U.S. patent application number 14/026677 was filed with the patent office on 2014-03-20 for downhole heater assembly and power line communications system.
This patent application is currently assigned to DH THERMAL LLC. The applicant listed for this patent is Jerry D. Crane, Alan Granger, William Masek, Duane L. Schreurs, Walter John Sutton. Invention is credited to Jerry D. Crane, Alan Granger, William Masek, Duane L. Schreurs, Walter John Sutton.
Application Number | 20140076545 14/026677 |
Document ID | / |
Family ID | 50273257 |
Filed Date | 2014-03-20 |
United States Patent
Application |
20140076545 |
Kind Code |
A1 |
Sutton; Walter John ; et
al. |
March 20, 2014 |
Downhole Heater Assembly and Power Line Communications System
Abstract
A hydrocarbon heating system comprises a surface control panel
and a subsurface heating system, connected by an external power
cable which also serves as the data communication link between the
two parts. The subsurface heating system includes a heating element
and two separate, thermally isolated temperature sensors. One
thermal sensor, mounted near the heating element, monitors the
temperature of the heating element. Another thermal sensor monitors
the ambient temperature of fluid in the borehole. The temperature
of the heating element may be varied to maintain an optimal well
temperature for the production of hydrocarbons. Downhole
electronics convert the thermal sensor outputs to digital data, and
modulate the digital data onto a power cable that carries power
from the surface to the heating element. A control system at the
surface controls the heating element via nested control loops
monitoring the temperatures of the borehole fluid and the heating
element.
Inventors: |
Sutton; Walter John;
(Wilmington, NC) ; Schreurs; Duane L.; (Baltic,
SD) ; Crane; Jerry D.; (Anderson, SC) ; Masek;
William; (Anderson, SC) ; Granger; Alan;
(Anderson, SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sutton; Walter John
Schreurs; Duane L.
Crane; Jerry D.
Masek; William
Granger; Alan |
Wilmington
Baltic
Anderson
Anderson
Anderson |
NC
SD
SC
SC
SC |
US
US
US
US
US |
|
|
Assignee: |
DH THERMAL LLC
Wilmington
NC
|
Family ID: |
50273257 |
Appl. No.: |
14/026677 |
Filed: |
September 13, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61703477 |
Sep 20, 2012 |
|
|
|
Current U.S.
Class: |
166/250.01 ;
166/53; 166/60 |
Current CPC
Class: |
E21B 47/12 20130101;
E21B 36/006 20130101; E21B 36/04 20130101; E21B 47/07 20200501 |
Class at
Publication: |
166/250.01 ;
166/60; 166/53 |
International
Class: |
E21B 36/04 20060101
E21B036/04; E21B 47/06 20060101 E21B047/06 |
Claims
1. A downhole hydrocarbon heating system operative to heat
hydrocarbon fluids in an oil or gas well comprising a borehole, the
system comprising: a surface control panel; a subsurface heating
system operative to be deployed down the borehole and including a
heating element; a first thermal sensor operative to sense the
temperature of the heating element; and a second thermal sensor
operative to sense the ambient temperature of fluid in the
borehole; and a power cable connecting the surface control panel
and the subsurface heating system, the power cable operative to
selectively carry power from the surface control panel to the
heating element, and further operative to carry temperature data
from the first and second thermal sensors to the surface control
panel.
2. The system of claim 1 wherein the heating element and the first
thermal sensor are disposed in a lower housing operative to be
deployed in the borehole at the depth of a hydrocarbon production
zone.
3. The system of claim 1 wherein the heating element is disposed
centrally in the lower housing and secured by a thermally
conductive concrete.
4. The system of claim 1 wherein the lower housing comprises
standoff elements secured to the exterior thereof in radially
spaced positions, the standoff elements operative to maintain the
lower housing generally centered in the borehole.
5. The system of claim 1 wherein the second thermal sensor is
disposed in a spaced relationship with the heating element such
that the temperature sensed by the second thermal sensor is not
directly influenced by the heating element.
6. The system of claim 5 wherein the subsurface heating system
further comprises an insulating section interposed between the
heating element and the second thermal sensor.
