OUTER TUBE FOR A PERFORATING GUN

Abstract

An outer tube for a perforating gun is provided that includes an inner wall and an outer wall and also a wall thickness (D) and a length (L), wherein the outer tube has a hardness over its entire longitudinal extent along the length (L) and its transverse extent along the wall thickness (D), wherein the hardness of the outer tube is reduced, in at least one region, to an extent (T) measured from the outer wall to the inner wall, wherein, in this region, the outer tube has a reduced hardness (HV) on its outer wall, said reduced hardness being reduced in this region by at least 5% in relation to the hardness (H) of the inner wall.

Claims

1. An outer tube for a perforating gun, comprising: an inner wall and an outer wall and also a wall thickness and a length, reduced hardness in at least one region of the outer wall, said reduced hardness extending into the wall thickness by an extent measured from the outer wall to the inner wall, said reduced hardness is at least 5% less than a hardness of the inner wall, and wherein the at least one region having the reduced hardness is established by a deep decarorization such that the hardness across the wall thickness in the at least one region having reduced hardness decreases continuously from the inner wall to the outer wall.

2. The outer tube as claimed in claim 1, comprising a metal.

3. The outer tube as claimed in claim 1, wherein the extent measured from the outer wall to the inner wall is at least 200 μm and at most 50% of the wall thickness.

4. The outer tube as claimed in claim 1, wherein the reduced hardness of the outer wall is at least 10% less than the hardness of the inner wall.

5. The outer tube as claimed in claim 1, further comprising a 0.2% offset yield strength R.sub.p,0.2 of at least 700 MPa.

6. The outer tube as claimed in claim 1, wherein the at least one region having the reduced hardness is only local and is enclosed all the way around a circumference by portions of a higher level of hardness.

7. The outer tube as claimed in claim 1, wherein the at least one region having the reduced hardness can be established by of a local heat treatment.

8. (canceled)

9. The outer tube as claimed in claim 1, further comprising: a multiplicity of depressions which extend radially from the outer wall in a direction of the inner wall.

10. The outer tube as claimed in claim 9, wherein the at least one region having the reduced hardness is arranged outside the depressions.

11. A perforating gun having an outer tube as claimed in claim 1 serving as a tubular housing, comprising: an inner part, which is arranged in the outer tube, and holders carrying explosive charges.

12. The outer tube as claimed in claim 3, wherein the reduced hardness of the outer wall is at least 10% less than the hardness of the inner wall.

13. The outer tube as claimed in claim 3, further comprising a 0.2% offset yield strength R.sub.p,0.2 of at least 700 MPa.

14. The outer tube as claimed in claim 4, further comprising a 0.2% offset yield strength R.sub.p,0.2 of least 700 MPa.

15. The outer tube as claimed in claim 3, wherein the at least one region having the reduced hardness is only local and is enclosed all the way around a circumference by portions of a higher level of hardness.

16. The outer tube as claimed in claim 4, wherein the at least one region having the reduced hardness is only local and is enclosed all the way around a circumference by portions of a higher level of hardness.

17. The outer tube as claimed in claim 5, wherein the at least one region having the reduced hardness is only local and is enclosed all the way around a circumference by portions of a higher level of hardness.

18. The outer tube as claimed in claim 3, further comprising a multiplicity of depressions which extend radially from the outer wall in a direction of the inner wall.

19. The outer tube as claimed in claim 4, further comprising a multiplicity of depressions which extend radially from the outer wall in a direction of the inner wall.

20. The outer tube as claimed in claim 7, further comprising a multiplicity of depressions which extend radially from the outer wall in a direction of the inner wall.

21. The outer tube as claimed in claim 2, comprising at least one of a steel and a steel alloy.

22. The outer tube as claimed in claim 7, wherein the region of reduced hardness is established by a local inductive heat treatment which takes place at a high frequency.

23. The outer tube as claimed in claim 1, further comprising: a non-reduced hardness in at least one region of the outer wall, said non-reduced hardness extending through the entire wall thickness such that said non-reduced hardness is substantially the same as the hardness of the inner wall

24. The outer tube as claimed in claim 9, wherein the reduced hardness of a region is offset from a depression in a circumferential direction about a longitudinal axis of the outer wall.

25. The outer tube as claimed in claim 24, wherein the offset is between 60° and 120° about the longitudinal axis of the outer wall.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In the drawing:

[0023] FIG. 1 shows a perspective illustration of a possible exemplary embodiment of an outer tube for a perforating gun according to the invention,

[0024] FIG. 2 shows a cross-sectional illustration of an outer tube according to the prior art, and

[0025] FIG. 3: shows a cross-sectional illustration of the outer tube according to the invention from FIG. 1.

