Patent Publication Number: US-10309910-B2

Title: System and method to measure salinity of multi-phase fluids

Description:
BACKGROUND 
     Embodiments of the present invention relates generally to the field of multi-phase flow metering and, more particularly, to a method and system for determining salinity in multi-phase fluids. 
     A multi-phase fluid refers to a composition that includes at least two phases of material. For example, multi-phase fluids may include some combination of oil, water, and gas. In process industries, oil and gas industries and other such areas, it is often necessary to accurately measure fractions and flow rate of phases of the multi-phase fluid flowing inside a pipeline. With smaller and deeper oil/gas wells with higher water content becoming more common around the globe, there is an enhanced need for multi-phase flow measurement techniques. 
     Commercially available sensors for measuring fractions in fluids in the petroleum industry are based on a variety of principles (either a single technique or a combination of several techniques). For example, impedance sensors, capacitive and/or inductive sensors, dual-energy gamma sensors, venturi meters, and microwave sensors (attenuation/phase/resonance) have all been used. Currently, there are numerous microwave-based flow metering sensors available offering varying degrees of sensitivity, complexity and costs. 
     Accuracy of current fraction measurement systems may be affected by the presence of saline content in the water phase of the multi-phase fluid. Presence of saline content leads to changes in the permittivity of the multi-phase fluid. If salinity is not determined accurately, changes in permittivity can be incorrectly attributed to changes in water fraction for instance. The measurements therefore need to be compensated for salinity for accurate fraction measurements. 
     Further, salinity determination helps users of the measurement facility to take control actions. Control actions pertaining to descaling of conduits are particularly dependent on measuring salinity in the multi-phase fluids flowing through the conduits. Metallic conduits may experience corrosion due to deposition of saline material on the inner surface of the conduits that is exposed to the multi-phase fluid. Hence, measuring saline content in the fluid flowing through the conduit is important. 
     Current salinity measurement systems include systems that are dependent on using phase differences observed in electromagnetic waves received at different sensing antennas. However, phase difference methodologies have been observed to provide accurate results in limited cases for multi-phase fluids with low dielectric losses (for example: oil-continuous fluids and wet gas streams). 
     Other existing systems and methods include determining reflection coefficients of reflected electromagnetic waves received from the multi-phase fluid, determining conductivity from the reflection coefficients and estimating salinity based on a conductive loss term in the permittivity associated with the fluid. Permittivity of water (∈ r w) can be expressed as follows: 
     
       
         
           
             
               
                 ɛ 
                 r 
               
               ⁡ 
               
                 ( 
                 w 
                 ) 
               
             
             = 
             
               
                 ɛ 
                 r 
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               - 
               
                 j 
                 ⁡ 
                 
                   ( 
                   
                     
                       ɛ 
                       r 
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     where, ∈′ r  corresponds to a real part of permittivity, ∈″ r  corresponds to the dielectric loss term, 
             σ     ω   ⁢           ⁢     ɛ   0             
represents the conductive loss term, where σ is the conductivity, ω is the angular frequency and ∈ 0  is the permittivity of free space.
 
