CN110853138B - Construction method of dual-medium carbonate pore-crack dual-network model - Google Patents
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Abstract
The invention relates to the technical field of oil gas development, in particular to a method for constructing a dual-medium carbonate pore-crack dual-network model. The method comprises the following steps: scanning the dual-medium carbonate rock sample to obtain a three-dimensional image; performing image segmentation processing on the three-dimensional image to extract a space to be identified; performing morphological analysis on the space to be identified, and completing separation of a pore space and a crack space according to morphological analysis results; respectively constructing a network model of the separated pore space and the separated crack space by adopting a sphere filling method to obtain a pore network model and a crack network model; and adding a communication throat between the pore network model and the crack network model to complete the construction of the pore-crack dual network model. The invention can accurately construct the pore network model and the crack network model when constructing the dual-medium carbonate network model, and simultaneously combine the pore network model and the crack network model into the pore-crack dual-network model.
Description
Technical Field
The invention relates to the technical field of oil gas development, in particular to a method for constructing a dual-medium carbonate pore-crack dual-network model.
Background
With the continuous enhancement of the exploration and development of China, the types of oil and gas reservoirs encountered at present are more and more complex, and particularly the exploration reserves of pore-fracture type carbonate reservoirs are continuously increased. The pore-crack type carbonate gas reservoir is different from the conventional sandstone gas reservoir, and a crack and pore dual-medium system is formed in the pore-crack type carbonate gas reservoir due to the existence of a large number of natural cracks, so that the seepage characteristics and the fluid exchange relationship are more complex, and the difficulty in developing a development scheme is greater.
For the research of the seepage characteristics of carbonate rock with cracks and pores simultaneously developed, the common practice is to construct a rock mass system with the cracks and the common pore medium, and solve and calculate the flow characteristics of coupling fluid in different pore and crack mediums by using a finite element method. Because the operation process of the method is complex and a large enough model needs to be constructed for the core sample with strong heterogeneity, the research period is greatly prolonged, and the method cannot be popularized and used on a large scale.
The pore network model has become an important tool for the characterization of the microscopic pore structure and the prediction of the microscopic seepage characteristics of the core since the introduction of the core analysis field in the 50 th century of 20 th year. The traditional pore network model construction method is mainly used for porous media, and due to continuity of crack space and wide three-dimensional expansion, the conventional modeling method can lose part of information so that the true three-dimensional topological structure of the crack cannot be accurately captured. In addition, for dual-medium carbonate rock with pores and cracks which develop simultaneously, fluid exchange exists between the pores and the cracks, and a certain error obviously exists in the simultaneous characterization of the pores and the cracks by using a set of network models, so that the later research and analysis are influenced.
To sum up, when constructing a dual-medium carbonate network model, two problems need to be solved simultaneously: firstly, realizing the accurate construction of a fracture network model; secondly, after a network model is respectively constructed for two mediums of the pore crack, the two mediums are fused into a set of pore-crack dual network model.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention provides a dual-medium carbonate pore-crack dual-network model construction method, which can accurately construct a pore network model and a crack network model when constructing a dual-medium carbonate network model in application, and simultaneously fuse the pore network model and the crack network model into a pore-crack dual-network model.
The technical scheme adopted by the invention is as follows:
the construction method of the dual-medium carbonate pore-crack dual-network model comprises the following steps:
step one: collecting a dual-medium carbonate sample, and scanning the dual-medium carbonate sample to obtain a nondestructive three-dimensional image;
step two: performing image segmentation processing on the three-dimensional image, and extracting a space to be identified, which contains a pore space and a crack space, from the three-dimensional image;
step three: performing morphological analysis on the space to be identified, and completing separation of a pore space and a crack space according to morphological analysis results;
step four: respectively constructing a network model of the separated pore space and the separated crack space by adopting a sphere filling method to obtain a pore network model and a crack network model;
step five: and adding a communication throat between the pore network model and the crack network model to complete the construction of the pore-crack dual network model.
In the first step, a CT scanner is used to perform CT scanning on the dual-medium carbonate sample to obtain a nondestructive three-dimensional image.
