CN112461812A - Method for measuring gas saturation of gas hydrate - Google Patents
Method for measuring gas saturation of gas hydrate Download PDFInfo
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- CN112461812A CN112461812A CN202011383000.6A CN202011383000A CN112461812A CN 112461812 A CN112461812 A CN 112461812A CN 202011383000 A CN202011383000 A CN 202011383000A CN 112461812 A CN112461812 A CN 112461812A
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
Abstract
The invention discloses a method for measuring gas saturation of a gas hydrate, which adopts a characteristic peak of water molecules in the gas hydrate as a reference peak, and carries out dimensionless transformation on peak intensity integrals of the characteristic peak of the gas molecules in the hydrate, namely, the ratio of the peak intensity integrals of the characteristic peak of the gas in the hydrate to the peak intensity integrals of the characteristic peak of the water molecules in the hydrate is calculated, and the relative peak intensity integrals of the characteristic peaks of the gas molecules in the hydrate are obtained; meanwhile, the gas saturation of the hydrate is quantitatively calculated by means of a macroscopic measurement method, a function of the relative peak intensity integral of the characteristic peak of the gas molecule in the hydrate on the gas content in the hydrate is established, and the gas saturation of the gas hydrate is calculated. The method solves the problem that the gas saturation of the gas hydrate can not be rapidly and accurately determined for a long time in the field of gas hydrate research, and has important significance for the research on the aspects of rapid quantitative measurement of the gas saturation of the gas hydrate, gas reserve evaluation in a gas hydrate reservoir and the like.
Description
Technical Field
The invention relates to the field of measurement of physical properties of hydrates, in particular to a method for measuring gas saturation in a gas hydrate.
Background
Gas hydrates are non-stoichiometric, cage-like crystalline substances formed by water and small molecule gases such as methane, carbon dioxide, nitrogen, and the like. As a new clean energy, naturally occurring natural gas hydrates are widely distributed in seabed continental shelves or plateau frozen soil layers under high pressure and low temperature conditions. The huge reserves of the energy source make the energy source become an important alternative energy source and are widely regarded by various countries all over the world.
Gas hydrates widely present in nature mainly comprise three types, I, II and H. The crystal structure of the hydrate is determined primarily by the gas components and concentrations in the hydrate. At the same time, the gas saturation in hydrates is also closely related to the environment in which they are located, for example the gas saturation of form I hydrates can vary between 75-99%. Therefore, how to determine the concentration of gas molecules in the hydrate phase has important significance for analyzing the crystal structure of the hydrate, calculating the gas storage density of the hydrate and evaluating the gas reserve in the hydrate reservoir.
Currently, gas saturation measurements of hydrates are mainly calculated by measuring the amount of gas and free water content after rapid decomposition of a hydrate sample. The method needs a large amount of samples, and meanwhile, free water and adsorbed gas carried in the sediment bring large errors to the measurement of the saturation degree of the hydrate gas. The confocal Raman spectrometer is an ideal measuring device, and can obtain the spectral characteristics of the hydrate without damaging the crystal structure of a hydrate sample. In the Raman spectrum of the hydrate, the integral area of the Raman characteristic peak intensity of the gas in the hydrate phase is in direct proportion to the concentration of the gas in the hydrate. However, since the positional deviation of the laser measurement point significantly deviates the characteristic peak intensity of the raman spectrum of the hydrate, the integral area of the raman characteristic peak intensity of the gas in the hydrate phase cannot be directly applied to the calculation of the gas saturation of the hydrate. The key for measuring the gas saturation in the hydrate is to utilize the traditional measuring method and measuring instrument and adopt a novel measuring idea to avoid the defects in the measurement of the physical property of the gas hydrate.
