Method for analyzing freezing and thawing well wall load transfer mechanism of deep and thick water-rich soft rock stratum

Abstract

The invention discloses a deep and thick water-rich soft rock freeze-thaw well wall load transfer mechanism analysis method. A deep and thick water-rich soft rock freeze-thaw well wall load transfer model is constructed according to a frozen well wall load characteristic evolution mechanism; a deep and thick water-rich soft rock freezing and thawing well wall similar model is manufactured in equal proportion based on the similarity ratio principle; determining a proportional relation between surrounding rock water pressure and solid-phase pressure in different stages in freezing pipes of the brine well wall similar models with different temperatures; the well wall load transmission mechanism is obtained by combining the well wall load transmission model, obtaining the proportional relation between the surrounding rock water pressure and the solid phase pressure and combining field actual measurement well wall data comparison. The method can serve well wall design optimization and construction key node control, the engineering cost is effectively reduced, the construction risk is reduced, and the engineering safety and economical efficiency are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of coal mining technology, specifically relating to a method for analyzing the load transfer mechanism of well walls in deep, water-rich, and weak rock formations during freeze-thaw cycles. Background Technology

[0002] Western my country is an important coal energy base. The vertical shafts in the mines of this region are generally characterized by depths exceeding 800 meters and large diameters, and they need to traverse water-rich, soft rock strata of the Cretaceous and Jurassic periods. These rock strata have problems such as low strength, weak cementation, softening upon contact with cement, strong hydraulic connectivity, and significant seepage weakening effects, resulting in an extremely complex stress environment for the walls of freeze-thaw vertical shafts.

[0003] The current theoretical system for frozen vertical shaft design in my country and the "Code for Design of Coal Mine Vertical Shafts and Chambers" (GB50384-2016) are mainly based on the geological characteristics of the deep and loose strata in the central and eastern regions, making it difficult to adapt to the unique geological and hydrological conditions of the water-rich and weak rock strata in the western regions. Existing codes and technologies have the following main shortcomings: they fail to reveal the dynamic evolution mechanism of shaft wall loads in the water-rich and weak rock strata of the western regions; they lack specific mechanical models for the thawing of frozen walls and the steady-state seepage stage of pore water; they cannot achieve accurate numerical simulation of multi-field coupling of seepage, stress, and temperature; and the combination of field measurements with theoretical and simulation analysis is insufficient, leading to either conservative and wasteful shaft wall designs or potential safety hazards.

[0004] Therefore, there is an urgent need to develop a method that can comprehensively and accurately analyze the load transfer mechanism of freeze-thaw well walls in deep, water-rich, and weak rock formations. Summary of the Invention

[0005] The purpose of this invention is to provide an analysis method for the load transfer mechanism of freeze-thaw wellbore in deep, water-rich, and weak rock formations, which solves the problem that existing dynamic evolution mechanisms of wellbore loads do not have a specific load transfer model for analyzing water-rich and weak rock formations in western China.

[0006] The purpose of this invention is to provide an analysis method for the load transfer mechanism of freeze-thaw well walls in deep, water-rich, and weak rock formations.

[0007] The technical solution adopted in this invention is: a method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, and weak rock strata. The specific operation steps are as follows: A load transfer model for deep, water-rich soft rock freeze-thaw well walls was constructed based on the evolution mechanism of the loading characteristics of frozen well walls. Step 2: Based on the principle of similarity ratio, create a similar model of the well wall of a deep, water-rich, soft rock freeze-thaw well at the same scale; Step 3: Determine the ratio of water pressure to solid pressure in the surrounding rock at different stages in the freezing tubes of similar models of brine well walls at different temperatures; Step 4: Combine the well wall load transfer model, the ratio of surrounding rock water pressure to solid phase pressure obtained in Step 3, and the well wall load transfer mechanism obtained by comparing with the field measured well wall data.

