Isotopic molecular markers for fluid resources or contaminants

Abstract

Systems and methods are provided for chemically tagging dry natural gas and other fluids. In one example, at least 1 ppbv of a first isotopic species of a first hydrocarbon is added to the dry natural gas as a chemical marker. The first isotopic species has at least three deuterium atoms. Some embodiments described herein provide for the addition of one or more chemical markers to a fluid and subsequent identification of the one or more chemical markers in the fluid. The method can be used to associate information associated with the one or more chemical markers to the fluid.

Description

[Technical field]

[0001] Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 63 / 362,867, entitled "ISOTOPOLOGUE MARKER FOR FLUID," which is incorporated herein by reference. [Background technology]

[0002] background Many different operators process fluids such as natural gas, crude oil, water, and carbon dioxide. Often, shipping or storage of these fluids results in fluids from different operators that are commingled. Once the fluids are commingled, it may be difficult or impossible to determine which operator supplied the fluid and in what quantities. For example, natural gas is often transported from processors to consumers via a network of pipelines. Many different operators may supply natural gas to the same network of pipelines and reservoirs. It is difficult to determine which operator's gas is present in a given pipeline or reservoir.

[0003] Natural resource producers and processors are also required to adopt environmentally conscious technologies and equipment to minimize the environmental impact of their operations. For example, natural gas producers are required to minimize emissions of fossil fuels into the environment during the extraction / production, processing, and / or transmission of natural gas. However, it is difficult to distinguish between environmentally conscious entrants in the natural resource space and those who fail to adopt proper resources and management, especially when most such resources are indiscriminately commingled at some point during transportation to distributors and users. Summary of the Invention [Means for solving the problem]

[0004] Short Description Some embodiments described herein provide for the addition of one or more chemical markers to a fluid and subsequent identification of the one or more chemical markers in the fluid. This method can be used to associate information associated with the one or more chemical markers to the fluid. Any desired information can be associated with the marker and thus the fluid it is in, such as the supplier of the fluid, whether the fluid meets certain specifications (e.g., any specifications created to ensure environmentally sustainable operations), whether the fluid meets pipeline content specifications, whether the fluid originates from a particular oil / gas field or geographic region, etc.

[0005] A chemical marker may be a unique molecule or a combination of two or more molecules in a unique ratio. As an example, a chemical marker may be one or more isotopic species of a component of the main fluid of interest or a chemically similar compound. To illustrate, a chemical marker for methane (CH4) or dry natural gas may be one or more isotopic species of methane, such as CDH2, CD2H, CD3H, and / or CD4, and / or one or more isotopic species of related compounds, such as isotopic species of ethane (e.g., C2DH5, C2D2H4, C2D3H3, C2D4H2, C2D5H, and / or C2D6), and / or isotopic species of propane (e.g., C3DH7, C3D2H6, C3D3H5, C3D4H4, C3D5H3, C3D6H2, C3D7H, and / or C3D8). The chemical markers may be one of each of these molecules or a combination of such molecules in a unique ratio.

[0006] One objective of the present invention is to identify fluids that may be mixed with other fluids of the same general nature. For example, dry natural gas (or any other fluid) supplied by a first manufacturer may be mixed with dry natural gas (or any other fluid) supplied by a second manufacturer. The fluids of interest may be any other natural resource (e.g., crude oil, propane, etc.) or pollutants (e.g., carbon dioxide, carbon monoxide, sulfuric acid, etc.).

[0007] It is another object of the present invention to provide an apparatus and method for producing chemical markers.

[0008] It is another object of the present invention to provide an apparatus and method for detecting the presence and amount of chemical markers in a fluid.

[0009] Example embodiments will be described with additional specificity and detail through the use of the accompanying drawings, with the understanding that the drawings illustrate exemplary embodiments only and are therefore not to be considered limiting of the scope. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram of an exemplary system for transporting a fluid.

[0011] [Diagram 2] FIG. 2 is an example chromatograph of a sample of chemically pure (CP) grade methane, showing that trace amounts of ethane can be separated by the CP technique.

[0012] [Diagram 3] FIG. 3 is another example chromatograph of the sample of FIG. 3 with SIM selection of perdeuterated ethane.

[0013] [Figure 4] FIG. 4 is a calibration curve for perdeuterated ethane in methane.

