U.S. patent application number 11/074124 was filed with the patent office on 2006-09-07 for downhole uses of piezoelectric motors.
This patent application is currently assigned to BAKER HUGHES, INCORPORATED. Invention is credited to Rocco DiFoggio, Jaedong Lee, T. Rajasingham.
Application Number | 20060198742 11/074124 |
Document ID | / |
Family ID | 36944280 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060198742 |
Kind Code |
A1 |
DiFoggio; Rocco ; et
al. |
September 7, 2006 |
Downhole uses of piezoelectric motors
Abstract
A sampling system used in collecting samples of connate fluid
from within hydrocarbon bearing formations. The sampling system
comprises a sonde disposed within a wellbore formed proximate to
the formation of interest. The sonde includes a sample probe
insertable into the formation and a drawdown pump in fluid
communication with the sample probe. The drawdown pump is motivated
by an associated electrically responsive material, where the
electrically responsive material can be comprised of a
piezoelectric material, a electroactive polymer, or some other
electrically responsive material.
Inventors: |
DiFoggio; Rocco; (Houston,
TX) ; Lee; Jaedong; (Houston, TX) ;
Rajasingham; T.; (Dundalk, IE) |
Correspondence
Address: |
GILBRETH ROEBUCK BYNUM DERRINGTON SCHMIDT WALKER &TRAN LLP
FROST BANK BUILDING
6750 WEST LOOP SOUTH, SUITE 920
BELLAIRE
TX
77401
US
|
Assignee: |
BAKER HUGHES, INCORPORATED
|
Family ID: |
36944280 |
Appl. No.: |
11/074124 |
Filed: |
March 7, 2005 |
Current U.S.
Class: |
417/410.1 ;
166/264; 417/411 |
Current CPC
Class: |
E21B 49/087
20130101 |
Class at
Publication: |
417/410.1 ;
417/411; 166/264 |
International
Class: |
E21B 49/08 20060101
E21B049/08 |
Claims
1. A formation fluid testing drawdown pump comprising: a piston; a
cylinder formed to receive said piston therein; and a motive device
operatively coupled to said piston, wherein said motive device is
comprised of material responsive to electrical stimuli.
2. The formation testing drawdown pump of claim 1, wherein said
material is comprised of a piezoelectric composition.
3. The formation testing drawdown pump of claim 2, further
comprising a piezoelectric motor.
4. The formation testing drawdown pump of claim 3, wherein said
piezoelectric motor is selected from the group comprising a linear
piezoelectric motor and a rotary piezoelectric motor.
5. The formation testing drawdown pump of claim 1, wherein said
material is comprised of an electroactive polymer.
6. The formation testing drawdown pump of claim 1, wherein said
operative coupling is comprised of a direct mechanical attachment
between said motive device and said piston.
7. The formation testing drawdown pump of claim 1 wherein said
operative coupling is comprised of a hydraulic circuit.
8. The formation testing drawdown pump of claim 3, wherein said
piezoelectric composition comprises at least two distinct
piezoelectric segments.
9. The formation testing drawdown pump of claim 1 further
comprising a feed back loop and a pump control, said feed back loop
comprising a pressure monitoring device in operative cooperation
with the pump control.
10. The formation testing drawdown pump of claim 9 wherein said
pressure monitoring device provides data representative of fluid
pressure within the cylinder and wherein the pump control is
programmable for controlling the operation of said drawdown pump in
response to the data representative of fluid pressure within the
cylinder to ensure the fluid pressure within the cylinder remains
above its bubble-point pressure.
11. A method of sampling connate fluid from within a subterranean
formation comprising: inserting a drawdown pump within a wellbore
adjacent the subterranean formation; providing a fluid
communicative path between said drawdown pump and the subterranean
formation; and operating said drawdown pump with a motive device,
wherein said motive device is operatively coupled to said drawdown
pump and comprises material responsive to electrical stimuli.
12. The method of claim 11 further comprising providing electrical
energy to said motive device.
13. The method of claim 11, wherein said material is comprised of a
piezoelectric composition.
14. The method of claim 13, wherein said piezoelectric composition
comprises a piezoelectric motor.
15. The method of claim 14, wherein said piezoelectric motor is
selected from the group comprising a linear piezoelectric motor and
a rotary piezoelectric motor.
16. The method of claim 11, wherein said material is comprised of
an electroactive polymer.
17. The method of claim 11, wherein said operative coupling is
comprised of a direct mechanical attachment between said motive
device and said piston.
18. The method of claim 11 wherein said operative coupling is
comprised of a hydraulic circuit.
19. The method of claim 13, wherein said piezoelectric composition
comprises at least two distinct piezoelectric segments.
