U.S. patent application number 13/759182 was filed with the patent office on 2013-06-13 for apparatus for testing swellable materials.
This patent application is currently assigned to SWELLTEC LIMITED. The applicant listed for this patent is Swelltec Limited. Invention is credited to Brian Nutley, Kim Nutley.
Application Number | 20130151154 13/759182 |
Document ID | / |
Family ID | 40133948 |
Filed Date | 2013-06-13 |
United States Patent
Application |
20130151154 |
Kind Code |
A1 |
Nutley; Kim ; et
al. |
June 13, 2013 |
Apparatus for Testing Swellable Materials
Abstract
The invention provides an apparatus for use in testing the swell
characteristics of swellable components used in downhole
exploration or production equipment, such as swellable packers. A
method of measuring a test piece using a testing apparatus with a
fluid chamber and a transducer is described. Measured data can be
compared with data measured from a sample section of a tool to
determine a relationship between swell characteristics. The
determined relationships can then be used to calculate or predict
swelling characteristics of swellable components, for example
particular packer designs, in specific fluid samples.
Inventors: |
Nutley; Kim; (Inverurie,
GB) ; Nutley; Brian; (Bridge of Don, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Swelltec Limited; |
Dyce |
|
GB |
|
|
Assignee: |
SWELLTEC LIMITED
Dyce
GB
|
Family ID: |
40133948 |
Appl. No.: |
13/759182 |
Filed: |
February 5, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12607452 |
Oct 28, 2009 |
8396667 |
|
|
13759182 |
|
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|
Current U.S.
Class: |
702/6 ; 156/242;
156/60; 428/172; 428/64.1 |
Current CPC
Class: |
E21B 47/00 20130101;
G06F 19/00 20130101; Y10T 156/10 20150115; B32B 3/30 20130101; G01N
15/08 20130101; G16Z 99/00 20190201; G01N 19/00 20130101; Y10T
428/21 20150115; E21B 33/1208 20130101; Y10T 428/24612
20150115 |
Class at
Publication: |
702/6 ; 156/60;
156/242; 428/172; 428/64.1 |
International
Class: |
E21B 47/00 20060101
E21B047/00; B32B 3/30 20060101 B32B003/30; G06F 19/00 20060101
G06F019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 28, 2008 |
GB |
0819749.3 |
Claims
1. A portable apparatus for testing a swell characteristic of a
test piece comprising a swellable material used in a swellable
component of downhole hydrocarbon exploration or production
equipment, the portable apparatus comprising: a fluid chamber
configured to receive a triggering fluid and the test piece
comprising a swellable material such that the test piece is exposed
to the triggering fluid; a transducer for measuring a swell
characteristic of the test piece due to exposure of the test piece
to the triggering fluid; and an output line for outputting
measurement data from the transducer.
2. The portable apparatus of claim 1, wherein the transducer is
operable to measure a dimension of the test piece.
3. The portable apparatus of claim 1, wherein the transducer is a
non-contact transducer which tracks movement of the test piece or a
target coupled to the test piece.
4. The portable apparatus of claim 3, wherein the target is
configured to move in correspondence with an increase in volume of
the swellable material of the test piece.
5. The portable apparatus of claim 3, wherein the transducer is an
eddy current transducer and is disposed to measure an eddy current
in the test piece or a target coupled to the test piece.
6. The portable apparatus of claim 1, wherein the transducer is a
contact transducer.
7. The portable apparatus of claim 6, wherein the transducer is
configured to measure a pressure or force exerted by swelling of
the test piece.
8. The portable apparatus of claim 1, further comprising a
mechanism for adjusting a position of the transducer.
9. The portable apparatus of claim 1, wherein the apparatus is
further configured to measure a time series of the swell
characteristic of the test piece.
10. The portable apparatus of claim 1, further comprising a
temperature control system.
11. The portable apparatus of claim 10, wherein the temperature
control system comprises a heating element operable to heat fluid
in the fluid chamber.
12. The portable apparatus of claim 1, configured for circulation
of fluid in the fluid chamber via an inlet and outlet of the fluid
chamber.
13. The portable apparatus of claim 1, further comprising a data
logging unit.
14. The portable apparatus of claim 1, further comprising a power
supply unit.
15. The portable apparatus of claim 1, further comprising an
interface for a portable computer.
16. The portable apparatus of claim 1, wherein the apparatus is
configured to measure a test piece swell characteristic which has a
known relationship with a swellable component swell
characteristic.
17. The portable apparatus of claim 1, wherein the fluid chamber is
configured to receive a substantially planar test piece.
18. The portable apparatus of claim 17, wherein the substantially
planar test piece comprises a substrate, and wherein the substrate
comprises a disc of metallic material, having a recess formed in
one face of the disc.
19. The portable apparatus of claim 18, wherein the disc has a
thickness in a range of 1 mm to 5 mm.
20. A test piece for use in a method of testing a swelling
characteristic of a swellable component for downhole exploration or
production equipment, the test piece comprising a planar substrate
having a recess; and a swellable material selected to increase in
volume on exposure at least one triggering fluid moulded into the
recess.
21. The test piece of claim 20, wherein the substrate comprises
metal.
22. The test piece of claim 20, wherein the substrate comprises a
disc, and the recess is formed in one face of the disc.
23. The test piece of claim 22, wherein the disc has a thickness in
the range of 1 mm to 5 mm.
24. The test piece of claim 20, wherein the swellable material is
bonded to the substrate on the base of the recess.
25. The test piece of claim 20, wherein the swellable material is
bonded to the substrate on the side walls of the recess.
26. The test piece of claim 20, wherein the recess has a depth in
the range of 0.5 mm to 4 mm.
27. The test piece of claim 20, wherein the recess has a depth of
approximately 2 mm.
28. A method of forming a test piece for a swellable component for
downhole exploration or production equipment, the method
comprising: providing a substantially planar substrate of a
non-swellable material; and bonding a layer of swellable material
selected to increase in volume on exposure at least one triggering
fluid onto the substrate.
29. The method of claim 28, wherein the swellable material has a
thickness in the range of 0.5 mm to 4 mm.
30. The method of claim 28, wherein the swellable material has a
thickness of approximately 2 mm.
31. The method of claim 28, wherein the substrate comprises a
recess, further comprising: moulding the layer of swellable
material into the recess.
32. The method of claim 31, wherein bonding a layer of swellable
material comprises bonding the swellable material to the substrate
on the base of the recess.
33. The method of claim 31, wherein bonding a layer of swellable
material comprises bonding the swellable material to the substrate
on the side walls of the recess.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/607,452, entitled "Method and Apparatus for
Testing Swellable Materials," filed Oct. 28, 2009, which claims
priority to United Kingdom Patent Application No. GB0819749.3,
filed on Oct. 28, 2008, both of which are hereby incorporated by
reference in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to a method and apparatus for
testing of swellable materials and in particular to a method and
apparatus for testing of swell characteristics of materials and
components used in downhole equipment for the oil and gas
exploration and production industries.
BACKGROUND ART
[0003] Swellable materials have been used in a range of oil and gas
exploration and production equipment. Most notably, swellable
materials have been used in wellbore packers for creating a seal in
an annular space between a tubing and a surrounding wall of a cased
hole or openhole well. A typical swellable packer includes a mantle
of swellable elastomeric material formed around a tubular body. The
swellable elastomer is selected to increase in volume on exposure
to at least one triggering fluid, which may be hydrocarbon fluid or
an aqueous fluid or brine. The packer is run to a downhole location
in its unexpanded, unswollen state where it is exposed to a
wellbore fluid and caused to swell. The design, dimensions, and
swelling characteristics are selected such that the swellable
mantle creates a fluid seal in the annulus, thereby isolating one
wellbore section from another. Swellable packers have several
advantages over conventional packers, including passive actuation,
simplicity of construction, and robustness in long term isolation
applications. Examples of swellable packers and suitable materials
are described in GB 2411918.
[0004] The swell characteristics of the packer are critical to
proper performance of the packer. Important swell characteristics
include the swell rate, the time taken for the outer surface of the
mantle to reach and contact the exterior surface (which may be
referred to generally as "contact time") and the time taken to
reach the point of maximum internal pressure exerted by the packer
on the surrounding surface (which may be referred to generally as
"pack-off time"). The swell characteristics are dependent on
various factors including the materials used, the dimensions and
design of the tool, the wellbore conditions (including temperature
and pressure), and the fluid or fluids to which the tool is
exposed.
[0005] It is known in the art to carry out tests on swellable
packers by placing a representative sample of the packer in a
fluid. A typical sample packer section is shown in FIG. 1,
generally depicted at 10. A swellable mantle 12 is formed on a pipe
or mandrel 14 according to conventional manufacturing techniques
and has a known outer diameter and thus a known mantle thickness.
