A split two-stage casing head specially designed for oil wells

Abstract

The present invention discloses a split-type two-stage casing head for oil wells, which relates to the technical field of casing heads. The split-type two-stage casing head for oil wells comprises a first-stage casing head, a first-stage flange located at both ends of the first-stage casing head, a second-stage casing head and second-stage flanges located at both ends of the second-stage casing head, wherein the lower second-stage flange is connected to the upper first-stage flange, and further comprises: a limiting groove, wherein the limiting groove is provided in an area on the upper surface of the second-stage flange opposite to two flange holes, and the diameter of the limiting groove is larger than the diameter of the flange hole; a limiting head, wherein the limiting head is located in the limiting groove, and a lifting spring is provided between the lower end of the limiting head and the bottom of the limiting groove, and the lifting spring can push the limiting head upward; the present invention ensures that the second-stage casing head falls vertically, thereby preventing the cut casing in the first-stage casing head from squeezing the BT sealing ring; and also avoids an imbalance in the load distribution between the two sections, thereby ensuring the sealing effect of the flange.

Description

Technical Field

[0001] The invention relates to the technical field of casing heads, in particular to a split double-stage casing head special for oil wells. Background Art

[0002] In the prior art split double-stage oil well casing head, the upper and lower casing heads are connected by original bolts 100. Figure 1 The original bolt 100 includes an original head 101 and a rod 103 located below the original head 101. An upper threaded portion 102 is provided at the upper end of the rod 103, and the upper threaded portion 102 is threadedly connected to the original head 101. A lower threaded portion 104 is provided at the lower end of the rod 103, and the lower threaded portion 104 passes through the flange hole of the lower casing head and is threadedly connected to the original nut 105.

[0003] The specific installation steps are: after removing the replacement four-way joint, hoist the upper casing head on the large hook lifting equipment. Specifically, during hoisting, step one: first, pass two or four of the original bolts 100 (symmetrically arranged) through the upper end of the upper threaded part 102 from bottom to top through the flange hole of the upper casing head, and then install the original head 101 on the upper threaded part 102; step two: gradually move the upper casing head downward. As the upper casing head moves downward, the lower end of the original bolt 100 can be inserted into the flange hole of the lower casing head, thereby ensuring that the installation positions of the upper and lower casing heads are correct on the one hand, and on the other hand, the flange hole of the lower casing head can also guide the original bolt 100, thereby ensuring that the upper casing head descends vertically, avoiding the cut casing 200 hanging in the lower casing head from squeezing the BT sealing ring when entering the interior of the upper casing head.

[0004] However, in reality, the original bolt 100 is not fixed in the flange hole of the upper casing head, resulting in its instability. When it is subjected to upward pressure (friction generated by the side wall of the flange hole of the lower casing head), it will move upward to a certain extent, causing the entire rod 103 to be unstable during guidance, resulting in the opportunity for the cut casing 200 to squeeze the BT sealing ring, which may damage the BT sealing ring.

[0005] In addition, if the rod 103 is fixed to the flange hole of the upper casing head by threading the rod 103 to the flange hole of the upper casing head, the rod 103 will rely on the preload of the nut and the threaded hole, which may cause an imbalance in the load distribution between the two sections. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention provides a split two-stage casing head specifically for oil wells, which solves the problem in the prior art that the rod portion is unstable during guidance.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions: a split two-stage oil well casing head, comprising a first-stage casing head, first-stage flanges located at both ends of the first-stage casing head, a second-stage casing head, and second-stage flanges located at both ends of the second-stage casing head, wherein the lower second-stage flange is connected to the upper first-stage flange, and further comprising:

[0008] A limiting groove is provided in an area of ​​the upper surface of the secondary flange opposite to two of the flange holes, and the diameter of the limiting groove is larger than the diameter of the flange holes;

[0009] A limit head is located in the limit slot, and a lifting spring is provided between the lower end of the limit head and the bottom of the limit slot, and the lifting spring can push the limit head upward;

[0010] A guide connector, the guide connector comprising a bolt head, a thickened threaded portion, a bolt shank, a threaded portion 1, and an extended portion arranged in sequence from top to bottom, the thickened threaded portion being threadedly connected to the limit head, and the bolt shank being located in the flange hole;

[0011] The extension portion can be inserted into the flange hole of the primary flange during the process of hoisting and lowering the secondary casing head to the primary casing head after disassembling the replacement spool, thereby playing a role in straightening the secondary casing head;

[0012] The elastic force release structure is used to release the upward elastic force of the lifting spring on the limit head after the threaded part is installed with the nut.