20. The method of claim 13 further comprising monitoring the
pressure within the cylinder.
21. The method of claim 20 further comprising controlling operation
of the drawdown pump based on the monitored pressure within the
cylinder thereby ensuring the pressure within the cylinder remains
above the bubble-point pressure of the sampled fluid.
22. The method of claim 11, wherein the operating mode of said
drawdown pump is selected from the group consisting of operating at
a constant pressure and operating at a constant volumetric flow
rate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates generally to the field of hydrocarbon
production. More specifically, the present invention relates to an
apparatus for sampling connate fluid of a hydrocarbon bearing
formation.
[0003] 2. Description of Related Art
[0004] The sampling of connate fluid contained in subterranean
formations provides a method of testing formation zones of possible
interest with regard to hydrocarbon bearing potential. This method
involves recovering a sample of any formation fluids present for
later analysis in a laboratory environment while causing a minimum
of damage to the tested formations. The formation sample is
essentially a point test of the possible productivity of subsurface
earth formations. Additionally, a continuous record of the control
and sequence of events during the test is made at the surface. From
this record, valuable formation pressure and permeability data as
well as data determinative of fluid compressibility, density and
relative viscosity can be obtained for formation reservoir
analysis.
[0005] Generally connate fluid sampling involves disposing a sonde
10 into a wellbore 5 via a wireline 8. Oppositely located on the
outer portion of the sonde 10 usually are a sample port 14 and an
urging means 12. When the sample port 14 is proximate to a
formation of interest 6, the urging means 12 is extended against
the inner surface of the wellbore 5 thereby engaging the sample
port 14 into the formation 6. The engagement of the sample port 14
pierces the outer diameter of the wellbore 5 and enables fluid
communication between the connate fluid in the formation 6 and the
sample port 14. As will be described in more detail below, after
pushing the sample port 14 into the formation 6, the connate fluid
can be siphoned into the sonde 10 with a pumping means disposed
therein.
[0006] Early formation fluid sampling instruments, such as the one
described in U.S. Pat. No. 2,674,313, were not fully successful as
a commercial service because they were limited to a single test on
each trip into the borehole. Later instruments were suitable for
multiple testing; however, the success of these testers depended to
some extent on the characteristics of the particular formations to
be tested. For example, where earth formations were unconsolidated,
a different sampling apparatus was required than in the case of
consolidated formations.
[0007] Down-hole multi-tester instruments have been developed with
extendable sampling probes that engage the borehole wall and
withdraw fluid samples from a formation of interest as well as
measure pressure of the fluid within the formation. Traditionally
these downhole instruments comprise an internal draw-down piston
that is reciprocated hydraulically or electrically for drawing
connate fluid from the formation to the instrument.
[0008] Generally, the down-hole multi-test sampling devices
incorporate a fluid circuit for the sampling system which requires
the connate fluid extracted from the formation, together with any
foreign matter such as fine sand, rocks, mud-cake, etc. encountered
by the sampling probe, to be drawn into a relatively small volume
chamber and which is discharged into the borehole when the tool is
closed. An example of such a device can be found in U.S. Pat. No.
4,416,152. Before closing, a sample can be allowed to flow into a
sample tank through a separate but parallel circuit. Other methods
provide for the sample to be collected through the same fluid
circuit.
[0009] Another example of a circuit used in the sampling of connate
fluid is shown in FIG. 2. Here connate fluid is motivated from the
formation 6 via the sample port 14 and a sampling circuit 22 with a
pump 20. Reciprocating action of a piston 19 within the pump 20
causes pressure differentials that draw the connate fluid into the
pump 20. The actuation means for the pump 20 is, produced by a
pressure source 26 and delivered to the pump 20 by a hydraulic
circuit 24. Check valves 28 strategically located within the
hydraulic circuit 24 and the sampling circuit 22 direct the fluid
flow within these circuits. A more detailed description of this
circuit can be found in Michaels et al., U.S. Pat. No.
5,303,775.
[0010] Mud filtrate is forced into the formation during the
drilling process. This filtrate must be flushed out of the
formation before a true, uncontaminated sample of the connate fluid
can be collected. Often this filtrate becomes lodged within the
sample port 14 and hinders connate fluid flow to the sampling
device. Prior art sampling devices have a first sample tank to
collect filtrate and a second to collect connate fluid. The problem
with this procedure is that the volume of filtrate to be removed is
not known. For this reason it is desirable to pump formation fluid
that is contaminated with filtrate from the formation until
uncontaminated connate fluid can be identified and produced.