The packer section 10 is formed by cutting a short length, for
example 8 to 15 cm, through the mantle 12 and the pipe 14. The
sample packer section 10 is placed in a fluid bath (not shown),
which contains a hydrocarbon or aqueous fluid or brine used for the
test. The fluid bath is located inside an oven, which can be heated
to typical wellbore temperatures. For example, the oven may be
operable to heat the fluid and packer section 10 to temperature of
around 80.degree. C. to 150.degree. C. The packer section 10 is
left in the fluid bath for the duration of the test (which may be
several days). At regular intervals during the test, the oven is
opened, the packer section is removed, and the outer diameter is
measured manually using a calliper gauge. The measurement data for
such packer sections 10 are generally considered by the industry to
be representative of the swell times of a complete tool of the same
radial dimensions and configuration in a wellbore environment.
[0006] FIG. 2 is a plot of thickness change, expressed as a
percentage of the original thickness, versus exposure time of a
sample packer section 10 with an initial outer diameter of 5.75
inches (approximately 146 mm) on a base pipe having outer diameter
of 4.5 inches (around 114 mm). The packer section 10 of this
example had a swellable mantle 12 formed from ethylene propylene
diene M-class rubber (EPDM) rubber and was exposed to Clairsol.RTM.
(a hydrocarbon fluid) at 90.degree. C. The data show that the time
taken for the sample section to swell to its maximum volume (with a
percentage thickness increase of around 80%) is around 600 hours or
25 days.
[0007] A packer will be deployed in and sealing with a wellbore of
known inner diameter. For example, the packer 10 for the test data
of FIG. 2 is designed for sealing with a bore of inner diameter in
the range of 6 to 6.8 inches (about 152.4 mm to 172.7 mm). The
measurements of particular interest are the time taken for a
swellable mantle to increase in outer diameter to contact a
surrounding surface of a wellbore of a particular inner diameter
(the "contact time") and the time taken for the swellable mantle to
exert its maximum internal pressure against a sealing surface of a
particular inner diameter (the "pack-off time"). In the example of
FIG. 2, the packer has a contact time of 60 hours with a 6.125 inch
(about 155.6 mm) wellbore.
[0008] Performing such tests on packer sections requires an oven
and a suitable fluid chamber, which typically lacks portability and
takes up valuable space at an exploration or production
installation. Carrying out the tests is labour intensive, and may
be hazardous due to the nature of the fluids used and the elevated
temperatures. Physical handling of the sample sections may be
difficult or unsafe when the packer sections have been exposed to
fluid, particularly at high temperatures. Measurement of the outer
diameter is prone to error, particularly because the swellable
material is soft and may be deformed by the callipers. Multiple
personnel may be required to measure the outer diameter at
different measurement times, and each individual may take a
measurement by a slightly different technique, introducing further
uncertainty into the measurement data. The long swelling times of
the sample packer sections are inconvenient for rapid measurement
of swell characteristics. The long test times also increase the
likelihood of multiple personnel being used to measure the outer
diameter, and therefore increase the likelihood of inconsistent
measurements. Long test times limit the repeatability of the tests,
and reduce the practicability of tests being carried out for
multiple fluid samples. These factors combine to reduce the quality
of the available measurement data.
[0009] With packer sample section 10 of the prior art, the ends of
the swellable member 12 are exposed to the test fluid, which
increases the surface area-to-volume ratio at each end of the
section 10, relative to the surface area-to-volume ratio at its
axial midpoint. This means that the swelling rate of the swellable
member at the end of the sample section 10 is likely to be greater
than the swelling rate at its axial midpoint, causing non-uniform
swelling which can have an adverse effect on the accuracy of the
measurements of the outer diameter.
[0010] The industry tends to make assumptions about the swell
characteristics of swellable materials in different fluids. For
example, a simplified model of volume increase of swellable
elastomers assumes that the swell rate of a swellable material
depends primarily on the viscosity of the fluid to which it has
exposed. Accordingly, a sample packer section 10 may be tested in a
fluid of low viscosity (for example 1 cP), with measurements of
percentage change in thickness over time being made. Measurements
may also be made for an identical sample packer section in a higher
viscosity of fluid (for example 100 cP or 100 mPa). In order to
predict the swell characteristics of a packer section in a given
wellbore fluid sample with a different viscosity, the measurement
data will be interpolated or extrapolated rather than repeating the
tests in the wellbore fluid sample.
[0011] Additionally, in some simplified models, the pack-off time
for a particular inner diameter is assumed to be constant
multiplier of the contact time. This simplified model is flawed,
because it does not account for different swelling end points of a
swellable material in different fluid samples. For example, a
packer sample section exposed to one hydrocarbon fluid with 1 cP
viscosity might have a maximum swelling extent of, for example 75%
of the original mantle thickness, whereas the swelling end point of
an identical tool sample in a different hydrocarbon fluid, also
having a viscosity of 1 cP, may have a swelling end point of 80% of
the original thickness of the mantle. FIG. 3 is a plot of swelling
profile of two identical sample sections in different
hydrocarbon-based fluids with the same viscosity (1.5 cP). The plot
shows that the swell characteristics of the sample in Fluid 1
(which was the special kerosine Clairsol 350 MHF.TM.) are different
from the swell characteristics of the sample in Fluid 2 (which was
a gas oil) despite the test fluids having the same fluid viscosity.
Different swelling end points have an effect on the contact time
and pack-off time, which is not accounted for in a model which
relies on viscosity effects only. This illustrates that it would be
advantageous to account for fluid types when assessing swell
characteristics.
[0012] It is amongst the aims and the objects of the invention to
provide methods, testing apparatus, and test pieces which overcome
or mitigate the drawbacks of conventional testing procedures and
apparatus.
[0013] Further aims and objects of the invention will become
apparent from the following description.
SUMMARY OF INVENTION
[0014] According to a first aspect of the invention, there is
provided a method of testing a swellable component for downhole
hydrocarbon exploration or production equipment, the method
comprising the steps of: providing a test piece comprising a
swellable material in a fluid chamber of a testing apparatus;
exposing the test piece to a triggering fluid; measuring, using a
transducer of the testing apparatus, a swell characteristic of the
test piece to provide a test piece measurement data set.
[0015] The test piece may be a small, portable test piece which is
easy to handle and which can be tested in a small, portable test
apparatus. The swell characteristics measured may for example be
thickness of the test piece (or another dimension) or a pressure
exerted by the test piece during swelling.
[0016] The method may comprise the additional step of outputting
the measurement data set to a data processing means. The data
processing means may be a personal computer, or alternatively maybe
a dedicated data processing module.
[0017] The method may comprise generating a report of the swell
characteristic. Preferably, the measurement data set comprises a
time series of a swell characteristic, and the method comprises
generating a report of the measurement data set as a changing swell
characteristic or parameter over time.
[0018] The fluid may comprise a hydrocarbon fluid. Alternatively,
or in addition, the fluid may comprise an aqueous fluid or brine.
The fluid may be a sample of a fluid to which downhole equipment
will be exposed in a wellbore. Thus, when testing a swellable
material for use in downhole equipment for a particular wellbore
installation, a sample of wellbore fluid used in that installation
may be used in the method to measure a swell characteristic of the
sample in that fluid. The fluid may be a drilling mud, a completion
fluid, or a production fluid. Other fluids are within the scope of
the invention.
[0019] The method may comprise the step of exposing the sample to a
second fluid or to a second fluid mixture. Thus the sample may be
exposed to a first fluid for a period of time, with swell
characteristics measured during that period. The sample may be
exposed to a second fluid, different from the first, for a second
period of time in order to measure the swell characteristic of the
sample when exposed to the second fluid.
[0020] The method may comprise the additional step of circulating
fluid in the chamber. Thus, according to one embodiment, the sample
may be exposed to a first fluid for a period of time, following
which the first fluid may be circulated out of a chamber and
replaced by a second fluid. After a further period, the first fluid
may be circulated in the chamber to replace the second fluid.
Alternatively, a third fluid may replace the second fluid.
According to this embodiment, the method may simulate the exposure
of the sample to different fluids, as might occur during deployment
of downhole equipment, or during the operational lifetime of the
downhole equipment. For example, the method may be used to monitor
the effect of circulating a completion fluid such as a brine, past
the equipment, before being exposed to hydrocarbon fluid such as a
drilling fluid or produced hydrocarbons. The method allows a swell
characteristic to be measured throughout exposure to different
fluid types.
[0021] The method may comprise the step of heating and/or cooling
the chamber of the apparatus. The method may therefore simulate
wellbore conditions, and in particular may expose the sample to an
environment similar to that found in a downhole wellbore
installation. In particular the method may comprise the step of
increasing the temperature of the test piece. Thus the method may
simulate an increasing temperature experienced by downhole
equipment during run-in. The method may comprise the step of
introducing a sharp temperature change to the chamber. This may
simulate the injection of a fluid passed the swellable apparatus,
the fluid being at a different temperature from the ambient
conditions in the wellbore. Such conditions may for example occur
during a wellbore clean-up operation.
[0022] Changing the temperature profile of the chamber may comprise
the step of circulating a fluid in the chamber at a different
temperature. The method may include the step of heating or cooling
the sample or fluid by a joule heater or Peltier device.
