CN105551004A - Core CT image processing-based remaining oil micro-occurrence representing method - Google Patents

Abstract

The invention relates to the fields of petroleum reservoirs, image processing and the like, in particular to a microcosmic occurrence representation method of remaining oil based on core CT image processing. The method includes the following steps: preprocessing of CT images, CT image interpolation based on cubic Lagrange interpolation; segmentation and correction of CT images; modeling of pore and throat networks based on CT images, and quantitative characterization of remaining oil microscopic occurrence. The microcosmic occurrence representation method of remaining oil based on core CT image processing of the present invention is based on the acquisition of core CT scan images, through CT image preprocessing, image interpolation, image-based medium segmentation, three-dimensional reconstruction of core models, pore throat Through steps such as segmentation and pore-throat topological structure reconstruction, the three-dimensional shape of all pores and throats in the core model and their topological connection relationship are obtained, and finally the quantitative characterization of the microscopic occurrence of remaining oil is obtained.

Description

A microscopic representation method of remaining oil based on core CT image processing

technical field

The invention relates to the fields of petroleum reservoirs, image processing and the like, in particular to a microcosmic occurrence representation method of remaining oil based on core CT image processing.

Background technique

Because many macroscopic properties of the reservoir (such as permeability, capillary pressure, etc.) depend on its microstructure. Therefore, in order to achieve the development goal of greatly enhancing oil recovery, its theoretical research and technical development cannot only stay at the macro level, but must go deep into the storage and migration space of oil—the interior of porous media, from the micro level Research.

Only by studying the essential issues that determine the macroscopic fluid flow phenomenon inside the porous medium (such as the influence of the topological distribution of the pore space on the fluid seepage, the distribution of the fluid in it and the mechanism of mutual influence, etc.), can we fundamentally understand the microcosmic and macroscopic phenomena. On this basis, we can really find the correct direction and technical means to study enhanced oil recovery technology, and provide reliable guidance for taking advanced and reasonable measures to enhance oil recovery. Prior to this, the microcosmic mechanism of oil-water distribution in high water-cut reservoirs was mostly studied qualitatively through experiments. Therefore, the theory of occurrence and migration obtained from the research still remained at the macroscopic scale, and many microcosmic mechanisms had not been revealed.

Therefore, it is necessary to rely on advanced computer analysis methods and algorithms and physical simulation experiment technology to conduct in-depth research on the microcosmic occurrence state of remaining oil in ultra-high water-cut reservoirs to achieve an organic combination of qualitative understanding and quantitative description. It provides a reliable guidance basis for enhancing oil recovery.

Contents of the invention

In order to solve the shortcomings and deficiencies in the prior art, the present invention proposes a microcosmic occurrence representation method of remaining oil based on core CT image processing. Microscopic test and analysis technology, through the research on the remaining oil occurrence and occurrence state in the pores and throats of porous media, the test analysis technology and characterization method of remaining oil at the CT micron scale are established. The technical scheme adopted is as follows:

A microcosmic occurrence representation method of remaining oil based on core CT image processing, characterized in that it includes the following steps:

Step 1, the processing of CT images, including CT image preprocessing, interpolation operation, image segmentation;

Step 2, modeling the pore and throat network on the basis of CT image processing;

Step 3, quantitative statistics of remaining oil microscopic occurrence;

Step 4, state characterization of remaining oil microscopic occurrence.

The processing of CT image in described step 1 comprises:

(1) Mainly perform contrast enhancement and sharpening on the acquired image first;

(2) Perform appropriate interpolation operation on the sliced image, and generate a new image by interpolation in the middle of the sliced image to ensure that the distance between the image layers is equal to the resolution of the plane image;

(3) With the help of image segmentation technology, the pores and remaining oil in the microscopic displacement image can be segmented.