[0014] [Diagram 5] FIG. 5 is a block diagram of an exemplary system for compounding fluid markers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Detailed Description FIG. 1 is a block diagram of a system 100 for transporting a fluid. The system 100 may include a number of suppliers 102 that supply the fluid to a network of pipes 104. The network 104 delivers the fluid to one or more destinations 106 for the fluid. The fluid may be any fluid that is desirable to transport in gaseous or liquid form, such as dry natural gas, wet natural gas, crude oil, water, carbon dioxide, ethane, or propane. Each supplier 102 may be any suitable entity involved in the supply or transportation of the fluid to or within the network 104, such as a manufacturer, processor, refiner, or wholesaler. The destination(s) may be any suitable entity that receives the fluid, such as a power plant, industrial plant, municipality, processing facility, refiner, transportation swap point, or storage facility for the fluid. The network of pipes 104 may include one or more pipes of any suitable size or design for transporting the fluid, including regional and interstate pipelines.

[0016] Each supply line 108 transports fluid from a respective supplier 102 to the network of pipes 104. Each supply line 108 transports fluid from a supplier 102 to the network 104. In some examples, only fluid from a single supplier 102 is included in each supply line 108. Fluid from each supplier 102 in each supply line 108 may be mixed with fluid from other suppliers 102 in the network of pipes 104. That is, the network of pipes 104 may contain a mixture of fluids from multiple suppliers 102 (e.g., a mixture of dry natural gas).

[0017] In some examples, each supplier 102 may process the fluid before supplying it to the network 104 (e.g., before supplying the fluid to a regional or interstate pipeline). This processing may be done to separate components of the fluid and / or otherwise modify the fluid to be of suitable quality for introduction into the network 104 (e.g., a regional or interstate pipeline). In examples where the fluid is dry natural gas, the supplier 102 may receive wet natural gas, for example, from one or more oil fields, storage facilities, and / or transportation vehicles, and may process the wet natural gas to separate heavy hydrocarbons (e.g., ethane, propane, etc.) from methane as well as remove non-hydrocarbon gases as needed. The output of processing is gas that is primarily methane and known as dry natural gas (also referred to as pipeline quality natural gas). The dry natural gas is then supplied to the network 104 for consumption by one or more destinations. Regional and interstate pipeline operators often provide specifications for the dry natural gas transported in their pipelines, and supplier 102 ensures that its processing produces dry natural gas that meets the specifications of the pipelines that transport the gas.

[0018] Before the fluid from the supplier 102 is introduced into the network 104 (i.e., before the fluid is mixed with fluids supplied by other suppliers 102), one or more chemical markers may be added to the fluid. Chemical markers can be used as indicators that can be detected in the fluid and used to indicate something about the fluid. The markers can indicate anything that is desired, and a list identifying each marker along with information associated with that marker can be stored in any suitable form (e.g., in a written or electronic data table) for marker detection, as discussed below. Exemplary information that the markers can indicate can include, but are not limited to, the supplier 102 from which the fluid originates, the specifications the fluid meets (e.g., pipeline specifications, or standards related to environmentally sustainable production methods), or the quality of the fluid, whether the fluid meets the specifications for the pipeline contents, or whether the fluid originates from a particular oil / gas field or geographic region. As described above, the markers can indicate that the fluid has a certain property or meets a certain specification. For example, a marker may be added to any fluid, regardless of source, if the fluid meets a first industry standard, such as the standard for responsible production and processing of natural gas. Such a marker can then be detected in the fluid to determine whether the fluid (and, if desired, what percentage of the fluid) is a fluid that meets the relevant standard. Other information can also be associated with the marker.

[0019] Each marker may be unique among the markers added to the network 104 such that each marker may be independently detected in the fluid as discussed below. As an example of a unique marker identifying a unique source provider 102, a first unique marker may be added to the fluid in a first supply line 108 from a first supplier 102 and a second unique marker may be added to the fluid in a second supply line 108 from a second supplier 102. The first unique marker may be associated with the first supplier 102 and the second unique marker may be associated with the second supplier 102 such that the fluid in the network 104 may be analyzed to detect whether the first and / or second markers are present and thus whether gas from the first and / or second provider 102 is present. The first and second unique markers may be comprised of different molecules, or different sets of molecules, or sets of the same molecules in different ratios. If markers from different suppliers are made using different ratios of the same set of molecules, detection would involve assessment of the amount of each of the different molecules along with a deconvolution calculation to separate the amounts due to each molecule present, so that the markers present can be identified by determining what ratio and amount of the markers when mixed will result in the amount of each molecule present.