Disclosure of Invention
The invention aims to provide a method for measuring gas saturation in a gas hydrate, which fully utilizes the existing basic means of experimental measurement and combines a confocal Raman spectrometer and a gas chromatograph to measure the gas saturation in the gas hydrate, and the measurement result has higher reliability and better consistency.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a method of measuring gas saturation in a gas hydrate, comprising:
generating a gas hydrate by using a high-pressure reaction kettle under the set conditions of temperature and pressure, obtaining the gas content of each component consumed by the generation of the hydrate by using a gas state equation according to the temperature, the pressure and gas phase components before and after the generation of the gas hydrate, and calculating the saturation of each component gas in the hydrate according to the crystal structure of the generated gas hydrate;
taking a small amount of gas hydrate samples from the high-pressure reaction kettle, measuring the Raman spectrum of the samples at the liquid nitrogen temperature to obtain the characteristic peaks and peak intensity integrals of gas molecules and water molecules in the hydrate phase, and calculating the ratio of the peak intensity integrals of the characteristic peaks of the gas molecules to the peak intensity integrals of the characteristic peaks of the water molecules by taking the characteristic peaks of the water molecules as reference peaks to obtain the relative peak intensity integrals of the characteristic peaks of the gas molecules in the gas hydrates;
establishing a function of the saturation of different component gases to the relative peak intensity integral of the characteristic peak through linear fitting according to the saturation of each component gas in the hydrate and the relative peak intensity integral of the characteristic peak measured for multiple times;
measuring and calculating the relative peak intensity integral of a characteristic peak of a gas component in a hydrate sample, and calculating the gas saturation of the gas in the hydrate sample by using a function of the saturation of the gas to the relative peak intensity integral of the characteristic peak.
Further, the gas saturation in the gas hydrate is measured by a confocal raman spectrometer.
Further, in the measurement process of the confocal Raman spectrometer, argon ion laser with power of 20-50 milliwatts and wavelength of 532 nanometers is adopted as a measurement light source, a grating line is 1800 or 2400 lines/mm, and the measurement wave number range is 100-5000 cm--1And performing point scanning on the crystal surface of the gas hydrate to obtain Raman characteristic peaks of gas molecules and water molecules in the gas hydrate.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the method, the function of the relative peak intensity integral of the characteristic peak of the gas molecule in the gas hydrate on the gas saturation in the hydrate is established, so that the accurate measurement of the gas saturation of the gas hydrate by the confocal Raman spectrum is realized, and the high dependence of the classical Raman spectrum on position parameters of Raman instruments and Raman laser measuring points on the surface of the hydrate in the quantitative measurement process of the gas hydrate is overcome.
2. The invention fully utilizes the existing experimental measuring instruments and measuring means, utilizes various measuring instruments and the crystal structure characteristics of the gas hydrate to finish the accurate measurement of the gas saturation in the gas hydrate, has low cost of the measuring method, simultaneously has better measuring accuracy and is more close to practical application.
Drawings
FIG. 1 is a schematic flow chart of the process of establishing the integral function of the relative peak intensities of the saturation of gases of different compositions versus the characteristic peak.
FIG. 2 is a flow chart of a method for calculating the saturation of hydrate gas according to the measurement method of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
The method for measuring the gas saturation in the gas hydrate mainly comprises 2 parts.
In the first part, a gas hydrate is generated by adopting single-component gas and multi-component mixed gas under the condition of constant temperature and constant volume through a macroscopic measurement device such as a gas chromatograph, a high-pressure resistant reaction kettle and the like, and the gas saturation in a hydrate sample is calculated according to the pressure before and after the hydrate is generated and the change of gas components;
in the second part, a small amount of gas hydrate samples are taken out from a macroscopic measuring device, the Raman spectrum of the samples is measured at the liquid nitrogen temperature, the positions of characteristic peaks and peak intensity integral areas of gas and water molecules in the hydrate phase are determined and analyzed, the relative peak intensity integral of the characteristic peaks is calculated and correlated with the saturation of gas in the hydrate obtained from the macroscopic measuring result, and then a function of the relative peak intensity integral of the characteristic peaks of different gases in the Raman spectrum on the gas content in the hydrate is established. And finally, calculating the gas saturation of the hydrate by obtaining the total content of the gas in the hydrate.
