Screening method for deep well return storage target layer of well water of high-salt mine

Abstract

The invention discloses a screening method for a deep well return storage target layer of well water of a high-salt mine. The screening method comprises the following steps: 1, collecting various geological data of a research area; 2, determining distribution of structures, faults and the like, and dividing structure grade areas; 3, determining engineering geology and hydrogeology characteristics of stratums of the research area; 4, analyzing the diameter filling conditions and water quality characteristics of hydrogeology, and dividing hydrogeology units; 5, eliminating mineral resource development potential stratums in the research area; 6, analyzing a tectonic stress field, identifying a brittle formation, and determining a main control stress direction and a formation hydraulic fracturing capability; 7, screening a crack type stratum or a karst type stratum; and 8, implementing a mine water restorage project. The invention provides a scientific and feasible technical thought for mine water treatment in a coal mine area.

Description

Technical Field

[0001] The present invention belongs to the technical field of geological storage of coal mine shaft water, and particularly relates to a method for screening deep well injection target layers of high-salt mine shaft water. Background Art

[0002] In arid and semi-arid regions in the central and western parts of China, water resources are scarce and the ecological environment is fragile. It is difficult to naturally restore the damaged mine ecological environment caused by coal mining. At the same time, affected by mining technology and hydrogeological structure characteristics, mine shaft water has the characteristics of high salt, large water volume, and high pH value. Its main water source is the sandstone aquifer in the overlying rock of the coal seam roof, while the deep strata have the characteristics of poor water, worse water quality, low pH value, no mineral resources, and do not affect the safe production of the energy industry. The water inflow of some mine shafts is huge, forcing coal mining enterprises to drain a large amount of mine shaft water to ensure the safe production of the mine. From an environmental protection perspective, it is required that coal mine shaft water be "zero-discharged", that is, after being treated to meet the standards, it is recycled within the mining area. However, in arid and semi-arid mining areas, the treatment of a large amount of high-salt mine shaft water has a large volume, and the treatment cost per ton is generally 20-30 yuan, greatly increasing the economic burden. Therefore, there is an urgent need to reform the technologies and methods for green and harmless treatment of mine shaft water. Summary of the Invention

[0003] Object of the Invention: In order to solve the problems existing in the above-mentioned prior art, the present invention provides a method for screening deep well injection target layers of high-salt mine shaft water.

[0004] Technical Solution: The present invention provides a method for screening deep well injection target layers of high-salt mine shaft water, specifically including the following steps:

[0005] Step 1: Collect geological data in the research area;

[0006] Step 2: Select data that can reflect the complexity of the structure according to the geological data in Step 1, and construct a structural grade zoning map of the research area; select alternative layers as the injection target layers according to the grade zoning map;

[0007] Step 3: Screen candidate layers according to the compressive strength in the alternative layers;

[0008] Step 4: Based on the geological data of the i-th layer in the candidate layers, score the geological engineering geological and hydrogeological characteristics of the i-th layer;

[0009] Step 5: Score the hydrogeological characteristics of the i-th layer according to the hydrogeological conditions of the i-th layer in the candidate layers;

[0010] Step 6: Score the non-industrial value of the i-th layer according to the mineral resources of the i-th layer;

[0011] Step 7: Divide the tectonic stress levels for the i-th layer of strata according to the evolution of the geological tectonic stress field and tectonic movement data, combined with the physical and mechanical properties and parameters of the strata rocks.

[0012] Step 8: Determine the type of the i-th layer of strata; and perform type scoring for this layer of strata based on the type and comprehensive geological characteristics of this layer of strata.

[0013] Step 9: Perform weighted summation on the scores obtained in Steps 4 - 8 to obtain the overall score of the i-th layer of strata, and select the layer of strata with the highest overall score function as the final target layer for backfilling.

[0014] Further, in Step 2, select geophysical gravity data and process this data using the singular value decomposition algorithm. Specifically:

[0015] Step 3.1: Take the geophysical gravity data as matrix X, and decompose matrix X into the product of the left eigenvector matrix U, the diagonal matrix S, and the right eigenvector matrix V; the diagonal matrix S is the singular value matrix, S = diag(σ1, σ2, ···, σ r , ···, σ R ), where σ r represents the r-th diagonal element, R is the rank of matrix X, and σ1 ≥ σ2 ≥ ··· ≥ σ r ;

[0016] Step 3.2: Make a selection from σ1, σ2, ···, σ r , ···, σ R according to the situation, set the unselected diagonal elements to 0, and obtain a two-dimensional map including curves and concave-convex regions.

