Soluble graded cementing device and application thereof

Abstract

The invention provides a soluble graded cementing device and application thereof, and belongs to the field of petroleum and natural gas exploration and development. The soluble graded cementing device comprises a body, a sliding sleeve, an opening plug and a closing plug. The body is of a cylindrical structure with two open ends; the sliding sleeve is arranged in an inner cavity of the body; a closing plug seat is arranged at the upper end of the inner cavity of the sliding sleeve, and an opening plug seat is arranged at the lower end of the inner cavity of the sliding sleeve; the closing plug seat can be matched with the closing plug; the opening plug seat can be matched with the opening plug; the closing plug seat, the opening plug seat, the opening plug and the closing plug are all made of dissoluble materials, on one hand, the well cementation problem of deep wells and ultra-deep wells is solved, on the other hand, the drilling time after well cementation is effectively shortened, and the operation efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the field of oil and gas exploration and development, and in particular relates to a soluble graded cementing device and application thereof. Background Art

[0002] During cementing construction of oil and gas wells, cementing cement needs to be injected into the wellbore, and then a cement plug is lowered into the well to squeeze the cementing cement in the wellbore into the space between the open hole wall and the oil pipe. However, when the depth of the wellbore is deep, it will be extremely difficult to lower the cement plug. Moreover, when the pressure of the cement plug is too high, there will be a risk of ground leakage; therefore, graded cementing operations are required, and when the graded cementing device completes the cementing operation, its internal accessories need to be drilled out to achieve wellbore penetration. At present, due to the anti-rotation performance of the internal accessories and the aluminum alloy material itself, the drilling and removal operation time is relatively long. The drilling and removal operation will not only extend the completion cycle, but also may cause drilling deviation, leakage of the graded cementing device, etc., which will greatly affect the subsequent oil production operations.

[0003] In view of the above problems, it is particularly important to design a soluble graded cementing device and its process in accordance with the objective demand of efficient, economical and harmless development. Summary of the invention

[0004] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a soluble graded cementing device and its application, which can solve the cementing problems of deep wells and ultra-deep wells on the one hand, and effectively reduce the drilling time after cementing on the other hand, and improve the operation efficiency.

[0005] The present invention is achieved through the following technical solutions:

[0006] A first aspect of the present invention provides a soluble graded cementing device, the soluble graded cementing device comprising a body, a sliding sleeve, an opening plug and a closing plug;

[0007] The body is a cylindrical structure with two ends open; the sliding sleeve is arranged in the inner cavity of the body;

[0008] A closing plug seat is provided at the upper end of the inner cavity of the sliding sleeve, and an opening plug seat is provided at the lower end of the inner cavity of the sliding sleeve; the closing plug seat can cooperate with the closing plug; the opening plug seat can cooperate with the opening plug;

[0009] The closing plug seat, the opening plug seat, the opening plug and the closing plug are all made of soluble materials.

[0010] A further improvement of the present invention is:

[0011] A pressure transmission hole and a body circulation hole are sequentially arranged in the middle of the body from top to bottom;

[0012] The pressure transmission hole and the main body circulation hole both connect the inner cavity of the main body with the outside of the main body.

[0013] Preferably, the plurality of pressure transmission holes are evenly distributed on the circumference;

[0014] A plurality of body circulation holes are evenly distributed on the circumference.

[0015] A further improvement of the present invention is:

[0016] The sliding sleeve is a cylindrical structure with openings at both ends;

[0017] The sliding sleeve is provided with a block hole, a pin hole and a sliding sleeve circulation hole in sequence from top to bottom;

[0018] The block hole, the pin hole and the sleeve circulation hole all connect the inner cavity of the sleeve with the outside of the sleeve;

[0019] An annular step is arranged on the upper inner wall of the sliding sleeve.

[0020] Preferably, the plurality of block holes are evenly distributed on the circumference;

[0021] A plurality of pin holes are evenly distributed on the circumference;

[0022] A plurality of sleeve circulation holes are evenly distributed on the circumference.

[0023] Preferably, a thread is provided on the inner wall of the lower end of the sliding sleeve.

[0024] A further improvement of the present invention is:

[0025] An annulus is provided on the outer wall of the sleeve between the pin hole and the sleeve circulation hole;

[0026] The annulus is communicated with the pressure transmission hole.

