U.S. patent number RE43,960 [Application Number 13/079,546] was granted by the patent office on 2013-02-05 for system for measuring stress in downhole tubulars.
This patent grant is currently assigned to Baker Hughes Incorporated. The grantee listed for this patent is Joseph Gregory Barolak. Invention is credited to Joseph Gregory Barolak.
United States Patent |
RE43,960 |
Barolak |
February 5, 2013 |
System for measuring stress in downhole tubulars
Abstract
An apparatus for evaluating a tubular in a borehole of includes
at least two electromagnetic acoustic transducers. The transducers
are configured to generate and receive first and second acoustic
waves in the tubular. A difference in velocity of the two acoustic
waves is indicative of a stress field in the tubular.
Inventors: |
Barolak; Joseph Gregory
(Spring, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
Barolak; Joseph Gregory |
Spring |
TX |
US |
|
|
Assignee: |
Baker Hughes Incorporated
(Houston, TX)
|
Family
ID: |
39321473 |
Appl.
No.: |
13/079,546 |
Filed: |
April 4, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
11622101 |
Jan 11, 2007 |
7660197 |
Feb 9, 2010 |
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Current U.S.
Class: |
367/35;
181/105 |
Current CPC
Class: |
G01N
29/2412 (20130101); E21B 47/007 (20200501); G01N
29/07 (20130101); G01N 2291/02827 (20130101); G01N
2291/2636 (20130101) |
Current International
Class: |
G01V
1/40 (20060101) |
Field of
Search: |
;367/35 ;181/105 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1020716 |
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Jul 2000 |
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EP |
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1467060 |
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Oct 2004 |
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EP |
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WO2004106913 |
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Dec 2004 |
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WO |
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Other References
Innerspec Technologies, EMAT Technology,
http://www.innerspec.com/site/emat.asp, Oct. 10, 2006, pp. 1-2.
cited by applicant .
NDT Resource Center, Pulser-Receivers,
http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/
. . . Oct. 5, 2006, pp. 1-2. cited by applicant .
NDT Resource Center, Ultrasonic Measurement of Stress,
http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/
. . . Oct. 5, 2006, pp. 1-2. cited by applicant .
NDT Resource Center, Electromagnetic Acoustic Transducers (EMATs),
http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/
. . . Oct. 5, 2006, pp. 1-2. cited by applicant .
NDT Resource Center, Precision Velocity Measurements,
http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/
. . . Oct. 5, 2006, pp. 1-2. cited by applicant .
Cantrell, Jr. et al.; Relative Slope Invariance of Velocity-Stress
and Strain-Stress Curves, 1981 Ultrasonics Symposium, pp. 434-437,
1 Fig., 1 Table. cited by applicant .
Frankel et al.; Residual Stress Measurement in Circular Steel
Cylinders, 1983 Ultrasonics Symposium, pp. 1009-1012, 3 Figs. cited
by applicant.
|
Primary Examiner: Lobo; Ian
Attorney, Agent or Firm: Mossman Kumar & Tyler PC
Claims
What is claimed is:
1. An apparatus configured to evaluate a tubular within a borehole,
the apparatus comprising: a plurality of acoustic transducers
configured to generate and receive first and second acoustic waves
in a body of the tubular, the second acoustic wave differing from
the first acoustic wave in at least one of (A) a direction of
propagation, and (B) a direction of polarizations; and a processor
configured to determine from a velocity of the first acoustic wave
and a velocity of the second acoustic wave an indication of stress
in the tubular, wherein the first and second acoustic waves are
generated at a substantially similar stress condition of the
tubular.
2. The apparatus of claim 1 wherein the acoustic transducers are
selected from the group consisting of: (i) electro-magnetic
acoustic transducers, (ii) piezoelectric transducers, and (iii)
wedge transducers.
3. The apparatus claim 1 wherein the plurality of acoustic
transducers are disposed on at one least pad extendable from a body
of a logging tool.
4. The apparatus of claim 3 wherein the at least one pad comprises
a plurality of pads.
5. The apparatus of claim 1 wherein the first acoustic wave
comprises a horizontally-polarized shear wave propagating in a
first direction, and the second acoustic wave comprises a
horizontally-polarized shear waves propagating in a direction
substantially orthogonal to the first direction.
