A shale adsorbed gas content calculation method

Abstract

The application discloses a shale adsorbed gas content calculation method, and belongs to the technical field of shale oil and gas resource evaluation, and comprises the following steps: obtaining sample adsorbed gas content by performing isothermal adsorption experiment; obtaining sample TOC value by performing organic carbon content determination experiment; obtaining clay mineral content by performing mineral content analysis experiment; obtaining fractal dimension by performing low-temperature nitrogen adsorption experiment; obtaining organic pore surface porosity by performing backscattering two-dimensional large-area scanning electron microscope experiment; performing element analysis experiment on shale samples in a research area to obtain biological quartz content; and establishing a shale adsorbed gas content calculation model by taking adsorbed gas content as a dependent variable, taking TOC, clay mineral content, fractal dimension, organic pore surface porosity and biological quartz content as dependent variables, and performing multiple linear fitting. The application realizes quantitative calculation of organic pore content under the condition that a scanning electron microscope is not available by screening a plurality of sensitive parameters which have influence on development of organic pores and introducing the sensitive parameters into a quantitative calculation model of the organic pore surface porosity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of shale oil and gas resource evaluation, and particularly relates to a shale adsorbed gas content calculation method. BACKGROUND

[0002] The occurrence state of shale gas in shale reservoir mainly includes three kinds, namely adsorbed gas, free gas and dissolved gas. The adsorbed gas is mainly attached to the surface of organic matter and clay mineral particles, and the proportion is usually more than 50%; the free gas is mainly present in the micro-nano pore system and micro-cracks, and the proportion is usually 20%-30%; the dissolved gas is shale gas dissolved in casein and asphaltene, and the proportion is usually less than 10%. In the shale gas production process, the free gas is first produced, and at the same time, with the decrease of formation pressure, the adsorbed gas continues to be released and desorbed, and the released adsorbed gas is produced together with the free gas to form the gas well productivity, and the contribution of the dissolved gas to the shale gas well productivity can be ignored. Shale gas production is a dynamic process of free gas release-adsorbed gas desorption-free gas release. Therefore, the calculation of shale adsorbed gas content is an important parameter for resource evaluation and favorable target optimization in shale gas exploration and development.

[0003] However, due to the various occurrence states of shale gas, both adsorbed gas and free gas exist, and dynamic conversion and mixed flow exist between them in the shale gas development process. The adsorbed gas released by desorption and the free gas have no essential difference in nature, and the respective proportions change constantly during production, so that it is very difficult to calculate the shale adsorbed gas content, which brings great trouble to the development and research of shale gas reservoirs.

[0004] At present, the adsorbed gas content is mainly tested by isothermal adsorption experiment, and this method has the defect of complex experimental operation, and whether the adsorbed gas content can be accurately obtained depends largely on the experience of the experimental personnel. Therefore, it is necessary to invent a new method to replace the isothermal adsorption experiment. SUMMARY

[0005] In order to solve the above problems, the application provides a shale adsorbed gas content calculation method, which comprises the following steps:

[0006] S1, performing isothermal adsorption experiment on shale samples in a research area to obtain the adsorbed gas content of the samples;

[0007] S2, performing organic carbon content determination experiment on the shale samples in the research area to obtain the TOC value of the samples;

[0008] S3, performing mineral content analysis experiment on the shale samples in the research area to obtain the clay mineral content;

[0009] S4, performing low-temperature nitrogen adsorption experiment on the shale samples in the research area to calculate and obtain the fractal dimension;

[0010] S5, carry out backscattered two-dimensional large-area scanning electron microscopy experiment on shale samples in the study area to obtain organic pore surface porosity;

[0011] S6, carry out element analysis experiment on shale samples in the study area to calculate and obtain biogenic quartz content;

[0012] S7, taking adsorbed gas content as dependent variable, TOC, clay mineral content, fractal dimension, organic pore surface porosity and biogenic quartz content as independent variables, establishing shale adsorbed gas content calculation model through multiple linear fitting.

