Well completion casing string and method based on coal bed gas horizontal communication well

Abstract

The invention discloses a well completion casing string based on a coal bed gas horizontal communicating well, which is characterized in that a casing string is tripped into a horizontal well and a vertical well which are communicated in an opposite manner, the casing string can be directly tripped through a vertical well section, and a casing is cut in the vertical well in a milling manner, so that the horizontal well and vertical well communicating well section is protected, and a throat well section is prevented from being blocked. According to the using method of the well completion casing string based on the coal bed gas horizontal communication well, after communication of the horizontal well and the vertical well is completed, eccentricity verification is conducted through a well repairing pipe column, it is determined that the communication point is directly facing communication or eccentrically communicating, if the communication point is eccentrically communicating, directly facing communication can be achieved in a repeated reaming mode, and if the communication point is not eccentrically communicating, directly facing communication is achieved; and the opposite relation between the horizontal well casing string and the communicating vertical well and the specific communicating well depth can be more conveniently defined.

Description

Technical Field

[0001] The invention belongs to the technical field of coalbed methane drilling and completion, and in particular relates to a completion casing string and method based on a coalbed methane horizontally connected well. Background Art

[0002] CBM development in broken, soft, and low-permeability coal seams usually adopts a wellbore structure in which horizontal wells are connected to vertical wells, and casing cementing is used for well completion. Staged fracturing is performed in the horizontal well section to connect a larger reservoir, and gas is produced by draining water and reducing pressure through the vertical well. Cementing of horizontally connected wells often adopts the method of filling the vertical well with sand, and inserting a screen pipe + blind plug at the end of the horizontal well. A 1.5-3m interval is reserved between the horizontal well casing and the vertical well to prevent the horizontal well casing from interfering with the vertical well pump.

[0003] This method has shortcomings in the cementing and production process. Since the cement slurry in the cementing section of the horizontal well has a high specific gravity, if there is leakage to varying degrees in the vertical well, the cement slurry will enter the vertical well cave, resulting in the inability to connect the horizontal well and the vertical well under the eccentric connection condition; at the same time, due to the distance between the horizontal well casing and the vertical well cave, this well section is an open hole section. As the throat section of the connecting well, once blocked, it will greatly affect the gas production. At the same time, horizontal well repair is required, which is very expensive and causes great damage to the wellbore.

[0004] Although with the improvement of the technology for connecting horizontal wells and vertical wells, precise connection between horizontal wells and vertical wells has been achieved, and the connection between horizontal wells and vertical wells after cementing has been achieved by drilling through cement plugs, the problem of unprotected open holes in the connecting sections between horizontal wells and vertical wells cannot be solved, and blockage of throat sections often occurs. Summary of the invention

[0005] The purpose of the present invention is to provide a completion casing string and method based on a coalbed methane horizontal connecting well, so as to solve the problem in the prior art that the open hole connecting the horizontal well and the vertical well is unprotected, resulting in blockage of the throat section.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0007] A completion casing string based on a coalbed methane horizontally connected well includes a hydraulic rotary guide shoe, the rear of which is sequentially connected to a milling casing nipple, a floating collar, a pressure-holding plugging mechanism, a packer, a pressure differential grading collar and a casing;

[0008] The pressure-holding and sealing mechanism comprises a pressure-holding seat and a sealing plug;

[0009] The front and rear parts of the pressure-holding seat are connected to the floating collar and the packer respectively; the front part of the pressure-holding seat is provided with a circle of mounting grooves along the circumferential direction, and a spring clamp is installed in the mounting groove, and the spring clamp is an open spring ring;

[0010] The inner diameter of the pressure-holding seat gradually increases from the middle to the rear to form a sealing slope; the front part of the sealing plug is a connecting part, and the middle part is a sealing part; the shape of the sealing part of the sealing plug matches the sealing slope; a circle of clamp grooves is circumferentially arranged on the outer wall of the connecting part of the sealing plug, and the spring clamp can enter the inside of the clamp groove when in a natural state;

[0011] The sealing plug can enter the interior of the pressure-holding seat, and at this time, the spring clamp enters the interior of the clamp groove, and the sealing portion of the sealing plug is sealed and fitted with the sealing inclined surface of the pressure-holding seat.

