A method for quantitatively evaluating micro-heterogeneity of flow channels in a tight sandstone reservoir

Abstract

The present application relates to the field of oil and gas engineering, especially to a kind of tight sandstone reservoir flow channel microheterogeneity quantitative evaluation method in exploration and development process.A kind of tight sandstone reservoir flow channel microheterogeneity quantitative evaluation method, method as follows: obtain the throat-pore microstructure parameters of target reservoir rock sample;According to the relationship between average throat width and the throat width connected by different coordination number pores, an overall average throat diameter calculation formula is established;A linear fitting equation of coordination number and average throat width is established, the linear fitting equation is substituted into the overall average throat diameter calculation formula, and the fitting coefficient of the linear fitting equation is solved;Microheterogeneity coefficient is calculated by fitting coefficient, and non-heterogeneity grade is classified by establishing non-heterogeneity grade classification standard with microheterogeneity coefficient.The present application can be quickly applied to on-site geological feature fine evaluation and sweet spot optimization.

Description

Technical Field

[0001] This invention relates to the field of oil and gas engineering, and in particular to a quantitative evaluation method for the microscopic heterogeneity of flow channels in tight sandstone reservoirs during exploration and development. Background Technology

[0002] China is extremely rich in tight oil and gas resources, mainly distributed in large basins such as the Ordos, Songliao, Junggar, and Sichuan Basins. They have huge development potential and will become the main force for future oil and gas reserve and production increases. China's tight gas reservoirs are characterized by vertically stacked thin-layer composite lithology and strong heterogeneity. Among them, the heterogeneity of oil and gas fluids in the micropores of rocks has always been the core indicator for evaluating the resource potential and development effect of oil fields, especially the key factors affecting the flow law of fluids in reservoirs, the enrichment of remaining oil and gas, and the selection of geological engineering sweet spots. A large number of literature surveys have been carried out on the vertical heterogeneity of unconventional reservoirs. At present, there are relatively few studies on the quantitative evaluation of reservoir heterogeneity. The main ones are as follows: (1) Qin Minjun et al. A method for evaluating reservoir heterogeneity, patent application number: CN202110438517.9. This method selects multiple sets of measurement points between and within each stratum of the reservoir to measure permeability. The permeability is used to obtain the coefficient of variation, advance coefficient and grade difference between and within each stratum to characterize the heterogeneity of the reservoir; (2) Meng Zhiyong et al. Shale heterogeneity division and comparison method, patent application number: CN201611268787.5. This method first divides and compares high-frequency sequences to establish an isochronous stratigraphic comparison framework for the vertical heterogeneity division of shale reservoirs; secondly, it studies the macroscopic heterogeneity in the isochronous stratigraphic comparison framework, analyzes and establishes the longitudinal and lateral variation characteristics of macroscopic heterogeneity of different high-frequency sequence segments of shale reservoirs in the isochronous stratigraphic comparison framework, establishes the longitudinal and lateral variation characteristics of microscopic heterogeneity of shale reservoirs in different high-frequency sequence segments, and finally divides and compares small layers. Based on the research results of macroscopic and microscopic heterogeneity in the isochronous stratigraphic comparison framework, it determines the heterogeneity characteristics of shale reservoirs.

[0003] Existing technical solutions mainly evaluate reservoir heterogeneity through methods such as differences in core test physical parameters and stratigraphic lithology comparison, which are conventional single-factor static macroscopic evaluation methods. Microscopic heterogeneity of the reservoir can more objectively and realistically evaluate the flow patterns of fluids in unconventional tight reservoirs within the micropores of the rock. Currently, conventional macroscopic evaluation methods have poor adaptability in unconventional micro- and nano-pores. Research shows that there are few reports on the microscopic heterogeneity of fluid flow channels in rock pores in published solutions. For unconventional reservoirs, the core factor affecting oil and gas flow capacity and dynamic development effectiveness lies in the microscopic heterogeneity of fluid flow channels. Therefore, this invention patent application calculates the heterogeneity coefficient of flow channels based on the actual core micropore and throat-related combination structure, achieving a quantitative evaluation of microscopic heterogeneity. The method is simple and feasible and can be quickly applied to the detailed evaluation of in-situ geological characteristics. Summary of the Invention

[0004] The present invention aims to propose a quantitative evaluation method for the microscopic heterogeneity of flow channels in tight sandstone reservoirs.

