Tunable laser spectral measurement of C13 ethane

Abstract

An apparatus for isotope ethane measurement of a gas sample includes: a tunable infrared laser configured to emit an infrared laser beam; an infrared sensor configured to receive the infrared laser beam; a gas chamber disposed in a path between the tunable infrared laser and the infrared sensor such that the infrared laser beam passes through the gas chamber, the gas chamber configured to receive the gas sample; and a controller configured to evaluate the received infrared laser beam to estimate a ratio of C13 ethane to C12 ethane in the gas sample.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to European patent application No. EP22305942.9, filed on June 29, 2022, and incorporated herein by reference in its entirety. Background Art

[0003] Formation gas composition is often measured when drilling oil and gas wells to enable geologists to characterize reservoir fluid composition while drilling. In situ gas chromatography (GC) is often combined with a flame ionization detector (FID) to make such measurements. While GC and FID sensors can provide accurate measurements, they are not well suited for continuous gas monitoring due to the long GC cycle times (e.g., about 5 minutes).

[0004] There is currently no known method suitable for in situ measurement of isotopic ethane ratios. U.S. Patent 8,810,794 discloses a cavity enhanced spectroscopy method for measuring the isotopic ratio of methane (C1) in the near infrared spectral region. However, the disclosed method is not suitable for measuring heavier hydrocarbons, such as ethane (C2) and propane (C3), which are used for geochemical evaluation in the oil and gas exploration industry.

[0005] The common method used in laboratory environment to measure C1 to C3 isotope ratio is based on the separation and measurement of these hydrocarbons, using gas chromatograph (GC), high temperature combustion furnace and isotope ratio mass spectrometry (GC-IRMS). For commercial GC-IRMS technology, chromatographic analysis is often performed using a general-purpose gas chromatograph, which is not optimized for online real-time measurement. In addition, the combustion furnace is easily damaged and leaks easily at high operating temperatures (about 900 ° C).

[0006] This traditional laboratory method is not suitable for field deployment due to its complexity, low reliability and high cost. Long GC cycle times (about 5 minutes) further limit continuous gas measurements at the well site, while the industry's goal is to achieve the best possible vertical logging resolution. The industry needs to make rapid measurements (e.g., intervals of less than 1 minute) of the isotope ratios of naturally occurring ethane. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] For a more complete understanding of the disclosed subject matter and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0008] Figure 1 An example drilling rig including an apparatus for measuring the isotopic ratio of naturally occurring ethane gas is depicted.

[0009] Figure 2 An example isotope ratio measurement apparatus is depicted.

[0010] Figure 3 Another example isotope ratio measurement apparatus is depicted.

[0011] Figure 4 Yet another example isotope ratio measurement apparatus is depicted.

[0012] Figure 5 A flow chart depicting an example method for estimating the isotopic ratio of naturally occurring ethane.

[0013] Figure 6 Depicted is a flow chart of another example method for estimating the isotopic ratio of naturally occurring ethane.

[0014] Fig. 7A and Figure 7B (collectively, FIG. 7 ) depicts absorbance as a function of wavelength calculated and linearized using a 2.54 cm long germanium etalon with a free spectral range (FSR) of 1.44 GHz ( 7A ) and a calibration model ( 7B ) for converting spectral channels (or data points) to corresponding wavenumbers.

[0015] Fig. 8A and Figure 8B (collectively, FIG8 ) depicts theoretical ( 8A ) and experimental ( 8B ) methane absorption spectra.

[0016] Fig.9A and Fig. 9B (collectively, FIG. 9 ) depicts C13 ethane spectral line identification ( 9A ) and detection limit estimation ( 9B ).

[0017] Fig.10 The wave numbers are about 2986 to about 2987 cm -1 The C13 ethane spectrum (solid line) and the standard C12 ethane (dashed line) spectrum at .

[0018] Fig.11A and Fig. 11B (collectively, FIG. 11 ) depict peak ratio plots at high ( 11A ) and low ( 11B ) ethane gas concentrations.

[0019] Fig. 12A and Fig. 12B (collectively referred to as Figure 12) depicts Fig.11A and Fig. 11B Allen-Waller deviation analysis of ethane isotope ratios for the indicated gas compositions.

[0020] Fig.13 Depicted are C12 and C13 ethane spectra obtained by high resolution FTIR at low pressure (10 mbar) with C12 ethane as a dashed line, C13 ethane as a solid line and ambient air as a dotted line.

[0021] Fig.14 A Pacific Northwest National Laboratory (PNNL) Fourier transform infrared (FTIR) spectrum depicting light hydrocarbons.

[0022] Fig.15A and Fig. 15B (collectively referred to as FIG. 15 ) depicts the pressure at 10 mbar and at a wave number of 2986 cm -1 High Resolution Transmission Molecular Absorption (HITRAN) simulations of the ethane (C12) line and the methane (C12 and C13) lines at (15A) and at the position of the C13 ethane line relative to the C12 ethane line estimated based on FTIR data (15B).

[0023] Fig.16A and Fig. 16B (collectively referred to as FIG. 16 ) depicts the -1 HITRAN simulation of the ethane (C12) line and the methane (C12 and C13) lines at (16A) and at the position of the C13 ethane line relative to the C12 ethane line estimated based on FTIR data (16B). DETAILED DESCRIPTION

[0024] Embodiments of the present disclosure include apparatus and methods for performing isotopic ethane measurements on a gas sample. In an exemplary embodiment, the disclosed apparatus includes: a tunable infrared laser configured to emit an infrared laser beam; an infrared sensor configured to receive the infrared laser beam; a gas chamber disposed in a path between the tunable infrared laser and the infrared sensor such that the infrared laser beam passes through the gas chamber, the gas chamber being configured to receive the gas sample via a gas inlet and discharge the gas sample via a gas outlet; and a controller configured to evaluate the received infrared laser beam to at least estimate the ratio of C13 ethane to C12 ethane in the gas sample. In certain advantageous embodiments, the gas chamber may include a hollow waveguide, and the apparatus may further include a GC column configured to separate an ethane sample from the gas sample and inject the ethane sample into the hollow waveguide.

[0025] An example method for performing isotopic ethane measurements on a gas sample may include introducing the gas sample into a gas chamber; scanning a tunable infrared laser between a first wavelength and a second wavelength; measuring a spectrum corresponding to the infrared laser scan; identifying a first absorption peak and a second absorption peak corresponding to C13 ethane and C12 ethane in the measured spectrum; calculating a first amplitude and a second amplitude of the first absorption peak and the second absorption peak; and calculating a ratio of the first amplitude and the second amplitude to estimate the ratio of C13 ethane to C12 ethane in the gas sample.