[0027] A further improvement of the present invention is:

[0028] The closing plug seat is a cylindrical structure with two ends open, an inclined surface matching the closing plug is arranged on the inner wall of the upper end, and an annular step is arranged on the outer wall of the upper end;

[0029] A pin groove is provided below the annular step.

[0030] Preferably, the plurality of pin grooves are evenly distributed on the circumference;

[0031] The pin grooves correspond to the pin holes on the sliding sleeve one by one.

[0032] Further, a stopper groove is provided on the outer surface of the closing plug seat;

[0033] The stopper groove is located above the pin groove.

[0034] Preferably, the plurality of block grooves are evenly distributed on the circumference;

[0035] The stopper passes through the stopper hole on the sliding sleeve and is inserted into the stopper groove;

[0036] An inclined surface is arranged at the upper end of each stopper groove.

[0037] Preferably, on the closing plug seat, no coating is provided on the outer cylindrical surface from the annular step to the lower end, and coating is provided on other positions of the closing plug seat.

[0038] A further improvement of the present invention is:

[0039] The opening plug seat is a cylindrical structure with two ends open, an inclined surface matching the opening plug is arranged on the inner wall of the upper end, and a thread is arranged on the outer wall;

[0040] Coatings are provided on both the inner and outer surfaces of the opening plug seat.

[0041] A further improvement of the present invention is:

[0042] The opening plug is a conical structure with one end larger than the other end, and an annular step is provided on the outer wall of the large end of the opening plug;

[0043] An impact mechanism is provided at the annular step;

[0044] The striking mechanism includes a mounting ring and a plurality of strikers;

[0045] The mounting ring is fixed to the annular step of the opening plug;

[0046] Each of the strikers is a sheet-like structure, the upper end of which is connected to the lower edge of the mounting ring, and the other end is suspended and provided with a blade.

[0047] Preferably, the plurality of firing pins are evenly distributed on the circumference.

[0048] Preferably, the opening plug is a solid structure with a coating provided on its surface.

[0049] Preferably, the closing plug seat, the opening plug seat and the opening plug are all made of magnesium-aluminum alloy;

[0050] The closing plug is made of polyurethane rubber material.

[0051] Preferably, the coatings are all aluminum oxide coatings.

[0052] A second aspect of the present invention provides a method for cementing a well using the above-mentioned soluble graded cementer, the method comprising:

[0053] The soluble graded cementing device is lowered to the designated position, and then cement slurry is injected to perform the first-level cementing operation;

[0054] After the first-level cementing operation is completed, the opening plug is put into operation, and cement slurry is continuously injected. The opening plug moves downward until it contacts the opening plug seat. The sliding sleeve moves downward, and the sliding sleeve circulation hole on the sliding sleeve is aligned with the body circulation hole on the body, and the second-level cementing operation is carried out. At the same time, the opening plug and the opening plug seat begin to dissolve.

[0055] After the secondary cementing operation is completed, the closing plug is put in and mud is injected at the same time. The closing plug moves down until it contacts the closing plug seat, the sleeve moves down, and the sleeve circulation hole on the sleeve is staggered with the body circulation hole on the body; the pin is sheared off, the closing plug seat moves down, and the block comes out of the block groove at the same time, and the closing plug and the closing plug seat begin to dissolve;

[0056] After the closing plug, the closing plug seat, the opening plug and the opening plug seat are all dissolved, the cementing operation is completed.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] The present invention solves the cementing problem of deep wells and ultra-deep wells on the one hand, and effectively reduces the drilling time after cementing on the other hand, thereby improving the operation efficiency.

[0059] In the present invention, the opening plug seat and the opening plug for realizing the hole opening action start to dissolve after completing the hole opening action, and the closing plug seat and the closing plug for realizing the hole closing action start to dissolve after completing the hole closing action, which does not affect the quality of the first and second stage cementing. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 The overall structural diagram of the soluble graded cementing device of the present invention;

[0061] Figure 2 A structural diagram of an opening plug in a soluble graded cementing device of the present invention;

[0062] Figure 3 A structural diagram of a closing plug seat in a soluble graded cementing device of the present invention;

[0063] Figure 4 Structural diagram of the closing plug of the soluble graded cementing device of the present invention. DETAILED DESCRIPTION

[0064] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0065] The present invention provides a soluble graded cementing device, which solves the cementing problem of deep wells and ultra-deep wells on the one hand, and on the other hand, the internal accessories of the graded water injector are designed as soluble structures, which effectively reduces the drilling time after cementing and improves the operation efficiency.