[0017] Step 3.3: Take the curves as faults, the convex regions as anticlines, and the concave regions as synclines, and assign weights to the faults, anticlines, and synclines to construct a hierarchical partition map.

[0018] Step 3.4: Take the regions with weight values exceeding the preset weight threshold range as candidate layers.

[0019] Further, Step 3 is specifically: Set the first and second compressive strength ranges. If there are brittle sandstone strata in the alternative layers that meet the first compressive strength range, then take these strata as candidate layers; if not, select the karst limestone strata that meet the second compressive strength range as candidate layers.

[0020] Further, the first compressive strength range is 30 MPa - 35 MPa, and the second compressive strength range is 40 MPa - 60 MPa.

[0021] Further, Step 5 is specifically:

[0022] Step 5.1: Score the water storage conditions of the i-th layer of strata according to the proportion of the number of effective water-bearing layers and effective water-resistant layers in the i-th layer of strata; the effective water-bearing layer is a stratum where the groundwater recharge, runoff, and discharge conditions do not meet the preset water storage conditions; the effective water-resistant layer is a stratum located at the top or bottom and having thick mudstone or sandy mudstone developed.

[0023] Step 5.2: Score the water quality of the i-th layer of strata.

[0024] Step 5.3: Score the characteristics of the i-th layer of strata based on the porosity, permeability, saturation, temperature, whether there are large water-conducting channels, petrological characteristics, whether there are soluble cements, and the potential for the infiltration characteristics to evolve and change of the i-th layer of strata.

[0025] Step 5.4: Obtain the comprehensive score of the hydrogeological characteristics of the i-th layer of strata based on the scores obtained in Steps 5.1 - 5.3.

[0026] Further, when scoring the characteristics of the i-th layer of strata in 5.3, if any of the following conditions are met, the characteristic score is increased:

[0027] Condition 1: The porosity is less than the porosity threshold, the permeability is less than the permeability threshold, the saturation is less than the saturation threshold, and the temperature is greater than the temperature threshold;

[0028] Condition 2: There are no large water-conducting channels;

[0029] Condition 3: The proportion of quartz in the petrological characteristics is greater than the preset threshold;

[0030] Condition 4: It contains erodible or soluble cements;

[0031] Condition 5: The infiltration characteristics have the potential to evolve and change.

[0032] Further, in Step 6, if the i-th layer of strata has mineral resources with industrial value, score the industrial production value of the i-th layer of strata according to the specific mineral resources possessed by the i-th layer of strata, and this score is less than the non-commercial value score threshold; if the i-th layer of strata does not have mineral resources with industrial value, the score of the i-th layer of strata is greater than the non-commercial value score threshold.

[0033] Further, the mineral resources with industrial value include: groundwater, coal, petroleum, natural gas, oil shale, or potassium salt.

[0034] Further, Step 7 comprehensively considers the geological structure background, stress state, in-situ stress measurement data, and the stability of the strata, and quantifies the tectonic stress level from 1 to 10 according to geology and tectonic stress research.

[0035] Further, the greater the change amplitude of the resistivity in the well logging curve of the i-th layer of the formation in step 8, the higher the type score of the formation.

[0036] Beneficial effects: By comprehensively analyzing various geological data and combining big data mining and in-depth analysis techniques, the present invention obtains multi-dimensional information such as formation lithology, structural characteristics, tectonic stress field, rock physical and mechanical properties, aquifer system, hydrogeological conditions, water quality characteristics, and fractured and karst formations. On this basis, fractured sandstone weak aquifers or karst limestone are determined as the target horizons for deep well recharge of high-salt mine water. The present invention provides an innovative method for the green and harmless treatment of high-salt mine water and the recycling of underground water resources, with significant environmental and economic benefits. Brief Description of the Drawings

[0037] Figure 1 is a flowchart of the present invention.