[0008] The invention is further characterized in that, The evolution mechanism of the loading characteristics of the frozen wellbore described in step 1 is as follows: During the wellbore construction phase, the frozen wall is in a frozen state and bears the external formation pressure. The wellbore is not directly subjected to pore water pressure, but only bears the initial stress caused by construction and temperature. During the thawing stage of the well wall, the frozen wall begins to melt, loses its bearing capacity, and the pore water pressure suddenly acts on the surface of the well wall, forming a peak hydrostatic pressure and causing a sudden change in the stress of the well wall. During the load formation stage, pore water forms a stable radial seepage between the surrounding rock and the well wall, and the water pressure decreases radially to a stable value; the solid phase stress of the surrounding rock is gradually released, and the well wall load is composed of the stable water pressure and the residual solid phase pressure and reaches equilibrium.

[0009] The well wall load transfer model is a three-dimensional structural model constructed based on the measured well wall parameters on site, defining the model boundaries and parameters; The parameters include the inner diameter of the inner wall layer. Inner wall outer diameter Outer diameter of outer wall layer The elastic modulus of the inner wall layer Poisson's ratio Effective stress coefficient Penetration rate ; Elastic modulus of the outer wall layer Poisson's ratio Effective stress coefficient Penetration rate Elastic modulus of surrounding rock Poisson's ratio Effective stress coefficient Penetration rate Water pressure on the outer side of the inner wall layer Water pressure on the outer side of the outer wall layer The total stresses of the surrounding rock, the outer side of the outer wall layer, and the inner side of the inner wall layer are respectively , , .

[0010] The total stress on the surrounding rock layer It is caused by pore water pressure and solid-phase horizontal stress Composed of, that is .

[0011] The specific steps for constructing the wellbore load transfer model in Step 1 are as follows: During the freeze-thaw process, the temperature field and the seepage field are significantly coupled. The freezing phase transition leads to changes in the pore water pressure gradient, while the permeability of the surrounding rock increases with increasing temperature. Therefore, a permeability function considering temperature is introduced:

[0012] in: Initial penetration rate; Temperature sensitivity coefficient; This is the freezing temperature; For reference temperature; Freeze-thaw load transfer formula:

[0013] in: This refers to the water pressure outside the well wall; This refers to the static pore water pressure. is the increase in water pressure caused by the temperature gradient; S is the release of solid stress in the surrounding rock, which gradually decreases over time. r Indicates radius, t For time; The increment of pore water pressure under the influence of temperature field is expressed as:

[0014] in, For water density, The coefficient of dynamic viscosity, For hydraulic gradient; After the frozen wall is completely melted, the boundary of the frozen wall is removed, and the structure of the inner wall layer (1), the outer wall layer (2), and the surrounding rock layer (3) is retained; the radial steady-state seepage of pore water between the surrounding rock and the well wall is considered; During the steady-state seepage stage, the seepage-stress coupling effect should be considered, that is, seepage causes changes in the effective stress of the surrounding rock, which in turn affects the deformation of the surrounding rock and the stress on the wellbore. A coupling function between permeability and stress should be introduced:

[0015] in, The uniaxial compressive strength of the surrounding rock. For effective stress, This is an empirical coefficient, with a value range of 1.5 to 3.5; Load transfer formula for steady-state seepage stage:

[0016]

[0017]

[0018] In the formula: Radial effective stress; The specific gravity of water; The dynamic viscosity of water; : Radius of the outer boundary of the seepage flow; The outer radius of the outer wall layer; For time; Water head height; Stress release rate coefficient.

[0019] The well wall similar model constructed in step 2 includes, from the inside out, an inner wall layer, an outer wall layer, and a frozen wall. The frozen wall is equipped with a longitudinal freezing pipe and is located within the surrounding rock layer. Miniature water pressure gauges and miniature pressure boxes are installed in the middle and on the outer side of the inner wall layer. A miniature pressure box is located in the surrounding rock layer and is located at the freezing pipe.