[0026] Figure 1 An example drilling rig 20 including a gas chromatography apparatus 100 for evaluating formation gas composition is depicted. The drilling rig 20 may be positioned above a subterranean formation (not shown). The drilling rig 20 may include, for example, a derrick and a hoisting device (also not shown) for raising and lowering a drill string 30, which extends into a wellbore 40 as shown and includes, for example, a drill bit 32 and one or more downhole measurement tools 38 (e.g., logging while drilling tools or measurement while drilling tools) in a bottom hole assembly (BHA) above the drill bit 32. Suitable drilling systems, for example, including drilling, steering, logging, and other downhole tools, are well known in the art.

[0027] The drilling rig 20 also includes a surface system 50 for controlling the flow of drilling fluid used on the drilling rig (e.g., used when drilling out the wellbore 40). In the depicted example drilling rig, drilling fluid 35 is pumped downhole (as depicted at 92) via a conventional mud pump 57. The drilling fluid 35 may be pumped, for example, through a riser 58 and a mud hose 59 on its way to the drill string 30. The drilling fluid 35 typically emerges from the drill string 30 at or near the drill bit 32 and creates an upward flow 94 of mud through the wellbore annulus 42 (the annular space between the drill string and the wellbore wall). The drilling fluid 35 then flows to a mud pit system 56 through a return pipe 52. It will be appreciated that the terms drilling fluid and mud are used synonymously herein.

[0028] The circulating drilling fluid 35 is used to perform a variety of functions during the drilling operation, one of which is to carry drill cuttings 45 to the surface (in the upflow 94). The drill cuttings 45 are typically removed from the returning mud via a shale shaker 55 (or other similar solids control equipment) in a return pipeline (e.g., directly upstream of the mud pit 56). Formation gases released during drilling can also be brought to the surface in the circulating drilling fluid. These gases are typically removed from the drilling fluid, for example, via a degasser or degasser 54 located in or near the head tank 53, which in the example depicted is directly upstream of the shale shaker 55. The drill cuttings 45 and gases are typically inspected at the surface to evaluate the formation layers drilled through by the wellbore.

[0029] The disclosed embodiments include methods and systems for estimating (e.g., measuring) the ratio of carbon-13 ethane (referred to herein as C13 ethane) to carbon-12 ethane (referred to herein as C12 ethane) in naturally occurring ethane gas. By naturally occurring, it is meant that the ethane gas originates from underground formations. It is known to those of ordinary skill in the art that formation gas (including ethane) can be released into the wellbore 40 via the drilling process (e.g., by breaking formation rock through the mechanical action of a drill bit), and can also migrate into the wellbore 40, for example, via cracks in formation rock. Once in the wellbore, the formation gas can be transported to the surface via the drilling fluid (in the upwardly flowing fluid 94). The formation gas can be a solution in the drilling fluid and / or in the form of bubbles, and can be sampled in the surface system, for example, via one or more drilling fluid degassers 54 and / or headspace gas probes. The disclosed embodiments explicitly do not limit how to sample the gas.

[0030] Further references Figure 1 The drilling rig 20 may also include a testing facility 60 (e.g., a laboratory trailer including one or more instruments suitable for making various measurements of drill cuttings and formation gas in the drilling fluid). The testing facility 60 includes an apparatus 100 (described in more detail below) configured to estimate the isotopic ratio of ethane gas (e.g., the ratio of C13 ethane to C12 ethane). Of course, the testing facility 60 may include many other testing instruments known to those of ordinary skill in the art.

[0031] Figure 2 An example embodiment of a gas testing device 100 is depicted. Figure 2 In the depicted embodiment, the apparatus 100 includes an infrared laser 110 configured to emit infrared radiation (e.g., an infrared laser beam) and an infrared sensor 170 configured to receive the infrared laser beam. A gas chamber 150 is configured to receive a formation gas sample (e.g., via a gas inlet) and is disposed between the laser 110 and the sensor 170 such that the emitted radiation passes through the gas sample in the gas chamber 150. A controller 190 is configured to process the received infrared radiation to estimate a ratio of C13 ethane to C12 ethane in the gas sample.

[0032] Figure 3Another example apparatus 100' for making isotopic ethane measurements is depicted. Apparatus 100' includes a laser (IRL) 110, such as a near infrared or mid infrared laser emitting in the 2-5 μm wavelength range. Laser 110 may include, for example, a near infrared (near IR) distributed feedback (DFB) laser diode having a wavelength up to about 3 μm, a quantum cascade laser (QCL) in the mid infrared (mid IR) region exceeding about 4 μm, or a GaSb baseband interband cascade laser (ICL) emitting in the 3-4 μm wavelength range. Advantageous embodiments may utilize commercially available ICL lasers, such as those available from Nanoplus Nanosystems and Technologies GmbH. Advantageous ICLs are small in size, operate in continuous wave (CW) at room temperature, and have low power requirements. The ICL may be tunable and may advantageously be configured to emit at a wavenumber of about 2980 cm -1 To about 2990cm -1 Infrared radiation in the range (e.g., from about 2985 cm -1 Wavenumbers less than or equal to about 2988 cm -1 wave number, or from about 2986cm -1 to about 2987cm -1 ). As described in more detail below, the -1 to about 2987cm -1 C12 and C13 ethane lines (absorption peaks) are identified at wave numbers of . These lines can be advantageously used to calculate the ratio of C13 ethane to C12 ethane in the gas sample.

[0033] In an advantageous embodiment, the mid-infrared laser beam emitted by the ICL passes through a dichroic mirror 120 and a beam mode matching lens 130 to a gas cell 150, such as a multi-pass gas cell (MPGC) or a hollow waveguide (HWG). The focal point of the lens 130 is located at the entrance of the gas cell 150 to achieve optimal power transfer from the ICL to the gas cell 150. The lens 130 can be configured to have essentially any suitable focal length, for example in the range of about 100 mm to about 400 mm (such as about 200 mm). The laser beam can be directed to the gas cell 150 by one or more plane mirrors 140a, 140b. Although not required, the use of plane mirrors can enable the construction of a more compact instrument (by enabling the beam to pass through the focal length of the lens 130 in a compact area).

