Cluster sliding sleeve staged fracturing completion string and construction method thereof

Abstract

The invention discloses a cluster sliding sleeve segmented fracturing completion string, comprising a floating collar, a first-stage sliding sleeve unit, a second-stage sliding sleeve unit, ..., and an Nth sliding sleeve unit connected sequentially through casing from bottom to top; the sliding sleeve units at each stage have the same structure, and all comprise a segment sliding sleeve and a plurality of cluster sliding sleeves with the same structure connected sequentially through casing from bottom to top, and a sealing ball matched with the inner diameter of the central channel of the segment sliding sleeve and the cluster sliding sleeve; the inner diameter of the central channel of each stage sliding sleeve increases step by step from bottom to top, and the diameter of the sealing ball matched with each stage sliding sleeve increases step by step from bottom to top; the cluster sliding sleeve segmented fracturing completion string can realize unlimited fracturing operations within a section of oil layer; multiple cluster sliding sleeves can be opened at one time in a single group operation, which simplifies the construction steps and saves the construction time; the wellhead does not need to be equipped with special equipment, and only a conventional fracturing tree can meet the construction requirements.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum development, and in particular to a cluster sliding sleeve segmented fracturing completion pipe string and a construction method thereof. Background Art

[0002] Horizontal well staged fracturing completion is currently recognized by the world as an efficient measure to increase oil well production. After years of development, the current commonly used horizontal well staged fracturing completion methods mainly include bridge plug multi-cluster perforation staged fracturing completion technology and dragging continuous tubing staged fracturing completion technology. Bridge plug cluster perforation staged fracturing completion requires the bridge plug to be lowered into the wellbore and sealed. The construction cycle is long, the efficiency is low, it is easy to encounter obstacles during the lowering process, and the sealing process has high requirements. There is a high risk of bridge plug sealing failure during construction. The dragging continuous tubing sandblasting perforation staged fracturing completion has the problem of inaccurate transformation points and cannot meet the requirements of precise fracturing. Summary of the invention

[0003] The purpose of the present invention is to provide a cluster sliding sleeve staged fracturing completion string that meets the requirements of large drift diameter, large displacement, precise fracturing, etc., and realizes staged fracturing transformation of low-porosity and low-permeability oil reservoirs in a simple manner.

[0004] Another object of the present invention is to provide a construction method using a cluster sliding sleeve staged fracturing completion string.

[0005] To this end, the technical solution of the present invention is as follows:

[0006] A cluster sliding sleeve staged fracturing completion string comprises a floating collar, a first sliding sleeve unit, a second sliding sleeve unit, ..., and an Nth sliding sleeve unit connected sequentially through casing from bottom to top; wherein:

[0007] Each level of the sliding sleeve unit has the same structure, which includes a segment sliding sleeve and a plurality of cluster sliding sleeves with the same structure connected sequentially through sleeves from bottom to top, and a sealing ball matched with the inner diameter of the central channel of the segment sliding sleeve and the cluster sliding sleeve;

[0008] The segment sleeve includes a segment outer sleeve and a segment inner sleeve; the inner diameter of the lower part of the segment outer sleeve is larger than the inner diameter of the upper part, and a plurality of segment fracturing holes are evenly distributed in the circumferential direction on the upper side wall of the segment outer sleeve; the segment inner sleeve is sleeved on the inner side of the upper part of the segment outer sleeve and is fixed as a whole by a plurality of segment shear pins arranged in the circumferential direction; the segment inner sleeve is composed of an upper cylinder and a lower petal claw, and the inner side surface and the outer side surface of the bottom end of each claw body of the lower petal claw are respectively provided with an inner convex block and an outer convex block, so that the lower petal claw is initially placed on the upper part of the segment outer sleeve in a contracted state, and opens when it moves downward as the segment shear pin is cut off, so that the sealing ball falls into the segment ball seat formed by the inner convex blocks at the bottom end of each claw body of the lower petal claw;

