Analysis method and whole-process detection method for inorganic carbon isotope dissolved in water body

Abstract

The invention relates to the technical field of isotope analysis and detection, discloses an analysis method and a whole-process detection method for inorganic carbon isotopes dissolved in a water body, and aims at the complexity (enrichment of a water sample mixed with oil, grease and organic acid, a turbid water sample or a water sample mixed with various suspended solids, a relatively clean water sample and a low-concentration DIC sample) of oilfield water types. The extraction method of the oil field water sample is designed for the first time, and the influence of organic matters on inorganic carbon isotopes in isotope exchange reaction balance is solved; in addition, design is carried out from the aspects of preparation and valuing of a standard solution, sample preservation, instrument analysis condition parameters, a program analysis method, a detection process, quality requirements and the like; according to the program analysis method, the specific time of sample introduction and sampling is set. According to the technical scheme, the operability and practicability are higher, the analysis data precision is high, the analysis time is short, and technical support is provided for judging the oil field water type, the oil field water source, the formation mechanism, the deposition environment and the like and predicting the oil and gas gathering rule.

Description

Technical Field

[0001] The present invention relates to the technical field of isotope analysis and detection, and particularly relates to an analysis method and a whole-process detection method for dissolved inorganic carbon isotope in water bodies. Background Art

[0002] The forms of occurrence of dissolved inorganic carbon (DIC) in water are HCO3 - , CO3 2- and CO2 (including free CO2 and H2CO3). Due to the chemical tracer effect of carbon isotopes, dissolved inorganic carbon isotopes in water are widely used in the research of geochemistry such as climate, biology, environment, petroleum geology, etc. (W.G. Deuser et al, 1969; McKenzie et al, 1985; William L et al, 1995; Wan Guojiang et al, 1996).

[0003] Over the years, the analysis methods for dissolved inorganic carbon isotopes in water generally used the precipitation method and the standard precipitation method (Hassan A A, 1982; Philip K. Bishop, 1990), and relatively accurate carbon isotope values could be obtained. However, if SrCl2-NH4OH or BaCl2-NaOH solution is added to the water body, isotope exchange may occur with CO2 in the atmosphere during the filtration and drying processes; if in a high-concentration sulfate water body environment, DIC will not precipitate completely, resulting in distortion of carbon isotope values. Since the above precipitation method has more steps and the salinity differences in different water bodies are very large, in order to enable inorganic carbon ions in water to participate in the reaction completely, the classical phosphoric acid method was later adopted, that is, the pretreatment and isotope determination are carried out separately. Its principle is that phosphoric acid directly reacts with the water body to generate CO2, and then it is sent to an isotope mass spectrometer for carbon isotope ratio determination (Tan F C et al, 1973; Grossman E I, 1984). E.A. Atekwana et al (1998) placed the sample in a sealed and pre-evacuated chromatographic vial and used the phosphoric acid method to analyze the content and carbon isotope of DIC in surface water and groundwater, with precisions of 1% and 0.1‰ respectively. He also used an off-line analysis method, which has certain requirements for the preservation of the generated CO2 gas, and the analysis precision is the result of a single extraction. With the development of continuous flow mass spectrometry technology, the on-line analysis method for dissolved inorganic carbon isotopes in water is also used more and more widely. G.G. Salata et al (2000) adopted the gas-liquid equilibrium method of phosphoric acid analysis, and then used the on-line analysis method of gas chromatography-separation-combustion-isotope mass spectrometer (GC-C-IRMS). The measured results are affected by the solution equilibrium time. It is proved that when the equilibrium time is 15-36 hours, the standard deviation is less than ±0.2‰. C (2005) reported the use of continuous-flow helium flushing method for groundwater, and the mixture of CO2 and He entered the mass spectrometer for analysis simultaneously, with an accuracy of about 0.1‰. Nelly Assayag et al (2006) introduced in detail the on-line analysis method of continuous-flow helium flushing. Experiments were carried out in terms of preparing standard solutions with different concentrations and sampling volumes of water samples. The whole analysis process took about 2 days, including sampling, CO2 (gas-liquid) equilibrium, and isotope mass spectrometry analysis, with an accuracy better than 0.1‰. After 2000, the continuous-flow on-line mode of connecting the GasBench on-line sample preparation device with the isotope mass spectrometer was developed, which simplified the analysis process and was a relatively fast and accurate analysis method.

[0004] Generally speaking, oilfield water generally comes from sedimentary water in water basins, infiltrated water from the atmosphere, primary water in clay minerals, and connate water deep in the earth. The long-term interaction between oilfield water and rocks, oil, and natural gas makes the chemical composition of oilfield water very complex. In addition to inorganic metal and non-metal ion components, there are also gas components, organic components (oil, fat, organic acids, etc.), and trace elements, which are much more complex than hot spring water, groundwater, surface water, and pore water. For some high-salinity brine samples and oilfield water with relatively high salinity, the interaction between the concentration of dissolved inorganic carbon and the pH value of the solution causes isotope fractionation during the equilibrium process. In addition, most oilfield produced waters contain organic acids, which will have a great impact on inorganic carbon isotopes in the isotope exchange reaction equilibrium and directly interfere with the determination results of inorganic carbon isotopes. Therefore, the extraction of oilfield water is crucial for the analysis of dissolved inorganic carbon isotopes in water. In the prior art, the literature "Research on the Method for Determining the Content and Carbon Isotope Composition of Dissolved Inorganic Carbon in Water by Continuous-Flow Isotope Mass Spectrometry" (Yang Tao et al, 2006) was found. It carried out research starting from the reaction process, equilibrium time, signal intensity, data accuracy, and standard stability. However, it did not make a normative description of the sample pretreatment, instrument analysis method, analysis steps, quality requirements, precautions, etc. required by the analysis method. For complex oilfield water samples, it is not yet mature enough in specific operations, so accurate detection data cannot be obtained. Summary of the Invention

[0005] The present application provides an analysis method and a whole-process detection method for dissolved inorganic carbon isotopes in water bodies to solve the above technical problems that the inorganic carbon isotopes in the prior art are affected and interfere with the determination results.