The pore and throat network modeling is based on the results of CT image processing and is used to analyze and display rock structure information. Firstly, the three-dimensional data field is obtained by performing difference on the obtained two-dimensional CT scan images; then the MarchingCube (MC) algorithm is used to construct the three-dimensional data volume, and on this basis, the visualization of the three-dimensional image and the statistics of the remaining oil information are completed; next , to create a pore and throat network model containing topological information, so as to realize the description of the microscopic pore level of the remaining oil.

The quantitative statistics of the remaining oil microscopic occurrence include the number, volume and surface area of the remaining oil microscopic occurrence. Among them, the number and volume of microcosmic occurrence of remaining oil are statistically divided by using the principle of distinguishing different substances in the core data volume by gray value. Among them, the gray value of matrix core is 0, the gray value of water is 255, and the gray value of remaining oil is 128. Therefore, in order to obtain the block number and volume information of the remaining oil, it is only necessary to count the voxels with a gray value of 128.

Using the moving cube algorithm can make the discrete three-dimensional data volume continuous, so the remaining oil surface changes from a cube to a relatively smooth polygon. When counting the surface area, according to the numbering order of the remaining oil, for the remaining oil numbered i, for each volume element to search. If all the voxels that have a 26-connected relationship with this voxel are oil, it means that the voxel is located inside the real remaining oil, and it is not counted; if a voxel adjacent to it is a rock particle, the statistics of the two The contact area between voxels and add it to the remaining oil area and the contact area; if an adjacent voxel is water, count the contact area between these two voxels and add it to the remaining oil area . After the statistics, it can be obtained that the surface area of the remaining oil numbered i is set as S ₁ (i) and the contact area with the rock surface is set as S ₂ (i).

The state characterization description of the remaining oil microscopic occurrence includes the remaining oil microscopic occurrence amount, occurrence location and occurrence form. In order to further quantitatively characterize the occurrence of remaining oil, the average volume of remaining oil is defined as:

$\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\mathrm{<span\; class="notranslate">\; N</span>}}$

In the formula: is the average volume of remaining oil, N is the number of remaining oil blocks, and v _i is the volume of the i-th block of remaining oil. Through the comprehensive analysis of the number of remaining oil lumps and the average volume of remaining oil, the occurrence of remaining oil in the process of remaining oil displacement can be quantitatively characterized.

In order to further quantitatively characterize the location of remaining oil, the contact area ratio C is defined as:

$\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>}$

In the formula, C—contact area ratio, S ₂ (i)—contact area between remaining oil and pores, S ₁ (i)—surface area of remaining oil. The contact area of remaining oil is the percentage of the contact area between remaining oil and pores in the total surface area of remaining oil, which reflects the relative positional relationship between remaining oil and pore surfaces. The smaller the contact area ratio, the smaller the proportion of remaining oil attached to the pore surface, and the better the corresponding water flooding effect.

In order to quantitatively describe the occurrence form of remaining oil, the shape factor G of remaining oil is defined as:

G=V/S _1.5

In the formula, V—the volume of a single block of remaining oil, S—the surface area of a single block of remaining oil. From the definition of the remaining oil shape factor, it can be seen that the smaller the shape factor, the larger the surface area of the remaining oil under the same volume, the greater the degree of surface unevenness, and the more irregular the shape. Based on the size of the shape factor, the remaining oil in each displacement stage is divided into four types: single pore, oil film, porous and continuous sheet.

Beneficial effects: A microcosmic occurrence representation method of remaining oil based on core CT image processing, which overcomes the shortcomings of the existing research on the occurrence and migration theory that still stays at the macro scale, and many microcosmic mechanisms have not been revealed. Processing, longitudinal image interpolation, image-based medium segmentation, core model 3D reconstruction, pore throat segmentation and pore throat topology reconstruction, etc., to obtain the 3D shape of all pores and throats in the core model and their topological connections, and propose Quantitative characterization indicators of microscopic occurrence of remaining oil, combined with the distribution of remaining oil in core samples at different stages, statistics on the shape, distribution mode, and migration law of oil and water in the pores and throats of core samples, and on this basis can be obtained Qualitative and quantitative analysis and research on the influencing factors of microcosmic occurrence state of remaining oil, so as to provide reliable guidance basis for improving oilfield recovery.

