U.S. patent application number 12/533292 was filed with the patent office on 2010-01-21 for pressure measurement of a reservoir fluid in a microfluidic device.
This patent application is currently assigned to Schlumberger Technology Corporation. Invention is credited to Farshid Mostowfi.
Application Number | 20100017135 12/533292 |
Document ID | / |
Family ID | 40638161 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100017135 |
Kind Code |
A1 |
Mostowfi; Farshid |
January 21, 2010 |
PRESSURE MEASUREMENT OF A RESERVOIR FLUID IN A MICROFLUIDIC
DEVICE
Abstract
Methods and related systems are described for measuring fluid
pressure in a microchannel. A number of flexible membranes are
positioned at locations along the microchannel such that pressure
of the fluid in the microchannel causes a deformation of the
membranes. An optical sensing system adapted and positioned to
detect deformation of the membranes that thereby determine the
pressure of the fluid flowing in the microchannel at a number of
locations along the microchannel.
Inventors: |
Mostowfi; Farshid;
(Edmonton, CA) |
Correspondence
Address: |
SCHLUMBERGER-DOLL RESEARCH;ATTN: INTELLECTUAL PROPERTY LAW DEPARTMENT
P.O. BOX 425045
CAMBRIDGE
MA
02142
US
|
Assignee: |
Schlumberger Technology
Corporation
Cambridge
MA
|
Family ID: |
40638161 |
Appl. No.: |
12/533292 |
Filed: |
July 31, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/IB09/50500 |
Feb 7, 2009 |
|
|
|
12533292 |
|
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Current U.S.
Class: |
702/8 |
Current CPC
Class: |
B01L 2300/0654 20130101;
B01L 3/502784 20130101; G01L 11/02 20130101; G01N 25/02 20130101;
B01L 9/527 20130101; B01L 2400/0463 20130101; B01L 2300/0887
20130101; B01L 2400/0487 20130101; G01N 33/2823 20130101 |
Class at
Publication: |
702/8 |
International
Class: |
G01V 5/04 20060101
G01V005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2008 |
CA |
2623793 |
Claims
1. A system for measuring fluid pressure in a microchannel
comprising: a microchannel adapted to carry a fluid; a first
flexible member adapted and positioned such that pressure of the
fluid in the microchannel causes a deformation of the first
flexible member; and an optical sensing system adapted and
positioned to detect deformation of the first flexible member.
2. A system according to claim 1, wherein the first flexible member
is a first membrane.
3. A system according to claim 2, further comprising a first cavity
defined in part by the first membrane, wherein the first cavity is
in fluid communication with the microchannel at a first location
such that a fluid pressure within the first cavity corresponds to
the fluid pressure in the microchannel at the first location, and
the deformation of the first membrane is representative of the
fluid pressure within the first cavity.
4. A system according to claim 3, wherein the cavity and the
microchannel are defined at least in part by a first substrate.
5. A system according to claim 4, wherein the first substrate
comprises silicon.
6. A system according to claim 3, further comprising: a second
cavity defined in part by a second membrane and positioned to be in
fluid communication with the microchannel at a second location such
that a fluid pressure in the second cavity corresponds to the fluid
pressure in the microchannel at the second location, and a
deformation of the second membrane is representative of the fluid
pressure within the second cavity; and a third cavity defined in
part by a third membrane and positioned to be in fluid
communication with the microchannel at a third location such that a
fluid pressure in the third cavity corresponds to the fluid
pressure in the microchannel at the third location and the
deformation of the third membrane is representative of the fluid
pressure within the third cavity.
7. A system according to claim 6, wherein the optical sensing
system includes first, second and third optical sensors that are
adapted and positioned to detect deformation of the first, second
and third membranes respectively.
8. A system according to claim 1, wherein the microchannel exhibits
a serpentine shape and a length of at least one meter.
9. A system according to claim 1, wherein the microchannel exhibits
a width within a range of tens of micrometers to hundreds of
micrometers.
10. A system according to claim 1, wherein the optical sensing
system comprises an optical sensor, a spectrometer and a computer
system.
11. A system according to claim 9, wherein the optical sensor is a
confocal chromatic sensor.
12. A system according to claim 1, wherein the microchannel is part
of a microfluidic apparatus for measuring thermo-physical
properties of a fluid that is of a type selected from the group
consisting of: reservoir fluid, biomedical fluid, and a fluid being
monitored in connection with environmental monitoring.
13. A system according to claim 1, further comprising an optical
sensing system adapted and positioned to detect phase states of the
fluid at a plurality of locations along the microchannel.
