Control method and system for maintaining sandstone geothermal well full life cycle recharge

Abstract

This invention belongs to the field of new energy development technology. It discloses a control method and system for maintaining reinjection throughout the entire lifecycle of sandstone geothermal wells. The method includes: extracting continuous core samples and obtaining reservoir property data to establish a set of characteristic parameters for sandstone reservoirs; conducting reinjection condition simulation tests to obtain an optimal combination of parameters for the wellbore filtration structure; performing pumping and reinjection tests on the target geothermal well based on the optimal combination of parameters to determine initial reinjection parameters; acquiring chemical and microbial component data to determine the formation law of blockage substances under different reinjection flow rates, reinjection water temperatures, and system tightness conditions, and screening out an optimal combination of reinjection process parameters; implementing well washing operations; performing reinjection capacity retesting after well washing; comparing the retest results with the initial reinjection parameters; and dynamically adjusting the optimal combination of reinjection process parameters based on the comparison results. This significantly improves the service life of sandstone geothermal wells.

Description

Technical Field

[0001] This invention relates to the field of new energy development technology, and more specifically, to a control method and system for maintaining reinjection of sandstone geothermal wells throughout their entire life cycle. Background Technology

[0002] Geothermal resources are widely valued as a stable and reliable renewable energy source. In the process of geothermal development and utilization, the balance between production and reinjection is the core requirement for the sustainable utilization of geothermal resources. The effective implementation of reinjection technology directly determines the operating efficiency and service life of the geothermal system. Sandstone reservoirs have become an important target stratum for medium-deep geothermal development due to their wide distribution and abundant reserves. As a key link in maintaining reservoir pressure and realizing tailwater recycling, the long-term stability of reinjection throughout its entire life cycle has a decisive impact on the economic feasibility of geothermal projects.

[0003] Sandstone geothermal wells face a significant challenge during long-term reinjection: the gradual decline in formation water absorption capacity. Specifically, sandstone formations contain numerous tiny pores and channels. During continuous reinjection, these channels undergo multiple blockage processes. Fine particulate impurities carried in the reinjection tailwater continuously deposit in narrow channels, forming a blockage layer. Simultaneously, the long-term contact and reaction between the reinjection water and the rock generates new mineral deposits that gradually fill existing water flow channels. Furthermore, temperature changes can cause minerals in the rock to dissolve and then redeposit elsewhere. These factors combined exacerbate formation blockage over time. With increasing service life, the... The continuous decline in reinjection capacity can lead to premature failure of reinjection wells in severe cases. Currently, the main approach to this problem is to take remedial measures after a significant decrease in reinjection capacity, such as injecting chemical agents to dissolve blockages or flushing the wellbore with high-pressure water. However, these methods can only restore part of the reinjection capacity in the short term and cannot fundamentally prevent the continued development of formation blockage. Moreover, frequent repair operations not only increase operating costs but may also cause additional damage to the formation structure. Existing technologies lack an active control method that can maintain the long-term stability of reinjection capacity throughout the entire operating cycle. This problem seriously restricts the large-scale sustainable development and utilization of sandstone geothermal resources.

[0004] In view of this, the present invention proposes a control method and system for maintaining reinjection of sandstone geothermal wells throughout their entire life cycle to solve the above problems. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of the prior art and to achieve the above objectives, the present invention provides the following technical solution: a control method for maintaining reinjection throughout the entire life cycle of sandstone geothermal wells, comprising:

[0006] Step S1: Conduct drilling and coring operations on the target geothermal well, extract continuous core samples from the sandstone geothermal reservoir section, and obtain reservoir physical property data through electrical logging and sonic logging. Based on the continuous core samples and reservoir physical property data, establish a set of characteristic parameters for the sandstone reservoir.

[0007] Step S2: Conduct reinjection simulation tests on continuous core samples based on the sandstone reservoir characteristic parameter set. By adjusting the configuration combination of filter media particle size, filter pipe porosity, opening diameter and mesh specifications, obtain the optimal parameter combination of wellbore filtration structure.

[0008] Step S3: Based on the optimal parameter combination of the wellbore filtration structure, conduct pumping and reinjection tests on the target geothermal well, determine the comprehensive permeability of the aquifer and the relationship between pressure head and reinjection volume, and determine the initial reinjection parameters accordingly.

[0009] Step S4: Conduct water quality characteristic testing on the recharge tailwater to obtain chemical composition data and microbial composition data. Based on the chemical composition data and microbial composition data, determine the generation law of blockage substances under different recharge flow rates, recharge water temperatures and system airtightness, and screen out the optimal combination of recharge process parameters.

[0010] Step S5: Perform well washing operation on the target geothermal well according to the preset operating cycle. After the well washing operation is completed, perform reinjection capacity retest, compare the retest results with the initial reinjection parameters, and dynamically adjust the optimal combination of reinjection process parameters based on the comparison results.

[0011] The control system used to maintain reinjection throughout the entire life cycle of sandstone geothermal wells includes:

[0012] Data extraction module: Drilling and coring operations are carried out on the target geothermal well to extract continuous core samples from the sandstone geothermal reservoir section, and reservoir physical property data are obtained through electrical logging and sonic logging. Based on the continuous core samples and reservoir physical property data, a set of characteristic parameters of the sandstone reservoir is established.

[0013] Configuration module: Based on the characteristic parameter set of sandstone reservoir, a simulation test of reinjection conditions was carried out on continuous core samples. By adjusting the configuration combination of filter media particle size, filter pipe porosity, porosity and mesh specifications, the optimal parameter combination of wellbore filtration structure was obtained.

[0014] Parameter determination module: Based on the optimal parameter combination of the wellbore filtration structure, pumping and reinjection tests are carried out on the target geothermal well to determine the comprehensive permeability of the aquifer and the correspondence between pressure head and reinjection volume, and the initial reinjection parameters are determined accordingly.

[0015] Process optimization module: Water quality characteristics of the reinjection tailwater are detected to obtain chemical and microbial composition data. Based on the chemical and microbial composition data, the generation pattern of blockage substances under different reinjection flow rates, reinjection water temperatures and system airtightness is determined, and the optimal combination of reinjection process parameters is screened.

[0016] Adjustment module: Perform well washing operation on the target geothermal well according to the preset operation cycle. After the well washing operation is completed, perform reinjection capacity retest, compare the retest results with the initial reinjection parameters, and dynamically adjust the optimal combination of reinjection process parameters based on the comparison results.