[0013] Further, in the 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 a agate mortar;

[0015] S12, place the powdered shale sample in a constant temperature drying oven and dry at 105℃ for 24 hours;

[0016] S13, under the condition of 105℃, vacuum degassing treatment is carried out on the dried shale powder sample for 8 hours.

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

[0018] Further, in the 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 a agate mortar;

[0020] S22, add the shale powder to dilute hydrochloric acid and react for 2 hours to completely remove inorganic minerals;

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

[0022] S24, place the powdered shale sample in a constant temperature drying oven and dry at 60℃ for 24 hours.

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

[0024] S31, wash the shale sample with oil, and the organic solvent used for oil washing is chloroform, and the treatment is carried out until the fluorescence is below grade four;

[0025] S32, drying the shale sample after washing oil by using constant temperature drying oven, temperature is 50℃, time is 24 hours;

[0026] S33, grinding the shale sample after drying by using agate mortar into 100 mesh powder.

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

[0028] S41, washing oil treatment is performed on the shale sample by using Soxhlet extraction method, the organic solvent is chloroform, and the time is 12 hours;

[0029] S42, drying treatment is performed on the sample after washing oil by using constant temperature drying oven, the temperature is 105℃, and the time is 12 hours;

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

[0031] Further, in the step S4, FHH model is used to calculate the fractal dimension of shale pore, which is represented 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 the constant.

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

[0035] D=K+3 (2)

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

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

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

[0039] Further, in the 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] Formula (3): SiO 2-Bio is the calculated biogenic quartz content, %; SiO 2-Sam is the quartz content of the shale sample, %; (SiO2 / Al2O3) Avg is the average shale SiO2 to Al2O3 ratio of the upper crust, dimensionless; Al2O 3-Sam is the alumina content of the shale sample, %.

[0042] The present application has the beneficial effects that: the present application introduces a plurality of sensitive parameters which have an influence on the development of organic pores into a quantitative calculation model of the organic pore surface porosity, so as to realize the quantitative calculation of the organic pore content without a scanning electron microscope, and the key parameter of the biogenic quartz content is included in the quantitative calculation model of the organic pore, so as to effectively improve the calculation accuracy of the model. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 : total organic carbon TOC and adsorbed gas amount crossplot;

[0044] Figure 2 : clay mineral content and adsorbed gas amount crossplot;

[0045] Figure 3 : fractal dimension D2 and adsorbed gas amount crossplot;

[0046] Figure 4 : organic pore surface porosity and adsorbed gas amount crossplot;

[0047] Figure 5 : biogenic quartz content and adsorbed gas amount crossplot;

[0048] Figure 6 : model calculated adsorbed gas amount and isotherm adsorption experiment calculated adsorbed gas amount crossplot. DETAILED DESCRIPTION

[0049] In order to make the technical means adopted by the present application and the purposes easy to understand, the present application is further described below in combination with specific embodiments, a shale adsorbed gas content calculation method, comprising the following steps:

[0050] S1, performing isotherm adsorption experiment on the shale samples in the study area to obtain the sample adsorbed gas content;

[0051] S2, performing organic carbon content determination experiment on the shale samples in the study area to obtain the sample TOC value;

[0052] S3, mineral content analysis experiment is carried out on shale samples in the research area to obtain clay mineral content;

[0053] S4, low-temperature nitrogen adsorption experiment is carried out on shale samples in the research area to calculate and obtain fractal dimension;

[0054] S5, backscattered two-dimensional large-area scanning electron microscope experiment is carried out on shale samples in the research area to obtain organic pore surface porosity;

[0055] S6, element analysis experiment is carried out on shale samples in the research area to calculate and obtain biogenic quartz content;

[0056] S7, taking adsorbed gas content as the dependent variable, taking TOC, clay mineral content, fractal dimension, organic pore surface porosity and biogenic quartz content as the independent variable, a shale adsorbed gas content calculation model is established through multiple linear fitting.