Description of drawings

Fig. 1 is the general flowchart of the present invention;

Fig. 2 is the pore, throat mesh modeling flowchart in the present invention;

Fig. 3 is the flow chart of remaining oil block number and volume statistics in the present invention;

Fig. 4 is a statistical flow chart of remaining oil surface area among the present invention;

Fig. 5 is a schematic diagram of remaining oil numbers in the present invention;

Fig. 6 is a statistical schematic diagram of the number of remaining oil blocks and the average volume of a single block of remaining oil in the present invention;

Fig. 7 is a schematic diagram of remaining oil occurrence positions at different displacement times in the present invention;

Fig. 8 is a schematic diagram of the residual oil occurrence state of slices at different positions at different times of saturated oil in the present invention.

detailed description

The present invention will be described in detail below through specific examples.

As shown in Figure 1, the present invention’s microcosmic occurrence representation method of remaining oil based on core CT image processing includes: CT image processing, modeling of pores and throat networks on the basis of CT image processing, microcosmic occurrence of remaining oil Quantitative statistics of remaining oil deposits, state characterization of remaining oil microscopic occurrences.

In Figure 1, the processing of CT images includes:

(1) Mainly perform contrast enhancement and sharpening on the acquired image first;

(2) Perform appropriate interpolation operation on the sliced image, and generate a new image by interpolation in the middle of the sliced image to ensure that the distance between the image layers is equal to the resolution of the plane image;

(3) With the help of image segmentation technology, the pores and remaining oil in the microscopic displacement image can be segmented.

In Fig. 2, Fig. 2 is a flow chart of modeling pores and throats in the present invention. Pore and throat network modeling is based on the results of CT image processing to analyze and display rock structure information more intuitively. The specific steps are as follows: firstly, the three-dimensional data field is obtained by performing difference on the acquired two-dimensional CT scanning images; then, the MarchingCube (MC) algorithm is used to construct the three-dimensional data volume, and on this basis, the visualization of the three-dimensional image and the remaining oil information are completed Statistics; Next, create a pore and throat network model containing topological information, so as to realize the description of the microscopic pore level of the remaining oil.

In Fig. 3 and Fig. 4, Fig. 3 is a flow chart flow chart of remaining oil block number and volume statistics in the present invention, and Fig. 4 is a flow chart flow chart of remaining oil surface area statistics in the present invention. Quantitative statistics of remaining oil microscopic occurrence, including the number, volume and surface area of remaining oil microscopic occurrence. Among them, the number and volume of microcosmic occurrence of remaining oil are statistically divided by using the principle of distinguishing different substances in the core data volume by gray value. Among them, the gray value of matrix core is 0, the gray value of water is 255, and the gray value of remaining oil is 128. Therefore, in order to obtain the block number and volume information of the remaining oil, it is only necessary to count the voxels with a gray value of 128, and the results are shown in Figure 5.

Using the moving cube algorithm can make the discrete three-dimensional data volume continuous, so the remaining oil surface changes from a cube to a relatively smooth polygon. When counting the surface area, according to the numbering order of the remaining oil, for the remaining oil numbered i, for each volume element to search. If all the voxels that have a 26-connected relationship with this voxel are oil, it means that the voxel is located inside the real remaining oil, and it is not counted; if a voxel adjacent to it is a rock particle, the statistics of the two The contact area between voxels and add it to the remaining oil area and the contact area; if an adjacent voxel is water, count the contact area between these two voxels and add it to the remaining oil area . After the statistics, it can be obtained that the surface area of the remaining oil numbered i is set as S ₁ (i) and the contact area with the rock surface is set as S ₂ (i).

State characterization of remaining oil microscopic occurrence, including microscopic occurrence amount, occurrence location and description of occurrence form.

