Methods and apparatus for acoustically investigating earth formations using shear waves

Claim 3

The method of claim 1 wherein said predominant frequency content of said detected acoustic energy is no greater than about 100-KHz.

Claim 4

The method of claim 1 wherein said one end of said travel path and said other end of said travel path are circumferentially spaced on said well bore wall.

Claim 7

The method of claim 4 wherein said predominant frequency content of said detected acoustic energy is no greater than about 100-KHz.

Claim 8

The method of claim 4 wherein said first and second spaced locations are circumferentially spaced from one another.

Claim 9

The method of claim 4 including the further steps of: direction broad band damped acoustic energy centered about said selected frequency into said well bore walls at a third one of said spaced locations for only a selected time interval which is no greater than about 80 percent of the arithmetical product of the estimated travel time of compressional acoustic energy through said well bore material multiplied by the shortest distance along said well bore wall between said third location and a fourth one of said spaced locations for developing a distinguishable shear-wave of acoustic energy having a predominant frequency content below said selected frequency to be propagated through said well bore material between said third and fourth spaced locations; and detecting said shear-wave acoustic energy arriving at said fourth location for producing a second electrical signal representative of the influence of said well bore material on the propagation of said shear-wave acoustic energy between said third and fourth spaced locations.

Claim 10

The method of claim 7 wherein said first and second spaced locations are circumferentially spaced from one another, and said third and fourth spaced locations are circumferentially spaced from one another.

Claim 11

The method of claim 8 wherein the circumferential spacing between said first and second spaced locations is equal to the circumferential spacing between said third and fourth spaced locations.

Claim 12

The method of claim 8 wherein said first spaced location is spaced from said third spaced location.

Claim 13

The method of claim 8 wherein the circumferential spacing between said first and second spaced locations is equal to the circumferential spacing between said third and fourth spaced locations, and said first spaced location is spaced circumferentially from said third spaced location.

Claim 14

The method of claim 8 wherein said first and third spaced locations are circumferentially spaced, said second spaced location is located at a selected circumferential distance in one direction around said well bore wall from said first spaced location, and said fourth spaced location is located at said selected circumferential distance in the opposite direction around said well bore wall from said third spaced location.

Claim 15

The method of claim 12 wherein said selected circumferential distance is about one-fourth of the circumference of said well bore wall.

Claim 16

The method of claim 13 wherein said predominant frequency content of said detected acoustic energy is no greater than about 100-KHz.

Claim 19

The method of claim 15 wherein said predominant frequency content of said detected acoustic energy is no greater than about 100-KHz.

Claim 20

The method of claim 15 wherein said successive waves of acoustic energy are detected at first and second ones of said spaced locations for producing first and second ones of said electrical signals for comparison to determine whether such formation anomalies are lying between said first and second locations and said one location.

Claim 21

The method of claim 15 wherein a first group of said series of broad band damped acoustic pulses are directed into a first one of said spaced locations and said successive shear-waves of acoustic energy developed from said first group of broad band damped acoustic pulses are detected at a second one of said spaced locations for producing a first electrical signal representative of the shear-wave acoustic energy successively propagated through said earth formations between said first and second spaced locations, and wherein a second group of said series of broad band damped acoustic pulses are directed into a third one of said spaced locations and said successive shear-waves of acoustic energy developed from said second group of broad band damped acoustic pulses are detected at a fourth one of said spaced locations for producing a second electrical signal representative of the shear-wave acoustic energy successively propagated through said earth formations between said third and fourth spaced locations for comparison with first electrical signal to determine whether such formation anomalies are present between either said first and second spaced locations or said third and fourth spaced locations.

Claim 22

The method of claim 18 wherein said first and second spaced locations are about 90* apart and said third and fourth spaced locations are about 90* apart.

Claim 23

The method of claim 18 wherein said first and third spaced locations are about 180* apart and said second and fourth spaced locations are about 180* apart.

Claim 24

The method of claim 20 wherein said second and fourth locations are about 90* apart from said first and third locations respectively.

Claim 27

The method of claim 22 wherein said predominant frequency content of said detected acoustic energy is no greater than about 100-KHz.

