Shale adsorption gas content calculation method

Abstract

A shale adsorbed gas content calculation method belongs to the technical field of shale oil and gas resource evaluation, and comprises the following steps: carrying out an isothermal adsorption experiment to obtain a sample adsorbed gas content; carrying out an organic carbon content determination experiment to obtain a TOC value of the sample; carrying out a mineral content analysis experiment to obtain the clay mineral content; carrying out a low-temperature nitrogen adsorption experiment to calculate fractal dimensions; carrying out a back scattering two-dimensional large-area scanning electron microscope experiment to obtain the porosity of an organic pore surface; carrying out an element analysis experiment on the shale sample in the research area, and calculating to obtain the biological quartz content; the shale adsorbed gas content calculation model is established through multivariate linear fitting by taking the adsorbed gas content as a dependent variable and TOC, the clay mineral content, the fractal dimension, the organic pore surface porosity and the biological quartz content as dependent 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.

Description

Technical Field

[0001] The invention belongs to the technical field of shale oil and gas resource evaluation, and particularly relates to a method for calculating shale adsorbed gas content. Background Art

[0002] There are three main states of shale gas in shale reservoirs, namely adsorbed gas, free gas and dissolved gas. Adsorbed gas is mainly attached to the surface of organic matter and clay mineral particles, accounting for more than 50%; free gas is mainly present in micro-nano pore systems and microcracks, accounting for 20%-30%; dissolved gas is shale gas dissolved in kerogen and asphaltene, accounting for less than 10%. In the process of shale gas extraction, free gas is first produced. At the same time, as the formation pressure decreases, adsorbed gas will continue to desorb and release. The released adsorbed gas is produced together with free gas to form gas well production capacity, while the contribution of dissolved gas to shale gas well production capacity can be ignored. Shale gas extraction is a dynamic process of free gas release-adsorbed gas desorption-free gas release. Therefore, the calculation of shale adsorbed gas volume is an important parameter for resource evaluation and favorable target selection in shale gas exploration and development.

[0003] However, due to the diverse occurrence of shale gas, there is both adsorbed gas and free gas, and there is dynamic transformation and mixed flow between the two during shale gas development. There is no essential difference in the properties of adsorbed gas and free gas released by desorption, and the proportion of each gas changes continuously during production, making it very difficult to calculate the adsorbed gas content in shale, which brings great trouble to the development and research of shale gas reservoirs.

[0004] At present, the adsorbed gas content is mainly tested by conducting isothermal adsorption experiments. This method has the disadvantage of complex experimental operation, and whether the adsorbed gas content can be accurately obtained depends largely on the experience of the experimenter. Therefore, it is necessary to invent a new method to replace the isothermal adsorption experiment. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes: a method for calculating the adsorbed gas content of shale, comprising the following steps:

[0006] S1. Conduct isothermal adsorption experiments on shale samples in the study area to obtain the adsorbed gas content of the samples;

[0007] S2. Conduct an organic carbon content measurement experiment on shale samples in the study area to obtain the TOC value of the samples;

[0008] S3. Conduct mineral content analysis experiments on shale samples in the study area to obtain clay mineral content;

[0009] S4. Conduct low-temperature nitrogen adsorption experiments on shale samples in the study area and calculate the fractal dimension;

[0010] S5. Conduct backscattered two-dimensional large-area scanning electron microscopy experiments on shale samples in the study area to obtain the porosity of organic pores;

[0011] S6. Conduct elemental analysis experiments on shale samples in the study area and calculate the biogenic quartz content;

[0012] S7. Taking the adsorbed gas content as the dependent variable, TOC, clay mineral content, fractal dimension, organic pore surface ratio and biogenic quartz content as dependent variables, a shale adsorbed gas content calculation model was established through multivariate linear fitting.

[0013] Furthermore, in step S1, the shale sample is pretreated before the isothermal adsorption experiment, and the process is as follows:

[0014] S11. Grind the shale sample into 60 mesh powder using an agate mortar;

[0015] S12, placing the powdered shale sample in a constant temperature drying oven and drying it at 105° C. for 24 hours;

[0016] S13. Under the condition of 105°C, the dried shale powder sample was subjected to vacuum degassing treatment for 8 hours.

