Shale gas reservoir classification evaluation method

Abstract

The invention relates to a shale gas reservoir classification evaluation method, and belongs to the technical field of shale oil and gas resource evaluation. The method comprises the following specific steps: obtaining the total gas content GTot, the total organic carbon TOC value, the quartz content SiO2-Bio and the organic pore surface porosity POrg of a sample; obtaining pore volumes in different pore diameter ranges; respectively drawing intersection curves of pore volumes in different pore diameter ranges and GTot, TOC, SiO2-Bio and POrg, and determining intersection points of the intersection curves; and classifying the shale gas reservoir according to the GTot value, the TOC value, the SiO2-Bio value and the POrg value corresponding to the intersection points. According to the method, different types of pore volumes and shale gas-bearing master control parameters are brought into a shale gas reservoir classification evaluation scheme for the first time, the microscopic heterogeneity of the shale gas reservoir and the influence on the gas-bearing property of the shale gas reservoir are comprehensively and accurately represented, and the method has good applicability to the shale gas reservoir with a complex pore structure; and scientific guidance can be provided for shale gas dessert optimization and development scheme compilation.

Description

Technical Field

[0001] The present invention relates to a shale gas reservoir classification evaluation method, belonging to the technical field of shale oil and gas resource evaluation. Background Art

[0002] Shale gas reservoirs typically undergo complex tectonic and diagenetic evolution during their formation, resulting in significant reservoir heterogeneity, leading to unclear key factors controlling reservoir gas content. Efficiently and rapidly identifying shale gas "sweet spots" has become a crucial research topic, hindering shale gas exploration and development. Reservoir classification and evaluation is a key step in shale gas exploration and development, and is crucial for scientifically guiding the selection of shale gas "sweet spots."

[0003] On October 16, 2023, Zhang Linlin, Wang Kongjie, Lai Fengpeng and others published a paper on the classification and evaluation of sweet spots in marine shale gas reservoirs in the Ordos Basin in the Journal of Experimental Petroleum Geology. The paper analyzed the influence of different factors on the evaluation and optimization of sweet spots in marine shale gas reservoirs in the Ordos Basin, and clarified that the content of silica minerals, clay minerals, pore specific surface area, total organic carbon content TOC and vitrinite reflectance Ro control the adsorption capacity of shale gas, the pore size and pore number control the storage capacity of shale, and the brittle mineral content and rock mechanics parameters control the compressibility of the reservoir. Based on the above geological Sweet spot evaluation parameters and engineering sweet spot compressibility parameters were used to preliminarily establish a classification and evaluation scheme for shale gas reservoirs; Chen Xiangyang, Chen Meijun, Rui Yun and others published a paper on the detailed evaluation of shale gas reservoir logging in the Journal of Well Logging Technology on December 20, 2022. The paper started from the logging response of shale gas reservoirs, comprehensively considered multiple factors such as geology, reservoirs, and gas reservoirs, and combined with core analysis data to establish a detailed evaluation method for shale gas reservoirs based on parameters such as sedimentary environment, lithology and facies, total organic carbon content, physical properties, gas content, degree of fracture and bedding development, stress state, and pore pressure coefficient.

[0004] The invention patent with authorization announcement number CN112855126 B provides a classification method, device and storage medium for shale gas reservoirs. The method constructs a shale gas reservoir quality coefficient based on total organic carbon (TOC), porosity, total gas content and brittleness index, and classifies shale gas reservoirs according to the relationship between the reservoir quality coefficient and the gas recovery index.

[0005] In summary, while the above methods provide shale gas reservoir classification and evaluation schemes from various perspectives, none address the strong heterogeneity of shale gas reservoirs and provide a method that can both describe the microscopic pore structure heterogeneity of shale gas reservoirs and characterize the gas content of shale. Therefore, it is necessary to seek a new method for shale gas reservoir classification and evaluation that incorporates the microscopic pore structure heterogeneity of shale gas reservoirs and its relationship with shale gas content into the reservoir classification and evaluation scheme, thereby scientifically guiding the efficient development of shale gas. Summary of the Invention

[0006] The present invention discloses a shale gas reservoir classification and evaluation method, which provides scientific guidance for shale gas resource evaluation and sweet spot selection.