     As can be seen from the equation the conductive loss term is inversely proportional to frequency and hence decreases with an increase in frequency and becomes an insignificant value at higher frequencies. On the other hand, the dielectric loss term increases with frequency until resonance is achieved and then decreases with frequency. The resonance frequency, depending on the composition of multi-phase fluids, may be in the range of tens of GHz. When the operating range are in the range where the dielectric loss term is significant, current methods that depend on determining only the conductive loss term and ignore the dielectric loss term may produce erroneous results. 
     Accordingly, there is an ongoing need for multi-phase flow metering systems and methods that determine saline content in multi-phase fluids across all frequency ranges and for multi-phase fluids that contain substantial amounts of lossy medium. 
     BRIEF DESCRIPTION 
     In accordance with one embodiment of the present invention, a method of determining salinity of a multi-phase fluid in a conduit is provided. The method includes exciting a sensing device to cause the sensing device to emit electromagnetic waves of one or more frequencies into a multi-phase fluid. The method also includes receiving at least one of transmitted or reflected electromagnetic waves from the multi-phase fluid. The method further includes determining an intermediate parameter from the transmitted or reflected electromagnetic waves. Furthermore, the method includes obtaining estimated values of a plurality of parameters. The estimated values include at least one of an estimated value of conductance, an estimated value of susceptance, an estimated value of differential conductance, an estimated value of differential susceptance, an estimated value of a real part of complex permittivity, and an estimated value of an imaginary part of complex permittivity. The method includes determining the salinity of the multi-phase fluid based, at least in part, on the estimated values of the plurality of parameters. 
     In accordance with another embodiment of the present invention, a system for determining salinity of a multi-phase fluid flowing in a conduit is provided. The system includes a sensing device placed on or about the conduit and configured to emit electromagnetic waves of one or more frequencies. Further, the system also includes a controller that is configured to excite the sensing device to emit electromagnetic waves of the one or more frequencies towards the multi-phase fluid. The controller is further configured to acquire transmitted or reflected electromagnetic waves corresponding to the one or more frequencies from the multi-phase fluid. Further, the controller is configured to obtain estimated values of a plurality of parameters from the transmitted or reflected electromagnetic waves. The estimated values of the plurality of parameters include at least one of an estimated value of conductance, an estimated value of susceptance, an estimated value of differential conductance, an estimated value of differential susceptance, an estimated value of a real part of complex permittivity, and an estimated value of an imaginary part of complex permittivity. Furthermore, the controller is configured to determine the salinity of the multi-phase fluid based, at least in part, on at least one of the plurality of parameters. 
    
    
     
