RU2796819C1 - Method for determining the group composition of bitumen in rock using low-frequency nmr relaxometry - Google Patents

Abstract

FIELD: oil development and production.

SUBSTANCE: methods for express analysis of the group composition of bitumen, which consists in the simultaneous registration of the decay signal of free induction and the envelope of echo signals in the Carr, Purcell, Meiboom, Gill sequence. A method for determining the group composition of bitumen in rock using low-frequency NMR relaxometry is disclosed, which consists in taking a sample of bitumen-saturated rock and crushing it to grains with a diameter of not more than 5 mm, then the ground sample is dried at a temperature T = (60±0.2)°C for 12 hours with the possibility of ensuring the removal of residual water, then the prepared sample is placed in a test tube with the possibility of ensuring maximum filling in the area of the measuring coil of the NMR analyzer, then the test tube with the sample is thermostatically controlled, then the NMR analyzer is adjusted, while measuring two free induction decay signals and the envelope of the echo signals in the Carr-Purcell-Meiboom-Gill sequence, performed in parallel on the NMR analyzer, the measurement parameters are entered, then the results are mathematically processed, which consists in fitting the experimental free induction decays and the decay envelope in the series Carr, Purcell, Meiboom, Gill sequence; then, from the envelope of the echo signals in the Carr-Purcell-Meiboom-Gill sequence, the amplitudes of the liquid-phase components are determined, then the relative content of each component is determined as the ratio of the corresponding amplitude to the total amplitude, the asphaltene content is determined from the free induction decay signal as the ratio of the amplitude of the solid-phase signal to the total amplitude with obtaining the parameters of the group composition of the bitumen in the rock.

EFFECT: rapid determination of bitumen group composition in rock samples; exclusion of complex and lengthy sample preparation operations; exclusion of the extraction process; exclusion of multi-stage chemical analysis; exclusion of the use of any reagents and solvents; improving the manufacturability of the analysis of bitumen in the rock.

1 cl, 1 tbl, 1 ex

Description

The invention relates to the field of oil development and oil production, and in particular to methods for express analysis of the group composition of bitumen, which consists in the simultaneous registration of the FSI signal (decay of free induction) and the envelope of echo signals in the KPMG (Carr-Parcell-Meibum-Gill) series in rock samples in initial state without prior preparation by low-frequency NMR relaxometry.

Due to the depletion of traditional reserves of light oil, natural bitumen is the main alternative source of hydrocarbons. However, the industrial development of efficient methods for the extraction of hydrocarbons from bituminous rocks is a complex scientific, technical and economic problem, especially for old oil-producing regions with high industrial potential. Bulk (or SARA) analysis of bitumen is a fundamental study necessary for modeling processes that affect enhanced oil recovery (polymer flooding, in situ combustion, the use of surfactants, etc.).

The claimed method can be used for operational control of technological processes of production, transportation and processing of ultra-high-viscosity oil.

An analysis of the studied prior art showed that the main methods for analyzing bituminous rocks in assessing deposits are Rock-Eval pyrolysis [Espitalié, J., Laporte, J. L., Madec, M., Marquis, F., Leplat, P., Paulet, J., Boutefeu, A., 1977 Rev. Inst. fr. Pet. 32, 23–42. https://doi.org/10.2516/ogst:1977002], CHNS elemental analysis method [Zauer, E.A., 2018. Modern automatic CHNS/O/X organic compound analyzers. Anal. i Kontrol 22, 6–19. https://doi.org/10.15826/analitika.2018.22.1.001], thermogravimetric analysis (TGA) [Ganeeva, Y.M., Yusupova, T.N., Okhotnikova, E.S., 2020. Thermal analysis methods to study the reservoir bitumens. J. Therm. Anal. Calorim. 139, 273-278. https://doi.org/10.1007/s10973-019-08410-6] and extraction methods [Tikhonova M.S., Ivanova D.A., Kalmykov A.G., Borisov R.S., Kalmykov G.A. ., 2019. Method of stepwise extraction of rocks of high-carbon formations to study the component distribution of bitumoids and the variability of their main geochemical parameters. Georesources 21, 172–182. https://doi.org/10.18599/grs.2019.2.172-182]. However, all of the above methods are used to quantify the content of organic matter and separate organic matter into a solid and liquid part.

From the studied prior art, a method for determining the group (SARA) composition of bitumens, standardized in the USA (ASTM D4124-09 (2018)) [ASTM D4124-09 (2018)), is known. Standard Test Method for Separation of Asphalt into Four Fractions. – Text: electronic // ASTM: official site. - 2018. - URL: https://www.astm.org/Standards/D4124.html (date of access: 08/01/2022)] and Russia as GOST 32269-2013 [GOST 32269-2013. Oil bitumen. Quadruple separation method = Petroleum bitumen. Method of separation into four fractions : Interstate standard : official edition : put into effect as the national standard of the Russian Federation by Order of the Federal Agency for Technical Regulation and Metrology dated August 28, 2013 No. 751-st : introduced for the first time : introduction date 2015-01- 01 / Prepared by the Technical Committee for Standardization TC 160 "Products of the petrochemical complex", Federal State Unitary Enterprise All-Russian Research Center for Standardization, Information and Certification of Raw Materials, Materials and Substances (VNITSSMV). - Moscow: Standartinform, 2014. - V, 20 p. - 31 copies. – Text : direct]. Currently, the known method is widely used. The essence of the method is the sequential separation of high-viscosity oil and bitumen into 4 fractions on a chromatographic column, followed by measurement of the content of each.