[0007] The technical solution adopted by the present invention is: a shale gas reservoir classification and evaluation method, the specific steps are as follows:

[0008] Step 1: Conduct on-site gas content measurement experiments on shale samples to obtain the total gas content G of the samples. Tot ;

[0009] Step 2: Conduct an indoor total organic carbon content measurement experiment on the shale sample to obtain the total organic carbon TOC value of the sample;

[0010] Step 3: Conduct indoor major element determination experiments on shale samples to calculate the biogenic quartz content SiO2 in the samples -Bio ;

[0011] Step 4: Conduct indoor scanning electron microscopy experiments on shale samples to calculate the organic pore porosity P of the samples. Org ;

[0012] Step 5: Conduct low-temperature CO2 and low-temperature N2 adsorption experiments on shale samples to obtain pore volumes in different pore size ranges;

[0013] Step 6: Calculate the pore volume and G of different pore size ranges respectively Tot , TOC, SiO2 -Bio and P Org The intersection curve of the intersection curve is determined;

[0014] Step 7: According to the G corresponding to the intersection Tot , TOC, SiO2 -Bio and P Org The values ​​are used to classify shale gas reservoirs.

[0015] Furthermore, in the step 1, specifically: the standard process of the on-site gas content determination experiment is carried out in accordance with the petroleum and natural gas industry standard SY / T 6940-2020 "Shale Gas Content Determination Method";

[0016] Furthermore, the total gas content G in step 1 Tot Calculated by formula 1:

[0017] G Tot =G Ds +G Rs +G Ls (1)

[0018] Where: G Ds , G Rs , GLs Respectively, the decomposed gas content, residual gas content and loss gas content, cm 3 / g.

[0019] Furthermore, in step 2, the shale sample needs to be pretreated before the total organic carbon content determination experiment. The specific process is as follows:

[0020] (1) Grind the shale sample into 100-mesh powder using an agate mortar;

[0021] (2) adding shale powder to dilute hydrochloric acid for 2 hours to completely remove inorganic minerals;

[0022] (3) Rinse the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until it becomes neutral;

[0023] (4) The powdered shale sample was placed in a constant temperature drying oven and dried at 60°C for 24 hours.

[0024] Furthermore, in step 3, the bioquartz content of the shale sample is SiO2 -Bio Calculated by formula 2:

[0025] SiO 2-Bio =SiO 2-Sam -(SiO2 / Al2O3) Avg ×Al2O 3-Sam (2)

[0026] Where: SiO 2-Bio is the calculated bioquartz 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, %.

[0027] Furthermore, in step 4, specifically, before the scanning electron microscope experiment, the shale surface is polished using argon ions.

[0028] Furthermore, in step 5, the shale samples need to be pretreated before the low-temperature CO2 and low-temperature N2 adsorption experiments are performed on them. The specific process is as follows:

[0029] (1) The shale samples were subjected to oil washing treatment using the Soxhlet extraction method with chloroform as the organic solvent for 12 hours;

[0030] (2) Dry the oil-washed samples in a constant temperature drying oven at 105°C for 12 hours;

[0031] (3) Use an agate mortar to grind the dried shale sample after washing oil into a powder with a mesh size of 80.

[0032] Further, in the step 5, to obtain the pore volumes in different pore size ranges, the different pore sizes respectively refer to: micropores (r < 2 nm), mesopores (2 < r < 50 nm), and macropores (r > 50 nm).

[0033] Further, in the step 5, the micropore volume is obtained through a low-temperature CO2 adsorption experiment, and the mesopore and macropore volumes are obtained through a low-temperature N2 adsorption experiment.

[0034] The present invention discloses a classification and evaluation method for shale gas reservoirs. The beneficial effect is that compared with the prior art, for the first time, the present invention incorporates different types of pore volumes and the main controlling parameters of shale gas content into the classification and evaluation scheme for shale gas reservoirs, comprehensively and accurately characterizing the microscopic heterogeneity of shale gas reservoirs and its influence on gas content, having good applicability to shale gas reservoirs with complex pore structures, and can provide scientific guidance for the optimization of shale gas sweet spots and the formulation of development plans. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 Shown is the total gas content G Tot Crossplot with pore volumes in different pore size ranges;

[0037] Figure 2 Shown is the crossplot of total organic carbon TOC with pore volumes in different pore size ranges;

[0038] Figure 3 Shown is the content of biogenic quartz SiO2 -Bio Crossplot with pore volumes in different pore size ranges;

[0039] Figure 4 Shown is the organic pore surface area ratio P Org Crossplot with pore volumes in different pore size ranges.

