Split type two-stage casing head special for oil well

Abstract

The invention discloses a split type two-stage casing head special for an oil well, and relates to the technical field of casing heads. The split type double-stage casing head special for the oil well comprises a first-stage casing head, first-stage flanges located at the two ends of the first-stage casing head, a second-stage casing head and second-stage flanges located at the two ends of the second-stage casing head, and further comprises a limiting groove, a first-stage flange and a second-stage flange, the limiting groove is formed in the area, opposite to two flange holes, of the upper surface of the secondary flange, and the diameter of the limiting groove is larger than that of the flange holes; the limiting head is located in the limiting groove, a jacking spring is arranged between the lower end of the limiting head and the groove bottom of the limiting groove, and the jacking spring can jack the limiting head upwards; according to the device, it is guaranteed that the second-stage casing head vertically falls, and a cut casing in the first-stage casing head is prevented from extruding a BT sealing ring; and the condition of unbalanced load distribution of the two sections is avoided, and the sealing effect of the flange is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of casing heads, and specifically provides a split-type double-stage special casing head for oil wells. Background Art

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

[0003] The specific installation steps are as follows. After removing the replacement cross, hoist the upper casing head with a hook hoisting device. Specifically, during hoisting, Step 1: First, pass two or four of the original bolts 100 (symmetrically arranged) from bottom to top through the flange holes of the upper casing head through the upper ends of the upper thread portions 102, and then install the original head 101 on the upper thread portion 102; Step 2: 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. Thus, on the one hand, it can ensure the correct installation positions of the upper and lower casing heads, and on the other hand, the flange hole of the lower casing head can also guide the original bolt 100, so as to ensure the vertical descent of the upper casing head and prevent the cut casing 200 seated in the lower casing head from squeezing and damaging the BT seal ring when entering the upper casing head.

[0004] However, in essence, the original bolt 100 is not fixed in the flange hole of the upper casing head, resulting in instability. When it is subjected to an upward pressure (the frictional force 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 portion 103 to be unstable during guiding, so that the cut casing 200 has the opportunity to squeeze the BT seal ring and may damage the BT seal ring.

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

[0006] Aiming at the deficiencies of the prior art, the present invention provides a split-type double-stage special casing head for oil wells, which solves the problem that the rod portion is unstable during guiding in the prior art.

[0007] To achieve the above object, the present invention is realized through the following technical solutions: A split-type double-stage special casing head for oil wells, including 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. The second-stage flange below is connected to the first-stage flange above. It further includes: A limiting groove, which is opened in the area of the upper surface of the second-stage flange opposite to two of the flange holes. The diameter of the limiting groove is larger than the diameter of the flange hole; A limiting head, which is located in the limiting groove. There is a jacking spring between the lower end of the limiting head and the bottom of the limiting groove, and the jacking spring can jack the limiting head upward; A guiding connecting piece, which includes a bolt head, a thickened threaded part, a bolt rod part, a first threaded part, and an extended part arranged in sequence from top to bottom. The thickened threaded part is threadedly connected to the limiting head, and the bolt rod part is located in the flange hole; The extended part can be inserted into the flange hole of the first-stage flange during the process of hoisting and lowering the second-stage casing head to the first-stage casing head after the replacement of the cross joint, playing a role in straightening the second-stage casing head; A elastic force release structure, which is used to release the upward elastic force of the jacking spring on the limiting head after the first threaded part is fitted with a nut.

[0008] Further, the limiting head can axially slide within the second-stage flange, and the lower end of the limiting head is limited within the limiting groove; A first annular groove is opened at the lower end of the limiting head, and the upper end of the jacking spring is arranged within the first annular groove; The elastic force release structure is used to control the relative position between the jacking spring and the first annular groove, so that the relative position between the jacking spring and the first annular groove has two states. State one is that the upper end of the jacking spring is limited at the lower end of the first annular groove, and state two is that the upper end of the jacking spring is limited at the upper end of the first annular groove.