[0006] According to one aspect of the present application, an embodiment provides an analysis method for dissolved inorganic carbon isotopes in water bodies, including the following steps:

[0007] S41. Set parameters according to the analysis conditions and establish a method suitable for sample analysis for the isotope mass spectrometer and the automatic gas sample preparation device;

[0008] S42. Place the quartz glass bottle into the constant-temperature sample tray, inject phosphoric acid, and then seal the quartz glass bottle.

[0009] S43. Fix the gas injection needle and start the instrument to fill with the carrier gas.

[0010] S44. Inject standard solutions with different concentrations respectively; among them, the standard solutions are prepared from chromatographically pure reagents, and the selection of the standard solutions is based on the stability of the sample's occurrence form in water, and to meet the sensitivity and linear range requirements of the detection instrument and detection method for dissolved inorganic carbon samples with various different concentrations in geological bodies.

[0011] S45. Take the sample to be tested, and the volume of the sample to be tested is determined according to the concentration of dissolved inorganic carbon and with reference to the volumes of standard solutions with different concentrations.

[0012] S46. After the established equilibrium reaches the set duration, fix the injection needle and run the instrument program corresponding to the method established in S41 to perform the isotope ratio determination.

[0013] In one embodiment, the analysis conditions of the isotope mass spectrometer refer to the general conditions; the analysis conditions of the automatic gas sampling device include: the temperature of the gas chromatography column, the pressure of the reference gas, the pressure of the carrier gas, and the equilibrium temperature of the constant-temperature sample tray.

[0014] In one embodiment, the reference gas is carbon dioxide and the carrier gas is helium.

[0015] In one embodiment, measure the blank sample before measuring the sample; the analysis sequence of the isotope ratio determination is: blank sample - standard solution - sample to be tested - standard solution - sample to be tested; among them, the blank sample is a blank sample with acid added and filled with gas.

[0016] In one embodiment, the set duration required for equilibrium is controlled within 6 hours to 24 hours.

[0017] In one embodiment, the quality control standards in the isotope ratio determination include:

[0018] The generated carbon dioxide peak shape is symmetric, the next carbon dioxide peak is completely separated from the adjacent previous peak, and there are no other impurity peaks in the entire chromatogram; and / or,

[0019] In the sample analysis result, when the peak height of the target voltage signal peak > 1V, the deviation of the repeated determination results of the sample ≤ ±0.3‰; when the peak height ≤ 1V, the deviation of the repeated determination results of the sample ≤ ±0.5‰.

[0020] According to one aspect of the present application, one embodiment provides a full-process detection method for dissolved inorganic carbon isotopes in water bodies, including the following steps:

[0021] S1. Pretreat the water sample to obtain the sample to be tested; wherein, the pretreatment of the water sample includes at least one of the following situations: removing oil, fat and organic acids from the water sample; filtering suspended solids in the water sample; filtering the relatively clean water sample through a water system filter membrane; concentrating and enriching the low-concentration DIC sample;

[0022] S2. Preparation and calibration of reference materials;

[0023] S3. Phosphoric acid preparation;

[0024] S4. Detect and analyze the sample to be tested by using the analysis method for dissolved inorganic carbon isotope in water body described in any one of claims 1-6.

[0025] In one embodiment, in the pretreated water sample of step S1:

[0026] For the water sample that may be mixed with oil, fat and organic acids, use a C18 pretreatment column or a Dionex On Guard RP column to extract the oil and fat in the water sample, and then pass through a silica column to remove the organic acids in the water sample to obtain the sample; and / or,

[0027] For the water sample mixed with suspended solids, use activated carbon particles to adsorb the suspended solids and / or filter the suspended solids with filter paper or absorbent cotton, and take the clarified water sample after standing precipitation to obtain the sample; and / or,

[0028] Filter the water sample obtained after the previous two treatments through a water system filter membrane to obtain the sample; and / or,

[0029] For the low-concentration DIC sample, concentrate it with a vacuum evaporation concentrator, and then take the water sample for testing; wherein, the concentration of DIC in the low-concentration DIC sample ≤ 0.5 mmol / L.

[0030] In one embodiment, the concentration of DIC in the sample is determined in combination with the value of anions in the chemical composition analysis of the sample; and / or,

[0031] The method of dropping a phosphoric acid solution into the sample is used to qualitatively judge the level of DIC concentration.