[0034] The apparatus 100, 100' can utilize substantially any suitable gas chamber 150, such as an MPGC. The MPGC is configured to enable the laser beam to pass through the gas chamber multiple times and thus pass through the sample before leaving the gas chamber. An advantageous MPGC is typically compact and may include an astigmatic mirror that reflects the laser beam within the gas chamber. In an exemplary embodiment, the MPGC includes a Herrickt multi-pass gas chamber having a path length of 10m and a volume of 700mL (available from Thorlabs, Inc.). In other exemplary embodiments, the gas chamber 150 may include a hollow waveguide (HWG), such as a low volume HWG. In such an embodiment, the HWG may be a single-pass HWG or a multi-pass HWG. In certain advantageous embodiments, a suitable HWG may have a small gas chamber volume, for example, having an inner diameter ranging from about 0.2mm to 1mm and a length ranging from about 0.2m to 10m. Using a small volume HWG may advantageously enable rapid isotope ethane measurements using the disclosed embodiments.

[0035] The laser beam is received at the infrared sensor 170 as soon as it leaves the gas chamber 150. In some embodiments, the beam can be reflected from the parabolic mirror 160 to focus the beam at the sensor 170. Suitable parabolic mirrors can have substantially any suitable focal length, for example, from about 10 mm to about 100 mm (such as about 35 mm). The sensor can include substantially any suitable infrared sensor, including, for example, a mercury cadmium telluride (MCT) detector.

[0036] Although not limited in this regard, the depicted embodiment may include a temperature controller 112 programmed to control the temperature of the ICL at a constant value, such as 25° C. The current driver 114 may be configured to provide a low noise current to the ICL. Although not depicted, the apparatus may also include a second temperature controller configured to control the temperature of the gas in the gas chamber 150.

[0037] The gas chamber 150 may include a gas inlet 151 and a gas outlet 152 for receiving and discharging a gas sample. A pressure controller 155 and a vacuum pump 157 may be configured to regulate the gas pressure in the gas chamber. Generally, it is best to measure at low pressure, for example, at a pressure less than about 100 mbar (such as about 10 mbar).

[0038] The device 100' may also include a controller 190 (such as a desktop or laptop PC) configured to control the current driver and receive and digitize the infrared sensor output. The controller may also include software configured to process the received sensor output to estimate (e.g., calculate) the isotopic ratio of ethane in the gas sample. For example, the controller may be configured to identify a first absorption peak and a second absorption peak in the received sensor output and process the ratio of these peaks to at least estimate the ratio of C13 ethane to C12 ethane in the gas sample.

[0039] Figure 4 Another example apparatus for making isotopic ethane measurements is depicted. The depicted example includes a dilution module 182 and a purge module 184 deployed upstream of one of the previously described apparatuses 100, 100'. The dilution module 182 can be configured to receive and dilute a gas sample (formation gas obtained from a well). For example, the gas sample can be diluted with air or nitrogen so that the ethane concentration is in the range of about 100 ppm to about 1000 ppm.

[0040] In certain embodiments, the purification module 184 can be configured to, for example, remove hydrocarbons having three or more carbon atoms (e.g., C3, C4, C5, etc.). In such an embodiment, the purification module can be configured to heat the gas in a catalytic furnace (e.g., as disclosed in U.S. Pat. No. 9,671,381) to remove larger hydrocarbons while retaining methane and ethane (C1 and C2). Light-off curves reported in the literature using commercial Pt-Rh / CeO2-Al2O3 catalysts indicate that the temperature of 50% conversion is: for alkanes, methane 515°C> ethane 435°C, 435°C> propane, 290°C> hexane, and for olefins, acetylene 285°C> ethylene 205°C. Dilution before catalytic combustion may be beneficial to limit HC concentration (C2 (maximum): 100-1000 ppm) and extend catalyst life. The purification module may additionally and / or alternatively include a molecular sieve to capture larger hydrocarbons.

[0041] In an embodiment using an HWG gas chamber, the purification module 184 may advantageously include a gas chromatography (GC) column configured to separate the various gas components in the gas sample. Since the HWG gas chamber has a small volume, a GC column may be used. In such an embodiment, the gas sample may be diluted using a dilution module at 182 and then transmitted through a GC column 184 to obtain an ethane gas sample. The ethane gas sample may then be transmitted to the HWG gas chamber 150, where the ethane gas sample may be evaluated to estimate the ratio of C13 ethane to C12 ethane in the gas sample. The use of an HWG gas chamber and a GC column purification module may advantageously avoid the need to separate methane peaks and ethane peaks in infrared measurements, and may further enable rapid isotope ethane measurements.

[0042] Figure 5 A flow chart of an example method 200 for processing infrared sensor measurements to estimate the isotopic ratio of naturally occurring ethane is depicted. Figure 2 and Figure 3 The sensor 170 described in the embodiment of the present invention receives an infrared signal at 202. The received signal is evaluated at 204 to identify a first absorption peak and a second absorption peak, and the ratio of the peaks is processed at 206 to estimate the ratio of C13 ethane to C12 ethane in the gas sample.

[0043] Figure 6 A flow chart of another example method 220 for estimating the isotopic ratio of naturally occurring ethane is depicted. A tunable infrared laser is provided at 222, which is coupled to, for example, a laser as described above with respect to Figure 2 and Figure 3 The gas cell and the infrared detector are aligned. A gas sample is introduced into the gas cell and at 224 between the first wave number and the second wave number (e.g., at about 2986 cm -1 The first wave number (such as 2986.2cm -1 ) and about 2987cm -1 The second wave number (such as 2987.3cm -1 ) between 224 and 298. The infrared radiation is measured (received) on an infrared detector and used to generate a spectrum corresponding to the wavenumber scan at 226 (the spectrum may include, for example, measured infrared intensity as a function of the measured number or wavenumber). The spectrum is evaluated to identify a first absorption peak and a second absorption peak in the spectrum at 228. For example, the peaks may be identified based on the wavenumber of each peak (e.g., at about 2986 cm -1 to about 2987cm -1The peaks may be identified based on a pattern recognition program in which the relative positions of the first peak and the second peak and other peaks in the scan are identified. The use of such pattern recognition programs is common in spectroscopy. After the peaks are identified, the peak amplitudes may be determined at 230 by removing background signals from the spectrum (e.g., using techniques known to those of ordinary skill in the art). The ratio of the peak amplitudes may be calculated at 232 and used to estimate the ratio of C13 ethane to C12 ethane in the gas sample (e.g., the ratio of the second peak to the first peak).

[0044] Reference again Figure 3 , describes in more detail an example setup used to make preliminary measurements. A CW, DFB ICL 110 from Nanoplus GmbH (Germany) was packaged as a 5×5×5 cm TO66 assembly including a thermoelectric cooler (TEC). The TEC and MCT detector 170 (Vigo System SA) configuration had a preamplifier occupying an area of ​​40×81×40 mm. A beam mode matching lens with a focal length of 200 mm located at the entrance of the MPGC was used to provide optimal power transfer from the ICL 110 to the MPGC 150.