[0020] Chemical markers may be added to a fluid so that the marker becomes and remains part of the fluid so that it can be detected in the fluid at a later time. The chemical composition of the marker can be selected so that the marker remains with the fluid while the fluid is at rest (e.g., during storage) and travels with the fluid while the fluid is flowing (e.g., during transportation via a pipeline).

[0021] A respective marker input station 110 may be disposed in each supply line 108 to add one or more markers to the fluid. The marker input stations 110 may have any suitable configuration, such as being part of a discharge station.

[0022] A centralized database or operator may be established for the purpose of establishing markers and allocating (associating) markers to particular operators 102 (e.g., particular suppliers), fluids that meet certain specifications (e.g., any specifications created to ensure environmentally sustainable operations), fluids originating from particular oil / gas fields or geographic regions, etc. The centralized operator may also be the source of certified marker addition stations 110 for operators 102 to use to add their markers to their fluids. The centralized operator may limit the allocation of markers to operators 102 based on predefined criteria, such as demonstrating compliance with certain environmentally conscious specifications defined by the centralized operator.

[0023] One or more marker detectors 112 may be located at one or more locations in the system 100 to detect markers in the fluid. For example, one or more marker detectors 112 may be provided at a gas storage facility or at multiple supply lines 108 served by the network 104 to determine the presence and / or amount of a marker in the received fluid associated with a particular marker. As another example, the marker detectors 112 may be provided at a compression station, a consumer location, or a city gate. As another example, the power generation station 106 may have a marker detector 112 to detect a marker in the received fluid.

[0024] The detector 112 may use any suitable method for detecting the markers in the fluid. In one example, the detector 112 uses a suitable analytical technique, such as a combination of gas chromatography and mass spectrometry (GC-MS) to detect and optionally quantify the markers in the fluid. Mass spectrometry may be used to quantify low concentrations of the marker. Gas chromatography may be used to separate the markers from other components as much as possible to improve the sensitivity of the MS detector to the markers. Any suitable device may be used, and examples are provided below.

[0025] As previously mentioned, chemical markers can be associated with information, and identification of chemical markers in a fluid can be used to associate that information with the fluid. Once one or more markers are identified in a fluid, information associated with those markers can be associated with the fluid to identify, for example, which entity 102 is supplying the fluid and / or what standards (e.g., specifications) the fluid meets. In one example, the detector 112 can frequently analyze the fluid from time to time (e.g., periodically) to provide data about the contents of the fluid. In another example, the detector 112 can frequently analyze the fluid to provide ongoing data about the contents of the fluid.

[0026] The system 100 shown in FIG. 1 is one example of a system for tagging a fluid, such as natural gas, that is mixed with other fluids in a reservoir, such as a network of pipes 104. In other examples, the fluid may be dispensed or mixed in the reservoir during storage (e.g., in a man-made or naturally constructed container) or during transportation (e.g., in a container that may be placed on a truck, train, ship, etc.). In such other systems, the markers may be dispensed into the fluid before it is mixed with other fluids. In some examples, the markers may be dispensed into a fluid that is already a mixture from multiple providers, including before the mixture is further mixed with other fluids. Such markers may be added to identify a regional mixture of fluids and may be used in addition to markers that identify individual providers 102. Markers may be added to a fluid at any time during its life and for any desired reason, so long as each marker is uniquely detectable.

[0027] The chemical composition of the marker as well as the specific amount of the marker added to the fluid can be selected so that the marker is detectable as an artificially occurring amount of a specific chemical composition. That is, to be definitively identifiable as a marker, the chemical composition of the marker is present in the fluid in an amount that exceeds the normal (e.g., naturally occurring) amount of that chemical. The specific amount of the marker required to exceed the normal amount of the chemical depends on the chemical composition of the marker and the possible / expected chemical composition in the fluid. In one example, isotopic species of molecules are used as molecules for the marker because they naturally occur in small amounts in the majority of fluids. Because they are present in small amounts, small amounts of the molecules are required to exceed the normal (e.g., naturally occurring) amount. In a particular example, the isotopic species is a deuterated version of the molecule, where a deuterium atom replaces a hydrogen atom in the molecule.

[0028] In some examples, the chemical composition of each marker can be selected such that the marker can be detected by the detector 112 and specifically distinguished from other chemical markers. For example, if the detector uses chromatography to identify some or all of the markers, the chemical composition of each marker can be selected such that each marker provides a specific chromatographic signal. In some examples, a specific chromatographic signal can be achieved by selecting molecules that have different retention times, for example, retention times that are at least 10 seconds apart. In some examples, a number of different techniques can be used to detect molecules of a marker, so a given marker need not be specifically identifiable by a single technique, provided that the marker is specifically identifiable by the combination of techniques used.

