Shale organic pore content calculation method considering biogenesis

Abstract

The invention belongs to the technical field of shale oil and gas resource evaluation, and discloses a shale organic pore content calculation method considering biogenesis. The method comprises the following steps: carrying out a back scattering two-dimensional large-area scanning electron microscope experiment on a shale sample in a research area to obtain an organic pore surface porosity; measuring the total organic carbon content, the mineral content and the major element content of the shale sample in the research area, and respectively obtaining the TOC content, the clay mineral content and the biological quartz content of the sample; and establishing a shale organic pore content calculation model through multivariate linear fitting by taking the organic pore surface porosity as a dependent variable and TOC, clay mineral and biological quartz content as independent variables. According to the method disclosed by the invention, various sensitive parameters influencing the development of the organic pores are screened out and introduced into an organic pore surface porosity quantitative calculation model, so that the quantitative calculation of the content of the organic pores is realized under the condition that a scanning electron microscope is not provided. The organic pore quantitative calculation model comprises a key parameter of biological quartz content, so that the calculation precision of the model can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of shale oil and gas resource evaluation, and relates to a method for calculating the content of shale organic pores considering biogenesis. Background Art

[0002] Organic pores are an important type of reservoir space in shale, and are of great significance for the enrichment and migration of shale oil and gas. Research shows that the organic matter content controls the development of shale organic pores. The research by Loucks shows (Loucks, Reed, Ruppel, et al. Morphology, Genesis, and distribution of nanometer-scale pores in siliceous mudstones of the mississippian barnett shale[J]. Journal of Sedimentary Research, 2009, 79(12):848-861) that there is a positive correlation between the content of shale organic pores and the TOC content. The type and maturity of organic matter also affect the number of organic pores. In shale formations with the same TOC content, due to differences in the type and maturity of organic matter, the number of organic pores will also be different. Therefore, the content of organic pores cannot be calculated solely based on a single parameter of the TOC content; traditional methods quantitatively characterize the content of shale organic pores based on scanning electron microscope experiments.

[0003] The invention patent with the application publication number CN 115239600 A provides a method for multi-component division of shale scanning electron microscope images. Based on scanning electron microscope experiments, this method performs threshold segmentation on the images according to the differences in the gray values of different components in the scanning electron microscope images, and divides shale components such as organic pores, organic matter, and minerals. In recent years, CT scanning and focused ion beam scanning electron microscope (FIB-SEM) experiments have been developed, which can further obtain the three-dimensional spatial distribution characteristics of shale organic pores. However, these methods are expensive in experiments and do not have the prospect of large-scale popularization and application. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for calculating the content of shale organic pores considering biogenesis, so as to provide scientific guidance for shale oil and gas resource evaluation and sweet spot optimization.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A method for calculating the content of shale organic pores considering biogenesis, comprising the following steps:

[0007] Step 1: Perform backscattered two-dimensional large-area scanning electron microscope experiments on shale samples in the study area to obtain the organic pore surface area ratio;

[0008] Step 2: Conduct experiments on the determination of total organic carbon, mineral content, and major elements of shale samples in the study area, and obtain the TOC, clay mineral, and biogenic quartz content of the samples respectively;

[0009] Step 3: Taking the organic pore porosity as the dependent variable and the TOC, clay mineral, and biogenic quartz content as the independent variables, establish a calculation model for the organic pore content of shale through multiple linear fitting.

[0010] Furthermore, in Step 1, the standard process of the backscattered two-dimensional large-area scanning electron microscope experiment is carried out with reference to the petroleum and natural gas industry standard SY / T 5162-2021 "Analysis Method of Scanning Electron Microscope for Rock Samples".

[0011] Furthermore, in Step 1, before the backscattered two-dimensional large-area scanning electron microscope experiment, the shale surface is polished with argon ions;

[0012] Furthermore, in Step 2, before the total organic carbon content determination experiment, the shale samples need to be pretreated, and the specific process is as follows:

[0013] (1) Grind the shale samples into 100-mesh powder using an agate mortar;

[0014] (2) Add the shale powder to dilute hydrochloric acid and react for 2 hours to completely remove inorganic minerals;

[0015] (3) Rinse the shale samples treated with dilute hydrochloric acid with distilled water for 10 minutes until neutral;

[0016] (4) Place the powdered shale samples in a constant temperature drying oven and dry them at 60°C for 24 hours.