Conventional down-hole testing instruments do not have an unlimited
fluid pumping capability and therefore cannot ensure complete
flushing of the filtrate; contaminant prior to sampling.
[0011] Estimates of formation permeability are routinely made from
the pressure change produced with one or more draw-down piston.
These analyses require that the viscosity of the fluid flowing
during pumping be known. This can be achieved by injecting a fluid
of known viscosity from the tool into the formation and comparing
its viscosity with recovered formation fluid. The permeability
determined in this manner can then be reliably compared to the
formations in off-site wells to optimize recovery of fluid.
[0012] When exposed to an open hole, the fluid characteristics of
formation fluid can change rapidly, thus it is important that the
formation fluid be removed as quickly as possible. However, it is
important that the formation flow rate be regulated in order to
prevent dropping the fluid pressure below its "bubble-point" since
measuring separated fluids does not result in a representative
sample. After having these components come out of solution, they
typically cannot be recombined which results in an unrepresentative
sample having altered fluid properties.
[0013] Recently developed reservoir testing devices are capable of
measuring the bubble-point pressures of the connate fluid at the
time of sample collection. This can be accomplished using known
techniques of light transmissibility to detect bubbles in the
liquid. However this method has some drawbacks when particulate
matter is present in the fluid thereby resulting in sometimes
erroneous results. Other methods include trapping a known volume of
formation fluid and increasing its volume gradually at a constant
temperature. The measured changes in volume and pressure provide a
plot of pressure vs. volume in order to ascertain the value of the
bubble-point. This value is estimated within the region of the plot
where the pressure and volume graph is no longer linear.
[0014] Unfortunately the pumping devices currently in use with the
sampling devices have inherent drawbacks. For example, control of
the electrical or hydraulic actuation means of the presently used
pumping systems is not accurate that in turn results in an
inability to fully control the speed of the pumps. Not being able
to fully control pump speed prohibits the capability of ceasing
pumping operations should the pressure of the connate fluid fall
below its bubble point and also hinders the ability to accurately
measure the bubble point. Since sampling connate fluid at pressures
below its bubble point negatively affects the accuracy of the
sampling data results. Therefore a need exists for a means of
sampling connate fluid whereby the connate fluid can be obtained
and analyzed at known pressures without altering the state of the
sample.
BRIEF SUMMARY OF THE INVENTION
[0015] The device of the present disclosure includes a formation
fluid testing drawdown pump comprising a piston, a cylinder formed
to receive the piston therein, and a motive device operatively
coupled to the piston. The motive device is comprised of material
responsive to electrical stimuli. Alternatively the material
responsive to electrical stimuli can be a piezoelectric composition
or a electroactive polymer. Optionally the piezoelectric
composition may be a single piezoelectric segment or at least two
distinct piezoelectric segments. The motive device of the drawdown
pump can optionally be a piezoelectric motor, where the
piezoelectric motor is selected from the group comprising a linear
piezoelectric motor and a rotary piezoelectric motor. The operative
coupling of the drawdown pump may be comprised of a direct
mechanical attachment between said motive device and said piston as
well as a hydraulic circuit.
[0016] The formation testing drawdown pump may further comprise a
feed back loop and a pump control, where the feed back loop
comprises a pressure monitoring device in operative cooperation
with the pump control. The pressure monitoring device provides data
representative of fluid pressure within the cylinder and wherein
the pump control is programmable for controlling the operation of
said drawdown pump in response to the data representative of fluid
pressure within the cylinder to ensure the fluid pressure within
the cylinder remains above its bubble-point pressure.
[0017] A method of sampling connate fluid from within a
subterranean formation is disclosed herein comprising inserting a
drawdown pump within a wellbore adjacent the subterranean
formation, providing a fluid communicative path between the
drawdown pump and the subterranean formation, and operating the
drawdown pump with a motive device. The motive device of the
present method is operatively coupled to the drawdown pump and
comprises material responsive to electrical stimuli. The method
further comprises providing electrical energy to the motive device.
The material of the present method may be comprised of a
piezoelectric composition that is a single segment or at least two
distinct segments. The piezoelectric composition of the present
method may comprise a piezoelectric motor, where the piezoelectric
motor is selected from the group comprising a linear piezoelectric
motor and a rotary piezoelectric motor. Optionally, the material
responsive to electrical stimuli of the present method may be
comprised of an electroactive polymer.
[0018] The operative coupling of the present method may be
comprised of a direct mechanical attachment between the motive
device and the piston and may also include a hydraulic circuit. The
method may further comprise monitoring the pressure within the
cylinder. The present method may further comprise controlling
operation of the drawdown pump based on the monitored pressure
within the cylinder thereby ensuring the pressure within the
cylinder remains above the bubble-point pressure of the sampled
fluid. The drawdown pump may operate under constant pressure or
under constant volumetric flow.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING.
