A variable-density heating self-dissolving sand-preventing screen pipe suitable for hydrate mining

Abstract

This invention relates to the field of downhole sand control tools in oil and gas extraction, and provides a variable-density heated self-dissolving sand control screen suitable for hydrate extraction. It includes a pre-filling system and a sand control screen body; the sidewall of the sand control screen body has an annular hollow interlayer; the pre-filling system is filled within the annular hollow interlayer; the pre-filling system includes a mixture of sand-blocking medium and a soluble medium; the ratio x of the total volume of the pre-filling system to the volume of the soluble medium satisfies: 0 < x < 6.25. The sand-blocking medium acts as a sand-blocking agent. During natural gas extraction, the soluble medium gradually dissolves in the reservoir fluid until it is completely dissolved. Therefore, during the dissolution process, it gradually changes the filling density of the sand-blocking medium, reduces the local pressure of the sand-blocking medium, thereby inhibiting the growth of secondary hydrate crystals, enhancing the permeability of the sand control screen, and solving the problem of easy clogging of existing sand control screens during natural gas hydrate reservoir extraction.

Description

Technical Field

[0001] This invention relates to the field of downhole sand control tools in oil and gas extraction, and in particular to a variable density heating type self-dissolving sand control screen suitable for hydrate extraction. Background Technology

[0002] Sand production is a common problem in conventional loose sandstone oil and gas reservoirs, but natural gas hydrate reservoirs (especially marine natural gas hydrate reservoirs) are characterized by weak consolidation and high clay content. The median particle size of fine sand in typical marine natural gas hydrate mud reaches 8 to 15 micrometers, and the clay content can be as high as 25% to 36%, which puts forward higher requirements for sand control technology.

[0003] Looking at the current global natural gas trial production situation, each trial has been constrained to varying degrees by sand production issues. In the field, mechanical sand control is generally the mainstream technology, including independent mechanical screen sand control, expandable screen sand control, screen-based gravel packing sand control, and fracturing packing sand control. Independent mechanical screen sand control technology is simple and easy to manufacture, but its sand-blocking accuracy is limited. Fine sand or clay produced from the formation can fill the annulus of the screen sleeve and the perforated wellbore, clogging the mechanical screen's permeable medium, reducing production, and resulting in low sand control accuracy. Furthermore, in terms of manufacturing technology, it is impossible to achieve micron-level screen sand control, making it only suitable for reservoirs with low clay content and coarse sand particles. Screen-based gravel packing sand control utilizes high-strength, highly permeable gravel layers, providing good sand control, long-lasting effectiveness, and a wide range of applications, but it is more expensive and is primarily suitable for controlling medium and fine silt sand with severe sand production. For wells such as long horizontal wells or highly deviated wells where gravel packing is difficult or costly, pre-filled screens are often used for sand control. However, pre-filled screens are prone to clogging under conditions of high clay content and fine particle size, which can reduce the production of natural gas hydrates.

[0004] Furthermore, during the extraction of natural gas hydrates, reservoir mud and sand can penetrate the sand-control screen, causing blockage of the capillary channels within the porous medium. This leads to a localized increase in pressure within the sand-control medium, which can easily cause secondary hydrate formation. Consequently, this affects the extraction efficiency of natural gas hydrates and may even cause gas accumulation, resulting in rock deformation or collapse and the leakage of large amounts of natural gas into the ocean and atmosphere. Summary of the Invention

[0005] This invention provides a variable density heating type self-dissolving sand-prevention screen pipe suitable for hydrate mining, which solves the problem that sand-prevention screen pipes in the prior art are prone to clogging during the mining of natural gas hydrate reservoirs.

[0006] This invention provides a variable density heated self-dissolving sand-prevention screen pipe suitable for hydrate mining, comprising a pre-filling system and a sand-prevention screen pipe body; the sidewall of the sand-prevention screen pipe body has an annular hollow interlayer; the pre-filling system fills the annular hollow interlayer;

[0007] The pre-filling system includes a sand-blocking medium and a soluble medium mixed together; the ratio x of the total volume of the pre-filling system to the volume of the soluble medium satisfies: 0 < x < 6.25.