[0040] SPECIFIC IMPLEMENTATION METHODS

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0042] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention, its application, or use. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention. Example 1

[0043] This embodiment provides a shale gas reservoir classification and evaluation method based on shale gas reservoir samples in a certain oil field study area. The specific steps are as follows:

[0044] Step 1: Conduct on-site gas content measurement experiments on shale samples to obtain the total gas content G of the samples. Tot ;

[0045] Specifically, the standard process for on-site gas content determination experiments is carried out in accordance with the petroleum and natural gas industry standard SY / T 6940-2020 "Shale Gas Content Determination Method"; the on-site gas content determination experiment instrument model is: CQJC-QT-2 shale gas and coalbed methane gas content test system;

[0046] Furthermore, the total gas content G in step 1 Tot Calculated by formula 1:

[0047] G Tot =G Ds +G Rs +G Ls (1)

[0048] Where: G Ds , G Rs , G Ls Respectively, the decomposed gas content, residual gas content and loss gas content, cm 3 / g.

[0049] Step 2: Conduct an indoor total organic carbon content measurement experiment on the shale sample to obtain the total organic carbon TOC value of the sample;

[0050] Specifically, the instrument model for the total organic carbon content determination experiment is: CS744 carbon-sulfur analyzer; before the total organic carbon content determination experiment, the shale sample needs to be pretreated. The specific process is as follows:

[0051] (1) Grind the shale sample into 100-mesh powder using an agate mortar;

[0052] (2) adding shale powder to dilute hydrochloric acid for 2 hours to completely remove inorganic minerals;

[0053] (3) Rinse the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until it becomes neutral;

[0054] (4) The powdered shale sample was placed in a constant temperature drying oven and dried at 60°C for 24 hours.

[0055] Step 3: Conduct indoor major element determination experiments on shale samples to calculate the biogenic quartz content SiO2 in the samples -Bio ;

[0056] The main element analysis experimental instrument model is: ZetiumAB104L / AL104 X-ray fluorescence spectrometer (XRF);

[0057] The major elements were measured by the alkali-fused glass disc method. The specific experimental steps are as follows:

[0058] The shale samples were ground into 200-mesh powder using an agate mortar;

[0059] The powdered shale sample was placed in a ceramic crucible and calcined at 1000°C for 1 hour to measure the weight loss of the sample.

[0060] 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 add

[0061] Heat to 1050℃ to make the required molten glass sheet;

[0062] Measurements were performed on an X-ray fluorescence spectrometer (XRF). Compton scattered radiation was used as an internal standard to correct for matrix effects for nickel, copper, strontium, and zirconium. The theoretical α coefficients were used to correct for interelement absorption-enhancement effects for the remaining analyzed elements. The amounts of major and minor components were calculated based on the fluorescence intensity.

[0063] The content of SiO in shale samples 2-Bio Calculated by formula 2:

[0064] SiO 2-Bio =SiO 2-Sam -(SiO2 / Al2O3) Avg ×Al2O 3-Sam (2)

[0065] Where: SiO 2-Bio is the calculated bioquartz 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; Al2O3-Sam is the alumina content of shale sample, %.

[0066] Step 4: Conduct indoor scanning electron microscopy experiments on shale samples to calculate the organic pore porosity P of the samples. Org ;

[0067] Before the SEM experiment, the shale surface was polished using argon ions;

[0068] Scanning electron microscope experimental instrument model: Leica TIX / Thermo Fisher Helios650 / 5CX;

[0069] The shale samples treated with argon ion profiling were imaged and tested according to the following steps:

[0070] 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.

[0071] Sample testing: Place the prepared sample into the instrument's sample chamber, focus, select the backscattered image mode, choose 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.

[0072] 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 splicing. At the same time, the images are quantitatively analyzed to obtain the organic pore surface ratio P Org .