       DRAWINGS 
       The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which: 
         FIG. 1  is a diagrammatical representation of a multi-phase flow measurement system using at least one sensing device; 
         FIG. 2  is diagrammatical representation of a multi-phase flow measurement system configured to determine saline content in a multi-phase fluid, according to an embodiment of the present invention; and 
         FIG. 3  is a flow chart representing a method for determination of saline content in multi-phase fluid, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     While embodiments of the present invention have been shown and described herein, such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims. 
     As will be discussed in detail below, embodiments of the invention include a method and system to detect saline content in multi-phase fluids. The term ‘multi-phase,’ as used herein, is used to refer to a composition that includes at least two phases of materials. Multi-phase fluids may include some combination of oil, water, and gas. For example, a particular sample of multi-phase fluid flowing through a conduit may include gas and water. In one example, the water may be saline water. In another example, the fluid may include gas and oil. The term ‘conduit,’ as used herein, refers to any structure that permits a flow of the multi-phase fluid. Further, the term conduit is not limited to elements that have a substantially circular cross-section, are substantially closed, or are longitudinal elements. 
     In accordance with embodiments of the invention, the determination of saline content includes emitting one or more frequencies in the microwave frequency range in the multi-phase fluid flowing through the conduit and measuring the reflected and/or transmitted signals. The term ‘microwave frequency range’ is used to refer to electromagnetic frequencies between hundreds of MHz to several hundreds of GHz. The electromagnetic waves are emitted by an antenna that is a part of a sensing device. The term ‘antenna,’ as used herein, may be used to refer to a transmitting and/or receiving element that is capable of operating at microwave frequencies. The antenna may be an open-ended coaxial probe that is configured to emit electromagnetic waves and receive transmitted or reflected electromagnetic waves from the multi-phase fluid. In another embodiment, the antenna may also include one or more metal portions over a ground plane, where the one or more metal portions and the ground plane are separated by one or more substrates. 
     In one embodiment, the antennas in the sensing devices emit electromagnetic waves over a range of frequencies and the transmitted or reflected electromagnetic waves are measured over that frequency range. The transmitted or reflected electromagnetic waves are utilized to determine a plurality of intermediate parameters. These intermediate parameters include a reflection coefficient associated with the reflected electromagnetic waves or transmission coefficient associated with the transmitted electromagnetic waves. The intermediate parameters may be utilized to determine a permittivity (dielectric constant) of the multi-phase fluid inside the conduit. The dielectric constant is a complex property including a real part and an imaginary part. Salinity in the multi-phase fluid causes changes in the dielectric properties of the fluid. These changes in the dielectric properties are utilized to measure the volume of salinity in the multi-phase fluid. Salinity changes also affect different parameters such as conductance, susceptance, and admittance. These parameters are determined from the reflection or transmission coefficients and utilized to measure the saline content in the multi-phase fluid. 
       FIG. 1  depicts a diagrammatical representation of a multi-phase flow measurement system  100  including one or more sensing devices  102 . Each sensing device  102  includes an antenna that is configured to emit electromagnetic waves in the microwave frequency range. The sensing devices  102  may be disposed on a conduit  104 . In particular, the sensing devices  102  may be placed in close proximity to a multi-phase fluid  106  flowing through the conduit  104 . The multi-phase fluid may include fractions of different phases such as oil, water, and gas. In certain embodiments, the multi-phase fluid may include one or more lossy phases. Examples of lossy phase include, but are not limited to, water and water that may have dissolved in it, different components such as salts. Salts such as Sodium Chloride, Magnesium Chloride, and the like may be present in the multi-phase fluid. Based on the fluid that has a major contribution in the multi-phase fluid, the multi-phase fluid flow state may be categorized as an oil-continuous flow state or a water-continuous flow state. In the oil-continuous flow state, the multi-phase fluid  106  has water dispersed in oil and oil constitutes the continuous medium. Whereas, in the water-continuous state, oil is dispersed in water. 
     The sensing devices  102  may be excited to emit electromagnetic waves over a range of frequencies. The range of frequencies may include a range of microwave frequencies. By way of example, the range of frequencies may range from about 300 MHz to about 300 GHz. 
     The system  100  may also include an electromagnetic frequency generation and reception (EMFGR) unit  108 . The EMFGR unit  108  may be configured to cause the one or more sensing devices  102  to emit electromagnetic waves of the desired range of frequencies. The EMFGR unit  108  may include an electronic device. In one example, the electronic device may include a vector network analyzer (VNA). Furthermore, the EMFGR unit  108  may be operatively coupled to a controller  110 . The controller  110  may be programmable logic controller (PLC) or programmable automation controller (PAC). The controller  110  may include a graphical user interface  114  and a processing unit  112  that may be configured to control the operations of the EMFGR unit  108 . In one example, the graphical user interface  114  may include a display unit. In one example, the graphical user interface  114  may be configured to display the data processed by the processing unit  112 . 
     The antennas from the sensing devices  102  and the multi-phase fluid  106  in the conduit  104  may be represented as an electrical network that has a plurality of ports. The electrical network may be represented as a two-port network and may be analyzed using S-parameters. The ports are points at which electrical signals either enter and/or exit the electrical network. The S-parameter may be represented by a unit-less complex number that represents a magnitude and an angle, such as amplitude and a phase angle of the transmitted or reflected electromagnetic waves. A two-port electrical network may be represented by the S-parameters S 11 , S 12 , S 21 , and S 22 . S 11  parameters represent amplitude and phase angle, associated with reflected electromagnetic wave at each frequency received at a first port in response to electromagnetic waves incident at the first port. Similarly, S 12  parameters represent amplitude and phase angle, associated with transmitted electromagnetic wave received at the first port in response to electromagnetic waves incident at the second port. Moreover, S 21  parameters are associated with electromagnetic waves received at the second port in response to incident electromagnetic waves emitted by the first port, while S 22  represents parameters associated with electromagnetic waves received at the second port in response to electromagnetic waves incident at the second port. 