[0038] Figure 2 is a schematic diagram of the recharge structure of a fractured sandstone formation. Detailed Embodiments

[0039] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0040] As Figure 1 shown, the present invention specifically includes the following steps:

[0041] Step 1: Collect data such as regional geology (sedimentary geology, engineering geology), formations (formations deeper than 1000 m and shallower than 3000 m), structures (faults, depressions, uplifts, etc.), geophysical field exploration drawings and profiles, mineral resources (including various industrial and large-scale exploitable mineral resources), in-situ stress (tectonic stress, maximum in-situ stress direction), rock physical and mechanical properties (mainly compressive strength, shear strength, etc.), hydrogeology, fractured data, borehole columnar diagrams, and various well logging curves from publicly available papers, patents, reports, drawings, etc. in the study area, and conduct big data mining and in-depth analysis.

[0042] Step 2: Determine the engineering geological and hydrogeological characteristics of the formations in the study area according to the regional geological formation data, including formation lithology, thickness, sedimentary environment, spatial distribution law, rock composition and clay composition, strength, mechanical parameters, permeability coefficient, porosity, etc., mainly focusing on the engineering geological and hydrogeological characteristics of various formations deeper than 1000 m and shallower than 3000 m.

[0043] Step 3: Collect and organize the data that can indicate complex structures in the study area. In this embodiment, geophysical gravity anomaly data is used, and the gravity data is processed using the singular value decomposition algorithm on the MATLAB platform.

[0044] Based on the singular value decomposition method, the gravity data is regarded as the target matrix X, and the matrix X is decomposed into the left eigenvector matrix U m×m , diagonal matrix S m×n and right eigenvector matrix V n×n The product of, that is:

[0045] X m×n =U m×m S m×n V n×n T

[0046] Among them, the diagonal matrix S is the singular value matrix, and its singular values are arranged in descending order along the main diagonal. The value of it is the positive square root of the eigenvalue λ, that is:

[0047]

[0048] S=diag(σ1,σ2,······,σ R )

[0049] R is the rank of matrix X, and σ1≥σ2≥···≥σ r .

[0050] According to the situation, select σ1 from the diagonal matrix, and the rest are 0 to remove data noise and obtain the overall trend; or select σ1 and σ2 according to the situation, and the rest are 0, then on the basis of the overall trend, add data details; or continue to select σ1, σ2, ···, σ r , then the gravity data tends to the initial form.

[0051] By successively selecting σ1≥σ2≥···≥σ r , obtain the gravity and magnetic anomaly data with different processing effects, and get some curves and convex and concave areas. The curves are regarded as faults, the convex places are anticlines, and the concave places are synclines. Then assign weights to these curves, convex places and concave places, and regard the faults as high-structural-level areas, and the anticlines and synclines as low-structural-level areas to form the structural level zoning map of a certain study area, and regard the high-level areas as the alternative layers for the storage target layer.

[0052] Step 4: Based on the regional hydrogeological conditions, combined with previous exploration data, pumping tests, aquifer water quality analysis, isotope dating, and groundwater balance calculations, etc., determine the boundary conditions and water control structures of different closed or semi-closed hydrogeological units in the study area. Consider the strata with extremely poor groundwater recharge, runoff, and discharge conditions as potential effective aquifers; at the same time, if thick mudstones and sandy mudstones are developed at the top and bottom, they can be regarded as effective aquitards (cap rocks) that can prevent mine water leakage induced by pressure shock or damage. Score the water storage conditions of the strata based on the proportion of effective aquifers and effective aquitards. From the perspective of water quality, the quality of the original formation water is generally inferior to that of mine water. Although a few conventional ions in high-salt mine water exceed the limits of Class III standards in the "Groundwater Quality Standard" (GB / T 14848-2017), it can still be used as a storage medium for mine water in general. The sandstone aquifer should be a formation with low porosity, low permeability, low saturation, high temperature, and low in-situ stress. Its microscopic pore structure has solution pores, karst caves, and microfractures, which can provide channels and sites for the mesoscopic migration of mine water and water-rock interaction. Within the regional scope, there are no large-scale water-conducting channels to ensure the safe re-injection of mine water. In addition, the petrological characteristics of the target formation should be mainly quartz, supplemented by feldspar, and contain a certain amount of erodible and soluble cement. Its permeability characteristics should have the potential for evolution and change; in this embodiment, the improved Nemerow index method is used for the comprehensive comparison of mine water and formation water:

[0053]

[0054] In the formula, Pcomprehensive is the Nemerow comprehensive index, Ci is the measured value of the i-th ion in the water quality, and Si is the Class III standard value of the groundwater environmental quality standard for the i-th ion in the water quality. is the single index, is the maximum value of the single index of the i-th ion.

