4D Chemical Fingerprinting Oil Well Monitoring

Abstract

A sensing system (16) for monitoring a composition of a downhole fluid (15) in an oil well (12), the sensing system (16) including a light source (41), a waveguide (21), an evanescent field sensing element (22) in indirect contact with the downhole fluid (15), and a detector (25, 43, 53, 63). The light source (41) is operable to emit a beam and includes a frequency comb generator (42) configured to modify at least a portion of the beam into a sensing comb beam. The evanescent field sensing element (22) provides an attenuated internal reflection of the sensing comb beam at an interface between the evanescent field sensing element (22) and the downhole fluid (15), and a portion of the sensing comb beam interacts with the downhole fluid (15) to form at least a portion of an interaction beam. The detector (25, 43, 53, 63) obtains a spectral distribution of the interaction beam.

Description

[Technical field]

[0001] The oil and gas industry is incorporating elements from the Fourth Industrial Revolution (4IR) into its operations, especially comprehensive data acquisition to monitor and control a given process. Four-dimensional (4D) chemical fingerprinting well monitoring allows for real-time monitoring of downhole fluid composition at specific depths in a well. [Background technology]

[0002] Monitoring the composition of the downhole fluid allows prediction of oil type, water cut, and corrosive or toxic elements such as H2S or CO2. Additional maintenance in logging operations may also be avoided. Furthermore, this allows for optimization of the downhole fluid when deployed simultaneously with inflow and injection control devices (ICDs) by mitigating water cut and corrosive or toxic elements. Summary of the Invention [Problem to be solved by the invention]

[0003] This Summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. [Means for solving the problem]

[0004] In one aspect, embodiments disclosed herein relate to a sensing system for monitoring a composition of downhole fluid in an oil well, the sensing system comprising a light source, a waveguide, an evanescent field sensing element in indirect contact with the downhole fluid, and a detector. The light source is operable to emit a beam and comprises a frequency comb generator configured to modify at least a portion of the beam into a sensing comb beam. The evanescent field sensing element provides an attenuated internal reflection of the sensing comb beam at an interface between the evanescent field sensing element and the downhole fluid, a portion of the sensing comb beam interacting with the fluid to form at least a portion of a fingerprint beam. The detector is configured to obtain a spectral distribution of the fingerprint beam.

[0005] In some embodiments, the detector of the sensing system may be a Fourier transform spectrometer.

[0006] In some embodiments, the waveguide is a hollow core optical fiber.

[0007] In some embodiments, the light source of the detection system may be an array of lasers or a broadband light source capable of emitting light at infrared, visible, or ultraviolet wavelengths.

[0008] In some embodiments, the sensing system may further comprise a first optical switch, which splits the beam into a reference beam and a sensing beam.

[0009] In some embodiments, each of the reference and sensing beams may be modified by a frequency comb generator.

[0010] In some embodiments, the detection system may further comprise a second optical switch that combines the detection beam after interacting with the downhole fluid with the reference beam to form an interaction beam having an interferogram.

[0011] In some embodiments, the detector of the sensing system may be an opto-electrical detector configured to convert the fingerprint beam into an electrical signal.

[0012] In some embodiments, the sensing system may further comprise a digitizer configured to digitize the signal from the detector for storage or transmission.

[0013] In some embodiments, the sensing system may further comprise a transmission line configured to transmit data or power optically or electrically.

[0014] In some embodiments, the evanescent field sensing element may be a crystal with total or partial internal reflection, or an optical fiber, or other waveguide configuration.

[0015] In some embodiments, the evanescent field sensing element may be a metasurface or a metamaterial.

[0016] In some embodiments, the surface of the evanescent field sensing element may be modified with a protective layer, a sensitivity enhancing layer, or a self-cleaning layer.

[0017] In some embodiments, the surface of the evanescent field sensing element may be modified with a metasurface or metamaterial.

[0018] In one aspect, embodiments disclosed herein relate to a method of chemical fingerprint well monitoring, the method including inserting a sensing system downhole to a desired depth, the sensing system comprising an evanescent field sensing element in direct contact with the downhole fluid and providing partial or total internal reflection of a beam interacting with the downhole fluid at an interface between the evanescent field sensing element and the downhole fluid, detecting a spectral distribution of the interacting beam to monitor a composition of the downhole fluid in real time, and controlling an actuator with an inflow and injection control device (ICD) based on the composition of the downhole fluid.

