Method for calibrating lithology of hidden geothermal resource reservoir of spring water sediment

Abstract

The invention discloses a method for calibrating lithology of a hidden geothermal resource reservoir of spring water sediments, which comprises the following steps of: collecting unweathered spring water sediments and bedrocks of different rock types in surrounding areas of the spring water sediments, and testing strontium isotopes and rare earth elements of the spring water sediments and the bedrocks; historical data of strontium isotopes and rare earth elements of spring water sediments in the geological area and different rock types of bed rocks in the surrounding area of the spring water sediments are collected, and an analysis data set is formed; basic characteristics of rare earth elements in the spring water sediments and the bedrocks of different rock types in the surrounding areas of the spring water sediments in the analysis data set are obtained, and the basic characteristics of strontium isotopes and rare earth elements in the spring water sediments and the bedrocks of different rock types in the surrounding areas of the spring water sediments are compared; screening out a bed rock type with the best matching property with the spring water sediment characteristics as the lithology of the hidden geothermal resource reservoir indicated by the spring water sediment; the method makes up the defect that geothermal fluid is severely relied on when geothermal resources are explored through a water chemical means.

Description

Technical Field

[0001] The invention relates to the technical field of sediment lithology calibration, and in particular to a method for calibrating the lithology of a hidden geothermal resource reservoir of a spring sediment. Background Art

[0002] Identifying geothermal reservoir lithology is the key to assessing the potential of geothermal resources, which can provide important information about the depth, range, porosity, permeability, etc. of the heat reservoir. Conventional identification of heat reservoir lithology is mainly completed through hydrochemical means, which requires the presence of geothermal displays represented by hot springs on the surface of the geothermal system. However, due to factors such as climate change, tectonic activity, and self-closure of fluid channels, surface hot springs may gradually disappear during the evolution of the geothermal system, turning geothermal resources into hidden geothermal resources, which seriously hinders the identification of heat reservoir lithology. Although drilling, geological and geophysical methods may also effectively identify the lithology of hidden geothermal resource reservoirs, their high risk, high cost, and complex and difficult operating procedures limit their use in the initial exploration of hidden geothermal resources, especially in areas with insufficient preliminary exploration.

[0003] Spring water sediments are (bio)chemical sediments precipitated by spring water, mainly including calcareous spring water sediments composed of calcium carbonate (i.e. travertine) and siliceous spring water sediments composed of silicon dioxide (i.e. siliceous calcite). Hot springs with long-extinct hidden geothermal resources may precipitate spring water sediments of sufficient scale on the surface. If these spring water sediments inherit the geochemical characteristics of the spring water during the precipitation process, then the geochemical characteristics of the spring water sediments also have the potential to calibrate the lithology of geothermal resource reservoirs. However, there is still a lack of methods to calibrate the lithology of geothermal resource reservoirs through the geochemical characteristics of spring water sediments. Summary of the invention

[0004] The purpose of the present invention is to provide a method for calibrating the lithology of hidden geothermal resource reservoirs in spring water sediments, so as to solve the technical problem that the prior art lacks a method for calibrating the lithology of geothermal resource reservoirs through the geochemical characteristics of spring water sediments.

[0005] In order to solve the above technical problems, the present invention specifically provides the following technical solutions:

[0006] A method for calibrating the lithology of a hidden geothermal resource reservoir in a spring sediment comprises the following steps:

[0007] Step 100, collecting unweathered spring sediments for multiple times, and collecting bedrock in the surrounding area of ​​the spring sediments at the same time, performing actual petrological and mineralogical analysis on the spring sediments and bedrock, respectively, and testing the strontium isotope and rare earth element composition of the spring sediments and bedrock;

[0008] Step 200, combining historical data of strontium isotopes and rare earth elements obtained from bedrock tests in spring water sediments in the geological area and surrounding areas to form an analysis data set;

[0009] Step 300, obtaining the basic characteristics of rare earth elements in the bedrock of the spring water sediments and the surrounding areas within the analysis data set, comparing the basic characteristics of strontium isotopes and rare earth elements of the bedrock of the spring water sediments and the surrounding areas, and screening out the bedrock type that best matches the strontium isotope and rare earth element characteristics of the spring water sediments as the hidden geothermal resource reservoir lithology indicated by the spring water sediments.

[0010] As a preferred embodiment of the present invention, in step 100, the method for testing the strontium isotope and rare earth element composition of the spring water sediment and bedrock is specifically as follows:

[0011] The spring sediment and the bedrock are prepared into thin slices, block samples and powder samples, and the thin slices, block samples and powder samples of the spring sediment and the bedrock are observed and analyzed respectively to determine the rock type and mineral composition corresponding to the spring sediment and the bedrock in the surrounding area;

[0012] Based on the identification results of the rock type and mineral composition of the spring water sediments and bedrock, corresponding pre-treatment methods are matched to the spring water sediments and bedrock of different rock types, and the strontium isotope and rare earth element composition of the spring water sediments and bedrock after pre-treatment are tested.