[0013] Furthermore, the limiting head can slide axially in the secondary flange, and the lower end of the limiting head is limited in the limiting groove;

[0014] A ring groove 1 is provided at the lower end of the limit head, and the upper end of the lifting spring is arranged in the ring groove 1;

[0015] The elastic force release structure is used to control the relative position of the lifting spring and the ring groove one, so that the relative position of the lifting spring and the ring groove one has two states. State one is that the upper end limit of the lifting spring is located at the lower end of the ring groove, and state two is that the upper end limit of the lifting spring is located at the upper end of the ring groove one.

[0016] Furthermore, an upper spring seat is fixedly provided at the upper end of the lifting spring, and the upper spring seat is located in the first ring groove. A lower spring seat is provided at the lower end of the lifting spring, and a second ring groove is provided at the bottom of the limiting groove, and the lower spring seat is fixed in the second ring groove.

[0017] Furthermore, the elastic force release structure includes: pressure threaded holes are opened in the areas opposite to the ring groove on both sides of the upper end of the limit head, a pressure rod is provided in the pressure threaded hole, and the lower end of the pressure rod is a threaded part 2, which is threadedly connected to the pressure threaded hole, so that the pressure rod can move axially when it rotates to adjust the descending height of the pressure rod, so that the pressure rod can press down the upper spring seat to different degrees.

[0018] Furthermore, an insertion hole is provided on the bolt head in the axial direction for accommodating a pressure rod, and the upper end of the pressure rod is exposed on the upper end surface of the bolt head.

[0019] Furthermore, a rotatable rotating cylinder is provided in the annular groove, and a guide rail is provided on the inner wall of the rotating cylinder. The guide rail includes a flat groove located below the inner wall of the rotating cylinder and an inclined groove located above the flat groove. A lifting block is provided on the arc surface of the upper spring seat, and the lifting block is located in the guide rail.

[0020] Furthermore, a handle is fixedly provided on one side of the upper end of the rotating cylinder, a compensation groove 1 is provided on the area of ​​the limit head opposite to the handle, and a compensation groove 2 is provided on the area of ​​the bolt head opposite to the handle.

[0021] Furthermore, when the limit head is fully pressed down into the secondary flange, the height of the upper surface of the limit head is no higher than the upper surface of the secondary flange.

[0022] Furthermore, sliders are provided at the lower ends of both sides of the limit head, and guide grooves are provided in the area of ​​the inner wall of the secondary flange opposite to the sliders. The upper ends of the guide grooves are sealing structures that can limit the sliders from detaching upward from the secondary flange.

[0023] Furthermore, the remaining flange holes of the primary flange and the secondary flange are connected by flange bolts.

[0024] The present invention has the following beneficial effects:

[0025] The nut is then tightened to the stopper, and the guide connector is inserted into the flange hole of the primary flange before the secondary casing head is lowered, and the thickened threaded portion is fixed on the limit head. As a result, when the secondary casing head is lowered and moved downward, the guide connector can enter the flange hole of the primary flange, thereby guiding the lowering of the secondary casing head, ensuring that the secondary casing head falls vertically, and preventing the cut casing in the primary casing head from squeezing the BT sealing ring. Furthermore, after the two casing heads are aligned and the nuts are assembled, the elastic force of the lifting spring can be eliminated, so that the bolt head, the limit head and the thickened threaded portion form an integrated structure. The three are integrated as a bolt head in the prior art. In this way, even if the pre-tightening force of the nut and the threaded portion, and the pre-tightening force of the thickened threaded portion and the limit head are different, there will be no imbalance in the load distribution between the two sections, thereby ensuring the sealing effect of the flange.