[0073] Step 5: Conduct low-temperature CO2 and low-temperature N2 adsorption experiments on shale samples to obtain pore volumes in different pore size ranges;

[0074] The model of the low-temperature CO2 and low-temperature N2 adsorption experiment instrument is: ASAP 2460 surface area / pore size analyzer;

[0075] Before conducting low-temperature CO2 and low-temperature N2 adsorption experiments on shale samples, the samples need to be pretreated. The specific process is as follows:

[0076] (1) The shale samples were subjected to oil washing treatment using the Soxhlet extraction method with chloroform as the organic solvent for 12 hours;

[0077] (2) Dry the oil-washed samples in a constant temperature drying oven at 105°C for 12 hours;

[0078] (3) Grind the oil-washed and dried shale sample into 80-mesh powder using an agate mortar;

[0079] The micropore (r < 2 nm) volume is obtained through low-temperature CO2 adsorption experiments, and the mesopore (2 < r < 50 nm) and macropore (r > 50 nm) volumes are obtained through low-temperature N2 adsorption experiments;

[0080] Step 6: Respectively plot the cross plots of the pore volumes in different pore size ranges against G Tot , TOC, SiO2 -Bio and P Org to determine the intersection points of the cross plots.

[0081] As Figures 1 to 4 shown, the cross plots of G Tot , TOC, SiO 2-Bio and P Org against the pore volumes in different pore size ranges are respectively;

[0082] Taking Figure 1 as an example, there are two intersection points in the cross plot; among them, the red represents micropores, the yellow represents mesopores, and the blue represents macropores; the X-axis is the total gas content G Tot , and the Y-axis is the pore volume;

[0083] Mesopores: y = 0.0044x + 0.0097 Correlation coefficient R <000006​0>= 0.9666 (3)

[0084] Micropores: y = -0.0019x + 0.0181 R 2 = 0.9728 (4)

[0085] Macropores: y = 0.0025x + 0.0008 R 2 ​>= 0.9759 (5)

[0086] Intersection point 1 is calculated by联立公式(3)和(4), and intersection point 2 is calculated by联立公式(5)和(4); intersection point 1 is G Tot = 1.33 mL / g, and intersection point 2 is G Tot = 3.93 mL / g. <0​000270>Similarly, the intersection points of the cross plot in Figures 2-4 can be calculated;

[0088] Figure 2 The two intersection points in [[ID=​​​​60]]

[0089] Figure 3 are TOC = 0.81% and TOC = 2.15% respectively; ​>

[0090] Figure 4 The two intersection points in

[0090] Figure 4 are POrg =0.53% and P Org =1.03%;

[0091] Step 7: According to the G corresponding to the intersection Tot 、TOC、SiO 2-Bio and P Org The values ​​are used to classify shale gas reservoirs;

[0092] G calculated according to step 6 Tot 、TOC、SiO 2-Bio and P Org Value, the reservoir can be divided into 3 categories;

[0093] The specific classification criteria are shown in Table 1;

[0094] Table 1

[0095]

[0096] When there is a contradiction in the classification of shale gas reservoirs using the above four parameters, the shale gas reservoirs are classified according to the following principles;

[0097] For a specific shale sample, the four parameters G corresponding to the sample are Tot 、TOC、SiO 2-Bio and P Org Assign points, calculate the average value of the assigned points, and determine the type of the shale sample based on the average value of the assigned points;

[0098] Specifically: Class I, Class II, and Class III are assigned scores of 1, 2, and 3 respectively;

[0099] Taking sample A as an example, the sample G Tot 、TOC、SiO 2-Bio and P Org G Tot =1.05mL / g, TOC=1.33%, SiO 2-Bio =3.55%, P Org =0.88%;

[0100] Then sample A follows G Tot 、TOC、SiO 2-Bio and P Org The four parameters are classified into categories III, II, III, and II, with corresponding scores of 3, 2, 3, and 2, respectively, and an average of 10 / 4 = 2.5;