[0029] In some examples, the chemical composition of the marker can be selected and the marker can be added using a method that allows the amount and / or percentage of the fluid corresponding to the marker to be determined after the fluid is mixed with other fluids that do not have the same marker. For example, it may be desirable to know not only if a particular entity 102's fluid is present in the composition, but also how much of that entity's 102's fluid is present in the composition. To accomplish this, a chemical marker can be selected that is uniquely identifiable by the detector 112 and that also allows the detector 112 to measure the amount of the marker present. The amount can be an absolute amount or a relative amount, so that the amount of the marker relative to the other markers is determined. In such examples, the addition of the marker to the corresponding fluid (e.g., to the first entity's 102's fluid before mixing) can be timed such that the amount of the marker added corresponds to the amount of the corresponding fluid present. The amount of the marker added can be maintained in a constant ratio to the amount of the fluid present. For example, a first marker corresponding to a first entity 102 can be added such that the first marker 102 is present in the first entity's fluid in an amount of 1 ppm by volume (ppmv). The detector 112 can then determine the amount of fluid from the first operator 102 in the composition based on the amount of the first marker detected. That is, if the first marker is detected in an amount of 1 ppmv, 100% of the composition is the first operator's fluid. If the first marker is detected in an amount of 0.5 ppmv, 50% of the composition is the first operator's fluid. This example uses a concentration of 1 ppmv, but any suitable amount can be used. To allow the amount of the marker to correspond to the amount of its corresponding fluid, the chemical composition of the marker can be selected to be deterministically diluted in the composition (e.g., in the same proportion or ratio as its corresponding fluid). For example, if 50% of the composition is made up of a fluid from the first operator 102 that has the first marker, the first marker is selected to be present in the composition in an amount that is 50% of the level at which it is added. Other methods of addition and detection can also be used.

[0030] As discussed above, a chemical marker may include a combination of two or more molecules (e.g., isotopic species) in a defined ratio. For example, a 1:1 molar (or volume) mixture of C2D6 and C2H3D3 can be added to dry natural gas at a concentration of 1000 ppbv (500 ppbv each). Other ratios of C2D6 and C2H3D3 can also be used, such as 1:5, 1:3, 1:2, 2:3, 3:2, 3:1, or 5:1. A specific fingerprint can be formed by using a chemical marker that is a defined ratio of multiple isotopic species. In one example, a mixture of multiple such defined ratios of two or more isotopic species can be used as a marker, which is selected so that the mixture can then be deconvoluted even if multiple such markers are present in a single fluid. Furthermore, the use of multiple isotopic species in defined ratios can provide a ratiometric method for detecting the amount of the marker and its corresponding fluid present.

[0031] To determine which markers are present in the fluid, and optionally the amount of markers present, the detector 112 can perform mass spectrometry on the fluid to determine which molecules used as markers are present in the fluid. A set of information corresponding to the molecular weight of each molecule used as a marker can be provided. For example, if the molecules used as markers consist of C2D6 and C2D4H2, the set of information includes about 36 for C2D6 and about 34 for C2D4H2. The detector 112 analyzes the output of the mass spectrometry to determine whether molecules with molecular weights of about 36 and about 34 were detected. In one example, if the area under the curve can be reliably integrated at molecular weights that are in the set, then molecules with molecular weights that are in the set are detected. The detector 112 can then determine which markers are present based on which molecules are detected. For example, if each marker is a single molecule, then detection of a molecule with a molecular weight that corresponds to the set of marker molecules is detection of the marker. In another example, if each marker is a defined ratio of multiple molecules, the detector 112 can deconvolute the results to determine which markers are present. Such deconvolution can use a linear programming algorithm that takes as input data the amount of each relevant molecule detected in the fluid using mass spectrometry along with information about each marker, the molecules that make up the marker, and the ratios of those molecules. The linear programming algorithm then calculates and outputs a set of one or more markers (e.g., a set of one or more ratios of molecules corresponding to each marker) that make up the amount of the molecule detected, and optionally the amount. This output identifies the markers present in the fluid. A calibration curve may be provided for each molecule used as a marker, which shows the correlation between the area under the detection curve (obtained by integration) from mass spectrometry for a particular molecular weight and the amount of the molecule present. The detector 112 can compare the area obtained for a molecular weight to the calibration curve for that molecular weight to determine the amount of the molecule present.