[0020] Step 2 is as follows: Step 2.1: Use low-temperature brine circulation to cool and freeze the surrounding rock model in the freezing hole corresponding to the freezing pipe to simulate the freezing state; during the construction of the freezing wall, the temperature sensor pre-embedded in the freezing wall monitors the temperature change at different locations in the freezing wall and is used to adjust the cooling parameters. The freezing temperature of the freezing wall is -15~-10℃. Step 2.2: After the frozen wall reaches the predetermined freezing state, the inner wall layer (1) and the outer wall layer (2) are made according to the similarity ratio; during the well wall model making process, micro pressure boxes and micro water pressure gauges are installed in the middle and outer sides of the inner wall layer (1) and the middle and outer sides of the outer wall layer (2), and displacement gauges (9) are arranged on the inner side of the inner wall layer (1). Step 2.3: Using a step-by-step loading method, water pressure corresponding to the prototype well wall is applied to the surrounding area of ​​the well wall similar model by water pump, and the freezing temperature is controlled to realize the freezing and melting process of the model water load. The pore water pressure and solid force of the inner wall layer (1), outer wall layer (2) and surrounding rock layer (3) during the freezing stage, melting stage and seepage stabilization stage are recorded.

[0021] Step 3 is as follows: Freezing stage: Cool the brine to -15℃ and adjust the circulation pump to a flow rate of 0.03m / s; apply water pressure corresponding to the prototype, and record temperature, stress and water pressure data every 2 hours until the frozen wall temperature stabilizes at -12~-10℃, which lasts for 24 hours. Melting stage: The temperature of the brine was increased from -15℃ to 5℃ at a rate of 2℃ / h, and the circulation pump maintained a flow rate of 0.03m / s; the water pressure was kept stable, and the evolution of stress and water pressure with temperature was recorded in real time every 1h for a period of 10h. Seepage stabilization stage: After the temperature rise is completed, maintain the brine temperature at 5℃ and shut down the brine circulation system; collect stress and water pressure data every 0.5 hours until the stress and water pressure changes are no more than 2%, and determine that the seepage stabilization state has been reached, and end the test. The duration is 10 hours. The confining pressure effect and pore water pressure effect of surrounding rock water pressure on the well wall are quantified to determine the proportional relationship between water pressure and solid phase pressure at different stages of load transfer.

[0022] Step 4, collecting on-site measured wellbore data, is as follows: During the construction of the vertical shaft, water pressure sensors, stress sensors, displacement sensors and temperature sensors are arranged at a monitoring section every 50 meters along the depth direction of the shaft wall. Using an automated data acquisition system, the sampling frequency was set to 2 hours / time during the freezing phase, 1 hour / time during the freeze-thaw phase, and 0.5 hours / time during the steady-state runoff phase. Monitoring data was continuously collected for at least 6 months to form a time series database. Step 5 is as follows: Step 5.1: Compare the calculated values ​​of the load transfer model with the proportional relationship between the surrounding rock water pressure and solid phase pressure at different stages in Step 3, and correct the effective stress coefficient and permeability parameters of the load transfer model to ensure that the error is less than 5%; Step 5.2: Compare the test results of water pressure, stress, and displacement in the well wall similar model with the field measured data to ensure that the data error is within 10%.

[0023] The beneficial effects of this invention are: This invention discloses a method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, weak rock strata. It accurately captures the stress characteristics of the well wall during the thawing stage and the steady-state flow stage of pore water, achieving a precise description of the dynamic changes in load transfer. Similar model tests are conducted to record the load during the freeze-thaw process of the well wall. A systematic field measurement system is built, covering monitoring of multiple parameters such as water pressure, stress, displacement, and temperature, forming a closed loop of theory-experiment-field verification to ensure the reliability of the analysis results and a high level of verification accuracy. Ultimately, this invention can serve the optimization of well wall design and the control of key construction nodes, effectively reducing engineering costs, minimizing construction risks, and significantly improving engineering safety and economy. Attached Figure Description

[0024] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of a three-dimensional cross-section of the well wall; Figure 2 A schematic cross-sectional view of the sensor arrangement for a wellbore-like model; Figure 3 This is a schematic diagram illustrating the loading characteristics of the wellbore during the construction phase. Figure 4 This is a schematic diagram illustrating the loading characteristics of the wellbore during the thawing stage. Figure 5 This is a schematic diagram of the loading characteristics of the well wall during the load formation stage; Figure 6 This is a schematic diagram of the mechanical model during the melting stage; Figure 7 This is a schematic diagram of the mechanical model for the steady-state seepage stage.

