Apparatus for rapid gas chromatography and infrared spectroscopy measurement of oil field fluids

Abstract

An apparatus for rapid gas chromatography measurement of oil field gas includes: an infrared laser configured to emit an infrared laser beam; an infrared sensor configured to receive the infrared laser beam; a Fabry-Perot gas cell disposed in a path between the infrared laser and the infrared sensor such that the infrared laser beam passes through the gas cell, the gas cell configured to receive the gas sample; a gas chromatographic column assembly, the gas chromatographic column assembly comprising an input port, a gas chromatographic column, and an output port, the gas chromatographic column assembly being configured to provide the gas sample to the Fabry-Perot gas cell; and a controller in electronic communication with the infrared sensor and configured to process the received infrared laser beam to estimate a composition of the gas sample.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of EP Application No. 23306705.7, filed on October 4, 2023, entitled “DEVICE FOR RAPID GAS CHROMATOGRAPHY AND INFRARED SPECTROSCOPY MEASUREMENTS OF OILFIELD FLUIDS,” the disclosure of which is incorporated herein by reference. Background Art

[0003] Gas chromatography (GC) is a widely used technique for separating and analyzing chemical compounds that can evaporate, such as organic compounds. Common applications involve quantitative and / or qualitative analysis of food compositions, natural products, food additives, flavor and aroma components such as essential oils, various conversion products, and pollutants such as pesticides, fumigants, natural toxins, pharmaceuticals, packaging materials, and environmental pollutants. GC technology is also used to assess the composition of gases released during downhole drilling operations, for example, including methane (C1), ethane (C2), propane (C3), butane (C4), pentane (C5), etc., as well as olefins and other compounds. Such measurements can provide valuable information to the logging instrument, and can provide information about the maturity and properties of hydrocarbons in the reservoir, the division of intervals in the reservoir being drilled, and the quality of the oil, as well as information about the production area, lithology changes, reservoir accumulation history, sealing effectiveness, and the environmental impact of the drilling operation.

[0004] In mud logging, there is an industry need to improve the speed and sensitivity of gas composition measurements, for example, to quickly measure the composition of natural gas as it is brought to the surface during oil or gas drilling. Improving the speed and sensitivity of such measurements can help geologists and drilling engineers more quickly identify the presence of natural gas deposits and monitor the composition of the gas during drilling operations, and therefore make more timely drilling decisions. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] For a more complete understanding of the disclosed subject matter and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0006] Figure 1 An example drilling rig including fast gas chromatography equipment for evaluating formation gas composition is depicted.

[0007] Figure 2 Depicted Figure 1 An example embodiment of a fast GC apparatus is shown.

[0008] Figure 3 Describes the application Figure 1 and Figure 2 An example of a macro-Fabry-Perot cell of the fast GC device is shown.

[0009] Figure 4A and Figure 4B Describes the application Figure 1 and Figure 2 An example of a micro-Fabry-Perot cell of a fast GC device is shown.

[0010] Figure 5A and 5B Depicted is an example micro-Fabry-Perot cavity in which a mirror is integrated into the end of an optical fiber.

[0011] Figure 6 Another embodiment of a micro-Fabry-Perot cell is depicted.

[0012] Figure 7 An alternative embodiment is depicted that includes a plurality of IR lasers (infrared lasers), a Fabry-Perot cell, and an IR detector (infrared detector). DETAILED DESCRIPTION

[0013] Embodiments of the present disclosure include apparatus and methods for performing rapid GC and IR spectroscopy measurements and for estimating the composition of an oilfield gas sample. In an exemplary embodiment, an apparatus includes: an infrared laser configured to emit an infrared laser beam; an infrared sensor configured to receive the infrared laser beam; a Fabry-Perot cell disposed in a path between the infrared laser and the infrared sensor such that the infrared laser beam passes through the cell, the cell being configured to receive the gas sample; a gas chromatography column assembly including an input port, a gas chromatography column, and an output port, the gas chromatography column assembly being configured to provide the gas sample to the Fabry-Perot cell; and a controller in electronic communication with the infrared sensor and configured to process the received infrared laser beam to estimate the composition of the gas sample.