[0019] In some embodiments, the method may further include analyzing the spectral distribution of the interaction beam using a Fourier transform.

[0020] Other aspects and advantages of the claimed subject matter will become apparent from the following description and the appended claims. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 illustrates an oil well with a detection system according to an embodiment of the present disclosure. [Figure 2A] FIG. 1 illustrates a scheme of a detection system according to an embodiment of the present disclosure. [Figure 2B] FIG. 2 illustrates another scheme of a detection system according to an embodiment of the present disclosure. [Figure 2C] FIG. 2 illustrates another scheme of a detection system according to an embodiment of the present disclosure. [Figure 3A] FIG. 1 illustrates an arrangement of evanescent field sensing elements according to an embodiment of the present disclosure. [Figure 3B] FIG. 13 is another diagram illustrating an arrangement of evanescent field sensing elements according to an embodiment of the present disclosure. [Figure 4] FIG. 1 illustrates a sensing system according to an embodiment of the present disclosure used in conjunction with at least one frequency comb. [Diagram 5] FIG. 1 illustrates a sensing system according to an embodiment of the present disclosure used in conjunction with at least one frequency comb and a Fourier transform spectrometer (FTS). [Figure 6] FIG. 1 illustrates a sensing system according to an embodiment of the present disclosure used in a dual comb configuration. [Figure 7] FIG. 1 illustrates a method for chemical fingerprint well monitoring according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Certain embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings, in which like elements in the various figures are designated with like reference numerals for consistency.

[0023] In the following detailed description of the embodiments of the present disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that the present disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0024] Throughout this application, ordinal numbers (e.g., first, second, third, etc.) may be used as adjectives of elements (i.e., any noun in this application). The use of ordinal numbers does not imply or create a particular order of elements, nor does it limit any element to only a single element, unless expressly disclosed, such as by using the terms "before," "after," "single," and other such terms. Rather, the use of ordinal numbers is to distinguish elements. As an example, a first element is different from a second element, and a first element may encompass two or more elements and follow (or precede) the second element in the order of elements.

[0025] The embodiments disclosed herein generally relate to a four-dimensional (4D) chemical fingerprinting well monitoring system and method using a frequency comb, a Fourier transform spectrometer, and an evanescent field sensor. For example, the monitoring system may utilize dual comb spectroscopy (DCS), Fourier transform infrared spectroscopy (FTIR), attenuated total reflectance (ATR), or any combination thereof, for real-time depth monitoring of downhole fluids. Real-time depth monitoring of downhole fluid composition, including the presence of compounds (e.g., H2S and CO2) that affect produced oil, water cut, and corrosion, allows optimization of drilling parameters for maximum production and minimum maintenance.

[0026] The embodiments disclosed herein relate to a system and method based on downhole deployment of evanescent field sensing elements for analyzing the chemical fingerprint of downhole fluids in real time. The evanescent field sensing element is in direct contact with the downhole fluid. The optical signal (i.e., beam) may be partially or totally reflected inside the evanescent field sensing element. At the interface between the evanescent field sensing element and the downhole fluid, the evanescent field interacts directly with the downhole fluid, causing a change in the energy distribution (i.e., intensity) of the electromagnetic field (i.e., sensing beam) and generating an absorption spectrum. Chemical characterization of the downhole fluid is performed by applying a Fourier Transform Spectrometer (FTS) to the absorption fingerprint present in the spectrum.

[0027] The embodiments disclosed herein generally relate to utilizing optical frequency combs (OFCs) to improve selectivity and sensitivity while ensuring thermal and mechanical stability. OFCs provide simultaneously recorded well resolved absorption and dispersion spectra, providing sensitive detection of multiple chemical species over a wide spectral window. OFCs can be utilized over a wide range of frequencies, ranging from the terahertz to the UV region. Its high spatial coherence allows for longer interrogation paths, higher sensitivity, high frequency resolution, and high accuracy. The aforementioned advantages can enable dynamic and real-time sensing with fast spectrum and data acquisition, as well as immediate feedback to controllers for optimization of oil production.

