Geothermal resource positioning method based on heat control construction

Abstract

The application discloses a geothermal resource positioning method based on heat control construction, relates to the technical field of geothermal resource survey positioning, and comprises the following steps: acquiring geological structure data at different depths and ranges, determining the distribution range and depth of structures at various levels through geological investigation and geophysical exploration; determining a main channel of a geothermal source through first-level structure discrimination; determining a groundwater and geothermal circulation fusion approach through second-level structure discrimination; determining a geothermal reservoir through third-level structure discrimination; constructing a regional structure system; and combining the analysis results of the first-level, second-level and third-level structures with the regional structure system to analyze and predict the position of a geothermal enrichment area. The application has the beneficial effect that the method of the regional structure system can quickly identify and analyze the geological structure, effectively position the geothermal range, and improve the positioning accuracy of the geothermal resource, and the method has very important guiding significance for future geothermal exploration and development and utilization.

Description

Technical Field

[0001] This invention relates to the field of geothermal resource exploration and location technology, and more specifically, to a geothermal resource location method based on tectonic heat control. Background Technology

[0002] Geothermal resources, as a clean and renewable energy source, have broad application prospects. However, current methods are insufficient to accurately reveal the enrichment patterns and distribution characteristics of geothermal resources, and they also involve high costs. Therefore, this paper proposes a method for geothermal resource location by controlling structural positioning, which has significant scientific and practical application value for the exploration, development, and utilization of geothermal resources. Summary of the Invention

[0003] To address the above deficiencies, this invention provides a geothermal resource location method based on tectonic heat control, thus solving the aforementioned problems.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] The geothermal resource location method based on tectonic heat control includes the following steps;

[0006] 1) Obtain geological structural data at different depths and ranges, and determine the distribution range and depth of structures at various levels through geological surveys and geophysical exploration;

[0007] 2) First-level structural identification to determine the main geothermal source channel;

[0008] 3) Secondary structural identification to determine the fusion pathway of groundwater and geothermal circulation;

[0009] 4) Three-level structural identification to determine geothermal reservoirs;

[0010] 5) Construct a regional tectonic system;

[0011] 6) The analysis results of primary, secondary and tertiary structures, combined with the regional tectonic system, are used to analyze and predict the location of geothermal enrichment areas.

[0012] Criteria for determining first-order structures;

[0013] 2.1) The mantle fault structure from the upper mantle to the deep lithosphere is a deep and large fault that regionally cuts through the asthenosphere of the upper mantle. It is the main channel for the migration of high-temperature mantle-derived material to the shallow part, providing abundant heat source conditions for regional geothermal hot spring resources.

[0014] Furthermore, the temperature range of the mantle fracture structure is 750-1000 degrees Celsius, and the depth range is 30km-80km.

[0015] Criteria for identifying secondary structures;

[0016] 3.1) Faulted crustal structures extending from the deep lithosphere to the upper crust. Faulted fracture zones are located near these structures. High-temperature mantle heat is transported to the shallow crust via conduction or convection, where it mixes with shallow groundwater to form geothermal fields.

[0017] Furthermore, the temperature range of the fractured crust structure is 280-750 degrees Celsius, and the depth range is 10km-30km.

[0018] Furthermore, the criteria for determining tertiary structures;

[0019] 4.1) Small-scale extensional faults in the shallow crust connect with primary and secondary structures to form a structural network system, which is the key structural network for deep geothermal energy to connect the shallow crust and emerge to form hot springs.

[0020] The third-level structure directly receives replenishment from atmospheric precipitation, which mixes with deep geothermal water during downward infiltration to form hot springs.

[0021] Furthermore, the steps for constructing a regional tectonic system include:

[0022] 5.1) Using GIS spatial overlay analysis, identify first-order mantle fault structures based on gravity anomaly maps and seismic tomography data;

[0023] 5.2) Identify secondary fracture structures by combining CSAMT profiling technology, magnetic anomalies, and magnetic data;

[0024] 5.3) High-resolution seismic exploration instruments and UAV aeromagnetic identification were used to identify third-order tensional faults;

[0025] 5.4) Analyze the connectivity of each level by analyzing the fracture direction angle and the vertical superposition of resistivity;

[0026] 5.5) Establish a three-dimensional structural model and calculate the geothermal enrichment index Qh;

[0027] a. Import borehole and seismic profiles to establish a base frame model;

[0028] b. Simulate the spatial distribution of the fault zone using Petrel software;

[0029] c. Add attribute fields (first-level structure: temperature at the Moho surface 800℃; third-level structure: gradient at 1km > 50℃ / km);

[0030] d. Calculate and output the geothermal enrichment index Qh.