As shown in Figure 6, Figure 6 is a statistical diagram of the number of remaining oil lumps and the average volume of a single remaining oil in the present invention. In order to further quantitatively characterize the occurrence of remaining oil, the average volume of remaining oil is defined as:

$\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\mathrm{<span\; class="notranslate">\; N</span>}}$

In the formula: is the average volume of remaining oil, N is the number of remaining oil blocks, and v _i is the volume of the i-th block of remaining oil. Through the comprehensive analysis of the number of remaining oil lumps and the average volume of remaining oil, the occurrence of remaining oil in the process of remaining oil displacement can be quantitatively characterized.

As shown in Fig. 7, Fig. 7 is a schematic diagram of remaining oil occurrence positions at different displacement times in the present invention. In order to further quantitatively characterize the location of remaining oil, the contact area ratio C is defined as:

$\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>}$

In the formula, C—contact area ratio, S ₂ (i)—contact area between remaining oil and pores, S ₁ (i)—surface area of remaining oil. The contact area of remaining oil is the percentage of the contact area between remaining oil and pores in the total surface area of remaining oil, which reflects the relative positional relationship between remaining oil and pore surfaces. The smaller the contact area ratio, the smaller the proportion of remaining oil attached to the pore surface, and the better the corresponding water flooding effect.

As shown in Fig. 8, Fig. 8 is a schematic diagram of the state of remaining oil in slices at different positions at different times of saturated oil in the present invention. In order to quantitatively describe the occurrence form of remaining oil, the shape factor G of remaining oil is defined as:

G=V/S _1.5

In the formula, V—the volume of a single block of remaining oil, S—the surface area of a single block of remaining oil. From the definition of the remaining oil shape factor, it can be seen that the smaller the shape factor, the larger the surface area of the remaining oil under the same volume, the greater the degree of surface unevenness, and the more irregular the shape. Based on the size of the shape factor, the remaining oil in each displacement stage is divided into four types: single pore, oil film, porous and continuous sheet.

A microcosmic occurrence representation method of remaining oil based on core CT image processing of the present invention is based on the acquisition of core CT scan images, through CT image preprocessing, longitudinal image interpolation, image-based medium segmentation, core model three-dimensional reconstruction, hole Throat segmentation and pore-throat topological structure reconstruction, etc., to obtain the three-dimensional shape of all pores and throats in the core model and their topological connections, and to propose a quantitative characterization description of the microscopic occurrence of remaining oil, which can analyze the microscopic occurrence state of remaining oil. Qualitative and quantitative analysis of influencing factors are studied to provide reliable guidance for improving oil recovery.

Claims (5)

1. A microcosmic occurrence representation method of residual oil based on core CT image processing, characterized in that: comprising the steps: Step 1, the processing of CT images, including CT image preprocessing, interpolation operation, image segmentation; Step 2, modeling the pore and throat network on the basis of CT image processing; Step 3, quantitative statistics of remaining oil microscopic occurrence; Step 4, state characterization of remaining oil microscopic occurrence. 2. a kind of residual oil microscopic representation method based on rock core CT image processing according to claim 1, is characterized in that: the processing of CT image in step 1 comprises: (1) Mainly perform contrast enhancement and sharpening on the acquired image first; (2) Perform appropriate interpolation operation on the sliced image, and generate a new image by interpolation in the middle of the sliced image to ensure that the distance between the image layers is equal to the resolution of the plane image; (3) With the help of image segmentation technology, the pores and remaining oil in the microscopic displacement image can be segmented. 3. A method for representing microcosmic occurrence of remaining oil based on core CT image processing according to claim 1, characterized in that: the modeling of pores and throat networks is based on the results of CT image processing for analyzing and displaying rocks structure information. 4. A method for expressing remaining oil microscopic occurrences based on core CT image processing according to claim 1, characterized in that: the quantitative statistics of remaining oil microscopic occurrences include the block number, volume and surface area. 5. A method for expressing remaining oil microscopic occurrence based on core CT image processing according to claim 1, characterized in that: the state characterization description of remaining oil microscopic occurrence includes remaining oil microscopic occurrence, occurrence location and Existing form.