[0032] In one embodiment, a NaHCO3 solution is selected as the reference sample in step S2, and step S2 includes the following sub-steps:

[0033] S21. Prepare standard solutions of 1.19 mmol / L, 2.45 mmol / L and 4.76 mmol / L from chromatographically pure NaHCO3 reagent;

[0034] S22. For the NaHCO3 reagent, use the phosphoric acid method of Gasbench-IRMS carbonate rock carbon and oxygen isotope analysis to analyze the carbon isotope value of the parent material NaHCO3; at the same time, use the oxidation combustion method of EA-IRMS elemental-isotope mass spectrometer as evidence to determine the carbon isotope value of the parent material NaHCO3.

[0035] The technical solution of the above embodiment of the present application solves the problem of poor operability of experimental personnel in detecting the dissolved inorganic carbon isotope in complex oilfield water sample types, and solves the problem of the influence of organic matter on inorganic carbon isotope in the isotope exchange reaction equilibrium. The technical solution of the present application is more operable and practical, with high-precision analysis data, short analysis time, and is easy to be widely promoted and applied, providing technical support for judging oilfield water types, the origin, formation mechanism, sedimentary environment, etc. of oilfield water, and predicting the law of oil and gas accumulation. Brief Description of the Drawings

[0036] Figure 1 It is a chromatogram of carbon dioxide ion current detected by an isotope mass spectrometer for the treated oilfield water in an embodiment. Detailed Embodiments

[0037] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0038] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0039] It should be noted that the terms "first", "second", etc. in the present application are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances for the embodiments of the present application described here. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0040] It should be understood that when an element (such as a layer, film, region, or substrate) is described as being "on" another element, the element can be directly on the other element or there can also be intermediate elements. Moreover, in this application, when an element is described as being "connected" to another element, the element can be "directly connected" to the other element or "connected" to the other element through a third element.

[0041] Example 1

[0042] An embodiment provides a method for analyzing the dissolved inorganic carbon isotope in water bodies, including the following steps:

[0043] S41. Set parameters according to the analysis conditions to establish a method suitable for sample analysis for the isotope mass spectrometer and the automatic gas sampling device. Among them, the analysis conditions of the isotope mass spectrometer refer to the general conditions; the analysis conditions of the automatic gas sampling device include: the temperature of the gas chromatography column, the reference gas pressure, the carrier gas pressure, and the equilibrium temperature of the constant-temperature sample disk. Generally, carbon dioxide is selected as the reference gas and helium is selected as the carrier gas.

[0044] S42. Place the quartz glass bottle in the constant-temperature sample disk and inject phosphoric acid, then seal the quartz glass bottle. Preferably, the temperature of the constant-temperature sample disk is 25°C and the concentration of phosphoric acid is 103%.

[0045] S43. Fix the inflation needle and start the instrument to fill with the carrier gas.

[0046] S44. Inject standard solutions with different concentrations respectively; among them, the standard solutions are prepared from chromatographically pure NaHCO3 reagents, and the selection of the standard solutions is based on the stability of the sample's occurrence form in water and to meet the sensitivity and linear range requirements of the detection instrument and detection method for dissolved inorganic carbon samples with various different concentrations in geological bodies. In one embodiment, 2 ml, 1 ml, and 0.5 ml of standard solutions with different concentrations of 1.19 mmol / L, 2.45 mmol / L, and 4.76 mmol / L are injected respectively.

[0047] S45. Take the sample to be measured, and the volume of the sample to be measured is determined according to the concentration of the dissolved inorganic carbon and with reference to the volumes of the standard solutions with different concentrations.

[0048] S46. After the established equilibrium reaches the set duration (generally more than 6 hours, and the equilibrium time is controlled within 6 hours - 24 hours), fix the injection needle and run the instrument program corresponding to the method established in S41 to perform isotope ratio determination.

[0049] In one embodiment, a blank sample is measured first before measuring the sample; the analysis order of the isotope ratio determination is: blank sample - standard solution - sample to be measured - standard solution - sample to be measured; among them, the blank sample is a blank sample with acid added and filled with gas.

[0050] In one embodiment, the quality control standards in isotope ratio determination include: chromatogram requirements. Whether the ion current signal peaks detected by the mass spectrometer are normal is a prerequisite for testing the success of the analysis method for dissolved inorganic carbon isotopes in the water body of this application. Specifically, the generated carbon dioxide peak shape is symmetrical, the next carbon dioxide peak is completely separated from the adjacent previous peak, and there are no other impurity peaks in the entire chromatogram. Among them, there should be no other impurity peaks such as air in the entire chromatogram, and the air peak seriously interferes with the true value of the sample.

[0051] In one embodiment, the quality control standards in isotope ratio determination include: requirements for the deviation of sample repeatability determination results. Specifically, in the sample analysis results, when the peak height of the target voltage signal peak > 1V, the deviation of the sample repeat determination results ≤ ±0.3‰; when the peak height ≤ 1V, the deviation of the sample repeat determination results ≤ ±0.5‰.

[0052] Embodiment Two

[0053] One embodiment provides a full-process detection method for dissolved inorganic carbon isotopes in water bodies. In view of the complexity of oilfield water samples, several extraction methods for oilfield water samples are designed. For water samples mixed with oil stains and organic acids, C18 pretreatment columns (C18-bonded silica gel ODS) or Dionex On Guard RP columns (porous divinylbenzene resin) are used to extract and remove organic substances such as oils, and then organic acids are removed through a silica column, avoiding the influence of organic substances on inorganic carbon isotopes during the isotope exchange equilibrium process; for water samples mixed with various suspended solids or turbidity, the method of adsorbing with activated carbon particles is adopted; for relatively clean water samples, the method of directly sucking and filtering with a syringe with a microporous system (0.45um) water filter membrane is used; for low-concentration DIC water samples, the enrichment method of concentrating with a vacuum evaporation concentrator is adopted. The program analysis method sets the specific time for sample injection and sampling, and is automatically controlled by computer program instructions. The entire full-process detection method includes aspects such as extraction of oilfield water samples, preparation and calibration of standard solutions, sample preservation, setting of instrument analysis condition parameters and program analysis methods, sample detection process, and quality control.