[0101] According to the principle of rounding, the average value of 2.5 is approximately 3, which means that sample A belongs to Class III.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for classifying and evaluating shale gas reservoirs, characterized in that, it includes the following steps: Step 1: Conduct an in-situ gas content determination experiment on the shale sample to obtain the total gas content G of the sample Tot ; Step 2: Conduct an indoor total organic carbon content determination experiment on shale samples to obtain the total organic carbon TOC value of the samples; Step 3: Conduct an indoor experiment on the determination of major elements of the shale sample, and calculate the biogenic quartz content SiO2 of the sample -Bio ; Step 4: Conduct an indoor scanning electron microscope experiment on the shale sample and calculate the organic pore surface porosity P of the sample Org ; Step 5; Conduct low-temperature CO 2 and low-temperature N 2 adsorption experiments on shale samples to obtain pore volumes in different pore size ranges; Step 6; separately make crossplot curves of pore volume within different pore size ranges and G Tot , TOC, SiO2 -Bio and P Org and determine the intersection points of the crossplot curves; Step 7: Classify the shale gas reservoir according to the G Tot , TOC, SiO2 -Bio and P Org values at the intersection point.

2. The method for classifying and evaluating shale gas reservoirs according to claim 1, characterized in that, Total air content G in Step 1 Tot Calculated by Formula 1: G Tot = G Ds + G Rs + G Ls (1) Where: G Ds , G Rs , G Ls are the analytical gas content, residual gas content, and lost gas content, respectively, in cm 3 / g.

3. The method for classifying and evaluating shale gas reservoirs according to claim 1, characterized in that, 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: Step 2.1: Use an agate mortar to grind the shale samples into 100-mesh powder; Step 2.2: Add the shale powder to dilute hydrochloric acid and react for 2 hours to completely remove inorganic minerals; Step 2.3: Rinse the shale samples treated with dilute hydrochloric acid with distilled water for 10 minutes until neutral; Step 2.4: Place the powdered shale samples in a constant temperature drying oven and dry them at 60°C for 24 hours.

4. The method for classifying and evaluating shale gas reservoirs according to claim 1, characterized in that, In step 3, the content of biogenic quartz in the shale sample, SiO2 -Bio is calculated by Formula 2: SiO 2-Bio = SiO 2-Sam -(SiO 2 / Al 2 O 3 ) Avg ×Al 2 O 3-Sam (2) where: 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, %.

5. The method for classifying and evaluating shale gas reservoirs according to claim 1, characterized in that, In step 4, specifically: Before the scanning electron microscope experiment, use argon ions to polish the surface of the shale.

6. The method for classifying and evaluating shale gas reservoirs according to claim 1, characterized in that, In step 5, before the low-temperature CO2 and low-temperature N2 adsorption experiments on the shale samples, the samples need to be pretreated, and the specific process is as follows: Step 5.1: Conduct an oil washing treatment on the shale samples. The method is Soxhlet extraction, the organic solvent is chloroform, and the time is 12 hours; Step 5.2: Conduct a drying treatment on the oil-washed samples. The instrument is a constant temperature drying oven, the temperature is 105°C, and the time is 12 hours; Step 5.3: Use an agate mortar to grind the oil-washed and dried shale samples into 80-mesh powder.

7. The method for classifying and evaluating shale gas reservoirs according to claim 1, characterized in that, In step 5, the pore volumes in different pore size ranges are obtained. The different pore sizes respectively refer to: micropores (r < 2 nm), mesopores (2 < r < 50 nm), and macropores (r > 50 nm).

8. The method for classifying and evaluating shale gas reservoirs according to claim 1, characterized in that, In step 5, the micropore volume is obtained through the low-temperature CO2 adsorption experiment, and the mesopore and macropore volumes are obtained through the low-temperature N2 adsorption experiment.

9. The method for classifying and evaluating shale gas reservoirs according to claim 1, characterized in that, Step 7 specifically involves classifying the reservoir into three categories based on the G Tot , TOC, SiO 2-Bio and P Org values obtained in Step 6; The specific classification criteria are shown in Table 1; Table 1 When the above 4 parameters conflict in classifying the shale gas reservoir, classify the shale gas reservoir according to the following principles; For a specific shale sample, four parameters G Tot , TOC, SiO 2-Bio and P Org corresponding to the sample are scored respectively, and the average value after scoring the sample is calculated. The type of the shale sample is judged according to the average score after scoring. Specifically, the scores for Class I, Class II and Class III are 1, 2 and 3 respectively.

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