[0032] Figure 2 is an example chromatograph of a sample containing ethane (C2H6) and perdeuterated ethane (C2D6) in methane using a PLOT column and an instrument with a 300 μL injection volume. As shown, the CH4 peak elutes at approximately 3.4 minutes, while the C2H6 peak has a retention time of approximately 4.6 minutes. The concentration of ethane in the test sample was 10.3 ppmv in chemically pure methane, which, once compared to the calibration curve, is within the SIM m / z 30 (C2H6 + ) peak (A30=141280). 573 ppbv of C2D6, also with a retention time of 4.6 min, is also contained in this sample. Figure 3 shows the SIMs detected at m / z=36 (C2D6 + ) is a chromatograph showing the profile from a sample when the A36 peak is set to 0. As shown, despite co-elution with the much larger ethane peak, the much smaller C2D6 peak is seen and the area can be quantified. The C2D6 concentration matches the value obtained when the area of ​​the A36 peak is compared to the calibration curve. Due to variability in instrument performance, instruments are individually calibrated and a unique calibration curve is generated for each analyte.

[0033] Figure 4 shows an example of a calibration curve for various concentrations of C2D6 in chemically pure methane in the range 50-1000 ppbv. Open circles and error bars indicate the mean and standard deviation of triplicate measurements at each concentration. A linear fit to the data is also shown, with a correlation coefficient of 0.9997. MSD was used in SIM mode with m / z=36. The table below shows the measurements included in the calibration curve. [Table 1] The calibration curve showed an excellent linear fit to the data, good reproducibility at any given measurement, and quantitative detection (LOQ) down to 50 ppbv. The curve has a slope of 14.6 ± 0.13 and a y-intercept of -37.2 ± 61.2. The quantitative expression of this fit is A36 / 14.6 = [C2D6] (ppbv). The limit of detection is about half this value, about 25 ppbv. Larger injection volumes (>300 μL) and splitless injections can be used, but the most stable performance was seen with a 0.5:1 split. A split is when the analyte gas is mixed with the carrier gas in a mixing chamber prior to introduction to the column. Splitless means that no such premixing takes place. Without splitting, the local pressure cannot function and poor separation is obtained. In this example, 150 μL of helium was mixed with 300 μL of sample with a 0.5:1 split.

[0034] In some examples, the chemical composition of the marker can be selected so that the marker does not significantly change the chemical properties of the fluid. This can be achieved by selecting a marker that has similar chemical properties to molecules already present in the fluid. In this way, the marker can be added without significantly affecting the properties of the fluid, for example, without affecting the energy efficiency of the fluid. In one example, the marker molecule is an isotopic species of a molecule or type of molecule that is typically present in the fluid. The molecule (e.g., ethane) or type of molecule (e.g., hydrocarbon) of which the marker is an isotopic species is ideally present at relatively low concentrations or is not present at all in the fluid to which the molecule has not been intentionally introduced. For example, it is preferred that the molecules that make up the marker are naturally present in the fluid, typically at concentrations of less than about 1000 ppmv, more preferably less than about 100 ppmv, and most preferably less than about 10 ppmv, or 1 ppmv. In examples where the fluid is a gas, the concentration is measured as a volume percentage of the fluid (e.g., 10 ppmv). In examples where the fluid is a liquid, the concentration can be measured as a mass percent of the fluid. As an example, each molecule of the marker is added at a concentration of more than about 0.1 ppbv, for example between 0.1 ppbv and 1000 ppmv. For example, the molecules may be added at a concentration of more than about 0.1 ppbv, 0.25 ppbv, 0.5 ppbv, 1 pbbv, 2.5 ppbv, 5 ppbv, 10 ppbv, 25 ppbv, 50 ppbv, 100 ppbv, 250 ppbv, 500 ppbv, 1 ppmv, 2.5 ppmv, 5 ppmv, 10 ppmv, 25 ppmv, 50 ppmv, 100 ppmv, 250 ppmv, 500 ppmv, or 1000 ppmv. For the liquids to be labeled, the units used herein (included in the above concentrations) are parts per mass fraction (e.g., ppb, ppm) instead of parts per volume (e.g., ppbv, ppmv). This means, for example, that the concentration for the liquid is greater than about 0.1 ppb, for example between 0.1 ppb and 1000 ppm.

