Microsystem With Fluidic and Optical Interface for Inline ... - IEEE Xplore

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IEEE SENSORS JOURNAL, VOL. 8, NO. 5, MAY 2008

Microsystem With Fluidic and Optical Interface for Inline Measurement of CO2 in Oil Fields

Emmanuel Tavernier, Julien Sellier, Frédéric Marty, Patrick Tabeling, and Tarik Bourouina, Senior Member, IEEE

Abstract—Motivated by the need for inline measurements in natural gas and oil exploitation, we developed a microfluidic system which is suitable for chemical measurements by optical methods. It consists of a microfluidic system allowing the separation of gas and liquid phases so that gas can be optically analyzed. This system takes advantage of surface tension effects in tiny microchannels. The application is the measurement of carbon dioxide (CO2 ) concentration by evaluating absorption of infrared light at a wavelength of 4.24 m. Measurements have been successfully performed in the 0–70 bars pressure range. Index Terms— CO2 , gas sensing, infrared (IR) absorption, microfluidics, oil field, phase separation.

I. INTRODUCTION

A

T CURRENT consumption rate, the proven reserves are expected to last 40 years and 60 years for oil and gas, respectively [1]. The models used to establish these previsions take into account and anticipate the future technology advances in oil industry [2]. These trends maintain a continuous evolution of the needs for improving the conditions of exploitation, storage, and distribution. Thus, the development of new technological tools is crucial. For instance, no specific solution exists in the market today to address the applications of real-time monitoring of gas reserves and underground storage facilities. For gas reserves, measurements are currently performed on reservoir fluid samples obtained with a wireline tool. However, even with the best techniques, when the samples are brought to the surface, there is an overall change of the environment; at least temperature and pressure are no longer the same, so that the sample may no longer represent the fluid within the reservoir. Moreover,

Manuscript received July 31, 2006; revised April 13, 2007 and April 29, 2007; accepted May 6, 2007. This work was supported in part by the CIFRE Program jointly between ANRT, Schlumberger and ESIEE and in part by the SESAME Program of Conseil Régional d’Ile-de-France. The associate editor coordinating the review of this paper and approving it for publication was Prof. Ooi Kiang Tan. E. Tavernier is with the Université Paris-Est, ESIEE, Ecole Supérieure d’Ingénieurs en Electronique et Electrotechnique, and ESYCOM Laboratory, F-93162 Noisy-le-Grand Cedex, France, and also with the Schlumberger MEMS Group, Elancourt, France (e-mail: [email protected]). J. Sellier and P. Tabeling are with ESPCI, Ecole Supérieure de Physique et Chimie Industrielles, 75231 Paris, France (e-mail: [email protected]; [email protected]). F. Marty is with the Université Paris-Est, ESIEE, Ecole Supérieure d’Ingénieurs en Electronique et Electrotechnique, and ESYCOM Laboratory, F-93162 Noisy-le-Grand Cedex, France (e-mail: [email protected]). T. Bourouina is with the Université Paris-Est, ESIEE, Ecole Supérieure d’Ingénieurs en Electronique et Electrotechnique and ESYCOM Laboratory, F-93162, Noisy-le-Grand Cedex, France (e-mail: [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2008.918170

these measurements are typically performed with macroscopic equipment, which in most cases is available only in laboratories located far from the well site. Consequently, the delays between sampling and analysis of a fluid can be on order for weeks. Real-time knowledge of these parameters would increase significantly the performance of the whole production. Inline integration of various kinds of sensors in portable instruments allows fast measurement of a number of physical and chemical properties in the reservoir. Microsystem technologies, which are based either on silicon or on other substrate materials, are being extensively used for this kind of applications because they enable the maximum level of integration allowing the design of microsystems containing miniaturized microelectromechanical systems (MEMS)-type sensing elements. Reduced size for the electronics is also achieved by the development of Application Specific Integrated Circuits (ASICs). Miniaturization is a key factor because only small sized devices can be deployed in the reservoirs and storage facilities. It also has an impact on the cost reduction, a higher level of reliability, as well as a smaller packaging. concentration is one of the properties Carbon dioxide to be determined using sensing systems for assessing quality of natural gas during exploitation, from exploration to production content in natural gas is indeed an indiand storage. The cation factor of its quality. However, natural gas has other contents including water and oil. Then, motivated by the need for concentration in multiphase quantitative measurements of mixtures, we developed a microsystem, which makes use of optical sensing in a specifically designed microfluidic channel. Gas chromatography and mass spectrometry are among the most precise methods for gas sensing and analysis. These methods still require heavy laboratory equipment though there are some reported attempts for miniaturization [3]–[5]. On the other hand, there are mainly two types of portable, low-cost gas sensors. The first ones are based on the use of a solid electrolyte whose physical properties are modified by adsorption or desorption of gas molecules [6]–[8]. Among these, one can mention: (i) capacitive sensors based on a changes in the dielectric properties of a polymer; (ii) microhotplate membranes exploiting a resistance change upon gas exposure of thick-film for instance) at medium temperature; (iii) thermoelectric ( calorimeters based on temperature variations due to enthalpy changes upon analyte absorption on a polymer film; and (iv) resonating cantilevers based on the change of mechanical resonance frequency due to added mass upon adsorption of gas molecules on a polymer layer deposited on the cantilever. The second type of gas sensors are based on absorption of infrared (IR) light by gas molecules [9], [10]. Beside their higher stability and lower power consumption, the main advantage of these