14. A system according to claim 1 wherein the first flexible member
is formed from the same material that at least partially defines
the microchannel.
15. A system according to claim 14 wherein the material is
silicon.
16. A method for measuring fluid pressure in a microchannel
comprising: providing a microchannel adapted to carry a fluid, and
a first flexible member adapted and positioned such that pressure
of the fluid in the microchannel causes a deformation of the first
flexible member; introducing fluid under pressure into the
microchannel, thereby causing a deformation of the first flexible
member; and optically detecting the deformation of the first
flexible member.
17. A method according to claim 16, further comprising determining
a value representing the pressure at a location in the microchannel
based at least in part on the optically detected deformation of the
first flexible member.
18. A method according to claim 16, wherein the first flexible
member is a first membrane.
19. A method according to claim 17, wherein a first cavity is
defined in part by the first membrane, and the first cavity is in
fluid communication with the microchannel at a first location such
that fluid pressure within the first cavity corresponds to the
fluid pressure in the microchannel at the first location, and
wherein the optically detected deformation of the first membrane is
representative of the fluid pressure in the microchannel at the
first location.
20. A method according to claim 19, further comprising optically
detecting deformation of a second membrane and a third membrane
both being adapted and positioned to deform according to fluid
pressures in the microchannel at second and third locations on the
microchannel respectively.
21. A method according to claim 16, wherein the microchannel
exhibits a width within a range of tens of micrometers to hundreds
of micrometers.
22. A method according to claim 16, wherein the deformation is
detected using a confocal chromatic sensor.
23. A method according to claim 16, wherein the introduced fluid is
of a type selected from the group consisting of: reservoir fluid,
biomedical fluid, and a fluid being monitored in connection with
environmental monitoring, and the method further comprises
determining one or more thermo physical properties of the
introduced fluid flowing through the microchannel.
24. A method according to claim 23, further comprising optically
sensing phase states of the fluid at a plurality of locations along
the microchannel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a continuation-in-part of
International Patent Application No. PCT/IB09/50500, filed Feb. 7,
2009, which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This patent specification relates to an apparatus and method
for measuring thermo-physical properties of a reservoir fluid. More
particularly, the patent specification relates to an apparatus and
method for measuring pressure of a reservoir fluid flowing in a
microfluidic device.
[0004] 2. Description of Related Art
[0005] The measurement of reservoir fluid properties is a key step
in the planning and development of a potential oilfield. It is
often desirable to perform such measurements frequently on a
producing well to provide an indication of the performance and
behavior of the production process. Examples of such measurements
are pressure, volume, and temperature measurements, often referred
to as "PVT" measurements, which are instrumental in predicting
complicated thermo-physical behavior of reservoir fluids. One
important use of PVT measurements is the construction of an
equation of state describing the state of oil in the reservoir
fluid. Other properties of interest that may be determined using
PVT measurements include fluid viscosity, density, chemical
composition, gas-oil-ratio, and the like. Once a PVT analysis is
complete, the equation of state and other parameters can be input
into reservoir modeling software to predict the behavior of the
oilfield formation.
[0006] Conventional PVT measurements are performed using a cylinder
containing the reservoir fluid. A piston disposed in the cylinder
maintains the desired pressure on the fluid, while the heights of
the liquid and gaseous phases are measured using, for example, a
cathetometer. International Patent Application No. PCT/IB09/50500,
filed Feb. 7, 2009, discusses microfluidic technique form measuring
thermo-physical properties of a reservoir fluid. The microfluidic
techniques can provide certain advantages including: (1) providing
a way to measure thermo-physical properties of a reservoir fluid
with small amounts of reservoir fluid; (2) providing a way to
perform pressure-volume-temperature analyses of a reservoir fluid
in a timely fashion; and (3) providing a way to measure
thermo-physical properties of a reservoir fluid using image
analysis. However, in some cases the microfluidic based
measurements and analysis can benefit from pressure measurement at
various points along the microchannel.
[0007] Pressure sensors based on deformation of a membrane have
long been developed. These membranes are usually micro-fabricated
using SOI or silicone-on-insulator wafers. For example, see, U.S.
Pat. Nos. 5,095,401, 5,155,061, 5,165,282, and 5,177,661, each of
which is incorporated by reference herein. Numerous techniques have
been used to correlate deformation of the membrane with pressure.
These techniques include piezo-resistive element (see, e.g., U.S.
