Well pipe perforation detector

Apparatus is provided to detect a discontinuity indicative of a hole in the bore wall of an axially extending tubular member. It comprises: PA0 (a) a carrier to be traveled axially lengthwise in the bore of the tubular member, PA0 (b) an acoustical wave transmitter located on the carrier to transmit acoustical waves for travel toward the bore wall and for reflection therefrom, PA0 (c) an acoustical wave detector at least partially located on the carrier to receive acoustical waves reflected from the bore wall and to detect the presence or absence of such reflected waves, and PA0 (d) a control for providing an indication of such discontinuity, and for controlling the transmission to the detector of the reflected acoustical waves, and characterized in that the detector is controllably exposed to reception of a sequential succession of reflected acoustical waves corresponding to a sequential succession of bore wall portions from which the waves are reflected.

BACKGROUND OF THE INVENTION 
This invention relates generally to the detection of discontinuities, such 
as holes for example, in tubular members, and more particularly concerns 
apparatus adapted to be traveled in a well bore and operable to scan the 
bore and detect the existence of holes in well casing, pipe or tubing. 
It is frequently necessary or desirable to obtain information as to the 
location or depth of holes, cracks or leaks in well casing. For example, 
such holes may have been produced, as by firing bullets through the 
casing, to enhance production of well fluid. Accordingly, it may be 
desirable later to perforate the casing at a selected vertical spacing 
from the previously formed holes, and the location of the latter must be 
determined in order to accurately locate that selected spacing. There are 
other reasons for the need to locate previously formed holes, perforations 
or cracks in well pipe. 
One device usable to inspect tubular members is disclosed in U.S. Pat. No. 
4,212,207 to Conradi. That device employs a rotating reflector to reflect 
ultrasonic waves transmitted toward and received from a bore of a tubular 
member. One difficulty with using that device in a well bore containing 
well fluid such as petroleum is the apparent production of cavitation due 
to rotation of the reflector, and leading to formation of vapor bubbles in 
the path of ultrasonic wave transmission, and consequent poor signal 
detection, or signal to noise readings. In addition, the hydrodynamic drag 
on the rotating reflector requires undesirably high power input to the 
motor. 
SUMMARY OF THE INVENTION 
It is a major object of the invention to provide apparatus and method 
characterized as meeting the above need, while avoiding difficulties with 
the described prior device or devices. 
Basically, the apparatus of the invention comprises: 
(a) a carrier adapted to be traveled axially lengthwise in the bore of an 
axially extending tubular member such as a well casing containing holes or 
perforations, 
(b) acoustical wave transmitting means located on the carrier to transmit 
acoustical waves for travel toward the bore wall and reflection therefrom, 
(c) acoustical wave detector means (which may be associated with the 
transmitter) located on the carrier to receive acoustical waves reflected 
from the bore wall and to detect the presence, absence or modification of 
such reflected waves, and 
(d) means for providing an indication of such discontinuity, and including 
means for controlling the transmission to the detector means of the 
reflected acoustical waves. The detector is controllably exposed to 
reception of a sequential succession of reflected acoustical waves 
corresponding to a sequential succession of bore wall portions from which 
the waves are reflected. 
In one form of the invention, an acoustical wave reflector is utilized to 
reflect both transmitted waves traveling toward the well bore, and return 
waves reflected back from the well bore. That reflector is typically at 
least partially encapsulated in such manner that its rotation at high 
speed does not produce fluid cavitation; also, fluid drag is reduced with 
attendant decrease in rotational power requirements. Further, the 
provision of a computer controlled stepping motor to rotate the reflector 
provides precise angular velocity, position control and indexing. 
Reflected signal conditioning or processing circuitry may be employed to 
delay and invert the output, so as to attenuate the output indicative of 
no holes or flaws in the casing, and to increase the gain of the output 
indicative of the presence of holes and flows in the casing, and to 
provide vertical and azimuthal indication of the presence of such holes. 
These and other objects and advantages of the invention, as well as the 
details of illustrative embodiments, will be more fully understood from 
the following drawings and description, in which:

DETAILED DESCRIPTION 
In FIGS. 1 and 4, a well is shown at 10 and is cased at 11. The casing may 
contain perforations indicated at 100 formed for example by bullets fired 
through the casing and into the surrounding formation 12, in an effort to 
initiate fluid flow, i.e. production of oil or gas into the well. At times 
it is desired to know the exact depth of the perforations, so that the 
production of additional perforations may be effected in selected 
vertically spaced relation to the existing perforations, for example. 
In accordance with the invention, the apparatus 13 to detect a 
discontinuity (indicative of a perforation or hole) includes a carrier 13a 
adapted to be traveled axially lengthwise in the bore 11a of the casing 11 
or other tubular member. The carrier may include a body or cap 14 
suspended in the well, as via a wire line 15 which is suitably spooled at 
16 and 17 at the well surface, with a readout 18 indicative of the depth 
of the carrier in the well. 
