantle source contribution is greater than or equal to the preset heat source identification threshold, the dominant heat source type of the current wellhead measuring point is determined to be mantle source type. When the proportion of mantle source contribution is less than the preset heat source identification threshold, the dominant heat source type of the current wellhead measuring point is determined to be shell source type.

[0010] In a preferred embodiment, in step S2, the radon gas water sample is sent to a radon concentration detector for detection, and the measured radon concentration at the current detection time is obtained by using alpha particle counting. Read the sampling timestamp and record the detection timestamp corresponding to the current time when the radon concentration detection is completed. Subtract the sampling timestamp from the detection timestamp to calculate the sample storage time. Based on the radioactive decay law of radon, the measured radon concentration is corrected for radon decay by using the sample storage time, and the initial radon concentration corresponding to the sampling time is restored.

[0011] In a preferred embodiment, in step S3, when the cumulative drainage time of drainage gas collection sampling reaches the preset drainage stabilization time, the current wellhead fluid temperature is collected. Using the current wellhead fluid temperature and initial radon concentration as inversion inputs, the fluid circulation depth at each wellhead measuring point is inverted using a weighted algorithm to obtain the fluid circulation depth. Compare the fluid circulation depth at each wellhead measuring point with the fluid circulation depth screening threshold: When the fluid circulation depth is greater than or equal to the fluid circulation depth screening threshold, the wellhead measuring point is marked. Conversely, the wellhead measuring points are not marked; The sodium ion content of each marked wellhead measuring point is detected: another water sample collected in the same well and at the same time as the radon water sample in step S1 is taken, and its sodium ion concentration is used as the sodium ion content of the corresponding marked wellhead measuring point.

[0012] In a preferred embodiment, in step S4, the sodium ion content and initial radon concentration at the marked wellhead measuring point are normalized using the interval scaling method to obtain the normalized sodium ion value and the normalized initial radon value. Calculate the spatial overlap coefficient between any two marked wellhead measuring points; Compare the spatial superposition coefficient with the spatial superposition coefficient threshold: When the spatial superposition coefficient is greater than or equal to the spatial superposition coefficient threshold, the corresponding two marked wellhead measuring points are retained on the surface plane projection map in the form of connecting edges. Conversely, the connection edge between the two marked wellhead measuring points is not retained; Construct a graph structure from all the retained connecting edges and their endpoints, and extract the largest connected subgraph that contains the most marked wellhead measuring points.

[0013] In a preferred embodiment, in step S4, principal component analysis is performed on the surface plane coordinates of all marked wellhead measuring points in the maximum connected subgraph, and the azimuth of the unit direction vector corresponding to the first principal component in the surface plane is taken as the direction of the water supply fracture in the intersection area of ​​the target fracture zone. The arithmetic mean of the normalized sodium ion values ​​at all marked wellhead measuring points in the maximally connected subgraph is denoted as . ; when When the water supply intensity level is greater than or equal to the high threshold, the water supply intensity level will be marked as high. when When the water supply intensity level is greater than or equal to the low threshold and less than the high threshold, the water supply intensity level is marked as medium. when When the water supply intensity is less than the low threshold, the water supply intensity level will be marked as low. The orientation of water supply faults and the level of water supply intensity together constitute the characteristics of water supply development.

[0014] In a preferred embodiment, in step S4, when the dominant heat source type is mantle source and the water supply intensity level is medium or low, or when the dominant heat source type is shell source and the water supply intensity level is high, the target fault zone intersection area is classified as a Class B candidate target area. When the dominant heat source type is shell source and the water supply intensity level is medium or low, the intersection area of ​​the target fault zone is classified as a Class C general target area. When the dominant heat source type is mantle source and the water supply intensity level is high, the intersection area of ​​the target fault zone is classified as a Class A preferred target area.

[0015] The technical effects and advantages of this invention are as follows: This invention monitors the escape state of bubbles at the wellhead and automatically collects samples of the escaped gas and radon water when conditions are met. Mass spectrometry analysis is performed on the gas samples to calculate helium isotope ratios and identify the heat source type. Simultaneously, decay correction is applied to the radon concentration to obtain the initial radon concentration. Furthermore, the fluid circulation depth is derived by inverting the wellhead fluid temperature, and data interfered with by shallow cold water mixing is automatically identified and removed. Finally, spatial superposition analysis is conducted by integrating the initial radon concentration and sodium ion content of effective measuring points to identify the development direction of underground water supply faults. The target area classification results are output based on the dominant heat source type, reducing the impact of shallow mixed fluids on geochemical analysis results. This achieves independent identification of water supply channels based on geochemical evidence chains, improving the automation and reliability of geothermal resource exploration target area screening. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the implementation of a fluid geochemical characteristic fusion analysis method for geothermal resource evaluation according to the present invention.