[0055] Step 5: Exclude potential strata for mineral resource development. According to the occurrence, exploration, development, and production information of existing mineral resources (including but not limited to groundwater, coal, oil, natural gas, oil shale, potassium salt, etc.), exclude the above-mentioned strata with industrial production value, and screen out the strata with fracture characteristics or karst characteristics as candidate layers for the subsequent target layer of mine water re-injection.

[0056] Step 6: Tectonic stress field analysis and formation screening. According to the evolution and movement data of the geological tectonic stress field, combined with the physical and mechanical properties and parameters of rocks in each formation, first screen the brittle sandstone formations with a rock compressive strength of about 30 MPa to 35 MPa, with coarse sandstone, medium sandstone, and fine sandstone as the main selection conditions. Such sandstones should have the potential to develop a three-dimensional fracture network system; secondly, screen the karst limestone formations with a rock compressive strength of 40 MPa to 60 MPa, and the deep karst void space should be well developed. In this embodiment, candidate formations are screened from the alternative formations according to the compressive conditions and formation rock types; at the same time, the main controlling direction of in-situ stress is determined according to the regional tectonic stress field. The assignment of tectonic stress levels comprehensively considers the geological tectonic background, stress state, in-situ stress measurement data, and formation stability of the formation. According to the existing geological and tectonic stress research, the tectonic stress level is quantified from 1 to 10, where 10 represents the best and 1 represents the worst.

[0057] Step 8: Combining the regional fracture type, karst type characteristics and well logging data, a large fracture type strength indicates that the formation fracture network is widely developed, and a high karst development intensity indicates that it has rich water storage space. These characteristics usually show a large change amplitude of the deep and shallow lateral resistivity in the well logging curve. Therefore, the fracture type or karst type phenomenon can be used as the main basis for formation optimization.

[0058] Step 9: Synthesize and evaluate the results of the above steps 2 to 7, evaluate from multiple aspects such as formation, structure, caprock, physical and chemical properties of the reservoir, and water quality, and comprehensively calculate according to engineering geology and hydrogeology characteristics, hydrogeology characteristics, excluding potential mineral resources, tectonic stress level, and formation type angles, and define a scoring calculation function S i , which will comprehensively consider the above calculation factors and set the weight coefficients α i , β i , χ i , γ i , η i , which respectively represent the weights of engineering geology and hydrogeology characteristics, hydrogeology characteristics, non-industrial value score, tectonic stress level, and formation type in the screening of the i-th formation target layer in the candidate formation. Then, establish the comprehensive calculation scoring formula for the i-th formation target layer as:

[0059] S i =α i ·A i +β i ·B i +χ i ·C i +γ i ·D i +η i ·E i

[0060] Among them, Ai is the score for the i-th engineering geological and hydrogeological characteristics; B i is the score for the hydrogeological characteristics of the i-th stratum; C i is the score for the non-industrial value of the i-th stratum; D i is the score for the tectonic stress level of the i-th stratum; E i is the score for the i-th stratum type. The stratum type score is a comprehensive score of the stratum type and geological comprehensive characteristics.

[0061] In this embodiment, the hydrogeological characteristic score is specifically obtained by scoring the water quality of the i-th stratum according to the proportion of the number of effective aquifers and effective aquitards in the i-th stratum; scoring the characteristics of the i-th stratum based on the porosity, permeability, saturation, temperature, whether there is a large water-conducting channel, petrological characteristics, whether there is a soluble cement, and the potential for the evolution and change of the permeability characteristics of the i-th stratum; and comprehensively obtaining the score of the hydrogeological characteristics of the i-th stratum by combining the scores of the above three aspects. When scoring the characteristics of the i-th stratum, if any of the following conditions is met, the characteristic score is increased:

[0062] Condition 1: The porosity is less than the porosity threshold, the permeability is less than the permeability threshold, the saturation is less than the saturation threshold, and the temperature is greater than the temperature threshold;

[0063] Condition 2: There is no large water-conducting channel;

[0064] Condition 3: The proportion of quartz in the petrological characteristics is greater than the preset threshold;

[0065] Condition 4: It contains erodible or soluble cement;

[0066] Condition 5: The permeability characteristics should have the potential for evolution and change.