DETAILED DESCRIPTION

[0026] FIG. 1 illustrates a possible exemplary embodiment of an outer tube for a perforating gun according to the invention. The outer tube here has an inner wall 1 and an outer wall 2, wherein the outer wall has a wall thickness D and a length L. Such an outer tube for a perforating gun serves, at the same time, as a housing 4 for the perforating gun.

[0027] As can be gathered from FIG. 1, depressions 3 are arranged on the outer wall 2 of the outer tube, each offset, in particular helically, through 60°. This outer tube is also referred to as a 60°-phase perforating gun.

[0028] The outer tube, which serves as a housing 4 for the perforating gun, has introduced into it an inner part 5, which contains holders 7 for explosive charges 6, said holders being offset helically through 60° in a manner corresponding to the depressions 3 on the outer wall 2 of the outer tube. In other words, it is also the case that the explosive charges 6 and/or the holders 7 of the inner part 5 are arranged within the outer tube, serving as a housing 4 for the perforating gun, in a manner in which they are offset through 60° in each case in relation to one another.

[0029] FIG. 2 shows such an arrangement for an outer tube of a perforating gun as is known from the prior art. The outer tube for the perforating gun, said outer tube serving as housing 4, has a wall thickness D here, wherein the hardness of the wall has a constant value H over its entire wall thickness D.

[0030] FIG. 2 shows this at the bottom left with a corresponding diagram, which illustrates the hardness of the outer tube as a constant value H over the wall thickness D of the outer tube. It is evident from this that the hardness of the material of the outer tube, usually produced from a steel, within the outer tube has the constant hardness value H over the entire wall thickness D from the outer wall 2 to the inner wall 1.

[0031] If, then, use is made, within the holders 7 of the inner part 5, of explosive charges 6 which exceed a certain explosive force, this gives rise, on account of the propagation of shear waves and pressure waves within the outer tube, to overlapping of said shear waves and pressure waves in the outer tube between the inner wall 1 and the outer wall 2. This results in points of failure 8. The breakage or crack in the outer tube starts here on the outer wall 2 of the outer tube and propagates to the inner wall 1 of the outer tube. In the worst-case scenario, this can result in plastic deformation of the outer tube as a whole, and it is therefore no longer possible for said outer tube, or the perforating gun as a whole, to be removed from the protective tube within the well.

[0032] FIG. 3 illustrates the outer tube according to the invention from FIG. 1 in a cross-sectional illustration taken along plane A-A from FIG. 1. Here too, the outer tube, which serves as a housing 4 for the perforating gun, has arranged within it an inner part 5, which has holders 7, which correspond to the depressions 3 and in which explosive charges 6 may be arranged. It is also the case here that the outer tube according to the invention has a wall thickness D, as is also given in the prior art according to the illustration of FIG. 2. However, in the case of the outer tube according to the invention, the hardness is not constant over the wall thickness D of the outer tube. Rather, the hardness is reduced by at least 5%, in the region of the outer wall, to an extent T. In other words, the outer tube for the perforating gun according to the invention has a hardness which decreases from the inner wall 1 to the outer wall 2. The reduced hardness HV on the outer wall 2 of the outer tube should be a maximum of 95% of the hardness H on the inner wall 1 of the outer tube. FIG. 3 uses a corresponding diagram at the bottom left to illustrate the hardness of the outer tube over its wall thickness. It is clearly evident here that the hardness of the outer tube decreases continuously over its wall thickness D from the hardness H on the inner wall 1 to the hardness HV on the outer wall 2 of the outer tube.

[0033] Such a drop in hardness from the inner wall to the outer wall can be achieved, for example, by high-frequency inductive heat treatment or deep decarburization. As a result of the reduction in the hardness to the value HV, the tendency of the outer tube to fail is less than in outer tubes of constant hardness H. To this extent, in the case of the outer tube according to the invention, it is also possible to use considerably stronger explosive charges, as a result of which deeper-level perforation of the rock or earth is achieved, and this results in a higher level of efficiency or in a higher production rate per source or per explosion.

[0034] The regions of reduced hardness HV on the outer wall 2 of the outer tube may be arranged individually on the outer tube. However, it is also possible for these regions of reduced hardness to be used over the entire outer tube. It is also possible for regions of reduced hardness HV to be arranged over the circumference of the outer tube adjacent to regions of non-reduced hardness H. In particular, it is also preferred for those regions of the outer tube which are located opposite the depressions 3 to be provided with reduced hardness HV on the outer wall of the tube.

LIST OF REFERENCE SIGNS

[0035] 1 Inner wall [0036] 2 Outer wall [0037] 3 Depression [0038] 4 Housing [0039] 5 Inner part [0040] 6 Explosive charge [0041] 7 Holder [0042] 8 Point of failure [0043] H Hardness [0044] HV Reduced hardness [0045] D Wall thickness [0046] L Length [0047] T Extent