[0017] Figure 2 This is a schematic diagram illustrating the steps of a fluid geochemical characteristic fusion analysis method for geothermal resource assessment according to the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention monitors the escape state of bubbles at the wellhead and automatically collects samples of the escaped gas and radon water when conditions are met. Mass spectrometry analysis is performed on the gas samples to calculate helium isotope ratios and identify the heat source type. Simultaneously, decay correction is applied to the radon concentration to obtain the initial radon concentration. Furthermore, the fluid circulation depth is derived by inverting the wellhead fluid temperature, and data interfered with by shallow cold water mixing is automatically identified and removed. Finally, spatial superposition analysis is conducted by integrating the initial radon concentration and sodium ion content of effective measuring points to identify the development direction of underground water supply faults. Target area classification results are output based on the dominant heat source type, reducing the impact of shallow mixed fluids on geochemical analysis results.

[0020] Example 1, such as Figures 1 to 2 As shown, a fluid geochemical characteristic fusion analysis method for geothermal resource assessment includes the following steps: Step S1: Collect bubble escape data from each wellhead measuring point in the intersection area of ​​the target fault zone and evaluate the fluid escape state. Based on the fluid escape state, determine whether to perform drainage gas collection and sampling treatment and obtain gas samples and radon water samples. Step S2: Perform mass spectrometry analysis on the gas sample and collect isotope ratio data. Calculate the mantle source contribution ratio based on the isotope ratio data and analyze the dominant heat source type. Detect the radon concentration in the radon gas water sample, perform radon decay correction on the radon concentration, and calculate the initial radon concentration. Step S3: Collect the current wellhead fluid temperature at each wellhead measuring point, invert the fluid circulation depth based on the initial radon concentration, screen and mark each wellhead measuring point according to the fluid circulation depth, and detect the sodium ion content at the marked wellhead measuring points; Step S4: Perform spatial overlay analysis on the sodium ion content and initial radon concentration at the wellhead measuring points, assess the water supply development characteristics based on the spatial overlay analysis results, and output the target area classification results of the target fault zone intersection area in combination with the dominant heat source type.

[0021] The specific implementation is as follows: In step S1, continuous monitoring is performed on each wellhead measuring point within the intersection area of ​​the target fault zone to obtain bubble escape data from each wellhead measuring point. The fluid escape state is assessed based on the bubble escape data, and it is determined whether to perform drainage and gas collection sampling based on the fluid escape state. When the sampling conditions are met, gas samples and radon water samples from the corresponding wellhead measuring points are acquired simultaneously to provide basic data for subsequent heat source type analysis and geochemical characteristic analysis.

[0022] The target fault zone intersection area refers to the subsurface structural area formed by the intersection or cutting of two or more regional faults, and is used as the target area for fluid geochemical monitoring and geothermal resource evaluation using this method. Wellhead monitoring points are fixed monitoring locations set at the outcrops of geothermal wells, hot springs, or natural hot springs within the target fault zone intersection area for continuous collection of fluid geochemical parameters. Each wellhead monitoring point corresponds to a unique spatial coordinate and number. Specifically, the scope of the target fault zone intersection area is determined based on the regional geological structure map. Then, combined with existing drilling data and spring distribution, wellheads with stable outflow conditions are selected as candidate locations. Subsequently, the position coordinates of each candidate wellhead are determined using a global positioning module, and a fixed monitoring point is established with the wellhead center as the reference. For the same wellhead, only one corresponding wellhead monitoring point is set to ensure a consistent spatial correspondence between data collected at different times.

[0023] Specifically, in-situ bubble flow monitoring devices are installed at each wellhead measuring point. The in-situ bubble flow monitoring devices use a combination of bubble image recognition unit and volumetric flow meter to continuously count the total volume of bubbles escaping from the wellhead per unit time and update the data once at a fixed sampling period, where the fixed sampling period is a preset data acquisition time interval.

[0024] It should be noted that the in-situ bubble flow monitoring device is a field detection device installed at the wellhead measuring point for real-time monitoring of the total volume and flow rate of bubbles escaping from the wellhead; the bubble image recognition unit is an industrial vision inspection module located outside the transparent observation cavity; and the volumetric flow meter is a gas volume measurement device installed at the outlet of the transparent observation cavity to detect the cumulative gas volume after the escaping gas passes through the observation cavity. When the wellhead fluid continuously escapes, the escaping bubbles first enter the transparent observation cavity. The bubble image recognition unit continuously identifies each bubble and calculates its corresponding volume, while the volumetric flow meter simultaneously measures the cumulative gas volume passing through the outlet. Real-time consistency checks are performed on the two sets of data. When the deviation is less than the preset allowable error, the cumulative volume of the volumetric flow meter is used as the final total bubble volume; when the deviation exceeds the allowable error, the output value of the volumetric flow meter is recalibrated based on the image recognition results, ultimately obtaining the total volume of bubbles escaping from the wellhead per unit time within the current sampling period.

