Method for quickly delineating geothermal target area based on chemical characteristics of surface water

Abstract

The present application belongs to the technical field of geothermal resource exploration, and particularly relates to a method for quickly delineating a geothermal target area based on chemical characteristics of surface water. + + 2+ 2+ ‑ 2‑ ‑ , SiO2, TDS and pH; based on the water chemical parameters, Na-K geothermal temperature scale values and SiO2 geothermal temperature scale values are calculated, and candidate abnormal sample points meeting the consistency condition of the double temperature scales are screened; combined with Cl ‑ , TDS, water temperature and the double temperature scale results, a surface water hydrothermal fluid influence abnormal index is constructed, and spatial continuity of the abnormal index is identified to form an abnormal zone; then, the abnormal zone and a fracture structure buffer zone are spatially superimposed to delineate the geothermal target area. The present application can quickly identify a potential hydrothermal fluid activity area using surface water chemical abnormalities in a large-scale general survey stage, and has the advantages of low cost, high efficiency and strong applicability.​​​​​​

Description

Technical Field

[0001] This invention belongs to the field of geothermal resource exploration technology, specifically relating to a method for rapidly delineating geothermal target areas based on the chemical characteristics of surface water. Background Technology

[0002] Geothermal resources, as a clean, stable, and renewable energy source, have broad application prospects in heating, power generation, agricultural use, and industrial applications. The key to geothermal resource exploration lies in rapidly identifying potential hydrothermal activity zones and favorable geothermal reservoirs, thereby providing target area information for subsequent geophysical exploration, drilling, and resource assessment.

[0003] Existing geothermal exploration methods mainly include geophysical exploration, drilling verification, geochemical exploration, and comprehensive evaluation of multi-source information. Among these, drilling verification offers high accuracy but is costly and time-consuming; geophysical methods can reflect underground structures and reservoir conditions, but often involve high investment and significant interpretability issues in large-scale surveys; geochemical methods, on the other hand, can indirectly reflect underground hydrothermal activity through changes in the composition of fluid media, thus possessing high application value in rapid geothermal resource exploration.

[0004] During the surface water cycle, if deep hydrothermal fluids rise along fractures and fissures and mix with shallow water, it usually leads to abnormal changes in surface water in terms of temperature, ionic composition, dissolved silica content, and total dissolved solids. Therefore, using the chemical characteristics of surface water to identify potential hydrothermal influence zones is feasible for rapidly delineating geothermal target areas.

[0005] However, common approaches in existing technologies typically focus on the following categories: one is using geothermal temperature scales to estimate reservoir temperature; another is using GIS or ArcGIS technology for spatial evaluation of geothermal resources; and yet another is using multi-source data such as remote sensing, geophysics, and geochemistry to predict favorable geothermal areas or target areas. While each of these approaches has its value, in large-scale survey scenarios, relying directly on comprehensive analysis of multi-source data often results in high data requirements, implementation complexity, and high costs; conversely, using only a single temperature scale or a single spatial analysis method can easily lead to unstable judgments and a high rate of misjudgment.

[0006] Therefore, it is necessary to provide a rapid delineation method that takes the chemical characteristics of surface water as the main line and integrates sampling layout, water chemical detection, dual temperature scale consistency judgment, hydrothermal influence anomaly identification, extraction of spatial continuous anomaly zones, and fracture structure coupling verification into a linked process, so as to improve the efficiency of geothermal target area identification and enhance its practicality for the general survey stage. Summary of the Invention

[0007] (a) Technical problems to be solved The purpose of this invention is to provide a method for rapidly delineating geothermal target areas based on surface water chemical characteristics, in order to solve the problems of high dependence on multi-source data, insufficient utilization of surface water chemical information, and low target area identification efficiency in the large-scale rapid survey stage in the existing technology.

[0008] (II) Technical Solution To achieve the above objectives, the present invention adopts the following technical solution: A method for rapidly delineating geothermal target areas based on surface water chemical characteristics includes the following steps: Step 1: Obtain basic data for the study area Data on the study area's extent, topography, drainage system distribution, and fault structures were acquired. The fault structure data was used for subsequent tectonic channel identification and target area verification.

[0009] Step 2: Grid division of the study area and layout of sampling points Based on the area, water system development, and geomorphological conditions of the study area, a regular grid was divided into the study area. Preferably, the grid side length is 1km to 5km.

