Note: Descriptions are shown in the official language in which they were submitted.
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DOWNHOLE ULTRASONIC WELL CLEANING DEVICE
Field of Invention
This invention relates to downhole cleaning using an ultrasonic device. More
particularly, this invention relates to downhole cleaning utilizing ultrasonic
generator(s)
powered by piezoelectric element(s), not requiring external electric power.
The ultrasonic
generator and piezoelectric element are placed within the completion equipment
and the
piezoelectric element(s) is normally in an unstrained state, generating no
electrical current, but
when subjected to mechanical force, it generates electricity to power the
ultrasonic device.
Background of the Invention
Well productivity is often impaired by fine particles lodged in restrictions
or caked on
the wellbore. Chemical cleaning has limited effectiveness in removal of these
materials.
Ultrasonic devices have been shown to enhance cleaning and particle separation
from liquids.
Current downhole ultrasonic cleaning devices are powered by external electric
sources
connected to the device by wires or cables.
It is known to enhance well cleaning using acoustic excitation. U.S. 4,280,557
discloses an apparatus for cleaning an extended number of apertured portions
of the lower
region of an oil well casing, which includes a sonic oscillator, a stem member
in the form of
an elongated elastic tube which runs along said extended number of apertured
portions, said
oscillator to be attached to the top end of said stem member in the region of
the apertured
portions to be cleaned, and means for driving said oscillator. U.S. 5,458,860
discloses the use
of sonic energy to enhance the removal of alkaline earth scale using an
aqueous solution
having a pH of about 8 to 14 and comprising a chelating agent.
The use of an external electric power source connected by a cable to power an
electroacoustic ultrasonic energy producing transducer is disclosed in U.S.
5,109,922 which
describes a power supply adjacent to the well and an electrical conductor
means of a length
sufficient to extend from ground level to at least the level of oil in the
well for conducting
alternating electrical power from said power supply to said transducer.
U.S. 5,184,678 discloses an apparatus for stimulating fluid production in a
producing well
wherein a well stimulating tool comprising a sealed tool housing with an
acoustic transducer
in the housing is run into a producing well on an electric wireline and placed
at a depth
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U. S. 5,184,678 discloses an apparatus for stimulating fluid production in a
producing well
wherein a well stimulating tool comprising a sealed tool housing with an
acoustic transducer
in the housing is run into a producing well on an electric wireline and placed
at a depth
opposite perforations in the producing zone. Similarly, U.S. 5,595,243
discloses a method
and apparatus for cleaning the wellbore and the near wellbore region in which
a sonde is
provided which is adapted to be lowered into a borehole and which includes a
plurality of
acoustic transducers arranged around the sonde, and wherein electrical power
provided by a
cable is converted to acoustic energy.
The use of mechanical coupling to produce low frequency waves is disclosed in
U. S.
4,469, 1 75, which describes a mechanoacoustic transducer, which comprises a
plurality of .
circumferentially spaced contiguous vibratile plate members, which are driven
in phase. by a
rotating cylindrical cam. The cam is shaped to provide radial oscillatory
displacements of the.
vibratile plates of sufficient amplitude to'generate acoustic power density
levels in liquids..
The use of fluid coupling to produce vibration to enhance well cementing is
disclosed
in U.S. 4,658,897. The transducer members are within a sleeve that is filled
with oil and
communicates vibrationsbfrom the transducer members.
U.S. 4,788,467 discloses in combination a housing, at least one transducer
disposed in
the housing and having properties of receiving electrical energy and convening
the electrical
energy into expansions and contractions of the transducer for the pumping of
oil in the oil well
in accordance with such expansions and contractions, passages extending into
and out of the
housing at opposite ends of the housing at a position below the transducer, a
piston disposed in
the housing for movement in accordance with the pressure of the fluid in the
oil well, and a
spring supported between the piston and the housing for compression and
expansion to inhibit
any cavitation of the oil in the oil well as a result of such expansion and
contraction of the
transducer and as a result of changes in the temperature of the oil in the oil
well.
