Field of the invention
[0001] The present invention relates, generally, to the field of crude oil thermal maturity assessment. More particularly, the present invention relates to a system for optimized quantitative estimation of thermal maturity of crude oil.
Background of the invention
[0002] Crude oil is generally formed from sedimentary organic matter in high temperature and pressure conditions under the earth's surface and seabed over a long period of time. Estimation of thermal maturity of crude oil aids in oil to oil and oil to source correlation studies. It has been observed that estimation of thermal maturity of crude oil with conventional techniques provides ambiguous results in late oil window. It has been observed that there is a reversal in Vitrinite Reflectance calculated (VRc) values associated with the crude oil after attaining certain maturity by the crude oil, therefore yielding anomalous VRc values for high maturity of oils/condensates.
[0003] Furthermore, the existing thermal maturity determination techniques use one or more biomarkers (e.g. Hopane (C32) , Sterane (C29) , etc.) for thermal maturity determination of crude oil, however, it has been observed that the biomarkers have narrow dynamic range of maturity and many reach equilibrium before the main stage of crude oil generation, thus limiting the maturity range in which accurate data may be interpreted.
[0004] In light of the aforementioned drawbacks, there is a need for a system, which provides for optimized quantitative estimation of thermal maturity of crude oil. Further, there is a need for a system, which provides for

estimation of thermal maturity of crude oil which extends up to post peak maturity.
Summary of the invention
[0005] In various embodiments of the present invention, system for optimized quantitative estimation of thermal maturity of a crude oil is provided. The system comprises a distillation unit for distilling crude oil at a temperature of up to 210°C for removing lighter fraction of the crude oil. Further, the system comprises a deasphalting unit for deasphalting the crude oil by refluxing with n-hexane for removing asphaltenes and obtaining maltene present in the crude oil. Further, the system comprises an aromatic fraction separation unit for separating a saturated fraction and an aromatic fraction from the maltene. The system further comprises a spectroscopic unit, executed by a processor, for obtaining spectrum of the aromatic fraction. Lastly, the system comprises a thermal maturity estimation unit, executed by the processor, for determining thermal maturity of the crude oil by determining a Fourier Transform Infrared (FTIR) ratio of aromatic to aliphatic spectral peaks obtained in FTIR spectrum and correlating the determined FTIR ratio with a crude oil maturity parameter.
Brief description of the accompanying drawings
[0006] The present invention is described by way of embodiments illustrated in the accompanying drawings wherein:
[0007] Fig. 1 illustrates a system 100 for optimized estimation of thermal maturity of crude oil, in accordance with an embodiment of the present invention;

[0008] FIG. 2 illustrates a graphical representation of stacked Fourier Transform Infrared (FTIR) spectrum plotted against wavenumber (cm-1) on x-axis and absorbance on y axis providing Vitrinite Reflectance calculated (VRC%) of crude oil against each spectrum, in accordance with an embodiment of the present invention; and
[0009] FIG. 3 illustrates a graphical representation of increasing FTIR ratio (=C-H/CH2+CH3) with increasing VRc% of crude oil along with a calibration curve plotted between the FTIR ratio and VRc%, in accordance with an embodiment of the present invention.
Detailed description of the invention
[0010] The present invention discloses a system for quantitative estimation of thermal maturity of crude oil. In particular, the present invention discloses a system for quantitative estimation of thermal maturity of crude oil by performing spectroscopic analysis on a hydrocarbon fraction of the crude oil. The present invention provides for analyzing aromatic fraction of crude oil for estimating thermal maturity of crude oil. The present invention further provides for efficiently determining thermal maturity parameters associated with the crude oil in an early to post peak maturation stage. Further, the present invention provides for estimating thermal maturity of crude oil using ratio values derived from Fourier Transform Infrared (FTIR) spectrum of the aromatic fraction of crude oil comprising aromatic (=C-H)/aliphatic (CH2+CH3) moieties ratio. Further, the present invention provides for correlating Fourier Transform Infrared (FTIR) derived maturity parameter with vitrinite reflectance calculated (%VRc) (Radke). Furthermore, the present invention provides for estimating thermal maturity of unknown crude oil samples from an equation derived from calibration plot. Yet

further, the present invention provides for non-ambiguous quantitative estimation of thermal maturity of crude oil.
[0011] The disclosure is provided in order to enable a person having ordinary skill in the art to practice the invention. Exemplary embodiments herein are provided only for illustrative purposes and various modifications will be readily apparent to persons skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the scope of the invention. The terminology and phraseology used herein is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed herein. For purposes of clarity, details relating to technical material that is known in the technical fields related to the invention have been briefly described or omitted so as not to unnecessarily obscure the present invention.
[0012] The present invention would now be discussed in context of embodiments as illustrated in the accompanying drawings.
[0013] Fig. 1 illustrates a system 100 for optimized estimation of thermal maturity of crude oil, in accordance with an embodiment of the present invention. In various embodiments of the present invention, the system 100 comprises multiple units, which operate in conjunction with each other for optimized estimation of thermal maturity of crude oil. In an embodiment of the present invention, the system 100 comprises a distillation unit 102, a deasphalting unit 114, an aromatic fraction separation unit 104, a spectroscopic unit 106 and a thermal maturity estimation