[0023] The method may comprise the additional step of determining a
relationship between a swell characteristic of the test piece and a
swell characteristic of a downhole tool. The relationship may in
particular be a time domain scaling between the respective time
series. The method also may comprise calculating swelling data for
a swellable component of hydrocarbon exploration or production
equipment from the test piece measurement data, using a determined
relationship between a test piece swell characteristic and a
swellable component swell characteristic.
[0024] The method may comprise providing swellable component
configuration data, and storing the swellable component
configuration data in a database with the determined relationship.
The swellable component configuration data is data about the
component, and may for example include at least one of: dimensions
of the swellable component; shape of the swellable component;
materials used in the swellable component; and construction
techniques used to form the swellable component. Therefore a
determined relationship can be assigned to or identified with a
particular swellable component.
[0025] The method may comprise deriving a ratio of a dimension of
the swellable component to a dimension of the test piece from the
swellable component configuration data. For example a ratio of the
thickness of a swellable component to the thickness of the
swellable material in the test piece may be derived from the
swellable component configuration data.
[0026] The method may comprise the steps of: a. providing an
additional measurement data set comprising measurement data
corresponding to an additional swellable component swell
characteristic; b. comparing the first and additional measurement
data sets to determine an additional relationship between a test
piece swell characteristic and the additional swellable component
swell characteristic.
[0027] Therefore for a single test of a test piece, relationships
can be determined with swellable components of different
configurations and stored in a database.
[0028] The method as claimed may comprise repeating steps a. and b.
for at least one further swellable component, and storing the
plurality of determined relationships in a database with the
swellable component configuration data.
[0029] For example, in the context of swellable packers,
relationships with swelling profiles of packers of different sizes
can be calculated. This can be repeated, with the relationships
stored in the database.
[0030] The method may also comprise deriving a further relationship
between the swellable component configuration data and the
plurality of determined relationships. For example, a further
relationship between the ratio of the thickness of a swellable
component to the thickness of the swellable material in the test
piece, and the time domain scaling multiplier can be determined.
This allows prediction of swell characteristics of a tool
configuration, even where a specific tool configuration has not
been tested.
[0031] According to a second aspect of the invention there is
provide an apparatus for testing a swell characteristic of a
material used in a swellable component of downhole hydrocarbon
exploration or production equipment, the apparatus comprising: a
fluid chamber configured to receive a fluid and a test piece
comprising a swellable material; and a transducer for measuring a
swell characteristic of the test piece.
[0032] The apparatus may comprise an output line for outputting
measurement data from the transducer, which may be operable to
measure a dimension of the test piece, such as a thickness. The
transducer may be a non-contact transducer which tracks movement of
a target coupled to the test piece. In one embodiment, the
transducer is an eddy current transducer and is disposed to measure
an eddy current in the target. The target may be configured to move
in correspondence with an increase in volume of the swellable
material of the test piece. Alternatively, the transducer may be a
contact transducer.
[0033] A movable plate may be provided which may be provided, and
may be configured for movement in a single direction (which is
preferably vertical). The movable plate moves in correspondence to
an increase in volume of the swellable material of the test piece.
Wherein the transducer is a contact transducer, the movable member
is disposed to contact the head of the transducer. The movable
member may impart a force or pressure on to the transducer
[0034] The apparatus may include a temperature control system,
which may have a heating element operable to heat fluid in the
fluid chamber and may comprise a temperature feedback loop. The
apparatus may comprise an inlet and/or an outlet for the chamber,
and may be configured for the circulation of fluid in the fluid
chamber via the inlet and outlet.
[0035] The apparatus may be part of a system of portable
components, which may comprise one or more of a data logging unit,
a power supply unit, and/or an interface for a portable
computer.
[0036] According to a third aspect of the invention there is
provided method of analysing data obtained from a test of a
swellable component of downhole hydrocarbon exploration or
production equipment, the method comprising the steps of: providing
a first measurement data set comprising measurement data
corresponding to a test piece swell characteristic; providing a
second measurement data set comprising measurement data
corresponding to a swellable component swell characteristic;
comparing the first and second measurement data sets to determine a
relationship between a test piece swell characteristic and a
swellable component swell characteristic.
[0037] The first measurement data set may comprise data
corresponding to a thickness of the test piece, and the second
measurement data set may comprise data corresponding to a dimension
of the swellable component. The second measurement data set may for
example be data corresponding to an outer diameter of the swellable
component (which may be a swellable wellbore packer).
[0038] The second measurement data set may be measured from a
swellable component sample, such as a packer section sample or a
model of a tool, or may be from a full scale tool test.
[0039] Preferably the data sets are time series, which may be
compared to derive a time domain scaling multiplier for the time
values of one of the time series. Thus the relationship between the
respective swell characteristics may be a time scaling factor. Thus
where the swellable component is a packer, the test piece may
comprise a thin piece of swellable material which swells faster
than a full size packer. The time domain multiplier may be applied
to the time values for the test piece to provide a swell profile
which matches that of the packer.
[0040] In one embodiment, a plurality of determined relationships
is obtained for different swellable components or tool designs, and
the determined relationships may have correlation with parameters
or features of the swellable components. For example, a
relationship may be determined between the time-domain scaling
multiplier and the ratio of thickness of the swellable material of
the test piece and the thickness of a mantle of a swellable packer.
This allows prediction or calculation of a relationship for a tool
design from the measured data, which in turn can be used to predict
the swelling characteristics of a tool, even when the tool design
itself has not been tested. A database may be built up from the
determined relationships.
[0041] According to a fourth aspect of the invention, there is
provided a method of calculating swelling data for a swellable
component of downhole hydrocarbon exploration or production
equipment, the method comprising the steps of: providing a test
piece measurement data set, obtained by disposing a test piece
comprising a swellable material in a fluid chamber of a testing
apparatus, exposing the test piece to a fluid, and measuring a test
piece swell characteristic; calculating swelling data for the
swellable component from the test piece measurement data set, using
a relationship between a test piece swell characteristic and a
swellable component swell characteristic.
[0042] The method may comprise obtaining the test piece measurement
data set by performing a test on the test piece, or the steps of
obtaining the data may be performed separately (at another
location) with the data later used in the method of this aspect of
the invention.
[0043] A wellbore operation may be simulated, for example by
altering one or more of the fluid composition, the fluid volume,
the fluid temperature, or the test piece temperature during the
test. The fluid may be selected to correspond to a fluid to which
the swellable component will be exposed during a downhole
operation, and may be an actual sample of wellbore fluid to which
the swellable component will be exposed during a wellbore
operation.
[0044] The suitability of the swellable component for a downhole
operation may be assessed, based on the calculated swelling data.
The method may be repeated to calculate swelling data for a
plurality of different swellable components using relationships
between a test piece swell characteristic and the respective
swellable component characteristics.
[0045] Where the swellable component is a part of a wellbore
packer, one or more of the following parameters may be calculated
to assess the performance and/or suitability of the packer for a
particular operation: a time at which the packer will contact a
borehole wall of known dimensions; a time at which the packer will
exert its maximum pressure against a borehole wall; or a pressure
differential rating for the packer in a borehole of known
dimensions.
[0046] According to a fifth aspect of the invention, there is
provided a method of forming a test piece for a swellable component
for downhole exploration or production equipment, the method
comprising: providing a substantially planar substrate of a
non-swellable material; bonding a layer of swellable material
selected to increase in volume on exposure at least one triggering
fluid onto the substrate.
[0047] Preferably, the test piece is substantially planar. The
substrate may be metal, and most preferably is steel. The substrate
may be a disc of metallic material, having a recess formed in one
face of the disc. The swellable material may be moulded into the
recess of the disc.
[0048] The swellable material may be bonded to the substrate on the
base of the recess, and may also be bonded on the side walls of the
recess.
[0049] The disc may have a thickness in the range of 1 mm to 5 mm.
The recess may have a depth in the range of 0.5 mm to 4 mm. The
recess preferably has a depth of approximately 2 mm. The swellable
material may have a thickness corresponding to the depth of the
recess. The thickness is selected to provide portability, along
with a rapid swelling rate, balanced with reasonably long overall
swelling time to allow sufficient data to be gathered.
[0050] According to a sixth aspect of the invention, there is
provided a test piece for use in a method of testing a swelling
characteristic of a swellable component for downhole exploration or
production equipment, the test piece comprising a planar substrate
having a recess, and a swellable material selected to increase in
volume on exposure at least one triggering fluid moulded into the
recess.
[0051] According to a seventh aspect of the invention, there is
provided a packer section for testing a swelling characteristic of
a swellable wellbore packer in a controlled environment, the packer
section comprising: a substantially cylindrical body portion having
an outer surface; at least one annular recess defined on the body;
and a swellable material disposed in the annular recess, the
swellable material selected to increase in volume on exposure to at
least one triggering fluid; wherein the outer diameter of the outer
surface corresponds to the outer diameter of an end ring on the
wellbore packer, and the outer diameter defined by a base of the
recess corresponds to the outer diameter of a base pipe of the
wellbore packer, such that the swellable material defines a
swellable body which corresponds to the radial dimensions of a
swellable mantle of the wellbore packer.