[0066] like Figures 1 to 4As shown, the soluble graded cementing device includes a body 1, a sleeve 2, an opening plug 11 and a closing plug 14; the body 1 is a cylindrical structure with openings at both ends, and the sleeve 2 is arranged in the inner cavity of the body 1; a closing plug seat 3 is arranged at the upper end of the inner cavity of the sleeve 2, and an opening plug seat 4 is arranged at the lower end of the inner cavity of the sleeve 2, the closing plug seat 3 can cooperate with the closing plug 14, and the opening plug seat 4 can cooperate with the opening plug 11.

[0067] The closing plug seat 3, the opening plug seat 4, the opening plug 11 and the closing plug 14 are all made of soluble materials, and the aluminum oxide coating prevents the soluble material from dissolving during the primary cementing process on the one hand, and does not affect the secondary cementing quality on the other hand.

[0068] The embodiments of the soluble graded cementing device are as follows:

[0069] Embodiment 1:

[0070] A pressure transmission hole 7 and a body circulation hole 8 are sequentially arranged in the middle of the body 1 from top to bottom, and the pressure transmission hole 7 and the body circulation hole 8 both connect the inner cavity of the body 1 with the outside of the body 1. Preferably, the plurality of pressure transmission holes 7 are evenly distributed on the circumference, and the plurality of body circulation holes 8 are evenly distributed on the circumference.

[0071] Furthermore, a thread is provided on the upper inner wall of the body 1 for connecting with the upper joint 10. After the body 1 and the upper joint 10 are connected by threads, they may become loose later. Therefore, a screw hole is provided on the upper part of the body 1. A screw is screwed into the screw hole. The screw can be squeezed on the thread where the upper joint 10 and the body 1 are connected, which can further prevent the body 1 and the upper joint 10 from becoming loose. A thread is provided on the lower outer wall of the body 1 for connecting with the lower joint.

[0072] Embodiment 2:

[0073] The sliding sleeve 2 is a cylindrical structure with two ends open, and a block hole, a pin hole 6 and a sliding sleeve circulation hole 9 are sequentially arranged on the sliding sleeve 2 from top to bottom. The block hole, the pin hole 6 and the sliding sleeve circulation hole 9 all connect the inner cavity of the sliding sleeve 2 with the outside of the sliding sleeve 2. An annular step is arranged on the upper inner wall of the sliding sleeve 2.

[0074] Preferably, a plurality of block holes are evenly distributed on the circumference, a plurality of pin holes 6 are evenly distributed on the circumference, and a plurality of sleeve circulation holes 9 are evenly distributed on the circumference. A thread is provided on the inner wall of the lower end of the sleeve 2 for connecting with the opening plug seat 4.

[0075] After the sleeve 2 is installed in the body 1, the sleeve circulation hole 9 is located between the pressure transmission hole 7 and the body circulation hole 8. Therefore, in the initial state, the sleeve circulation hole 9 is not connected with the body circulation hole 8, that is, the body circulation hole 8 is in a closed state.

[0076] Furthermore, an annulus is provided on the outer wall of the sleeve 2 between the pin hole 6 and the sleeve circulation hole 9, and the annulus is connected to the pressure transmission hole 7 on the body. The downhole pressure is high, and the pressure inside and outside the pipe can be balanced through the pressure transmission hole 7 and the annulus, thereby ensuring that the body 1 does not deform. Because if the body 1 is deformed, the sleeve 2 will be stuck and it will be impossible to open the hole.

[0077] During installation, the sleeve 2 is directly pressed into the inner cavity of the body 1, and the two are matched with each other. In order to seal, a plurality of annular grooves are provided on the outer wall of the sleeve 2, and a sealing ring is placed in each annular groove, and the sealing between the body 1 and the sleeve 2 is achieved by the sealing ring. Preferably, sealing rings are provided on the outer wall of the sleeve 2 above and below the annulus, above and below the sleeve circulation hole 9, and above and below the body circulation hole 8.