unit 108. The spectroscopic unit 106 and a thermal maturity estimation unit 108 are operated via a processor 110 specifically programmed to execute instructions stored in a memory 112 for executing respective functionalities of the spectroscopic unit 106 and the thermal maturity estimation unit 108, in accordance with various embodiments of the present invention.
[0014] In an embodiment of the present invention, the system 100 performs an infrared spectroscopic analysis on a hydrocarbon fraction of the crude oil for estimating thermal maturity of crude oil. In an embodiment of the present invention, the system 100 performs the spectroscopic analysis based on an Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopic technique. In various embodiments of the present invention, the system 100 analyzes and characterizes crude oil samples in totality with respect to chemical functionalities of the crude oil samples for determining gross chemical changes associated with the thermal maturation of the crude oil.
[0015] In an embodiment of the present invention, the distillation unit 102 of the system 100 distills the crude oil at a temperature of up to 210°C, for removing lighter fractions of the crude oil. Subsequently the crude oil above 210°C temperature is deasphaltened, by the deasphalting unit 114, for removing asphaltenes, which are present in the crude oil, by refluxing with n-hexane and to obtain maltene present in the crude oil. Asphaltenes, being relatively polar macromolecules may interfere in ATR-FTIR spectroscopic analysis and column chromatography, therefore are removed by deasphalting process. Maltene is passed on to the aromatic fraction separation unit 104 for obtaining an aromatic fraction from the crude oil. In an exemplary embodiment of the present invention, the aromatic fraction

separation unit 104 applies a column chromatography technique on the maltene for separating a saturated fraction from maltene using n-hexane and separating an aromatic fraction using toluene from the maltene. The column chromatography technique includes, but is not limited to, Saturate, Aromatic, Resin and Asphaltene (SARA) analysis.
[0016] In an embodiment of the present invention, before passing the aromatic fraction to a spectroscopic unit 106, a background spectrum of the aromatic fraction is obtained. A single beam spectrum is obtained without a sample induced by the spectroscopic unit 106 and the surrounding environment is used for obtaining the background spectrum. Further, subsequent to obtaining the background spectrum of the aromatic fraction, spectrum of the aromatic fraction is obtained by the spectroscopic unit 106. In an embodiment of the present invention, the spectrum of the aromatic fraction is obtained by analyzing the aromatic fraction using the ATR-FTIR spectroscopic technique. In an embodiment of the present invention, the aromatic fraction is diluted in a pre-defined amount (e.g. minimum amount) of organic solvent such as, but is not limited to, dichloromethane (DCM) . Thereafter, the aromatic fraction, diluted with DCM, is uniformly spread over a zinc-selenide crystal present in the spectroscopic unit 106 using a syringe. The DCM having lower boiling point (~40°C), evaporates at a faster rate at a room temperature and only the aromatic fraction remains on the zinc-selenide crystal, thus peaks due to DCM are not observed in spectrum. In an exemplary embodiment of the present invention, refractive index of the zinc-selenide crystal is 2.4.
[0017] In an embodiment of the present invention, the spectroscopic unit 106 is an ATR-FTIR spectroscopic unit configured to obtain the spectrum of the aromatic fraction.

In an embodiment of the present invention, the spectrum of aromatic fraction comprising different peaks is obtained by passing radiation through the aromatic fraction spread over the zinc-selenide crystal using the ATR-FTIR spectroscopic technique. In an exemplary embodiment of the present invention, the spectrum of aromatic fraction (also referred to as FTIR spectrum) is obtained by the spectroscopic unit 106 in a mid infrared range of 4000-650 cm-1 by collecting at least 32 scans per aromatic fraction. In an exemplary embodiment of the present invention, resolution of the spectroscopic unit 106 is maintained at 4 cm-1 in an absorbance mode. In an exemplary embodiment of the present invention, the spectroscopic unit 106 comprises a spectrometer such as, but is not limited to, a Thermo Scientific Nicolet iS5 FTIR spectrometer for effectively obtaining the FTIR spectrum. The Thermo Scientific Nicolet iS5 FTIR spectrometer comprises of an infrared (IR) source, a potassium bromide (KBr) beam splitter and a Deuterated Triglycine Sulphate (DTGS) detector for carrying out mid infrared (MIR) measurements. In an exemplary embodiment of the present invention, the effective pathlength of the spectrum obtained varies with the wavelength of the radiation, therefore, an ATR correction is performed on the obtained spectrum in order to correct the variation in effective pathlength.
[0018] In an embodiment of the present invention, the thermal maturity estimation unit 108 performs a quantitative estimation of the obtained spectrum of the aromatic fraction. The obtained spectrum of the aromatic fraction comprises of multiple spectral peaks. In an exemplary embodiment of the present invention, the multiple peaks include aromatic =C-H stretching peaks, aliphatic C-H asymmetric and symmetric stretching peaks, aromatic C=C stretching peaks, aliphatic C-H bending peaks and aromatic