[0031] Furthermore, in step d, Qh = K·ΔLΔT·A·Φ;

[0032] Parameter description:

[0033] Qh: Geothermal enrichment index;

[0034] K: Thermal conductivity of the fracture zone (W / m·K);

[0035] ΔT / ΔL: Geothermal gradient of the tectonic zone (°C / km);

[0036] A: Area of ​​the fault intersection zone (km²) 2 );

[0037] Φ: Connectivity coefficient;

[0038] Geothermal enrichment index Qh threshold setting:

[0039] The primary target area is defined as 70 > Qh > 50.

[0040] A target range of 100 > Qh > 70 is considered a secondary target region.

[0041] A target area with a value of Qh > 100 is considered a Level 3 target area.

[0042] Furthermore, the first and second levels, and the second and third levels are directly connected: Φ = 1.0;

[0043] The intersection angle between primary and secondary structures, and between secondary and tertiary structures, is <30°: Φ=0.8;

[0044] Isolated faults of grade I and II, and grade II and III: Φ = 0.3.

[0045] The beneficial effects of this invention are: the method fully reveals the formation mechanism of the "five major geothermal enrichment zones" and the "five major geothermal enrichment basins". Different structural systems with different structural scales and types contain different types of geothermal enrichment areas; the formation of first-, second-, and third-order structures and the formation of a network structure in the crust for heat generation, transfer, and storage.

[0046] The regional tectonic system approach can quickly identify and analyze geographical structures, enabling effective location of geothermal areas and improving the accuracy of geothermal resource location. Currently, geothermal areas have been successfully located in Baoshan, Yunnan and Tanyang, Fujian using this method. This method has significant guiding significance for future geothermal exploration and development. Attached Figure Description

[0047] Figure 1 This is a spatial schematic diagram of the geothermal resource location method based on structural heat control described in this invention;

[0048] Figure 2 This is a schematic diagram of the method flow of the present invention;

[0049] Figure 3 This is a schematic diagram of geothermal temperature. Detailed Implementation

[0050] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0051] This application provides a method for locating geothermal resources based on tectonic heat control. Please refer to [reference needed]. Figures 1-3 Includes the following steps;

[0052] 1) Obtain geological structural data at different depths and ranges, and determine the distribution range and depth of structures at various levels through geological surveys and geophysical exploration;

[0053] 2) First-level structural identification to determine the main geothermal source channel;

[0054] 3) Secondary structural identification to determine the fusion pathway of groundwater and geothermal circulation;

[0055] 4) Three-level structural identification to determine geothermal reservoirs;

[0056] 5) Construct a regional tectonic system;

[0057] 6) The analysis results of primary, secondary and tertiary structures, combined with the regional tectonic system, are used to analyze and predict the location of geothermal enrichment areas.

[0058] Criteria for determining first-order structures;

[0059] 2.1) The mantle fault structure from the upper mantle to the deep lithosphere is a deep and large fault that regionally cuts through the asthenosphere of the upper mantle. It is the main channel for the migration of high-temperature mantle-derived material to the shallow part, providing abundant heat source conditions for regional geothermal hot spring resources.

[0060] The temperature range of the mantle fracture structure is 750-1000 degrees Celsius, and the depth range is 30km-80km.

[0061] Criteria for identifying secondary structures;

[0062] 3.1) Faulted crustal structures extending from the deep lithosphere to the upper crust. Faulted fracture zones are located near these structures. High-temperature mantle heat is transported to the shallow crust via conduction or convection, where it mixes with shallow groundwater to form geothermal fields.

[0063] The temperature range of the fractured crust structure is 280-750 degrees Celsius, and the depth range is 10km-30km.

[0064] Criteria for determining tertiary structures;

[0065] 4.1) Small-scale extensional faults in the shallow crust connect with primary and secondary structures to form a structural network system, which is the key structural network for deep geothermal energy to connect the shallow crust and emerge to form hot springs.