[0026] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of a double-stage casing head in the prior art;

[0028] Figure 2 It is an overall diagram of the present invention;

[0029] Figure 3 This is a schematic diagram of the guide connector connecting the primary flange and the secondary flange in the first embodiment of the present invention;

[0030] Figure 4 This is a cross-sectional view of the connection between the guide fitting and the secondary flange in the first embodiment of the present invention (the lifting spring lifts the limit head);

[0031] Figure 5 This is a diagram showing the state in which the secondary casing head is hoisted above the primary casing head and the guide connector is inserted;

[0032] Figure 6 This is an exploded view of the guide fitting in the first embodiment of the present invention;

[0033] Figure 7 This is a diagram showing the position of the lifting spring in the limiting groove in the first embodiment of the present invention;

[0034] Figure 8 Schematic diagram of the structure of the guide connector in the first embodiment of the present invention;

[0035] Figure 9 This is an exploded view of the bolt shank and extension portion in Example 1 of the present invention;

[0036] Figure 10 This is a diagram showing the state in which the secondary casing head is hoisted above the primary casing head according to the present invention;

[0037] Figure 11 A diagram showing a state in which the secondary casing head is continuously moved downward and guided by a guide fitting according to the present invention;

[0038] Figure 12 This is a diagram showing the state of the secondary casing head and the primary casing head being aligned with each other according to the present invention;

[0039] Figure 13 This is a state diagram after the extension portion of the present invention is disassembled;

[0040] Figure 14 This is a state diagram after the nut is assembled according to the present invention;

[0041] Figure 15This is a diagram showing the state in which the pressure rod releases pressure on the upper spring seat in the first embodiment of the present invention;

[0042] Figure 16 For the present invention Figure 15 Stereoscopic image of

[0043] Figure 17 This is a schematic diagram of the installation of the guide connector on the secondary flange in the second embodiment of the present invention;

[0044] Figure 18 This is a schematic diagram of the lifting spring lifting the limit head in the second embodiment of the present invention;

[0045] Figure 19 This is a diagram showing the relative positions of the lifting spring and the limiting head of the present invention;

[0046] Figure 20 For the present invention Figure 19 Exploded diagram of .

[0047] In the figure, 100, original bolt; 101, original head; 102, upper threaded portion; 103, rod; 104, lower threaded portion; 105, original nut; 1, flange bolt; 200, casing; 3, primary casing head; 31, primary flange; 4, secondary casing head; 41, secondary flange; 411, limiting groove; 412, guide groove; 413, annular groove 2; 5, guide connector; 51, bolt head; 511, socket; 512, compensation groove 2; 52, bolt rod; 53, threaded portion 1; 54, Nut; 55, thickened threaded portion; 56, extended portion; 561, connector; 6, guide fitting; 61, limit head; 611, pressure threaded hole; 612, ring groove one; 613, compensation groove one; 614, threaded cavity; 62, lifting spring; 63, upper spring seat; 64, lower spring seat; 65, pressure rod; 651, hexagonal head; 652, threaded portion two; 66, slider; 67, handle; 68, rotating cylinder; 681, limit ring; 682, flat groove; 683, inclined groove; 69, lifting block. DETAILED DESCRIPTION

[0048] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0049] In the description of the present invention, it should be understood that the terms "opening", "upper", "lower", "thickness", "top", "middle", "length", "inside", "around" and the like indicating orientation or positional relationship are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the components or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0050] The following is based on Figures 1-20 The present invention provides a split double-stage casing head specifically for oil wells.

[0051] Example 1:

[0052] See also Figure 2-Figure 4 As shown, an embodiment of the present invention provides a split-type two-stage oil well casing head, which includes the following components:

[0053] The primary casing head 3 and the primary flanges 31 located at both ends of the primary casing head 3 .

[0054] The secondary casing head 4 and the secondary flanges 41 at both ends of the secondary casing head 4 , the lower secondary flange 41 is connected to the upper primary flange 31 , so that the primary casing head 3 and the secondary casing head 4 can be connected.

[0055] The flange bolt 1 is used to connect the flange holes of the primary flange 31 and the secondary flange 41 . The flange bolt 1 here is the original bolt 100 in the prior art.