[0045] Although not required, an alignment diode laser (λ=630 nm) and a dichroic mirror (ISOoptics, Model BSP-DI-25-3) are utilized to assist in the optical alignment of the MPGC 150 and the MCT detector 170. After the ICL beam and the visible alignment beam are collinearly aligned using a mirror, the combined beam is coupled into the MPGC using a mode matching lens 130. Figure 3 As depicted, mirrors M1 and M2 (142, 144) change the beam direction by 180 degrees to provide the required 200-mm distance for the mode matching lens, thereby folding the optical path and reducing the size of the sensor optical core. A 35 mm focal length parabolic mirror is used to focus the collimated ICL beam leaving the MPGC onto the TEC, MCT detector.

[0046] Although not depicted, embodiments of apparatus 100' may include an online reference unit located between infrared laser 110 and dichroic mirror 120 (or lens 130 in embodiments where a dichroic mirror is not employed). When target gas is not present, the reference unit may provide a reference signal to identify the laser wavelength in real time and avoid wavelength drift.

[0047] Continue to refer Figure 3, the controller 190 can be configured to control the ICL temperature controller 112 and the current driver 114. To minimize the laser frequency noise, a developed low noise laser driver board (e.g., ITC4002QCL available from Thorlabs) can be selected. In an example measurement described in more detail below, the ICL 110 was operated at a current of 57 mA and a temperature of 25° C., providing approximately 8 mW of optical power. To avoid spectral overlap, the pressure in the MPGC 150 was reduced to 10 mbar.

[0048] In the exemplary embodiment, the controller 190 also includes a laptop equipped with a NI data acquisition (DAQ) card and a two-channel arbitrary function generator to generate a 500 Hz sawtooth wave with a DC offset. The offset determines the ICL center wavelength, and the sawtooth wave is used to scan the ICL wavelength center wavelength. The amplitude of the offset depends on the characteristics of the ICL and the wavelength of the target absorption line. The laptop DAQ combination acquires spectral data from the MTC detector at a sampling rate of 500 kS / s to 1000 kS / s.

[0049] Data processing was performed as described below. First, 500 spectra were averaged by ramping the laser current at 500 Hz to cover the target spectral region and the detector output was collected using a DAQ. Each spectrum contained 2000 or 8000 data points. In order to obtain the baseline of the spectral scan, the absorption peak was removed from the average spectrum. Subsequently, the remaining data points were fitted with the aid of a fifth-order polynomial. The absorbance was calculated based on the baseline fitting and then linearized using a quadratic polynomial obtained in advance based on the fringe spacing of the Ge standard. Finally, the Voigt line shape (or a simple Gaussian distribution) was fit to the linearized absorbance using the Levenberg-Marquardt least squares fitting process to retrieve the target gas concentration. The output rate of the spectral output was 1 Hz.

[0050] Fig. 7A and Figure 7B (collectively, FIG. 7 ) depicts absorbance as a function of wavelength calculated and linearized using a 2.54 cm long germanium etalon with a free spectral range (FSR) of 1.44 GHz ( 7A ) and a calibration model ( 7B ) for converting spectral channels (or data points) to corresponding wavenumbers. A calibration curve based on a fifth-order polynomial regression is used to convert spectral channels (or data points) to corresponding wavenumbers.

[0051] Sawtooth scanning of the ICL current around the 55mA center current resulted in a 2986.2cm -1 Up to 2987.3cm -1Since the sawtooth signal was not registered for spectral sampling using the full DAQ bandwidth, the laser was systematically turned off by setting the initial current below the laser threshold (approximately 24 mA). A HITRAN simulation of methane was performed to confirm the initial wavelength assignment: 2986.2 cm -1 and etalon FSR. These parameters are fine-tuned to match the HITRAN simulations, in particular, the etalon FSR can vary slightly depending on the ambient temperature. Figure 8 depicts a typical 500 average (1 Hz acquisition rate) methane spectrum obtained from a known concentration level of 19% and the corresponding HITRAN simulation. Zero air was used to measure the spectral baseline and subtract it from the raw methane transmission spectrum. Good agreement between the experimental spectrum (8B) and the simulated spectrum (8A) was observed.

[0052] Although good agreement between experimental and simulated spectra is observed for methane, it should be noted that the ethane C13 absorption line is not available in the HITRAN database in this spectral region (3.4 μm) and needs to be determined experimentally (as described below).

[0053] Fig.9A and Fig. 9B (collectively, FIG. 9 ) depicts C13 ethane spectral line identification ( 9A ) and detection limit estimation ( 9B ). An example C13 ethane absorption peak is shown at 302 . In previous studies, FTIR spectrometers were used to measure the infrared absorption lines of ethane isotopologues in the mid-infrared range for the first time. In this study, the 2986 cm -1 The high resolution absorption cross section of the same isotopomer was measured by a nearby ICL. Using ethane C13 diluted to 2500 ppb (100 ppm N2 balance gas) provided by CalGas / Air Liquid, the presence of a strong ethane C13 line near 2986.4 cm- was confirmed, as shown in Figure 9.

[0054] The signal-to-noise ratio (SNR) is usually defined as the ratio of the signal power to the background noise power and is usually expressed in decibels (dB). In this study, the SNR was calculated by dividing the highest possible absorption signal (S max ) divided by the standard deviation of the background signal during nitrogen measurement: SNR = S max / (σN2), where σN2 is regarded as the noise level.

[0055] The LOD is specified as the lowest amount / concentration that can be distinguished from the absence of the substance. The SNR can be used to calculate the LOD of a substance, for example as follows: LOD = c / SNR, where c is the concentration of the substance during the SNR measurement. The obtained LOD is idealized, because if the amplitude of the meaningful signal and the noise level are the same, it will be difficult to distinguish between the two. Therefore, the value represents only a rough estimate of the experimentally achievable LOD. In order to measure the noise level of the above-mentioned device, the MPGC was flushed with pure nitrogen and the measurements were performed at ambient temperature and a gas pressure of 10 mbar. For an ethane C13 sample with a concentration of 2500 ppb, the estimated LOD of the ethane C13 line is about 25 ppb corresponding to an SNR of 100. The noise level is about 4×10 -4 RMS, which is consistent with the specifications provided by the MPGC manufacturer.

[0056] like Fig.10 As shown, the amplitude of the identified C13 ethane peak matches the corresponding peak of the standard ethane sample at about 250 ppm (2986.7 cm reported in HITRAN). -1 The interference between ethane C13 and the potential ethane C12 line is estimated to be weak and can be corrected using accurate calibration ethane concentrations. In order to experimentally determine an accurate estimate of ethane C12, the absorption lines need to be separated out into ethane C12 molecules. However, this process is extremely expensive and has never been used in practice. Another approach would require improving the current optical setup to remove the baseline spectrum using better optics (i.e., neutral density) or a less sensitive infrared detector (that does not saturate when using about 8 mW of optical power).

