U.S. patent number 10,385,694 [Application Number 15/948,847] was granted by the patent office on 2019-08-20 for enhanced pdm performance testing device.
This patent grant is currently assigned to Abaco Drilling Technologies LLC. The grantee listed for this patent is Basintek, LLC. Invention is credited to Peter Thomas Cariveau, Jing Lu, Timothy Mark Miller.
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United States Patent |
10,385,694 |
Cariveau , et al. |
August 20, 2019 |
Enhanced PDM performance testing device
Abstract
A method for evaluating load performance of a rotor/stator test
coupon, advantageously within a sealable test chamber comprising
test fluid. In some embodiments, the test coupon comprises at least
a partial length of a PDM stage, and in others the test coupon
comprises a splined rotor/stator. The method includes rotating
either the rotor section or the stator section, wherein such
rotation actuates corresponding rotation of the other of the rotor
section and the stator section. A braking torque is applied to the
actuated one of the rotor section and the stator section such that
load performance of the test coupon may be evaluated. Embodiments
include selectively applying non-linear torque to load the test
coupon, and evaluating load performance of the test coupon with
reference to relative angular positions of the rotor section and
the stator section over time.
Inventors: |
Cariveau; Peter Thomas
(Houston, TX), Miller; Timothy Mark (Klein, TX), Lu;
Jing (Houston, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
Basintek, LLC |
Houston |
TX |
US |
|
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Assignee: |
Abaco Drilling Technologies LLC
(Houston, TX)
|
Family
ID: |
63039161 |
Appl.
No.: |
15/948,847 |
Filed: |
April 9, 2018 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180223665 A1 |
Aug 9, 2018 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15464640 |
Mar 21, 2017 |
9938829 |
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62311278 |
Mar 21, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F03C
2/08 (20130101); F01C 20/28 (20130101); F04C
13/008 (20130101); F04C 2/1071 (20130101); G01M
99/002 (20130101); G01M 99/007 (20130101); G01M
15/02 (20130101); F04C 2270/80 (20130101); F01C
1/103 (20130101) |
Current International
Class: |
G01M
15/00 (20060101); G01M 99/00 (20110101); F01C
20/28 (20060101); G01M 15/02 (20060101); F01C
1/10 (20060101) |
Field of
Search: |
;73/788 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Noori; Max H
Attorney, Agent or Firm: Zeman-Mullen & Ford, LLP
Parent Case Text
RELATED APPLICATIONS
This application is a continuation-in-part of co-pending,
commonly-invented and commonly-assigned U.S. patent application
Ser. No. 15/464,640 filed Mar. 21, 2017 (now U.S. Pat. No.
9,938,829). Ser. No. 15/464,640 claims the benefit of and priority
to, commonly-invented and commonly-assigned U.S. Provisional Patent
Application Ser. No. 62/311,278 filed Mar. 21, 2016. The entire
disclosures of Ser. Nos. 15/464,640 and 62/311,278 are further
incorporated herein by reference.
Claims
We claim:
1. A method for evaluating load performance of a rotor/stator test
coupon, the method comprising the steps of: (a) providing a test
coupon, the test coupon including a splined rotor section received
inside a splined stator section, wherein an exterior of the splined
rotor section provides a plurality of rotor splines and an interior
of the stator section provides a plurality of splined stator
cutouts for receiving rotor splines; (b) rotating a rotated first
one of the splined rotor section and the splined stator section,
wherein rotation of the rotated first one of the splined rotor
section and the splined stator section actuates corresponding
rotation of an actuated second one of the splined rotor section and
the splined stator section; (c) applying a braking torque to the
actuated second one of the splined rotor section and the splined
stator section; and (d) responsive to step (c), evaluating load
performance of the test coupon.
2. The method of claim 1, in which the splined rotor section
rotates about a longitudinal rotor rotation axis and the splined
stator section rotates about a longitudinal stator rotation axis,
and in which step (b) includes setting a preselected offset
distance between the rotor rotation axis and the stator rotation
axis.
3. The method of claim 1, in which the splined rotor section
rotates about a longitudinal rotor rotation axis and the splined
stator section rotates about a longitudinal stator rotation axis,
and in which the rotor splines are disposed parallel to the
longitudinal rotor rotation axis and the splined stator section
cutouts are disposed parallel to the longitudinal stator rotation
axis.
4. The method of claim 1, in which step (d) includes at least one
substep selected from the group consisting of: (d1) controlling
torque across the splined rotor section and the splined stator
section; (d2) counting, through to failure of the test coupon, at
least one of (1) splined rotor section rotation cycles and (2)
splined stator section rotation cycles; and (d3) examining at least
one of (1) the splined rotor section and (2) the splined stator
section for wear.
5. The method of claim 1, further comprising, after step (a) and
before step (b), the substeps of: (a1) receiving the test coupon
inside a sealable test chamber; (a2) filling the test chamber with
test fluid; and (a3) sealing the test chamber.
6. The method of claim 5, in which step (d) further includes the
substep of monitoring temperature change over time in the test
chamber.
7. The method of claim 1, in which the splined stator section
provides an elastomer interface at a contact surface with the
splined rotor section inside the test coupon, and in which step (d)
includes at least one substep selected from the group consisting
of: (d1) controlling torque across the splined rotor section and
the splined stator section; (d2) counting, through to failure of
the test coupon, at least one of (1) splined rotor section rotation
cycles and (2) splined stator section rotation cycles; (d3)
examining at least one of (1) the splined rotor section and (2) the
splined stator section for wear; and (d4) monitoring temperature
change over time in the elastomer interface.
8. The method of claim 5, in which the splined stator section
provides an elastomer interface at a contact surface with the
splined rotor section inside the test coupon, and in which step (d)
further includes the substep of monitoring temperature change over
time in the test chamber.
9. A method for evaluating load performance of a rotor/stator test
coupon, the method comprising the steps of: (a) providing a test
coupon, the test coupon including a rotor section received inside a
stator section; (b) rotating a rotated first one of the rotor
section and the stator section with non-linear torque, wherein
rotation of the rotated first one of the rotor section and the
stator section actuates corresponding rotation of an actuated
second one of the rotor section and the stator section; (c)
applying a braking torque to the actuated second one of the rotor
section and the stator section; and (d) responsive to step (c),
evaluating load performance of the test coupon.
10. The method of claim 9, in which the non-linear torque in step
(b) is delivered by at least one technique selected from the group
consisting of: (1) engaging an impact hammer-pin clutch when
rotating the rotated first one of the rotor section and the stator
section; (2) deploying a variable frequency drive motor to vary
rotation speed of the rotated first one of the rotor section and
the stator section; and (3) variably applying a braking torque to
the actuated second one of the rotor section and the stator
section.
11. The method of claim 9, in which the rotor section rotates about
a longitudinal rotor rotation axis and the stator section rotates
about a longitudinal stator rotation axis, and in which step (b)
includes setting a preselected offset distance between the rotor
rotation axis and the stator rotation axis.
12. The method of claim 9, in which step (d) includes at least one
substep selected from the group consisting of: (d1) controlling
torque across the rotor section and the stator section; (d2)
counting, through to failure of the test coupon, at least one of
(1) rotor section rotation cycles and (2) stator section rotation
cycles; and (d3) examining at least one of (1) the rotor section
and (2) the stator section for wear.
13. The method of claim 9, in which the test coupon comprises at
least a partial length of a positive displacement motor (PDM)
stage.
14. The method of claim 9, in which, in step (a), at least one
progressing gap on a helical pathway is formed between the rotor
section and the stator section when the rotor section and the
stator section are differentially rotated.
15. The method of claim 9, further comprising, after step (a) and
before step (b), the substeps of: (a1) receiving the test coupon
inside a sealable test chamber; (a2) filling the test chamber with
test fluid; and (a3) sealing the test chamber.
16. The method of claim 15, in which step (d) further includes the
substep of monitoring temperature change over time in the test
chamber.
17. The method of claim 9, in which the stator section provides an
elastomer interface at a contact surface with the rotor section
inside the test coupon, and in which step (d) includes at least one
substep selected from the group consisting of: (d1) controlling
torque across the rotor section and the stator section; (d2)
counting, through to failure of the test coupon, at least one of
(1) rotor section rotation cycles and (2) stator section rotation
cycles; (d3) examining at least one of (1) the rotor section and
(2) the stator section for wear, and (d4) monitoring temperature
change over time in the elastomer interface.
18. The method of claim 15, in which the stator section provides an
elastomer interface at a contact surface with the rotor section
inside the test coupon, and in which step (d) further includes the
substep of monitoring temperature change over time in the test
chamber.
19. A method for evaluating load performance of a rotor/stator test
coupon, the method comprising the steps of: (a) providing a test
coupon, the test coupon including a rotor section received inside a
stator section; (b) rotating a rotated first one of the rotor
section and the stator section, wherein rotation of the rotated
first one of the rotor section and the stator section actuates
corresponding rotation of an actuated second one of the rotor
section and the stator section; (c) applying a braking torque to
the actuated second one of the rotor section and the stator
section; (d) during steps (b) and (c), independently monitoring at
least one of (1) an angular position of the rotor section over
time, and (2) an angular position of the stator section over time;
and (e) responsive to steps (b) through (d), evaluating load
performance of the test coupon with reference to angular position
as monitored in step (d) over time.
20. The method of claim 19, in which angular position in step (d)
is monitored using at least one rotary encoder.
21. The method of claim 19, in which the rotor section rotates
about a longitudinal rotor rotation axis and the stator section
rotates about a longitudinal stator rotation axis, and in which
step (b) includes setting a preselected offset distance between the
rotor rotation axis and the stator rotation axis.
22. The method of claim 19, in which step (e) includes at least one
substep selected from the group consisting of: (e1) controlling
torque across the rotor section and the stator section; (2)
counting, through to failure of the test coupon, at least one of
(1) rotor section rotation cycles and (2) stator section rotation
cycles; and (e3) examining at least one of (1) the rotor section
and (2) the stator section for wear.
23. The method of claim 19, in which the test coupon comprises at
least a partial length of a positive displacement motor (PDM)
stage.
24. The method of claim 19, in which, in step (a), at least one
progressing gap on a helical pathway is formed between the rotor
section and the stator section when the rotor section and the
stator section are differentially rotated.
25. The method of claim 19, further comprising, after step (a) and
before step (b), the substeps of: (a1) receiving the test coupon
inside a sealable test chamber; (a2) filling the test chamber with
test fluid; and (a3) sealing the test chamber.
26. The method of claim 25, in which step (e) further includes the
substep of monitoring temperature change over time in the test
chamber.
27. The method of claim 19, in which the stator section provides an
elastomer interface at a contact surface with the rotor section
inside the test coupon, and in which step (e) includes at least one
substep selected from the group consisting of: (e1) controlling
torque across the rotor section and the stator section; (e2)
counting, through to failure of the test coupon, at least one of
(1) rotor section rotation cycles and (2) stator section rotation
cycles; (e3) examining at least one of (1) the rotor section and
(2) the stator section for wear; and (e4) monitoring temperature
change over time in the elastomer interface.
