Sand blasting perforator for drilling well wall

Abstract

The invention relates to the technical field of oil well punching, in particular to a sand blasting perforator for well wall punching. According to the sand blasting perforator, the structure comprising the jet pipe and the expansion clamping part is designed, so that circumferential positioning and clamping of the jet pipe at an oil well perforating working position are achieved. And the expansion clamping part can be automatically butted, communicated and propped against the well wall under the action of gravity by utilizing the ingenious combination of two flow guide pipes and a plurality of hinge double connecting rods, so that the jet pipe is effectively prevented from shaking due to counter-acting force, and the punching precision and the working efficiency are greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of oil well drilling, in particular to a sandblasting perforator for drilling holes in a well wall. Background Art

[0002] The hydraulic sandblasting perforation technology uses a spray gun to spray water slurry mixed with abrasives (quartz sand, expanded clay, etc.) at high pressure and high speed to penetrate the near-well formation and form perforation holes to improve the flow efficiency of oil and gas in the oil well.

[0003] At present, the commonly used jet tubes mostly adopt an integrated, straight-cylinder design, and their diameter is smaller than the inner diameter of the oil well, so as to facilitate the lowering of the jet tube into the well. During the jet drilling operation, the ground pressure equipment applies pressure, and the water slurry is ejected from the nozzle at high speed to form a high-pressure jet, which impacts the well wall to achieve the purpose of drilling. However, the reaction force when the high-pressure jet impacts the well wall will cause the jet tube to shake, which will lead to uncontrolled swinging of the high-pressure jet, making it impossible to accurately perforate. Although in many cases, the diameter of the jet tube with an integrated straight-cylinder design will be as close to the inner diameter of the oil well as possible, in order for the jet tube to be smoothly lowered into the well, there will always be a certain gap between the jet tube and the wall of the oil well, so that during the drilling operation, the above-mentioned jet tube shaking will inevitably occur, which is also a problem that urgently needs to be solved in the current oil well drilling work. Summary of the invention

[0004] In order to avoid and overcome the technical problems existing in the prior art, the present invention provides a sandblasting perforator for drilling holes in a well wall. The present invention performs circumferential positioning on the jet tube, thereby preventing the jet tube from shaking due to the reaction force, thereby improving the drilling accuracy.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A sandblasting perforator for drilling holes in a well wall comprises a jet tube and an expansion clamping part installed at both ends of the jet tube, and the expansion clamping part can perform a circumferential expansion action to clamp the jet tube in an oil well drilling working position; the expansion clamping part comprises two guide tubes coaxially arranged with the jet tube; the two guide tubes are hinged to each other through a plurality of hinged double connecting rods, and each group of hinged double connecting rods is distributed in turn and equidistantly along the circumference of the guide tube; the two guide tubes can approach each other and be connected to each other along their axial direction under the action of gravity, and at the same time drive the joints of each group of hinged double connecting rods to expand outward and press against the well wall; the two ports of the jet tube are respectively fixedly connected to the corresponding guide tubes; in the expansion clamping part at the top of the jet tube, the guide tube located on the upper side is fixedly connected to the supply tube for providing high-pressure jet; in the expansion clamping part at the bottom of the jet tube, the guide tube located on the lower side is pressed against the bottom of the oil well.

[0007] As a further solution of the present invention: each set of hinged double-links includes two links, one long and one short, and the long and short links in two adjacent sets of hinged double-links are arranged opposite to each other.

[0008] As a further solution of the present invention: an elastic sleeve is coaxially sleeved on the outer side of the flow guide tube.

[0009] As a further solution of the present invention: in the expansion clamping part at the bottom of the jet tube, the bottom of the guide tube located on the lower side is fixed with a guide shoe for abutting against the bottom of the oil well, and a one-way valve is encapsulated in the guide tube to prevent the high-pressure jet from flowing out of the guide tube.