[0008] According to the present invention, a variable-density heated self-dissolving sand-preventing screen suitable for hydrate mining is provided, wherein the soluble medium comprises soluble aluminum alloy particles prepared from soluble aluminum alloy materials and / or soluble magnesium alloy particles prepared from soluble magnesium alloy materials; the dissolution rate of the soluble aluminum alloy particles is 0.5–70 mg / cm³. 2 The dissolution rate of the soluble magnesium alloy particles is 30–90 mg / cm³. 2 ·h.

[0009] According to the present invention, a variable density heating type self-dissolving sand-preventing screen pipe suitable for hydrate mining is provided, wherein the soluble aluminum alloy particles are Al-Li soluble aluminum alloy particles, Al-Mg soluble aluminum alloy particles, Al-Zn soluble aluminum alloy particles and / or Al-Cu soluble aluminum alloy particles; the strength of the soluble aluminum alloy particles exceeds 500 MPa.

[0010] According to the present invention, a variable density heating type self-dissolving sand-preventing screen pipe suitable for hydrate mining is provided, wherein the soluble magnesium alloy particles are Mg-Li soluble magnesium alloy particles, Mg-Zn soluble magnesium alloy particles and / or Mg-Al soluble magnesium alloy particles, and the strength of the soluble magnesium alloy particles exceeds 400 MPa.

[0011] According to the present invention, a variable density heated self-dissolving sand-blocking screen pipe suitable for hydrate mining is provided, wherein the sand-blocking medium is one or a combination of several of the following: lightweight ceramsite, quartz sand, gravel, and gravel-shell mixture.

[0012] According to the present invention, a variable density heating type self-dissolving sand-preventing screen pipe suitable for hydrate mining is provided, wherein the soluble medium further includes soluble metal exothermic particles, the soluble metal exothermic particles include an outer shell and contents disposed within the outer shell; the outer shell is a soluble metal coating, and the contents are chemicals capable of reacting with water to release heat.

[0013] According to the present invention, a variable density heating type self-dissolving sand-preventing screen pipe suitable for hydrate mining is provided, wherein the soluble metal coating is a soluble aluminum alloy coating and / or a soluble magnesium alloy coating.

[0014] According to the present invention, a variable density heated self-dissolving sand-preventing screen pipe suitable for hydrate mining is provided, wherein the contents are calcium oxide and / or sodium oxide.

[0015] According to the present invention, a variable density heating type self-dissolving sand-prevention screen pipe suitable for hydrate mining is provided, wherein the sand-prevention screen pipe body includes a base pipe, an inner screen pipe and an outer screen pipe;

[0016] The inner screen tube is arranged around and fits the outer wall of the base tube, and the outer screen tube is arranged around the periphery of the inner screen tube, forming the annular hollow interlayer between them.

[0017] According to the present invention, a variable density heating type self-dissolving sand-preventing screen pipe suitable for hydrate mining is provided. The sand-preventing screen pipe body further includes two end caps. Each end cap is sleeved around the base pipe. The end cap covers the ends of the inner screen pipe and the outer screen pipe to close the ends of the annular hollow interlayer.

[0018] According to the present invention, a variable density heating type self-dissolving sand-preventing screen pipe suitable for hydrate mining is provided, wherein the end cap comprises:

[0019] An end plate is provided with a through hole for the base tube, and the end plate covers the ends of the inner sieve tube and the outer sieve tube to seal the annular hollow interlayer.

[0020] A side panel is connected to the edge of the end plate and is located on the side of the end plate facing the inner screen tube and the outer screen tube. The side panel is attached to the outer side wall of the outer screen tube.

[0021] This invention provides a variable-density heated self-dissolving sand-blocking screen suitable for hydrate extraction. It utilizes a sand-blocking medium to prevent sand accumulation. The soluble medium gradually dissolves in the high-temperature liquid during natural gas extraction until it is completely dissolved. Because the soluble medium and the sand-blocking medium are mixed together, the dissolution process gradually changes the packing density of the sand-blocking medium, reducing its local pressure and thus inhibiting hydrate growth. This enhances the permeability of the sand-blocking screen and solves the problem of clogging that easily occurs in existing sand-blocking screens during natural gas hydrate reservoir extraction. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a cross-sectional structural diagram of a variable density heating type self-dissolving sand-preventing screen pipe suitable for hydrate mining provided by the present invention;