[0026] The labels in the diagram are as follows: 1-Inner wall layer, 2-Outer wall layer, 3-Surrounding rock, 4-Frozen wall, 5-Frozen pipe, 6-Sealing ring, 7-Miniature pressure box, 8-Miniature water pressure gauge, 9-Displacement gauge. Detailed Implementation

[0027] 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, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Example 1 This invention provides a method for analyzing the load transfer mechanism of freeze-thaw wellbore in deep, water-rich, and weak rock formations. The specific operation steps are as follows: Step 1: Construct a load transfer model for the freeze-thaw well wall of deep, water-rich soft rock based on the evolution mechanism of the loading characteristics of the frozen well wall; Step 2: Based on the principle of similarity ratio, create a similar model of the well wall of a deep, water-rich, soft rock freeze-thaw well at the same scale; Step 3: Determine the ratio of water pressure to solid pressure in the surrounding rock at different stages in the freezing tubes of similar models of brine well walls at different temperatures; Step 4: Combine the well wall load transfer model, the ratio of surrounding rock water pressure to solid phase pressure obtained in Step 3, and the well wall load transfer mechanism obtained by comparing with the field measured well wall data.

[0029] Example 2 As described in Example 1, the wellbore load transfer mechanism analysis method for freeze-thaw cycles in deep, water-rich, and weak rock formations yields the following wellbore loading characteristic evolution mechanism: 1.1: During the wellbore construction phase, the frozen wall is in a frozen state and bears the external formation pressure. The wellbore is not directly subjected to pore water pressure, but only to the initial stress caused by construction and temperature.

[0030] 1.2: During the thawing stage of the well wall, the frozen wall begins to melt, loses its bearing capacity, and the pore water pressure suddenly acts on the surface of the well wall, forming a peak hydrostatic pressure and causing a sudden change in the stress of the well wall. 1.3: During the load formation stage, pore water forms a stable radial seepage flow between the surrounding rock and the well wall, and the water pressure decreases radially to a stable value. The solid phase stress of the surrounding rock is gradually released, and the well wall load is composed of the stable water pressure and the residual solid phase pressure, which reach equilibrium.

[0031] Example 3 Based on Example 2, step 2 specifically includes the following steps: 2.1 Similarity Ratio Design: The prototype well wall parameters were designed by proportionally scaling down the model using geometric similarity constants. The inner radius of the well wall model is 320mm, the thickness of inner wall layer 1 is 100mm, the thickness of outer wall layer 2 is 40mm, and the thickness of surrounding rock layer 3 is 80mm. The concrete strength grade of inner wall layer 1 is C60, that of outer wall layer 2 is C50, and that of surrounding rock layer 3 is C25. The pore water pressure of the prototype well wall is consistent with that of the well wall model; the freezing temperature of the frozen wall 4 is -15~-10℃, the thawing temperature is 0~5℃, and the frozen brine flow rate is 0.03m / s.

[0032] 2.2 According to the similarity ratio of the design, the surrounding rock layer 3 is made of a material with similar physical and mechanical properties to the prototype surrounding rock layer. A micro pressure box and a micro water pressure gauge are arranged in the middle of the surrounding rock layer, and a freezing pipe 5 is reserved.

[0033] 2.3 Low-temperature brine circulation was used to cool and freeze the surrounding rock model in the freezing borehole to simulate a frozen state. Temperature sensors embedded during the construction of the freezing wall monitored temperature changes at different locations within the freezing wall to adjust cooling parameters. The freezing temperature of the wellbore model's freezing wall was -15 to -10℃.