     In the system  100 , the two ports of the electrical network may correspond to the ports of the sensing devices  102  that are coupled to the EMFGR unit  108 . The sensing devices  102  may be excited to emit electromagnetic waves of the range of frequencies via use of an incident signal generated by the EMFGR unit  108 . The incident signal is representative of a signal which is provided as an input to a port associated with one of the sensing devices  102  by the EMFGR unit  108 . The electromagnetic waves emitted by the one of the sensing devices  102  may either be transmitted to an opposite end of the conduit  104  and received by another of the sensing devices  102  or may be reflected and received by the transmitting sensing device  102 . Accordingly, transmitted and/or reflected electromagnetic waves may be acquired at one of the ports. The term ‘transmitted’ and ‘reflected’ electromagnetic waves as used herein may be used to refer to transmitted/reflected electrical signals. Such electrical signals may be measured using at least one of a voltage value, a current value, and a power value. The electronic device of the EMFGR unit  108  may be configured to measure S-parameters corresponding to the transmitted or reflected electromagnetic waves received at the ports. The controller  110  may be configured to determine the amplitude and the phase angle corresponding to the transmitted or reflected electromagnetic waves based on the S-parameters. 
     Further, the controller  110  may be employed to determine the salinity in the multi-phase fluid based on the transmission or reflection coefficients of the transmitted or reflected electromagnetic waves. The determination of salinity in the multi-phase fluid is used to compensate measurements made for phase fraction determination in the fluid. The phase-fractions may be determined by measuring a complex permittivity of the fluid and utilizing a relationship between the complex permittivity and the phase fractions of phases in the fluid. 
       FIG. 2  is diagrammatical representation of a multi-phase flow measurement system configured to determine saline content in a multi-phase fluid, according to an embodiment of the present invention. The system  200  includes a sensing device  202  that is configured to emit electromagnetic waves of a range of frequencies in the multi-phase fluid  206  flowing through the conduit  204 . The sensing device  202  includes among others an antenna  208 , an RF connector  210  and a metallic holder  212 . 
     In one embodiment, the antenna  208  is an open-ended coaxial probe that is configured to receive control signals from the RF connector  210  and emit electromagnetic waves into the multi-phase fluid. Some electromagnetic waves transmit through the multi-phase fluid  206  flowing through the conduit  204 . However, some waves are reflected back from the multi-phase fluid  206 . Fluid analysis is dependent on the transmitted or reflected electromagnetic waves. The antenna  208  is configured to receive these transmitted or reflected electromagnetic waves. The antenna  208 , according to certain other embodiments, may be a patch antenna. In other embodiments, the antenna  208  may include a monopole antenna, a dipole antenna, or a multi-pole antenna. 
     The RF connector  210  of the sensing device  202  is coupled with the antenna  208 . The RF connector  210 , in turn, may be coupled to the EMFGR unit  214 . The RF connector  210  is configured to be coupled to the EMFGR unit  214  to receive inputs from the controller  216  through the EMFGR unit  214 . Signals from the controller  216  provide instructions on the amount of power to be supplied to the antenna  208 . 
     The antenna  208  may be covered by the metallic holder  212  such that a substantial portion of the antenna  208  is covered leaving at least one surface open for direct contact with the multi-phase fluid  206  flowing through the conduit  204 . In certain other embodiments, a surface of the sensing device  202  that is placed in the conduit  202  may also include one or more protective layers. The protective layers may be configured to protect the antenna  208  from coming in direct contact with the fluid  206  while allowing for electromagnetic waves to flow into the conduit  202 . The protective layers may be made from non-conductive materials and also may include materials that are flexible in nature. 
     In operation, one or more sensing devices  202  are placed along the circumference of the conduit  204  to measure various parameters of the multi-phase fluid  206 . The EMFGR unit  214  receives an input from the controller  216  to excite one or more sensing devices  202  with appropriate amount of power so that at least one of the antennas  208  coupled to the EMFGR unit  214  emits electromagnetic waves of a range of frequencies into the multi-phase fluid  206 . Further, the sensing devices  202  are also configured to receive transmitted or reflected electromagnetic waves from the multi-phase fluid  206  in the conduit  204 . 
     The transmitted or reflected electromagnetic waves that are received by the sensing devices  202  are communicated to the controller  216  through the EMFGR unit  214 . The processing unit  218 , which may be a part of the controller  216 , is configured to determine a plurality of parameters from at least one of the transmitted and reflected electromagnetic waves. Examples of the plurality of parameters determined by the processing unit  218  include, but are not limited to, conductance (G), susceptance (B), differential conductance (ΔG), differential susceptance (ΔB), a real part of complex permittivity, and an imaginary part of complex permittivity. 
     According to one embodiment, the processing unit  218  is configured to determine an intermediate parameter related to the transmitted or reflected electromagnetic waves. Examples of intermediate parameter determined by the processing unit  218  include, but are not limited to, a complex reflection coefficient associated with the reflected electromagnetic waves, and a complex transmission coefficient associated with the transmitted electromagnetic waves. The intermediate parameter is utilized to obtain values of the plurality of parameters. According to one embodiment, when the intermediate parameter is the complex reflection coefficient, a value of admittance (Y) is determined using Equation 1: 
     
