METHOD FOR ESTIMATING A QUANTITY OF A HYDROCARBON IN MUD RECOVERED FROM A WELL, AND A DEVICE AND PROGRAM USING THE METHOD

Abstract

A method for estimating a concentration of a hydrocarbon in mud recovered from a well includes acquiring a measurement representative of a concentration of the hydrocarbon in mud. An indicator of drill bit metamorphism in the mud is estimated. At least one measurement representative of the concentration of the hydrocarbon in the mud is corrected based on the indicator of drill bit metamorphism.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Indonesian Patent Application No. P00202112264, filed Dec. 29, 2021, and U.S. Provisional Patent Application No. 63/215,628, filed Jun. 28, 2021. Each of the patent applications identified above is incorporated herein by reference in its entirety.

BACKGROUND

During the drilling of a well containing oil or another effluent (in particular gas, steam, water), gaseous compounds contained in the drilling muds emerging from the well can be analyzed. This analysis facilitates the reconstruction of the geological sequence of the formations passed through during the drilling process and helps to determine possible uses for the fluid deposits encountered.

This analysis, which is carried out continuously, includes two main phases. The first phase includes extracting the gases conveyed by the mud (for example, hydrocarbon compounds, carbon dioxide, carbon monoxide, hydrogen and hydrogen sulphide). The second phase includes quantifying the extracted gases.

In the following, “hydrogen” can include gaseous hydrogen, also called di-hydrogen, which is a molecule having two hydrogen atoms.

A degasser having mechanical stirring means of the type described in U.S. Pat. No. 6,443,001 (the entirety of which is incorporated herein by reference) is frequently used for extracting the gases from the mud. The gases extracted from the mud, which are mixed with a carrier gas introduced into the degasser, can be conveyed by suction through a gas extraction conduit up to an analyzer, which allows the extracted gases to be quantified.

In some cases, the concentration which is obtained from the extraction in the degasser is not representative of the concentration of the hydrocarbon in the geological formation. For example, when drilling, heat may be generated at the interaction of the bit and the formation which is sufficient to crack alkanes, i.e., when heat that surpasses activation energy of a liquid alkane in the oil-based mud (or a hydrocarbon containing mud), hydrocarbons in the drilling liquid are partially transformed into short chain alkanes. Such a phenomenon is known as “drill bit metamorphism” (DBM). This phenomenon is related to many drilling and rock parameters, such as rock strength, abrasiveness, hardness of cutter, sliding surface areas, friction areas, weight on bit, vibrations, torque, effectiveness of bit cooling which corresponds to the mud flow rate and mud and cutter/bit heat transfer rate. As an example, such cracking might happen when the drilling rotation speed is particularly high, such as in turbo-drilling or power-drilling operations. However, such alkanes are indistinguishable from the alkanes collected from the geological formation.

Consequently, when DBM is present, the measured concentration of hydrocarbon is generally higher than the hydrocarbon concentration from the formation. This may lead to an overestimation of the amount of oil or gas in the wellbore.

SUMMARY

Embodiments of the present disclosure relate to a method for estimating a concentration of a hydrocarbon in mud recovered from a well, an estimating device implementing the aforementioned method, and a computer program including software instructions, which implements an estimation method for estimating a concentration of at least a hydrocarbon in mud, when a computer executes them.

In some embodiments, the method allows estimation of a concentration of a predefined type of hydrocarbon in mud recovered from a well.

In some embodiments, a method for estimating a concentration of at least one hydrocarbon in mud recovered from a well, e.g., implemented in an estimation device, includes acquiring a measurement representative of a concentration of the at least one hydrocarbon in mud. An indicator of drill bit metamorphism in the mud is estimated. At least one measurement representative of the concentration of the at least one hydrocarbon in the mud is corrected based on the indicator of drill bit metamorphism.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of estimating a concentration of a hydrocarbon in mud and devices and software for doing the same as disclosed herein will be appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings where:

FIG. 1 is a schematic view of an estimation system including a drilling system and an estimating device for estimating a concentration of hydrocarbon in mud;

FIG. 2 is a cross-plot relating a measured concentration of a DBM indicating compound to a concentration of alkane generated by DBM, the curve being used in embodiments of the disclosure;

FIG. 3 is a projection curve relating a concentration of carbon in an alkane, to an estimated concentration of another alkane produced by DBM;

FIG. 4 is a cross-plot relating a ratio depending on measured concentrations of alkane and DBM indicating compound to a carbon isotope signature of a hydrocarbon, the curve being used in embodiments of the disclosure; and

FIG. 5 is a diagram of a method for estimating a concentration of hydrocarbon in mud.

DESCRIPTION

According to some embodiments, the measurement representative of a concentration of the at least one hydrocarbon in the mud can be corrected taking into account the DBM to accurately estimate a concentration of hydrocarbon recovered from the well.

In some embodiments, a method for estimating a concentration of at least one hydrocarbon in mud recovered from a well includes acquiring a measurement representative of a concentration of at least one hydrocarbon in mud. An indicator of drill bit metamorphism in the mud is estimated. At least one measurement representative of the concentration of the at least one hydrocarbon in the mud is corrected based on the indicator of drill bit metamorphism.

In some embodiments, acquiring includes acquiring a first measurement of a concentration of a first type of hydrocarbon present in the formation and acquiring a second measurement of a concentration of a DBM indicating compound generated by DBM, the first type of hydrocarbon and the DBM indicating compound being distinct. The indicator of drill bit metamorphism in the mud is an estimated concentration of the first type of hydrocarbon produced by drill bit metamorphism.

In some embodiments estimating the indicator of DBM includes determining a concentration of the first type of hydrocarbon produced by drill bit metamorphism, from a concentration cross-plot and the second measurement of the DBM indicating compound. In some embodiments determining includes using a regression curve relating the concentration of the DBM indicating compound in the mud recovered from the well, to the estimated concentration of the first type of hydrocarbon produced by DBM obtained from the concentration cross-plot. The concentration of the first type of hydrocarbon is a concentration of alkane or benzene in the mud recovered from the well.