[0034] 2.4 After the frozen wall reaches the predetermined freezing state, concrete and steel materials similar to those used in the prototype well wall are selected, such as... Figure 1-2 As shown, inner wall layer 1 and outer wall layer 2 are fabricated according to a similarity ratio. During the fabrication of the well wall model, miniature pressure cells and miniature hydraulic gauges are installed in the middle and on the outer side of inner wall layer 1, and in the middle and on the outer side of outer wall layer 2. Displacement gauges 9 are arranged on the inner side of the well wall model. Sealing rings 6 are also installed at inner wall layer 1 and surrounding rock layer 3. The load is applied using hydraulic pressure, and the sealing rings 6 serve a sealing function to prevent oil leakage during the process.

[0035] 2.5. Using a gradual loading method, water pressure corresponding to the prototype is applied to the well wall model via a water pump. The freezing temperature is controlled to realize the freezing and thawing process of the model under water load. The pore water pressure and solid stress of the inner wall layer 1, outer wall layer 2, and surrounding rock layer 3 are recorded during the freezing stage, thawing stage, and seepage stabilization stage.

[0036] Example 4 Based on Example 1, step 3 is as follows: Freezing stage: Cool the brine to -15℃ and adjust the circulation pump to a flow rate of 0.03m / s; apply water pressure corresponding to the prototype, and record temperature, stress and water pressure data every 2 hours until the frozen wall temperature stabilizes at -12~-10℃, which lasts for 24 hours.

[0037] Melting stage: The temperature of the brine was increased from -15℃ to 5℃ at a rate of 2℃ / h, and the circulation pump maintained a flow rate of 0.03m / s. The water pressure was kept stable, and the evolution of stress and water pressure with temperature was recorded in real time every 1h for a period of 10h.

[0038] Seepage stabilization stage: After the temperature rise is completed, maintain the brine temperature at 5℃ and shut down the brine circulation system; collect stress and water pressure data every 0.5 hours until the stress and water pressure changes are no more than 2%, and determine that the seepage stabilization state has been reached, and end the test. The duration is 10 hours.

[0039] Example 5 The present invention provides a method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, and weak rock formations. Based on the principles of generalized effective stress and stress superposition, it constructs well wall load transfer models for the stages from the moment the frozen wall begins to melt to the instant of complete melting and from the moment the frozen wall completely melts to the stage of steady-state seepage flow formed by pore water.

[0040] (1) Construct a load transfer model for the thawing stage of the frozen wall. The model boundary and parameter definitions are as follows: inner diameter of the inner wall layer. The inner diameter and outer diameter of the inner wall layer are The outer diameter of the outer wall layer is outer diameter of surrounding rock layer The fluid viscosity coefficient is The total stresses on the outer side of the surrounding rock layer, the outer wall layer, and the inner side of the inner wall layer are respectively... , , ; , , and The elastic modulus, Poisson's ratio, effective stress coefficient, and permeability of the inner wall layer 1 are used to represent these parameters. , , and The elastic modulus, Poisson's ratio, effective stress coefficient, and permeability of the outer wall layer 2 are used to represent these parameters. , , and Let represent the elastic modulus, Poisson's ratio, effective stress coefficient, and permeability of the surrounding rock layer 3. The water pressure outside the inner wall layer 1 is... The water pressure on the outer side of the outer wall layer 2 is The total stress on the surrounding rock layer 3 It is caused by pore water pressure and solid-phase horizontal stress Composed of, that is .

[0041] During the freeze-thaw process, the temperature field and the seepage field are significantly coupled. The freezing phase transition leads to changes in the pore water pressure gradient, while the permeability of the surrounding rock increases with increasing temperature. A temperature-dependent permeability function is introduced:

[0042] in: Initial penetration rate; Temperature sensitivity coefficient; This is the freezing temperature; This is a reference temperature.

[0043] Freeze-thaw load transfer formula:

[0044] in: This refers to the water pressure outside the well wall; This refers to the static pore water pressure. is the increase in water pressure caused by the temperature gradient; S is the release of solid stress in the surrounding rock, which gradually decreases over time. r Indicates radius, t For time; The increase in pore water pressure under the influence of temperature field can be expressed as:

[0045] in, For water density, The coefficient of dynamic viscosity, This represents the hydraulic gradient.