[0056] The guide connector 5 is essentially a special flange bolt, which is used to be inserted into the flange hole of the primary flange 31 during the process of hoisting the secondary casing head 4 and moving it down to the primary casing head 3 after the replacement cross is disassembled, thereby playing the role of straightening the secondary casing head 4 and preventing the severed casing in the primary casing head 3 from squeezing the BT sealing ring due to the lack of a guide structure in the secondary casing head 4 during the process of hoisting the secondary casing head 4 down (the above-mentioned flange bolt 1 is used to connect the flange hole without the guide connector 5).

[0057] The guide fitting member 6 is used to cooperate with the guide connecting member 5 so that the guide connecting member 5 can perform a guiding operation.

[0058] like Figure 4Specifically, a limiting groove 411 is provided in an area on the upper surface of the secondary flange 41 opposite to two of the flange holes (the positions of the two flange holes should be symmetrical), the diameter of the limiting groove 411 is larger than the diameter of the flange hole, the guide fitting 6 includes a limiting head 61, a limiting head 61 is provided in the limiting groove 411, the limiting head 61 is limited to being able to move up and down only in the limiting groove 411, a lifting spring 62 is provided between the lower end of the limiting head 61 and the bottom of the limiting groove 411, the lifting spring 62 can lift the limiting head 61 upward to a state where the upper surface of the limiting head 61 is higher than the upper surface of the secondary flange 41, the guide connecting member 5 includes a bolt head 51, a thickened threaded portion 55, a bolt rod 52, a threaded portion 53 and an extension portion 56 arranged in sequence from top to bottom, and a threaded cavity 614 (such as Figure 6 ), the thickened threaded portion 55 is threadedly connected to the limiting head 61, as shown Figure 5 In the state shown, the lifting spring 62 lifts the limit head 61 and the guide connecting member 5 installed on the limit head 61 upward.

[0059] After the replacement cross is disassembled, the secondary casing head 4 is hoisted, and the thickened threaded portion 55 is threadedly installed on the limit head 61 on the secondary casing head 4. When the secondary casing head 4 is hoisted downward, the extended portion 56 can be inserted into the flange hole of the primary flange 31 during the process of moving down to the primary casing head 3, thereby playing a role in straightening the secondary casing head 4. Then, the entire guide connector 5 is pressed down, so that the guide connector 5 presses the limit head 61 down into the limit groove 411, and then the nut 54 is installed.

[0060] In order to avoid the above-mentioned lifting spring 62 always generating an upward elastic force on the limit head 61 and the bolt head 51 after the nut 54 is installed, resulting in instability of the entire guide fitting 6, an elastic force release structure is also provided here. The elastic force release structure is used to release the upward elastic force of the lifting spring 62 on the limit head 61 after the threaded part 53 is installed into the nut 54.

[0061] Therefore, although the split-type two-stage oil well special casing head provided in the embodiment of the present invention also has two sections of threads (thickened threaded portion 55 and threaded portion 1 53) on the bolt shank 52, the thickened threaded portion 55 is connected to the limit head 61. Even if the pre-tightening force of the thickened threaded portion 55 on the limit head 61 is different from the pre-tightening force of the threaded portion 1 53 on the nut 54, it will not affect the tight connection type of the two flanges and the sealing effect of the two. In addition, since the entire guide connector 5 is fixed on the secondary casing head 4, it also has good guiding performance, avoiding the situation where the severed casing squeezes the BT sealing ring due to the deviation of the secondary casing head 4 when the secondary casing head 4 is lowered, thereby avoiding the situation where the BT sealing ring is damaged due to the severed casing.

[0062] Preferably, the lower end of the above-mentioned limit head 61 is limited in the limit groove 411. Specifically, a slider 66 is provided at the lower end of both sides of the limit head 61, and a guide groove 412 is provided in the area of ​​the inner wall of the secondary flange 41 opposite to the slider 66. The upper end of the guide groove 412 is a sealing structure to limit the slider 66 from upwardly separating from the secondary flange 41, so as to avoid the extension part 56 being unstable due to the friction force of the flange hole of the primary casing head 3 when the secondary casing head 4 is hung down, thereby pushing the guide connecting part 5 upward.

