Hot dry rock resource target assessment method based on multi-parameter fusion

Abstract

The invention discloses a hot dry rock resource target region assessment method based on multi-parameter fusion, and the method comprises the steps: dividing resource target region assessment parameters into five index layers: geophysical characteristics, surface geothermal characteristics, geothermal geological conditions, rock mass economy and geological safety; the indexes are further divided into 20 indexes such as gravity and magnetic force abnormity, inhabitation burial depth, earth heat flow value, 5km earth temperature, unit area resource quantity, earthquake area / earthquake activity, residential area / scale and the like. Weights are distributed to the indexes according to importance, the indexes are divided into five grades from a suitable grade to an unsuitable grade, the hot dry rock resource target areas are graded and sorted accordingly, and the optimal target area is optimized. According to the method, hot dry rock resource target region evaluation parameters and grades are subdivided, and target region evaluation conditions are clearer and finer; progressive elimination is adopted, and the evaluation method is reasonable; economic and safety evaluation is increased, and the problems that in the prior art, evaluation parameters of the hot dry rock resource target area are incomplete, and economical efficiency and safety are not considered are effectively solved.

Description

Technical Field

[0001] This invention patent relates to the field of geological exploration, and specifically relates to a method for evaluating the target area of hot dry rock resources based on the fusion of multi-parameters such as geophysical characteristics and surface geothermal characteristics. Background Art

[0002] Hot Dry Rock refers to a high-temperature rock mass buried 3 - 10 km underground, with a temperature above 180°C (150°C in some literature), without water or steam, and being dense and impermeable. It can be widely used for power generation, heating, enhanced oil recovery, etc. The "geothermal energy" guided by hot dry rock is one of the most cost-effective energies in the new energy field. Compared with hydrothermal geothermal energy, hot dry rock resources are more stable and uniform, will not cause water level decline or resource depletion due to over-exploitation, and will not cause disaster problems such as ground settlement. It is a new type of clean, efficient, and safe energy recognized by the international community. For more than 50 years, developed countries such as the United States, Japan, France, the United Kingdom, and Germany have successively invested heavily in research and have established 31 EGS projects, with a cumulative power generation capacity of about 12.2 MW. Currently, the international hot dry rock power generation technology is transitioning to the second-generation supercritical CO2 medium. The exploration and development of hot dry rock resources in China are still in the experimental stage. In the entire exploration and development process, target area evaluation is a very important link, which is directly related to the economic, environmental benefits, and production safety of hot dry rock resources. Due to the large burial depth of hot dry rock resources, conventional geological exploration means such as surface geological survey and hydrogeology, engineering geology, and environmental geology surveys have limited constraints on the evaluation of hot dry rock target areas; at the same time, the development of hot dry rock is similar to that of shale gas, and a heat storage area needs to be constructed through hydraulic fracturing technology. Research shows that unconventional oil and gas hydraulic fracturing (HF) and enhanced geothermal systems (EGS) can both cause deep fault creep and induce earthquakes, thereby affecting the living and production safety of residents around the development site. Therefore, how to systematically and accurately evaluate and delineate the target area of hot dry rock resources has become a key issue restricting the exploration and development of hot dry rock resources. Only by scientifically evaluating and accurately delineating the resource target area can the efficient, safe, and orderly development and utilization of hot dry rock resources be achieved.