In some embodiments, the estimating can include determining the concentration of methane, ethane, propane, and/or benzene, produced by DBM from the concentration cross-plot(s). Estimating can also include estimating a concentration of butane and/or a concentration of pentane produced by DBM from a projection curve interpolating the estimated concentrations of methane, ethane, and propane produced by DBM. In some embodiments, correcting can include subtracting the estimated concentration of the first type of hydrocarbon produced by DBM from the first measurement.

In some embodiments, acquiring includes acquiring a third measurement of an isotope signature of the hydrocarbon in the mud recovered from the drilling, and a fourth measurement of an isotope signature of the hydrocarbon in a drilling liquid used for drilling the geological formation. In such embodiments, correcting includes correcting the third measurement based on: the fourth measurement, the corrected measurement representative of the concentration of the at least one hydrocarbon in the mud, the first measurement, and the indicator of drill bit metamorphism.

In some embodiments, acquiring includes acquiring a third measurement of an isotope signature of the hydrocarbon in the mud recovered from the drilling, and a fourth measurement of an isotope signature of the hydrocarbon in a drilling liquid used for drilling the geological formation. The indicator of drill bit metamorphism in the mud is an estimated isotope signature of the hydrocarbon in the geological formation. Estimating an indicator of DBM includes calculating the estimated isotope signature from an isotopic cross-plot of the third measurement, versus a ratio calculated from the first and the second measurements. In some embodiments, estimating an indicator of DBM includes calculating from a generative curve an isotope signature of the hydrocarbon in the mud recovered from the drilling at the point where the concentration of the DBM indicating compound is null. The correcting includes computing an estimated concentration of first type produced by DBM as a function of the third measurement, the fourth measurement and the indicator of DBM. The correcting step includes subtracting the estimated concentration of the first type of hydrocarbon produced by DBM from the first measurement.

In some embodiments, the first type of hydrocarbon is an alkane and the DBM indicating compound is an alkene, carbon monoxide, and/or hydrogen. In some embodiments, the first type of hydrocarbon is benzene.

In some embodiments, correcting includes calculating an estimation of a concentration of at least a hydrocarbon in the geological formation.

In some embodiments, a computer program includes software instructions which, when implemented by a piece of computer equipment, carry out the method for estimating a concentration of at least a hydrocarbon according to the disclosure.

In some embodiments, an estimation device for estimating a concentration of hydrocarbon in the mud recovered from a well includes an acquisition unit configured to acquire a measurement representative of a concentration of the at least one the hydrocarbons in mud. The device also includes an estimation unit configured to estimate an indicator of drill bit metamorphism in the mud. The device also includes a correction unit configured to correct the measurement representative of the concentration of the at least one hydrocarbon in the mud, based on the indicator of drill bit metamorphism.

FIG. 1 discloses a device 2 for hydrocarbon content estimation. The device 2 may be included in a drilling facility 5. Such a facility 5 may include a drilling installation 12, and the device 2 as mentioned above.

In FIG. 1, the drilling installation 12 generally includes a rotary drilling tool 14 able to drill a cavity 16, a surface installation 18 such as a rig, and an analysis unit 19 for analyzing drilling cuttings.

A borehole 20, defining the cavity 16, is formed in the formation 21 by the rotary drilling tool 14. The geological formation is for example a subsurface formation. At the surface 22, a well head 23 having a discharge pipe 25 closes the borehole 20.

The drilling tool 14 generally comprises a drill bit 27, a drill string 29 and a liquid injection head 31.

The drill bit 27 includes cutting elements 33 for drilling through the rocks of the substratum 21. It is mounted on the lower portion of the drill string 29 and is positioned in the bottom of the borehole 20.

The drill string 29 includes a set of hollow drilling pipes. These pipes define an internal space 35 which makes it possible to bring a drilling liquid from the surface 22 to the drill bit 27. To this end, the liquid injection head 31 is screwed onto the upper portion of the drill string 29.

The drilling liquid (e.g., drilling fluid or drilling mud) may be a water-based mud or an oil-based mud. Oil-based drilling mud may include natural or synthetic oils. Synthetic oil-based muds have typically narrow range of the dominant compounds, usually C11-C15 hydrocarbons. This range will likely be broader for natural oil or diesel based muds. The concentration of these hydrocarbons remains generally constant in the drilling liquid during the entire drilling of the well. Hence, under the drilling action, the cracking of these alkanes produces two types of hydrocarbons with a lower amount of carbon. These two types of hydrocarbons are primarily short-chain alkanes and alkenes. The alkane cracking may also produce hydrogen, carbon monoxide, and some other gasses in lower proportions. DBM is generally more pronounced in oil-based muds owing to the higher concentrations of hydrocarbons in these muds. However, DBM may also occur at lower levels in water-based muds that include a significant fraction of hydrocarbons.

The surface installation 18 comprises a support 41 for supporting the drilling tool 14 and driving it in rotation (e.g., a top drive or a kelly), an injector 43 for injecting the drilling liquid, and a shale shaker 48. The drilling liquid circulates downwards in the center of drill string 35, to the bit 33, and flowing upwards in the cavity 16 to the surface, bringing along drilling residue and formation gases.

The injector 43 is hydraulically connected to the injection head 31 in order to introduce and circulate the drilling liquid in the center 35 of the drill string 29.

The shale shaker 48 collects the mud recovered from the well including the drilling residue, the recovered mud flowing out from the discharge pipe 25. The shale shaker includes a sieve 46 allowing the separation of the solid drill cuttings from the mud recovered from the well.

The shale shaker includes a holding tank intended to collect the mud after separating the cuttings. The mud collected in the holding tank is recycled to the injector 43 by a mud recycling pipe.

As illustrated in FIG. 1, the surface installation 18 includes a system 50 for extracting gas from the mud recovered from the well and conveyed through the drainpipe 25. The system 50 includes a liquid sampling head, which projects into the drainpipe 25 upstream of the shale shaker 48, a connection tube, and a pump with an adjustable flow. The extracting system 50 also includes an enclosure, a pipe for conveying mud into the enclosure, a pipe for removing mud from the enclosure, an inlet for admitting a carrier gas into the enclosure and a pipe for extracting the extracted gases from the enclosure.

The extracted gases include hydrocarbon compounds, such as alkanes, alkenes, and/or benzene. Other extracted gases may include carbon dioxide, carbon monoxide, and hydrogen.