       
         
           
             
               
                 
                   
                     Y 
                     L 
                     * 
                   
                   = 
                   
                     
                       Y 
                       0 
                       * 
                     
                     ⁡ 
                     
                       ( 
                       
                         
                           1 
                           - 
                           
                             Γ 
                             * 
                           
                         
                         
                           1 
                           + 
                           
                             Γ 
                             * 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
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                   1 
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     where YL* is the admittance associated with the antenna  208 , Y 0 * is characteristic admittance, and Γ* is the complex reflection coefficient. 
     The admittance (YL*) associated with the antenna  208  may be expressed in terms of conductance (G) and susceptance (B) as shown in Equation 2:
 
 Y*   L   =G+jB   (2)
 
     The computed value of YL* is a complex number that is equated to the complex equation shown in Equation 2. The real part of the complex value of YL* is equated with the real part of Equation 2 and the imaginary part of the complex value of YL* is equated with the imaginary part of Equation 2. The values of G and B thus obtained are utilized to determine the estimated value of the real part (∈′) of complex permittivity and the estimated value of the imaginary part (∈″) of complex permittivity. 
     Further, complex admittance is also expressed in terms of real part of complex permittivity and imaginary part of complex permittivity using Equation 3:
 
 Y*   L   =ωC   f   ∈″ +G rad ∈′ 5/2 +ω( C   0 +∈′( C   f ))  (3)
 
     where, ω is the frequency of the transmitted or reflected electromagnetic waves, C 0  and Cf are calibration constants associated with the sensing device  202 , and Grad is value of conductance dependent on the frequency of the emitted electromagnetic waves. 
     Equations 2 and 3 are compared to establish a relationship between the real part (∈′) of complex permittivity and the imaginary part (∈″) of complex permittivity with conductance (G) and susceptance (B). This relationship is expressed in Equations 4 and 5.
 
 G=ωC   f   ∈″+G   rad ∈′ 5/2   (4)
 
 B =ω( C   0 +∈′( C   f ))  (5)
 