[0010] Surface water sampling points are set up within each grid cell, with priority given to the following locations: 1. Near a fracture structure; 2. The spring and its surrounding area; 3. Location of the valley's water catchment area; 4. Locations with relatively abnormal water temperatures.

[0011] Ideally, 1 to 3 surface water sampling points should be set up within each grid cell. During sampling, the latitude and longitude coordinates, elevation, water temperature, sampling time, and water type of each sampling point should be recorded. The water type includes one or more of the following: spring water, river water, lake water, valley stream water, and shallow seepage water.

[0012] Step 3: Surface water sampling and water chemical analysis Experimental testing was conducted on the collected surface water samples to obtain the following water chemical parameters: Na + K + Ca 2+ Mg 2+ Cl - SO4 2- HCO3 - SiO2, TDS and pH.

[0013] Of the parameters mentioned above, Na + K + And SiO2 is used for geothermal temperature scale calculation, Cl -TDS and water temperature are used to reflect the degree of hydrothermal influence and anomalous characteristics.

[0014] Step 4: Geothermal temperature scale calculation and candidate anomaly point screening The Na-K geothermal temperature scale and SiO2 geothermal temperature scale were calculated based on the aforementioned hydrochemical parameters to characterize the underground thermal reservoir temperature information.

[0015] Preferably, the Na-K geothermal temperature scale value can be calculated using the following formula: T1 = 1217 / [log(Na / K) + 1.483] - 273 The geothermal temperature scale value of SiO2 can be calculated using the following formula: T2 = 1309 / [5.19 - log(SiO2)] - 273 Where Na, K, and SiO2 represent the concentrations of the corresponding chemical components.

[0016] Based on the comparison results of T1 and T2, candidate anomalous sample points that meet the dual-temperature scale consistency condition are selected. The dual-temperature scale consistency condition means that the difference between T1 and T2 is within a preset consistency range. When a surface water sample point simultaneously shows a high geothermal reservoir temperature indication and the dual-temperature scale results are close to each other, it indicates that the sample point is more likely to be affected by deep hydrothermal activity.

[0017] Step 5: Construct anomaly indices for the impact of surface hydrothermal fluids Based on candidate anomaly sampling points, a surface water hydrothermal influence anomaly index is constructed to comprehensively characterize the degree to which surface water is affected by deep hydrothermal activity.

[0018] The surface hydrothermal fluid impact anomaly index is preferably composed of at least three of the following factors: 1. Na-K geothermal temperature scale index; 2. SiO2 geothermal temperature scale index; 3. Cl - Concentration index; 4. TDS index; 5. Water temperature index.

[0019] If necessary, HCO3 can also be introduced. - Index, pH index, or other auxiliary factors related to hydrothermal activity.

[0020] To eliminate the influence of different dimensions, the factors are standardized. The preferred standardization method is any one of range standardization, Z-score standardization, or quantile standardization.

[0021] Preferably, when range standardization is used, the calculation formula is: X' = ​​(X - Xmin) / (Xmax - Xmin) After obtaining the standardized results, the factors can be weighted and summed according to the preset weights to form the surface hydrothermal influence anomaly index.

[0022] Step 6: Identification of Spatial Continuity of Anomaly Index Based on the surface hydrothermal anomaly index, spatial analysis was conducted on the study area to identify continuously distributed high-value anomaly zones.

[0023] Preferably, spatial analysis is performed using a GIS platform, and anomaly index distribution maps can be generated using Kriging interpolation, inverse distance weighting, or spline function interpolation.

[0024] Compared with single anomalous points, spatially continuous high-value anomaly zones better reflect the spatial characteristics of hydrothermal activity rising along tectonic channels and having a continuous impact on surface water bodies, and therefore can serve as an important basis for subsequent target area delineation.

[0025] Step 7: Coupled analysis of fracture structure and delineation of target area Based on the fault structure data of the study area, buffer zones are established for the main fault structures. The extent of the buffer zones can be determined according to the fault level, extension scale, regional geological background, and range of influence.

[0026] By spatially superimposing the anomaly zone and the fault tectonic buffer zone, the corresponding area is identified as a geothermal target area when the following conditions are met: 1. The sampling points meet the consistency requirements of the two temperature scales; 2. The surface hydrothermal anomaly index shows a continuous high-value band; 3. Continuous high-value zones are adjacent to or spatially overlap with fault structures in buffer zones.

[0027] This enables the rapid delineation of geothermal target areas using the chemical characteristics of surface water.