[0024] Figure 2 yes Figure 1 Schematic diagram of the cross-sectional structure at section AA;

[0025] Figure 3 yes Figure 1 Enlarged structural diagram at point B;

[0026] Figure 4 This is a cross-sectional structural schematic diagram of the soluble metal exothermic particles of the present invention;

[0027] Figure 5 yes Figure 1 Enlarged structural diagram at point C;

[0028] Figure 6 This shows the change of pressure differential over time under different filling density conditions; Curve A represents the change of pressure differential over time when the filling density is 94%; Curve B represents the change of pressure differential over time when the filling density is 98%; Curve C represents the change of pressure differential over time when the filling density is 96%; and Curve D represents the change of pressure differential over time when the filling density is 100%.

[0029] Figure 7 These curves represent the changes in sand output over time under different filling density conditions. Curve A represents the changes in sand output over time when the filling density is 94%; Curve B represents the changes in sand output over time when the filling density is 98%; Curve C represents the changes in sand output over time when the filling density is 96%; and Curve D represents the changes in sand output over time when the filling density is 100%.

[0030] Figure label:

[0031] 1: Pre-filling system; 2: Sand control screen body;

[0032] 21: Base tube; 22: Inner sieve tube; 23: Outer sieve tube; 24: End cap;

[0033] 211: Flow hole. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this 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 this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0035] In combination Figure 1The present invention describes a variable density heated self-dissolving sand-prevention screen pipe suitable for hydrate mining. This embodiment provides a variable density heated self-dissolving sand-prevention screen pipe suitable for hydrate mining, including a pre-filling system 1 and a sand-prevention screen pipe body 2; the side wall of the sand-prevention screen pipe body 2 is formed with an annular hollow interlayer; the pre-filling system 1 is filled in the annular hollow interlayer;

[0036] The prefilling system 1 includes sand-blocking medium and soluble medium mixed together; the ratio x of the total volume of the prefilling system to the volume of the soluble medium satisfies: 0 < x < 6.25.

[0037] The sand-blocking medium pre-filling system serves to prevent and block sand. The soluble medium gradually dissolves in the reservoir fluid during natural gas extraction until it is completely dissolved. Because the soluble medium and the sand-blocking medium are mixed together, the dissolution process of the soluble medium gradually changes the filling density of the sand-blocking medium, reducing the local pressure and thus inhibiting hydrate growth. This enhances the permeability of the sand-blocking screen and solves the problem of clogging that easily occurs in existing sand-blocking screens during natural gas hydrate reservoir extraction. Furthermore, the sand-blocking capacity of the pre-filling system must be maintained during the dissolution process of the soluble medium. Therefore, the filling rate of the soluble medium needs to be limited. In this embodiment, the ratio x of the total volume of the pre-filling system to the volume of the soluble medium satisfies: 0 < x < 6.25. This ensures that after the soluble medium is completely dissolved, the filling density of the pre-filling system remains at approximately 96%.

[0038] In a specific embodiment, the soluble medium includes soluble aluminum alloy particles prepared from soluble aluminum alloy materials and / or soluble magnesium alloy particles prepared from soluble magnesium alloy materials; the dissolution rate of the soluble aluminum alloy particles is 0.5–70 mg / cm³. 2 The dissolution rate of soluble magnesium alloy particles is 30–90 mg / cm³. 2 ·h.

[0039] In a specific embodiment, the soluble medium may be selected from soluble aluminum alloy particles or soluble magnesium alloy particles.

[0040] During the experimental phase:

[0041] First, the relationship between the spatial release rate of the soluble medium and the dissolution rate of various soluble metal particles is calculated according to formulas (1) and (2):

[0042] V 现 =V 原 -α 和 ×H (1)

[0043] η = V 现 / V 原 (2)

[0044] Among them, V 现 V is the volume of the pre-filled system after the soluble medium has dissolved. 原 α is the initial volume of the pre-filled system. 和 This is the union of the dissolution rates of various soluble metal particles.

[0045] In this embodiment, α 和 =αAL∪α Mg ;where α AL α represents the dissolution rate of soluble aluminum alloy particles. Mg The dissolution rate of soluble magnesium alloy particles.

