Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B47/00—Survey of boreholes or wells
  • E21B47/12—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling
  • E21B47/13—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling by electromagnetic energy, e.g. radio frequency
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F38/00—Adaptations of transformers or inductances for specific applications or functions
  • H01F38/18—Rotary transformers

Definitions

• This invention relates to a coupling for transmitting electrical signals between first and second members which undergo relative rotation.
• the invention is particularly, but not exclusively, of relevance to the inspection of long hollow cylindrical objects, such as drill collars for oil boreholes.
• a drill collar typically has a length of 10 m and an internal bore of about 78 mm; this makes i ⁇ .ternal inspection for cracks and the like difficult-
• an electro.— magnetic inspection apparatus using a probe with twin windings This apparatus is suitable for detecting defects of interest in drill collars and the like, but it is necessary to scan the probe over the internal surface. One way of doing this would be to draw through the bore on which the probe is rotatably mounted, so that spiral scan is performed. However, it is necessary to couple the signals from the rotating probe to a non-rotating instrument including a bridge circuit.
• the parameter of interest is a small out-of-balance quantity, it is very easy for this to be swamped by noise in the coupling. It has also been found that the signal of interest can be swamped by spurious signals arising from non-uniformity of rotational and translational movement.
• an object of the present invention is to provide a coupling of the kind stated and which provides low noise and a high immunity to non-uniform movemen .
• the invention provides a rotary coupling for transferring an electrical signal between first and second members arranged to undergo relative rotation, comprising a primary winding on the first member, and a secondary winding on the second member adjacent the primary winding for inductive coupling therewith, the primary winding having a given linear extent and the secondary winding being positioned within a minor part of and spaced from the ends of said linear extent.
• the first member is a shaft and the second member a surrounding sleeve.
• the primary winding is a'single-layer coil of length A on the shaft surface, and the secondary a multi- ⁇ 0 layer coil of length B on the sleeve adjacent the centre of the primary.
• the face of the primary winding away from the secondary winding is covered with a ferrite material.
• Fig 1 is a perspective view of an inspection apparatus incorporating the invention
• Fig 2 is a diagrammatic cross-section of a coupling embodying the invention for use in the apparatus of Fig 1; 20 Fi 3 is a similar view of an alternative embodiment of the coupling; and
• Fig 4 is a side view, partly in cross-section, of a further embodiment.
• the inspection apparatus shown in Fig 1 comprises a cylindrical 25 body 10 dimensioned to be pulled through the bore of a tubular member by a cable 12.
• the body 10 has spring-biased wheels 14 for engagement with the bore.
• a probe 16 suitably of the type described in EP-A-0033802, is mounted in a holder 18 which is rotatable with respect to the body 10, to produce a helical scanning pattern.
• the probe and holder are attached to a shaft 20 rotatable within a sleeve 22.
• the two windings of the probe 16 are connected each to a respective primary winding 24a, 24b, which are single-layer windings formed over ferrite layers 26a, 26b in circumferential grooves in the outer surface of the 35 shaft 20.
• Each primary winding 24a, 24b is inductively coupled with a respective secondary winding 28a, 28b, these being multi-layer windings formed in narrow slots in the sleeve 22.
• the linear extent A of the primary windings 24 is considerably larger than the linear extent B of the secondary windings.
• the purpose is to position the secondary winding in an area of uniform flux from its primary, and to avoid coupling in the end zone of the primary where flux concentration occurs.
• Fig 3 operates in a similar manner and like parts are denoted by like references.
• the primary windings 24 are disc-shaped in a transversely extending flange 30 and are coupled with secondary windings 28 in an annular housing 32.
• Bearings.34 journal the shaft 20 for rotation in the housing 32.
• Fig 4 illustrates the invention applied to the inspection of a narrow-bore tube 40 having a bore too small to accept the rotary coupling.
• a probe 16 is mounted on the end of a rod 42 for rotation and translation within the tube 40.
• Bearing means indicated at 44 are provided for locating the probe 16 within the tube 40.
• the rod 42 is rotated b.y a drive assembly 46 embodying the coupling described above and located outside the tube 40. It will be understood that the rod 42 houses conductors connecting the probe 16 to the inductive coupling.
• the rod 42 is sectional, the sections being provided with mechanical screw or bayonet connectors and mating electrical contacts. This permits long tubing to be inspected with the drive assembly requiring axial movement only by the section length.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Geology (AREA)
• Remote Sensing (AREA)
• Life Sciences & Earth Sciences (AREA)
• Power Engineering (AREA)
• Mining & Mineral Resources (AREA)
• Electromagnetism (AREA)
• Geophysics (AREA)
• Environmental & Geological Engineering (AREA)
• Fluid Mechanics (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 1986
  • 1986-08-07 GB GB868619316A patent/GB8619316D0/en active Pending
• 1987
  • 1987-08-03 EP EP87904924A patent/EP0277169A1/de not_active Withdrawn
  • 1987-08-03 WO PCT/GB1987/000554 patent/WO1988001096A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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