[0013] The spring sediments and bedrock of different rock types in the surrounding area were tested for strontium isotopes and rare earth elements using the solution method.

[0014] As a preferred embodiment of the present invention, in step 100, after completing the strontium isotope and rare earth element tests, the test results of the spring water sediment and the bedrock in the surrounding area are screened respectively, and the strontium isotope and rare earth element data of the calcareous spring water sediment and bedrock obtained are screened by analyzing the zirconium (Zr) content and correlation diagram to screen out the strontium isotope and rare earth element test results of the calcareous spring water sediment and bedrock that are obviously contaminated by exogenous silicate components. The specific implementation method is:

[0015] When the zirconium (Zr) content Zr is less than 4μg / g per unit mass, or there is no correlation between zirconium (Zr) and thorium (Th), or there is no correlation between thorium (Th) and strontium isotopes, it means that the strontium isotope and rare earth element data of the calcareous spring sediment samples and bedrock are not significantly contaminated by exogenous silicate components.

[0016] As a preferred embodiment of the present invention, in step 300, basic characteristics of rare earth elements in bedrock of different rock types in the spring sediments and surrounding areas in the analysis data set are obtained, and the basic characteristics of the rare earth elements specifically include a rare earth element distribution pattern diagram, a relative enrichment degree of rare earth elements, and a rare earth element anomaly index;

[0017] Among them, the implementation method of obtaining the basic characteristics of rare earth elements is:

[0018] Standardizing the rare earth element data values ​​in the bedrock of different rock types in the spring sediment and its surrounding areas;

[0019] Based on the rare earth elements in the bedrock of different rock types in the spring water sediment and its surrounding areas and the standard data values ​​corresponding to each rare earth element, a rare earth element distribution pattern diagram of the bedrock of different rock types in the spring water sediment and its surrounding areas is formed;

[0020] Based on the types of rare earth elements, light rare earth, medium rare earth and heavy rare earth are distinguished, and based on the standard data values ​​corresponding to light rare earth, medium rare earth and heavy rare earth, the relative enrichment and relative depletion of light rare earth, medium rare earth and heavy rare earth are calculated respectively;

[0021] Based on the rare earth elements in the bedrock of different rock types in the spring water sediments and the surrounding areas and the standard data value corresponding to each rare earth element, the rare earth element anomaly index of the bedrock of different rock types in the spring water sediments and the surrounding areas is calculated.

[0022] As a preferred embodiment of the present invention, the implementation method of standardizing the rare earth elements in the bedrock of different rock types in the spring sediment and its surrounding areas is as follows:

[0023] The ratio of the content of each rare earth element in the bedrock of the spring water sediment and its surrounding areas to the content of the rare earth element in the corresponding standard is used as the standardized value of each rare earth element in the bedrock of the spring water sediment and its surrounding areas.

[0024] As a preferred embodiment of the present invention, the total types of rare earth elements in the spring sediments and bedrocks of different rock types in the surrounding areas include: La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Y (yttrium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium);

[0025] Among them, La (lanthanum), Ce (cerium), Pr (praseodymium), and Nd (neodymium) are light rare earths, Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Y (yttrium), and Ho (holmium) are medium rare earths, and Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium) are heavy rare earths.

[0026] As a preferred embodiment of the present invention, when calculating the relative enrichment of light rare earth (La, Ce, Pr, Nd), medium rare earth (Sm, Eu, Gd, Tb, Dy, Ho) and heavy rare earth (Er, Tm, Yb, Lu) elements, the ratio of the standard data value of the light rare earth element after standardization to the standard data value of the medium rare earth element after standardization is used as the relative enrichment of the light rare earth relative to the medium rare earth;

[0027] The ratio of the standard data value of the light rare earth element after the standardization treatment to the standard data value of the heavy rare earth element after the standardization treatment is used as the relative enrichment degree of the light rare earth relative to the heavy rare earth;

[0028] The ratio of the standardized standard data value of the middle rare earth element to the standardized standard data value of the heavy rare earth element is used as the relative enrichment degree of the middle rare earth relative to the heavy rare earth.

[0029] As a preferred embodiment of the present invention, when the ratio of the standard data value of the light rare earth element after standardization to the standard data value of the medium rare earth element after standardization is greater than 1, it indicates that the light rare earth is enriched relative to the medium rare earth;

[0030] When the ratio of the standard data value of the light rare earth element after normalization to the standard data value of the medium rare earth element after normalization is less than 1, it indicates that the light rare earth is deficient relative to the medium rare earth;

[0031] By analogy, the enrichment and depletion of light rare earths relative to heavy rare earths, as well as the enrichment and depletion of medium rare earths relative to heavy rare earths, are obtained respectively.