[0028] (III) Beneficial Effects Compared with the prior art, the present invention has the following beneficial effects: 1. This invention can complete the initial screening of geothermal target areas by relying only on surface water chemical characteristics and basic structural data, reducing the dependence on remote sensing, geophysical exploration and borehole data, and is suitable for areas with weak data and large-scale survey stages.

[0029] 2. This invention integrates surface water sampling deployment, water chemical detection, dual temperature scale consistency judgment, anomaly index construction, spatial continuity identification, and fracture structure coupling verification into a linked process, which can improve the systematicness and reliability of target area identification.

[0030] 3. This invention reduces the instability caused by the use of a single temperature scale by combining the Na-K geothermal temperature scale and the SiO2 geothermal temperature scale, thereby improving the reliability of the geothermal storage temperature indication results.

[0031] 4. This invention identifies the spatial continuity of anomaly indices, avoiding judgment based solely on discrete anomaly points, which helps improve the accuracy of geothermal target area delineation.

[0032] 5. This invention is applicable to large-scale and rapid investigation of geothermal resources, and can provide preferred areas for subsequent geophysical verification, drilling deployment and resource evaluation. It has the advantages of low implementation cost, high efficiency and strong scalability. Attached Figure Description

[0033] Figure 1 This is a flowchart of the method of the present invention; Figure 2 A schematic diagram of the grid layout of surface water sampling points in the study area; Figure 3 A schematic diagram for identifying geothermal anomaly zones and delineating geothermal target areas. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the following embodiments.

[0035] Example 1: A geothermal resource survey was conducted in a mountainous area, with a study area of ​​approximately 120 km². 2 The area has well-developed fault structures and numerous springs and valley streams. First, topographic, hydrological, and fault structure distribution data of the study area were obtained, and the area was divided into 2km × 2km grid units.

[0036] Surface water sampling points were set up within each grid cell, totaling 72 sampling points. Sampling points were preferentially located near faults, springs, gully catchment areas, and locations of localized anomalous water temperatures. During the sampling process, the latitude, longitude, water temperature, elevation, and water type information of each sampling point were recorded.

[0037] Experimental testing was conducted on the collected surface water samples, and the results showed that: Na + The concentration is 30 mg / L to 45 mg / L. K + The concentration is 5 mg / L to 8 mg / L. Ca 2+ The concentration is 17 mg / L to 21 mg / L. Mg 2+ The concentration is 5.5 mg / L to 6.5 mg / L. Cl- The concentration is 40 mg / L to 50 mg / L. The SiO2 concentration is 35 mg / L to 45 mg / L. TDS ranges from 280 mg / L to 360 mg / L.

[0038] Based on the detection results, the Na-K geothermal temperature scale values ​​and SiO2 geothermal temperature scale values ​​were calculated respectively. The results showed that the two types of temperature scale results of some sample points had good consistency and met the conditions for candidate abnormal sample points.

[0039] Further, using the Na-K geothermal temperature scale index, SiO2 geothermal temperature scale index, and Cl... - Concentration index, TDS index, and water temperature index were used to construct anomaly indices for surface hydrothermal influence. After standardization of each factor, spatial interpolation analysis was performed using GIS to generate anomaly index distribution maps. The results show that continuous high-value anomaly zones are formed along the fault zone in the northern and central parts of the study area.

[0040] Finally, the continuous high-value anomaly zone was overlaid with the fault structure buffer zone for analysis. Two regions were identified that simultaneously met the conditions of dual-temperature scale consistency, continuous anomaly zone distribution, and proximity to fault structure channels. These were ultimately designated as preferred thermal target areas, with areas of approximately 4.2 km². 2 and 3.6km 2 .

[0041] Example 2: A rapid geothermal resource survey was conducted in a basin area, covering approximately 80 km². 2 The area contains several hidden faults. The study area was divided into a 2km × 2km grid, with a total of 50 surface water sampling points set up. The sampling objects included river water and shallow seepage water.

[0042] After testing the collected surface water samples, the Na-K geothermal temperature scale values ​​and SiO2 geothermal temperature scale values ​​were calculated, and candidate anomaly points were screened based on the consistency of the two temperature scales. This was then combined with Cl... - An anomaly index of surface hydrothermal influence was constructed using indicators such as TDS and water temperature, and interpolation analysis was performed on a GIS platform.

[0043] Analysis results indicate that high-value anomaly indices are mainly distributed in the fault intersection area in the northern part of the basin, forming a relatively continuous anomaly zone. By overlaying this anomaly zone with the fault buffer zone, a key geothermal target area of ​​approximately 3.8 km² was delineated. 2 .