Pat. Nos. 5,081,437, 5,172,205, and 6,843,121), optical fibers
(See. e.g. U.S. Pat. Nos. 7,000,477, and 7,149,374; and U.S. Patent
Publication Nos. 2005/0041905, and 2008/0175529), and capacitive
sensors (See. e.g. U.S. Pat. Nos. 7,254,008, 5,470,797, and
6,945,116, and PCT Patent Publication Nos. WO 96/16319, and WO
98/23934). Each of the foregoing patents and patent publications
are incorporated by reference herein.
[0008] Most of these techniques have been developed for
conventional pressure sensors. Incorporating such tools inside a
microchannel is either too difficult or otherwise impractical.
Practical and cost effective measurement techniques for
microchannels are rare. To measure pressure inside a microfluidic
channel, some techniques have been described. For example, R.
Baviere, F. Ayela, Meas. Sci. Technol., 15, (2004), 377,
incorporated by reference herein, discusses the use of
piezo-resistive elements; and M. J. Kohl, S. I. Abdel-Khalik, S. M.
Jeter, D. L. Sadowski, Sensors and Actuators a-Physical, 118,
(2005), 212; and M. J. Kohl, S. I. Abdel-Khalik, S. M. Jeter, D. L.
Sadowski, Int. J. Heat Mass Transfer, 48, (2005), 1518, both
incorporated by reference herein, discuss the use of lasers.
[0009] However, there remains a need for simple non-invasive
techniques to measure pressure inside a microfluidic channel.
BRIEF SUMMARY OF THE INVENTION
[0010] According to embodiments, a system for measuring fluid
pressure in a microchannel is provided. The system includes a
microchannel adapted to carry a fluid; a first flexible member
adapted and positioned such that pressure of the fluid in the
microchannel causes a deformation of the first flexible member; and
an optical sensing system adapted and positioned to detect
deformation of the first flexible member.
[0011] The flexible member is preferably a membrane partially
defining a cavity that is in fluid communication with the
microchannel at a first location such that deformation of the
membrane is representative of the fluid pressure in the
microchannel at the first location. According to some embodiments,
second and third membranes also can be provided to provide
detecting of pressure at second and third locations on the
microchannel.
[0012] Additionally, according to some embodiments a method for
measuring fluid pressure in a microchannel is provided. The method
includes providing a microchannel adapted to carry a fluid, and a
first flexible member adapted and positioned such that pressure of
the fluid in the microchannel causes a deformation of the first
flexible member. Fluid is introduced under pressure into the
microchannel, thereby causing a deformation of the first flexible
member, and deformation of the first flexible member is optically
detected. A value can be determined representing the pressure at a
location in the microchannel based at least in part on the
optically detected deformation of the first flexible member.
[0013] Further features and advantages of the invention will become
more readily apparent from the following detailed description when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present invention is further described in the detailed
description which follows, in reference to the noted plurality of
drawings by way of non-limiting examples of exemplary embodiments
of the present invention, in which like reference numerals
represent similar parts throughout the several views of the
drawings, and wherein:
[0015] FIG. 1 is a stylized, exploded, perspective view of a first
illustrative embodiment of a microfluidic device for measuring
thermo-physical properties of a reservoir fluid;
[0016] FIG. 2 is a stylized, schematic representation of a reaction
of reservoir fluid as the reservoir fluid flows through the
microfluidic device of FIG. 1;
[0017] FIG. 3 is a top, plan view of the microfluidic device of
FIG. 1 depicting three reservoir fluid flow regimes;
[0018] FIG. 4 is a stylized, side, elevational view of a reservoir
fluid measurement system, including the microfluidic device of FIG.
1 and a camera for generating images of the microfluidic device in
use;
[0019] FIG. 5 is a top, plan view of a second illustrative
embodiment of a microfluidic device for measuring thermo-physical
properties of a reservoir fluid;
[0020] FIG. 6 is a side, elevational view of the microfluidic
device of FIG. 5;
[0021] FIGS. 7-9 depict exemplary microchannel constrictions of the
microfluidic device of FIG. 5;
[0022] FIGS. 10A and 10B are schematic cross sections of an
un-deformed and deformed membrane respectively, according to some
embodiments;
[0023] FIG. 11 is a stylized, schematic representation a membrane
deformation measurement setup, according to some embodiments;
[0024] FIG. 12 is a stylized, schematic representation a membrane
deformation measurement setup having multiple optical sensors,
according to some embodiments;
[0025] FIG. 13 shows plots of exemplary measurements of a membrane
in undeformed and deformed states, according to embodiments;
[0026] FIG. 14 shows a plot of repeated measured deformations as a
function of hydrostatic pressure, according to embodiments; and
[0027] FIG. 15 shows plots of the measured pressures in cavities
for different input pressures, according to embodiments.
