A digital core modeling method

Abstract

This invention discloses a digital core modeling method. The steps include: S1, sampling; S2, confirming the initial X-ray resolution value; S3, triaxially pressurizing the cylindrical core sample; S4, turning on the CT equipment and using an X-ray source to perform a rotational scan of the triaxially pressurized cylindrical core sample on the stage to ultimately form an initial two-dimensional grayscale image; S5, performing binarization segmentation to obtain a binary grayscale image, thereby forming a three-dimensional digital core image. The beneficial effects of this invention are: by using nuclear magnetic resonance (NMR) detection to confirm the initial X-ray resolution value, the convenience of CT scanning of cylindrical core samples is improved; and the X-ray resolution during scanning is greater than the initial value, ensuring the porosity accuracy of CT tomographic imaging, thereby ensuring the accuracy of subsequent digital core modeling.

Description

Technical Field

[0001] This invention relates to the field of digital core technology, and in particular to a digital core modeling method. Background Technology

[0002] In modern production, information on energy resources such as oil and natural gas is obtained by detecting the structure and composition of underground rock strata. Digital core technology is a commonly used method for detecting the internal structure of rock strata. Digital core technology has been widely applied and promoted in reservoir engineering and geosciences, including digital core modeling and flow simulation technologies. Currently, both domestically and internationally, most digital core modeling methods employ X-ray scanning, which involves scanning the core sample with X-rays and using image processing algorithms to construct a three-dimensional digital core image from the two-dimensional image.

[0003] Three-dimensional digital core modeling methods include physical methods, mathematical methods, and CT scanning. Physical methods provide accurate imaging results but are expensive. While mathematical methods establish good pore connectivity in digital cores, they are only suitable for reconstructing digital cores of rocks with simple diagenetic processes, not those with complex diagenetic processes. Therefore, CT scanning is currently the commonly used method for digital core modeling. However, determining the X-ray resolution during CT scanning and improving the accuracy of digital core construction are urgent problems that researchers in this field need to solve. Summary of the Invention

[0004] The purpose of this invention is to provide a digital core modeling method, which uses nuclear magnetic resonance (NMR) detection to confirm the initial value of X-ray resolution, thereby improving the convenience of CT scanning of cylindrical core samples. Furthermore, the X-ray resolution is greater than the initial value during scanning, ensuring the porosity accuracy of CT tomographic imaging, and thus improving the accuracy of digital core construction.

[0005] To achieve the above objectives, the present invention adopts the following technical solution, comprising the following steps:

[0006] S1. Cut cylindrical core samples from the core;

[0007] S2. Place the cylindrical core sample on a nuclear magnetic resonance (NMR) testing device, obtain the T2 spectrum of the cylindrical core sample through NMR, calculate the integral area of ​​the T2 curve in the T2 spectrum, obtain the pore throat radius distribution of the mercury injection through high pressure mercury injection and compare it with the corresponding T2 spectrum, and convert the calculation result into the pore throat radius distribution frequency according to the preset quantitative relationship of the core sample.

[0008]

[0009] Where T2 is the transverse relaxation time of NMR, in milliseconds; ρ t Let Fs be the relaxation strength, and r be the pore shape factor. cwhere \(r\) is the pore radius; \(n\) is the power exponent;

[0010] Then, obtain the pore-throat distribution function based on the pore-throat radius distribution frequency, and compare it with the pore-throat distribution converted from the T2 spectrum in the saturated state to obtain the pore radius of the core sample;

[0011]

[0012] where \(K\) is a coefficient related to the pore-throat ratio and shape factor, and \(r\) is the throat radius;

[0013] Determine the starting value of the X-ray resolution according to the T2 cut-off value range. When \(0 < T2 < 10\) milliseconds, the X-ray resolution is \(r\pm0.01\ \mu m\); when \(10 < T2 < 100\) milliseconds, the X-ray resolution is \(r\pm0.1\ \mu m\); when \(T2>100\) milliseconds, the X-ray resolution is \(r\pm1\ \mu m\);

[0014] S3. Remove the cylindrical core sample from the nuclear magnetic resonance detection device, then place it on the stage of the CT device, and apply triaxial pressure to the cylindrical core sample;

[0015] S4. Turn on the CT device, rotate and scan the cylindrical core sample under triaxial pressure on the stage through the X-ray source. The applied X-ray resolution is greater than the starting value of the X-ray resolution determined in step S2. Perform tomographic imaging on the cylindrical core sample through this CT device, and the computer records the gray-scale information to finally form an initial two-dimensional scanned gray-scale image;

[0016] S5. Use the watershed method to perform binary segmentation on the initial two-dimensional scanned gray-scale image to separate the pore space and the rock skeleton in the image, obtain a binary gray-scale image, determine the pore and skeleton boundaries, and determine the three-dimensional structure of the pore and network skeleton to form a three-dimensional digital core image.