[0010] As a further solution of the present invention: an eccentric hole is opened in the jet tube along the axial direction thereof, and a plurality of conical positioning holes are opened in sequence along the axial direction on the thick-walled side thereof, the axial direction of each conical positioning hole extends along the radial direction of the jet tube where the conical positioning hole is located, and the diameter of each conical positioning hole gradually decreases from the inside to the outside; a conical straight nozzle is coaxially fixed in the injection positioning hole; an inner sleeve is coaxially arranged in the eccentric hole, and the inner sleeve can perform a reciprocating linear sliding action along the axial direction of the eccentric hole to block or open the conical straight nozzles one by one.

[0011] As a further solution of the present invention: With the centroid of the jet tube as the coordinate origin, the axis of the jet tube as the Y axis, and the straight line passing through the origin and perpendicular to the Y axis as the X axis, a plane rectangular coordinate system O-XY is established, and the axis of the eccentric hole is also located in the plane rectangular coordinate system O-XY, then the centroid coordinate (x g ,y g ) is calculated as follows:

[0012]

[0013] In the formula, x g represents the horizontal coordinate of the center of mass of the jet tube, in mm; g Indicates the ordinate of the center of mass of the jet tube, in mm; D indicates the diameter of the jet tube, in mm; d1 indicates the maximum wall thickness of the jet tube, in mm; d2 indicates the minimum wall thickness of the jet tube, in mm; A1 indicates the area of ​​the thick wall circle, in mm 2 ; A2 represents the thin-walled circle area, in mm 2 ; x1 represents the abscissa of the mass center of the thick-walled tube; y1 represents the ordinate of the mass center of the thick-walled tube; x2 represents the abscissa of the mass center of the thin-walled tube; y2 represents the ordinate of the mass center of the thin-walled tube;

[0014] Along the axial direction of the jet tube, the plane that divides the jet tube and the eccentric hole into two is called the section plane, and the section plane and the eccentric hole form two intersecting lines; among them, the intersecting line close to the thick-walled side of the jet tube is recorded as the first axis, and the other intersecting line is recorded as the second axis; a cylinder is drawn around the first axis with d1 as the radius, and the part where the cylinder and the jet tube overlap each other constitutes a thick-walled tube; a cylinder is drawn around the second axis with d2 as the radius, and the part where the cylinder and the jet tube overlap each other constitutes a thin-walled tube.

[0015] As a further solution of the present invention: a telescopic rod is installed on the inner wall surface of the eccentric hole, the telescopic direction of the telescopic rod is parallel to the axial direction of the jet tube, and the telescopic end of the telescopic rod is fixedly connected to the inner sleeve.

[0016] As a further solution of the present invention: a guide groove is opened on the hole wall of the eccentric hole, and the groove length direction of the guide groove is parallel to the axis of the eccentric hole; a slider is fixedly connected to the outer wall of the inner sleeve, and the slider is inserted in the guide groove; the telescopic rod is installed in the guide groove, and the slider is fixed on the telescopic end of the telescopic rod, and the telescopic rod drives the inner sleeve through the slider to complete the reciprocating linear sliding action.

[0017] As a further solution of the present invention: there are three injection positioning holes, and one of the injection positioning holes is located at the thickest wall in the middle of the jet tube, and the other two injection positioning holes are equidistantly arranged on the upper and lower sides of the injection positioning hole; the three injection positioning holes are spirally distributed on the jet tube, and adjacent injection positioning holes differ by 30° along the circumference of the jet tube.

[0018] As a further solution of the present invention: the guide tube coaxially connected to the jet tube is fixedly connected to each other through an eccentric tube, and the eccentric tube is coaxially arranged with the jet tube.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The sandblasting perforator is designed with a structure including a jet tube and an expansion clamping part, which realizes the circumferential positioning and clamping of the jet tube at the oil well drilling work position. The expansion clamping part uses a clever combination of two guide tubes and multiple hinged double connecting rods, which can automatically connect and press against the well wall under the action of gravity, effectively preventing the jet tube from shaking due to the reaction force, thereby greatly improving the drilling accuracy and operation efficiency.

[0021] 2. Each set of hinged double links includes two links, one long and one short, and the long and short links in two adjacent sets of hinged double links are arranged in opposite directions, so that the joints in adjacent hinged double links are arranged alternately up and down. Each joint point on the upper side cooperates to form an expansion ring, and each joint point on the lower side also cooperates to form an expansion ring. Two coaxial and co-diameter expansion rings cooperate up and down to form a collision column, which expands the annular support surface into a columnar support surface, effectively improving the stability of the support.