The apparatus also includes acoustical wave transmitting means located on 
the carrier to transmit acoustical waves for travel toward the bore wall 
for reflection therefrom (or for lack of full reflection, or reduced 
reflection, in the event of the presence of a hole or discontinuity in the 
wall); and acoustical wave detector means located on the carrier to 
receive acoustical waves reflected from the bore wall and to detect the 
presence or absence of such reflected waves. 
As shown in FIG. 5, acoustical wave transmitting means such as 
transmitter/receiver (or transceiver) 18, 19, transmits acoustical waves 
for travel toward the bore wall for reflection therefrom (or for lack of 
full reflection, or reduced reflection, in the event of presence of a hole 
in the wall). The acoustical wave detector may be associated with the 
transmitter to detect the presence or absence of the bore wall reflected 
waves. As shown, the transmitter-detector may be supported or carried at 
20 by the body or housing 14a. 
The control means includes an optimized acoustical quarter wave plate or 
surface 21 angled at about 45.degree. to the body axis 22, to receive 
transmitted waves traveling at 23 along that axis and to reflect them 
laterally or radially for travel at 24 toward the bore wall. The waves 
reflected from that wall travel reversely back along path 24 for 
reflection by the plate and subsequent travel reversely along path 23 to 
the detector. The transmission of such waves may be intermittent to allow 
time for their reflection and reception by detector 19. A drive means such 
as stepping motor 25 rotates the reflector about axis 22 so that the 
detector is controllably exposed to reception of a sequential succession 
of reflected waves corresponding to a sequential succession of bore wall 
portions from which the waves are reflected. Thus, the bore wall is 
spirally completely scanned for the presence or absence of holes 101 as 
the apparatus is traveled lengthwise of the bore. 
Means is also provided to at least partially encapsulate the reflector and 
also to pass or transmit the acoustical waves along paths 23 and 24. Such 
means may take the form of a synthetic resin cylinder 26 whose axis 
coincides with axis 22, and which extends parallel to the axis of casing 
11. The resin may consist of EPON 815, a product of Shell Oil Co. The 
cylinder has a straight side wall 26b normal to path 24, (typically 
acoustically transparent at the chosen frequency, such as 1 MHz) whereby 
acoustic wave transmission through the cylinder wall is not deviated. 
Also, the cylinder 26 is supported as shown by body or cap 14. Lower end 
cap for cylinder 26 appears at 14b. The body and caps may consist of 
brass. 
Motor 25 is also carried by body 14, and its shaft 25a rotates and supports 
a metallic cup 27, filled with resin 27a as shown, and which in turn 
supports reflector 21 for rotation in fluid filled zone 28. Plastic such 
as polyurethane provides acoustical damping, and it may contain lead shot 
to enhance this effect. Synthetic resin body 29 at the face of the 
reflector forms a continuation of cup or cylinder 27, whereby there is no 
turbulence, bubbles or cavitation produced in the fluid in annular zone 28 
during reflector rotation. Body 29 may consist of epoxide (EPON 815) 
resin. The acoustic impedance of fluid in zone 28 is closely matched to 
that of the synthetic resin 29, to provide optimal acoustic coupling and 
transmission, interface reflection being minimized. An annular EPON window 
40 is provided in the body 14, to pass the acoustic pulses as the plate 21 
rotates. 
Cables from transducer 18/19 extend at 30 and 30a back upwardly through 
window 40 and wall 26 and emerge at 30b for extension along side wire line 
15 to the surface. Power to motor 25 may be transmitted by cable from the 
surface. 
Devices 32 and 32a on body 14 project for engagement with the casing bore 
11a for spacing the apparatus from that bore. Such devices are outwardly 
urged by springs 33. A sensor 42 may be coupled to pivoted device 32a to 
sense the pivoting of that device, for providing a signal indicative of 
pipe bore diameter. Three devices 32 and 32a may be spaced about axis 22, 
to center the instrument in the pipe or well bore. 
Acoustic coupling liquid such as glycerine or silicone oil may be filled 
into zone 28, whereby ultrasonic pulses are transmitted in liquid, and in 
solid plastic during their transmission from and to the transceiver 18/19. 
Also provided is circuitry connected with the detector to provide an output 
indicative of the presence of a perforation in the wall of the tubular 
member, in response to operation of the detector means when a reduced 
acoustic wave reflection, or no reflection, is received by the detector 
means. As shown, the circuitry may for example include surface recorder 
apparatus 60 receiving multiplexed or non-multiplexed signals from the 
transmitter and detector via a lead in the wire line or cable 15. The 
recorder includes circuitry 61 to amplify and process the signals, for 
transmission to printers 62 and 63. The latter incorporate media (such as 
paper) charts 64 and 65 whose feed is synchronized with the rate of 
travel, i.e. velocity, of the carrier 13 vertically in the well. Printer 
63 prints a horizontal line or bar 65a on strip or chart 65 each time an 
acoustic pulse is transmitted, the length of the lines being indicative of 
the amplitude of the acoutic pulse. Printer 62 similarly prints a 
horizontal line or bar 64a on strip or chart 64 each time a reflected 
pulse detected, the length of the line being indicative of the amplitude 
of the detected pulse. FIG. 2 shows that all the bars 65a corresponding to 
transmitted pulses have approximately the same amplitudes. FIG. 3 shows 
that nearly all of the reflected and detected pulses have approximately 
the same amplitudes, the remaining pulses at 64a' having significantly 
reduced amplitudes. These correspond to the attenuated pulse reflections 
(or absence of same) from the holes 100 in the casing. Circuitry 61 may 
incorporate signal inverting elements (amplifiers, for example) to 
attenuate the lines 64a and amplify the lines 64a', so that detection of 
the holes may be enhanced. 