[0012] The present invention also has the following features:

[0013] Furthermore, the front and rear parts of the pressure-holding seat are respectively screwed to the floating collar and the packer.

[0014] Furthermore, at least one sealing gasket is provided on the sealing portion of the sealing plug;

[0015] The rear part of the sealing plug is provided with a plurality of reinforcing skirts; the plurality of reinforcing skirts are evenly distributed along the circumference and axial direction of the sealing plug and are all inclined backwards;

[0016] The reinforced skirt is made of elastic material.

[0017] Furthermore, the reinforcement skirt is made of rubber material, and the reinforcement skirt is fixed to the rear of the sealing plug by vulcanization of nitrile rubber;

[0018] The outer diameter of the reinforced skirt in a free state is at least 10% greater than the inner diameter of the casing, and the reinforced skirt does not turn over when the pressure is not greater than 5MPa.

[0019] Furthermore, the length of the sealing plug is not less than twice the inner diameter of the sleeve.

[0020] Furthermore, a retaining ring is provided in the installation groove; the spring clamp is fixedly installed in the installation groove through the retaining ring.

[0021] A method for using a completion casing string based on a coalbed methane horizontally connected well, the method is based on the above-mentioned completion casing string based on a coalbed methane horizontally connected well, and comprises the following steps:

[0022] Step 1: Drill a horizontal well using a horizontal well drilling tool. When the drilling is 100-120m away from the vertical well, a strong magnetic joint and a connecting instrument are respectively lowered into the horizontal well and the vertical well;

[0023] When drilling to 5-8m away from the vertical well, retrieve the connecting instrument in the vertical well and carry out the connecting operation until the vertical wellhead shows signs of connection;

[0024] Step 2: After drilling the horizontal well for 5-8 m, run a connection verification pipe string into the vertical well, wherein the lower end of the connection verification pipe string is run 5 m below the connection point between the horizontal well and the vertical well;

[0025] Step 3, adjusting the face angle of the horizontal well drilling tool and continuing drilling, and determining whether the horizontal well drilling tool collides with the connection verification pipe string;

[0026] If not, it means that the horizontal well and the vertical well are eccentrically connected, and the slotting operation is performed until the horizontal well drilling tool collides with the connection verification pipe string to achieve the positive connection between the horizontal well and the vertical well; the precise well depth is determined by the collision position of the connection verification pipe string and then step 4 is entered;

[0027] If a collision occurs, it means that the horizontal well and the vertical well are directly connected. After verifying the collision position of the pipe string through connection and determining the precise well depth, proceed to step 4.

[0028] Step 4, connecting the hydraulic rotary guide shoe, the milling casing nipple, the floating collar, the pressure holding plugging mechanism, the packer, the pressure differential grading collar and the casing to form a casing string;

[0029] Run the casing string into the horizontal well to the precise well depth determined in step 3, and allow the milling casing short section to enter the overlapping section of the vertical well and the horizontal well;

[0030] Step 5, using an external circulation pump to circulate the annular space in the casing string until the annular space in the casing string is unobstructed and then inserting the sealing plug; allowing the sealing plug to continue to move forward under the pump pressure of the external circulation pump until the spring clamp enters the inside of the clamp groove, and the sealing portion of the sealing plug is sealed and fitted with the sealing inclined surface of the pressure holding seat, so that the channel in the sealing plug is blocked to achieve pressure holding;

[0031] Step 6: Use an external pump truck to continuously pressurize the inside of the casing string until the opening pressure of the packer is reached, and then the injection port of the injection mechanism of the packer is opened; inject clean water into the packer, and continue to pressurize the inside of the casing string until the closing pressure of the packer is reached, and then the injection port of the injection mechanism of the packer is closed, thereby achieving the plugging of the packer;

[0032] Step 7: Use an external pump truck to continuously pressurize the inside of the casing string until the opening pressure of the differential pressure grading collar is reached; inject cement slurry into the horizontal well, lower the shut-off plug into the casing string and then inject water until it contacts the differential pressure grading collar, and continue to pressurize until the closing pressure of the differential pressure grading collar is reached, and complete cementing and wait for solidification;

[0033] Step 8, drilling down into the horizontal well to remove the hydraulic rotary guide shoe, floating collar, pressure-holding plugging mechanism, packer and differential pressure grading collar to achieve connectivity between the vertical wellbore and the horizontal wellbore.