[0017] Furthermore, in step S1, the reagents required for the isothermal adsorption experiment include: a supersaturated potassium sulfate solution, methane gas with a purity of 99.99%, helium with a purity of 99.99%, and distilled water.

[0018] Furthermore, in step S2, the shale sample is pretreated before the TOC content determination experiment, and the process is as follows:

[0019] S21. Grind the shale sample into 100-mesh powder using an agate mortar;

[0020] S22, adding shale powder to dilute hydrochloric acid for 2 hours to completely remove inorganic minerals;

[0021] S23, washing the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until it becomes neutral;

[0022] S24. Place the powdered shale sample in a constant temperature drying oven and dry it at 60°C for 24 hours.

[0023] Furthermore, in step S3, the sample is pretreated before the mineral content determination experiment, and the process is as follows:

[0024] S31, washing the shale sample with chloroform as the organic solvent, and treating the sample to a fluorescence level below level 4;

[0025] S32, drying the shale sample after oil washing in a constant temperature drying oven at a temperature of 50°C for 24 hours;

[0026] S33. Grind the shale sample after washing and drying into 100 mesh powder using an agate mortar.

[0027] Furthermore, in step S4, the shale sample is pretreated before the low-temperature nitrogen adsorption experiment is performed on the sample, and the process is as follows:

[0028] S41, washing the shale sample with oil by Soxhlet extraction, using chloroform as the organic solvent, for 12 hours;

[0029] S42, drying the sample after oil washing, the instrument is a constant temperature drying oven, the temperature is 105°C, and the time is 12 hours;

[0030] S43, grinding the shale sample after washing and drying into 80 mesh powder using an agate mortar;

[0031] Furthermore, in step S4, the FHH model is used to calculate the fractal dimension of shale pores, which is expressed by formula (1):

[0032] LnV=KLn(Ln(P0 / P))+C (1);

[0033] In formula (1): P0 is the saturated vapor pressure, MPa; P is the equilibrium pressure, MPa; V is the adsorption volume, cm 3 / g; K is the linear correlation coefficient; C is a constant.

[0034] The fractal dimension is expressed by formula (2):

[0035] D=K+3 (2)

[0036] In formula (2), D is the fractal dimension of shale pores, dimensionless; K is the linear correlation coefficient fitted by formula (1), dimensionless.

[0037] Furthermore, in step S4, two types of fractal dimensions of shale are calculated respectively with relative pressure P / P0=0.5 as the limit, and are recorded as D1 and D2 respectively; fractal dimension D1 is obtained when P / P0<0.5, and fractal dimension D2 is obtained when P / P0>0.5;

[0038] Furthermore, in step S5, the shale surface is polished using argon ions before the backscattering two-dimensional large-area scanning electron microscope experiment.

[0039] Furthermore, in step S6, the biogenic quartz content of the shale sample is calculated by formula (3):

[0040] SiO2-Bio =SiO 2-Sam -(SiO2 / Al2O3) Avg ×Al2O 3-Sam (3)

[0041] In formula (3): SiO 2-Bio is the calculated biogenic quartz content, %; SiO 2-Sam is the quartz content of shale samples, %; (SiO2 / Al2O3) Avg is the average shale SiO2 to Al2O3 ratio in the upper crust, dimensionless; Al2O 3-Sam is the alumina content of shale sample, %.

[0042] The beneficial effects of the present invention are as follows: the present invention screens out a variety of sensitive parameters that affect the development of organic pores, introduces them into the quantitative calculation model of organic pore surface ratio, and realizes the quantitative calculation of organic pore content without 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

[0043] Figure 1 : Cross-plot of total organic carbon TOC and adsorbed gas volume;

[0044] Figure 2 : Cross-plot of clay mineral content and adsorbed gas volume;

[0045] Figure 3 : The cross plot of fractal dimension D2 and adsorbed gas volume;

[0046] Figure 4 : Cross-plot of organic pore surface ratio and adsorbed gas volume;

[0047] Figure 5 : Cross plot of biogenic quartz content and adsorbed gas volume;