28. The method of claim 25, in which the stator section provides an
elastomer interface at a contact surface with the rotor section
inside the test coupon, and in which step (e) further includes the
substep of monitoring temperature change over time in the test
chamber.
Description
FIELD OF THE DISCLOSURE
This disclosure is directed generally to devices that test the
performance of a subterranean positive displacement motor ("PDM"),
and more particularly to a device that miniaturizes the performance
testing of full-scale PDMs while still maintaining accurate
simulation of downhole conditions during such miniaturized
performance testing.
BACKGROUND OF THE DISCLOSED TECHNOLOGY
Currently, PDMs are tested using standardized ASTM protocols in
order to simulate performance of parameters such as elastomer
material performance and elastomer bonding performance under
projected drilling loads. Conventional testing may be performed on
failed PDM parts (typically stators) that have been retrieved from
downhole service as part of an investigation into the cause of the
failure. Alternatively, conventional testing may be performed as
part of well planning activity, prior to drilling, in order to
optimize selection of PDM components such as stator elastomer in
view of the expected downhole environmental conditions and
anticipated loading.
Conventional testing is done according to current applicable ASTM
protocols. The ASTM tests are not particularly representative of
specific expected or encountered downhole environments. First, the
ASTM tests are not able to replicate the cyclic loading stresses
encountered by PDMs in service. Second, the ASTM tests only
peripherally simulate the elevated temperatures and pressures
encountered by PDMs in service.
Generally, the ASTM tests are basic immersion tests in which an
elastomer sample from a stator is first exposed to drilling fluid
for a prescribed period at elevated temperatures, followed by
performance evaluation by pull or tear testing. The performance
evaluation is normally done at ambient temperatures and pressures.
The purpose of the ASTM testing is to evaluate loss of physical
properties in the rubber material and/or bond integrity. The ASTM
testing may be done with a small volume of drilling fluid used in
the specific drilling application. The drilling fluid sample may be
taken from the actual drilling site.
Examples of specific conventional ASTM protocols include the
following:
ASTM D2240--Durometer Hardness (Shore A)
ASTM D412--Tensile properties (Die C)
ASTM D5289--Vulcanization using Rotorless Cure Meter (MDR
tests)
ASTM D624--Tear Strength (Die C)
ASTM D3182--Practice for preparing standard vulcanized sheets (for
tensile and tear bars)
ASTM D429--Adhesion
ASTM D6370--Compositional Analysis by Thermogravimetry (TGA)
ASTM D471--Rubber Property--Effect of Liquids (Swell or immersion
test)
In addition to the traditional ASTM testing, two other conventional
test methods are known to evaluate the performance of PDM power
sections. In contrast to the traditional ASTM protocols described
above, however, these two test methods require large volumes of
test drilling fluid to perform each test.
Flow loop testing attempts to simulate downhole PDM service by
placing a full downhole motor in an enclosed dynamometer ("dyno").
Drilling fluid is introduced at full operating pressure to drive
the PDM power section. It often takes hundreds or even thousands of
gallons of drilling fluid to fill and operate the flow loop. Each
well drilled may have different drilling fluid types, making a full
scale dyno test cost prohibitive to perform on a frequent basis.
Further, the specialized equipment required to handle drilling
fluids under pressure and high temperature make this approach
logistically challenging and often not economically viable.
Recirculating pump vessels have also been used in the past to
evaluate the performance of PDMs. While pump vessels do not require
the volume of drilling fluid needed by flow loops, pump vessels
still require a minimum of 25 gallons of drilling fluid to operate.
Further, pump vessels have limited load ranges that correspondingly
limit the range of downhole environments that can be simulated.
The volumes of drilling fluid needed by flow loop testing and
recirculating pump vessel testing present a further drawback that
is inherent to these conventional tests. Often the need for testing
and evaluation arises after there has been a specific downhole PDM
failure. Investigation of the failure advantageously includes
evaluation and testing of the power section in an environment that
closely simulates the downhole conditions in which the failure
occurred. Such simulation is enhanced greatly when the evaluation
and testing can be done using a sample of the actual drilling fluid
flowing through the power section at the time the failure occurred.
Such samples can be taken, and are available, but they come in
small volumes, typically 0.5 to 2 gallons--not nearly enough to do
flow loop or recirculating pump vessel testing.
There is therefore a need in the art for a test apparatus that can
closely simulate, evaluate and measure PDM performance under (1)
the elevated temperatures encountered downhole, and (2) the cyclic
loads encountered downhole. The test apparatus should nonetheless
provide embodiments in which only small quantities of drilling
fluid are required, ideally less than about 10 gallons of drilling
fluid, preferably less than about 5 gallons and most preferably,
less than about 2 gallons. Embodiments of the test apparatus should
also ideally have a small enough footprint to be suitable to be
housed in a conventional laboratory or at a wellsite location.
SUMMARY AND TECHNICAL ADVANTAGES
These and other drawbacks in the prior art are addressed by a test
apparatus using a PDM test coupon that is a partial length of one
stage of power section, mounted within a test chamber. In some
embodiments, the longitudinal length of the test coupon is up to
about 12 inches. The test chamber also holds a small volume of test
fluid, sufficient to immerse the test coupon and occupy all of its
internal progressing gaps. In some embodiments, the test fluid is
drilling fluid maintained at predetermined and monitored elevated
temperatures so as to simulate temperature performance in desired
downhole conditions. The volume of test fluid/drilling fluid
required to fill the test apparatus is further advantageously small
enough to allow, if desired, use of actual drilling fluid samples
drawn from full operational power sections that may have failed
downhole. It will be appreciated that the test coupon cannot be
sealed because it is only a partial length of one stage of a PDM
power section, and thus presents less than one complete progressing
cavity. Therefore, the test apparatus does not pump drilling fluid
through the test coupon per the conventional operation of a PDM.
Instead, an external motor rotates the rotor section in the test
coupon, actuating corresponding rotation of the stator section by
contact between rotor section and the stator section. The rotation
of the rotor section, with corresponding actuated rotation of the
stator section, is all in the presence of test fluid in the
progressing gap(s) between rotor section and stator section in the
test coupon. In this way, traditional PDM interaction between rotor
and stator via drilling fluid flow can be simulated without pumping
drilling fluid. The test fluid in the test coupon is present to
interact with the test coupon materials to simulate degradation
that might be seen in actual downhole conditions. Note that the
relative differential rotation of the rotor section and the stator
section in the test coupon may cause the test fluid to flow under
low pressure through progressing gaps between rotor and stator
sections. In some embodiments, a flow loop of test fluid may form
through two or more progressing gaps. In other embodiments where
openings are provided in the stator section, a flow loop of test
fluid may form through the progressing gaps, out of the stator
section openings, into the annular space between the test coupon
and the test chamber, and back into the progressing gaps again.
Once the rotor section and stator section are rotating, an external
brake mechanism intentionally applies a braking torque to the
rotation of the stator section against the externally-driven
rotation of the rotor, causing the test coupon to come under
controlled load. The braking force may be controlled, for example,
by measuring the output torque of the stator section and adjusting
the braking force to obtain a desired torque. This ensures the
interface stress between the rotor and stator sections remains
constant, resulting in a highly controlled fatigue loading being
placed on the test coupon. Controlling the applied torque in this
way enables multiple modes of evaluating performance of the test
coupon. The performance of the test coupon in the test fluid
environment can be monitored continuously over a wide range of
loads placed cyclically on the coupon over time. In this way, a
stress field can be generated between the rotor and stator sections
in the test coupon that simulates very closely the same loading
placed on a corresponding full scale power section in downhole
service. Variables such as materials selection, performance
optimization and useful downhole life, for example, can all be
evaluated against the fatigue caused by the loading placed on the
test coupon. Performance of the test coupon may be evaluated via
measuring metrics including, but not limited to: (1) recording
cycles to test coupon failure, via, for example, counting rotor
section and/or stator section cycles through to failure, (2)
examining the rotor section and/or the stator section for wear, (3)
monitoring temperature change over time in the test chamber, and
(4) monitoring temperature change over time in an elastomer layer
provided by the stator section at its contact surface with the
rotor section.
In other embodiments, an external motor may drive the stator
section in the test coupon, and an external brake mechanism may
intentionally slow the rotor section in order to place load on the
test coupon.
In other embodiments, the separate external motors may drive the
rotor section and the stator section in the test coupon. Controlled
differential rotation of separate motors driving the rotor and
stator may be used to place the test coupon under desired
loads.
In other embodiments, the disclosed test apparatus provides a
method of evaluating PDM power section materials at elevated
drilling temperatures and under similar stress profiles as seen in
downhole service by full scale PDM power sections. According to
currently preferred embodiments, the test apparatus design uses a
small section of the full scale PDM power section as a test coupon
and preferably less than about two gallons of drilling fluid within
the test chamber. Many of the advantages of conventional flow loop
or recirculating pump vessel testing can thus be obtained using the
disclosed test apparatus, while at the same time obviating the need
for large footprint or high volumes of drilling fluid.
In some embodiments, the disclosed test apparatus provides
interoperating rotor and stator sections in which the rotor section
has straight splines engaged within straight cutouts formed in the
stator section. It will be appreciated that in these embodiments,
the test coupon does not provide progressing cavities (or
progressing gaps) on helical pathways formed between rotor and
stator as seen in conventional PDMs. However, the
artificially-created rotor/stator gear sections provided in these
splined test coupon embodiments may be used to simulate desired
conditions in the test chamber for evaluation of, for example,
specific loading or environmental conditions of interest. A
specific stress field between rotor and stator sections, for
example, or a specific downhole environment, again for example, may
be artificially created, simulated and tested. As such, therefore,
the scope of this disclosure is not limited to evaluating test
coupons that are partial sections of a PDM. Artificially-created
splined gearing designs, coupled with specifically selected test
fluids and environmental controls, enable simulations and
evaluations of load performances outside the boundaries of PDM
designs. Such splined gearing designs are particularly useful in
evaluating stator performance, although they are not limited to
stator evaluation. Such designs are also useful in evaluating the
performance of other PDM components, such as rotors,
elastomers/rubbers or drilling fluids.
In some embodiments, the disclosed test apparatus provides a
variable frequency drive motor (VFDM) to cause external rotation of
the rotor section within the test chamber. The VFDM is programmable
to deliver varying rotation patterns (e.g. designed increased
rotation pulses) to simulate various types of load patterns on the
test chamber. In other embodiments, varying braking patterns may be
exerted on the stator section within the test chamber by
controlling the braking torque exerted on the stator. For example,
in embodiments in which braking torque is applied using a
pneumatically-driven continuous-slip brake, air pressure pulses
delivered to the brake will cause corresponding braking patterns on
the stator section, simulating torque pulses on the stator section.
Again, various types of load patterns may be simulated on the test
chamber.