[0078] Embodiment 3

[0079] like Figure 3 As shown, the closing plug seat 3 is a cylindrical structure with two ends open, and an inclined surface matching the closing plug 14 is provided on the inner wall of the upper end thereof, and an annular step 303 is provided on the outer wall of the upper end thereof. A pin groove 301 is provided below the annular step 303, and preferably, a plurality of pin grooves 301 are evenly distributed on the circumference, and the pin grooves 301 correspond to the pin holes 6 on the sliding sleeve 2 one by one. The pin grooves 301 do not penetrate the closing plug seat 3.

[0080] During installation, the closing plug seat 3 is directly pressed into the inner cavity of the sliding sleeve 2, and the pin groove 301 is aligned with the pin hole 6 one by one. The pin passes through the pin hole 6 on the sliding sleeve 2 and is inserted into the pin groove 301. In this way, the connection between the closing plug seat 3 and the sliding sleeve 2 is achieved through the pin.

[0081] Furthermore, a block groove 302 is provided on the outer surface of the closing plug seat 3, and the block groove 302 is located above the pin groove 301, the block groove is slightly larger than the block hole, and the block groove 302 does not penetrate the closing plug seat 3. Preferably, a plurality of block grooves 302 are evenly distributed on the circumference. The block 5 is inserted into the block groove 302 after passing through the block hole on the sleeve 2, and the limit between the sleeve 2 and the closing plug seat 3 is achieved by the block 5. During the first-level cementing process, the block 5 limits the closing plug seat 3 to prevent the pin from being cut off in advance. An inclined surface is provided at the upper end of each of the block grooves 302, and when the closing plug seat 3 moves downward, the block 5 can leave the block groove 302 along the inclined surface. In order to increase the bearing capacity, the contact area between the block and the block groove 302 needs to be increased. Therefore, preferably, the block hole and the block groove 302 are designed as long holes and long grooves. Correspondingly, the block is a long arc block that can be inserted into the block hole and the block groove 302.

[0082] Furthermore, an annular groove 304 is provided at the lower portion of the closing plug seat 3 for accommodating a sealing ring.

[0083] Preferably, the contact position between the shut-off plug seat 3 and the sleeve 2 is not coated, that is, the outer cylindrical surface from the annular step 303 to the lower end is not provided with an alumina coating, and the other positions of the shut-off plug seat 3 are provided with an alumina coating. The shut-off plug seat 3 is not coated with an alumina coating only on a part of the outer surface, so that the uncoated part does not contact the external cement slurry when the shut-off plug seat 3 does not move during the primary cementing process, and the part in contact with the cement slurry is provided with a coating, so that the shut-off plug seat 3 will not dissolve. After the shut-off plug 14 is put in, the shut-off plug seat 3 moves downward, so that the part of the shut-off plug seat 3 that is not coated is exposed, and after contacting the cement slurry, the entire shut-off plug seat 3 begins to dissolve.

[0084] When the closing plug 14 reaches the closing plug seat 3, the closing plug 14 closes the inner cavity of the closing plug seat 3 through the inclined surface at the upper end of the closing plug seat 3. Under the push of the liquid pressure, the closing plug 14 pushes the closing plug seat 3 to move (such as Figure 1 As shown, the closing plug 14 moves downward), the closing plug seat 3 moves downward, the stopper 5 is pushed out of the stopper groove 302, and the closing plug seat 3 moves downward for a short distance and is blocked by the annular step on the inner wall of the sliding sleeve 2. At this time, the stopper 5 is aligned with the annular step at the upper end of the closing plug seat 3. At this time, the cement slurry will enter the gap between the outer wall of the closing plug seat 3 and the inner wall of the sliding sleeve 2. The unprocessed coating part on the closing plug seat 3 contacts the cement slurry, that is, the soluble material contacts the cement slurry, and the closing plug seat 3 begins to dissolve.

[0085] Embodiment 4

[0086] like Figure 1 As shown, the opening plug seat 4 is a cylindrical structure with two ends open, and an inclined surface matching the opening plug 11 is arranged on the inner wall of the upper end thereof, and a thread is arranged on the outer wall thereof for connecting with the thread of the lower end of the sliding sleeve 2, and the opening plug seat 4 is connected to the inner cavity of the lower end of the sliding sleeve 2 through the threaded connection. An aluminum oxide coating is arranged on both the inner and outer surfaces of the opening plug seat 4, that is, the aluminum oxide coating covers the entire opening plug seat 4.

