A shale young's modulus calculation method

Abstract

The application discloses a shale Young's modulus calculation method, and belongs to the technical field of oil and gas field development. mea The method comprises the following steps: step 1, preparing a shale sample into a standard core column; step 2, performing a rock mechanics experiment to obtain a Young's modulus E ; step 3, performing a total organic carbon experiment to obtain TOC; step 4, performing a rock pyrolysis experiment to obtain free hydrocarbon S1 and pyrolysis hydrocarbon S2; step 5, performing an X-ray diffraction whole rock quantitative analysis experiment to obtain the content of brittle minerals and clay minerals; step 6, performing a low-temperature nitrogen adsorption experiment to calculate a fractal dimension D; step 7, constructing a shale Young's modulus calculation model; and step 8, verifying the effectiveness of the model. The technical method provided by the application is simple in principle and high in practicability, a Young's modulus calculation model based on shale micro-pore structure and shale components is established, and the method has important significance for guiding shale brittleness evaluation and engineering sweet spot optimization.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas reservoir development technology, specifically relating to a method for calculating the Young's modulus of shale. Background Technology

[0002] With the increasing maturity of large-scale horizontal well fracturing technology, the proportion of shale oil and gas resources in my country's energy structure has been rising year by year. Shale reservoirs are extremely dense, characterized by low porosity and extremely low permeability, making development difficult. Fracturing is crucial for ensuring high production of shale oil and gas wells. During fracturing, hydraulic fracturing fluid is injected into the formation to create a fracture network, thereby improving the permeability of the shale reservoir. The effectiveness of fracturing depends on external factors such as the pressure of the injected fracturing fluid, the amount of proppant added, and the amount of fluid added, as well as the brittleness of the shale. The greater the reservoir brittleness, the more fractures are generated after fracturing, and the easier it is to form a large-area interconnected fracture network. Therefore, accurately assessing shale brittleness is of great significance for improving the development effect of shale.

[0003] Young's modulus of shale is a rock mechanics parameter widely used in reservoir brittleness and compressibility assessment, and is particularly important for fracturing layer selection and construction parameter design. Patent CN109580906B provides a method and system for creating a shale brittleness identification chart based on rock physics. It obtains the static Young's modulus and static Poisson's ratio by performing triaxial stress-strain tests on shale samples, and then calculates the brittleness index using these parameters.

[0004] The Young's modulus is influenced by the pore structure and composition of shale. Patent application CN110057853A provides a method for calculating the Young's modulus of rocks based on low-field nuclear magnetic resonance (NMR) response. It uses the T2 spectrum signal from NMR experiments to calibrate the Young's modulus in rock mechanics experiments and employs a multivariate regression method to establish a Young's modulus calculation model based on NMR response. This patent calculates the Young's modulus from the perspective of shale micropore structure. Patent application CN105021458A provides a quantitative evaluation method for the Young's modulus of oil-bearing shale. It uses a multivariate regression method to establish a Young's modulus calculation model based on shale composition. This patent calculates the Young's modulus from the perspective of shale composition. These studies indicate that currently, there is no existing technology that can simultaneously calculate the Young's modulus based on both the micropore structure and composition of shale. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for calculating the Young's modulus of shale. This method can simultaneously consider the microstructure and composition of shale, which is of great significance for guiding the evaluation of shale brittleness and the selection of optimal sweet spots in engineering applications.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] Step 1: Prepare standard core columns from shale samples;

[0008] Step 2: Conduct rock mechanics experiments to obtain Young's modulus E. mea ;

[0009] Step 3: Conduct a total organic carbon (TOC) experiment to obtain the TOC;

[0010] Step 4: Conduct rock pyrolysis experiments to obtain free hydrocarbon S1 and pyrolytic hydrocarbon S2;

[0011] Step 5: Conduct X-ray diffraction whole-rock quantitative analysis to obtain the content of brittle minerals and clay minerals;

[0012] Step 6: Conduct a low-temperature nitrogen adsorption experiment and calculate the fractal dimension D;

[0013] Step 7: Construct a Young's modulus calculation model for shale;

[0014] Step 8: Verify the effectiveness of the model.