[0003] At present, there are few evaluation methods for the development target areas of hot dry rock resources. "Optimization of Exploration Target Areas for Hot Dry Rock in the Chinese Continental Area: Insights from the Genetic Mechanisms of Domestic and Foreign Hot Dry Rock Systems" published in "Earth Science" comprehensively analyzed the site selection indicators of hot dry rock resources from aspects such as the tectonic background, terrestrial heat flow distribution, deep formation temperature, Cenozoic volcanic distribution, and Moho depth; "Evaluation Indicators and Formation Conditions for Hot Dry Rock Exploration" published in "Earth Science and Technology Bulletin" comprehensively evaluated the exploration evaluation indicators of hot dry rock from 6 aspects including lithosphere thickness and Moho burial depth, Curie depth, geothermal gradient, terrestrial heat flow, neotectonic movement, high-temperature hot springs and gas fields; "Thermal Reservoir Evaluation of Hot Dry Rock Geothermal Resources Based on Factor Analysis" published in "Journal of Chengdu University of Technology (Natural Science Edition)" selected 6 evaluation indicators including thermal reservoir burial depth, thermal reservoir temperature, terrestrial heat flow value, geothermal gradient, thermal reservoir lithology, and thermal reservoir physical properties, and ranked the thermal reservoir conditions of 11 hot dry rock resource research areas in China; "Construction and Application of the Evaluation System for Favorable Areas of Hot Dry Rock" published in "Petroleum Exploration and Development" evaluated the hot dry rock in the central Inner Mongolia Basin using 11 evaluation parameters including Moho depth, Curie depth, depth of melt or magma chamber, time of magmatic and volcanic activities, terrestrial heat flow, geothermal gradient, surface heat anomaly, earthquake magnitude and focal depth, distribution of deep major faults, thermal reservoir burial depth, and caprock type and thickness.

[0004] However, the above-mentioned intellectual properties still lack constraints on the evaluation of hot dry rock target areas, and none of them involve the extremely important economic and safety evaluations in the development and utilization of hot dry rock. Therefore, in order to effectively develop hot dry rock resources, reduce exploration costs, improve economic benefits, and ensure mining safety, an evaluation method for hot dry rock resource target areas is needed. Summary of the Invention

[0005] Aiming at the above-mentioned existing technical deficiencies, the purpose of the present invention is to provide an evaluation method for hot dry rock target areas that integrates 5 categories of parameters including geophysical characteristics, surface geothermal characteristics, geothermal geological conditions, rock mass economy, and geological safety, so as to solve the problems of incomplete evaluation parameters for hot dry rock resource target areas and the lack of consideration of economy and safety in the prior art.

[0006] The present invention adopts the following technical solutions:

[0007] S1. Divide the evaluation index layer of hot dry rock resource target areas into 5 aspects: geophysical characteristics, surface geothermal characteristics, geothermal geological conditions, rock mass economy, and geological safety.

[0008] S2. Further divide the geophysical characteristics into 6 indicators: gravity anomaly, magnetic anomaly, Curie depth, Moho depth, terrestrial heat flow value, and low-velocity and high-conductivity layer within the crust; divide the surface geothermal characteristics into 4 indicators: thermal infrared remote sensing image characteristics, surface fluid temperature, geothermal gradient, and fluid temperature scale; divide the geothermal geological conditions into 5 indicators: radioactive heat production rate, rock mass age, rock mass scale, fault scale, and reservoir-cap rock combination; divide the economic viability of the rock mass into 3 indicators: geothermal temperature at 5 km, estimated resource volume, and resource volume per unit area; divide the geological safety into 2 indicators: whether it is a seismic area / earthquake activity, and whether it is a residential area / size.

[0009] S3. Combining the basic geological conditions of the dry hot rock resources in China, conduct a 3-level classification for 2 geological safety indicators, and assign scores of 1.5, 1, and 0.5 respectively from suitable to unsuitable; conduct a 5-level classification for the remaining 18 indicators, namely suitable, relatively suitable, generally suitable, relatively unsuitable, and unsuitable, and assign scores of 5, 4, 3, 2, and 1 respectively from suitable to unsuitable; allocate weights to them according to the subjective weighting method based on the importance of each indicator for the development of dry hot rock resources.

[0010] Decomposition and Weight Assignment Diagram of Evaluation Indicators for Dry Hot Rock Resource Target Areas

[0011] S4. Conduct geological exploration and data collection for the region, and screen out at least 1 gravity and magnetic anomaly area above the unsuitable level in the region as the S4 target area.