[0034] Furthermore, the outer diameter of the connectivity verification pipe string in step 2 is not less than the outer diameter of the external drainage pump hook.

[0035] Furthermore, in step 3, the facing angles of the horizontal well drilling tool are adjusted to 90° and 270° respectively before drilling continues.

[0036] Compared with the prior art, the present invention has the following technical effects:

[0037] (I) The completion casing string based on the coalbed methane horizontal connecting well of the present invention is to lower the casing string into the horizontal well and the vertical well to achieve the connection. The casing string can be directly lowered through the vertical well section, and the casing is cut by milling in the vertical well to achieve protection of the connecting section between the horizontal well and the vertical well, thereby avoiding blockage of the throat section.

[0038] (II) In the method for using the completion casing string based on the coalbed methane horizontal connecting well of the present invention, after the horizontal well and the vertical well are connected, the eccentricity verification is carried out through the well repair pipe string to determine whether the connection point is directly connected or eccentrically connected. If it is eccentrically connected, directly connected can be achieved by repeated eye-marking, which makes it easier to clarify the directly connected relationship between the horizontal well casing string and the connected vertical well and the specific connected well depth.

[0039] (III) The completion casing string based on the coalbed methane horizontal connecting well of the present invention realizes that the connected casing string does not contain a screen pipe, and the lower end is connected to a rotating guide shoe; this arrangement can realize pump circulation and bottom well stirring during the casing lowering process, avoiding the problem of difficulty in lowering caused by the existence of the screen pipe section during the conventional casing connection process.

[0040] (IV) The completion casing string based on the coalbed methane horizontal connecting well of the present invention realizes that the connected casing string can be directly lowered through the vertical well section, and the casing of the vertical well is cut by milling to realize the protection of the entire horizontal section; the lower part of the completion casing string is connected to the drillable packer and the pressure difference grading hoop to realize cementing above the horizontal section packer, avoiding cement slurry from entering the vertical well, which is suitable for large-scale use and promotion in industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the overall structure of a completion casing string based on a coalbed methane horizontally connected well of the present invention;

[0042] Figure 2 It is a schematic diagram of cementing effect of completion casing string based on coalbed methane horizontal connecting well of the present invention;

[0043] Figure 3 It is a schematic diagram of the structure of the pressure holding seat in the present invention;

[0044] Figure 4 It is a schematic diagram of the spring clamp structure in the present invention;

[0045] Figure 5It is a schematic diagram of the sealing plug structure of the present invention;

[0046] Figure 6 It is a schematic diagram of the overall structure of a casing string using a row of screen tube short sections in one embodiment of the present invention.

[0047] The meaning of the symbols in the figure is:

[0048] 1. Hydraulic rotary guide shoe; 2. Milling casing short section; 3. Floating hoop; 4. Packer; 5. Pressure differential grading hoop; 6. Casing; 7. Pressure holding seat; 8. Sealing plug; 9. Installation groove; 10. Spring clamp; 11. Sealing bevel; 12. Clamp groove; 13. Sealing gasket; 14. Reinforced skirt; 15. Circlip retaining ring. DETAILED DESCRIPTION

[0049] It should be noted that, unless otherwise specified, all components of the present invention are components known in the prior art. For example, the hydraulic rotary guide shoe adopts a known and commonly used hydraulic rotary guide shoe.

[0050] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0051] like Figure 1 , 3 , 4 and 5, a completion casing string based on a coalbed methane horizontally connected well comprises a hydraulic rotary guide shoe 1, the rear of which is sequentially connected with a milling casing nipple 2, a floating collar 3, a pressure-holding plugging mechanism, a packer 4, a pressure differential grading collar 5 and a casing 6;

[0052] The pressure-holding and sealing mechanism comprises a pressure-holding seat 7 and a sealing plug 8;

[0053] The front and rear parts of the pressure-holding seat 7 are connected to the floating collar 3 and the packer 4 respectively; the front part of the pressure-holding seat 7 is provided with a circle of mounting grooves 9 along the circumferential direction, and a spring clamp 10 is installed in the mounting groove 9, and the spring clamp 10 is an open spring ring;