[0046] Then, considering the actual conditions of the natural gas hydrate reservoir, the planned extraction time, and the respective dissolution rates of soluble aluminum alloy particles and soluble magnesium alloy particles, the relationship between the space release rate of the pre-filling system and the dissolution rates of various soluble metal particles can be obtained: η=1-(αAL∪α Mg )×H / V 原 .

[0047] Finally, by adjusting the respective ratios of soluble aluminum alloy particles and soluble magnesium alloy particles, the theoretically suitable space release rate and the ratio of soluble aluminum alloy particles and soluble magnesium alloy particles for the current actual natural gas hydrate reservoir were determined.

[0048] Furthermore, when applying the aforementioned pre-filling system to the natural gas extraction process, the ratio of soluble aluminum alloy particles and soluble magnesium alloy particles needs to be adjusted in real time according to the specific circumstances to achieve a better ratio.

[0049] In specific embodiments, the soluble aluminum alloy particles are aluminum-lithium (Al-Li) soluble aluminum alloy particles, aluminum-magnesium (Al-Mg) soluble aluminum alloy particles, aluminum-zinc (Al-Zn) soluble aluminum alloy particles, and / or aluminum-copper (Al-Cu) soluble aluminum alloy particles. These different series of soluble aluminum alloy particles have advantages such as excellent performance and multiple dissolution rates, and the tensile strength of these series of soluble aluminum alloy particles exceeds 500 MPa.

[0050] In specific embodiments, the soluble magnesium alloy particles are magnesium-lithium (Mg-Li) soluble magnesium alloy particles, magnesium-zinc (Mg-Zn) soluble magnesium alloy particles and / or magnesium-aluminum (Mg-Al) soluble magnesium alloy particles. These different series of soluble magnesium alloy particles have advantages such as low density, high specific strength and specific stiffness, good dimensional stability, and tensile strength exceeding 400 MPa.

[0051] In a specific embodiment, the sand-blocking medium is one or a combination of several of the following: lightweight ceramsite, quartz sand, gravel, and a mixture of gravel and nutshells. In this embodiment, because lightweight ceramsite is lightweight, has good flowability, and meets the sand-blocking precision requirement of 140 mesh (106 micrometers), considering the particle size, flowability, strength, and manufacturing precision of the silty clay in the natural gas reservoir, this embodiment preferably uses lightweight ceramsite. Moreover, the size of the lightweight ceramsite in this embodiment is no greater than 40 mesh, which allows fine clay-grade sand to pass through. This indicates that the pre-filling system of this embodiment can be used in natural gas hydrate reservoirs with high clay content and fine particle size.

[0052] The use of soluble aluminum alloys and soluble magnesium alloys is related to the mining time. Generally speaking, the dissolution rate of soluble aluminum alloys is lower than that of soluble magnesium alloys, and their use depends on the production situation.

[0053] In a specific embodiment, such as Figure 4 As shown, the soluble medium also includes soluble exothermic metal particles, which consist of an outer shell and contents within the shell. The outer shell is coated with a soluble metal, and the contents are chemicals that react with water to release heat. During the dissolution process of the soluble metal coating, it also regulates the local pressure of the sand-blocking medium. Furthermore, after the soluble metal coating dissolves, its contents, calcium oxide and / or sodium oxide, react with the formation fluid to generate heat, causing the secondary hydrates in the sand-blocking screen to depressurize and decompose under heat. This eliminates the secondary hydrates formed within the sand-blocking screen during extraction, solves the blockage problem caused by secondary hydrates, and ensures the continuous high-yield extraction of natural gas.

[0054] In a specific embodiment, the soluble metal coating is a soluble aluminum alloy coating and / or a soluble magnesium alloy coating.

[0055] In a specific embodiment, the contents are calcium oxide and / or sodium oxide. In this embodiment, calcium oxide is preferred.

[0056] In a specific embodiment, such as Figure 1 and Figure 2 As shown, the sand control screen body 2 includes a hollow base pipe 21, an inner screen pipe 22 and an outer screen pipe 23; the inner screen pipe 22 is arranged around and attached to the outer side wall of the base pipe 21, and the outer screen pipe 23 is arranged around the periphery of the inner screen pipe 22, forming an annular hollow interlayer between the inner screen pipe 22 and the outer screen pipe 23.