[0035] In some instances, the chemical composition of the marker can be selected such that its composition does not violate the requirements of the fluid, for example, there may be industry standards for the composition of dry natural gas, in which case the marker is selected to be an acceptable additive.

[0036] In one example, the fluid is natural gas and the marker molecules are isotopic species of hydrocarbons such as alkanes or alkenes. Some exemplary alkanes and alkenes are those having 1-3 carbon atoms (e.g., perdeuterated ethane, perdeuterated ethylene, perdeuterated propane, perdeuterated propene). Examples of molecules that can form isotopic species include methane, ethane, propane, butane, ethylene, propylene, or butene. Natural gas is primarily composed of hydrocarbons, so having the marker be an isotopic species of a hydrocarbon means that the marker does not significantly change the chemical properties of the gas. Alternatively, the marker may be various molecules naturally occurring in natural gas, such as carbon dioxide, nitrogen, hydrogen sulfide, or helium. Natural gas may contain low concentrations of isotopic species of alkanes. In such cases, the amount of the particular isotopic species used is selected to be higher than the natural abundance of the isotopic species discussed below.

[0037] In one example, the marker molecules are deuterium isotopic species of hydrocarbons. This can include, for example, deuterium isotopic species of methane, including one or more of CD4, CD3H, CD2H2, CDH3, and / or deuterium isotopic species of ethane, such as C2D6, C2H2D4, C2H3D3, etc. Such isotopic species include deuterium ( 2 H or D) 1 H, protium, or simply H). In another example, the isotopic species may be a carbon-based isotopic species (e.g., 13-carbon isotope). Such carbon-based isotopic species may or may not also include a deuterium isotope. A preferred chemical marker for use with methane is C2H6. A preferred chemical marker for carbon dioxide is CD4.

[0038] The selected molecules to be used as isotopic molecular species markers, alone or in combination with other molecules, may naturally occur in small amounts in the fluid. In this environment, the isotopic molecular species may be used in concentrations well above the amount that naturally occurs so that an artificially high level of the isotopic molecular species can be identified as a marker (or a component of the marker if multiple molecules are used as a single marker). It may be advantageous to use isotopic molecular species with more isotopes (e.g., more deuterium atoms) as molecules in the marker, because the more isotopes in the isotopic molecular species, the lower the natural abundance of the isotopic molecular species. Hydrocarbon isotopic molecular species with a few deuterium atoms (e.g., one deuterium atom) may naturally occur in small amounts in the fluid. However, the more deuterium atoms present in the isotopic molecular species, the lower the amount of that isotopic molecular species naturally occurring in the fluid. For example, C2D2H4 naturally occurs in natural gas at or below approximately 24 ppbv, and C2D3H3 occurs at approximately 3.17 e -12 In one example, the molecules in the marker have at least three deuterium atoms to ensure that the molecules naturally occur in sufficiently low amounts in the fluid. In another example, the molecules in the marker have at least four deuterium atoms to further ensure that the molecules naturally occur in sufficiently low amounts in the fluid. In hydrocarbons having more than three carbon atoms (e.g., butane), at least six deuterium atoms may be included in the molecules of the isotopic species used as the marker. In another example, at least half of the hydrogen atoms in the molecules of the marker are replaced with deuterium atoms. That is, the molecules in the marker have at least N / 2 deuterium atoms, where N corresponds to the number of hydrogen atoms in the corresponding molecule. For ethane, since ethane has six hydrogen atoms, this means that the molecules of the marker will have at least three deuterium atoms (i.e., including C2D3H3, C2D4H2, C2D5H, and C2H6). The following table lists the natural abundances of the deuterium-based isotopic species of methane in natural gas. [Table 2]

[0039] A gas chromatograph and mass spectrometer combination may be optimized for separation of methane and ethane, such as by using a Shimadzu TQ8030 to detect isotopic species of ethane. Mass spectrometric detection of trace isotopic species in natural gas is very sensitive and can therefore provide unambiguous identification and quantification of the isotopic species. For example, separation of trace ethane, propane, and butane (including their isotopic species) from methane can be achieved with a 50 meter Al2O3 / KCl porous layer hollow tube (PLOT) column using selected ion mode (SIM). Oven temperatures between 100°C and 0°C can be used, with improved separations obtained at lower temperatures (e.g., 10-50°C, preferably 20-40°C, more preferably 25-35°C, most preferably 30°C). Different detection parameters and equipment may be used for different fluids or marker molecules.