[0052] Preferably, the swellable material is bonded to the body
portion at the surface defining the base of the annular recess. The
swellable material may alternatively or in addition be bonded to
the body portion at the radially extending side walls which define
the annular recess.
[0053] The annular recess may be formed in the body portion by a
machining process. Alternatively, or in addition, the annular
recess may be at least partially defined by a ring upstanding from
a cylindrical base member or mandrel of the body portion. The ring
may be slipped on to the cylindrical base member, or alternatively
may be threaded on to the cylindrical base member.
[0054] The swellable material may substantially fill the annular
recess such that the outer surface of the swellable body is flush
with the outer cylindrical surface of the body portion.
[0055] The packer model may comprise a plurality of annular
recesses. The annular recesses may be formed to different
depths.
[0056] The swellable material may be selected to increase in volume
on exposure to a hydrocarbon triggering fluid, an aqueous
triggering fluid, or may be a hybrid swellable material which
increases in volume on exposure to either of a hydrocarbon or
aqueous triggering fluid. The swellable material may comprise an
ethylene propylene diene monomer rubber (EPDM).
[0057] Embodiments of the different aspects of the invention may
comprise optional or preferred features of any of the other
preferred aspect of the invention.
BRIEF DESCRIPTION OF DRAWINGS
[0058] FIG. 1 is a perspective view of a sample section of a
swellable packer.
[0059] FIG. 2 is a plot of swelling profile of a sample section of
a swellable mantle.
[0060] FIG. 3 is a plot of swelling profile of two identical sample
sections in different hydrocarbon fluids with the same
viscosity.
[0061] FIGS. 4A and 4B are respectively perspective and sectional
views of a test piece in accordance with an embodiment of the
invention.
[0062] FIG. 5 is a sectional view of a mould used to form the test
piece of FIG. 4 in accordance with an embodiment of the
invention.
[0063] FIG. 6 is a sectional view of a testing apparatus in
accordance with an embodiment of the invention.
[0064] FIG. 7 is a sectional view of a testing apparatus in
accordance with an alternative embodiment of the invention.
[0065] FIG. 8 is a plot of thickness change versus time for a test
piece of an embodiment of the invention.
[0066] FIG. 9 is a sectional view of a part of a testing apparatus
in accordance with a further alternative embodiment of the
invention.
[0067] FIG. 10 is a plot of pressure versus time measured using the
apparatus of FIG. 9.
[0068] FIG. 11 is a block diagram showing schematically the steps
of a method of collecting test data in accordance with an
embodiment of the invention.
[0069] FIG. 12 is a block diagram showing schematically the steps
of a method of predicting a swell characteristic of a tool in
accordance with an embodiment of the invention.
[0070] FIG. 13 is a plot of predicted swell profiles of tools with
different configurations.
[0071] FIG. 14 is a plot of tool measurement data and rescaled test
piece measurement data.
[0072] FIG. 15 is a plot of scaling multipliers determined by the
method of FIG. 11 against ratio of tool component thickness to test
piece thickness.
[0073] FIG. 16 is a plot comparing a predicted swell profile of a
tool with a measured swell profile.
[0074] FIGS. 17A and 17B are respectively perspective and sectional
views of a packer sample section in accordance with an embodiment
of the invention.
[0075] FIG. 18 shows components of a portable system in accordance
with an embodiment of the invention.
[0076] FIG. 19 is a sectional view of the testing apparatus in
accordance with an alternative embodiment of the invention.
DESCRIPTION OF EMBODIMENTS
[0077] Referring to FIGS. 4A and 4B, there is shown a test piece,
generally depicted at 30, in the form of a planar coupon. The test
piece 30 facilitates improved methods of testing swell
characteristics, and may be used with apparatus according to
embodiments of the invention. The test piece 30 comprises a
substrate 32 which acts as a carrier and support for a swellable
material 34. The substrate 32 is in the form of a planar disc,
having a thickness of approximately 0.12 inches (3.05 mm). The disc
is formed from a suitable metal, such as carbon steel. A circular
recess 36 is formed in a face 38 of the disc to a depth of
approximately 0.085 inches (2.16 mm). The recess 36 is filled with
a swellable material 34, which may be any material used in
swellable components of oilfield equipment which are designed to
increase in volume on exposure to a triggering fluid. In this
example, the swellable material is ethylene propylene diene M-class
(EPDM) rubber, typically used for forming the swellable mantle in a
downhole packer. EPDM rubber increases in volume on exposure to a
hydrocarbon fluid, such as produced oil. Other materials which are
known to swell in hydrocarbon or aqueous fluids or brines are known
in the art and are within the scope of the invention.
[0078] The substrate 32 is machined, and the test piece 30 is
completed in a moulding process. FIG. 5 shows schematically a
section through a mould, generally depicted at 40, used to form the
test piece 30. The substrate 32 is placed inside a chamber 42 in
the mould 40. A bonding agent is applied to the lower surface and
side walls of the recess 36, and the uncured swellable material is
injected into the recess 36. The mould 40 is assembled and pressure
will be applied to the upper surface of the swellable material 34
in order to ensure bonding to the substrate and to form the test
piece 30 into the desired shape. Depending on the properties of the
swellable material used, heat may be applied to cure the swellable
material. The resulting test piece 30 may be finished, for example
by machining, to provide an upper surface 37 of the swellable
material which is flush with the face 38 of the substrate 32. The
test piece is bonded to the substrate on its lower surface and its
sides, with one unbonded surface 37. This is comparable to the
swellable member of a wellbore packer which will typically bonded
to a base pipe on its lower surface and to gauge rings or end rings
at the radially extending surfaces at its opposing ends.
[0079] The test piece 30 is convenient for conducting tests of
swell characteristics in an efficient and repeatable manner. The
test piece 30 has several advantages over the packer sections 10 of
the prior art (and as shown in FIG. 1). Notably, the test piece 30
is simple to manufacture. It is compact and uses a small quantity
of swellable material. This facilitates the production and storage
of large numbers of test pieces 30, optionally with different
swellable materials 34. The test piece is portable and facilitates
use in compact swell testing apparatus. The substrate provides
support to the swellable material and allows consistent production
of samples. It is envisaged that for each batch of swellable
material delivered to a manufacturer of oilfield equipment, a
number of test pieces could be created for testing the swellable
characteristics before deployment of manufactured equipment, or
stored for use in post-deployment testing.
[0080] FIG. 6 shows a testing apparatus in accordance with an
embodiment of the invention. The apparatus, generally shown at 50,
is configured for testing a swell characteristic of a swellable
material used in oilfield equipment. The apparatus has particular
application to testing of the test pieces 30 described with
reference to FIGS. 4A and 4B, but it will be apparent to one
skilled in the art that the testing apparatus 50 may also be used
with different test pieces.
[0081] The apparatus 50 comprises a substantially cylindrical body
with longitudinal axis A, and is shown in FIG. 5 in longitudinal
section. The body comprises a base section 52 and a cap section 56,
which together define an internal chamber 54. The base section 52
and the cap section 56 are formed from a suitable metal such as
stainless steel. The cap section 56 fits onto an annular wall 58
which up stands from the base section 52 to define the internal
chamber 54. The apparatus 50 is substantially symmetrical about a
longitudinal axis A, with fasteners 64 circumferentially
distributed around the apparatus to fix the cap section 56 to the
base section 52 and close the chamber 54. The fasteners 64 are
securing pins which extend through co-aligned bores in the cap
section and the annular bore 58, with threaded portions cooperating
with thumb screws 66. Other securing means can be used in
alternative embodiments of the invention. A central portion 60 of
the cap section 56 extends into the inner diameter defined by the
annular wall 58. An o-ring 62 is provided between the upper surface
of the annular wall 58 and the lower surface of the cap section 56
to create a fluid seal with the interior of the chamber.
[0082] The apparatus 50 comprises a transducer 70 extending through
a central aperture in the cap section 56 from the outside of the
apparatus into the internal chamber 54. In this embodiment, the
transducer 70 is an eddy current transducer, such as Micro-Epsilon
Group's DT3010-A series of sensors. An o-ring 78 is provided
between the transducer body 74 and the cap section 56 to provide a
fluid seal with the chamber 54.
[0083] The apparatus 50 is configured to receive a test piece 30 as
described with reference to FIGS. 4A and 4B in a mounting assembly,
generally shown at 79. The test piece 30 is located on a surface of
the base section 52 beneath a target plate 80, formed in this case
from aluminium. The target plate 80 is mounted to the base section
52 via hexagonal pillars 82, which allow vertical movement of the
plate (in the direction of the axis A) but are keyed with the plate
to prevent relative rotation. The transducer 70 is located at a
distance of approximately 5-10 mm from the target plate 80,
although the position of the transducer may be adjusted, for
example by a micrometer adjuster (not shown), to take account of
desired operational parameters of the particular eddy current
transducer used.
