Abstract:
The present invention relates to a system of analysis, which can be used in a mobile laboratory in a drilling site situation or in a similar situation, suitable for measuring (preferably in relation to at least two partially gaseous species, which derive preferably from a mixture extracted from a drilling mud, for example, methane, ethane, propane and/or any other heavier hydrocarbons) the quantities of the different isotopes of at least a same chemical element (preferably the quantities of  13 C, carbon isotope with 6 protons and 7 neutrons, and of  12 C, carbon isotope with 6 protons and 6 neutrons, respectively) by means of a laser isotopes analyser regulated for a single, at least partially gaseous species which contains said chemical element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of the priority filing date in Italian patent application no. MI2011A001647 filed on Sep. 14, 2011. The earliest priority date claimed is Sep. 14, 2011. 
       FEDERALLY SPONSORED RESEARCH 
       [0002]    None 
       SEQUENCE LISTING OR PROGRAM 
       [0003]    None 
       STATEMENT REGARDING COPYRIGHTED MATERIAL 
       [0004]    Portions of the disclosure of this patent document contain material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office file or records, but otherwise reserves all copyright rights whatsoever. 
       BACKGROUND OF THE INVENTION 
       [0005]    The present invention relates to a system of analysis, which can be used in a mobile laboratory in a drilling site situation or in a similar situation, suitable for measuring (preferably in relation to at least two at least partially gaseous species, which derive preferably from a mixture extracted from a drilling mud, for example, methane, ethane, propane and/or any other heavier hydrocarbons) the quantities of the different isotopes of at least a same chemical element(preferably the quantities of  13 C, carbon isotope with 6 protons and 7 neutrons, and of  12 C, carbon isotope with 6 protons and 6 neutrons, respectively) by means of a laser isotopes analyser regulated for a single, at least partially gaseous species which contains said chemical element. 
         [0006]    At the current state of the art, the instruments which are commonly used for measuring the isotope ratio of carbon in hydrocarbons, which is linked to the quantities in mass of the two isotopes mentioned, are mass spectrometers of the IRMS (isotope ratio mass spectrometer) type, which in fact allows for separate investigation of the relative concentration of stable isotopes,  12 C and  13 C, in different gaseous species. However, instruments of this type are not suitable for site analysis because of their dimensions and because they have to be used in particular environmental conditions free from vibrations and with stable temperature and pressure. These facts preclude their use in drilling sites, both on land and at sea, where said analysis has to take place in a continuous process. 
         [0007]    The object of the present invention is that of producing a system of analysis which is able to measure the isotopic content of a chemical element, as a continuous process on site, and in relation to at least two different, partially gaseous species containing that element. Said species is contained in at least one partially gaseous mixture, which in turn was originally extracted, preferably from drilling mud. This allows accurate analyses to be carried out in a continuous and easily manageable manner, even in difficult environmental conditions, such as remote site locations on land or on a sea platform. 
         [0008]    Another type of instrumentation for analysing the isotope ratio of carbon is known and described in patent application EP 1887342. This application is based on laser optical spectrometry, which allows the production of an instrument of simpler application and management and which can be used on site. However, because this instrument is configured in such a way that the laser spectrometer is able to quantify the relative abundance of the two stable isotopes of the carbon only in a single hydrocarbon species, it is not possible to analyse, the relative abundance of the two stable isotopes of the carbon also in other hydrocarbon species in a single analysis cycle and without modifying the configuration of the same laser spectrometer. In fact, the operation of changing the configuration of the analyzer leads to an unacceptable discrepancy between the analysis and the current depth. 
