Method for quantitatively characterizing content of different occurrence state water in shale by TG-MS

Abstract

The embodiment of the application provides a method for quantitatively characterizing water content in different states in shale by using TG-MS, target laminae are identified on a shale plug or rock block taken in situ, a micro drill is used to drill a micro area sample of the target laminae under a preset environment; the micro area sample is placed in a liquid nitrogen environment for frozen grinding; the ground powder sample is transferred to a sample boat of a thermogravimetric-mass spectrometer, and is heated by programmed temperature rising, so that a mass spectrum curve of the micro area sample is measured; under the same experimental conditions, calcium oxalate monohydrate is selected as a standard substance, a standard curve of water mass and mass spectrum integral peak area is established; the measured mass spectrum curve of the micro area sample is integrated, so that the integral peak area of the sample is obtained; the integral peak area of the sample is substituted into the established standard curve, so that the mass of water in the shale micro area sample is determined, and then the mass moisture content of the laminae is determined according to the initial mass of the micro area sample, so that accurate quantitative analysis of water content in different laminae of shale is realized.

Description

Technical Field

[0001] This application relates to the field of oil and gas geological exploration and development technology, and specifically to a method for quantitatively characterizing the water content of shale in different occurrence states using TG-MS. Background Technology

[0002] The occurrence and content of oil and water in shale have a decisive impact on the exploration potential and development effectiveness of shale oil. Accurate determination of shale water content is fundamental to evaluating reservoir properties and analyzing oil-water distribution patterns. Currently, various methods have been developed for macroscopic water content testing in shale, mainly including well logging interpretation and nuclear magnetic resonance imaging. These methods can provide continuous water content profiles at the core or wellbore scale.

[0003] However, shale exhibits strong heterogeneity and abundant laminar structure, with significant differences in water-bearing capacity among different laminae (such as clay laminae, silt laminae, and organic laminae). Macroscopic testing methods lack sufficient spatial resolution, making it difficult to distinguish water content differences at the laminar scale and failing to meet the needs for detailed research on the microscopic mechanisms of oil and water occurrence in shale. Although nuclear magnetic resonance (NMR) technology can be used to analyze pore fluids, it suffers from the following problems: 1. Shale contains both oil and water phases, and their signals may overlap on the NMR spectrum, making clear differentiation difficult. 2. For two-dimensional NMR, magnetic minerals within the shale (such as pyrite and magnetite) generate internal magnetic field gradients, leading to rapid signal attenuation (shortened relaxation time T2), making some water signals undetectable. In summary, current NMR methods struggle to accurately obtain the absolute water content in situ within laminae. Therefore, a method that can overcome signal interference and achieve precise quantitative analysis of water content at the shale laminar scale is urgently needed. Summary of the Invention

[0004] This application provides a method for quantitatively characterizing the water content of shale in different occurrence states using TG-MS.

[0005] The first aspect of this application provides a method for quantitatively characterizing the water content of shale in different occurrence states using TG-MS, comprising: On shale plungers or rock blocks that are cored in situ, the target laminae are observed and identified using a microscope, and micro-drills are used to extract micro-area samples of the target laminae under a preset environment. The obtained micro-area samples were placed in a liquid nitrogen environment for cryogenic grinding to pulverize them into powder, so as to fully expose the pores and retain the original moisture. The ground powder was transferred to the sample boat of the thermogravimetric-mass spectrometer and heated by programmed temperature rise to obtain the mass spectrum curve of the shale micro-region sample. Under the same experimental conditions, calcium oxalate monohydrate was selected as the standard substance, and a standard curve of water mass versus mass spectrometry integrated peak area was established. The integrated peak area of ​​the sample is obtained by integrating the mass spectrometry curve of the measured shale micro-region sample. Substitute the integrated peak area of ​​the sample into the established standard curve to determine the mass of water in the shale micro-region sample, and then determine the mass water content of the laminar layer based on the initial mass of the micro-region sample.

[0006] In an optional embodiment of this application, the measurement of the mass spectrometry curve of the shale micro-region sample includes: During the programmed heating process, characteristic ion fragments of water molecules are recorded in the mass spectrum. The monitored nucleus-mass ratio includes the main peak of water molecules and the peaks of water molecule fragments to eliminate interference from other gases and ensure the accuracy of the detection signal.

[0007] In an optional embodiment of this application, the preset environment is between -10°C and 0°C.