[0032] As a preferred embodiment of the present invention, when calculating the rare earth element anomaly index, the rare earth element standardized values ​​of the bedrock of different rock types in the spring water sediment and its surrounding areas are used to calculate its rare earth element anomaly index, mainly including Y / Ho, Ce anomaly value and Eu anomaly value;

[0033] Wherein, Y / Ho = the ratio of the unstandardized Y element data value to the Ho element data value;

[0034] Ce abnormal value: δCe=(Ce / Ce*) SN =Ce SN / (Pr SN ×(Pr SN / Nd SN ));

[0035] Eu abnormal value: δEu=(Eu / Eu*) SN =Eu SN / (Sm SN 2 ×Tb SN ) 1 / 3 ;

[0036] Wherein, Ce* and Eu* are the normal values ​​of Ce (cerium element) and Eu (europium element), SN represents the standard value of the element for standardization, Pr is praseodymium element, Nd is neodymium element, Sm is samarium element, and Tb is terbium element;

[0037] When the value of δCe is greater than 1, it indicates a positive Ce anomaly, and when the value of δCe is less than 1, it indicates a negative Ce anomaly;

[0038] When the value of δEu is greater than 1, it indicates a positive anomaly of Eu, and when the value of δEu is less than 1, it indicates a negative anomaly of Eu.

[0039] As a preferred embodiment of the present invention, in step 300, after obtaining the relative enrichment of light rare earth to medium rare earth, the relative enrichment of light rare earth to heavy rare earth, and the relative enrichment of medium rare earth to heavy rare earth, the rare earth element anomaly index, the rare earth element distribution pattern diagram, and the strontium isotope range of all bedrock and spring sediments, the bedrock type with the best matching performance with the strontium isotope and rare earth element characteristics of the spring sediments is screened out as the hidden geothermal resource reservoir lithology indicated by the spring sediments, and the specific matching method is:

[0040] Compare all bedrock and spring sediments in terms of REE distribution pattern diagrams, REE relative enrichment, and REE anomaly index;

[0041] Determining the strontium isotope range of the spring sediments, and comparing the strontium isotopes in all bedrocks to the strontium isotope range of the spring sediments;

[0042] Among them, the bedrock that is most similar to the rare earth element distribution pattern diagram of the spring water sediments, with the smallest relative enrichment of rare earth elements, the smallest difference in rare earth element anomaly index, and the closest strontium isotope range will be regarded as the hidden geothermal resource reservoir lithology indicated by the spring water sediments.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention relies on sedimentary geochemical methods such as strontium isotopes and rare earth elements to create a new method for calibrating the reservoir lithology of hidden geothermal resources through spring water sediments, which makes up for the deficiency of heavy reliance on geothermal fluids when exploring geothermal resources using hydrochemical methods. It can be used as an important supplementary means for exploring hidden geothermal resources in addition to drilling, geology and geophysics. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0046] Figure 1 A schematic flow chart of a method for calibrating lithology of a hidden geothermal resource reservoir provided in an embodiment of the present invention.

[0047] Figure 2 A high-scale regional geological map (Figure A) and a geological profile map (Figure B) of the area surrounding the Rehai spring water sediments in Tengchong, Yunnan, China provided in an embodiment of the present invention.

[0048] Figure 3 A comparative diagram of rare earth element distribution patterns of the Rehai spring water sediments in Tengchong, Yunnan, China (Figure A) and bedrock of different rock types in its surrounding areas (Figure B) provided in an embodiment of the present invention.

[0049] Figure 4 A comparison chart of the relative enrichment and anomaly index of rare earth elements in the spring water sediments of Rehai, Tengchong, Yunnan, China and bedrock of different rock types in its surrounding areas provided in an embodiment of the present invention.

[0050] Figure 5 A comparison diagram of bedrock strontium isotopes of different rock types in the Rehai spring water sediments in Tengchong, Yunnan, China and its surrounding areas provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] It should be noted that strontium isotopes are mainly used in earth science. 87 Sr / 86Sr is used to represent the ratio of strontium in different rocks and minerals. The ratio of strontium in different rocks and minerals varies significantly. During the underground migration of geothermal fluids, they will undergo chemical exchange with the surrounding rocks, dissolving the strontium elements in the rocks and minerals, resulting in the degradation of the surrounding rocks. 87 Sr / 86 The Sr ratio is inherited by the geothermal fluid, especially the surrounding rock as the geothermal fluid reservoir lithology, because it has a longer contact time with the geothermal fluid, a more complete water-rock reaction will occur, making the geothermal fluid 87 Sr / 86 The Sr ratio is closer to the reservoir lithology of the geothermal fluid. 87 Sr / 86 The Sr ratio is inherited by the precipitated spring sediments. In addition, under common geological conditions, the chemical behavior of strontium is relatively stable and is not easily affected by temperature, pH or redox environment. Therefore, the strontium isotope ratio can better preserve the source area information of the fluid and is not easily changed by later effects.