[0057] Fig.11A and Fig. 11B (collectively referred to as FIG. 11 ) depicts peak ratio graphs at high ( 11A) and low ( 11B) ethane gas concentrations. The isotope ratio (C13 / C12) is calculated using the ratio between the peak maxima of the C13 line and the C12 line (as described above), as shown in FIG. 11 , where the spectrum acquisition time is 20 seconds, at a gas pressure of 10 mbar, and the two ethane concentrations are 2500 ppm and 220 ppm. As depicted in FIG. 11 , the peak ratio (on the vertical axis) is approximately linear with respect to the isotope ratio (on the horizontal axis).

[0058] To evaluate the linearity of the ethane isotope ratio measurement, C13 ethane was mixed stepwise (100 ppm) with a standard ethane sample (2500 ppm, delta ethane -29‰). Figure 11 shows the measured changes in the isotope ratio (C13 / C12) as a function of the estimated isotope ratio. For the high concentration (2500 ppm) gas sample (11A), high sensitivity of delta ethane measurement was achieved: <0.1‰ (delta resolution) and good linearity (R 2>0.9). For low concentration (220ppm) gas samples (11B), lower sensitivity <0.1‰ (δ resolution) and good linearity (R2>0.9) were achieved. The δ resolution was also confirmed by an uncertainty assessment based on a one-second standard deviation estimate (<0.1‰). It should be noted that these measurements were performed in a laboratory at a relatively stable ambient temperature (<1K). By controlling the temperature of the MPGC, any temperature changes that affect the linearity of the isotope measurements can be improved. Temperature changes in the gas chamber are considered to be one of the most important parameters affecting measurement drift and are typically controlled to within 0.1°C in commercial isotope analyzers. Further experimental measurements are needed to better evaluate the required stability of the gas chamber temperature, however, it will be understood that a temperature controller configured to control the gas chamber temperature can be easily implemented by an ordinary technician.

[0059] Allen-Waller Deviation Analysis allows determining the amount of time to average the optical sensor signal in order to improve detection sensitivity. To assess long-term stability, calculate Fig.10 The ratio between the peak maxima of the C13 absorption line and the C12 absorption line (peak) depicted in , with an acquisition time of 20 seconds and a gas pressure of 10 mbar. The calculated sensitivity limit is plotted in FIG12 as a function of the integration time based on the Allen-Waller deviation.

[0060] Fig. 12A and Fig. 12B (collectively referred to as Figure 12) depicts Fig.11A and Fig. 11B Allen-Waller deviation analysis of ethane isotope ratios for the gas compositions shown. Within an integration time of approximately 50 seconds, the standard deviations for high (2500 ppm) (12A) and low (220 ppm) (12B) ethane concentrations are reduced to 0.1‰ and 0.5‰, respectively. These results are consistent with the linearity and uncertainty analysis discussed previously. Based on the above, it can be concluded that for low ethane samples (200 ppm), isotope ratio stability better than 0.5‰ can be achieved. In order to achieve better performance at lower concentrations, one may consider selecting a gas cell with a longer path length and increasing the gas pressure in the range (e.g., 20-50 mbar). Analyzer performance is primarily limited by laboratory temperature drift and can be easily improved by controlling the temperature of the gas cell as described above.

[0061] A feasibility study was performed using an optical bench (many optical components are mounted on the optical bench) to simplify the control of the optical components (lasers, optics), electronics (laser drivers) and gas conditions (flow, pressure and temperature) and to select the most suitable configuration for isotope analysis. The wavelength was chosen to be 2986 cm based on theoretical analysis using the HITRAN database and preliminary high-resolution FTIR measurements. -1(3.349mm) as the center of the ICL light source. The experimental results confirmed that 2986cm -1 The study also showed that in this spectral region, there is limited interference between the minor C12 absorption line and the C13 absorption line. Despite the lack of published data on ethane spectra in this spectral region, it was shown for the first time that it is possible to directly measure ethane isotope variations without the need for a complex laboratory setup based on GC-IRM.

[0062] In the foregoing disclosure, it has been shown that the ratio of C13 ethane to C12 ethane can be determined for a substantially pure ethane composition (i.e., without significant interference from other hydrocarbons in the gas). As described above, hydrocarbons having three or more carbon atoms can be removed from the gas sample. The following analysis shows that the presence of methane in the gas composition is not expected to significantly interfere with the ethane isotope ratio measurement.

[0063] Ethane spectra with sufficient resolution are available in the literature, but this is not the case for ethane with the isotope C13. Therefore, we chose to collect both spectra (C12 and C13) to obtain two easily comparable spectra. In addition, the ethane spectrum of C12 is partially available in the HITRAN database, as only strong lines in the 3-4 μm region are reported. It was observed that the spectrum of ethane C13 is similar in appearance to that of C12, with the peak shifted by an average of 0.4-0.8 cm towards the weaker waves of C13 ethane. -1 Since infrared lasers (QCL or ICL) can usually be transmitted at several wave numbers (1-4cm -1 ) and therefore both isotopes can be advantageously detected with a single laser.

[0064] In general, absorption peaks tend to broaden as gas pressure increases due to molecular collisions in the gas cell. For example, the peak may broaden slightly, reaching a width of 0.5 cm at half height. -1 Up to 1cm -1 In order to differentiate isotopic absorption peaks using a single laser, it may be advantageous to reduce the gas pressure in the gas cell to less than 100 mbar.

[0065] refer to Fig.13 In the spectra shown, it is important to note that the C13 ethane peak is often split, probably due to the fact that only one carbon atom, C13, is substituted in the ethane molecule. Therefore, the frequency of the rotational vibration line will change slightly depending on the proximity of the C12 or C13 carbon atom. This is not visible in the standard ethane spectrum because of the low proportion of C13. Peaks attributed specifically to the C13 ethane present in standard ethane can sometimes be seen in the previous figures (e.g., 2986cm -1). The peaks in this region are very steep, and no very steep water peaks can be seen. As mentioned above, Figure 3 The depicted ICL laser emits infrared radiation in this spectral region.