As a preferred aspect of the above technical solution, the specific process for obtaining a three-dimensional image of a dual medium carbonate sample includes: firstly, scanning a dual-medium carbonate rock sample by using a CT scanner to obtain projection data; then, reconstructing the projection data into a core gray image by using an image reconstruction method; and finally, preprocessing the gray level image to obtain a three-dimensional image of the dual-medium carbonate rock sample.
As a preferred aspect of the above-mentioned aspect, in the third step, the process of performing morphological analysis on the void space and the crack space includes:
s31, measuring and obtaining three-dimensional length and three-dimensional minimum width data of a pore space and a crack space;
s32, calculating to obtain the ratio of the three-dimensional length to the three-dimensional minimum width;
s33, setting a threshold value, comparing the calculated ratio with the threshold value, and judging the crack space or the pore space according to the comparison result.
As a preferable mode of the above technical solution, in the fourth step, the sphere filling method includes: the three-dimensional space spreading and topological structure is depicted by adopting a central line extraction method, then an inscribed sphere is established by taking a central line voxel as a sphere center and taking a space boundary point as a tangent point, finally, a rod body is established to connect all continuous inscribed spheres in a centering manner, the opening degree of the space is represented by the interconnected inscribed spheres, and the connectivity and seepage channel information of the connected rod body represent the space.
As the optimization of the technical scheme, the specific steps of constructing the network model for the crack space are as follows:
s41, center line extraction: extracting continuous voxel chains, wherein the voxel chains are crack center lines of a crack space;
s42, determining an expandable space by using each voxel on a central line as a basic point and adopting an expansion algorithm, after finding the range of the double-medium carbonate skeleton voxels nearest to each voxel, identifying an inscribed sphere corresponding to the basic point by adopting a contraction algorithm, and finally calculating to obtain an upper limit and a lower limit of the inscribed sphere radius;
s43, after a series of inscribed spheres taking a central line voxel as a sphere center are extracted, optimizing the extracted inscribed spheres to obtain a residual inscribed sphere set;
and S43, sequentially centering and connecting the rest inscribed sphere sets through the rod bodies to form a crack space for a network model.
As a preferred embodiment of the present invention, in step S43, the process of optimizing the extracted inscribed sphere includes: firstly, according to the square size of the radius of each voxel corresponding to the inscribed sphere, each voxel is represented in a linked list form; and searching the linked list for the inscribed sphere corresponding to the voxel with the inclusion relationship, deleting the included inscribed sphere with the inclusion relationship, and finally leaving the rest inscribed sphere set which is not included.
As a preferred embodiment of the above technical solution, in the fifth step, the specific step of constructing the pore-crack dual network model includes:
s51, marking contact surfaces of a pore space and a crack space, finding out respective maximum inscribed spheres in a pore network model and a crack network model corresponding to the contact surfaces, and numbering the maximum inscribed spheres;
s52, obtaining a throat radius and coordination number distribution relation communicated between the pore network model and the crack network model according to the number and the area of the contact surfaces and the corresponding number of the maximum inscribed sphere;
and S53, connecting the largest inscribed spheres in the pore network model and the crack network model corresponding to the contact surface through the throat according to the throat radius and coordination number distribution relation to form a pore-crack dual network model.
The beneficial effects of the invention are as follows:
1. the invention can accurately construct the pore network model and the crack network model when constructing the dual-medium carbonate network model, and simultaneously combine the pore network model and the crack network model into a set of pore-crack dual-network model.
2. The invention utilizes a method of combining central line extraction with maximum inscribed sphere to establish a fracture network model for finely representing the real fracture space topological structure in the rock, and the model can be directly used for parameter representation and seepage characteristic simulation of the fracture space.
3. The pore-crack dual network model constructed by the invention can be regarded as a quasi-static model, the fluid flow in the model is controlled by the capillary pressure, and the problem of singular points caused by the flow in cracks when the physical properties of the fluid change can be ignored. By utilizing the invasion-percolation theory, the relative permeability prediction of each phase of fluid can be realized when multiphase fluid flows simultaneously during dual-medium carbonate rock seepage simulation and oilfield development.