[0066] The third-level structure directly receives replenishment from atmospheric precipitation, which mixes with deep geothermal water during downward infiltration to form hot springs.

[0067] The steps involved in constructing a regional tectonic system include:

[0068] 5.1) Using GIS spatial overlay analysis, identify first-order mantle fault structures based on gravity anomaly maps and seismic tomography data;

[0069] 5.2) Identify secondary fracture structures by combining CSAMT profiling technology, magnetic anomalies, and magnetic data;

[0070] 5.3) High-resolution seismic exploration instruments and UAV aeromagnetic identification were used to identify third-order tensional faults;

[0071] 5.4) Analyze the connectivity of each level by analyzing the fracture direction angle and the vertical superposition of resistivity;

[0072] 5.5) Establish a three-dimensional structural model and calculate the geothermal enrichment index Qh;

[0073] a. Import borehole and seismic profiles to establish a base frame model;

[0074] b. Simulate the spatial distribution of the fault zone using Petrel software;

[0075] c. Add attribute fields (first-level structure: temperature at the Moho surface 800℃; third-level structure: gradient at 1km > 50℃ / km);

[0076] d. Calculate and output the geothermal enrichment index Qh.

[0077] In step d, Qh = K·ΔLΔT·A·Φ;

[0078] Parameter description:

[0079] Qh: Geothermal enrichment index;

[0080] K: Thermal conductivity of the fracture zone (W / m·K);

[0081] ΔT / ΔL: Geothermal gradient of the tectonic zone (°C / km);

[0082] A: Area of ​​the fault intersection zone (km²) 2 );

[0083] Φ: Connectivity coefficient;

[0084] Geothermal enrichment index Qh threshold setting:

[0085] The primary target area is defined as 70 > Qh > 50.

[0086] A target range of 100 > Qh > 70 is considered a secondary target region.

[0087] A target area with a value of Qh > 100 is considered a Level 3 target area.

[0088] The first and second levels, and the second and third levels are directly connected: Φ = 1.0;

[0089] The intersection angle between primary and secondary structures, and between secondary and tertiary structures, is <30°: Φ=0.8;

[0090] Isolated faults of grade I and II, and grade II and III: Φ = 0.3.

[0091] Specifically, taking the geothermal resource location method based on structure-controlled heat as an example, the first optimization complete step is as follows:

[0092] 1) Obtain geological structural data at different depths and ranges, and determine the distribution range and depth of structures at various levels through geological surveys and geophysical exploration;

[0093] 2) First-level structural identification to determine the main geothermal source channel;

[0094] 3) Secondary structural identification to determine the fusion pathway of groundwater and geothermal circulation;

[0095] 4) Three-level structural identification to determine geothermal reservoirs;

[0096] 5) Construct a regional tectonic system;

[0097] 6) The analysis results of primary, secondary and tertiary structures, combined with the regional tectonic system, are used to analyze and predict the location of geothermal enrichment areas.

[0098] Detailed data on first-, second-, and third-order structures can be obtained using corresponding monitoring tools (GIS, CSAMT, high-resolution seismic exploration instruments). This data is then input into the regional tectonic system for analysis. The specific analysis includes the thermal conductivity of fault zones; geothermal gradient of tectonic zones; area of ​​fault intersection zones; and connectivity coefficients. The corresponding values ​​are then obtained from the analysis.

[0099] Then, the specific value is obtained by applying the geothermal enrichment index formula Qh=K·ΔLΔT·A·Φ; the Qh value is classified into levels as follows;

[0100] The primary target area is defined as 70 > Qh > 50.

[0101] A target range of 100 > Qh > 70 is considered a secondary target region.

[0102] A target area with a value of Qh > 100 is considered a Level 3 target area.

[0103] Meeting the criteria for a Level 1 target area means meeting the criteria for a geothermal enrichment zone.

[0104] Criteria for determining first-order structures;

[0105] 2.1) The mantle fault structure from the upper mantle to the deep lithosphere is a deep and large fault that regionally cuts through the asthenosphere of the upper mantle. It is the main channel for the migration of high-temperature mantle-derived material to the shallow part, providing abundant heat source conditions for regional geothermal hot spring resources.

[0106] The temperature of the mantle fracture structure is 750 degrees Celsius, and the depth is 30 km.