[0019] FIG. 1 depicts in a partial cutaway side view of a sampling
sonde disposed in a wellbore.
[0020] FIG. 2 illustrates a prior art drawdown pump.
[0021] FIGS. 3A-3D portray electrically responsive materials in a
perspective view.
[0022] FIG. 4 shows a cutaway view of one embodiment of a drawdown
pump in accordance with the disclosure herein.
[0023] FIG. 5 illustrates an embodiment of a drawdown pump in
accordance with the disclosure herein.
[0024] FIG. 6 depicts a partial cutaway view of an embodiment of a
drawdown pump in accordance with the disclosure herein.
DETAILED DESCRIPTION OF THE INVENTION
[0025] With reference now to the drawings herein, one embodiment of
a drawdown pump 56 in accordance with the present invention is
illustrated in a cutaway view in FIG. 4. In this embodiment the
drawdown pump 56 comprises a housing 57 that encompasses a cylinder
58 on one end and having a cavity 66 on its other end. The cylinder
58 should be substantially cylindrical and formed to receive a
piston 68 within. The piston 68, having a disklike configuration,
should likewise have an outer diameter that is substantially
circular and formed for reciprocating axial travel within the
cylinder 58. The cavity 66, while shown as substantially
cylindrical, can have other shapes and can also have a varying
cross sectional area along its length. As will be described in more
detail later, the cavity 66 should be formed to receive a section
of electrically responsive material.
[0026] A seal 69 can be provided on the outermost circumference of
the piston 68. The seal 69 should preferably be comprised of a
resilient pliable material, such as a polymer, that is capable of
providing a pressure seal across the outer diameter of the piston
68. This pressure seal should thereby isolate the pressure within
the cylinder 58 on the side of the piston face 71 from the cylinder
pressure along the piston rod 70.
[0027] The drawdown pump 56 of FIG. 4 further comprises a fluid
inlet line 60 that terminates on one of its ends at an inlet port
61 formed in the pump housing 57. Since the inlet port 61 traverses
the through the outside of the housing 57 and into the cylinder 58,
the fluid inlet line 60 is therefore in fluid communication with
the cylinder 58. The other end of the fluid inlet line 60 is in
fluid communication with a sample probe 14. An inlet check valve 62
is included with the fluid inlet line 60. Fluid can flow across the
inlet check valve 62 only in the direction towards the inlet port
61 but is prevented from flowing across the inlet check valve 62
from the inlet check valve 62 towards the sample probe 14.
[0028] This embodiment of the drawdown pump 56 further includes a
fluid exit line 64 connected on one of its ends at an outlet port
65 and in fluid communication on its other end with a fluid storage
tank (not shown). An outlet check valve 63 resides on the fluid
exit line 64 whose orientation allows fluid flow from the drawdown
pump 56 to fluid storage, but prevents flow from the fluid storage
tank to the drawdown pump 56. Like the inlet port 61, the outlet
port 65 is formed through the outer surface of the housing 57
thereby allowing fluid communication between the fluid exit line 64
and the cylinder 58.
[0029] With reference now to FIGS. 3A-3D, examples of electrically
responsive material (ERM) are shown in a perspective view.
Electrically responsive material converts electrical energy into
mechanical energy and can expand or contract when exposed to
electrical stimuli. The electrically responsive material can
include piezoelectric composites, electroactive polymers,
artificial muscles and the like.
[0030] When a voltage is applied to the piezoelectric material, the
material will experience a strain that causes it to expand. When
the voltage is removed, the strain is removed and the material
contracts. A non-limiting list of potential piezoelectric materials
for use with embodiments of the present invention includes
ceramics, quartz, poly-crystalline piezoelectric ceramics, and
quartz analogue crystals like berlinite (AlPO4) and gallium
orthophosphate (GaPO4), ceramics with perovskite or tungsten-bronze
structures (BaTiO3, KNbO3, LiNbO3, LiTaO3, BiFeO3, NaxWO3,
Ba2NaNb5O5, Pb2KNb5O15).
[0031] Suitable electroactive polymer materials include any
substantially insulating polymer or rubber (or combination thereof)
that deforms in response to an electrostatic force or whose
deformation results in a change in electric field. More
specifically, exemplary materials include silicone elastomers,
acrylic elastomers such as VHB 4910 acrylic elastomer,
polyurethanes, thermoplastic elastomers, copolymers comprising
PVDF, pressure-sensitive adhesives, fluoroelastomers, polymers
comprising silicone and acrylic moieties, and the like. Polymers
comprising silicone and acrylic moieties may include copolymers
comprising silicone and acrylic moieties, polymer blends comprising
a silicone elastomer and an acrylic elastomer, for example.
