Apparatus and method for acoustically investigating a casing set in a borehole
First Claim
1. An apparatus for investigating a borehole having a borehole wall with a casing having a casing wall penetrating an earth formation comprising:
- a tool shaped to move along the borehole, said tool having an axis which is generally parallel to the wall of the borehole;
a substantially continuous array of acoustic transducers concentrically mounted on the tool around the tool axis, said array being oriented to transmit and then detect acoustic energy traveling along a path generally parallel to the tool axis;
a substantially radially continuous acoustic reflection surface which is generally concentric with the tool axis and is axially spaced from the array and is interposed in the path of acoustic energy transmitted from and to be detected by the array;
means for selectively actuating the transducers in the array to produce circumferentially discrete pulsed beams of acoustic energy from the array with the beams distributed around the tool axis and being directed onto the reflection surface;
said reflection surface being inclined at such angle relative to the tool axis so as to reflect transmitted beams primarily onto discrete circumferential casing segments of the casing wall with an angle of incidence that is substantially normal to the casing wall and with a circumferentially curved acoustic wavefront;
the acoustic transducers that are energized to produce said pulsed beams being of a number so selected that the casing segments onto which the beams are incident circumferentially overlap; and
means for deriving from acoustic energy detected by the transducers an indication of a characteristic of the casing wall at said casing segments.
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Accused Products
Abstract
A method and apparatus for acoustically investigating a casing in a borehole are described. An electronically scannable acoustic transducer is formed on a planar circular surface and is oriented on a tool so as to direct circumferentially scannable beams of acoustic energy initially in an axial direction and subsequently in a radial direction onto the casing. Acoustic reflections from casing wall segments are detected and the frequencies of the casing reverberations present in the reflections are measured. One frequency measuring technique employs a reiterative technique whereby a previously measured frequency of a reflection attributable to one wall segment is used to generate a subsequent pulsed acoustic beam at the same wall segment. The number of reiterations may vary and is selected to accurately determine the thickness resonance of the casing. The scanning speed of the array and the number of transducers are selected so that the casing segments onto which the beams are incident circumferentially overlap.
97 Citations
11 Claims
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1. An apparatus for investigating a borehole having a borehole wall with a casing having a casing wall penetrating an earth formation comprising:
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a tool shaped to move along the borehole, said tool having an axis which is generally parallel to the wall of the borehole; a substantially continuous array of acoustic transducers concentrically mounted on the tool around the tool axis, said array being oriented to transmit and then detect acoustic energy traveling along a path generally parallel to the tool axis; a substantially radially continuous acoustic reflection surface which is generally concentric with the tool axis and is axially spaced from the array and is interposed in the path of acoustic energy transmitted from and to be detected by the array; means for selectively actuating the transducers in the array to produce circumferentially discrete pulsed beams of acoustic energy from the array with the beams distributed around the tool axis and being directed onto the reflection surface; said reflection surface being inclined at such angle relative to the tool axis so as to reflect transmitted beams primarily onto discrete circumferential casing segments of the casing wall with an angle of incidence that is substantially normal to the casing wall and with a circumferentially curved acoustic wavefront; the acoustic transducers that are energized to produce said pulsed beams being of a number so selected that the casing segments onto which the beams are incident circumferentially overlap; and means for deriving from acoustic energy detected by the transducers an indication of a characteristic of the casing wall at said casing segments. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for acoustically investigating a wall of a casing in a borehole penetrating an earth formation with a tool moved along the borehole, said casing wall having a circumference, the method comprising the steps of:
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generating from different acoustic sources circumferentially separate non-interfering pulsed beams of acoustic energy in a direction that is generally parallel to the axis of the tool, reflecting the beams towards the wall of the casing so as to be incident upon respective casing wall segments, said separate beams being so circumferentially spaced as to provide a circumferential overlap of casing wall segments upon which the beams are incident to investigate the casing wall along its entire circumference, and detecting acoustic energy which is reflected from the wall segments. - View Dependent Claims (9, 10, 11)
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Specification