In some embodiments, the disclosed test apparatus provides rotary
encoders to measure/map rotary position separately on the rotor
section and the stator section within the test chamber. Comparison
of rotary position data from each rotary encoder enables
measurement and evaluation of rotary displacement between the rotor
section and the stator section under load.
In some embodiments, the disclosed test apparatus provides an
impact hammer-pin clutch interposed between the external motor and
the test chamber. Engagement of the clutch allows torque to be
delivered with controlled impacts, thereby simulating torsional
impact loading within the test chamber.
In some embodiments, the disclosed test apparatus provides at least
one accelerometer on or near the test chamber to monitor/map
vibration (and changes in vibration patterns) within the test
chamber over time during operation.
According to a first aspect, therefore, this disclosure describes
an embodiment of a method for measuring load performance of a
positive displacement motor (PDM) test coupon, the method
comprising the steps of: (a) providing a PDM test coupon, the test
coupon comprising a partial length of a PDM stage, the test coupon
including a rotor section received inside a stator section, wherein
the rotor section and the stator section are independently
rotatable, wherein further at least one progressing gap on a
helical pathway is formed between the rotor section and the stator
section when the rotor section and the stator section are
differentially rotated; (b) receiving the test coupon inside a
sealable test chamber; (c) filling the test chamber with test
fluid; (d) sealing the test chamber, (e) rotating the rotor
section, thereby actuating corresponding rotation of the stator
section in the presence of test fluid in the progressing gap; (f)
applying a braking torque to said stator section rotation actuated
in step (e); and (g) responsive to step (f), evaluating performance
of the test coupon, wherein said evaluating step includes at least
one substep selected from the group consisting of: (g1) controlling
torque across the rotor section and the stator section; (g2)
counting, through to failure of the test coupon, at least one of
(1) rotor section rotation cycles and (2) stator section rotation
cycles; (g3) examining at least one of (1) the rotor section and
(2) the stator section for wear; and (g4) monitoring temperature
change over time in the test chamber.
According to a second aspect, this disclosure describes an
embodiment of a method for measuring load performance of a positive
displacement motor (PDM) test coupon, the method comprising the
steps of: (a) providing a PDM test coupon, the test coupon
comprising a partial length of a PDM stage, the test coupon
including a rotor section received inside a stator section, wherein
the rotor section and the stator section are independently
rotatable about a longitudinal rotor axis and a longitudinal stator
axis respectively, wherein further the rotor axis and the stator
axis are substantially parallel and offset by a preselected axis
offset distance, wherein further at least one progressing gap on a
helical pathway is formed between the rotor section and the stator
section when the rotor section and the stator section are
differentially rotated; (b) receiving the test coupon inside a
sealable test chamber; (c) filling the test chamber with test
fluid; (d) sealing the test chamber; (e) rotating the rotor
section, thereby actuating corresponding rotation of the stator
section in the presence of test fluid in the progressing gap; (f)
applying a braking torque to said stator section rotation actuated
in step (e); and (g) responsive to step (f), evaluating performance
of the test coupon, wherein said evaluating step includes at least
one substep selected from the group consisting of: (g1) controlling
torque across the rotor section and the stator section; (g2)
counting, through to failure of the test coupon, at least one of
(1) rotor section rotation cycles and (2) stator section rotation
cycles; (g3) examining at least one of (1) the rotor section and
(2) the stator section for wear, and (g4) monitoring temperature
change over time in the test chamber. According further to the
second aspect, embodiments of the test coupon may be selected to be
representative of a full size PDM stage having a known rotor/stator
eccentricity, in which case the preselected axis offset distance is
selected to be substantially the same as the known rotor/stator
eccentricity.
Embodiments according to the first or second aspects may also
include the stator section providing an elastomer interface at a
contact surface with the rotor section inside the test coupon, and
in which the evaluating step (g) includes at least one substep
selected from the group consisting of: (g1) controlling torque
across the rotor section and the stator section; (g2) counting,
through to failure of the test coupon, at least one of (1) rotor
section rotation cycles and (2) stator section rotation cycles;
(g3) examining at least one of (1) the rotor section and (2) the
stator section for wear; (g4) monitoring temperature change over
time in the test chamber; and (g5) monitoring temperature change
over time in the elastomer interface.
In other embodiments according to the first or second aspects, the
at least one progressing gap comprises a plurality of progressing
gaps, and in which a first flow loop of test fluid is formed
through the plurality of progressing gaps when the test chamber is
sealed and the rotor section is rotated.
In other embodiments according to the first or second aspects, an
annular cavity is formed between an external periphery of the
stator section and an internal periphery of the test chamber,
wherein the at least one progressing gap, a plurality of openings
in the stator section, and the annular cavity form a second flow
loop of test fluid when the test chamber is sealed and the rotor
section is rotated.
According to third and other aspects and embodiments, step (c) of
the method according to the first or second aspects requires no
more than about 25 gallons of test fluid, and most preferably, no
more than about 2 gallons of test fluid. Embodiments of the test
coupon may have an overall longitudinal length of no more than
about 12 inches. Embodiments of the method according the first or
second aspects may further comprise further steps of maintaining a
preselected temperature and/or pressure inside the test chamber
during at least steps (e) and (f). Embodiments of the test coupon
may further be cut from a full size PDM stage through which
drilling fluid was previously caused to flow. Step (f) of the
method according to the first or second aspects may be accomplished
using a continuous-slip brake.
According to a fourth aspect, this disclosure describes an
embodiment of a method for evaluating load performance of a
rotor/stator test coupon, the method comprising the steps of: (a)
providing a test coupon, the test coupon including a splined rotor
section received inside a splined stator section, wherein an
exterior of the splined rotor section provides a plurality of rotor
splines and an interior of the stator section provides a plurality
of splined stator cutouts for receiving rotor splines; (b) rotating
a rotated first one of the splined rotor section and the splined
stator section, wherein rotation of the rotated first one of the
splined rotor section and the splined stator section actuates
corresponding rotation of an actuated second one of the splined
rotor section and the splined stator section; (c) applying a
braking torque to the actuated second one of the splined rotor
section and the splined stator section, and (d) responsive to step
(c), evaluating load performance of the test coupon. In some
embodiments, the splined rotor section rotates about a longitudinal
rotor rotation axis and the splined stator section rotates about a
longitudinal stator rotation axis. In such embodiments, step (b)
may include setting a preselected offset distance between the rotor
rotation axis and the stator rotation axis. In such embodiments,
the rotor splines may be disposed parallel to the longitudinal
rotor rotation axis and the splined stator section cutouts may be
disposed parallel to the longitudinal stator rotation axis. In
other embodiments, the splined stator section may provide an
elastomer interface at a contact surface with the splined rotor
section inside the test coupon. In such embodiments, step (d) may
include at least one substep selected from the group consisting of:
(d1) controlling torque across the splined rotor section and the
splined stator section; (d2) counting, through to failure of the
test coupon, at least one of (1) splined rotor section rotation
cycles and (2) splined stator section rotation cycles; (d3)
examining at least one of (1) the splined rotor section and (2) the
splined stator section for wear, and (d4) monitoring temperature
change over time in the elastomer interface.
In other embodiments according to the fourth aspect, step (d) may
in elude at least one substep selected from the group consisting
of: (d1) controlling torque across the splined rotor section and
the splined stator section; (d2) counting, through to failure of
the test coupon, at least one of (1) splined rotor section rotation
cycles and (2) splined stator section rotation cycles; and (d3)
examining at least one of (1) the splined rotor section and (2) the
splined stator section for wear. In other embodiments according to
the fourth aspect, the method may further comprise, after step (a)
and before step (b), the substeps of: (a1) receiving the test
coupon inside a sealable test chamber; (a2) filling the test
chamber with test fluid; and (a3) sealing the test chamber. In such
embodiments, step (d) may further include the substep of monitoring
temperature change over time in the test chamber. In such
embodiments, the splined stator section may provide an elastomer
interface at a contact surface with the splined rotor section
inside the test coupon, wherein step (d) further includes the
substep of monitoring temperature change over time in the test
chamber.
According to a fifth aspect, this disclosure describes an
embodiment of a method for evaluating load performance of a
rotor/stator test coupon, the method comprising the steps of: (a)
providing a test coupon, the test coupon including a rotor section
received inside a stator section; (b) rotating a rotated first one
of the rotor section and the stator section with non-linear torque,
wherein rotation of the rotated first one of the rotor section and
the stator section actuates corresponding rotation of an actuated
second one of the rotor section and the stator section; (c)
applying a braking torque to the actuated second one of the rotor
section and the stator section; and (d) responsive to step (c),
evaluating load performance of the test coupon. In some embodiments
according to the fifth aspect, the non-linear torque in step (b)
may be delivered by at least one technique selected from the group
consisting of: (1) engaging an impact hammer-pin clutch when
rotating the rotated first one of the rotor section and the stator
section; (2) deploying a variable frequency drive motor to vary
rotation speed of the rotated first one of the rotor section and
the stator section; and (3) variably applying a braking torque to
the actuated second one of the rotor section and the stator
section.
According to a sixth aspect, this disclosure describes an
embodiment of a method for evaluating load performance of a
rotor/stator test coupon, the method comprising the steps of: (a)
providing a test coupon, the test coupon including a rotor section
received inside a stator section; (b) rotating a rotated first one
of the rotor section and the stator section, wherein rotation of
the rotated first one of the rotor section and the stator section
actuates corresponding rotation of an actuated second one of the
rotor section and the stator section; (c) applying a braking torque
to the actuated second one of the rotor section and the stator
section; (d) during steps (b) and (c), independently monitoring at
least one of (1) an angular position of the rotor section over
time, and (2) an angular position of the stator section over time;
and (e) responsive to steps (b) through (d), evaluating load
performance of the test coupon with reference to angular position
as monitored in step (d) over time. In some embodiments according
to the sixth aspect, angular position in step (d) may be monitored
using at least one rotary encoder.
In some embodiments according to the fifth, sixth and other
aspects, the rotor section rotates about a longitudinal rotor
rotation axis and the stator section rotates about a longitudinal
stator rotation axis. In such embodiments, step (b) may include
setting a preselected offset distance between the rotor rotation
axis and the stator rotation axis. In other embodiments, step (d)
may include at least one substep selected from the group consisting
of: (d1) controlling torque across the rotor section and the stator
section; (d2) counting, through to failure of the test coupon, at
least one of (1) rotor section rotation cycles and (2) stator
section rotation cycles; and (d3) examining at least one of (1) the
rotor section and (2) the stator section for wear. In other
embodiments, the test coupon may comprise at least a partial length
of a positive displacement motor (PDM) stage. In other embodiments,
at least one progressing gap on a helical pathway may form between
the rotor section and the stator section when the rotor section and
the stator section are differentially rotated. In other
embodiments, the stator section may provide an elastomer interface
at a contact surface with the rotor section inside the test coupon,
wherein step (d) includes at least one substep selected from the
group consisting of: (d1) controlling torque across the rotor
section and the stator section; (d2) counting, through to failure
of the test coupon, at least one of (1) rotor section rotation
cycles and (2) stator section rotation cycles; (d3) examining at
least one of (1) the rotor section and (2) the stator section for
wear; and (d4) monitoring temperature change over time in the
elastomer interface.
