CN111179296A - Novel method for researching heat conduction characteristic of rock based on digital rock core technology - Google Patents
Novel method for researching heat conduction characteristic of rock based on digital rock core technology Download PDFInfo
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- CN111179296A CN111179296A CN202010016328.8A CN202010016328A CN111179296A CN 111179296 A CN111179296 A CN 111179296A CN 202010016328 A CN202010016328 A CN 202010016328A CN 111179296 A CN111179296 A CN 111179296A
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Abstract
The invention discloses a novel method for researching heat conduction characteristics of rocks based on a digital core technology, and belongs to the field of digital core processing and application. The method is characterized in that: carrying out micro-CT scanning on a real rock core to obtain a plurality of two-dimensional images, and converting the two-dimensional images into binary images through image processing operations such as noise reduction, threshold segmentation and the like; then stacking the binary images and reconstructing the binary images into a three-dimensional model; then based on
Description
Technical Field
The invention relates to an application technology of a digital core, namely, the heat conduction characteristic of a porous core is analyzed on a microscale by researching the heat conduction characteristic of a rock through a digital core technology and a numerical simulation method.
Background
The thermal physical properties of the rock have important significance in a plurality of fields applying the earth science, wherein the thermal conductivity has important theoretical significance and application value in the development of geothermal energy and the application of rock thermal engineering. In recent years, in order to improve the recovery of oil and gas and the application of thermal engineering of rocks such as geothermal energy development, research on oil and gas reservoirs is gradually shifted from a macro scale to a micro scale. Many macroscopic properties of the reservoir medium depend on the microstructure and the composition of the reservoir medium, namely, various physical properties of fluids in a rock solid framework and a pore space of the rock solid framework, so that the micro-and macroscopic relations can be fundamentally known only by carrying out research on a micro-level, and the correct direction for researching the application of the rock thermal engineering technology and the technical means which should be adopted can be really found only on the basis, thereby providing powerful technical guidance for field production.
The digital core technology can accurately represent the core skeleton and the pore structure on the micrometer scale, and is more and more applied to the research of the core thermophysical property in recent years. How to convert the micro-CT image accurately describing the internal structure of the core into a high-precision volume grid structure that can be identified by current general analog calculation software and develop high-precision rock thermophysical property calculation research is a hotspot and difficulty of current digital core technologies.
Disclosure of Invention
Aiming at the current development situation, the invention provides an advanced digital core technology and a novel method for researching the heat conduction characteristic of the core by matching with a numerical simulation method, the internal structure of the rock can be accurately reconstructed based on the high-precision micro CT image of the core, and then the high-precision numerical simulation research on the microcosmic heat conduction characteristic of the rock is carried out by utilizing general commercial software.
The technical scheme adopted by the invention is as follows:
a new method for researching the heat conduction characteristic of rock based on a digital core technology is summarized as follows: firstly, scanning a real rock core by utilizing Micro-CT (Micro-CT) equipment to obtain a CT image; image processing operations such as noise reduction, threshold segmentation and the like are carried out on the image by using image software to obtain a binary image; then, stacking the binary image, performing three-dimensional reconstruction on an internal framework of the binary image, and outputting a reconstruction model into a universal stl file; use of
The platform carries out calculation pretreatment such as optimization treatment, grid division and the like on the model; finally utilize
And the software carries out numerical simulation on the heat conduction characteristic of the reconstructed microcosmic rock core.
And scanning the rock core through high-precision Micro-CT to obtain a series of scanned 2D images in the vertical direction of the rock core. Many miscellaneous points exist in rocks and other irreversible factors such as noise interference in the CT scanning process require that an image must be processed, and the definition and the accuracy of the image are improved by utilizing a miscellaneous point removing function and a median filter noise reduction function. The purpose of threshold segmentation is to segment the pores and the skeleton in the rock core, and the accuracy of threshold segmentation is ensured by adopting a manual threshold segmentation method and taking the porosity of the segmented image and the porosity measured by experiments as the standard, and the grayscale image is processed into a binary image, wherein the grayscale value 0 represents the pores, and the grayscale value 255 represents the skeleton. For convenience of calculation, a region with a proper scale and capable of representing the physical properties of the rock sample is selected as a characterization volume (REV), and the output of the REV is saved.
And further processing the binary image, filling holes with undersize pixel values by utilizing a closing function in image processing software, and processing the connectivity of the image by using triaxial continuity, wherein the operations do not influence the characteristics of the rock core and lay a foundation for subsequent numerical simulation. And finally, reconstructing the finely processed binary image into a 3D skeleton model and outputting the model as an stl format file.