[0009] The cluster sleeve comprises a cluster outer sleeve and a cluster inner sleeve; the inner diameter of the lower part of the cluster outer sleeve is larger than the inner diameter of the upper part, and a plurality of cluster fracturing holes are evenly distributed on the upper side wall thereof in the circumferential direction; the cluster inner sleeve is sleeved on the inner side of the upper part of the cluster outer sleeve and fixed as a whole by a plurality of cluster shear pins arranged in the circumferential direction; the cluster inner sleeve is composed of an upper cylinder and lower petal claws, and the outer side surface of the bottom end of each claw body of the lower petal claw is provided with an outer convex block, so that the lower petal claw is initially placed on the upper part of the cluster outer sleeve in a contracted state, and opens when the cluster shear pin is cut and moves downward, so that the sealing ball falls and leaves the cluster sleeve;

[0010] The inner diameter of the central channel of each level of the sliding sleeve increases step by step from bottom to top, and the diameter of the sealing ball matched with each level of the sliding sleeve increases step by step from bottom to top.

[0011] Furthermore, the segment sleeve also includes a segment upper joint and a segment lower joint; wherein, the bottom end of the segment upper joint is threadedly connected to the top inner wall of the segment sleeve; the top end of the segment lower joint is threadedly connected to the bottom inner wall of the segment sleeve, so that an annular groove-shaped segment claw groove is formed between the segment sleeve and the segment lower joint.

[0012] Furthermore, the inner diameter of the upper joint of the segment, the inner diameter of the upper cylinder of the inner sleeve of the segment, and the inner diameter of the lower joint of the segment are all the same.

[0013] Furthermore, the cluster sleeve also includes a cluster upper joint and a cluster lower joint; wherein, the bottom end of the cluster upper joint is threadedly connected to the top inner wall of the cluster sleeve; the top end of the cluster lower joint is threadedly connected to the bottom inner wall of the cluster sleeve, so that an annular groove-shaped cluster claw groove is formed between the cluster sleeve and the cluster lower joint.

[0014] Furthermore, the inner diameter of the cluster upper joint, the inner diameter of the upper cylinder of the cluster inner sleeve, and the inner diameter of the cluster lower joint are all the same.

[0015] Furthermore, in each stage of the sliding sleeve unit, the top end surfaces of the inner protrusions at the bottom ends of the claw bodies on the lower petal claws of the inner sleeve are processed to be able to cooperate with the sealing balls of this stage to form a sealed conical surface.

[0016] Furthermore, the value of N is consistent with the number of layers of the underground oil layer to be fractured.

[0017] Furthermore, the length of the casing connected between the floating collar, the first-stage sliding sleeve unit, the second-stage sliding sleeve unit, ..., and the N-th sliding sleeve unit is adapted to the depth of each oil layer to be fractured and reconstructed underground, so that the first-stage sliding sleeve unit, the second-stage sliding sleeve unit, ..., and the N-th sliding sleeve unit are correspondingly inserted into each oil layer to be fractured and reconstructed underground from deep to shallow.

[0018] A construction method using the cluster sliding sleeve staged fracturing completion string is implemented, and the steps are as follows:

[0019] S1. Lower the completion string into the open hole wellbore to complete the cementing construction;

[0020] S2, drop a first sealing ball into the completion string, the first sealing ball directly passes through the second-stage sliding sleeve unit and falls into the first upper cluster sliding sleeve of the first-stage sliding sleeve unit and is stuck at the lower petal claw of the cluster inner sleeve of the first upper cluster sliding sleeve, blocking the passage of the first upper cluster sliding sleeve; pressurize the completion string, the first sealing ball is pressed to break four cluster shear pins, push the cluster inner sleeve downward, open the cluster fracturing hole that is initially in a blocked state, and at the same time, the first sealing ball falls into the first lower cluster sliding sleeve, and the first upper cluster sliding sleeve is now in an open state;

[0021] Continue to pressurize the completion string. The first sealing ball is pressed to break the four cluster shear pins of the first lower cluster sliding sleeve, pushing the cluster inner sleeve downward to open the cluster fracturing hole that was initially in a blocked state. At the same time, the first sealing ball falls into the first section sliding sleeve, and the cluster fracturing holes of the first upper cluster sliding sleeve and the first lower cluster sliding sleeve are both in an open state.

[0022] Continue to pressurize the completion string. The first sealing ball breaks the four cluster shear pins of the first section sliding sleeve under pressure, pushing the inner sleeve of the section downward, opening the section fracturing hole that was initially in a blocked state. At the same time, the first sealing ball falls to the section ball seat. At this time, the cluster fracturing holes of the first upper cluster sliding sleeve and the first lower cluster sliding sleeve, as well as the section fracturing holes of the first section sliding sleeve are all in an open state. After that, the first stage fracturing construction can be started.