[0032] With regard to the electrically responsive material of the
embodiment of FIGS. 3A-3D and FIG. 4, the electrically responsive
material expands with the application of an electrical stimulus.
This expansion is illustrated with reference to a comparison of
FIGS. 3A and 3B. An example of an ERM 50 of length L.sub.1 is shown
in FIG. 3A in its relaxed or unresponsive state. Illustrating the
expansive nature of electrically responsive material, FIG. 3B
depicts an ERM 50a illustrating how the material responds to an
applied electrical stimuli. In FIG. 3B, the ERM 50 a has expanded
over that of the ERM 50 of FIG. 3A and its length has increased
from L.sub.1 to L.sub.1+.DELTA.L.sub.1; where
L.sub.1+.DELTA.L.sub.1 is greater than L.sub.1. The increase is a
function of the dimensions of the un-stimulated material as well as
the amount of current or voltage applied to the material. It is
believed that it is well within the capabilities of those skilled
in the art to determine appropriate dimensions and applied
electrical power in order to attain the desired means and ends of
the present invention.
[0033] Alternatively, with reference now to FIGS. 3C and 3D, the
electrically responsive material can be a segmented ERM 52
comprised of at least two segments 54 sequentially stacked in an
axial configuration. FIG. 3C depicts in perspective view a
segmented ERM 52 in a relaxed state, upon application of applied
electrical energy to the segmented ERM 52 it expands to an expanded
ERM 52a (FIG. 3D) from a length L.sub.2 to a length
L.sub.2+.DELTA.L.sub.2, where L.sub.2+.DELTA.L.sub.2 is greater
than L.sub.2. An advantage of greater control and flexibility of
ERM expansion can be realized by the segmented embodiment. Here a
single segment 54 can be expanded by selectively applying
electrical energy, or the collective segments 54 can be
sequentially expanded to affect a manner of the expansive stroke
applied by expansion of the segmented ERM 52. It should be pointed
out that while linear expansion is illustrated in FIGS. 3A-3D, the
ERMs (50, 52) can expand in a radial fashion as well.
[0034] In operation, connate fluid resident within the formation of
interest 6 enters the sample probe 14, travels through the fluid
inlet line 60 and into inlet port 61, thereby filling the cylinder
58. Generally when the cylinder 58 is being filled with connate
fluid the piston 68 is in the downstroke mode and moving towards
the cavity 66. This movement of the piston 68 can be produced by
the pressure differential across the piston 68 caused by the
presence of the fluid, or by a spring (not shown) disposed within
the cylinder 58 driving the piston backwards.
[0035] When a desired amount of fluid fills the cylinder 58, an
electrical stimulus is applied to the ERM 50 disposed within the
cavity 66. It should be pointed out that the segmented ERM 52 can
be used in lieu of the ERM 50, or these varying embodiments can be
used concurrently. As previously discussed, the electrical stimulus
causes the ERM 50 to expand; this expansion in turn pushes against
the piston rod 70 and urges it out of the cavity 66. As the piston
rod 70 is moved out of the cavity 66 (the upstroke mode) the piston
68 travels across the cylinder 58 thereby imparting a motivating
force onto the fluid within the cylinder 58. This motivating force
pressurizes the fluid thereby causing it to move from the cylinder
58 through the outlet port 65 onto the fluid storage tank via the
fluid exit line 64. As is well known, the strategic positioning and
orientation of the inlet and outlet check valves (62, 63) allows
fluid flow into the cylinder 58 from the formation 6 during the
downstroke mode and from the cylinder 58 to fluid storage during
the upstroke mode.
[0036] Optionally, as shown in dashed lines in FIG. 4, the connate
fluid inlet line 60a connects to the housing 57 at the inlet port
61a. Here the inlet port 61a pierces the connate pump 56 in an area
of the housing 57 proximate to the ERM cavity 66. In this
configuration urging the piston 68 into the cylinder 58 by
expansion of the ERM 50 reduces the pressure on the backside of the
piston 68 thus drawing fluid in from the formation 6. Furthermore,
like the inlet port 61a, the outlet port 65a of this alternative
embodiment is similarly positioned proximate to the ERM cavity 66.
Thus the fluid drawn into the cylinder 58 during expansion of the
ERM 50 is urged out of the cylinder 58 on the downstroke of the
piston 68.