[0063] In addition, the extension portion 56 mentioned here should be provided with a threaded connector 561, which is connected to the bolt rod portion 52 through the connector to facilitate its disassembly and assembly.

[0064] like Figure 7 As shown, preferably, the specific installation method of the above-mentioned lifting spring 62 is as follows: an annular groove 612 is provided at the lower end of the limiting head 61, and the upper end of the lifting spring 62 is arranged in the annular groove 612. The elastic force release structure is used to control the relative position of the lifting spring 62 and the annular groove 612, so that the relative position of the lifting spring 62 and the annular groove 612 has two states, state one is that the upper end of the lifting spring 62 is limited to the lower end of the annular groove 612, and state two is that the upper end of the lifting spring 62 is limited to the upper end of the annular groove 612.

[0065] Before the secondary casing head 4 is hoisted and moved downward, the lifting spring 62 is in state one, with its upper end located at the lower end of the annular groove 1 612. After the hoisting and moving downward is completed and the nut 54 is assembled on the guide connector 5, the lifting spring 62 is controlled to be in the second state through the elastic release structure, thereby preventing the lifting spring 62 from generating upward stress on the guide connector 5 and affecting the connection performance of the guide connector 5 to the secondary flange 41 and the primary flange 31.

[0066] Preferably, an upper spring seat 63 is fixedly provided at the upper end of the lifting spring 62, and the upper spring seat 63 is located in the annular groove 1 612. A lower spring seat 64 is provided at the lower end of the lifting spring 62, and an annular groove 2 413 is provided at the bottom of the limiting groove 411, and the lower spring seat 64 is fixed in the annular groove 2 413.

[0067] The elastic force release structure mentioned above includes the following: pressure threaded holes 611 are opened in the areas opposite to the ring groove 1 612 on both sides of the upper end of the limit head 61, and a pressure rod 65 is provided in the pressure threaded hole 611. The lower end of the pressure rod 65 is a threaded portion 2 652, and the threaded portion 2 652 is threadedly connected to the pressure threaded hole 611, so that the pressure rod 65 can move axially when it rotates, so as to adjust the descending height of the pressure rod 65, so that the pressure rod 65 presses down the upper spring seat 63 to different degrees.

[0068] In addition, in order to facilitate the operation of the pressure rod 65, an axially provided socket 511 is provided on the bolt head 51 to accommodate the pressure rod 65. The upper end of the pressure rod 65 is exposed on the upper end surface of the bolt head 51. The upper end of the pressure rod 65 is a hexagonal head 651, which facilitates the rotation of the pressure rod 65.

[0069] When using (working) it is as follows:

[0070] Step 1: Disassemble and replace the four-way pipe, and hoist the secondary casing head 4 above the primary casing head 3 to form Figure 10 The status shown;

[0071] Step 2: Pass the bolt shank 52 through the threaded cavity 614 and rotate the bolt head 51 so that the thickened threaded portion 55 is threadedly connected in the threaded cavity 614 to form a Figure 5 The status shown;

[0072] Step 3: Continue to move the secondary casing head 4 downwards, so that the extension portion 56 gradually passes through the flange hole of the primary casing head 3, referring to Figure 11 The state reaches Figure 12 Status;

[0073] Step 4: Remove the extension 56 to form Figure 13 The status shown;

[0074] Step 5: Press down the bolt head 51 to make the limiting head 61 enter the limiting groove 411, and assemble the nut 54 to the bolt rod 52 to form Figure 14 state (when the limiting head 61 is fully pressed down into the limiting groove 411, the height of the upper surface of the limiting head 61 is not higher than the upper surface of the secondary flange 41, that is, the axial length of the limiting groove 411 is greater than the axial length of the limiting head 61);

[0075] Step 6: Figure 14 In the state shown, rotate the hexagonal head 651 to make the upper end of the lifting spring 62 reach the inner upper end of the ring groove 612 to release the elastic force, forming Figure 15 and Figure 16 The status shown.