[0008] In an optional embodiment of this application, the step of selecting calcium oxalate monohydrate as a standard substance and establishing a standard curve of water mass versus mass spectrometry integrated peak area includes: At least three samples of calcium oxalate monohydrate of different masses were weighed and measured by thermogravimetric-mass spectrometry. The characteristic peaks of water molecules released from each standard sample were integrated to obtain the peak area. Using the mass of the standard sample as the x-axis and the corresponding mass spectrometry integrated peak area as the y-axis, a linear fit was performed to obtain the standard curve of moisture mass versus mass spectrometry integrated peak area.

[0009] In an optional embodiment of this application, after establishing the standard curve of moisture mass versus mass spectrometry integrated peak area, the method further includes: Verify the correlation of the standard curve; If the correlation of the standard curve reaches a preset threshold, the step of substituting the integral peak area of ​​the sample into the established standard curve is executed.

[0010] Compared with the prior art, the technical solutions provided in this application have at least some or all of the following advantages: The method for quantitatively characterizing the water content of shale in different occurrence states using TG-MS, as described in this application embodiment, involves observing and identifying target laminae on shale plungers or blocks obtained from in-situ core samples using a microscope, and drilling micro-area samples of the target laminae under a preset environment using a micro-drill. The obtained micro-area samples are then subjected to cryogenic grinding in a liquid nitrogen environment to pulverize them into powder, fully exposing the pores and preventing the loss of original moisture. The ground powder is transferred to the sample boat of a thermogravimetric-mass spectrometer (TGA), and heated using a programmed temperature rise method. The mass spectrometry curve of the shale micro-area sample is then measured. Under the same experimental conditions, calcium oxalate monohydrate is selected... As a standard material, a standard curve was established to correlate water mass with the integrated peak area of ​​the mass spectrometer. The mass spectrometer curves of the measured shale micro-region samples were integrated to obtain the integrated peak area of ​​the samples. The integrated peak area of ​​the samples was substituted into the established standard curve to determine the water mass in the shale micro-region samples. Based on the initial mass of the micro-region samples, the mass water content of the laminae was determined. This method overcomes the shortcomings of insufficient spatial resolution in macroscopic logging and nuclear magnetic resonance methods, and for the first time, it has achieved accurate quantitative analysis of water content in different shale laminae (millimeter-level or even smaller scale), providing key data support for the study of the microscopic occurrence mechanism of shale oil. Attached Figure Description

[0011] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a flowchart illustrating a method for quantitatively characterizing the water content of shale in different occurrence states using TG-MS, as provided in one embodiment of this application. Detailed Implementation

[0012] To make the technical solutions and advantages of the embodiments of this application clearer, the exemplary embodiments of this application will be described in further detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not an exhaustive list of all embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0013] Please see Figure 1 The method for quantitatively characterizing the water content of shale in different occurrence states using TG-MS provided in this application includes the following steps S100~S600: S100: On shale plungers or rock blocks that are cored in situ, the target laminae are observed and identified using a microscope, and micro-drills are used to drill micro-area samples of the target laminae under a preset environment. S200 involves placing the obtained micro-area sample in a liquid nitrogen environment for cryogenic grinding to pulverize it into powder, thereby fully exposing the pores and preventing the loss of original moisture. S300: The ground powder sample is transferred to the sample boat of the thermogravimetric-mass spectrometer, heated by programmed temperature rise, and the mass spectrum curve of the shale micro-area sample is measured. S400, under the same experimental conditions, calcium oxalate monohydrate was selected as the standard substance, and a standard curve of water mass versus mass spectrometry integrated peak area was established. S500 integrates the mass spectrometry curves of the measured shale micro-region samples to obtain the integrated peak area of ​​the samples. S600: Substitute the integrated peak area of ​​the sample into the established standard curve to determine the mass of water in the shale micro-region sample, and then determine the mass water content of the laminar layer based on the initial mass of the micro-region sample.

[0014] In an optional embodiment of this application, the measurement of the mass spectrometry curve of the shale micro-region sample includes: During the programmed heating process, characteristic ion fragments of water molecules are recorded in the mass spectrum. The monitored nucleus-mass ratio includes the main peak of water molecules and the peaks of water molecule fragments to eliminate interference from other gases and ensure the accuracy of the detection signal.

[0015] In an optional embodiment of this application, the preset environment is between -10°C and 0°C.