In some embodiments, the enclosure includes a leak-tight container with an internal volume which may, for example, range between 0.4 liters and 3 liters. This enclosure has a lower section in which the mud circulates and an upper section which has gaseous vapor. The enclosure is also equipped with an impeller having an agitator, projecting into the enclosure and rotated by a motor fitted to the top part of the enclosure. The agitator is immersed in the mud.

The mud transfer pipe extends between the outlet from the pump (e.g., a roller pump) and an inlet opening created in the lower or upper part of the enclosure. The transfer pipe may be equipped with a heater for heating the mud so as to increase the temperature of the mud to values ranging between 25 and 100° C., preferably between 60 and 90° C.

The analysis system 19 includes a sampling port 52 and an analysis unit 54. The sampling port 52 is configured to sample a part of the gases extracted through the extraction system 50 to generate mud gas spot sample(s) that could be further analyzed, e.g., they could be transported to a laboratory to perform lab analysis on the extracted gas. The laboratory is for example remote from the wellbore. The analysis unit 54 is configured to analyze the remainder of the extracted gas in order to carry out measurement of different concentrations, as it will be described hereinafter.

As known to those of ordinary skill in the art, CX refers to a carbon containing compound with a number of carbon equal to X. As an example, C2 is a two carbon containing compound and could be, e.g., ethane or ethene. C6 could refer to benzene, hexane, or hexene. A CX couple refers to alkanes and alkenes having the same number of carbon. The CX couple of C2 would be ethane and ethene.

The analysis unit 54 includes one or several analyzers for measuring a concentration of at least one hydrocarbon in the gases. More specifically, the analysis unit 54 is configured to measure a concentration of a first type of hydrocarbon present in the formation and measure a concentration of a DBM indicating compound present in the drill liquid. In some embodiments, the analysis unit 54 is configured to proceed to the first and the second measurements simultaneously.

In some embodiments, the first measurement is a measured concentration C_X,AN,LOG of at least one type of alkane or benzene in the mud recovered from the well and the second measurement is a measured concentration C_X,EN,LOG of at least one type of alkene, carbon monoxide, or hydrogen in the mud recovered from the well. In some embodiments, the alkane is methane, ethane, propane, butane, or pentane.

As used herein, C_6,AN,LOG refers to the measured concentration of benzene instead of a measured concentration of hexane, however, the disclosure is not limited to the measurement of benzene and hexane could also be measured.

In some embodiments, when alkanes are measured, if the concentration of each isomer (e.g., butane isomers, such as iso-butane, n-butane, or pentane isomers, such as iso-pentane, neo-pentane, n-pentane) is higher than a corresponding threshold, the isomers could each be considered as a separate type of alkane. The measurement for an alkene could therefore, for example, include the concentration of iso-butane and the concentration of n-butane independently.

The type of alkene may be ethene, propene, butene, and/or pentene. The analysis unit 54 can be configured to measure the concentration C_X,AN,LOG of each alkane with less than six carbons in the mud recovered from the well, and to measure the concentration C_X,EN,LOG of each alkene with less than or equal to six carbons, of carbon monoxide, or hydrogen in the mud recovered from the well.

In some embodiments, the analysis unit 54 is also configured to measure a carbon isotope signature δ¹³C_X,EX,LOG of a hydrocarbon in the mud recovered from the well. The isotope signature δ¹³C_X,EX,LOG is a ratio of stable carbon isotopes ¹³C:¹²C and is a well-known ratio. The analysis unit 54 can be configured to also receive a measurement of an isotope signature δ¹³C_X,OBM,LOG of a hydrocarbon in the drill liquid used for drilling the geological formation. The fourth measurement is, for example, obtained via lab analysis before, or after, drilling the well.

In some embodiments, the analysis unit 54 is configured to take the third and fourth measurements for each hydrocarbon with less than four carbons.

In some embodiments, the estimation device 2 includes a calculator having a processor and a memory. The memory contains software modules and/or units adapted to be executed by the processor. In some embodiments, the calculator is designed at least partially as logic programmable component, or as dedicated integrated circuits.

In FIG. 1, the memory contains an acquisition unit 56, an estimation unit 58, and a correction unit 60. The estimation device 2 connected to the output of the analysis unit 54 and is configured to estimate a concentration of at least one hydrocarbon in mud recovered from a well. The estimation device 2 may be directly connected to the analysis unit 54 through a wire. In some embodiments, the estimation device 2 is distant from the analysis unit (e.g., several kilometers away) and the analysis unit 54 and the estimation device 2 communicate through a wireless connection.

The acquisition unit 56 is configured to acquire measurements representative of hydrocarbons from the analysis unit 54. More specifically, the acquisition unit 56 is configured to acquire C_X,AN,LOG and C_X,EN,LOG measurements. In other words, the acquisition unit 56 is configured to acquire the measured concentrations in the mud recovered from the well of at least one alkane and at least one DBM indicating compound, e.g., at least one of the alkanes methane C_1,AN,LOG, ethane C_2,AN,LOG, propane C_3,AN,LOG, butane C_4,AN,LOG, and pentane C_5,AN,LOG, and at least one of the DBM indicating compounds benzene C_6,AN,LOG, ethene C_2,EN,LOG, propene C_3,EN,LOG, carbon monoxide, hydrogen, butene C_4,EN,LOG, and/or pentene C_5,EN,LOG.

While certain embodiment may include directly measuring DBM indicating compounds butene C_4,EN,LOG, and/or pentene C_5,EN,LOG, in certain other embodiments the measured concentrations of butene C_4,EN,LOG and pentene C_5,EN,LOG may be too low to be used by the estimation device 2. Hence, in some embodiments, the analysis unit 54 is not configured to measure butene and/or pentene. However, in some embodiments, the analysis unit 54 is configured to measure butene and/or pentene.

The estimation unit 58 is configured to estimate, from the measurements of the at least one alkane and at least one DBM indicating compound, an indicator of drill bit metamorphism in the mud. In some embodiments, the estimation unit 58 is configured to estimate the indicator of drill bit metamorphism from the first C_X,AN,LOG and the second C_X,EN,LOG measurements.