[0076] Therefore, the split two-stage oil well special casing head provided by the present invention has a guide connector 5 as a special bolt inserted into the flange hole on the secondary flange 41 before the secondary casing head 4 is lowered, and the thickened threaded portion 55 is fixed on the limit head 61, so that when the secondary casing head 4 is lowered and moved downward, the extended portion 56 can enter the flange hole of the primary flange 31, thereby guiding the lowering of the secondary casing head 4, ensuring that the secondary casing head 4 falls vertically, and avoiding the casing inside the primary casing head 3 being cut off. 200 pairs of BT sealing rings are squeezed; furthermore, after the two sleeve heads are matched and the nut 54 is assembled, the elastic force of the lifting spring 62 can be eliminated, so that the bolt head 51, the limit head 61 and the thickened threaded portion 55 form an integrated structure at this time. After the three are integrated into one, they serve as the bolt head in the prior art. In this way, even if the pre-tightening force of the nut 54 and the threaded portion 53, and the pre-tightening force of the thickened threaded portion 55 and the limit head 61 are different, there will be no imbalance in the load distribution between the two sections.

[0077] Example 2:

[0078] Reference Figures 17-20 As shown, the difference between this embodiment and the first embodiment is that the elastic force release structure includes the following: a rotatable rotating cylinder 68 is provided in the annular groove 1 612, and a guide rail is provided on the inner wall of the rotating cylinder 68. The guide rail includes a flat groove 682 located below the inner wall of the rotating cylinder 68 and an inclined groove 683 located above the flat groove 682. A lifting block 69 is provided on the arc surface of the upper spring seat 63, and the lifting block 69 is located in the guide rail. When the lifting block 69 is located in the flat groove 682, it is blocked by the flat groove 682, and the upper spring seat 63 is located in the annular groove 1. The lower end of 612, that is, the lifting spring 62 is in a state of being able to lift the limit head 61. Conversely, when the rotating cylinder 68 is rotated, the lifting block 69 loses the obstruction of the flat groove 682 and enters the inclined groove 683, so that the lifting spring 62 can rebound, allowing the upper spring seat 63 to enter the upper end of the inner part of the annular groove 612; conversely, when the rotating cylinder 68 is rotated in the opposite direction, the inclined groove 683 pushes the lifting block 69 to descend and enter the inner part of the flat groove 682, so that the upper end of the upper spring seat 63 can also return to the lower end of the annular groove 612.

[0079] Preferably, in order to facilitate manual rotation of the rotating cylinder 68, a handle 67 is fixed on one side of the upper end of the rotating cylinder 68, a compensation groove 1 613 is opened in the area opposite to the handle 67 on the limit head 61, and a compensation groove 2 512 is opened in the area opposite to the handle 67 on the bolt head 51, so that the handle 67 can be operated outside the bolt head 51.

[0080] Preferably, a vertical track is provided on the inner side wall of the annular groove 1 612 , and a sliding block cooperating with the vertical track is provided on the inner wall of the upper spring seat 63 to ensure the vertical movement of the upper spring seat 63 .

[0081] Preferably, a limiting ring 681 is provided on the outer surface of the rotating cylinder 68 to limit it inside the ring groove 1 612 .

Claims

1. A split double-stage oil well casing head, comprising a first-stage casing head (3), first-stage flanges (31) located at both ends of the first-stage casing head (3), a second-stage casing head (4), and second-stage flanges (41) located at both ends of the second-stage casing head (4), wherein the lower second-stage flange (41) is connected to the upper first-stage flange (31), and is characterized in that: Also includes: A limiting groove (411), wherein the limiting groove (411) is provided in an area of ​​the upper surface of the secondary flange (41) opposite to two flange holes, and the diameter of the limiting groove (411) is larger than the diameter of the flange holes; A limiting head (61), the limiting head (61) is located in the limiting groove (411), and a lifting spring (62) is provided between the lower end of the limiting head (61) and the bottom of the limiting groove (411), and the lifting spring (62) can push the limiting head (61) upward; A guide connecting member (5), the guide connecting member (5) comprising a bolt head (51), a thickened threaded portion (55), a bolt shank (52), a first threaded portion (53) and an extended portion (56) arranged in sequence from top to bottom, the thickened threaded portion (55) being threadedly connected to the limiting head (61), and the bolt shank (52) being located in the flange hole; The extension portion (56) can be inserted into the flange hole of the primary flange (31) during the process of hoisting and lowering the secondary casing head (4) to the primary casing head (3) after disassembling the replacement cross; An elastic force release structure is used to release the upward elastic force of the lifting spring (62) on the limit head (61) after the threaded portion (53) is installed into the nut (54).