[0022] 3. The design of coaxially sleeved elastic sleeve on the outside of the flow guide tube further improves the fit and sealing between the perforator and the well wall. The elastic sleeve can absorb and buffer the impact and vibration during the operation, protect the flow guide tube and the well wall from damage, and also help to maintain the stability of the jet tube.

[0023] 4. The eccentric hole and multiple conical positioning holes in the jet tube, as well as the arrangement of the conical straight nozzle, enable the jet to more accurately control the injection direction and angle, improving the flexibility and efficiency of drilling. The reciprocating linear sliding action of the inner sleeve can block or open the nozzles one by one as needed, achieving more precise drilling operations. The setting of the eccentric hole can increase the wall thickness of one side of the jet tube, so that a longer conical straight nozzle can be installed in the corresponding conical positioning hole, and then the initial degree of the jet can be increased by the longer conical straight nozzle, thereby increasing the kinetic energy of the jet, and providing sufficient pressure shock to achieve rock breaking and drilling.

[0024] 5. The design of the guide groove and the slider makes the movement of the inner sleeve more stable and controllable. The slider is inserted in the guide groove, and the telescopic rod drives the inner sleeve through the slider to complete the reciprocating linear sliding action, effectively avoiding operational errors caused by shaking or offset during movement. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0026] Figure 2 It is a schematic diagram of the internal cross-sectional structure of the present invention.

[0027] Figure 3 It is a schematic diagram of the structure of the tapered positioning hole in the present invention.

[0028] Figure 4 It is a schematic structural diagram of the expansion clamping part in the present invention.

[0029] Figure 5 It is a schematic diagram of the dimensions of the jet tube in the present invention.

[0030] In the figure: 1. jet tube; 11. eccentric hole; 111. guide groove; 12. inner sleeve; 121. slider; 13. telescopic rod; 14. jet positioning hole; 15. conical straight nozzle; 16. perforating matrix; 2. expansion clamping part; 21. guide tube; 22. hinged double connecting rod; 23. elastic sleeve; 3. valve seat; 4. ball valve; 5. guide shoe; 6. flow supply tube; 7. eccentric tube; 8. thick-walled circle; 9. thin-walled circle. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0032] See also Figure 1 to Figure 4 A sandblasting perforator for drilling holes in a well wall mainly comprises a jet tube 1, an expansion clamping part 2, and various assembly accessories thereof.

[0033] like Figure 2 As shown, the jet tube 1 is cylindrical, and its two ends are also provided with threaded sections for threaded detachable connection with the eccentric tube 7. An eccentric hole 11 is opened in the jet tube 1 along its axial direction, and the axis of the eccentric hole 11 is parallel to the axis of the jet tube 1.

[0034] A plurality of conical positioning holes are sequentially opened along the axial direction on the thick wall side of the jet tube 1, and the axial direction of each conical positioning hole extends along the radial direction of the jet tube 1 where the conical positioning hole is located, and the diameter of each conical positioning hole gradually decreases from the inside to the outside. Figure 3 As shown, a conical straight nozzle 15 is coaxially fixed in each conical positioning hole, and a conical hollow perforating matrix 16 is also provided between the conical positioning hole and the conical straight nozzle 15, and the conical straight nozzle 15 and the perforating matrix 16, as well as the conical positioning hole and the perforating matrix 16, are sealed and sleeved with each other in a labyrinth seal manner. In this embodiment, there are three injection positioning holes 14, one of which is located at the thickest part of the middle wall of the jet tube 1, and the other two injection positioning holes 14 are equidistantly arranged on the upper and lower sides of the injection positioning hole 14. The three injection positioning holes 14 are spirally distributed on the jet tube 1, and adjacent injection positioning holes 14 differ by 30° along the circumference of the jet tube 1.

[0035] An inner sleeve 12 is coaxially arranged in the eccentric hole 11. The inner sleeve 12 can slide axially along the eccentric hole 11 to block or open the conical straight nozzles 15 one by one in a reciprocating linear sliding motion.