         [0009]    Another object of the present invention is that of producing an instrument that is able to quantify the isotope ratio of a chemical element contained in at least two partially gaseous species in a continuous process on site. The partially gaseous species derive from a mixture previously contained in a drilling mud, without modifying the configuration of the isotope analyser. Thus, there is a good correlation between the analysis and the current depth. The latter analyser uses laser spectrometry and is intended to measure the relative quantity of two stable isotopes of a chemical element contained in each of said gaseous species. The gaseous species are previously separated from the mixture by means of a gas chromatograph controlled by software, and then transformed one by one into a gas species, such as carbon dioxide CO 2 , for which this analyser is configured. In this way, the isotope content of several gaseous species can be analysed, continuously and at different depths, without having to work on the analyser. Such an operation would take too much time for numerous analyses, which cannot be prolonged excessively because the analyses have to be correlated to the depth in approximate real time considering that the mixture flows continuously. 
         [0010]    Moreover, at the state of the art, no site instrument for the analysis of the isotope ratio of carbon in hydrocarbon gases internally provides a system of chromatographic separation of each gaseous species constituting the mixture sampled and comprising a flame ionization detector or FID. This detector was introduced in order to check the correct separation of the single gas species, and therefore to define the correct sampling thereof before carrying out the analysis. Without the flame ionization detector, the instrument would be considered “blind” and therefore not able to ensure that the same gas species is sampled in every phase in which the analysis is to be performed. 
         [0011]    A further object of the present invention is that of producing an instrument which is able to quantify, also in a continuous process on site, at least one isotope ratio of a chemical element contained in at least two partially gaseous species. The partially gaseous species derives from at least a mixture previously contained in drilling mud. The instrument is able to ensure that the gas species is exactly the same in every phase whereof in which the analysis is performed. 
         [0012]    To date, it has not been possible to perform isotope analyses of continuous flows sufficiently in real time by means of laser isotopes analysers. This is because it was not possible to have sufficiently distanced times in sending a single gas species to said analyser so as to allow the laser isotope analysis. In any case, it was not possible to conclude the cycle of analysis in a sufficiently rapid manner for all the gaseous species of geological interest, which are usually methane, ethane and propane. 
         [0013]    Therefore, an important object of the present invention is that of providing an instrument with which it is possible to send single gaseous species extracted from a mixture which flows continuously, to a laser analyser at sufficiently large intervals of time, and which can rapidly conclude the entire cycle of analysis for all the gaseous species of interest in order to perform several analyzes in real time. Thanks to the particular configuration given here to the gas chromatograph, the gaseous species to be analysed are sent to the isotope analyser at sufficiently distanced intervals of time, so as to allow the same to perform the analysis of each individual species. All the gas species not yet analysed remain trapped in a column of the gas chromatograph, while only one of these species is sent towards the analyser, in such a way as to obtain a sufficient interval of time between two successive analyses. In any case, the device takes a sufficiently reduced time to conclude the entire cycle of analysis of the gas species extracted at a certain depth, and in such a way that it is possible to perform analyses at many levels of depth. 
         [0014]    On these bases, the present invention uses the technology known as gas chromatography for the separation of gaseous species, combined with a flame ionization detector (FID). The FID is intended to correctly identify the times of gas retention under investigation inside the various components of the gas chromatograph. Gas chromatography, together with laser spectrometry, is used to detect the isotopic content, and so the isotopic ratio, of the carbon contained in each of said gaseous species. 
       SUMMARY OF THE INVENTION 
       [0015]    Firstly, it is noted that, in the present application, and thus with reference also to the claims: 
         [0000]    the term “valve” can denote any means for distributing at least one fluid flow and which preferably allows, on the bases of the configuration it takes on, the placing in contact, according to several combinations, of at least two sections or ways or outlets formed therein;
 