The known method has significant disadvantages:

- analysis requires a well-equipped chemical laboratory and experienced personnel, since fractionation requires careful conduct;

– significant analysis time and difficulty of automation;

– a large amount of spent reagents;

- there is information showing the low accuracy of the known method [Bissada, K. K., Tan, J., Szymczyk, E., Darnell, M., Mei, M. 2016. Group-type characterization of crude oil and bitumen. Part I: Enhanced separation and quantification of saturates, aromatics, resins and asphaltenes (SARA). Organic Geochemistry 95, 21–28. https://doi.org/10.1016/j.orggeochem.2016.02.007].

For group analysis of bitumen, it is required to preliminarily carry out extraction from a rock sample. Invasive extraction requires grinding the sample, followed by exposure to a solvent such as chloroform. Non-invasive extraction, according to some reports [ASTM D5369-93(2008)e1. Standard Practice for Extraction of Solid Waste Samples for Chemical Analysis Using Soxhlet Extraction. – Text: electronic // ASTM: official site. - 2016. - URL: https://www.astm.org/d5369-93r08e01.html (date of access: 08/01/2022)], does not provide complete extraction of hydrocarbons from closed pores. Also, extraction without crushing the rock takes an average of 10 to 120 hours, and for rocks with low reservoir properties, it can reach up to 3 weeks or more. When grinding the rock, extraction takes up to 72 hours.

There is a method for determining the group analysis of petroleum fractions in a porous medium [Mirotchnik, K., Kantzas, A., Aikman, M., 2001. A New Method for Group Analysis of Petroleum Fractions in Unconsolidated Porous Media. J. Can. Pet. Tech. 40(7), 38-44. https://doi.org/10.2118/01-07-02]. This non-invasive method is based on the use of low frequency NMR relaxometry. The essence of the known method is that the spectrum of transverse relaxation times of oil components can be divided into frames. The fastest relaxation frame represents asphaltenes, the second shortest relaxation frame represents resins, and the next two slower frames represent aromatic and saturated compounds.

Disadvantages of the known method:

– use of solvents to increase the mobility of heavy oil molecules;

– the method is demonstrated on model samples imitating a real rock.

A known method for determining the content of paraffins and asphaltenes in oil according to the patent of the Russian Federation No. 2333476 "Method for determining the content of paraffins and asphaltenes in oil", the essence is a method for determining the content of paraffins and asphaltenes in oil, including precipitation of asphaltenes with a solvent, characterized in that three samples of crude oil are taken , two of the selected samples are dissolved in a solvent, asphaltenes are removed from one of the solvent-treated samples, for all three samples, the decay curves of free induction are measured by nuclear magnetic resonance and the ratio of hydrogen-containing solid fractions suspended in oil and hydrogen-containing liquid fractions is determined by the content of hydrogen-containing solid fractions in a solvent-treated sample from which asphaltenes have been removed, the paraffin content is judged, the asphaltene concentration is judged by the content of hydrogen-containing solid fractions in another solvent-treated sample, taking into account the established concentration of paraffins, and the content of paraffins and asphaltenes in the original oil is determined based on the established ratio paraffins and asphaltenes in hydrogen-containing solid fractions. The method for determining the content of paraffins and asphaltenes in oil according to claim 1, characterized in that after the dissolution of two samples in the solvent, the solvent is removed along with light oil fractions.

Thus, the known method involves taking three samples of crude oil, two of which are treated with a solvent, after which the solvent is removed along with light oil fractions, and asphaltenes are removed from one of the solvent-treated samples. The free induction decay curves (FID) are then measured for all three samples. The ratio of the FID amplitudes for the solid and liquid phases determines the concentration of paraffins and asphaltenes.

Disadvantages of the known method:

– the need to measure three samples;

– use of solvents;

- the initial structure of the sample changes, which does not occur during the implementation of the claimed method, which increases the manufacturability of the claimed method.

An invention is known according to RF patent No. 2383884 “Method for determining the content of liquid-phase and solid-state components in a mixture of hydrocarbons”, the essence is a method for determining the content of liquid-phase and solid-state components in a mixture of hydrocarbons, including the selection of at least one sample of the hydrocarbon mixture, characterized in that for of this sample, the method of nuclear magnetic resonance is used to measure a series of decay curves of the free induction of a mixture of hydrocarbons in the temperature range from -150 to +150 ° C, for each curve of the decay of free induction, the value of the proportion of the solid component P _s in the ¹ H signal of nuclear magnetic resonance is determined at that temperature, at which it was measured, the obtained values are used to build the temperature dependence of the proportion of the solid component P _s in the signal ¹ H of nuclear magnetic resonance and the change in the proportion P _s -ΔP _si due to the phase transition of the i-component due to heating or cooling, determine the content of solid and / or liquid-phase components in a mixture of hydrocarbons by assigning the values of ΔP _si to the respective components of the mixture.

Thus, the known method for determining the content of liquid-phase and solid-state components in a mixture of hydrocarbons is based on determining the temperature dependence of the SSI signal of the solid-state component. The method excludes chemical processing and preserves the non-invasiveness of the sample.