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TAVERNIER et al.: MICROSYSTEM WITH FLUIDIC AND OPTICAL INTERFACE FOR INLINE MEASUREMENT OF

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Fig. 2. Side view of the channel, illustrating the flow of water from a thin to a deep area.

Fig. 1. Side view of the channel with a liquid-gas interface. As the channel thickness (and width) decrease, surface tension effects increase, causing a pressure barrier. The higher pressure corresponds to the smallest radius of curvature of the liquid surface (c).

sensors is their high selectivity due to the absorption of light at specific wavelengths, corresponding to resonance of molecular vibrations. Another advantage of optical sensing is the ability to perform measurements in harsh environments, especially those where electrical wires must be avoided. This second type of sensors is, therefore, the most suitable for measurements in oil fields, where temperature and pressure levels are also high. This paper describes a microfluidic system allowing the separation of gas and water phases in a straight channel. The system makes use of surface tension to drive the water phase into the central part of the channel and allows easy separation of gaseous contents. Capillary separation of gas from liquid usually makes use of various channel sizes [11]. In this paper, we implement it in the main channel itself. The microfluidic system is to be immeasurement by plemented in an experimental setup for an optical method based on IR light absorption. II. DESIGN

becomes very large on their fluid flow. This pressure barrier as the radius of curvature or the dimensions of the channel decreases. A higher pressure barrier develops in the case illustrated in Fig. 1(c) as compared with the case of Fig. 1(b). Fig. 1(a) illustrates the case of a fluid flow in a channel in which surface tension effects are not taken into account (for instance, a channel of large dimensions). In this case, the pressure-flow characteristic for laminar flow is given by the Hagen–Poiseuille equation (3) where is an applied differential pressure and the resulting flow-rate. is the fluid viscosity. , , and are the channel length, width, and thickness, respectively. In both cases of Fig. 1(b) and (c), the effect of surface tension can be taken into account as follows, where the characteristics approaches somehow the behavior of a passive valve (4) Flow can occur only if the applied differential pressure is larger than the pressure barrier ; otherwise, the fluid is retained in the microchannel. B. Operation Principle of Phase Separation Microsystems

A. Liquid Flow Involving Surface Tension Effects in a Microchannel Wetting involves three kinds of interfaces: gas-liquid, gassolid, and liquid-solid, the solid surface being the microchannel boundary [12], [13]. Let us consider first the simple case depicted in Fig. 1. Surface tension between liquid and gas causes a pressure barrier, which is given by Laplace law (1)

Let us consider now the microsystem schematically depicted in Fig. 2, which illustrates the principle of using surface tension to separate two phases. The microsystem consists of a transition between two microchannels where lateral dimensions are increased in the flow transition from channels 1 to 2. According to (2), the pressure barrier decreases with an increase of lateral dimensions. As a result of these different interactions between the hydrophobic material and water in channels 1 and 2, water is expelled from the thin area (channel 1) into the deep trench (channel 2). In this case, the pressure difference is given by

and are the two radii of curvature of the surface and where is the surface tension, which characterizes the liquid-air interand are related to the angle of face. The radii of curvature contact and the channel dimensions. One finally obtains for (2) where and are the width and thickness of the channel, respectively. Due to the tiny dimensions of microchannels, surface tension effects involved in wetting have a non-negligible impact

(5)

III. EXPERIMENTAL RESULTS The systems presented here are obtained in two etching steps on a polymethylsiloxane (PDMS) substrate and can easily be implemented in existing processes for complex microfluidic systems manufacturing.