[0005] The technical solution of this invention is as follows:

[0006] A quantitative evaluation method for the microscopic heterogeneity of flow channels in tight sandstone reservoirs is as follows:

[0007] Obtain throat-pore microstructure parameters of the target reservoir rock sample;

[0008] Based on the relationship between the average throat diameter and the throat diameter connected by pores with different coordination numbers, a formula for calculating the overall average throat diameter is established.

[0009] A linear fitting equation between coordination number and average larynx diameter is established. The linear fitting equation is then substituted into the formula for calculating the overall average larynx diameter, and the fitting coefficient of the linear fitting equation is obtained by solving the equation.

[0010] The micro-heterogeneity coefficient is calculated by fitting coefficient, and a heterogeneity level classification standard is established based on the micro-heterogeneity coefficient to classify the heterogeneity level.

[0011] The specific calculation process for the micro-heterogeneity coefficient is as follows:

[0012] (5)

[0013] In the formula: is a microscopic non-homogeneous coefficient, dimensionless; The number of coordination numbers; The maximum coordination number is 1; The slope of the linear fitting equation is dimensionless. The intercept of the linear fitting equation is the minimum throat diameter, which is dimensionless. for Number of pores under each coordination number.

[0014] The specific criteria for classifying heterogeneity levels are as follows: when 0.70 < micro heterogeneity coefficient ≤ 1, it is a Class I heterogeneous reservoir; when 0.35 < micro heterogeneity coefficient ≤ 0.70, it is a Class II heterogeneous reservoir; and when 0 < micro heterogeneity coefficient ≤ 0.35, it is a Class III heterogeneous reservoir.

[0015] The specific formula for calculating the overall average throat diameter is as follows:

[0016] (1)

[0017] In the formula: The overall average throat diameter, in μm; The number of coordination numbers; The maximum coordination number is 1; for Number of pores under a coordination number of ; for Average canal diameter, μm, for each coordination number.

[0018] The linear fitting equation is specifically as follows:

[0019] (2)

[0020] In the formula: Let be the slope of the linear fitting equation, which is dimensionless; The intercept of the linear fitting equation is the minimum throat diameter, which is dimensionless.

[0021] The specific process for solving the slope of the linear fitting equation is as follows:

[0022] Substituting the linear fitting equation into the overall average throat diameter calculation formula, specifically:

[0023] (3)

[0024] The specific slope of the linear fitting equation is as follows:

[0025] (4).

[0026] The throat-pore microstructure parameters include pore-throat attribute parameters and pore attribute parameters; the pore-throat attribute parameters include the diameter distribution of the pore throats and the number of pore throats at the corresponding diameters; the pore attribute parameters include the number of pores with different coordination numbers.

[0027] The pore throat attribute parameters were obtained through image analysis of the cast thin section.

[0028] The overall average throat diameter is the average diameter of the overall throat.

[0029] The technical advantages of this invention are as follows:

[0030] (1) For the first time, the key parameters of the microstructure of the pore-throat channel that affect the heterogeneity of the fluid flow channel were obtained by combining the analysis results of the thin section images of the core casting in the mine. The throat diameter of the pore with different coordination numbers was established, and the calculation formula of the overall average throat diameter was obtained. The diameter of the throat connected by the pore with different coordination numbers was quantitatively distinguished. The larger the coordination number of the pore, the larger the throat diameter and the stronger the flow capacity. The micro heterogeneity coefficient was calculated by combining the linear fitting equation, and the classification standard of the micro heterogeneity of the rock pore flow channel was established to realize the quantitative evaluation of the heterogeneity of the flow channel.