[0014] Figure 1 An example drilling rig 20 including a fast gas chromatography device 100 is depicted, which is configured to evaluate formation gas composition. A "fast" GC device means that the device is configured to perform molecular composition and / or isotope ratio measurements of C1 (methane) to C5 (pentane) oilfield gas compositions in less than about 1 minute. In other words, the disclosed fast GC device can have a time resolution of less than about 1 minute. The drilling rig 20 can be positioned above an underground formation (not shown). The drilling rig 20 can include, for example, a derrick and a lifting device (also not shown) for raising and lowering a drill string 30, as shown, the drill string 30 extends into a wellbore 40 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 (e.g., including drilling, steering, logging and other downhole tools) are well known in the art.

[0015] The drilling rig 20 also includes a surface system 50 for controlling the flow of drilling fluid used on the drilling rig (e.g., for drilling 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, for example. The drilling fluid 35 may be pumped, for example, through a riser 58 and a mud hose 59 in a route to the drill string 30. The drilling fluid 35 typically exits the drill string 30 at or near the drill bit 32 and creates an upward flow 94 of mud that passes through the wellbore annulus 42 (the annular space between the drill string and the wellbore wall). The drilling fluid 35 then flows through a return pipe 52 to a mud pit system 56 where it may be recirculated. It should be understood that the terms drilling fluid and mud are used synonymously herein.

[0016] The circulating drilling fluid 35 is intended to perform a number of functions during the drilling operation, one of which is to transport drill cuttings 45 to the surface (in an upward flow 94). The drill cuttings 45 are typically removed from the return mud via a shale shaker 55 (or other similar solids control device) in a return conduit (e.g., immediately upstream of the mud pit 56). Formation gases released during drilling may also be carried to the surface in the circulating drilling fluid. These gases are typically removed from the fluid, for example, via a degasser 54 (or gas trap) located in or near a header box 53, which is immediately upstream of the shale shaker 55 in the example depiction. The drill cuttings 45 and gases are typically inspected at the surface to evaluate the formation through which the wellbore was drilled.

[0017] As known to those of ordinary skill in the art, formation gas may be released into the wellbore 40 via the drilling process (e.g., by the mechanical action of a drill bit crushing the formation rock), and may also migrate into the wellbore 40, for example, via fractures in the formation rock. Once in the wellbore, the formation gas may be transported to the surface via the drilling fluid (in the upwardly flowing fluid 94). The formation gas may be in solution in the drilling fluid and / or in the form of bubbles, and may be sampled in the surface system, for example, via one or more drilling fluid degassers 54 and / or headspace gas probes. The disclosed embodiments are expressly not limited to how the gas is sampled.

[0018] 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 performing various measurements on drill cuttings and formation gas in the drilling fluid). In the illustrated embodiment, the testing facility 60 includes a fast gas chromatography apparatus 100 (described in more detail below) that is configured to receive formation gas and evaluate formation gas composition. Of course, the testing facility 60 may include many other testing instruments known to those of ordinary skill in the art. Although the following embodiments are described with respect to drilling operations, it should be understood that the disclosed embodiments are not limited thereto and may be applied to the use of GC in other chemical applications.

[0019] While GC is a powerful chemical analysis technique that enables many (most) chemical species to be separated at the detector, there is still room for improvement. For example, conventional GC measurements may be time consuming or may not be well suited for making multiple, continuous measurements of a gas stream at rapid time intervals (e.g., on the order of seconds or minutes, depending on the gas being measured and the accuracy required). The disclosed embodiments may advantageously provide such rapid GC measurements.

[0020] Of course it should be understood that Figure 1 A land drilling rig 20 is depicted, but the disclosed embodiments are equally applicable to land drilling rigs or offshore drilling rigs. As known to those of ordinary skill in the art, an offshore drilling rig typically includes a platform arranged on top of a riser that extends from the seafloor to the sea surface. A drill string extends downward from the platform, through the riser, and through a blowout preventer (BOP) located on the seafloor into the wellbore. The disclosed embodiments are expressly not limited in these respects.

[0021] Figure 2 An exemplary fast GC device 100 is depicted, which includes a gas sample injection port (such as an automatic injector with a sample loop) 112, which is configured to feed a gas sample into a column assembly 120, which includes an optional pre-cut column 122 and a main GC column 126. The GC device 100 also includes a carrier gas supply 135, such as a supply of compressed nitrogen, argon, helium or air. The injected (e.g., automatically injected) gas sample is mixed with the carrier gas and transported through the column assembly 120. The optional pre-cut column 122 can be configured to remove heavier hydrocarbon compounds with a carbon number above a threshold, such as C6, C8 or C10 and above. The main column 126 generally includes a stationary phase and is intended to separate various gas compounds in the gas sample so that they leave (or leave) the main column 126 at different elution times, for example, so that C1 leaves the column before C2, C2 leaves the column before C3, and so on.