[0023] S3, after the first stage fracturing is completed, a second sealing ball is dropped into the completion string, and step S2 is repeated until the second sealing ball sequentially opens the fracturing holes on the second upper cluster sliding sleeve, the second lower cluster sliding sleeve, and the second section sliding sleeve, after which the second stage fracturing construction can be started;

[0024] S4, repeating the above step S3 until the N-stage fracturing construction corresponding to the N-stage sliding sleeve unit is completed.

[0025] Compared with the existing technology, the cluster sleeve segmented fracturing completion string is suitable for completion and fracturing transformation of horizontal wells in low-porosity and low-permeability oil reservoirs. It is simple and easy to operate, and can achieve unlimited fracturing operations within a section of the oil layer. Multiple cluster sleeves can be opened at one time in a single group operation, simplifying the construction steps and saving construction time. The wellhead does not need to be equipped with special equipment, and only conventional fracturing trees can meet the construction requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the structure of the cluster sliding sleeve staged fracturing completion string of the present invention;

[0027] Figure 2 It is a schematic structural diagram of the first section of the sliding sleeve of the cluster sliding sleeve staged fracturing completion string of the present invention in an initial state;

[0028] Figure 3It is a schematic structural diagram of the first section of the sliding sleeve of the cluster sliding sleeve staged fracturing completion string of the present invention in an open state;

[0029] Figure 4 It is a schematic structural diagram of the first cluster of sliding sleeves of the cluster sliding sleeve staged fracturing completion string of the present invention in an initial state;

[0030] Figure 5 It is a schematic structural diagram of the first cluster of sliding sleeves of the cluster sliding sleeve staged fracturing completion string of the present invention in an open state. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention in any way.

[0032] In this embodiment, there are two uneven oil layers that need to be subjected to staged fracturing. Figure 1 As shown, the cluster sleeve staged fracturing completion string 100 includes a floating collar 7, a first-stage sleeve unit and a second-stage sleeve unit connected sequentially through a casing 9 from bottom to top; wherein the first-stage sleeve unit is arranged at the depth of a first oil layer 101 located deep in the formation, and the second-stage sleeve unit is arranged at the depth of a second oil layer 102 close to the ground; specifically,

[0033] The floating collar 7 is arranged at the bottom end of the completion string 100 and located at the bottom of the well, and is used to complete the cementing construction;

[0034] The first-stage sliding sleeve unit includes a first-stage sliding sleeve 1, a first-cluster sliding sleeve group and a first sealing ball 801; wherein the first-cluster sliding sleeve group is composed of a first lower cluster sliding sleeve 2 and a first upper cluster sliding sleeve 3 having the same structure;

[0035] like Figure 2 and Figure 3 As shown, the first section sliding sleeve 1 includes a section upper joint 11, a section inner sleeve 12, a section outer sleeve 13, a section lower joint 14 and four section shear pins 15; specifically,

[0036] The segment outer sleeve 13 is a cylinder with an upper inner diameter smaller than a lower inner diameter, and a plurality of segment fracturing holes 131 are evenly distributed on the upper side wall thereof along the circumferential direction; the bottom end of the segment upper joint 11 is threadedly connected to the top inner wall of the segment outer sleeve 13; the segment inner sleeve 12 is sleeved on the upper inner side of the segment outer sleeve 13, and the two are connected and fixed as a whole through four segment shear nails 15 arranged along the circumferential direction, at this time, the top end of the segment inner sleeve 12 is against the bottom end face of the segment upper joint 11, and at the same time, the segment inner sleeve 12 blocks all the segment fracturing holes 131;

[0037] The segment inner sleeve 12 is composed of an upper cylinder and lower petal claws 121, and the inner side surface and outer side surface of the bottom end of each claw body of the lower petal claw 121 are respectively provided with an inner convex block and an outer convex block; the outer convex block at the bottom end of each claw body of the lower petal claw 121 makes the lower petal claw 121 initially arranged in a contracted state on the inner side of the upper part of the segment outer sleeve 13, and the inner convex block at the bottom end of each claw body of the lower petal claw 121 forms a segment ball seat 122 capable of cooperating with the first sealing ball 801; the top end of the segment lower joint 14 is threadedly connected to the inner wall of the bottom end of the segment outer sleeve 13, so that an annular groove-shaped segment claw groove 132 is formed between the segment outer sleeve 13 and the segment lower joint 14; wherein, the inner diameters of the segment upper joint 11, the upper cylinder of the segment inner sleeve 12, and the inner diameter of the segment lower joint 14 are consistent;