[0017] The technical effects and advantages of the control method and system for maintaining reinjection throughout the entire life cycle of sandstone geothermal wells, as described in this invention, are as follows:

[0018] This invention optimizes the configuration of filter media particle size, filter pipe porosity, opening diameter, and mesh specifications through reinjection condition simulation tests, reducing the risk of blockage caused by mechanical particles entering the reservoir from the source. Based on the correlation between the comprehensive permeability and pressure head of the aquifer and the reinjection volume determined by pumping and reinjection well tests, scientifically reasonable initial reinjection parameters are determined to avoid reservoir damage due to improper reinjection pressure or flow rate settings. By detecting the chemical and microbial components of the reinjection tailwater, the generation patterns of blockage substances under different reinjection flow rates, reinjection water temperatures, and system tightness conditions are systematically analyzed, and effective inhibitors of chemical scaling and microbial scaling are screened. The optimal combination of reinjection process parameters for biofilm formation enables proactive prevention of various blockage mechanisms. Well washing operations are carried out according to a preset operating cycle, and reinjection capacity is retested. The reinjection process parameters are dynamically adjusted based on the trend of reinjection capacity decay and the dominant blockage type, achieving optimized dynamic control throughout the entire life cycle. This breaks through the passive response mode of existing technologies that only adopt ex-post remedial measures, and constructs a full-process proactive control system covering reservoir evaluation, structural optimization, parameter determination, blockage prevention, and dynamic control. This effectively delays the reservoir blockage process, maintains long-term stable reinjection capacity, and significantly extends the service life of sandstone geothermal wells. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the control method for maintaining reinjection throughout the entire life cycle of sandstone geothermal wells according to the present invention;

[0020] Figure 2 This is a schematic diagram of the control system for maintaining reinjection of sandstone geothermal wells throughout their entire life cycle, as described in this invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1

[0023] Please see Figure 1 As shown in the figure, this embodiment describes a control method for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well, including:

[0024] Step S1: Conduct drilling and coring operations on the target geothermal well, extract continuous core samples from the sandstone geothermal reservoir section, and obtain reservoir physical property data through electrical logging and sonic logging. Based on the continuous core samples and reservoir physical property data, establish a set of characteristic parameters for the sandstone reservoir.

[0025] In this embodiment, the target geothermal well is located in a sandstone reservoir development area, with the reservoir section ranging from 1800 meters to 2200 meters in depth and approximately 400 meters in thickness. Wireline coring drilling is used to conduct drilling and coring operations on the target geothermal well, with a coring recovery rate of no less than 85%, ensuring that the obtained continuous core samples can accurately reflect the lithological variation characteristics of the reservoir.

[0026] It should be noted that the drilling and coring process used in this embodiment is a conventional technology in the field, and the coring yield is an industry standard, which is highly representative in the field of reservoir property analysis.

[0027] Electrical logging and sonic logging are effective means of obtaining reservoir property data. Electrical logging inverts the reservoir porosity distribution by measuring changes in formation resistivity, while sonic logging evaluates the reservoir's compaction and porosity development by measuring the propagation speed of sound waves in the formation. This embodiment uses a joint interpretation of electrical logging curves and sonic logging curves to obtain reservoir property data.

[0028] Preferably, in some possible implementations of the embodiments of the present invention, the method for establishing the characteristic parameter set of sandstone reservoirs includes:

[0029] Multiple core samples were taken from the sandstone reservoir at preset depth intervals. Mineral composition and grain size were determined for each core sample to obtain sandstone skeleton characteristic data. In this embodiment, the preset depth interval was 5 meters, meaning a core sample was taken every 5 meters. Sandstone reservoirs typically exhibit distinct rhythmic sedimentary characteristics, and a 5-meter interval effectively captures lithological variations across different sedimentary rhythm layers, balancing sampling efficiency and analysis cost. The preset depth interval ranged from 3 to 10 meters. In areas with drastic changes in reservoir lithology, the interval could be appropriately reduced to 3 meters, while in areas with homogeneous lithology, it could be increased to 10 meters.

[0030] The mineral composition of the core was identified using X-ray diffraction analysis to determine the percentage content of major minerals such as quartz, feldspar, mica, and clay minerals. Particle size classification was performed using a laser particle size analyzer, dividing particles into four grades based on diameter: gravel (greater than 2 mm), sand (0.0625 mm to 2 mm), silt (0.004 mm to 0.0625 mm), and clay (less than 0.004 mm). The mass percentage of each grade was then calculated. The mineral composition and particle size together constitute the characteristic data of the sandstone skeleton, reflecting the reservoir's skeletal structure and particle support characteristics.

[0031] Vertical distribution data of reservoir porosity is obtained through electrical logging curves, and vertical distribution data of reservoir layer velocity is obtained through sonic logging. The vertical distribution data of reservoir porosity and reservoir layer velocity are then subjected to depth realignment processing to generate a reservoir property distribution sequence. Depth realignment processing refers to the uniform calibration of the depth scales of different logging curves to eliminate depth errors generated during the well running of logging instruments, ensuring that the property data at the same depth point have a corresponding relationship. In this embodiment, the natural gamma curve is used as the reference curve for depth realignment, and the realignment accuracy is controlled within 0.1 meters.

[0032] The reservoir property distribution sequence contains continuous property variation information from the top to the bottom boundary of the thermal reservoir. Taking this embodiment as an example, within the range of 1800 meters to 2200 meters in the thermal reservoir section, the porosity distribution ranges from 8% to 22%, with an average value of 15.6%; the layer velocity distribution ranges from 3200 m / s to 4100 m / s, with an average value of 3650 m / s. Porosity and layer velocity are negatively correlated; the layer with higher porosity has a lower acoustic propagation velocity, reflecting more developed reservoir pores and better water flow channel conditions.

[0033] Permeability tests were conducted on core sections under multiple confining pressure levels to obtain the overall permeability of the cores at each confining pressure level. The confining pressure levels were set based on simulating the overlying formation pressure on the reservoir under different burial depths; in this embodiment, five confining pressure levels were set, namely 5 MPa, 10 MPa, 20 MPa, 30 MPa, and 40 MPa, corresponding to the effective stress conditions at simulated burial depths of approximately 200 meters, 400 meters, 800 meters, 1200 meters, and 1600 meters.

[0034] The permeability measurement experiment employed the steady-state method, measuring the volume of fluid passing through the core sample per unit time under constant pressure differential conditions. The permeability value was calculated based on Darcy's law, and the permeability values ​​under various constant pressure conditions were considered to be stable (permeability fluctuations within a certain range). The value of 2 millidarcy is used as the overall permeability under that pressure. Taking the core sample at a depth of 1950 meters in this embodiment as an example, the permeability is 856 millidarcy under a confining pressure of 5 MPa, and decreases to 412 millidarcy under a confining pressure of 40 MPa.

[0035] By performing stratigraphic correlation and data integration on sandstone framework characteristic data, reservoir physical property distribution sequences, and comprehensive permeability, a sandstone reservoir characteristic parameter set is generated. Stratigraphic correlation refers to matching the analysis depth of core samples with the measurement depth of well logging curves to ensure that various data can be integrated according to a unified depth coordinate system. The sandstone reservoir characteristic parameter set is indexed by depth and includes multi-dimensional parameter information such as mineral composition, grain size distribution, porosity, layer velocity, and permeability at each depth point, providing complete reservoir background data for subsequent wellbore filtration structure design and reinjection process optimization.

[0036] Step S2: Conduct reinjection simulation tests on continuous core samples based on the sandstone reservoir characteristic parameter set. By adjusting the configuration combination of filter media particle size, filter pipe porosity, opening diameter and mesh specifications, obtain the optimal parameter combination of wellbore filtration structure.

[0037] The wellbore filtration structure is a crucial interface connecting reinjection water and the reservoir. Its design directly impacts the efficiency of reinjection water entering the reservoir and the interception of suspended particles. Improper filtration design can lead to two extremes: excessively high filtration precision, while effectively intercepting fine particles, results in excessive seepage resistance, affecting reinjection capacity; conversely, insufficient filtration precision allows fine particles to enter deeper into the reservoir with the reinjection water, causing blockages at narrow pore throats that are difficult to remove through well washing. Therefore, it is necessary to determine the optimal combination of filtration structure parameters through reinjection condition simulation tests.