In some embodiments, the estimation unit 58 acquires or determines a regression curve relating the concentration of the DBM indicating compound in the mud recovered from the well to the estimated concentration of the first type of hydrocarbon produced by drill bit metamorphism from a regression curve of a cross plot. In other words, the at least one concentration cross-plot is used to determine a regression curve relating the second measurement C_X,EN,LOG to a concentration of alkane, or benzene, produced by DBM C_X,AN,DBM. In some embodiments, the regression curve is linear. A suitable regression curve may be estimated manually (e.g. via evaluating a concentration cross-plot) or automatically (e.g., as described in more detail below).

In some embodiments, the estimation unit 58 acquires or determines a respective concentration cross-plot for the C2-couple, and one respective concentration cross-plot for the C3-couple, one respective concentration cross-plot for the C4-couple, one respective cross-plot for the C5-couple, and/or one respective cross-plot for the C6-couple.

Such cross-plots can be obtained by measurements carried out during the drilling of the well. As shown in FIG. 2, a cross plot includes data D1 representative of a zone without DBM and data D2 representative of a zone with DBM. When drilling a well where the geological formation does not include any gaseous hydrocarbon, the entire quantities of hydrocarbon gasses in the mud recovered from the well is due to DBM of the drilling fluid. Representing the measurements of a CX-couple in a cross plot reveals data D2 which shows where DBM is occurring. The estimation unit 58 is configured to determine a regression equation of a regression curve, from the second data D2. The regression curve relates, for the considered CX-couple, the measured concentration of DBM indicating compound in the mud recovered from the well C_X,EN,LOG to the concentration of alkane, or benzene, produced by drill bit metamorphism C_X,AN,DBM. In FIG. 2, one example regression curve is depicted as a dashed line.

To do so, the estimation unit 58 is configured, from the DBM indicating gas data greater than a cut-off value, to determine the parameters of the regression curve. The cut-off value could be any suitable value, e.g., between 25 ppm and 30 ppm. The regression curve is a baseline of the second set of data D2 resulting of a tradeoff between a correlation factor R² greater than a specific threshold and a minimized amount of data below the baseline minimized.

In some embodiments, the estimation unit 58 is configured to receive one or more cross plots, one or more regression curves, and/or one or more parameters of a regression equation. These plots, curves, and/or parameters might be obtained in a lab before drilling the well or the parameters can be obtained from previous wells (e.g. an average) in the same field, assuming the same rig and drilling fluid are used.

FIG. 2 shows an example of a concentration cross-plot relating the measured concentration C_2,EN,LOG of ethene in the mud recovered from the well to the concentration of ethane recovered from the well C_2,AN,DBM. The estimation unit 58 is configured to estimate the indicator of drill bit metamorphism as the concentration of ethane produced by drill bit metamorphism C_2,AN,DBM by reading the value of the regression curve (the dashed line) corresponding to the measured concentration of ethene C_2,EN,LOG.

As shown in FIG. 2, the height of the regression curve from the X axis corresponds to the value of the concentration of a particular hydrocarbon (here ethane) produced by DBM, when a particular concentration of DBM indicating compound C_X,EN,LOG is measured. The same process can be used with methane, propane, butane, and/or pentane by replacing ethene with propene, carbon monoxide, hydrogen, butene, or pentene.

As already discussed, in certain operations the concentrations of butene C_4,EN,LOG and pentene C_5,EN,LOG in the mud recovered from the well may be too low to be used by the estimation device 2 to obtain a concentration cross-plot. Therefore, in some embodiments, the estimation unit 58 may be configured to derive the concentrations of butane C_4,AN,DBM, pentane C_5,AN,DBM, and benzene C_6,AN,DBM produced by drill bit metamorphism from the estimated concentrations of methane C_1,AN,DBM, ethane C_2,AN,DBM, and/or propane C_3,AN,DBM produced by drill bit metamorphism. In some embodiments, the estimation unit 58 is configured to determine a projection curve, represented as a dotted curve on FIG. 3, relating the concentration of alkane or benzene produced by DBM C_X,AN,DBM as a function of the amount of carbon in the alkane. In the depicted embodiment, the projection curve is a decreasing logarithmic curve interpolating points corresponding to the estimated concentration of alkane or benzene produced by drill bit metamorphism C_X,AN,DBM. Where the concentrations of alkane produced by drill bit metamorphism are estimated for methane C_1,AN,DBM, ethane C_2,AN,DBM, and propane C_3,AN,DBM, the projection curve interpolates each of the points of coordinates (1, C_1,AN,DBM), (2, C_2,AN,DBM), and (3, C_3,AN,DBM). Such a curve could be obtained by any suitable method, e.g., by the method disclosed in U.S. Pat. No. 7,392,138, which is incorporated herein by reference in its entirety.

Using the projection curve, the estimation unit 58 estimates the concentration of butanes produced by drill bit metamorphism C_4,AN,DBM as the value of the projection curve for a number of carbons equal to 4. Similarly, the estimation unit 58 is configured to estimate the concentration of pentanes produced by drill bit metamorphism C_5,AN,DBM as the value of the projection curve for a number of carbons equal to 5. On FIG. 4, the points corresponding to the concentration of butane C_4,AN,DBM and pentane C_5,AN,DBM produced by DBM, are respectively represented by a star.

The correction unit 60 is configured to correct the at least one measurement representative of the concentration of hydrocarbons in the mud, based on the indicator of drill bit metamorphism. In other words, the correcting unit 60 is configured to determine at least one of a corrected concentration of methane C_1,AN,COR, a corrected concentration of ethane C_2,AN,COR, a corrected concentration of propane C_3,AN,COR, a corrected concentration of butane C_4,AN,COR, or a corrected concentration of pentane C_5,AN,COR.

In some embodiments, the correction unit is configured to compute a difference between the measurement of alkanes and the indicator of drill bit metamorphism. In other words, the correcting unit 60 is configured, for each type of alkane, to compute a corrected concentration of alkane or benzene, C_X,AN,COR according to the following equation:

$\begin{array}{cc}{C}_{X,\mathrm{AN},COR}=C_{X,\mathrm{AN},\mathrm{LOG}}-C_{X,\mathrm{AN},\mathrm{DBM}}& \mathrm{Equation}1\end{array}$

where X is an integer comprised between 1 and 6.