[0009] Further, an upper spring seat is fixedly arranged at the upper end of the jacking spring. The upper spring seat is located within the first annular groove. A lower spring seat is arranged at the lower end of the jacking spring. A second annular groove is arranged at the bottom of the limiting groove, and the lower spring seat is fixed within the second annular groove.

[0010] Further, the elastic force release structure includes: Pressure threaded holes are opened in the areas on both sides of the upper end of the limiting head opposite to the first annular groove. Pressure rods are arranged within the pressure threaded holes. The lower end of the pressure rod is a second threaded part, and the second threaded part is threadedly connected to the pressure threaded hole, so that the pressure rod can axially move itself when rotating to adjust the descending height of the pressure rod, so that the pressure rod can press the upper spring seat to different degrees.

[0011] Further, an insertion hole is axially opened on the bolt head for accommodating the pressure rod, and the upper end of the pressure rod is exposed on the upper end surface of the bolt head.

[0012] Further, a rotatable rotary cylinder is provided in the first annular groove. A guide rail is provided on the inner wall of the rotary cylinder. The guide rail includes a flat groove located below the inner wall of the rotary 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.

[0013] Further, a handle is fixedly provided on one side of the upper end of the rotary cylinder. A first compensation groove is provided in the area of the limit head opposite to the handle. A second compensation groove is provided in the area of the bolt head opposite to the handle.

[0014] Further, when the limit head is completely pressed down into the second-level flange, the height of the upper surface of the limit head is not higher than the upper surface of the second-level flange.

[0015] Further, sliders are provided at both lower ends of the limit head. Guide grooves are provided in the areas of the inner wall of the second-level flange opposite to the sliders. The upper ends of the guide grooves are of a sealed structure, which can limit the sliders from disengaging upward from the second-level flange.

[0016] Further, the first-level flange and the remaining flange holes of the second-level flange are connected by flange bolts.

[0017] The present invention has the following beneficial effects: For this split-type double-stage oil well special casing head, before the second-stage casing head is lifted and lowered, as a guiding connecting piece of a special bolt, it is inserted into the flange hole on the second-level flange, and the thickened threaded part is fixed on the limit head. Thus, when the second-stage casing head is lifted and lowered and moves downward, the guiding connecting piece can enter the flange hole of the first-level flange, and further guide the lifting and lowering of the second-stage casing head, ensuring that the second-stage casing head falls vertically, and avoiding the cut casing in the first-level casing head from squeezing the BT sealing ring; furthermore, after the two casing heads are aligned and the nut is assembled, the elastic force of the jacking spring can be eliminated. Thus, at this time, the bolt head, the limit head, and the thickened threaded part form an integral structure. After the three are integrated, they serve as the bolt head in the prior art. In this way, even if the pre-tightening force between the nut and the first threaded part and the pre-tightening force between the thickened threaded part and the limit head are different, the situation of unbalanced load distribution in two sections will not occur, ensuring the sealing effect of the flange.

[0018] Of course, it is not necessary for any product implementing the present invention to achieve all the above-mentioned advantages simultaneously. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of a double-stage casing head in the prior art; Figure 2 It is an overall view of the present invention; Figure 3 It is a schematic diagram of the guiding connecting piece connecting the first-level flange and the second-level flange in the first embodiment of the present invention; Figure 4 Cross-sectional view of the connection between the guiding fitting and the secondary flange in the first embodiment of the present invention (when the jacking spring jacks up the limiting head); Figure 5 State diagram of hoisting the secondary casing head above the primary casing head and inserting it into the guiding connecting member in the present invention; Figure 6 Exploded view of the guiding fitting in the first embodiment of the present invention; Figure 7 Position diagram of the jacking spring in the limiting groove in the first embodiment of the present invention; Figure 8 Structural schematic diagram of the guiding connecting member in the first embodiment of the present invention; Figure 9 Exploded view of the bolt rod part and the lengthening part in the first embodiment of the present invention; Figure 10 State diagram of hoisting the secondary casing head above the primary casing head in the present invention; Figure 11 State diagram of continuously lowering the secondary casing head and guiding it with the guiding fitting in the present invention; Figure 12 State diagram of aligning the secondary casing head with the primary casing head in the present invention; Figure 13 State diagram after disassembling the lengthening part in the present invention; Figure 14 State diagram after assembling the nut in the present invention; Figure 15 State diagram of the pressure rod releasing pressure on the upper spring seat in the first embodiment of the present invention; Figure 16 For the present invention Figure 15 Three-dimensional view; Figure 17 Installation schematic diagram of the guiding connecting member on the secondary flange in the second embodiment of the present invention; Figure 18 Schematic diagram of the jacking spring jacking up the limiting head in the second embodiment of the present invention; Figure 19 Relative position diagram of the jacking spring and the limiting head in the present invention; Figure 20 For the present invention Figure 19 Exploded view.