In other embodiments according to the fifth, sixth and other
aspects, the method may further comprise, after step (a) and before
step (b), the substeps of: (a1) receiving the test coupon inside a
sealable test chamber; (a2) filling the test chamber with test
fluid; and (a3) sealing the test chamber. In such embodiments, step
(d) further may further include the substep of monitoring
temperature change over time in the test chamber. In such
embodiments, the stator section may also provide an elastomer
interface at a contact surface with the rotor section inside the
test coupon, wherein step (d) further includes the substep of
monitoring temperature change over time in the test chamber.
It is therefore a technical advantage of the disclosed test
apparatus to miniaturize the performance testing of PDM power
sections in downhole conditions by accurately simulating such
conditions (for example, temperature and stress loading) in a
partial section of one stage of a PDM power section. The footprint
of the disclosed test apparatus is suitable to house the apparatus
in a conventional laboratory or even at the wellsite.
A further technical advantage of the disclosed test apparatus is to
provide a PDM test apparatus that enables performance testing using
a small volume of drilling fluid. In this way, if desired, the
disclosed test apparatus can accurately simulate downhole service
conditions using samples of actual drilling fluid extracted from a
PDM previously in downhole service (such samples known to be
available only in small quantities).
A further technical advantage of the disclosed test apparatus is to
avoid eccentric rotation vibration in the PDM power section test
coupon during testing. By avoiding such vibration, the disclosed
test apparatus enables performance evaluation of a PDM power
section test coupon that is isolated from the effects of vibration
caused by the eccentric rotation of the rotor within the stator.
Conventionally, the construction of PDM power sections provides a
hard (e.g. metal) rotor surface contacting a resilient stator
(usually providing an elastomer or rubber through part or all of
its cross-section). In normal PDM power section operations, the
eccentric rotation of the rotor within the stator imparts cyclic
loads (including, without limitation, compressive, shear and
tensile loads) on the resilient stator material, particularly on
the stator lobes. These loads imparted by cyclic contact are all
included in the suite of performance metrics sought to be simulated
and evaluated by the disclosed test apparatus.
However, the eccentric rotation of the rotor during normal PDM
power section operations also creates many modes of vibration
throughout the PDM assembly and elsewhere on the drill string. The
rotor on a full-size downhole PDM distributes torque and tilting
reaction forces along the full length of the elastomer component of
the stator. The large length to diameter ratio of the power section
allows these forces to be distributed along the length of multiple
power section stages. The PDM, over its entire multi-stage length,
can therefore absorb the vigorous dynamic forces created as the
rotor orbits eccentrically in the stator. In contrast, the
disclosed test apparatus evaluates performance on only a partial
section of one PDM power section stage. It is therefore not
possible in the disclosed test apparatus to stabilize the rotor
section within the test coupon against the vibrational effect of
eccentric rotation and tilting forces as might be seen in "live"
downhole operations, since the length of the rotor section in the
test coupon is too short to have sufficient longitudinal flexure to
compensate for eccentric rotation vibration.
Embodiments of the disclosed test apparatus therefore substantially
eliminate eccentric rotation vibration from the test coupon by
setting and holding the rotor rotation axis on a predetermined,
fixed offset from the stator rotation axis. The offset is selected
to be approximately equal to the design eccentricity of the
full-size, operational power section whose performance the test
coupon seeks to replicate and evaluate. The disclosed test
apparatus thus generates test results that reflect performance
isolated from substantially all eccentric rotation vibration, in a
test coupon that can be very short in length and requiring only a
small volume of drilling fluid. In this way, the results generated
by the disclosed test apparatus will more accurately predict
corresponding or vibration-compensated or vibration-isolated
performance expected in full-size PDM power sections operating
downhole.
The disclosed test apparatus provides yet a further advantage in
embodiments in which eccentric rotation vibration is substantially
eliminated. In embodiments where an offset is provided between axes
of rotor rotation and stator rotation (in order to elimination
eccentric rotation vibration), the external drive train rotating
the rotor is greatly reduced in complexity which still giving a
very accurate stress field within the test coupon. In embodiments
where an offset is not provided between axes of rotor rotation and
stator rotation, a transmission is required in the external drive
train to counteract or eliminate eccentric rotation vibration. The
rotor must also be longer in such embodiments in order to generate
flexure. Such an additional transmission and rotor length adds
cost, complexity, and inevitably (1) increases potential footprint
and (2) requires a higher volume of drilling fluid.
The disclosed test apparatus provides yet a further advantage in
embodiments in which non-linear torque may be applied to the test
coupon within the test chamber. Non-linear torque may be used to
simulate loading conditions on the test coupon found, for example,
in downhole environments where inhomogeneous formations are
encountered. Such non-linear torque may be provided by programming
speed pulses, for example, into the rotation delivered to the rotor
section by a variable frequency drive motor (VFDM). Alternatively,
braking torque pulses, for example, may be applied to the stator
section via pulsing the air supply to a pneumatically-drive brake
applying load to the rotating test coupon. Alternatively, an impact
hammer-pin clutch may be interposed between the external motor and
the test chamber to generate non-linear torque or impact
loading.
The disclosed test apparatus provides yet a further advantage in
embodiments in which independent rotary encoders are provided on
each of the rotor and stator sections. Comparison of data from the
rotary encoders enable evaluation of load performance with
reference to relative angular positions of the rotor section and
the stator section over time. In this way, torsional flex of the
rotor section may be monitored. Alternatively, rotary displacement
between the rotor and stator sections may be monitored during
operation. It will be understood that such rotary displacement is
often caused by torsional compression of elastomer lobes on the
stator section responsive to torque exerted thereon by lobes on the
rotor section.
The foregoing has rather broadly outlined some features and
technical advantages of the disclosed test apparatus, in order that
the following detailed description may be better understood.
Additional features and advantages of the disclosed technology may
be described. It should be appreciated by those skilled in the art
that the conception and the specific embodiments disclosed may be
readily utilized as a basis for modifying or designing other
structures for carrying out the same inventive purposes of the
disclosed technology, and that these equivalent constructions do
not depart from the spirit and scope of the technology as
described.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of embodiments described in
detail below, and the advantages thereof, reference is now made to
the following drawings, in which:
FIGS. 1-A through 1-J depict the operation of a conventional power
section 100 in a series of freeze-frame cutaway section views of
the conventional power section in operation;
FIGS. 2-A through 2-J depict movement of corresponding components
to FIGS. 1-A through 1-J in the disclosed new test apparatus 200,
wherein such movement is also depicted in a series of freeze-frame
cutaway section views;
FIG. 3 shows an exemplary layout for test bed 300 on which
components may be secured for enabling the disclosed new test
apparatus 200;
FIG. 4 illustrates test chamber 325 in cutaway view with internals
and surrounding components;
FIGS. 5 and 5A illustrate two different embodiments of test chamber
325 in cutaway view, in which test fluid 323 may follow different
flow loops FL1 and FL2;
FIG. 5B illustrates a third embodiment of test chamber in 325 in
cutaway view, in which stator section 321 is externally rotated to
drive rotor section 315 within test chamber 325;
FIG. 5C illustrates a fourth embodiment of test chamber 325 in
cutaway view, in which splined rotor section 415 is externally
rotated to drive splined stator section 421 within test chamber
325;
FIG. 6 illustrates exemplary embodiments of drive train 310 as more
generally illustrated on FIG. 3;
FIGS. 7A and 7B illustrate alternative test bed embodiments 700 and
702, respectively;
FIG. 8 illustrates expected rotary displacement RD between rotor
section 315 and stator section 321 in test chamber 325 during
operation of test bed embodiments such as shown on FIGS. 3, 5A, 5B,
7A and 7B, for example;
FIGS. 9A, 9B and 9C are sections as shown on FIGURE SC.
DETAILED DESCRIPTION
As discussed summarily above in this disclosure, this application
is directed to a PDM testing apparatus using a rotor/stator test
coupon that is a partial length of one stage of a power section. A
stage of a power section is defined by the minimum length to seal a
single helical progressing cavity. The relationship describing the
helical length of a single progressing cavity is based on the rotor
to stator lobe count ratio and can be expressed as: Stator Pitch
Length=(N+I)/N.times.Rotor Pitch Length Stator pitch length is a
PDM design parameter chosen to give the desired volumetric fluid
flow ratio for the selected rotor/stator configuration.
FIGS. 1-A through 1-J depict the mechanics of a conventional
progressing cavity power section, as is well known in the prior
art. Such progressing cavity power sections are also well known as
"Moineau" devices. FIGS. 1-A through 1-J depict the operation of
such a conventional power section 100 in a series of freeze-frame
cutaway section views of the power section in operation. The series
of freeze-frame views depicted in FIGURES I-A through 1-J are in
sequence. Parts and other features of conventional power section
100 are identified by reference number or letter, as described in
detail further below. Where the same reference number or letter is
used in FIGS. 1-B through 1-J, the same part or feature of power
section 100 is being identified on that Figure as depicted on FIG.
1-A. In this way, reference numbers and letters on FIGS. 1-B
through 1-J can be omitted for clarity on some views while still
allowing the reader to understand the subject matter depicted on
FIGS. 1-B through 1-J.
As noted, power section 100 as depicted in FIGURES I-A through 1-J
is conventional. Such power sections are designed using
intermeshing continuous helical pathways that provide, in cross
section, cooperating lobed gear profiles that intermesh with one
another in an "n" and "n+1" combination. Typically, the inner rotor
has n lobes and the outer stator gear has n+1 lobes. Referring to
FIG. 1A, rotor 120 is depicted with 6 lobes, and stator 110 has 7
lobes, although these values are purely by way of example. As will
be seen generally from FIGURES IA through 1-J viewed in sequence,
the precise cross-sectional profiles of these
these-gear-within-a-gear devices are normally described by
hypocycloid geometry created by rolling circle techniques. The
resulting gear devices are helically swept over the axial lengths
of the rotor and stator. The intermeshing along the axial length
creates progressing cavities on a helical pathway between the rotor
and stator, identified in cross-section on FIG. 1A as PC, through
which a flow of fluid drives rotor 120 around the inner periphery
of stator 110.
The hypocycloid geometry of the intermeshed lobes on rotor 120 and
stator 110 thus compels that in conventional PDM power sections
such as power section 100 on FIG. 1-A, rotor 120 orbits within
stator 110 at a known eccentricity from a central longitudinal
axis. This eccentricity is a derived relationship and is related to
the curvature and lobe heights generated from the mathematical
expressions defining hypocycloid and true rolling motion used in
the rotor and stator geometries. Review of FIGS. 1-A through 1-J in
sequence illustrate this conventional eccentricity in more
detail.