[0107] The region from the upper mantle to the deep lithosphere is the main area of ​​mantle-fault tectonics. This region has deep and large fault zones that can provide a continuous heat source for small-scale extensional faults, with a temperature of 750 degrees Celsius and a depth of 30 km.

[0108] Criteria for identifying secondary structures;

[0109] 3.1) Faulted crustal structures extending from the deep lithosphere to the upper crust. Faulted fracture zones are located near these structures. High-temperature mantle heat is transported to the shallow crust via conduction or convection, where it mixes with shallow groundwater to form geothermal fields.

[0110] The temperature range of the fractured crust structure is 280 degrees Celsius, and the depth range is 10 km.

[0111] This area serves as a transit zone for heat transfer, containing numerous fracture zones. Heat can be transferred to locations near the Earth's surface through the gaps in these fracture zones.

[0112] Criteria for determining tertiary structures;

[0113] 4.1) Small-scale extensional faults in the shallow crust connect with primary and secondary structures to form a structural network system, which is the key structural network for deep geothermal energy to connect the shallow crust and emerge to form hot springs.

[0114] The third-level structure directly receives replenishment from atmospheric precipitation, which mixes with deep geothermal water during downward infiltration to form hot springs.

[0115] This area is typically distributed from the surface to 5 kilometers underground, with numerous small branches, and is an essential channel for deep geothermal energy to connect to the shallow crust.

[0116] The steps involved in constructing a regional tectonic system include:

[0117] 5.1) Using GIS spatial overlay analysis, identify first-order mantle fault structures based on gravity anomaly maps and seismic tomography data;

[0118] 5.2) Identify secondary fracture structures by combining CSAMT profiling technology, magnetic anomalies, and magnetic data;

[0119] 5.3) High-resolution seismic exploration instruments and UAV aeromagnetic identification were used to identify third-order tensional faults;

[0120] 5.4) Analyze the connectivity of each level by analyzing the fracture direction angle and the vertical superposition of resistivity;

[0121] 5.5) Establish a three-dimensional structural model and calculate the geothermal enrichment index Qh;

[0122] a. Import borehole and seismic profiles to establish a base frame model;

[0123] b. Simulate the spatial distribution of the fault zone using Petrel software;

[0124] c. Add attribute fields (first-level structure: temperature at the Moho surface 800℃; third-level structure: gradient at 1km > 50℃ / km);

[0125] d. Calculate and output the geothermal enrichment index Qh.

[0126] In step d, Qh = K·ΔLΔT·A·Φ;

[0127] Parameter description:

[0128] Qh: Geothermal enrichment index;

[0129] K: Thermal conductivity of the fracture zone (W / m·K);

[0130] ΔT / ΔL: Geothermal gradient of the tectonic zone (°C / km);

[0131] A: Area of ​​the fault intersection zone (km²) 2 );

[0132] Φ: Connectivity coefficient;

[0133] Geothermal enrichment index Qh threshold setting:

[0134] The primary target area is defined as 70 > Qh > 50.

[0135] A target range of 100 > Qh > 70 is considered a secondary target region.

[0136] A target area with a value of Qh > 100 is considered a Level 3 target area.

[0137] By analyzing the data through this structural system, it is possible to quickly determine whether the data in a region meets the standards and classify it into different levels.

[0138] The first and second levels, and the second and third levels are directly connected: Φ = 1.0;

[0139] The intersection angle between primary and secondary structures, and between secondary and tertiary structures, is <30°: Φ=0.8;

[0140] Isolated faults of grade I and II, and grade II and III: Φ = 0.3.

[0141] Example 1 of calculating the geothermal enrichment index;

[0142] First-level structural discrimination data;

[0143] Gravity anomaly map data: NE-directed Bouguer anomaly gradient band (Δg=18mGal / km);

[0144] Seismic tomography: The low-velocity zone extends to a mantle fault structure at a depth of 30-80 km and a temperature of 800±20℃.

[0145] Secondary structural discrimination data;

[0146] CSAMT profile: Low-resistivity (5Ω·m) fractured shell structure with vertical depth of 15-28km;

[0147] Magnetic anomaly: superimposed linear negative ΔT band;

[0148] Third-level structural discrimination data;

[0149] UAV aeromagnetic analysis: Identification of conjugate tensile fractures (strike at N40°E);

[0150] Shallow earthquake: fracture zone width 22m (Vp=2.8km / s, drop 17%).