4. The pore-crack dual network model constructed by the invention can be regarded as a quasi-static model, the calculation speed is greatly improved compared with the traditional method for solving and calculating the flow characteristics of coupling fluid in different media of pores and cracks by using a finite element method, the method can be directly applied to development and production of oil and gas fields, and mechanism recognition and data support are provided for the design of an oil and gas field development scheme.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic flow chart of the steps of the present invention;
FIG. 2 is a micrometer CT scan image of dual media carbonate;
FIG. 3 is a diagram of a pore network model, a fracture network model and a constituent pore-fracture dual network model of dual medium carbonate;
FIG. 4 is a schematic drawing of extraction of void space and crack space from CT images;
FIG. 5 is a schematic view of a three-dimensional length search angle in example 2;
FIG. 6 is a schematic illustration of the void space and fracture space separated;
FIG. 7 is a schematic view of the centerline extraction in example 3;
FIG. 8 is a schematic diagram of the maximum inscribed sphere and percolation path partitioning in example 3 showing the crack space;
FIG. 9 is a schematic diagram of a method for characterizing a split network model in example 3;
FIG. 10 is a schematic illustration of the pore and crack interface markings of example 4;
FIG. 11 is a schematic diagram of the embodiment 4 before the throat is connected between the pores and the cracks;
FIG. 12 is a schematic representation of example 4 after the throat is connected between the pores and the cracks.
Detailed Description
The invention is further described with reference to the drawings and specific examples. It should be noted that the description of these examples is for aiding in understanding the present invention, but is not intended to limit the present invention. Specific structural and functional details disclosed herein are merely representative of example embodiments of the invention. This invention may, however, be embodied in many alternate forms and should not be construed as limited to the embodiments set forth herein.
It should be appreciated that the terms first, second, etc. are used merely to distinguish between descriptions and should not be construed as indicating or implying relative importance. Although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments of the present invention.
It should be understood that the term "and/or" is merely an association relationship describing the associated object, and means that three relationships may exist, for example, a and/or B may mean: the terms "/and" herein describe another associative object relationship, indicating that there may be two relationships, e.g., a/and B, may indicate that: the character "/" herein generally indicates that the associated object is an "or" relationship.
It should be understood that in the description of the present invention, the terms "upper", "vertical", "inner", "outer", etc. indicate an azimuth or a positional relationship in which the inventive product is conventionally put in use, or an azimuth or a positional relationship that are conventionally understood by those skilled in the art, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the apparatus or elements referred to must have a specific azimuth, be configured and operated in a specific azimuth, and thus should not be construed as limiting the present invention.
It will be understood that when an element is referred to as being "connected," "connected," or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. Other words used to describe relationships between elements (e.g., "between … …" pair "directly between … …", "adjacent" pair "directly adjacent", etc.) should be interpreted in a similar manner.
In the description of the present invention, it should also be noted that, unless explicitly specified and limited otherwise, the terms "disposed," "mounted," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates to the contrary. It will be further understood that the terms "comprises," "comprising," "includes," "including" and/or "including," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, and do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and/or groups thereof.
It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or the figures may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
In the following description, specific details are provided to provide a thorough understanding of example embodiments. However, it will be understood by those of ordinary skill in the art that the example embodiments may be practiced without these specific details. For example, a system may be shown in block diagrams in order to avoid obscuring the examples with unnecessary detail. In other embodiments, well-known processes, structures, and techniques may not be shown in unnecessary detail in order to avoid obscuring the example embodiments.
Example 1:
the embodiment provides a dual-medium carbonate pore-crack dual-network model construction method, which is as shown in fig. 1:
the method comprises the following steps:
step one: and carrying out CT scanning on the dual-medium carbonate rock sample by using the micron CT to obtain a nondestructive real sample three-dimensional image.
Step two: and (3) extracting pore spaces and crack spaces from the three-dimensional image obtained in the step one by utilizing an image segmentation technology. Because the pores and the cracks are extracted as the same phase, the pores and the cracks need to be further separated, and the aim of respectively constructing the network model is fulfilled.
Step three: and (3) carrying out morphological analysis on the pore and crack space extracted in the step two, calculating the three-dimensional length and the three-dimensional minimum width information of each pore/crack, and dividing the pore and the crack through the ratio of the two.