     Further, the processing unit  218  is configured to determine the salinity of the multi-phase fluid based on the values of estimated value of the real part (∈′) of complex permittivity and the estimated value of the imaginary part (∈″) of complex permittivity the multi-phase fluid. The processing unit  218 , according to one embodiment, is configured to identify one or more records from a data repository, such as the data repository  220 , corresponding to a first ratio between the estimated values of the imaginary part (∈″) of complex permittivity and the estimated values of the real part (∈′) of complex permittivity. Each record in the repository  220  corresponds to a particular value of salinity of the multi-phase fluid  206  for a particular value of the first ratio between the values of the imaginary part (∈″) of complex permittivity and the values of the real part (∈′) of complex permittivity. 
     According to one embodiment, the processing unit  218  may compute an average of salinity values from the one or more records and estimate the salinity of the multi-phase fluid  206 . Further, the processing unit  218  may also be configured to select a maximum value of salinity among the one or more records as the salinity of the multi-phase fluid  206 . 
     In another embodiment, the processing unit  218  may be configured to determine salinity of the multi-phase fluid  206  based on the estimated values of the real and imaginary parts of permittivity and computed values of real and imaginary parts of permittivity. In this embodiment, the processing unit  218  is configured to determine computed values of the real part of complex permittivity and computed values of the imaginary part of complex permittivity using a feed-forward model. The feed-forward model includes a relationship between the real and imaginary parts of complex permittivity, the one or more frequencies of the electromagnetic waves, temperature of the multi-phase fluid  206 , and salinity of the multi-phase fluid. In one embodiment, the feed-forward model comprises Stogryn model that relates permittivity, salinity and temperature of water in the multi-phase fluid. The Stogryn model is described in “Equations for calculating the dielectric constant of saline water”, IEEE Transactions on Microwave Theory and Techniques, August 1971, pp. 733-36. The processing unit  218  is configured to insert different values of salinity in the feed-forward model to determine computed values of the real and imaginary part of complex permittivity. 
     Further, the processing unit  218  is also configured to determine a second ratio between the computed value of the imaginary part of permittivity and the computed value of the real part of permittivity. The processing unit  218  is then configured to compare the second ratio and the first ratio between the estimated values of real part of complex permittivity and imaginary part of complex permittivity. Furthermore, the processing unit  218  selects that value of salinity from the different values of salinity inserted in the feed-forward model as the actual salinity value of the multi-phase fluid  206  for which the difference between the first ratio and the second ratio is less than or equal to a first threshold. In one embodiment, a minimum value of the difference between the first ratio and the second ratio is selected as the first threshold. 
     According to another embodiment, the processing unit  218  may be configured to compute the salinity values based on values of conductance (G) and susceptance (B) determined from Equations 1 and 2. The processing unit  218 , according to one embodiment, is configured to determine a third ratio between the estimated value of conductance and the estimated value of susceptance. The processing unit  218  is further configured to determine one or more records from the data repository  220  corresponding to the third ratio. The one or more records may relate values of the third ratio with the salinity value for multi-phase fluid. The processing unit  218  is further configured to determine the salinity value of the multi-phase fluid based on the one or more records. 
     Further, the processing unit  218  may also or instead be configured to determine salinity of the multi-phase fluid  206  based on a fourth ratio between the estimated values of differential conductance and the estimated values of differential susceptance. The values for differential conductance (ΔG) and differential susceptance (ΔB) may be computed by computing values of G and B for different values of complex reflection coefficient or complex transmission coefficient. The values for G and B may be computed using Equations 1 and 2. 
     In one embodiment, the processing unit  218  may be configured to estimate salinity values based on one or more records stored in the data repository  220  that correlate the values of the fourth ratio with salinity values. 
     The data repository  220  may be populated with correlation data between the first ratio and salinity, third ratio and salinity, and fourth ratio and salinity utilizing test multi-phase fluid samples with known salinity values. Values of G, B, ΔG, ΔB, ∈′, and ∈″ are estimated from the transmitted and reflected electromagnetic waves received from the test samples. The estimated values are then correlated with the known salinity values to populate the repository  220 . 