Referring first to FIG. 1-A, stator 110 includes rotational marker
112 and point marker 113. Rotational marker 112 sets a fixed point
on the outer periphery of stator 110, and point marker 113 sets a
fixed point on the inner periphery of stator 110 (adjacent
reference point "S1" on stator 110). It will be seen that the
location of markers 112 and 113 on subsequent views in FIGS. 1-B
through 1-J does not change, indicating that stator 110 is
stationary throughout the operation of conventional power section
100 depicted by FIGS. 1-A through 1-J.
With further reference to FIG. 1-A, rotor 120 includes fixed
reference point "R1" on the outer periphery of one of its lobes.
FIG. 1-A also shows progressing cavity (PC) position marker 130, on
which PC marker line 132 indicates the position of the approximate
most open point of progressing cavity PC. PC position marker 130
rotates in synch with progressing cavity PC around a central
longitudinal axis through stator 110. PC position marker 130 thus
also serves to illustrate and highlight the eccentric rotation of
rotor 120 within stator 110. It will be seen on FIG. 1-A that that
PC position marker 130 is offset from a central longitudinal axis
through rotor 120.
Referring now to FIG. 1-B, a flow of drilling fluid (not
illustrated) has displaced rotor 120 within stator 110 such that
progressing cavity PC has rotated approximately 90 degrees
clockwise within stator 110 from the corresponding progressing
cavity position depicted on FIG. 1-A. This rotation of progressing
cavity PC is illustrated by the new position of PC marker line 132
on FIG. 1-B, as well as a new general position on FIG. 1-B of
progressing cavity PC. FIG. 1-B also shows that in response to
clockwise movement of PC, rotor 120 has rotated counterclockwise as
shown by the new position of rotor reference point R1. FIG. 1-B
illustrates the clockwise movement of progressing cavity PC by
arrow R.sub.PC, and the responsive counterclockwise movement of
rotor 120 by arrow R.sub.R.
FIG. 1-C illustrates that the flow of drilling fluid has displaced
rotor 120 within stator 110 such that progressing cavity PC has
rotated approximately a further 90 degrees clockwise within stator
110 from the corresponding progressing cavity position depicted on
FIG. 1-B. The relative movement of components within stator 110 can
be seen from the new positions of progressing cavity PC, PC marker
line 132, and rotor reference point R1 on FIG. 1-C, as compared to
their corresponding positions on FIGS. 1-A and 1-B.
FIGS. 1-D and 1-E each show a further rotation of approximately 90
degrees clockwise of progressing cavity PC over the previously
illustrated positions. Again, the relative movement of components
within stator 110 can be seen from the new positions of progressing
cavity PC, PC marker line 132, and rotor reference point R1 on each
advancing view on FIGS. 1-A through 1-E. It will be appreciated
that on FIG. 1-E, progressing cavity PC has made one complete
revolution of stator 110 over the starting position on FIG.
1-A.
FIGS. 1-F through 1-J illustrate the counterclockwise rotation of
rotor 120 within stator 110 responsive to subsequent full
revolutions clockwise of progressing cavity PC. In each of FIGS.
1-A, and then 1-F through 1-J, progressing cavity PC has made one
further full clockwise revolution over the previously illustrated
view. When FIGS. 1-A, and then 1-F through 1-J are viewed in
sequence, the new position of rotor reference point R1 can be seen
in response to one additional revolution of progressing cavity PC.
It will be appreciated that in FIG. 1-J, progressing cavity PC has
made 6 clockwise revolutions of stator 110 over the view depicted
in FIG. 1-A, during which time rotor reference point R1 has made
one counterclockwise revolution, indicating that the eccentricity
of rotor 120 within stator 110 is in the same state in FIG. 1-J as
it was initially in FIG. 1-A.
As noted throughout the disclosure immediately above, FIGURES I-A
through 1-J illustrate movement of components within a conventional
power section 100. FIGS. 2-A through 2-J depict movement of
corresponding components within the disclosed new test apparatus
200. As with FIGS. 1-A through 1-J, FIGS. 2-A through 2-J depict
such movement within test apparatus 200 in a series of freeze-frame
cutaway section views of the test apparatus in operation. The
series of freeze-frame views depicted in FIGS. 2-A through 2-J are
in sequence. Similar to conventional power section 100 depicted in
FIGS. 1-A through 1-J, test apparatus 200 in FIGS. 2-A through 2-J
provides a rotor 220 with 6 lobes operating inside a stator 210
with 7 lobes. Where the same reference number or letter is used in
FIGS. 2-A through 2-J, the same part or feature of test apparatus
200 is being identified. In this way, reference numbers and letters
on FIGS. 2-A through 2-J can be omitted for clarity on some views
while still allowing the reader to understand the subject matter
depicted on FIGS. 2-A through 2-J.
The "Summary" section describes above how the disclosed test
apparatus 200 tests less than one full length of a full downhole
PDM power section stage, and thus necessarily cannot provide a
series of full progressing cavities (one full stage of a power
section being defined by the minimum length to seal a single
helical progressing cavity, see above). Test apparatus 200 thus
cannot be sealed to operate conventionally with moving drilling
fluid driving a rotor in a stationary stator (as illustrated and
described above with reference to FIGS. 1-A through 1-J). Test
apparatus 200 thus does not provide progressing cavities as
illustrated as PC on FIGS. 1-A through 1-J. In contrast, as
illustrated on FIGS. 2-A though 2-J, test apparatus 200 provides
progressing gaps PG on helical pathways formed between rotor 220
and stator 210 when rotor 220 and stator 210 are differentially
rotated. Progressing gaps PG on FIGS. 2-A though 2-J are
necessarily only a partial section of corresponding progressing
cavities PC found on a full PDM power stage, as illustrated on
FIGS. 1-A through 1-J.
In operation, currently preferred embodiments of test apparatus 200
on FIGS. 2-A through 2-J provide an external motor (not illustrated
on FIGS. 2-A through 2-J) to rotate rotor 220 while submersed in
test fluid/drilling fluid inside stator 210. As rotor 220 rotates,
it actuates corresponding rotation of stator 210 via contact
between rotor 220 and stator 210. An external brake mechanism
(again not illustrated on FIGS. 2-A through 2-J) is then activated
to apply braking torque to intentionally slow the rotation of
stator 210 against the powered rotation of rotor 220. Applied
braking torque can be finely controlled. In this way, a controlled
stress field can be intentionally introduced on the components
inside test apparatus 200 that approximate closely in kind,
location, and strength the operational stresses experienced inside
conventional power section 100 on FIGS. 1-A through 1-J when
drilling fluid is pumped through progressing cavity PC to rotate
rotor 120 within stationary stator 110.
Looking at FIGS. 2-A through 2-J in more detail, FIG. 2-A
illustrates test apparatus 200 with the following parts and
features, many of which are counterparts to the corresponding parts
and features described above with respect to FIGS. 1-A through
1-J:
Stator 210
Stator rotational marker 212
Stator point marker 213
Stator reference point S1
Rotor 220
Rotor reference point R1
Progressing gap PG along the axial length of rotor 220 and stator
210, on a helical pathway formed between rotor 220 and stator 210
when rotor 220 and stator 210 are differentially rotated.
Additionally, FIG. 2-A illustrates rotor rotation marker line 222,
which, along with rotor reference point R1, indicates rotation of
rotor 220 relative to other components in test apparatus 200 as
views advance through FIGS. 2-A through 2-J.
Referring now to FIG. 2-B, external rotor motor (not illustrated)
has rotated rotor 220 approximately 90 degrees counterclockwise
within stator 210 from the corresponding position of rotor 220
depicted on FIG. 2-A. As a result, rotational motion forces from
rotor 220 have exerted themselves on stator 210, actuating rotation
of stator 210 in a counterclockwise direction. This displacement of
stator 210 can be seen by comparing the relative positions of
stator rotational marker 212, stator point marker 213 and stator
reference point S1 on FIG. 2-B as compared to FIG. 2-A.
Additionally, the displacement of rotor 220 by approximately 90
degrees counterclockwise in FIG. 2-B has caused progressing gap PG
to move in a clockwise direction away from its corresponding
position in FIG. 2-A. This clockwise movement of progressing gap PG
is best seen by comparing its displaced position relative to stator
rotational marker 212 in FIG. 2-A and then FIG. 2-B. FIG. 2-B
illustrates the counterclockwise movement of rotor 220 by arrow
R.sub.R, the responsive counterclockwise movement of stator 210 by
arrow R.sub.S, and the resulting clockwise movement of progressing
gap PG by arrow R.sub.PG.
FIG. 2-C illustrates that external rotor motor (not illustrated)
has rotated rotor 220 approximately 90 degrees further
counterclockwise within stator 210 from the corresponding position
of rotor 220 depicted on FIG. 2-B. As a result, rotational motion
forces from rotor 220 have acted on stator 210, causing stator 210
to rotate further in a counterclockwise direction. This
displacement of stator 210 can be seen by comparing the relative
positions of stator rotational marker 212, stator point marker 213
and stator reference point S1 on FIG. 2-C as compared to FIG. 2-B.
Additionally, the displacement of rotor 220 by approximately 90
degrees further counterclockwise in FIG. 2-C has caused progressing
gap PG to move in a clockwise direction away from its corresponding
position in FIG. 2-B, as seen by comparing the position of
progressing gap PG in FIG. 2-C relative to stator rotational marker
212 in FIG. 2-B.
FIGS. 2-D and 2-E each show a further rotation of approximately 90
degrees counterclockwise of rotor 220 over the previously
illustrated positions. Again, the relative movement of components
within stator 210 can be seen from the new positions of rotor
rotation marker line 222, rotor reference point R1, stator
rotational marker 212, stator point marker 213, stator reference
point S1, and progressing gap PG on each advancing view on FIGS.
2-A through 2-E. It will be appreciated that on FIG. 2-E, external
rotor motor (not illustrated) has caused rotor 220 to make one
complete revolution of stator 210 over the starting position on
FIG. 2-A.
FIGS. 2-F through 2-J illustrate the counterclockwise rotation of
stator 210 responsive to subsequent full revolutions
counterclockwise of rotor 220. In each of FIGS. 2-A, and then 2-F
through 2-J, rotor 220 has made one further full counterclockwise
revolution over the previously illustrated view. When FIGS. 2-A,
and then 2-F through 2-J are viewed in sequence, the new relative
position of stator rotational marker 212, stator point marker 213,
stator reference point S1, and progressing gap PG can be seen in
response to one additional revolution of rotor 220. It will be
appreciated that in FIG. 2-J, rotor reference point R1 has made 6
counterclockwise revolutions as compared to the view depicted in
FIG. 2-A, during which time stator reference point S1 has made
almost one counterclockwise revolution in the orbital distance
separating rotor reference point R1 and stator reference point R1
during rotation. It will be appreciated that with one further
complete counterclockwise revolution of rotor reference point R1 (a
seventh overall rotation), stator reference point S1 will have made
one complete counterclockwise revolution in the orbital distance
separating rotor reference point R1 and stator reference point S1,
and will further have returned to the same position relative to
rotor reference point R1 as depicted in FIG. 2-A.