[0053] Rare earth elements are similar to strontium isotopes. They can be released from rocks when interacting with geothermal fluids and remain stable in geothermal fluids. They show consistent trivalent behavior in chemical reactions (except Ce (cerium) and Eu (europium)), so their distribution is more controlled by physical conditions and sources rather than complex chemical reactions. Although divalent Ce (cerium) and Eu (europium) are easily affected by temperature and redox environment, rare earth elements still have the potential to calibrate the lithology of hidden geothermal resource reservoirs.

[0054] Therefore, strontium isotopes and rare earth elements can be used to indicate the compatibility between spring sediments and their surrounding bedrock, and the bedrock with the best match can be taken as the reservoir lithology of the hidden geothermal resources indicated by the spring sediments.

[0055] like Figure 1 As shown, the present invention provides a method for calibrating the lithology of a hidden geothermal resource reservoir of a spring sediment, which specifically includes the following steps:

[0056] Step 100, collecting unweathered spring sediments for multiple times, and collecting bedrock in the surrounding area of ​​the spring sediments at the same time, performing actual petrological and mineralogical analysis on the spring sediments and the bedrock, respectively, and testing the strontium isotope and rare earth element composition of the spring sediments and the bedrock.

[0057] During the collection process, the collection of spring sediment samples should try to avoid contamination by exogenous debris, and the collection of bedrock should try to include all types of rock types exposed in the surrounding areas of the spring sediments.

[0058] In step 100, the method for testing the strontium isotope and rare earth element composition of spring water sediments and bedrock is specifically as follows:

[0059] (1) The spring sediments and bedrock were prepared into thin sections, block samples, and powder samples. The thin sections, block samples, and powder samples of the spring sediments and bedrock were observed and analyzed to determine the rock type and mineral composition corresponding to the bedrock of the spring sediments and the surrounding areas.

[0060] In this step, thin sections, block samples and 200-mesh powder samples of spring sediments and bedrock are observed and analyzed using optical microscopy, scanning electron microscopy, XRD and other means to determine the rock type and mineral composition corresponding to the bedrock of the spring sediments and its surrounding areas.

[0061] (2) Based on the identification results of the rock types and mineral compositions of spring water sediments and bedrock, the corresponding pre-treatment methods are matched to the spring water sediments and bedrocks of different rock types, and the strontium isotope and rare earth element compositions of the spring water sediments and bedrocks after pre-treatment are tested.

[0062] Among them, based on the identification results of the rock types and mineral compositions of spring sediments and bedrock, different pre-treatment methods should be selected for samples of different rock types. The rock types corresponding to the bedrock of spring sediments and their surrounding areas include calcareous samples and siliceous samples. Low-concentration weak acid is used to dissolve the carbonate components in calcareous spring sediments and bedrock; high-concentration strong acid is used to perform full-rock dissolution on siliceous spring sediments and bedrock.

[0063] For example, for carbonate samples, it is recommended to use weak acid (such as 0.5N acetic acid) for sample dissolution to avoid contamination by silicate components; for silicate samples, it is recommended to use strong acid (such as nitric acid + hydrofluoric acid) for sample dissolution to ensure sufficient dissolution of the sample.

[0064] When conducting relevant tests on the strontium isotope and rare earth element composition of spring sediments and bedrock, it is recommended to use the solution method to conduct whole-rock strontium isotope and rare earth element composition tests on rocks composed of a single mineral. For rocks composed of multiple minerals, it is recommended to use the laser in-situ method to conduct single-mineral strontium isotope and rare earth element composition tests on spring sediments and bedrock.

[0065] After completing the strontium isotope and rare earth element tests, the feasibility evaluation of the test results of the spring water sediments and the bedrock in the surrounding areas is carried out. The feasibility evaluation of the strontium isotope and rare earth element data of the calcareous spring water sediments and bedrock can be carried out by analyzing the zirconium (Zr) content and correlation diagram to screen out the strontium isotope and rare earth element test results of the calcareous spring water sediments and bedrock that are obviously contaminated by exogenous silicate components. The specific implementation method is:

[0066] Within unit mass, when the zirconium (Zr) content Zr is less than 4μg / g or when there is no correlation between zirconium (Zr) and thorium (Th), and when there is no correlation between thorium (Th) and strontium isotopes, the strontium isotope and rare earth element data of calcareous spring sediment samples and bedrock are not obviously contaminated by exogenous silicate components.

[0067] Figure 2 This is a high-proportion regional geological map (Figure A) and geological profile map (Figure B) of the area surrounding the Rehai spring water sediments in Tengchong, Yunnan, China. It is determined that the area surrounding the Rehai spring water sediments in Tengchong, Yunnan, China mainly exposes Quaternary sediments, Quaternary volcanic rocks, Neogene clastic rocks, Neogene volcanic rocks, and Gaoligong Group metamorphic rocks, and there are several types of bedrock such as Cretaceous-Paleogene granites widely distributed underground.