the term “conduit” can denote any means for the containing of at least one fluid flow;
 
the term “chromatographic column” can denote any means capable of separating at least partially, preferably on the bases of different weight, at least two gaseous species flowing in the same column;
 
the term “processor” can denote a software together with all the physical devices, which constitute the hardware and which allow the software to operate.
 
         [0016]    The present invention is, therefore, a system of analysis that is able to: 
         [0000]    separate at least two different partially gaseous species from a mixture and extracted from drilling mudto be analyzed, such as methane, ethane and/or propane, as well as other possible superior equivalents including aromatic hydrocarbons;
 
quantifyat least two different isotopes and optionally at least one isotope ratio of at least one chemical element for at least two of said gaseous species, which is preferably carbon, and coming from the latter species to be analyzed.
 
         [0017]    The instrument developed as part of the present invention is therefore constituted mainly at least by the following components: 
         [0000]    at least one gas chromatograph for the mutual separation of said gaseous species;
 
at least one oxidation oven for heating separated gaseous species and consequently producing at least one other partially gaseous species;
 
at least one laser isotopes analyser configured to analyse said gaseous species produced by heating;
 
means for transferring each of said gaseous species to be analysed from said gas chromatograph to said oxidation oven;
 
means for transferring said gaseous species produced by heating from said oxidation oven to said laser isotopes analyser.
 
         [0018]    Moreover, the system preferably comprises at least the following components: 
         [0000]    means for collecting and concentrating said gaseous species produced by heating before isotope analysis;
 
at least one processor suitable for controlling at least part of the components of said system.
 
         [0019]    It is to be noted that the present device foresees the following features: 
         [0000]    said oxidation oven transforms said gas species to be analysed, at least into carbon dioxide CO 2 ;
 
said laser isotopes analyser is configured to analyse isotopes of carbon contained in carbon dioxide CO 2 ;
 
said gas chromatograph is connected to at least one flame ionization detector or FID, and intended to measure the retention times of gas species and to calibrate the system.
 
         [0020]    The preferred embodiment of the device is configured, by at least one known means, so as to be used with a process that comprises a sequence formed by the following steps (at least partially controlled by said processor and whereof at least two steps can be partially simultaneous): 
         [0000]    a) part of a partially gaseous mixture enters said gas chromatograph;
 
b) said part of said mixture is partially separated into two portions, at least one partially gaseous species contained in one of these portions being different from at least one partially gaseous species contained in the other of said portions;
 
c) at least part of one of said portions enters said oxidation oven;
 
d) said oxidation oven heats said part of said portion, and then generates at least one partially gaseous species;
 
e) at least part of the latter generated species enters said laser analyser, which analyses the isotope content relative to a chemical element which constitutes a part of the same generated species;
 
f) steps c) , d), e), are repeated for at least another of said portions.
 
         [0021]    The gas chromatograph of the preferred embodiment of the present device is constituted at least by the following components partially inside a heated chamber: 
         [0000]    one valve (called “sample valve”) for sampling gaseous mixture from drilling mud, along a line where said gaseous mixture flows continuously;
 
one conduit for the entry of at least a carrier gas (called “primary entry line”) connected to at least one way of said sample valve;
 
one other conduit for the entry of the gaseous mixture to be analysed (called “gas entry line”) connected to at least one way of said sample valve;
 
one other conduit which performs the function of chromatographic column (called “backwashing column”) connected to at least two ways of said sample valve;
 
one other conduit (hereinafter, “sampling cell”) where said gaseous mixture flows and where the same mixture is subsequently taken over by the carrier gas, said sampling cell being connected to at least two outlets or ways of said sample valve;
 
one other conduit (called “intermediate line”) connected to at least one way of said sample valve;
 
said sample valve being able to place in contact at least:
 
         [0022]    said sampling cell with gas entry line and a discharge conduit, or said sampling cell at least with said backwashing column and said primary entry line; 
         [0023]    said backwashing column with said primary entry line and with a discharge conduit, or said backwashing column with said intermediate line and said sampling cell; 
         [0024]    said gas entry line with said sampling cell or with a discharge conduit; 
         [0000]    one other valve (hereinafter, “storage valve”) connected to the sample valve by means of said “intermediate line”;
 
one other conduit for storing the gaseous species to be analyzed (hereinafter, “store column”) connected to at least two ways of said storage valve;
 
said store column performing the function of a chromatographic column;
 
one other conduit (called “connection line”) connected to at least one way of said storage valve;
 
said storage valve being able to place in contact at least:
 