[0038] like Figure 2 As shown, when the first sealing ball 801 enters the first section sliding sleeve 1, since the lower petal claw 121 of the inner sleeve 12 is in a contracted state, the first sealing ball 801 is stuck at the lower petal claw 121 and blocks the first section sliding sleeve 1 channel; Figure 3 As shown, after the four segment shear nails 15 are sheared off under pressure, the segment inner sleeve 12 falls freely under the action of gravity until its lower petal claw 121 abuts against the top end surface of the segment lower joint 14. At this time, all the segment fracturing holes 131 are opened and the fracturing operation can be started. At the same time, the bottom end of the lower petal claw 121 of the segment inner sleeve 12 springs into the segment claw groove 132, so that the lower petal claw 121 opens, and the first sealing ball 801 falls onto the segment ball seat 122 under the action of gravity and forms a sealing fit with the segment ball seat 122.

[0039] As a preferred technical solution of the present application, the top end surface of the inner protrusion at the bottom end of each claw body on the lower petal claw 121 of the inner sleeve 12 is processed to be able to cooperate with the first sealing ball 801 to form a sealed conical surface;

[0040] like Figure 4 and Figure 5 As shown, the first lower cluster sliding sleeve 2 includes a cluster upper joint 21, a cluster inner sleeve 22, a cluster outer sleeve 23, a cluster lower joint 24 and four cluster shear pins 25; specifically,

[0041] The cluster jacket 23 is a cylinder with an upper inner diameter smaller than a lower inner diameter, and a plurality of cluster fracturing holes 231 are evenly distributed on its upper side wall along the circumferential direction; the bottom end of the cluster upper joint 21 is threadedly connected to the top inner wall of the cluster jacket 23; the cluster inner sleeve 22 is sleeved on the upper inner side of the cluster jacket 23, and the two are connected and fixed as a whole through four cluster shear nails 25 arranged along the circumferential direction, at this time, the top end of the cluster inner sleeve 22 is against the bottom end face of the cluster upper joint 21, and the cluster inner sleeve 22 blocks all the cluster fracturing holes 231 at the same time;

[0042] The cluster inner sleeve 22 is composed of an upper cylinder and lower petal claws 221, and each claw body of the lower petal claws 221 is provided with an outer protrusion on the outer side surface of the bottom end, so that the lower petal claws 221 are initially arranged in a contracted state on the inner side of the upper part of the cluster outer sleeve 23; the top end of the cluster lower joint 24 is threadedly connected to the inner wall of the bottom end of the cluster outer sleeve 23, so that an annular groove-shaped cluster claw groove 232 is formed between the cluster outer sleeve 23 and the cluster lower joint 24; wherein, the inner diameter of the cluster upper joint 21, the inner diameter of the upper cylinder of the cluster inner sleeve 22, and the inner diameter of the cluster lower joint 24 are consistent;

[0043] like Figure 4 As shown, when the first sealing ball 801 enters the first lower cluster sliding sleeve 2, since the lower petal claw 221 of the cluster inner sleeve 22 is in a contracted state, the first sealing ball 801 is stuck at the lower petal claw 221 and blocks the passage of the first lower cluster sliding sleeve 2; Figure 5 As shown, when the four cluster shear pins 25 are sheared off under pressure, the cluster inner sleeve 22 falls freely under the action of gravity until its lower petal claw 221 abuts against the top end surface of the cluster lower joint 24. At this time, all cluster fracturing holes 231 are opened and the fracturing operation can be started. At the same time, the bottom end of the lower petal claw 221 of the cluster inner sleeve 22 springs into the cluster claw groove 232, so that the lower petal claw 221 opens, and the first sealing ball 801 falls freely under the action of gravity and leaves the first lower cluster sliding sleeve 2;

[0044] like Figure 1 As shown, the structure and size of the first upper cluster sliding sleeve 3 are completely the same as those of the first lower cluster sliding sleeve 2, and the distance between the two is preferably 10m.