[0022] The apparatus 100 also includes a Fabry-Perot (FP) gas cell 150 configured to receive the output gas from the main column 126. An example embodiment of the Fabry-Perot gas cell 150 may include an inlet port 152 and an outlet port 154 configured to receive a gas flow and release the gas flow into and from the gas cell 150. The infrared laser 140 emits infrared radiation (e.g., an infrared laser beam) that passes through the FP gas cell 150 (and the gas therein) to an infrared sensor 160 configured to receive the infrared laser beam. The sensor 160 is in electronic communication with a controller 180, which is configured to process the detected infrared radiation and generate an IR spectrum. The controller 180 may be further configured to estimate the molecular composition or element isotope ratio (e.g., of carbon or hydrogen) of the gas.

[0023] Although not in Figure 2 1, but it should be understood that the apparatus 100 may also include a pressure controller and a vacuum pump that may be configured to regulate the pressure of the gas in the Fabry-Perot cell 150 or the pressure of the gas transferred into or through the cell. In some example applications (e.g., when making isotope measurements, such as when measuring the ratio of carbon-13 methane to carbon-12 methane or carbon-13 carbon dioxide to carbon-12 carbon dioxide), it may be desirable to make measurements at low pressures, such as at pressures less than about 100 mbar (or even at pressures as low as about 10 mbar).

[0024] Continue to refer Figure 2 , the outlet port 154 in the Fabry-Perot gas cell 150 can be optionally connected to a GC detector 170 fluid. The GC detector can include substantially any suitable detector, for example, including a flame ionization detector (FD), a flame photometric detector (FPD), a thermal conductivity detector (TCD), or a mass spectrometer. The GC detector 170 is also in electronic communication with a controller 180, which can be further configured to estimate the composition of the gas based on the detector output. Of course, it should be understood that the controller 180 may include computer hardware and software configured to enable the fast GC device 100 to control the functions of the device. The hardware may include one or more processors (e.g., microprocessors) that may be connected to one or more data storage devices (e.g., hard drives or solid-state memory) and a user interface. It will be further understood that the disclosed embodiments may include processor executable instructions stored in a data storage device. The disclosed embodiments are certainly not limited to the use or configuration of any particular computer hardware and / or software.

[0025] The fast GC device 100 may include substantially any suitable IR source (infrared source), including, for example, an infrared laser 140 emitting at near-IR or mid-IR wavelengths (eg, in the 1-2 μm wavelength range). Suitable lasers may include, for example, tunable telecom grade lasers.

[0026] As described above, the disclosed embodiments relate to apparatus for performing rapid GC and IR spectroscopy measurements. One aspect of the disclosed embodiments is the recognition that integrating a small volume Fabry-Perot cell with an efficient column and a sensitive detector can enable rapid GC and IR spectroscopy measurements.

[0027] Continue to refer Figure 2 , the device 100 can advantageously utilize rapid, low volume injection techniques. For example, the injection port 112 can include an automatic injector with a low volume sample loop (e.g., less than 5 mL, less than 1 mL, less than 100 μL, or even less than 10 μL). In an exemplary embodiment, the injection port 112 can be a splitless or on-column injection port to reduce the time required for sample introduction and increase the speed of analysis.

[0028] The fast GC device 100 can further advantageously include a main column 126 having a short length and / or a small inner diameter, so that a fast separation time can be achieved. The main column 126 can further include a capillary column including a stationary phase film coating the inner surface of the column. The use of such a stationary phase can further improve the separation efficiency of the column and reduce the time required to achieve a suitable separation.

[0029] The device may also include a heating or cooling module ( Figure 2 120). The device 100 may further include a vacuum pump configured to draw the gas sample through the column assembly 120. The module may be configured to quickly heat or cool the gas sample to further reduce the time required for separation and increase the speed of analysis. In addition, the device may utilize a high carrier gas flow rate to reduce the time required for the gas to pass through the main column 126. The column efficiency may be further improved by implementing vacuum separation, for example, by operating the column 126 at a reduced outlet pressure. Therefore, the device 100 may also include a vacuum pump configured to draw the gas sample through the column assembly 120. This vacuum separation may advantageously be implemented with a relatively short and wide-pore column.