         [0025]    said store column with said intermediate line and said connection line, or said store column with at least two partially closed sections; 
         [0000]    a flame ionization analyser FID, connected to the system and in contact with said storage valve. Said FID carries out the synchronisation of the valves and monitors the output times of different gaseous species under examination in order to calibrate the device and to be sure that the same gaseous species are sent separately to the oxidation oven;
 
one other valve (called “final valve”) connected to said storage valve through said connection line;
 
one other conduit for the final sampling of the gaseous species to be analysed, which is conveyed towards the oxidation oven by the carrier gas. Said conduit being referred to as “holding chamber” and connected to at least two ways of said final valve;
 
one other conduit for the discharge of gas, connected to at least one way of said final valve;
 
one other conduit for the entry of the carrier gas (called “secondary entry line”) connected to at least one way of said final valve;
 
one other conduit (called “exit line”) for the exit of each gas species travelling towards said oxidation oven, said exit line being connected to at least one way of said final valve;
 
said final valve being able to place in contact at least:
 
         [0026]    said holding chamber st with said connection line and a discharge conduit, or said holding chamber with said secondary entry line and said exit line; 
         [0027]    said connection line with said holding chamber, or with a discharge conduit; 
         [0000]    said valves being able to place in contact different pairs of outlets or ways according to the configuration which they assume, and being controlled preferably by solenoid valves via pressurised air;
 
said valves preferably being pneumatic.
 
         [0028]    During the analysis cycle, these valves change configuration automatically via the processor which controls said solenoid valves, and at instants of time. These valves are programmed in such a way that the gaseous species of interest arrive separated at the oxidation oven. The initial gaseous mixture, transiting via the backwashing and store columns (preferably filled with active polymers able to slow down most the motion of heavier gases), separates into the single gaseous species, which are sent singly to the oxidation oven due to synchronisation of the same valves. 
         [0029]    Generically, the preferred embodiment of the present system is configured with adequate means so as to allow said chromatograph to be able to operate according to a process which comprises at least the sequence formed by the following steps—at least partially controlled by said processor, which in turn is preferably manually calibrated by the user, and whereof at least two steps can be at least partially simultaneous: 
         [0000]    at least part of a partially gaseous mixture (henceforth, “mixture”) arriving from the entry line for the gas, flows at least partially through the sampling cell and moves towards a discharge conduit;
 
said sample valve changes configuration so as to place said primary entry line in contact with said sampling cell;
 
at least a carrier gas partially enters the sampling cell, taking from it said part of the mixture, and drawing the latter at least partially into the backwashing column;
 
two or more partially gaseous species of said mixture (henceforth, “species”) are at least partially separated, or moved away, between them and within said backwashing column;
 
at least a carrier gas starts to draw at least two of said species (henceforth, “first species” and “second species”) are preferably the lighter components of said part of the mixture, inside said intermediate line;
 
after the heaviest species which is to be analysed has partially entered said intermediate line, the sample valve once again changes configuration, so as to prevent heavier species from entering said intermediate line;
 
at least one carrier gas draws said first and second species to be analyzed partially through said intermediate line and subsequently inside said store column, where the latter two species move away even more between them;
 
at least said first species exits from said store column, while said storage valve is places said store column in contact with said connection line, and enters said connection line;
 
said storage valve changes configuration so as to place said store column in contact with said two closed sections so that said second species remains trapped inside said store column;
 
at least one carrier gas draws said first species through said connection line, and subsequently inside said holding chamber, while said final valve places said holding chamber in contact with said connection line;
 
said final valve changes configuration so as to place said holding chamber in contact with said secondary entry line;
 
at least one carrier gas, arriving from said secondary entry line, flows through said holding chamber, taking said first species and conveying it into said exit line;
 
said storage valve changes configuration so as to place said store column in contact with said connection line so that said second species exits from said store column, and enters said connection line;
 
at least one carrier gas draws said second species through said connection line, and subsequently inside said holding chamber, while said final valve again places said holding chamber in contact with said connection line;
 
said final valve changes configuration so as to place said holding chamber in contact with said secondary entry line;
 
at least one carrier gas, arriving from said secondary entry line, flows through said holding chamber, taking said second species and conveying it into said exit line.
 