[0020] In the figure, 100 is the original bolt; 101 is the original head; 102 is the upper threaded part; 103 is the rod part; 104 is the lower threaded part; 105 is the original nut; 1 is the flange bolt; 200 is the sleeve; 3 is the first-stage casing head; 31 is the first-stage flange; 4 is the second-stage casing head; 41 is the second-stage flange; 411 is the limiting groove; 412 is the guiding groove; 413 is the second annular groove; 5 is the guiding connecting part; 51 is the bolt head; 511 is the jacking hole; 512 is the second compensation groove; 52 is the bolt rod part; 53 is the first threaded part; 54 is the nut; 55 is the thickened threaded part; 56 is the lengthened part; 561 is the connecting head; 6 is the guiding and fitting part; 61 is the limiting head; 611 is the pressure threaded hole; 612 is the first annular groove; 613 is the first compensation groove; 614 is the threaded cavity; 62 is the jacking spring; 63 is the upper spring seat; 64 is the lower spring seat; 65 is the pressure rod; 651 is the hexagonal head; 652 is the second threaded part; 66 is the sliding block; 67 is the handle; 68 is the rotating cylinder; 681 is the limiting ring; 682 is the flat groove; 683 is the inclined groove; 69 is the lifting block. Detailed implementation mode

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0022] In the description of the present invention, it should be understood that the terms "open hole", "upper", "lower", "thickness", "top", "middle", "length", "inner", "periphery", etc. indicating the orientation or position relationship are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the components or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present invention.

[0023] Next, according to Figures 1 - 20 Describe the split-type double-stage oil well special casing head provided by the embodiment of the present invention.

[0024] Embodiment 1: Please refer to Figures 2 - 4 As shown, the embodiment of the present invention provides a split-type double-stage oil well special casing head, which includes the following components: The first-stage casing head 3 and the first-stage flange 31 located at both ends of the first-stage casing head 3.

[0025] The second-stage casing head 4 and the second-stage flange 41 located at both ends of the second-stage casing head 4. The lower second-stage flange 41 is connected to the upper first-stage flange 31, so that the first-stage casing head 3 and the second-stage casing head 4 can be connected.

[0026] Flange bolt 1 is used to connect the flange holes of the first-stage flange 31 and the second-stage flange 41. Here, the flange bolt 1 is the original bolt 100 in the prior art.

[0027] Guide connecting piece 5 is essentially a special flange bolt. It is used to insert into the flange hole of the first-stage flange 31 during the process of hoisting the second-stage casing head 4 down to the first-stage casing head 3 after the replacement four-way is disassembled, so as to play a role in straightening the second-stage casing head 4 and avoid the casing cut in the first-stage casing head 3 squeezing the BT sealing ring due to the lack of a guiding structure for the second-stage casing head 4 during the process of hoisting the second-stage casing head 4 down (the above flange bolt 1 is used to connect the flange holes without the guide connecting piece 5 installed).

[0028] Guide fitting 6 is used to cooperate with the guide connecting piece 5 to enable the guide connecting piece 5 to perform guiding operations.