Claim 28

The method of claim 22 wherein N is equal to four.

Claim 29

The method of claim 22 wherein each of said successively broad band damped pulses occurs at about 2,000 Mu seconds following the immediately-preceding one of said damped pulses.

Claim 30

The method of claim 25 wherein N is equal to four.

Claim 31

The method of claim 22 wherein the next one of each of said broad band damped pulses is directed into said next-adjacent one of said spaced locations following the reception thereat of acoustic energy developed from the immediately-preceding broad band damped pulse for progressively exploring the perimeter of said borehole wall in a uniform fashion.

Claim 32

The method of claim 22 wherein said broad band damped pulses are respectively directed along axes of transmission which are substantially normal to said borehole wall at their respective spaced locations for minimizing the propagation of compressional-wave energy toward the others of said spaced locations.

Claim 33

The method of claim 22 further including the step of: successively recording said electrical signals as a function of the depth of said borehole for producing a logging record representative of such formation anomalies in each of said sectors of said earth formations versus depth.

Claim 34

Apparatus adapted for investigating acoustically-responsive characteristics of well bore material and comprising: a body adapted for suspension in a well bore; first acoustic transducer means having a low mechanical Q cooperatively arranged on said body and adapted for directing a pulse of damped acoustic energy centered about a selected frequency toward a first location on a well bore wall; second acoustic transducer means having a low mechanical Q cooperatively arranged on said body and adapted for detecting acoustic energy having a predominant frequency content below said selected frequency and arriving from a second location on a well bore wall spatially disposed at a selected distance from said first location; transducer-driving means cooperatively arranged to drive said first transducer means for only a selected time interval such that said damped pulse is no greater than about 80 percent of the arithmetical product of the estimated travel time of compressional acoustic energy through such well bore material multiplied by the length of the shortest path through such well bore material between said first and second spaced locations for developing a distinguishable shear-wave of acoustic energy propagated along said path through such well bore material between said first and second spaced locations; and circuit means coupled to said second transducer means and cooperatively arranged for producing an electrical signal representative of the influence of such well bore material on the propagation of shear-wave acoustic energy along said path between said spaced locations.

Claim 35

Apparatus adapted for investigating acoustically-responsive characteristics of well bore material and comprising: a body adapted for suspension in a well bore; first acoustic transducer means having a low mechanical Q cooperatively arranged on said body and adapted for directing a pulse of damped acoustic energy centered about a selected frequency toward a first location on a well bore wall; second acoustic transducer means having a low mechanical Q cooperatively arranged on said body and adapted for detecting acoustic energy having a predominant frequency content below said selected frequency and arriving from a second location on a well bore wall spatially disposed at a selected distance from said first location; transducer-driving means cooperatively arranged to drive said first transducer means for only a selected time interval such that said damped pulse is no greater than about 80 percent of the arithmetical product of the estimated travel time of compressional acoustic energy through such well bore material multiplied by the length of the shortest path through such well bore material between said first and second spaced locations for developing a distinguishable shear-wave of acoustic energy propagated along said path through such well bore material between said first and second spaced locations; and circuit means coupled to said second transducer means and cooperatively arranged for producing an electrical signal representative of the influence of such well bore material on the propagation of shear-wave acoustic energy along said path between said spaced locations.

Claim 36

The apparatus of claim 30 wherein said first and second acoustic transducer means are respectively directed along outwardly-diverging first and second operating axes.

Claim 37

The apparatus of claim 30 wherein said predominant frequency content detected by said second transducer means is no greater than about 100-KHz.

Claim 38

The apparatus of claim 30 wherein said first and second acoustic transducer means are respectively directed along outwardly-diverging first and second operating axes substantially lying in a common plane perpendicular to the longitudinal axis of said body so that said path will substantially lie in said common plane.

Claim 39

The apparatus of claim 33 wherein said first and second operating axes are substantially at right angles to one another.

