US20100017135A1

US20100017135A1 - Pressure measurement of a reservoir fluid in a microfluidic device

Info

Publication number: US20100017135A1
Application number: US12/533,292
Authority: US
Inventors: Farshid Mostowfi
Original assignee: Schlumberger Technology Corp
Current assignee: Schlumberger Technology Corp
Priority date: 2008-03-03
Filing date: 2009-07-31
Publication date: 2010-01-21
Also published as: AU2009220857A2; MY155889A; WO2009109868A1; AU2009220857B2; EP2252888B1; US8485026B2; BRPI0908452B1; RU2458344C2; CA2623793C; CA2623793A1; BRPI0908452A2; MX2010009569A; US20110030466A1; EP2252888A1; CN101971022A; CN101971022B; AU2009220857A1; RU2010140426A

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

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

1. Field of the Invention
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.
2. Description of Related Art
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.
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.
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.
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.
However, there remains a need for simple non-invasive techniques to measure pressure inside a microfluidic channel.

BRIEF SUMMARY OF THE INVENTION

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.
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.
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.
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

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:

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;

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;

FIG. 3 is a top, plan view of the microfluidic device of FIG. 1 depicting three reservoir fluid flow regimes;

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;

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;

FIG. 6 is a side, elevational view of the microfluidic device of FIG. 5;

FIGS. 7-9 depict exemplary microchannel constrictions of the microfluidic device of FIG. 5;

FIGS. 10A and 10B are schematic cross sections of an un-deformed and deformed membrane respectively, according to some embodiments;

FIG. 11 is a stylized, schematic representation a membrane deformation measurement setup, according to some embodiments;

FIG. 12 is a stylized, schematic representation a membrane deformation measurement setup having multiple optical sensors, according to some embodiments;

FIG. 13 shows plots of exemplary measurements of a membrane in undeformed and deformed states, according to embodiments;

FIG. 14 shows a plot of repeated measured deformations as a function of hydrostatic pressure, according to embodiments; and

FIG. 15 shows plots of the measured pressures in cavities for different input pressures, according to embodiments.

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

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.
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.
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.
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.
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.
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.
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.
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×, 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.
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.
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.
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.
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 W₁, which is smaller than a width W₂of 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 W₃, which are smaller than a width W₄of microchannel 505. Preferably, width W₁of nozzle opening 801 and widths W₃of constrictions 703 are about 20 micrometers, whereas the preferred width W₂and W₄of microchannel 505 is 100 micrometers. These restrictions increase the velocity of the reservoir fluid by up to about 500 percent.
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.
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.
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 Lumiére) 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.
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.
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.
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.
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.
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:
$\begin{matrix} Q = \frac{Δ P}{R}, & (1) \end{matrix}$
where Q, ΔP, 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:
$\begin{matrix} R = {\frac{12 µ L}{ω h^{3}} [1 - \frac{h}{ω} (\frac{192}{π^{5}} \sum_{n = 1, 3, 5}^{\infty} \frac{1}{n^{5}} \tanh (\frac{n πω}{2 h}))]}^{- 1}, & (2) \end{matrix}$
where ω 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.
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.
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.
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.

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.