[0038] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining the preferred combination of parameters for the wellbore filtration structure includes:

[0039] A recharge simulation device was constructed. Continuous core samples were filled into the annulus area of ​​the simulated well. Replaceable filter pipe components (with well pipes installed inside the components, and different filter pipes and filtration devices can be configured) and filter media filling layers were installed sequentially inside the simulated well. The filter media filling layers were covered with mesh materials of different mesh sizes. Simulated recharge fluid matching the water quality characteristics of the on-site recharge tailwater was injected into the simulated well.

[0040] The core structure of the reinjection simulation device includes: an outer cylinder (simulating the well wall and reservoir environment, made of cement components), an inner cylinder (installing filter pipe components), a filter media filling layer (located between the filter pipe and the mesh), and a mesh layer (the outermost filter barrier of the well pipe). The device dimensions are based on the actual well structure.

[0041] The simulated reinjection fluid was prepared by matching chemical and microbial component data to ensure that the concentration of major ions, suspended solids content, and microbial activity of the simulated reinjection fluid were consistent with those of the on-site reinjection tailwater. In this embodiment, the suspended solids concentration of the simulated reinjection fluid was controlled at 15 mg / L.

[0042] According to the orthogonal configuration scheme, filter media of different particle size grades, different porosities, different filter pipes, different filter devices and filter pipe components with different opening diameters, as well as meshing materials of different mesh sizes are replaced in sequence. Simulated reinjection fluid is continuously injected at a constant injection pressure under each configuration state to carry out multi-scenario reinjection simulation, and the decay curve of injection flow rate over time and the pressure accumulation curve in the simulated wellbore are recorded simultaneously.

[0043] This embodiment employs a four-factor, three-level orthogonal experimental design, with the levels of each factor set as follows:

[0044] Filter media particle size grades: coarse (2 mm to 4 mm), medium (1 mm to 2 mm), fine (0.5 mm to 1 mm); the filter media particle size is set based on the particle size classification results of sandstone reservoirs. The filter media particle size should be larger than the median particle size of sand particles in the reservoir to prevent reservoir particles from flowing back into the filter media layer and causing mixed-layer blockage.

[0045] Filter pipe opening ratio: low opening ratio (8%), medium opening ratio (15%), high opening ratio (22%); the opening ratio ranges from 5% to 25%. Too low an opening ratio will limit the flow area and increase the backflow resistance, while too high an opening ratio will reduce the structural strength of the filter pipe.

[0046] Opening diameter: small opening (8 mm), medium opening (12 mm), large opening (16 mm); the opening diameter is matched with the filter media particle size. The opening diameter should be less than twice the minimum particle size of the filter media to prevent the filter media from entering the well shaft through the opening.

[0047] Mesh count: coarse (20 mesh), medium (40 mesh), fine (60 mesh); the mesh count determines the final particle interception accuracy. A 20-mesh mesh corresponds to an aperture of approximately 0.85 mm, a 40-mesh mesh corresponds to an aperture of approximately 0.38 mm, and a 60-mesh mesh corresponds to an aperture of approximately 0.25 mm.

[0048] Nine configuration states were set up in the orthogonal experiment. In each configuration state, simulated reinjection fluid was continuously injected at a constant injection pressure of 0.3 MPa for 72 hours. A high-precision flow meter was used to record the instantaneous injection flow rate at 10-minute intervals, and a bottom hole pressure sensor was used to record the simulated wellbore bottom pressure value at 10-minute intervals. The decay curve of injection flow rate over time and the pressure accumulation curve were generated respectively.

[0049] The decay rate of the injection flow rate over time is extracted from the decay curve of the injection flow rate under each configuration state, and the pressure rise slope is extracted from the pressure accumulation curve. The filter media particle size, filter pipe porosity, opening diameter and mesh size corresponding to the configuration state where both the decay rate and the pressure rise slope are in the lowest range are determined as the optimal parameter combination for the well barrel filtration structure.

[0050] The decay rate is calculated as follows: the decay curve is divided into three stages: the early stage (0 to 24 hours), the middle stage (24 to 48 hours), and the late stage (48 to 72 hours). The percentage of flow decay in each stage is calculated, and the average of the three stages is taken as the comprehensive decay rate. The pressure rise slope is calculated as follows: the pressure accumulation curve is linearly fitted, and the slope of the fitted line is taken as the pressure rise slope, with the unit being kPa / h.

[0051] In this embodiment, the overall attenuation rate of the fifth configuration state (medium-sized filter media, medium porosity, medium pore size, 40-mesh screen) is 8.2%, and the pressure rise slope is 0.15 kPa / h. Both of these indicators are the lowest values ​​among all configuration states. Therefore, the filter media particle size of 1 mm to 2 mm, the filter pipe porosity of 15%, the pore diameter of 12 mm, and the screen mesh size of 40 mesh are determined as the preferred parameter combination for the well barrel filtration structure.

[0052] This optimal combination of parameters enables the medium-sized filter media to provide sufficient permeability while effectively supporting the mesh layer. The medium porosity balances the flow area and structural strength, and the 40-mesh mesh can intercept suspended particles larger than 0.38 mm in the recharge tailwater, preventing coarse particles from entering the reservoir and causing surface clogging, while maintaining low filtration resistance.

[0053] Step S3: Based on the optimal parameter combination of the wellbore filtration structure, conduct pumping and reinjection tests on the target geothermal well, determine the comprehensive permeability of the aquifer and the correspondence between pressure head and reinjection volume, and determine the initial reinjection parameters accordingly.

[0054] After completing the optimized design of the wellbore filtration structure, it is necessary to obtain the actual permeability and reinjection characteristic curves of the reservoir through field well testing. Pumping well testing reflects the reservoir's ability to supply water to the wellbore, while reinjection well testing reflects the wellbore's ability to inject water into the reservoir. Comparative analysis of the two helps to evaluate the bidirectional flow characteristics of the reservoir. Initial reinjection parameters serve as the benchmark for subsequent full life-cycle reinjection control, and their accurate measurement is of great significance for evaluating the trend of reinjection capacity changes.

[0055] Preferably, in some possible implementations of the embodiments of the present invention, the method for determining the initial reinjection parameters includes:

[0056] Based on the optimal parameter combination of the wellbore filtration structure, a multi-stage stable flow pumping test was carried out on the target geothermal well. After the water level stabilized at each pumping flow level, the corresponding dynamic water level depth was measured. The comprehensive permeability of the aquifer was calculated based on the corresponding data of each pumping flow level and dynamic water level depth.

[0057] The design of the multi-stage steady-flow pumping test is based on the technical requirements for pumping tests in the "Geological Exploration Specification for Geological Resources". This embodiment sets five pumping flow rates: 20 cubic meters / hour, 40 cubic meters / hour, 60 cubic meters / hour, 80 cubic meters / hour, and 100 cubic meters / hour. The stabilization time for each flow rate is no less than 8 hours, and the water level is considered to be in a stable state when the change in water level is less than 0.1 meters for two consecutive hours.

[0058] The dynamic water level depth is measured using an electrical level gauge with an accuracy of 0.01 meters. Taking this embodiment as an example, the static water level depth is 85.6 meters, and the stable dynamic water level depth is 142.3 meters at a pumping flow rate of 100 cubic meters per hour, with a drawdown of 56.7 meters.