[0029] Such as Figure 4 , specifically, a limit groove 411 is opened in the area of the upper surface of the second-stage flange 41 opposite to two of its flange holes (the positions of these two flange holes should be symmetrical). The diameter of the limit groove 411 is larger than the diameter of the flange hole. The guide fitting 6 includes a limit head 61. The limit head 61 is arranged in the limit groove 411 and is limited to move up and down only within the limit groove 411. A jacking spring 62 is provided between the lower end of the limit head 61 and the bottom of the limit groove 411. The jacking spring 62 can jack the limit head 61 upward to a state where the upper surface of the limit head 61 is higher than the upper surface of the second-stage flange 41. The guide connecting piece 5 includes a bolt head 51, a thickened thread part 55, a bolt rod part 52, a first thread part 53, and an extended part 56 arranged in sequence from top to bottom. A thread cavity 614 is opened at the center of the limit head 61 (such as Figure 6 ), and the thickened thread part 55 is threadedly connected to the inside of the limit head 61. As in Figure 5 the shown state, at this time, the jacking spring 62 jacks the limit head 61 and the guide connecting piece 5 installed on the limit head 61 upward.

[0030] After the replacement four-way is disassembled, the second-stage casing head 4 is hoisted, and the thickened thread part 55 is threadedly installed on the limit head 61 on the second-stage casing head 4. When the second-stage casing head 4 is hoisted downward, the extended part 56 can insert into the flange hole of the first-stage flange 31 during the process of moving down to the first-stage casing head 3, playing a role in straightening the second-stage casing head 4. Subsequently, the entire guide connecting piece 5 is pressed down, so that the guide connecting piece 5 presses the limit head 61 into the limit groove 411, and then the nut 54 is installed.

[0031] In order to avoid the instability of the entire guiding fitting 6 caused by the upward elastic force constantly exerted by the above-mentioned lifting spring 62 on the limiting head 61 and the bolt head 51 after the nut 54 is installed, a 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 limiting head 61 after the threaded part 53 is inserted into the nut 54.

[0032] Therefore, for the split-type double-stage oil well special casing head provided in the embodiment of the present invention, although two sections of threads (the thickened threaded part 55 and the threaded part 53) are also provided on the bolt rod part 52, the thickened threaded part 55 is connected to the limiting head 61. Even if the pre-tightening force of the thickened threaded part 55 on the limiting head 61 is different from the pre-tightening force of the threaded part 53 on the nut 54, it will not affect the connection tightness of the two flanges and will not affect their sealing effect. In addition, since the entire guiding connecting piece 5 is fixed on the second-stage casing head 4, it also has good guiding performance, avoiding the situation where the BT seal ring is damaged due to the squeezing of the cut casing on the BT seal ring caused by the deviation of the second-stage casing head 4 when the second-stage casing head 4 is lowered.

[0033] Preferably, the lower end of the above-mentioned limiting head 61 is limited in the limiting groove 411. Specifically, sliding blocks 66 are provided at both lower ends of the limiting head 61, and guiding grooves 412 are provided in the area of the inner wall of the second-stage flange 41 opposite to the sliding blocks 66. The upper end of the guiding groove 412 is a sealed structure to limit the upward detachment of the sliding blocks 66 from the second-stage flange 41, avoiding the instability of the lengthening part 56 caused by the upward pushing of the guiding connecting piece 5 by the lengthening part 56 under the action of the frictional force of the flange hole of the first-stage casing head 3 when the second-stage casing head 4 is lowered.

[0034] In addition, a threaded connection head 561 should be provided at the lengthening part 56 mentioned here, and it is connected to the bolt rod part 52 through a connecting part to facilitate its disassembly and assembly.

[0035] As Figure 7 shown, preferably, the specific installation method of the above-mentioned lifting spring 62 is as follows: a first annular groove 612 is opened at the lower end of the limiting head 61, the upper end of the lifting spring 62 is arranged in the first annular groove 612, and the elastic force release structure is used to control the relative position of the lifting spring 62 and the first annular groove 612, so that the relative position of the lifting spring 62 and the first annular groove 612 has two states. State one is that the upper end of the lifting spring 62 is limited at the lower end of the first annular groove 612, and state two is that the upper end of the lifting spring 62 is limited at the upper end of the first annular groove 612.