Returning now to view FIGS. 1-A through 1-E in sequence, it will be
appreciated rotor 120 is in an eccentric orbit within stator 110
during in the operation of conventional power section 100.
Conventionally, the construction of PDM power sections provides a
hard (e.g. metal) rotor surface contacting a resilient stator
(usually providing an elastomer or rubber through part or all of
its cross-section). As described above in the "Summary" section, in
normal PDM power section operations, the eccentric rotation of the
rotor within the stator imparts cyclic loads (including, without
limitation, compressive, shear and tensile loads) on the resilient
stator material, particularly on the stator lobes. The eccentric
rotation of the rotor during normal PDM power section operations
also creates many modes of vibration throughout the PDM assembly
and elsewhere on the drill string. It will be appreciated that
these vibrations, as experienced downhole, can be addressed over
the length of a full power section stage by fixing the ends of the
rotor and allowing the natural flexure of the rotor to compensate.
However, in short lengths of conventional power section configured
according to FIGS. 1-A through 1-E, such eccentric rotation
vibrations cannot easily be compensated for, since the rotor is too
short to have the required flexure.
Turning now to view FIGS. 2-A through 2-E in sequence, it will be
appreciated that embodiments of the disclosed test apparatus 200
are reconfigured in a way to optimize, and in some cases to
substantially eliminate, any eccentric rotation vibration that
might potentially arise in the test coupon, so that performance
evaluation of the components of the test coupon can be conducted
free of the effects of such vibration. FIGS. 2-A through 2-E show
that stator 210 and rotor 220 each rotate independently about their
own fixed, substantially parallel longitudinal axes, and that the
rotor rotation axis is set at a fixed offset distance from the
stator rotation axis. The fixed offset distance is a predetermined
design choice, selected according to the size and lobe count of the
rotor and stator, and further according to the amount of
operational contact desired by the rotor on the stator as the rotor
is externally rotated. Comparison should now be made with the
eccentric orbit of rotor 120 within stator 110 on FIGS. 1-A through
1-E in sequence, where rotor 120 makes operational contact on
stator 110 as rotor 120 moves around the inner periphery of stator
110. Returning to FIGS. 2-A through 2-E, it will be appreciated
that by selecting, setting and holding the rotor rotation axis of
rotor 220 at a fixed offset distance from the rotation axis of
stator 210, the same operational contact between rotor 220 and
stator 210 can be replicated in test apparatus 200 as is
experienced in conventional PDM power section 100 on FIGS. 1-A
through 1-E. In test apparatus 200 on FIGS. 2-A through 2-E,
however, there is no eccentric orbital rotation of rotor 220 within
stator 210, thereby substantially eliminating vibration that might
otherwise be caused by such eccentric orbital rotation.
Previous disclosure described how in most test environments, test
apparatus 200 will be configured such that the offset between of
rotor 220 and stator 210 is substantially the same as the
eccentricity of the rotor's orbit in a full-size PDM whose
performance the test coupon is designed to evaluate. For purposes
of this paragraph, such offset between longitudinal rotational axes
of rotor 210 and stator 220 will be referred to as the "ideal
eccentricity". Additional embodiments of test apparatus 200 may be
configured with variations in offset (greater or smaller) away from
the ideal eccentricity. Such additional embodiments will simulate
(and enable corresponding performance evaluation under) extreme
loading conditions experienced by full-length PDM power sections in
environments where the ambient dynamic loading conditions are
deflecting rotor's eccentric orbit beyond design.
Physical embodiments of the disclosed test apparatus are now
described with reference to FIGS. 3 through 9C. As before, where
the same reference number or letter is used in FIGS. 3 through 9C,
the same part or feature is being identified on more than one
Figure.
FIG. 3 shows an exemplary layout for test bed 300 on which
components may be secured for enabling the disclosed test
apparatus. External motor 305 provides rotational power to rotor
section 315 via drive train 310. External motor 305 is illustrated
on FIG. 3 as an electric motor. The scope of the disclosed test
apparatus is indifferent, however, to the type of external motor
selected. Drive train 310 is illustrated in FIG. 3 as a
belt-and-pulley drive train. Embodiments of test bed 300 that
provide drive train 310 as a belt-and-pulley train will gain
further advantages as described below with reference to FIG. 6.
However, this disclosure is not limited to embodiments whose drive
train 300 is a belt-and pulley train.
Rotor section 315 on FIG. 3 is set rotationally in place on rotor
bearings 318. It will be understood from momentary reference to
FIG. 5 that a distal end of rotor section 315 terminates inside
test chamber 325, and functions as the rotor portion of the test
coupon under analysis in test chamber 325. Test chamber 325 is
shown sealed on FIG. 3. Embodiments of the internals of test
chamber 325 are discussed further below with reference to FIG. 4
and FIGS. 5 through 5C. Returning to FIG. 3, stator shaft 320 exits
test chamber 325 and will be understood to be rotationally
connected to stator section 321 inside test chamber 325 (again,
refer momentarily to FIG. 4). Stator bearings 328 set stator shaft
320 rotationally in place. Stator shaft 320 is rotationally
connected to torque sensor 330, which measures the torque generated
by stator shaft 320 as stator shaft 320 rotates in response to
external motor 305 driving rotor 315. Torque sensor 330 is further
subject to intentional slowing of rotation via a braking torque
supplied by continuous-slip brake 335, whereby control of the
braking torque induces a controlled stress field (not illustrated)
between rotor 315 and stator 321 inside test chamber 325. While the
embodiments described with reference to FIG. 3 refer to a
continuous-slip brake 335, it will be understood that the scope of
the test apparatus is not limited in this regard, and that other
types of conventional brakes may be substituted for continuous-slip
brake 335.
Test chamber 325 will now be discussed in more detail with
reference to FIG. 4 and FIGS. 5 through 5C. FIG. 4 and FIGS. 5
through 5C are section views shown generally on FIG. 3. Note FIG. 3
omits specific reference to FIGS. 5A through 5C mainly for clarity,
it being understood from disclosure further below that FIGS. 5
through 5C are alternative embodiments and therefore the section
line for FIG. 5 shown on FIG. 3 is representative for all of FIGS.
5 through 5C.
Referring first to FIG. 4, test chamber 325 is seen in cutaway
view. Rotor section 315 is omitted for clarity. Stator section 321
is seen rotationally and coaxially fixed to stator shaft 320.
Sealable test chamber 325 also provides annular cavity 322 formed
between an external periphery of stator section 321 and an internal
periphery of test chamber 325. Per the embodiment of FIG. 5A,
described further below, FIG. 4 depicts openings 324 provided
stator section 321. (It will be appreciated from disclosure further
below that openings 324 are not provided in the embodiment of FIG.
5). In operation, test chamber 325 is filled with test fluid 323
(advantageously drilling fluid) prior to being sealed so that
stator section 321 is completely immersed.
FIGS. 5 through 5C illustrate four exemplary alternative
embodiments of test chamber 325 in more detail with surrounding
components, again in cutaway view. Referring first to FIGS. 5 and
5A, first and second embodiments of test chamber 325 are
illustrated in which progressing gaps PG are formed on helical
pathways between stator section 321 and rotor section 315. Test
chamber 325 is sealed and filled with test fluid 323. It was noted
in earlier disclosure that test fluid 323 is present in test
chamber 325 to interact with the materials from which rotor section
315 and stator section 321 are made, in order to simulate
degradation that might be seen in actual downhole conditions. It
was also noted in earlier disclosure, however, that once test
chamber 325 was sealed, the relative differential rotation of rotor
section 315 and stator section 321 may cause the test fluid 323 to
flow under low pressure through progressing gaps PG. Referring to
the embodiment of FIG. 5, and as illustrated by the darker arrows
on FIG. 5, first flow loop FL1 for test fluid 323 is formed through
progressing gaps PG. FIG. 5 depicts first flow loop FL1 in one
exemplary flow direction, although it will be understood that flow
loop FL1 may arise in either direction according to user selection
of the direction in which to rotate rotor section 315.
Referring now to the embodiment of FIG. 5A, openings 324 are
provided in stator section 321. The darker arrows on FIG. 5A
illustrate that second flow loop FL2 for test fluid 323 may form in
one exemplary flow direction, through progressing gaps PG in a
direction away from the end near rotor bearing 318, then through
openings 324 in stator section 321, then through annular cavity 322
back to the rotor bearing end of progressing gaps PG. Again,
although not specifically illustrated on FIG. 5A, it will be
understood that, according to user selection of the direction in
which to rotate rotor section 315, second flow loop FL2 may flow in
either direction. In general, first and second flow loops FL1 and
FL2 on FIGS. 5 and 5A are indifferent to the direction in which
test fluid 323 may be caused to flow.
FIGS. 5 and 5A further show rotor section 315 held rotationally in
place by one of rotor bearings 318. Stator shaft 320 is also shown
held rotationally in place by one of stator bearings 328. FIG. 5
further illustrates a cross-section cut for FIGS. 2-A through 2-J.
It will be understood that freeze-frame views seen on FIGS. 2-A
through 2-J represent movement of the disclosed test apparatus
within test chamber 325 along an exemplary cross-section cut line
as shown on FIG. 5.
FIGS. 5 and 5A also illustrate the preselected offset 317 between
rotor rotation axis 316 and stator rotation axis 326. As discussed
extensively above with reference to FIGS. 2-A through 2-E, for
example, offset 317 is introduced to eliminate eccentric rotation
vibration during operation of test chamber 325. It will be
understood that relative adjustment of rotor bearings 318 and
stator bearings 328 allows test chamber 325 to accommodate a range
of offsets 317 to be selected, set and held according to user
requirements.
FIG. 5B illustrates a third embodiment of test chamber 325. The
embodiment of FIG. 5B is similar to the embodiment of FIG. 5 in
many regards, except that rotor section 315 and section 321 have
"switched positions" within test chamber 325 in the embodiment
illustrated on FIG. 5B. That is, stator shaft 320 and stator
section 321 on FIG. 5B are externally rotated within test chamber
315 (by, for example, external motor 305 as depicted on FIG. 3).
Stator bearings 328 on FIG. 5B set stator shaft 320 rotationally in
place. External rotation of stator shaft 320 on FIG. 5B causes test
fluid 323 to flow through the progressing gaps on the helical
pathways between stator section 321 and rotor section 315 within
test chamber 325 (progressing gaps not labeled on FIG. 5B, refer to
item PG on FIG. 5 instead for corresponding identification of this
feature). Flow of test fluid 323 through the progressing gaps
between stator section 321 and rotor section 315 within test
chamber 325 on FIG. 5B causes rotor 315 to rotate. Rotor bearings
318 set rotor section 315 rotationally in place. It will be
understood by comparative reference to FIG. 3 as described above
that rotor section 315 is rotationally connected to torque sensor
330, which measures the torque generated by rotor section 315 as
rotor section 315 rotates in response to external motor 305 driving
stator shaft 320 and stator section 321. Torque sensor 330 is
further subject to intentional slowing of rotation via a braking
torque supplied by continuous-slip brake 335, whereby control of
the braking torque induces a controlled stress field (not
illustrated) between rotor section 315 and stator section 321
inside test chamber 325. The stress field and other
parameters/conditions regarding test chamber 325 (or rotor section
315, stator section 321 or test fluid 323 within test chamber 325)
may then be measured and evaluated.