     The processing unit  218 , in certain embodiments, may comprise one or more central processing units (CPU) such as a microprocessor, or may comprise any suitable number of application specific integrated circuits working in cooperation to accomplish the functions of a CPU. The processing unit  218  may include a memory. The memory can be an electronic, a magnetic, an optical, an electromagnetic, or an infrared system, apparatus, or device. Common forms of memory include hard disks, magnetic tape, Random Access Memory (RAM), a Programmable Read Only Memory (PROM), and EEPROM, or an optical storage device such as a re-writeable CDROM or DVD, for example. The processing unit  218  is capable of executing program instructions, related to the determination of phase fractions in the multi-phase fluid, and functioning in response to those instructions or other activities that may occur in the course of or after determining phase fractions. Such program instructions will comprise a listing of executable instructions for implementing logical functions. The listing can be embodied in any computer-readable medium for use by or in connection with a computer-based system that can retrieve, process, and execute the instructions. Alternatively, some or all of the processing may be performed remotely by additional processing units  218 . The controller  216 , and more specifically the processing unit  218  in the controller  216 , may perform operations implemented in the form of models such as those that are required to determine salinity, or those required to determine permittivity values as described herein. 
     To transmit electromagnetic waves into the multi-phase fluid and to gather reflected electromagnetic waves from the multi-phase fluid, the sensing device  202  may be placed proximate to the conduit  204  in various ways. Various configurations of the sensing device  202  placement along the conduit  204  depend on a material of the conduit  204  and may include using a strap-on device to strap a plurality of sensing device  202  along an outer surface of the conduit  204 . 
     In another embodiment, the antenna in the sensing device  202  may be a patch antenna. The patch antenna may have a plurality of substrates. In certain examples, the substrates may be manufactured from flexible material such as silicone, plastic, woven natural fibers, and other suitable polymers, copolymers, and combinations thereof. The material for the substrates may be selected such that the sensing device  202  is flexible in nature while being able to sustain high pressure and temperature. 
     Further, when the antenna is a patch antenna the sensing device  202  may also include a protective dielectric layer over a surface of the antenna such that the dielectric layer acts as a barrier between the antenna and the multi-phase fluid  206 . The dielectric layer may be placed on or over the antenna or the antenna may be printed on the dielectric layer or embedded into the dielectric layer such that the antenna may be covered by the dielectric layer. The dielectric layer, according to certain embodiments, may be made from material that leads to minimum attenuation of the electromagnetic waves emitted by the antenna. Further, the dielectric layer may be made from material that is flexible in nature to allow for the layer to conform to the inner diameter of the conduit  204  when the sensing device  202  is fitted on the conduit  204 . In certain examples, the dielectric layer can be fabricated using hard materials to conform to the inner surface of the conduit. Examples of materials that can be used to make the dielectric layer include, but are not limited to, polyetheretherketone (PEEK), silicone, PTFE-coated fabric, epoxy resin, fiberglass etc. 
     In case of patch antennas, the sensing device may also include a feed element that is coupled to the RF connector  210  of the sensing device  202  on one end and is coupled with the antenna on another end. The RF connector  210  may be coupled to the EMFGR unit  214  to receive inputs from the controller  216  through the EMFGR unit  214 . Signals from the controller  216  provide instructions on the amount of power to be supplied to the antenna. 
     Patch antennas may also be arranged in different configurations such as a helical arrangement. The patch antennas may be configured to substantially surround the circumference of the conduit. In various embodiments, the shape of the patch antennas from the sensing device  202  may vary. The shape of the sensing device  202  in  FIG. 2  may be a function of the shape used for the patch antenna in the sensing device  202 . The shape of the patch antenna may form virtually any polygonal shape or combinations thereof. For example, the patch antenna may be rectangular in shape. In another example, the patch antenna may have a circular shape, a square shape, as well as an elliptical shape. 
       FIG. 3  illustrates a flow diagram of a method for determination of salinity in a multi-phase fluid. The illustrated method, according to one embodiment, can be utilized to determine salinity of the multi-phase fluid  206  flowing in the conduit  204  of  FIG. 2 . To determine salinity, a sensing device (for example: sensing device  202 ) is placed proximate to the multi-phase fluid  206 . The sensing device, as described along with  FIG. 2 , includes an antenna  204 . 