[0028] FIG. 1 shows a scheme of a derrick 11 and an oil well 12. There is at least one piping 13 that is partially inside the well with at least one sensing system 16. The derrick includes a power module that provides power for sensing and communication. The well may include at least one packer 14. The packer separates the well into individual zones and allows selective access and control. At least one sensing system is embedded inside the piping and distributed along the well to obtain a chemical fingerprint of the downhole fluid 15 in real time.

[0029] In some embodiments, multiple sensing systems may be embedded inside one pipe to allow real-time monitoring at different locations. In some embodiments, multiple pipes may be placed inside an oil well. In such a configuration, the number of pipes is limited by the diameter of the well.

[0030] Tubing according to embodiments of the present disclosure may include an actuator controlled by an inflow and infusion control device (ICD) that restricts flow. The ICD may be an electrical actuator, a fluidic actuator, a mechanical actuator, etc. The ICD may be disposed along the tubing.

[0031] In some embodiments, at least a portion of the piping is above ground inside the derrick. The sensing system in the piping may include a light source configured to generate single or multiple frequency optical signals, or a detector (e.g., a spectrometer), or a communication device, or any combination thereof. The light source, detector, and communication device may be located above ground or below ground. The communication device receives real-time chemical fingerprint monitoring results from the spectrometer and provides feedback information to the ICD for immediate operational decisions based on the composition of produced oil in the well.

[0032] In some embodiments, the sensing system includes data and / or power lines connected to a power module in the derrick. The data and / or power lines transmit optical and / or electrical signals and / or provide power to the sensing system. The data and / or power lines can be optical (e.g., waveguide, fiber optic, etc.), electrical, or both.

[0033] The sensing system of Figure 1 includes at least one waveguide 21 configured to transmit an optical signal, at least one evanescent field sensing element 22, and a cladding 23. The evanescent field sensing element, surrounded by the cladding, is connected to the waveguide on both sides.

[0034] The waveguide may be an optical fiber or any other material with an increased refractive index for guiding an optical signal. For example, the waveguide may be a hollow optical fiber (e.g., hollow silica or sapphire tube) or a few-mode fiber filled with a gas (e.g., air, nitrogen, or helium). Alternatively, the waveguide may be a glass fiber (e.g., chalcogenide, fluoride), a (poly)crystal fiber (e.g., silver halide, sapphire), or a solid waveguide (e.g., thin-film planar GaAs / AlGaAs). In some embodiments, the sensing system may include multiple waveguides 21, each with multiple evanescent field sensing elements distributed along the waveguide. In such a configuration, the number of waveguides is limited by the outer diameter of the well.

[0035] The evanescent field sensing element provides total internal reflection of the beam and is in direct contact with the downhole fluid. The interaction between the evanescent field of the beam and the downhole fluid results in a spectral fingerprint of the downhole fluid. In other words, the interaction modifies the intensity and spectral distribution of the beam.

[0036] According to one or more embodiments of the present application, FIG. 2A, FIG. 2B, and FIG. 2C show a scheme of a portion of the detection system showing the placement of the evanescent field sensing element. In some embodiments, the beam is directly directed from the light source to the evanescent field sensing element for reaction at the interface. Alternatively, the beam may be split into a detection beam and a reference beam that pass through an optical switch 24 or a beam splitter and are directed to the evanescent field sensing element 22 for reaction. The length (or exposed area) of the evanescent field sensing element, in other words the contact area between the evanescent field sensing element and the downhole fluid, may affect the sensitivity of the detection system. The interaction beam may be monitored in situ by a detector 25 and the monitoring results may be transmitted to an ICD. Alternatively, the interaction beam may be reflected and optically transmitted to a detector for analysis. In some embodiments, another optical switch may be used to recombine the reaction beam and the reference beam. Data and / or power lines 26 may be used for transmission of power and / or beams before or after the interaction. More specifically, hollow optical fibers 28 may be used. In some embodiments, at least one actuator 27 may be controlled by the ICD and used to restrict flow.

[0037] In some embodiments, the beam directed to the evanescent field sensing element is a near-infrared (NIR) optical signal generated from a NIR light source. Alternatively, the beam may be ultraviolet (UV) or visible light. Alternatively, the frequency of the beam may span the entire electromagnetic spectrum from X-ray to radio frequency (RF). The light source according to the embodiments of the present disclosure may be a single band or a broadband light source. The broadband light source may be pulsed or continuous, including but not limited to lasers, light emitting diodes (LEDs), superluminescent diodes (SLEDs), blackbody radiators, plasma sources. The light source may be coupled with an electromagnetic wavelength selector, such as a dispersive, dichroic, or bandpass optical or electro-optical element, to select single or multiple frequencies.