[0046] (2) Construct a load transfer model for the steady-state seepage stage of pore water, and simplify the model and adjust the parameters: After the frozen wall is completely melted, remove the boundary of the frozen wall and retain the structure of inner wall layer 1, outer wall layer 2 and surrounding rock layer 3; consider the radial steady-state seepage of pore water between the surrounding rock and the well wall.

[0047] During the steady-state seepage stage, the seepage-stress coupling effect should be considered, that is, seepage causes changes in the effective stress of the surrounding rock, which in turn affects the deformation of the surrounding rock and the stress on the wellbore. A coupling function between permeability and stress should be introduced:

[0048] in The compressive strength of the surrounding rock. This is an empirical coefficient, with a value range of 1.5 to 3.5; Load transfer formula for steady-state seepage stage:

[0049]

[0050]

[0051] In the formula: Radial effective stress; The specific gravity of water; The dynamic viscosity of water; : Radius of the outer boundary of the seepage flow; The outer radius of the outer wall layer; For time; Water head height; Stress release rate coefficient.

[0052] Example 6 Based on Example 1, the method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, and weak rock formations of this invention, step 4, involves obtaining the field-measured well wall data as follows: During the construction of the vertical shaft, the following sensors are installed at monitoring sections every 50 meters along the depth direction of the shaft wall: Water pressure sensors: placed at the middle and outer sides of the inner wall layer, the middle and outer sides of the outer wall layer, and 2m, 4m, and 6m away from the well wall inside the surrounding rock to monitor the dynamic changes in pore water pressure; Stress sensors: arranged in the circumferential and radial directions of the inner and outer wall layers to monitor the evolution of wellbore stress; Displacement sensor: A multi-point displacement meter is used to monitor the radial displacement of the well wall and the deep displacement of the surrounding rock layer; Temperature sensor: placed at the interface between the frozen wall and the surrounding rock layer to monitor the change in the melting temperature of the frozen wall.

[0053] Data acquisition: An automated data acquisition system was adopted, with sampling frequencies set at 2 hours / time during the freezing phase, 1 hour / time during the thawing phase, and 0.5 hours / time during the steady-state phase. Monitoring data for at least 6 months was continuously collected to form a time series database.

[0054] Step 5 specifically includes the following steps: Step 5.1: Compare the calculated values ​​of the load transfer model with the proportional relationship between the surrounding rock water pressure and solid phase pressure at different stages in Step 3, and correct the effective stress coefficient and permeability parameters of the load transfer model to ensure that the error is less than 5%; Step 5.2: Compare the test results of water pressure, stress, and displacement in the well wall similar model with the field measured data to ensure that the data error is within 10%.

[0055] like Figure 3-5As shown, before the frozen wall thaws, the formation pressure acts directly on the outside of the frozen wall, and the well wall is not directly affected by the water pressure; after the frozen wall is completely thawed, the well wall is immediately subjected to the direct action of the water pressure, and as the water pressure penetrates, radial seepage gradually forms in the surrounding rock and well wall, and the water pressure gradually decreases to a stable state in the area of ​​the surrounding rock and well wall.

[0056] like Figure 6-7 As shown, based on the principles of generalized effective stress and stress superposition, a well wall external load transfer model is constructed for the stages from the start of the frozen wall to the instant of complete melting and from the complete melting of the frozen wall to the stage of steady-state seepage of pore water.

[0057] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, and weak rock formations, characterized in that... The specific operating steps are as follows: Step 1: Construct a load transfer model for the freeze-thaw well wall of deep, water-rich soft rock based on the evolution mechanism of the loading characteristics of the frozen well wall; Step 2: Based on the principle of similarity ratio, create a similar model of the well wall of a deep, water-rich, soft rock freeze-thaw well; Step 3: Determine the ratio of water pressure to solid pressure in the surrounding rock at different stages in the freezing tubes of similar models of brine well walls at different temperatures; Step 4: Combine the well wall load transfer model, the ratio of surrounding rock water pressure to solid phase pressure obtained in Step 3, and the well wall load transfer mechanism obtained by comparing with the field measured well wall data.