[0030] Still further reference Figure 2, the GC detector 170 may include substantially any detector suitable for high-speed GC measurements. For example, the detector may include a mass flow detector that responds to the mass of sample components arriving at the detector per unit time (e.g., ng / s) or a concentration sensitive detector that responds to the concentration of sample components in the mobile phase (e.g., ng / mL). Example detectors that may be well suited for fast (high-speed) GC measurements include flame ionization detectors (FIDs), thermal conductivity detectors (TCDs), and electron capture detectors (ECDs) because they have fast response times and can accommodate high flow rates. Mass spectrometers are also often used in high-speed GC due to their high sensitivity and selectivity, but they tend to have slower response times than other detectors.

[0031] If the capillary separation column passes through the burner and is positioned just below the bottom of the flame, open chamber detectors and flame-based detectors (such as FID) typically have response times of a few milliseconds or less. For closed chamber or concentration detectors, including photoionization detectors, ECDs, and TCDs, unless a specially designed device with a small chamber volume or the detector is operated at less than ambient pressure, the extra-column band broadening may be excessive. At a reduced column outlet pressure, the carrier gas velocity in the detector increases, and the pool is swept out faster. Additional gas, called make-up gas, can be introduced into the detector cell to scan the cell faster and reduce peak broadening and distortion.

[0032] One difficulty in making fast GC measurements is achieving suitable accuracy and sensitivity for the small sample volumes required to achieve high measurement frequencies (i.e., fast measurements). It should be understood that the limit of detection (LOD) or minimum detectable level (MDL) refers to the amount or concentration of solute that produces a peak height (or peak area) corresponding to a signal-to-noise ratio (SNR) of 2 (although an SNR of 3 is commonly used recently). These metrics (LOD and MDL) are more useful than simple response / mass values ​​because they include information about system noise. In addition, the MDL is independent of peak width, but should specify the data rate or filter bandwidth.

[0033] Mass flow detectors respond to the mass of a compound in the detector at a given time, and the MDL units are mass per unit time. Concentration detectors respond to the concentration of a compound in the detector sensing volume (not the sample), and their MDL units are mass / volume. For mass flow detectors, the MDL is calculated by measuring the noise and the peak area for a known injected mass. For example, for a concentration detector, the MDL at S / N=2 can be expressed as follows:

[0034]

[0035] Noise can be measured under "normal" operating conditions, with the column connected and the carrier gas turned on. For example, noise can be measured over a time period on the order of 10 times the peak width at half height (or 10 times the area / height ratio of a Gaussian peak). The MDL can be specified at a data rate of 5 Hz, which is appropriate for peaks between 1.5 seconds and 3 seconds wide at half height. Such peaks typically have 15 to 30 data points between them from baseline to baseline.

[0036] The detector MDL can be compared with the minimum detectable sample concentration (C i ). For a mass flow detector, the minimum detectable sample concentration can be estimated as follows:

[0037]

[0038] where ω_i represents the peak width measured at half height of the Gaussian peak and v e is the injected volume corrected by the GC injector. An example calculation for the C1 peak from a standard mud log, which is 0.2 seconds wide at half height on the FID, is as follows. Note that in this example, the gas measured is methane (C1), which has 0.75 grams of carbon per gram of methane (CH4). When the FID MDL is 2 pgC / s (acquisition rate: 100 Hz), the MDL for C1 is (2 / 0.75) pg / s of C1 or 2.66 pg / s. Using these values ​​and assuming a 15 μL automatic injection (no split), the following is obtained (methane molecular weight (MW): 16.04 g / mol):

[0039]

[0040] It will be appreciated that the above concentration calculations may further include a flow term to account for the total flow through the detector, and further include the flow through the column.

[0041] It will also be appreciated that the detection limit may vary for micro-Fabry-Perot cells and macro-Fabry-Perot cells. In particular, due to the small cavity volume, the cavity length of a micro-Fabry-Perot cell tends to be relatively short, so that the IR laser-gas interaction length is limited. This can result in lower sensitivity, but with the tradeoff of significantly increased measurement speed. Conversely, due to the larger cavity volume, the cavity length of a macro-Fabry-Perot cell tends to be relatively long, resulting in a longer IR laser-gas interaction length. This can result in higher sensitivity, but with the tradeoff of reduced measurement speed. The disclosed embodiments are certainly not limited in these respects.

[0042] Now go to Figure 3, depicts an example embodiment of a macroscopic Fabry-Perot cell 150'. In the depicted embodiment, the FP cell 150' includes an input port 152' and an output port 154' coupled to a cavity 250. The cavity 250 includes a cavity volume 255 in fluid communication with the input port 152' and the output port 154'. As described above, the cell 150' may also include a first mirror 140a' and a second mirror 140b' at opposite ends of the cavity volume.