[0048] Figure 6 : The cross plot of the adsorbed gas amount calculated by the model and the adsorbed gas amount calculated by the isothermal adsorption experiment. DETAILED DESCRIPTION

[0049] In order to make the technical means and objectives of the present invention easy to understand, the present invention is further described below in combination with a specific implementation method. A method for calculating the adsorbed gas content of shale includes the following steps:

[0050] S1. Conduct isothermal adsorption experiments on shale samples in the study area to obtain the adsorbed gas content of the samples;

[0051] S2. Conduct an organic carbon content measurement experiment on shale samples in the study area to obtain the TOC value of the samples;

[0052] S3. Conduct mineral content analysis experiments on shale samples in the study area to obtain clay mineral content;

[0053] S4. Conduct low-temperature nitrogen adsorption experiments on shale samples in the study area and calculate the fractal dimension;

[0054] S5. Conduct backscattered two-dimensional large-area scanning electron microscopy experiments on shale samples in the study area to obtain the porosity of organic pores;

[0055] S6. Conduct elemental analysis experiments on shale samples in the study area and calculate the biogenic quartz content;

[0056] S7. Taking the adsorbed gas content as the dependent variable, TOC, clay mineral content, fractal dimension, organic pore surface ratio and biogenic quartz content as dependent variables, a shale adsorbed gas content calculation model was established through multivariate linear fitting.

[0057] Reference Figures 1 to 6 , this specific implementation adopts the following technical solution: A method for calculating shale adsorbed gas content, comprising the following steps:

[0058] Step S1: Conduct an isothermal adsorption experiment on the shale samples in the study area to obtain the sample adsorption gas content

[0059] The shale samples of the present invention were taken from the Longmaxi Formation in the Zigong area in the southeastern part of the Sichuan Basin;

[0060] The isothermal adsorption experiment instrument is the RI-HP StaticⅢ isothermal adsorption instrument produced by Beijing Yuanhaiwei Company;

[0061] The parameters of the RI-HP StaticⅢ isothermal adsorption instrument are: the maximum test pressure is 35MPa, the maximum temperature is 150℃, the instrument uses a high-precision magnetic suspension balance with an accuracy of 10μg. The instrument uses a circulating oil bath heating method, and the temperature fluctuation range is less than 0.2℃;

[0062] The shale samples need to be pretreated before the isothermal adsorption experiment. The specific process is as follows:

[0063] (1) Grind the shale sample into 60 mesh powder using an agate mortar;

[0064] (2) The powdered shale sample was placed in a constant temperature drying oven and dried at 105°C for 24 hours;

[0065] (3) The dried shale powder sample was subjected to vacuum degassing treatment at 105°C for 8 hours.

[0066] The reagents required for the isothermal adsorption experiment include: supersaturated potassium sulfate solution, methane gas with a purity of 99.99%, helium with a purity of 99.99%, and distilled water.

[0067] Step S2: Conduct an organic carbon content test on the shale samples in the study area to obtain the TOC value of the samples

[0068] The TOC content determination experimental instrument model is CS744 carbon sulfur analyzer;

[0069] Before the TOC content determination experiment, the shale samples need to be pretreated. The specific process is as follows:

[0070] (1) Grind the shale sample into 100 mesh powder using an agate mortar;

[0071] (2) adding shale powder to dilute hydrochloric acid for 2 hours to completely remove inorganic minerals;

[0072] (3) Rinse the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until it becomes neutral;

[0073] (4) The powdered shale sample was placed in a constant temperature drying oven and dried at 60°C for 24 hours.

[0074] like Figure 1 As shown in Figure 2, TOC content has a good positive correlation with shale adsorbed gas content (R 2 =0.8150), indicating that TOC content can be involved in the calculation model of shale adsorbed gas content.

[0075] Step S3: Conduct mineral content analysis experiments on shale samples in the study area to obtain clay mineral content

[0076] The mineral analysis experiment instrument is a D8 DISCOVER X-ray diffractometer;

[0077] The samples need to be pretreated before the mineral content determination experiment. The specific process is as follows:

[0078] (1) Wash the shale sample with chloroform as the organic solvent and treat it to a fluorescence level below level 4;

[0079] (2) The shale samples after oil washing were dried in a constant temperature drying oven at a temperature of 50°C for 24 hours;

[0080] (3) Use an agate mortar to grind the shale sample after washing and drying into a 100-mesh powder.

