High-resolution magnetic anomaly detector for well bore piping

Claim 2

Apparatus adapted for detecting magnetic anomalies in a string of well bore pipe and comprising: an elongated support member adapted for movement through a string of such well bore pipe; magnet means cooperatively arranged on said support member with the north and south magnet poles of said magnet means being situated at longitudinally spaced intervals along said support member for producing a magnetic flux field; first pole-piece means cooperatively arranged on said support member immediately adjacent to one of said magnetic poles; second pole-piece means cooperatively arranged on said support member immediately adjacent to the other of said magnetic poles for defining a first shorter flux path extending between said magnetic poles; third pole-piece means cooperatively arranged on said support member magnetically coupled to said second pole-piece means and longitudinally separated from said second pole-piece means for defining a second longer flux path extending between said magnetic poles; magnetic flux-focusing means cooperatively arranged on said support and disposed exterior of and adjacent to said second pole-piece means for selectively reDucing the overall magnetic reluctance of said first flux path below the overall magnetic reluctance of said second flux path only so long as said first flux path is not traversing a magnetic anomaly on an adjacent wall section of a well bore pipe through which said apparatus is being moved; and detecting coil means on said support member and cooperatively arranged between said second and third pole-piece means for detecting changes in the flux intensities in said first and second flux paths.

Claim 3

The anomaly-detecting apparatus of claim 1 wherein said flux-focusing means include a member of a magnetic material which is laterally spaced from said second pole-piece means.

Claim 4

The anomaly detecting apparatus of claim 1 wherein said support member is a hollow body of a non-magnetic material respectively enclosing said magnet means, said first, second and third pole-piece means, and said detecting coil means.

Claim 5

The anomaly detecting apparatus of claim 1 wherein said support member is a hollow body of a non-magnetic material respectively enclosing said magnet means, said first, second and third pole-piece means, and said detecting coil means; and said flux-focusing means include a member of a magnetic material which is mounted on said support member around at at least a major portion of said second pole-piece means.

Claim 6

The anomaly detecting apparatus of claim 4 wherein said flux-focusing member is laterally spaced from said second pole-piece means.

Claim 7

Apparatus adapted for detecting magnetic anomalies in a string of well bore pipe and comprising: an elongated tubular support of a non-magnetic material adapted for passage through a string of such well bore pipe; a permanent magnet cooperatively arranged within said tubular support with the north and south magnetic poles of said magnet being spaced along the central axis of said tubular support for producing a magnetic flux field; a first pole piece cooperatively arranged within said tubular support immediately adjacent to one of said magnetic poles; a second pole piece cooperatively arranged within said tubular support immediately adjacent to the other of said magnetic poles for defining a first flux path between said magnetic poles to traverse a first adjacent longitudinal wall section of a well bore pipe in which said apparatus is situated; a third pole piece cooperatively arranged within said tubular support having one portion magnetically coupled to said second pole piece and extending longitudinally therefrom to another portion of said third pole piece for defining a second longer flux path between said magnetic poles to serially traverse the first longitudinal wall section as well as a second adjacent longitudinal wall section of such a well bore pipe; magnetic flux-focusing means cooperatively disposed on said tubular support around at least a portion of said second pole piece for selectively reducing the overall magnetic reluctance of said first flux path below the overall magnetic reluctance of said second flux path only so long as said first flux path is not traversing a magnetic anomaly of at least a predetermined magnitude in the first pipe wall section; and a detecting coil coaxially wound around said one portion of said third pole piece for detecting changes in the flux intensities in said first and second flux paths which are representative of the presence of such a magnetic anomaly.

Claim 8

Apparatus adapted for detecting magnetic anomalies in a string of well bore pipe and comprising: an elongated tubular support of a non-magnetic material adapted for passage through a string of such well bore pipe; a permanent magnet cooperatively arranged within said tubular support with the north and south magnetic poles of said magnet being spaced along the central axis of said tubular support for producing a magnetic flux field; a first pole piece cooperatively arranged within said tubular support immediately adjacent to one of said magnetic poles; a second pole piece cooperatively arranged within said tubular support immediately adjacent to the other of said magnetic poles for defining a first flux path between said magnetic poles to traverse a first adjacent longitudinal wall section of a well bore pipe in which said apparatus is situated; a third pole piece cooperatively arranged within said tubular support having one portion magnetically coupled to said second pole piece and extending longitudinally therefrom to another portion of said third pole piece for defining a second longer flux path between said magnetic poles to serially traverse the first longitudinal wall section as well as a second adjacent longitudinal wall section of such a well bore pipe; magnetic flux-focusing means cooperatively disposed on said tubular support around at least a portion of said second pole piece for selectively reducing the overall magnetic reluctance of said first flux path below the overall magnetic reluctance of said second flux path only so long as said first flux path is not traversing a magnetic anomaly of at least a predetermined magnitude in the first pipe wall section; and a detecting coil coaxially wound around said one portion of said third pole piece for detecting changes in the flux intensities in said first and second flux paths which are representative of the presence of such a magnetic anomaly.