[0016] In an optional embodiment of this application, the step of selecting calcium oxalate monohydrate as a standard substance and establishing a standard curve of water mass versus mass spectrometry integrated peak area includes: At least three samples of calcium oxalate monohydrate of different masses were weighed and measured by thermogravimetric-mass spectrometry. The characteristic peaks of water molecules released from each standard sample were integrated to obtain the peak area. Using the mass of the standard sample as the x-axis and the corresponding mass spectrometry integrated peak area as the y-axis, a linear fit was performed to obtain the standard curve of moisture mass versus mass spectrometry integrated peak area.

[0017] In an optional embodiment of this application, after establishing the standard curve of moisture mass versus mass spectrometry integrated peak area, the method further includes: Verify the correlation of the standard curve; If the correlation of the standard curve reaches a preset threshold, the step of substituting the integral peak area of ​​the sample into the established standard curve is executed.

[0018] Example 1 The method for quantitatively characterizing the water content of shale in different occurrence states using TG-MS, as described in this application, includes the following steps: Step 1: Micro-area sampling On shale plungers or blocks that are cored in situ, the target laminae are observed and identified using a microscope, and micro-drills are used to drill micro-area samples in a low-temperature environment (e.g., maintained between -10°C and 0°C to prevent moisture evaporation).

[0019] Step 2: Low-temperature sample preparation The obtained micro-area samples were rapidly placed in a liquid nitrogen environment for cryogenic grinding to pulverize them into powder, thereby fully exposing the pores and preventing the loss of original moisture.

[0020] Step 3: Sample Testing The ground powder was rapidly transferred to the sample boat of a thermogravimetric-mass spectrometer (TG-MS) for programmed temperature increase. During heating, characteristic ion fragments of water molecules were recorded in the mass spectrum. Specifically, the monitored mass-to-nucleus ratio (m / z) included the main water molecule peak (m / z=18) and the water molecule fragment peak (m / z=17) to eliminate interference from other gases and ensure the accuracy of the detection signal.

[0021] Step 4: Establishing the Standard Curve Under the same experimental conditions, calcium oxalate monohydrate (CaC2O4·H2O) was selected as the standard substance. At least three samples of calcium oxalate monohydrate with different masses (e.g., 20 mg, 50 mg, 80 mg) were weighed and analyzed by TG-MS. The characteristic peak (m / z=18) of the water molecules released from each standard sample was integrated to obtain the peak area. A linear fit was performed with the mass of the standard sample as the x-axis and the corresponding MS integrated peak area as the y-axis to establish a standard curve of water mass versus MS integrated peak area. The correlation (R²) was verified; a strong correlation indicates that this curve can be used for the next step.

[0022] Step 5: Moisture Content Conversion Integrate the MS curve (m / z=18) of the shale micro-area sample obtained in step 3 to obtain the integrated peak area of ​​the sample. Substitute this peak area into the standard curve established in step 4 to calculate the mass of water in the shale micro-area sample. Then, based on the initial mass of the micro-area sample, calculate the mass water content of the laminar layer.

[0023] Example 2 In-situ cored samples of shale from a certain region were selected, and the bright crystalline and mixed laminae were drilled separately using a micro-drill under liquid nitrogen conditions. Immediately after drilling, the samples were transferred to a cryogenic grinder and ground to a particle size of approximately 100 mesh. Two portions of the ground powder were accurately weighed and tested using thermogravimetric analysis-mass spectrometry (TG-MS). The testing conditions were: heating from room temperature to 800℃ at a rate of 10℃ / min. Under the same conditions, one blank sample and three different masses of calcium oxalate monohydrate (CaC2O4·H2O) standard samples were tested sequentially. The mass spectrometry (MS) signal data of the blank sample, shale sample, and calcium oxalate monohydrate sample were recorded. The MS signals of the shale sample and calcium oxalate sample were integrated after subtracting the baseline of the blank sample. A standard curve was established with the integrated peak area of ​​the three calcium oxalate monohydrate samples as the ordinate and the corresponding sample mass as the abscissa. The linear correlation coefficient R² reached 0.999. Substituting the MS integral peak areas of the two shale samples into the standard curve, the water content of the shale sample was calculated to be 20 mg / g.

[0024] In this application, micro-area sampling and low-temperature sample preparation are combined. Targeting the shale laminar scale, a low-temperature micro-drilling sampling technique combined with liquid nitrogen cryogenic grinding is adopted to avoid the loss of original moisture in the shale due to temperature rise during the sample preparation process, thus ensuring the original state of the micro-area sample.