Claim 40

Apparatus adapted for locating formation anomalies which are effective for impairing the circumferentially-directed propagation of shear-wave acoustic energy through earth formations surrounding a borehole and comprising: a body adapted for suspension in a borehole; acoustic transmitting means on said body,having a low mechanical Q and cooperatively arranged for directing pulses of damped acoustic energy centered about a selected frequency into a borehole wall for developing shear-wave acoustic energy along N equal paths through such earth formations to a corresponding number circumferentially-spaced locations on a borehole wall; acoustic receiving means on said body,having a low mechanical Q and cooperatively arranged for selectively detecting acoustic energy having a predominant frequency content below said selected frequency and respectively arriving at said spaced locations; first circuit means cooperatively arranged to successively drive said acoustic transmitting means for only selected time intervals such that said damped pulses are each no greater than about 80 percent of the arithmetical product of the estimated travel time of compressional acoustic energy through such earth formations multiplied by the length of one of said equal paths such that a series of successive distinguishable shear-waves of acoustic energy are propagated along said equal paths to said spaced locations respectively; and second circuit means cooperatively arranged for producing N electrical signals respectively representative of the shear-wave acoustic energy respectively arriving at said spaced locations.

Claim 41

Apparatus adapted for locating formation anomalies which are effective for impairing the circumferentially-directed propagation of shear-wave acoustic energy through earth formations surrounding a borehole and comprising: a body adapted for suspension in a borehole; acoustic transmitting means on said body,having a low mechanical Q and cooperatively arranged for directing pulses of damped acoustic energy centered about a selected frequency into a borehole wall for developing shear-wave acoustic energy along N equal paths through such earth formations to a corresponding number circumferentially-spaced locations on a borehole wall; acoustic receiving means on said body,having a low mechanical Q and cooperatively arranged for selectively detecting acoustic energy having a predominant frequency content below said selected frequency and respectively arriving at said spaced locations; first circuit means cooperatively arranged to successively drive said acoustic transmitting means for only selected time intervals such that said damped pulses are each no greater than about 80 percent of the arithmetical product of the estimated travel time of compressional acoustic energy through such earth formations multiplied by the length of one of said equal paths such that a series of successive distinguishable shear-waves of acoustic energy are propagated along said equal paths to said spaced locations respectively; and second circuit means cooperatively arranged for producing N electrical signals respectively representative of the shear-wave acoustic energy respectively arriving at said spaced locations.

Claim 42

The apparatus of claim 35 wherein said acoustic receiving means include first and second acoustic receiving transducers respectively directed outwardly along separate first and second operating axes intersecting first and second ones of said spaced locations respectively.

Claim 43

The apparatus of claim 36 wherein the angle defined by said first and second axes is at least about 90*.

Claim 44

The apparatus of claim 35 wherein said acoustic receiving means include first and second acoustic receiving transducers respectively directed outwardly along separate first and second receiving axes intersecting first and second ones of said spaced locations respectively; and said acoustic transmitting means include first and second acoustic transmitting transducers respectively directed outwardly along separate first and second transmitting axes which are respectively divergent in relation to said first and second receiving axes.

Claim 45

The apparatus of claim 35 further including: recording means cooperatively coupled to said second circuit means and adapted for individually recording said electrical signals as a function of the depth of said acoustic transmitting means and acoustic receiving means as they are being operated.

Claim 46

The apparatus of claim 35 wherein said acoustic receiving means includes N acoustic receiving transducers uniformly arranged around said body and respectively directed along individual receiving axes at equal angles to one another; and said acoustic transmitting means include N acoustic transmitting transducers uniformly arranged around sAid body and respectively directed along individual transmitting axes at equal angles to one another to respectively position each of said transmitting transducers at a uniform circumferential distance from an associated one of said receiving transducers.

Claim 47

The apparatus of claim 40 wherein N equals four.

Claim 48

The apparatus of claim 40 wherein N equals four and each of said transmitting transducers is respectively directed along a transmitting axis that is at right angles to the receiving axis of a given one of said receiving transducers for positioning each associated pair of said receiving and transmitting transducers at 90* from one another.

Claim 49

The apparatus of claim 30 wherein mechanical Q is less than 1.0.

Claim 50

The apparatus of claim 35 wherein mechanical Q is less than 1.0.