U-shaped well efficient sealing structure and sealing method

Abstract

The invention discloses a U-shaped well efficient sealing structure and a sealing method, the U-shaped well efficient sealing structure is composed of different functional layers in the well depth direction, and the U-shaped well efficient sealing structure belongs to the technical field of geothermal well sealing and comprises a well mouth sealing layer which is a rigid consolidation body formed after sealing slurry is chemically activated; the middle sealing layer is composed of a flexible sealing body formed by pouring and curing the sealing slurry, and a U-shaped heat exchange tube is embedded in the middle sealing layer; the bottom backfilling layer is composed of a composite structure jointly formed by the sealing slurry and a physical heat conduction reinforcing body arranged at the bottom of the well in advance and wraps the bottom elbow section of the U-shaped heat exchange pipe. Wherein the sealing slurry comprises pressure response expansion particles; low critical pressure type pressure response expansion particles are distributed in the middle sealing layer and used for responding and sealing pressure fluctuation of the middle water-bearing layer. High critical pressure type pressure response expansion particles are distributed in the bottom backfill layer and used for coping with deep high formation pressure and cyclic stress caused by thermal expansion and contraction of the U-shaped heat exchange pipes.

Description

Technical Field

[0001] This application relates to a high-efficiency sealing structure and sealing method for U-shaped wells, belonging to the field of geothermal well sealing technology. Background Technology

[0002] As a highly efficient and renewable energy utilization technology, ground source heat pump systems rely heavily on U-shaped buried pipe heat exchangers, which are vertically drilled and installed underground. Backfilling and sealing the annular gap between the borehole and the U-shaped heat exchanger is a crucial step in ensuring the system's long-term, efficient, and safe operation. This sealing structure must simultaneously fulfill three core functions: first, effectively isolating different aquifers to prevent groundwater contamination and protect groundwater resources; second, maintaining well wall stability and supporting the U-shaped pipe; and third, establishing a good heat conduction path to guarantee heat exchange efficiency. Currently, the sealing of U-shaped wells in ground source heat pumps commonly employs a traditional "three-stage" technique: backfilling with high thermal conductivity material (bottom), high sealing material (middle), and high-strength material (wellhead). This approach stems from the technical bias that thermal conductivity and sealing performance cannot be simultaneously achieved, leading to multiple material changes during construction, a complex process, low efficiency, and the risk of seal failure and thermal short circuits at the interfaces of different materials, severely impacting the system's long-term reliability and heat exchange efficiency. Summary of the Invention

[0003] According to one aspect of this application, a high-efficiency sealing structure for U-shaped wells is provided, comprising different functional layers along the well depth direction, including: The wellhead sealing layer is located at a predetermined depth below the surface. The wellhead sealing layer is a rigid solidified body formed by chemically activating the sealing slurry. The middle sealing layer is located below the wellhead sealing layer. The middle sealing layer is composed of a flexible sealing body formed by the injection and curing of the sealing slurry, and has a U-shaped heat exchange tube embedded inside. The bottom backfill layer is located below the middle sealing layer. The bottom backfill layer is a composite structure formed by the sealing slurry and a physical thermal conductivity enhancer pre-set at the bottom of the well, and it wraps the bottom elbow section of the U-shaped heat exchange tube. The sealing slurry includes pressure-responsive expanding particles; The central sealing layer contains low-critical-pressure type pressure-responsive expansion particles, which are used to respond to and seal pressure fluctuations in the central aquifer. The bottom backfill layer contains high-critical-pressure type pressure-responsive expansion particles to cope with the high pressure of deep formations and the cyclic stress caused by the thermal expansion and contraction of the U-shaped heat exchange tube.

[0004] Furthermore, the mass percentage of pressure-responsive expansion particles in the wellhead sealing layer is ≤10wt%, or the wellhead sealing layer does not contain pressure-responsive expansion particles, and the rigid consolidation body resists surface loads and freeze-thaw cycles.

[0005] Furthermore, the middle sealing layer near the interface between the top and bottom plates of the main aquifer forms one or more pressure-activated enhanced sealing rings through the concentrated activation of the low-critical-pressure type pressure-response expansion particles.

[0006] Furthermore, the sealing slurry is composed of a dry mix and water at a weight ratio of 1:(0.8-1.2), and the dry mix consists of the following components by weight percentage: 35%-50% sodium-based bentonite; 40%-55% thermally conductive filler; 0.2%-0.6% reinforcing fiber; 0.4%-1.0% retarder; And, 5%-10% of the pressure-responsive expanding particles.