[0017] Furthermore, in Step 2, before the mineral content determination experiment, the samples need to be pretreated, and the specific process is as follows:

[0018] (1) Wash the shale samples with oil, and the organic solvent used for washing oil is chloroform, and process until the fluorescence is below grade four;

[0019] (2) Use a constant temperature drying oven to dry the shale samples after washing oil, the temperature is 50°C, and the time is 24 hours;

[0020] (3) Grind the shale samples after washing oil and drying into 100-mesh powder using an agate mortar.

[0021] Furthermore, the major element determination experiment is based on the national standard GB / T 14506.28-2010 "Methods for Chemical Analysis of Silicate Rocks - Part 28: Determination of 16 Major and Minor Component Contents".

[0022] Further, in step 2, the content of biogenic quartz in the shale sample is calculated by formula (1):

[0023] SiO 2-Bio = SiO 2-Sam - (SiO 2 / Al 2 O 3 ) Avg × Al 2 O 3-Sam (1)

[0024] In formula (1): SiO 2-Bio is the calculated content of biogenic quartz, %; SiO 2-Sam is the quartz content in the shale sample, %; (SiO 2 / Al 2 O 3 ) Avg is the ratio of SiO 2 to Al 2 O 3 in the average shale of the upper crust, dimensionless; Al 2 O 3-Sam is the alumina content in the shale sample, %.

[0025] Further, in step 3, the calculation model of the organic pore content in the shale is: organic pore surface area porosity = 0.1559 × TOC - 0.0144 × clay content + 0.0175 × biogenic quartz content + 0.4282.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] By screening out a variety of sensitive parameters that affect the development of organic pores and introducing them into the quantitative calculation model of organic pore surface area porosity, the present invention realizes the quantitative calculation of the organic pore content without the condition of a scanning electron microscope. The quantitative calculation model of organic pores includes the key parameter of biogenic quartz content, which can effectively improve the calculation accuracy of the model. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the crossplot of total organic carbon TOC and experimentally calculated organic pore surface area porosity;

[0029] Figure 2 is the crossplot of clay mineral content and experimentally calculated organic pore surface area porosity;

[0030] Figure 3 is the crossplot of biogenic quartz content and experimentally calculated organic pore surface area porosity;

[0031] Figure 4 is the crossplot of model-calculated organic pore surface area porosity and experimentally calculated organic pore surface area porosity. Detailed implementation mode

[0032] To make the technical means and achieved purposes adopted by the present invention easy to understand, the present invention will be further described below in conjunction with specific implementation modes.

[0033] Unless otherwise specified, the experimental methods used in the following embodiments are all conventional methods.

[0034] Refer to Figures 1 to 4 , the following technical solutions are adopted in this specific implementation mode: A method for calculating the content of organic pores in shale considering biogenesis, comprising the following steps:

[0035] Step 1: Conduct a backscattered two-dimensional large-area scanning electron microscope experiment on shale samples in the study area to obtain the backscattered two-dimensional large-area scanning electron microscope imaging of the organic pore surface porosity. The instrument model is Helios650 / Helios5CX;

[0036] Backscattered two-dimensional large-area scanning electron microscope imaging is for samples that need to be observed in a large area, such as shale samples containing multi-scale pore structures. A series of continuous and edge-overlapping high-resolution small images are scanned and arranged in a selected area. After the scanning is completed, these small images will be stitched together to obtain an ultra-high-resolution and ultra-large-area two-dimensional backscattered electron image;

[0037] Before the backscattered two-dimensional large-area scanning electron microscope experiment, the shale surface is polished with argon ions.

[0038] The shale samples after argon ion polishing are subjected to large-area backscattered high-resolution imaging detection according to the following steps;

[0039] Sample preparation: Cut a sub-sample with the same diameter as the original sample and a thickness of 2 - 5 mm from the rock sample, polish the surface with ions, and then coat a carbon conductive film (with a thickness of 10 - 20 nm) on the surface to ensure the conductivity of the sample surface.

[0040] Sample testing: Put the prepared sample into the instrument sample chamber, focus, select the backscattered image mode, select appropriate voltage and beam current values, then set the size of a single small image and the size of the scanning area, and start scanning.