[0084] The transducer 70 tracks vertical movement of the target
plate through proportional changes in the eddy current between the
transducer sensor head 72 and target plate 80 as the position of
the target plate 80 moves upwards in the direction of the axis A.
The transducer 70 outputs this as measurement data via line 76.
[0085] The apparatus comprises an inlet 84 and an outlet 86 to the
fluid chamber 54. The inlet allows delivery of fluid into the
chamber 54. The inlet 84 and the outlet 86 are provided with
connectors for connection with a suitable fluid delivery system
such as a fluid hose. A fluid inlet and outlet allows continual
circulation of fluid. This allows a fluid to be exchanged or
circulated out of the apparatus during the measurement process, as
will be described below. In an alternative embodiment, the fluid
outlet may be sealed during use, and the fluid inlet may be in
communication with the reservoir to ensure that there is an
adequate supply of fluid to the fluid chamber. In other
embodiments, the fluid chamber may be filled with fluid prior to
commencement of the test, with the fluid supply disconnected and
the fluid chamber plugged.
[0086] The apparatus 50 is also provided with a thermal regulation
system 90. In this embodiment, the thermal regulation system 90
comprises a joule heater 92 disposed in the base section 52 and
coupled to a temperature controller 94. The heater 92 allows the
apparatus 52 to be operated at elevated temperatures to simulate
the conditions in a downhole environment. In other embodiments, the
system 90 may include alternative heating and/or cooling elements
such as Peltier devices. Optionally, a temperature sensor such as a
thermocouple may be provided in the chamber 54 for measurement of
the internal temperature of the apparatus. The measured temperature
may be fed back to a temperature controller. Insulating cladding
may also be provided on the exterior of the apparatus to improve
heat retention.
[0087] In use, the chamber 54 is filled with a fluid and the test
piece 30 is exposed to the fluid. Any increase in volume of the
swellable material in the test sample 30 due to exposure to the
fluid causes the target plate 80 to be displaced vertically. This
displacement is measured by the transducer 70, with the measurement
signal output from the apparatus via line 76. The apparatus
therefore allows regular, automated measurement of the swelling of
the swellable material in the test sample. The swell characteristic
is measured in situ, while the test sample is exposed to the fluid,
and avoids the need for interruption of the test. The apparatus is
capable of measuring an increase in thickness of the test sample
automatically with no manual intervention by a user. This increases
the consistency of the measurement. The transducer is also capable
of measuring the increase in thickness with a high degree of
precision, reducing errors caused by calliper measurement. The
transducer and measurement system may be configured for continuous
measurement of the transducer, or measurement at regular sample
intervals. This increases the quality of the measurement data.
[0088] FIG. 7 is a sectional view through a mounting assembly 100
of an apparatus in accordance with a preferred embodiment of the
invention. The apparatus in which the mounting assembly 100 is
located is similar to, and will be understood from the arrangement
50 shown in FIG. 6. The transducer 70, fluid chamber 54 and lid
section (not shown) are substantially identical to the embodiment
of FIG. 6. However, the mounting assembly 100 increases the fluid
exposure of the test piece 30.
[0089] Shown in FIG. 7 is a part of the base section 152, which is
similar to the base section 52 of apparatus 50. The base section
152 differs in that it is provided with a recess 156 in its upper
surface 154. The recess 156 is sized to receive a porous layer 158,
which is formed from a metallic mesh material. An annular ledge 159
is provided around the perimeter of the recess 156 and supports the
porous layer 158 above the bottom of the recess. The porous layer
158 provides a support for the test piece 30. The mesh of the
porous layer provides a network of pores which allow fluid flow
through the layer 158 and around the recess 156.
[0090] As with the embodiment of FIG. 6, the target plate 180 is
mounted on hexagonal pillars 82 which permit vertical movement of
the support plates, but prevent relative rotation.
[0091] The target plate 180 is provided with a similar recess 162
on its lower surface 160. The recess 162 is sized to receive a
porous layer 164, which is supported from the base of the recess
162 by an annular ledge 166. The arrangement allows fluid
communication from the fluid chamber 54 to the recess 162, via the
porous layer 164. The upper surface of the swellable layer 34 is
therefore exposed to fluid in the support layer 64 and recess 162,
and the recesses and porous layers provide a complete fluid
circulation path around the test piece, improving fluid access to
the swellable material 34.
[0092] In an embodiment of the invention, the apparatus of FIGS. 6
and 7 is used as follows. The test piece 30 is located in the fluid
chamber 54, and the fluid is delivered to the chamber via the inlet
84. The test piece 30 and the swellable material 34 in fluid
communication with the fluid in the chamber, and depending on the
nature of the swellable material and the type of fluid, this
exposure may trigger a change in volume of the swellable material
34. An increase in volume will be manifested as a change in
thickness and thus the upper surface of the swellable material 34
will impart a force on to the target plate, which in turn will be
measured by the eddy current transducer 70. Changes in thickness
are therefore detected by the transducer, and the measurement
signal can be output as a time series via line 76. The time series
data is recorded in a data storage means in communication with the
apparatus, which forms part of a personal computer. Alternatively,
or in addition, the data may be directly output to a display to a
user. The apparatus and method therefore enables a series of
measurements of the thickness of the swellable material over time
to be collected.
[0093] A typical measurement data set is plotted in FIG. 8, with
the change in thickness is plotted as a percentage of the initial
thickness (i.e. .DELTA.T/T, where T is the initial thickness and
.DELTA.T is the cumulative change in thickness). The plot shows an
initial increase of the thickness of the material during hours 0 to
5 at a relatively fast rate, with a gradual reduction of the rate
of change during hours 5 to 15 and a levelling off from
approximately hour 16.
[0094] The testing apparatus described above is configured for the
measurement of thickness data by using a contactless eddy current
transducer 70 to measure the vertical displacement of a target
plate. In an alternative embodiment, the testing apparatus is
configured for measurement of a pressure exerted by a support plate
on a transducer. FIG. 9 is a cross-sectional view of a part of an
apparatus 150 in accordance with such an alternative embodiment of
the invention. The testing apparatus 150 is similar to the testing
apparatus 50, with like-parts indicated by like-reference numerals.
However, the apparatus differs in the nature of the transducer,
which in apparatus 150 is a pressure transducer 170 which is
located at a fixed distance h above the target plate 180 when the
test piece 30 is in an unswelled condition. An example of a
suitable transducer is Impress Sensors & Systems Limited's DMP
343 low pressure transducer. The distance h is selected to
correspond to a separation distance between the outer surface of a
swellable component of a tool before swelling and the surface with
which it seals (i.e. the swelling distance before contact). In the
case of a swellable packer, this is the radial depth of the annular
space between a swellable tool and a surrounding wall.
[0095] As an example, a swellable packer having an initial mantle
thickness of 0.6275 inches (about 15.9 mm), may be configured to
run on a base pipe or mandrel with outer diameter of 4.5 inches
(about 114.3 mm), in a wellbore having inner diameter of 6.125
inches (about 155.6 mm). The annular space between the mandrel and
wellbore therefore has a radial distance of 0.8125 inches (about
20.6 mm), and the required change in thickness of the swellable
mantle for wellbore contact is 0.1875 inches (about 4.8 mm) or
around 30% of the original thickness of the swellable mantle. For
the test configuration of FIG. 9, the separation distance of the
support plate and the pressure transducer is calculated in
proportion. If the initial thickness of the swellable material 34
is 0.080 inches (about 2.0 mm), the distance h is 0.024 inches
(about 0.6 mm) for an equivalent thickness change of 30%. The
distance h is configurable in the testing apparatus.
[0096] In use, the test piece 30 is exposed to a fluid delivered to
the chamber. The fluid triggers an increase in volume of the
swellable material 34 and a vertical displacement of the target
plate. When the support plate has displaced by distance h, it is
brought into contact with the transducer and exerts pressure on the
transducer. The pressure is measured and output via line 76. The
data may be output as a time series of measured pressure data.
Continued swelling of the swellable material will tend to increase
the pressure on the transducer, until further swelling of the
material is prevented by a back pressure from the transducer. The
point at which the test sample exerts a maximum pressure on the
transducer (which corresponds to the pack-off time) can be
determined from the measurement data.
[0097] FIG. 10 is a typical plot of pressure data versus time using
the testing apparatus of FIG. 9. Between a time of t=0 and t=t1,
the pressure measured by the pressure transducer is zero, because
the support plate has not been brought into contact with the
transducer 170. At time t1, the plate 180 has moved to the distance
h, and the plate contacts the transducer. As the swellable material
of the test piece continues to swell, the pressure transducer
measures an increase in pressure between times t1 and t2. The rate
of increase of pressure reduces, until at t2, a maximum pressure,
Pmax has been reached: t2 therefore represents the pack-off time
described above. In practice, it may be preferred to calculate a
"guaranteed pack-off time" which is greater than t2. A guaranteed
pack-off time may be calculated by multiplying t2 by a factor (for
example 1.5) or adding a minimum additional time to t2.