[0066] Fig.14 A similar FTIR spectrum of ethane collected and published by Pacific Northwest National Laboratory (PNNL) is shown in Figure 1. A high resolution infrared spectrum of light hydrocarbons (C1-C5) is also shown. As shown, the ethane line does not interfere with the methane and hydrocarbon lines. However, if high concentrations of hydrocarbons (>1000ppm) are present in the gas sample, a shift in the baseline level can be expected, which can affect the isotope measurement accuracy. The ethane lines are 3.3cm apart. -1 And around 2986cm -1 The main C2 lines in this spectral region are referenced (p1, p2, etc.) according to their position relative to the center line (p0).

[0067] Since C13 ethane concentrations are low (ppb level) and methane concentrations are high (percent level), ultra-high resolution spectroscopy is required to investigate the overlap between ethane minor lines not captured in the FTIR data and methane minor lines. Methane absorption lines are well documented in the HITRAN database, so ultra-high resolution (<0.001 cm) at low pressure (10 mbar) can be simulated. -1 ) spectrum. Figure 15 shows the spectrum at P = 10 mbar and wavelength 2986 cm -1 HITRAN simulation of ethane (C12) line and methane (C12 and C13) line at .

[0068] Fig.15A and Fig. 15B (collectively referred to as FIG. 15 ) depicts the pressure at 10 mbar and at a wave number of 2986 cm -1 High Resolution Transmission Molecular Absorption (HITRAN) simulations of the ethane (C12) line and the methane (C12 and C13) lines at (15A) and at the position of the C13 ethane line relative to the C12 ethane line estimated based on FTIR data (15B). The position of the ethane C13 line relative to the ethane C12 line is based on the FTIR data (0.392 cm -1 ). The intensity of the C13 ethane peak is calculated based on the intensity of the corresponding C12 ethane line and its natural abundance (about 1%). Fig. 15B In the example, C13 ethane peak 312 is at about 2986.3 cm -1 (For example, at 2986.2cm -1 and 2986.4cm -1 observed between and corresponds to Fig.15A The line 314 in FIG. 316 of the exemplary C12 ethane peak is at about 2986.7 cm -1 (For example, at 2986.6cm -1 and 2986.8cm -1 observed between and corresponds to Fig.15A The ethane peak 318 in the image is shown in Figure 3. The ratio of ethane C13 to the overlapping methane line can be calculated and is called the methane retention rate. -1 For the central ethane line at (p0), this ratio is estimated to be 100.

[0069] In order to achieve the required measurement accuracy (1‰), this ratio can be higher than 1000 in cases where the ethane and methane concentrations in the sample are similar. However, in natural gas samples, ratios between C1 and C2 of 100 to 1000 are often encountered. In this case, a methane rejection of 10 is desired. 5 Order of magnitude.

[0070] Fig.16A and Fig. 16B (collectively referred to as FIG. 16 ) depicts the -1 HITRAN simulation of the ethane (C12) line and methane (C12 and C13) lines at (16A) and at the position of the C13 ethane line relative to the C12 ethane line estimated based on FTIR data (16B). As shown in FIG. 16 , for the wavelength 2983 cm -1 Ethane line at (p -1 ), the highest methane retention rate in this spectral region is about 10 4 In this case, an accurate calibration for high methane concentrations is required to correct for its effect on the C2 isotope ratio. The methane retention of the remaining ethane line is estimated to be less than 10 3 .exist Fig. 16B In the example, C13 ethane peaks 322 and 323 are at 2982.9 cm -1 (For example, at 2982.8cm -1 and 2983.0cm -1 Between) and 2983.0cm -1 (For example, at 2982.9cm -1 and 2983.1cm -1 observed between and corresponds to Fig.16A Lines 324 and 325 in Figure 3. Example C12 ethane peak 326 at 2983.4 cm -1 (For example, at 2983.3cm -1 and 2983.5cm -1 observed between and corresponds to Fig.16AThe C12 ethane peak is 328.

[0071] As described above, the feasibility of determining the ratio of C13 ethane to C12 ethane in naturally occurring formation gas has been demonstrated. The disclosed apparatus and method advantageously simplifies the control of the optical components (lasers, optics), electronics (laser driver), and gas conditions (flow, pressure, and temperature), and enables the selection of the most appropriate configuration for isotopic analysis. The wavelength was selected to be 2986 cm based on theoretical analysis using the HITRAN database and preliminary high resolution FTIR measurements. -1 The experimental results disclosed in this paper confirm that 2986cm -1 The spectral information (position and intensity) of the C13 line of ethane nearby was obtained. It was also shown that this spectral line is useful for the direct analysis of ethane isotope ratios. Despite the lack of published data on ethane spectra in this spectral region, it has been shown for the first time that ethane isotope variations can be measured directly without the need for a complex laboratory setup based on GC-IRMS.

[0072] It will be understood that the present disclosure includes many embodiments. These embodiments include but are not limited to the following embodiments.

[0073] In a first embodiment, an apparatus for performing isotopic ethane measurements on a gas sample comprises: a tunable infrared laser configured to emit an infrared laser beam; an infrared sensor configured to receive the infrared laser beam; a gas chamber disposed in a path between the tunable infrared laser and the infrared sensor such that the infrared laser beam passes through the gas chamber, the gas chamber being configured to receive the gas sample via a gas inlet and to discharge the gas sample via a gas outlet; and a controller configured to evaluate the received infrared laser beam to at least estimate the ratio of C13 ethane to C12 ethane in the gas sample.

[0074] A second embodiment may include the first embodiment, wherein the air chamber comprises a hollow waveguide air chamber having an inner diameter in the range of 0.2 mm to 1 mm and a length in the range of 0.2 m to 10 m.

[0075] A third embodiment may include the second embodiment, further comprising a gas chromatography column configured to separate an ethane sample from the gas sample and inject the ethane sample into the hollow waveguide.

[0076] A fourth embodiment may include any one of the first to third embodiments, wherein the tunable infrared laser comprises a continuous wave GaSb baseband inter-cascade laser (ICL) configured to emit the infrared laser beam; and the infrared sensor comprises a mercury cadmium telluride (MCT) infrared detector configured to receive the infrared laser beam.

[0077] A fifth embodiment may include the fourth embodiment, wherein the tunable infrared laser is configured to emit light from greater than or equal to 2985 cm -1 The first wave number is less than or equal to 2988cm -1 The emitted infrared laser beam is scanned at a second wave number.

[0078] The sixth embodiment may include any one of the first to fifth embodiments, and the sixth embodiment also includes a beam mode matching lens, which is deployed in the path between the tunable infrared laser and the gas chamber, so that the focus of the beam mode matching lens is located at the gas inlet of the gas chamber.

[0079] The seventh embodiment may include any one of the first to sixth embodiments, and the seventh embodiment also includes a parabolic mirror deployed in a path between the gas chamber and the infrared sensor, and the parabolic mirror is configured to focus the infrared laser beam leaving the gas chamber onto the infrared sensor.