[0059] The formula for calculating the overall permeability of an aquifer is: In the formula, The aquifer's overall permeability is expressed in meters per day. This is the pumping flow rate, expressed in cubic meters per day. To account for the radius of influence, based on experience, this embodiment uses a value of 500 meters; The radius of the wellbore is 0.15 meters in this embodiment; The effective thickness of the aquifer is determined to be 180 meters based on the reservoir property distribution sequence. The unit for water level drawdown is meters.

[0060] The wellhead temperature of the geothermal water produced by the target geothermal well is measured. The density of the geothermal water at the corresponding temperature is then determined, and the pressure head value for each pumping flow rate is calculated based on the dynamic water level depth. In this example, the wellhead temperature is 68℃, corresponding to a geothermal water density of 979.5 kg / m³. The formula for calculating the pressure head is: In the formula, The pressure head is expressed in kilopascals (kPa). The density of geothermal water is expressed in kilograms per cubic meter. The acceleration due to gravity is taken as 9.8 m / s². The depth is the dynamic water level, expressed in meters.

[0061] After the pumping test is completed, a reinjection test is carried out on the target geothermal well. Reinjection water filtered by the geothermal water treatment device in the ground heat exchange station is injected into the well at multiple pressure levels through the ground pressurization equipment. The injection is maintained at each pressure level until the pressure at the bottom of the well tends to stabilize. The pressure head value and the corresponding stable reinjection flow rate value under the stable state are recorded.

[0062] The reinjection test employed the variable pressure constant flow method. A plunger-type water injection pump with a rated pressure of 5 MPa and a rated flow rate of 150 cubic meters per hour was used as the surface booster equipment. This embodiment included five pressure levels: 0.5 MPa, 1.0 MPa, 1.5 MPa, 2.0 MPa, and 2.5 MPa. The injection time for each pressure level was no less than 6 hours. A stable state was defined as the bottom-hole pressure fluctuating by less than 0.02 MPa for one consecutive hour. A relationship curve between pressure and reinjection volume was constructed to provide a reference for subsequent engineering-scale reinjection.

[0063] The maximum value among the stable reinjection flow rates at each pressure level is used as the initial reinjection capacity benchmark value, and the corresponding pressure head value is recorded as the benchmark reinjection pressure value. The initial reinjection capacity benchmark value and the benchmark reinjection pressure value are used as the initial reinjection parameters.

[0064] In this embodiment, the initial reinjection capacity benchmark value is 108 cubic meters per hour (stable reinjection flow rate at a pressure level of 2.5 MPa), and the benchmark reinjection pressure value is 2.5 MPa. The initial reinjection parameters will serve as the benchmark for monitoring and evaluating the reinjection capacity during subsequent operating cycles. When the ratio of the reinjection capacity retested after well washing to the initial reinjection capacity benchmark value is lower than a preset threshold, it indicates that the reservoir blockage has exceeded the reversible range, and the reinjection process parameters need to be adjusted.

[0065] Step S4: Conduct water quality characteristic testing on the reinjection tailwater to obtain chemical composition data and microbial composition data. Based on the chemical composition data and microbial composition data, determine the generation law of blockage substances under different reinjection flow rates, reinjection water temperatures and system airtightness, and screen out the optimal combination of reinjection process parameters.

[0066] The water quality characteristics of the reinjection tailwater determine the type and rate of blockage material formation; chemical composition determines the likelihood of scaling and precipitation; and microbial composition determines the risk level of biofilm blockage. Different reinjection process conditions (flow rate, water temperature, and tightness) affect the formation rate of blockage material. Through systematic experimental research, it is possible to find the combination of process parameters that minimizes the formation rate of blockage material, thereby delaying the reservoir blockage process and extending the service life of the reinjection well.

[0067] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining chemical component data and microbial component data includes:

[0068] Samples of reinjection tailwater were collected from the outlet of the geothermal system heat exchange equipment. Multi-element ion analysis was performed on the reinjection tailwater samples to determine the concentrations of calcium ions, magnesium ions, carbonate ions, sulfate ions, and total dissolved solids. The results were then compiled to generate chemical composition data.

[0069] The collection of reinjection tailwater samples shall be carried out in accordance with the "Technical Guidelines for Water Quality Sampling". The sampling point shall be set at the sampling valve of the outlet pipe of the heat exchange equipment. Before sampling, flush the pipe with water for 3 to 5 minutes to remove residual water. Then, collect 2 liters of water sample using a polyethylene sampling bottle. The samples shall be delivered to the laboratory for analysis within 4 hours after collection. Samples exceeding the time limit shall be refrigerated.

[0070] Multi-element ion analysis employed inductively coupled plasma atomic emission spectrometry (ICP-AES) to determine the concentration of metal cations, ion chromatography to determine the concentration of anions, and gravimetric analysis to determine the total dissolved solids content. The product of calcium ion and carbonate concentrations was used to assess the risk of calcium carbonate scaling. In this embodiment, if the product of calcium ion and carbonate concentrations exceeds the calcium carbonate solubility product constant (approximately [value missing] at 25°C), [further analysis is required]. The converted equivalent threshold indicates a tendency for calcium carbonate scaling in the reinjection tailwater. The high sulfate concentration may lead to barium sulfate precipitate formation upon encountering barium ions in the reservoir.

[0071] Microbial culture experiments were conducted on the recharge tailwater samples under anaerobic and aerobic conditions to determine the number of sulfate-reducing bacteria, iron bacteria, and heterotrophic bacteria. The colony counts were then compiled to generate microbial component data.

[0072] Microbial culture experiments were conducted using the plate count method. Anaerobic cultures were performed in anaerobic jars at 37°C for 72 hours, while aerobic cultures were performed in a constant temperature incubator at 30°C for 48 hours. Sulfate-reducing bacteria were cultured on modified Postgate B medium, iron bacteria on Winogradsky medium, and heterotrophic bacteria on beef extract peptone medium.

[0073] Preferably, in some possible implementations of the embodiments of the present invention, the method for determining the generation law of blockage substances and screening the optimal combination of reinjection process parameters includes:

[0074] Based on chemical and microbial composition data, a multi-factor combined batch test scheme was designed. The reinjection flow rate was divided into three levels: low flow rate, medium flow rate, and high flow rate. The reinjection water temperature was set to a fixed temperature range. The system's airtightness was divided into three types: fully enclosed, semi-enclosed, and open. It should be noted that the geothermal water must be desanded before this experiment to achieve clear water and clean sand.

[0075] The levels of each factor are set based on the following criteria:

[0076] The recharge flow rate levels are set based on the initial recharge capacity baseline value measured in step S3. The low flow rate range is 30% to 50% of the baseline value (32 to 54 cubic meters per hour in this embodiment), the medium flow rate range is 50% to 80% of the baseline value (54 to 86 cubic meters per hour in this embodiment), and the high flow rate range is 80% to 100% of the baseline value (86 to 108 cubic meters per hour in this embodiment). The flow rate levels are determined as follows: under low flow rate conditions, the recharge water has a longer residence time in the reservoir, which is conducive to the formation of chemical precipitation; under high flow rate conditions, the hydraulic shearing effect is stronger, which may scour the surface blockage layer but may also push fine particles into the deeper parts of the reservoir.