[0038] When a coherent laser source is used, a frequency comb generator (e.g., a resonator with a resonant cavity) may be incorporated to generate a beam with a frequency comb. In some embodiments, the beam with the frequency comb beam is directed to the evanescent field sensing element and serves as a sensing beam. In some embodiments, the sensing system may include an optical switch, a digital micromirror, a filter, a polarizer, or a beam splitter to split the beam generated from the light source and couple only a portion of the beam to the evanescent field sensing element as a sensing beam. The other portion of the beam that is not directed to the evanescent field sensing element serves as a reference beam. In some embodiments, both the sensing beam and the reference beam may be coupled to the resonator to generate the frequency comb.

[0039] The sensing system according to the embodiments of the present disclosure generally relates to ATR, which utilizes total internal reflection and the resulting evanescent wave. When a beam (e.g., an IR beam) travels from a medium with a high refractive index (i.e., the evanescent field sensing element) to a medium with a low refractive index (e.g., the sample and the surrounding medium) at an angle of incidence, at least a portion of the light is reflected back to the low refractive index medium. If the angle of incidence is greater than a certain angle, almost all of the light is reflected back. When the beam passes through the evanescent field sensing element, the beam is reflected at least once from the internal surface at the interface with the sample. As a result of the internal reflection, a portion of the electromagnetic radiation from the beam propagating along the surface penetrates into the sample. The penetration depth into the sample is typically within a micrometer, and the exact value is determined by the wavelength of the light, the angle of incidence, the refractive index of the evanescent field sensing element, and the medium being probed. The number of reflections may be varied by changing the angle of incidence or the size of the evanescent field sensing element. At each location where an internal reflection occurs, the evanescent wave penetrates into the adjacent environment with a decaying amplitude and interacts with the sample at the interface. The beam may then exit the evanescent field sensing element and be collected by a detector. The interaction beam may be conditioned or filtered for in situ analysis or may be directed to the ground. For example, the interaction beam may be coupled back into a transmission or telemetry fiber using a 2x1 coupler or another optical switch. Alternatively, the post-interaction sensing beam may be captured by a detector buried in the underground portion of the sensing system.

[0040] The evanescent field sensing element of the embodiments of the present disclosure may be a few-mode or multimode optical fiber, or a crystal with total or partial internal reflection made of SiO2, F:SiO2, sapphire, or other material required for the application. The crystal used as the evanescent field sensing element may also be germanium (Ge), zinc selenide (ZnSe), zinc sulfide (ZnS), thallium bromide (e.g., KRS-5), or silicon (Si). The excellent mechanical properties of diamond make it an ideal material for the evanescent field sensing element, with a wavelength range of 2600-1900 cm.-1 The broad diamond phonon band at 1000 nm significantly reduces the signal-to-noise ratio in this region. The shape of the evanescent field sensing element depends on the type of spectrometer and the nature of the sample. For example, when used with a dispersive spectrometer, the evanescent field sensing element may have the shape of a rectangular slab with chamfered edges. Other geometric shapes may be prisms, trapezoids, rods, hemispheres, or thin films. Other waveguide configurations may be used, including but not limited to glass fibers (e.g., chalcogenides, fluorides), (poly)crystalline fibers (e.g., silver halide, sapphire), hollow waveguides (e.g., hollow silica or sapphire tubes), and solid waveguides (e.g., thin-film planar GaAs / AlGaAs).

[0041] In some embodiments, metamaterials or metasurfaces may be used as evanescent field sensing element materials. The metamaterials or metasurfaces disclosed herein may include materials with zero or near-zero refractive index, negative refractive index, plasmonic properties, Fano resonances, photonic band gaps, or phononic band gaps. The metamaterials or metasurfaces may also be photodiodes, photonic crystals, tunable metamaterials. The metamaterials or metasurfaces may be Moiré hyperbolic, bianisotropic, bianisotropic, 2D chiral, 3D chiral, or superlattices. The metamaterials or metasurfaces may be patterned or fabricated using metals (e.g., gold, silver, platinum, rhodium), 2D materials (e.g., graphene, hexagonal boron nitride, metal dichalcogenides, phosphorene, maxine), or metal-organic frameworks. In some embodiments, the metamaterials and metasurfaces may be coated on the evanescent field sensing element or the waveguide. Alternatively, the frequency comb generator may also be coated with metamaterials and metasurfaces to enhance and / or tune its optical performance. Metamaterials and metasurfaces may be patterned by a variety of methods, including but not limited to laser ablation, plasma etching, chemical etching, and lithography, or deposition may be performed by sputtering, pulsed laser deposition, pulsed plasma deposition, atomic layer deposition, atomic layer etching, electroplating, electron beam evaporation, chemical vapor deposition, surface solution, or slurry coating.