2. The method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, weak rock formations according to claim 1, characterized in that, The evolution mechanism of the loading characteristics of the frozen wellbore described in step 1 is as follows: During the wellbore construction phase, the frozen wall is in a frozen state and bears the external formation pressure. The wellbore is not directly subjected to pore water pressure, but only bears the initial stress caused by construction and temperature. During the thawing stage of the well wall, the frozen wall begins to melt, loses its bearing capacity, and the pore water pressure suddenly acts on the surface of the well wall, forming a peak hydrostatic pressure and causing a sudden change in the stress of the well wall. During the load formation stage, pore water forms a stable radial seepage between the surrounding rock and the well wall, and the water pressure decreases radially to a stable value; the solid phase stress of the surrounding rock is gradually released, and the well wall load is composed of the stable water pressure and the residual solid phase pressure and reaches equilibrium.

3. The method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, weak rock formations according to claim 1, characterized in that, The well wall load transfer model is a three-dimensional structural model constructed based on the measured well wall parameters on site, defining the model boundaries and parameters; The parameters include the inner diameter of the inner wall layer. Inner wall outer diameter Outer diameter of outer wall layer The elastic modulus of the inner wall layer Poisson's ratio Effective stress coefficient Penetration rate ; Elastic modulus of the outer wall layer Poisson's ratio Effective stress coefficient Penetration rate Elastic modulus of surrounding rock Poisson's ratio Effective stress coefficient Penetration rate Water pressure on the outer side of the inner wall layer Water pressure on the outer side of the outer wall layer The total stresses on the outer side of the surrounding rock layer, the outer wall layer, and the inner side of the inner wall layer are respectively... , , .

4. The method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, weak rock strata according to claim 3, characterized in that, The total stress on the surrounding rock layer It is caused by pore water pressure and solid-phase horizontal stress Composed of, that is .

5. The method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, weak rock formations according to claim 3, characterized in that, The specific steps for constructing the wellbore load transfer model in Step 1 are as follows: During the freeze-thaw process, the temperature field and the seepage field are significantly coupled. The freezing phase transition leads to changes in the pore water pressure gradient, while the permeability of the surrounding rock increases with increasing temperature. Therefore, a permeability function considering temperature is introduced: in: Initial penetration rate; This refers to the temperature sensitivity coefficient. This is the freezing temperature; For reference temperature; Freeze-thaw load transfer formula: in: The water pressure outside the well wall; This refers to the static pore water pressure. is the increase in water pressure caused by the temperature gradient; S is the release of solid stress in the surrounding rock, which gradually decreases over time. r Indicates radius, t For time; The increment of pore water pressure under the influence of temperature field is expressed as: in, For water density, The coefficient of dynamic viscosity, For hydraulic gradient; After the frozen wall is completely melted, the boundary of the frozen wall is removed, and the structure of the inner wall layer (1), the outer wall layer (2), and the surrounding rock layer (3) is retained; the radial steady-state seepage of pore water between the surrounding rock and the well wall is considered; During the steady-state seepage stage, the seepage-stress coupling effect should be considered, that is, seepage causes changes in the effective stress of the surrounding rock, which in turn affects the deformation of the surrounding rock and the stress on the wellbore. A coupling function between permeability and stress should be introduced: in, The uniaxial compressive strength of the surrounding rock. For effective stress, This is an empirical coefficient, with a value range of 1.5 to 3.5; Load transfer formula for steady-state seepage stage: In the formula: Radial effective stress; The specific gravity of water; The dynamic viscosity of water; : Radius of the outer boundary of the seepage flow; The outer radius of the outer wall layer; For time; Water head height; Stress release rate coefficient.