It is to be considered that, if said at least two gaseous species to be analyzed are more than two, when the second species is in the holding chamber, another species (called “third species”) remains trapped in the store column as a result of another configuration change of said storage valve.
 
         [0030]    The system is synchronized so that, separately and sequentially, for each single species of said at least two species: 
         [0000]    the single species flows through said exit line, enters said oxidation oven and is heated so as to produce carbon dioxide;
 
the carbon dioxide produced by the heating of said single species is collected and concentrated by known means;
 
said isotope analyzer detects the isotopic content of the carbon contained in said carbon dioxide, which is derived from said single species.
 
         [0031]    All these features will be made clearer by the following detailed description of a possible embodiment of the present invention, to be considered by way of a non-limiting example of the more general concepts claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The following description refers to the accompanying drawings, in which: 
           [0033]      FIG. 1  is a schematic representation of the gas chromatograph analysis circuit; 
           [0034]      FIG. 2  is an enlargement of the zone where the sample valve is disposed; 
           [0035]      FIG. 3  is an enlargement of the zone where the storage valve is disposed; 
           [0036]      FIG. 4  is an enlargement of the zone where the final valve is disposed; 
           [0037]      FIG. 5  is a block diagram of the initial phase in which the entire system undergoes washing; 
           [0038]      FIG. 6  is a block diagram of the phase during which the gaseous species to be analysed are taken by the carrier gas into the sampling cell; 
           [0039]      FIG. 7  is a block diagram of the phase during which a single gaseous species is transported towards the oxidation oven. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]    In  FIG. 1 , the lines schematically represent conduits or columns where the gaseous species can transit and, as a general rule, when two lines intersect completely, forming four equal angles, two by two. The relative conduits are not in contact with each other. The carrier gas, preferably nitrogen N 2 , comes in the direction of the arrow C from the primary entry line or conduit  10 , while the gas to be analysed comes in the direction of the arrow D from the conduit or entry line for the gas  11 , and can be a continuous flow or also only a sample. 
         [0041]    The three sample  20 , storage  40  and final  50  valves can be seen, each of which, as can be seen also in  FIGS. 2 ,  3  and  4 , is provided with a certain number of ways or inlets, schematically positioned at the vertices of a polygon and corresponding, only in  FIGS. 2 ,  3  and  4 , to progressive series of numbers. Said valves can take on at least two configurations, such that when they take on the first configuration they place the pairs of ways in direct contact corresponding to the pairs of vertices between which a continuous line is placed, whereas when they take on the second configuration they place the pairs of ways in contact corresponding to the pairs of vertices represented by a dotted line. Henceforth said first configuration will be referred to as configuration “A” while said second configuration will be referred to as configuration “B”. 
         [0042]    In  FIGS. 2 ,  3  and  4  some conduits connected to the valves are denoted by the corresponding number and, due to a space requirement, interrupted partially. 
         [0043]    As can be seen in detail in  FIG. 2 , configuration A, the sample valve  20  places in contact: 
         [0000]    the backwashing column  13  with the primary entry line  10  and a discharge line  14 , thus respectively the pairs of ways  21 ,  30  and  25 ,  24 ;
 
the sampling cell  64  with the primary entry line for the gas  11  and a discharge conduit  65 , thus respectively the pairs of ways  29 ,  28  and  26 ,  27 ;
 