[0040] Any other combination of ethane isotopic species may also be used in a unique ratio. Additionally, one hydrocarbon isotopic species may be used in a unique ratio with another hydrocarbon isotopic species, for example, ethane isotopic species may be used with C3D9. The table below shows other exemplary markers with associated physical data. [Table 3]

[0041] FIG. 5 is a block diagram of an exemplary method 200 for producing isotopic species of alkanes (e.g., C2D6) that can be used as a marker for natural gas. The method 500 of FIG. 5 can economically produce isotopic species of alkanes using a two-step reaction based on normal water (H2O), heavy water (D2O), and carbon monoxide (CO). The two stages 502, 504 of the method operate in series, with the output from the first stage 502 being sent to the second stage 504. The first stage 502 of the method 500 includes applying power to perform electrolysis on the heavy water and, optionally, on normal water to split deuterium and, if present, hydrogen from oxygen. The heavy water and normal water may be pumped from storage tanks to provide a continuous input of heavy water and normal water.

[0042] The oxygen product from this first stage 502 may be vented to the atmosphere or contained for some other use. The deuterium and optionally dihydrogen from the first stage 202 are sent to a second stage 204 of the process 200. Carbon monoxide is the input to the second stage 204, which uses a catalyst such as platinum and a heater to reduce alkane isotopes with CO and the deuterium / hydrogen inputs. The second stage of the reaction produces a mixture of alkane isotopes, heavy water, and optionally normal water.

[0043] A series of condensers operating at low temperatures, such as cryogenic temperatures, can be used to separate the mixture of isotopic species, heavy water, and normal water (506). The heavy water and normal water can be collected and recycled back to the input of the first stage 202. The isotopic species in the output of the second stage 504 can be controlled by adjusting the ratio of heavy water to normal water input to the first stage 502 along with the temperature and pressure used in the second stage 504. For example, if no normal water is input to the first stage 502 (i.e., only heavy water is input), only fully deuterated alkanes (e.g., CD4 and C2D6) will be produced from the second stage 504. The ratio of normal water input to the first stage 502 determines the ratio of deuterated alkanes produced in the second stage 504.

[0044] In a particular example, 99% pure heavy water may be input to the first stage 502 at a rate of 305 mL / day. Separated oxygen is a by-product and is produced from the first stage 502 at a rate of, for example, 15.7 cubic feet / day. In one example, carbon monoxide may be provided from a gas cylinder and input to the second stage 504 at a continuous rate of about 8.7 cubic feet / day. In this example, C2D6 is produced from the separator at a rate of about 5 cubic feet / day. Five cubic feet / day of C2D6 production can tag 100 million cubic feet of dry natural gas at a concentration of 50 ppbv. The two-stage process can be operated at low pressure (e.g., 20 psig or less) to efficiently produce C2D6.

[0045] In one example, other isotopic species of ethane can be made using the same two-step reaction as method 200, except that the heavy water input to the first step is replaced with a mixture of heavy water and regular water (H2O). The mixture of heavy water and regular water results in a mixture of methane, ethane, and their isotopic species, including, for example, C2D6 and C2H2D4, produced by the two-step reaction. The ratio of heavy water to regular water can be varied to vary the statistical mixture of isotopic species in the product. The ratio of heavy water and regular water can be selected so that the product from a given reaction results in a uniquely identifiable mixture of isotopic species that can be used as markers or modified to be used as markers. The different ethane isotopic species can be separated and used as individual markers or combined with each other in uniquely identifiable ratios as described above. In either case, the markers made can be compressed into cylinders for transport to the appropriate marker input station 110.

[0046] Similar techniques can be used for markers of other fluids such as carbon dioxide (CO2), crude oil, and water. In one example, an isotopic species of methane (e.g., CD4) can be used as a chemical marker for carbon dioxide. Other exemplary molecules for use alone or in combination as markers for carbon dioxide include those in the table below. [Table 4-1] [Table 4-2]

[0047] In an example where the fluid to be tagged is crude oil, exemplary molecules to be used in the marker include hydrocarbons in the C8-14 range (8-14 carbon atoms), including both straight or branched chain hydrocarbons and / or molecules containing fluorine or chlorine. Isotopically labeled paraffins and alcohols can be used as labels for water or crude oil. In another example, isotopic species of one or more aromatic compounds are used as markers for crude oil. The proposed reaction process described above for deuterated ethane can also be adapted to synthesize long-chain isotopically labeled paraffins and alcohols for labeling liquid products such as crude oil and water.