[0031] (2) The micro-heterogeneity of fluid flow channels was dynamically and quantitatively evaluated by calculating the micro-homogeneity coefficient, which is a significant improvement over conventional macro-evaluation. The method is simple and feasible and can be quickly applied to the fine evaluation of on-site geological features and the selection of sweet spots. Attached Figure Description

[0032] Figure 1 This is a diagram showing the diameter and number of larynxes.

[0033] Figure 2 This is a diagram showing the coordination number and the number of pores.

[0034] Figure 3 This is a diagram of a thin sheet of the cast metal. Detailed Implementation

[0035] A quantitative evaluation method for the microscopic heterogeneity of flow channels in tight sandstone reservoirs is as follows:

[0036] Step 1: Obtain the throat-pore microstructure parameters of the target reservoir rock sample; wherein, the throat-pore microstructure parameters include pore-throat attribute parameters and pore attribute parameters; the pore-throat attribute parameters include the diameter distribution of the pore throat and the number of pore throats at the corresponding diameter; the pore attribute parameters include the number of pores with different coordination numbers, which are obtained through analysis of thin section images of the cast body;

[0037] Step 2: Based on the relationship between the average throat diameter and the throat diameter connected by pores with different coordination numbers, establish the overall average throat diameter calculation formula as shown in formula (1);

[0038] Step 3: Establish a linear fitting equation between the coordination number and the average larynx diameter, as shown in formula (2); substitute formula (2) into the overall average larynx diameter calculation formula in formula (1) to obtain formula (3); then solve for the fitting slope of the linear fitting equation. For example, as in formula (4);

[0039] Step 4: Calculate the micro heterogeneity coefficient using formula (5), and establish a classification standard for heterogeneity levels to classify heterogeneity levels; when 0.70 < micro heterogeneity coefficient ≤ 1, it is a Class I heterogeneous reservoir; when 0.35 < micro heterogeneity coefficient ≤ 0.70, it is a Class II heterogeneous reservoir; when 0 < micro heterogeneity coefficient ≤ 0.35, it is a Class III heterogeneous reservoir.

[0040] A specific experimental case study was conducted, using typical tight sandstone reservoir samples from western China as examples. One vertical well, KN, was used as the main development zone, with the K1 sub-layer as the primary development zone. Samples from the K1 sub-layer were obtained, and the method proposed in this application was used to evaluate the microscopic heterogeneity of the flow channels in the tight sandstone reservoir in this area.

[0041] A quantitative evaluation method for the microscopic heterogeneity of flow channels in tight sandstone reservoirs is as follows:

[0042] Step 1: Obtain the throat-pore microstructure parameters of the target reservoir rock sample; the specific process is as follows:

[0043] 1. Pore throat attribute parameters: The diameter distribution of the pore throats and the number of pore throats at corresponding diameters were obtained through analysis of thin-section images of the cast body, as shown in Table 1 and... Figure 1 As shown:

[0044] Table 1. Throat Attribute Parameter Table

[0045] ;

[0046] 2. Pore property parameters: Combining pore throat property parameters, the number of pores with different coordination numbers is obtained, as shown in Table 2 and... Figure 2 As shown:

[0047] Table 2 Pore Property Parameters

[0048] ;

[0049] Step 2: Based on the relationship between the average throat diameter and the throat diameter connected by pores with different coordination numbers, establish the overall average throat diameter calculation formula as shown in formula (1); the specific process is as follows: the average throat diameter is 3.14 μm obtained from the analysis of the thin-film image of the casting, and the minimum throat diameter is... The diameter is 0.47 μm; based on this, a formula for calculating the overall average throat diameter as in formula (1) is established; a linear fitting equation as in formula (2) is established to quantitatively distinguish the diameter of the throats connected by pores with different coordination numbers. The larger the coordination number pore, the larger the corresponding throat diameter; substituting formula (2) into formula (1), the fitting slope of the linear fitting equation is obtained. It is 1.137;

[0050] Step 3: Calculate the micro heterogeneity coefficient using formula (5). The value is 0.25, which is defined as a Class III heterogeneous reservoir according to the heterogeneity classification standard.