The correcting unit 60 is only configured to determine the corrected concentration of an alkane or benzene C_X,AN,COR for the type(s) alkane or benzene for which a measured concentration C_X,AN,LOG and an estimated concentration produced by DBM C_X,AN,DBM are available. The estimated concentration of benzene produced by DBM is denoted C_6,AN,DBM.

As shown in FIG. 2, the value of the corrected alkane concentration C_X,AN,CRO corresponds to the height between the data point corresponding to the actual measurement of alkane concentration C_X,AN,LOG and the height of the regression curve at the same abscissa, corresponding to the value of the concentration of DBM indicating compound C_X,EN,LOG.

A method for estimating representative concentration of at least one hydrocarbon in mud recovered from a well will now be described with reference to FIG. 5. Initially, a well is drilled and some mud is recovered from the well. A measurement representative of the concentration of at least one hydrocarbon in the mud, is performed by the analysis unit 54. This measurement includes a measured concentration of an alkane or benzene in the mud recovered from the well C_X,AN,LOG and a measured concentration of DBM indicating compound in the mud recovered from the well C_X,EN,LOG.

In acquiring 110, the at least one measurement representative of the concentration of at least one hydrocarbon in the mud is acquired by the acquisition unit 56. At estimating 120, the indicator drill bit metamorphism in the mud is estimated. For this purpose, the estimation unit 58 optionally uses, for at least one CX-couple, the corresponding concentration cross-plot relating the measured concentration of DBM indicating compound in the mud recovered from the well C_X,EN,LOG, to the concentration of the alkane or benzene produced by drill bit metamorphism C_X,AN,DBM, in order to determine the parameters of the regression equation from a regression curve. More specifically, the estimation unit 58 estimates the concentration of an alkane or benzene produced by drill bit metamorphism C_X,AN,DBM based on a regression curve of the corresponding concentration cross-plot, as detailed above. The estimating 120 may include estimation of the concentrations of methane C_1,AN,DBM, ethane C_2,AN,DBM, propane C_3,AN,DBM, butanes C_4,AN,DBM, pentanes C_5,AN,DBM, and/or benzene C_6,AN,DBM produced by DBM.

In some embodiments, during estimating 120, the estimation unit 58 determines a projection curve from the estimated concentrations of methane C_1,AN,DBM, ethane C_2,AN,DBM, and propane C_3,AN,DBM produced by DBM. Then, based on such projection curve, the estimation unit 58 estimates the concentration of butane C_4,AN,DBM and/or pentane C_{5,AN DBM} produced by drill bit metamorphism, as detailed above.

During correcting 130, the correction unit 60 corrects the at least one measurement representative of the concentration of hydrocarbons in the mud, based on the indicator of drill bit metamorphism. The correction unit 60 for example determines, for at least one type of alkane or benzene, the corrected concentration of alkane or benzene in the geological formation C_X,AN,COR, by deducing the indicator of drill bit metamorphism from the alkene or benzene measurement C_X,AN,LOG. In other words, the correction unit 60 determines, for each type of alkane, the corrected concentration of alkane or benzene in the geological formation C_X,AN,COR, from the estimated concentration of the alkane or benzene produced by DBM C_X,AN,DBM and the measured concentration of the alkane or benzene in the mud recovered from the well C_X,AN,LOG, according to Equation 1.

In some embodiments, the acquisition unit 56 configured to acquire, from the analysis unit 54 and for at least one CX, a third measurement δ¹³C_X,EX,MES and a fourth measurement δ¹³C_X,OBM,LAB. For example, the acquisition unit 56 may be configured to acquire the third δ¹³C_X,EX,MES and the fourth δ¹³C_X,OBM,LAB measurements for methane, ethane, and/or propane. The correction unit 60 is configured to correct the measured isotope signature of carbon in mud recovered from the well δ¹³C_X,EX,MES. More specifically, the correction unit 60 is configured to compute, for each CX-couple for which isotope measurements have been acquired, the fraction f_X,AN,DBM of alkane produced by drill bit metamorphism among the measured concentration of alkane or benzene in the mud recovered from the well. The correction unit 60 is configured to use the following equation:

$\begin{array}{cc}{f}_{X,\mathrm{AN},\mathrm{DBM}}=\frac{C_{X,\mathrm{AN},\mathrm{DBM}}}{C_{X,\mathrm{AN},\mathrm{LOG}}}& \mathrm{Equation}2\end{array}$

where X is an integer comprised between 1 and 3.

The correction unit 56 is then configured, for the CX-couple(s), to compute the corrected quantity of ¹³C-isotope of carbon in the geological formation δ¹³C_X,EX,COR according to the following equation:

$\begin{array}{cc}{\delta }^{13}{C}_{X,\mathrm{EX},COR}=\frac{{\delta }^{13}{C}_{X,\mathrm{EX},\mathrm{MES}}-f_{X,\mathrm{AN},\mathrm{DBM}}{\delta }^{13}{C}_{X,\mathrm{OBM},\mathrm{LAB}}}{1-f_{X,\mathrm{AN},\mathrm{DBM}}}& \mathrm{Equation}3\end{array}$

where X is an integer comprised between 1 and 3.

Equation 3 can be obtained by considering that the measured quantity of ¹³C-isotope of carbon in molecules of CX-couples of the mud recovered from the well is proportional to the quantity of ¹³C-isotope of carbon in the same molecules in the reservoir and to the measured quantity of ¹³C-isotope of carbon in the same molecules of the oil-based mud or in alkene DBM-products of mud degradation.

The method for estimating a representative concentration of at least one hydrocarbon in the mud recovered from the well, also includes, during acquiring 110, the acquisitions of the third δ¹³C_X,EX,LOG and fourth δ¹³C_X,OBM,LAB measurements. During the correcting 130, for each CX-couple for which third and fourth measurements are acquired, the estimation unit 58 estimates the corrected quantity of ¹³C-isotope of carbon in the geological formation δ¹³C_X,EX,COR according to Equations 2 and 3.