[0025] Dividing the total volume of bubbles detected within the current sampling period by the duration of the sampling period yields the bubble escape flow rate corresponding to the wellhead measuring point. The bubble escape flow rate reflects the strength of gas release from deep underground fluids to the surface along the fracture channel. A higher value indicates that more deep gas is released per unit time, the underground fluid activity is more active, and there is a continuous migration process between the deep fluid and the surface; conversely, a lower value indicates weaker deep fluid activity or insufficient fracture conductivity.

[0026] To avoid misjudgments caused by instantaneous bubble disturbances, after obtaining the bubble escape flow rate for multiple consecutive sampling periods, the bubble escape flow rate within each consecutive sampling period is arithmetically averaged to obtain the average bubble escape flow rate. The average bubble escape flow rate reflects the overall stability of gas escape at the wellhead measuring point. The larger the value, the stronger the continuous gas escape capacity at the wellhead, the less affected by instantaneous fluctuations, and the more accurately it can characterize the continuous release state of underground fluids.

[0027] Subsequently, a preset escaping gas judgment threshold is invoked to compare and judge the average bubble escaping flow rate: When the average bubble escape flow rate is greater than or equal to the preset escape judgment threshold, the current wellhead measuring point is determined to be in an effective fluid escape state. When the average bubble escape flow rate is less than the preset escape judgment threshold, the current wellhead measuring point is determined to be in an invalid fluid escape state.

[0028] The preset gas escape judgment threshold is obtained based on the statistical data of historical wellhead gas escape monitoring in the target area. Specifically, the 95th percentile of the average bubble escape flow rate corresponding to the historical effective sampling wellhead is used as the judgment threshold, thereby ensuring that sampling is only carried out on wellheads with stable deep gas escape characteristics, and improving the reliability of subsequent analysis data.

[0029] Once the wellhead measuring point is determined to be in a state of effective fluid escape, the drainage gas collection sampling device is controlled to move to a preset depth below the liquid surface at the wellhead and the surface water at the wellhead is removed, allowing the escaped air bubbles to enter the sealed gas collection chamber. After gas-liquid separation is completed in the sealed gas collection chamber, the collected escaped gas is introduced into a vacuum gas collection bottle to form a gas sample.

[0030] It should be noted that the drainage gas collection sampling device is a closed sampling device used to collect gas escaping from the wellhead, including a lifting mechanism, a drainage unit, a closed gas collection chamber, and a gas guide pipeline; the vacuum gas collection bottle is a sealed gas storage container that has been pre-evacuated to a vacuum state, and its interior maintains a vacuum environment lower than the ambient pressure.

[0031] The entire sampling process is carried out in a closed environment to prevent outside air from mixing in and causing changes in the composition of rare gases such as helium and neon, thereby ensuring the authenticity of the isotope ratios obtained from subsequent mass spectrometry analysis.

[0032] Simultaneously, a vacuum diffusion sampling device is activated to collect radon-containing water samples. The vacuum diffusion sampling device draws the wellhead fluid into a sealed diffusion chamber, allowing the dissolved radon gas in the water to be fully released under a preset negative pressure condition, and then redissolved in a specified volume of standard sampling liquid, subsequently automatically sealed to form a radon-containing water sample.

[0033] It should be noted that the vacuum diffusion sampling device is a specialized sampling equipment used to extract dissolved radon from underground fluids. It consists of a sealed diffusion chamber, a negative pressure generator, a standard sampling liquid container, and an automatic packaging module.

[0034] The entire diffusion process is controlled by constant negative pressure and constant diffusion time to ensure that radon water samples collected from different wellhead measuring points have consistent extraction efficiency, providing a unified data basis for subsequent radon concentration detection.

[0035] After collecting gas and radon water samples, the built-in clock module is synchronously invoked to record the current sampling time and generate a corresponding sampling timestamp. The sampling timestamp represents the absolute time when the sample was completely sealed and collected. It serves as the time reference in the subsequent radon decay correction process, used to calculate the decay time between sample collection and experimental detection, thereby restoring the true radon concentration corresponding to the sampling time.

[0036] In step S2, mass spectrometry analysis is performed on the gas sample to obtain helium and neon isotope composition data. The contribution ratio of the mantle source is calculated based on the isotope ratio, and the dominant heat source type is analyzed. At the same time, radon concentration is detected in the radon gas water sample, and radon decay correction is completed in combination with the sampling timestamp to obtain the initial radon concentration at the corresponding sampling time, providing basic data for subsequent fluid circulation depth inversion.

[0037] Specifically, the gas sample was introduced into a rare gas mass spectrometer, and the abundance of He³ in the sample was detected under constant vacuum conditions. Abundance. Among them, ³He abundance refers to the helium-3 abundance detected in the sample, characterizing the dominant isotope originating from the deep mantle. The abundance is the helium-4 abundance detected in the sample, which originates from the radioactive decay process in the Earth's crust.

[0038] It should be noted that a rare gas mass spectrometer is an analytical instrument used to detect the composition of rare gas isotopes such as helium and neon in gas samples. It uses a vacuum ion source to ionize the sample gas into an ion beam, then separates the ions according to their mass-to-charge ratios, and uses an ion detector to statistically analyze the isotopes of He and neon. The corresponding ion signal intensity is then used to calculate the abundance and ratio of each isotope.