the compensation conduit  12  with the intermediate line  15 , thus the pairs of ways  23 ,  22 ;
 
whereas in configuration B, the sample valve  20  places in contact:
 
the backwashing column  13  with the sampling cell  64  and the intermediate line  15 , thus respectively the pairs of outlets  25 ,  26  and  21 ,  22 ;
 
the entry line for the gas  11  with a discharge conduit  65 , thus the pair of ways  28  and  27 ;
 
the sampling cell  64  with the primary entry line  10 , thus the pair of outlets  29 ,  30 ;
 
the compensation conduit  12  with a discharge conduit  14 , thus the pair of outlets  23 ,  24 .
 
         [0044]    As can be seen in  FIG. 3 , in configuration A, for example, the storage valve  40  places in contact the store column  16  with the closed ways  46  and  47 , thus respectively the pairs of ways  48 ,  47  and  45 ,  46 ; in configuration B, instead, it places the store column  16  in contact with the intermediate line  15  and the connection line  18 , thus respectively the pairs of ways  48 ,  41  and  45 ,  44 . 
         [0045]    As can be seen in  FIG. 4 , in configuration A, for example, the final valve  50  places the holding chamber  19  in contact with the secondary entry line  66  and the exit line  67 , thus respectively the pairs of ways  52 ,  53  and  55 ,  54 ; in configuration B, instead, it places the holding chamber  19  in contact with the connection line  18  and a discharge conduit  60 , thus respectively the pairs of ways  52 ,  51  and  55 ,  56 . 
         [0046]    In this example, the eventuality that the gases of interest are methane CH 4 , ethane C 2 H 6  and propane C 3 H 8 , whereof the first is the lightest and the last one is the heaviest, is taken into consideration. The process whereby the instrument operates from when the gas enters the gas chromatograph to when the heaviest gas species exits, moving towards the oxidation oven, consists of several phases, which are preferably controlled by specific software. 
         [0047]    In the first phase, the sampling valve  20  is set, automatically by the software, in configuration “A,” while the storage  40  and final valves  50  are in configuration “B”. In this way, part of the carrier gas which comes from the primary entry line  10 , as can be seen in  FIGS. 1 and 2 , enters the way  30 , exits from the way  21 , and travels along the backwashing column  13  in the direction of arrow E. Afterwards, it enters the way  25  and exits from the way  24  to move towards a discharge conduit  14 , thus cleaning said backwashing column  13 . 
         [0048]    The other part of the carrier gas, which branches off from the initial crossing, as can be seen in  FIGS. 1 and 2 , travels along the compensation conduit  12 , enters the way  23 , exits from the way  22  and moves, via the intermediate line  15 , towards the storage valve  40 . 
         [0049]    Subsequently, as can be seen in  FIGS. 1 and 3 , the carrier gas enters the way  41  of said storage valve  40 , then exits from the way  48  and subsequently travels in the direction of arrow G and cleans the store column  16 . Subsequently, said part of carrier gas enters the way  45 , exits from the way  44 , and arrives at a crossing in which it divides into two portions. 
         [0050]    The first of these portions is smaller, and reaches the flame ionization analyser or FID  17 , which is therefore intended to calculate the arrival times of the various gaseous species, while the other one travels along the connection line  18 , subsequently entering the way  51  of the final valve  50  as can be seen in  FIG. 4 . The latter portion then exits the way  52 , travels in the direction of arrow H and cleans the holding chamber  19 , so as to enter the way  55  and exit from the way  56 , to then reach the discharge  60 . 
         [0051]      FIG. 1  also shows the supply lines to the FID of air  61  and hydrogen  62 , as well as the discharge line for condensation  63 . 
         [0052]    As shown in  FIGS. 1 and 2 , the gas mixture to be analysed, comes from the entry line for the gas  11 , enters the way  28 , exits from the way  29 , travels in the direction of arrow L along the sampling cell  64 , enters the way  26  and exits, moving towards the discharge conduit  65 , from the way  27 . 