[0067] In this embodiment, the score for the non-industrial value of the i-th stratum is specifically as follows: If the i-th stratum has mineral resources with industrial value, the industrial production value of the i-th stratum is scored according to the specific mineral resources possessed by the i-th stratum, and this score is less than the non-commercial value score threshold; if the i-th stratum does not have mineral resources with industrial value, the score of the i-th stratum is greater than the non-commercial value score threshold.

[0068] The score for the i-th stratum type is specifically: The greater the change range of the resistivity in the logging curve of the i-th stratum, the higher the type score of the stratum.

[0069] Finally, the stratum with the highest comprehensive score is selected as the final backfill target layer. According to the calculation results, the fractured sandstone weak aquifer or karst limestone stratum is preferably selected as the deep well backfill target layer for high-salt mine water, and the mine water backfill project is implemented accordingly, such asFigure 2 As shown in Table 1, the Heshanggou Formation, Liujiagou Formation, and Shiqianfeng Formation can be used as the target layers for project implementation.

[0070] Table 1

[0071]

[0072]

[0073] During the implementation of the deep well re-injection test well for high-salt mine water, on-site tests and laboratory tests also need to be carried out for comprehensive scientific research. Among them, on-site tests include water level recovery test, pumping test, water pressure test, injection test, tracer test, geophysical logging, ultrasonic imaging, electrical tomography, core and cuttings logging, etc.; laboratory tests include but are not limited to mercury injection test, water quality analysis (total analysis, trace elements and isotopes, etc.), X-ray diffraction, scanning electron microscopy, rock physical and mechanical tests, core nano-CT scanning, permeability evolution test, hydraulic fracturing test, leaching test, soaking test, water-rock interaction test, water quality miscibility test, acid and corrosion resistance test, etc. Through the above on-site and laboratory tests, the water storage performance, water-rock interaction, and engineering safety of the target layer can be comprehensively evaluated, providing a scientific basis for the implementation of the deep well re-injection project for mine water.

[0074] Although the present invention is directed to the selection of the target layer for the re-injection of coal mine water, its technical idea is also applicable to the harmless green treatment of mine water and the mine water-CO2 combined capture and storage technology. Specifically, in the initial stage, the present invention can utilize mine water to expand and increase the storage space in the deep formation, creating favorable conditions for subsequent CO2 capture and storage; in the middle and late stages, it can be directly used for CO2 storage, significantly increasing the CO2 storage capacity. In this way, the present invention can provide an innovative technical idea with broad application prospects and important practical significance.

[0075] In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

Claims

1. A screening method for the target layer of deep well back-storage of high-salt mine water, characterized in that, Specifically, it includes the following steps: Step 1: Collect geological data within the research area; Step 2: Select data that can reflect complex structures based on the geological data in Step 1, and construct a structural grade zoning map for the research area; select alternative layers as the backfill target layer according to the grade zoning map; Step 3: Screen candidate layers according to the compressive strength in the alternative layers; Step 4: Based on the geological data of the i-th layer in the candidate layers, score the geological engineering geological and hydrogeological characteristics of the i-th layer; Step 5: Score the hydrogeological characteristics of the i-th layer according to the hydrogeological conditions of the i-th layer in the candidate layers; Step 6: Score the non-industrial value of the i-th layer according to the mineral resources of the i-th layer; Step 7: Divide the tectonic stress of the i-th layer into grades according to the evolution of the tectonic stress field and tectonic movement data, combined with the physical and mechanical properties and parameters of the formation rocks; Step 8: Determine the type of the i-th layer; and score the type of the formation based on the type and geological comprehensive characteristics of the formation; Step 9: Perform weighted summation on the scores obtained in Steps 4-8 to obtain the overall score of the i-th layer, and select the layer with the highest overall score function as the final backfill target layer.