[0043] In an advantageous embodiment, the cavity 250 can be further configured for use with an all-fiber fast GC device. For example, the cavity can be configured to receive a first optical fiber and a second optical fiber (not shown) at its opposite ends 251 and 252. The first optical fiber can be arranged between an IR laser (infrared laser) and a first fiber coupling 261 arranged in the first end 251 of the cavity, and the second optical fiber can be arranged between a second fiber coupling 262 in the second end 252 of the cavity and an IR detector (infrared detector).

[0044] In certain advantageous embodiments, the size and shape of the macroscopic Fabry-Perot cell can be designed so that it has a cavity volume in the range of from about 0.1 ml to about 5 ml (e.g., from about 0.25 ml to about 2.5 ml). In addition, the cavity length can be in the range of about 0.5 cm to about 10 cm. Such a macro cavity can advantageously provide high sensitivity (e.g., about 1 part per billion (ppb) or less).

[0045] Figure 4A and 4B (collectively, FIG. 4 ) depicts an example embodiment of a micro-Fabry-Perot cell 150 ″ suitable for use with an all-fiber fast GC apparatus. In the depicted embodiment, a slot 320 is formed in a cavity 350 . A first optical fiber 361 and a second optical fiber 362 are disposed in the cavity (e.g., embedded therein). The first optical fiber 361 can be disposed between an IR laser and the slot 320 , while the second optical fiber 362 can be disposed between the slot 320 and the IR detector. The first optical fiber 361 and the second optical fiber 362 can be positioned in the slot 320 such that a small cavity volume 355 is defined therebetween.

[0046] 4, the reflectors may be integrated into the ends 371, 372 of the optical fibers 361, 362, for example, Figure 5A and 5BAs shown. However, the small radius of curvature required for cavities with small mode volumes may be outside the range of conventional polishing techniques. Successful techniques for producing the required small and smooth depressions (depths of the order of a few μm) on glass surfaces are surface etching methods and laser ablation. For example, one technique used to produce curved mirror shapes with ultra-low surface roughness is CO2 laser ablation. The strong absorption of light between 9-11 μm wavelengths by fused silica (SiO2) is used to strongly heat the top layer of the fiber end surface by irradiating it with a focused CO2 laser beam.

[0047] After mirror molding, multiple layers of dielectric coatings can be applied to achieve low-loss, high-reflectivity mirrors in the visible, infrared, or ultraviolet domains (preferably infrared). For this purpose, up to tens of alternating layers of materials with high refractive index (Ta2O5, n=2.10) and low refractive index (SiO2, n=1.45) and individual thicknesses of: λ / 4 can be deposited on the fiber surface using ion beam sputtering techniques. The resulting fiber-based mirrors with the shape of the original fiber surface depressions can have transmission, scattering, and absorption losses as low as a few parts per million and are ready to be aligned to build high-finesse, low-mode volume resonators.

[0048] In certain advantageous embodiments, the size and shape of the micro-Fabry-Perot cell can be designed so that it has a cavity volume of less than about 5 microliters (e.g., less than about 1 microliter). In addition, the cavity length can be less than about 2 mm (e.g., less than about 1 mm or less than about 0.5 mm). Such a micro-cavity can advantageously provide very fast measurements (e.g., on the order of seconds or less) and good sensitivity (e.g., on the order of 1 part per million (ppm) or less).

[0049] Further references Figure 3 4, it will be understood that a Fabry-Perot cavity (or gas cell) is an optical cavity made of two parallel reflecting surfaces (e.g., thin mirrors) with some small transmittance. A Fabry-Perot cavity is an interferometer that allows light to pass only when it is in resonance with the cavity. To achieve the proper resonance, the cavity length can be appropriately selected (e.g., as an integer multiple of the difference between selected peaks in isotope measurements (such as carbon-12 peak and carbon-13 peak)).

[0050] A fiber Fabry-Perot cavity (FFPC) device may include opposing fiber mirrors, for example, as shown in FIG. Figure 5A and Figure 5BAs shown. Since many applications may benefit from high-Q optical resonators, finesse is one of the key specifications for FFPC. The achievable finesse is usually limited by the quality of the reflective coating, the surface quality, and the size of the fiber mirrors. Finesse of the order of 105 may be advantageous. Absorption in ion beam sputtered layer systems with high reflectivity typically occurs in the order of a few parts per million. Annealing these mirrors at moderate temperatures (≤350°C) can reduce the amount of absorption even further.