[0087] Embodiment five:

[0088] like Figure 4 As shown, the closing plug 14 is a multi-layer tower structure. The closing plug 14 can be inserted into the closing plug seat 3, and the central through hole of the closing plug seat 3 is blocked by the closing plug 14 cooperating with the inclined surface of the upper end of the closing plug seat 3. No coating is provided on the surface of the closing plug 14.

[0089] Embodiment six:

[0090] like Figure 2 As shown, the opening plug 11 is a conical structure with one end larger than the other end. An annular step is provided on the outer wall of the large end of the opening plug 11, and an impact mechanism is provided at the annular step. The opening plug 11 is made of soluble material. In order to ensure the strength of the impact mechanism, the impact mechanism is made of insoluble material.

[0091] Since the requirement of rapid lowering must be met during the lowering process, the heavier the opening plug 11 is, the faster it can be lowered. Therefore, preferably, the opening plug 11 is a solid structure with a coating provided on its surface.

[0092] The striking mechanism includes a mounting ring 12 and a plurality of strikers 13 fixedly connected to the mounting ring 12. The mounting ring 12 can be tightly clamped at the annular step of the open plug 11. Each striker 13 is a sheet-like structure, the upper end of which is connected to the lower edge of the mounting ring 12, and the other end is suspended and provided with a blade. Preferably, the plurality of strikers 13 are evenly distributed on the circumference.

[0093] The soluble opening plug 11 and the insoluble impact mechanism ensure effective opening and improve the efficiency of dissolution. After the opening plug 11 dissolves, only the impact mechanism remains. Since the impact mechanism is a ring structure, it hardly affects the diameter of the body 1.

[0094] During the cyclic cementing process, when the opening plug 11 is pressed against the inclined surface of the opening plug seat 4, the striker 13 on the opening plug 11 can pierce the aluminum oxide coating on the surface of the opening plug seat 4, and the cement slurry immediately contacts the portion under the coating, and the opening plug seat 4 begins to dissolve. At the same time, when the striker 13 of the opening plug 11 collides with the opening plug seat 4, the striker 13 will also destroy the aluminum oxide coating of the opening plug 11, and the opening plug 11 also begins to dissolve.

[0095] The closing plug seat 3, the opening plug seat 4, the opening plug 11, and the closing plug 14 are all made of soluble materials. Specifically, the closing plug seat 3, the opening plug seat 4, and the opening plug 11 are all made of magnesium-aluminum alloy. Since the closing plug 14 needs to have a certain elasticity, the closing plug 14 is made of polyurethane rubber material. Magnesium-aluminum alloy and polyurethane rubber materials are both soluble in water, and there is water in the cement slurry, so their dissolution can be achieved by injecting the cement slurry into the main body 1. In addition, in order to accelerate their dissolution, salt can be added to the cement slurry. In actual production, suitable magnesium-aluminum alloy and polyurethane rubber materials can be selected according to the well temperature and brine concentration, so that the demand for timely and efficient dissolution is achieved without affecting the quality of cementing.

[0096] The present invention also provides a method for cementing a well using the above-mentioned soluble graded cementing device, and an embodiment of the method is as follows:

[0097] Embodiment seven:

[0098] The soluble graded cementing device is lowered to the designated position, and then cement slurry is injected to perform the primary cementing operation. During the primary cementing operation, the cement slurry passes through the upper joint 10, the body 1, and the inner cavity of the lower joint and enters the annulus between the body 1 and the well wall. When the amount of cement slurry injected reaches the designed primary cementing injection amount, the primary cementing operation is completed.