Step four: firstly, a central line extraction method is utilized to truly draw out three-dimensional space spread and topology structures of the crack in the crack space separated in the step three, then, a continuous expansion searching method is adopted by taking each central line voxel as a sphere center, the crack boundary is ascertained, the mutually connected spheres are used for representing the real opening of the crack, stick-shaped construction is used for connecting the spheres, and connectivity and seepage channel information of the crack are represented; and simultaneously, constructing a network model for the pore space separated in the step three by using the sphere filling method to obtain a pore network model.
Step five: and (3) after the pore network model and the crack network model are respectively obtained according to the step four and the step five, constructing the pore-crack dual network model by adding a communication throat between the maximum spheres representing the pores and the cracks.
As shown in fig. 2, the original dual medium carbonate micron CT scan image is shown in fig. 3, which is the pore network model, fracture network model and final pore-fracture dual network model finally obtained by the present method.
The method for establishing the digital rock core by using the gray level image obtained by the micron CT scanning mainly comprises the following three steps: 1. scanning the processed rock sample by using CT equipment to obtain projection data of the rock sample; 2. reconstructing the obtained projection data into a core gray image by using an image reconstruction method, as shown in a part a in fig. 4; 3. after preprocessing the gray level image, the void and crack space in the gray level image is separated from the rock skeleton by using an image segmentation method, as shown in part b in fig. 4.
Example 2:
as an optimization of the above embodiment, the void space and the crack space can be distinguished by calculating the ratio of the three-dimensional length and the three-dimensional minimum width of the void and the crack, and selecting a suitable threshold value for effective separation. The three-dimensional length measurement is to place each pore/crack in a coordinate system as shown in fig. 5, take 18 degrees as a step length along the theta and phi directions, search from 0 degrees to 162 degrees, record the distance between the head and tail ends of each step, wherein the maximum distance is the three-dimensional length. Two planes which are parallel to each other and are in contact with the edges of the pores/cracks and are made in the three-dimensional length direction rotate by taking the three-dimensional length direction as an axis, and the minimum distance between the two planes is the three-dimensional minimum width. Because the crack is in a flat form, the ratio of the three-dimensional length to the minimum width is far greater than that of the pore, so that the crack and the pore can be distinguished by the size of the ratio. The result of distinguishing the pores and cracks of fig. 4 using the ratio of three-dimensional length to minimum width is shown in fig. 6.
Example 3:
as an optimization of the above embodiment, when the network model is constructed for the fracture space separated in the third step, the following operations are sequentially adopted to obtain a fracture network model:
1. extracting a central line: firstly, giving a value to each voxel of a fracture digital core model, wherein the value is the distance from the voxel to the nearest rock skeleton; and then continuously refining the digital core model of the fracture according to the distance map until a continuous voxel chain is left, wherein the voxel chain is the extracted fracture center line as shown in fig. 7.
2. With each centerline voxel on the centerline as a base point, a dilation algorithm is first used to determine the possible search space. After finding the nearest skeleton voxel range from each voxel, adopting a contraction algorithm to identify the inscribed sphere corresponding to the center voxel; and finally, calculating to obtain the upper limit value and the lower limit value of the radius of the inscribed sphere.
3. After a series of inscribed spheres centered on the centerline voxels are extracted, the extracted inscribed spheres need to be optimized because some spheres are a subset of other spheres. The optimization method is characterized in that each voxel is represented in a linked list mode according to the square size of the inscribed sphere radius corresponding to the voxel. When the loop calculation is to r2=0, the operation is stopped. For an inscribed sphere with a sphere center of p0= (x 0, y0, z 0) and a radius of R0, searching an inscribed sphere corresponding to a voxel p meeting the condition dist2 (p, p 0) < R02 in the generated linked list, and judging whether an inclusion relationship exists between the inscribed sphere and the appointed sphere. The found inscribed sphere with the containing relation is deleted from the linked list, and finally the largest inscribed sphere set which is not contained by other spheres is left in the linked list.