[0037] The embodiment of the drawdown pump 56a shown in FIG. 5
comprises an elongated housing 57a having a substantially
cylindrical cylinder 58a formed to receive a piston 68a axially
therein. Like the piston 68 of the embodiment of FIG. 4, the piston
69a has a disk-like configuration suitable for axial travel within
the cylinder 58a. However the associated piston rods (74, 75) of
this embodiment extend respectively from both the first and the
second piston face (71a, 72a). The piston rods (74, 75) extend into
corresponding forward and rearward cavities (76, 73) disposed at
the opposite ends of the cylinder 58a. Further, in this embodiment,
fluid inlet lines 60a connect to the cylinder 58a via inlet ports
61a on both sides of the piston 68a. Similarly, fluid outlet lines
connect to the cylinder 58a via outlet ports 65a that are also
situated on both sides of the piston 68a. The inlet lines 60a are
in fluid communication on their other end with the sample probe
thereby enabling connate fluid to flow into the cylinder 58a
through these lines. As in the case of the embodiment of FIG. 5, in
this embodiment the other end of the fluid exit lines 64a connects
to a fluid sample tank. Inlet check valves 62a are included within
the inlet line 60a that limit fluid flow direction only to the
cylinder 58a. Outlet check valves 63a are also provided with the
exit lines 64a that allow fluid flow from the cylinder to the fluid
sample tank but prevents flow reverse directional flow. A quantity
of ERM 50 is included within each cavity (76, 73).
[0038] In the operation of the embodiment of FIG. 5 axial movement
of the piston 68a is effectuated by stimulating one of either ERM
51 within the forward cavity 76, or ERM 53 within the rearward
cavity 73. As noted above, stimulation of any electrically
responsive material can cause it to expand. In the case of the
drawdown pump 56a, expansion of either ERM 51 or ERM 53 urges the
piston 68a along the axis of the cylinder 58a. Movement of the
piston 68a in either direction increases the fluid pressure within
the cylinder 58a in the portion that the piston 68a is moving
towards, thus urging any fluid within that portion to the fluid
storage tank via the corresponding fluid exit line 64a. Moreover,
in the other portion of the cylinder 58a, the fluid pressure is
decreasing, thus drawing the connate fluid out of the formation 6,
into the sample port 14, and into that portion of the cylinder 58a.
When the piston 68a reaches the end of its stroke, the electrical
power stimulating the expanded ERM (51 or 53) is terminated and
electrical power is then applied to the other ERM (51 or 53) to
repeat the process of simultaneously urging fluid from one portion
of the cylinder 58a and drawing fluid into the other portion.
Accordingly, the electrical stimulus should not be applied to both
ERM 51 and ERM 53 simultaneously, but instead should be applied in
discrete sequences. Use of the present invention thereby enables
samples of connate fluid to be drawn, at pressure, from a formation
of interest 6 and stored within a storage tank for later analysis.
Sustaining the connate fluid at pressure maintains the sample above
its bubble point thereby preserving all the constituents within the
sample.
[0039] The embodiment of the drawdown pump 78 of FIG. 6 comprises a
piston 80, a cylinder 82, a piston rod 86, an ERM segment 88, an
anchor rod 92, a base 94, an expansion stroke pinch brake 100, a
compression stroke pinch brake 102, and an optional dashpot 98. The
base 94 further includes legs 95 that extend perpendicularly away
from the main body of the base 94. The legs 95 contain a first
aperture 97 and a second aperture 99 in which the pinch brakes
(100, 102) are respectively disposed. The cylinder 82 is elongated
and is formed within a generally cylindrical cylinder housing 84.
The inner diameter of the cylinder 82 is formed to axially receive
the piston 80 therein and allow for axial reciprocation of the
piston 80. The piston 80 has a disklike configuration with a
circular outer diameter that should match the dimensions and
configuration of the inner diameter of the cylinder 80. Preferably
the respective dimensions of the outer circumference of the piston
80 and the inner diameter of the cylinder 82 are sufficiently close
to create a pressure seal along the outer diameter of the piston
80. Seals (not shown) may be disposed on the outer diameter of the
piston 80 for providing the pressure seal.
[0040] The piston rod 86 is attached to the rearward side of piston
80 and extends outside of the cylinder housing 84 through an
opening 85 formed on the rear face of the housing 84. The piston
rod 86 is connected to the forward side of the ERM 88 on its other
end. An annular seal 96 can be included around the piston rod 86
within the cylinder 82 and adjacent the opening 85 for preventing
fluid flow through the opening 85.
[0041] Between the cylinder housing 84 and the ERM 88, the piston
rod 86 passes through the expansion stroke pinch brake 100. The
expansion stroke pinch brake 100 fits within a first aperture 97
formed through one of the legs 95. The inner diameter of the first
aperture 97 is greater than the outer diameter of the piston rod 86
thus providing a space for the pinch brake 100 to reside therein.