[0054] The full-process detection method for dissolved inorganic carbon isotopes in the water body of this application is mainly used for detecting the dissolved inorganic carbon isotope composition in water body samples such as oilfield water and formation water. Specifically, it includes the following steps:

[0055] S1. Pretreat the water sample to obtain a sample to be tested; among them, the pretreatment of the water sample includes at least one of the following situations: removing oils, fats, and organic acids in the water sample; filtering suspended solids in the water sample; filtering relatively clean water samples through a water filter membrane; concentrating and enriching low-concentration DIC samples.

[0056] S2. Preparation and calibration of reference materials. The reference materials are the standard solutions in Embodiment One.

[0057] S3. Phosphoric acid preparation.

[0058] S3. The sample to be tested is detected and analyzed by using the analysis method of dissolved inorganic carbon isotope in water body described in Example 1.

[0059] In one embodiment, the pretreated water sample in step S1 has one or more of the following situations:

[0060] 1. For a water sample that may be mixed with oil, grease and organic acids, use a C18 pretreatment column (C18-bonded silica gel ODS) or Dionex On Guard RP (porous divinylbenzene resin) column to extract organic substances such as oil and grease in the water sample, and then pass through a silica column to remove organic acids in the water sample, and finally obtain a sample; after the above treatment, oil, grease and organic acids in the water sample can be removed.

[0061] 2. For a water sample mixed with suspended solids, use activated carbon particles to adsorb the suspended solids and / or filter the suspended solids with filter paper or absorbent cotton. After static precipitation, take the clarified water sample, and finally suck the clean water sample into a container to obtain a sample. Among them, in the filtration operation of filter paper and absorbent cotton, the clarification effect of the water sample is worse than that of activated carbon adsorption, but the filtration time is shorter.

[0062] 3. Filter the water sample obtained after the first two treatments (i.e., items 1 and 2) through a water system filter membrane to obtain a sample. In addition, for a relatively clean water sample, it can also be directly sucked and filtered into a container bottle with a syringe equipped with a 0.45um water system filter membrane at the top to obtain a sample.

[0063] 4. Enrich the low-concentration DIC sample in the sample obtained above. Specifically, it is concentrated by a vacuum evaporation concentrator, and then the sample is taken for testing. Among them, the concentration of DIC in the low-concentration DIC sample is ≤ 0.5 mmol / L.

[0064] In one embodiment, the concentration of DIC in the sample is determined in combination with the value of anions in the chemical composition analysis of the sample. In addition, the method of dropping a phosphoric acid solution into the sample can be used to qualitatively judge the high or low concentration of DIC.

[0065] In one embodiment, step S2 selects a NaHCO3 solution as a standard sample, and step S2 includes the following sub-steps:

[0066] S21. Prepare standard solutions of 1.19 mmol / L, 2.45 mmol / L and 4.76 mmol / L with chromatographically pure NaHCO3 reagent.

[0067] S22. For the NaHCO3 reagent, the phosphoric acid method for the analysis of carbon and oxygen isotopes of carbonate rocks by Gasbench-IRMS is used to analyze the carbon isotope value of the parent material NaHCO3. At the same time, the oxidation combustion method of the EA-IRMS elemental-isotope mass spectrometer is used as evidence to determine the carbon isotope value of the parent material NaHCO3.

[0068] The combination of the above Example 1 and Example 2 forms a method for the whole-process detection of dissolved inorganic carbon isotopes in water bodies (especially oilfield water), which can solve the operability of experimental personnel in detecting dissolved inorganic carbon isotopes in complex oilfield water sample types. Among them: 1. In view of the complexity of oilfield water types (water samples mixed with grease and organic acids, water samples mixed with various suspended solids or turbidity, relatively clean water samples, enrichment of low-concentration DIC samples), a method for extracting oilfield water samples is designed for the first time to solve the influence of organic matter on inorganic carbon isotopes in the isotope exchange reaction equilibrium. 2. The program analysis method sets the specific time for sample injection and sampling. 3. In addition, it is designed from aspects such as the preparation and determination of standard solutions, sample preservation, instrument analysis condition parameters and program analysis methods, detection flow, and quality requirements.

[0069] The whole-process detection method for dissolved inorganic carbon isotopes in the water body of the present application is a rapid and accurate whole-process detection method for dissolved inorganic carbon isotopes in oilfield water. The whole-process detection of dissolved inorganic carbon isotopes in oilfield water is realized from aspects such as the extraction of oilfield water samples, detection flow and analysis conditions, instrument program analysis methods, analysis precautions, and quality control. It solves the problem of poor operability of experimental personnel in detecting dissolved inorganic carbon isotopes in complex oilfield water sample types and solves the problem of the influence of organic matter on inorganic carbon isotopes in the isotope exchange reaction equilibrium.