[0099] After the primary cementing operation is completed, the opening plug 11 is put in, and cement slurry is continuously injected. The opening plug 11 moves downward until it contacts the opening plug seat 4. Since the opening plug 11 seals the opening plug seat 4, the cement slurry that continues to be injected will increase the pressure. The opening plug 11 pushes the sleeve 2 downward under the pressure. After the sleeve 2 moves downward, the sleeve circulation hole 9 on the sleeve 2 is aligned with the body circulation hole 8 on the body 1. At this time, the secondary cementing circulation hole of the soluble graded cementing device is opened. The cement slurry flows through the sleeve circulation hole 9 and the body circulation hole 8 and flows out into the annulus between the body 1 and the well wall. The pressure decreases, so the sleeve 2 does not continue to move downward, and cement slurry is continuously injected for the secondary cementing operation; at the same time, since the striker 13 pierces the coating of the opening plug 11 and the opening plug seat 4, the opening plug 11 and the opening plug seat 4 begin to dissolve. When the amount of cement slurry injected reaches the designed secondary cementing injection amount, the secondary cementing operation is completed. At this time, the closing plug seat 3 does not dissolve, so the safety of the secondary cementing is fully guaranteed. Both the primary cementing operation and the secondary cementing operation are existing mature technologies and will not be described in detail here.

[0100] After the secondary cementing operation is completed, the closing plug 14 is put in, and mud is injected at the same time. The closing plug 14 moves down to contact the inclined surface of the closing plug seat 3, and continues to squeeze the cement slurry below into the annulus between the body 1 and the well wall. Continuing to inject mud will increase the pressure. The closing plug 14 pushes the sliding sleeve 2 downward under the action of pressure. The sliding sleeve circulation hole 9 on the sliding sleeve 2 is staggered with the body circulation hole 8 on the body 1, and the cement slurry no longer flows out from the circulation hole. Continue to inject mud, the pressure continues to increase, the pin used to connect the sliding sleeve 2 and the closing plug seat 3 is sheared off, the closing plug seat 3 moves down, and the stopper 5 comes out of the stopper groove and is located at the annular step on the closing plug seat 3. At this time, the uncoated part of the closing plug seat 3 contacts the cement slurry, and the closing plug seat 3 begins to dissolve, and the closing plug 14 also begins to dissolve. After the closing plug 14, the closing plug seat 3, the opening plug 11, and the opening plug seat 4 are all dissolved, the wellbore is connected, and the cementing operation is completed. Then, the subsequent operation can be carried out after the mud is returned. The process of cementing wells by using the above-mentioned soluble graded cementing device is mechanized, and the graded operation is completed by plugging.

[0101] On the one hand, the present invention can effectively solve the problem of low cementing quality in deep wells and ultra-deep wells, and on the other hand, it can avoid the operation of drilling out internal accessories after the cementing operation is completed, thereby further improving the cementing quality and shortening the operation cycle.

[0102] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0103] In the description of the present invention, unless otherwise specified, the terms "upper", "lower", "left", "right", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the present invention.

[0104] The above technical solution is only one implementation mode of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the principles disclosed in the present invention, and it is not limited to the technical solution described in the above specific embodiments of the present invention. Therefore, the above description is only preferred and does not have a restrictive meaning.

Claims

1. A soluble graded cementing device, characterized in that: The soluble graded cementing device comprises a body, a sliding sleeve, an opening plug and a closing plug; The body is a cylindrical structure with two ends open; the sliding sleeve is arranged in the inner cavity of the body; A closing plug seat is arranged at the upper end of the inner cavity of the sliding sleeve, and an opening plug seat is arranged at the lower end of the inner cavity of the sliding sleeve; The closing plug seat can cooperate with the closing plug; the opening plug seat can cooperate with the opening plug; The closing plug seat, the opening plug seat, the opening plug and the closing plug are all made of soluble materials.

2. The soluble graded cementing device according to claim 1, characterized in that: A pressure transmission hole and a body circulation hole are sequentially arranged in the middle of the body from top to bottom; The pressure transmission hole and the main body circulation hole both connect the inner cavity of the main body with the outside of the main body.

3. The soluble graded cementing device according to claim 2, characterized in that: Multiple pressure transmission holes are evenly distributed on the circumference; A plurality of body circulation holes are evenly distributed on the circumference.

4. The soluble graded cementing device according to claim 2, characterized in that: The sliding sleeve is a cylindrical structure with openings at both ends; The sliding sleeve is provided with a block hole, a pin hole and a sliding sleeve circulation hole in sequence from top to bottom; The block hole, the pin hole and the sleeve circulation hole all connect the inner cavity of the sleeve with the outside of the sleeve; An annular step is arranged on the upper inner wall of the sliding sleeve.