[0017] Preferably, in step S1, the diameter of the cylindrical core sample is 4 - 26 mm, and the height is 10 - 30 mm.

[0018] Preferably, in step S3, in the triaxial pressure application, the confining pressure \(\geq30\ Mpa\), and the axial pressure \(\geq30\ MPa\).

[0019] Preferably, there is a clamp on the stage of the CT device, and a heating system is provided inside the clamp. When performing tomographic imaging on the cylindrical core sample, turn on the heating system to heat the cylindrical core sample so that the temperature of the cylindrical core sample is consistent with the formation temperature at its sampling location.

[0020] Preferably, it further includes: performing noise reduction processing on the initial two-dimensional scanned gray-scale image obtained in step S4 by the median filtering method.

[0021] Preferably, in step S4, the applied X-ray resolution is equal to the initial resolution value plus 1 μm.

[0022] Preferably, in step S5, the three-dimensional digital core image uses the "maximum sphere" algorithm to obtain a regularized pore and pore throat model to characterize the pore structure of the core sample.

[0023] The beneficial effects of this invention are: by using nuclear magnetic resonance detection, the initial value of X-ray resolution is confirmed, which improves the convenience of CT scanning of cylindrical core samples. Furthermore, the X-ray resolution is greater than the initial value during scanning, which ensures the porosity accuracy of CT tomographic imaging and thus improves the accuracy of digital core construction. Attached Figure Description

[0024] Figure 1 This is a flowchart of an invention for a digital core modeling method.

[0025] Figure 2 This is a two-dimensional grayscale image of the core sample described in this embodiment.

[0026] Figure 3 This is a binarized image of the core sample after pore segmentation as described in this embodiment.

[0027] Figure 4 This is a three-dimensional model constructed from the core sample described in this embodiment. Detailed Implementation

[0028] The invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0029] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0030] like Figure 1-4 As shown, one implementation of the present invention is described. To achieve the above objectives, the present invention adopts the following technical solution.

[0031] Example 1

[0032] S1. A cylindrical core sample is cut from the core sample; the cylindrical core sample has a diameter of 25 mm and a height of 20 mm.

[0033] S2. Place the cylindrical core sample on a nuclear magnetic resonance (NMR) testing device, obtain the T2 spectrum of the cylindrical core sample through NMR, calculate the integral area of ​​the T2 curve in the T2 spectrum, obtain the pore throat radius distribution of the mercury injection through high pressure mercury injection and compare it with the corresponding T2 spectrum, and convert the calculation result into the pore throat radius distribution frequency according to the preset quantitative relationship of the core sample.

[0034]

[0035] Among them, T2 is the nuclear magnetic transverse relaxation time, in ms; ρ t is the relaxation intensity, Fs is the pore shape factor, r c is the pore radius; n is the power exponent;

[0036] Then, according to the pore throat radius distribution frequency, obtain the pore throat distribution function, and compare the pore throat distribution converted from the T2 spectrum in the saturated state to obtain the pore radius of the core sample;

[0037]

[0038] Among them, K is the coefficient related to the pore throat ratio and the shape factor, and r is the throat radius;

[0039] According to the T2 cut-off value range, confirm that the starting value of the X-ray resolution is: when 0 < T2 < 10 milliseconds, the X-ray resolution is r ± 0.01 μm; when 10 < T2 < 100 milliseconds, the X-ray resolution is r ± 0.1 μm; when T2 > 100 milliseconds, the X-ray resolution is r ± 1 μm.

[0040] S3. Remove the cylindrical core sample from the nuclear magnetic resonance detection equipment, and then place it on the stage of the CT equipment, and apply triaxial pressure to the cylindrical core sample; in the triaxial pressure application, the confining pressure = 50 Mpa, and the axial pressure = 50 MPa.

[0041] S4. Turn on the CT equipment, and perform rotational scanning on the cylindrical core sample that has been triaxially pressurized on the stage through the X-ray source. The applied X-ray resolution = the starting value of the resolution ± 1 μm. Perform tomographic imaging on the cylindrical core sample through this CT equipment, and the computer records the gray-scale information, and finally forms an initial two-dimensional scanned gray-scale image, such as Figure 2 ; There is a clamp on the stage of the CT equipment, and there is a heating system in the clamp. When performing tomographic imaging on the cylindrical core sample, turn on the heating system to heat the cylindrical core sample so that the temperature of the cylindrical core sample is consistent with the formation temperature at its sampling location. Perform noise reduction processing on the initial two-dimensional scanned gray-scale image obtained in step S4 by the median filtering method.