[0036] Before the second-stage casing head 4 is hoisted and lowered, the jacking spring 62 is in the first state, and its upper end is located at the lower end of the first annular groove 612. After the hoisting and lowering are completed and the nut 54 is assembled to the guiding connecting member 5, the jacking spring 62 is controlled to be in the second state through the elastic force releasing structure, so as to prevent the jacking spring 62 from generating an upward stress on the guiding connecting member 5 and affecting the connection performance of the guiding connecting member 5 to the second-stage flange 41 and the first-stage flange 31.

[0037] Preferably, an upper spring seat 63 is fixedly provided at the upper end of the jacking spring 62. The upper spring seat 63 is located in the first annular groove 612. A lower spring seat 64 is provided at the lower end of the jacking spring 62. An annular groove 413 is provided at the bottom of the limiting groove 411, and the lower spring seat 64 is fixed in the annular groove 413.

[0038] The above-mentioned elastic force releasing structure includes the following: Pressure threaded holes 611 are provided in the areas on both sides of the upper end of the limiting head 61 opposite to the first annular groove 612. Pressure rods 65 are provided in the pressure threaded holes 611. The lower end of the pressure rod 65 is a second threaded portion 652, and the second threaded portion 652 is threadedly connected to the pressure threaded hole 611, so that the pressure rod 65 can axially move itself when rotating to adjust the lowering height of the pressure rod 65 and press the upper spring seat 63 by different degrees.

[0039] In addition, in order to facilitate the operation of the pressure rod 65, an insertion hole 511 is axially provided on the bolt head 51 for accommodating 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 is convenient for rotating the pressure rod 65.

[0040] The usage (working) method is as follows: Step 1: Disassemble the replacement cross joint, and hoist the second-stage casing head 4 above the first-stage casing head 3 to form the Figure 10 state shown; Step 2: Pass the bolt rod portion 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 the Figure 5 state shown; Step 3: Continuously lower the second-stage casing head 4 so that the lengthened portion 56 gradually passes through the flange hole of the first-stage casing head 3, and reach the Figure 11 state with reference to the Figure 12 state; Step 4: Disassemble the lengthened portion 56 to form the Figure 13 state shown; Step 5: Press down the bolt head 51 to make the limiting head 61 enter the inside of the limiting groove 411, and assemble the nut 54 to the bolt rod portion 52 to form the Figure 14the state (when the limit head 61 is fully pressed down into the limit groove 411, the height of the upper surface of the limit head 61 is not higher than the upper surface of the secondary flange 41, that is, the axial length of the limit groove 411 is greater than the axial length of the limit head 61); Step Six: Figure 14 In the state shown, rotate the hexagonal head 651 so that the upper end of the jacking spring 62 reaches the inner upper end of the first annular groove 612 to release the elastic force, forming Figure 15 and Figure 16 the state shown.

[0041] Therefore, for the split-type double-stage special casing head for oil wells provided by the present invention, before the secondary casing head 4 is lowered, the guiding connecting piece 5 as a special bolt is inserted into the flange hole on the secondary flange 41, and the thickened threaded portion 55 is fixed on the limit head 61. Thus, when the secondary casing head 4 is lowered and moved down, the lengthening 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 extrusion of the cut casing 200 in the primary casing head 3 on the BT sealing ring. Moreover, after the two casing heads are aligned and the nut 54 is assembled, the elastic force of the jacking spring 62 can be eliminated. At this time, the bolt head 51, the limit head 61, and the thickened threaded portion 55 form an integral structure. After the three are integrated, they serve as the bolt head in the prior art. In this way, even if the pre-tightening forces between the nut 54 and the first threaded portion 53 and between the thickened threaded portion 55 and the limit head 61 are different, the situation of unbalanced load distribution in two segments will not occur.