[0070] Example 3

[0071] An embodiment provides a method for the whole-process detection of dissolved inorganic carbon isotopes in a water body. The technical solution of the present application will be elaborated below according to the inventor's thinking, which is conducive to those skilled in the art to be familiar with the idea of the present application. Among them, for some technical key points, detailed explanations are made in order that those skilled in the art can fully understand the technical solution of the present application.

[0072] The method for the whole-process detection of dissolved inorganic carbon isotopes in a water body is described by taking oilfield water as an example. The steps are as follows:

[0073] I. Pretreatment of oilfield water samples

[0074] 1. For water samples that may be mixed with oil, grease, and organic acids, first extract organic substances such as oil and grease with a C18 pretreatment column (C18-bonded silica gel ODS) or a Dionex On Guard RP column (porous divinylbenzene resin), then remove organic acids through a silica column, and then take the water sample for testing.

[0075] 2. For turbid water samples or those mixed with various suspended solids, first adsorb with activated carbon particles and let it stand overnight for precipitation, and then take the clarified water sample for testing. Or filter 2 - 3 times with filter paper, absorbent cotton, and a funnel; its filtration and clarification effect is worse than that of activated carbon adsorption but the filtration time is shorter.

[0076] 3. For relatively clean water samples, directly aspirate and filter them into a container bottle for testing with a syringe equipped with a 0.45um water-based filter membrane at the top. In addition, water samples treated in items 1 and 2 can be further treated in this step 3.

[0077] 4. Enrich low-concentration DIC samples. Among them, combined with the analysis of the chemical composition of oilfield water (anions), if there is no known quantitative concentration value, phosphoric acid solution can also be dropped into the sample to qualitatively judge the concentration level, and phosphoric acid waste liquid can be selected. For the enrichment method of low-concentration (≤0.5 mmol / L) DIC samples, a vacuum evaporation concentrator is used for concentration.

[0078] II. Preparation and certification of reference materials

[0079] 1. There is no unified reference material for dissolved inorganic carbon isotopes in water, and it needs to be prepared by the laboratory itself. The selection of the reference sample is mainly based on the stability of the occurrence form of the sample in water. In this application, a NaHCO3 solution is used as the reference sample. Chromatographically pure NaHCO3 reagent is prepared into standard solutions with different concentrations (1.19 mmol / L, 2.45 mmol / L, and 4.76 mmol / L) to meet the sensitivity and linear range requirements of the instrument and method for dissolved inorganic carbon samples with various concentrations in geological bodies.

[0080] 2. For this batch of purchased chromatographically pure NaHCO3 reagent, analyze the carbon isotope value of the parent NaHCO3 using the phosphoric acid method for carbonate rock carbon and oxygen isotope analysis by Gasbench-IRMS (using gbw04405 as the reference material), and at the same time, use the oxidation combustion method of an EA-IRMS elemental-isotope mass spectrometer (using gbw04407 as the reference material) as a corroboration to certify the carbon isotope value of the parent NaHCO3.

[0081] III. Preservation of samples and reference materials

[0082] The pretreated samples and the prepared standard solutions should be tested in a timely manner and should not be stored for a long time. They can be sealed with a rubber stopper and stored in the refrigerator for short-term preservation.

[0083] IV. Phosphoric Acid Preparation

[0084] Prepare 103% orthophosphoric acid (with a density of approximately 1.93 g / cm 3 ) by adding phosphorus pentoxide to commercially available phosphoric acid crystals, and store it in a desiccator for short-term use. The freshly prepared phosphoric acid solution should not be stored for a long time.

[0085] V. Instrument Analysis Condition Parameters and Program Analysis Method Setting

[0086] 1. Set the instrument analysis condition parameters, including the analysis conditions of the isotope mass spectrometer and the analysis conditions of the automatic gas sampling device.

[0087] The analysis conditions of the isotope mass spectrometer refer to the general conditions. The main analysis conditions of the automatic gas sampling device include the temperature of the gas chromatographic column, the pressures of the reference gas (carbon dioxide) and the carrier gas (helium), and the equilibrium temperature of the constant-temperature sample disk.

[0088] 2. Set the instrument program analysis method. Through the automatic gas sampling device, computer program instructions for on-line sample analysis, and experimental exploration, establish a method suitable for the analysis of this sample and automate the control.

[0089] VI. Sample Analysis Procedure

[0090] 1. Place the quartz glass vial in the constant-temperature sample disk at 25°C, inject 0.5 ml of the 103% orthophosphoric acid prepared in Step IV, and tighten the bottle cap.

[0091] 2. Fix the inflation needle, start the instrument software program, and inflate with helium for about 14 minutes.

[0092] 3. Inject 2 ml, 1 ml, and 0.5 ml of standard solutions with different concentrations (1.19 mmol / L, 2.45 mmol / L, and 4.76 mmol / L) respectively.

[0093] 4. Estimate the sampling volume of the sample to be measured according to the concentration of dissolved inorganic carbon in it, referring to the injection volumes of the standard solutions with various concentrations in Step 3 above.

[0094] 5. To ensure the success of each batch of analysis, be sure to measure the blank sample (the blank with acid added and filled with gas) before measuring the sample. The analysis sequence follows: blank - standard solution - sample to be measured (10) - standard solution - sample to be measured (10).

[0095] 6. After the equilibrium time reaches 6 hours (generally, the equilibrium time is controlled within 6 hours - 24 hours), fix the injection needle, run the instrument program analysis method established in Step V, and start the isotope ratio measurement. The entire program analysis time is about 11 minutes.