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Fig. 3. Channel design with a deep trench for separation of water from gas.

Fig. 5. Design for multiple phase separation.

Fig. 4. Decomposition of a movie taken during the flow of a water slug in the trench. The water is fluorescent and thus appears in white on the gray background of the channel. The width of the channel is 240 m, the ratio between deep and thin heights is 5, and the differential pressure of the system is 0.1 bar.

A. Gas and Water Separation A channel is etched in a hydrophobic material (PDMS), and is separated in the center by a trench, thus designing two thin sides separated by a deep area (Fig. 3). When a mix of water and gas enters the filtering part of the channel, water rushes in the trench due to the hydrophobic surface properties of the material, while gas fills the thin parts on the sides. The gaseous phase is thereafter easily removed by side channels. The system has been tested in a flow of water and air at a differential pressure of 0.1 bar. At a differential pressure higher than 2 bars, the entire channel is filled with water. It is worth noting that the absolute pressure can be up to 1500 bars. Gaseous sweeping afterwards resumes the state where the sides are free of water. The separating power and the working pressure range are given by the channel geometry and hydrophobicity of the material. The main application of this system is to maintain part of the channel free of liquid for optical analysis of gas, but this filtering is clearly also adapted to the removal of bubbles from a liquid sample as reported before with a similar structure [14]. Fig. 4 shows a decomposition of a movie taken during the flow of a water slug in the trench. The water is fluorescent and, thus, appears in white on the gray background of the channel. The width of the channel is 240 m, the ratio between deep and thin heights is 5, and the differential pressure of the system is 0.1 bar.

Fig. 6. Photographs of the filtering microsystem in operation (silicon trenches with glass cap). The thin part depth is 5 m, trenches are 100 m-deep, and inlet width is 200 m. (a) Initial state; channels are empty or filled with gas. (b) At 2 bars differential pressure, water not only exits through the deep water outlets, but also overflows the thin outlet. (c) Oil invades the system regardless of differential pressure and can exit through the thin outlet.

B. Multiple Phase Separation: Gas Water and Oil For inline phase filtering, we proposed the design illustrated in Fig. 5 to allow elimination of oil, as well as water. As in the previous design, water flows in the deep parts of the channels, leading to its separation through outlet (B) and (D) from the remaining contents of the fluid. When oil is introduced in the system, it flows in the thinner parts of the channels and, therefore, it escapes through the gas outlet (C). The operation of the phase separation system is illustrated in the pictures shown in Fig. 6. The system is empty in Fig. 6(a). Fig. 6(b) relates to a situation in which water invades the thin

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Fig. 7. (a) Principle of attenuated total reflection (ATR) optical measurement. The IR light is brought to the window and then to the detector through infrared CIR fibers, not shown here. (b) Implementation in the microfluidic phase separation system.

part due to the high pressure difference of 2 bars. Fig. 6(c) shows an oil flow in the thin part of the channel, regardless to the pressure difference. C. Optical Measurement of Optical measurement is the most suitable for gas analysis, especially in harsh environment, namely, high pressure (up to 100 bars) and high temperature (200 C). The signal is indeed carried by an optical fiber from the down hole to the surface. The measurement is achieved by evaluating the optical absorption contained in the sample. An optical of IR radiation by the window is designed for this purpose at the entrance of the gas outlet (Fig. 7). It is designed to satisfy conditions of total internal reflection. Thus, light absorption process is enhanced due to the multiple reflections at the interface between the window and fluid media. The measurement is performed by comparing the optical energy at two different wavelengths: one reference wavelength (3.95 m), which is not absorbed by any compound and one which is strongly absorbed by the presence of (4.24 m). The measurement of the ratio of the two intensities allows to get rid of any drift in the system. Fig. 8(a) shows an example from 0 to of measurement in the pressure range of pure 70 bars. The characteristic is quite linear until the discontinuity at 57 bars, corresponding to the transition of from the gas phase to a mix of gas and liquid phases. The pressure range up to 57 bars is enough for the application since the partial presin a gas field does not exceed this level, which corsure of responds to nearly 4% of typical absolute pressure. Fig. 8(b) relates to similar absorption measurements for Argon. As expected, no absorption was recorded at both wavelengths. It is noteworthy that the flatness of this response is an indication of the quality of the measurement setup. Fig. 9 shows the contrast between air and water environments, corresponding to the flow of a series of water slugs of different lengths in the channel shown in Fig. 4.Fig. 10 shows a transient response of the sensor