[0077] The reinjection water temperature is set based on the operating temperature range of the heat exchange system, which is 25℃ to 35℃. The temperature range is set based on experience; at low temperatures, microbial activity is lower but the solubility of some minerals decreases; at high temperatures, microbial activity is inhibited but the chemical reaction rate is accelerated.

[0078] The system's airtightness setting is based on the reinjection system's process configuration. A fully airtight system means the reinjection water is transported in a completely sealed manner from the heat exchanger outlet to the wellhead, without contact with the atmosphere. A semi-airtight system means a sealed storage tank is installed, but a breather valve is provided on the top of the tank. An open system means the reinjection water is injected into the well after passing through an open sedimentation tank. The airtightness affects the dissolved oxygen content of the reinjection water, which in turn affects the activity of iron bacteria and the formation of oxidative precipitates.

[0079] Test reaction units were configured to correspond to the number of factor level combinations in the multi-factor combination batch test scheme. Core components with lithology consistent with the sandstone thermal reservoir section were filled into each test reaction unit. This embodiment adopted a three-factor, three-level full-factor experimental design, with a total of 27 factor level combinations, corresponding to 27 test reaction units. The test reaction units were stainless steel cylindrical containers with an inner diameter of 50 mm and a length of 200 mm. The core components were sand grains with a particle size of 0.1 mm to 0.5 mm obtained from the continuous core sample obtained in step S1 after crushing and sieving. The filling density was controlled according to the reservoir porosity of 15.6%.

[0080] Recharge tailwater samples, adjusted to the corresponding temperature level, are continuously injected into each test reaction unit according to the corresponding flow rate level. Each test reaction unit is configured to the corresponding closed state type, and continuous injection is maintained until the end of the preset test cycle.

[0081] The preset test period is 30 days. This value is based on the following: according to preliminary survey data, the blockage effect of sandstone thermal reservoirs can show a significant trend in the early stage of reinjection operation (within 1 month). The 30-day test period can effectively reflect the formation pattern of blockage materials while controlling test costs. The range is 20 to 45 days. In systems where the blockage effect develops rapidly, it can be shortened to 20 days, and in systems where the blockage effect develops slowly, it can be extended to 45 days.

[0082] After the test cycle was completed, each test reaction unit was disassembled, and sediment samples from the surface of the core components and blockage samples from the pores of the core components were extracted. The sediment samples were identified and weighed, and the thickness of the microbial film on the blockage samples was measured.

[0083] X-ray diffraction was used to identify the mineral phase composition of the sediment samples. Common plugging minerals included calcium carbonate, barium sulfate, ferric hydroxide, and ferric sulfide. Weighing was performed using an analytical balance with an accuracy of 0.1 mg. Biofilm thickness was measured using a confocal laser scanning microscope. Ten random fields of view were selected on the surface of the core sample to measure the biofilm thickness, and the average value was taken as the biofilm thickness of that reaction unit.

[0084] Establish a data matrix corresponding to the combination of various factor levels and sediment quality and microbial film thickness. Select the factor level combination with the lowest comprehensive index of sediment quality and microbial film thickness from the corresponding data matrix. Determine the reinjection flow rate, reinjection water temperature and system sealing status corresponding to the factor level combination as the optimal combination of reinjection process parameters.

[0085] The comprehensive index is calculated as follows: the sediment mass of the experimental results is normalized to obtain a normalized sediment mass value (0 to 1), and the microbial film thickness is normalized to obtain a normalized microbial film thickness value (0 to 1). The comprehensive index is equal to the weighted average of the two normalized values, with each weighting 0.5. Taking this embodiment as an example, the comprehensive index of the 14th factor level combination (medium flow range, low temperature range, and fully enclosed state) is 0.18, which is the lowest value among the 27 groups; therefore, the recharge flow rate of 70 cubic meters per hour (median value of the medium flow range), the recharge water temperature of 30℃ (median value of the low temperature range), and the fully enclosed state are determined as the preferred combination of recharge process parameters.

[0086] Step S5: Perform well washing operation on the target geothermal well according to the preset operating cycle. After the well washing operation is completed, perform reinjection capacity retest, compare the retest results with the initial reinjection parameters, and dynamically adjust the optimal combination of reinjection process parameters based on the comparison results.

[0087] Despite optimized wellbore filtration structures and reinjection process parameters, reservoir blockage will still gradually accumulate over time. Regular well flushing is a necessary measure to maintain reinjection capacity. The purpose of well flushing is to remove accumulated blockages in the wellbore and near-wellbore area, restoring the smooth flow of water. Retesting the reinjection capacity after well flushing can evaluate the flushing effect and provide a basis for determining whether adjustments to reinjection process parameters are necessary. By comparing the retest results with the initial reinjection parameters, changes in blockage trends can be detected in a timely manner, allowing for targeted control measures and proactive maintenance of reinjection capacity throughout its entire lifecycle.

[0088] Preferably, in some possible implementations of the embodiments of the present invention, the method for carrying out well washing operations includes:

[0089] During the intermittent period after the end of each heating season operation cycle, the bottom sand is first explored and flushed. Then, a well-washing tool string is lowered into the target geothermal well. The well-washing tool string includes a high-pressure rotary nozzle, a mechanical scraper and a centering guide connected in sequence along the axis. The well-washing tool string is lowered to the well depth position corresponding to the sandstone thermal reservoir section.

[0090] The preset operating cycle is one heating season (approximately 4 months), with a range of 3 to 6 months. For wells with rapid blockage development, the cycle can be shortened to 3 months, while for wells with slow blockage development, it can be extended to 6 months.

[0091] The structural configuration of the well-washing tool string is based on the following: a high-pressure rotary nozzle uses the impact force of high-pressure water flow to peel off the blockage layer on the well wall and filter pipe surface; a mechanical scraper uses elastic scrapers to physically scrape the pipe wall, removing hard scale layers that are difficult to wash away by high-pressure water flow; and a centering guide keeps the tool string running centrally within the well barrel, preventing uneven wear on the well wall. In this embodiment, the high-pressure rotary nozzle is equipped with 8 nozzles, each with a diameter of 3 mm and a spray angle of 45 degrees; the mechanical scraper is equipped with 6 sets of elastic scrapers, the outer diameter of which is 10 mm smaller than the inner diameter of the well barrel.

[0092] The surface high-pressure pump unit is started and the well-washing working fluid is injected through the wellhead. The well-washing working fluid forms a circumferentially distributed high-pressure jet through the high-pressure rotating nozzle, which impacts the well wall and the inner surface of the filter pipe. At the same time, it drives the mechanical scraper to perform up-and-down reciprocating scraping motion along the well shaft axis, peeling off the blockage layer attached to the well wall and the surface of the filter pipe and dispersing it in the well-washing working fluid to form a polluted suspension.

[0093] The formulation of the well-washing working fluid is determined according to the type of blockage: for chemical scaling blockage, a 5% hydrochloric acid solution is used to dissolve carbonate precipitates; for biological mucus blockage, a 0.5% sodium hypochlorite solution is used to kill microorganisms and decompose the mucus; for mechanical particle blockage, clean water combined with high-pressure jet is used for physical flushing. In this embodiment, based on the blockage formation pattern determined in step S4, clean water is selected as the well-washing working fluid, with an injection pressure of 8 MPa and an injection flow rate of 120 cubic meters per hour.