[0054] The inner diameter of the pressure-holding seat 7 gradually increases from the middle to the rear, forming a sealing slope 11; the front part of the sealing plug 8 is a connecting part, and the middle part is a sealing part; the shape of the sealing part of the sealing plug 8 matches the sealing slope 11; a circle of clamp grooves 12 are formed on the outer wall of the front part of the sealing plug 8 along the circumferential direction, and the spring clamp 10 can enter the inside of the clamp groove 12 when it is in a natural state;

[0055] The sealing plug 8 can enter the interior of the pressure-holding seat 7 , and at this time, the spring clamp 10 enters the clamp groove 12 , and the sealing portion of the sealing plug 8 is sealed and fitted with the sealing inclined surface 11 of the pressure-holding seat 7 .

[0056] When in use, the diameter of the clamp groove 12 in the pressure-holding seat 7 is larger than the inner diameter of the pressure-holding seat 7. The spring clamp 10 is installed in the clamp groove 12. Since the spring clamp 10 is an open spring ring, it can expand when subjected to impact force, and return to a natural state to shrink and clamp when the impact force disappears. In the actual working process, when the sealing plug 8 enters the pressure-holding seat 7, the front part of the sealing plug 8 opens the spring clamp 10. As the sealing plug 10 continues to move forward, the spring clamp 10 enters the clamp groove 12, the impact force disappears, and the spring clamp 10 returns to a natural state and tightens until it completely enters the clamp groove 12 to achieve fixation.

[0057] At this time, since the sealing portion and the sealing inclined surface 11 have the same shape, the sealing portion of the sealing plug 8 is in sealing contact with the sealing inclined surface 11 of the pressure holding seat 7, and sealing can be achieved under pressure.

[0058] As a preferred solution, the front and rear parts of the pressure holding seat 7 are respectively screwed with the floating collar 3 and the packer 4, so as to achieve detachable installation while ensuring the sealing performance and connection strength.

[0059] As a preferred solution, a sealing gasket 13 is provided on the sealing portion of the sealing plug 8;

[0060] A plurality of reinforcing skirts 14 are provided at the rear of the sealing plug 8; the plurality of reinforcing skirts 14 are evenly distributed along the circumference and axial direction of the sealing plug 8 and are all inclined backwards;

[0061] The reinforcement skirt 14 is made of elastic material.

[0062] Further preferably, the reinforcement skirt 14 is made of rubber material and is fixed to the rear of the sealing plug 8 by vulcanization of nitrile rubber;

[0063] The outer diameter of the reinforcement skirt 14 in a free state is at least 10% greater than the inner diameter of the sleeve 6 , and the reinforcement skirt 14 does not turn over when the pressure is not greater than 5 MPa.

[0064] Among them, the sealing gasket 13 strengthens the sealing performance of the sealing plug 8, and cooperates with multiple reinforced skirts 14 to prevent the sealing plug 8 from moving after entering the pressure-holding seat 7, thereby further improving the sealing performance while ensuring the tightness of the connection.

[0065] As a preferred solution, the length of the sealing plug 8 is not less than twice the inner diameter of the sleeve 6. On the premise of safely passing through the through hole in the grading hoop, the angle between the axis of the sealing plug 8 and the axis of the pressure-holding seat is not greater than 10°. After the sealing plug 8 moves to the sealing bevel 11, it can be guided by the sealing bevel 11, and then tightly fit to achieve sealing; avoid the problem of blocking the sealing plug 8 and the sealing bevel 11 caused by excessive angle.

[0066] Further preferably, a retaining ring 15 is further provided in the installation groove 9 ; the spring clamp 10 is fixedly installed in the installation groove 9 via the retaining ring 15 .

[0067] The retaining ring 15 is connected to the pressure-holding seat 7 through a thread, and together with the clamp groove 12, the retaining ring 15 is axially locked so that it does not move axially when subjected to an axial force.