[0039] Calculate the abundance of He³ in a gas sample and The abundance ratios yield isotope ratio data. Isotope ratio data reflect the degree of mantle-derived fluid involvement in subsurface fluids. The higher the value, the higher the proportion of mantle-derived helium in the sample, and the more significant the contribution of deep mantle-derived material; conversely, it indicates that the fluid is mainly controlled by crustal origin.

[0040] Subsequently, the isotope ratio data was normalized by calling the preset atmospheric helium isotope standard values ​​to obtain the standardized isotope ratio values, the calculation expression of which is: ; in, To standardize isotope ratios, This is isotope ratio data. This is the standard value for atmospheric helium isotopes.

[0041] It should be noted that the standard values ​​of atmospheric helium isotopes refer to the values ​​of ³He and ³He in the modern standard atmosphere. An internationally unified reference value for abundance ratios is used to eliminate measurement differences caused by different instruments and experimental conditions.

[0042] The standardized isotope ratio eliminates the influence of different instrument ranges and experimental environments. The larger the value, the more significantly the sample deviates from the atmospheric composition and the higher the contribution of deep mantle-derived fluids.

[0043] Since natural geothermal fluids are typically a mixture of mantle-derived and crust-derived fluids, the mantle-derived contribution ratio is further calculated based on standardized isotope ratios using the two-terminal mixing method. The calculation expression is as follows: ; in, Contribution ratio to mantle source Normalized isotope ratios for mantle-derived endmembers. The isotope ratio is the shell-source endmember normalized value. To standardize isotope ratios.

[0044] It should be noted that the two-end-member mixing method is a geochemical mixing ratio calculation method. It assumes that subsurface fluids are formed by the mixing of two stable sources: mantle-derived fluid endmembers and crustal-derived fluid endmembers. The proportion of mantle-derived contribution is calculated based on the ratio of the standardized isotope ratios of the samples located between the two endmembers, thereby quantitatively evaluating the degree of mantle-derived material participation in subsurface fluids. The standardized isotope ratio of the mantle-derived endmembers refers to the standardized helium isotope ratio corresponding to typical mantle-derived fluids in the region. It represents the theoretical standard value of pure mantle-derived fluids and is obtained by statistical averaging of known magmatic hydrothermal samples in the region. The standardized isotope ratio of the crustal endmembers refers to the standardized helium isotope ratio corresponding to typical crustal-derived fluids in the region. It represents the theoretical standard value of pure crustal radiogenic fluids and is obtained by statistical averaging of known crustal-derived groundwater samples in the region.

[0045] The calculated mantle-derived contribution ratio is limited to between 0 and 1. When the result is greater than 1, it is taken as 1, and when the result is less than 0, it is taken as 0. The mantle-derived contribution ratio reflects the degree of contribution of mantle volatiles to underground fluids. The larger the value, the stronger the effect of deep magmatic activity on fluid supply; the smaller the value, the more the fluid mainly originates from crustal radioactive decay and shallow groundwater circulation.

[0046] After calculating the mantle-derived contribution ratio, the dominant heat source type is analyzed based on a preset heat source identification threshold. The preset heat source identification threshold is established based on the statistical analysis of heat source types in known geothermal fields in the region, with the average mantle-derived contribution ratio of known mantle-derived hydrothermal samples used as the judgment criterion.

[0047] When the proportion of mantle source contribution is greater than or equal to the preset heat source identification threshold, the dominant heat source type of the current wellhead measuring point is determined to be mantle source type. When the proportion of mantle source contribution is less than the preset heat source identification threshold, the dominant heat source type of the current wellhead measuring point is determined to be shell source type.

[0048] The dominant heat source type reflects the main source of underground thermal energy, and its results serve as an important basis for determining the development type of the target area.

[0049] Simultaneously, radon gas samples were sent to a radon concentration detector for analysis. The detector uses alpha particle counting to count the number of alpha particles produced by radon decay per unit volume of water sample, and automatically calculates the measured radon concentration at the current detection time based on the instrument's calibration curve. The measured radon concentration reflects the residual radon activity level in the water sample at the detection time; a higher value indicates more radioactive radon retained in the current water sample. However, because radon continues to undergo radioactive decay after sampling, the measured radon concentration does not accurately reflect the radon concentration in the underground fluid at the time of sampling.

[0050] It should be noted that the radon concentration detector is a radioactive measuring device used to detect the radon activity concentration in radon-containing water samples. It includes a degassing unit, a detection chamber, an alpha particle detector, and a data processing module. During the detection process, radon is first released from the water sample into the detection chamber. Then, the alpha particle detector counts the number of alpha particles produced by radon decay per unit time. The alpha particle counting method calculates radon activity based on the number of alpha particles released from the decay of radon and its progeny. The detector records the alpha particle count per unit time, and the corresponding radon concentration is calculated by combining this count with the instrument's calibration curve.