6. The apparatus of claim 1 wherein the first acoustic wave
comprises a horizontally polarized shear-wave and the second
acoustic wave comprises a vertically polarized shear-wave
propagating in a direction that is the same as a direction of
propagation of the horizontal the polarized shear wave.
7. The apparatus of claim 1 wherein the indication is related to at
least one of (i) a torque, (ii) an axial stress, (iii) a bending
load, (iv) a crushing load, (v) corrosion of the tubular, and (vi)
a mechanical defect in the tubular.
8. The apparatus of claim 2 further comprising a conveyance device
configured for conveying the logging tool into the borehole, the
conveyance device selected from (i) a wireline, (ii) a drilling
tubular, (iii) a slickline, and (iv) coiled tubing.
9. The apparatus of claim 1 wherein the tubular is selected from
the group consisting of: (i) production tubing, (ii) casing, and
(iii) a drilling tubular.
10. A method of evaluating a tubular within a borehole, the method
comprising: propagating and receiving first and second acoustic
waves in a body of the tubular, the second acoustic wave differing
from the first acoustic wave in at least one of (A) a direction of
propagation, and (B) a direction of polarizations; and determining
from a velocity of the first acoustic wave and a velocity of the
second acoustic wave an indication of stress in the tubular;
wherein the first and second waves are propagated at a
substantially similar stress condition of the tubular.
11. The method of claim 10 further comprising generating the first
acoustic wave and the second acoustic wave using a plurality of
acoustic transducers disposed on at least pad extendable from a
body of a logging tool.
12. The method of claim 11 further comprising disposing the
plurality of acoustic transducers on a plurality of pads.
13. The method of claim 10 wherein the first acoustic wave and the
second acoustic wave comprise horizontally-polarized shear waves
propagating in substantially orthogonal directions.
14. The method of claim 10 wherein the first acoustic wave
comprises a horizontally polarized shear-wave and the second
acoustic wave comprises a vertically polarized shear-wave
propagating in a direction that is the same as a direction of
propagation of the horizontal the polarized shear wave.
15. The method of claim 10 wherein the indicator is related to at
least one of (i) a torque, (ii) an axial stress, (iii) a bending
load, (iv) a crushing load, (v) corrosion of the tubular, and (vi)
a mechanical defect in the tubular.
16. The method of claim 10 further comprising conveying the logging
tool into the borehole using a conveyance device selected from (i)
a wireline, (ii) a drilling tubular, (iii) a slickline, and (iv)
coiled tubing.
17. The method of claim 10 wherein the tubular is selected from the
group consisting of: (i) production tubing, (ii) casing, and (iii)
a drillstring.
18. A computer-readable medium product having stored thereon
instructions that when read by a processor, cause the processor to
perform a method, the method comprising: determining an indication
of a stress field in a tubular from a velocity of a first acoustic
wave and a velocity of second acoustic wave generated and received
in a body of the tubular by a plurality of acoustic transducers,
the second acoustic wave differing from the first acoustic wave in
at least one of: (A) a direction of propagation, and (B) a
direction of polarization; wherein the first and second acoustic
waves are generated at a substantially similar stress condition of
the tubular.
19. The medium of claim 18 further comprising at least one of (i) a
ROM, (ii) an EPROM, (iii) an EEPROM, (iv) a flash memory, and (v)
an optical disk.
.Iadd.20. A non-transitory computer-readable medium product having
stored thereon instructions that when read by a processor, cause
the processor to perform a method, the method comprising:
propagating first and second acoustic waves in a body of a tubular,
the second acoustic wave differing from the first acoustic wave in
at least one of (A) a direction of propagation, and (B) a direction
of polarizations; and determining from a velocity of the first
acoustic wave and a velocity of the second acoustic wave an
indication of one of: (i) stress and (ii) a mechanical defect in
the tubular; wherein the first and second waves are propagated at a
substantially similar stress condition of the tubular..Iaddend.
.Iadd.21. The non-transitory computer-readable medium product of
claim 20 further comprising at least one of (i) a ROM, (ii) an
EPROM, (iii) an EEPROM, (iv) a flash memory, and (v) an optical
disk..Iaddend.