[0151] The secondary structure dips towards the NW direction and intersects with the tertiary fault at an angle of 25°.

[0152] Substituting into the formula Qh=K2.8×ΔT / ΔL58×A 1.6×Φ0.8=207 Level 3 target area.

[0153] The second preferred complete step is as follows:

[0154] 1) Obtain geological structural data at different depths and ranges, and determine the distribution range and depth of structures at various levels through geological surveys and geophysical exploration;

[0155] 2) First-level structural identification to determine the main geothermal source channel;

[0156] 3) Secondary structural identification to determine the fusion pathway of groundwater and geothermal circulation;

[0157] 4) Three-level structural identification to determine geothermal reservoirs;

[0158] 5) Construct a regional tectonic system;

[0159] 6) The analysis results of primary, secondary and tertiary structures, combined with the regional tectonic system, are used to analyze and predict the location of geothermal enrichment areas.

[0160] Criteria for determining first-order structures;

[0161] 2.1) The mantle fault structure from the upper mantle to the deep lithosphere is a deep and large fault that regionally cuts through the asthenosphere of the upper mantle. It is the main channel for the migration of high-temperature mantle-derived material to the shallow part, providing abundant heat source conditions for regional geothermal hot spring resources.

[0162] The temperature of the mantle fracture structure is 1000 degrees Celsius, and the depth is 80 km.

[0163] Criteria for identifying secondary structures;

[0164] 3.1) Faulted crustal structures extending from the deep lithosphere to the upper crust. Faulted fracture zones are located near these structures. High-temperature mantle heat is transported to the shallow crust via conduction or convection, where it mixes with shallow groundwater to form geothermal fields.

[0165] The temperature of the fractured crust is 750 degrees Celsius, and the depth is 30 km.

[0166] Criteria for determining tertiary structures;

[0167] 4.1) Small-scale extensional faults in the shallow crust connect with primary and secondary structures to form a structural network system, which is the key structural network for deep geothermal energy to connect the shallow crust and emerge to form hot springs.

[0168] The third-level structure directly receives replenishment from atmospheric precipitation, which mixes with deep geothermal water during downward infiltration to form hot springs.

[0169] The steps involved in constructing a regional tectonic system include:

[0170] 5.1) Using GIS spatial overlay analysis, identify first-order mantle fault structures based on gravity anomaly maps and seismic tomography data;

[0171] 5.2) Identify secondary fracture structures by combining CSAMT profiling technology, magnetic anomalies, and magnetic data;

[0172] 5.3) High-resolution seismic exploration instruments and UAV aeromagnetic identification were used to identify third-order tensional faults;

[0173] 5.4) Analyze the connectivity of each level by analyzing the fracture direction angle and the vertical superposition of resistivity;

[0174] 5.5) Establish a three-dimensional structural model and calculate the geothermal enrichment index Qh;

[0175] a. Import borehole and seismic profiles to establish a base frame model;

[0176] b. Simulate the spatial distribution of the fault zone using Petrel software;

[0177] c. Add attribute fields (first-level structure: temperature at the Moho surface 800℃; third-level structure: gradient at 1km > 50℃ / km);

[0178] d. Calculate and output the geothermal enrichment index Qh.

[0179] In step d, Qh = K·ΔLΔT·A·Φ;

[0180] Parameter description:

[0181] Qh: Geothermal enrichment index;

[0182] K: Thermal conductivity of the fracture zone (W / m·K);

[0183] ΔT / ΔL: Geothermal gradient of the tectonic zone (°C / km);

[0184] A: Area of ​​the fault intersection zone (km²) 2 );

[0185] Φ: Connectivity coefficient;

[0186] Geothermal enrichment index Qh threshold setting:

[0187] The primary target area is defined as 70 > Qh > 50.

[0188] A target range of 100 > Qh > 70 is considered a secondary target region.

[0189] A target area with a value of Qh > 100 is considered a Level 3 target area.

[0190] Further methods for determining the connectivity coefficient Φ.

[0191] The first and second levels, and the second and third levels are directly connected: Φ = 1.0;

[0192] The intersection angle between first- and second-order structures, and between second- and third-order structures, is <30°: Φ = 0.8; the isolated faults between first- and second-order structures, and between second- and third-order structures, are: Φ = 0.3.