7. The system of claim 1 wherein the subsurface heating system
further comprises a downhole printed circuit board (PCB) containing
electronics to convert the first and second thermal sensor outputs
to digital data, and to modulate the digital temperature data onto
the power cable.
8. The system of claim 7 further comprising a transformer operative
to tap power from the power cable and to power the downhole
PCB.
9. The system of claim 7 wherein power cable carries 3-phase power,
and wherein the electronics on the downhole PCB are operative to
modulate digital data across two phases of the power cable.
10. The system of claim 1 wherein the subsurface heating system is
deployed below production tubing operative to extract hydrocarbons
from the well.
11. The system of claim 1 wherein the surface control panel
comprises: a power line controller operative to receive sensed
temperature data from the power cable; and a temperature controller
operative to control power to the heating element by selectively
connecting the power cable to a power source in response to the
sensed temperature data received from the power line
controller.
12. The system of claim 10 wherein the temperature controller is
operative to control power to the heating element by: in an outer
control loop, applying power to the heating element in response to
the ambient temperature of fluid in the borehole being below a
predetermined lower limit; and in an inner control loop, applying
power to the heating element only if the temperature of the heating
element is at or below a predetermined setpoint, without regard to
the outer control loop.
13. The system of claim 10 wherein the temperature controller is
operative to control power to the heating element by periodically
applying power to the heating element for brief durations without
regard to the ambient fluid or heating element temperature
values.
14. A method of controlling the temperature of hydrocarbons in a
well comprising a borehole, in which is disposed a subsurface
heating system including a heating element, a first thermal sensor
operative to sense the temperature of the heating element, and a
second thermal sensor operative to sense the ambient temperature of
fluid in the borehole, the method comprising: monitoring the
temperature of the heating element and the ambient temperature of
fluid in the borehole; applying power to the heating element in
response to the sensed ambient temperature of fluid in the borehole
being below a lower limit, and the sensed temperature of the
heating element being below a setpoint; and removing power from the
heating element in response to the sensed ambient temperature of
fluid in the borehole being above an upper limit or between the
lower and upper limit, or the sensed temperature of the heating
element being above the setpoint.
15. The method of claim 11, further comprising periodically
applying power to the heating element for brief durations without
regard to the values sensed by the first and second thermal
sensors.
16. The method of claim 12 wherein periodically applying power to
the heating element for brief durations comprises applying power to
the heating element for two seconds every thirty seconds.
Description
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 61/703,477, titled "Downhole Heater Assembly
and Power Line Communications System," filed Sep. 20, 2012, the
disclosure of which is incorporated herein by reference in its
entirety.
FIELD OF INVENTION
[0002] The present invention relates generally to subsurface
hydrocarbon extraction, and in particular to a downhole heater
assembly and method of temperature communications.
BACKGROUND
[0003] Hydrocarbon (e.g., crude oil and natural gas) extraction
from subsurface formations is a costly and complex endeavor. After
drilling, a well is cased, and tubing is installed in the borehole
to carry the target fluids to the surface. If the subsurface
pressure is insufficient to flow the oil and gas to the surface, as
is the case in many wells that have been in production for some
time, a pump is required to pump the fluids out. In many cases,
particularly in older wells, the remaining hydrocarbons have such
low viscosity, or are clogged with paraffin or other substances,
that pumping is inefficient or impossible. In the case of natural
gas, iron oxides and other residues may build up and impede the
free flow of gas.
[0004] It is known in the art to position a heating element
downhole, to increase the temperature and hence lower the viscosity
of hydrocarbons, melt interfering paraffin, break up concentrations
of iron oxides or other residues, and generally facilitate
efficiently pumping hydrocarbons to the surface. For example, U.S.
Pat. No. 7,363,979 discloses a downhole heater and system of rugged
electrical connectors necessary to survive the downhole
environment. Proper control of such a downhole heater is essential
to optimally heating the downhole fluids. However, control of a
downhole heater is complicated by the need to transmit temperature
data to the surface for monitoring and control.
[0005] The Background section of this document is provided to place
embodiments of the present invention in technological and
operational context, to assist those of skill in the art in
understanding their scope and utility. Unless explicitly identified
as such, no statement herein is admitted to be prior art merely by
its inclusion in the Background section.