In some embodiments, the acquisition unit 56 is configured to acquire for at least one CX-couple the first C_X,AN,LOG, the second C_X,EN,LOG, the third δ¹³C_X,EX,LOG and fourth δ¹³C_X,OBM,LAB measurements. The acquisition unit 56 is configured to acquire the first measurement C_X,AN,LOG for methane, ethane, propane, butane, pentane, and/or benzene, and the third and fourth measurements for each CX-couple with less than four carbon atoms. The estimation unit 58 is configured to estimate an indicator of drill bit metamorphism in the mud. However, unlike the above described embodiments, the indicator of drill bit metamorphism includes an isotope signature δ¹³C_X,f of the hydrocarbon in the reservoir.

The estimation unit 58 is able to acquire or determine a generative curve from an isotopic cross-plot relating the quantity of ¹³C-isotope of carbon of a CX-couple δ¹³C_X,EX,LOG to a ratio Rx depending on the measured concentration of DBM indicating compound in the mud recovered from the well C_X,EN,LOG and on the measured concentration of alkane or benzene in the mud recovered from the well C_X,AN,LOG. Such ratio Rx is calculated with the following equation:

$\begin{array}{cc}{R}_X=\frac{C_{X,\mathrm{AN},\mathrm{LOG}}}{C_{X,\mathrm{EN},\mathrm{LOG}}+C_{X,\mathrm{AN},\mathrm{LOG}}}& \mathrm{Equation}4\end{array}$

where X is an integer between 1 and 3.

For each CX-couple when the ratio Rx is equal to one, the measured concentration of alkene in the mud recovered from the well C_X,EN,LOG is equal to zero. Since the geological formation does not naturally include alkenes, the ratio Rx equal to one indicates that the gas is derived from the geological formation. Indeed, all (e.g., substantially all) the alkenes in the mud recovered from the well come from the drilling mud. Consequently, when the ratio Rx is equal to one, the corresponding quantity of ¹³C-isotope of carbon δ¹³C_X,EX,LOG corresponds to a quantity of ¹³C-isotope of carbon in the fluid in the geological formation δ¹³C_X,f. In addition, when the ratio Rx is equal to zero, the mud recovered from the well only includes gasses derived from DBM from the drilling liquid since the concentration of alkane, or benzene, in the mud recovered from the well C_X,AN is equal to zero.

For each CX-couple, the generative curve relates the ratio Rx of the specific CX-couple to the quantity of ¹³C-isotope of carbon in the molecules of this CX-couple in the mud recovered from the well δ¹³C_X,EX,LOG. Each generative curve is, for example, a regression curve obtained by applying an optimization algorithm to several measurements for different values of a same ratio Rx and starting at the same origin at the carbon isotope signature δ¹³C_X,EX,LOG of the drilling oil for a ratio Rx equal to one, translating to pure DBM product. The generative curve may be obtained, based on several ratios and isotope signatures obtained through measurements when drilling the well, based on measurements carried out in a laboratory on samples taken from the well, or based on measurements of a previously drilled well or wells.

A second degree polynomial regression curve provides an efficient result for the generative curve 70 relating the ratio Rx, to the quantity of ¹³C-isotope of carbon in the molecules of C1 in the mud recovered from the well δ¹³C_1,EX,LOG. However, for larger molecules, such as the molecules of C2 or C3, a linear regression curve can be used for the corresponding generative curves 75, 80. The isotopic cross-plot is for example represented on FIG. 4.

The estimation unit 58 is configured, for each CX-couple for which the acquisition unit 56 acquired the first and the second measurements, to compute the corresponding ratio Rx. Then for each CX′-couple, potentially different than the CX-couple, for which the acquisition unit 56 acquired the third δ¹³C_X′,EX,MES and the fourth δ¹³C_X′,OBM,LAB measurements, the estimation unit 58 is configured to, from a point of coordinates (Rx, δ¹³C_X′,EX,MES) in the second cross-plot, to follow, in a parallel manner, the corresponding generative curve, by making the ratio Rx increase until reaching a ratio Rx equal to one. The estimation unit 58 is thus configured to read the value of the corresponding quantity of 13C-isotope of carbon in the geological formation δ¹³C_X′,f.

In embodiments where the acquisition unit 56 acquires the first C_2,AN,LOG and the second C_2,EN,LOG measurements corresponding to C2-couple (for example ethane and ethene), and a third δ¹³C_1,EX,LOG and fourth δ¹³C_1,OBM,LAB measurements for C1-couple, the estimation unit 58 is to compute the corresponding ratio R₁ according to the second equation, as follows:

$\begin{array}{cc}{R}_2=\frac{C_{2,\mathrm{AN},\mathrm{LOG}}}{C_{2,\mathrm{AN},\mathrm{LOG}}+C_{2,\mathrm{EN},\mathrm{LOG}}}& \mathrm{Equation}5\end{array}$

The estimation unit 58 is thus configured, from a point of coordinates (R₂, δ¹³C_1,EX,LOG) in the isotopic cross-plot, to follow an interpolating curve, parallel to the corresponding generative curve 70, make the ratio R₂ increase to one as shown by the parallel curves XX and YY on FIG. 4. The interpolating curve XX, YY is the curve parallel to the generative curve, which interpolate the point of coordinates (R₁, δ¹³C_1,EX,MES). Thus, the estimation unit 58 is configured to read the value of the quantity of ¹³C-isotope of carbon of methane in the geological formation δ¹³C_1,f.

In some embodiments, the estimation unit 58 is configured to use the R₂ to generate the curve for the C2-couple and the C3-couple (e.g., in addition to using R₃).

The correction unit 60 is configured to correct the at least one measurement representative of the concentration of the at least one hydrocarbon in the mud. For example, the correction unit 60 is configured to estimate, for at least one CX-couple, the concentration of the corresponding alkane produced by drill bit metamorphism C_X,AN,DBM, based on the third measurement δ¹³C_X,EX,MES, the fourth measurement δ¹³C_X,OBM,MES and the indicator of drill bit metamorphism. The indicator of drill bit metamorphism, in some embodiments, corresponds to the isotope signature of carbon indigenous in the formation 13C_X,f. Such estimation can be obtained using the following equation:

$\begin{array}{cc}{C}_{X,\mathrm{AN},\mathrm{DBM}}=C_{X,\mathrm{AN},\mathrm{LOG}}\frac{{\delta }^{13}{C}_{X,\mathrm{EX},\mathrm{LOG}}-{\delta }^{13}{C}_{X,f}}{{\delta }^{13}{C}_{X,\mathrm{OBM},\mathrm{LAB}}-{\delta }^{13}{C}_{X,f}}& \mathrm{Equation}6\end{array}$

where X is an integer comprised between 1 and 3.