[0051] The traditional method for evaluating the microscopic heterogeneity of tight sandstone reservoirs is to calculate the porosity-to-permeability ratio of the target reservoir. A higher porosity-to-permeability ratio indicates stronger microscopic heterogeneity. Given that the target reservoir sample has a porosity of 7.8% and a permeability of 0.18 mD, its porosity-to-permeability ratio is 43.33% / mD. Similar reservoirs typically have porosity-to-permeability ratios ranging from 16.67% / mD to 110.33% / mD. The following formula is used to evaluate the microscopic heterogeneity of the tight sandstone reservoir, and the calculated values ​​are... The value is 0.28, which, according to the heterogeneous reservoir classification in this application, also classifies it as a Class III heterogeneous reservoir.

[0052] ;

[0053] In the formula: This is a traditional method for calculating the microscopic heterogeneity coefficient of dense sandstone, which is dimensionless. The ratio of reservoir porosity to permeability, % / mD; The minimum porosity to permeability ratio for similar reservoirs, % / mD; This represents the maximum porosity to permeability ratio for similar reservoirs, expressed as % / mD.

[0054] The present invention has been specifically described above through embodiments. It should be noted that these embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way, nor are they limited to the forms disclosed herein, and should not be construed as excluding other embodiments. Modifications and simple variations made by those skilled in the art that do not depart from the technical concept and scope of the present invention are all within the protection scope of the present invention.

Claims

1. A method for quantitatively evaluating the microscopic heterogeneity of flow channels in tight sandstone reservoirs, characterized in that, The method is as follows: Obtain the throat-pore microstructure parameters of the target reservoir rock sample; Based on the relationship between the average throat diameter and the throat diameter connected by pores with different coordination numbers, a formula for calculating the overall average throat diameter is established. A linear fitting equation between coordination number and average larynx diameter is established. The linear fitting equation is then substituted into the formula for calculating the overall average larynx diameter, and the fitting coefficient of the linear fitting equation is obtained by solving the equation. The micro-heterogeneity coefficient is calculated by fitting coefficient, and a heterogeneity level classification standard is established based on the micro-heterogeneity coefficient to classify the heterogeneity level. The specific calculation process for the micro-heterogeneity coefficient is as follows: （5） The specific formula for calculating the overall average throat diameter is as follows: （1） The linear fitting equation is specifically as follows: （2） In the formula: is a microscopic non-homogeneous coefficient, dimensionless; The number of coordination numbers; The maximum coordination number is 1; The slope of the linear fitting equation is dimensionless. The intercept of the linear fitting equation is the minimum throat diameter, which is dimensionless. for Number of pores under a coordination number of ; The overall average throat diameter, in μm; for Average canal diameter, μm, for each coordination number.

2. The method for quantitatively evaluating the microscopic heterogeneity of flow channels in tight sandstone reservoirs according to claim 1, characterized in that, The specific criteria for classifying heterogeneity levels are as follows: when 0.70 < micro heterogeneity coefficient ≤ 1, it is a Class I heterogeneous reservoir; when 0.35 < micro heterogeneity coefficient ≤ 0.70, it is a Class II heterogeneous reservoir; and when 0 < micro heterogeneity coefficient ≤ 0.35, it is a Class III heterogeneous reservoir.

3. The method for quantitatively evaluating the microscopic heterogeneity of flow channels in tight sandstone reservoirs according to claim 1, characterized in that, The throat-pore microstructure parameters include pore-throat attribute parameters and pore attribute parameters; the pore-throat attribute parameters include the diameter distribution of the pore throats and the number of pore throats at the corresponding diameters; the pore attribute parameters include the number of pores with different coordination numbers.

4. The method for quantitatively evaluating the microscopic heterogeneity of flow channels in tight sandstone reservoirs according to claim 3, characterized in that, The pore throat attribute parameters were obtained through image analysis of the cast thin section.

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