[0057] Referring to Figures 1 to 6 , the specific embodiment adopts the following technical scheme: a shale adsorbed gas content calculation method, comprising the following steps:

[0058] Step S1: isothermal adsorption experiment is carried out on shale samples in the research area to obtain sample adsorbed gas content

[0059] The shale sample in the example of the present application is taken from the Longmaxi Formation in Zigong area in the southeast of Sichuan Basin;

[0060] The isothermal adsorption experiment instrument is R-I-HP Static III type isothermal adsorption instrument produced by Beijing Yuanhaiwei Company;

[0061] The parameters of the R-I-HP Static III type isothermal adsorption instrument are: the highest test pressure is 35 MPa, the highest temperature is 150 DEG C, the instrument adopts high-precision magnetic suspension balance, and the precision is 10 mu g. The instrument adopts circulating oil bath heating mode, and the temperature fluctuation range is less than 0.2 DEG C;

[0062] Before the isothermal adsorption experiment, the shale sample needs to be pretreated, and the specific process is as follows:

[0063] (1) use agate mortar to grind the shale sample into 60 mesh powder;

[0064] (2) place the powder shale sample in a constant temperature drying oven, and dry at 105 DEG C for 24 hours;

[0065] (3) under the condition of 105 DEG C, the vacuum degassing treatment is carried out on the dried shale powder sample, and the time is 8 hours.

[0066] The reagents required for the isothermal adsorption experiment include: potassium sulfate supersaturated 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 determination experiment on shale samples from the study area to obtain the TOC value of the samples.

[0068] The instrument used for TOC content determination was a CS744 carbon and sulfur analyzer.

[0069] The shale sample needs to be pretreated before the TOC content determination experiment. The specific procedure is as follows:

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

[0071] (2) Add shale powder to dilute hydrochloric acid and react 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 neutral;

[0073] (4) Place the powdered shale sample in a constant temperature drying oven and dry it at 60°C for 24 hours.

[0074] like Figure 1 As shown, TOC content and shale adsorbed gas content have a strong positive correlation (RT). 2 =0.8150), indicating that TOC content can be included in the calculation model of shale adsorbed gas content.

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

[0076] The mineral analysis experiment was conducted using a D8 DISCOVER X-ray diffractometer.

[0077] Before conducting mineral content determination experiments, sample pretreatment is required. The specific procedure is as follows:

[0078] (1) The shale samples were washed with oil using chloroform as the organic solvent, and the treatment was carried out until the fluorescence level was below level four;

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

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

[0081] like Figure 2 As shown, there is a strong negative correlation between clay mineral content and shale adsorbed gas content (R0). 2 =0.7659), indicating that clay mineral content can be included in the calculation model of shale adsorbed gas content.

[0082] Step S4: Perform low-temperature nitrogen adsorption experiment on the shale sample in the study area to calculate the fractal dimension

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

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

[0085] Before performing the low-temperature nitrogen adsorption experiment on the shale sample, the sample needs to be pretreated, and the specific process is as follows:

[0086] (1) The shale sample is treated with oil, and the method is Soxhlet extraction, the organic solvent is chloroform, and the time is 12 hours;

[0087] (2) The sample after oil washing is dried, the instrument is a constant temperature drying oven, the temperature is 105°C, and the time is 12 hours;

[0088] (3) The shale sample after oil drying is ground into 80-mesh powder using a maroon mortar;

[0089] The FHH model is used to calculate the fractal dimension of the shale pore, which is represented 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 the constant.

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

[0093] D=K+3 (2)

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

[0095] Take the relative pressure P / P0=0.5 as the boundary to calculate two types of fractal dimensions of the shale, respectively denoted as D1 and D2;

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

[0097] As Figure 3 shown, 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 included in the calculation model of shale adsorbed gas content.