[0028] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and are herein described in
detail. It should be understood, however, that the description
herein of specific embodiments is not intended to limit the
invention to the particular forms disclosed, but on the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the scope of the invention as defined
by the appended claims.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0029] Illustrative embodiments of the invention are described
below. In the interest of clarity, not all features of an actual
implementation are described in this specification. It will be
appreciated that in the development of any such actual embodiment,
numerous implementation-specific decisions must be made to achieve
the developer's specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure. Further, like reference numbers and designations in the
various drawings indicated like elements.
[0030] According to embodiments, systems and methods for measuring
pressure of a reservoir fluid in a microfluidic device are
provided. For the purposes of this disclosure, the term "reservoir
fluid" means a fluid stored in or transmitted from a subsurface
body of permeable rock. Thus "reservoir fluid" may include, without
limitation, hydrocarbon fluids, saline fluids such as saline water,
as well as other formation water, and other fluids such as carbon
dioxide in a supercritical phase. Moreover, for the purposes of
this disclosure, the term "microfluidic" means having a
fluid-carrying channel exhibiting a width within a range of tens to
hundreds of micrometers, but exhibiting a length that is many times
longer than the width of the channel. Similarly the term
"microchannel" means a fluid-carrying channel exhibiting a width
within a range of tens to hundreds of micrometers. Although many of
the microchannels described herein are of rectangular cross section
due to the practicalities of fabrication techniques, the cross
section of a microchannel can be of any shape, including round,
oval, ellipsoid, square, etc.
[0031] FIG. 1 depicts a stylized, exploded, perspective view of a
microfluidic device 101 in which pressure can be measured,
according to some embodiments of the invention. In the illustrated
embodiment, microfluidic device 101 comprises a first substrate 103
defining a microchannel 105, an entrance well 107 and an exit well
109. Microchannel 105 extends between and is in fluid communication
with entrance well 107 and exit well 109. Microchannel 105 forms a
serpentine pattern in first substrate 103, thus allowing
microchannel 105 to extend a significant length but occupy a
relatively small area. According to one embodiment, microchannel
105 exhibits a length of one or more meters, a width of about 100
micrometers, and a depth of about 50 micrometers, although the
present invention also contemplates other dimensions for
microchannel 105. Microfluidic device 101 further comprises a
second substrate 111 having a lower surface 113 that is bonded to
an upper surface 115 of first substrate 103. When second substrate
111 is bonded to first substrate 103, microchannel 105 is sealed
except for an inlet 117 at entrance well 107 and an outlet 119 at
exit well 109. Second substrate 111 defines an entrance passageway
121 and an exit passageway 123 therethrough, which are in fluid
communication with entrance well 107 and exit well 109,
respectively, of first substrate 103. Also shown in FIG. 1 are a
number of cavities such as cavity 150, each connected to the main
microchannel 105 using a small side channel. As is explained in
further detail below, each cavity such as cavity 150 is partially
defined by a deformable membrane that allows for pressure
measurement. According to preferred embodiments substrate 103 is
fabricated with circular openings and the cavities are defined on
the sides by the walls of the openings in substrate 103, on the
bottom with the deformable membrane, and on the top by the second
substrate 111.
[0032] In FIG. 1, first substrate 103 is preferably made of silicon
and is approximately 500 micrometers thick, and second substrate
111 is made of glass, such as borosilicate glass, although the
present invention contemplates other materials for first substrate
103, as is discussed in greater detail herein. According some
preferred embodiments substrate 103 is a conventional silicon on
insulator (SOI) wafer. Exemplary borosilicate glasses are
manufactured by Schott North America, Inc. of Elmsford, N.Y., USA,
and by Corning Incorporated of Corning, N.Y., USA.
[0033] In operation, pressurized reservoir fluid is urged through
entrance passageway 121, entrance well 107, and inlet 117 into
microchannel 105. The reservoir fluid exits microchannel 105
through outlet 119, exit well 109, and exit passageway 123.
Microchannel 105 provides substantial resistance to the flow of
reservoir fluid therethrough because microchannel 105 is very small
in cross-section in relation to the length of microchannel 105.
When fluid flow is established between inlet 117 and outlet 119 of
microchannel 105, the pressure of the reservoir fluid within
microchannel 105 drops from an input pressure, e.g., reservoir
pressure, at inlet 117 to an output pressure, e.g., atmospheric
pressure, at outlet 119. The overall pressure drop between inlet
117 and outlet 119 depends upon the inlet pressure and the
viscosity of the reservoir fluid. Fluid flow through microchannel
105 is laminar and, thus the pressure drop between inlet 117 and
outlet 119 is linear when the reservoir fluid exhibits single-phase
flow. For further details of microfluidic devices and method for
measuring thermo-physical properties of reservoir fluid, see e.g.