The disadvantage of the known method is a significant change in the group composition of the analyzed mixture with a change in temperature, tk. resins are involved in the formation of asphaltene supramolecular structures, which leads to an incorrect determination of the amount of asphaltenes in the sample, which reduces the efficiency of using the invention for its intended purpose.

A known method for determining bitumen and free water in rock samples [Yang, K., Connolly, P.R.J., Li, M., Seltzer, S.J., McCarty, D.K., Mahmoud, M., El-Husseiny, A., May, E.F., Johns , M.L., 2020. Shale rock core analysis using NMR: Effect of bitumen and water content. J. Pet. sci. Eng. 195, 107847. https://doi.org/10.1016/j.petrol.2020.107847]. The essence of the known method is to determine the composition of shale rocks containing viscous semi-solid bitumen and capillary trapped water in organic/inorganic pores by changing the saturation relative humidity by low-frequency NMR relaxometry. The method is based on the simultaneous processing of the combined SSI and KPMG data for the interpretation of the population of protons related to various components in the rock.

The known method can only be used to quantify the content of organic matter and water, as a result of which it cannot be used to determine the group composition of bitumen in the rock.

The closest solution to a technical solution that matches the declared set of matching features, but does not match the purpose of the object of study, chosen by the applicant as a prototype, is the method described in [In situ analysis of the component composition and properties of heavy oils in situ by NMR relaxation in low magnetic fields / V.Ya. Volkov, B.V. Sakharov, N.M. Khasanova, D.K. Nurgaliev – DOI 10.18599/grs.2018.4.308-323. – Text: direct // Georesources. - 2018. - T. 20, No. 4. – S. 308–323]. The essence of the known method is the sequential measurement of the free induction decay signal (FID) and the envelope of the echo signals in the Carr-Purcell-Meibum-Gill (KPMG) series, followed by mathematical processing of the received signals, which makes it possible to determine the amplitudes of the NMR signals and the times of transverse or spin-spin relaxation T ₂ protons of all components. The envelope of spin echo signals in the KPMG series is described by the sum of the exponents:

(1) $$A_{CPMG}(t)={\displaystyle \sum _{i=1}^n{A}_i\cdot \exp \left(-\frac{t}{T_{2i}}\right)},$$

(1)

where A _i are the amplitudes of the components, which make it possible to estimate the content of liquid components (saturated compounds, aromatic compounds and resins) with relaxation times T _{2 i} in the range from 0.1 ms to several seconds.

The FID signal has a complex shape, which is mainly determined by the inhomogeneity of the magnetic field in the sample volume. In the initial section in the range from 10 to 100 μs, when the influence of the field inhomogeneity is insignificant, the FID shape is described by the sum of the Gaussian and exponential functions. The rest of the FID up to 2 ms is described by the exponent and the product of the exponent and the function that describes the inhomogeneity of the magnetic field in the sensor coil. The full form of the SSI is well approximated by the set of functions:

(2) $$\begin{array}{l}{A}_{FID}(t)=A_{S0}\cdot \left[(1-f_{Sam})\cdot \exp \left(-{\left(\frac{t}{T_{2Sg}}\right)}^2\right)+f_{Sam}\cdot \exp \left(-\frac{t}{T_{2Sam}}\right)\right]+\\ A_{le0}\cdot \exp \left(-\frac{t}{T_{2le}}\right)+A_{lm0}\cdot \exp \left(-\frac{t}{T_{2lm}}\right)\cdot \exp \left(-{\left(\frac{t}{T_{2ll}}\right)}^2\right),\end{array}$$

(2)

WhereA _{S 0} is the amplitude of solid-phase components (asphaltenes),A _{le 0} – amplitude of high-viscosity resins,A _{lm 0} – amplitude of liquid maltenes (saturated, aromatic compounds and resins);T _{2 Sg} is the relaxation time of the crystalline part of the solid phase component;T _{2 Sam} is the relaxation time of the amorphous part of the solid phase component;T _{2 le} is the relaxation time of the short exponential function of the liquid phase component;T _{2 lm} is the relaxation time of the Voigt function of the liquid-phase component;T _{2 ll} is the relaxation time of the component describing the inhomogeneity of the magnetic field;f _Sam is the proportion of the amorphous part of the solid phase component.

The method was tested on two samples of crude oil from different wells of the Ashalchinskoye field with different asphaltene content. Two more samples were prepared by diluting the first two samples of the deasphalted residue and the fifth sample was the deasphalted residue.

The disadvantage of the method described in the prototype is that it is a theoretical description and experimental study of high-viscosity oil, carried out exclusively in a laboratory using five test samples in a narrow range of variation in the composition of the oil. At the same time, two samples were prepared in advance in a special way, namely, to reduce the asphaltene content, a deasphalted residue obtained from the original oil samples was added to them. And one sample completely represented this residue. At the same time, the prototype does not have a really developed industrial method, including a description of the methodology and sequence of operations for implementing the method at an oil production, transportation and processing facility, which limits the possibility of its intended use.

In addition, under the conditions of the prototype (laboratory conditions) there is no possibility of obtaining real-time data on changes in the composition of oil during its production or transportation.