[0042] When metamaterials and metasurfaces are used as evanescent field sensing elements, they may generate linear or planar distribution evanescent waves instead of point distribution. For example, Figures 3A and 3B show the arrangement of evanescent field sensing elements according to embodiments of the present disclosure. Other types of evanescent field sensing elements may generate discrete evanescent fields 31 at each location where total internal reflection occurs, while the continuous evanescent field 32 from metamaterials and metasurfaces is uniformly distributed at the interface between the evanescent field sensing element 22 and the downhole fluid 15. Thus, metamaterials and metasurfaces enable improved conversion of electromagnetic waves into evanescent waves, as well as improved sensitivity and responsiveness of the interaction between the downhole fluid and the evanescent field sensing element.

[0043] In some embodiments, a modification layer may be coated, added, or patterned to modify the surface of the evanescent field sensing element or waveguide. The modification layer may be a protection layer, a sensitivity enhancement layer, a self-cleaning layer, or a combination thereof. The modification layer may be made of polymers, ceramics, oxides, diamond, metals, metamaterials, or other materials as required by their function. The sensitivity enhancement layer may be a thin film that modifies the propagation of the evanescent wave and improves the sensing capability by providing a continuous evanescent wave along the waveguide surface, and may avoid the generation of discrete evanescent waves. The thickness of the modification layer may be adjusted as required. The self-cleaning layer may be coated to improve the stability and durability of the evanescent field sensing element or waveguide. Measurements in extreme conditions, such as in oil producing wells, require a robust sensing system for sampling and analysis. Surfaces treated with the self-cleaning material are configured to repel water and oil, or be switchable between hydrophobic and oleophobic, and be omniphobic or superomniphobic to minimize damage from hazardous and extreme environments.

[0044] An embodiment of the present disclosure may include a detector. The detector may be a dispersive spectrometer that allows detection at different wavelengths. A dispersive spectrometer may be coupled with a virtual imaging phased array (VIPA) to achieve time resolution in microseconds, allowing dynamic and real-time monitoring of chemical fingerprints. Alternatively, if a laser is used, a single detector without a dispersive element may be sufficient. The detector may also be a cooled (solid-state) or uncooled photodiode or photoelectric sensor. The type of detector depends mainly on the range of wavelengths to be measured. For example, silicon-based charge-coupled devices (CCDs) are suitable for the shorter end of the UV, visible, and IR ranges. For detection at longer wavelengths, IR detectors may be used. IR detectors include optical detectors (photon detectors) that have sensitivity in the relatively long wavelength region, and thermal detectors that are based on sensing small temperature changes caused by the absorption of IR light. At longer wavelengths, semiconductor materials with lower band gap energy are required, so that photons with lower energy are sufficient to generate carriers that contribute to some photocurrent. Indium gallium arsenide (InGaAs) detectors are suitable for wavelengths up to about 1.7 μm. Similarly, germanium (Ge) photodiodes can be used from about 0.9 μm to 1.6 μm. For longer wavelengths beyond 5 μm, indium antimonide (InSb) photodiodes are suitable. IR detectors may be mercury cadmium telluride (MCT) detectors, quantum dot infrared photodetectors (QDIPs), or quantum well infrared photodetectors (QWIPs) based on GaAs / AlGaAs. Thermal IR detectors may include pyroelectric detectors based on ferroelectric materials such as lithium tantalate, or bolometers that include thin IR absorbing plates made of amorphous silicon or vanadium oxide. Alternatively, detectors that upconvert crystals or nanoparticles such as lithium niobate can be used as sensors with lower temperature noise sensitivity.