2. The split-type two-stage oil well casing head according to claim 1, characterized in that: The limiting head (61) is capable of axially sliding in the secondary flange (41), and the lower end of the limiting head (61) is limited in the limiting groove (411); The lower end of the limiting head (61) is provided with an annular groove (612), and the upper end of the lifting spring (62) is arranged in the annular groove (612); The elastic force release structure is used to control the relative position of the lifting spring (62) and the annular groove (612), so that the relative position of the lifting spring (62) and the annular groove (612) has two states, state one is that the upper end of the lifting spring (62) is limited to the lower end of the annular groove (612), and state two is that the upper end of the lifting spring (62) is limited to the upper end of the annular groove (612).

3. The split-type two-stage oil well casing head according to claim 2, characterized in that: An upper spring seat (63) is fixedly provided at the upper end of the lifting spring (62), and the upper spring seat (63) is located in the annular groove 1 (612). A lower spring seat (64) is provided at the lower end of the lifting spring (62), and an annular groove 2 (413) is provided at the bottom of the limiting groove (411), and the lower spring seat (64) is fixed in the annular groove 2 (413).

4. The split-type two-stage oil well casing head according to claim 3, characterized in that: The elastic force release structure includes: pressure threaded holes (611) are opened in the areas opposite to the annular groove 1 (612) on both sides of the upper end of the limit head (61), a pressure rod (65) is provided in the pressure threaded hole (611), the lower end of the pressure rod (65) is a threaded portion 2 (652), the threaded portion 2 (652) is threadedly connected to the pressure threaded hole (611), and the pressure rod (65) can press down the upper spring seat (63) to varying degrees.

5. The split-type two-stage oil well casing head according to claim 4, characterized in that: The bolt head (51) is provided with an insertion hole (511) along the axial direction for accommodating a pressure rod (65), and the upper end of the pressure rod (65) is exposed on the upper end surface of the bolt head (51).

6. The split-type two-stage oil well casing head according to claim 3, characterized in that: The elastic force release structure includes: a rotatable rotating cylinder (68) is provided in the annular groove (612), a guide rail is provided on the inner wall of the rotating cylinder (68), and the guide rail includes a flat groove (682) located below the inner wall of the rotating cylinder (68) and an inclined groove (683) located above the flat groove (682); a lifting block (69) is provided on the arc surface of the upper spring seat (63), and the lifting block (69) is located in the guide rail.

7. The split-type two-stage oil well casing head according to claim 6, characterized in that: A handle (67) is fixedly provided on one side of the upper end of the rotating cylinder (68), a compensation groove 1 (613) is provided on the area of ​​the limiting head (61) opposite to the handle (67), and a compensation groove 2 (512) is provided on the area of ​​the bolt head (51) opposite to the handle (67).

8. The split-type two-stage special casing head for oil wells according to any one of claims 2 to 7, characterized in that: When the limiting head (61) is completely pressed down into the secondary flange (41), the height of the upper surface of the limiting head (61) is no higher than the upper surface of the secondary flange (41).

9. The split-type two-stage oil well casing head according to claim 8, characterized in that: Slide blocks (66) are provided at the lower ends of both sides of the limit head (61), and a guide groove (412) is provided in the area of ​​the inner wall of the secondary flange (41) opposite to the slide blocks (66). The upper end of the guide groove (412) is a sealing structure that can limit the slide blocks (66) from detaching upward from the secondary flange (41).

10. The split-type two-stage oil well casing head according to claim 1, characterized in that: The primary flange (31) and the remaining flange holes of the secondary flange (41) are connected via flange bolts (1).

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