[0098] Measurement data sets collected by the swell tests described
above may be used to predict a swelling characteristic of a
swellable component of downhole equipment. For example, the test
piece data may be compared with measurement data from the swelling
of a packer or packer section to derive a relationship between the
swelling rates of the test piece and the packer. The relationship
can then be used to predict the swell characteristics, such as the
contact time and the maximum pressure) of the packer. Data from a
new test on a test piece, for example using a fluid sample
recovered from a wellbore, can be input into the derived
relationship in order to calculate the predicted swell
characteristics of the packer.
[0099] FIG. 11 is a block diagram which schematically shows a
method 200 for collecting test data for use in analysis of swelling
characteristics. In step 210 a test piece measurement data set is
collected from a test piece exposed to a reference fluid, using the
method and apparatus described above. In step 220, a tool
measurement data set is collected by exposing a tool, or a sample
section of a tool, to the same reference fluid used in step 210. It
should be noted that in step 220, the tool measurement data set
need not be measurement of data of the complete tool itself, but
may be a measurement of the swell characteristics of a sample
section generally considered to correspond to the swell
characteristics of the tool, for example the sample packer section
described with reference to FIG. 1. In this embodiment the tool is
a swellable packer, and the tool measurement data set is collected
by measuring a packer section as described with reference to FIG.
1.
[0100] The respective measurement data sets are stored in a
database 230 as time series of measurement data. As described
above, the measurement data may be thickness data or pressure data,
or a combination of the two. In step 240, the measurement data sets
are compared, using any of a number of conventional statistical
techniques. The comparison may be performed using software on a
personal computer or in a dedicated processing module. In step 250
a relationship between the swell profile of the test piece in the
reference fluid and the swell profile of the tool in the reference
fluid is determined from the comparison of data. The determined
relationship is stored in a database, for later use in predicting
the swelling characteristics of a tool.
[0101] One example of a relationship between a test piece data set
and tool data sets is by a numerical time domain scaling multiplier
S. Such a multiplier may be applied to a time value of the test
piece swell data, such that the swell profiles match one another.
Such an operation is equivalent to rescaling the time axis for a
plot of the percentage thickness change against the time value
data. Time domain scaling multipliers may be calculated by any of a
number of statistical or numerical processing techniques. One
simple method involves optimising the scaling multiplier to
minimise a difference between the scaled and unscaled time series.
Any of a number of different optimisation techniques may be used.
One simple method includes the steps of: setting a starting value
to a time domain scaling multiplier; applying it to time values of
the test piece data for each data point; replotting the thickness
change data for the test piece against the rescaled time axis;
calculating a difference between the respective swell profiles of
the rescaled test piece data and the tool data; and perturbing the
time domain scaling multiplier. The new time domain scaling
multiplier is applied to the time values of the test-piece data for
each data point, and the thickness change data for the test piece
is replotted against scaled time axis. A difference between the
respective swell profiles of the rescaled test piece data and the
tool data is calculated, and compared with the previously
calculated difference. The process can be repeated until the
difference between the respective plots is minimised.
[0102] FIG. 12 is a block diagram which schematically shows a
method 300 that uses a determined relationship from the method 200
to predict the swell characteristics of a swellable component or
swellable tool. In step 310, a fluid sample is selected and
provided in the test apparatus 50. This may be an actual fluid
sample from the wellbore environment in which a tool is planned to
be deployed. Alternatively, it may be a fluid representative of the
fluid in the wellbore environment, for example a synthesised fluid
to approximate the fluid conditions expected in the wellbore. It
may also be a combination of fluids, and may be a number of
separate volumes of different fluids to which the test piece will
be exposed during different parts of the test, as will be described
in more detail below.
[0103] The test piece is subject to the test in step 320 as
described with reference to FIGS. 6, 7 and/or 9 above, and the test
piece measurement data is output as a time series and recorded in a
data storage apparatus 330. Optionally, a display representative of
the swell characteristic from the measurement data set may be
generated and displayed to a user. For example, the test piece
swell profile can be displayed to a user in real time via a graphic
display (not shown).
[0104] The test piece data set is then used in step 340 to
calculate the predicted swell profile of one or more tools. This is
carried out by applying to the measured test piece data the
relationship between a test piece swell profile and a tool swell
profile determined using the method of 200. This may be for example
the time domain scaling multiplier S, as described above. Synthetic
tool datasets 350, 360 are generated for each tool design for which
a relationship (or multiplier S) has been determined. Each
synthetic tool dataset represents the predicted swelling behaviour
of the respective tool in the sample fluid. Swelling profiles can
be output as a time series of swell data to a data storage
apparatus 330, and/or can be displayed (step 370) to a user via
graphical display. The information can be used to generate (at step
380) a report on the swelling behaviour of the specific tool
designs in the sample fluid. For example, the report may include a
predicted contact time for a swellable packer and/or a predicted
pack-off time. In certain embodiments of the invention, the report
also provides an expected pack-off pressure, which may be used in
conjunction with information on the surface area of the packer and
the expected co-efficient of friction with the surrounding wall, to
derive information representative of the pressure capability of the
packer.
[0105] Optionally, the method may include the additional steps of
selecting or recommending a particular tool design, according to
desired swell parameters input into the system at step 390. For
example, an operator may input a maximum initial outer diameter of
a packer, and may specify a minimum contact time. Alternatively, a
user may specify a fixed base pipe size, and/or may require that
the tool must have a pack-off time not greater than a particular
value. The system is capable of providing a synthetic swell profile
data for a number of specific tool designs in a sample fluid, and
then assisting a user with the selection of the tool design for the
specific application.
[0106] FIG. 13 shows the predicted swell profiles of a number of
different tool designs calculated using the method 300. Plot A
shows schematically the predicted swell profiles for three wellbore
packers having the same initial outer diameter of the swellable
mantle, and different size base pipes. The Figure shows graphically
how the method can be used to select or eliminate particular tool
configurations (which in this case are base pipe diameters)
depending on constraints on swelling time and/or final OD of the
packer.
[0107] The method 200 can be repeated to obtain a number of
different time domain scaling multipliers S for different tool
configurations. It is then possible to determine a relationship
between the time domain scaling multipliers and various parameters
of the tool configuration. For example, a relationship can be
derived which describes the dependence of time domain scaling
multipliers on the ratio of test piece thickness to test packer
element thickness, by plotting calculated scaling multipliers
against the ratios of the packer swellable mantle thickness Tp to
the thickness of the test piece Tc. Using standard statistical
techniques, it is possible to determine a relationship, for example
a quadratic relationship in the form
S=aR.sup.2+bR-c (Equation 1),
[0108] where R is Tp/Tc, between the scaling multiplier S and the
tool parameters.
[0109] The invention therefore provides a method by which swell
profile information for a proposed new packer size can be obtained
on the basis of the derived relationships and the measurement data
from a test piece. For the proposed packer design, the appropriate
time domain scaling multiplier can be derived from of the ratio of
the test piece thickness and the thickness of the swellable member
in the packer. This is then applied to the swell test data measured
from a test piece to obtain a predicted swell profile of the packer
design.
[0110] The techniques described above can be applied to a
measurement of pressure exerted by the swellable member during an
increase in volume. Again, the time series pressure data are
collected for a test sample, and compared with the time series of
pressure data collected using the conventional testing of a packer
section to derive a relationship between the swelling profiles.
[0111] One specific example of the method 200 of the invention is
described here. In this example, a test piece 30 was tested using
the apparatus 50 in order to obtain a time series of test piece
data which corresponds to thickness changes of the swellable
material. The test piece 30 was exposed to a fluid sample selected
to approximate the fluid encountered in the wellbore into which it
is planned to run a packer. The temperature of the fluid was
maintained at a constant 80.degree. C.
[0112] A wellbore packer sample section, similar to section 10
shown in FIG. 1, was placed in a fluid bath containing the same
reference fluid, also maintained at a temperature of 80.degree. C.
The sample section was a packer section having a 4.5 inch (about
114.3 mm) base pipe with a swellable mantle which had an outer
diameter of 5.5 inches (about 146.1 mm). Measurements were taken
manually using a calliper gauge over a period of days to obtain a
tool measurement data set. The test piece data set and the tool
data set were compared, and it was determined that the data
provided a good match when the test piece data had applied to it a
time domain scaling multiplier S of 35. In other words, for each
data point, a multiplier of 35 was applied to the time value at
which the measurement was taken before plotting on the same scale
as the tool measurement data. FIG. 14 plots a percentage thickness
change against time for the tool (dashed line) and the percentage
thickness change of the test piece versus a scaled time, after the
time domain multiplier of 35 is applied. The plot shows a close
match between the respective plots. The method 200 has therefore
been used to determine a relationship between the swelling
characteristics of a test piece 30 and the swelling characteristics
of a sample section of a packer.