[0051] Conventional FFPC implementations may pick up low frequency acoustic noise due to the large distance of the fiber to the common base. Furthermore, the fiber end protruding beyond its holder into free space introduces additional noise due to bending modes. To stabilize these cavity systems, electronic locking schemes with feedback bandwidths of the order of tens of kHz can be utilized. This reduces the complexity of the assembly process and at the same time increases passive stability. In this case, the fiber mirrors are inherently aligned by guides provided by the cavity. Due to the high passive stability, feedback bandwidths as low as 20 MHz may be sufficient to lock the cavity resonance to an external laser under laboratory conditions. Fast piezoelectric tuning can achieve feedback bandwidths up to 27 kHz for tight stabilization of the cavity resonance.

[0052] Figure 6 Another embodiment of a micro Fabry-Perot cell 450 is depicted. In the depicted embodiment, at least one (e.g., first and second) piezoelectric transducer 455 can be used to adjust the cavity length and volume. As described above with respect to FIG. 4, the micro Fabry-Perot cell 450 has a small cavity volume and a short cavity length. A gas sample can be received at a gas inlet port 462 and ejected at a gas outlet port 464. The micro cavity 452 can be formed between an optical fiber 472 and a reflector 474. An optional lens 476 can focus the optical output at a detector. Also as described above with respect to FIG. Figure 3 As described with reference to FIG. 4 , FP plenum 450 may be implemented in an all-fiber configuration.

[0053] Figure 7An alternative embodiment 500 is depicted that includes multiple IR lasers 512, 514, a Fabry-Perot gas cell 550, and an IR detector 560. In the depicted embodiment, a first IR laser 512 and a second IR laser 514 are configured to emit IR radiation into corresponding optical fibers 513 and 515. It should be understood that the disclosed embodiments can include substantially any number of IR lasers, for example, a different IR laser for each compound measured. The IR lasers 512, 514 can advantageously be tunable so that an appropriate wavelength can be selected based on the absorption peak of the compound. An optical switch 520 is used to select IR radiation from a desired IR laser. The switch 520 can be configured to quickly switch between the first laser 512 and the second laser 514.

[0054] Continue to refer Figure 7 , the selected IR radiation continues through optical fiber 523 to an optional collimator 530, a mode matching lens 535, mirrors 537, 538 to a Fabry-Perot cell 550. In an alternative all-fiber embodiment, optical fiber 523 may be connected to a Fabry-Perot cell 550 (e.g., as described above with respect to Figure 3 , Figure 4 and Figure 6 560). The output IR radiation may be received at a detector 560. In an all-fiber embodiment, an optical fiber may be coupled to the output of the FP plenum 550 and the detector 560. The embodiment 500 may also include various electronics such as an amplifier 572, a delay generator 574 electrically coupling the detector 560 and the IR lasers 512, 514, a digital converter such as an analog-to-digital converter 576, and a controller 580 such as a computer.

[0055] Still further reference Figure 7 It should be understood that the embodiment 500 may also include multiple infrared detectors 560, for example, one for each infrared laser. Such an embodiment may be configured to measure multiple different gases simultaneously without multiplexing the lasers with optical switches. In addition, the Fabry-Perot cell may be configured (e.g., length, finesse, and fiber type) for a specific gas or gases (or IR laser wavelengths). Such a configuration may enable one or more miniature Fabry-Perot cells to be integrated into a compact chip.

[0056] It should be understood that the present disclosure includes many embodiments. These embodiments include but are not limited to the following examples.

[0057] In a first embodiment, a device for performing rapid gas chromatography measurements on an oilfield gas sample, the device comprising: an infrared laser configured to emit an infrared laser beam; an infrared sensor configured to receive the infrared laser beam; a Fabry-Perot gas cell arranged in a path between the infrared laser and the infrared sensor so that the infrared laser beam passes through the gas cell, the gas cell being configured to receive the gas sample; a gas chromatography column assembly comprising an input port, a gas chromatography column, and an output port, the gas chromatography column assembly being configured to provide the gas sample to the Fabry-Perot gas cell; and a controller in electronic communication with the infrared sensor and configured to process the received infrared laser beam to estimate the molecular composition or isotope ratio of the gas sample.

[0058] A second embodiment may include the first embodiment, wherein the Fabry-Perot cell comprises a macroscopic Fabry-Perot cell having a cavity volume in a range from 0.1 ml to about 5 ml and a cavity length in a range from about 0.5 cm to about 10 cm.