[0068] A method for using a completion casing string based on a coalbed methane horizontally connected well, the method is based on the above-mentioned completion casing string based on a coalbed methane horizontally connected well, and comprises the following steps:

[0069] Step 1, use a horizontal well drilling tool to drill a horizontal well. When the drilling is 100 to 120 meters away from the vertical well, a strong magnetic joint and a connecting instrument are respectively lowered into the horizontal well and the vertical well to guide the horizontal well to connect with the vertical well;

[0070] Among them, when drilling to 40-50m away from the vertical well, the well inclination and azimuth need to be adjusted;

[0071] When drilling to a distance of 5 to 8 meters from the vertical well, the connecting instrument in the vertical well is recovered and connecting operations are carried out until signs of connection appear at the wellhead of the vertical well; wherein, the signs of connection include water spraying, air jetting and other phenomena. Technical personnel in this field can judge the signs of connection by combining relevant knowledge in this field and local actual conditions.

[0072] Step 2: After drilling the horizontal well for 5-8 m, run a connection verification pipe string into the vertical well, wherein the lower end of the connection verification pipe string is run 5 m below the connection point between the horizontal well and the vertical well;

[0073] Step 3, adjusting the face angle of the horizontal well drilling tool and continuing drilling, and determining whether the horizontal well drilling tool collides with the connection verification pipe string;

[0074] If not, it means that the horizontal well and the vertical well are eccentrically connected, and the slotting operation is performed until the horizontal well drilling tool collides with the connection verification pipe string to achieve the positive connection between the horizontal well and the vertical well; the precise well depth is determined by the collision position of the connection verification pipe string and then step 4 is entered;

[0075] If yes, it means that the horizontal well and the vertical well are directly connected. After verifying the collision position of the pipe string through the connection and determining the precise well depth, proceed to step 4.

[0076] When adjusting the facing angle of the horizontal well drilling tool, the facing angle of the horizontal well drilling tool is adjusted to 90° and 270° respectively;

[0077] Before the slotting operation, the horizontal well continues to be drilled for 5 to 8 meters, the last measuring point is measured, and then the connected data is recalculated to clarify the positional relationship between the actual wellbore trajectory and the vertical well axis. If the vertical well axis increases the azimuth direction, the tool face is adjusted to 220 to 230 degrees, and the slotting operation is repeated. The azimuth is quickly lowered while the drilling tool's deadweight is used to reduce the well inclination until the drilling tool string collides with the verification pipe string; if the vertical well axis increases the azimuth direction, the tool face is adjusted to 130 to 140 degrees, and the slotting operation is repeated. The azimuth is quickly increased while the drilling tool's deadweight is used to reduce the well inclination until the drilling tool string collides with the verification pipe string.

[0078] Step 4, connecting the hydraulic rotary guide shoe 1, the milling casing short section 2, the floating collar 3, the pressure holding plugging mechanism, the packer 4, the pressure differential grading collar 5 and the casing 6 to form a casing string;

[0079] The casing string is lowered into the horizontal well to the precise well depth determined in step 3, and the milling casing sub 2 is allowed to enter the overlapping well section of the vertical well and the horizontal well;

[0080] Among them, when the casing string encounters resistance during the lowering process, according to the conventional selection, the external circulation pump is turned on to clean the sediment at the bottom of the horizontal well;

[0081] Step 5, use an external circulation pump to perform 1-2 cycles, and then put in the sealing plug 8 after the annulus in the casing is unobstructed, and let the sealing plug 8 continue to move forward under the action of the pump pressure until the spring clamp 10 enters the clamp groove 12, and the sealing part of the sealing plug 8 is sealed and fitted with the sealing inclined surface 11 of the pressure holding seat 7, so that the channel in the sealing plug 8 is blocked to achieve pressure holding;

[0082] Step 6: Use an external pump truck to continuously pressurize the inside of the casing string until the opening pressure of the packer 4 is reached, then the injection port of the injection mechanism of the packer 4 is opened and clean water is injected into the packer 4; continue to pressurize the inside of the casing string until the closing pressure of the packer 4 is reached, then the injection port of the injection mechanism of the packer 4 is closed, and the packer 4 is plugged;