.Iadd.22. An apparatus configured to evaluate a tubular within a
borehole, the apparatus comprising: a plurality of acoustic
transducers configured to generate and receive first and second
acoustic waves in a body of the tubular, the second acoustic wave
differing from the first acoustic wave in at least one of (A) a
direction of propagation, and (B) a direction of polarizations; and
a processor configured to determine from a velocity of the first
acoustic wave and a velocity of the second acoustic wave an
indication of one of: (i) stress and (ii) a mechanical defect in
the tubular, wherein the first and second acoustic waves are
generated at a substantially similar stress condition of the
tubular..Iaddend.
.Iadd.23. The apparatus of claim 22 wherein the acoustic
transducers are selected from the group consisting of: (i)
electro-magnetic acoustic transducers, (ii) piezoelectric
transducers, and (iii) wedge transducers..Iaddend.
.Iadd.24. The apparatus claim 22 wherein the plurality of acoustic
transducers are disposed on at least one pad extendable from a body
of a logging tool..Iaddend.
.Iadd.25. The apparatus of claim 24 wherein the at least one pad
comprises a plurality of pads..Iaddend.
.Iadd.26. The apparatus of claim 22 wherein the first acoustic wave
comprises a horizontally-polarized shear wave propagating in a
first direction, and the second acoustic wave comprises a
horizontally-polarized shear wave propagating in a direction
substantially orthogonal to the first direction..Iaddend.
.Iadd.27. The apparatus of claim 22 wherein the first acoustic wave
comprises a horizontally polarized shear-wave and the second
acoustic wave comprises a vertically polarized shear-wave
propagating in a direction that is the same as a direction of
propagation of the horizontally polarized shear wave..Iaddend.
.Iadd.28. The apparatus of claim 22 wherein the indication is
related to at least one of (i) a torque, (ii) an axial stress,
(iii) a bending load, (iv) a crushing load, (v) corrosion of the
tubular, and (vi) a mechanical defect in the tubular..Iaddend.
.Iadd.29. The apparatus of claim 22 further comprising a conveyance
device configured for conveying the logging tool into the borehole,
the conveyance device selected from (i) a wireline, (ii) a drilling
tubular, (iii) a slickline, and (iv) coiled tubing..Iaddend.
.Iadd.30. The apparatus of claim 22 wherein the tubular is selected
from the group consisting of: (i) production tubing, (ii) casing,
and (iii) a drilling tubular..Iaddend.
.Iadd.31. A method of evaluating a tubular within a borehole, the
method comprising: propagating first and second acoustic waves in a
body of the tubular, the second acoustic wave differing from the
first acoustic wave in at least one of (A) a direction of
propagation, and (B) a direction of polarization; and determining
from a velocity of the first acoustic wave and a velocity of the
second acoustic wave an indication of one of: (i) stress and (ii) a
mechanical defect in the tubular; wherein the first and second
waves are propagated at a substantially similar stress condition of
the tubular..Iaddend.
.Iadd.32. The method of claim 31 further comprising generating the
first acoustic wave and the second acoustic wave using a plurality
of acoustic transducers disposed on at least one pad extendable
from a body of a logging tool..Iaddend.
.Iadd.33. The method of claim 32 further comprising disposing the
plurality of acoustic transducers on a plurality of
pads..Iaddend.
.Iadd.34. The method of claim 31 wherein the first acoustic wave
and the second acoustic wave comprise horizontally-polarized shear
waves propagating in substantially orthogonal
directions..Iaddend.
.Iadd.35. The method of claim 31 wherein the first acoustic wave
comprises a horizontally polarized shear-wave and the second
acoustic wave comprises a vertically polarized shear-wave
propagating in a direction that is the same as a direction of
propagation of the horizontally polarized shear wave..Iaddend.
.Iadd.36. The method of claim 31 wherein the indicator is related
to at least one of (i) a torque, (ii) an axial stress, (iii) a
bending load, (iv) a crushing load, (v) corrosion of the tubular,
and (vi) a mechanical defect in the tubular..Iaddend.
.Iadd.37. The method of claim 31 further comprising conveying the
logging tool into the borehole using a conveyance device selected
from (i) a wireline, (ii) a drilling tubular, (iii) a slickline,
and (iv) coiled tubing..Iaddend.
.Iadd.38. The method of claim 31 wherein the tubular is selected
from the group consisting of: (i) production tubing, (ii) casing,
and (iii) a drillstring..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present disclosure provides an apparatus and method for testing
the structural integrity of tubing and casings used in a borehole.