[0113] The method 200 was repeated for a number of sample sections
of packer elements having different dimensions. In a second
example, the test piece data was compared with a data set measured
from a sample section of a packer element having a base pipe of 5.5
inches (about 139.7 mm) and a swellable mantle with an initial
outer diameter of 8 inches (about 203.2 mm). A comparison of the
data sets revealed that a time domain multiplier of 120 led to a
correspondence of the swelling profiles.
[0114] Similar tests were carried out on a number of different
packer configurations, with the results as shown in Table 1.
TABLE-US-00001 TABLE 1 Actual Test Base Mantle Piece pipe Mantle
Thick- Thick- Packer OD OD ness T.sub.p ness T.sub.c
T.sub.p/T.sub.c Scaling configuration (inches) (inches) (inches)
(inches) Ratio Multiplier 7.00 .times. 8.00 7.00 8.00 0.50 0.08
6.24 20 7.00 .times. 8.15 7.00 8.15 0.58 0.08 7.24 30 4.50 .times.
5.75 4.50 5.75 0.64 0.08 7.98 35 4.50 .times. 5.85 4.50 5.85 0.68
0.08 8.50 39 6.625 .times. 8.15 6.625 8.15 0.77 0.08 9.61 52 5.50
.times. 8.00 5.50 8.00 1.26 0.08 15.73 120 5.50 .times. 8.15 5.50
8.15 1.33 0.08 16.60 135
[0115] The numbers in the first column indicate the packer
configuration in notation commonly used in the industry. The outer
diameter (OD) of the base pipe and the outer diameter of the
swellable mantle are given in inches in columns two and three
respectively. The fourth column specifies the actual thickness of
the test packer element in inches, as measured. This is the radial
thickness of the swellable mantle Tp, which represents
approximately half of the difference between the dimensions in
columns two and three, with the differences due to engineering
tolerances. In all cases, the test coupon thickness Tc was 0.08
inches (column five). The ratio of the radial thickness of the
swellable mantle Tp and the test coupon thickness Tc is given in
column six, and the derived scaling multiplier, which provides a
suitable concordance between the swell profile of the test piece
and the swell profile of a packer element, is given in column
seven.
[0116] From the calculation of the time domain scaling multipliers
for different ratios of test coupon to test packer element
thickness, it a relationship was determined between the time domain
scaling multipliers and the ratios. The calculated scaling
multipliers were plotted against the ratios of the packer swellable
mantle thickness Tp to the thickness of the test piece Tc, with the
results shown in FIG. 15. Using standard statistical techniques, a
relationship between the scaling multiplier and the thickness ratio
was determined to be:
S=0.2765R.sup.2+4.5989R-18.94 (Equation 2),
[0117] where S is the scaling multiplier and R is the ratio
Tp/Tc.
[0118] An appropriate scaling multiplier for the time domain S can
now be determined from this relationship for a new proposed packer
design, on the basis of the ratio of the test coupon thickness and
the thickness of the swellable member in the packer, even where no
previous swelling test has been performed on that packer
configuration. This is then applied to the swell test data measured
from a test piece to obtain a predicted swell profile of the packer
design.
[0119] FIG. 16 is a plot of measured data from a tool test and
synthetic data for the same tool design calculated using the method
300. In this example, sample packer section tested had a
pre-swollen element OD of 5.755 inches (about 146.2 mm) and a base
pipe OD of 4.5 inches (about 114.3 inches). The test piece has a
rubber thickness of 0.080 inches (about 2 mm). This means the Tp/Tc
ratio R is about 7.84, which when input into Equation 2 gives a
time domain multiplier S of about 34.14. This is the time domain
multiplier that is applied to the test piece measurement data to
accurately portray the packer swell profile. The plot shows a high
level of concordance with the predicted swell profile, shown by the
dashed line D, and the actual measured swell profile, shown by the
line E.
[0120] The present invention also allows the simulation of
different wellbore conditions. For example, during different
periods of a swell test, the temperature of the test piece and/or
fluid can be varied. The temperature of the test piece could begin
at an ambient surface temperature (for example 20.degree. C.) and
be gradually increased to simulate an increase in temperature
experienced by a swellable packer as it is run to a downhole
location and as it is exposed to wellbore fluids. The temperature
could be changed rapidly for periods of the test, which may for
example simulate the exposure of a packer to a different, cooler
fluid (such as an injected fluid stream). Optionally, a temperature
sensor such as a thermocouple is provided in the interior of the
fluid chamber, or in thermal contact with the test sample. The
signal from the temperature sensor may be fed back to the
temperature controller. The thermal regulation system 90 may
operate in a simple power control mode (similar to a thermostat) or
in a continuous variation mode.
[0121] The test apparatus also allows different fluids to be
circulated passed the test piece during the test. This offers
another mechanism for changing the temperature inside the testing
apparatus. For example, a fluid at a temperature of 90.degree. C.
may be replaced with a fluid at a temperature of 15.degree. C. for
a two hour period of the test. The measurement data will be
continually to be sampled during the change in temperature.
[0122] A fluid of a different nature can be circulated in the
testing apparatus. For example, the early stages of a test may
expose the test sample to an aqueous fluid or brine, with a later
stage of the test exposing the test sample to a drilling fluid or
wellbore clean-up fluid. Subsequent stages of the test may expose
the test sample to hydrocarbon fluids such as are typically be
encountered in the production system. Numerous variations are
possible within the scope of the invention. The invention allows
the simulation of wellbore conditions likely to be encountered by a
typical downhole apparatus. The conditions may be pre-programmed
into the apparatus to automatically simulate a fluid circulation
schedule for a particular well. Throughout the process, the
measurement data is continually taken. Thus the effect on swelling
characteristics can be predicted to obtain a swelling profile for
the wellbore conditions a tool will experience. A long period of
exposure to a hydrocarbon fluid could be interjected with exposure
to an aqueous fluid (which may be at a lower temperature) to
simulate the injection of a fluid into the wellbore from surface.
During such simulation programmes, due account must be given to the
time domain relationship between the swell profile of the test
piece and swelling profile of the packer, for example by dividing
the typical time for which the packer would be exposed to a
particular fluid in a wellbore operation by the time domain scaling
multiplier to obtain a time for which the test piece should be
exposed to that fluid during the test.
[0123] The above-described embodiments of the invention relate the
swelling characteristics of a test piece with swelling
characteristics of a sample packer section 10 which is
representative of the swelling of a swellable wellbore packer.
FIGS. 17A and 17B illustrate an alternative sample section which
may be used with certain embodiments of the invention. The sample
section, generally depicted at 400, comprises a cylindrical base
pipe 402 formed from a metal such as steel. Machined into the outer
surface of the base pipe are annular recesses 404, 406. Recess 404
is formed to a first depth, and recess 406 is formed to a second
depth, greater than the first depth. Located in the recesses is
swellable material selected to increase in volume on exposure to
the wellbore fluid, which in this case is EPDM rubber. The
swellable material creates swellable bodies 408 and 410 which fill
the recesses to provide an outer surface 412 which is flush with
the surface of the pipe 402. The swellable bodies are bonded to the
pipe 402 on their lower surfaces and on the radially extending side
walls of the recesses.
[0124] The sample section 400 has certain advantages over the
sample section 10 of the prior art. Firstly, the swellable bodies
have a swelling behaviour which more closely resembles the swelling
of a swellable member of a wellbore packer. By bonding the lower
and side surfaces of the swellable bodies onto the base pipe, the
swellable bodies resembles the form of a swellable packer, which is
typically bonded on its lower surface to a base pipe, and to gauge
rings or end rings which are upstanding from the base pipe to abut
the radially extending surfaces which define the ends of the
swellable member. In contrast, with the sample section 10, the ends
of the swellable member 12 are exposed to the wellbore fluid, which
increases the surface area to volume ratio at the opposing ends of
the sample section 10 and creates non-uniform swelling which is not
characteristic of a typical wellbore packer configuration. The
sample section 400 thus more closely resembles the structure of a
typical wellbore packer. Forming the swellable bodies in annular
recesses also provides advantages in the manufacturing process. The
swellable material which makes up the swellable bodies can be
applied, moulded, compressed and bonded into the recesses, and the
outer surface of the bodies can be easily machined to be flush with
the outer diameter of the pipe 402.
[0125] The recesses 404 and 406 are formed to different depths, to
form corresponding swellable bodies 408, 410 with different
thicknesses. This facilitates the simultaneously testing of
swellable bodies which correspond to packers of different
dimensions. Although two recesses are formed in the sample section
400, a single recess may be provided in an alternative embodiment,
and other embodiments may comprise three or more recesses.
Different recesses may be formed with different depths and/or
shapes, and the swellable bodies with different swellable materials
may be provided in different recesses on the same sample section.
It will also be appreciated that the sample section may be formed
on a solid mandrel, in place of the base pipe 402. The mandrel or
base pipe may be provided with formations to facilitate handling of
the sample section.
[0126] The invention also contemplates that a measurement data set
could be obtained from a full scale trial of downhole equipment.
For example, a full scale packer could be deployed in a test bore,
with regular outer diameter measurements taken in order to provide
reliable measurement data.
