US4685091A — Method and apparatus for acoustic well logging

Claim 1

Independent Claim 205 words

A method of establishing multipole acoustic waves in a subsurface earth formation traversed by a borehole with a sonde, having a central longitudinal axis, disposed therein, comprising the steps of: simultaneously generating 2N acoustic pressure waves, where N is an integer not less than one, originating from a corresponding number of discrete locations spaced radially outward from said central longitudinal axis so that said waves will propagate initially along respective wave axes in directions substantially parallel to said central longitudinal axis, said wave axes being oriented so that the projections, in a plane perpendicular to the central longitudinal axis, of lines intersecting the central longitudinal axis and the wave axes define a plurality of approximately equal angles α, wherein α is approximately equal to 360°/2N, and so that any first one of the waves traveling along a corresponding first one of the wave axes is substantially out of phase with respect to any second one of the waves traveling along a corresponding second one of the wave axes, where the first wave axis and the second wave axis are separated by angle α with respect to the central longitudinal axis; and reflecting said waves substantially radially outward from said central longitudinal axis into said formation.

Claim 2

Independent Claim 205 words

A method of establishing multipole acoustic waves in a subsurface earth formation traversed by a borehole with a sonde, having a central longitudinal axis, disposed therein, comprising the steps of: simultaneously generating 2N acoustic pressure waves, where N is an integer not less than one, originating from a corresponding number of discrete locations spaced radially outward from said central longitudinal axis so that said waves will propagate initially along respective wave axes in directions substantially parallel to said central longitudinal axis, said wave axes being oriented so that the projections, in a plane perpendicular to the central longitudinal axis, of lines intersecting the central longitudinal axis and the wave axes define a plurality of approximately equal angles α, wherein α is approximately equal to 360°/2N, and so that any first one of the waves traveling along a corresponding first one of the wave axes is substantially out of phase with respect to any second one of the waves traveling along a corresponding second one of the wave axes, where the first wave axis and the second wave axis are separated by angle α with respect to the central longitudinal axis; and reflecting said waves substantially radially outward from said central longitudinal axis into said formation.

Claim 3

Dependent Claim 24 words

The method of claim 1, wherein said pressure waves are initially propagated within said sonde and are thereafter reflected radially outward from said sonde.

Claim 4

Dependent Claim 16 words

The method of claim 2, wherein said wave axes are substantially equidistant from said central axis.

Claim 5

Dependent Claim 31 words

The method of claim 1, wherein said reflected waves include lobes reflected at an angle θ from a plane perpendicular to said central longitudinal axis, where θ is greater than zero.

Claim 6

Dependent Claim 7 words

The method of claim 4, wherein N=2.

Claim 7

Dependent Claim 58 words

The method of claim 4, wherein the directions of said radially outward reflected waves, when projected onto a plane perpendicular to said central axis, define said plurality of angles α, and wherein said generated pressure waves have an amplitude and frequency such that said reflected waves will interfere to generate an acoustic multipole shear wave in said formation.

Claim 8

Dependent Claim 212 words

Apparatus for establishing multipole acoustic waves in a subsurface earth formation traversed by a borehole with a sonde, having a central longitudinal axis, disposed therein, comprising: acoustic wave generator means for simultaneously generating 2N acoustic pressure waves, where N is an integer not less than one, originating from a corresponding number of discrete locations spaced radially outward from said central longitudinal axis so that said waves will propagate along respective wave axes in directions substantially parallel to said central longitudinal axis, said wave axes being oriented so that the projections, in a plane perpendicular to the central longitudinal axis, of lines intersecting the central longitudinal axis and the wave axes define a plurality of approximately equal angles α, wherein α is approximately equal to 360°/2N, and so that any first one of the waves traveling along a corresponding first one of the wave axes is substantially out of phase with respect to any second one of the waves traveling along and corresponding second one of the wave axes, where the first wave axis and the second waves axis are separated by angle α with respect to the central longitudinal axis; and acoustic wave reflector means for reflecting said waves in substantially radially outward directions from said central longitudinal axis into said formation.

Claim 9

Dependent Claim 212 words

Apparatus for establishing multipole acoustic waves in a subsurface earth formation traversed by a borehole with a sonde, having a central longitudinal axis, disposed therein, comprising: acoustic wave generator means for simultaneously generating 2N acoustic pressure waves, where N is an integer not less than one, originating from a corresponding number of discrete locations spaced radially outward from said central longitudinal axis so that said waves will propagate along respective wave axes in directions substantially parallel to said central longitudinal axis, said wave axes being oriented so that the projections, in a plane perpendicular to the central longitudinal axis, of lines intersecting the central longitudinal axis and the wave axes define a plurality of approximately equal angles α, wherein α is approximately equal to 360°/2N, and so that any first one of the waves traveling along a corresponding first one of the wave axes is substantially out of phase with respect to any second one of the waves traveling along and corresponding second one of the wave axes, where the first wave axis and the second waves axis are separated by angle α with respect to the central longitudinal axis; and acoustic wave reflector means for reflecting said waves in substantially radially outward directions from said central longitudinal axis into said formation.