         [0053]    The second phase starts up when the initial valve  20  changes configuration at the command of the synchronised processor, so that the portion of carrier gas which arrives at the way  30  is forced to travel along the sampling cell  64 , passing from the way  29  and in the direction of arrow L, taking the gas content thereof. Subsequently this flow of carrier gas, together with the mixture collected, traverses the way  26 , exits from the way  25  and travels along the backwashing column  13  in the direction of arrow F, to then pass through the ways  21  and  22  and flow into the intermediate line  15 . 
         [0054]    When the gases exit from the way  22 , the gases are already at least partially separated because they have travelled along the backwashing column  13 , which is a separation chromatographic column, i.e., it has the capacity to slow down most of the heavier gases. During this phase, the gaseous mixture, coming from the entry line for the gas  11 , flows continuously in the case of continuous analysis. The gaseous mixture flows through the ways  28  and  27 , directly towards the discharge conduit  65 , in such a way that successive analyses are fairly faithful to the current depth. 
         [0055]    The system is synchronised, preferably by means of the processor. This is done in such a way that the sample valve  20  returns to configuration A, triggering the third phase, when the gas species of interest (in this case methane, ethane and propane) are drawn into the intermediate line  15 , so that they alone are transported towards the storage valve  40 . Since propane is the heaviest gas, the sample valve  20  returns to configuration A when the entire propane portion has exited from the way  22 . Methane and ethane are lighter, and are in a more advanced position, along said intermediate line  15 , towards the storage valve  40 . 
         [0056]    During said third phase, the carrier gas returns to wash in the countercurrent from the backwashing column  13 , cleaning the gaseous species from the backwashing column  13  that are not of interest, while the in-coming gaseous mixture continues to travel continuously along the sampling cell  64 . The gaseous mixture then moves towards the discharge  65  to ensure that the analyses are correlated to depth at a reduced time lag. The compensation conduit  12  is so called because it serves to ensure that, in this phase, the carrier gas (which arrives from said compensation conduit  12  and flows into the intermediate line  15 ) arrives with the same load losses whereto the flow of carrier gas was subject. In the previous phase, the carrier gas flowed into said intermediate line  15  after having travelled along the backwashing column  13 . 
         [0057]    Methane, which is the lightest of the three gases, arrives first at the storage valve  40  and traverses (as seen in  FIGS. 1 and 3 ) the ways  41  and  48  sequentially—said storage valve  40  being in configuration B—to then enter the store column  16 . Subsequently, Methane enters the way  45  and exits definitively from said storage valve  40  through the way  44 , to then move towards the FID in part and the final valve  50  in part. 
         [0058]    The first of said parts, which is usually smaller, only serves to calculate the arrival times of the various gases during calibration and synchronise the valves, preferably by means of the processor and preferably manually by the user. On the other hand, the second of said parts travels along the connection line  18  and arrives at the final valve  50 . Said part of methane (as shown in  FIGS. 1 and 4 ) enters the way  51  and exits from the way  52 —said final valve  50  being in configuration B—to then travel along the holding chamber  19 . 
         [0059]    When all the methane is inside the holding chamber  19 , the storage valve  40  passes automatically into configuration A, as a result of the synchronised processor, so as to trap ethane and propane in the store column  16 . The store column  16  is in direct contact with the closed ways  47  and  46  in this case, as can be seen in  FIG. 2 . This condition is known as “store column” and corresponds with the fourth phase, during which the carrier gas that arrives from the intermediate line  15  traverses the valve  68  (referred to as “tap valve”) connected to the ways  42  and  43  of the storage valve  40 . After the carrier gas flows into the connection line  18 , the carrier gas enters the discharge line  60 , and passes through the final valve  50  (as seen in  FIG. 1 ). 