[0036] A guide groove 111 is provided on the hole wall of the eccentric hole 11, and the groove length direction of the guide groove 111 is parallel to the axis of the eccentric hole 11. A slider 121 is fixedly connected to the outer wall of the inner sleeve, and the slider 121 is inserted into the guide groove 111. A hydraulic cylinder serving as the telescopic rod 13 and remotely controlled on the ground is installed in the guide groove 111, and the slider 121 is fixed on the telescopic end of the hydraulic cylinder. The hydraulic cylinder drives the inner sleeve through the slider 121 to complete the reciprocating linear sliding action.

[0037] With the centroid of the jet tube 1 as the coordinate origin, the axis of the jet tube 1 as the Y axis, and the straight line passing through the origin and perpendicular to the Y axis as the X axis, a plane rectangular coordinate system O-XY is established. Figure 5 As shown, along the axial direction of the jet tube 1, the plane that divides the jet tube 1 and the eccentric hole 11 into two is a section plane, and the section plane and the eccentric hole 11 form two intersecting lines; wherein, the intersecting line close to the thick-walled side of the jet tube 1 is recorded as the first axis, and the other intersecting line is recorded as the second axis; a cylinder is drawn around the first axis with d1 as the radius, and the portion where the cylinder and the jet tube 1 overlap each other constitutes a thick-walled tube 8; a cylinder is drawn around the second axis with d2 as the radius, and the portion where the cylinder and the jet tube 1 overlap each other constitutes a thin-walled tube 9.

[0038] The axis of the eccentric hole 11 is also located in the plane rectangular coordinate system O-XY, so the centroid coordinate (x g ,y g ) is calculated as follows:

[0039]

[0040] In this embodiment, D is 60 mm, d1 is 20 mm, and d2 is 40 mm.

[0041] Then we can calculate: A1 is 800πmm 2 , A1 is 500πmm 2 .

[0042] Calculate the center of mass coordinates (x g ,y g ) is the centroid coordinate (x g ,y g ); and through the centroid coordinates (x c ,y c ) is compared with the eccentricity of the jet tube 1 by formula (2).

[0043]

[0044] Substituting the data, we can calculate that the eccentricity is E=5mm.

[0045] Through the eccentric setting, the specific size design of the nozzle can be achieved to meet the displacement and injection pressure of the high temperature and high pressure environment underground.

[0046] like Figure 4 As shown, the expansion clamping part 2 includes two guide tubes 21 arranged coaxially with the jet tube 1, and the two guide tubes 21 are hinged to each other through a plurality of hinged double-link rods 22, and each group of hinged double-link rods 22 are distributed equidistantly along the circumference of the guide tube 21, and at the same time, each hinge axis in the same hinged double-link rod 22 is arranged parallel to each other.

[0047] The two flow guide tubes 21 can approach each other and connect with each other along their axial direction under the action of gravity, and at the same time drive the joints of each group of hinged double connecting rods 22 to expand outward and press against the well wall. The two ports of the jet tube 1 are respectively fixedly connected with the corresponding flow guide tubes 21. Among them, in the expansion clamping part 2 at the top of the jet tube 1, the flow guide tube 21 located on the upper side is fixedly connected with the flow supply tube 6 providing high-pressure jet through the eccentric tube 7; in the expansion clamping part 2 at the bottom of the jet tube 1, the flow guide tube 21 located on the lower side is pressed against the bottom of the oil well. The flow guide tubes 21 in the upper and lower expansion clamping parts 2 are coaxially arranged with the jet tube 1.

[0048] Each set of hinged double links 22 includes two links, one long and one short, and the long and short links in two adjacent sets of hinged double links 22 are arranged opposite to each other, so that the joints in adjacent hinged double links 22 are arranged alternately up and down. Each joint point on the upper side cooperates to form an expansion ring, and each joint point on the lower side also cooperates to form an expansion ring. Two coaxial and co-diameter expansion rings cooperate up and down to form a collision column, which expands the annular support surface into a columnar support surface, effectively improving the stability of the support.