     The method includes, at step  302 , exciting the sensing device to cause the sensing device to emit electromagnetic waves of one or more frequencies into the multi-phase fluid. In one embodiment, the one or more frequencies may be in the microwave frequency range. The electromagnetic waves may be emitted into the multi-phase fluid sequentially. At step  304  a plurality of transmitted or reflected electromagnetic waves are received by the sensing device from the multi-phase fluid. A part of the emitted electromagnetic waves travel through the multi-phase fluid to a side of the conduit that is opposite to the sensing device while some parts of the emitted waves are reflected back to the side of the conduit where the sensing device is placed. The electromagnetic waves that travel through the multi-phase fluid from the emission port (for example: ports  1 ) to the opposite side of the conduit (port  2 ) are termed as transmitted electromagnetic waves. On the other hand, the electromagnetic waves that get reflected after interaction with the multi-phase and collected back by the emission port (for example: port  1 ) are termed as reflected electromagnetic waves. 
     Further, at step  306 , the transmitted or reflected electromagnetic waves are used to determine an intermediate parameter associated with the multi-phase fluid. Examples of intermediate parameter determined by the processing unit  218  include, but are not limited to, a complex reflection coefficient associated with the reflected electromagnetic waves, a complex transmission coefficient associated with the transmitted electromagnetic waves, amplitude of the reflected or transmitted electromagnetic waves, and phase angle of the reflected or transmitted electromagnetic waves. At step  308 , the intermediate parameters are utilized to obtain an estimated value of a plurality of parameters of the multi-phase fluid  206 . The estimated values of plurality of parameters include, but are not limited to, estimated value of conductance, estimated value of susceptance, estimated value of differential conductance, estimated value of differential susceptance, an estimated value of real part of complex permittivity and an estimated value of an imaginary part of complex permittivity. According to one embodiment, estimated values are determined utilizing the intermediate parameters determined from the transmitted or reflected electromagnetic waves. An example methodology to determine the estimated values involves utilizing Equations 1-5. At step  310 , a salinity value associated with the multi-phase fluid is determined based on a relationship between at least one of the plurality of parameters and the salinity value. 
     In one embodiment, the relationship between the real and imaginary parts of permittivity and salinity may be expressed in terms of one or more records in a data repository. The records in the data repository, such as the data repository  220 , may be populated by determining values of imaginary and real parts of permittivity for test fluid samples with known salinity values. 
     In another embodiment, the relationship between the real and imaginary parts of permittivity and salinity may be determined using a feed-forward model. The feed-forward model may be utilized to determine computed values of real and imaginary parts of permittivity by feeding one or more salinity values. The feed-forward model includes a relationship between permittivity, temperature, and salinity of water in the multi-phase fluid. The computed values are then compared with estimated values to determine the salinity of multi-phase fluid  206 . The salinity value for which the difference between computed values and estimated values is less than or equal to a threshold may be identified as the salinity value for the multi-phase fluid  206 . 
     According to other embodiments, the method also includes determining the estimated values of the real part of permittivity and imaginary part of permittivity from differential conductance and differential susceptance. The values for differential conductance (ΔG) and differential susceptance (ΔB) may be computed by computing values of G and B for different values of complex reflection coefficient or complex transmission coefficient. The values for G and B may be computed using Equations 1 and 2. According to some embodiments, salinity values can be determined using values of conductance and susceptance, or differential conductance and differential susceptance. The method may include determining one or more records that relate salinity values of test fluids with values of a ratio between conductance and susceptance for the test fluids. Further, the method may also include determining one or more records that relate salinity values of test fluids with values of a ratio between differential conductance and differential susceptance for the test fluids. The salinity value of the multi-phase fluid may be determined based on a comparison between the values of the ratios in the one or more records with the ratios of estimated values of conductance, susceptance, differential conductance, and differential susceptance. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of ordinary skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” etc. are used merely as labels, and are not intended to impose numerical or positional requirements on their objects. 
     This written description uses examples to disclose several embodiments of the invention, including the best mode, and also to enable any person of ordinary skill in the art to practice the embodiments of invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising,” “including,” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. 
     Since certain changes may be made in the above-described method and system for determining salinity in multi-phase fluids, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.