[0045] like Figure 1 As shown, the second-stage sleeve unit includes a second-stage sleeve 4, a second cluster sleeve group and a second sealing ball 802; the first cluster sleeve group is composed of a second lower cluster sleeve 5 and a second upper cluster sleeve 6 having the same structure; wherein the second-stage sleeve 4 has the same structure as the first-stage sleeve 1, and the second lower cluster sleeve 5, the second upper cluster sleeve 6 have the same structure as the first lower cluster sleeve 2 (or the first upper cluster sleeve 3); the difference between the second-stage sleeve unit and the first-stage sleeve unit is that the diameter of the second sealing ball 802 is greater than the diameter of the first sealing ball 801, and correspondingly, the minimum inner diameter of the second-stage sleeve unit is greater than the minimum inner diameter of the first-stage sleeve unit, so as to realize the segmented fracturing of two uneven oil layers by two-stage fracturing construction.

[0046] For the cluster sleeve segmented fracturing completion string of the present embodiment, in its structural design, each level of the sleeve unit gradually opens the three-level fracturing channel for one oil layer through one ball throwing. Compared with the structural design of completing the first-level fracturing channel with one ball throwing commonly used in the past, the structural design of the present application can shorten the total time from the initial ball throwing to the complete opening of all the fracturing holes in the three-level fracturing channel and reaching the fracturing construction conditions by at least half, and the pressure of pumping liquid to achieve the ball throwing pressure is also reduced by half accordingly, thereby effectively improving the construction efficiency and reducing the construction cost.

[0047] Example 2

[0048] A construction method for a cluster sliding sleeve staged fracturing completion string using Example 1, the specific steps of which are:

[0049] First, the completion string 100 is lowered into the open hole wellbore to complete the cementing construction;

[0050] Then, the first sealing ball 801 is thrown into the completion string 100. Since the diameter of the first sealing ball 801 is smaller than the minimum diameter of the second-stage sliding sleeve unit, the first sealing ball 801 directly passes through the second-stage sliding sleeve unit and falls into the first upper cluster sliding sleeve 3 of the first-stage sliding sleeve unit and is stuck at the lower petal claw 221 of the cluster inner sleeve of the first upper cluster sliding sleeve 3, thereby blocking the passage of the first upper cluster sliding sleeve 3. The completion string 100 is pressurized, and the first sealing ball 801 is pressed to apply a downward force to the cluster inner sleeve, so that the four cluster shear pins are cut off, and the cluster inner sleeve moves downward, opening the cluster fracturing hole that is initially in a blocked state. At the same time, the lower petal claw of the cluster inner sleeve opens, so that the first sealing ball 801 falls into the first lower cluster sliding sleeve 2. At this time, the first upper cluster sliding sleeve 3 is in an open state.

[0051] Continue to pressurize the completion string 100, the first sealing ball 801 exerts downward force on the cluster sleeve under pressure, so that the four cluster shear nails are cut off, the cluster sleeve moves downward, and the cluster fracturing hole that is initially in a blocked state is opened. At the same time, the lower petal claws of the cluster sleeve are opened, so that the first sealing ball 801 falls into the first section sliding sleeve 1. At this time, the cluster fracturing holes of the first upper cluster sliding sleeve 3 and the first lower cluster sliding sleeve 2 are both in an open state;

[0052] Continue to pressurize the completion string 100, the first sealing ball 801 exerts downward force on the segment inner sleeve under pressure, so that the four segment shear nails are cut off, and the segment inner sleeve moves downward, opening the segment fracturing hole that is initially in a blocked state, and at the same time, the lower petal claws of the segment inner sleeve open, so that the first sealing ball 801 falls to the segment ball seat 122, at which time the cluster fracturing holes of the first upper cluster sliding sleeve 3 and the first lower cluster sliding sleeve 2, as well as the segment fracturing holes of the first segment sliding sleeve 1 are all in an open state; thereafter, the first-stage fracturing operation can be started;

[0053] Next, after the first-stage fracturing is completed, a second sealing ball 802 is dropped into the completion string 100, and falls into the second upper cluster sliding sleeve 6 of the second-stage sliding sleeve unit; the above steps are repeated in the same manner as the cooperation between the first sealing ball 801 and the first-stage sliding sleeve unit, and the second sealing ball 802 opens the fracturing holes on the second upper cluster sliding sleeve 6, the second lower cluster sliding sleeve 5 and the second section sliding sleeve 4 in turn by applying pressure to the completion string 100, and then the second-stage fracturing construction can be started.