[0012] S5. Calculate the burial depths of the Moho and Curie surfaces in the region through gravity and magnetic data; calculate the burial depth of the low-velocity and high-conductivity layer within the crust in the region based on the terrestrial heat flow value data; eliminate the regions in the S4 target area where the cumulative number of indicators exceeds two and are at the unsuitable level, and the remaining regions are used as the S5 target areas for further evaluation. Among them, the Curie depth is calculated using the frequency-domain high-order derivative power spectrum method based on the regional magnetic anomaly combination, the calculation data grid is 5 km × 5 km, and the window size is 100 km × 100 km. Among them, it is compiled using gravity data with the deep seismic exploration results as control points. The formula for calculating the high-conductivity and low-velocity layer is h = h0q -a , for the high-conductivity layer within the crust, h0 = 35 km, a = 1.30; for the high-conductivity layer in the upper mantle, h0 = 155 km, a = 1.46, q is the terrestrial heat flow value, and the unit is HFU.

[0013] S6. Use thermal infrared remote sensing, surface geological survey and other means to find out the thermal infrared inversion temperature, hot spring fluid temperature and geothermal gradient in the S5 target area; calculate the fluid temperature scale temperature by geochemical methods; eliminate the areas in the S5 target area that have accumulated more than two indicators and are unsuitable, and the remaining areas are used as the S6 target area for further evaluation. Among them, the thermal infrared remote sensing inversion uses ENVI5.3 software as the information extraction platform, and performs geometric correction, georeferencing and necessary interference removal and masking processing on each required scene remote sensing data to eliminate and suppress the influence of various interference factors on remote sensing anomalies. The atmospheric correction method is used to perform surface temperature inversion calculation in units of scenes. Among them, the hot spring fluid temperature scale temperature is mainly calculated by the SiO2 temperature scale method, and the formula used is: T℃=1309 / (5.19-lgC1)-273.15. C1 is the SiO2 content, in mg / L.

[0014] S7, calculate the radioactive heat generation rate of the rock mass through major and trace elements; calculate the age of the rock mass through zircon isotopes; determine the size of the rock mass through remote sensing, ground geological surveys and geophysical gravity and magnetic comprehensive inversion; determine the distribution of deep and large faults around the rock mass, the distribution conditions of heat reservoirs and caprocks through basic geological research; eliminate areas in the S6 target area that have accumulated more than two indicators and are unsuitable, and the remaining areas are used as S7 target areas for further evaluation. The radioactive heat generation rate is calculated as follows: A = 0.01ρ (9.52C U +2.56C Th +3.48C K ), A is the radioactive heat generation rate of rock, unit is μW / m 3 ; ρ is the rock density, in g / cm 3 ; C U , C Th are the U and Th contents in rocks, respectively, in units of 10 -6 ; C K is the K2O content in the rock, in %. The geophysical gravity and magnetic comprehensive inversion to determine the rock mass scale mainly uses Bouguer gravity anomaly map, residual gravity anomaly map, aeromagnetic △T anomaly map, aeromagnetic △T minimum wave 3rd order detail map, G H Comprehensive judgment of field cross-section diagram and two-dimensional magnetic intensity imaging results.

[0015] S8. Calculate the crustal heat flow through the crust-mantle heat flow ratio, and calculate the thickness of the radioactive enrichment layer in combination with the radioactive heat production rate; calculate the geothermal temperature at a depth of 5 km of the rock mass according to the trend that the radioactive heat production rate decays exponentially with depth by combining the thickness of the radioactive enrichment layer with the steady-state heat conduction formula and the radioactive heat production rate exponential formula; take 1 km as the slice thickness, slice the rock mass to calculate the volume, and calculate the heat resources in the slice volume and the total resources of the rock mass in combination with the top and bottom plate temperatures of the slice; calculate the resource amount per unit area of the rock mass in combination with the outcropping area of the rock mass; exclude the areas in the S7 target area where more than two indicators exceed the unsuitable level, and the remaining areas are used as the S8 target area for further evaluation. The formula for calculating the deep temperature is: Tz = T0 + q0z / k - Az 2 / 2k, Az = Aexp(-z / D). T z is the temperature at depth Z; T0 is the surface temperature; q0 is the surface terrestrial heat flow value; A is the rock heat production rate; k is the rock thermal conductivity; D is the thickness of the radioactive heat-producing element enrichment layer; Z is the depth. The formula for calculating the dry hot rock resource amount is: Q = ρ•Cρ•V•(T - Tc), where ρ is the rock density, taking 2.6 g / cm 3 ; Cρ is the specific heat of the rock, taking 794 J / kg•°C; V is the rock volume; T is the rock temperature at a specific depth, and Tc is the surface temperature.