[0044] Example 3: A verification experiment was conducted in a fault-rich area, covering an area of ​​approximately 60 km². 2 A total of 38 surface water sampling points were set up, and the sampling objects were mainly spring water and shallow seepage water distributed along the main fault and secondary fault.

[0045] After conducting hydrochemical tests on samples from each sampling point, the Na-K geothermal thermoscale values ​​and SiO2 geothermal thermoscale values ​​were calculated, and candidate anomalous sampling points were screened based on the consistency of the two thermoscales. Subsequently, a surface hydrothermal influence anomaly index was constructed, and a continuous high-value anomaly zone distributed in a band along a north-trending fault was identified through spatial analysis.

[0046] Further spatial overlay of the continuous high-value anomaly zone with the fault tectonic buffer zone ultimately delineated a potential geothermal target area with an area of ​​approximately 2.7 km². 2 .

[0047] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. All equivalent substitutions, improvements, and modifications made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for rapidly delineating geothermal target areas based on surface water chemical characteristics, characterized in that, Includes the following steps: S1. Obtain basic data of the study area, including at least the scope of the study area, topographic and geomorphological data, water system distribution data, and fault structure data; S2. Divide the study area into grids and prioritize the placement of surface water sampling points near fault structures, springs, valley catchment locations, or locations with abnormal water temperatures. Collect surface water samples from the sampling points and record the coordinates, water temperature, elevation, and water type information of the sampling points. S3. Perform water chemistry analysis on the surface water sample to obtain information including Na. + K + Ca 2+ Mg 2+ Cl - SO4 2- HCO3 - Water chemical parameters including SiO2, TDS and pH; S4. Calculate the Na-K geothermal temperature scale value and the SiO2 geothermal temperature scale value according to the water chemical parameters, and screen candidate abnormal sample points that meet the dual temperature scale consistency condition. S5, Cl based on candidate anomaly samples - The surface hydrothermal influence anomaly index was constructed using TDS, water temperature, and dual temperature scale results. The anomaly index was then standardized and its spatial continuity was identified to form anomaly zones. S6. The anomalous zone and the fracture structure buffer zone are spatially superimposed, and the area that simultaneously meets the conditions of dual temperature scale consistency, continuous distribution of anomalous zone and adjacent fracture structure channel is determined as the geothermal target area.

2. The method according to claim 1, characterized in that, The grid division in step S2 adopts a regular grid division method, with a grid side length of 1km to 5km.

3. The method according to claim 1, characterized in that, In step S2, one to three surface water sampling points are set up in each grid cell.

4. The method according to claim 1, characterized in that, The water body type mentioned in step S2 includes one or more of spring water, river water, lake water, valley water and shallow seepage water.

5. The method according to claim 1, characterized in that, In step S4, the Na-K geothermal temperature scale value and the SiO2 geothermal temperature scale value are used to characterize the underground thermal reservoir temperature information, and candidate abnormal sample points are screened according to whether the difference between the two is within a preset consistency range.

6. The method according to claim 5, characterized in that, The dual-temperature scale consistency condition is that the difference between the Na-K geothermal temperature scale value and the SiO2 geothermal temperature scale value does not exceed a preset threshold.

7. The method according to claim 1, characterized in that, The surface hydrothermal influence anomaly index mentioned in step S5 is composed of the Na-K geothermal temperature scale index, the SiO2 geothermal temperature scale index, and the Cl... - It consists of at least three of the following: concentration index, TDS index, and water temperature index.

8. The method according to claim 1, characterized in that, The standardization process described in step S5 uses any one of range standardization, Z-score standardization, or quantile standardization.

9. The method according to claim 1, characterized in that, The spatial continuity identification in step S5 includes generating an anomaly index distribution map using a spatial interpolation method and identifying continuously distributed high-value anomaly areas. The spatial interpolation method is any one of Kriging interpolation, inverse distance weighting, or spline function interpolation.

10. The method according to claim 1, characterized in that, The fracture structure buffer zone described in step S6 is set according to the fracture level, extension scale, or scope of influence.

11. The method according to claim 1, characterized in that, In step S6, when the high-value area of ​​the surface hydrothermal influence anomaly index, the concentrated distribution area of ​​candidate anomaly samples, and the fault structure buffer zone overlap spatially, the overlapping area is determined as the geothermal target area.

12. The method according to claim 1, characterized in that, The method is used for rapid initial screening of target areas during the large-scale survey of geothermal resources.

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