6. The method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, weak rock formations according to claim 3, is characterized in that... The well wall similar model constructed in step 2 includes an inner wall layer (1), an outer wall layer (2), and a frozen wall (4) from the inside out. The frozen wall (4) is equipped with a longitudinal freezing pipe (5) and is located in the surrounding rock layer (3). The inner wall layer (1) is equipped with a micro water pressure gauge (8) and a micro pressure box in the middle and on the outside. The surrounding rock layer (3) is equipped with a micro pressure box (7) and is located at the freezing pipe (5).

7. The method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, weak rock formations according to claim 3, is characterized in that, Step 2 is as follows: Step 2.1: Use low-temperature brine circulation to cool and freeze the surrounding rock model in the freezing hole corresponding to the freezing pipe to simulate the freezing state; during the construction of the freezing wall, the temperature sensor pre-embedded in the freezing wall monitors the temperature change at different locations in the freezing wall and is used to adjust the cooling parameters. The freezing temperature of the freezing wall is -15~-10℃. Step 2.2: After the frozen wall reaches the predetermined freezing state, the inner wall layer (1) and the outer wall layer (2) are made according to the similarity ratio; during the well wall model making process, micro pressure boxes and micro water pressure gauges are installed in the middle and outer sides of the inner wall layer (1) and the middle and outer sides of the outer wall layer (2), and displacement gauges (9) are arranged on the inner side of the inner wall layer (1). Step 2.3: Using a step-by-step loading method, water pressure corresponding to the prototype well wall is applied to the surrounding area of ​​the well wall similar model by water pump, and the freezing temperature is controlled to realize the freezing and melting process of the model water load. The pore water pressure and solid force of the inner wall layer (1), outer wall layer (2) and surrounding rock layer (3) during the freezing stage, melting stage and seepage stabilization stage are recorded.

8. The method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, weak rock formations according to claim 3, characterized in that, Step 3 is as follows: Freezing stage: Cool the brine to -15℃ and adjust the circulation pump to a flow rate of 0.03m / s; apply water pressure corresponding to the prototype, and record temperature, stress and water pressure data every 2 hours until the frozen wall temperature stabilizes at -12~-10℃, which lasts for 24 hours. Melting stage: The temperature of the brine was increased from -15℃ to 5℃ at a rate of 2℃ / h, and the circulation pump maintained a flow rate of 0.03m / s; the water pressure was kept stable, and the evolution of stress and water pressure with temperature was recorded in real time every 1h for a period of 10h. Seepage stabilization stage: After the temperature rise is completed, maintain the brine temperature at 5℃ and shut down the brine circulation system; collect stress and water pressure data every 0.5 hours until the stress and water pressure changes are no more than 2%, and determine that the seepage stabilization state has been reached, and end the test. The duration is 10 hours. The confining pressure effect and pore water pressure effect of surrounding rock water pressure on the well wall are quantified to determine the proportional relationship between water pressure and solid phase pressure at different stages of load transfer.

9. The method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, weak rock formations according to claim 3, characterized in that, The steps for collecting the field-measured wellbore data in step 4 are as follows: During the construction of the vertical shaft, water pressure sensors, stress sensors, displacement sensors and temperature sensors are arranged at a monitoring section every 50 meters along the depth direction of the shaft wall. Using an automated data acquisition system, the sampling frequency was set to 2 hours / time during the freezing phase, 1 hour / time during the freeze-thaw phase, and 0.5 hours / time during the steady-state runoff phase. Monitoring data was continuously collected for at least 6 months to form a time series database.

10. The method for analyzing the load transfer mechanism of freeze-thaw well walls in deep, water-rich, weak rock formations according to claim 3, characterized in that, Step 5 is as follows: Step 5.1: Compare the calculated values ​​of the load transfer model with the proportional relationship between the surrounding rock water pressure and solid phase pressure at different stages in Step 3, and correct the effective stress coefficient and permeability parameters of the load transfer model to ensure that the error is less than 5%; Step 5.2: Compare the test results of water pressure, stress, and displacement in the well wall similar model with the field measured data to ensure that the data error is within 10%.

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