As shown, the pinch brake 100 is a single annularly shaped element
circumscribing a portion of the length of the piston rod 86; but
the pinch brake 100 can also be comprised of one or more elements
radially disposed within the space between the piston rod 86 and
the diameter of the first aperture 97.
[0042] Selective activation of the pinch brake 100 impinges the
brake 100 upon the piston rod 86 with sufficient force to
effectively bind the piston rod 86 to the leg 95 thereby preventing
movement of the piston rod 86 with respect to the leg 95. Examples
of suitable material for the brake include an inflatable packer,
extending members, and electrically responsive materials, such as
piezoelectric material and electroactive polymers.
[0043] The anchor rod 92 is connected to the rearward side of the
ERM 88 on one end and passes through the compression stroke pinch
brake 102 before terminating within the optional dashpot 98.
Optionally, the other end of the anchor rod 92 is inserted into the
dashpot 98 via an opening 93 formed through the wall of the dashpot
98. The dashpot 98 should contain a compressible fluid, such as for
example but not limited to silicone oil, brine, or formation fluid.
Seals 96 are provided adjacent the opening 93 for retaining the
fluid within the dashpot 98.
[0044] The ERM segment 88 is preferably comprised of an
electrically responsive material such as a piezoelectric composite,
an electroactive polymer, or any other substance responsive to
external electrical stimuli. The ERM segment 88 of the embodiment
of FIG. 6 is shown as a series of stacked elements 90, where each
element has substantially the same dimensions. However, the ERM
segment 88 can alternatively be comprised of a single non-segmented
portion of electrically responsive material. Further, the stacked
elements 90 can also be of varying dimensions. Additionally, the
specific material of the individual elements 90 can vary, for
example, one or more of the elements 90 might be comprised of a
piezoelectric material while the remaining elements 90 may be
comprised of an electroactive polymer.
[0045] In operation, the embodiment of the drawdown pump 78 of FIG.
6 operates in a similar fashion to the above described drawdown
pumps (56, 56a), that is the drawdown pump 78 is in fluid
communication with the sample probe 14 via a conduit 15. Connate
fluid is drawn into the cylinder 82 by the pressure differential
that exists between the cylinder 82 and the formation 6. The
differential pressure can be created by lowering the pressure
within the cylinder by urging the piston 80 axially rearward
through the cylinder housing 84. Movement of the piston 80 is
accomplished by selectively activating the ERM segment 88 in
combination with both the expansion stroke pinch brake 100 and the
compression stroke pinch brake 102. For example, stimulating the
ERM segment 88 while simultaneously releasing the compression
stroke pinch brake 102 allows the ERM segment 88 to expand in
response to the applied external electrical stimulus. Expansion of
the ERM segment 88 thereby slides the anchor rod 92 through the
compression stroke pinch brake 102 in a direction away from the ERM
segment 88. Upon completion of the expansion stroke of the ERM
segment 88 the compression stroke pinch brake 102 is activated
thereby clamping the anchor rod 92 therein. Then the external
stimulus is removed from the ERM segment 88 while the expansion
stroke pinch brake 100 is in the release mode. Removing the
electrical stimulus from the ERM segment 88 allows the ERM segment
88 to contract in size to its normal or relaxed state. Contraction
of the ERM 88 in combination with the release of the expansion
stroke pinch brake 100 pulls the piston rod 86 in the direction of
the ERM segment 88 thereby urging the piston 80 through the
cylinder 82 in a rearward direction.
[0046] The piston stroke length realized during each sequence of
release/activation steps is dependent upon the amount and type of
the electrically responsive material of the ERM segment 88 as well
as the amount and type of external stimulus applied. Consecutively
repeating the above described release/activation and stimulus steps
produces an "inch-worm" effect on the piston travel enabling the
drawdown pump 78 to draw in a suitable amount of connate fluid
within the cylinder 82 for subsequent analysis. Typical fluid
sampling volumes can range from about 30 cc to in excess of 900 cc,
and often in the range of about 56 cc. However the actual amount of
fluid sampled is dependent on the particular formation from which
the fluid is being drawn, thus the volume of the cylinder 82 should
be able to accommodate the amount of fluid to be sampled.
[0047] Due to the highly responsive qualities of electrically
responsive materials, the speed and stroke of the piston 80 can be
tightly controlled to ensure that the pressure within the cylinder
82 remains above the bubble point pressure of the connate fluid.