[0015] In the above method, in step 1, the standard core column is 5cm long and 2.5cm in diameter.

[0016] In the above method, step 2, the rock mechanics experiment procedure is carried out in accordance with the national standard GB / T23561 "Methods for Determination of Physical and Mechanical Properties of Coal and Rock".

[0017] In the above method, step 3, the total organic carbon experimental procedure refers to the national standard GB / T19145-2003 "Determination of Total Organic Carbon in Sedimentary Rocks".

[0018] In the above method, in step 4, the rock pyrolysis experiment is conducted in accordance with the national standard GB / T18602-2012 "Rock Pyrolysis Analysis".

[0019] In the above method, step 5, the experimental procedure for whole-rock quantitative analysis by X-ray diffraction refers to the industry standard SY / T5163-2010 "X-ray diffraction analysis method for clay minerals and common non-clay minerals in sedimentary rocks".

[0020] In the above method, step 6, the low-temperature nitrogen adsorption experimental procedure refers to the national standard GB.T19587-2004 "Method for determining the specific surface area of ​​solid substances by gas adsorption BET principle".

[0021] In the above method, in step 6, the FHH model is used, and the two types of fractal dimensions of the sample pores are calculated with the relative pressure P / P0 = 0.5 as the boundary. They are denoted as D1 and D2 respectively.

[0022] In the above method, in step 6, the FHH model is:

[0023] LnV=KLn(Ln(P0 / P))+C;

[0024] In the formula, P0 is the saturated vapor pressure (MPa); P is the equilibrium pressure (MPa); and V is the adsorption volume (cm³). 3 / g; K is the linear correlation coefficient; C is a constant.

[0025] In the above method, in step 6, the fractal dimension D = K + 3. When P / P0 > 0.5, the fractal dimension D1 is obtained, and when P / P0 < 0.5, the fractal dimension D2 is obtained.

[0026] In the above method, in step 7, E mea As the dependent variable, TOC, S1, S2, M clay and M bri Using the independent variable, a multivariate linear fitting method was used to establish a calculation model for the Young's modulus of shale:

[0027] E cal =A·TOC+B·S1+C·S2+D·M clay +E·M bri +F·D1+G·D2+H

[0028] In the formula, E cal Young's modulus calculated for the model, GPa; TOC is organic carbon content, %; S1 is free hydrocarbon content, mg / g; S2 is pyrolytic hydrocarbon content, mg / g; M clay Clay mineral content, %; M bri , represents the content of brittle minerals, %; D1 and D2 are the fractal dimensions, dimensionless; A, B, C, D, E, F, G, and H are constants.

[0029] Compared with existing technologies, the advantages of this invention are as follows: This invention simultaneously considers both the microstructure and composition of shale, and employs a multivariate linear fitting method to establish a Young's modulus calculation model for shale. In the Young's modulus calculation model provided by this invention, TOC, S1, S2, and M... bri and M clay The influence of shale composition on Young's modulus is represented by the fractal dimensions D1 and D2, which represent the influence of shale micropore structure on Young's modulus. Incorporating these multiple parameters into the Young's modulus calculation model enhances its scientific rigor. The technical method provided by this invention is simple in principle and highly practical, and is of great significance for guiding the evaluation of shale brittleness and the selection of optimal sweet spots in engineering applications. Attached Figure Description

[0030] Figure 1 The figure shown is TOC-E in an example of the present invention.mea Intersection diagram;

[0031] Figure 2 The figure shown is S1-E in the example of the present invention. mea Intersection diagram;

[0032] Figure 3 The figure shown is S2-E in the example of the present invention. mea Intersection diagram;

[0033] Figure 4 The image shows M in an example of the present invention. clay -E mea Intersection diagram;

[0034] Figure 5 The image shows M in an example of the present invention. bri -E mea Intersection diagram;

[0035] Figure 6 The figure shown is D1-E in the example of the present invention. mea Intersection diagram;

[0036] Figure 7 The figure shown is D2-E in the example of the present invention. mea Intersection diagram;

[0037] Figure 8 The figure shown is E in an example of the present invention. cal -E mea Intersection diagram. Specific implementation methods

[0038] To make the technical means and objectives of this invention easier to understand, the invention is further described below in conjunction with specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods.