[0098] Step S5: Perform backscattered two-dimensional large-area scanning electron microscopy experiments on shale samples from the study area to obtain the porosity of organic pores.

[0099] The backscatter two-dimensional large-area scanning electron microscope imaging instrument is model Helios650 / Helios5CX;

[0100] Backscattered two-dimensional large-area scanning electron microscopy (SEM) is used for samples that require large-area observation, such as shale samples with multi-scale porosity. A series of continuous and overlapping high-resolution small images are arranged and scanned in a selected area. After scanning, these small images are stitched together to obtain an ultra-high resolution, ultra-large area two-dimensional backscattered electron image.

[0101] Argon ions were used to perform a backscattering two-dimensional large-area scanning electron microscope experiment to polish the shale surface.

[0102] The shale samples after argon ion spectroscopy were subjected to large-area backscatter high-resolution imaging detection according to the following steps.

[0103] 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, perform ion polishing on the surface, and then deposit a carbon conductive film (10-20 nm thick) on the surface to ensure the conductivity of the sample surface.

[0104] Sample testing: Place the prepared sample into the instrument's sample chamber, focus, select the backscatter image mode, select the appropriate voltage and beam current values, 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 image acquisition, all resulting images are input into image processing software for combination and stitching. At the same time, quantitative analysis is performed on the images to obtain parameters such as pore size distribution and organic porosity.

[0106] like Figure 4 As shown, the porosity of organic pores is positively correlated with the adsorbed gas content in shale (R0). 2 =0.6371), indicating that the porosity of organic pores can be included in the calculation model of shale adsorbed gas content.

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

[0108] The major element analysis instrument was a Zetium AB104L / AL104 X-ray fluorescence spectrometer (XRF).

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

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

[0111] In formula (3): SiO 2-Bio The calculated bio-quartz content is %; SiO2 2-Sam The quartz content of the shale sample is expressed as % (SiO2 / Al2O3). Avg The ratio of SiO2 to Al2O3 in the average upper crustal shale is dimensionless; Al2O3 3-Sam The alumina content of the shale sample is %.

[0112] Major elements were determined by the alkali fusion glass slide method. The specific experimental steps are as follows:

[0113] The shale sample was ground into 200-mesh powder using an agate mortar and pestle.

[0114] The powdered shale sample was placed in a ceramic crucible and calcined at 1000℃ for 1 hour. The weight reduction of the sample was then measured.

[0115] Weigh 1g of the calcined shale powder sample to be tested, add 6g of anhydrous lithium tetraborate and mix evenly in a ceramic crucible, and heat to 1050℃ to prepare the required molten glass slide.

[0116] Measurements were performed on an X-ray fluorescence spectrometer (XRF). Except for nickel, copper, strontium, and zirconium, which were corrected for matrix effects using Compton scattering as internal standards, the absorption-enhancement effects between elements were corrected using theoretical α coefficients for all other analytical elements. The amounts of the primary and secondary components were calculated based on the fluorescence intensity.

[0117] like Figure 5 As shown, the content of biogenic quartz and the content of adsorbed gas in shale have a strong positive correlation (Rb). 2 =0.819), indicating that the biogenic quartz content can be included in the calculation model of shale adsorbed gas content.

[0118] Step S7: Using adsorbed gas content as the dependent variable and TOC, clay mineral content, fractal dimension, organic porosity, and biogenic quartz content as independent variables, a multivariate linear fitting model is established to calculate the adsorbed gas content of shale.

[0119] Table 1 shows the TOC content, clay mineral content, fractal dimension D2, organic porosity, bio-quartz content, adsorbed gas content from isothermal adsorption experiments, adsorbed gas content calculated from models, and relative errors, calculated through various experiments.

[0120] Table 1

[0121]

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

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

[0124] like Figure 6 As shown, the model-calculated adsorbed gas content has a very strong correlation with the adsorbed gas content in the isothermal adsorption experiment (R0). 2 =0.9905), with a relative error of only 0.1%, indicating that the calculation model provided by the present invention has high accuracy.