The technical result of the claimed technical solution is the creation of an easy-to-implement, fast and efficient method for analyzing the group composition of bitumen in rock samples in the initial state without prior preparation, including in the field, which ensures the implementation of the following possibilities:

1 - rapid determination of the group composition of bitumen in rock samples;

2 – exclusion of complex and lengthy sample preparation operations;

3 - exclusion of the extraction process;

4 - exclusion of multi-stage chemical analysis;

5 - exclusion of the use of any reagents and solvents;

6 - improving the manufacturability of the analysis of bitumen in the rock.

The essence of the claimed technical solution is a method for determining the group composition of bitumen in rock using low-frequency NMR relaxometry, which consists in taking a sample of bituminous rock and crushing it to grains with a diameter of not more than 5 mm, then the ground sample is dried at a temperature T = (60 ± 0 ,2) °С for 12 hours with the possibility of ensuring the removal of residual water, then the prepared sample is placed in a test tube with the possibility of ensuring maximum filling in the area of the measuring coil of the NMR analyzer, then the test tube with the sample is thermostated, then the NMR analyzer is adjusted, at In order to measure two free induction decay signals and the envelope of echo signals in the Carr-Purcell-Meiboom-Gill series, performed in parallel on an NMR analyzer, the measurement parameters are entered, namely, for free induction decay signals: registration time is 6 ms, the number accumulations - 225, repetition time - 2 s; and for the envelope of echo signals in the Carr-Purcell-Meiboom-Gill series: the time between echo signals is 100 μs, the number of echo signals is 5000, the number of accumulations is 225, the repetition time is 2 s; then the measurement process is started, as a result of which the free induction decay signal and the envelope of the echo signals are recorded in the Carr-Purcell-Meibum-Gill series, then the results are mathematically processed, which consists in performing the procedure of fitting the experimental free induction decays according to the formula

$$\begin{array}{l}{A}_{FID}(t)=A_{S0}\cdot \left[(1-f_{Sam})\cdot \exp \left(-{\left(\frac{t}{T_{2Sg}}\right)}^2\right)+f_{Sam}\cdot \exp \left(-\frac{t}{T_{2Sam}}\right)\right]+\\ A_{le0}\cdot \exp \left(-\frac{t}{T_{2le}}\right)+A_{lm0}\cdot \exp \left(-\frac{t}{T_{2lm}}\right)\cdot \exp \left(-{\left(\frac{t}{T_{2ll}}\right)}^2\right),\end{array}$$

WhereA _{S 0} – amplitude of solid-phase components – asphaltenes),A _{le 0} – amplitude of high-viscosity resins,A _{lm 0} – range of liquid maltenes – saturated, aromatic compounds and resins,T _{2 Sg} is the relaxation time of the crystalline part of the solid phase component,T _{2 Sam} is the relaxation time of the amorphous part of the solid phase component,T _{2 le} is the relaxation time of the short exponential function of the liquid phase component,T _{2 lm} is the relaxation time of the Voigt function of the liquid phase component,T _{2 ll} is the relaxation time of the component describing the inhomogeneity of the magnetic field;f _Sam is the proportion of the amorphous part of the solid phase component and the decay envelope in the Carr-Purcell-Meibum-Gill series according to the formula

$$A_{CPMG}(t)={\displaystyle \sum _{i=1}^n{A}_i\cdot \exp \left(-\frac{t}{T_{2i}}\right)},$$

$$$$

в начальный момент времени, которая пропорциональна количеству атомов водорода в битуме; далее из огибающей эхо-сигналов в последовательности Карра-Парселла-Мейбума-Гилла определяют амплитуды жидкофазных компонент, причем компонента с самым длинным временем релаксации T ₂₁ соответствует протонной популяции насыщенных углеводородов с амплитудой А ₁ , следующая с более коротким временем релаксации T ₂₂ компонента соответствует протонной популяции ароматических углеводородов с амплитудой А ₂ , компонента с наиболее коротким временем релаксации T ₂₃ соответствует протонной популяции группы смол с амплитудой А ₃ ; далее определяют относительное содержание каждой компоненты как отношение соответствующей амплитуды А _i к общей амплитуде А ₀ , содержание асфальтенов определяют из сигнала спада свободной индукции как отношение амплитуды твердофазного сигнала А _{S 0} к общей амплитуде А ₀ с получением параметров группового состава битума, находящегося в породе.where T _2i is the relaxation time, A _i are the amplitudes of the components that make it possible to estimate the content of liquid components - saturated compounds, aromatic compounds and resins, characterizing the distribution of the components and the correlation according to the group composition of bitumen in the test sample, then the total amplitude is determined from the free induction decay signal according to the formula: $$A_0=A_{S0}+A_{l0}=A_{S0}+A_{le0}+A_{lm0}$$

$$$$

at the initial moment of time, which is proportional to the number of hydrogen atoms in the bitumen; then, from the envelope of the echo signals in the Carr-Purcell-Meiboom-Gill sequence, the amplitudes of the liquid-phase components are determined, and the component with the longest relaxation time T ₂₁ corresponds to the proton population of saturated hydrocarbons with amplitude A ₁ , the next component with a shorter relaxation time T ₂₂ corresponds to the proton populations of aromatic hydrocarbons with amplitude A ₂ , the component with the shortest relaxation time T ₂₃ corresponds to the proton population of the group of resins with amplitude A ₃ ; then, the relative content of each component is determined as the ratio of the corresponding amplitude A _i to the total amplitude A ₀ , the asphaltene content is determined from the decay signal of free induction as the ratio of the amplitude of the solid phase signal A _{S 0} to the total amplitude A ₀ to obtain the parameters of the group composition of the bitumen in the rock.