[0081] like Figure 2 As shown in Figure 2, the clay mineral content has a good negative correlation with the shale adsorbed gas content (R 2 =0.7659), indicating that clay mineral content can be involved in the calculation model of shale adsorbed gas content.

[0082] Step S4: Conduct low-temperature nitrogen adsorption experiments on shale samples in the study area and calculate the fractal dimension

[0083] The model of the low-temperature nitrogen adsorption experiment instrument is ASAP 2460 surface area / pore size analyzer;

[0084] The temperature of low-temperature nitrogen adsorption experiment is -195.70℃, and the relative pressure is 0.005-1.0 (absolute pressure is 0.0006-0.1112Mpa);

[0085] Before conducting low-temperature nitrogen adsorption experiments on shale samples, the samples need to be pretreated. The specific process is as follows:

[0086] (1) The shale samples were subjected to oil washing treatment by Soxhlet extraction, with chloroform as the organic solvent, for 12 hours;

[0087] (2) Drying the sample after oil washing in a constant temperature drying oven at 105°C for 12 hours;

[0088] (3) Grind the shale sample after washing and drying into 80 mesh powder using an agate mortar;

[0089] The FHH model is used to calculate the fractal dimension of shale pores, which is expressed by formula (1):

[0090] LnV=KLn(Ln(P0 / P))+C (1);

[0091] In formula (1): P0 is the saturated vapor pressure, MPa; P is the equilibrium pressure, MPa; V is the adsorption volume, cm 3 / g; K is the linear correlation coefficient; C is a constant.

[0092] The fractal dimension can be expressed by formula (2):

[0093] D=K+3 (2)

[0094] In formula (2), D is the fractal dimension of shale pores, dimensionless; K is the linear correlation coefficient fitted by formula (1), dimensionless.

[0095] Taking the relative pressure P / P0 = 0.5 as the limit, two types of fractal dimensions of shale are calculated, which are recorded as D1 and D2 respectively;

[0096] When P / P0<0.5, the fractal dimension D1 is obtained, and when P / P0>0.5, the fractal dimension D2 is obtained;

[0097] like Figure 3 As shown in Figure 2, the fractal dimension D2 has a good positive correlation with the shale adsorbed gas content (R 2=0.7682), indicating that the fractal dimension D2 can be involved in the calculation model of shale adsorbed gas content.

[0098] Step S5: Perform a backscattered two-dimensional large-area scanning electron microscope experiment on the shale samples in the study area to obtain the organic pore surface ratio

[0099] The backscattered 2D large-area SEM imaging instrument model is Helios650 / Helios5CX;

[0100] Backscattered 2D large-area SEM imaging is used for samples that need to be observed over a large area, such as shale samples with multi-scale pore structures. A series of continuous and overlapping high-resolution small images are arranged and scanned in the selected area. After scanning, these small images are spliced ​​to obtain an ultra-high-resolution, ultra-large-area 2D backscattered electron image.

[0101] Before the backscattering 2D large-area scanning electron microscopy experiment, the shale surface was polished using argon ions;

[0102] The shale samples treated with argon ion profiling were subjected to large-area backscattering high-resolution imaging detection according to the following steps:

[0103] Sample preparation: A sub-sample with the same diameter as the original sample and a thickness of 2-5 mm was cut from the rock sample, the surface was ion polished, and then a carbon conductive film (thickness of 10-20 nm) was coated on the surface to ensure the conductivity of the sample surface.

[0104] Sample test: Place the prepared sample into the instrument sample chamber, focus, select the backscattering image mode, select the appropriate voltage and beam current value, then set the size of the single small image and the size of the scanning area, and start scanning.

[0105] 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. At the same time, the images are quantitatively analyzed to obtain parameters such as pore size distribution and organic pore surface ratio.