[0016] S9. Judge whether the selected S6 target area is located in a seismic area and whether the seismic activity is active through past seismic data, and exclude the areas in the S8 target area where more than two indicators exceed the unsuitable level according to whether it is a residential area and the scale of the residential area. The remaining areas are the finally selected dry hot rock resource target area S9 target area.

[0017] S10. Score the S9 target area according to the evaluation index decomposition and weighting diagram of the dry hot rock resource target area, rank the dry hot rock resource target areas according to the higher the score, and select the best target area. The scoring formula is: I = , I is the total score value of the target area, Ki is the grade score value of each evaluation index, Ai is the weight value of each evaluation index, and n is the number of indicators, which is taken as 20 in the present invention.

[0018] Compared with the prior art, the advantages of the present invention are:

[0019] 1. The evaluation parameters of the dry hot rock resource target area are subdivided, and the target area evaluation conditions are clearer.

[0020] At present, the evaluation of dry hot rock resource targets that meet China's geological conditions is still in the practice stage. Many scholars and researchers have put forward their own views. However, most of them lack medium-scale basic geological data and fail to consider the impact of this part of data on the evaluation of dry hot rock resources, resulting in the lack of evaluation indicators. As a result, the data scale for regional tectonic research is extremely small, and the target range at the kilometer scale cannot be accurately delimited; while in point location research, the data is scarce and the universality is poor. Based on the comprehensive study of medium-scale basic geological data and evaluation practice, the present invention proposes to initially select targets based on regional gravity and magnetic anomalies, and refine the evaluation indicators of dry hot rock resource targets by inverting the depth of the Curie surface, the depth of the Moho surface, the value of the terrestrial heat flow, the low-velocity and high-conductivity layer in the crust, and the characteristics of thermal infrared remote sensing images, making the delineation of the target range more accurate.

[0021] 2. Subdivide the index levels of dry hot rock resource targets, and the target selection is more refined.

[0022] Combined with the basic geological conditions of China's dry hot rock resources, the geological safety index is divided into 3 levels, and the remaining 18 indicators are divided into 5 levels. The division is more refined, effectively avoiding the problem of inability to rank due to rough level division.

[0023] 3. Adopt progressive elimination, and the evaluation method is reasonable.

[0024] The present invention uses progressive screening and elimination of 19 indicators. Each target is deleted when it reaches two unsuitable levels. This method reduces the range from large to small, ensuring that the dry hot rock resources in the region are neither mis-evaluated nor missed, effectively reducing the workload of field geological surveys. At the same time, the constraint condition of two unsuitable levels not only has the universality of evaluation, but also ensures that a small number of rock masses with extremely good overall thermal conditions but poor individual conditions are not prematurely eliminated, and the evaluation method is relatively reasonable.

[0025] 4. Increase the evaluation of the economy and safety of rock masses, and the evaluation results have utilizable value.

[0026] The purpose of evaluating dry hot rock resource targets is for development and utilization. Previous studies mainly focused on the research and evaluation of the thermal formation mechanism of dry hot rock, and did not consider the economy and safety of its exploitation, resulting in the inability to develop and utilize the evaluated targets. The present invention increases the calculation of the geothermal temperature at a depth of 5 km of the rock mass, the resource volume of the rock mass and the resource volume per unit area, reducing the resource exploration cost and ensuring the economy of the development and utilization of dry hot rock resources; at the same time, considering the safety of the development of dry hot rock resources from two aspects of seismic activity and residential areas, the evaluation results have utilizable value.

[0027] 5. Assign weights to the evaluation indicators of dry hot rock targets, and the results are unique.

[0028] Combined with the basic conditions of dry hot rock resources in China, 20 evaluation indicators for dry hot rock resource target areas are divided. Three grades are divided for 2 geological safety indicators; the remaining 18 indicators are classified into 5 levels; according to the importance of different indicators for the exploration and development of dry hot rock resources, weights are assigned to each indicator. The detailed classification, grading and scoring make the scoring of each target area more accurate, and the results are unique, which is more conducive to the ranking of target areas. Description of the Drawings

[0029] The present invention will be further described in detail below with reference to the drawings.