[0068] Step 200, combining historical data of strontium isotopes and rare earth elements obtained from tests of spring sediments in the geological area and bedrock in the surrounding area to form an analysis data set;

[0069] Step 300, obtaining the basic characteristics of rare earth elements in the bedrock of the spring sediments and the surrounding areas in the analysis data set, comparing the basic characteristics of strontium isotopes and rare earth elements in the bedrock of the spring sediments and the surrounding areas, and screening out the bedrock type that best matches the strontium isotope and rare earth element characteristics of the spring sediments as the hidden geothermal resource reservoir lithology indicated by the spring sediments.

[0070] In step 300, basic characteristics of rare earth elements in bedrock of different rock types in spring sediments and surrounding areas in the analysis data set are obtained. The basic characteristics of rare earth elements specifically include rare earth element distribution pattern diagram, relative enrichment degree of rare earth elements and rare earth element anomaly index.

[0071] The rare earth element distribution pattern diagram is a qualitative diagram that can reflect the relative enrichment of rare earth elements and the rare earth element anomaly index. The relative enrichment of rare earth elements and the rare earth element anomaly index are quantitative values ​​that reflect the characteristics of the rare earth element distribution pattern diagram. The specific matching method is the similarity between the bedrock and spring water sediments in the rare earth element distribution pattern diagram, the relative enrichment of rare earth elements and the rare earth element anomaly index. The concept with the best rare earth element characteristic matching is that the rare earth element distribution pattern diagrams of the bedrock and spring water sediments are most similar, and the relative enrichment of rare earth elements and the rare earth element anomaly index are closest.

[0072] Among them, the implementation method of obtaining the basic characteristics of rare earth elements is:

[0073] (1) The rare earth element data values ​​in the bedrock of different rock types in the spring water sediments and the surrounding areas are standardized, wherein the rare earth element content of the bedrock of different rock types in the spring water sediments and the surrounding areas is divided by the rare earth element content of the corresponding standard, and the obtained ratio is the standardized value of the rare earth elements in the bedrock of different rock types in the spring water sediments and the surrounding areas.

[0074] For example, the Post-Archaean Australian Shale (PAAS) standard is selected, and its standard values ​​are as follows:

[0075] La Ce Pr Nd Sm Eu G Tb Dy Y Ho Er Tm Yb Lu 38 80 8.9 32 5.6 1.1 4.7 0.77 4.4 27 1 2.9 0.4 2.8 0.43

[0076] (2) Based on the rare earth elements in the bedrock of different rock types in the spring sediments and the surrounding areas and the standard data values ​​corresponding to each rare earth element, a rare earth element distribution pattern diagram of the bedrock of different rock types in the spring sediments and the surrounding areas is formed.

[0077] The standardized values ​​of rare earth elements of bedrock of different rock types in spring sediments and surrounding areas obtained through the above steps are taken logarithmically to the base 10 as the ordinate and the order of elements La to Lu as the abscissa to obtain a diagram of the rare earth element distribution pattern of bedrock of different rock types in spring sediments and surrounding areas.

[0078] Illustration of the rare earth element distribution pattern of different rock types in the spring sediments and surrounding areas Figure 3 As shown, Figure 3 This is a comparison of the rare earth element distribution patterns of the spring water sediments in Tengchong Rehai, Yunnan, China and the bedrock of different rock types in the surrounding areas. Figure 3 A is a diagram of the distribution pattern of rare earth elements in the spring water sediments of Rehai, Tengchong, Yunnan, China. Figure 3 B is an illustration of the rare earth element distribution patterns of bedrock of different rock types in the area surrounding the Rehai spring water sediments in Tengchong, Yunnan, China. The comparison results show that the rare earth element distribution pattern of the Rehai spring water sediments in Tengchong, Yunnan, China has a good similarity with the Gaoligong Group metamorphic rocks and Cretaceous-Paleogene granites, but a poor similarity with Quaternary volcanic rocks.

[0079] (3) Based on the type of rare earth elements, light rare earth, medium rare earth and heavy rare earth are distinguished, and based on the standard data values ​​corresponding to light rare earth, medium rare earth and heavy rare earth, the relative enrichment and relative depletion of light rare earth, medium rare earth and heavy rare earth are calculated respectively.

[0080] When the ratio of the standard data value of the light rare earth element after normalization to the standard data value of the medium rare earth element after normalization is greater than 1, it indicates that the light rare earth is enriched relative to the medium rare earth.

[0081] When the ratio of the standard data value of the light rare earth element after normalization to the standard data value of the medium rare earth element after normalization is less than 1, it indicates a loss of light rare earth relative to medium rare earth.

[0082] By analogy, the enrichment and depletion of light rare earths relative to heavy rare earths, as well as the enrichment and depletion of medium rare earths relative to heavy rare earths, are obtained respectively.

[0083] The total types of rare earth elements in spring sediments and bedrock of different rock types in the surrounding areas include: La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Y (yttrium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium);

[0084] Among them, La (lanthanum), Ce (cerium), Pr (praseodymium), and Nd (neodymium) are light rare earths, Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Y (yttrium), and Ho (holmium) are medium rare earths, and Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium) are heavy rare earths.