Further, the applicant provides a description of the claimed technical solution.

$$$$

сигнала ССИ в начальный момент времени, которая пропорциональна количеству атомов водорода в битуме, затем из огибающей эхо-сигналов в последовательности КМПГ определяют амплитуды жидкофазных компонент, причем компонента с самым длинным временем релаксации T ₂₁ соответствует протонной популяции насыщенных углеводородов с амплитудой А ₁ , следующая с более коротким временем релаксации T ₂₂ компонента соответствует протонной популяции ароматических углеводородов с амплитудой А ₂ , компонента с наиболее коротким временем релаксации T ₂₃ соответствует протонной популяции группы смол с амплитудой А ₃ , после этого относительное содержание каждой компоненты определяют как отношение соответствующей амплитуды А _i к общей амплитуде А ₀ , содержание асфальтенов определяют из сигнала ССИ как отношение амплитуды твердофазного сигнала А _{S 0} к общей амплитуде А ₀ .The claimed method for determining the group composition of bitumen in rock using low-frequency NMR relaxometry as a whole consists in the fact that the studied rock samples are pre-dried at a temperature of T = 60 ° C for 12 hours to ensure the removal of residual water, then placed in a glass test tube with a diameter of 10 mm to a height of 15 mm, ensuring maximum filling in the region of the transceiver coil, then the sample is thermostated for at least 15 minutes at a temperature of T = (40 ± 0.2) ° C and then placed in an NMR relaxometer, then the FSI signal is recorded with minimum "dead time" equal to 10 µs, registration frequency 1 µs (receiver bandwidth - 1 MHz), registration time - 6 ms, number of accumulations - 225 and repetition time - 2 s, after that, the envelope of echo signals in the KPMG series is recorded with a minimum the time between echo signals is equal to 100 μs and the number of echoes is 5000, the number of accumulations is 225 and the repetition time is 2 s, after which the mathematical processing of the results is performed, which consists in the procedure of fitting the experimental SSI decays and the KPMG decay envelope with the model functions presented in the prototype, characterizing the distribution of the components and the correlation by the group composition of bitumen, determine the overall amplitude $$A_0=A_{S0}+A_{l0}=A_{S0}+A_{le0}+A_{lm0}$$

$$$$

of the FSI signal at the initial moment of time, which is proportional to the number of hydrogen atoms in the bitumen, then from the envelope of the echo signals in the CMPG sequence, the amplitudes of the liquid-phase components are determined, and the component with the longest relaxation time T ₂₁ corresponds to the proton population of saturated hydrocarbons with the amplitude A ₁ , following with the shorter relaxation time T ₂₂ of the component corresponds to the proton population of aromatic hydrocarbons with amplitude A ₂ , the component with the shortest relaxation time T ₂₃ corresponds to the proton population of the resin group with amplitude A ₃ , after that the relative content of each component is determined as the ratio of the corresponding amplitude A _i to the total amplitude A ₀ , the content of asphaltenes is determined from the FSI signal as the ratio of the amplitude of the solid-phase signal A _{S 0} to the total amplitude A ₀ .

For the practical implementation of the proposed method, an NMR relaxometer (NMR analyzer) is required, which allows recording the solid-state component of the proton NMR signal. The dead time (not more than 10 µs) and the signal-to-noise ratio (not less than 200 at the resonance frequency of 20 MHz) should ensure the registration of NMR signals with transverse relaxation times of the order of 10 µs.

The following is a detailed description of the claimed method by the applicant:

1. Take a sample of bituminous rock and crush it to grains with a diameter of not more than 5 mm. A larger grind value leads to incomplete filling of the tube in the resonant region, which, in turn, leads to a decrease in the signal-to-noise ratio.

2. The ground sample is dried at a temperature of T = (60 ± 0.2) ° C for 12 hours with the possibility of removing residual water. These temperature and time parameters have been confirmed by numerous experimental studies. It is shown that a decrease in temperature leads to an increase in the drying time, which is inappropriate within the working cycle of a research laboratory, and an increase in temperature with a decrease in drying time leads to the evaporation of low-boiling bitumen components.

3. The prepared sample is placed in a glass tube with a diameter of 10 mm to a height of 15 mm, with the possibility of ensuring maximum filling in the resonant region of the measuring coil of the NMR analyzer.

4. Next, the test tube with the sample is thermostated for at least 15 minutes at a temperature T = (40 ± 0.2) °C.

5. Next, the NMR analyzer is tuned to ensure the achievement of the claimed technical result, namely, the measurement parameters are entered, i.e. for the free induction decay signal: registration frequency - 1 μs (a value sufficient to ensure the required accuracy of obtaining the claimed technical result, at the same time not leading to overflow of the ADC of the NMR analyzer receiving path), registration time - 6 ms (time at which the useful signal ends), the number of accumulations is 225 (to obtain a signal-to-noise ratio of at least 100), the repetition time is 2 s (the repetition period must be at least _5T1 - the transverse relaxation time of the sample to eliminate signal suppression); for the envelope of echo signals in the Carr-Purcell-Meiboom-Gill series: the time between echo signals is 100 μs (the minimum possible value for an NMR relaxometer), the number of echo signals is 5000 (the number sufficient to register the entire useful signal), the number accumulations - 225 (to obtain a signal-to-noise ratio of at least 100), repetition time - 2 s (the repetition period must be at least _5T1 - the transverse relaxation time of the sample to eliminate signal suppression).