[0106] like Figure 4 As shown in Figure 2, the organic pore surface ratio has a positive correlation with the shale adsorbed gas content (R 2 =0.6371), indicating that the porosity of organic pores can be involved in the calculation model of shale adsorbed gas content.

[0107] Step S6: Conduct major element analysis experiments on shale samples in the study area to calculate the biogenic quartz content

[0108] The main element analysis experimental instrument model is Zetium AB104L / AL104 X-ray fluorescence spectrometer (XRF);

[0109] The biogenic quartz content of shale samples is calculated by formula (3):

[0110] SiO 2-Bio =SiO 2-Sam -(SiO2 / Al2O3) Avg ×Al2O 3-Sam (3)

[0111] In formula (3): SiO 2-Bio is the calculated biogenic quartz content, %; SiO 2-Sam is the quartz content of shale samples, %; (SiO2 / Al2O3) Avg is the average shale SiO2 to Al2O3 ratio in the upper crust, dimensionless; Al2O 3-Sam is the alumina content of shale sample, %.

[0112] The major elements were measured by the alkali fused glass disk method. The specific experimental steps are as follows:

[0113] The shale samples were ground into 200 mesh powder using an agate mortar;

[0114] The powdered shale sample was placed in a ceramic crucible and calcined at 1000°C for 1 hour to test the weight loss of the sample.

[0115] Weigh 1g of the calcined shale powder sample to be tested, add 6g of anhydrous lithium tetraborate, mix evenly in a ceramic crucible, and heat to 1050°C to make the required molten glass sheet;

[0116] The measurement was carried out on an X-ray fluorescence spectrometer (XRF). Except for nickel, copper, strontium and zirconium, which used Compton scattered rays as internal standards to correct the matrix effect, the absorption-enhancement effect between elements was corrected by theoretical α coefficients for the other analyzed elements. The amount of the main and minor components was calculated based on the fluorescence intensity.

[0117] like Figure 5 As shown in Figure 2, the biogenic quartz content has a good positive correlation with the shale adsorbed gas content (R 2 =0.819), indicating that the biogenic quartz content can be involved in the calculation model of shale adsorbed gas content.

[0118] Step S7: Taking the adsorbed gas content as the dependent variable, TOC, clay mineral content, fractal dimension, organic pore surface ratio and biogenic quartz content as the dependent variables, a shale adsorbed gas content calculation model is established through multivariate linear fitting.

[0119] As shown in Table 1: TOC content, clay mineral content, fractal dimension D2, organic pore porosity, biogenic quartz content, adsorbed gas content of isothermal adsorption experiment, adsorbed gas content calculated by the model, and relative error calculated by various experiments;

[0120] Table 1

[0121]

[0122] The calculation model of shale adsorbed gas content can be expressed by formula (1):

[0123] Shale adsorbed gas content = 0.2006 × TOC - 0.0283 × clay content + 20.62 × D2 - 0.1642 × organic pore porosity + 0.0464 × biogenic quartz content - 51.96 (1)

[0124] like Figure 6 As shown in Figure 2, the adsorbed gas content calculated by the model has a strong correlation with the adsorbed gas content in the isothermal adsorption experiment (R 2 =0.9905), with a relative error of only 0.1%, indicating that the calculation model provided by the example of the present invention has a high accuracy.

[0125] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for calculating shale adsorbed gas content, characterized in that: The steps include: S1. Conduct isothermal adsorption experiments on shale samples in the study area to obtain the adsorbed gas content of the samples; S2. Conduct an organic carbon content measurement experiment on shale samples in the study area to obtain the TOC value of the samples; S3. Conduct mineral content analysis experiments on shale samples in the study area to obtain clay mineral content; S4. Conduct low-temperature nitrogen adsorption experiments on shale samples in the study area and calculate the fractal dimension; S5. Conduct backscattered two-dimensional large-area scanning electron microscopy experiments on shale samples in the study area to obtain the porosity of organic pores; S6. Conduct elemental analysis experiments on shale samples in the study area and calculate the biogenic quartz content; S7. Taking the adsorbed gas content as the dependent variable, TOC, clay mineral content, fractal dimension, organic pore surface ratio and biogenic quartz content as dependent variables, a shale adsorbed gas content calculation model was established through multivariate linear fitting.