[0125] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for calculating the adsorbed gas content in shale, characterized in that, Includes the following steps: S1. Conduct isothermal adsorption experiments on shale samples from the study area to obtain the adsorbed gas content of the samples; S2. Conduct organic carbon content determination experiments on shale samples from the study area to obtain the TOC values ​​of the samples; S3. Conduct mineral content analysis experiments on shale samples from the study area to obtain the clay mineral content; S4. Conduct low-temperature nitrogen adsorption experiments on shale samples from the study area and calculate the fractal dimension. S5. Backscatter two-dimensional large-area scanning electron microscopy experiments were conducted on shale samples from the study area to obtain the porosity of organic pores. S6. Conduct elemental analysis experiments on shale samples from the study area to calculate and obtain the biogenic quartz content; S7. Using adsorbed gas content as the dependent variable and TOC, clay mineral content, fractal dimension, organic porosity, and bio-quartz content as independent variables, a multivariate linear fitting model for calculating shale adsorbed gas content was established.

2. The method for calculating the adsorbed gas content in shale 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 and pestle; S12. Place the powdered shale sample in a constant temperature drying oven and dry it at 105℃ for 24 hours. Under conditions of S13 and 105℃, the dried shale powder sample was subjected to vacuum degassing for 8 hours.

3. The method for calculating the adsorbed gas content in shale according to claim 1, characterized in that, 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 gas with a purity of 99.99%, and distilled water.

4. The method for calculating the adsorbed gas content in shale according to claim 1, characterized in that, In step S2, the shale samples are pretreated before the TOC content determination experiment. The procedure is as follows: S21. Grind the shale sample into 100-mesh powder using an agate mortar and pestle; S22. Add shale powder to dilute hydrochloric acid and react for 2 hours to completely remove inorganic minerals. S23. Rinse the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until 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 the adsorbed gas content in shale as described in claim 1, characterized in that, In step S3, the sample is pretreated before the mineral content determination experiment, and the process is as follows: S31. Wash the shale sample with oil using chloroform as the organic solvent, and treat until the fluorescence level is below level four. S32. The shale samples after washing oil were dried in a constant temperature drying oven at 50℃ for 24 hours. S33. Use an agate mortar to grind the washed and dried shale sample into 100-mesh powder.

6. The method for calculating the adsorbed gas content in shale according to claim 1, characterized in that, In step S4, the shale sample is pretreated before the low-temperature nitrogen adsorption experiment. The procedure is as follows: S41. The shale sample was washed with oil using Soxhlet extraction with chloroform as the organic solvent for 12 hours. S42. The sample after washing with oil is dried using a constant temperature drying oven at 105℃ for 12 hours. S43. Use an agate mortar to grind the washed and dried shale sample into 80-mesh powder.

7. The method for calculating the adsorbed gas content in shale according to claim 1, characterized in that, In step S4, the fractal dimension of shale pores is calculated using the FHH model, as 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, cm³. 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, which is dimensionless; K is the linear correlation coefficient fitted by formula (1), which is dimensionless.

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

5.

9. The method for calculating the adsorbed gas content in shale according to claim 1, characterized in that, In step S5, the shale surface is subjected to argon ion beam processing before the backscattered two-dimensional large-area scanning electron microscope experiment.

10. The method for calculating the adsorbed gas content in shale according to claim 1, characterized in that, In step S6, the biogenic quartz content of the shale sample is calculated using formula (3): Not. 2-Bio = SiO 2-Sam -(SiO2 / Al2O3) Avg ×Al2O 3-Sam (3) In formula (3): SiO 2-Bio The calculated bio-quartz content is %; SiO2 2-Sam The quartz content of the shale sample is expressed as % (SiO2 / Al2O3). Avg The ratio of SiO2 to Al2O3 in the average upper crustal shale is dimensionless; Al2O3 3-Sam The alumina content of the shale sample is %.

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