U.S. 5,554,922 discloses a system for the conversion of pressure fluctuations
prevailing in a fluid distribution piping system into electrical energy,
characterized in that it
includes a casing, at least one chamber formed in the casing which may be
linked to a fluid
system and which is limited on one side by a wall which may be moved back and
forth under
the influence of the pressure prevailing in the fluid system, and at least one
apparatus which is
connected to the movable wall and which converts the mechanical
T111547FF C,RST 2
AMENDED SHEET
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As mentioned above, current downhole ultrasonic cleaning devices are powered
by
external electric sources connected to the device by wires or cables. It would
be extremely
valuable in the art if there were an alternative, lower cost, simpler way to
power such devices
using mechanical force to generate electrical power using a piezoelectric
device. In many
industrial applications, particularly those involved in the drilling,
completion, and workover of
oil and gas production wells, equipment normally used in these applications is
already
designed to apply large magnitude, controlled loads or stresses from the
surface or other
remote location to the equipment at the bottom of the well. On the other hand
delivering
external electrical power as required in the prior art requires additional
equipment not
normally installed in the well. The prior art does not recognize the
opportunity to use the
available mechanical force to create electricity to power the downhole
ultrasonic device.
Summary of the Invention
In accordance with the foregoing the present invention is a cleaning apparatus
for any
structure where caking of particles may affect productivity, characterized in
that it requires no
. external electrical source and includes the following elements:
1) At least one ultrasonic sonde or horn that produces ultra high frequency
pressure
oscillations in a fluid when energized by an electrical signal;
2) A generator to deliver the necessary electrical signal to the sonde or
horn, said
generator containing appropriate circuitry to provide the appropriate voltage,
power, and
frequency of electrical excitation to the ultrasonic sonde in item 1);
3) At least one apparatus which converts mechanical energy into electrical
energy,
preferably a piezoelectric element, also placed or inserted within said
structure connected to
the generator described in item 2) and through it able to provide electrical
excitation to the
ultrasonic sonde; and
4) A means for applying mechanical force to said apparatus to generate
electricity to
power said mechanical electrical converter. The invention is also a method of
cleaning a
structure that is enclosed, or otherwise difficult to access, and where
mechanical force can be
applied more readily or at lower cost than electrical power, such as, for
example, an enclosed
tank or vessel, or a pipeline or subterranean well, such as those used for oil
and gas
production, using an ultrasonic source, characterized in that no external
electric source is
required, which includes the elements of:
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1) Placing in the completion equipment one or more ultrasonic
generator(s);
2) Placing within the completion equipment in close proximity to the
ultrasonic generator(s) one or more apparatus(s) for converting mechanical
force to
electrical energy, preferably piezoelectric element(s), said element(s)
normally in an
unstrained or relaxed state; and
3) Applying mechanical force to said piezoelectric element when it is
desirable to generate ultrasonic excitation to enhance well cleaning.
According to one aspect of the present invention, there is provided a
cleaning apparatus for dislodging caked particles from a production tubing in
a
wellbore comprising: at least one ultrasonic generator for conditioning
electrical
energy to excite an ultrasonic energy sonde; at least one ultrasonic energy
sonde,
which while excited, converts the electrical energy into ultrasound energy for
dislodging caked particles; at least one converter apparatus, which upon
application
of a tension or compression force converts mechanical energy into the
electrical
energy and the tension or compression force is applied to the at least one
converter
apparatus by a second tubing which is inserted into or around the production
tubing
or by a mechanical device which is inserted into the well on a non-conducting
wire.
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Brief Description of the Diagrams
Figure 1 is a block diagram of the invention configured for temporary
insertion into
the well or other structure of fixed diameter with a packer on tubing.
Figure 2 is a diagram of the invention configured for permanent installation
in the
wellbore and activation by inserted tubing.
Figure 3 is a graph showing voltage vs. current for a piezo generator.
Figures 4(a) and 4(b) are diagrams of compression and tension generators,
respectively.
Figures 5(a) and 5(b) are diagrams of parallel and transverse shear
generators,
respectively.
Figures 6(a) and 6(b) are diagrams of series and parallel bending generators,
respectively.
Detailed Description of the Invention
Piezoelectric materials transform energy from mechanical to electrical and
vice-versa.
Piezoelectric materials produce an electric field when exposed to a change in
dimension
caused by an imposed mechanical force (mechanical to electrical conversion)
and conversely,
an applied electric field will produce a mechanical stress (electrical to
mechanical conversion).