6. Next, the test tube with the prepared sample is placed in the NMR relaxometer and the measurement process is started, as a result of which the free induction decay signal and the envelope of the echo signals are recorded in the Carr-Purcell-Meiboom-Gill series.

7. Next, mathematical processing of the results is performed, which consists in performing the procedure of fitting the experimental free induction decays according to formula (2) and the decay envelope in the Carr-Purcell-Meiboom-Gill series according to formula (1), characterizing the distribution of the components and the correlation by the group composition of bitumen in sample under study.

в начальный момент времени, которая пропорциональна количеству атомов водорода в битуме.8. Further, from the decay signal of free induction, the total amplitude is determined by the formula: $$A_0=A_{S0}+A_{l0}=A_{S0}+A_{le0}+A_{lm0}$$

at the initial moment of time, which is proportional to the number of hydrogen atoms in the bitumen.

9. Next, from the envelope of the echo signals in the Carr-Purcell-Meiboom-Gill sequence, the amplitudes of the liquid-phase components are determined, and the component with the longest relaxation time T ₂₁ corresponds to the proton population of saturated hydrocarbons with amplitude A ₁ , the next with a shorter relaxation time T ₂₂ component corresponds to the proton population of aromatic hydrocarbons with amplitude A ₂ , the component with the shortest relaxation time T ₂₃ corresponds to the proton population of the resin group with amplitude A ₃ .

10. Next, the relative content of each component is determined as the ratio of the corresponding amplitude A _i to the total amplitude A ₀ , the asphaltene content is determined from the decay signal of free induction as the ratio of the amplitude of the solid phase signal A _{S 0} to the total amplitude A ₀ .

Further, the applicant gives an example of a specific implementation of the claimed method on rock samples.

The claimed method was implemented and tested in practice on 6 weakly cemented samples of bitumen-saturated carbonate rocks with a clay mineral content of 0 to 50%, where the amount of bitumen and its group composition could not be determined only by one of the above standard methods. Any mechanical and chemical impact could lead to the loss of light hydrocarbons or the destruction of the mineral matrix with asphaltenes blocking the pore space. To implement the claimed method, a sample of bitumen-saturated rock was crushed to grains with a diameter of not more than 5 mm, then the ground sample was dried at a temperature of T = (60 ± 0.2) ° C for 12 hours with the possibility of ensuring the removal of residual water, then the prepared sample was placed, for example , into a glass test tube with a diameter of 10 mm to a height of 15 mm with the possibility of ensuring maximum filling in the resonant region of the measuring coil of the NMR analyzer, then the test tube with the sample was thermostated, for example, for 15 minutes, at a temperature T = (40 ± 0.2) °C, then the NMR analyzer was tuned to ensure the achievement of the declared technical result, while to measure the free induction decay signals and the envelope of the echo signals in the Carr-Purcell-Meiboom-Gill series, performed sequentially on the NMR analyzer, the measurement parameters were introduced, namely, for free induction decay signals: registration time - 6 ms, number of accumulations - 225, repetition time - 2 s; and for the envelope of echo signals in the Carr-Purcell-Meiboom-Gill series: the time between echo signals is 100 μs, the number of echo signals is 5000, the number of accumulations is 225, the repetition time is 2 s; then the measurement process was started, as a result of which the free induction decay signal and the envelope of the echo signals in the Carr-Purcell-Meibum-Gill series were recorded, then the mathematical processing of the results was carried out, which consisted in performing the procedure of fitting the experimental free induction decays according to the formula

$$\begin{array}{l}{A}_{FID}(t)=A_{S0}\cdot \left[(1-f_{Sam})\cdot \exp \left(-{\left(\frac{t}{T_{2Sg}}\right)}^2\right)+f_{Sam}\cdot \exp \left(-\frac{t}{T_{2Sam}}\right)\right]+\\ A_{le0}\cdot \exp \left(-\frac{t}{T_{2le}}\right)+A_{lm0}\cdot \exp \left(-\frac{t}{T_{2lm}}\right)\cdot \exp \left(-{\left(\frac{t}{T_{2ll}}\right)}^2\right),\end{array}$$