[0007] Furthermore, the pressure-responsive expansion particles have a core-shell structure, with the core being a water-absorbing polymer and the outer shell being a microporous membrane sensitive to formation pressure. The critical rupture pressure of the low-critical-pressure type pressure-responsive expansion particles is 0.5-2 MPa; the critical rupture pressure of the high-critical-pressure type pressure-responsive expansion particles is 2-5 MPa.

[0008] Furthermore, the chemical activation is achieved by adding a pH adjuster into the annulus of the slurry at the wellhead. The pH adjuster is quicklime or solid cement.

[0009] Furthermore, the physical thermal conductivity enhancement is preformed from the following components in weight percentages: 70%-85% thermally conductive components, including metal shavings, graphite blocks, or artificial thermally conductive ceramic particles; 15%-30% skeleton component, wherein the skeleton component is the dry mix; In this process, the thermally conductive component, the skeleton component, and water are mixed and pressed into a cylinder with through pores to allow the sealing slurry to penetrate.

[0010] According to another aspect of this application, a method for high-efficiency sealing of a U-shaped well is provided, for forming a high-efficiency sealing structure of a U-shaped well, comprising the following steps: S1: After drilling and cleaning the well, the aforementioned physical heat-conducting reinforcement is pre-installed at the bottom of the well; S2: Lower the U-shaped heat exchange tube into the well; S3: Through a grouting pipe extending to the bottom of the well, the uniform sealing slurry is pumped into the annulus inside the well, and the pump pressure is kept stable and below the critical rupture pressure of all types of pressure-responsive expanding particles during the pumping process; S4: The slurry continuously replaces the water in the well from the bottom up until the slurry overflows from the wellhead, and the density of the returned slurry is basically the same as that of the pumped slurry. S5: Add a pH adjuster into the annular gap of the slurry at the wellhead to mix it with the surface slurry and form the wellhead sealing layer; S6: Static curing allows the slurry to solidify throughout the entire well section; during curing, as well pressure recovers and formation stress occurs, the pressure-response expansion particles at different depths expand according to their P... c The values ​​are activated sequentially, ultimately forming an integrated sealing structure with gradient functionality and pressure self-adaptation capability along the well depth direction.

[0011] Furthermore, in S5, after the slurry overflows from the wellhead, a pH adjuster is immediately added into the wellhead annulus, and a special tool is used to stir and mix to a limited depth, so that the slurry in this section will rapidly solidify.

[0012] The beneficial effects that this application can produce include: The low-critical-pressure type pressure-responsive expansion particles (pressure 0.5-2 MPa) are mainly distributed in the middle sealing layer, while the high-critical-pressure type pressure-responsive expansion particles (pressure 2-5 MPa) are mainly distributed in the bottom backfill layer. After the geothermal well completes grouting and enters the curing stage, the hydrostatic pressure within the wellbore and the geostress of the surrounding formation will gradually recover and act on the solidified sealant grout. In the middle section, when the formation pressure recovers to the range of 0.5-2 MPa, the outer shell of the low-critical-pressure type particles first reaches its mechanical strength limit and ruptures. The water-absorbing polymer inside is rapidly released, drawing free water from the surrounding grout and causing significant volume expansion. This expansion is not uniform and gentle, but rather generates significant expansion stress in a localized area. This stress effectively compresses the surrounding solidified grout, actively filling any microscopic cracks and pores that may be caused by grout shrinkage due to water loss or minor changes in geological stress, thereby forming a dense zone with enhanced sealing performance in this area. As depth increases, formation pressure rises further. When it reaches a threshold of 2-5 MPa, the hypercritical pressure particles distributed in the bottom backfill layer are activated and begin their expansion process. The bottom layer not only bears higher formation pressure but also directly experiences thermal cycling stress caused by drastic temperature changes in the U-shaped heat exchange tubes, placing more stringent demands on the durability of the sealing material. The activation and expansion of the hypercritical pressure particles at this location generates expansion stress that counteracts the high formation pressure and thermal stress at depth, effectively compensating for material fatigue or interfacial micro-gap that may result from long-term thermal cycling and high pressure, ensuring the long-term sealing integrity of the core heat exchange area.