In particular, the present disclosure discusses an apparatus and
method using ultrasonic waves to estimate the stress on tubulars in
a borehole environment.
2. Description of the Related Art
The environmental conditions encountered by production casing and
tubing used in hydrocarbon recovery can result in stress buildup in
the tubing. This stress in the tubing may come from pressure and
temperature variations during production, movement of the formation
due to pressure depletion, "flow" of salt formations, etc. This
stress may eventually lead to casing or tubing collapse or shear,
rendering the well inoperable. Prior art methods have generally
involved waiting for the buildup of this stress to a point where
mechanical deformation occurs before the stress can be
detected.
Stress buildup may also occur in a drillstring during the drilling
of a borehole. During drilling operations, it is not uncommon for
the drillstring to get stuck. To recover the stuck pipe, it is
first required to determine the upper most `free` point of the
drillpipe. This is done by measuring the torque and/or pull induced
from the surface or the physical stretching of the drillpipe due to
this torque or pull.
Stress in a casing or tubing may be in the form of an axial load,
circumferential torque, or a bending moment. Although stresses are
applied on the drilling equipment while in use in the borehole
environment, testing for wear typically occurs uphole or in a
laboratory, often by observing the residual stress on the mandrel
from its use. In general, when a stress is applied to a material
and then removed, a residual stress remains on the material. This
residual stress is often observed by checking for atomic
dislocations at the crystalline level of the material and can be
used to determine properties related to the structural integrity of
the material. Various methods have been designed to observe
residual stress on materials, including X-ray diffraction
techniques, determining magnetic permeability, and ultrasonic
testing.
Changes in ultrasonic wave propagation speed, along with energy
losses from interactions with materials microstructures are often
used to nondestructively gain information about properties of the
material. An ultrasonic wave may be created in a material sample,
such as a solid beam, by creating an impulse at one region of the
sample. As the wave propagates through the sample, stresses and
other material changes or defects affect the wave. Once the
affected wave is recorded, the nature of the stresses of the
material can be determined. Measurements of sound velocity and
ultrasonic wave attenuation can be related to the elastic
properties that can be used to characterize the texture of
polycrystalline metals.
Velocity measurements are of interest in longitudinal waves
propagating in gases, liquids, and solids. In solids, transverse
(shear) waves are also of interest. The velocity of a longitudinal
wave is independent of a sample's geometry when the dimensions at
right angles to the sample are large compared to the sample area
and to the wavelength. The velocity of a transverse wave is
affected little by the physical dimensions of the sample. The
relationship between stress and velocity has been discussed for
example by Cantrell and Chern, "Relative Slope Invariance of
Velocity-Stress and Strain-Stress Curves," Ultrasonics Symposium,
1981.
Measurement of ultrasonic velocity is performed by measuring the
time it takes for a pulse of ultrasound to travel from one
transducer to another (pitch-catch scenario) or return to the same
transducer (pulse-echo scenario). Another measurement method
compares the phase of the detected sound wave with that of a
reference signal, wherein slight changes in the transducer
separation are seen as slight phase changes, from which the sound
velocity can be calculated. These methods are suitable for
estimating acoustic velocity to about 1 part in 100. Standard
practice for measuring velocity in materials is detailed in
American Society for Testing and Materials (ASTM) Publication E494.
Residual stress measurements in cylinders have been discussed for
example by Frankel et al., "Residual Stress Measurement in Circular
Steel Cylinders," Ultrasonics Symposium, 1983.
An oriented measurement of magnetic permeability has also been used
to determine stress. Several patents discuss the use of magnetic
permeability to measure stress. U.S. Pat. No. 4,708,204 to Stroud
discusses a system for determining the stuck point of pipe in a
borehole including a wireline tool having an exciter coil and a
receiver coil axially spaced from one another. The exciter coil is
driven at a pre-selected low frequency and the voltage induced into
the receiver coil is related to the magnetic permeability of a pipe
through which the tool is run. A receiver coil voltage log is run
of the section of pipe in the region of the stuck point first while
that region is substantially free of mechanical stress. A second
log of the same region is run with the pipe under mechanical
stress. Comparison of the two logs determines the stuck point from
the difference in magnetic permeability of the stressed pipe above
the stuck point and the unstressed pipe below the stuck point.