[0051] Therefore, the sampling timestamp is read, and the detection timestamp corresponding to the current moment when the radon concentration detection is completed is recorded. The sampling timestamp is subtracted from the detection timestamp to calculate the sample preservation time. The sample preservation time reflects the length of time from the completion of sample collection to the completion of detection. The larger the value, the higher the degree of natural radon decay, and the greater the decay compensation required.

[0052] Subsequently, based on the radioactive decay law of radon, the measured radon concentration was corrected for radon decay using the sample storage time to restore the initial radon concentration corresponding to the sampling time. The calculation expression is as follows: ; in, This represents the initial radon concentration. To measure radon concentration, The preset radon decay constant, This refers to the sample storage time.

[0053] It should be noted that the radon decay constant is a physical constant describing the natural radioactive decay rate of radon, which is derived from the radioactive decay law of radon-222.

[0054] The initial radon concentration reflects the actual radon activity level carried by the underground fluid at the time of sampling. The higher the value, the longer the contact time between the underground fluid and the deep uranium- or radium-bearing strata, and the more obvious the deep circulation. It also indicates that the underground fluid has a stronger ability to carry radioactive gases during its migration along the fracture channel. Therefore, it can more realistically reflect the characteristics of the deep underground circulating fluid.

[0055] In step S3, the current wellhead fluid temperature refers to the fluid temperature measured by the wellhead temperature measuring device after the drainage and gas collection sampling operation is completed and the wellhead fluid outflow is stable.

[0056] It should be added that the wellhead temperature measuring device is a contact-type high-temperature temperature measuring instrument adapted to the wellhead pipe of hot spring / geothermal wells. In this case, it is used to continuously read the wellhead fluid temperature within the time window from the end of drainage and gas collection to the first batch of samples being sent for testing.

[0057] Specifically, when the cumulative drainage time of drainage gas collection sampling reaches the preset drainage stabilization time, it is determined that the wellhead fluid has switched to a deep source-dominated state, triggering the collection of the current wellhead fluid temperature; The data acquisition time window starts from this moment and continues for a preset stable temperature reading duration. The arithmetic mean of the readings from the wellhead temperature measuring device within this window is taken as the current wellhead fluid temperature.

[0058] The preset drainage stabilization time and preset temperature stabilization reading time are determined based on the wellbore volume of existing geothermal wells in the target fault zone intersection area and the median value of the stable water production flow rate of a single well, which will not be elaborated here.

[0059] Using the current wellhead fluid temperature and initial radon concentration as inversion inputs, the fluid circulation depth at each wellhead measuring point is inverted. The inversion formula is as follows: ; Where D is the fluid circulation depth. The current wellhead fluid temperature, The temperature of the surface isothermal layer is taken as the multi-year average air temperature of the area where the target fault zone intersects, and G is the regional geothermal gradient. This represents the initial radon concentration. The radon concentration for shallow cold water is the statistical mean of the radon concentration in shallow cold water wells in the vicinity of the target fault zone without geothermal background. α is the temperature coupling weighting coefficient, which is dimensionless, and β is the radon coupling weighting coefficient, with the unit being m.

[0060] Fluid circulation depth refers to the maximum vertical reciprocating distance of the hot fluid in the target fault zone intersection area as it travels up to the wellhead front, infiltrates down the fault, heats up, and returns. It reflects the extent to which the fluid undergoes deep heating and interacts with water and rock.

[0061] The regional geothermal gradient was obtained by: constructing data pairs based on well depth and temperature from wells below the isothermal layer in existing wells surrounding the intersection of the target fault zone, and then performing univariate linear regression using the least squares method. The slope obtained from the regression is taken as G, where z is the well depth and T is the logging temperature at the corresponding well depth. This is the intercept.

[0062] The temperature coupling weighting coefficient and the radon coupling weighting coefficient are determined as follows: Several calibration wells around the intersection of the target fault zone, whose fluid circulation depth has been confirmed by hydrological drilling or geophysical data, are selected as calibration samples; for each calibration sample, the following is used: Item and The terms are the independent variables, and the known fluid circulation depth is the dependent variable. The least squares regression method is used to obtain α and β.

[0063] By employing the least squares regression method, the estimation of the linear superposition weights under small sample calibration conditions exhibits the minimum variance property, stably separating the contributions of the temperature and radon terms to the fluid circulation depth without introducing additional regularization terms.

[0064] The higher the current wellhead fluid temperature, the greater the initial radon concentration, and the greater the fluid circulation depth, the more it reflects that the fluid corresponding to the wellhead measuring point has undergone deeper circulation heating and has a longer contact time with the uranium- and radium-bearing surrounding rock before ascending to the wellhead, which is closer to the deep original state without shallow cold water mixing.