Claim 9

The anomaly detecting apparatus of claim 6 wherein said flux-focusing means include a ring of a magnetic material which is coaxially mounted on said tubular support.

Claim 10

The anomaly detecting apparatus of claim 7 wherein said ring is radially spaced from said second pole piece.

Claim 11

Apparatus adapted for detecting magnetic anomalies in a string of tandemly coupled pipe joints in a well bore and comprising: an elongated tubular support of a non-magnetic material adapted for movement through string of such pipe joints; first and second permanent magnets cooperaTively arranged at longitudinally spaced positions within said tubular support with their magnetic poles being spaced along the central axis of said tubular support and oppositely oriented in relation to one another with opposed like poles longitudinally spaced apart; first and second pole pieces cooperatively arranged within said tubular support and respectively positioned immediately adjacent to the unopposed poles of said first and second magnets; third and fourth pole pieces cooperatively arranged within said tubular support and respectively positioned immediately adjacent to said opposed poles of said first and second magnets for defining first and second longitudinally spaced flux paths respectively looping between said magnetic poles of each of said first and second magnets to respectively traverse first and second longitudinally spaced adjacent wall sections of a string of such pipe joints through which said apparatus is then being moved; a fifth pole piece cooperatively arranged within said tubular support between said third and fourth pole pieces and magnetically coupled thereto and having an intermediate pole portion for defining third and fourth longitudinally spaced longer flux paths respectively looping between said magnetic poles of each of said first and second magnets to respectively serially traverse such first and second wall sections as well as third and fourth longitudinally spaced adjacent wall sections of a string of such pipe joints which lie therebetween; first and second magnetic flux-focusing means cooperatively disposed on said tubular support and respectively positioned around at least a portion of said third and fourth pole pieces for selectively reducing the combined magnetic reluctances of each of said first and second flux paths respectively below the combined reluctances of each of said third and fourth flux paths, respectively only so long as either of said first and second flux paths is not traversing a junction of adjacent ones of such pipes joints which has a magnetic reluctance of at least a predetermined magnitude; and first and second electrically intercoupled detecting coils positioned between said fifth pole piece and said third and fourth pole pieces respectively and cooperatively arranged for detecting changes in the flux intensities in said flux paths which are representative of the presence of a pipe joint junction in either of such first and second wall sections.

Claim 12

Apparatus adapted for detecting magnetic anomalies in a string of tandemly coupled pipe joints in a well bore and comprising: an elongated tubular support of a non-magnetic material adapted for movement through string of such pipe joints; first and second permanent magnets cooperaTively arranged at longitudinally spaced positions within said tubular support with their magnetic poles being spaced along the central axis of said tubular support and oppositely oriented in relation to one another with opposed like poles longitudinally spaced apart; first and second pole pieces cooperatively arranged within said tubular support and respectively positioned immediately adjacent to the unopposed poles of said first and second magnets; third and fourth pole pieces cooperatively arranged within said tubular support and respectively positioned immediately adjacent to said opposed poles of said first and second magnets for defining first and second longitudinally spaced flux paths respectively looping between said magnetic poles of each of said first and second magnets to respectively traverse first and second longitudinally spaced adjacent wall sections of a string of such pipe joints through which said apparatus is then being moved; a fifth pole piece cooperatively arranged within said tubular support between said third and fourth pole pieces and magnetically coupled thereto and having an intermediate pole portion for defining third and fourth longitudinally spaced longer flux paths respectively looping between said magnetic poles of each of said first and second magnets to respectively serially traverse such first and second wall sections as well as third and fourth longitudinally spaced adjacent wall sections of a string of such pipe joints which lie therebetween; first and second magnetic flux-focusing means cooperatively disposed on said tubular support and respectively positioned around at least a portion of said third and fourth pole pieces for selectively reducing the combined magnetic reluctances of each of said first and second flux paths respectively below the combined reluctances of each of said third and fourth flux paths, respectively only so long as either of said first and second flux paths is not traversing a junction of adjacent ones of such pipes joints which has a magnetic reluctance of at least a predetermined magnitude; and first and second electrically intercoupled detecting coils positioned between said fifth pole piece and said third and fourth pole pieces respectively and cooperatively arranged for detecting changes in the flux intensities in said flux paths which are representative of the presence of a pipe joint junction in either of such first and second wall sections.

Claim 13

The anomaly detecting apparatus of claim 9 further including third flux-focusing means cooperatively disposed on said tubular support and around at least a portion of said fifth pole piece for selectively enhancing the sensitivity of said detecting coils.

Claim 14

The anomaly detecting apparatus of claim 9 wherein said first and second flux-focusing means are respectively comprised of first and second rings of magnetic material coaxially mounted on said tubular support.

Claim 15

The anomaly detecting apparatus of claim 11 wherein said first and second rings are each spaced radially from said third and fourth pole pieces respectively.

Claim 16

The anomaly detecting apparatus of claim 11 further including a third ring of magnetic material coaxially mounted on said tubular support around said fifth pole piece for focusing said third and fourth flux paths to selectively enhance the sensitivity of said detecting coils.