[0094] The well-washing tool string moves up and down in the hot reservoir section, with each reciprocating stroke covering the full thickness of the hot reservoir (180 meters in this embodiment). The reciprocating speed is controlled between 5 meters / minute and 10 meters / minute, and the number of reciprocating strokes is no less than 10.

[0095] The continuous injection of well-washing working fluid will displace and discharge the contaminated suspension from the bottom of the well toward the wellhead. The fluid will then be introduced into the surface sedimentation and separation device through the wellhead sewage pipeline. Once the clarity of the return fluid from the wellhead reaches the preset cleanliness standard, the injection of well-washing working fluid will be stopped and the well-washing tool string will be retrieved.

[0096] Collect the materials removed during well washing and conduct physical, chemical, and microbiological monitoring. Analyze the physical, chemical, and microbiological components and characteristics of the clogging materials to provide a reference for subsequent reinjection water treatment and reinjection process optimization.

[0097] The preset cleanliness standard is based on the following criteria: the suspended solids concentration in the wellhead return fluid should be below 50 mg / L, and the color of the return fluid should change from turbid to clear. Clarity is determined on-site using a turbidimeter; a turbidity value below 20 NTU is considered to meet the cleanliness standard. In this embodiment, the well-washing operation lasted approximately 8 hours, with a cumulative injection volume of approximately 960 cubic meters of working fluid and a cumulative discharge volume of approximately 1100 cubic meters of contaminated suspension (including the original water stored in the wellbore).

[0098] Preferably, in some possible implementations of the embodiments of the present invention, the method for retesting and comparing reinjection capacity includes:

[0099] After the well washing operation is completed and the residual sewage in the wellbore is drained, clean reinjection water is injected into the target geothermal well according to the same pressure level sequence as when the initial reinjection parameters were determined to conduct a reinjection capacity retest. The pressure level sequence is consistent with the reinjection test in step S3, namely five levels: 0.5 MPa, 1.0 MPa, 1.5 MPa, 2.0 MPa, and 2.5 MPa, to ensure that the retest data is comparable to the initial data.

[0100] During the retesting process, the instantaneous reinjection flow rate under stable injection conditions at each pressure level was recorded. The maximum value among the recorded instantaneous reinjection flow rates was extracted as the retesting value for the current reinjection capacity. Taking the retesting after the end of the first heating season in this embodiment as an example, the stable reinjection flow rates at each pressure level were 29 cubic meters / hour, 52 cubic meters / hour, 71 cubic meters / hour, 86 cubic meters / hour, and 98 cubic meters / hour, respectively. The maximum value of 98 cubic meters / hour was used as the retesting value for the current reinjection capacity.

[0101] The reinjection capacity recovery coefficient is obtained by dividing the current reinjection capacity remeasurement value by the initial reinjection capacity benchmark value. The reinjection capacity recovery coefficient is then compared with a preset recovery degree threshold to determine the recovery degree level of the target geothermal well's reinjection capacity after the current well-washing operation. The preset recovery degree threshold is 0.85 (i.e., 85%). According to statistical data from sandstone geothermal reservoir reinjection projects, a reinjection capacity recovery to above 85% of the initial capacity is within the normal attenuation range, and the reinjection capacity can be maintained through conventional well-washing maintenance. A value below 85% indicates that deep reservoir blockages have formed that are difficult to remove, requiring adjustments to the reinjection process parameters to slow down the blockage development. The value range is 0.80 to 0.90; a higher threshold of 0.90 can be used for wells with better reservoir conditions, while a lower threshold of 0.80 can be used for wells with poorer reservoir conditions.

[0102] Preferably, in some possible implementations of the embodiments of the present invention, the method for dynamically adjusting the preferred combination of reinjection process parameters includes:

[0103] When the recharge capacity recovery coefficient is higher than the preset recovery threshold, the recharge flow rate, recharge water temperature, and system closed state in the current optimal combination of recharge process parameters are kept unchanged and applied to the next operating cycle. When the recharge capacity recovery coefficient is lower than the preset recovery threshold, the current recharge capacity remeasurement values ​​from previous operating cycles are retrieved, arranged in chronological order to generate a recharge capacity evolution sequence, and the decay trend characteristics of the recharge capacity evolution sequence are extracted.

[0104] Based on the attenuation trend characteristics and the composition identification results of the blockage samples after each well washing operation, the dominant blockage type at the current stage is determined. The dominant blockage types include mechanical particle blockage, chemical scaling blockage, and microbial mucus blockage.

[0105] The criteria for determining the dominant blockage type are as follows: if mineral particles (quartz, feldspar, etc.) account for more than 60% of the blockage sample, it is classified as mechanical particle blockage; if chemical precipitates (calcium carbonate, barium sulfate, ferric hydroxide, etc.) account for more than 50% of the blockage sample, it is classified as chemical scaling blockage; if the organic matter content of the blockage sample exceeds 30% or the thickness of the microbial film exceeds 100 micrometers, it is classified as microbial mucus blockage. When multiple conditions are met simultaneously, the dominant blockage type is determined by the type with the highest percentage.

[0106] Targeted adjustments are made to the corresponding parameters in the optimal combination of reinjection process parameters based on the dominant blockage type:

[0107] For mechanical particle clogging, the reinjection flow rate is reduced to a low flow range. Mechanical particle clogging is mainly caused by the deposition of suspended particles in the reinjection water at the reservoir pore throat. Reducing the reinjection flow rate can decrease the water flow's ability to carry particles, allowing particles to be effectively intercepted at the wellbore filtration structure, thus reducing the amount of particles entering the reservoir. In this embodiment, the reinjection flow rate is reduced from 70 cubic meters per hour to 45 cubic meters per hour.

[0108] For chemical scaling and clogging, the reinjection water temperature is lowered to a lower temperature range. Chemical scaling is mainly caused by the supersaturated precipitation of minerals due to temperature changes. Lowering the reinjection water temperature can reduce the amplitude of mineral solubility changes and slow down the scaling rate. It should be noted that the lower temperature range is 25℃ to 30℃. Chemical scaling (such as calcium carbonate, barium sulfate, etc.) is mainly affected by temperature, pressure, and ion concentration. Lowering the temperature will reduce the amplitude of mineral solubility changes and slow down the scaling rate. If the water temperature is too low, although the scaling tendency will be further reduced, it may lead to problems such as decreased heat exchange efficiency and formation cold shock. In this embodiment, the reinjection water temperature is lowered from 30℃ to 25℃.

[0109] For microbial mucus blockage, adjust the system from a closed to a fully closed state. The microbial mucus is mainly composed of extracellular polysaccharides produced by aerobic and facultative anaerobic bacteria. A fully closed system can minimize the dissolved oxygen content in the recharge water, inhibiting the growth and reproduction of aerobic bacteria. If the system is already in a fully closed state, further add a bactericide (such as chlorine dioxide, at a concentration of 0.5 mg / L) to the recharge water.

[0110] The adjusted reinjection flow rate, reinjection water temperature, and system sealing status are updated to the optimal combination of reinjection process parameters, and the reinjection operation is performed in the next operating cycle according to the updated optimal combination of reinjection process parameters.