[0041] Image processing and quantitative analysis: After the image acquisition is completed, all the result images are input into the image processing software for combination and stitching, and at the same time, quantitative analysis is performed on the images to obtain the organic pore surface porosity.

[0042] Step 2: Conduct experiments on the total organic carbon, mineral content, and major elements of shale samples in the study area to obtain the TOC, clay mineral, and biogenic quartz content of the samples respectively

[0043] The experimental instrument for TOC content determination is a CS744 carbon-sulfur analyzer;

[0044] Before the TOC content determination experiment, the shale samples need to be pretreated. The specific process is as follows:

[0045] (1) Use an agate mortar to grind the shale samples into 100-mesh powder;

[0046] (2) Add the shale powder to dilute hydrochloric acid and react for 2 hours to completely remove inorganic minerals;

[0047] (3) Rinse the shale samples treated with dilute hydrochloric acid with distilled water for 10 minutes until neutral;

[0048] (4) Place the powdered shale samples in a constant-temperature drying oven and dry them at 60 °C for 24 hours.

[0049] As Figure 1 shown, there is a good positive correlation between TOC content and organic pore surface area porosity (R 2 = 0.8072), indicating that the TOC content can be involved in the calculation model of organic pore surface area porosity.

[0050] The experimental instrument for mineral analysis is a D8 DISCOVER X-ray diffractometer;

[0051] Before the mineral content determination experiment, the samples need to be pretreated. The specific process is as follows:

[0052] (1) Wash the shale samples with oil. The organic solvent used for oil washing is chloroform, and the treatment is carried out until the fluorescence level is below four;

[0053] (2) Use a constant-temperature drying oven to dry the shale samples after oil washing. The temperature is 50 °C and the time is 24 hours;

[0054] (3) Use an agate mortar to grind the shale samples after oil washing and drying into 100-mesh powder.

[0055] As Figure 2 shown, there is a good negative correlation between clay mineral content and organic pore surface area porosity (R 2 = 0.72), indicating that the clay mineral content can be involved in the calculation model of organic pore surface area porosity.

[0056] The experimental instrument model for major element analysis is a Zetium AB104L / AL104 X-ray fluorescence spectrometer (XRF);

[0057] The biogenic quartz content of the shale samples is calculated by formula (1):

[0058] SiO 2-Bio = SiO 2-Sam-(SiO 2 / Al 2 O 3 ) Avg ×Al 2 O 3-Sam (1)

[0059] In formula (1): SiO 2-Bio is the calculated content of biogenic quartz, %; SiO 2-Sam is the quartz content in the shale sample, %; (SiO 2 / Al 2 O 3 ) Avg is the ratio of SiO 2 to Al 2 O 3 in the average shale of the upper crust, dimensionless; Al 2 O 3-Sam is the alumina content in the shale sample, %.

[0060] The major elements were measured by the alkali fusion glass chip method. The specific experimental steps are as follows:

[0061] Use an agate mortar to grind the shale sample into 200-mesh powder;

[0062] Place the powdered shale sample in a ceramic crucible and calcine it at 1000 °C for 1 h to measure the weight reduction of the sample;

[0063] Weigh 1 g of the calcined shale powder sample to be measured, add 6 g of anhydrous lithium tetraborate, mix evenly in a ceramic crucible, and heat it to 1050 °C to make the required molten glass chip;

[0064] Measure on an X-ray fluorescence spectrometer (XRF). Except for nickel, copper, strontium, and zirconium, which are corrected for matrix effects using Compton scattered rays as internal standards, the absorption-enhancement effects between the remaining analytical elements are corrected using the theoretical α coefficient. Calculate the amounts of the major and minor components based on the fluorescence intensity;

[0065] As Figure 3 shown, there is a good positive correlation between the biogenic quartz content and the organic pore surface porosity (R 2 = 0.8585), indicating that the biogenic quartz content can be involved in the calculation model of the organic pore surface porosity.

[0066] Step 3: Taking the organic pore surface porosity as the dependent variable and taking the TOC, clay minerals, and biogenic quartz content as the independent variables, establish a calculation model for the organic pore content of shale through multiple linear fitting

[0067] As shown in Table 1 is the experimental data table

[0068] Table 1

[0069]

[0070]

[0071] The calculation model of the organic pore surface area ratio can be expressed by the following formula:

[0072] Organic pore surface area ratio = 0.1559 × TOC - 0.0144 × clay content + 0.0175 × biogenic quartz content + 0.4282.