In the two parts, the measurement process is repeatedly measured for many times, which is beneficial to reducing measurement errors. The structure of the hydrate crystals must be determined in establishing a function of the relative peak intensity integral of the characteristic peaks of the gas as a function of the gas content in the hydrate. In hydrates with different crystal structures, the function of the relative peak intensity integral of the characteristic peak of the gas on the gas content in the hydrate is different.
Examples
The details of the process for methane (CH) are described below in conjunction with FIGS. 1 and 24) And carbon dioxide (CO)2) Establishing function of relative peak intensity integral of characteristic peak to gas content in hydrate and measuring CH4-CO2Use of gas saturation in mixed gas hydrates.
The specific operation steps are as follows:
in the first step, a function of the saturation of the different component gases in the gas hydrate as a function of the relative peak intensity integrals of the characteristic peaks is established.
The macroscopic measurement part is that deionized water is cooled and ground into ice powder in the liquid nitrogen environment, and the ice powder is takenThe mass is M g and the volume is ViceThe ice powder is put into a high pressure resistant reaction kettle with volume V and precooled to minus 10 ℃. Then, injecting a molar quantity n into the reaction kettle through a gas buffer tank0CH (A) of4-CO2Mixing the gas and CH in the reaction kettle4-CO2The mixed gas begins to combine with the ice powder to form CH under certain temperature and pressure conditions4-CO2A mixed gas hydrate. When the pressure in the reaction kettle reaches a stable value, recording the temperature T in the reaction kettle1And pressure P1And respectively taking out a small amount of gas from the gas buffer tank and the high-pressure resistant reaction kettle, and measuring the gas sample by adopting a gas chromatograph. Respectively measuring the contents of the methane gas in the gas buffer tank and the high-pressure resistant reaction kettle as y0mAnd y1m。
According to CH4-CO2Pressure P after formation of mixed gas hydrate1Temperature T1Volume of gas phase V-ViceAnd the concentration of methane, and the CH in the gas phase of the reaction kettle can be calculated by utilizing a P-R gas state equation4And CO2Content n of1mAnd n1cObtaining CH4-CO2Consumption of CH by formation of mixed gas hydrates4And CO2Molar amount of gas NmAnd Nc：
Nm＝n0·y0m–n1m
Nc＝n0·(1-y0m)–n1c
Finally obtaining CH4And CO2Saturation in mixed gas hydrate samples SmAnd ScAnd the gas saturation S of the mixed gas hydrate:
Sm＝5.75·Nm/(M/18)·100％
Sc＝5.75·Nc/(M/18)·100％
S＝Sm+Sc
microscopic measurement in CH4-CO2After the mixed gas hydrate is generated, taking out the mixed gas hydrate from the high-pressure resistant reaction kettle in a liquid nitrogen environmentA portion of the hydrate sample was subjected to raman spectroscopy. After multiple measurements on the hydrate sample, a Raman spectrum with stronger peak intensity is selected as an analysis spectrum. First, the characteristic peak positions of methane and carbon dioxide in the hydrate are determined. The characteristic peak of methane in the type I hydrate is 2915cm-1And 2916cm-1Respectively, methane molecule in type I hydrate 512And 51262Peak position in a cage-like structure; the characteristic peak position of carbon dioxide in the type I hydrate is 1278cm-1And 1382cm-1. Then, after baseline leveling of the Raman spectrum, selecting spectral band 1350--1，2880-2940cm-1Respectively integrating the characteristic peak intensities of the methane and the carbon dioxide to obtain the characteristic peak areas A of the methane and the carbon dioxidemAnd Ac. The integration of the characteristic peak intensity of water molecule requires to calculate the band 2700--1Integral calculation is carried out, then the integral value of the characteristic peak intensity of methane is subtracted, and the characteristic peak area A of water molecules is obtainedw. Finally, carrying out dimensionless operation on the peak intensity integral of the characteristic peak of the gas molecule in the gas hydrate to obtain the relative peak intensity integral I of the characteristic peak of the methane and the carbon dioxide in the gas hydratemAnd Ic：
Im＝Am/Aw
Ic＝Ac/Aw
Then, by changing the initial gas components to obtain a methane and carbon dioxide mixed gas hydrate with different component contents, repeating the steps, and establishing a function of the relative peak intensity integral of the methane and carbon dioxide saturation degrees to the Raman characteristic peak in the mixed gas hydrate through linear fitting:
Sm＝Km·Im
Sc＝Kc·Ic
S＝Sm+Sc
wherein, KmAnd KcThe slopes of the relative peak intensity integral functions of methane and carbon dioxide saturation versus methane and carbon dioxide raman signature peaks, respectively.