[0085] It should be noted that, in this embodiment, light rare earth elements, medium rare earth elements and heavy rare earth elements are specifically distinguished according to atomic numbers.

[0086] In earth science research, there is no unified classification of rare earth elements, including the two-way classification (light rare earth elements: La, Ce, Pr, Nd, Sm, Eu; heavy rare earth elements: Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and the three-way classification (the method used in the present invention). The choice of classification method usually depends on the personal habits of the researcher. The three-way classification is currently a more common classification method. Therefore, the present invention recommends using the three-way classification to divide rare earth elements into light rare earth elements, medium rare earth elements and heavy rare earth elements. In addition, due to similar chemical properties, although Y (yttrium) is often discussed with other rare earth elements in carbonate (rock) research and inserted between Dy (dysprosium) and Ho (holmium) in the drawing, it is not included in the classification of light, medium and heavy rare earth elements. Therefore, the correct three-part division of rare earth elements is as follows: light rare earth elements include La, Ce, Pr, and Nd; medium rare earth elements include Sm, Eu, Gd, Tb, Dy, and Ho; heavy rare earth elements include Er, Tm, Yb, and Lu.

[0087] (4) Based on the rare earth elements in the bedrock of different rock types in the spring sediments and the surrounding areas and the standard data values ​​corresponding to each rare earth element, the rare earth element anomaly index of the bedrock of different rock types in the spring sediments and the surrounding areas is calculated.

[0088] When calculating the rare earth element anomaly index, the rare earth element standardized values ​​of bedrock of different rock types in the spring sediments and surrounding areas are used to calculate its rare earth element anomaly index, mainly including Y / Ho, Ce anomaly value and Eu anomaly value;

[0089] Wherein, Y / Ho = the ratio of the unstandardized Y element data value to the Ho element data value;

[0090] Ce abnormal value: δCe=(Ce / Ce*)SN=CeSN / (PrSN×(PrSN / NdSN));

[0091] Eu abnormal value: δEu = (Eu / Eu*)SN = EuSN / (SmSN2×TbSN)1 / 3;

[0092] Wherein, Ce* and Eu* are the normal values ​​of Ce (cerium element) and Eu (europium element), SN represents the standard value of the element for standardization, Pr is praseodymium element, Nd is neodymium element, Sm is samarium element, and Tb is terbium element;

[0093] When the value of δCe is greater than 1, it indicates a positive Ce anomaly, and when the value of δCe is less than 1, it indicates a negative Ce anomaly;

[0094] When the value of δEu is greater than 1, it indicates a positive anomaly of Eu, and when the value of δEu is less than 1, it indicates a negative anomaly of Eu.

[0095] After obtaining the relative enrichment of light rare earth to medium rare earth, the relative enrichment of light rare earth to heavy rare earth, and the relative enrichment of medium rare earth to heavy rare earth, the rare earth element anomaly index, the rare earth element distribution pattern diagram, and the strontium isotope range of all bedrock and spring sediments, the bedrock type with the best match with the strontium isotope and rare earth element characteristics of the spring sediments is selected as the hidden geothermal resource reservoir lithology indicated by the spring sediments. The specific matching method is:

[0096] Compare all bedrock and spring sediments in terms of REE distribution pattern diagrams, REE relative enrichment, and REE anomaly index;

[0097] Determine the strontium isotope range of the spring sediments and compare the strontium isotopes in all bedrocks to the strontium isotope range of the spring sediments;

[0098] Among them, the bedrock with the most similar rare earth element distribution pattern diagram to the spring water sediments, the smallest rare earth element relative enrichment, the smallest rare earth element anomaly index difference, and the closest strontium isotope range will be regarded as the hidden geothermal resource reservoir lithology indicated by the spring water sediments.

[0099] Figure 4 This is a comparison chart of the relative enrichment and anomaly index of rare earth elements in the spring water sediments of Rehai in Tengchong, Yunnan, China and the bedrock of different rock types in the surrounding areas. Figure 4 A, Figure 4 B and Figure 4 C are the comparison diagrams of light rare earth relative to heavy rare earth - light rare earth relative to medium rare earth, light rare earth relative to heavy rare earth - Y / Ho, Eu anomaly - Ce anomaly distribution of the spring water sediments of Rehai, Tengchong, Yunnan, China and bedrock of different rock types in the surrounding areas. The comparison results show that the relative enrichment degree and anomaly index of rare earth elements in the spring water sediments of Rehai, Tengchong, Yunnan, China are well similar to the metamorphic rocks of the Gaoligong Group and the Cretaceous-Paleogene granites, but poorly similar to the Quaternary volcanic rocks.

[0100] Figure 5 This is a comparison of strontium isotopes between spring water sediments in Rehai, Tengchong, Yunnan, China and bedrock of different rock types in the surrounding areas. The comparison results show that the strontium isotopes of spring water sediments in Rehai, Tengchong, Yunnan, China have good similarity with Gaoligong Group metamorphic rocks and Cretaceous-Paleogene granites, but poor similarity with Quaternary volcanic rocks.

