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 
       [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&#39;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×, 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 1 , which is smaller than a width W 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 3 , which are smaller than a width W 4  of microchannel  505 . Preferably, width W 1  of nozzle opening  801  and widths W 3  of constrictions  703  are about 20 micrometers, whereas the preferred width W 2  and W 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 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 . 
         [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: 
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         [0049]    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: 
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                   ) 
                 
               
             
           
         
       
     
         [0050]    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. 
         [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.