2. The screening method of the deep well re-injection target layer for the high-salt mine water according to claim 1, wherein, In Step 2, select geophysical gravity data and process the data using the singular value decomposition algorithm. Specifically: Step 3.1: Take the geophysical gravity data as matrix X, and decompose matrix X into the product of a left eigenvector matrix U, a diagonal matrix S, and a right eigenvector matrix V; the diagonal matrix S is the singular value matrix, S = diag(σ1, σ2, ···, σ r , ···, σ R ), where σ r represents the r-th diagonal element, R is the rank of matrix X, and σ1 ≥ σ2 ≥ ··· ≥ σ r ; Step 3.2: Select from σ1, σ2, ···, σ r , ···, σ R as appropriate, set the unselected diagonal elements to 0 to obtain a two-dimensional graph including curves and concave-convex regions; Step 3.3: Take the curve as a fault, the convex area as an anticline, and the concave area as a syncline, and assign weights to the fault, anticline, and syncline to construct a grade zoning map; Step 3.4: Take the area where the weight value exceeds the preset weight threshold range as the candidate layer.

3. The screening method for the deep well re-injection target layer of high-salt mine water depth according to claim 1, characterized in that, Step 3 is specifically: Set the first and second compressive strength ranges. If there are brittle sandstone formations in the alternative layers that meet the first compressive strength range, these formations are used as candidate layers; if not, select karst limestone formations that meet the second compressive strength range as candidate layers.

4. The screening method of the deep well back - storage target layer for the high - salinity mine water according to claim 3, characterized in that, The first compressive strength range is 30 MPa to 35 MPa, and the second compressive strength range is 40 MPa to 60 MPa.

5. The screening method for the deep well re-injection target layer of high-salt mine water according to claim 1, wherein The specific content of Step 5 is: Step 5.1: Score the water storage conditions of the i-th layer according to the proportion of the number of effective water storage layers and effective water isolation layers in the i-th layer; the effective water storage layer is a formation where the groundwater recharge, runoff, and discharge conditions do not meet the preset water storage conditions; the effective water isolation layer is a formation located at the top or bottom and having thick-layered mudstone or sandy mudstone developed; Step 5.2: Score the water quality of the i-th layer; Step 5.3: Score the characteristics of the i-th layer based on the porosity, permeability, saturation, temperature, whether there are large water-conducting channels, petrological characteristics, whether there are soluble cements, and the potential for evolution and change of the permeation characteristics of the i-th layer; Step 5.4: Based on the scores obtained in Steps 5.1 - 5.3, obtain the comprehensive score of the hydrogeological characteristics of the i-th layer.

6. The screening method of the deep well re-injection target layer for the high-salt mine water according to claim 5, wherein When scoring the characteristics of the i-th layer in 5.3, if any of the following conditions are met, the characteristic score is increased: Condition 1: Porosity is less than the porosity threshold, permeability is less than the permeability threshold, saturation is less than the saturation threshold, and temperature is greater than the temperature threshold; Condition 2: There are no large water-conducting channels; Condition 3: The proportion of quartz in the petrological characteristics is greater than the preset threshold; Condition 4: It contains erodible or soluble cement; Condition 5: The permeability characteristics have the potential to evolve and change.

7. A screening method for the target layer of deep well back-injection of high-salt mine water according to claim 1, characterized in that, In step 6, if the i-th formation has mineral resources with industrial value, the industrial production value of the i-th formation is scored according to the specific mineral resources possessed by the i-th formation, and this score is less than the non-commercial value score threshold; if the i-th formation does not have mineral resources with industrial value, the score of the i-th formation is greater than the non-commercial value score threshold.

8. The screening method for the target layer of deep well backstorage of high-salt mine water depth according to claim 7, wherein Mineral resources with industrial value include: groundwater, coal, petroleum, natural gas, oil shale or potash.

9. The screening method for the target layer of deep well back - storage of high - salinity mine water according to claim 1, wherein, Step 7 comprehensively considers the geological structure background, stress state, in-situ stress measurement data and the stability of the formation, and quantifies the tectonic stress level from 1 to 10 according to geological and tectonic stress research.

10. The screening method for the target layer of deep well back - storage of high - salinity mine water according to claim 1, wherein, In step 8, the greater the change amplitude of the resistivity in the logging curve of the i-th formation, the higher the type score of the formation.

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