[0096] VII. Quality Control

[0097] 1. Requirements for chromatogram

[0098] Whether the ion current signal peaks detected by the mass spectrometer are normal is a prerequisite for verifying the success of the full - process detection method for dissolved inorganic carbon isotopes in the water body of this application. It is required that the generated carbon dioxide peak shape is symmetrical, and the next carbon dioxide peak can be completely separated from the adjacent previous peak shape (preferably, the resolution > 95%). There should be no other impurity peaks such as air in the entire chromatogram, as the air peak seriously interferes with the true value of the sample.

[0099] 2. Requirements for the deviation of sample repeatability determination results

[0100] According to the sample analysis results detected by the full - process detection method for dissolved inorganic carbon isotopes in this water body, when the peak height of the target voltage signal peak > 1V, the deviation of sample repeated determination ≤ ±0.3‰; when the peak height ≤ 1V, the deviation of sample repeated determination ≤ ±0.5‰.

[0101] The full - process detection method for dissolved inorganic carbon isotopes in the water body of this application provides a highly operable and accurate full - process detection method from aspects such as sample pretreatment (extraction of oilfield water samples, preparation and calibration of standard solutions, sample preservation), instrument analysis condition parameters and program analysis method setting, sample detection process, and quality control. It provides technical support for using isotope indicators to judge the origin, formation mechanism, sedimentary environment, etc. of oilfield water and predict the law of oil and gas accumulation.

[0102] Example 4

[0103] The full - process detection method for dissolved inorganic carbon isotopes in oilfield water is based on an automatic gas sampling device - isotope mass spectrometer (such as Gasbench - IRMS). The following is an explanation starting from an actual application case, including the following steps:

[0104] I. Pretreatment of oilfield water samples

[0105] 1. For water samples that may be mixed with oil stains and soluble organic matter, use a glass syringe to extract 10 ml of water sample and pre - extract it with a C18 pretreatment column (C18 - bonded silica gel ODS) or a Dionex On Guard RP column (porous divinylbenzene resin) to remove organic substances such as grease, and then pass through a silica column to remove organic acids, avoiding the influence of organic substances on inorganic carbon isotopes during the isotope exchange equilibrium process.

[0106] 2. If the water sample is turbid or mixed with various suspended solids, use a glass syringe to extract 10 ml of the water sample and transfer it to a transparent glass bottle. Add a certain amount of activated carbon particles for adsorption and let it stand overnight for sedimentation. Then take the clarified water sample. Or filter it 2 - 3 times with filter paper, absorbent cotton, and a funnel. Among them, the filtration clarification effect is worse than that of activated carbon adsorption, but the filtration time is shorter.

[0107] 3. For relatively clean water samples, directly draw 10 ml of the water sample with a syringe equipped with a 0.45 - um water - based filter membrane at the top and filter it into a container bottle. The water samples treated in the above steps 1 and 2 are then processed through step 4.

[0108] 4. Enrichment of low - concentration DIC samples; among them, to judge the DIC concentration of the sample, the chemical composition analysis (anion) value of the oil - field water can be combined. If there is no known quantitative concentration value, phosphoric acid solution (phosphoric acid waste solution is fine) can also be dropped into the sample to qualitatively judge the concentration level. For the enrichment method of low - concentration (≤0.5 mmol / L) DIC samples, first extract 100 ml of the water sample and process it according to steps 1, 2, and 3, and then concentrate it to about 10 - 20 ml with a vacuum evaporation concentrator for later measurement.

[0109] II. Preparation and certification of reference materials

[0110] 1. There is no unified reference material for dissolved inorganic carbon isotope in water, and it needs to be prepared by the laboratory itself. The selection of the reference sample is mainly based on the stability of the sample's occurrence form in water. In this application, NaHCO3 is used as the reference material, and standard solutions with low, medium, and high concentrations are prepared to meet the sensitivity and linear range requirements of the instrument and method for dissolved inorganic carbon samples with various different concentrations in geological bodies. Weigh 5 mg, 25 mg, 50 mg, and 100 mg of chromatographically pure NaHCO3 reagents with an electronic balance and put them into 250 - mL volumetric flasks respectively. Dissolve them with CO2 - free distilled water to prepare 4 standard solutions with concentrations of 0.24 mmol / L, 1.19 mmol / L, 2.45 mmol / L, and 4.76 mmol / L respectively, and seal them for standby.

[0111] In this application, a large number of conditional tests have been carried out on parameters such as sampling volume, equilibration time, and chromatographic conditions. The analysis results are shown in Table 1. The results show that the carbon dioxide peak signal obtained by instrument analysis for the NaHCO3 solution with a low concentration of 0.24 mmol / L is very low, the value is unstable, and the standard deviation is relatively large at 0.56. It is considered that the data measured for low - concentration samples are unreliable and are excluded. In the detection of a large number of samples, it is found that the analysis data for concentrations above 0.5 mmol / L are relatively reliable.

[0112] Table 1 Analysis results of dissolved inorganic carbon isotope in four different - concentration NaHCO3 solutions

[0113]

[0114] 2. For the batch of purchased chromatographically pure NaHCO3 reagent, two analytical methods were used to determine the carbon isotope value of the parent material NaHCO3.