WhereA _{S 0} – amplitude of solid-phase components – asphaltenes),A _{le 0} – amplitude of high-viscosity resins,A _{lm 0} – range of liquid maltenes – saturated, aromatic compounds and resins,T _{2 Sg} is the relaxation time of the crystalline part of the solid phase component,T _{2 Sam} is the relaxation time of the amorphous part of the solid phase component,T _{2 le} is the relaxation time of the short exponential function of the liquid phase component,T _{2 lm} is the relaxation time of the Voigt function of the liquid phase component,T _{2 ll} is the relaxation time of the component describing the inhomogeneity of the magnetic field;f _Sam is the proportion of the amorphous part of the solid phase component and the decay envelope in the Carr-Purcell-Meibum-Gill series according to the formula

$$A_{CPMG}(t)={\displaystyle \sum _{i=1}^n{A}_i\cdot \exp \left(-\frac{t}{T_{2i}}\right)},$$

$$$$

в начальный момент времени, которая пропорциональна количеству атомов водорода в битуме; далее из огибающей эхо-сигналов в последовательности Карра-Парселла-Мейбума-Гилла определялись амплитуды жидкофазных компонент, причем компонента с самым длинным временем релаксации T ₂₁ соответствует протонной популяции насыщенных углеводородов с амплитудой А ₁ , следующая с более коротким временем релаксации T ₂₂ компонента соответствует протонной популяции ароматических углеводородов с амплитудой А ₂ , компонента с наиболее коротким временем релаксации T ₂₃ соответствует протонной популяции группы смол с амплитудой А ₃ ; далее определяют относительное содержание каждой компоненты как отношение соответствующей амплитуды А _i к общей амплитуде А ₀ , содержание асфальтенов определяют из сигнала спада свободной индукции как отношение амплитуды твердофазного сигнала А _{S 0} к общей амплитуде А ₀ с получением заявленных параметров группового состава битума, находящегося в породе.where A _i are the amplitudes of the components that make it possible to estimate the content of liquid components - saturated compounds, aromatic compounds and resins, characterizing the distribution of the components and the correlation according to the group composition of bitumen in the test sample, then the total amplitude was determined from the signal of the decay of free induction by the formula: $$A_0=A_{S0}+A_{l0}=A_{S0}+A_{le0}+A_{lm0}$$

$$$$

at the initial moment of time, which is proportional to the number of hydrogen atoms in the bitumen; further, from the envelope of the echo signals in the Carr-Purcell-Meiboom-Gill sequence, the amplitudes of the liquid-phase components were determined, and the component with the longest relaxation time T ₂₁ corresponds to the proton population of saturated hydrocarbons with amplitude A ₁ , the next component with a shorter relaxation time T ₂₂ corresponds to the proton populations of aromatic hydrocarbons with amplitude A ₂ , the component with the shortest relaxation time T ₂₃ corresponds to the proton population of the group of resins with amplitude A ₃ ; then, the relative content of each component is determined as the ratio of the corresponding amplitude A _i to the total amplitude A ₀ , the asphaltene content is determined from the decay signal of free induction as the ratio of the amplitude of the solid phase signal A _{S 0} to the total amplitude A ₀ to obtain the declared parameters of the group composition of bitumen in the rock .

SARA analysis of extracts from six samples according to ASTM D4124-09 was performed to assess the accuracy of determination of group composition (SARA) by NMR. SARA results according to ASTM D4124-09 and NMR method are shown in the Table where HC are hydrocarbons.

Table. Group composition of extracts from rock samples

(1 - ASTM D4124-09, 2 - NMR relaxation)

Sample No. Saturated hydrocarbons, % Aromatic hydrocarbons, % Resins, % Asphaltenes, % 1 2 1 2 1 2 1 2 1 7.4 3.4 18.4 18.5 37.3 24.8 36.9 53.3 2 15.3 8.9 28.0 27.9 23.4 26.7 33.3 36.5 3 0.8 2.6 9.6 14.9 31.0 21.0 58.6 61.6 4 1.0 1.4 6.8 13.1 42.0 30.5 55.2 55.0 5 0.8 1.8 9.2 14.7 34.3 24.5 55.6 59.1 6 8.3 9.6 26.0 19.6 24.9 19.0 40.8 51.8

An analysis of the results presented in the Table allows us to conclude that the values obtained in accordance with ASTM D4124-09 and the NMR method do not differ by more than 17%, which shows a high degree of convergence of the results of both methods. Comparison of the SSI and KPMG data showed that the bituminous rock and extract have almost the same relaxation signals, which confirms the correctness of the data obtained by the claimed method.

The presented embodiment of the claimed technical solution shows the effectiveness of its use on bitumen-saturated rock samples to determine the group composition of bitumen in explored and exploited hydrocarbon deposits, including deposits that were not previously used due to the high cost of extracting a viscous fluid and low profitability.

Thus, taking into account the results of the experiments, it seems possible to draw a logical conclusion about the achievement of the claimed technical result, namely, an easy-to-implement, fast and efficient method for analyzing the group composition of bitumen in rock samples in the initial state without preliminary preparation, including in the field, ensuring the implementation of the possibilities:

1 - rapid determination of the group composition of bitumen in rock samples, due to the use of the method of pulsed low-frequency NMR relaxometry;

2 – exclusion of complex and lengthy sample preparation operations due to
the fact that the method of NMR-relaxometry directly receives a signal from the paramagnetic nuclei (protons) of bitumen in the original rock;

3 - exclusion of the extraction process due to the fact that the proposed method does not require the separation of the bitumen sample from the mineral matrix;

4 – exclusion of multistage chemical analysis due to the use of pulsed low-frequency NMR relaxometry;

5 - exclusion of the use of any reagents and solvents due to the use of the method of pulsed low-frequency NMR relaxometry;

6 - increasing the manufacturability of the analysis of bitumen in the rock also through the use of the method of pulsed low-frequency NMR relaxometry.