[0049] The outer side of the guide tube 21 is coaxially sleeved with an elastic sleeve 23 to prevent the joints of the hinged double link 22 from directly contacting the well wall, prevent particles on the well wall from falling into the joints, reduce the probability of wear of the joints due to interference from particles, and reduce the failure rate of the hinged double link 22.

[0050] The guide pipe 21 on the lower side of the expansion clamping part 2 at the lower end is connected to a valve seat 3, the minimum inner diameter of the valve seat 3 is 22mm, a 60° inclined groove is opened at the rear end of the valve seat 3, and the inclined groove cooperates with the valve ball 4 to form a one-way valve, and a valve baffle is installed at the end of the valve seat 3, which can always be located in the working area. A guide shoe 5 is provided at the lower end of the valve seat 3, and there is a 100mm through hole to improve the flow capacity during backwashing.

[0051] When the present invention is used, all the equipment is assembled, and then the sandblasting perforator is hoisted and slowly lowered into the oil well. During the lowering process, due to the effect of gravity, the two guide tubes 21 in the same group are far away from each other. When the sandblasting perforator is placed at the bottom of the well, the two guide tubes 21 in the same group are close to each other, and the hinged double connecting rod 22 is stretched open and pressed against the well wall. When the two guide tubes 21 in the same group are aligned with each other, the pipe above the sandblasting perforator stops pressing down. Then, the ground pressurizing equipment starts to input high-pressure jets, and the high-pressure jets enter the jet tube 1 through the flow supply pipe 6 and are ejected by the conical straight nozzle 15. At the same time, according to the drilling requirements, the hydraulic cylinder action is started to close or open a set number of conical straight nozzles 15 to achieve multi-stage drilling. After drilling the hole, the sandblasting perforator is lifted up to release the clamping and locking effect of the expansion clamping part 2, and then the sandblasting perforator is pulled out of the oil well.

[0052] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A sandblasting perforator for drilling holes in a well wall, characterized in that: The invention comprises a jet tube (1), and expansion clamping parts (2) installed at both ends of the jet tube (1), and the expansion clamping parts (2) can perform a circumferential expansion action to clamp the jet tube (1) at the oil well drilling working position; the expansion clamping part (2) comprises two guide tubes (21) arranged coaxially with the jet tube (1); the two guide tubes (21) are hinged to each other through a plurality of hinged double connecting rods (22), and each group of hinged double connecting rods (22) are distributed in sequence at equal intervals along the circumference of the guide tube (21); the two guide tubes (21) can be externally Under the action of force, they approach each other along their axial direction and are connected to each other, and at the same time, the joints of each group of hinged double connecting rods (22) are driven to expand outward and press against the well wall; the two ends of the jet tube (1) are respectively fixedly connected to the corresponding guide tubes (21); in the expansion clamping part (2) at the top of the jet tube (1), the guide tube (21) located on the upper side is fixedly connected to the supply tube (6) for providing high-pressure jet; in the expansion clamping part (2) at the bottom of the jet tube (1), the guide tube (21) located on the lower side is pressed against the bottom of the oil well.

2. A sandblasting perforator for drilling a hole in a well wall according to claim 1, characterized in that: Each set of hinged double connecting rods (22) comprises two connecting rods, one long and one short, and the long and short connecting rods in two adjacent sets of hinged double connecting rods (22) are arranged in opposite directions to each other.

3. A sandblasting perforator for drilling a hole in a well wall according to claim 2, characterized in that: An elastic sleeve (23) is coaxially sleeved on the outer side of the flow guide tube (21).

4. A sandblasting perforator for drilling a hole in a well wall according to claim 3, characterized in that: In the expansion clamping portion (2) at the bottom of the jet tube (1), a guide shoe (5) for contacting the bottom of the oil well is fixedly connected to the bottom of the guide tube (21) located at the lower side, and a one-way valve is encapsulated in the guide tube (21) to prevent the high-pressure jet from flowing out of the guide tube (21).