The numerical simulation comprises three basic steps of pretreatment, simulation and post-treatment, wherein the pretreatment comprises model treatment, grid division and the like. Importing a reconstructed skeletal model
Platform, use of
The software carries out simplified optimization processing on the data and specifies boundaries, and then uses the data
The software divides the hexahedral core mesh into the hexahedral core mesh and improves the quality of the hexahedral core mesh, and finally
And (3) specifying a control equation, boundary conditions, a dispersion method and the like in software, and carrying out heat conduction numerical simulation on the core framework. The simulation can obtain the visual distribution of the temperature on the microscopic scale in the framework, so that the characteristics and the mechanism of the heat conduction can be researched on the microscopic scale. Meanwhile, the equivalent thermal conductivity coefficient of the core skeleton can be calculated by using the result of numerical simulation and combining with the Fourier law. The equivalent thermal conductivity coefficients in different directions obtained by performing simulation calculation on the reconstructed REV through the above process are shown in the following table:
TABLE 1 equivalent thermal conductivity in different directions
The invention has the beneficial effects that: the method has the advantages that a whole set of flow from CT scanning images to heat conduction characteristic simulation analysis is realized by utilizing an advanced digital core technology, the complex and anisotropic three-dimensional structure in the core can be accurately represented, subjective simplification and homogenization are not needed, the method can be applied to the related fields of porous media such as geological geography, oil exploitation and stratum storage, and the accuracy, digitization and visualization of core research on a microscale are really realized. In addition, the characteristics and mechanism of the rock core can be analyzed on a micro scale by a numerical simulation means, so that micro scale analysis which cannot be realized by macro research is obtained, related experiments of the rock core can be simulated, some physical parameters are calculated, and macro characteristics and rules are predicted, so that the method can be better applied to geothermal energy development and rock thermal engineering application.
Drawings
Fig. 1 shows an original image of a CT scan.
Fig. 2 shows an image subjected to noise reduction processing.
Fig. 3 shows a binarized image after threshold segmentation.
Fig. 4 shows the image after cutting.
Fig. 5 shows a reconstructed core skeleton model.
FIG. 6 shows the results of pretreatment for thermal property calculation.
Fig. 7 shows a temperature distribution diagram of a plurality of cross sections after numerical simulation.
Detailed Description
The invention is described in detail below with reference to the accompanying drawings:
FIG. 1 is a diagram of an original image of CT scanning, which is processed by image processing operations such as removing noise and reducing noise to obtain a diagram 2; obtaining a binary image shown in figure 3 by threshold segmentation; selecting an appropriate region as the REV, as shown in fig. 4; further processing and reconstructing the three-dimensional model of the skeleton shown in fig. 5 by commercial image software; then, preprocessing the reconstructed model by thermophysical property calculation, and outputting the model shown in the figure 6; by using
Conducting heat conduction numerical simulation on the temperature distribution data by software to obtain the temperature distribution shown in the figure 7; and finally, calculating to obtain the equivalent thermal conductivity coefficient shown in the table 1 based on the Fourier law, and realizing the analysis of the thermal conductivity characteristics and mechanism of the rock core on a microscale.
The above embodiments are merely illustrative and not restrictive of the technical solutions of the present invention. Any modification or partial replacement without departing from the spirit of the present invention should be covered in the scope of the claims of the present invention.
Claims (4)
1. A new method for researching heat conduction characteristics of rocks based on a digital rock core technology is characterized in that: carrying out micro-CT scanning on a real rock core to obtain a plurality of sequentially arranged two-dimensional images, and firstly converting the two-dimensional images into binary images by processing operations such as noise reduction, threshold segmentation and the like by using image processing software; then stacking the multiple binary images and reconstructing a three-dimensional body model of the core skeleton; then is at
The platform carries out optimization processing and calculation pre-processing on the reconstruction model; finally pass through
The software carries out numerical simulation on the heat conduction characteristic of the core framework, and carries out analysis and research on the heat conduction characteristic and mechanism of the rock from a microscopic angle.
2. The image processing process according to claim 1, characterized in that: the influence of the external environment on the CT image is removed through operations of removing impurity points, reducing noise and the like, and the image definition is improved; the thresholding is to separate the skeleton from the pores to facilitate later three-dimensional reconstruction.
3. The image stack and skeletal model reconstruction process of claim 1, characterized in that: and removing undersized features by utilizing closing operation, processing the communication performance of three shafts, and finally reconstructing the core framework into a three-dimensional model.
4. A numerical simulation process according to claim 1, characterized in that: based on
And
the platform carries out simulation research on the heat conduction characteristic of the rock core,the method has the advantages of microscopic visualization, reality and accuracy, and can calculate heat conduction and calculate physical parameters, analyze characteristic mechanisms, realize microscopic and macroscopic relation and further deeply understand the macroscopic heat conduction characteristic of the rock based on a real skeleton model in the rock core.
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Cited By (2)
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| CN111862306A (en) * | 2020-07-03 | 2020-10-30 | 大连理工大学 | CT image-based three-dimensional modeling method for pore filling type hydrate sediment |
| CN112326524A (en) * | 2020-10-22 | 2021-02-05 | 中国石油大学(华东) | Rock pore permeability measurement method based on CT scanning image |
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Application publication date: 20200519 |