[0115] One is the phosphoric acid method for carbon and oxygen isotope analysis of carbonate rocks by Gasbench-IRMS (using gbw04405 as the reference material) to analyze the carbon isotope value of the parent material NaHCO3. The detection standard is SY / T 5238-2019 "Analysis Methods for Carbon and Oxygen Isotopes of Organic Substances and Carbonate Rocks". The analysis result is δ13C = -7.8‰.

[0116] The other is the oxidation combustion method of EA-IRMS elemental-isotope mass spectrometer (using gbw04407 as the reference material) as corroboration. The method is SY / T 5238-2019 "Analysis Methods for Carbon and Oxygen Isotopes of Organic Substances and Carbonate Rocks". The analysis result is δ13C = -7.7‰, which is consistent with the average carbon isotope value δ13C = -7.9‰ in the NaHCO3 solution.

[0117] III. Preservation of Samples and Reference Materials

[0118] The pretreated sample water and the prepared standard solution should be detected in a timely manner and are not suitable for long-term storage. They can be sealed with a rubber stopper and stored in the refrigerator for short-term use.

[0119] IV. Preparation of Phosphoric Acid Solution

[0120] Add phosphorus pentoxide to commercially available phosphoric acid crystals, stir, and heat in an oven at 120°C for 1 hour to prepare 103% orthophosphoric acid (density about 1.93 g / cm3). Store it in a desiccator for short-term use. The freshly prepared phosphoric acid solution is not suitable for long-term storage.

[0121] V. Setting of Instrument Analysis Condition Parameters and Program Analysis Methods

[0122] 1. Set the instrument analysis condition parameters, including the analysis conditions of the isotope mass spectrometer and the analysis conditions of the automatic gas sampling device. The analysis conditions of the isotope mass spectrometer refer to the general conditions. The main analysis conditions of the automatic gas sampling device include the gas chromatography column temperature, the pressures of the reference gas (carbon dioxide) and the carrier gas (helium), and the equilibrium temperature of the constant-temperature sample tray. The gas chromatography column temperature can be referred to as 65°C; the pressure of the reference gas (carbon dioxide): 10 psi; the pressure of the carrier gas (helium): 20 psi; the temperature of the constant-temperature sample tray: 25°C.

[0123] 2. Set the instrument program analysis method.

[0124] Through an automatic gas sampling device, with the instructions of the sample online analysis computer program and experimental exploration, a method suitable for the analysis of this sample is established for automatic control. The design of this application refers to the appropriate time for the reference gas to close and open, sample injection, and sampling. Specifically: 5S load - 20S reference on - 30S inject - 40S reference off - 65S load - 70S reference on - 90S reference off - 120S reference on - 135S inject - 140S reference off - 170S load - 240S inject - 275S load - 345S inject - 415S load - 440S inject - 510S load - 545S inject - 630S reference on - 650S reference off.

[0125] VI. Sample Analysis Process

[0126] 1. Place the quartz glass vial in a constant-temperature sample tray at 25°C, inject 0.5 ml of the 103% orthophosphoric acid prepared in Step 4, and tighten the bottle cap.

[0127] 2. Fix the inflation needle, start the instrument software program, and inflate helium for about 14 minutes.

[0128] 3. Inject 2 ml, 1 ml, and 0.5 ml of standard solutions with different concentrations (1.19 mmol / L, 2.4 mmol / L 5, and 4.76 mmol / L) respectively.

[0129] 4. The sampling volume of the sample to be tested is estimated according to the concentration of its dissolved inorganic carbon, referring to the injection volumes of the standard solutions with various concentrations in Step 3.

[0130] 5. To ensure the success of each batch of analysis, be sure to measure the blank first (this blank refers to the blank with acid added and filled with gas) before measuring the sample. The analysis sequence follows: blank - standard solution - sample to be tested (10) - standard solution - sample to be tested (10).

[0131] 6. After the equilibrium time reaches 6 hours (the equilibrium time is controlled within 6 hours - 24 hours), fix the injection needle, run the instrument program analysis method established in Step 5, and start the isotope ratio determination. The entire program analysis time is about 11 minutes.

[0132] VII. Quality Control

[0133] 1. Chromatogram Requirements

[0134] Whether the ion current signal peaks detected by the mass spectrometer are normal is a prerequisite for verifying the success of the detection method. It is required that the generated carbon dioxide peak shape is symmetric, and the next carbon dioxide peak can be completely separated from the adjacent previous peak (resolution > 95%). There should be no air peaks or other impurity peaks in the entire chromatogram. Since air peaks seriously interfere with the true value of the sample, if impurity peaks appear, the data is not available and the reason needs to be analyzed and re-measured. The standard carbon dioxide ion current chromatogram is as Figure 1 。

[0135] 2. Requirements for the deviation of the sample repeatability determination results

[0136] For the sample analysis results detected by the method of the present application, when the peak height of the target voltage signal peak > 1V, the deviation of the sample repeated determination ≤ ±0.2‰; when the peak height ≤ 1V, the deviation of the sample repeated determination ≤ ±0.3‰.

[0137] The present application selected 3 DIC crude oil-water mixture samples with different concentrations from the Sichuan Chengdu Sag for repeatability experiment analysis. The results are shown in Table 2, and the analysis deviations are 0.11, 0.11, and 0.16 respectively. Among them, the DIC concentration of S3 is 0.3 mmol / L. After being re-measured after the concentration treatment in item 4 of step 1, the analysis deviation is 0.16, realizing the high-precision detection of low-concentration DIC oilfield water.