And secondly, selecting a hydrate sample to be detected containing methane or carbon dioxide, and performing Raman spectrum measurement on the sample. Obtaining the relative peak intensity integral I of the characteristic peak of methane or carbon dioxide in the gas hydrate by the calculation method in the first stepmAnd Ic. Finally, calculating the saturation S of methane or carbon dioxide in the hydrate sample to be detected according to the function of the relative peak intensity integral of the methane and carbon dioxide saturation to the Raman characteristic peakmOr Sc。
The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention accordingly, and not to limit the protection scope of the present invention accordingly. All equivalent changes or modifications made in accordance with the spirit of the present disclosure are intended to be covered by the scope of the present disclosure.
Claims (3)
1. A method for measuring the saturation of gas in a gas hydrate, comprising:
generating a gas hydrate by using a high-pressure reaction kettle under the set conditions of temperature and pressure, obtaining the gas content of each component consumed by the generation of the hydrate by using a gas state equation according to the temperature, the pressure and gas phase components before and after the generation of the gas hydrate, and calculating the saturation of each component gas in the hydrate according to the crystal structure of the generated gas hydrate;
taking a small amount of gas hydrate samples from the high-pressure reaction kettle, measuring the Raman spectrum of the samples at the liquid nitrogen temperature to obtain the characteristic peaks and peak intensity integrals of gas molecules and water molecules in the hydrate phase, and calculating the ratio of the peak intensity integrals of the characteristic peaks of the gas molecules to the peak intensity integrals of the characteristic peaks of the water molecules by taking the characteristic peaks of the water molecules as reference peaks to obtain the relative peak intensity integrals of the characteristic peaks of the gas molecules in the gas hydrates;
establishing a function of the saturation of different component gases to the relative peak intensity integral of the characteristic peak through linear fitting according to the saturation of each component gas in the hydrate and the relative peak intensity integral of the characteristic peak measured for multiple times;
measuring and calculating the relative peak intensity integral of a characteristic peak of a gas component in a hydrate sample, and calculating the gas saturation of the gas in the hydrate sample by using a function of the saturation of the gas to the relative peak intensity integral of the characteristic peak.
2. A method of measuring gas saturation in a gas hydrate as claimed in claim 1, wherein: and (3) measuring the gas saturation in the gas hydrate by using a confocal Raman spectrometer.
3. A method of measuring gas saturation in a gas hydrate as claimed in claim 2, wherein: in the measurement process of the confocal Raman spectrometer, argon ion laser with power of 20-50 milliwatts and wavelength of 532 nanometers is used as a measurement light source, a grating groove is 1800 or 2400 groove/mm, and the measurement wave number range is 100-5000 cm--1And performing point scanning on the crystal surface of the gas hydrate to obtain Raman characteristic peaks of gas molecules and water molecules in the gas hydrate.
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| PCT/CN2020/140523 WO2021212903A1 (en) | 2020-12-01 | 2020-12-29 | Method for measuring gas saturation of gas hydrate |
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