[0065] Compare the fluid circulation depth at each wellhead measuring point with the fluid circulation depth screening threshold: When the fluid circulation depth is greater than or equal to the fluid circulation depth screening threshold, it is determined that the fluid corresponding to the wellhead measuring point is mainly deep circulating hot water, and the wellhead measuring point is marked. Conversely, if the wellhead measuring point is determined to have significant shallow cold water mixing interference, and its conventional inorganic salt indicators can no longer accurately characterize the deep reservoir information, it will not be marked.

[0066] It should be noted that the method for determining the fluid circulation depth screening threshold is as follows: search the historical drilling database of the geothermal field where the target fault zone intersection area is located, and search for all wells with exposed geothermal reservoirs and stable daily water production per well. Calculate the corresponding fluid circulation depth of each well according to the above inversion formula to obtain a fluid circulation depth sequence. Take the lower quartile of this sequence as the fluid circulation depth screening threshold.

[0067] The sodium ion content of each marked wellhead measuring point was detected: another water sample collected in the same well and at the same time as the radon gas water sample in step S1 was sent to an ion chromatograph to determine the sodium ion concentration in the fluid, and the obtained concentration value was taken as the sodium ion content of the corresponding marked wellhead measuring point.

[0068] Sodium ion content reflects the cumulative degree of water-rock interaction between the fluid and the sodium-bearing feldspar surrounding rock along the water-conducting channel. The higher the content, the more developed the water-rock exchange channel and the smoother the replenishment path of the fluid.

[0069] In step S4, the sodium ion content and initial radon concentration at all marked wellhead measuring points are normalized using the interval scaling method, and the calculation formula is as follows: ; ; in, The normalized value of sodium ions at the i-th marked wellhead measuring point; The initial normalized radon value for the i-th marked wellhead measuring point; , These represent the sodium ion content and initial radon concentration at the i-th marked wellhead measuring point, respectively. , These are the minimum and maximum sodium ion contents at all marked wellhead measuring points within the intersection zone of the target fault zone; , These are the minimum and maximum initial radon concentrations at all marked wellhead measuring points within the intersection zone of the target fault zone.

[0070] For any two marked wellhead measuring points, calculate the spatial overlap coefficient between them using the following formula: ; in, To mark the spatial overlap coefficient between wellhead measuring points i and j; The Euclidean distance between wellhead measuring points i and j projected onto the Earth's surface is calculated from the GPS coordinates of each wellhead measuring point. The distance represents the spatial attenuation characteristic.

[0071] The spatial overlap coefficient reflects the possibility that two marked wellhead measuring points are located on the same water-conducting structure and are supplied by the same water supply path.

[0072] The spatial attenuation characteristic distance is determined as follows: the average length of the main fault segment is measured on the existing regional tectonic interpretation map of the target fault zone intersection area, and one-third of it is taken as the spatial attenuation characteristic distance.

[0073] Compare the spatial overlap coefficients between all pairs of marked wellhead measuring points with the spatial overlap coefficient threshold: When the spatial superposition coefficient is greater than or equal to the spatial superposition coefficient threshold, it is determined that there is a significant water supply co-source relationship between the two corresponding marked wellhead measuring points, and it is preserved in the form of a connecting edge on the surface plane projection map. When the spatial overlap coefficient is less than the spatial overlap coefficient threshold, it is determined that the two corresponding wellhead measuring points do not belong to the same water supply path, and the connection edge is not retained.

[0074] The spatial overlap coefficient threshold is determined as follows: sort the spatial overlap coefficients of all marked wellhead measuring points in the intersection area of ​​the target fault zone from largest to smallest, and take the upper quartile of the sequence as the spatial overlap coefficient threshold.

[0075] Construct a graph structure from all the remaining connecting edges and their endpoints, and extract the largest connected subgraph containing the most marked wellhead measuring points. Perform principal component analysis on the surface plane coordinates of all marked wellhead measuring points in the largest connected subgraph, and use the azimuth of the unit direction vector corresponding to the first principal component in the surface plane as the direction of the water supply fault in the intersection area of ​​the target fault zone.

[0076] The strike of the water supply fault refers to the azimuth angle of the extension of the hidden fault that undertakes the function of deep hot water supply and conduction in the intersection area of ​​the target fault zone under the surface plane projection, which is independent of the fault strike obtained by existing geophysical interpretation.

[0077] The water supply intensity level is assessed based on the arithmetic mean of the normalized sodium ion values ​​at all marked wellhead measuring points in the maximally connected subgraph. The formula for calculating this arithmetic mean is as follows: ,in, is the arithmetic mean of the normalized sodium ion values ​​at all marked wellhead measuring points in the maximum connected subgraph; N is the number of marked wellhead measuring points in the maximum connected subgraph. is the normalized value of sodium ions at the i-th marked wellhead measuring point.

[0078] when When the water supply intensity level is greater than or equal to the high threshold, the water supply intensity level will be marked as high. when When the water supply intensity level is greater than or equal to the low threshold and less than the high threshold, the water supply intensity level is marked as medium. when When the water supply intensity is below the low threshold, the water supply intensity level will be marked as low.