[0013] The sealing structure consists of a wellhead sealing layer, a middle sealing layer, and a bottom backfill layer. All three layers originate from the same slurry containing functional components such as pressure-responsive expansion particles and thermally conductive fillers. During construction, the slurry is injected throughout the entire well section in a single pumping operation, ensuring the uniformity and continuity of the material in its initial state. Subsequently, a differentiated activation mechanism comes into play: in the wellhead area, a locally strong alkaline, high-calcium ion environment is created by artificially adding pH adjusters (such as quicklime or solid cement). This environment not only neutralizes the effect of the retarder but, more importantly, stimulates the slurry system (especially the bentonite component) to undergo a pozzolanic reaction and rapid hydration reaction. This transforms the slurry in this section from a flexible gel state based on bentonite hydration into a rigid solidified body similar to cement-based materials, thereby achieving the high strength required to resist surface loads and freeze-thaw cycles. In the middle and bottom of the well, the slurry undergoes normal hydration and solidification under natural formation conditions and temperatures, forming a seal with extremely low permeability and good flexibility to adapt to minor formation deformations. The formation of this gradient function is seamless and gradual. Since there are no abrupt changes in materials between layers, but rather the evolution of the same material's physicochemical state under different conditions, there are no obvious physical interfaces between layers that could easily lead to sealing failure. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of a U-shaped well high-efficiency sealing structure in one embodiment of this application; List of components and attached diagrams: 1-Wellhead sealing layer; 2-Middle sealing layer; 3-U-shaped heat exchange tube; 4-Bottom backfill layer. Detailed Implementation

[0015] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0016] See Figure 1 A U-shaped well high-efficiency sealing structure, composed of different functional layers along the well depth direction, including: Wellhead sealing layer 1 is located at a predetermined depth below the surface. Wellhead sealing layer 1 is a rigid solidified body formed by chemical activation of sealing slurry. The middle sealing layer 2 is located below the wellhead sealing layer 1. The middle sealing layer 2 is composed of a flexible sealing body formed by the injection and curing of the sealing slurry, and a U-shaped heat exchange tube 3 is embedded inside it. The bottom backfill layer 4 is located below the middle sealing layer 2. The bottom backfill layer 4 is a composite structure formed by the sealing slurry and a physical thermal conductivity enhancer pre-set at the bottom of the well, and it wraps the bottom elbow section of the U-shaped heat exchange tube 3. The sealing slurry includes pressure-responsive expanding particles; The middle sealing layer 2 contains low-critical-pressure type pressure-responsive expansion particles, which are used to respond to and seal the pressure fluctuations of the middle aquifer. The bottom backfill layer 4 contains high-critical-pressure type pressure-response expansion particles to cope with the high pressure of deep formations and the cyclic stress caused by the thermal expansion and contraction of the U-shaped heat exchange tube.

[0017] Furthermore, the mass percentage of pressure-responsive expansion particles in the wellhead sealing layer 1 is ≤10wt%, or the wellhead sealing layer 1 does not contain pressure-responsive expansion particles, and the rigid consolidation body relies on its strength to resist surface loads and freeze-thaw cycles.

[0018] Furthermore, the middle sealing layer 2, near the interface between the top and bottom plates of the main aquifer, forms one or more pressure-activated enhanced sealing rings through the concentrated activation of the low-critical-pressure type pressure-response expansion particles.

[0019] Furthermore, the sealing slurry is composed of a dry mix and water at a weight ratio of 1:(0.8-1.2), wherein the dry mix consists of the following components by weight percentage: 35%-50% sodium-based bentonite; 40%-55% thermally conductive filler; 0.2%-0.6% reinforcing fiber; 0.4%-1.0% retarder; And, 5%-10% of the pressure-responsive expanding particles.

[0020] Furthermore, the pressure-responsive expansion particles have a core-shell structure, with the core being a water-absorbing polymer and the outer shell being a microporous membrane sensitive to formation pressure; the critical rupture pressure of the low-critical-pressure type pressure-responsive expansion particles is 0.5-2 MPa; and the critical rupture pressure of the high-critical-pressure type pressure-responsive expansion particles is 2-5 MPa.

[0021] Furthermore, the chemical activation is achieved by adding a pH adjuster into the annular space of the slurry at the wellhead; the pH adjuster is quicklime or solid cement.