C-H bending peaks, as illustrated in Fig. 2. The aliphatic C-H asymmetric stretching peaks are the most dominant in the obtained spectrum. In an embodiment of the present invention the thermal maturity estimation unit 108 is further configured to carry out a curve fitting technique in a spectral range of between 2800 cm-1 to 3100 cm-1. The curve fitting technique aids in deconvoluting various overlapping spectral peaks. Further, subsequent to curve fitting, area of a particular peak is determined for computing an FTIR ratio. The obtained spectrum are stacked in a graphical representation, as illustrated in Fig. 2, where x-axis denotes the wavenumber and y-axis denotes the absorbance values. The stacked spectrum show increasing absorption peak intensities of aromatic =C-H stretching, aromatic C=C stretching and aromatic C-H bending peaks with increasing maturity (VRc%) of crude oils, as illustrated in Fig. 2.
[0019] In an embodiment of the present invention, the thermal maturity estimation unit 108 determines various FTIR ratios of aromatic to aliphatic spectral peaks obtained in FTIR spectrum. The FTIR ratio comprises =C-H (aromatic stretching) /CH2+CH3 (aliphatic stretching), C=C
(aromatic/olefinic stretching) /CH2+CH3 (aliphatic stretching) and C-H (aromatic bending)/CH2+CH3 (aliphatic stretching). The three FTIR ratios, as thermal maturity parameters, are correlated with a maturity parameter of crude oil (i.e. Vitrinite Reflectance calculated, VRc%) for quantitatively estimating the thermal maturity of crude oil. In an embodiment of the present invention, the FTIR ratio =C-H (aromatic stretching)/CH2+CH3 (aliphatic stretching) provides the most effective correlation with the VRc%. The FTIR ratio values for =C-H (aromatic stretching)/CH2+CH3
(aliphatic stretching) are determined. The determined FTIR

ratio values are correlated and analyzed against the VRc%, as illustrated in Fig. 3. Referring to Fig. 3, the VRc% values are plotted on the x-axis and the FTIR ratio values are plotted on the y-axis. The calibration plot, as illustrated in Fig. 3, provides an increasing =C-H/CH2+CH3 ratio with increasing maturity or VRc% of crude oil. In an exemplary embodiment of the present invention, the FTIR ratio values are plotted on the y-axis in the range of between 0.052 to 0.35. Further, the plot between the FTIR ratio values and the VRc% values provides a calibration curve. In an embodiment of the present invention, the calibration curve is used to quantitatively estimate the thermal maturity of unknown crude oil samples.
[0020] In an embodiment of the present invention, the thermal maturity estimation unit 108 estimates the thermal maturity of the crude oil based on the correlation between FTIR ratio values and VRc% values using the calibration curve and further based on the below mentioned formula:
y = 0. 0093e2-8647x
wherein, y represents FTIR ratio (=C-H/CH2+CH3 ratio);
e represents exponential function; and
x represents VRc% value
In an embodiment of the present invention, the correlation between the FTIR ratio values and the crude oil maturity parameter (VRc%) values is represented by a correlation coefficient value (R2) determined from the calibration curve. In an exemplary embodiment of the present invention, the correlation coefficient value (R2) is 0.9043, which provides an efficient thermal maturity estimation of the crude oils.

[0021] Advantageously, in accordance with various embodiments of the present invention, the present invention provides an efficient quantitative estimation of thermal maturity of crude oil. The present invention further provides determination of thermal maturity parameter associated with the crude oil in entire maturity range from early to post peak maturation stage, therefore providing non-ambiguous quantitative estimation of thermal maturity of crude oil. Further, the present invention provides for accurate determination of thermal maturity of higher maturity crude oils based on determined FTIR ratio i.e. aromatic stretching (=C-H)/aliphatic stretching (CH2+CH3) ratio. Further, the present invention provides for analyzing aromatic fraction of crude oil for effective estimation of thermal maturity of crude oil. Furthermore, the present invention provides for estimating thermal maturity of unknown crude oil samples based on equation derived from calibration curve between FTIR ratio values and VRc% values. Yet further, the process of present invention provides for effective thermal maturity estimation based on the calibration curve plotted between the determined FTIR ratio values and the VRc% values for the crude oil samples.
[0022] While the exemplary embodiments of the present invention are described and illustrated herein, it will be appreciated that they are merely illustrative. It will be understood by those skilled in the art that various modifications in form and detail may be made therein without departing from the scope of the invention.