SUMMARY
[0006] The following presents a simplified summary of the
disclosure in order to provide a basic understanding to those of
skill in the art. This summary is not an extensive overview of the
disclosure and is not intended to identify key/critical elements of
embodiments of the invention or to delineate the scope of the
invention. The sole purpose of this summary is to present some
concepts disclosed herein in a simplified form as a prelude to the
more detailed description that is presented later.
[0007] According to one or more embodiments described and claimed
herein, a hydrocarbon heating system comprises a surface control
panel and a subsurface heating system, connected by an external
power cable which also serves as the data communication link
between the two parts. The subsurface heating system includes a
heating element and two separate, thermally isolated temperature
sensors. One thermal sensor, mounted near the heating element,
monitors the temperature of the heating element, to ensure that it
operates within an optimal temperature range, and to prevent damage
from overheating. Another thermal sensor, preferably isolated from
the heating element sensor, monitors the ambient temperature in the
well. The temperature of the heating element may be varied to
maintain an optimal well temperature for the production of
hydrocarbons. Downhole electronics convert the thermal sensor
outputs to digital data, and modulate the digital data onto a power
cable that carries power from the surface to the heating element. A
control system at the surface controls the heating element via
nested control loops monitoring the temperatures of the borehole
fluid and the heating element.
[0008] One embodiment relates to a downhole hydrocarbon heating
system operative to heat hydrocarbon fluids in an oil or gas well
comprising a borehole. The system includes a surface control panel
and a subsurface heating system operative to be deployed down the
borehole. The subsurface heating system includes a heating element;
a first thermal sensor operative to sense the temperature of the
heating element; and a second thermal sensor operative to sense the
ambient temperature of fluid in the borehole. The system further
includes a power cable connecting the surface control panel and the
subsurface heating system. The power cable is operative to
selectively carry power from the surface control panel to the
heating element. The power cable is further operative to carry
temperature data from the first and second thermal sensors to the
surface control panel.
[0009] Another embodiment relates to a method of controlling the
temperature of hydrocarbons in a well comprising a borehole.
Disposed in the borehole is a subsurface heating system including a
heating element, a first thermal sensor operative to sense the
temperature of the heating element, and a second thermal sensor
operative to sense the ambient temperature of fluid in the
borehole. The temperature of the heating element and the ambient
temperature of fluid in the borehole are monitored. Power is
applied to the heating element in response to the sensed ambient
temperature of fluid in the borehole being below a lower limit, and
the sensed temperature of the heating element being below a
setpoint. Power is removed from the heating element in response to
the sensed ambient temperature of fluid in the borehole being above
an upper limit or between the lower and upper limit, or the sensed
temperature of the heating element being above the setpoint.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will now be described more fully
hereinafter with reference to the accompanying drawings, in which
embodiments of the invention are shown. However, this invention
should not be construed as limited to the embodiments set forth
herein. Rather, these embodiments are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the invention to those skilled in the art. Like numbers
refer to like elements throughout.
[0011] FIG. 1 is a sectional diagram of a producing oil well with a
downhole heating and control system according to one embodiment of
the present invention.
[0012] FIG. 2 is a more detailed sectional view of the downhole
heating and control system according to one embodiment of the
present invention.
[0013] FIG. 3 is a functional block diagram of a temperature sensor
control and communication system according to one embodiment of the
invention.
[0014] FIG. 4 is a flow diagram of a method of controlling the
temperature of hydrocarbons in a well.
DETAILED DESCRIPTION
[0015] It should be understood at the outset that although
illustrative implementations of one or more embodiments of the
present disclosure are provided below, the disclosed systems and/or
methods may be implemented using any number of techniques, whether
currently known or in existence. The disclosure should in no way be
limited to the illustrative implementations, drawings, and
techniques illustrated below, including the exemplary designs and
implementations illustrated and described herein, but may be
modified within the scope of the appended claims along with their
full scope of equivalents.