FIG. 5B also illustrates the preselected offset 317 between rotor
rotation axis 316 and stator rotation axis 326. Preselected offset
317 will be understood to be available and operable on the
embodiment of FIG. 5B even though rotor section 315 and stator
section 321 have "switched positions" within test chamber 325 as
compared to, say, FIG. 5. As discussed extensively above with
reference to FIGS. 2-A through 2-E, for example, offset 317 is
introduced to eliminate eccentric rotation vibration during
operation of test chamber 325. It will be understood that relative
adjustment of rotor bearings 318 and stator bearings 328 allows
test chamber 325 to accommodate a range of offsets 317 to be
selected, set and held according to user requirements.
It will be also appreciated that the scope of this disclosure is
not limited to the "switching of positions" of rotor and stator
sections 315 and 321 as depicted in the embodiment of FIG. 5B as
compared to the embodiment of FIG. 5, as described above. The scope
of this disclosure includes the rotor and stator sections
"switching positions" inside the test chamber for all test chamber
embodiments, including the embodiments depicted on FIGS. 5A and
5C.
FIG. 5C illustrates a fourth embodiment of test chamber 325. FIGS.
9A, 9B and 9C are sections as shown on FIG. 5C. The embodiment of
FIG. 5C depicts straight, longitudinal engagement between splined
rotor section 415 and splined stator section 421 within test
chamber 325. It will therefore be understood that the embodiment of
FIG. 5C does not act like a conventional "Moineau" stator/rotor
assembly (such as described in the embodiments of FIGS. 5, 5A and
5B), since the embodiment of FIG. 5C does not provide helical
pathways between splined rotor section 415 and splined stator
section 421. Instead, with momentary reference to FIGS. 9A through
9C, splined rotor section 415 provides a plurality of straight,
longitudinal splines 419 for engagement with straight, longitudinal
splined stator cutouts 427 formed in splined stator section 421. It
will be further understood that although FIG. 5C depicts straight,
longitudinal splines 419 formed in splined rotor section 415, the
scope if this disclosure is not limited in this regard, and that
other embodiments (not illustrated) may deploy non-longitudinal
straight splines on a rotor section disposed to be received in
corresponding non-longitudinal, straight splined stator cutouts
formed in the stator section.
As noted above in the "Summary" section, the artificially-created
gearings between splined rotor section 415 and splined stator
section 421 provided in splined embodiments such as depicted on
FIG. 5C may be used to simulate desired conditions in test chamber
325 for evaluation of, for example, specific loading or
environmental conditions of interest. A specific stress field
between splined rotor section 415 and splined stator section 421,
for example, or a specific downhole environment, again for example,
may be artificially created, simulated and tested. As such,
therefore, the scope of this disclosure is not limited to
evaluating test coupons that are partial sections of a PDM, such as
are illustrated and described above with reference to the
embodiments of FIGS. 5, 5A and 5B.
FIG. 5C also illustrates preselected offset 417 between splined
rotor rotation axis 416 and splined stator rotation axis 426. It
will be understood that relative adjustment of rotor bearings 318
and stator bearings 328 allows test chamber 325 on FIG. 5C to
accommodate a range of offsets 417 to be selected, set and held
according to user requirements.
FIGS. 9A through 9C illustrate just one example of a specific
loading condition and stress field that may be created, simulated,
varied and evaluated using splined embodiments such as are depicted
on FIG. 5C. FIGS. 9A through 9C are sections as shown on FIG. 5C,
and should be viewed in conjunction with FIG. 5C. FIGS. 9A through
9C show three exemplary alternative sections through splined rotor
section 415 and splined stator section 421. Each of FIGS. 9A
through 9C are illustrated with different offsets 417 between
splined rotor rotation axis 416 and splined stator rotation axis
426 (compare and refer with FIG. 5C). Each offset 417 will be
understood to be selected via relative adjustment of rotor bearings
318 and stator bearings 328 on FIG. 5C. FIG. 9A reflects the most
offset 417 between splined rotor rotation axis 416 and splined
stator rotation axis 426 on FIG. 5C. FIG. 9C reflects the least
offset 417 between splined rotor rotation axis 416 and splined
stator rotation axis 426 on FIG. 5C. FIG. 9B reflects an offset 417
on FIG. 5C that is between offset 417 reflected on FIG. 9A and
offset 417 reflected on FIG. 9C.
In each of FIGS. 9A through 9C, contact zone CZ2 at "6 o'clock", or
180 degrees azimuth between splined rotor section 415 and splined
stator section 421 is one exemplary stress field variable being
evaluated for load performance in the splined embodiment of FIG.
5C. It will be appreciated from FIGS. 9A through 9C that as splined
rotor section 415 is rotated, torque transfer into splined stator
section 421 is through rotor splines 419 engaged in splined stator
cutouts 427 at contact zone CZ2 at 180 degrees azimuth. Splined
stator section 421 rotates responsive to rotation of splined rotor
section 415. Portions of splined stator section 421 thus move into
and then out of contact zone CZ2 as splined stator section 421
rotates. In FIG. 9A, reflecting the most offset 417 between splined
rotor rotation axis 416 and splined stator rotation axis 426 on
FIG. 5C, portions of splined stator section 421 are in compression
as they move into and out of contact zone CZ2. Load performance of
splined stator section 421 in this compressed condition may be
evaluated in the presence of controlled test fluids or
environmental conditions. In FIG. 9C, reflecting the least offset
417 between splined rotor rotation axis 416 and splined stator
rotation axis 426 on FIG. 5C, there is a small gap (and thus no
compression) between splined rotor section 415 and splined stator
section 421 as portions of splined stator section 421 move into and
out of contact zone CZ2. Torque transfer between splined rotor
section 415 and splined stator section 421 is carried almost
entirely through lobes on splined stator section 421 to the side of
contact zone CZ2. Load performance of splined stator section 421 in
this uncompressed/lobe-compressed condition may be evaluated in the
presence of controlled test fluids or environmental conditions. In
FIG. 9B, reflecting an offset 417 on FIG. 5C that is between offset
417 reflected on FIG. 9A and offset 417 reflected on FIG. 9C,
portions of splined stator section 421 are merely in contact with
splined rotor section 415 as they move into and out of contact zone
CZ2. Load performance of splined stator section 421 in this
uncompressed but contacted condition may be evaluated in the
presence of controlled test fluids or environmental conditions.
It will be understood from the above example with reference to
FIGS. 9A through 9C that many performance variables may be isolated
or combined, and then simulated and evaluated a splined embodiment
such as illustrated in FIG. 5C. FIG. 5C and FIGS. 9A through 9C
illustrate an embodiment where splined rotor section 415 provides
six (6) rotor splines 419 engaged at contact zone CZ2 at 180
degrees azimuth in seven (7) splined stator cutouts 427 in splined
stator section 421. Splined rotor section 415 in FIGS. 5C and 9A
though 9C is further sized for a "near full fit" within splined
stator section 421. It will be appreciated that the scope of this
disclosure, however, is not limited in any of the foregoing
regards. Design choices within the scope of this disclosure
include, for example and without limitation: number and size of
rotor splines; number and size of splined stator cutouts; relative
sizes and lengths of splined rotor section and splined stator
section; azimuthal points of engagement between rotor splines and
splined stator cutouts; amount of offset (and azimuth of offset)
between splined rotor rotation axis and splined stator rotation
axis; materials used for splined rotor section and splined stator
section (including hybrid constructions); test fluid
characteristics (such as chemistry or historical source); and
environmental conditions such as temperature and internal
pressure.
With further reference to FIG. 5C, and comparing with FIGS. 5 and
5A, it will also be appreciated that the splined embodiment of FIG.
5C does not create designated flow loops of test fluid 323 within
test chamber 325, such as flow loops FL1 or FL2 described above
with reference to FIGS. 5 and 5A. Instead, test fluid 323 in FIG.
5C is turbulent within test chamber 325, and the rotation of
splined rotor section 415 as engaged on splined stator section 421
creates local eddies and flow patterns within test fluid 323. As
such, test fluid 323 acts in part as a lubricant and coolant in
splined embodiments such as in FIG. 5C. Test fluid 323 may also be
selected in such embodiments for simulation evaluation of its
specific chemical or mechanical effect on elastomer/rubber deployed
on splined stator section 421.
FIG. 6 illustrates exemplary embodiments of drive train 310 as more
generally illustrated on FIG. 3. On FIG. 6, three alternatives are
illustrated in which varying drive speeds and torques may be
delivered to rotor section 315 by external motor 305 via drive
train 310. It will be understood, however, that the disclosed test
apparatus is not limited to the three alternatives illustrated on
FIG. 6, and that the scope of the disclosed test apparatus
contemplates many alternative drive speeds and torques delivered to
rotor section 315. It will be further appreciated that by providing
different drive speeds and torques to rotor section 315, the
disclosed test apparatus can simulate the mutation speed of a PDM
power section, i.e. the "step down" effect of the "gear within the
gear".
As suggested in earlier disclosure, external motor 305, drive train
310, rotor and stator bearings 318 and 328, torque sensor 330,
continuous-slip brake 335, and other seals not called out by part
number are all off-the-shelf components whose performance
characteristics are selected to suit a particular design of the
disclosed test apparatus. In presently preferred embodiments, a
suitable external motor 305 is a Brook Crompton 75 HP AC 3-phase
230/460 V motor delivering up to 1800 rpm; a suitable
continuous-slip brake 335 is a Wichita Clutch model KKB 208;
suitable seals for test chamber 325 are UTEX models MP; suitable
rotor/stator bearings 318/328 are available from Dodge; and a
suitable torque transmitter 330 is a Himmelstein MRCT 39000X. The
scope of the disclosed test apparatus is nonetheless not limited to
any particular selection or combination of such off-the-shelf
components. Likewise, the control of the disclosed test apparatus
is advantageously via conventional PLC and PID control, and the
scope of the disclosed test apparatus is not limited in this
regard.
FIGS. 7A and 7B illustrate test bed embodiments 700 and 702,
respectively, and should be viewed in conjunction and comparison
with test bed embodiment 300 illustrated on FIG. 3. Generally, test
bed 700 on FIG. 7A is functionally similar to test bed 300 on FIG.
3, except that additional and/or different equipment is deployed on
test bed 700 to render test bed 700 capable of measuring and
evaluating additional and/or different conditions within and around
test chamber 325 on test bed 700. Specifically, test bed 700 on
FIG. 7A provides the following equipment: external variable
frequency drive motor (VFDM) 405; clutch 340 interposed between
VFDM 405 and test chamber 325; and rotary encoders 345A/345B
deployed either side of test chamber 325. FIG. 7A shows rotary
encoder 345A positioned to measure/map rotation and angular
position of rotor section 315, and rotary encoder 345B positioned
to measure/map rotation and angular position of stator shaft 320
(attached to stator section 321, hidden from view within test
chamber 325).