[0127] A preferred embodiment of the invention is configured as a
system of portable apparatus, as shown in FIG. 18. The system 500
comprises an apparatus 50, an auxiliary unit 510, and a portable
computer 520, and a case 530. The auxiliary unit 510 contains a
power supply for the apparatus 50, and an interface for data input
to and output from the apparatus 50 and the computer 520. The power
supply in this example is a mains adaptor, although in other
embodiments it may comprise a battery pack to increase portability.
A data logger and microcontroller are also included in the
auxiliary unit. The case 530 is configured to house the apparatus
50 and the auxiliary unit 510, and comprises receptacles 532, 534
for test pieces 30 and fluid sample containers 536. The portable
computer is capable of analysing and displaying data from the
auxiliary unit, and may also be used to configure the operation of
the system. However, the system may be left to run without being
connected to the portable computer 520.
[0128] The invention in this aspect allows the apparatus to be
taken to a site, such as an offshore location or laboratory, for
performance of the methods of the invention. The apparatus may be
used to test the swell profile of a test piece in a fluid sample
extracted from a wellbore at the drill site. It may be used to
demonstrate performance of a particular swellable tool
configuration at a client site.
[0129] FIG. 19 shows a testing apparatus in accordance with a
further alternative embodiment of the invention, which may be used
as an alternative or in addition to the testing apparatus of FIG.
6, 7 or 9. The apparatus, generally shown at 500, is configured for
testing the swell characteristic of a swellable material used in
oilfield equipment. The apparatus 500 is similar to and will be
understood from the apparatus 50 of FIG. 6, although differs in
various structural and functional features as will be described
below.
[0130] The apparatus 500 comprises a substantially cylindrical body
comprising a base section 502 and a cap section 506, which together
define the internal chamber 504. The base section 502 and the cap
section 506 are formed from a suitable metal such as aluminium or
an aluminium alloy. The body is shaped and sized to be accommodated
in a recess 508 in an aluminium block heater 510. The cap section
506 is fixed to the base section 502 to close the chamber 504. A
central aperture 512 in the cap section 506 accommodates an eddy
current transducer 514, which extends through the cap section into
the fluid chamber 504. The eddy current transducer is for example a
Micro-Epsilon group DT3010-A series sensor.
[0131] The apparatus 500 comprises a mounting arrangement 516 for a
test piece 530. The test piece 530 is similar to test piece 30 and
will be understood from FIGS. 4A and 4B and the corresponding
description. However, the test piece 530 differs in that the
substrate 532, which acts as a carrier and support for the
swellable material 534, is formed from aluminium. A recess 536
formed in the face of the disc is filled with a swellable material
534. In this embodiment, the swellable material 534 is not moulded
into the recess 536. Rather, the swellable material is a piece of
material punched, machined, or cut from a larger body of swellable
material. The swellable material 534 is bonded to the substrate 532
on its lower surface and its sides, leaving one exposed
surface.
[0132] In the previous embodiments, the mounting arrangement 516
included a plate which was moved by the swelling of the test piece,
with the position of the plate (or contact pressure in the case of
the embodiment of FIG. 9) measured by the transducer. However, in
this embodiment, the test piece 530 is mounted in an inverted
orientation, with the substrate 532 uppermost, and the swellable
material 534 lowermost. The test piece 530 is supported on a
support member 518, which in this case includes a plurality of
needle points 520. The needle points 520 provide a number of point
contacts for the test piece, while still allowing fluid circulation
and sufficient exposure of the test piece 532 to fluid in the
chamber 504.
[0133] In use, fluid present in the chamber contacts the swellable
material 534 and causes an increase in volume. This increase in
volume imparts an upward force on the test piece 532, moving the
substrate towards the transducer 514. The transducer measures the
displacement of the substrate 532 and the measurement data is
recorded.
[0134] Omitting a separate plate from the design simplifies the
apparatus, reducing its cost and weight and improving its
portability. The mounting arrangement 516 is preferable to using of
a mesh or porous support for the test piece in some circumstances.
For example, water-swellable elastomers such as those including
Super-Absorbent Polymers (SAPs) may exude a residue which has a
tendency to block pores in a porous or mesh-like support, reducing
fluid access and diminishing the quality of the data. The mounting
arrangement 516 offers the advantage that any substance which
exudes from the swellable material 534 will pass into the fluid in
the chamber 504.
[0135] In the foregoing description, the invention is described in
the context of testing swellable packers. However, it will be
appreciated by one skilled in the art that the principles of the
invention may be used wherever swellable components are employed in
downhole environments. For example, swellable components are used
in a variety of seals, anchors and centralisers. Use of swellable
components has also been proposed in downhole actuation mechanisms,
valves and flow stemming members. Using the principles of the
invention, a relationship may be determined between the swelling of
a test piece, and the swelling of a swellable component having a
particular configuration. This can then be used to predict the
swelling profile of the tool in specific fluids, and may be
extended to predict the swelling configuration of components having
different dimensions and/or configurations.
[0136] The principles and techniques of the invention may also be
used in applications to testing of oilfield components and
apparatus which are used downhole, and which are not specifically
designed to swell. For example, elastomeric materials which are
used downhole in a wide range of apparatus, such as o-ring seals
and components of downhole pumps, may be selected to avoid or limit
the swelling due to fluid exposure where an increase in volume is
detrimental to the performance of the apparatus. The invention in
its various aspects may therefore be applied to testing and/or
predicting the swelling characteristics of components and materials
to enable the design and/or specification of oilfield apparatus to
mitigate against undesired swelling.
[0137] In embodiments described above, the apparatus 50 comprises
an eddy current transducer. It may be advantageous to use eddy
current transducers with fluids at high temperatures or large
variations in temperature. Other transducer types may be used in
alternative embodiments. For example non-contacting transducers
such as optical, laser and capacitive transducers may be used. In
another example, a contacting linear transducer capable of
measuring displacement of a piston relative to a body is used. One
suitable linear transducer 70 is a contacting linear transducer
sold by Positek Limited with product reference number P103. The
transducer is in contact with a support plate which moves upwards
in the direction of the axis A on swelling of the swellable
material, and outputs the displacement measurements as measurement
data.
[0138] The methods described above make the assumption that the
relationships between the swelling characteristics of a test piece
and the swelling characteristics of a tool in a given fluid depends
on the relative geometry of the tool, and are not dependent on the
fluid. However, for a particular tool design, the test can be
repeated in a number of different fluids or the same fluid at
different activation temperatures. In each case, the test piece
measurement data and the tool measurement data are collected from
tests carried out in the same format (i.e. the same reference
fluids and test temperatures).
[0139] If any variations in the swelling profile of test pieces in
different fluids are apparent, they can be recorded in the
database, for example as separate time-series. When predicting the
swelling characteristics in a particular wellbore fluid, data from
tests performed with an appropriate fluid (i.e. one with similar
composition) can be used. For example, a time-domain scaling
multiplier may be selected from a test performed using the closest
match of fluid type recorded in the database.
[0140] Variations in the swelling profile of test pieces in the
same fluid at different temperatures may also be apparent,
particularly in the case of water-swelling elastomers and "hybrid"
elastomers which swell in aqueous and hydrocarbon fluids. An
increase in temperature may increase the maximum swell volume ratio
and may also increase the swell rate, reducing the contact time
and/or pack-off time. In such circumstances the method may include
performing multiple swell-tests at different temperature conditions
and deriving a relationship between the swelling characteristics of
a test piece and the swelling characteristics of a swellable
component which is temperature dependent. One simple method is to
calculate time-domain scaling multipliers in the manner described
above for multiple different temperature tests and to plot the
results against temperature to derive a relationship between the
temperature and the multiplier. For given wellbore conditions with
a known temperature, an appropriate time scale multiplier may be
selected for predicting the performance of a swelling component
based on test-piece measurement data.
[0141] In another simple example method, the maximum swelling
volume may be determined from multiple different temperature tests
with the results plotted against temperature to allow derivation of
a relationship between the temperature and the maximum swelling
volume. This allows determination of swell volume scaling
multipliers, which may be applied to the swell volume data to
normalise the data for different temperature conditions. For given
wellbore conditions with a known temperature, the normalised or
rescaled volume data can be used in conjunction with the
time-domain scaling multiplier in the manner described above to
predict the performance of a swelling component based on test-piece
measurement data.
[0142] The invention provides a method and apparatus for use in
testing the swell characteristics of swellable components used in
downhole exploration or production equipment, such as swellable
packers. A method of measuring a test piece using a testing
apparatus with a fluid chamber and a transducer is described.
Measured data can be compared with data measured from a sample
section of a tool to determine a relationship between swell
characteristics. The determined relationships can then be used to
calculate or predict swelling characteristics of swellable
components, for example particular packer designs, in specific
fluid samples.
[0143] Variations to the above-described embodiments of the
invention are within the scope of the invention, and the invention
extends to combinations of features other than those expressly
claimed herein.
* * * * *