Fig. 8. Measurement by optical absorption at 4.24 m. A second wavelength of 3.95 m is used as a reference. (a) Measurement of pure CO revealing a nearly linear absorption in the pressure range from 0 to 70 bars. Discontinuity at 57 bars corresponds to the transition from gaseous state to liquid state. (b) Measurements of Argon. As expected, no absorption is recorded.

Fig. 9. Contrast between air and water environment.

to 2 bar pressure pulse of of 90 s duration. The ratio of the adsorbed/reference light intensity, which reflects the real-time content, is plotted along with the applied squared-shape pressure pulse. This measurement reveals the actual sensitivity of the sensor, which is better than 1 bar relative pressure. The time needed for the sensor to return to its idle state is also highlighted as being nearly 3 min, which (although this time constant depends on the number of measurement averaging) is in the same order of magnitude of other sensors [15].

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[14] C. P. Steinert, H. Sandmaier, M. Daub, B. de Heij, and R. Zengerle, “Bubble-Free priming of blind channels,” in Proc. 17th IEEE Int. Conf. Micro Electro Mechan. Syst., MEMS 2004, Maastritch, The Netherlands, Jan. 21–25, 2004, pp. 224–228. [15] S. Herber, J. Bomer, W. Olthuis, P. Bergveld, and A. van den Berg, “A micro CO gas sensor based on sensing of PH-sensitive hydrogel swelling by means of a pressure sensor,” in Proc. 13th Int. Conf. SolidState Sensors and Actuators, TRANSDUCERS’05, Seoul, Korea, Jun. 5–9, 2005, pp. 1146–1149.

Fig. 10. Transient response to a 2 bar pressure pulse of CO , revealing a time constant of nearly 3 min.

IV. CONCLUSION A microsystem was designed and fabricated for inline meain oil fields. IR light absorption was used as it surement of is the most suitable for operation in harsh environment. Separation of multiple phase mixtures of gas, water, and oil was demonstrated in a microfluidic chip, allowing reliable optical measure. Experiments were performed for the measurement ment of of pure in the 0–70 pressure range. This pressure level , when considering a is equivalent to 4% concentration of typical absolute pressure of 1500 bars in a field. The transient response revealed a time constant of nearly 3 min for the sensor. REFERENCES [1] “Statistical Review of World Energy. 2006”, ser. Historical data series. London, U.K.: British Petroleum, 2006. [2] “Annual Energy Outlook 2007 With Projections to 2030,” U.S. Dept. Energy, Energy Information Administration, Rep. DOE/EIA-0383, 2007. [3] M. Agah, G. R. Lambertus, R. Sacks, and K. D. Wise, “High speed MEMS-based chromatography,” J. Microelectromech. Syst., vol. 15, pp. 1371–1378, 2006. [4] P. R. Lewis, P. Manginell, D. R. Adkins, R. J. Kottenstette, D. R. Wheeler, S. S. Sokolowski, D. E. Trudell, J. E. Byrnes, M. Okandan, J. M. Bauer, R. G. Manley, and C. Frye-Mason, “Recent advancements in the gas-phase microchemlab,” IEEE Sensors J., vol. 6, no. 3, pp. 784–795, 2006. [5] S. A. Ecelberger, T. J. Cornish, B. F. Collins, D. L. Lewis, and W. A. Bryden, “Suitcase TOF: A man-portable time-of-flight mass spectrometer,” Johns Hopkins APL Tech. Dig., vol. 25, no. 1, pp. 14–19, 2004. [6] A. Hierlemann, Integrated Chemical Microsensor Systems in CMOSTechnology. Heidelberg, Germany: Springer-Verlag, 2005. [7] C. Hagleitner, A. Hierlemann, and H. Baltes, CMOS Single-Chip Gas Detection Systems Part I, Sensors Update, H. Baltes, J. Korvink, and G. Fedder, Eds. New York: Wiley, 2003, vol. 11, pp. 101–155. [8] C. Hagleitner, A. Hierlemann, and H. Baltes, CMOS Single-Chip Gas Detection Systems Part II, Sensors Update, H. Baltes, J. Korvink, and G. Fedder, Eds. New York: Wiley, 2003, vol. 12, pp. 51–120. [9] N. Neumann, K. Hiller, and S. Kurth, “Micromachined mid-infrared tunable Fabry-Perot filter,” in Proc. 13th Int. Conf. Solid-State Sensors and Actuators, TRANSDUCERS’05, Seoul, Korea, Jun. 5–9, 2005, pp. 1010–1013. [10] M. Noro, K. Suzuki, N. Kishi, H. Hara, T. Watanabe, and H. Iwaoka, “ CO =H O gas sensor using tunable fabry-perot filter with wide wavelength range,” in Proc. 16th IEEE Int. Conf. Micro Electro Mech. Syst., Kyoto, Jan. 2003, pp. 319–322. [11] B. Zhao, J. S. Moore, and D. J. Beebe, “Surface-directed liquid flow inside microchannels,” Science, vol. 291, no. 5506, pp. 1023–1026, 2001. [12] Bhuhan, Ed., Handbook of Nanotechnology. Berlin, Germany: Springer Verlag, 2004, ch. Surface Forces, pp. 543–603. [13] P. Tabeling and S. Chen, Introduction to Microfluidics. Oxford, U.K.: Oxford Univ. Press, 2006.