[0045] As mentioned above, the pulsed laser source may incorporate a frequency comb generator to obtain a beam with a frequency comb. The frequency comb allows real-time monitoring of the produced oil composition, as well as water cut and corrosive or toxic elements, with high speed and sensitivity. Figure 4 shows a sensing system according to an embodiment of the present disclosure used with at least one frequency comb.

[0046] A coherent light source such as a frequency comb allows for higher brightness, increased signal-to-noise ratio, and shorter measurement time. In some embodiments, the beam generated from the light source 41 may be coupled to at least one frequency comb generator 42 (e.g., a resonator) to generate a frequency comb. The spectrum of the frequency comb beam has a series of discrete, equally spaced frequency lines, and the intensity of the comb lines can vary substantially. A frequency comb beam can be generated by periodic modulation (amplitude and / or phase) of a continuous wave laser, four-wave mixing in a nonlinear medium, or stabilization of a pulse train generated by a mode-locked laser. For example, a nonlinear optical resonator with a resonant cavity can be used in conjunction with a pulsed laser source to generate a frequency comb. The nonlinear optical resonator can nonlinearly convert light from a continuous laser with a single frequency into comb light with multiple frequencies.

[0047] The frequency comb beam is directed to the evanescent field sensing element 22 for interaction with the downhole fluid. The interaction beam is then captured by a dispersive spectrometer 43, which allows detection at different wavelengths. The dispersive spectrometer can be coupled with a virtual imaging phased array (VIPA) to achieve time resolution in microseconds, allowing dynamic and real-time monitoring of chemical fingerprints.

[0048] In some embodiments, a Fourier transform spectrometer (FTS) may be utilized as a detector. The optical spectrum with the chemical fingerprint is the Fourier transform of the interferogram in the time domain interference waveform. A laser array or a broadband light source that can be rapidly switched through different lengths of fiber may provide the time delay required to capture the time domain interferogram of the FTS. For example, FIG. 5 shows a detection system based on a frequency comb combined with a Fourier transform spectrometer. A beam generated from a light source 41 may be coupled to at least one frequency comb generator (e.g., resonator) 42 to generate a frequency comb. The frequency comb beam, which contains light at many frequencies at once, is directed to an evanescent field sensing element 22 to interact with the downhole fluid at the interface. The beam is modified by the interaction at the interface due to absorption by the downhole fluid, exhibiting a chemical fingerprint for real-time monitoring. This process is repeated many times rapidly over a short time span. The interacting beam is then directed to an FTS 53 with multiple mirrors on a movable arm 54 for analysis.

[0049] FTS is a measurement technique that uses time- or spatial-domain measurements of electromagnetic or other types of radiation to obtain a spectrum (transmittance, reflectance, or absorbance) based on a measurement of the coherence of the radiation source. The Fourier transform is applied to convert the raw data into an actual spectrum, often applied to optical systems including interferometers. For example, FTS may use an interferometer to generate a broadband interferogram in the time domain whose Fourier transform is the optical spectrum. FTS may be applied to a variety of spectroscopic techniques including optical spectroscopy, infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), magnetic resonance spectroscopic imaging (MRSI), mass spectrometry, and electron spin resonance spectroscopy.

[0050] In some embodiments, the FTS includes a scanning Michelson interferometer that measures the interference between the two time-delayed signals from the two arms as a function of the optical path difference on a single photodetector. The beams used herein can be generated by starting with a broadband light source that includes the entire spectrum of wavelengths to be measured. The time-domain interferogram can be obtained by a scanning Michelson interferometer with mirrors on a movable arm. The interacting beam is incident on a Michelson interferometer that includes a specific configuration of mirrors, at least one of which is moved by a motor. As this mirror moves, each wavelength of light in the beam is periodically blocked, transmitted, blocked, and transmitted by the interferometer due to wave interference. Different wavelengths are modulated at different rates, so that at each instant or mirror position, the beams emerging from the interferometer have different spectra.

[0051] According to an embodiment of the present disclosure, FTIR is combined with ATR for detection and analysis in the IR spectral range, with advantages over conventional IR spectroscopy. FTIR may also be combined with ATR in other spectral ranges. For example, when ultraviolet (UV) or visible light is used, the evanescent light path is short enough that the interaction between the evanescent wave and the sample decreases with wavelength. For optically dense samples, this may allow measurements in the UV range.