International Patent Application No. PCT/IB09/50500, filed Feb. 7,
2009, which is incorporated by reference herein, and in co-pending
U.S. Pat. No. ______, entitled "PHASE BEHAVIOR ANAYSIS USING A
MICROFLUIDIC PLATFORM," Attorney Docket No. 117.0043 US NP, filed
on even date herewith, which is incorporated by reference herein.
Once the flow is established, the membrane in each cavity, such as
cavity 150, deforms due to the fluid pressure and the deformation
can be optically detected, as is described more fully below.
[0034] FIG. 2 provides a stylized, schematic representation of the
reaction of reservoir fluid 201 as the reservoir fluid flows
through microchannel 105 in a direction generally corresponding to
arrow 202, according to some embodiments. When the reservoir fluid
enters inlet 117 of microchannel 105, the reservoir fluid is at a
pressure above the "bubble point pressure" of the reservoir fluid.
The bubble point pressure of a fluid is the pressure at or below
which the fluid begins to boil, i.e., bubble, at a given
temperature. When the reservoir fluid exits outlet 119 of
microchannel 105, the reservoir fluid is at a pressure below the
bubble point pressure of the reservoir fluid. Thus, a "first"
bubble 203 forms in the reservoir fluid at some location, e.g., at
205 in FIG. 2, within microchannel 105 where the reservoir fluid is
at the bubble point pressure. Downstream of location 205,
multi-phase flow, e.g., gas and liquid flow, of reservoir fluid 201
occurs in microchannel 105. Previously-formed bubbles, e.g. bubbles
207, 209, 211, 213, 215, and the like, grow in size as reservoir
fluid 201 flows within microchannel 105 beyond the location
corresponding to the formation of the first bubble due to decreased
pressure in this portion of microchannel 105 and more evaporation
of the lighter components of reservoir fluid 201. The bubbles are
separated by slugs of liquid, such as slugs 217, 219, 221, 223,
225, and the like. Expansion of the bubbles, such as bubbles 207,
209, 211, 213, 215, results in an increased flow velocity of the
bubbles and liquid slugs, such as slugs 217, 219, 221, 223, 225,
within microchannel 105. The mass flow rate of reservoir fluid 201
is substantially constant along microchannel 105; however, the
volume flow rate of reservoir fluid 201 increases as reservoir
fluid flows along microchannel 105. The reservoir fluid also enters
cavity 150 through small channel 152. According to some embodiments
the width of small side channel 152 is approximately 50
micrometers, or about half of the width of microchannel 105, and is
about 50 micrometers deep.
[0035] Thermo-physical properties of the reservoir fluid, such as
reservoir fluid 201 of FIG. 2, for example gas-oil-ratio, phase
envelope, and equation of state, can be determined by measuring the
size and concentration of bubbles within microchannel 105.
Referring now to FIG. 3, the flow of the reservoir fluid through
microchannel 105 is depicted in three regimes. A first bubble, such
as first bubble 203 of FIG. 2, is formed at 301 along microchannel
105. From inlet 117 of microchannel 105 to location 301 of the
first bubble, indicated in FIG. 3 as a first region 303, the
pressure of the reservoir fluid is above the bubble point. No
bubbles are observed within first region 303. In first region 303,
the flow of the reservoir fluid is laminar due to a low Reynolds
number and the pressure drops linearly therein. Once bubbles are
formed, the bubbles move along within microchannel 105 toward
outlet 119 and the volumes of the bubbles increases. In a second
region 305, the void fraction, i.e., the volume of gas to total
volume, of the reservoir fluid is less than one. In a third region
307, the flow of the reservoir fluid is dominated by high-speed gas
flow. The gas bubbles are separated by small droplets of liquid,
such as water. The pressure of the reservoir fluid within third
region 307 decreases rapidly. Gas bubbles flow within second region
305 at a slower rate than in third region 307, where they are often
nearly impossible to follow with the naked eye.