European Patent Application EP 1 647 669 A1 discusses a method and
apparatus for determining a stuck pipe. In one embodiment, a free
point logging tool, having a freepoint sensor and, optionally, an
acoustic sensor, is attached to a working line such as a wireline.
The freepoint sensor acquires magnetic permeability data in a
string of pipe, while the acoustic sensor acquires acoustic data in
the pipe. Two sets of data for each sensor are acquired: one in
which the pipe is unstressed, and one in which the pipe is
stressed. The first set and second sets of magnetic permeability
data are compared to determine the stuck point location of the
pipe. The first and second sets of acoustic data are compared to
determine the matter in which the pipe is stuck. EP 1 647 669 A1
references the use of travel time to measure stress but anticipates
only a measure of axial travel time.
In petroleum exploration, time spent raising and lowering a
drilling apparatus from and into a borehole is time that could
otherwise be used in exploration and is thus costly. Historically,
stress on a tubular containing drilling equipment used in a
borehole has only been determined by looking for actual physical
movement of the tubular (i.e., freepoint indicators) or by physical
distortion of the tubular (i.e., casing inspection). Thus, it is
desirable to perform stress testing of a drilling apparatus
obtaining measurements downhole.
SUMMARY OF THE INVENTION
One embodiment of the invention is an apparatus for evaluating a
tubular within a borehole. The apparatus includes a plurality of
acoustic transducers configured to generate and receive first and
second acoustic waves in the tubular. The first and second acoustic
waves differ from each other in a direction of propagation and/or a
direction of polarization. The apparatus further includes a
processor configured to determine from the velocity of the first
acoustic wave and the velocity of the second acoustic wave an
indication of stress in the tubular. The acoustic transducers may
include electromagnetic acoustic transducers, piezoelectric
transducers, and/or wedge transducers. The acoustic transducers may
be disposed on at least one pad extending from a body of for
logging tool. The at least one pad may include a plurality of pads.
The first and second acoustic waves may include a horizontally
polarized shear wave and a vertically polarized shear wave
propagating in the same direction. The indicator may be related to
a torque, an axial stress, a bending load, a crushing load,
corrosion of the tubular, and a mechanical defect in the tubular.
The apparatus may further include a conveyance device used for
conveying the logging tool into the borehole. The conveying device
may be selected from a wireline, a drilling tubular, a slickline,
and/or coiled tubing. The tubular may be production tubing, casing,
and/or a drilling tubular.
Another embodiment of the invention is a method of evaluating a
tubular within a borehole. The method includes propagating first
and said second acoustic waves in the tubular. The second acoustic
wave differs from the first acoustic wave in a direction of
propagation and/or a direction of polarization. The method further
determines from the velocity of the first acoustic wave and the
velocity of the second acoustic wave an indication of the stress
field in the tubular. The first and second acoustic waves may be
generated using a plurality of acoustic transducers positioned on
at least one pad extendable from a body of a logging tool. The
first acoustic wave may include a horizontally polarized shear wave
and the second acoustic wave may include a vertically polarize
shear wave propagating in the same direction as the horizontally
polarized shear wave. The indicator may be related to a torque, an
axial stress, a bending load, a crushing load, corrosion, and a
mechanical defect in the tubular. The method may further include
conveying the logging tool into the borehole using a conveyance
device that may be a wireline, a drilling tubular, a slickline,
and/or coiled tubing. The tubular may be a production tubing, a
casing, and/or a drillstring.
Another embodiment of the invention is a computer-readable medium
for use with an apparatus for evaluating a tubular within a
borehole. The apparatus includes a plurality of acoustic
transducers configured to propagate and receive first and second
acoustic waves in the tubular. The first acoustic wave and the
second acoustic wave differ in at least one of a directional
propagation, and a direction of polarization. The medium includes
instructions which enable a processor to determine from the
velocity of the first acoustic wave and the velocity of the second
acoustic wave an indication of a stress in the tubular. The medium
may include a ROM, an EPROM, and EEPROM, a flash memory and/or an
optical disk.