[0048] The two-stage reaction in any of the above methods may use a stainless steel tube reactor filled with catalyst and controlled in temperature and pressure. The two stages may be carried out at the same or different pressures, for example in the range of 1-50 bar, more preferably 1-20 bar, or most preferably 1-5 bar. In one example, the first stage is carried out at a pressure less than about 3 bar and the second stage is carried out at a pressure greater than about 3 bar. In one example, the second stage is maintained at a temperature between about 100 and about 1200 degrees Celsius, for example between about 200 and about 400 degrees Celsius. The temperature may be controlled by an electric heater and a control system that monitors the temperature at multiple locations. The reactor length and diameter are sized for the designed flow rate along with the amount of catalyst.

[0049] Markers produced by any of the methods described herein may be compressed and then injected into a desired fluid or stored in a cylinder for transport or later use.

Claims

1. 1. A dry natural gas comprising at least 1 ppbv of a first isotopic species of a first hydrocarbon, said first isotopic species having at least three deuterium atoms.

2. 2. The dry natural gas of claim 1, wherein the first hydrocarbon is an alkane.

3. 3. The dry natural gas of claim 2, wherein the alkane is ethane.

4. The first isotopic species is C ２ D ６ 4. The dry natural gas of claim 3,

5. 5. The dry natural gas of claim 1, comprising at least 1 ppbv of a second isotopic species of a second hydrocarbon other than methane, the second isotopic species having at least three deuterium atoms and different from the first isotopic species.

6. 6. The dry natural gas of claim 5, wherein the second hydrocarbon is an alkane.

7. 7. The dry natural gas of claim 6, wherein the alkane is one of ethane or propane.

8. The second isotopic species is C ２ H ２ D ４ Or C ３ D ８ 8. The dry natural gas of claim 7, wherein

9. The second isotopic species is perdeuterated propane (C ３ D ９ 6. The dry natural gas according to claim 5,

10. 1. A method comprising adding at least 1 ppbv of a first isotopic species of a first hydrocarbon other than methane to dry natural gas, wherein the first isotopic species has at least three deuterium atoms.

11. The method of claim 1 , wherein the first hydrocarbon is an alkane.

12. The method of claim 2 wherein the alkane is ethane.

13. The first isotopic species is C ２ D ６ The method according to claim 3, wherein

14. 14. The method of claim 10, further comprising adding at least 1 ppbv of a second isotopic species of a second hydrocarbon other than methane to the dry natural gas, wherein the second isotopic species has at least three deuterium atoms and is different from the first isotopic species.

15. 15. The method of claim 14, wherein the second hydrocarbon is an alkane.

16. 16. The method of claim 15, wherein the alkane is one of ethane or propane.

17. The second isotopic species is C ２ H ２ D ４ Or C ３ D ８ 17. The method of claim 16, wherein the

18. The second isotopic species is perdeuterated propane (C ３ D ９ 15. The method of claim 14, wherein

19. receiving wet natural gas; processing the wet natural gas to produce the dry natural gas; 19. The method of claim 10, comprising: supplying the dry natural gas to a first storage facility, the first storage facility comprising a pipeline transporting dry natural gas from a plurality of processing plants or a container receiving dry natural gas from a plurality of processing plants; and adding at least 1 ppb of a first isotopic species comprises adding the at least 1 ppb before supplying the dry natural gas to the first storage facility.

20. analyzing the dry natural gas by a combination of gas chromatography and mass spectrometry, the analysis being performed downstream from where the at least 1 ppb of a first isotopic species was added; determining whether the first isotopic species is present in the analyzed dry natural gas based on the analysis; 20. The method of claim 19, comprising:

21. 21. The method of claim 20, wherein the determining step comprises deconvoluting results from the analysis to identify a plurality of unique chemical markers having a defined ratio of at least two different molecules.

22. Heavy water (D ２ O) continuously into the first reactor; electrolyzing the heavy water to produce deuterium and dioxygen; continuously passing the deuterium from the first reactor to a second reactor; continuously passing carbon monoxide (CO) to the second reactor; The deuterium oxide and carbon monoxide are passed over a catalyst to ２ D ６ obtaining a continuous product comprising: C from the other components of the product of the second reactor ２ D ６ and isolating Including C ２ D ６ A method for manufacturing the same.

23. 23. The method of claim 22, wherein the catalyst is platinum, cobalt, nickel, ruthenium, or a mixture thereof.

24. 24. The method of claim 22 or 23, further comprising the step of separating heavy water from the output of the second reactor and using the separated heavy water in the first reactor.

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