[0083] Step 7, use an external pump truck to continuously pressurize the inside of the casing string until the opening pressure of the differential pressure grading collar 5 is reached; when injecting cement slurry, according to the cementing design, inject cement slurry of the required quantity and specific gravity for annular sealing into the horizontal well, lower the closing plug into the casing string, and then inject clean water post-flushing liquid until the closing plug contacts the differential pressure grading collar 5, and continue to pressurize to the closing pressure of the differential pressure grading collar 5 to complete cementing;

[0084] The amount and specific gravity of cement slurry used for cementing belong to the conventional cementing design content and are not specifically studied in this embodiment; the replacement slurry is used because the amount of cement slurry is sufficient to seal the annulus. Using clean water post-flushing fluid as the replacement slurry, in addition to assisting in the displacement of cement slurry in the casing, can also send the closing plug to the predetermined position of the predetermined grading collar to achieve the closure of the grading collar.

[0085] Step 8, after the solidification is completed, drill down into the horizontal well to remove the hydraulic rotary guide shoe 1, the floating collar 3, the pressure-holding plugging mechanism, the packer 4 and the pressure difference grading collar 5 to achieve the connection between the vertical wellbore and the horizontal wellbore.

[0086] Specifically, the outer diameter of the connectivity verification pipe string in step 2 is not less than the outer diameter of the external drainage pump hook.

[0087] An optional implementation method is given below. In the actual operation process, it may happen that the horizontal well and the vertical well cannot be directly connected. Figure 6 As shown, at this time, the milling casing short section 2 in the casing string in the present application is replaced with a drainage screen short section, and the hydraulic rotary guide shoe 1 is replaced with a self-rotating guide shoe. In this way, after the cement plug is swept in the horizontal well, the horizontal well and the vertical well can be reconnected, and the screen protection is realized in the entire well section of the horizontal well.

Claims

1. A completion casing string based on a coalbed methane horizontally connected well, characterized in that: It comprises a hydraulic rotary guide shoe (1), the rear part of which is sequentially connected with a milling casing nipple (2), a floating collar (3), a pressure-holding plugging mechanism, a packer (4), a pressure differential grading collar (5) and a casing (6); The pressure-holding and sealing mechanism comprises a pressure-holding seat (7) and a sealing plug (8); The front and rear parts of the pressure-holding seat (7) are connected to the floating collar (3) and the packer (4) respectively; the front part of the pressure-holding seat (7) is provided with a circle of mounting grooves (9) along the circumferential direction, and a spring clamp (10) is installed in the mounting groove (9), and the spring clamp (10) is an open spring ring; The inner diameter of the pressure-holding seat (7) gradually increases from the middle to the rear, forming a sealing slope (11); the front part of the sealing plug (8) is a connecting part, and the middle part is a sealing part; the shape of the sealing part of the sealing plug (8) matches the sealing slope (11); a circle of clamp grooves (12) are arranged on the outer wall of the connecting part of the sealing plug (8) along the circumferential direction, and the spring clamp (10) can enter the inside of the clamp groove (12) when in a natural state; The sealing plug (8) can enter the interior of the pressure-holding seat (7), and at this time, the spring clamp (10) enters the interior of the clamp groove (12), and the sealing portion of the sealing plug (8) is sealed and fitted with the sealing inclined surface (11) of the pressure-holding seat (7).

2. The completion casing string based on the coalbed methane horizontal connecting well according to claim 1, characterized in that: The front and rear parts of the pressure-holding seat (7) are respectively screwed to the floating collar (3) and the packer (4).

3. The completion casing string based on the coalbed methane horizontal connecting well according to claim 1, characterized in that: At least one sealing gasket (13) is provided on the sealing portion of the sealing plug (8); The rear portion of the sealing plug (8) is provided with a plurality of reinforcing skirts (14); the plurality of reinforcing skirts (14) are evenly distributed along the circumference and axial direction of the sealing plug (8) and are all inclined backwards; The reinforced skirt (14) is made of elastic material.

4. The completion casing string based on the coalbed methane horizontal connecting well according to claim 3, characterized in that: The reinforcing skirt (14) is made of rubber material, and the reinforcing skirt (14) is fixed to the rear of the sealing plug (8) by vulcanization of nitrile rubber; The outer diameter of the reinforcement skirt (14) in a free state is at least 10% greater than the inner diameter of the sleeve (6), and when the pressure is not greater than 5 MPa, the reinforcement skirt (14) does not turn over.