BRIEF DESCRIPTION OF THE DRAWINGS
For a detailed understanding of the present invention, reference
should be made to the following detailed description of the
invention, taken in conjunction with the accompanying drawing and
in which:
FIG. 1 is a schematic illustration of a wireline logging
system;
FIG. 2A is an illustration of a logging tool according to the
present invention within a cased borehole with poor cementing;
FIG. 2B shows an exemplary pad containing an array of transducers
capable of performing the method of the present disclosure;
FIGS. 3A-E shows various practical transducer configurations that
may be used on a material and resultant forces on the surface of
the material for producing acoustic pulses; and
FIG. 4 is a schematic illustrations of two EMATs configured to
generate shear-waves in two different directions.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is discussed with reference to specific
logging instruments that may form part of a string of several
logging instruments for conducting wireline logging operations. It
is to be understood that the choice of the specific instruments
discussed herein is not to be construed as a limitation and that
the method of the present invention may also be used with other
logging instruments as well.
FIG. 1 shows a logging tool 10 suspended in a borehole 12 that
penetrates earth formations such as 13, from a suitable cable 14
that passes over a sheave 16 mounted on drilling rig 18. By
industry standard, the cable 14 includes a stress member and seven
conductors for transmitting commands to the tool and for receiving
data back from the tool as well as power for the tool. The tool 10
is raised and lowered by draw works 20. Electronic module 22, on
the surface 23, transmits the required operating commands downhole
and in return, receives data back which may be recorded on an
archival storage medium of any desired type for concurrent or later
processing. The data may be transmitted in analog or digital form.
Data processors such as a suitable computer 24, may be provided for
performing data analysis in the field in real time or the recorded
data may be sent to a processing center or both for post processing
of the data.
FIG. 2A is a schematic external view of a borehole system according
to the present invention. The tool 10 comprises the arrays 26 and
is suspended from cable 14. Electronics modules 28 and 38 may be
located at suitable locations in the system and not necessarily in
the locations indicated. The components may be mounted on a mandrel
34 in a conventional well-known manner. In an exemplary assembly,
the outer diameter of the assembly is about 5 inches and about
fifteen feet long. An orientation module 36 including a
magnetometer and an accelerometer or inertial guidance system may
be mounted above the imaging assemblies 26 and 32. The upper
portion 38 of the tool 10 contains a telemetry module for sampling,
digitizing and transmission of the data samples from the various
components uphole to surface electronics 22 (FIG. 1) in a
conventional manner. If acoustic data are acquired, they are
preferably digitized, although in an alternate arrangement, the
data may be retained in analog form for transmission to the surface
where it is later digitized by surface electronics 22.
FIG. 2B shows an exemplary pad containing transducers capable of
performing the method of the present disclosure. Pad 40 includes
one or more acoustic sensors 45. In one embodiment of the
invention, the acoustic sensors comprise electromagnetic acoustic
transducers (EMATS) assembled in a pattern to obtain measurements
of ultrasonic velocities for the purpose of determining a stress on
a material. The pad 40 is attached to the mandrel 34 of FIG. 2A by
way of supports 42. The pattern of EMATS shown in FIG. 2B is only
an example of many possible configurations that may be used.
In another embodiment of the invention, the sensors may be disposed
on two or more vertically spaced apart pads. Such an arrangement
makes it easier to make axial measurements as a described
below.
The present disclosure generally uses orthogonal acoustic velocity
measurements in the steel tubulars to determine in-situ stress. In
one possible embodiment, the velocity of a vibrational (acoustic)
wave traveling axially in a casing is compared to the velocity of a
similar wave traveling circumferentially at substantially the same
point in the casing. Differences in the resulting measured
velocities indicate either torque or axial stress in the casing.
With a more complex arrangement using segmented circumferential or
axial measurements, differences in axial stress around the
circumference of the casing may indicate bending or crushing loads
being applied to the casing by the formation. Also, localized
stress measurements made in the area of casing corrosion or
mechanical defects can be used to predict potential points of
casing rupture. Since the properties of casing steel may vary, the
use of orthogonal measurements is critical to identifying changes
caused by stress from background changes in materials.
Measurement of acoustic travel time may be substituted with
alternative measurements that are affected by casing stress. One
alternative measurement might be magnetic permeability. The angle
between the two measurements may be something other than
orthogonal. A 90.degree. angle, however, maximizes sensitivity of
the measurement.
Measurements of stress in casing or tubing downhole have multiple
potential uses. These uses potentially include casing deformation,
freepoint indicators, and formation stresses (as transferred to the
casing). The disclosed method offers a potential method of making
an absolute stress measurement in a casing or tubing.