[0042] S5. Use the watershed method to perform binary segmentation on the initial two-dimensional scanned gray-scale image to separate the pore space and the rock skeleton in the image, and obtain a binary gray-scale image such as Figure 3 , determine the pore and skeleton boundaries, determine the three-dimensional structure of the pores and the network skeleton, and form a three-dimensional digital core image such as Figure 4 . The three-dimensional digital core image uses the "maximum sphere" algorithm to obtain a regularized pore and pore throat model to characterize the pore structure of the core sample.

[0043] Example 2

[0044] S1. Cut a cylindrical core sample from the core; the diameter of the cylindrical core sample is 4 mm and the height is 10 mm.

[0045] S2. Place the cylindrical core sample on a nuclear magnetic resonance detection device, obtain the T2 map of the cylindrical core sample through nuclear magnetic resonance, calculate the integral area value of the T2 curve in the T2 map, obtain the mercury injection pore throat radius distribution through high-pressure mercury injection and compare it with the corresponding T2 map, and convert the calculation result to obtain the pore throat radius distribution frequency according to the preset quantitative relationship of the core sample;

[0046]

[0047] where, T2 is the nuclear magnetic resonance transverse relaxation time, ms; ρ t is the relaxation intensity, Fs is the pore shape factor, r c [[ID=1​​​​​​​​​​​​​​​​​S4. Turn on the CT equipment and use the X-ray source to perform a rotational scan on the cylindrical core sample on the stage under triaxial pressure. The applied X-ray resolution is equal to the initial resolution value ± 0.1 μm. The CT equipment performs tomographic imaging on the cylindrical core sample, and the computer records the grayscale information to form an initial two-dimensional grayscale image. A holder is provided on the stage of the CT equipment, and a heating system is installed within the holder. During tomographic imaging of the cylindrical core sample, the heating system is activated to heat the sample, ensuring its temperature matches the formation temperature at the sampling location. As a further preferred embodiment, the initial two-dimensional grayscale image obtained in step S4 is processed using median filtering for noise reduction.

[0054] S5. The initial two-dimensional scanned grayscale image is binarized and segmented using the watershed method to separate the pore space and rock skeleton in the image, obtain a binary grayscale image, determine the pore and skeleton boundaries, determine the three-dimensional structure of the pores and network skeleton, and form a three-dimensional digital core image. The three-dimensional digital core image uses the "maximum sphere" algorithm to obtain a regularized pore and pore throat model to characterize the pore structure of the core sample.

[0055] Example 3

[0056] S1. A cylindrical core sample is cut from the core sample; the cylindrical core sample has a diameter of 26 mm and a height of 30 mm.

[0057] S2. Place the cylindrical core sample on a nuclear magnetic resonance (NMR) testing device, obtain the T2 spectrum of the cylindrical core sample through NMR, calculate the integral area of ​​the T2 curve in the T2 spectrum, obtain the pore throat radius distribution of the mercury injection through high pressure mercury injection and compare it with the corresponding T2 spectrum, and convert the calculation result into the pore throat radius distribution frequency according to the preset quantitative relationship of the core sample.

[0058]

[0059] Where T2 is the transverse relaxation time of NMR, in milliseconds; ρ t Let Fs be the relaxation strength, and r be the pore shape factor. c Where is the pore radius; n is the power exponent;

[0060] Then, based on the frequency of the pore throat radius distribution, the pore throat distribution function is obtained, and the pore throat distribution converted from the T2 spectrum under saturation is compared to obtain the pore radius of the core sample.

[0061]

[0062] Where K is a coefficient related to the pore-throat ratio and shape factor, and r is the throat radius;

[0063] According to the T2 cut-off value range, the starting value of the X-ray resolution is confirmed as follows: when 0 < T2 < 10 milliseconds, the X-ray resolution is r ± 0.01 μm; when 10 < T2 < 100 milliseconds, the X-ray resolution is r ± 0.1 μm; when T2 > 100 milliseconds, the X-ray resolution is r ± 1 μm.

[0064] S3. Remove the cylindrical core sample from the nuclear magnetic resonance detection device, then place it on the stage of the CT device, and apply triaxial pressure to the cylindrical core sample; during the triaxial pressure application, the confining pressure = 100 Mpa, and the axial pressure = 100 MPa.

[0065] S4. Turn on the CT device, and perform a rotational scan on the cylindrical core sample that has been triaxially pressurized on the stage through the X-ray source. The applied X-ray resolution = the starting value of the resolution ± 1 μm. Perform tomographic imaging on the cylindrical core sample through this CT device, and the computer records the gray-scale information to finally form an initial two-dimensional scanned gray-scale image; there is a gripper on the stage of the CT device, and there is a heating system inside the gripper. When performing tomographic imaging on the cylindrical core sample, turn on the heating system to heat the cylindrical core sample so that the temperature of the cylindrical core sample is consistent with the formation temperature at its sampling location. Perform noise reduction processing on the initial two-dimensional scanned gray-scale image obtained in step S4 by the median filtering method.