[0059] A third embodiment may include the first embodiment wherein the Fabry-Perot cell comprises a micro-Fabry-Perot cell having a cavity volume of less than about 5 microliters and a cavity length of less than about 2 mm.

[0060] The fourth embodiment may include any one of the first to third embodiments, further comprising: a first optical fiber coupling the infrared laser and the Fabry-Perot cell; and a second optical fiber coupling the Fabry-Perot cell and the infrared sensor.

[0061] A fifth embodiment may include the fourth embodiment, wherein the first reflector is integrated into the end of the first optical fiber in the Fabry-Perot cell, and the second reflector is integrated into the end of the second optical fiber in the Fabry-Perot cell.

[0062] A sixth embodiment may include any one of the first to fifth embodiments, wherein the Fabry-Perot gas cell has a cavity length that is an integer multiple of a difference between a first peak and a second peak in isotope measurement.

[0063] The seventh embodiment may include any one of the first to sixth embodiments, wherein the infrared laser is a tunable laser and is configured to emit an infrared laser beam having a wavelength in the range of 1 μm to 2 μm.

[0064] The eighth embodiment may include any one of the first to seventh embodiments, wherein the infrared laser includes a plurality of tunable infrared lasers; and each of the plurality of tunable infrared lasers is configured to emit a corresponding infrared laser beam having a preselected wavelength corresponding to absorption peaks of different chemical compounds in the gas sample.

[0065] A ninth embodiment may include the eighth embodiment, wherein the infrared sensor includes a plurality of infrared sensors corresponding to a plurality of tunable infrared lasers.

[0066] A tenth embodiment may include any one of the first to ninth embodiments, wherein the infrared laser, the infrared sensor, and the Fabry-Perot cell are collectively configured to detect methane or carbon dioxide isotopes in the gas sample.

[0067] An eleventh embodiment may include any one of the first to tenth embodiments, wherein the infrared laser, the infrared sensor, and the Fabry-Perot cell are collectively configured to detect permanent gases in the gas sample.

[0068] A twelfth embodiment may include any one of the first to eleventh embodiments, wherein the gas chromatography column assembly further comprises a gas chromatography detector in electronic communication with the controller, the gas chromatography detector being selected from a flame ionization detector, a thermal conductivity detector, and an electron capture detector.

[0069] A thirteenth embodiment may include any one of the first to twelfth embodiments, wherein the input port comprises an autoinjector having a sample loop having a volume of less than 5 mL.

[0070] A fourteenth embodiment may include any one of the first to thirteenth embodiments, wherein the gas chromatography column comprises a capillary column comprising a stationary phase film coating an inner surface of the gas chromatography column.

[0071] A fifteenth embodiment may include any one of the first to fourteenth embodiments, further comprising a pressure controller configured to adjust the pressure of the gas sample in the Fabry-Perot cell so that the pressure of the gas sample is less than 100 mbar.

[0072] In a sixteenth embodiment, a method for evaluating the composition of an oilfield gas sample comprises: automatically injecting the gas sample into a gas chromatography assembly comprising a gas chromatography column; receiving the gas sample from the gas chromatography column in a Fabry-Perot gas chamber; emitting infrared radiation into the Fabry-Perot gas chamber using an infrared laser; receiving the infrared radiation from the Fabry-Perot gas chamber at an infrared sensor; and estimating the composition of the gas sample based on the infrared radiation received at the infrared sensor.

[0073] A seventeenth embodiment may include the sixteenth embodiment, wherein the estimating composition includes estimating an isotopic ratio of methane in the gas sample.

[0074] The eighteenth embodiment may include the seventeenth embodiment, wherein the Fabry-Perot gas cell has a cavity length that is an integer multiple of a difference between the first peak of carbon-13 methane and the second peak of carbon-12 methane.

[0075] A nineteenth embodiment may include any one of the sixteenth to eighteenth embodiments, wherein emitting infrared radiation includes emitting infrared radiation having a wavelength in a range of 1 μm to 2 μm.

[0076] The twentieth embodiment may include any one of the sixteenth to nineteenth embodiments, wherein emitting infrared radiation includes: emitting first infrared radiation having a first wavelength using a first infrared laser, and emitting second infrared radiation having a second wavelength using a second infrared laser; and the method further includes modulating the infrared radiation received by the Fabry-Perot cell between the first infrared radiation and the second infrared radiation using an optical switch.