[0138] Table 2 Analysis results of dissolved inorganic carbon isotopes in oilfield water samples

[0139]

[0140] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for analyzing the isotopes of dissolved inorganic carbon in water, characterized in that, It includes the following steps: S41. Set parameters according to the analysis conditions and establish a method suitable for sample analysis for the isotope mass spectrometer and the automatic gas sample preparation device; S42. Place the quartz glass bottle in the constant-temperature sample tray, inject phosphoric acid, and then seal the quartz glass bottle; S43. Fix the inflation needle and start the instrument to fill with the carrier gas; S44. Inject standard solutions with different concentrations respectively; among them, the standard solutions are prepared from chromatographically pure reagents, and the selection of the standard solutions is based on the stability of the sample's occurrence form in water, and to meet the sensitivity and linear range requirements of the detection instrument and detection method for dissolved inorganic carbon samples with various different concentrations in geological bodies; S45. Take the sample to be tested, where the volume of the sample to be tested is determined according to the concentration of dissolved inorganic carbon and refers to the volume of standard solutions with different concentrations; After the established equilibrium reaches the set duration, fix the injection needle and run the instrument program corresponding to the method established in S41 to measure the isotope ratio.

2. The method for analyzing the dissolved inorganic carbon isotope in water according to claim 1, characterized in that The analysis conditions of the isotope mass spectrometer refer to the general conditions; the analysis conditions of the automatic gas sample preparation device include: the temperature of the gas chromatographic column, the pressure of the reference gas, the pressure of the carrier gas, and the equilibrium temperature of the constant-temperature sample tray.

3. The method for analyzing the dissolved inorganic carbon isotope in water according to claim 2, characterized in that, The reference gas is carbon dioxide, and the carrier gas is helium.

4. The analysis method of dissolved inorganic carbon isotope in water body according to claim 1, characterized in that, Measure the blank sample before measuring the sample; the analysis sequence for measuring the isotope ratio is: blank sample - standard solution - sample to be tested - standard solution - sample to be tested; among them, the blank sample is a blank sample with acid added and filled with gas.

5. A method for analyzing the isotope of dissolved inorganic carbon in water bodies according to any one of claims 1-4, characterized in that, The set duration required for equilibrium is controlled within 6 hours - 24 hours.

6. A method for analyzing the dissolved inorganic carbon isotope in water body according to any one of claims 1-4, characterized in that, The quality control standards in the isotope ratio measurement include: The generated carbon dioxide peak shape is symmetric, the next carbon dioxide peak is completely separated from the adjacent previous peak, and there are no other impurity peaks in the entire chromatogram; and / or, In the sample analysis results, when the peak height of the target voltage signal peak > 1V, the deviation of the repeated measurement results of the sample ≤ ±0.3‰; when the peak height ≤ 1V, the deviation of the repeated measurement results of the sample ≤ ±0.5‰.

7. A method for the whole-process detection of dissolved inorganic carbon isotope in water body, characterized in that, It includes the following steps: S1. Pretreat the water sample to obtain the sample to be tested; among them, the pretreatment of the water sample includes at least one of the following situations: removing oil, grease, and organic acids in the water sample; filtering suspended solids in the water sample; filtering the relatively clean water sample through a water system filter membrane; concentrating and enriching low-concentration DIC samples; S2. Preparation and calibration of reference substances; S3. Configuration of phosphoric acid; S4. Detect and analyze the sample to be tested by using the analysis method for dissolved inorganic carbon isotope in water body described in any one of claims 1 - 6.

8. The whole-process detection method for dissolved inorganic carbon isotope in water body according to claim 7, characterized in that, In the pretreated water sample in step S1: For the water sample that may be mixed with oil, grease, and organic acids, use a C18 pretreatment column or a Dionex On Guard RP column to extract oil and grease in the water sample, and then pass through a silica column to remove organic acids in the water sample to obtain the sample; and / or, For the water sample mixed with suspended solids, use activated carbon particles to adsorb suspended solids and / or filter suspended solids with filter paper and absorbent cotton, and take the clarified water sample after standing and sedimentation to obtain the sample; and / or, Filter the water sample obtained after the first two treatments through a water system filter membrane to obtain the sample; and / or, For low-concentration DIC samples, they are concentrated using a vacuum evaporation concentrator, and then the samples are taken for measurement; among them, the concentration of DIC in the low-concentration DIC samples is ≤ 0.5 mmol / L.

9. The whole-process detection method for dissolved inorganic carbon isotope in water body according to claim 8, characterized in that The concentration of DIC in the sample is determined in combination with the value of anions in the chemical composition analysis of the sample; and / or, The method of dropping phosphoric acid solution into the sample is used to qualitatively judge the level of DIC concentration.

10. The whole-process detection method for dissolved inorganic carbon isotope in water body according to claim 7, characterized in that In step S2, a NaHCO3 solution is selected as the standard sample, and step S2 includes the following sub-steps: S21. Prepare standard solutions of 1.19 mmol / L, 2.45 mmol / L, and 4.76 mmol / L from chromatographically pure NaHCO3 reagent. S22. For the NaHCO3 reagent, analyze the carbon isotope value of the parent material NaHCO3 using the phosphoric acid method for carbonate rock carbon and oxygen isotope analysis with Gasbench-IRMS; meanwhile, as a corroboration, determine the carbon isotope value of the parent material NaHCO3 using the oxidation combustion method with an EA-IRMS element-isotope mass spectrometer.

Images