[0079] The high and low thresholds for water supply intensity are determined as follows: For water supply fracture samples in the exploited geothermal fields where the target fracture zone intersects, whose water conductivity levels (strong, medium, and weak) have been confirmed through pumping tests, the arithmetic mean of their corresponding sodium ion normalized values ​​is calculated according to the normalization method in this step, resulting in the median values ​​for the strong, medium, and weak water supply fracture sample groups. The arithmetic mean of the median values ​​of the strong and medium water supply fracture sample groups is taken as the high threshold for water supply intensity, and the arithmetic mean of the median values ​​of the medium and weak water supply fracture sample groups is taken as the low threshold for water supply intensity.

[0080] The orientation of water supply faults and the level of water supply intensity together constitute the characteristics of water supply development, reflecting the degree of development maturity of the "connectivity" element in the intersection area of ​​the target fault zone.

[0081] When the dominant heat source type is mantle source and the water supply intensity level is medium or low, or when the dominant heat source type is crust source and the water supply intensity level is high, the intersection area of ​​the target fault zone is classified as a Class B candidate target area, indicating that at least one of the two elements of "source" and "connection" is satisfied, and the other element needs to be confirmed through supplementary exploration. When the dominant heat source type is shell source and the water supply intensity level is medium or low, the intersection area of ​​the target fault zone is classified as a Class C general target area, indicating that neither its heat source nor water conduit has met the preferred criteria, and subsequent geothermal drilling well locations are not prioritized.

[0082] When the dominant heat source type is mantle source and the water supply intensity level is high, the intersection area of ​​the target fault zone is classified as a Class A preferred target area, indicating that both the "source" and "connection" elements meet the preferred criteria, and subsequent geothermal drilling well locations are prioritized.

[0083] Based on the comprehensive analysis results of the above-mentioned dominant heat source types and water supply development characteristics, the target area classification results of the intersection of the target fault zones are output, and they are used as the basis for decision-making on the deployment of well locations for subsequent geothermal resource development.

[0084] Finally, it should be noted that in this paper, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0085] Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0086] In this document, the singular forms “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that terms such as “comprising / including” or “having” specify the presence of the stated features, integrals, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, integrals, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0087] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0088] The above description of the disclosed embodiments will enable those skilled in the art to make or use various modifications to these embodiments. It will be readily apparent to those skilled in the art that the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A fluid geochemical characteristic fusion analysis method for geothermal resource assessment, characterized in that: Includes the following steps: Step S1: Collect bubble escape data from each wellhead measuring point in the intersection area of ​​the target fault zone and evaluate the fluid escape state. Based on the fluid escape state, determine whether to perform drainage gas collection and sampling treatment and obtain gas samples and radon water samples. Step S2: Perform mass spectrometry analysis on the gas sample and collect isotope ratio data. Calculate the mantle source contribution ratio based on the isotope ratio data and analyze the dominant heat source type. Detect the radon concentration in the radon gas water sample, perform radon decay correction on the radon concentration, and calculate the initial radon concentration. Step S3: Collect the current wellhead fluid temperature at each wellhead measuring point, invert the fluid circulation depth based on the initial radon concentration, screen and mark each wellhead measuring point according to the fluid circulation depth, and detect the sodium ion content at the marked wellhead measuring points; Step S4: Perform spatial overlay analysis on the sodium ion content and initial radon concentration at the wellhead measuring points, assess the water supply development characteristics based on the spatial overlay analysis results, and output the target area classification results of the target fault zone intersection area in combination with the dominant heat source type.

2. The fluid geochemical characteristic fusion analysis method for geothermal resource assessment according to claim 1, characterized in that: In step S1, the target fault zone intersection area refers to the underground structural area formed by the intersection or cutting of two or more regional faults. Wellhead monitoring points refer to fixed monitoring locations set at geothermal wells, hot spring wells, or natural hot springs in the intersection area of ​​the target fault zone for the continuous collection of fluid geochemical parameters. In-situ bubble flow monitoring devices are installed at each wellhead measuring point to continuously count the total volume of bubbles escaping from the wellhead per unit time. Divide the total volume of bubbles detected within the current sampling period by the duration of the sampling period to obtain the bubble escaping flow rate corresponding to the wellhead measuring point.

3. The fluid geochemical characteristic fusion analysis method for geothermal resource assessment according to claim 2, characterized in that: In step S1, the bubble escaping flow rate within the continuous sampling period is arithmetically averaged to obtain the average bubble escaping flow rate. When the average bubble escape flow rate is greater than or equal to the preset escape judgment threshold, the current wellhead measuring point is determined to be in an effective fluid escape state. Otherwise, the current wellhead measuring point is determined to be in an invalid fluid escape state; Once the wellhead measuring point is determined to be in an effective fluid escape state, the drainage gas collection sampling device is controlled to move to a preset depth below the wellhead liquid surface and the surface water of the wellhead is removed, allowing the escaped air bubbles to enter the sealed gas collection chamber. After gas-liquid separation is completed in the sealed gas collection chamber, the collected escaped gas is introduced into the vacuum gas collection bottle to form a gas sample. At the same time, a vacuum diffusion sampling device was activated to collect radon gas water samples.