[0054] It should be noted that in a completion string 100, the number of segment sleeves is not limited to 2 as described above, and can also be adjusted to 1 to 4 segment sleeves according to the actual number of corresponding underground oil layers; correspondingly, the cluster sleeves associated with each segment sleeve are also not limited to the two described above, and can be adjusted to associate several cluster sleeves with each segment sleeve according to the corresponding oil layer thickness, that is, one segment sleeve and several cluster sleeves constitute a group of sleeve units, and are equipped with a sealing ball of corresponding size; specifically, a single segment sleeve is placed at a position slightly below the corresponding oil layer, and a cluster sleeve is placed upward at intervals of 10 to 30 m. More sleeves can be placed if the oil layer is thick, and fewer sleeves can be placed if the oil layer is thin, and all sleeves are finally evenly distributed in the entire oil layer section; the size of each group of sleeve units and sealing balls increases step by step from bottom to top, and multiple groups of sleeve units can be added to the completion string to achieve staged fracturing transformation for one or more oil layers of varying thicknesses.

Claims

1. A cluster sliding sleeve staged fracturing completion string, characterized in that: It includes a floating collar, a first-stage sliding sleeve unit, a second-stage sliding sleeve unit, ..., and an N-stage sliding sleeve unit which are sequentially connected through casing from bottom to top; Each level of sliding sleeve unit has the same structure, which includes a segment sliding sleeve and a plurality of cluster sliding sleeves with the same structure connected sequentially through casing from bottom to top, and a sealing ball matched with the inner diameter of the central channel of the segment sliding sleeve and the cluster sliding sleeve; a plurality of cluster sliding sleeves with the same structure are arranged at intervals of 10 to 30 m according to the thickness of the oil layer, so as to be evenly distributed in the entire oil layer section; The segment sleeve comprises a segment outer sleeve and a segment inner sleeve; the inner diameter of the lower part of the segment outer sleeve is larger than the inner diameter of the upper part, and a plurality of segment fracturing holes are evenly distributed in the circumferential direction on the upper side wall thereof; the segment inner sleeve is sleeved on the inner side of the upper part of the segment outer sleeve and is fixed as a whole by a plurality of segment shear pins arranged in the circumferential direction; the segment inner sleeve is composed of an upper cylinder and a lower petal claw, and the inner side surface and the outer side surface of the bottom end of each claw body of the lower petal claw are respectively provided with an inner convex block and an outer convex block, so that the lower petal claw is initially placed on the upper part of the segment outer sleeve in a contracted state, and opens when it moves downward as the segment shear pin is cut off, so that the sealing ball falls into the segment ball seat formed by the inner convex blocks at the bottom end of each claw body of the lower petal claw; the segment sleeve also comprises a segment upper joint and a segment lower joint; wherein, the bottom end of the segment upper joint is threadedly connected to the inner wall of the top end of the segment outer sleeve; the top end of the segment lower joint is threadedly connected to the inner wall of the bottom end of the segment outer sleeve, so that an annular groove-shaped segment claw groove is formed between the segment outer sleeve and the segment lower joint; The cluster sleeve comprises a cluster outer sleeve and a cluster inner sleeve; the inner diameter of the lower part of the cluster outer sleeve is larger than the inner diameter of the upper part, and a plurality of cluster fracturing holes are evenly distributed in the circumferential direction on the upper side wall thereof; the cluster inner sleeve is mounted on the inner side of the upper part of the cluster outer sleeve and fixed as a whole by a plurality of cluster shear pins arranged in the circumferential direction; the cluster inner sleeve is composed of an upper cylinder and a lower petal claw, and an outer protrusion is arranged on the outer side surface of the bottom end of each claw body of the lower petal claw, so that the lower petal claw is initially placed on the upper part of the cluster outer sleeve in a contracted state, and opens when the cluster shear pin is cut off and moves downward, so that the sealing ball falls off the cluster sleeve; the cluster sleeve also comprises a cluster upper joint and a cluster lower joint; wherein, the bottom end of the cluster upper joint is threadedly connected to the inner wall of the top end of the cluster outer sleeve; the top end of the cluster lower joint is threadedly connected to the inner wall of the bottom end of the cluster outer sleeve, so that an annular groove-shaped cluster claw groove is formed between the cluster outer sleeve and the cluster lower joint; The inner diameter of the central channel of each level of the sliding sleeve increases step by step from bottom to top, and the diameter of the matching sealing ball corresponding to each level of the sliding sleeve increases step by step from bottom to top.