Test bed 702 on FIG. 7B is functionally similar to test bed 700 on
FIG. 7A, except that test bed 702 on FIG. 7B is a direct drive
embodiment, in contrast to test bed 700's belt drive embodiment
shown on FIG. 7A. Test bed 702 on FIG. 7B also provides external
variable frequency drive motor (VFDM) 405; clutch 340 interposed
between VFDM 405 and test chamber 325; and rotary encoders
345A/345B deployed either side of test chamber 325 to measure/map
rotation and angular position of rotor section 315 and stator shaft
320, respectively. It will be appreciated that much of the
following description with reference to test bed 700 on FIG. 7A
will be equally applicable to test bed 702 on FIG. 7B.
Test bed 700 on FIG. 7A provides rotary encoders 345A/345B to
measure and evaluate operational rotary displacement between stator
section 321 and rotor section 315 during operation. Rotary encoders
345A/345B each measure and compare incremental or absolute angular
position of stator section 321 and rotor section 315 at moments in
time. An example of suitable rotary encoder for use as rotary
encoders 345A/345B on FIG. 7A is a Maxon Tacho 103935 encoder.
FIG. 8 illustrates expected rotary displacement RD between rotor
section 315 and stator section 321 in test chamber 325 during
operation of test bed embodiments such as shown on FIGS. 3, 5, 5A,
5B, 7A and 7B, for example. It will be understood on FIG. 8 that as
rotor section 315 is externally rotated (or as stator section 321
is externally rotated in the embodiment of FIG. 5B), compression of
stator section 321 during torque transfer will be expected in areas
such as contact zone CZ1. This compression of stator section 321 in
contact zone CZ1 will in turn cause rotary displacement RD, at a
given moment in time, between (A) the centerline running from rotor
rotation axis 316 to bisect a lobe of interest on rotor section
315, and (B) the centerline running from stator rotation axis 326
to theoretically bisect (in an uncompressed state) the cutout in
stator section 321 in which the lobe of interest on rotor section
315 is located. It will be further seen on FIG. 8 that rotary
displacement RD subtends a compound angle because rotor and stator
rotation axes 316 and 326 are separated in operation by preselected
offset 317.
With momentary reference now to FIG. 7A, it will be understood that
comparison of data from rotary encoders 345A/345B will enable
rotary displacement RD on FIG. 8 to be measured and evaluated.
Correction of comparison data may be required to account for the
compound angle subtended by rotary displacement RD if preselected
offset 317 between rotor and stator rotation axes 316 and 326 is
sufficiently large to affect the accuracy or reliability of
uncorrected comparison data.
In other embodiments (not illustrated) rotary displacement RD may
arise as a result of torsional flex of rotor section 315 with
respect to stator section 321. Rotary encoders 345A/345B may also
be configured to measure and evaluate rotary displacement RD in the
presence of such torsional flex of rotor section 315.
FIG. 8 is illustrated with respect to "Moineau"-design embodiments
of stator section 321 and rotor section 315 having progressing gaps
PG (and associated helical pathways). It will nonetheless be
understood that although not specifically illustrated, deployments
of rotary encoders 345A/345B such as on test bed embodiment 700 may
also be used to measure and evaluate operational rotary
displacement of splined rotor and stator sections 415 and 421 on
the splined embodiments illustrated on FIG. 5C.
Test bed embodiment 700 on FIG. 7A further provides external
variable frequency drive motor (VFDM) 405 to provide external
rotation of rotor section 315. VFDM 405 is an alternative to
conventional fixed-frequency external motor 305 shown on test bed
300 on FIG. 3. VFDM 405 is conventional, and suitable VFDMs are
commercially available from GE, Delta or AC Tech Lenze, for
example. It will be understood that variable frequency drive motors
such as VFDM 405 on FIG. 7A conventionally have controllers to vary
the voltage or alternating current frequency supplied to the motor,
and thus vary the speed (and thus, indirectly, the torque) with
which the motor rotates. The controllers may be governed by
programmable software so that the motor may be customized to rotate
in accordance with designed rotational speed patterns. Test bed
embodiments providing VFDM 405 may thus provide external rotation
of rotor section 315 (e.g. on FIG. 7A) in which the rotation is
pulsed, for example. As a result, VFDM 405 may be programmed to
simulate the small rotation pulses (and thus, indirectly, the small
torque pulses) created when a PDM is used to drill inhomogeneous
rock formations. Such a simulation is just one example of PDM
drilling processes that may be simulated by varying the programming
parameters in the VFDM software to provide different load pulsing.
The scope of this disclosure is not limited to any particular
rotation variations over time that may be generated by VFDM
405.
Although VFDM 405 has been described above with reference to test
bed embodiment 700 on FIG. 7A, it will be understood that VFDM 405
may also be deployed in conjunction with other test bed
embodiments, including those illustrated on FIGS. 3, 5, 5A, 5B, 5C
and 7B, for example.
Alternatively, torque pulses may be simulated on test bed
embodiment 700 on FIG. 7A (and indeed on test bed embodiments 300
and 702 on FIGS. 3 and 7B) by pulsing the braking torque applied by
continuous-slip brake 335. In embodiments where continuous-slip
brake 335 is driven pneumatically, the air supply to brake 335 may
be pulsed. Pulses on brake 335 may be any size, shape or frequency
pattern, including sinusoidal or stepped (square wave) patterns,
for example. The scope of this disclosure is not limited to any
particular pattern of braking torque that may be delivered by brake
335, or the manner in which it is delivered.
Test bed embodiment 700 on FIG. 7A also provides alternative
embodiments of clutch 340. In some embodiments, clutch 340 is a
conventional clutch acting simply to apply torque to rotor section
315 smoothly and gradually, and/or to limit rotation speed or
torque delivered. In another embodiment, clutch 340 may be an
impact hammer-pin clutch. In this embodiment, torsional impact
testing may be simulated within test chamber 325. Energy is
preferably stored up in a flywheel or heavy drive shaft (not
illustrated) on the motor side of clutch 340. When engaged, clutch
340 allows drive pins within impact hammer-pin clutch to transfer
torque to rotor section 315. The drive pins are received into
corresponding sockets within impact hammer-pin clutch as torque is
transferred through clutch 340. An impact is created each time a
drive pin is received into a socket. Typically, a suitable impact
hammer-pin clutch embodiment of clutch 340 will deliver one (1) to
six (6) impacts per rotation, although the scope of this disclosure
is not limited in this regard. Impact hammer-pin embodiments of
clutch 340 are conventional, and are widely commercially available
as also used in in impact wrenches, for example.
Although embodiments of clutch 340 have been described above with
reference to test bed embodiment 700 on FIG. 7A, it will be
understood that such embodiments of clutch 340 may also be deployed
in conjunction with other test bed embodiments, including those
illustrated on FIGS. 3, 5, 5A, 5B, 5C and 7B, for example.
Referring now to commonly-invented and commonly-assigned U.S.
Provisional Patent Application Ser. No. 62/311,278 (the
"Provisional Application"), to which this disclosure claims
priority and whose provisional disclosure is incorporated herein by
reference, FIG. 7 of the Provisional Application is an exemplary
finite element analysis (FEA) image of static displacement (strain)
based upon known torque stresses placed on a rotor to be used in
conjunction with the disclosed test apparatus. The image is color
coded to show increasing strain. FEA images of the type shown on
FIG. 7 of the Provisional Application are useful, for example, for
sizing the external motor driving the rotor and deriving
specifications for the interconnecting drive train.
There now follows description of an exemplary operation of the
disclosed test apparatus. It will be understood that the following
disclosure is for illustration only, and that the disclosed test
apparatus is not limited thereby.
The objectives of an exemplary test protocol may include to
evaluate new elastomer compounds in an environment that accurately
simulates expected downhole service in an operational PDM power
section. With this in mind, a test stator section is prepared with
the elastomer, molded into the actual stator profile to be expected
downhole. The test stator section is placed into the test chamber.
In accordance with the disclosed test apparatus, the stator section
is then (1) exposed the actual drilling fluids expected downhole;
(2) exposed to the actual elevated temperatures expected downhole;
(3) loaded with comparative (or higher) forces and cycle
frequencies expected downhole. The disclosed test apparatus may
then, for example, measure the number of cycles to failure under
defined loads and conditions. In some embodiments, the cycles to
failure may be determined by counting, through to failure, the
rotor section cycles and/or the stator section cycles. In other
embodiments, the rotor section and/or stator section may be
examined for wear. In other embodiments, temperature change over
time inside the test chamber may be monitored. In other
embodiments, temperature change over time may be monitored in an
elastomer layer provided by the stator section at its contact
surface with the rotor section. The test data yielded by the
disclosed test apparatus will be expected to correlate closely to
comparative test data that might have been extracted from a
hypothetical power section in downhole service, and may be used to
develop elastomer compounds with improved performance
characteristics according to the service. Alternatively, without
limitation, the disclosed test apparatus may be used to test the
performance of actual test coupons and surrounding drilling fluids
taken from PDMs in service in wells with their own chemistry.
Embodiments of the disclosed test apparatus may be expected to
achieve the following exemplary target performance parameters
(again, the following list is not exhaustive, and the scope of the
disclosed test apparatus is not limited in any of the following
regards):
Test chamber temperatures up to 350-400 degrees F.;
Ability to use stator sections or rotor sections cut from actual
downhole tools; and
Ability to load stator elastomers up to approximately 40%
strain.
It will be appreciated that the scope of the disclosed test
apparatus is not limited to the construction of stator sections
that may be put in the test coupon, and includes, without
limitation, all-elastomer construction, hybrid metal/elastomer
constructions ("evenwall") or other types of construction.
Likewise, the disclosed test apparatus is not limited to the size,
type or construction of rotor that may be put in the test
coupon.
Alternative embodiments of the disclosed test apparatus could
further include, without limitation, the following features and
aspects:
(a) Substituting the disclosed offset shaft mounting of rotor and
stator and convert the rotor to an eccentric transmission by which
to receive rotational torque.
(b) Adapting the disclosed test apparatus to evaluate miniaturized
1.0 to 2.0 stage motors, advantageously with small diameters.
(c) Varying the number and locations of rotor/stator bearings for
support of the rotor/stator.
(d) Varying the number and locations of the test chamber fluid
seals.
(e) Deploying one or more accelerometers on or near the test
chamber to monitor/map vibration (and changes in vibration
patterns) within the test chamber over time during operation.
Although the inventive material in this disclosure has been
described in detail along with some of its technical advantages, it
will be understood that various changes, substitutions and
alternations may be made to the detailed embodiments without
departing from the broader spirit and scope of such inventive
material as set forth in the following claims.
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