Claim 10

Dependent Claim 7 words

The apparatus of claim 7, wherein N=2.

Claim 11

Dependent Claim 32 words

The apparatus of claim 7, wherein said vibrations have an amplitude and frequency such that said reflected waves are capable of interfering to generate an acoustic multipole shear wave in said formation.

Claim 12

Dependent Claim 16 words

The apparatus of claim 7, wherein said wave axes are substantially equidistant from said central axis.

Claim 13

Dependent Claim 37 words

The apparatus of claim 7, wherein said generator means includes a plurality of rod means each longitudinally coaxial to a different corresponding one of said wave axes for establishing vibrations in the direction of said wave axes.

Claim 14

Dependent Claim 36 words

The apparatus of claim 11, wherein each of said plurality of rod means is comprised of piezoelectric material which vibrates in the direction of the wave axis corresponding thereto when energized by a changing electrical potential.

Claim 15

Dependent Claim 66 words

The apparatus of claim 11, wherein said acoustic wave reflector means comprises a plurality of acoustic reflector face means each for a different one of said waves and facing a different one of said substantially radially outward directions from said central axis, for reflecting each of said different ones of said plurality of waves in a respective said different one of said substantially radially outward directions.

Claim 16

Dependent Claim 44 words

The apparatus of claim 11, wherein each of said rod means is comprised of a magnetostrictive material having a strain constant, which vibrates in the direction of the wave axis corresponding thereto when in the presence of a changing magnetic field in said direction.

Claim 17

Dependent Claim 103 words

The apparatus of claim 14, wherein a next one of said plurality of rod means, and each one of said plurality of rod means having a wave axis separated from the wave axis corresponding to said next one of said plurality of rod means by an angle equal to 2nα with respect to said central axis are comprised of a first magnetostrictive material having a first strain constant, and wherein every other one of said plurality of rod means is comprised of a second magnetostrictive material having a second strain constant different from said first strain constant, where n is a positive integer.

Claim 18

Dependent Claim 20 words

The apparatus of claim 15, wherein said first magnetostrictive material is nickel and second magnetostrictive material is 2 V Permendur.

Claim 19

Dependent Claim 79 words

The apparatus of claim 15, wherein the absolute value of the first strain constant is larger than that of the second strain constant, and also comprising: an electrically conducting metal element wrapped about each of said rod means comprised of a material having said first strain constant so that the absolute value of the effective strain constant of each of said wrapped rod means is reduced to a value less than the absolute value of said first strain constant.

Claim 20

Dependent Claim 19 words

The apparatus of claim 14, wherein each of said plurality of rod means has substantially the same strain constant.

Claim 21

Dependent Claim 25 words

The apparatus of claim 18, also comprising: pre-biasing means for establishing a constant selected magnetic field adjacent predetermined ones of said plurality of rod means.

Claim 22

Dependent Claim 13 words

The apparatus of claim 19, wherein said pre-biasing means comprises a permanent magnet.

Claim 23

Dependent Claim 13 words

The apparatus of claim 19, wherein said pre-biasing means comprises an electromagnetic coil.

Claim 24

Dependent Claim 33 words

The apparatus of claim 12, wherein each of said rod means is comprised of a plurality of discs of said piezoelectric material stacked longitudinally in the direction of the wave axis corresponding thereto.

Claim 25

Dependent Claim 41 words

The apparatus of claim 22, wherein each of said plurality of face means is oriented for reflecting a different one of said waves at an angle θ from a plane perpendicular to said central axis, where θ is greater than zero.

Claim 26

Dependent Claim 31 words

The apparatus of claim 13, wherein the number of said plurality of rod means is equal to 2N and the number of said plurality of face means is equal to 2N.

Claim 27

Dependent Claim 72 words

The apparatus of claim 13, wherein said acoustic wave reflector means defines an inverted pyramid in coaxial alignment with said central axis, said pyramid having faces, each of which comprises a different one of said plurality of face means, each of said faces being oriented above a respective one of said rod means and being further intersected by one of said wave axes corresponding to said respective one of said rod means.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1990-08-03	1991-02-02	1991-08-04	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1994-08-03	1995-02-02	1995-08-04	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1998-08-03	1999-02-02	1999-08-04	$7700.00	Window Closed / Lapsed

Method and apparatus for acoustic well logging

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