These materials can be used for sensing purposes, including actuatoUnd sensor
applications.
In the present invention a downhole ultrasonic well cleaning device is powered
by an
apparatus that converts mechanical force into electrical energy, preferably a
piezoelectric
generator. Both are installed or inserted within the completion equipment of
any structure
where the caking of particles may affect productivity. The preferred
application is in cleaning
wells and subterranean formations. The ultrasonic generator and piezoelectric
element would
be placed within the completion equipment (e.g. pipeline, tubing, packer, sand
control. screen,
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or other element) of a pipeline or subterranean well such as those used for
oil or gas
production. Figure 1 illustrates a configuration for temporary insertion in
the well. The
mechanical electrical converter 1, ultrasonic generator 2, and the ultrasonic
sonde 3 are
inserted on the end of a temporarily installed tubing 4, which is anchored in
place by a
5 temporary packer sealing element S. Tension or compression as denoted by the
arrow 6 is
applied to this tubing from an oil field drilling rig, workover rig, or
workover hoist.
Figure 2 illustrates a configuration for permanent installation. In this case
the
mechanical electrical converter 1, ultrasonic generator 2, and the ultrasonic
sonde 3 are
permanently affixed to the permanent production tubing of the well 4 which may
be affixed
to with a permanent packer sealing element 5. In this configuration the force
6 is applied to a
second tubing 7 that is temporarily inserted. into the bore of the permanent
tubing 4. In this
configuration a flow passage 8 exists. The principle differences between the
two are the
passageway to allow fluid production in the second example and the arrangement
of packers
and alignment of tubing to allow easy removal in the first application. Other
configurations
could be envisioned but these diagrams capture the key elements of two broad
classes.
The piezoelectric element of the mechanical electrical converter is normally
in a
relaxed (unstrained) state and generates no electrical current, however the
piezoelectric
element(s) are mounted or inserted in the pipeline or well equipment in a
manner which allows
the operator to apply mechanical force as required. When the operator desires
to generate
ultrasonic excitation to enhance well cleaning, mechanical force would be
applied to the
piezoelectric element to generate electricity to power the ultrasonic sonde.
Ultrasonic sondes convert electrical energy to ultra high frequency pressure
oscillations when electrical energy is applied to the sonde at its operational
resonant
frequency. The operational resonant frequency and range of the sonde is
determined by its
design, specifically geometry and materials of construction. Varions equipment
manufacturers
accomplish this in a number of ways. The present invention is not intended to
be limited to
any particular ultrasonic sonde. Suitable acoustic sondes and transducers are
described, for
example, in U.S. 5,595,243 and U.S. 5,184,678..
The ultrasonic generator converts normal sources of electricity, such as
direct current
from batteries or alternating current, typically 20 to 80 Hz, to ultra high
frequency alternating
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current to excite the operational resonant frequency of the ultrasonic sonde.
The principles to
be applied in designing a suitable generator for this application are known to
those skilled in
the art. Examples are given in U. S. 5,184,678 and U. S. 5,595,243. Use of
direct current
from a battery has been revealed by Y. Bar-Cohen, S. Sherrit, B. Dolgin, T.
Peterson, D. Pal
and J. Kroh, "Ultrasonic/Sonic Driller/Corer (USDC) With Integrated Sensors,"
New
Technology Report, Submitted on August 30, 1999. Docket No. 20856, Item No.
0448b,
November 17, 1999. U.S. Provisional Patent, filed on May 3, 2000, Application
No.
60/201,650. The ultrasonic generator receives input signals from the
piezoelectric element
when it is placed in tension or compression or it is otherwise strained.