[0111] This embodiment establishes a complete reservoir characteristic parameter system, optimizes the wellbore filtration structure, screens reinjection process parameters, and implements periodic well cleaning and dynamic adjustments, forming a proactive maintenance mechanism for reinjection capacity throughout the entire life cycle of geothermal wells. Compared with existing passive repair methods, this solution can take targeted measures in the early stages of blockage development, effectively delaying the reservoir blockage process, extending the service life of reinjection wells, and significantly reducing operation and maintenance costs, thus providing technical support for the large-scale sustainable development and utilization of sandstone geothermal resources.

[0112] Example 2

[0113] Please see Figure 2 As shown, parts not described in detail in this embodiment are described in Embodiment 1. A control system for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well is provided, including:

[0114] Data extraction module: Drilling and coring operations are carried out on the target geothermal well to extract continuous core samples from the sandstone geothermal reservoir section, and reservoir physical property data are obtained through electrical logging and sonic logging. Based on the continuous core samples and reservoir physical property data, a set of characteristic parameters of the sandstone reservoir is established.

[0115] Configuration module: Based on the characteristic parameter set of sandstone reservoir, a simulation test of reinjection conditions was carried out on continuous core samples. By adjusting the configuration combination of filter media particle size, filter pipe porosity, porosity and mesh specifications, the optimal parameter combination of wellbore filtration structure was obtained.

[0116] Parameter determination module: Based on the optimal parameter combination of the wellbore filtration structure, pumping and reinjection tests are carried out on the target geothermal well to determine the comprehensive permeability of the aquifer and the correspondence between pressure head and reinjection volume, and the initial reinjection parameters are determined accordingly.

[0117] Process optimization module: Water quality characteristics of the reinjection tailwater are detected to obtain chemical and microbial composition data. Based on the chemical and microbial composition data, the generation pattern of blockage substances under different reinjection flow rates, reinjection water temperatures and system airtightness is determined, and the optimal combination of reinjection process parameters is screened.

[0118] Adjustment module: Perform well washing operation on the target geothermal well according to the preset operation cycle. After the well washing operation is completed, perform reinjection capacity retest, compare the retest results with the initial reinjection parameters, and dynamically adjust the optimal combination of reinjection process parameters based on the comparison results.

[0119] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A control method for maintaining sandstone geothermal well full life cycle recharge, characterized by, include: Step S1: Conduct drilling and coring operations on the target geothermal well, extract continuous core samples from the sandstone geothermal reservoir section, and obtain reservoir physical property data through electrical logging and sonic logging. Based on the continuous core samples and reservoir physical property data, establish a set of characteristic parameters for the sandstone reservoir. Step S2: Conduct reinjection simulation tests on continuous core samples based on the sandstone reservoir characteristic parameter set. By adjusting the configuration combination of filter media particle size, filter pipe porosity, opening diameter and mesh specifications, obtain the optimal parameter combination of wellbore filtration structure. Step S3: Based on the optimal parameter combination of the wellbore filtration structure, conduct pumping and reinjection tests on the target geothermal well, determine the comprehensive permeability of the aquifer and the relationship between pressure head and reinjection volume, and determine the initial reinjection parameters accordingly. Step S4: Conduct water quality characteristic testing on the recharge tailwater to obtain chemical composition data and microbial composition data. Based on the chemical composition data and microbial composition data, determine the generation law of blockage substances under different recharge flow rates, recharge water temperatures and system airtightness, and screen out the optimal combination of recharge process parameters. Step S5: Perform well washing operation on the target geothermal well according to the preset operating cycle. After the well washing operation is completed, perform reinjection capacity retest, compare the retest results with the initial reinjection parameters, and dynamically adjust the optimal combination of reinjection process parameters based on the comparison results.

2. The control method for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well according to claim 1, characterized in that, A set of characteristic parameters for sandstone reservoirs was established based on continuous core samples and reservoir property data, including: Multiple core samples were taken from the sandstone reservoir at preset depth intervals. Mineral composition and particle size classification were performed on each core sample to obtain sandstone skeleton characteristic data. The vertical distribution data of reservoir porosity is obtained by electrical logging curves, and the vertical distribution data of reservoir layer velocity is obtained by sonic logging. The vertical distribution data of reservoir porosity and the vertical distribution data of reservoir layer velocity are then processed for depth alignment to generate a reservoir property distribution sequence. Permeability tests were conducted on the core section under multiple confining pressure levels to obtain the comprehensive permeability of the core under each confining pressure level. By performing stratigraphic correlation and data integration on sandstone skeleton characteristic data, reservoir physical property distribution sequence and comprehensive permeability, a set of sandstone reservoir characteristic parameters is generated.

3. The control method for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well according to claim 1, characterized in that, By adjusting the configuration combination of filter media particle size, filter pipe porosity, porosity, and mesh specifications, an optimal combination of parameters for the well shaft filtration structure is obtained, including: A recharge simulation device was constructed. Continuous core samples were filled into the annulus of the simulated well. Replaceable filter pipe components and filter media filling layers were installed sequentially inside the simulated well. The filter media filling layers were covered with mesh materials of different mesh sizes. Simulated recharge fluid matching the water quality characteristics of the on-site recharge tailwater was injected into the simulated well. According to the orthogonal configuration scheme, filter media of different particle size grades, filter pipe components of different porosity and porosity, and mesh material of different mesh size are replaced in sequence. Simulated reinjection fluid is continuously injected at constant injection pressure under each configuration state to carry out multi-scenario reinjection simulation, and the decay curve of injection flow rate over time and the pressure accumulation curve in the simulated wellbore are recorded simultaneously. The decay rate of the injection flow rate over time is extracted from the decay curve of the injection flow rate under each configuration state, and the pressure rise slope is extracted from the pressure accumulation curve. The filter media particle size, filter pipe porosity, opening diameter and mesh size corresponding to the configuration state where both the decay rate and the pressure rise slope are in the lowest range are determined as the optimal parameter combination for the well barrel filtration structure.

4. The control method for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well according to claim 1, characterized in that, The overall permeability of the aquifer and the relationship between pressure head and reinjection volume were determined, and the initial reinjection parameters were determined accordingly, including: Based on the optimal parameter combination of the wellbore filtration structure, a multi-stage stable flow pumping test was carried out on the target geothermal well. After the water level stabilized at each pumping flow level, the corresponding dynamic water level depth was measured. The comprehensive permeability of the aquifer was calculated based on the corresponding data of each pumping flow level and dynamic water level depth. Measure the wellhead temperature of the geothermal water produced by the target geothermal well, find the density value of the geothermal water at the corresponding temperature based on the wellhead temperature, and calculate the pressure head value at each pumping flow rate level by combining the dynamic water level depth. After the pumping test is completed, a reinjection test is carried out on the target geothermal well. Reinjection water is injected into the well at multiple pressure levels through ground pressurization equipment. The injection is maintained at each pressure level until the pressure at the bottom of the well tends to stabilize. The pressure head value and the corresponding stable reinjection flow rate value under the stable state are recorded. The maximum value among the stable reinjection flow rates at each pressure level is used as the initial reinjection capacity benchmark value, and the corresponding pressure head value is recorded as the benchmark reinjection pressure value. The initial reinjection capacity benchmark value and the benchmark reinjection pressure value are used as the initial reinjection parameters.