[0052] In some embodiments, the digitizer 55, in addition to digitizing the signal obtained from the detector, may be used for storage or transmission to the surface via data and / or power lines. The data and / or power lines may be electrical, optical, or a combination thereof. Optionally, data processing may be performed downhole electronically or optically and stored in situ using a storage unit.

[0053] In some embodiments, the detection system may include two or more frequency combs for the measurement, i.e., dual comb spectroscopy (DCS). DCS is a two-comb approach that does not require moving arms. For example, as shown in FIG. 6, the beam generated from the light source 41 is split into a reference beam and a detection beam by an optical switch 62 (or a beam splitter). Each of the reference beam and the detection beam is modified by a resonator 42 (e.g., a Kerr frequency comb microresonator) to generate a reference comb beam and a detection comb beam. The detection comb beam is directed to the evanescent field sensing element 22 for interaction with the downhole fluid. The interaction modifies the intensity and spectral distribution of the detection comb beam, causing a slightly different repetition frequency. The reference comb beam and the interacted detection comb beam are subsequently recombined using a recombiner 64 (e.g., another optical switch) to generate a recombined beam having an interferogram spectrum that interferes with both the detection comb beam and the reference comb beam. The recombined beam is recorded as a function of time and Fourier transformed to reveal the spectrum. This may be analyzed in situ by detector 63 or may be coupled back to a telemetry or feed fiber for analysis on land. In both cases, the line spacing of the interferogram spectrum is converted into a radio frequency (RF) signal having a signature reflecting the chemical fingerprint of the downhole fluid. The information, including the fingerprint, is then fed back to the ICD for control and optimization.

[0054] In some embodiments, after interaction, the detection comb beam may be converted to an electrical signal for analysis via an opto-electric detector or an array thereof (e.g., thermopile, photodetector, pyroelectric detector, electrocalorimetric detector, microbolometer, diode, pyrometer, or radiometer). A digitizer 55 may be used to digitize the signal obtained from the detector as well as for storage or transmission to the surface via data and / or power lines. The data and / or power lines may be electrical, optical, or a combination thereof. Optionally, data processing may be performed downhole electronically or optically and stored in situ using a storage unit.

[0055] The sensing system according to an embodiment of the present disclosure may include a communication device that receives real-time chemical fingerprint monitoring results from the detector and may provide feedback information to the ICD for immediate operational decisions based on the composition of the produced oil in the well. According to an embodiment of the present disclosure, a method of chemical fingerprint well monitoring is shown in FIG. 7. In step 701, the sensing system is inserted downhole to a desired depth. At least one beam is directed to an evanescent field sensing element using a waveguide. The beam may be generated from a light source located on the surface or underground and may optionally pass through an optical switch, a frequency comb generator, or both. Multiple beams used for either reference or sensing may be used. The beam interacts with the downhole fluid with an evanescent field generated at the interface between the evanescent field sensing element and the downhole fluid. Step 702 includes detecting a spectrum of the downhole fluid. The interacting beam is directed to a detector, either in situ or on the surface, to capture the chemical fingerprint in real time. In step 703, the obtained data (e.g., spectra) is analyzed to determine the composition of the downhole fluid, including oil type, water cut, gas, and corrosive and toxic chemicals. In step 704, the communication device transmits the monitoring results to the ICD, which controls the operation to optimize the produced downhole fluid. In step 705, the composition or composition change of the produced downhole fluid is monitored in real time. A determination of whether the expected composition is achieved is achieved in step 706 based on the monitoring results. If so, a report of the chemical composition of the operating segment may be generated. If not, real-time monitoring may continue by cycling back to step 702.

[0056] While the present disclosure has been described with respect to a limited number of embodiments, it will be appreciated that those skilled in the art having the benefit of this disclosure may devise other embodiments that do not depart from the scope of the present disclosure as disclosed herein. Accordingly, the scope of the present disclosure should be limited only by the scope of the appended claims. [Explanation of symbols]

[0057] 11. Derrick 12 Oil well 13 Piping 14 Pakka 15 Downhole Fluids 16 Detection Systems 21 Waveguide 22 Evanescent field sensing element 23 Clad 24 Optical Switch 25 Detector 26 Data and / or power lines 27 Actuator 28 Hollow Optical Fiber 31 Discrete evanescent fields 32 Continuous evanescent field 41 Light source 42 Frequency Comb Generator 43 Dispersive Spectrometer 53 Fourier transform spectrometer 54 Mirror on a movable arm 55 Digitizer 62 Optical Switch 63 Detector 64 Recombiner