[0022] Furthermore, the physical thermal conductivity enhancer is preformed from the following components in weight percentages: 70%-85% thermally conductive components, including metal shavings, graphite blocks, or artificial thermally conductive ceramic particles; 15%-30% skeleton component, wherein the skeleton component is the dry mix; In this process, the thermally conductive component, the skeleton component, and water are mixed and pressed into a cylinder with through pores to allow the sealing slurry to penetrate.

[0023] A method for high-efficiency sealing of a U-shaped well, used to form the aforementioned high-efficiency sealing structure, includes the following steps: S1: After drilling and cleaning the well, the aforementioned physical heat-conducting reinforcement is pre-installed at the bottom of the well; S2: Lower the U-shaped heat exchange tube into the well; S3: Through a grouting pipe extending to the bottom of the well, the uniform sealing slurry is pumped into the annulus inside the well, and the pump pressure is kept stable and below the critical rupture pressure of all types of pressure-responsive expanding particles during the pumping process; S4: The slurry continuously replaces the water in the well from the bottom up until the slurry overflows from the wellhead, and the density of the returned slurry is basically the same as that of the pumped slurry. S5: Add a pH adjuster into the annular gap of the slurry at the wellhead to mix it with the surface slurry and form the wellhead sealing layer; S6: Static curing allows the slurry to solidify throughout the entire well section; during curing, as well pressure recovers and formation stress occurs, the pressure-response expansion particles at different depths expand according to their P... c The values ​​are activated sequentially, ultimately forming an integrated sealing structure with gradient functionality and pressure self-adaptation capability along the well depth direction.

[0024] Furthermore, in S5, after the slurry overflows from the wellhead, a pH adjuster is immediately added into the wellhead annulus, and a special tool is used to stir and mix to a limited depth, so that the slurry in this section will rapidly solidify.

[0025] The low-critical-pressure type pressure-responsive expansion particles (pressure 0.5-2 MPa) described in this application are mainly distributed in the middle sealing layer, while the high-critical-pressure type pressure-responsive expansion particles (pressure 2-5 MPa) are mainly distributed in the bottom backfill layer. After the geothermal well completes grouting and enters the curing stage, the hydrostatic pressure inside the wellbore and the geostress of the surrounding formation will gradually recover and act on the injected sealing grout solidified body. In the middle section of the well, when the formation pressure recovers to the range of 0.5-2 MPa, the outer shell of the low-critical-pressure type particles here first reaches its mechanical strength limit and ruptures. The water-absorbing polymer inside is rapidly released, absorbing free water from the surrounding grout, resulting in significant volume expansion. This expansion is not a uniform and gentle expansion, but rather generates significant expansion stress in a localized area. This stress can effectively squeeze the surrounding grout solidified body, actively filling any micro-cracks and pores that may be caused by grout shrinkage due to water loss or small changes in geological stress, thereby forming a dense zone with enhanced sealing performance in this area. As depth increases, formation pressure rises further. When it reaches a threshold of 2-5 MPa, the hypercritical pressure particles distributed in the bottom backfill layer are activated and begin their expansion process. The bottom layer not only bears higher formation pressure but also directly experiences thermal cycling stress caused by drastic temperature changes in the U-shaped heat exchange tubes, placing more stringent demands on the durability of the sealing material. The activation and expansion of the hypercritical pressure particles at this location generates expansion stress that counteracts the high formation pressure and thermal stress at depth, effectively compensating for material fatigue or interfacial micro-gap that may result from long-term thermal cycling and high pressure, ensuring the long-term sealing integrity of the core heat exchange area.

[0026] The sealing structure consists of a wellhead sealing layer, a middle sealing layer, and a bottom backfill layer. All three layers originate from the same slurry containing functional components such as pressure-responsive expansion particles and thermally conductive fillers. During construction, the slurry is injected throughout the entire well section in a single pumping operation, ensuring the uniformity and continuity of the material in its initial state. Subsequently, a differentiated activation mechanism comes into play: in the wellhead area, a locally strong alkaline, high-calcium ion environment is created by artificially adding pH adjusters (such as quicklime or solid cement). This environment not only neutralizes the effect of the retarder but, more importantly, stimulates the slurry system (especially the bentonite component) to undergo a pozzolanic reaction and rapid hydration reaction. This transforms the slurry in this section from a flexible gel state based on bentonite hydration into a rigid solidified body similar to cement-based materials, thereby achieving the high strength required to resist surface loads and freeze-thaw cycles. In the middle and bottom of the well, the slurry undergoes normal hydration and solidification under natural formation conditions and temperatures, forming a seal with extremely low permeability and good flexibility to adapt to minor formation deformations. The formation of this gradient function is seamless and gradual. Since there are no abrupt changes in materials between layers, but rather the evolution of the same material's physicochemical state under different conditions, there are no obvious physical interfaces between layers that could easily lead to sealing failure.