[0036] Once a stabilized flow of reservoir fluid is established in
microchannel 105, a camera 401 is used to capture snapshots of the
flow, as shown in FIG. 4. Note that the flow of reservoir fluid
into inlet 117 (shown in FIGS. 1 and 3) is represented by an arrow
403 and that the flow of reservoir fluid from outlet 119 (shown in
FIGS. 1 and 3) is represented by an arrow 405. In one embodiment,
camera 401 is a charge-coupled device (CCD) type camera. The images
produced by camera 401 are processed using image analysis software,
such as ImageJ 1.38.times., available from the United States
National Institutes of Health, of Bethesda, Md., USA, and
ProAnalyst, available from Xcitex, Inc. of Cambridge, Mass., USA,
to measure the size and concentration of the bubbles in the
reservoir fluid disposed in microchannel 105. Using this technique,
many thermo-physical properties of the reservoir fluid, such as
gas-oil-ratio, phase envelope, and equation of state, can be
determined.
[0037] FIGS. 5 and 6 depict a microfluidic device 501, according to
some embodiments. As in microfluidic device 101 of FIG. 1,
microfluidic device 501 comprises a first substrate 503 defining a
microchannel 505, an entrance well 507, and an exit well 509.
Microchannel 505 extends between and is in fluid communication with
entrance well 507 and exit well 509. In the illustrated embodiment,
first substrate 503 is made from silicon; however, first substrate
503 may be made from glass. Microchannel 505, entrance well 507,
and exit well 509 are, in one embodiment, first patterned onto
first substrate 503 using a photolithography technique and then
etched into first substrate 503 using a deep reactive ion etching
technique. As in the first embodiment shown in FIG. 1, in a
preferred embodiment, microchannel 505 exhibits a length of one or
more meters, a width of about 100 micrometers, and a depth of about
50 micrometers, although the present invention also contemplates
other dimensions for microchannel 505. A number small side
channels, such as side channels 552 and 556 lead from the main
microchannel 505 to circular cavities such as cavities 550 and 554.
Also shown in a side channel 560 that leads to cavity 558.
According to some embodiments, twelve cavities are spaced out along
the length of microchannel 505 and each of the cavities are about 2
mm in diameter, although the present invention also contemplates
other numbers of cavities and diameters for each cavity.
[0038] Microfluidic device 501 further comprises a second substrate
511 defining an entrance passageway 513 and an exit passageway 515
in fluid communication with entrance well 507 and exit well 509.
Second substrate 511 is made from glass, as discussed herein
concerning second substrate 111 (shown in FIG. 1). In one
embodiment, entrance passageway 513 and exit passageway 515 are
generated in second substrate 511 using a water jet or abrasive
water jet technique. First substrate 503 and second substrate 511
are preferably fused using an anodic bonding method after careful
cleaning of the bonding surfaces of substrates 503 and 511. The
cavities can be fabricated using a verity of techniques. According
to some embodiments, a deep ion reaction (DRIE) etching process is
used.
[0039] The present invention contemplates microfluidic device 501
having any suitable size and/or shape needed for a particular
implementation. In one embodiment, microfluidic device 501 exhibits
an overall length A of about 80 millimeters and an overall width B
of about 15 millimeters. In such an embodiment, passageways 513 and
515 are spaced apart a distance C of about 72 millimeters, cavities
558 and 550 are spaced apart a distance D of about 3 millimeters,
and cavities along the serpentine section of microchannel 505, such
as cavities 550 and 554 are spaced apart by a distance E of about 5
millimeters. It should be noted that microfluidic device 101 may
also exhibit dimensions corresponding to microfluidic device 501.
However, the scope of the present invention is not so limited.
[0040] Referring to FIG. 7, one or more portions of microchannel
505 include zones of reduced cross-sectional area to induce the
formation of bubble nuclei in the reservoir fluid. For example, as
shown in FIGS. 7 and 8, a micro-venturi 701 is incorporated into an
inlet of microchannel 505. Micro-venturi 701 includes a nozzle
opening 801 having a width W.sub.1, which is smaller than a width
W.sub.2 of microchannel 505. The contraction provided by
micro-venturi 701 causes a substantial pressure drop in the
reservoir fluid at nozzle opening 801 along with an increased
velocity of reservoir fluid flow. The combined effect of the
pressure drop and the increased velocity induces formation of
bubble nuclei in the reservoir fluid. Preferably, microchannel 505
further includes one or more additional constrictions 703, as shown
in FIGS. 7 and 9. Constrictions 703 exhibit widths W.sub.3, which
are smaller than a width W.sub.4 of microchannel 505. Preferably,
width W.sub.1 of nozzle opening 801 and widths W.sub.3 of
constrictions 703 are about 20 micrometers, whereas the preferred
width W.sub.2 and W.sub.4 of microchannel 505 is 100 micrometers.
These restrictions increase the velocity of the reservoir fluid by
up to about 500 percent.