[0073] As Figure 4 shown, the organic pore surface area ratio calculated by the model has a very strong correlation with the organic pore surface area ratio calculated by the backscattered two-dimensional large-area scanning electron microscope experiment (R 2 = 0.9691), and the average relative error is only 6.97%, indicating that the calculation model provided by the examples of the present invention has high accuracy.

[0074] Although some embodiments of the present invention have been given in this article, those skilled in the art should understand that the embodiments in this article can be changed without departing from the spirit of the present invention. The above embodiments are only exemplary and should not be used as a limitation of the scope of the rights of the present invention.

Claims

1. A calculation method for the content of organic pores in shale considering biogenesis, characterized in that, it includes the following steps: Step 1: Conduct a backscattered two-dimensional large-area scanning electron microscopy experiment on shale samples in the study area to obtain the pore surface porosity of organic pores; Step 2: Conduct experiments on the total organic carbon, mineral content, and major elements of shale samples in the study area to obtain the TOC, clay mineral, and biogenic quartz content of the samples respectively; Step 3: Take the pore surface porosity of organic pores as the dependent variable, and the TOC, clay mineral, and biogenic quartz content as independent variables, and establish a calculation model for the content of organic pores in shale through multiple linear fitting.

2. The calculation method for the content of organic pores in shale considering biogenesis according to claim 1, characterized in that, in Step 1, the standard process of the backscattered two-dimensional large-area scanning electron microscopy experiment is carried out with reference to the petroleum and natural gas industry standard SY / T 5162-2021 "Analysis Method of Scanning Electron Microscope for Rock Samples".

3. The calculation method for the content of organic pores in shale considering biogenesis according to claim 1, characterized in that, before the backscattered two-dimensional large-area scanning electron microscopy experiment in Step 1, the shale surface is polished with argon ions.

4. The calculation method for the content of organic pores in shale considering biogenesis according to claim 1, characterized in that, before the total organic carbon content determination experiment in Step 2, the shale samples need to be pretreated, and the specific process is as follows: (1) Grind the shale samples into 100-mesh powder using an agate mortar; (2) Add the shale powder to dilute hydrochloric acid and react for 2 hours to completely remove inorganic minerals; (3) Rinse the shale samples treated with dilute hydrochloric acid with distilled water for 10 minutes until neutral; (4) Place the powdered shale samples in a constant-temperature drying oven and dry them at 60°C for 24 hours.

5. The calculation method for the content of organic pores in shale considering biogenesis according to claim 1, characterized in that, before the mineral content determination experiment in Step 2, the samples need to be pretreated, and the specific process is as follows: (1) Wash the shale samples with an organic solvent of chloroform until the fluorescence is below level 4; (2) Use a constant-temperature drying oven to dry the shale samples after washing with oil at a temperature of 50°C for 24 hours; (3) Grind the shale samples after washing and drying with oil into 100-mesh powder using an agate mortar.

6. The calculation method for the content of organic pores in shale considering biogenesis according to claim 1, characterized in that, the major element determination experiment is based on the national standard GB / T 14506.28-2010 "Chemical Analysis Methods of Silicate Rocks - Part 28: Determination of 16 Major and Minor Component Contents".

7. The calculation method for the content of organic pores in shale considering biogenesis according to claim 1, characterized in that, in Step 2, the biogenic quartz content of the shale samples is calculated by formula (1): SiO 2-Bio = SiO 2-Sam -(SiO 2 / Al 2 O 3 ) Avg ×Al 2 O 3-Sam (1) In formula (1): SiO 2-Bio is the calculated content of biogenic quartz, %; SiO 2-Sam is the quartz content of the shale sample, %; (SiO 2 / Al 2 O 3 ) Avg is the ratio of the average shale SiO 2 in the upper crust to Al 2 O 3 , dimensionless; Al 2 O 3-Sam is the alumina content of the shale sample, %.

8. The calculation method for the content of organic pores in shale considering biogenesis according to claim 1, characterized in that, In Step 3, the calculation model for the organic pore content in shale is: Organic pore surface area ratio = 0.1559 × TOC - 0.0144 × clay content + 0.0175 × biogenic quartz content + 0.4282.

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