[0057] In this embodiment, the annular hollow interlayer is filled with a pre-filling system, which includes lightweight ceramic particles, soluble aluminum alloy particles, soluble magnesium alloy particles, and soluble exothermic metal particles, such as... Figure 3As shown. The soluble metal exothermic particles comprise a soluble aluminum alloy coating, and calcium oxide and / or sodium oxide encapsulated within the soluble aluminum alloy coating. Alternatively, the soluble metal exothermic particles comprise a soluble magnesium alloy coating, and calcium oxide and / or sodium oxide encapsulated within the soluble magnesium alloy coating.

[0058] In a specific embodiment, the inner screen tube 22 is a slotted screen tube or a wire mesh.

[0059] In a specific embodiment, the mesh size of both the inner sieve tube 22 and the outer sieve tube 23 should be smaller than the size of the lightweight ceramsite.

[0060] In a specific embodiment, an overflow hole 211 is formed on the wall of the base pipe 21.

[0061] In specific embodiments, the flow orifice 211 can be circular, square, polygonal, or other shapes. In this embodiment, the flow orifice 211 is circular, with a diameter of 8–13 mm.

[0062] In a specific embodiment, such as Figure 1 and Figure 5 As shown, the sand-proof screen pipe body 2 also includes two end caps 24. Each end cap 24 is sleeved around the base pipe 21. The end caps 24 cover the ends of the inner screen pipe 22 and the outer screen pipe 23 to close the ends of the annular hollow interlayer.

[0063] In a specific embodiment, such as Figure 5 As shown, the end cap 24 includes an end plate and a side plate; the end plate has a through hole for the base tube 21, and the end plate covers the ends of the inner sieve tube 22 and the outer sieve tube 23 to seal the annular hollow interlayer; the side plate is connected to the edge of the end plate and is located on the side of the end plate facing the inner sieve tube 22 and the outer sieve tube 23, and the side plate is attached to the outer side wall of the outer sieve tube 23. In this embodiment, the height of the side plate is 10-20 mm.

[0064] In a specific embodiment, an O-ring is provided between the end cap 24 and the pre-filling system, the purpose of which is to seal the pre-filling system in the annular hollow interlayer.

[0065] The sand control screen body 2 in any of the above embodiments was used in a sand control simulation experiment. The sand control simulation experiment simulated a natural gas hydrate reservoir with a median particle size (d50) of 8 micrometers, a clay content of 38%, and a non-uniformity coefficient of 6.5. Under this reservoir condition, the filling density of the pre-filling system in the annular hollow interlayer of the sand control screen body 2 was selected as 100%, 98%, 96%, and 94%, respectively. At this time, the pre-filling system only contained sand-blocking media, which was preferably lightweight ceramsite. The above sand control screen was used for sand control simulation, and the pressure difference over time was measured under different filling density conditions, such as... Figure 6As shown in the figure. The variation of sand output over time under different filling density conditions was also measured. Figure 7 As shown.

[0066] from Figure 6 It can be seen that when the filling density is 100%, the pressure increases rapidly and blockage occurs. When the filling density is 98%, 96%, and 94%, the production pressure differential stabilizes and production can remain stable for a period of time. However, after half an hour of stable production at 98% filling density, the pressure rises rapidly and blockage occurs. Figure 7 It can be seen that the sand output when the filling density is 100%, 98%, 96% and 94% is 38.6g, 43.15g, 65.65g and 120.79g respectively. The sand output is large when the filling density is 94%, and the sand control effect is poor.

[0067] Taking into account the changes in sand output and pressure difference over time, it can be seen that a sand control screen with a filling density of 96% can ensure that both the sand output and pressure difference meet the experimental requirements.

[0068] The above experiments show that when using the pre-filling system of the present invention for sand control, it is also necessary to ensure that the filling density of the pre-filling system is around 96%. In order to ensure that the filling density of the pre-filling system still meets the sand control requirements after the soluble medium is completely dissolved, the volume ratio of the soluble medium must be limited.