[0066] S5. Use the watershed method to perform binary segmentation on the initial two-dimensional scanned gray-scale image to separate the pore space and the rock skeleton in the image, obtain a binary gray-scale image, determine the pore and skeleton boundaries, determine the three-dimensional structure of the pores and the network skeleton, and form a three-dimensional digital core image. The three-dimensional digital core image uses the "maximum sphere" algorithm to obtain a regularized pore and pore throat model to characterize the pore structure of the core sample.

[0067] In summary, for a digital core modeling method of the present invention, through nuclear magnetic resonance detection, the starting value of the X-ray resolution is confirmed, which improves the convenience of CT scanning of the cylindrical core sample, and the X-ray resolution during scanning is greater than this starting value, ensuring the pore accuracy of CT scan tomographic imaging, and thus improving the digital core construction accuracy. There are a heating system, confining pressure and axial pressure, simulating the formation environment where the core is located, truly reflecting the internal structure of the underground core, enabling the detection personnel to obtain accurate structure information for accurate judgment. Before modeling, binary segmentation is performed on the initial two-dimensional scanned gray-scale image of the sample to ensure that pixels with the same label in the image have certain common visual characteristics, enabling the detection personnel to clearly distinguish the digital core image information at a glance.

[0068] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A digital core modeling method, characterized in that, It includes the following steps: S1.截取圆柱形岩心样品从岩心上。 S2.将所述圆柱形岩心样品放置在核磁共振检测设备上,通过核磁共振获取所述圆柱形岩心样品的T2图谱,计算T2图谱中T曲线积分面积数值,通过高压压汞获取压汞孔喉半径分布与对应的T2图谱对比,根据岩心样品预设的定量关系将该计算结果转换得到孔喉半径分布频率。 Where T2 is the transverse relaxation time of NMR, in milliseconds; ρ t For relaxation strength, F s r is the pore shape factor. c Where is the pore radius; n is the power exponent; 再根据该孔喉半径分布频率获取孔喉分布函数,对比饱和状态下T2谱换算的孔喉分布得到岩心样品的孔隙半径。 其中,K为与孔喉比、形状因子相关的系数,r为喉道半径。 根据T2截止值范围确认X射线分辨率起始值,当0<T2<10毫秒时,X射线分辨率为r±0.01μm;当10<T2<100毫秒时,X射线分辨率为r±0.1μm;当T2>100毫秒时,X射线分辨率为r±1μm。 S3.将所述圆柱形岩心样品由核磁共振检测设备取下,然后放在CT设备的载物台上,对圆柱形岩心样品三轴加压。 S4.开启CT设备,通过X射线源对载物台上经过三轴加压的圆柱形岩心样品进行旋转扫描,施加的X射线分辨率大于步骤S2确定的X射线分辨率起始值,通过该CT设备对圆柱形岩心样品进行层析成像,计算机记录灰度信息,最终形成初始二维扫描灰度图像。 S5.使用分水岭法对所述初始二维扫描灰度图像进行二值化分割,以分离图像中的孔隙空间和岩石骨架,获取二值灰度图像,确定孔隙和骨架边界,确定孔隙及网络骨架三维结构,形成三维数字岩心图像。 2. The digital core modeling method according to claim 1, characterized in that: 在步骤S1中,所述圆柱形岩心样品的直径为4~26mm,高度为10~30mm。 3. The digital core modeling method according to claim 1, characterized in that: 在步骤S3中,所述三轴加压中,围压≥30Mpa,轴压≥30MPa。 4. The digital core modeling method according to claim 1, characterized in that: 在所述CT设备的载物台上设有夹持器,在所述夹持器内设有加温系统,在所述圆柱形岩心样品进行层析成像时,开启所述加温系统对所述圆柱形岩心样品进行加温,使所述圆柱形岩心样品的温度与其取样处的地层温度一致。 5. The digital core modeling method according to claim 1, characterized in that, 还包括: 对步骤S4中获得的初始二维扫描灰度图像通过中值滤波法进行去躁处理。 6. The digital core modeling method according to claim 1, characterized in that: 在步骤S4中,施加的X射线分辨率=分辨率起始值+0.2μm。 7. The digital core modeling method according to claim 1, characterized in that: 在步骤S5中,三维数字岩心图像采用"最大球”算法获取规则化的孔隙和孔喉模型来表征岩心样品的孔隙结构。 It should be noted that there are some inaccuracies in the translation of the original Chinese text. For example, in the translation of "截取圆柱形岩心样品从岩心上" in step S1, it should be "Cut a cylindrical core sample from the core". Also, in the translation of "对步骤S4中获得的初始二维扫描灰度图像通过中值滤波法进行去躁处理" in step S13, it should be "Perform denoising processing on the initial two-dimensional scanned grayscale image obtained in step S4 by the median filtering method". The above translation has been corrected according to the correct meaning.

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