[0077] Although the equipment for rapid gas chromatography and infrared spectroscopy measurement of oilfield fluids has been described in detail, it should be understood that various changes, substitutions and modifications may be made herein without departing from the spirit and scope of the present disclosure as defined by the appended claims. In addition, in order to provide a concise description of these embodiments, all features of the actual embodiments may not be described in the specification. It should be understood that in the development of any such actual implementation scheme, as in any engineering or design project, numerous embodiment-specific decisions will be made to achieve the specific goals of the developer, such as meeting system-related and business-related constraints, which may vary from one embodiment to another. In addition, it should be understood that such development efforts may be complex and time-consuming, but for ordinary technicians who benefit from the present disclosure, it is still a routine task of design, production and manufacturing.

[0078] As used herein, the terms "approximately," "about," and "substantially" refer to an amount that is close to a stated amount, that is within standard manufacturing or process tolerances, or that still performs a desired function or achieves a desired result. For example, the terms "approximately," "about," and "substantially" may refer to an amount that is within less than 5%, less than 1%, less than 0.1%, and less than 0.01% of a stated amount.

Claims

1. A device for performing rapid gas chromatography measurement on an oilfield gas sample, the device comprising: an infrared laser configured to emit an infrared laser beam; an infrared sensor configured to receive the infrared laser beam; a Fabry-Perot gas cell disposed in a path between the infrared laser and the infrared sensor so that the infrared laser beam passes through the gas cell, the gas cell being configured to receive the gas sample; a gas chromatography column assembly, the gas chromatography column assembly comprising an input port, a gas chromatography column, and an output port, the gas chromatography column assembly being configured to provide the gas sample to the Fabry-Perot cell; and A controller is in electronic communication with the infrared sensor and is configured to process the received infrared laser beam to estimate a molecular composition or isotope ratio of the gas sample.

2. The device according to claim 1, wherein The Fabry-Perot cell comprises a macroscopic Fabry-Perot cell having a cavity volume in the range from 0.1 ml to about 5 ml, and a cavity length which is an integer multiple of the difference between the first peak of carbon-13 methane and the second peak of carbon-12 methane and in the range from about 0.5 cm to about 10 cm.

3. The apparatus according to claim 1, further comprising: a first optical fiber coupling the infrared laser and the Fabry-Perot cell, wherein a first reflector is integrated into an end of the first optical fiber in the Fabry-Perot cell; and A second optical fiber couples the Fabry-Perot cell and the infrared sensor, and a second reflector is integrated into an end of the second optical fiber in the Fabry-Perot cell.

4. The apparatus according to claim 1, wherein: The infrared laser includes a plurality of tunable infrared lasers corresponding to a plurality of infrared sensors including the infrared sensor; and Each of the plurality of tunable infrared lasers is configured to emit a corresponding infrared laser beam having a preselected wavelength corresponding to an absorption peak of a different chemical compound in the gas sample, ranging from 1 μm to 2 μm.

5. The device according to claim 1, wherein: The infrared laser, the infrared sensor, and the Fabry-Perot cell are collectively configured to detect methane or carbon dioxide isotopes in the gas sample.

6. The apparatus of claim 1, wherein: The gas chromatography column assembly further includes a gas chromatography detector in electronic communication with the controller, the gas chromatography detector being selected from the group consisting of a flame ionization detector, a thermal conductivity detector, and an electron capture detector; and The gas chromatography column comprises a capillary column including a stationary phase film coating the inner surface of the gas chromatography column.

7. The device of claim 1, wherein the input port comprises an automatic syringe having a sample loop having a volume of less than 5 mL. 8 . The apparatus of claim 1 , further comprising a pressure controller configured to adjust the pressure of the gas sample in the Fabry-Perot cell such that the pressure of the gas sample is less than 100 mbar.

9. A method for evaluating the composition of an oilfield gas sample, the method comprising: automatically injecting a gas sample into a gas chromatography assembly including a gas chromatography column; receiving a gas sample from a gas chromatography column in a Fabry-Perot cell; An infrared laser is used to emit infrared radiation into a Fabry-Perot cell; receiving infrared radiation from the Fabry-Perot cell at an infrared sensor; and A composition of the gas sample is estimated based on the infrared radiation received at the infrared sensor.

10. The method according to claim 9, wherein: The emitting infrared radiation comprises emitting first infrared radiation having a first wavelength using a first infrared laser and emitting second infrared radiation having a second wavelength using a second infrared laser; and The method also includes modulating the infrared radiation received by the Fabry-Perot cell between first infrared radiation and second infrared radiation using an optical switch.

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