[0016] FIG. 1 depicts a modern, mature, production oil well the
well 10 comprises a borehole 12 in which production tubing 14 has
been installed. A pump jack 16 creates a pressure differential that
pulls hydrocarbons from a subsurface production zone 18 into the
borehole 12. The hydrocarbons enter the production tubing 14
through a perforated section 20, and are pumped to the surface. In
many cases, the hydrocarbon fluids are of low viscosity, clogged
with paraffin or iron oxides, or otherwise present obstructions to
efficient pumping. In these cases, a hydrocarbon heating system 8
according to one or more embodiments of the present invention may
be deployed to heat the fluids. The hydrocarbon heating system 8
comprises two parts: a surface control panel 58 and a subsurface
heating system 22, connected by an external power cable 54 which
also serves as the data communication link between the two
parts.
[0017] The subsurface heating system 22, depicted in greater detail
in FIG. 2, is attached to the downhole side of production tubing
14, below the perforated section 20. The core of the subsurface
heating system 22 is a heating element 24. The heating element 24
is a long, thin element, e.g., in one embodiment, approximately ten
feet in length and less than one inch in diameter. The heating
element 24 is disposed in a lower housing 26, such as a section of
2.5 inch stainless steel pipe. The heating element 24 is generally
centered within the lower housing 26, and is preferably held in
position by thermally conductive cement 28, such as ceramic heat
transfer cement. In operation, the lower housing 26 is disposed in
the borehole 12 at a target depth corresponding to the subsurface
production zone 18, to heat the hydrocarbon fluids. In one
embodiment, upper and lower standoffs 30 welded to the exterior of
lower housing 26 maintain the lower housing 26 generally centered
within the borehole 12. In one embodiment, the lower housing 26 is
approximately ten feet in length.
[0018] One example of a suitable heating element 24 is a 12 kW
Maxizone heater, available from Chromalox of Pittsburgh, Pa. The
heating element 24 preferably operates in the range of 500-600
degrees Fahrenheit (F). The heating element 24 is powered, in one
embodiment, by a three-phase, 12-gauge, Teflon stranded internal
power cable 32 carrying, e.g., 480 VAC, 3-phase power obtained from
the surface control panel 56 via external power cable 54. A first
thermal sensor 34, such as a K type thermocouple, is embedded in,
or disposed proximate to, the heating element 24. The first thermal
sensor 34 monitors the temperature of the heating element 24.
[0019] In one embodiment, an insulating section 36 separates the
lower housing 26 from the upper housing 38. The insulating section
36 ensures separation between the heating element 24 and control
electronics and a second sensor 40 housed in the upper housing 38.
In one embodiment, the insulating section 38 is in the range of
eight to ten feet long. This distance allows the second sensor 40
to monitor the ambient temperature of fluids in the borehole 12,
without undue influence from the heating element 24. The internal
power cable 32 passes through the insulating section 36.
[0020] An upper housing 38, disposed opposite the insulating
section 36 from the lower housing 26, includes downhole printed
circuit board (PCB) 42, which contains the downhole control
electronics. The downhole PCB 42 is powered from the internal power
cable 32 via a transformer 44. A second thermal sensor 40 is
disposed in the upper housing 38, and connected to the downhole PCB
42. The second thermal sensor 40 is operative to monitor the
ambient temperature of fluids in the borehole 12, which are
preferably maintained in the range of 150-200 degrees F., and more
preferably in the range of 160-180 degrees F. The transformer 44,
PCB 42, second thermal sensor 40, and power cable 32 are preferably
encased in an inert compound 46. The transformer 44 and PCB 42 may
comprise any suitable components--for example, components designed
and certified for use in harsh environments. In one embodiment,
separation of the second thermal sensor 40 from the heating element
24 is provided, not by a separate insulating section 36, but by
locating the second thermal sensor 40 in the upper region of the
upper housing 38. In this embodiment, the upper housing 38 is
preferably eight to ten feet long.
[0021] Above the upper housing 38, a cable admission connector 48,
connected thereto by a coupler 47, includes a port 50, to which is
attached a connector 52. The connector 52 provides a quick-detach
connection between the internal power cable 32 providing power to
the PCB 42 and heating element 24, and an external power cable 54
that extends up the borehole 12 external to the production tubing
14. The external power cable 54 is preferably an armored cable
designed for operation in the harsh environment of the borehole 12.
One example of a suitable external power cable 54 is a 3.times., 4
AWG flat armored cable available from Schlumberger of Houston,
Tex.