         [0060]    During the successive fifth phase, the final valve  50  also takes on configuration A, so that the carrier gas that arrives from the secondary entry line  66  (as seen in  FIGS. 1 and 4 ) travels along said holding chamber  19  after having traversed the ways  53  and  52 . The carrier gas can then take on the methane located in said holding chamber  19 . Subsequently, the methane is transported into the exit line  67 , passing through the ways  55  and  54 , and heads for the oxidation oven. 
         [0061]    In the sixth phase, the storage  40  and final  50  valves are once again in configuration B, so that the carrier gas coming from the holding chamber  19  travels to the discharge  60 , passing sequentially through the ways  55  and  56  of said final valve  50 . On the other hand, ethane, which is trapped in the storage column  16 , can travel towards the final valve  50  and the FID  17 . The system is preferably synchronised so that until all the ethane reaches the holding chamber  19 , the propane, which is heavier, does not yet travel along the entire store column  16 . In this way, the previous trapping effect acts effectively only on the portion of ethane. 
         [0062]    The seventh phase starts when, the storage valve  40  moves into configuration A at the moment at which all the ethane is in the holding chamber  19 . This traps the propane in the store column  16 , restoring the condition of “store column”. Subsequently, the final valve  50  also moves into configuration A, triggering the eighth phase. 
         [0063]    In the eighth phase, the carrier gas coming from the secondary line  66  conveys the ethane towards the oxidation oven through the exit line  67 . 
         [0064]    In phase nine phase, both the storage  40  and final  50  valves are again in configuration B. Thanks to the flow of carrier gas arriving from the intermediate line  15 , a portion of propane flows towards the final valve  50  through the connection line  18 , while the other portion of this gas moves towards the FID, which calibrates the retention times. 
         [0065]    Phase ten starts when the final valve  50  takes on configuration A (i.e., after the entire portion of propane heading for the final valve  50  has entered the holding chamber  19 ). Said portion is conveyed by the carrier gas coming from the secondary entry line  66  (as seen in  FIG. 4 ) into the exit line  67 , and then drawn towards the oxidation oven. 
         [0066]    In phase eleven, the final valve  50  is once again in configuration B. The system therefore returns to the initial conditions and the analysis sampling cycle begins again. 
         [0067]    All valve configuration changes are managed by the processor, so that the user only has to start the instrument, which is controlled by software. The phase of preliminary calibration, and therefore of software programming, is preferably performed manually by the user. 
         [0068]    In  FIG. 5 , the second phase is schematised. It shows the carrier gas, N 2 , entering the sampling cell, taking the gas species indicated as C 1 , C 2 , and C 3 , and transporting them to the store column. The other portion of carrier gas travels along the compensation conduit to the discharge. 
         [0069]    In  FIG. 6 , the third phase is schematised, during which C 1 , the lightest of the gases to be analysed (i.e., methane) is transported into the holding chamber, while C 2  and C 3  remain trapped in the store column. The path of the incoming carrier gas can be seen, part of which washes in against the backwashing column to then go to the discharge. Another part of the carrier gas travels along the compensation conduit, entering the store column and drawing the lightest of the gases towards the holding chamber and the FID. 
         [0070]      FIG. 7  schematises the fifth phase, during which the carrier gas coming from the secondary entry line enters the holding chamber, takes the content of C 1 , and transports the gas to the oxidation oven. 
         [0071]    Said gas is transformed preferably into carbon dioxide which, after having passed through a sampler that collects the gas and concentrates it, goes to an isotopes analyser (preferably laser) that is configured appropriately and whose functions are known in the art. Said analyser is mainly based on detecting light absorption by atoms  12 C and  12 C at two different wavelengths. The configuration has to be regulated especially on the basis of the gas to be analysed, in our case CO 2 . 
         [0072]    Variations in the constitution of the system described and of the process whereby it operates are possible, in any case coming within the scope of protection of the present patent according to what is expressed in the claims.