Cable system for downhole use and method of perforating a wellbore tubular
A system for providing information through a metal wall employs a device adapted to be arranged on one side of the metal wall and a magnetic-permeability element, provided at, near or connected to the device. The magnetic-permeability element is based on a material having a relative magnetic permeability of at least 2000. The disclosure also provides use of said system. The use may involve the step of optimizing the magnetic-permeability element using equivalent inductive mass (EIm). The system can for example be used to magnetically sense the location of a cable present on the outside of a wellbore tubular using a magnetic orienting tool that is located within the wellbore tubular.
1. A cable system for downhole use, comprising cable and a magnetic-permeability element configured along a length of the cable, wherein said magnetic-permeability element comprises a material having a relative magnetic permeability μ r,m of at least 2,000, and wherein the magnetic-permeability element is provided as a strip extending along at least part of the length of the cable wherein said strip comprises multiple layers of sheet of said material.
2. The cable system of claim 1 , the material having an EM contrast ratio of at least 50 μΩ −1 ·cm −1 , wherein said EM contrast ratio is defined as μ r,m ·σ m , wherein σ m is electrical conductivity of the material.
3. The cable system of claim 1 , the material having relative magnetic permeability μ r of at least 4,000.
4. The cable system of claim 1 , wherein the material is selected from the group consisting of: mumetal, permalloy, and electrical steel.
5. The cable system of claim 1 , wherein the material comprises electrical steel.
6. The cable system of claim 1 , wherein said strip comprises a laminate of said multiple layers of sheet.
7. The cable system of claim 1 , wherein the cable is a fiber-optic cable comprising a fiber optic line.
8. The cable system of claim 7 , wherein the magnetic-permeability element and the fiber optic line are encapsulated together within an encapsulation.
9. The cable system of claim 1 , wherein the magnetic-permeability element is configured external to the cable.
10. The cable system of claim 1 , wherein the cable and the magnetic-permeability element are arranged on one side of a metal wall.
11. The cable system of claim 10 , wherein said relative magnetic permeability μ r,m of at least 2,000 exceeds a relative magnetic permeability μ r,w of said metal wall.
12. The cable system of claim 10 , wherein an EM contrast ratio of the material exceeds the EM contrast ratio of said metal wall, wherein EM contrast ratio of the material is defined as μ r,m ·σ m , and wherein EM contrast ratio of the metal wall is defined as μ r,w ·σ w wherein σ m is an electrical conductivity of the material and σ w is an electrical conductivity of the metal wall.
13. The cable system of claim 10 , further comprising a magnetic orienting tool positioned on a second side of said metal wall opposite from said one side to locate the magnetic-permeability element through the metal wall.
14. The cable system of claim 10 , wherein a target-to-background ratio of equivalent inductive mass of the cable relative to the metal wall exceeds 5.
15. The cable system of claim 10 , wherein said metal wall comprises a wall of a wellbore tubular.
16. A method of perforating a wellbore, comprising:
providing a cable system for downhole use, comprising cable and a magnetic-permeability element configured along a length of the cable, wherein said magnetic-permeability element comprises a material having a relative magnetic permeability μ r,m of at least 2,000, and wherein the magnetic-permeability element is provided as a strip extending along at least part of the length of the cable wherein said strip comprises multiple layers of sheet of said material;
providing a wellbore tubular downhole, said wellbore tubular comprising a metal wellbore tubular wall whereby the cable system is arranged on an outside of said wellbore tubular;
lowering a magnetic orienting tool into the wellbore tubular;
locating the cable system through the metal wellbore tubular wall with the magnetic orienting tool;
subsequently perforating the metal wellbore tubular wall away from the cable system.
17. The method of claim 16 , the material having relative magnetic permeability μ r of at least 4,000.
18. The method of claim 16 , wherein the material is selected from the group consisting of: mumetal, permalloy, and electrical steel.
19. The method of claim 16 , wherein the material comprises electrical steel.
20. The method of claim 16 , wherein said strip comprises a laminate of said multiple layers of sheet.