2. The method for calculating shale adsorbed gas content according to claim 1, characterized in that: In step S1, the shale sample is pretreated before the isothermal adsorption experiment, and the process is as follows: S11. Grind the shale sample into 60 mesh powder using an agate mortar; S12, placing the powdered shale sample in a constant temperature drying oven and drying it at 105° C. for 24 hours; S13. Under the condition of 105°C, the dried shale powder sample was subjected to vacuum degassing treatment for 8 hours.

3. The method for calculating shale adsorbed gas content according to claim 1, characterized in that: In the step S1, the reagents required for the isothermal adsorption experiment include: a supersaturated potassium sulfate solution, methane gas with a purity of 99.99%, helium with a purity of 99.99%, and distilled water.

4. The method for calculating shale adsorbed gas content according to claim 1, characterized in that: In step S2, the shale sample is pretreated before the TOC content determination experiment, and the process is as follows: S21. Grind the shale sample into 100-mesh powder using an agate mortar; S22, adding shale powder to dilute hydrochloric acid for 2 hours to completely remove inorganic minerals; S23, washing the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until it becomes neutral; S24. Place the powdered shale sample in a constant temperature drying oven and dry it at 60°C for 24 hours.

5. The method for calculating shale adsorbed gas content according to claim 1, characterized in that: In step S3, the sample is pre-treated before the mineral content determination experiment, and the process is as follows: S31, washing the shale sample with chloroform as the organic solvent, and treating the sample to a fluorescence level below level 4; S32, drying the shale sample after oil washing in a constant temperature drying oven at a temperature of 50°C for 24 hours; S33. Grind the shale sample after washing and drying into 100 mesh powder using an agate mortar.

6. The method for calculating shale adsorbed gas content according to claim 1, characterized in that: In step S4, the shale sample is pretreated before the low-temperature nitrogen adsorption experiment is performed on the sample, and the process is as follows: S41, washing the shale sample with oil by Soxhlet extraction, using chloroform as the organic solvent, for 12 hours; S42, drying the sample after oil washing, the instrument is a constant temperature drying oven, the temperature is 105°C, and the time is 12 hours; S43. Grind the shale sample after oil washing and drying into 80 mesh powder using an agate mortar.

7. The method for calculating shale adsorbed gas content according to claim 1, characterized in that: In step S4, the FHH model is used to calculate the fractal dimension of shale pores, which is expressed by formula (1): LnV=KLn(Ln(P0 / P))+C (1); In formula (1): P0 is the saturated vapor pressure, MPa; P is the equilibrium pressure, MPa; V is the adsorption volume, cm 3 / g; K is the linear correlation coefficient; C is a constant, The fractal dimension is expressed by formula (2): D=K+3 (2) In formula (2), D is the fractal dimension of shale pores, dimensionless; K is the linear correlation coefficient fitted by formula (1), dimensionless.

8. The method for calculating shale adsorbed gas content according to claim 1, characterized in that: In step S4, two types of fractal dimensions of shale are calculated respectively with relative pressure P / P0=0.5 as the limit, and are recorded as D1 and D2 respectively; fractal dimension D1 is obtained when P / P0<0.5, and fractal dimension D2 is obtained when P / P0>0.

5.

9. The method for calculating shale adsorbed gas content according to claim 1, characterized in that: In step S5, the shale surface is polished using argon ions before the backscattering two-dimensional large-area scanning electron microscope experiment.

10. The method for calculating shale adsorbed gas content according to claim 1, characterized in that: In step S6, the biogenic quartz content of the shale sample is calculated by formula (3): Not. 2-Bio =No 2-Sam -(SiO2 / Al2O3) Avg ×Al2O 3-Sam (3) In formula (3): SiO 2-Bio is the calculated biogenic quartz content, %; SiO 2-Sam is the quartz content of shale samples, %; (SiO2 / Al2O3) Avg is the average shale SiO2 to Al2O3 ratio in the upper crust, dimensionless; Al2O 3-Sam is the alumina content of shale sample, %.

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