[0041] FIGS. 10A and 10B are schematic cross sections of an
un-deformed and deformed membrane respectively, according to some
embodiments. Cavity 554 is shown defined on the sides by the first
substrate 503, on the top by a second substrate 511, and on the
bottom by deformable membrane 570. According to some embodiments,
membrane 570 is micro-fabricated in the device 501 using
conventional SOI (Silicon one insulator) wafers. According to some
embodiments, the membranes, such as membrane 570 are not separate
parts from the first substrate 503. Rather they are formed the same
material as substrate 503. According to such embodiments, starting
with substrate 503 is a 500 micrometer thick silicon wafer. The
cavities, such as cavity 554 are etched down to about 400
micrometers. This leaves a 100 micrometer wall at the bottom of
each cavity, which forms the flexible membrane, such as membrane
570.
[0042] In FIG. 10B, membrane 570 is shown in a deformed state. Once
the pressure inside the microchannel 505 (not shown) and inside
cavity 554 exceeds that of the atmosphere, the membrane 570 will
expand outward. Membrane 570 is designed such that deformation of
the membrane 570 is linear within the expected pressure range for
the device 501. It has been found that for many downhole
applications a membrane diameter of about 2 mm in diameter and
about 100 micrometers in thickness, although other membrane
dimensions, including thickness, are contemplated. According to
some embodiments, modeling such as finite element modeling can be
used to ensure the membrane will behave linearly within the
expected range of pressures.
[0043] FIG. 11 is a stylized, schematic representation a membrane
deformation measurement setup, according to some embodiments. The
setup includes a microfluidic device 501, confocal sensor 1110,
spectrometer 1120, and a computer system 1130. Due to changing
pressure inside the microchannel of device 501, the pressure
changes in cavity 554 and membrane 570 deforms. The deformation is
detected and measured by the sensor 1110. To measure deformation of
the membrane 570, according to some embodiments, a confocal
chromatic sensor, or an optical pen, is used. Suitable sensors
include the chromatic confocal distance sensors made by STIL
(Sciences et Techniques Industrielles de la Lumiere) SA, of France.
The confocal sensor uses the wide spectrum of the white light. It
then disperses the white light into monochromatic light using a
series of lenses. The distance of the object from the sensors is
measured by spectroscopy of the reflected light using spectrometer
1120 which receives optical signals from the sensor via fiber optic
connection 1112. The setup is controlled by and the results are
interpreted and displayed using computer system 1130. Computer
system 1130 includes a one or more processors, a storage system
1132 (which includes one or more removable storage devices that
accept computer readable media), display 1136, and one or more
human input devices 1134, such as a keyboard and/or a mouse.
Computer system 1130 also includes a data acquisition system for
collecting data from the spectrometer 1120.
[0044] According to one embodiment, the microfluidic device 501 is
mounted on a chip holder perpendicular to the main axis of the
confocal sensor 1110. The sensor is also mounted on a holder that
can move the sensor in two orthogonal directions using two
micro-stages. In this way, the sensor 1110 can be focused, one at a
time, on any of the other membranes of the other cavities located
on device 501.
[0045] FIG. 12 is a stylized, schematic representation a membrane
deformation measurement setup having multiple optical sensors,
according to some embodiments. As in the case of FIG. 11, the setup
includes a microfluidic device 501, spectrometer 1120, and a
computer system 1130. The setup in FIG. 12 includes a plurality of
optical sensors 1210 with one optical sensor focused on each
membrane of device 510. For example, sensor 1212 is focused on the
membrane of cavity 558, and sensor 1214 is focused on the membrane
of cavity 550. The signals form the sensors 1210 that represent
various states of deformation of the membranes are fed to
spectrometer 1120 and then stored, evaluated and/or displayed by
computer system 1130. According to some embodiments, the sensor
1210 are mounted on a micro-stage such that each optical sensor can
be positioned to focus on several points with respect to the
membrane. For example, the micro-stage can be programmed such that
each optical sensor focuses on three points corresponding to points
A, B and C on the curves 1310 and 1320 of FIG. 13, which is
described more fully below.
[0046] FIG. 13 shows plots of exemplary measurements of a membrane
in undeformed and deformed states, according to embodiments. To
measure the deformation of the membrane, the optical sensor was
moved across the membrane using a micro-stage. Curve 1310 is the
membrane profile under no (i.e. atmospheric) pressure and curve
1320 is the membrane profile under 400 psi pressure. It can be seen
that the flat membrane assumes a bell-shape under the applied
pressure. Two reference points "A" and "B" were selected on either
side of the membrane an the line 1312 represents the device plane
in the case of curve 1310 and the line 1322 represents the device
plane in the case of curve 1320. From curve 1310, it can be seen
that approximately 1 micrometer offset exists between the device
plane and the undeformed membrane surface. The deformation of the
center point "C" of the membrane is used as a measure of the
applied pressure. According to curve 1320 the deformation from the
device plane is slightly more than 4 micrometers.