The present disclosure discusses an apparatus and method for
performing acoustic testing on a casing or tubular. An ultrasonic
wave can be produced at one location on the tubular and the wave
can later be detected at the same or another location on the
tubular. One way to create ultrasound within a material is via an
EMAT. An EMAT comprises a magnetic element, such as a permanent
magnet, and a set of wires. In general, the EMAT is placed against
the material to be tested such that the set of wires are located
between the magnetic element and the material to be tested. When a
wire or coil is placed near to the surface of an electrically
conducting object and is driven by a current at a desired
ultrasonic frequency, eddy currents are induced in a near surface
region. If a static magnetic field is also present, these currents
experience a Lorentz force of the form {right arrow over
(F)}={right arrow over (J)}.times.{right arrow over (B)} (1) where
{right arrow over (F)} is a body force per unit volume, {right
arrow over (J)} is the induced dynamic current density, and {right
arrow over (B)} is the static magnetic induction. Thus the Lorentz
force converts the electrical energy into a mechanical vibration,
which can be used to test the material. Alternatively, EMATs may
also be based on the use of magnetostrictive properties of the
casing/tubing.
Since no coupling device is used between the EMAT and the tested
material, the EMAT can operate without contact at elevated
temperatures and in remote locations. Thus EMATs can eliminate
errors associated with coupling variation in contact measurements
and thereby provide precise velocity or attenuation
measurements.
The coil and magnet structure used in an EMAT can be designed to
excite complex wave patterns and polarizations. FIGS. 3A-3F shows a
number of practical EMAT configurations including a biasing magnet
structure, a coil configuration, and resultant forces on the
surface of the solid for producing acoustic pulses using EMATS. The
configurations of FIGS. 3A, 3B, and 3C excite beams propagating
normal to the surface of a half-space and produce, respectively,
beams with radial, longitudinal, and transverse polarizations. The
configurations of FIGS. 3D and 3E use spatially varying stresses to
excite beams propagating at oblique angles or along the surface of
a component. These configurations are considered for illustrative
purposes although any number of variations on these configurations
can be used.
FIG. 3A shows a cross-sectional view of a spiral coil EMAT
configuration for exciting radially polarized shear waves
propagating normal to the surface. Permanent magnet 301 and tubular
307 are separated by a space containing a wire represented by one
or more wires as shown as wire segments 303 and 305. The wire
segments 303 and 305 represent separate groups of wire segments
carrying current in anti-parallel directions in the manner
illustrated in FIG. 3A, thereby exciting the radially polarized
shear waves propagating normal to the surface.
FIG. 3B shows a cross-sectional view of a tangential field EMAT
configuration for exciting longitudinally polarized compressional
waves propagating normal to the surface. Permanent magnet 311 is
placed against tubular to produce a magnetic field parallel to the
surface. A magnet such as the magnet 311 of FIG. 3B having a
horseshoe configuration may be used. Wires segments 313 provide a
current flowing between the magnetic poles perpendicular to the
direction of the local magnetic field of magnet 311. Wire segments
315 provide a current flowing anti-parallel to the current in wire
segments 313 in a region exterior to the magnetic poles.
FIG. 3C shows a cross-sectional view of a normal field EMAT
configuration for exciting plane polarized shear waves propagating
normal to the surface. The configuration comprises a pair of
magnets 321 and 323 assembled so as to provide two anti-parallel
magnetic fields at the surface of the tubular. The permanent
magnets 321 and 323 are separated from tubular 329 by a space
containing one or more wires 325 and 327 providing anti-parallel
current.
FIG. 3D shows a cross-sectional view of a meander coil EMAT
configuration for exciting obliquely propagating L (long) or SV
waves, Rayleigh waves, or guided modes (such as Lamb waves) of
plates. The configuration includes a permanent magnet and tubular
separated by a space containing wire segments such as one or more
wires 333 and 335 which provides current flowing in sequentially
alternating directions.
FIG. 3E shows a cross-sectional view of a periodic permanent magnet
EMAT for exciting grazing or obliquely propagating horizontally
polarized (SH) waves or guided SH modes of plates. Multiple
permanent magnets such as magnets 341 and 343 are assembled so as
to provide alternating magnetic polarities at the surface of the
tubular. The magnetic assembly and tubular are separated by a space
containing a wire 345 that provides a current in a single
direction.