[0027] Controlling the pumping pressure to maintain a stable pressure below the critical rupture pressure for all types of pressure-responsive expansion particles ensures the entire pumping process operates in laminar flow, protecting the functional components of the slurry and the integrity of the pressure-responsive expansion particles. Excessive pump pressure can cause premature particle rupture and failure during pumping or at the top of the wellbore, depleting their valuable pressure-responsive capacity before reaching the designed formation. Monitoring the density of the returned slurry and its consistency with the pumped slurry provides a direct indication of whether the well water has been completely replaced and whether the injection is continuous and complete.

[0028] The central sealing layer is formed by curing a uniform sealing slurry under natural formation conditions. This flexible nature allows it to better adapt to wellbore micro-deformation caused by formation creep, temperature changes, or minor geological activity, without being prone to brittle cracking like rigid materials. However, any material can develop micro-damage under long-term complex environments. This is where the low-critical-pressure-responsive expansion particles distributed within it play a crucial role. Throughout the sealing structure's lifespan, any newly generated micro-cracks due to stress or wet-dry cycles will lead to stress concentration and fluid pressure changes in that localized area. Once this pressure disturbance reaches the particle activation threshold (0.5-2 MPa), the surrounding particles rupture and expand, releasing water-absorbing polymers that rapidly seal and fill these newly formed micro-cracks.

[0029] This self-repair mechanism is proactive and occurs in situ, independent of external intervention or subsequent maintenance. The rigid consolidation of the wellhead layer provides robust structural protection, while the high thermal conductivity composite at the bottom layer resists deep high pressure and thermal fatigue. This not only significantly reduces the maintenance risks and costs of geothermal wells throughout their entire life cycle but also fundamentally ensures the safety of groundwater resources and the long-term efficiency and stability of geothermal energy extraction.

[0030] The sealing slurry itself is a high-performance heat-conducting medium. Its dry mix contains 40%-55% thermally conductive fillers, which, during the mixing and curing process, can overlap to form a three-dimensional continuous heat conduction network within the bentonite matrix. This allows the cured sealing layer, especially the central sealing layer penetrating the main well depth, to have a thermal conductivity consistently higher than 1.0 W / (m·K), far superior to traditional bentonite slurries (typically below 0.8 W / (m·K)). This means that heat between the circulating fluid in the U-shaped heat exchanger and the surrounding formation can be transferred more smoothly through the central sealing layer, reducing thermal resistance and directly improving heat exchange efficiency.

[0031] In the bottom bend section, where heat exchange is most concentrated, this application employs a more robust technical solution: a pre-installed physical thermal conductivity reinforcement composed of 70%-85% high thermal conductivity components. This reinforcement is designed as a cylinder with interconnected pores. When the sealing slurry is pumped in, it permeates and encapsulates this reinforcement, forming a composite structure of slurry and a high thermal conductivity skeleton after curing. The equivalent thermal conductivity of this composite structure is significantly higher than that of a single cured slurry. Materials such as metal shavings or thermally conductive ceramics possess extremely high thermal conductivity (tens to hundreds of W / (m·K)), forming preferential heat flow channels and greatly enhancing the heat extraction and injection capabilities of the bottom region. Furthermore, the high-critical-pressure type pressure-responsive expansion particles distributed in this layer, upon activation, expand, enhancing the seal while further compacting the contact between the slurry and the thermally conductive reinforcement skeleton, potentially reducing contact thermal resistance and further optimizing thermal conductivity.