[0039] Example 1: A method for calculating the Young's modulus of shale, comprising the following steps:

[0040] Step 1: Prepare a standard core column from the shale sample, 5 cm in length and 2.5 cm in diameter;

[0041] Step 2: Conduct rock mechanics experiments to obtain Young's modulus;

[0042] The RTR-2000 high-pressure triaxial dynamic acoustic wave testing system was used to conduct rock mechanics experiments on standard core samples, referring to the national standard GB / T23561 "Methods for Determination of Physical and Mechanical Properties of Coal and Rock", to obtain triaxial stress-strain curves. Young's modulus was calculated based on the obtained triaxial stress-strain curves using the following formula:

[0043]

[0044] (where E is Young's modulus, GPa; Δσ) c Δε represents the change in axial stress. α (This represents the increase in axial strain.)

[0045] Step 3: Conduct a total organic carbon (TOC) experiment to obtain the TOC value;

[0046] The total organic carbon (TOC) values ​​of standard core samples were obtained by using a CS-230 carbon-sulfur analyzer in accordance with the national standard GB / T19145-2003 "Determination of Total Organic Carbon in Sedimentary Rocks".

[0047] Step 4: Conduct rock pyrolysis experiments to obtain the values ​​of free hydrocarbon S1 and pyrolytic hydrocarbon S2;

[0048] Rock-Eval6plus300 source rock analyzer was used to conduct rock pyrolysis experiments on standard core samples in accordance with the national standard GB / T18602-2012 "Rock Pyrolysis Analysis" to obtain the values ​​of free hydrocarbon S1 and pyrolysis hydrocarbon S2.

[0049] Step 5: Conduct X-ray diffraction whole-rock quantitative analysis to obtain the content of brittle minerals and clay minerals;

[0050] A D8DISCOVER X-ray diffractometer was used to perform whole-rock quantitative X-ray diffraction analysis on standard core samples, following the industry standard SY / T5163-2010 "X-ray Diffraction Analysis Methods for Clay Minerals and Common Non-Clay Minerals in Sedimentary Rocks," to obtain the contents of brittle minerals and clay minerals. Brittle minerals refer to quartz, feldspar, and calcite.

[0051] Step 6: Conduct a low-temperature nitrogen adsorption experiment and calculate the fractal dimension D;

[0052] Low-temperature nitrogen adsorption experiments were conducted on standard core samples using an ASAP2460 surface area and porosity analyzer, following the industry standard SY / T5163-2010 "X-ray Diffraction Analysis Methods for Clay Minerals and Common Non-Clay Minerals in Sedimentary Rocks". The FHH model was used, with a relative pressure P / P0 = 0.5 as the boundary, to calculate the two types of fractal dimensions of the sample porosity, denoted as D1 and D2, respectively. The FHH model is as follows:

[0053] LnV=KLn(Ln(P0 / P))+C

[0054] (Where, P0 is the saturated vapor pressure, unit: MPa; P is the equilibrium pressure, unit: MPa; V is the adsorption volume, unit: cm³) 3 / g; K is the linear correlation coefficient; C is a constant.

[0055] The fractal dimension D = K + 3 is obtained when P / P0 > 0.5, and the fractal dimension D2 is obtained when P / P0 < 0.5.

[0056] The experimental data for steps 2-6 are shown in Table 1:

[0057] Table 1: Statistical Table of Experimental Results

[0058]

[0059] In Table 1, TOC represents total organic carbon content (%); D1 and D2 are fractal dimensions (dimensionless); S1 represents free hydrocarbon content (mg / g); S2 represents pyrolytic hydrocarbon content (mg / g); M... clay Clay mineral content, %; M bri Content of brittle minerals, %; E mea GPa is the Young's modulus measured experimentally.

[0060] Step 7: Construct a Young's modulus calculation model for shale;

[0061] like Figure 1-7 As shown, E mea and TOC, S1, S2, M clay M bri The good correlation between D1 and D2 indicates that parameters such as TOC can be used in the calculation of the Young's modulus model for shale.