Emmanuel Tavernier was born in 1981. He received the Engineer degree from the Sup’Elec school of Electrical Engineering, Gif-sur-Yvette, France, in 2003 and the M.Sc. degree in physics from both SUPELEC and the National University of Singapore (NUS), Singapore. He is currently working towards the Ph.D. degree in collaboration at the Ecole Supérieure d’Ingénieurs en Electronique et Electrotechnique (ESIEE), Paris, France In 2004, he joined Schlumberger MEMS Group in Elancourt, France. His interests include sensor design and microtehnology.

Julien Sellier, photograph and biography not available at the time of publication.

Frédéric Marty was born in Champigny-sur-Marne, France, in 1971. He received the ESTE degree in microelectronics from the Ecole Supérieure d’Ingénieurs en Electronique et Electrotechnique (ESIEE), Paris, France. He worked for six years at various companies involved in MEMS development and manufacturing, especially in the field of pressure measurement and acceleration for aerospace and automotive applications. Since 1998, he has been with the ESIEE Group, Noisy-le-Grand, France, where he is engaged in microelectronics and microsystems, and is in charge of different industrial projects, from the design to the fabrication in a clean room. His current research interests include development of new prototypes of fluidic and pressure MEMS.

Patrick Tabeling was born on September 25, 1951. He received the Engineer degree from the Ecole Supérieure d’Electricité (ESE) School of Electrical Engineering, Paris France, in 1974, the Ph.D. degree in 1976, and the Doctorat d’état degree in 1980 from the Ecole Supérieure d’Electricité (ESE) School of Electrical Engineering. He is Research Director with the French Center of National Research (CNRS), where he leads the Microfluidics and Micro Nanotechnology Group at Ecole Supérieure de Physique et Chimie Industrielle (ESPCI). He is coauthor of more than 100 papers in peer-reviewed journals and six patents. His interests include physics of fluids, turbulence and microfluidics. Dr. Tabeling was awarded the Schlichting Prize in 1997.

Tarik Bourouina (A’00–M’02–SM’05) was born in 1967. He received the M.Sc. degree in physics from the University Houari Boumedienne, Algeria, in 1987, the Diplôme d’Etudes Approfondies in electronics from the University of Paris-Sud Orsay in 1988, the Doctorat (Ph.D. degree), from the University of Paris XII Creteil in 1991, and the Habilitation à Diriger les Recherches degree from the University of Paris-Sud Orsay in 2000. In 1988, he started research in MEMS at the Ecole Supérieure d’Ingénieurs en Electronique et Electrotechnique (ESIEE), Paris, France, where he conducted projects in the field of silicon-based acoustic microsensors, including microphones and the acoustic microgyroscope. In 1995, he joined the Université Paris-Sud-Orsay in the Institut d’Electronique Fondamentale (IEF), a joint laboratory with CNRS. From 1998 to 2001, he was at the University of Tokyo, Tokyo, Japan, as an Invited Scientist in the framework of LIMMS. He is currently a Professor at ESIEE. His research interests include optical MEMS, microactuators, mechanical microsensors, and nanostructures.