The main advantages of the claimed method are non-invasiveness, ease of sample preparation, high analysis speed compared to currently used methods, for example, compared to the most common extraction method, the analysis speed increases up to a hundred times. At the same time, non-invasiveness makes it possible to keep the fluid saturation of rock samples and pore space intact during research.

The claimed technical solution meets the "novelty" criterion for inventions, since the claimed set of features given in the claims and the obtained technical solutions that ensure the achievement of the claimed results are unknown from the state of the art studied at the date of filing the application.

The claimed technical solution meets the "inventive step" criterion for inventions, since the claimed set of features and the technical results obtained are not obvious to specialists in this field, and, according to the applicant, a fundamentally new method for determining the group composition of bitumen in rock samples has been developed , which provides a significant superiority of the claimed technical solution over the known methods at the date of submission of the claimed technical solution.

The claimed technical solution meets the criterion of "industrial applicability" for inventions, since the claimed technical solution has been tested in laboratory conditions at the Institute of Geology and Petroleum Technologies of the Kazan (Volga Region) Federal University, and it can be implemented in industrial production for the production of extra heavy oil and natural bitumen with using standard equipment (desktop NMR relaxometer), well-known tools and materials.

Claims (5)

A method for determining the group composition of bitumen in rock using low-frequency NMR relaxometry, which consists in taking a sample of bitumen-saturated rock and crushing it to grains with a diameter of not more than 5 mm, then the ground sample is dried at a temperature of T = (60 ± 0.2) ° C for 12 hours with the possibility of ensuring the removal of residual water, then the prepared sample is placed in a test tube with the possibility of ensuring maximum filling in the area of the measuring coil of the NMR analyzer, then the test tube with the sample is thermostated, then the NMR analyzer is adjusted, while measuring two signals of the free induction decay and the envelope of the echo signals in the Carr-Purcell-Meiboom-Gill series, performed in parallel on the NMR analyzer, the measurement parameters are entered, namely, for the free induction decay signals: registration time is 6 ms, the number of accumulations is 225, the time repetitions - 2 s; and for the envelope of echo signals in the Carr-Purcell-Meiboom-Gill series: the time between echo signals is 100 μs, the number of echo signals is 5000, the number of accumulations is 225, the repetition time is 2 s; then the measurement process is started, as a result of which the free induction decay signal and the envelope of the echo signals are recorded in the Carr-Purcell-Meibum-Gill series, then the results are mathematically processed, which consists in performing the procedure of fitting the experimental free induction decays according to the formula $$\begin{array}{l}{A}_{FID}(t)=A_{S0}\cdot \left[(1-f_{Sam})\cdot \exp \left(-{\left(\frac{t}{T_{2Sg}}\right)}^2\right)+f_{Sam}\cdot \exp \left(-\frac{t}{T_{2Sam}}\right)\right]+\\ A_{le0}\cdot \exp \left(-\frac{t}{T_{2le}}\right)+A_{lm0}\cdot \exp \left(-\frac{t}{T_{2lm}}\right)\cdot \exp \left(-{\left(\frac{t}{T_{2ll}}\right)}^2\right),\end{array}$$

where A_S0 – amplitude of solid-phase components – asphaltenes, A_le0 – amplitude of high-viscosity resins, A_lm0 – amplitude of liquid maltenes – saturated, aromatic compounds and resins, T_2Sg is the relaxation time of the crystalline part of the solid phase component, T_2Sam is the relaxation time of the amorphous part of the solid phase component, T_2le is the relaxation time of the short exponential function of the liquid phase component, T_2lm is the relaxation time of the Voigt function of the liquid phase component, T_2ll is the relaxation time of the component describing the inhomogeneity of the magnetic field; f_Sam is the proportion of the amorphous part of the solid phase component and the decay envelope in the Carr-Purcell-Meibum-Gill series according to the formula $$A_{CPMG}(t)={\displaystyle \sum _{i=1}^n{A}_i\cdot \exp \left(-\frac{t}{T_{2i}}\right)},$$

where T _2i is the relaxation time, A _i are the amplitudes of the components that make it possible to estimate the content of liquid components - saturated compounds, aromatic compounds and resins, characterizing the distribution of the components and the correlation according to the group composition of bitumen in the test sample, then the total amplitude is determined from the free induction decay signal according to the formula: $$A_0=A_{S0}+A_{l0}=A_{S0}+A_{le0}+A_{lm0}$$

$$$$

at the initial moment of time, which is proportional to the number of hydrogen atoms in the bitumen; then, from the envelope of the echo signals in the Carr-Purcell-Meiboom-Gill sequence, the amplitudes of the liquid-phase components are determined, and the component with the longest relaxation time T ₂₁ corresponds to the proton population of saturated hydrocarbons with amplitude A ₁ , the next component with a shorter relaxation time T ₂₂ corresponds to the proton populations of aromatic hydrocarbons with amplitude A ₂ , the component with the shortest relaxation time T ₂₃ corresponds to the proton population of the group of resins with amplitude A ₃ ; further, the relative content of each component is determined as the ratio of the corresponding amplitude A _i to the total amplitude A ₀ , the asphaltene content is determined from the decay signal of free induction as the ratio of the amplitude of the solid phase signal A _S0 to the total amplitude A ₀ to obtain the parameters of the group composition of bitumen in the rock.