Method and apparatus for detecting the direction and distance to a target well casing

• US 4,443,762 A
• Filed: 06/12/1981
• Issued: 04/17/1984
• Est. Priority Date: 06/12/1981
• Status: Expired due to Fees

• Current Assignee: Case Corporation (CNH Industrial N.V.)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: Kuckes, Arthur F.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US06/273,138
• Time in Patent Office: 1,040 Days
• Field of Search: 324/221, 324/329, 324/339, 324/340, 324/342, 324/343, 324/346, 166/65 M, 166/255, 175/40, 175/45
• US Class Current: 324/346
• CPC Class Codes: E21B 47/0228 using electromagnetic energy or detectors therefor
• CPC Class Codes: G01V 3/26 operating with magnetic or electric fields produced or modified either by the surrounding earth formation or by the detecting device with electromagnetic waves G01V3/30

Abstract

A method and an apparatus for determining the exact direction of and distance to a nearby target well having a steel casing from a bore hole are disclosed. A long solenoid having a coil wound on a high permeability core for generating a source magnetic field which, in the absence of a target well, has axial symmetry and is characterized by having a magnetic pole at each end of the core is provided. Directly adjacent to one end of the core is a 3-component ring-type fluxgate magnetometer to detect magnetic field components perpendicular to the axis of the solenoid. The detection apparatus is located in a bore hole, and the magnetic field generated thereby is distorted when the solenoid approaches a target well.

The magnetic field source is mounted in a drill stem which includes one or more nonmagnetic drill collars, the solenoid source being mounted so that its lower end is located within the nonmagnetic collar while the upper end is magnetically connected to the rest of the drill stem. Accordingly, the upper magnetic pole of the solenoid is distributed over a large portion of the drill stem so that the lower portion is, in effect, a monopole source. A ring-type magnetometer is mounted below the monopole source and is co-axial with the solenoid to detect field distortion caused by the target well, and the output of the magnetometer provides a measure of the direction and distance to the target well casing.

Claims

1. A method for detecting the direction of and distance to a target well having a casing from a bore hole being drilled, comprising:

mounting within a drill stem for said bore hole a vertically oriented, coaxial, elongated solenoid having a core and a winding on said core;

mounting a magnetometer within said drill stem immediately adjacent one end of said solenoid;

providing a nonmagnetic collar in said drill stem, said nonmagnetic collar surrounding said one end of said solenoid and surrounding said magnetometer;

magnetically coupling the other end of said solenoid to said drill stem;

advancing said drill stem in said bore hole;

energizing said solenoid by means of a periodically varying current to produce a source magnetic field surrounding said bore hole, said magnetic field being symmetrical with the common axis of said solenoid and said bore hole in the absence of a nearby target well; and

energizing said magnetometer to detect distortions in said source magnetic field, the direction and amplitude of said distortions providing an exact measure of the direction and distance of said target well casing.

2. A well casing detector system for detecting the direction of and distance to a target well having a casing, comprising:

a housing having a magnetic portion and a nonmagnetic portion;

an elongated solenoid comprising a high permeability core and coil surrounding a major part of the length thereof;

means for energizing said solenoid coil to produce a source magnetic field axially symmetrical with respect to the axis of said solenoid;

means for securing said solenoid within and generally parallel to the axis of said housing, a first end of said solenoid being secured within said nonmagnetic portion of said housing and a second end of said solenoid being magnetically coupled to said magnetic portion of said housing for distribution of the magnetic pole corresponding to said second end, whereby said first end of said solenoid acts as a monopole magnetic field source;

a magnetometer mounted adjacent said first end of said solenoid; and

means for energizing said magnetometer to detect distortions in said magnetic field due to a target well casing, said magnetometer producing an output proportional to the vector components of said distorted field whereby the direction and distance of said target well casing from said detector system is measured.

3. The apparatus of claim 2, wherein said magnetometer includes a ring core coaxial with said solenoid core.

4. The apparatus of claim 3, further including gradiometer means adjacent said solenoid.

5. The apparatus of claim 3, wherein said solenoid core is of mu-metal, and wherein said solenoid coil extends along about two-thirds the length of said solenoid core.

6. The apparatus of claim 3, wherein said solenoid coil is energized by means of periodically varying current.

7. The apparatus of claim 3, wherein said ring core is insensitive to axial magnetic fields.

8. The apparatus of claim 3, wherein said housing is a drill stem.

9. The apparatus of claim 3, wherein said housing is an instrument Sonde.

10. A well casing detector system for detecting the direction of and distance to a target well having a casing, comprising:

a drill stem for a well bore having a first portion consisting of a plurality of drill rods of magnetic material and a second portion consisting of at least one nonmagnetic drill collar portion interposed in said drill stem;

an elongated solenoid comprising a high permeability core and a coil surrounding a major port of the length thereof;

means for securing said solenoid within said drill stem with at least a part of said solenoid being located within said nonmagnetic drill collar portion and at least a part of said solenoid being located within said drill rod portion, whereby one end of said solenoid is magnetically coupled to said drill stem, said solenoid being secured in longitudinal alignment with said drill stem;

a magnetometer mounted within said nonmagnetic collar portion in coaxial alignment with said solenoid and adjacent one end thereof;

means for energizing said solenoid coil to produce a source magnetic field axially symmetrical with respect to the axis of said solenoid and extending out of said nonmagnetic collar portion; and

means for energizing said magnetometer to detect distortions in the symmetry of said source magnetic field due to a target well casing, said magnetometer producing an output proportional to the vector components of the distorted field whereby the direction and distance of said target well casing from said detector system is measured.

11. The well casing detector system of claim 10, wherein said solenoid core is a rod approximately six feet long and 3/8 inch in diameter, and wherein said solenoid coil is wound around the central four feet thereof.

12. The well casing detector system of claim 10, wherein said means for energizing said solenoid core comprising a periodically varying source of current.

13. The well casing detector system of claim 10, wherein said magnetometer is a ring core fluxgate magnetometer and wherein said ring core is coaxial with said solenoid.

14. A method for detecting the direction of and distance to a target well having a casing of magnetic material from a nearby borehole, comprising:

mounting within a housing of magnetic material a vertically oriented, elongated solenoid having a core and a winding on said core;

mounting a magnetometer within said housing immediately adjacent one end of, and coaxial with, said solenoid;

providing a nonmagnetic portion in said housing adjacent at least said one end of said solenoid and adjacent said magnetometer;

magnetically coupling at least a portion of said solenoid to said housing;

moving said housing through said bore hole;

energizing said solenoid by means of a periodically varying current to produce a monopolar source magnetic field in the earth in the vicinity of said bore hole, said magnetic field being substantially symmetrical with respect to the common axis of said solenoid and said magnetometer in the absence of a nearby target well casing; and

energizing said magnetometer to detect distortions in said source magnetic field, the direction and amplitude of said distortions providing an exact measure of the direction of said well casing.

15. The method of claim 14, wherein the step of moving said housing comprises intermittently advancing said housing through said bore hole, and periodically detecting distortions in said source magnetic field.