The correction unit 60 is then configured to correct the first measure based on the estimated concentration of alkane, or benzene, produced by DBM C_X,AN,DBM. In other words, the correction unit 60 is configured, for at least one CX-couple, to determine the corresponding corrected concentration of alkane or benzene C_X,AN,COR as being the difference between the measured concentration of alkane or benzene in the mud recovered from the well C_X,AN,LOG and the estimated concentration of alkane or benzene produced by drill bit metamorphism C_X,AN,DBM.

A method for estimating the representative concentration of at least one hydrocarbon in mud recovered from a well, implemented by the estimation device describe above, will now be described with reference to FIG. 5. The following method is only described by its differences with the method implemented by the estimation device according to the earlier described embodiments.

During the acquiring step 110, the acquisition unit 56 acquires, for at least one CX-couple, C_X,AN,LOG, C_X,EN,LOG, δ¹³C_X,EX,LOG, and δ¹³C_X,EX,LOG. In some embodiments, the acquisition unit 56 acquires the first measurement C_X,AN,LOG for each alkane with less than six carbons and the third δ¹³C_X,EX,LOG, and the fourth δ¹³C_X,OBM,LOG measurements for each CX-couple with less than three carbons.

During the estimating 120, the estimation unit 58 estimates the indicator of drill bit metamorphism from the first C_X,AN,LOG, the second C_X,EN,LOG, and the third δ¹³C_X,EX,LOG measurements using the isotopic cross-plot. More specifically, the estimation unit 58 computes, for at least one of the CX-couple for which the acquisition unit 56 acquired measurements, the corresponding ratio Rx using Equation 4 and each generative curve. Then, from a point of coordinates (Rx, δ¹³C_X,EX,MES) in the isotopic cross-plot, the estimation unit 58 follows a parallel interpolation curve XX or YY to the corresponding generative curve by making the ratio Rx increase until reaching a ratio Rx equal to one. Then, the estimation unit 58 identifies the value of the corresponding quantity of ¹³C-isotope of carbon in the geological formation δ¹³C_X,f as the value of the corresponding generative curve at a point where the concentration of the corresponding alkene is null, i.e. at the point where the ratio R_X is equal to one. The identified quantity of ¹³C-isotope of carbon in the geological formation δ¹³C_X,f is the indicator of drill bit metamorphism.

During the correcting 130, the correction unit 60 corrects the at least one measurement representative of the concentration of the at least one hydrocarbons in the mud, based on the indicator of drill bit metamorphism. More specifically, the correction unit 60 computes the concentration of alkane or benzene produced by drill bit metamorphism C_X,AN,DBM, from: the indicator of drill bit metamorphism δ¹³C_X,f, the third measurement δ¹³C_X,EX,LOG, and the fourth measurement δ¹³C_X,OBM,LOG according to Equation 6. Then the correction unit 60 corrects the first measurement C_X,AN,LOG with the concentration of alkane or benzene produced by drill bit metamorphism C_X,AN,DBM, for example, by applying Equation 1.

In some embodiments, in formations without liquid phase (i.e., in formations that only produce gasses), benzene will be generated only from DBM along with alkenes, hydrogen, and/or carbon monoxide. The second measurement may be a measured concentration of benzene in the mud recovered from the well. Then the corrected concentration of alkane in the mud recovered from the well might be deduced from the measured concentration of benzene, as a DBM indicating compound.

With the estimating device, according to any of the disclosed embodiments, measurements representative of a concentration of each hydrocarbon in the mud are corrected to estimate a concentration of hydrocarbon in the mud, which removes the effect of DBM. The above described method also provides an estimation of the isotope signature of the formation alkane gases and is applicable to hydrocarbons with up to five carbons given sufficient concentration and measured carbon isotope signature δ¹³C_X,EX,LOG.

In some embodiments, correction to remove the effect of DBM makes it possible to accurately estimate the concentration of hydrocarbon in the geological formation without being biased by the effect of DBM. This provides a more accurate detection of hydrocarbon content in the formations in which the well is drill than is currently employed.

One or more embodiments of the present disclosure are described herein. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, not all features of an actual embodiment may be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous embodiment-specific decisions will be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one embodiment to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein. Numbers, percentages, ratios, or other values stated herein are intended to include that value, and also other values that are “about” or “approximately” the stated value, as would be appreciated by one of ordinary skill in the art encompassed by embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within 5%, within 1%, within 0.1%, or within 0.01% of a stated value.

A person having ordinary skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations may be made to embodiments disclosed herein without departing from the spirit and scope of the present disclosure. Equivalent constructions, including functional “means-plus-function” clauses are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in the same manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words ‘means for’ appear together with an associated function. Each addition, deletion, and modification to the embodiments that falls within the meaning and scope of the claims is to be embraced by the claims.

The terms “approximately,” “about,” and “substantially” as used herein represent an amount close to the stated amount that is within standard manufacturing or process tolerances, or which 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% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of a stated amount. Further, it should be understood that any directions or reference frames in the preceding description are merely relative directions or movements. For example, any references to “up” and “down” or “above” or “below” are merely descriptive of the relative position or movement of the related elements.

The present disclosure may be embodied in other specific forms without departing from its spirit or characteristics. The described embodiments are to be considered as illustrative and not restrictive. Changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. A method for estimating a concentration of a hydrocarbon in mud recovered from a well penetrating a formation, implemented in an estimation device (2), comprising:

acquiring (110) a measurement representative of a concentration of the hydrocarbon in the mud;

estimating (120) an indicator of drill bit metamorphism in the mud; and

correcting (130) at least one measurement representative of the concentration of the hydrocarbon in the mud, based on the indicator of drill bit metamorphism (DBM).