[0101] This implementation method relies on sedimentary geochemical methods such as strontium isotopes and rare earth elements to create a new method for calibrating the lithology of hidden geothermal resource reservoirs through spring water sediments, which makes up for the deficiency of heavy reliance on geothermal fluids when exploring geothermal resources using hydrochemical methods. It can be used as an important supplementary means for exploring hidden geothermal resources in addition to drilling, geology and geophysics.

[0102] The above embodiments are only exemplary embodiments of the present application and are not intended to limit the present application. The protection scope of the present application is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present application within the essence and protection scope of the present application, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present application.

Claims

1. A method for calibrating the lithology of hidden geothermal resource reservoirs in spring sediments, characterized in that: The following steps are involved: Step 100, collecting unweathered spring sediments, and at the same time collecting bedrock in the surrounding area of ​​the spring sediments, respectively performing actual petrological and mineralogical analysis on the spring sediments and bedrock, and testing the strontium isotope and rare earth element composition of the spring sediments and bedrock; Step 200, combining historical data of strontium isotopes and rare earth elements obtained from bedrock tests in spring water sediments in the geological area and surrounding areas to form an analysis data set; Step 300, obtaining the basic characteristics of rare earth elements in the bedrock of the spring water sediments and the surrounding areas within the analysis data set, comparing the basic characteristics of strontium isotopes and rare earth elements of the bedrock of the spring water sediments and the surrounding areas, and screening out the bedrock type that best matches the strontium isotope and rare earth element characteristics of the spring water sediments as the hidden geothermal resource reservoir lithology indicated by the spring water sediments.

2. A method for calibrating the lithology of hidden geothermal resource reservoirs in spring water sediments according to claim 1, characterized in that: In step 100, the method for testing the strontium isotope and rare earth element composition of the spring water sediment and bedrock is specifically as follows: The spring sediment and the bedrock are prepared into thin slices, block samples and powder samples, and the thin slices, block samples and powder samples of the spring sediment and the bedrock are observed and analyzed respectively to determine the rock type and mineral composition corresponding to the spring sediment and the bedrock in the surrounding area; Based on the identification results of the rock type and mineral composition of the spring water sediments and bedrock, corresponding pre-treatment methods are matched to the spring water sediments and bedrock of different rock types, and the strontium isotope and rare earth element composition of the spring water sediments and bedrock after pre-treatment are tested. The spring sediments and bedrock of different rock types in the surrounding area were tested for strontium isotopes and rare earth elements using the solution method.

3. A method for calibrating the lithology of hidden geothermal resource reservoirs in spring water sediments according to claim 2, characterized in that: In step 100, after completing the strontium isotope and rare earth element tests, the test results of the spring water sediment and the bedrock in the surrounding area are screened respectively, and the strontium isotope and rare earth element data of the calcareous spring water sediment and bedrock obtained are screened by analyzing the content of zirconium (Zr) and the correlation diagram to screen out the strontium isotope and rare earth element test results of the calcareous spring water sediment and bedrock that are obviously contaminated by exogenous silicate components. The specific implementation method is: When the zirconium (Zr) content Zr is less than 4μg / g per unit mass, or there is no correlation between zirconium (Zr) and thorium (Th), or there is no correlation between thorium (Th) and strontium isotopes, it means that the strontium isotope and rare earth element data of the calcareous spring sediment samples and bedrock are not significantly contaminated by exogenous silicate components.

4. A method for calibrating the lithology of hidden geothermal resource reservoirs in spring water sediments according to claim 1, characterized in that: In the step 300, basic characteristics of rare earth elements in the spring sediments and bedrock of different rock types in the surrounding areas in the analysis data set are obtained, wherein the basic characteristics of the rare earth elements specifically include a rare earth element distribution pattern diagram, a relative enrichment degree of the rare earth elements, and a rare earth element anomaly index; Among them, the implementation method of obtaining the basic characteristics of rare earth elements is: Standardizing the rare earth element data values ​​in the bedrock of different rock types in the spring sediment and its surrounding areas; Based on the rare earth elements in the bedrock of different rock types in the spring water sediment and its surrounding areas and the standard data values ​​corresponding to each rare earth element, a rare earth element distribution pattern diagram of the bedrock of different rock types in the spring water sediment and its surrounding areas is formed; Based on the types of rare earth elements, light rare earth, medium rare earth and heavy rare earth are distinguished, and based on the standard data values ​​corresponding to light rare earth, medium rare earth and heavy rare earth, the relative enrichment and relative depletion of light rare earth, medium rare earth and heavy rare earth are calculated respectively; Based on the rare earth elements in the bedrock of different rock types in the spring water sediments and the surrounding areas and the standard data value corresponding to each rare earth element, the rare earth element anomaly index of the bedrock of different rock types in the spring water sediments and the surrounding areas is calculated.