Accordingly one of the many advantages realized by the drawdown
pump of the present disclosure is that the measured discrete
movements of the piston 80 does not produce the large dynamic
forces caused by the acceleration/deceleration of typical currently
used drawdown pump motors. Furthermore, due to the highly
responsive nature of electrically responsive material, the speed of
operational cycles of drawdown pumps of the present disclosure is
well within acceptable limits of operational usage.
[0048] The pressure within the cylinder 82 may be monitored with
the attached pressure monitoring device 83. Implementation of the
pressure monitoring device 83 also provides the ability to control
the actuation of the drawdown pump 78 to ensure the pressure within
the cylinder 82 remains above the bubble point of the sampled fluid
therein. The drawdown sequence can occur under constant pressure or
under constant volumetric flow rate. The pressure measured by the
pressure monitoring device 83 is conveyed via a feed back loop 87
to the pump control 79. The pressure monitoring device 83 can be a
pressure gauge, and can detect the pressure in any currently known
or later developed means of pressure monitoring. For example, the
pressure monitoring device 83 can monitor pressure pneumatically or
with transducers that convert mechanical energy to electrical, such
as a quartz element or piezoelectric component. The measured
pressure can be measured and obtained in digital or analog
form.
[0049] The pump control 79, as is known in the art, may be
comprised of a programmable circuit, such as a computer or
microprocessor, having been programmed to analyze the value of the
measured pressure within the cylinder 82 and compare it to the
connate fluid bubble point pressure. Should these two pressures
both reside within a predetermined pressure range, the pressure
control 79 may be programmed to adjust the operation of the
drawdown pump 78 to ensure the pressure of the fluid in the
cylinder 82 remains above its bubble point pressure. The data
commands are preferably in digital form and are transferred to the
operational components 77 of the drawdown pump 78 via the control
loop 81. The operation components 77 include the items enclosed by
the dashed line of FIG. 6, as well as the components used to supply
and control the electrical signal(s) applied to the items within
the dashed line. Those skilled in the art are capable of
establishing a proper pressure range above that which the cylinder
pressure should remain. It is also within the capabilities of those
skilled in the art to program a control system for comparing
measured pressures with bubble point pressures and affecting pump
controls when these pressures fall within the specified range.
[0050] Furthermore, an additional advantage realized by the
responsive material of the ERM segment 88 is that the discrete
inch-worm movements of the drawdown pump 78 simulate a continuous
or analog movement of the piston 80 that minimizes or eliminates
the dynamic pumping effects experienced by current drawdown pumps.
When it is desired to empty the cylinder 82 of fluid, the
release/activation sequence may be reversed to urge the piston 80
into the cylinder 82 and thus force the fluid through a cylinder
outlet (not shown) for storage and/or fluid analysis.
[0051] Inclusion of the optional dashpot 98 with its compressible
fluid therein provides a resistive force to the movement of the
anchor rod 92 for pressure compensation with regard to the piston
80. The resistive force produced within the compressible fluid can
be useful in situations when the applied force of the pinch brakes
(100, 102) is limited and may not possess sufficient clamping force
to support the piston rod 86 against the fluid force imparted onto
the piston 80. Yet further optionally, the free end of the anchor
rod 92 may include a piston (not shown) for increasing the
resistive force provided by the dashpot 98. Additionally, the
resistive force is stored within the compressive fluid and can be
transferred into a translational force for pushing the piston 80
back into the cylinder 82 after the fluid sampling stroke is
completed. Alternatives to the fluid can include a spring or other
elastic device or material in which kinetic energy can be converted
to potential energy and temporarily stored therein.
[0052] The present invention described herein, therefore, is well
adapted to carry out the objects and attain the ends and advantages
mentioned, as well as others inherent therein. While a presently
preferred embodiment of the invention has been given for purposes
of disclosure, numerous changes exist in the details of procedures
for accomplishing the desired results. For example, the
electrically responsive material can be used for pressurizing
hydraulics, where the produced hydraulic pressure is utilized to
operate a drawdown pump as disclosed herein. Moreover, the
embodiments of the pumping devices disclosed herein can be utilized
for measuring fluid physical properties such for example fluid
density and fluid viscosity. Poiseuille's Law may be implemented
with regard to measuring fluid viscosity, fluid viscosity can be
determined by flowing a known amount of fluid through a length of
tube and measuring the pressure drop along the tube. Other ways of
determining viscosity include rotating a cylinder within the fluid
and measuring a corresponding torque produced within the fluid.
Rotation of the cylinder can be effectuated by adding a rotary
piezo-electric motor. These and other similar modifications will
readily suggest themselves to those skilled in the art, and are
intended to be encompassed within the spirit of the present
invention disclosed herein and the scope of the appended
claims.
* * * * *