We claim:
1. A system (100) for optimized quantitative estimation of
thermal maturity of a crude oil, the system (100)
comprising:
a distillation unit (102) for distilling crude oil at a temperature of up to 210°C for removing lighter fraction of the crude oil;
a deasphalting unit (114) for deasphalting the crude oil by refluxing with n-hexane for removing asphaltenes and obtaining maltene present in the crude oil;
an aromatic fraction separation unit (104) for separating a saturated fraction and an aromatic fraction from the maltene;
a spectroscopic unit (106), executed by a processor (110), for obtaining spectrum of the aromatic fraction; and
a thermal maturity estimation unit (108), executed by the processor (110), for determining thermal maturity of the crude oil by determining a Fourier Transform Infrared (FTIR) ratio of aromatic to aliphatic spectral peaks obtained in FTIR spectrum and correlating the determined FTIR ratio with a crude oil maturity parameter.
2. The system (100) as claimed in claim 1, wherein the
saturated fraction is separated from the maltene using
n-hexane and the aromatic fraction is separated from the
maltene using toluene.

3. The system (100) as claimed in claim 1, wherein the aromatic fraction separation unit (104) separates the saturated fraction and the aromatic fraction from the maltene by applying a column chromatography technique, wherein the column chromatography technique includes Saturate, Aromatic, Resin and Asphaltene (SARA) analysis.
4. The system as claimed in claim 1, wherein a background spectrum of the aromatic fraction is obtained, and wherein a single beam spectrum is obtained without a sample induced by the spectroscopic unit (106) using the surrounding environment for obtaining the background spectrum.
5. The system (100) as claimed in claim 1, wherein the spectroscopic unit (106), executed by the processor (110), obtains the spectrum of the aromatic fraction by
analyzing the aromatic fraction using an Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopic technique.
6. The system (100) as claimed in claim 5, wherein the
spectroscopic unit (106), executed by the processor
(110), obtains the spectrum of the aromatic fraction by:
diluting the aromatic fraction in a pre-defined amount of an organic solvent, wherein the organic solvent is dichloromethane (DCM);
spreading uniformly the aromatic fraction, diluted with DCM, over a zinc selenide crystal present in the spectroscopic unit (106) using a syringe, wherein DCM evaporates at a room temperature and the aromatic fraction remains on the zinc-selenide crystal, and

wherein refractive index of the zinc-selenide crystal is 2.4; and
obtaining spectrum of the aromatic fraction by passing radiation through the aromatic fraction spread over the zinc-selenide crystal using the ATR-FTIR spectroscopic technique, wherein the spectrum of aromatic fraction is obtained by the spectroscopic unit (106) in a mid infrared range of 4000-650 cm-1 by collecting at least 32 scans per aromatic fraction.
7. The system (100) as claimed in claim 1, wherein resolution of the spectroscopic unit (106), executed by the processor (110), is maintained at 4 cm-1 in an absorbance mode.
8. The system (100) as claimed in claim 1, wherein the obtained spectrum of the aromatic fraction comprises of multiple spectral peaks including aromatic =C-H stretching peaks, aliphatic C-H asymmetric and symmetric stretching peaks, aromatic C=C stretching peaks, aliphatic C-H bending peaks and aromatic C-H bending peaks.

9. The system (100) as claimed in claim 9, wherein the thermal maturity estimation unit (108), executed by the processor (110), is configured to carry out a curve fitting technique in a spectral range of between 2800 cm" 1 to 3100 cm-1 for deconvoluting overlapping spectral peaks.
10. The system (100) as claimed in claim 1, wherein the thermal maturity estimation unit (108), executed by the

processor (110), determines an area of a peak for computing the FTIR ratio.
11. The system (100) as claimed in claim 10, wherein the
FTIR ratio comprises =C-H (aromatic stretching)/CH2+CH3
(aliphatic stretching).
12. The system (100) as claimed in claim 1, wherein the maturity parameter of the crude oil is a Vitrinite Reflectance calculated (VRc%) value.
13. The system (100) as claimed in claim 12, wherein the thermal maturity of the crude oil is estimated by the thermal maturity estimation unit (108), executed by the processor (110), based on a correlation between the FTIR ratio values and the VRc% values using a calibration curve, and wherein a plot between the FTIR ratio values and the VRc% values provide the calibration curve.
14. The system (100) as claimed in claim 13, wherein the correlation between the FTIR ratio values and the crude oil maturity parameter (VRc%) is represented by a correlation coefficient value (R2) which is determined by the thermal maturity estimation unit (108), executed by the processor (110), from the calibration curve, and wherein the correlation coefficient value (R2) is 0.9043.