5. A method for calibrating the lithology of hidden geothermal resource reservoirs in spring water sediments according to claim 4, characterized in that: Standardization of the rare earth elements in the bedrock of the spring sediments and the different rock types in the surrounding area was achieved by: The ratio of the content of each rare earth element in the bedrock of the spring water sediment and its surrounding areas to the content of the rare earth element in the corresponding standard is used as the standardized value of each rare earth element in the bedrock of the spring water sediment and its surrounding areas.

6. A method for calibrating the lithology of hidden geothermal resource reservoirs in spring sediments according to claim 4, characterized in that: The total types of rare earth elements in the spring sediments and bedrock of different rock types in the surrounding areas include: La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Y (yttrium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium); Among them, La (lanthanum), Ce (cerium), Pr (praseodymium), and Nd (neodymium) are light rare earths, Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Y (yttrium), and Ho (holmium) are medium rare earths, and Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium) are heavy rare earths.

7. A method for calibrating the lithology of hidden geothermal resource reservoirs in spring sediments according to claim 6, characterized in that: When calculating the relative enrichment of light rare earth (La, Ce, Pr, Nd), medium rare earth (Sm, Eu, Gd, Tb, Dy, Ho) and heavy rare earth (Er, Tm, Yb, Lu) elements, the ratio of the standard data value of light rare earth elements after standardization to the standard data value of medium rare earth elements after standardization is used as the relative enrichment of light rare earth to medium rare earth; The ratio of the standard data value of the light rare earth element after the standardization treatment to the standard data value of the heavy rare earth element after the standardization treatment is used as the relative enrichment degree of the light rare earth relative to the heavy rare earth; The ratio of the standardized standard data value of the middle rare earth element to the standardized standard data value of the heavy rare earth element is used as the relative enrichment degree of the middle rare earth relative to the heavy rare earth.

8. A method for calibrating the lithology of hidden geothermal resource reservoirs in spring sediments according to claim 7, characterized in that: When the ratio of the standard data value of the light rare earth element after the standardization treatment to the standard data value of the medium rare earth element after the standardization treatment is greater than 1, it indicates that the light rare earth is enriched relative to the medium rare earth; When the ratio of the standard data value of the light rare earth element after normalization to the standard data value of the medium rare earth element after normalization is less than 1, it indicates that the light rare earth is deficient relative to the medium rare earth; By analogy, the enrichment and depletion of light rare earths relative to heavy rare earths, as well as the enrichment and depletion of medium rare earths relative to heavy rare earths, are obtained respectively.

9. A method for calibrating the lithology of hidden geothermal resource reservoirs in spring sediments according to claim 7, characterized in that: When calculating the rare earth element anomaly index, the rare earth element standardized values ​​of the bedrock of different rock types in the spring water sediment and its surrounding areas are used to calculate its rare earth element anomaly index, mainly including Y / Ho, Ce anomaly value and Eu anomaly value; Wherein, Y / Ho = the ratio of the unstandardized Y element data value to the Ho element data value; Ce abnormal value:δCe=(Ce / Ce*) SN =What SN / (Pr SN ×(Pr SN / Nd SN )); Eu abnormal value: δEu=(Eu / Eu*) SN =Eu SN / (Sm SN 2 ×Tb SN ) 1 / 3 ; Wherein, Ce* and Eu* are the normal values ​​of Ce (cerium element) and Eu (europium element), SN represents the standard value of the element for standardization, Pr is praseodymium element, Nd is neodymium element, Sm is samarium element, and Tb is terbium element; When the value of δCe is greater than 1, it indicates a positive Ce anomaly, and when the value of δCe is less than 1, it indicates a negative Ce anomaly; When the value of δEu is greater than 1, it indicates a positive anomaly of Eu, and when the value of δEu is less than 1, it indicates a negative anomaly of Eu.

10. A method for calibrating the lithology of hidden geothermal resource reservoirs in spring sediments according to claim 9, characterized in that: In step 300, after obtaining the relative enrichment of light rare earth to medium rare earth, the relative enrichment of light rare earth to heavy rare earth, and the relative enrichment of medium rare earth to heavy rare earth, the rare earth element anomaly index, the rare earth element distribution pattern diagram, and the strontium isotope range of all bedrock and spring sediments, the bedrock type with the best matching of strontium isotope and rare earth element characteristics of the spring sediment is screened out as the hidden geothermal resource reservoir lithology indicated by the spring sediment, and the specific matching method is: Compare all bedrock and spring sediments in terms of REE distribution pattern diagrams, REE relative enrichment, and REE anomaly index; Determining the strontium isotope range of the spring sediments, and comparing the strontium isotopes in all bedrocks to the strontium isotope range of the spring sediments; Among them, the bedrock that is most similar to the rare earth element distribution pattern diagram of the spring water sediments, with the smallest relative enrichment of rare earth elements, the smallest difference in rare earth element anomaly index, and the closest strontium isotope range will be regarded as the hidden geothermal resource reservoir lithology indicated by the spring water sediments.

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