The device for converting mechanical to electrical energy revealed in this
invention is
based on the phenomenon that piezoelectric elements can be used to generate
electrical power
when they are subjected to mechanical force, i.e. when they are placed in
compression or
tension and when they are strained. Piezoelectric materials include many
polymers, ceramics,
and molecules, such as water, which are permanently polarized. Suitable
piezoelectric
materials in the present invention for producing an electric field as the
result of an imposed
mechanical force include, for example, but are not limited to ceramic, quartz
(Si02), barium
titanate (BaTiO3), lithium niobate, polyvinyledene difluoride (PVDF), and lead
zirconate
titanate (PZT). (See: http://www.mse.comell.edu/courses/en igr 111//piezo.htm
)
They are ceramic materials manufactured of specific materials and under
specific conditions to
impart piezoelectric properties. Other classes of materials, such as certain
minerals and
combinations of metal and minerals may also create the same effect and could
be used in this
invention. The ceramic materials are preferred because their properties are
more reproducible
and controllable. The property that is exploited in this invention is that
when a mechanical
force is applied, placing the piezoceramic in tension, compression, or
inducing strain, an
electrical charge is generated. The charge generated is proportional to the
force applied. If
designed appropriately this charge will induce an electromotive force that can
supply current
to power electrical devices like the generator and sonde in this invention.
The material to be used in this invention will be chosen based on the
relationship
between the properties of the material, the mechanical design of the
installation or apparatus
3o delivering force, and the electrical properties (voltage and power)
required to power the sonde.
These are captured schematically in Figure 3, which illustrates a typical
curve of voltage
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produced versus current for a piezo ceramic. The value of voltage produced for
a given
mechanical loading is a property of the piezo ceramic know in the industry as
the "g" constant.
This constant is commonly known for commercially available materials suitable
for this
application. The maximum voltage (denoted Voc in Figure 3) is achieved if the
circuit is open,
i.e. no current or power is drawn from the device. As current is drawn from
the device the
voltage is reduced but power is generated. The maximum current is available if
the circuit is
closed (denoted Icc in Figure 3). The appropriate operating point (A in Figure
3) for the piezo
ceramic defined by a particular stress (Sop in Figure 3) above the threshold
stress for the
material (Si in Figure 3) will deliver the required voltage and current to the
generator to power
the sonde at the mechanical stress the apparatus is designed to impart.
The piezoelectric element in this invention is placed in a mechanical element
or
housing within the wellbore or inserted tubing such that mechanical force
imposed on the
tubing is transmitted to the element. As illustrated in Figures 4-6 this
mechanical force could
be used to place the piezo electric element in tension or compression or to
bend it. Each of
these modes of operations may be useful in specific designs. For example a
simple tension or
compression device, as illustrated in Figures 4(a) and (b), would be
applicable in the
application illustrated in Figure 1 where the apparatus is placed
symmetrically in the center of
the well. A shear type device as illustrated in Figures 5(a) and (b) would be
more applicable
in the apparatus illustrated in Figure 2 where the ultrasonic apparatus and
mechanical -
electrical energy converter is place asymmetrically on one side of the well
tubing.
Single sheets of piezo can be energized to produce motion in the thickness,
length, and
width directions. They may be stretched or compressed to generate electrical
output. Double
or multiple ceramic elements may be used in series or parallel as required to
generate the
required voltage and power. Other alternatives are bending or extension of two-
layer
generators including extension and bending generators. Applying mechanical
stress to a
laminated two layer element results in electrical generation depending on the
direction of the
force, the direction of polarization, and the wiring of the individual layers.
In the case of an
extension generator, when a mechanical stress causes both layers of a suitably
polarized 2-
layer element to stretch (or compress), a voltage is generated which tries to
return the piece to
its original dimensions. Essentially, the element acts like a single sheet of
piezo. The metal
shim sandwiched between the two piezo layers provides mechanical strength and
stiffness.
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Any of these or combinations thereof may be applied to deliver the voltage and
power required
to drive the sonde.
In multi-layer generators, one example of which is a stack generator, the
stack, which
comprises a large number of piezo layers, is a very stiff structure with a
high capacitance. It is
suitable for handling high force and collecting a large volume of charge.
Series operation refers to the case where supply voltage is applied across all
piezo
layers at once. The voltage on any individual layer is the supply voltage
divided by the total
number of layers. A 2-layer device wired for series operation uses only two
wires, one
attached to each outside electrode (figure 6a).
Parallel operation refers to the case where the supply voltage is applied to
each layer
individually. This means accessing and attaching wires to each layer. A 2-
layer bending
element wired for parallel operation requires three wires; one attached to
each outside.
electrode and one attached to the center shim (Figure 6b).