2. The method according to claim 1, wherein acquiring (110) comprises acquiring a first measurement (CX,AN,LOG) of a concentration of a first hydrocarbon present in the formation and acquiring a second measurement (CX,EN,LOG) of a concentration of DBM indicating compound generated by DBM, the first hydrocarbon and the DBM indicating compound being distinct.

3. The method according to claim 2, wherein the indicator of DBM in the mud is an estimated concentration (CX,AN,DBM) of the first hydrocarbon produced by DBM.

4. The method according to claim 3, wherein estimating an indicator of DBM in the mud comprises determining a concentration of the first hydrocarbon produced by DBM from a concentration cross-plot and the second measurement (CX,EN,LOG), and wherein determining comprises using a regression curve relating the concentration (CX,EN,LOG) of the DBM indicating compound in the mud to estimate a concentration (CX,AN,DBM) of the first hydrocarbon produced by DBM obtained from the concentration cross-plot.

5. The method according to claim 4, wherein the concentration of the first hydrocarbon is a concentration (CX,AN,LOG) of an alkane or benzene in the mud, and wherein the estimating (120) comprises determining a concentration of methane (C1,AN,DBM), ethane (C2,AN,DBM), propane (C3,AN,DBM), butane (C4,AN,DBM), pentane (C5,AN,DBM), or benzene (C6,AN,DBM) produced by drill bit metamorphism from the concentration cross-plot(s).

6. The method according to claim 4, wherein the estimating (120) comprises estimating a concentration of butane (C4,AN,DBM) and/or a concentration of pentane (C5,AN,DBM) produced by DBM from a projection curve interpolating estimated concentrations of methane (C1,AN,DBM), ethane (C2,AN,DBM), and/or propane (C3,AN,DBM) produced by DBM.

7. The method according to claim 6, wherein correcting (130) the measurement representative of the concentration of the hydrocarbon in the mud comprises subtracting the estimated concentration (CX,AN,DBM) of the first hydrocarbon produced by DBM from the first measurement (CX,AN,LOG).

8. The method according to claim 7, wherein the acquiring (110) further comprises acquiring a third measurement (δ13CX,EX,MES) of an isotope signature of the hydrocarbon in the mud, and a fourth measurement (δ13CX,OBM,MES) of an isotope signature of the hydrocarbon in the mud prior to being used in the well, and wherein the correcting (130) comprising correcting the third measurement (δ13CX,EX,MES) based on: the fourth measurement (δ13CX,OBM,MES), the corrected measurement (CX,AN,COR) representative of the concentration of the hydrocarbon in the mud, the first measurement (CX,AN,LOG), and the indicator of DBM (CX,AN,DBM).

9. The method according to claim 2, wherein the acquiring (110) further comprises acquiring a third measurement (δ13CX,EX,MES) of an isotope signature of the hydrocarbon in the mud, and a fourth measurement (δ13CX,OBM,MES) of an isotope signature of the hydrocarbon in the mud prior to being used in the well.

10. The method according to claim 9, wherein the indicator of DBM in the mud is an estimated isotope signature (δ13CX,f) of the hydrocarbon in the geological formation.

11. The method according to claim 10, wherein estimating (120) an indicator of DBM comprises calculating the estimated isotope signature (δ13CX,f) from an isotopic cross-plot of the third measurement (δ13CX,EX,MES), versus a ratio calculated from the first (CX,AN,LOG) and the second (CX,EN,LOG) measurements.

12. The method according to claim 11, wherein estimating (120) an indicator of drill bit metamorphism further comprises calculating from a generative curve, an isotope signature (δ13CX,f) of the hydrocarbon in the mud recovered from the drilling at the point where the concentration of the DBM indicating compound is zero.

13. The method according to claim 12, wherein the correcting (130) comprises computing an estimated concentration (CX,AN,DBM) of the first hydrocarbon produced by DBM as a function of the third measurement (δ13CX,EX,MES), the fourth measurement (δ13CX,OBM,MES), and the indicator of DBM (δ13CX,f).

14. The method according to claim 13, wherein the correcting (130) comprises subtracting the estimated concentration (CX,AN,DBM) of the first hydrocarbon produced by DBM, from the first measurement (CX,AN,LOG).

15. The method according to claim 14, wherein the first hydrocarbon is an alkane and the DBM indicating compound is an alkene, carbon monoxide, and/or hydrogen.

16. The method according to claim 14, wherein the first hydrocarbon is benzene and the DBM indicating compound is an alkene, carbon monoxide, and/or hydrogen.

17. The method according to claim 14, wherein the correcting (130) comprises a calculation of an estimation of a concentration of at least a hydrocarbon in the formation.

18. A computer program product comprising software instructions which, when implemented by a piece of computer equipment, carry out the method for estimating a concentration of at least a hydrocarbon according to any one of the preceding claims.

19. An estimation device (2) for estimating a concentration of a hydrocarbon in mud recovered from a well, the estimation device (2) comprising:

an acquisition unit (56) configured to acquire a measurement representative of a concentration of the hydrocarbon in the mud;

an estimation unit (58) configured to estimate an indicator of drill bit metamorphism (DBM) in the mud; and

a correction unit (60) configured to correct the measurement representative of the concentration of the hydrocarbon in the mud, based on the indicator of DBM.

20. The estimation device (2) of claim 19, wherein:

the acquisition unit (56) is configured to acquire a first measurement (CX,AN,LOG) of a concentration of a first hydrocarbon present in the mud and a second measurement (CX,EN,LOG) of a concentration of DBM indicating compound generated by DBM, the first hydrocarbon and the DBM indicating compound being distinct;

the estimation unit (58) is configured to determine a concentration of the first hydrocarbon produced by DBM from a concentration cross-plot and the second measurement (CX,EN,LOG), wherein the determining comprises using a regression curve relating the concentration (CX,EN,LOG) of the DBM indicating compound in the mud to estimate a concentration (CX,AN,DBM) of the first hydrocarbon produced by DBM obtained from the concentration cross-plot; and

the correction unit is configured to subtract the estimated concentration (CX,AN,DBM) of the first hydrocarbon produced by DBM from the first measurement (CX,AN,LOG) of the concentration of the first hydrocarbon present in the mud.