[0047] To calibrate membrane deformation, a series of hydrostatic
tests were performed. The exit port of the microfluidic device was
plugged to prevent any flow in the system. Then, the input pressure
was varied from 0 psig up to 800 psig. This guaranteed a uniform
hydrostatic pressure throughout the channel. FIG. 14 shows a plot
of repeated measured deformations as a function of hydrostatic
pressure, according to embodiments. As shown by curve 1410, good
linearity was achieved for the designed range. Reasonable
repeatability and reproducibility is achieved as shown by the
standard deviation bars at various points along curve 1410. Thus
curve 1410 indicates that the described techniques can be reliably
used to measure pressure inside a microchannel.
[0048] The accuracy and reliability of the described techniques is
further demonstrated by the following experiment. In a microchannel
where Reynolds number is extremely low, the pressure drop is
linear. In other words, if a fluid is injected at a give pressure
and the output pressure is atmospheric, the pressure inside the
channel maintains a linear relationship with the length of the
channel. In such a system, flow rate is calculated using:
Q = .DELTA. P R , ( 1 ) ##EQU00001##
[0049] where Q, .DELTA.P, and R represent flow rate, pressure drop,
and channels resistance respectively. For a rectangular
microchannel R can be calculated using the teachings of D. J.
Beebe, G. A. Mensing, G. M. Walker, Annual Review of Biomedical
Engineering, 4, (2002), 261, which is incorporated herein by
reference, namely:
R = 12 L .omega. h 3 [ 1 - h .omega. ( 192 .pi. 5 n = 1 , 3 , 5
.infin. 1 n 5 tanh ( n .pi..omega. 2 h ) ) ] - 1 , ( 2 )
##EQU00002##
[0050] where .omega. is the channel width and h is the channel
height. The above equations show that there is a linear
relationship between pressure inside the channel and the length.
Therefore, it can be expected that there is a linear pressure drop
along the channels.
[0051] The membranes were calibrated using the data shown in FIG.
14. Then the fluid (water) was injected into the channel. The
injection pressure was varied from 600 psig down to 100 psig. The
deformations of the membranes were measured at each pressure. Then,
the deformations were converted into pressure using the calibration
curve shown in FIG. 14. FIG. 15 shows plots of the measured
pressures in the cavities for different input pressures, according
to embodiments. The injected fluid is water. Each data point shows
the pressure at the corresponding cavity. The input pressure was
varied from 600 psi (curve 1510) down to 100 psi (curve 1520). From
the curves, a linear pressure distribution is evident in the
channel, which is in accord with the above analysis.
[0052] Although many embodiments have been described herein with
respect to analysis of reservoir fluids, the present invention is
also applicable to the analysis of many other types of fluids.
According to some embodiments analysis of one or more types of
biomedical fluids is provided including but not limited to bodily
fluids such as blood, urine, serum, mucus, and saliva. According to
other embodiments analysis of one or more fluids is provided in
relation to environmental monitoring, including by not limited to
water purification, water quality, and waste water processing, and
potable water and/or sea water processing and/or analysis.
According to yet other embodiments, analysis of other fluid
chemical compositions is provided.
[0053] Whereas many alterations and modifications of the present
invention will no doubt become apparent to a person of ordinary
skill in the art after having read the foregoing description, it is
to be understood that the particular embodiments shown and
described by way of illustration are in no way intended to be
considered limiting. Further, the invention has been described with
reference to particular preferred embodiments, but variations
within the spirit and scope of the invention will occur to those
skilled in the art. It is noted that the foregoing examples have
been provided merely for the purpose of explanation and are in no
way to be construed as limiting of the present invention. While the
present invention has been described with reference to exemplary
embodiments, it is understood that the words, which have been used
herein, are words of description and illustration, rather than
words of limitation. Changes may be made, within the purview of the
appended claims, as presently stated and as amended, without
departing from the scope and spirit of the present invention in its
aspects. Although the present invention has been described herein
with reference to particular means, materials and embodiments, the
present invention is not intended to be limited to the particulars
disclosed herein; rather, the present invention extends to all
functionally equivalent structures, methods and uses, such as are
within the scope of the appended claims.
* * * * *