[0030] Figure 1 It is a diagram for the decomposition and weighting of evaluation indicators for dry hot rock resource target areas

[0031] Figure 2 It is a flow chart for the evaluation of dry hot rock resource target areas Detailed Embodiment

[0032] The following further details the specific implementation of the present invention with reference to the drawings:

[0033] Please refer to Figure 1 As shown, the indicators for the evaluation of dry hot rock resource target areas are decomposed and weighted, mainly including the following steps:

[0034] 1 Subdivide the evaluation index layer of dry hot rock resource target areas.

[0035] 1.1 It is divided into 5 aspects: geophysical characteristics, surface geothermal characteristics, geothermal geological conditions, rock mass economy, and geological safety.

[0036] 1.2 The geophysical characteristics are divided into 6 indicators: gravity anomaly, magnetic anomaly, Curie depth, Moho depth, heat flow value, and low velocity and high conductivity layer in the crust; the surface geothermal characteristics are divided into 4 indicators: thermal infrared remote sensing image characteristics, surface fluid temperature, geothermal gradient, and fluid temperature scale; the geothermal geological conditions are divided into 5 indicators: radioactive heat generation rate, rock mass age, rock mass scale, fracture scale, and reservoir-cap combination; the rock mass economy is divided into 3 indicators: geothermal temperature at 5 km, estimated resource volume, and resource volume per unit area; the geological safety is divided into 2 indicators: whether it is a seismic area / earthquake activity and whether it is a residential area / size.

[0037] 2 Classify and weight each indicator.

[0038] 2.1 Combined with the existing characteristics of dry hot rocks in China, 3 grades are divided for 2 geological safety indicators, and scores of 1.5, 1, and 0.5 are assigned respectively from suitable to unsuitable; the remaining 18 indicators are divided into 5 grades: suitable, relatively suitable, generally suitable, relatively unsuitable, and unsuitable, and scores of 5, 4, 3, 2, and 1 are assigned respectively from suitable to unsuitable;

[0039] 2.2 Assign weights to each index according to its importance for the development of hot dry rock resources by the subjective weighting method.

[0040] Please refer to Figure 2 as shown, evaluate the target areas of hot dry rock resources.

[0041] 3 Optimize the target areas of hot dry rock resources.

[0042] 3.1 Screen out at least one area with gravity and magnetic anomalies above the unsuitable level in the area as the preliminary target area;

[0043] 3.2 Evaluate the burial depths of the Curie surface and the Moho surface, the burial depth of the low-velocity and high-conductivity layer in the crust, the temperature retrieved by thermal infrared, the temperature of hot spring fluid, the geothermal gradient, the temperature of fluid geothermometer, the radioactive heat generation rate of rock mass, the age of rock mass, the scale of rock mass, the distribution of deep major faults around the rock mass, the distribution conditions of heat reservoirs and caps, the geothermal temperature at a depth of 5 km of the rock mass, the total resource amount of the rock mass, and the resource amount per unit area of the rock mass for the preliminary target areas in turn. When evaluating each target area, if two unsuitable levels are reached, the target area will be excluded.

[0044] 3.3 After completing all index evaluations and target area exclusions, score the remaining target areas according to the decomposition and weighting diagram of the evaluation indexes of hot dry rock resource target areas, sort the hot dry rock resource target areas according to the higher the score, the better, and optimize the best target area, then complete the evaluation of the hot dry rock resource target area this time.

[0045] The above is the principle and implementation method of the present invention. It does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. A method for evaluating a hot dry rock target area, characterized in that: A variety of parameter fusion research is used to comprehensively analyze and judge the hot dry rock target area.

2. The method according to claim 1, characterized in that: The parameters used are divided into five index layers: geophysical characteristics, surface geothermal characteristics, geothermal geological conditions, rock mass economy, and geological safety.