[0080] The eighth embodiment may include any one of the first to seventh embodiments, and the eighth embodiment also includes at least one of the following: a temperature controller configured to control the temperature of the tunable infrared laser; and a pressure controller configured to control the pressure of the gas sample in the gas chamber.

[0081] The ninth embodiment may include any one of the first to eighth embodiments, and the ninth embodiment also includes at least one of the following: a dilution module configured to dilute the gas sample with air or nitrogen so that the ethane concentration in the gas sample is in the range of about 100 ppm to about 1000 ppm; and a purification module configured to remove hydrocarbons having three or more carbon atoms from the gas sample.

[0082] The tenth embodiment may include any one of the first to ninth embodiments, wherein the controller is further configured to: cause the tunable infrared laser to scan the emitted infrared laser beam between a first wave number and a second wave number; cause the infrared sensor to measure a spectrum corresponding to the scanned infrared laser beam; identify a first C13 ethane absorption peak and a second C12 ethane absorption peak in the measured spectrum; calculate a first amplitude and a second amplitude of the corresponding first absorption peak and second absorption peak by removing the spectral background; and calculate a ratio of the first amplitude to the second amplitude to estimate the ratio of C13 ethane to C12 ethane in the gas sample.

[0083] In an eleventh embodiment, a method for performing isotopic ethane measurement on a gas sample includes introducing the gas sample into a gas chamber, the gas chamber being disposed in a path between a tunable infrared laser and an infrared sensor, the tunable infrared laser being configured to emit an infrared laser beam, the infrared laser beam passing through the gas chamber and being received at the infrared sensor; scanning the emitted infrared laser beam between a first wavenumber and a second wavenumber; measuring a spectrum corresponding to the scanned infrared laser beam; identifying a first C13 ethane absorption peak and a second C12 ethane absorption peak in the measured spectrum; calculating a first amplitude and a second amplitude of the first absorption peak and the second absorption peak by removing the spectral background; and calculating a ratio of the first amplitude to the second amplitude to estimate the ratio of C13 ethane to C12 ethane in the gas sample.

[0084] The twelfth embodiment may include the eleventh embodiment, wherein the first wave number is greater than or equal to 2985 cm -1 And the second wave number is less than or equal to 2988cm -1 .

[0085] The thirteenth embodiment may include the twelfth embodiment, wherein the first C13 ethane absorption peak is at 2986.2 cm -1 and 2986.4cm -1 The second C12 ethane absorption peak is at 2986.6 cm -1 and 2986.8cm -1 The number of waves between.

[0086] A fourteenth embodiment may include any one of the eleventh to thirteenth embodiments, wherein the introducing comprises introducing the gas sample into a gas chamber comprising a hollow waveguide having an inner diameter in a range of 0.2 mm to 1 mm and a length in a range of 0.2 m to 10 m.

[0087] The fifteenth embodiment may include any one of the eleventh to fourteenth embodiments, wherein the introducing includes: introducing the gas sample into a dilution module to obtain a diluted gas sample including about 100 ppm to about 1000 ppm ethane; injecting the diluted gas sample into a gas chromatography column to separate an ethane sample; and introducing the ethane sample into a gas chamber including a hollow waveguide having an inner diameter in the range of 0.2 mm to 1 mm and a length in the range of 0.2 m to 10 m.

[0088] In a sixteenth embodiment, a device for performing isotope ethane measurement on a gas sample includes: a tunable infrared laser configured to emit an infrared laser beam; an infrared sensor configured to receive the infrared laser beam; a gas chromatography column configured to separate an ethane gas sample from the gas sample; a hollow waveguide disposed in a path between the tunable infrared laser and the infrared sensor so that the infrared laser beam passes through the hollow waveguide, the hollow waveguide being configured to receive the ethane gas sample via a gas inlet and discharge the ethane gas sample via a gas outlet, the hollow waveguide having an inner diameter in a range of 0.2 mm to 1 mm and a length in a range of 0.2 m to 10 m; and a controller configured to process a ratio of a first absorption peak to a second absorption peak in the received infrared laser beam to estimate a ratio of C13 ethane to C12 ethane in the gas sample.

[0089] The seventeenth embodiment may include the sixteenth embodiment, wherein the tunable infrared laser comprises a continuous wave GaSb baseband inter-cascade laser (ICL) configured to emit an infrared laser beam; and the infrared sensor comprises a mercury cadmium telluride (MCT) infrared detector configured to receive the infrared laser beam.

[0090] An eighteenth embodiment may include the seventeenth embodiment, wherein the tunable infrared laser is configured to emit light from greater than or equal to 2985 cm -1 The first wave number is less than or equal to 2988cm -1 The emitted infrared laser beam is scanned at a second wave number.

[0091] The nineteenth embodiment may include any one of the sixteenth to eighteenth embodiments, and the nineteenth embodiment also includes: a beam mode matching lens disposed in a path between the tunable infrared laser and the hollow waveguide, so that a focus of the beam mode matching lens is located at the gas inlet; and a parabolic mirror disposed in a path between the hollow waveguide and the infrared sensor, the parabolic mirror being configured to focus the infrared laser beam leaving the hollow waveguide onto the infrared sensor.

[0092] A twentieth embodiment may include any one of the sixteenth to nineteenth embodiments, wherein the controller is further configured to: make the tunable infrared laser at a frequency greater than or equal to 2985 cm -1 The first wave number is less than or equal to 2988cm -1 The method comprises the steps of: scanning the emitted infrared laser beam between a first wave number of a wavelength of 400 nm and a second wave number of a wavelength of 800 nm; causing the infrared sensor to measure a spectrum corresponding to the scanned infrared laser beam; identifying a first C13 ethane absorption peak and a second C12 ethane absorption peak in the measured spectrum; calculating a first amplitude and a second amplitude of the corresponding first absorption peak and second absorption peak by removing the spectral background; and calculating a ratio of the first amplitude to the second amplitude to estimate the ratio of C13 ethane to C12 ethane in the gas sample.

[0093] Although the tunable laser spectroscopy measurement of C13 ethane has been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims.

Claims

1. A device for measuring isotope ethane in a gas sample, the device comprising: a tunable infrared laser configured to emit an infrared laser beam; an infrared sensor configured to receive the infrared laser beam; a gas cell disposed in a path between the tunable infrared laser and the infrared sensor such that the infrared laser beam passes through the gas cell, the gas cell being configured to receive the gas sample via a gas inlet and to exhaust the gas sample via a gas outlet; as well as A controller is configured to evaluate the received infrared laser beam to at least estimate a ratio of C13 ethane to C12 ethane in the gas sample.