For sheet and plate specimens experiencing applied or residual
stress, the principal stresses .sigma..sub.a and .sigma..sub.b may
be inferred from orthogonal velocity measurements. Eq. (2) relates
ultrasonic velocities to the principle stresses experienced in a
sheet or plate:
2.rho.V.sub.avg[V(.theta.)-V(.theta.+.pi./2)]=.sigma..sub.a-.sigma..sub.b
(2). In Eq. (2), V.sub.avg is the average shear velocity and .rho.
is a density of a material. V(.theta.) and V(.theta.+.pi./2) are
mutually perpendicular wave velocities as can be detected at a
transducer. It is understood that velocity difference
V(.theta.)-V(.theta.+.pi./2) is maximized when the ultrasonic
propagation directions are aligned with the principal stress axes.
The magnitude of this difference, along with the density and mean
velocity can be used to estimate the principal stress
difference.
FIG. 4 shows an arrangement of two EMATS 145A and 145B. The pad 40
illustrated and FIG. 2B is not shown. When EMATS 145A and 145B are
of the type shown in FIG. 3E, they will produce horizontally
polarized shear-wave propagating along the tool axis and
circumferential to the tool axis, thus providing the necessary
measurements for solving eqn. (2). Those versed in the art would
appreciate that using an array of transducers as shown in FIG. 2B,
it would be possible to generate horizontally polarized shear waves
propagating in different directions. The EMATs, in addition to
acting as transmitters, can also act as receivers, so that by
having two EMATs with the same polarization at different spatial
positions, it is possible to determine the velocity of propagation
of the wave. In addition, by having such transducers mounted on
different pads on the downhole logging to it is possible to make
measurements of the stress differences circumferentially around the
borehole.
By using transducers of the type shown in FIG. 3B it would be
possible to make measurements of compression velocity at different
azimuthal positions along the borehole. Variations in this velocity
are indicative of circumferential variations of the stress. The
same is true using transducers of the type shown in FIG. 3C. But
using transducers of the type shown in FIG. 3D it would be possible
to generate Rayleigh waves on land waves along the surface of the
tubular.
In addition, those versed in the art would recognize that the
velocity of propagation of a vertically polarized shear-wave may
differ from the velocity of propagation of the horizontally
polarized shear-wave in the same direction. This difference may
also be indicative of the stress in the garden. Such measurements
may be obtained by using transducers of the type shown in FIGS. 3D
and 3E.
In one embodiment a velocity of an acoustic wave traveling axially
in the casing is compared to the velocity of a similar wave
traveling circumferentially at substantially the same point in the
casing. Differences in the measured velocities are indicative of
torque or axial stress in the casing. With a more complex
arrangement using segmented circumferential or axial measurements
made with pad-mounted EMATs, differences in axial stress around the
circumference of the casing are indicative of bending a crushing
load being applied to the casing by the formation. Localized test
measurements made in the area of casing corrosion or mechanical
defects are used to predict potential points of casing failure. As
would be known to those versed in the art, such casing corrosion or
mechanical defects would produce changes in the stress field. All
of these use measurements having orthogonal direction of
propagation or orthogonal polarization or both. Properties of
casings steel may vary, so that the use of such measurements is
important in identifying changes caused by stress from changes
caused by differences in the steel.
The invention has been described above is a specific example of
using EMATS as the acoustic sensors. This is not to be construed as
a limitation on the invention. The method of the invention could
also be carried out using other side types of sensors such as
piezoelectric transducers and wedge transducers. Wedge transducers
are discussed, for example, in U.S. Pat. No. 4,593,568 to Telford
et al.
The invention has been described above with reference to a device
conveyed on a wireline. However the method of invention may also be
practices using the tool conveyed on a tubular such as a
drillstring or coiled tubing, or on a slickline.
Implicit in the processing method of the present invention is the
use of a computer program implemented on a suitable machine
readable medium that enables the processor to perform the control
and processing. The machine readable medium may include ROMs,
EPROMs, EAROMs, Flash Memories and Optical disks. Such a computer
program may output the results of the processing, such as the
stress constraints, to a suitable tangible medium. This may include
a display device and/or a memory device.
* * * * *
References