3. The method according to claim 2, characterized in that: The geophysical characteristics are divided into six indicators: gravity anomaly, magnetic anomaly, Curie surface depth, Moho surface depth, geothermal heat flow value, and low-velocity and high-conductivity layer in the crust; the surface geothermal characteristics are divided into four indicators: thermal infrared remote sensing image characteristics, surface fluid temperature, geothermal gradient, and fluid temperature scale temperature; the geothermal geological conditions are divided into five indicators: radioactive heat generation rate, rock mass age, rock mass scale, fault scale, and reservoir-cap combination; the rock mass economy is divided into three indicators: ground temperature at 5km, estimated resources, and resources per unit area; the geological safety is divided into two indicators: whether it is an earthquake zone / earthquake activity and whether it is a residential area / scale, totaling 20 indicators.

4. The method according to claim 3, characterized in that: According to the average characteristic values ​​of existing hot dry rock resources in China, the geological safety indicators were divided into three levels, and scored 1.5, 1, and 0.5 points respectively from suitable to unsuitable; the remaining 18 indicators were divided into five levels of suitable, relatively suitable, generally suitable, relatively unsuitable, and unsuitable, and scored 5, 4, 3, 2, and 1 points respectively from suitable to unsuitable.

5. The method according to claim 4, characterized in that: The 20 indicators are assigned weights using the subjective weighting method based on their importance.

6. The method according to claim 5, characterized in that: The S9 target area is scored according to the dry hot rock resource target area assessment index decomposition and weighted map, and the dry hot rock resource target areas are ranked according to the higher the score, the better, and the best target area is selected. The scoring formula is: I = , I is the total score of the target area, Ki is the grade score of each evaluation indicator, Ai is the weight value of each evaluation index, n is the number of indicators, and the value is 20 in the present invention.

7. The evaluation steps for the S9 target area are as follows: S4. Conduct geological surveys and data collection in the region, and select at least one regional gravity and magnetic anomaly area above the unsuitable level as the S4 target area. S5. Calculate the burial depth of the regional Moho and Curie surface through gravity and magnetic data; calculate the burial depth of the low-velocity and high-conductivity layer in the regional crust based on the geothermal heat flow value data; eliminate the areas in the S4 target area that have accumulated more than two indicators and are at the unsuitable level, and the remaining areas are used as the S5 target area for further evaluation. S6. Use thermal infrared remote sensing, surface geological surveys and other means to find out the thermal infrared inversion temperature, hot spring fluid temperature, and geothermal gradient in the S5 target area; calculate the fluid temperature scale temperature through geochemical methods; eliminate the areas in the S5 target area that have accumulated more than two indicators and are at the unsuitable level, and the remaining areas are used as the S6 target area for further evaluation. S7. Calculate the radioactive heat generation rate of the rock mass through major and trace elements; calculate the age of the rock mass through zircon isotopes; determine the scale of the rock mass through remote sensing, ground geological surveys and geophysical gravity and magnetic inversion; determine the distribution of deep and large faults around the rock mass, the distribution conditions of heat reservoirs and caprocks through basic geological research; eliminate areas in the S6 target area that have accumulated more than two indicators and are unsuitable, and the remaining areas are used as S7 targets for further evaluation. S8. Calculate the crustal heat flow through the crust-mantle heat flow ratio, and calculate the thickness of the radioactive enriched layer in combination with the radioactive heat generation rate; calculate the ground temperature at a depth of 5km in the rock mass based on the thickness of the radioactive enriched layer combined with the steady-state heat conduction formula and the radioactive heat generation rate exponential formula, according to the exponential decay trend of the radioactive heat generation rate with depth; Taking 1km as the slice thickness, the rock mass is sliced ​​to calculate the volume, and the thermal resources in the slice volume and the total rock mass resources are calculated based on the top and bottom plate temperatures of the slices; the rock mass resources per unit area are calculated based on the exposed area of ​​the rock mass; Eliminate the areas in the S7 target area that have accumulated more than two indicators and are unsuitable, and the remaining areas are used as the S8 target area for further evaluation. S9. Determine whether the selected S6 target area is located in the earthquake zone and whether the earthquake activity is active, whether it is a residential area and the scale of the residential area through previous seismic data. Eliminate the areas in the S8 target area that have accumulated more than two indicators and are unsuitable, and the remaining areas are used as the final preferred regional hot dry rock resource target area S9 target area.

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