[0042] Embodiment Two: Referring to Figures 17 - 20 shown, the difference between this embodiment and the first embodiment is that the above-mentioned elastic force release structure includes the following: A rotatable rotating cylinder 68 is provided in the first annular groove 612. 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, due to the blocking effect of the flat groove 682, the upper spring seat 63 is located at the lowermost end of the first annular groove 612, that is, the jacking spring 62 is in a state where it can jack up the limit head 61. On the contrary, when the rotating cylinder 68 is rotated, the lifting block 69 loses the blocking of the flat groove 682 and enters the inclined groove 683, so that the jacking spring 62 can rebound, enabling the upper spring seat 63 to enter the inner upper end of the first annular groove 612. On the contrary, when the rotating cylinder 68 is rotated in the reverse direction, the inclined groove 683 pushes the lifting block 69 to descend and enter the inside 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 first annular groove 612.

[0043] Preferably, in order to facilitate manual rotation of the rotary cylinder 68, a handle 67 is fixedly provided on one side of the upper end of the rotary cylinder 68. A first compensation groove 613 is formed in the region of the limit head 61 opposite to the handle 67, and a second compensation groove 512 is formed in the region of the bolt head 51 opposite to the handle 67, so that the handle 67 can be operated outside the bolt head 51.

[0044] Preferably, a vertical track is provided on the inner side wall of the first annular groove 612, and a sliding block cooperating with the vertical track is arranged on the inner wall of the upper spring seat 63 to ensure the vertical movement of the upper spring seat 63.

[0045] Preferably, a limit ring 681 is arranged on the outer surface of the rotary cylinder 68, so as to limit it inside the first annular groove 612.

Claims

1. A split double-stage casing head for oil wells, comprising a primary casing head (3), primary flanges (31) located at both ends of the primary casing head (3), a secondary casing head (4), and secondary flanges (41) located at both ends of the secondary casing head (4), wherein the lower secondary flange (41) is connected to the upper primary flange (31), and is characterized in that: Also includes: A limiting groove (411), wherein the limiting groove (411) is provided in a region of the upper surface of the secondary flange (41) opposite to two of the flange holes, and the diameter of the limiting groove (411) is greater than the diameter of the flange hole; A limiting head (61), wherein 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 in a stopper head (61), and the bolt shank (52) being located in a 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, wherein 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 portion (53) is installed into the nut (54).

2. The split double-stage oil well casing head according to claim 1 is 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); A first annular groove (612) is formed at the lower end of the limit head (61), and the upper end of the lifting spring (62) is arranged in the first 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 double-stage oil well casing head according to claim 2 is 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 first annular groove (612). A lower spring seat (64) is provided at the lower end of the lifting spring (62), and a second annular groove (413) is provided at the bottom of the limiting groove (411), and the lower spring seat (64) is fixed in the second annular groove (413).

4. The split double-stage oil well casing head according to claim 3 is characterized in that: The elastic force release structure comprises: pressure threaded holes (611) are provided in areas opposite to the first ring groove (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 second threaded portion (652); the second threaded portion (652) is threadedly connected to the pressure threaded hole (611); the pressure rod (65) can press down the upper spring seat (63) to varying degrees.

5. The split double-stage oil well casing head according to claim 4 is characterized in that: The bolt head (51) is provided with an insertion hole (511) in 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 double-stage oil well casing head according to claim 3, characterized in that: The elastic force release structure comprises: a rotatable rotating cylinder (68) is arranged in the annular groove (612); a guide rail is provided on the inner wall of the rotating cylinder (68); the guide rail comprises 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 casing head for oil wells 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 first compensation groove (613) is provided on the limiting head (61) in an area opposite to the handle (67); and a second compensation groove (512) is provided on the bolt head (51) in an area opposite to the handle (67).

8. A 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 double-stage casing head for oil wells 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 guide grooves (412) are provided in the area of ​​the inner wall of the secondary flange (41) opposite to the slide blocks (66). The upper ends of the guide grooves (412) are sealing structures capable of limiting the slide blocks (66) from detaching upward from the secondary flange (41).

10. The split double-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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