[0022] The cable admission connector 48 connects to the upper
housing 38, via a coupler 47, in a manner that excludes borehole
fluids from the interior of the upper housing 38. Indeed, from the
coupler 47 downward, the system 22 is a sealed environment, with no
incursion of borehole 12 fluids into the interior of the upper
housing 38, insulating section 36, or lower housing 26. One example
of a suitable cable admission connector 48 is the ZPTC series
connector available from Taurus Engineering of Long Beach, Calif.
In one embodiment, the power cable 32 also carries temperature
monitoring signaling from the downhole thermal sensors 34, 40 to
the surface, as described further herein.
[0023] Above the cable admission connector 48--which constitutes
the upper extent of the subsurface heating system 22--is a
perforated tubing section 20. The perforated tubing section 20 is
the lower-most portion of the production tubing 14, and may be, for
example, four feet long. Perforations in the perforated tubing
section 20 allow hydrocarbon fluids to enter the production tubing
14, where they are pumped to the surface by the pump jack 16.
Intermittently, such as at intervals of 30 feet, straps 56 secure
the exterior power cable 54 to the production tubing 14. The straps
may be applied, as required or desired, as the subsurface heating
system 22 and production tubing 14 are lowered into the borehole
12. At the surface, the external power cable 54 enters a control
panel 56, which houses the surface electronics.
[0024] In general, the sections of the subsurface heating system
22--such as the lower housing 26, insulating section 36, and upper
housing 38--may be constructed from 2.5 inch steel pipe with
National Pipe Thread Taper (NPT), coupled together by 2
inch.times.2.5 inch NPT couplers, as well known in the drilling and
hydrocarbon production arts.
[0025] The first thermal sensor 34 monitors the temperature of the
heating element 24, and the second thermal sensor 40 monitors the
ambient borehole fluid temperature. Both thermal sensors 34, 40 are
connected to the downhole PCB 42, which converts the thermal sensor
34, 40 voltages to digital temperature data, and transmits the
temperature data to the surface control panel 56 using power line
communications.
[0026] FIG. 3 presents a functional block diagram of the electrical
and control system of the hydrocarbon heating system 8. The
subsurface heating system 22 comprises the heating element 24,
first thermal sensor 34 monitoring the heating element 24, second
thermal sensor 40 monitoring the ambient borehole fluid
temperature, and the downhole PCB 42. The PCB 42 is powered by a
transformer 44 connected to the internal power cable 32. The PCB
also connects across two phases of the internal power cable 32 to
communicate temperature data to the surface control panel 58 via
power line communications. The coupling across two phases obviates
the need for a neutral, or ground, conductor.
[0027] The PCB 42 includes a power line controller operative to
modulate digital data on a power line for communication to the
surface control panel 58. One example of a suitable power line
controller is a PL3120 power line smart transceiver, available from
Eschelon Corp. of San Jose, Calif. The PL3120 includes a power line
transceiver, a Neuron processor core, embedded memory, and
associated circuits. The PCB 42 additionally includes two Analog to
Digital Converters (ADC) to convert the output voltages of the
thermal sensors 34, 40 to digital values. One example of a suitable
ADC is a MAX31855 cold-junction compensated thermocouple-to-digital
converter, available from Maxim Integrated Products of San Jose,
Calif. The ADCs communicate with the power line controller, such as
via an I2C interface.
[0028] In one embodiment, the thermal sensor 34, 40 values are
converted to Lonworks protocol Standard Network Variable Type
(SNVT) temperature values. As known in the art, Lonworks is an
industry standard networking protocol targeted to address the needs
of control applications. The Lonworks protocol defines a plurality
of SNVTs for common control system variable types. For example, the
temperature SNVT defines a number between zero and 65535 that
corresponds to a temperature between -247 and 6279.5 degrees
Celsius. The Lonworks protocol also defines the standards for power
line communications, by which digital data is modulated onto an AC
power line.