Claims

1. 1. A sensing system (16) for monitoring a composition of a downhole fluid (15) in an oil well (12), said sensing system (16) comprising: at least one light source (41) having at least one frequency comb generator (42) emitting a beam; a first optical switch configured to split said beam into a reference beam and a sensing beam; a waveguide (21), an evanescent field sensing element (22) in direct contact with said downhole fluid (15), the frequency comb generator (42) configured to modify the reference beam into a reference comb beam and modify the detection beam into a detection comb beam; the evanescent field sensing element (22) is configured to provide an attenuated internal reflection of the sensing comb beam at an interface between the evanescent field sensing element (22) and the downhole fluid (15); an evanescent field sensing element (22) where the sensing comb beam interacts with the downhole fluid (15) to form at least a portion of an interaction beam; a second optical switch that combines the sensing beam after interaction with the downhole fluid with the reference comb beam to form the interaction beam having an interferogram, the downhole fluid is disposed between the first optical switch and the second optical switch; The sensing comb beam interacts with the downhole fluid at the evanescent field sensing element, and the reference comb beam bypasses the downhole fluid. A second optical switch; a detector (25, 43, 53, 63) configured to obtain the spectral distribution of said interaction beam; A detection system comprising:

2. The sensing system of claim 1 , wherein the detector is a Fourier transform spectrometer (53).

3. 3. The sensing system according to claim 1 or 2, wherein the waveguide (21) is a hollow optical fiber.

4. 4. The detection system of claim 1, wherein the light source (41) is an array of lasers or a broadband light source capable of emitting light at infrared, visible or ultraviolet wavelengths.

5. 2. The detection system of claim 1, wherein the detector (25, 63) is an opto-electrical detector configured to convert the interaction beam into an electrical signal.

6. The sensing system of claim 1 , further comprising a digitizer (55) configured to digitize a signal from the detector (63) for storage or transmission.

7. The sensing system of any one of claims 1 to 6, further comprising a transmission line (26) configured to transmit data or power optically or electrically.

8. 8. The sensing system of claim 1, wherein the evanescent field sensing element (22) is at least one of a crystal with total or partial internal reflection, an optical fiber, a waveguide, a metasurface, a metamaterial, or a combination thereof.

9. The sensing system of claim 1 , wherein a surface of the evanescent field sensing element (22) is modified with at least one of a protective layer, a sensitivity enhancing layer, a self-cleaning layer, or a combination thereof.

10. 10. The sensing system of claim 1, wherein a surface of the evanescent field sensing element (22) is modified with at least one of a crystal, an optical fiber, a waveguide, a metasurface, a metamaterial, or a combination thereof having total or partial internal reflection.

11. A cable comprising a plurality of sensing systems according to any one of claims 1 to 10.

12. 1. A method for oil well monitoring, the method comprising: inserting a sensing system (16) downhole to a desired depth, said sensing system (16) comprising an evanescent field sensing element (22) in direct contact with a downhole fluid (15) and providing partial or total internal reflection of a beam interacting with the downhole fluid (15) at an interface between said evanescent field sensing element (22) and said downhole fluid (15); The detection system comprises: at least one light source having at least one frequency comb generator emitting a beam, a first optical switch configured to split said beam into a reference beam and a sensing beam; - a waveguide, Equipped with the frequency comb generator configured to modify the reference beam into a reference comb beam and modify the detection beam into a detection comb beam; the sensing comb beam interacting with the downhole fluid to form at least a portion of an interaction beam; a second optical switch that combines the sensing beam after interaction with the downhole fluid with the reference comb beam to form the interaction beam having an interferogram, the downhole fluid is disposed between the first optical switch and the second optical switch; The sensing comb beam interacts with the downhole fluid at the evanescent field sensing element, and the reference comb beam bypasses the downhole fluid. A second optical switch; a detector configured to obtain a spectral distribution of said interaction beam; A detection system comprising: detecting a spectral distribution of the interaction beam with the detector to monitor the composition of the downhole fluid (15) in real time; controlling an actuator (27) with an inflow and injection control device (ICD) based on the composition of the downhole fluid (15); A method comprising:

13. The method of claim 12 further comprising analyzing the spectral distribution of the interaction beam using a Fourier transform.

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