Referring now to FIG. 6, control circuitry is there shown at 200 to process 
signal versions of the received acoustical waves, indicated as supplied at 
201 to such circuitry. The purpose of such circuitry is, for example, to 
provide substantially no output at 202 to the display 203 when no 
discontinuity in the bore wall is detected, and conversely to provide a 
positive output at 202 to the display when a discontinuity in the bore 
wall is detected. Normally, as shown in FIG. 7a, the transducer 18/19 will 
provide positive output signals seen at 204 and 205 indicative of the 
inner and outer surface respectively of the pipe or casing 11, whereas, as 
seen in FIG. 7b, the transducer 18/19 will provide very little or no 
output signals at 204a and 205a when a hole (discontinuity) is detected. 
Waves 204 and 205 are reflected signals off the pipe inner and outer 
walls. In FIGS. 7a and 7b, wave 207 is the outgoing (transmit) pulse, wave 
208 represents the reflection off the body 29, and waves 209 and 210 are 
reflections off the inner and outer walls of the housing window 40. Note 
in this regard, that the width ".omega..sub.1 " of the "transmit" surface 
of the transducer 18/19 is less than the width ".omega..sub.2 " of the 
"receive" surface of the body 29, so that all transmitted waves are passed 
into that body for reflection by mirror 21. 
The circuitry 200 in FIG. 6 includes sampling means to provide a selected 
number of samples of the received signal, per each revolution of the 
reflector. To this end, the circuitry may include rectifier and integrator 
circuits, as well as sampling circuitry, at 211. FIG. 8a shows a 
"reflected" signal 204' corresponding for example to reflected acoustic 
wave 204 (in FIG. 7a). A selected sampled portion of that signal 
corresponding to time interval "t" shown in FIG. 8a is rectified to 
produce signal 204", and integrated in FIG. 8c to produce signal 204". 
That sample is then digitized at 212 in FIG. 6, and passed at 213 to 
microprocessor 214. 
Merely for purposes of illustration, let there be 200 samples per 
revolution, i.e. transceiver 19 and circuitry 200 "looks at" each 
1.8.degree. of pipe bore to see if the signal reflected therefrom 
indicates, or does not indicate, any discontinuity therein. Other sample 
intervals could also be chosen, provided the interval is small enough to 
detect ("resolve") a discontinuity. 
The microprocessor receives the samples and typically combines them with 
averaged values of delayed sample values, so as to derive substantially no 
output at 202 when no discontinuities are detected, and positive output at 
202 when discontinuities are in fact present and detected. In the example 
of FIG. 9, 200 digitized samples per revolution are received at 215. (Note 
the sample switch 216 driven at 216' at the selected rate, as for example 
200 closings per revolution). Values at time t=o pass at 217 to the 
summing junction 218. Delayed values at t=one revolution, t=two 
revolutions and up to t=n revolutions are passed at 219-221 (via delay 
networks 219a-221a) to an averaging circuit (sum 222 and divider 223), and 
then passed at 224 to junction 218. When no discontinuity is present, the 
output at 225 is zero because of cancellation (subtraction) of positive 
inputs at 217 and 224. When a discontinuity is present, one of the inputs 
at 217 and 224 is almost zero, so that the output at 225 is positive. In 
this regard, the apparatus is being lifted or lowered in the well, so that 
the spiral scanning of the well pipe bore is being effected. Note in FIG. 
10 spiral scan lines 230 crossing a hole 231 in the pipe wall. The time 
interval "t" is represented by scan interval "d" in FIG. 10, less than the 
diameter of the hole. Referring to FIGS. 7 a and 7b again, if only one of 
the acoustic pulses 204 is detected, the interpretation is that the edge 
of the hole 231 is present. 
The azimuthal location of the hole 231 is also detected by means of 
circuitry shown at 240 in FIG. 9. That circuitry includes delay networks 
at 241a-243a receiving the sampled values at 215, and whose outputs are 
passed at 241-243 to an averaging circuit (sum 244 and divider 245). The 
output at 246 is passed to a summing junction 247 also receiving input 
from 215, as shown. The junction output at 248 provides a positive 
indication as to the presence or absence of the pipe wall opening 231 at 
each interval .DELTA.t (corresponding to .DELTA.d) i.e. azimuthally. The 
values at 224 and 246 may be averaged at 250 and summed with output 248 at 
a junction 251 to provide a further indication--i.e. a "coincidence" 
indicator at 253 of the vertical and azimuthal presence of a 
discontinuity, confirming its existence.