[0029] The surface control panel 56 includes also includes a power
line controller 60 operative to extract thermal 34, 40 data from
the external power cable 54. The surface power line controller 60
be the same as, or similar to, the power line controller on the
downhole PCB 42. In one embodiment, the surface power line
controller 60 converts the temperature data from the subsurface
heating system 22 into two 4-20 ma current loop signals for use as
feedback signals for two nested temperature control loops,
controlled by a temperature controller 62. An inner control loop
prevents the heating element 24 from operating beyond a maximum
setpoint, such as 600 degrees F. An outer control loop modulates
power to the heating element 24 to maintain a desired ambient
downhole fluid temperature, such as in the range of 150-200 degrees
F., and more preferably in the range of 160-180 degrees F. The
temperature controller 62 controls the downhole temperatures by
modulating the 480 VAC, 3-phase power to the heating element 24,
such via a solid state 3-phase relay. In one embodiment, regardless
of the control loop outputs, downhole power is periodically applied
for a brief duration--such as for two seconds every thirty
seconds--to allow the subsurface heating system 22 to obtain and
transmit updated temperature readings. One example of a suitable
temperature controller 62 is an EZ-Zone PM controller, available
from Watlow Electric Manufacturing Co. of St. Louis, Mo.
[0030] FIG. 4 depicts a method 100 of controlling the temperature
of hydrocarbons in a well. Although those of skill in the art will
appreciate that the method describes a continuous and ongoing
process, for the purpose of explanation it may be said to "begin"
by monitoring the temperature of the heating element 24, via the
first thermal sensor 34, and the ambient borehole fluid
temperature, via the second thermal sensor 40 (block 102). The
ambient borehole fluid temperature is controlled in an outer
control loop (block 104). If the ambient temperature is within a
predetermined range, such as 150-200 degrees F., or more preferably
160-180 degrees F., or if the ambient temperature exceeds the
maximum desired temperature, the heating element 24 is not
energized, and the system 8 continues to monitor the downhole
temperatures (block 104). If the ambient borehole fluid temperature
falls below the desired minimum temperature, then the heating
element 24 is energized to further heat the hydrocarbons, subject
to the operation of the inner control loop. If the temperature of
the heating element 24 is at or below a predetermined setpoint
(block 106), then the heating element 24 is energized by supplying
480 VAC, 3-phase power via the external power cable 54 and internal
power cable 32 (block 108). However, if the temperature of the
heating element 24 exceeds its setpoint (block 106), then the
heating element 24 is not energized, regardless of the ambient
borehole fluid temperature, to prevent damage to the heating
element 24. In either case, the system 8 then continues to monitor
the downhole temperatures (block 102).
[0031] Those of skill in the art will recognize that the method 100
as depicted in FIG. 4 is representative only, and many variations
are possible within the scope of the present invention. For
example, in one embodiment, once the ambient borehole fluid
temperature is within the desired range, a partial current may be
supplied to the heating element 24 to maintain its temperature,
with the power being removed only if the first thermal sensor 34
indicates a temperature above the setpoint. As another example, as
discussed above, even when the heating element 24 is not energized
by the control loops (i.e., method block 108 is not reached due to
the downhole temperatures reported), the power may be applied
periodically for brief durations (e.g., two seconds every thirty
seconds) to energize the downhole electronics and obtain updated
temperature readings. Furthermore, various timers may be
implemented to halt the method 100 in a state (e.g., block 108) for
predetermined durations. In general, those of skill in the art may
devise numerous temperature control schemes, given the teachings of
the present disclosure and the resources of two separate,
independent thermal sensors 34, 40 reporting both heating element
24 and ambient borehole fluid temperatures, respectively. All such
heating element 24 control schemes would fall within the broad
scope of the present invention.
[0032] The hydrocarbon heating system 8 of the present invention
presents numerous advantages over the prior art. By providing two
temperature sensors 34, 40 in the subsurface system 22, two
critical temperatures may be monitored. By controlling the heating
element 24 in a nested control loop, the ambient borehole fluid
temperature may be regulated as desired, subject to the protective
monitoring and control function of limiting the temperature of the
heating element 24. By employing power line communications to
convey temperature readings from the subsurface thermal sensors 34,
40 to the surface, the need for expensive and fragile dedicated
communication lines is obviated. This improves both lowers cost and
improves the reliability of operation in the hostile environment of
the borehole 12.
[0033] The present invention may, of course, be carried out in
other ways than those specifically set forth herein without
departing from essential characteristics of the invention. The
present embodiments are to be considered in all respects as
illustrative and not restrictive, and all changes coming within the
meaning and equivalency range of the appended claims are intended
to be embraced therein.
* * * * *