5. The completion casing string based on the coalbed methane horizontal connecting well according to claim 4, characterized in that: The length of the sealing plug (8) is not less than twice the inner diameter of the sleeve (6).

6. The completion casing string based on the coalbed methane horizontal connecting well according to claim 5, characterized in that: A retaining ring (15) is also provided in the installation groove (9); the spring clamp (10) is fixedly installed in the installation groove (9) via the retaining ring (15).

7. A method for using a completion casing string based on a coalbed methane horizontally connected well, the method is based on the completion casing string based on a coalbed methane horizontally connected well according to claim 6, characterized in that: The following steps are involved: Step 1: Drill a horizontal well using a horizontal well drilling tool. When the drilling is 100-120m away from the vertical well, a strong magnetic joint and a connecting instrument are respectively lowered into the horizontal well and the vertical well; When drilling to 5-8m away from the vertical well, retrieve the connecting instrument in the vertical well and carry out the connecting operation until the vertical wellhead shows signs of connection; Step 2: After drilling the horizontal well for 5-8 m, run a connection verification pipe string into the vertical well, wherein the lower end of the connection verification pipe string is run 5 m below the connection point between the horizontal well and the vertical well; Step 3, adjusting the face angle of the horizontal well drilling tool and continuing drilling, and determining whether the horizontal well drilling tool collides with the connection verification pipe string; If not, it means that the horizontal well and the vertical well are eccentrically connected, and the slotting operation is performed until the horizontal well drilling tool collides with the connection verification pipe string to achieve the positive connection between the horizontal well and the vertical well; the precise well depth is determined by the collision position of the connection verification pipe string and then step 4 is entered; If a collision occurs, it means that the horizontal well and the vertical well are directly connected. After verifying the collision position of the pipe string through connection and determining the precise well depth, proceed to step 4. Step 4, connecting the hydraulic rotary guide shoe (1), the milling casing short section (2), the floating collar (3), the pressure holding plugging mechanism, the packer (4), the pressure differential grading collar (5) and the casing (6) to form a casing string; The casing string is lowered into the horizontal well to the precise well depth determined in step 3, and the milling casing short section (2) is allowed to enter the overlapping well section of the vertical well and the horizontal well; Step 5, using an external circulation pump to circulate the annular space in the casing string until the annular space in the casing string is unobstructed and then inserting the sealing plug (8); allowing the sealing plug (8) to continue to move forward under the pump pressure of the external circulation pump until the spring clamp (10) enters the inside of the clamp groove (12), and the sealing part of the sealing plug (8) is sealed and fitted with the sealing inclined surface (11) of the pressure holding seat (7), so that the inner channel of the sealing plug (8) is blocked to achieve pressure holding; Step 6: Use an external pump truck to continuously pressurize the inside of the casing string until the opening pressure of the packer (4) is reached, and then the injection port of the injection mechanism of the packer (4) is opened; inject clean water into the packer (4), and continue to pressurize the inside of the casing string until the closing pressure of the packer (4) is reached, and then the injection port of the injection mechanism of the packer (4) is closed, thereby achieving the plugging of the packer (4); Step 7, using an external pump truck to continuously pressurize the inside of the casing string until the opening pressure of the differential pressure grading collar (5) is reached; injecting cement slurry into the horizontal well, inserting the closing plug into the casing string and then injecting water until it contacts the differential pressure grading collar (5), and then continuing to pressurize to the closing pressure of the differential pressure grading collar (5), completing cementing and waiting for solidification; Step 8, drilling down into the horizontal well to remove the hydraulic rotary guide shoe (1), the floating collar (3), the pressure-holding plugging mechanism, the packer (4) and the pressure differential grading collar (5), so as to achieve the connection between the vertical wellbore and the horizontal wellbore.

8. The method for using a completion casing string based on a coalbed methane horizontally connected well according to claim 7, characterized in that: The outer diameter of the connectivity verification pipe string in step 2 is not less than the outer diameter of the external drainage pump hook.

9. The method for using a completion casing string based on a coalbed methane horizontally connected well according to claim 7, characterized in that: In step 3, the facing angles of the horizontal well drilling tool are adjusted to 90° and 270° respectively before drilling continues.

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