4. The fluid geochemical characteristic fusion analysis method for geothermal resource assessment according to claim 3, characterized in that: In step S2, the gas sample is introduced into a rare gas mass spectrometer, and the abundance of He³ in the sample is detected under constant vacuum conditions. Abundance; Calculate the abundance of He³ in a gas sample and The abundance ratio is used to obtain isotope ratio data. The isotope ratio data is then normalized to obtain standardized isotope ratios. Based on standardized isotope ratios, the mantle source contribution ratio was calculated using the two-terminal mixing method. When the proportion of mantle source contribution is greater than or equal to the preset heat source identification threshold, the dominant heat source type of the current wellhead measuring point is determined to be mantle source type. When the proportion of mantle source contribution is less than the preset heat source identification threshold, the dominant heat source type of the current wellhead measuring point is determined to be shell source type.

5. The fluid geochemical characteristic fusion analysis method for geothermal resource assessment according to claim 4, characterized in that: In step S2, the radon gas water sample is sent to a radon concentration detector for detection, and the measured radon concentration at the current detection time is obtained by using alpha particle counting. Read the sampling timestamp and record the detection timestamp corresponding to the current time when the radon concentration detection is completed. Subtract the sampling timestamp from the detection timestamp to calculate the sample storage time. Based on the radioactive decay law of radon, the measured radon concentration is corrected for radon decay by using the sample storage time, and the initial radon concentration corresponding to the sampling time is restored.

6. The fluid geochemical characteristic fusion analysis method for geothermal resource assessment according to claim 1, characterized in that: In step S3, when the cumulative drainage time of drainage gas collection sampling reaches the preset drainage stabilization time, the current wellhead fluid temperature is collected. Using the current wellhead fluid temperature and initial radon concentration as inversion inputs, the fluid circulation depth at each wellhead measuring point is inverted using a weighted algorithm to obtain the fluid circulation depth. Compare the fluid circulation depth at each wellhead measuring point with the fluid circulation depth screening threshold: When the fluid circulation depth is greater than or equal to the fluid circulation depth screening threshold, the wellhead measuring point is marked. Conversely, the wellhead measuring points are not marked; The sodium ion content of each marked wellhead measuring point was tested: another water sample collected in the same well and at the same time as the radon water sample in step S1 was taken, and its sodium ion concentration was obtained as the sodium ion content of the corresponding marked wellhead measuring point.

7. The fluid geochemical characteristic fusion analysis method for geothermal resource assessment according to claim 1, characterized in that: In step S4, the sodium ion content and initial radon concentration at the marked wellhead measuring point are normalized using the interval scaling method to obtain the normalized sodium ion value and the normalized initial radon value. Calculate the spatial overlap coefficient between any two marked wellhead measuring points; Compare the spatial superposition coefficient with the spatial superposition coefficient threshold: When the spatial superposition coefficient is greater than or equal to the spatial superposition coefficient threshold, the corresponding two marked wellhead measuring points are retained on the surface plane projection map in the form of connecting edges. Conversely, the connection edge between the two marked wellhead measuring points is not retained; Construct a graph structure from all the retained connecting edges and their endpoints, and extract the largest connected subgraph that contains the most marked wellhead measuring points.

8. The fluid geochemical characteristic fusion analysis method for geothermal resource assessment according to claim 7, characterized in that: In step S4, principal component analysis is performed on the surface plane coordinates of all marked wellhead measuring points in the maximum connected subgraph, and the azimuth of the unit direction vector corresponding to the first principal component in the surface plane is taken as the direction of the water supply fault in the intersection area of ​​the target fault zone. The arithmetic mean of the normalized sodium ion values ​​at all marked wellhead measuring points in the maximally connected subgraph is denoted as . ; when When the water supply intensity level is greater than or equal to the high threshold, the water supply intensity level will be marked as high. when When the water supply intensity level is greater than or equal to the low threshold and less than the high threshold, the water supply intensity level is marked as medium. when When the water supply intensity is less than the low threshold, the water supply intensity level will be marked as low. The orientation of water supply faults and the level of water supply intensity together constitute the characteristics of water supply development.

9. A fluid geochemical characteristic fusion analysis method for geothermal resource assessment according to claim 8, characterized in that: In step S4, when the dominant heat source type is mantle source and the water supply intensity level is medium or low, or when the dominant heat source type is shell source and the water supply intensity level is high, the intersection area of ​​the target fault zone is classified as a Class B candidate target area. When the dominant heat source type is shell source and the water supply intensity level is medium or low, the intersection area of ​​the target fault zone is classified as a Class C general target area. When the dominant heat source type is mantle source and the water supply intensity level is high, the intersection area of ​​the target fault zone is classified as a Class A preferred target area.

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