In the present invention the ultrasonic generator and piezoelectric elements
would be
attached or installed in a structure or wellbore during completion. This could
be accomplished
in a number of ways, as would be apparent to those skilled in the art and the
present invention
is not intended to be limited to a particular method. The elements can be
secured by, for
example, welding, or cement adhesions, or by screwing in mounting brackets.
(See:
http://www.loadmonitors.com/services.htm )
The mechanical force could be applied by several means, including, but not
limited to:
1) Placing the well tubing in tension or compression; 2) Use of a second
tubing inserted into or
around the wells permanent tubing; or 3) Use of a mechanical device inserted
into the wellbore
on a non-conducting wire.
In another embodiment the apparatus could be situated on sectional tubing,
coiled
tubing, or non-electric wireline, then inserted into the wellbore and actuated
by mechanical
force, by one of the methods described above.
As mentioned above, the mechanical force could be applied by, for example: 1)
Placing the well tubing in tension or compression; 2) Use of a second tubing
inserted into or
around the wells permanent tubing; or 3) Use of a mechanical device inserted
into the wellbore
on a non-conducting wire. Well tubing can be placed in compression using a
packer or other
tubing anchor to lock the tubing in place. Such packers and tubing anchors are
commercial
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items available from a variety of vendors and widely used in well construction
activities, (See,
for example, http://www.bakerhughes.com/bot/service tools/index.htm) and can
be placed in
tension or compression using mechanical equipment normally available on rigs
and hoists
used for well operations. The techniques used to place tubing in compression
or tension in a
controlled manner are often practiced by those skilled in the art using
established techniques.
The piezoelectric elements could be situated such that when either tension or
compression of
the tubing occurs, the piezoelectric element is subjected to force, thus
generating electric
power for the ultrasonic transducer.
In another embodiment, a second tubing, of slightly smaller or larger diameter
could be
inserted into or around permanent tubing, and as it moves it would come in
contact with the
piezoelectric elements secured in the completion equipment, to create
mechanical force, which
is converted to electric power for the ultrasonic generator.
In yet another embodiment, a mechanical device could be introduced into the
wellbore
on a non-conducting wire, and as it comes into contact with the piezoelectric
element(s), the
element(s) would be bent or displaced.
Also within the concept of the present invention the ultrasonic sonde and
piezoelectric
mechanical to electrical converter could be situated on sectional tubing, or
coiled tubing, and
subject to compression or tension loads using the equipment and methods
described above.
Alternatively, a non-electric wireline could be inserted into the wellbore
with a device
designed to catch the mechanical electrical converter or an attachment to it.
The operator
would then pull on the non-electric wireline to apply a tension load to the
mechanical
electrical converter. This method would be limited by the strength of the non-
electric
wireline.
When mechanical force is applied to the piezoelectric generator, the movement
results
in an electrical voltage which can be measured at the electrical terminals of
the piezoelectric
converter and used to power the ultrasonic sonde by suitable electronics,
referred to herein as
the generator, which are not the object of the present invention.
This method can be used to clean enclosed tanks or vessels where access for
other
methods is limited.
It can be used to clean water production or injection wells or wells used for
the
injection of steam or production of hot water or steam from subterranean
geothermal deposits.
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Variations might include:
= Positioning of the respective elements (generator or oscillator) with
respect to
each other.
= Nature of the electrical circuitry used to transmit the electrical energy
5 generated to the sonic oscillator.
= Materials of construction of the various elements.
= Frequency of operation of the ultrasonic sonde.
= Whether the sonde is operated in a steady or pulsed mode.
= Characteristics of the electrical energy generated - voltage, current, and
power.
10 = Methods for positioning the elements in the structure to be cleaned.
= Size of the various pieces of equipment.
= The orientation of the equipment in the enclosure to be cleaned. This
includes
the direction in which the respective elements are pointed and whether they
are
mounted symmetrically or asymmetrically within the enclosure.
= In cases where a tubing element or non-electric wireline element is used to
apply mechanical force it may be inserted in the bore of a larger tubing or
alternatively in the annulus between concentric tubing or casing strings.
= Mechanical force may be applied to the element from any direction.
The invention as described is intended only as a means of illustration and
should not be
construed as limiting the scope of the invention in any way. Those skilled in
the art will
recognize many variations that may be made without departing from the spirit
of the disclosed
invention.