5. The control method for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well according to claim 1, characterized in that, Water quality characteristics of the reinjection effluent are analyzed to obtain chemical and microbiological composition data, including: Samples of reinjection tailwater were collected from the outlet of the geothermal system heat exchange equipment. Multi-element ion analysis was performed on the reinjection tailwater samples to determine the concentrations of calcium ions, magnesium ions, carbonate ions, sulfate ions, and total dissolved solids. The results of the above measurements were compiled to generate chemical composition data. Microbial culture experiments were conducted on the recharge tailwater samples under multi-stage anaerobic and aerobic conditions to determine the number of sulfate-reducing bacteria colonies, iron bacteria colonies, and total number of heterotrophic bacteria. The colony count results were then compiled to generate microbial component data.

6. The control method for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well according to claim 1, characterized in that, Based on chemical and microbial component data, the formation patterns of blockage substances under different reinjection flow rates, reinjection water temperatures, and system tightness were determined, including: Based on chemical and microbial component data, a multi-factor combined batch test scheme was designed. The reinjection flow rate was divided into three levels: low flow rate, medium flow rate and high flow rate. The reinjection water temperature was set to a fixed temperature range. The system's airtightness was divided into three types: fully closed, semi-closed and open. Configure test reaction units corresponding to the number of factor level combinations in the multi-factor combination batch test scheme, and fill each test reaction unit with core components consistent with the lithology of the sandstone thermal reservoir section; The recharge tailwater sample, adjusted to the corresponding temperature level, was continuously injected into each test reaction unit according to the corresponding flow rate level. Each test reaction unit was configured to the corresponding closed state type, and continuous injection was maintained until the end of the preset test cycle. After the test cycle was completed, each test reaction unit was disassembled, and sediment samples from the surface of the core components and blockage samples from the pores of the core components were extracted. The sediment samples were identified and weighed, and the thickness of the microbial film was measured in the blockage samples. Establish a data matrix corresponding to the combination of various factor levels and sediment quality and microbial film thickness. Select the factor level combination with the lowest comprehensive index of sediment quality and microbial film thickness from the corresponding data matrix. Determine the reinjection flow rate, reinjection water temperature and system sealing status corresponding to the factor level combination as the optimal combination of reinjection process parameters.

7. The control method for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well according to claim 1, characterized in that, The target geothermal well is cleaned according to a pre-set operating cycle, including: During the intermittent period after the end of each heating season operation cycle, the sand at the bottom of the well is first explored and flushed. Then, a well-washing tool string is lowered into the target geothermal well. The well-washing tool string includes a high-pressure rotary nozzle, a mechanical scraper and a centering guide connected in sequence along the axis. The well-washing tool string is lowered to the well depth position corresponding to the sandstone thermal reservoir section. The surface high-pressure pump unit is started and the well-washing working fluid is injected through the wellhead. The well-washing working fluid forms a high-pressure jet distributed in a ring through the high-pressure rotating nozzle, which impacts the well wall and the inner surface of the filter pipe. At the same time, it drives the mechanical scraper to perform up-and-down reciprocating scraping motion along the well shaft axis, peeling off the blockage layer attached to the well wall and the surface of the filter pipe and dispersing it in the well-washing working fluid to form a polluted suspension. The continuously injected well-washing working fluid replaces and discharges the contaminated suspension from the bottom of the well towards the wellhead. The solution is then introduced into the surface sedimentation and separation device through the wellhead sewage pipeline. Once the clarity of the returned liquid from the wellhead reaches the preset cleanliness standard, the injection of the well-washing working fluid is stopped and the well-washing tool string is retrieved.

8. The control method for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well according to claim 1, characterized in that, After the well washing operation is completed, the reinjection capacity is retested, and the retest results are compared with the initial reinjection parameters, including: After the well washing operation is completed and the residual sewage in the well is drained, clean reinjection water is injected into the target geothermal well according to the same pressure level sequence as when the initial reinjection parameters were determined to carry out the reinjection capacity retest. During the retesting process, the instantaneous reinjection flow rate under stable injection conditions at each pressure level was recorded, and the maximum value was extracted from each recorded instantaneous reinjection flow rate as the retesting value of the current reinjection capacity. Divide the current re-measured value of re-irrigation capacity by the initial re-irrigation capacity benchmark value to obtain the re-irrigation capacity recovery coefficient; The reinjection capacity recovery coefficient is compared with the preset recovery degree threshold to determine the reinjection capacity recovery degree level of the target geothermal well after the current well washing operation.

9. The control method for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well according to claim 1, characterized in that, Based on the comparison results, the optimal combination of reinjection process parameters is dynamically adjusted, including: When the recharge capacity recovery coefficient is higher than the preset recovery threshold, the recharge flow rate, recharge water temperature and system closed state in the current preferred combination of recharge process parameters will remain unchanged and continue to be applied to the next operating cycle. When the recovery coefficient of the re-irrigation capacity is lower than the preset recovery degree threshold, the current re-irrigation capacity retest value of each operating cycle is retrieved, and the re-irrigation capacity evolution sequence is generated in chronological order. The decay trend feature of the re-irrigation capacity evolution sequence is then extracted. Based on the attenuation trend characteristics and the composition identification results of the blockage samples after each well washing operation, the dominant blockage type at the current stage is determined. The dominant blockage types include mechanical particle blockage, chemical scaling blockage, and microbial mucus blockage. For the dominant clogging type, the corresponding parameters in the optimal combination of reinjection process parameters are adjusted in a targeted manner. For mechanical particle clogging, the reinjection flow rate is lowered to a low flow range; for chemical scaling clogging, the reinjection water temperature is lowered to a low temperature range; and for microbial mucus clogging, the system's closed state is adjusted to a fully closed state. The low temperature range is 25℃ to 30℃. The adjusted reinjection flow rate, reinjection water temperature, and system sealing status are updated to the optimal combination of reinjection process parameters, and the reinjection operation is performed in the next operating cycle according to the updated optimal combination of reinjection process parameters.

10. A control system for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well, comprising the means for implementing any one of claims 1 to 9 for maintaining reinjection throughout the entire life cycle of a sandstone geothermal well, characterized in that, include: Data extraction module: Drilling and coring operations are carried out on the target geothermal well to extract continuous core samples from the sandstone geothermal reservoir section, and reservoir physical property data are obtained through electrical logging and sonic logging. Based on the continuous core samples and reservoir physical property data, a set of characteristic parameters of the sandstone reservoir is established. Configuration module: Based on the characteristic parameter set of sandstone reservoir, a simulation test of reinjection conditions was carried out on continuous core samples. By adjusting the configuration combination of filter media particle size, filter pipe porosity, porosity and mesh specifications, the optimal parameter combination of wellbore filtration structure was obtained. Parameter determination module: Based on the optimal parameter combination of the wellbore filtration structure, pumping and reinjection tests are carried out on the target geothermal well to determine the comprehensive permeability of the aquifer and the correspondence between pressure head and reinjection volume, and the initial reinjection parameters are determined accordingly. Process optimization module: Water quality characteristics of the reinjection tailwater are detected to obtain chemical and microbial composition data. Based on the chemical and microbial composition data, the generation pattern of blockage substances under different reinjection flow rates, reinjection water temperatures and system airtightness is determined, and the optimal combination of reinjection process parameters is screened. Adjustment module: Perform well washing operation on the target geothermal well according to the preset operation cycle. After the well washing operation is completed, perform reinjection capacity retest, compare the retest results with the initial reinjection parameters, and dynamically adjust the optimal combination of reinjection process parameters based on the comparison results.

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