5. The soluble graded cementing device according to claim 4, characterized in that: A plurality of stopper holes are evenly distributed on the circumference; A plurality of pin holes are evenly distributed on the circumference; A plurality of sleeve circulation holes are evenly distributed on the circumference.

6. The soluble graded cementing device according to claim 4, characterized in that: A thread is arranged on the inner wall of the lower end of the sliding sleeve.

7. The soluble graded cementing device according to claim 4, characterized in that: An annulus is provided on the outer wall of the sleeve between the pin hole and the sleeve circulation hole; The annulus is communicated with the pressure transmission hole.

8. The soluble graded cementing device according to claim 4, characterized in that: The closing plug seat is a cylindrical structure with two ends open, an inclined surface matching the closing plug is arranged on the inner wall of the upper end, and an annular step is arranged on the outer wall of the upper end; A pin groove is provided below the annular step.

9. The soluble graded cementing device according to claim 8, characterized in that: A plurality of pin grooves are evenly distributed on the circumference; The pin grooves correspond to the pin holes on the sliding sleeve one by one.

10. The soluble graded cementing device according to claim 8, characterized in that: A stopper groove is provided on the outer surface of the closing plug seat; The stopper groove is located above the pin groove.

11. The soluble graded cementing device according to claim 10, characterized in that: A plurality of stopper grooves are evenly distributed on the circumference; The stopper passes through the stopper hole on the sliding sleeve and is inserted into the stopper groove; An inclined surface is arranged at the upper end of each stopper groove.

12. The soluble graded cementing device according to claim 8, characterized in that: On the closing plug seat, no coating is provided on the outer cylindrical surface from the annular step to the lower end, and coating is provided on other positions of the closing plug seat.

13. The soluble graded cementing device according to claim 1, characterized in that: The opening plug seat is a cylindrical structure with two ends open, an inclined surface matching the opening plug is arranged on the inner wall of the upper end, and a thread is arranged on the outer wall; Coatings are provided on both the inner and outer surfaces of the opening plug seat.

14. The soluble graded cementing device according to claim 1, characterized in that: The opening plug is a conical structure with one end larger than the other end, and an annular step is provided on the outer wall of the large end of the opening plug; An impact mechanism is provided at the annular step; The striking mechanism includes a mounting ring and a plurality of strikers; The mounting ring is fixed to the annular step of the opening plug; Each of the strikers is a sheet-like structure, the upper end of which is connected to the lower edge of the mounting ring, and the other end is suspended and provided with a blade.

15. The soluble graded cementing device according to claim 14, characterized in that: The plurality of strikers are evenly distributed on the circumference.

16. The soluble graded cementing device according to claim 14, characterized in that: The opening plug is a solid structure with a coating disposed on its surface.

17. The soluble graded cementing device according to claim 1, characterized in that: The closing plug seat, opening plug seat and opening plug are all made of magnesium-aluminum alloy; The closing plug is made of polyurethane rubber material.

18. The soluble graded cementer according to claim 12, 13 or 16, characterized in that: The coatings are all aluminum oxide coatings.

19. A method for cementing a well, characterized in that: The method comprises: The soluble graded cementing device is lowered to the designated location, and then cement slurry is injected to perform the first-level cementing operation; After the first-level cementing operation is completed, the opening plug is put into operation, and cement slurry is continuously injected. The opening plug moves downward until it contacts the opening plug seat. The sliding sleeve moves downward, and the sliding sleeve circulation hole on the sliding sleeve is aligned with the body circulation hole on the body, and the second-level cementing operation is carried out. At the same time, the opening plug and the opening plug seat begin to dissolve. After the secondary cementing operation is completed, the closing plug is put in and mud is injected at the same time. The closing plug moves down until it contacts the closing plug seat, the sleeve moves down, and the sleeve circulation hole on the sleeve is staggered with the body circulation hole on the body; the pin is sheared off, the closing plug seat moves down, and the block comes out of the block groove at the same time, and the closing plug and the closing plug seat begin to dissolve; After the closing plug, the closing plug seat, the opening plug and the opening plug seat are all dissolved, the cementing operation is completed.

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