[0032] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A U-shaped well high-efficiency sealing structure, comprising different functional layers along the well depth direction, characterized in that, include: Wellhead sealing layer (1) is located at a predetermined depth below the surface. The wellhead sealing layer (1) is a rigid solidified body formed by chemical activation of sealing slurry. The middle sealing layer (2) is located below the wellhead sealing layer (1). The middle sealing layer (2) is a flexible sealing body formed by the injection and curing of the sealing slurry, and a U-shaped heat exchange tube (3) is embedded inside it. The bottom backfill layer (4) is located below the middle sealing layer (2). The bottom backfill layer (4) is a composite structure formed by the sealing slurry and a physical thermally conductive reinforcement pre-set at the bottom of the well, and wraps the bottom bend of the U-shaped heat exchange tube (3). The sealing slurry includes pressure-responsive expanding particles; The middle sealing layer (2) contains low critical pressure type pressure response expansion particles, which are used to respond to and seal the pressure fluctuations of the middle aquifer. The bottom backfill layer (4) contains high critical pressure type pressure response expansion particles, which are used to cope with the high pressure of deep formations and the cyclic stress caused by the thermal expansion and contraction of U-shaped heat exchange tubes.

2. The U-shaped well high-efficiency sealing structure according to claim 1, characterized in that, The mass percentage of pressure-responsive expansion particles in the wellhead sealing layer (1) is ≤10wt%, or the wellhead sealing layer (1) does not contain pressure-responsive expansion particles, and the rigid solidified body resists surface loads and freeze-thaw cycles.

3. The U-shaped well high-efficiency sealing structure according to claim 1, characterized in that, The middle sealing layer (2) is located near the interface between the top and bottom plates of the main aquifer. Through the concentrated activation of the low critical pressure type pressure response expansion particles, it forms one or more pressure-activated enhanced sealing rings.

4. The U-shaped well high-efficiency sealing structure according to claim 1, characterized in that, The sealing slurry is composed of a dry mix and water at a weight ratio of 1:(0.8-1.2), and the dry mix consists of the following components by weight percentage: 35%-50% sodium-based bentonite; 40%-55% thermally conductive filler; 0.2%-0.6% reinforcing fiber; 0.4%-1.0% retarder; And, 5%-10% of the pressure-responsive expanding particles.

5. The U-shaped well high-efficiency sealing structure according to claim 4, characterized in that, The pressure-responsive expansion particles have a core-shell structure, with the core being a water-absorbing polymer and the outer shell being a microporous membrane sensitive to formation pressure. The critical rupture pressure of the low-critical-pressure type pressure-responsive expansion particles is 0.5-2 MPa; the critical rupture pressure of the high-critical-pressure type pressure-responsive expansion particles is 2-5 MPa.

6. The U-shaped well high-efficiency sealing structure according to claim 1, characterized in that, The chemical activation is achieved by adding a pH adjuster into the annulus of the slurry at the wellhead. The pH adjuster is quicklime or solid cement.

7. The U-shaped well high-efficiency sealing structure according to claim 1, characterized in that, The physical thermal conductivity enhancement is preformed from the following components in weight percentages: 70%-85% thermally conductive components, including metal shavings, graphite blocks, or artificial thermally conductive ceramic particles; 15%-30% skeleton component, wherein the skeleton component is the dry mix; In this process, the thermally conductive component, the skeleton component, and water are mixed and pressed into a cylinder with through pores to allow the sealing slurry to penetrate.

8. A method for efficient sealing of a U-shaped well, used to form a high-efficiency sealing structure for a U-shaped well as described in any one of claims 1-7, characterized in that, Includes the following steps: S1: After drilling and cleaning the well, the aforementioned physical thermal conductivity enhancement material is pre-installed at the bottom of the well; S2: Lower the U-shaped heat exchange tube into the well; S3: Through a grouting pipe extending to the bottom of the well, the uniform sealing slurry is pumped into the annulus inside the well, and the pump pressure is kept stable and below the critical rupture pressure of all types of pressure-responsive expanding particles during the pumping process; S4: The slurry continuously replaces the water in the well from the bottom up until the slurry overflows from the wellhead, and the density of the returned slurry is basically the same as that of the pumped slurry. S5: Add a pH adjuster into the annular gap of the slurry at the wellhead to mix it with the surface slurry and form the wellhead sealing layer; S6: Static curing allows the slurry to solidify throughout the entire well section; during curing, as well pressure recovers and formation stress occurs, the pressure-response expansion particles at different depths expand according to their P... c The values ​​are activated sequentially, ultimately forming an integrated sealing structure with gradient functionality and pressure self-adaptation capability along the well depth direction.

9. The efficient sealing method for U-shaped wells according to claim 8, characterized in that, In S5, after the slurry overflows from the wellhead, a pH adjuster is immediately added into the wellhead annulus, and a special tool is used to mix it to a limited depth, so that the slurry in this section will quickly solidify.

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