Claims

1. A geothermal resource location method based on tectonic heat control, characterized in that, Includes the following steps; 1) Obtain geological structural data at different depths and ranges, and determine the distribution range and depth of structures at various levels through geological surveys and geophysical exploration; 2) First-level structural identification to determine the main geothermal source channel; 3) Secondary structural identification to determine the fusion pathway of groundwater and geothermal circulation; 4) Three-level structural identification to determine geothermal reservoirs; 5) Construct a regional tectonic system; 6) The analysis results of primary, secondary and tertiary structures, combined with the regional tectonic system, are used to analyze and predict the location of geothermal enrichment areas.

2. The geothermal resource location method based on tectonic heat control according to claim 1, characterized in that, Criteria for determining first-order structures; 2.1) The mantle fault structure from the upper mantle to the deep lithosphere is a deep and large fault that regionally cuts through the asthenosphere of the upper mantle. It is the main channel for the migration of high-temperature mantle-derived material to the shallow part, providing abundant heat source conditions for regional geothermal hot spring resources.

3. The geothermal resource location method based on tectonic heat control according to claim 2, characterized in that, The temperature range of the mantle fracture structure is 750-1000 degrees Celsius, and the depth range is 30km-80km.

4. The geothermal resource location method based on tectonic heat control according to claim 2, characterized in that, Criteria for identifying secondary structures; 3.1) Faulted crustal structures extending from the deep lithosphere to the upper crust. Faulted fracture zones are located near these structures. High-temperature mantle heat is transported to the shallow crust via conduction or convection, where it mixes with shallow groundwater to form geothermal fields.

5. The geothermal resource location method based on tectonic heat control according to claim 4, characterized in that, The temperature range of the fractured crust structure is 280-750 degrees Celsius, and the depth range is 10km-30km.

6. The geothermal resource location method based on tectonic heat control according to claim 4, characterized in that, Criteria for determining tertiary structures; 4.1) Small-scale extensional faults in the shallow crust connect with primary and secondary structures to form a structural network system, which is the key structural network for deep geothermal energy to connect the shallow crust and emerge to form hot springs. The third-level structure directly receives replenishment from atmospheric precipitation, which mixes with deep geothermal water during downward infiltration to form hot springs.

7. The geothermal resource location method based on tectonic heat control according to any one of claims 1-6, characterized in that, The steps involved in constructing a regional tectonic system include: 5.1) Using GIS spatial overlay analysis, identify first-order mantle fault structures based on gravity anomaly maps and seismic tomography data; 5.2) Identify secondary fracture structures by combining CSAMT profiling technology, magnetic anomalies, and magnetic data; 5.3) High-resolution seismic exploration instruments and UAV aeromagnetic identification were used to identify third-order tensional faults; 5.4) Analyze the connectivity of each level by analyzing the fracture direction angle and the vertical superposition of resistivity; 5.5) Establish a three-dimensional structural model and calculate the geothermal enrichment index Qh; a. Import borehole and seismic profiles to establish a base frame model; b. Simulate the spatial distribution of the fault zone using Petrel software; c. Add attribute fields (first-level structure: temperature at the Moho surface 800℃; third-level structure: gradient at 1km > 50℃ / km); d. Calculate and output the geothermal enrichment index Qh.

8. The geothermal resource location method based on tectonic heat control according to claim 7, characterized in that, In step d, Qh = K·ΔLΔT·A·Φ; Parameter description: Qh: Geothermal enrichment index; K: Thermal conductivity of the fracture zone (W / m·K); ΔT / ΔL: Geothermal gradient of the tectonic zone (°C / km); A: Area of ​​the fault intersection zone (km²) 2 ); Φ: Connectivity coefficient; Geothermal enrichment index Qh threshold setting: The primary target area is defined as 70 > Qh > 50. A target range of 100 > Qh > 70 is considered a secondary target region. A target area with a value of Qh > 100 is classified as a Level 3 target area.

9. The geothermal resource location method based on tectonic heat control according to claim 8, characterized in that... ； The first and second levels, and the second and third levels are directly connected: Φ = 1.0; The intersection angle between primary and secondary structures, and between secondary and tertiary structures, is <30°: Φ=0.8; Isolated faults of grade I and II, and grade II and III: Φ = 0.3.

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