[0069] By changing the ratio x of the total volume of the prefilling system to the volume of the soluble medium, prefilling systems with different proportions of soluble medium volume were obtained. Sand control simulation experiments were conducted on these prefilling systems. It was found that when the ratio x of the total volume of the prefilling system to the volume of the soluble medium satisfies 0 < x < 6.25, the filling density of the prefilling system can be kept stable at about 96% after the soluble medium is completely dissolved.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A variable-density heating type self-dissolving and anti-sand screen pipe suitable for hydrate mining, characterized in that, It includes a pre-filling system (1) and a sand-proof screen tube body (2); the side wall of the sand-proof screen tube body (2) is formed with an annular hollow interlayer; the pre-filling system (1) is filled in the annular hollow interlayer; The pre-filling system (1) includes a sand-blocking medium and a soluble medium mixed together; the ratio x of the total volume of the pre-filling system to the volume of the soluble medium satisfies: 0 < x < 6.25, and the filling density of the pre-filling system (1) is 96%; The soluble medium includes soluble exothermic metal particles, each soluble exothermic metal particle comprising a shell and contents disposed within the shell; the shell is a soluble metal coating, and the contents are chemicals capable of reacting with water to release heat; the soluble metal coating is a soluble aluminum alloy coating and / or a soluble magnesium alloy coating. The soluble medium also includes soluble aluminum alloy particles prepared from soluble aluminum alloy materials and / or soluble magnesium alloy particles prepared from soluble magnesium alloy materials.

2. A variable-density heating type self-dissolving sand-preventing screen pipe suitable for hydrate mining according to claim 1, characterized in that, The dissolution rate of the soluble aluminum alloy particles is 0.5–70 mg / cm³. 2 The dissolution rate of the soluble magnesium alloy particles is 30–90 mg / cm³. 2 ·h.

3. A variable-density heating type self-dissolving sand-preventing screen pipe suitable for hydrate mining according to claim 2, characterized in that, The soluble aluminum alloy particles are Al-Li soluble aluminum alloy particles, Al-Mg soluble aluminum alloy particles, Al-Zn soluble aluminum alloy particles and / or Al-Cu soluble aluminum alloy particles; the strength of the soluble aluminum alloy particles exceeds 500 MPa.

4. A variable-density heating self-dissolving sand-preventing screen pipe suitable for hydrate mining according to claim 2, characterized in that, The soluble magnesium alloy particles are Mg-Li soluble magnesium alloy particles, Mg-Zn soluble magnesium alloy particles and / or Mg-Al soluble magnesium alloy particles, and the strength of the soluble magnesium alloy particles exceeds 400 MPa.

5. A variable-density heating self-dissolving sand-preventing screen pipe suitable for hydrate mining according to claim 1, characterized in that, The sand-blocking medium is one or a combination of several of the following: lightweight ceramsite, quartz sand, gravel, and gravel-shell mixture.

6. A variable-density heating self-dissolving sand-preventing screen pipe suitable for hydrate mining according to claim 1, characterized in that, The contents are calcium oxide and / or sodium oxide.

7. A variable-density heating type self-dissolving sand-preventing screen pipe suitable for hydrate mining according to any one of claims 1-6, characterized in that, The sand control screen body (2) includes a base pipe (21), an inner screen pipe (22) and an outer screen pipe (23). The inner sieve tube (22) is arranged around and attached to the outer wall of the base tube (21), and the outer sieve tube (23) is arranged around the periphery of the inner sieve tube (22), forming the annular hollow interlayer between the outer sieve tube (22) and the inner sieve tube (22).

8. A variable-density heating self-dissolving sand-preventing screen pipe suitable for hydrate mining according to claim 7, characterized in that, The sand-proof screen tube body (2) also includes two end caps (24), each end cap (24) is sleeved around the base tube (21), and the end caps (24) cover the ends of the inner screen tube (22) and the outer screen tube (23) to close the ends of the annular hollow interlayer.

9. A variable-density heating type self-dissolving sand-preventing screen pipe suitable for hydrate mining according to claim 8, characterized in that, The end cap (24) includes: End plate, the end plate having a through hole for the base tube (21), and the end plate covering the ends of the inner sieve tube (22) and the outer sieve tube (23) to seal the annular hollow interlayer; A side panel is connected to the edge of the end plate and is located on the side of the end plate facing the inner sieve tube (22) and the outer sieve tube (23). The side panel is attached to the outer side wall of the outer sieve tube (23).

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