[0025] The selection and identification of characteristic nucleus-mass ratio (m / z) in this application, along with the monitoring of the main peak (m / z=18) and fragment peak (m / z=17) of water molecules, effectively distinguishes and eliminates interference from other hydrocarbon gases produced by the pyrolysis of organic matter in shale on the water signal (m / z=18) through bimodal identification technology, thereby improving the specificity of detection.

[0026] In this application, calcium oxalate monohydrate was used as the standard reference material for selection and quantitative modeling. This material has a defined thermal decomposition temperature and a fixed water content, and its pyrolysis behavior is comparable to the water release process in shale. By establishing standard curves of MS peak integral area versus water mass for different masses of calcium oxalate monohydrate, absolute quantification of MS signals in shale micro-area samples was achieved, overcoming the limitations of traditional methods that only provide semi-quantitative or relative quantification.

[0027] This application achieves quantitative analysis at the lamellar scale, overcoming the shortcomings of insufficient spatial resolution in methods such as macroscopic logging and nuclear magnetic resonance. It is the first to realize accurate quantitative analysis of water content in different lamellars (millimeters or even smaller scale) of shale, providing key data support for the study of the microscopic occurrence mechanism of shale oil.

[0028] This application improves detection accuracy by using TG-MS coupled with the monitoring of characteristic nucleus-mass ratios of 17 and 18, effectively solving the problem of overlap between water signals and rock mineral / organic matter signals in traditional pyrolysis or NMR methods, and eliminating interference from non-aqueous hydrogen sources.

[0029] This application achieves absolute quantification by establishing a direct correlation between moisture mass and MS signal integral area using a calcium oxalate monohydrate standard sample. This converts the MS signal from relative intensity to absolute water content, significantly improving the accuracy and reliability of the measurement results.

[0030] This application preserves the original state of the sample, and low-temperature control is used throughout the entire process from sampling to sample preparation, so as to preserve the original water content in the shale laminae to the greatest extent and ensure the representativeness and authenticity of the test results.

[0031] It should be understood that although the steps in the flowchart are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order constraint on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the diagram may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0032] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0033] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for quantitatively characterizing the water content of shale in different occurrence states using TG-MS, characterized in that, include: On shale plungers or rock blocks that are cored in situ, the target laminae are observed and identified using a microscope, and micro-drills are used to extract micro-area samples of the target laminae under a preset environment. The obtained micro-area samples were placed in a liquid nitrogen environment for cryogenic grinding to pulverize them into powder, so as to fully expose the pores and retain the original moisture. The ground powder was transferred to the sample boat of the thermogravimetric-mass spectrometer and heated by programmed temperature rise to obtain the mass spectrum curve of the shale micro-region sample. Under the same experimental conditions, calcium oxalate monohydrate was selected as the standard substance, and a standard curve of water mass versus mass spectrometry integrated peak area was established. The integrated peak area of ​​the sample is obtained by integrating the mass spectrometry curve of the measured shale micro-region sample. Substitute the integrated peak area of ​​the sample into the established standard curve to determine the mass of water in the shale micro-region sample, and then determine the mass water content of the laminar layer based on the initial mass of the micro-region sample.

2. The method according to claim 1, characterized in that, The mass spectrometry curves of the measured shale micro-region samples include: During the programmed heating process, characteristic ion fragments of water molecules are recorded in the mass spectrum. The monitored nucleus-mass ratio includes the main peak of water molecules and the peaks of water molecule fragments to eliminate interference from other gases and ensure the accuracy of the detection signal.

3. The method according to claim 1, characterized in that, The preset environment is between -10℃ and 0℃.

4. The method according to claim 1, characterized in that, The step of selecting calcium oxalate monohydrate as a standard substance and establishing a standard curve of water mass versus mass spectrometry integrated peak area includes: At least three samples of calcium oxalate monohydrate of different masses were weighed and measured by thermogravimetric-mass spectrometry. The characteristic peaks of water molecules released from each standard sample were integrated to obtain the peak area. Using the mass of the standard sample as the x-axis and the corresponding mass spectrometry integrated peak area as the y-axis, a linear fit was performed to obtain the standard curve of moisture mass versus mass spectrometry integrated peak area.

5. The method according to claim 1, characterized in that, After establishing the standard curve of moisture mass versus mass spectrometry integrated peak area, the method further includes: Verify the correlation of the standard curve; If the correlation of the standard curve reaches a preset threshold, the step of substituting the integral peak area of ​​the sample into the established standard curve is executed.

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