5. A sandblasting perforator for drilling a hole in a well wall according to any one of claims 1 to 4, characterized in that: An eccentric hole (11) is formed in the jet tube (1) along its axial direction, and a plurality of conical positioning holes are formed in sequence along the axial direction on the thick wall side thereof, the axial direction of each conical positioning hole extending along the radial direction of the jet tube (1) where the conical positioning hole is located, and the diameter of each conical positioning hole gradually decreases from the inside to the outside; a conical straight nozzle (15) is coaxially fixedly connected in each of the jet positioning holes (14); an inner sleeve (12) is coaxially arranged in the eccentric hole (11), and the inner sleeve (12) can slide along the axial direction of the eccentric hole (11) to block or open the conical straight nozzles (15) one by one in a reciprocating linear sliding action.

6. A sandblasting perforator for drilling holes in a well wall according to claim 5, characterized in that: With the centroid of the jet tube (1) as the coordinate origin, the axis of the jet tube (1) as the Y axis, and the straight line passing through the origin and perpendicular to the Y axis as the X axis, a plane rectangular coordinate system O-XY is established, and the axis of the eccentric hole (11) is also located in the plane rectangular coordinate system O-XY, then the centroid coordinate (x g ,y g ) is calculated as follows: In the formula, x g represents the horizontal coordinate of the center of mass of the jet tube (1), in mm; g represents the ordinate of the center of mass of the jet tube (1), in mm; D represents the diameter of the jet tube (1), in mm; d1 represents the maximum wall thickness of the jet tube (1), in mm; d2 represents the minimum wall thickness of the jet tube (1), in mm; A1 represents the thick wall circle area, in mm 2 ; A2 represents the thin-walled circle area, in mm 2 ; x1 represents the abscissa of the center of mass of the thick-walled tube (8); y1 represents the ordinate of the center of mass of the thick-walled tube (8); x2 represents the abscissa of the center of mass of the thin-walled tube (9); y2 represents the ordinate of the center of mass of the thin-walled tube (9); Along the axial direction of the jet tube (1), a plane that simultaneously divides the jet tube (1) and the eccentric hole (11) into two is defined as a section plane, and the section plane and the eccentric hole (11) form two intersecting lines; wherein the intersecting line close to the thick-walled side of the jet tube (1) is recorded as a first axis, and the other intersecting line is recorded as a second axis; a cylinder is drawn around the first axis with a radius of d1, and the portion where the cylinder and the jet tube (1) overlap each other constitutes a thick-walled tube (8); a cylinder is drawn around the second axis with a radius of d2, and the portion where the cylinder and the jet tube (1) overlap each other constitutes a thin-walled tube (9).

7. A sandblasting perforator for drilling a hole in a well wall according to claim 6, characterized in that: A telescopic rod (13) is installed on the inner wall surface of the eccentric hole (11), the telescopic direction of the telescopic rod (13) is parallel to the axial direction of the jet tube (1), and the telescopic end of the telescopic rod (13) is fixedly connected to the inner sleeve (12).

8. A sandblasting perforator for drilling a hole in a well wall according to claim 7, characterized in that: A guide groove (111) is provided on the hole wall of the eccentric hole (11), and the groove length direction of the guide groove (111) is parallel to the axis of the eccentric hole (11); a slider (121) is fixedly connected to the outer wall of the inner sleeve, and the slider (121) is inserted into the guide groove (111); the telescopic rod (13) is installed in the guide groove (111), and the slider (121) is fixed on the telescopic end of the telescopic rod (13), and the telescopic rod (13) drives the inner sleeve through the slider (121) to complete the reciprocating linear sliding action.

9. A sandblasting perforator for drilling holes in a well wall according to claim 8, characterized in that: There are three injection positioning holes (14), one of which is located at the thickest part of the middle of the jet tube (1), and the other two injection positioning holes (14) are equidistantly arranged on the upper and lower sides of the injection positioning hole (14); the three injection positioning holes (14) are spirally distributed on the jet tube (1), and adjacent injection positioning holes (14) differ by 30 degrees along the circumference of the jet tube (1).

10. A sandblasting perforator for drilling holes in a well wall according to claim 9, characterized in that: The guide tube (21) coaxially connected to the jet tube (1) is fixedly connected to each other via an eccentric tube (7), and the eccentric tube (7) is coaxially arranged with the jet tube (1).

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