2. The apparatus of claim 1, wherein the air chamber comprises a hollow waveguide air chamber having an inner diameter in the range of 0.2 mm to 1 mm and a length in the range of 0.2 m to 10 m.

3. The apparatus of claim 2, further comprising a gas chromatography column configured to separate an ethane sample from the gas sample and inject the ethane sample into the hollow waveguide.

4. The device of claim 1, wherein: The tunable infrared laser comprises a continuous wave GaSb baseband inter-cascade laser (ICL) configured to emit the infrared laser beam; and The infrared sensor includes a mercury cadmium telluride (MCT) infrared detector configured to receive the infrared laser beam.

5. The apparatus of claim 4, wherein the tunable infrared laser is configured to emit light from greater than or equal to 2985 cm -1 The first wave number is less than or equal to 2988cm -1 The emitted infrared laser beam is scanned at a second wave number.

6. The apparatus of claim 1 , further comprising a beam mode matching lens disposed in a path between the tunable infrared laser and the gas cell such that a focus of the beam mode matching lens is located at the gas inlet of the gas cell.

7. The apparatus of claim 1, further comprising a parabolic mirror disposed in a path between the gas chamber and the infrared sensor, the parabolic mirror being configured to focus the infrared laser beam exiting the gas chamber onto the infrared sensor.

8. The device of claim 1, further comprising at least one of the following: a temperature controller configured to control the temperature of the tunable infrared laser; and A pressure controller is configured to control the pressure of the gas sample in the gas chamber.

9. The device of claim 1, further comprising at least one of the following: a dilution module configured to dilute the gas sample with air or nitrogen so that the ethane concentration in the gas sample is in the range of about 100 ppm to about 1000 ppm; and A purification module is configured to remove hydrocarbons having three or more carbon atoms from the gas sample.

10. The apparatus of claim 1, wherein the controller is further configured to: causing the tunable infrared laser to scan the emitted infrared laser beam between a first wave number and a second wave number; causing the infrared sensor to measure a spectrum corresponding to the scanned infrared laser beam; identifying a first C13 ethane absorption peak and a second C12 ethane absorption peak in the measured spectrum; Calculating the first amplitude and the second amplitude of the corresponding first absorption peak and the second absorption peak by removing the spectral background; and A ratio of the first amplitude to the second amplitude is calculated to estimate the ratio of C13 ethane to C12 ethane in the gas sample.

11. A method for measuring isotopic ethane in a gas sample, the method comprising: introducing the gas sample into a gas cell disposed in a path between a tunable infrared laser and an infrared sensor, the tunable infrared laser being configured to emit an infrared laser beam that passes through the gas cell and is received at the infrared sensor; scanning the emitted infrared laser beam between a first wave number and a second wave number; measuring a spectrum corresponding to the scanned infrared laser beam; identifying a first C13 ethane absorption peak and a second C12 ethane absorption peak in the measured spectrum; calculating a first amplitude and a second amplitude of the first absorption peak and the second absorption peak by removing the spectral background; as well as A ratio of the first amplitude to the second amplitude is calculated to estimate a ratio of C13 ethane to C12 ethane in the gas sample.

12. The method of claim 11, wherein the first wave number is greater than or equal to 2985 cm -1 And the second wave number is less than or equal to 2988cm -1 .

13. The method of claim 12, wherein the first C13 ethane absorption peak is at 2986.2 cm -1 and 2986.4cm -1 The second C12 ethane absorption peak is at 2986.6 cm -1 and 2986.8cm -1 The number of waves between.

14. The method of claim 11, wherein the introducing comprises introducing the gas sample into a gas chamber comprising a hollow waveguide having an inner diameter in a range of 0.2 mm to 1 mm and a length in a range of 0.2 m to 10 m.

15. The method of claim 11, wherein the introducing comprises: introducing the gas sample into a dilution module to obtain a diluted gas sample comprising about 100 ppm to about 1000 ppm ethane; injecting the dilution gas sample into a gas chromatography column to separate an ethane sample; as well as The ethane sample was introduced into a gas chamber comprising a hollow waveguide having an inner diameter in the range of 0.2 mm to 1 mm and a length in the range of 0.2 m to 10 m.

16. An apparatus for measuring isotopic ethane in a gas sample, the apparatus comprising: a tunable infrared laser configured to emit an infrared laser beam; an infrared sensor configured to receive the infrared laser beam; a gas chromatography column configured to separate an ethane gas sample from the gas sample; a hollow waveguide disposed in a path between the tunable infrared laser and the infrared sensor such that the infrared laser beam passes through the hollow waveguide, the hollow waveguide being configured to receive the ethane gas sample via a gas inlet and to discharge the ethane gas sample via a gas outlet, the hollow waveguide having an inner diameter in a range of 0.2 mm to 1 mm and a length in a range of 0.2 m to 10 m; as well as A controller is configured to process a ratio of a first absorption peak to a second absorption peak in the received infrared laser beam to estimate a ratio of C13 ethane to C12 ethane in the gas sample.

17. The apparatus of claim 16, wherein: The tunable infrared laser comprises a continuous wave GaSb baseband inter-cascade laser (ICL) configured to emit an infrared laser beam; and The infrared sensor includes a mercury cadmium telluride (MCT) infrared detector configured to receive the infrared laser beam.

18. The apparatus of claim 17, wherein the tunable infrared laser is configured to emit light from greater than or equal to 2985 cm -1 The first wave number is less than or equal to 2988cm -1 The emitted infrared laser beam is scanned at a second wave number.

19. The apparatus of claim 16, further comprising: a beam mode matching lens disposed in a path between the tunable infrared laser and the hollow waveguide such that a focus of the beam mode matching lens is located at the gas inlet; as well as A parabolic mirror is disposed in a path between the hollow waveguide and the infrared sensor, the parabolic mirror being configured to focus the infrared laser beam leaving the hollow waveguide onto the infrared sensor.

20. The apparatus of claim 1, wherein the controller is further configured to: The tunable infrared laser is made to have a wavelength greater than or equal to 2985 cm -1 The first wave number is less than or equal to 2988cm -1 scanning the emitted infrared laser beam between a second wave number of causing the infrared sensor to measure a spectrum corresponding to the scanned infrared laser beam; identifying a first C13 ethane absorption peak and a second C12 ethane absorption peak in the measured spectrum; Calculating the first amplitude and the second amplitude of the corresponding first absorption peak and the second absorption peak by removing the spectral background; and A ratio of the first amplitude to the second amplitude is calculated to estimate the ratio of C13 ethane to C12 ethane in the gas sample.

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