[0062] With E mea As the dependent variable, TOC, S1, S2, M clay and M bri Using the independent variable, a multivariate linear fitting method was used to establish a calculation model for the Young's modulus of shale:

[0063] E cal =-3.47TOC+5.63S1-0.78S2+0.0197M clay +0.7528M bri +9.64D1-60.26D2+110.78

[0064] In the formula, E cal Young's modulus calculated for the model, GPa; TOC is organic carbon content, %; S1 is free hydrocarbon content, mg / g; S2 is pyrolytic hydrocarbon content, mg / g; M clay Clay mineral content, %; M bri D1 and D2 represent the content of brittle minerals, in percentages; D1 and D2 are the fractal dimensions, dimensionless.

[0065] Step 8: Verify the model's effectiveness by calculating relative error and performing correlation analysis;

[0066] E was obtained based on the shale Young's modulus calculation model in step 7. cal And calculate E mea and E cal The relative error is shown in Table 2. The formula for calculating the relative error is:

[0067] Table 2: Statistical Table of Young's Modulus Calculation Results for Shale

[0068]

[0069] The relative error calculation results show that: E mea and E cal The relative error ranges from -4.68% to 6.09%, with an average of 0.08%, for E mea and E cal Perform correlation analysis, such as Figure 8 As shown, the results indicate that E cal and E mea Highly correlated (R) 2 =0.9808), thus proving the effectiveness of the Young's modulus calculation model of the present invention.

[0070] The above description is merely 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 inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for calculating the Young's modulus of shale, characterized in that, Includes the following steps: Step 1: Prepare standard core columns from shale samples; Step 2: Conduct rock mechanics experiments to obtain Young's modulus E. mea ; Step 3: Conduct a total organic carbon (TOC) experiment to obtain the TOC; Step 4: Conduct rock pyrolysis experiments to obtain free hydrocarbon S1 and pyrolytic hydrocarbon S2; Step 5: Conduct X-ray diffraction whole-rock quantitative analysis to obtain the content of brittle minerals and clay minerals; Step 6: Conduct a low-temperature nitrogen adsorption experiment and calculate the fractal dimension D; In step 6, the FHH model is used, with the relative pressure P / P0=0.5 as the boundary, to calculate the two types of fractal dimensions of the sample pores, denoted as D1 and D2 respectively; Step 7: Construct a shale Young's modulus calculation model; In step 7, the calculation model for the Young's modulus of shale is as follows: E cal =A·TOC+B·S1+C·S2+D·M clay +E·M bri +F·D1+G·D2+H In the formula, E cal Young's modulus calculated for the model, GPa; TOC is the organic carbon content, %; S1 is the free hydrocarbon content, mg / g; S2 is the pyrolytic hydrocarbon content, mg / g; M clay The content of clay minerals, %; M bri The content of brittle minerals is expressed as %; D1 and D2 are fractal dimensions, which are dimensionless; A, B, C, D, E, F, G, and H are constants. Step 8: Verify the effectiveness of the model.

2. The method according to claim 1, characterized in that, In step 1, the standard core column is 5cm long and 2.5cm in diameter.

3. The method according to claim 1, characterized in that, In step 6, the FHH model is: LnV=KLn(Ln(P0 / P))+C; In the formula, P0 is the saturated vapor pressure (MPa); P is the equilibrium pressure (MPa); and V is the adsorption volume (cm³). 3 / g; K is the linear correlation coefficient; C is a constant.

4. The method according to claim 1, characterized in that, In step 6, the fractal dimension D = K + 3. When P / P0 > 0.5, we obtain the fractal dimension D1, and when P / P0 < 0.5, we obtain the fractal dimension D2.

5. The method according to claim 1, characterized in that, In step 7, E mea As the dependent variable, TOC, S1, S2, M clay and M bri Using as the independent variable, a multivariate linear fitting method was used to establish a calculation model for the Young's modulus of shale.

6. The method according to claim 1, characterized in that, In step 8, the effectiveness of the shale Young's modulus calculation model is verified by calculating the relative error and performing correlation analysis.

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