2. The cluster sliding sleeve staged fracturing completion string according to claim 1, characterized in that: The inner diameter of the upper joint of the segment, the inner diameter of the upper cylinder of the inner sleeve of the segment, and the inner diameter of the lower joint of the segment are all the same.

3. The cluster sliding sleeve staged fracturing completion string according to claim 1, characterized in that: The inner diameter of the cluster upper joint, the inner diameter of the upper cylinder of the cluster inner sleeve, and the inner diameter of the cluster lower joint are all the same.

4. The cluster sliding sleeve staged fracturing completion string according to claim 1, characterized in that: In each stage of the sliding sleeve unit, the top end surface of the inner protrusion at the bottom end of each claw body on the lower petal claw of the inner sleeve of the segment is processed to be able to cooperate with the sealing ball of this stage to form a sealed conical surface.

5. The cluster sliding sleeve staged fracturing completion string according to claim 1, characterized in that: The value of N is consistent with the number of underground oil layers to be fractured.

6. The cluster sliding sleeve staged fracturing completion string according to claim 1, characterized in that: The length of the casing connected between the floating collar, the first-stage sliding sleeve unit, the second-stage sliding sleeve unit, ..., and the N-stage sliding sleeve unit is adapted to the depth of each oil layer to be fractured underground, so that the first-stage sliding sleeve unit, the second-stage sliding sleeve unit, ..., and the N-stage sliding sleeve unit are correspondingly inserted into each oil layer to be fractured underground from deep to shallow.

7. A construction method using the cluster sliding sleeve staged fracturing completion string according to any one of claims 1 to 6, the steps of which are as follows: S1. Lower the completion string into the open hole wellbore to complete the cementing construction; S2, drop a first sealing ball into the completion string, the first sealing ball directly passes through the second-stage sliding sleeve unit and falls into the first upper cluster sliding sleeve of the first-stage sliding sleeve unit and is stuck at the lower petal claw of the cluster inner sleeve of the first upper cluster sliding sleeve, blocking the passage of the first upper cluster sliding sleeve; pressurize the completion string, the first sealing ball is pressed to break four cluster shear pins, push the cluster inner sleeve downward, open the cluster fracturing hole that is initially in a blocked state, and at the same time, the first sealing ball falls into the first lower cluster sliding sleeve, and the first upper cluster sliding sleeve is now in an open state; Continue to pressurize the completion string. The first sealing ball is pressed to break the four cluster shear pins of the first lower cluster sliding sleeve, pushing the cluster inner sleeve downward to open the cluster fracturing holes that were initially blocked. At the same time, the first sealing ball falls into the first section sliding sleeve, and the cluster fracturing holes of the first upper cluster sliding sleeve and the first lower cluster sliding sleeve are both in an open state. Continue to pressurize the completion string. The first sealing ball breaks the four shear pins of the first sliding sleeve under pressure, pushing the inner sleeve downward to open the segment fracturing hole that was initially blocked. At the same time, the first sealing ball falls to the segment ball seat. At this time, the cluster fracturing holes of the first upper cluster sliding sleeve and the first lower cluster sliding sleeve, as well as the segment fracturing holes of the first sliding sleeve are all open. After that, the first stage fracturing construction can be started. S3, after the first stage fracturing is completed, a second sealing ball is dropped into the completion string, and step S2 is repeated until the second sealing ball sequentially opens the fracturing holes on the second upper cluster sliding sleeve, the second lower cluster sliding sleeve, and the second section sliding sleeve, after which the second stage fracturing construction can be started; S4, repeating the above step S3 until the N-stage fracturing construction corresponding to the N-stage sliding sleeve unit is completed.

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