4. Further, the largest inscribed ball set is converted into clusters connected with each other, as shown in fig. 8, the main balls in each cluster define the size of the crack space in the area where the cluster is located, the nodes connected between different clusters define the size of the seepage channels of the crack space, after one seepage channel is found, the links of the channel to two main balls can be obtained, and the links are composed of the seepage channels and all inscribed balls between the main balls. As shown in fig. 9, these links also actually form the skeleton of the overall fracture network model.
Example 4:
as an optimization for the above embodiment, after the fracture network model and the pore network model are respectively constructed, the following operation flows are sequentially adopted, and a communication throat is added between the largest inscribed spheres representing the pores and the fractures, so that the construction of the pore-fracture dual network model is realized:
1. after the pore space and the crack space are obtained, as shown in fig. 10, the contact surface of the pore space and the crack space, which are in contact with each other, is marked, and the largest inscribed sphere number in the pore network model and the crack network model corresponding to the contact surface is found.
2. According to the number N and the area S of each contact surface and the corresponding number I of the largest inscribed sphere, establishing a throat radius and coordination number distribution relation of communication between the pores and the cracks.
3. As shown in fig. 11 to 12, according to the distribution relation of the throat radius and coordination number, the pore and the maximum sphere of the crack corresponding to the contact surface are selected to connect the two throats with proper radius and number, so as to construct the pore-crack dual network model.
The method accurately describes the three-dimensional space topological structure of the crack by a method of extracting the central line and adding the maximum inscription sphere, finely characterizes the information of the space spread, the opening degree, the connectivity and the like of the crack, and solves the problem of accurately constructing the crack network model when constructing the dual-medium carbonate network model; in addition, the method builds a communication throat between the pore and the crack based on the real communication surface and the communication relation of the pore and the crack, and solves the problem that two mediums of the pore and the crack are respectively built into a network model and then are fused into a set of pore-crack dual network model.
The invention is not limited to the alternative embodiments described above, but any person may derive other various forms of products in the light of the present invention. The above detailed description should not be construed as limiting the scope of the invention, which is defined in the claims and the description may be used to interpret the claims.
Claims (4)
1. The method for constructing the dual-medium carbonate pore-crack dual-network model is characterized by comprising the following steps of:
step one: collecting a dual-medium carbonate sample, and scanning the dual-medium carbonate sample to obtain a nondestructive three-dimensional image;
step two: performing image segmentation processing on the three-dimensional image, and extracting a space to be identified, which contains a pore space and a crack space, from the three-dimensional image;
step three: performing morphological analysis on the space to be identified, and completing separation of the pore space and the crack space according to morphological analysis results, wherein the method comprises the following steps: s31, measuring and obtaining three-dimensional length and three-dimensional minimum width data of a pore space and a crack space; s32, calculating to obtain the ratio of the three-dimensional length to the three-dimensional minimum width; s33, setting a threshold value, comparing the calculated ratio with the threshold value, and judging a crack space or a pore space according to a comparison result;
step four: respectively constructing a network model for the separated pore space and the separated crack space by adopting a sphere filling method to obtain a pore network model and a crack network model, wherein the sphere filling method comprises the steps of adopting a central line extraction method to draw three-dimensional space spreading and topological structures, then taking a central line voxel as a sphere center, taking a space boundary point as a tangent point to establish an inscribed sphere, finally establishing a rod body to connect each continuous inscribed sphere in a centering manner, representing the opening degree of the space by the interconnected inscribed spheres, and representing the connectivity of the space and the seepage channel information by the connected rod body; the specific steps of constructing the network model for the crack space are as follows: s41, center line extraction: extracting continuous voxel chains, wherein the voxel chains are crack center lines of a crack space; s42, determining an expandable space by using each voxel on a central line as a basic point and adopting an expansion algorithm, after finding the range of the double-medium carbonate skeleton voxels nearest to each voxel, identifying an inscribed sphere corresponding to the basic point by adopting a contraction algorithm, and finally calculating to obtain an upper limit and a lower limit of the inscribed sphere radius; s43, after a series of inscribed spheres taking a central line voxel as a sphere center are extracted, optimizing the extracted inscribed spheres to obtain a residual inscribed sphere set; s43, sequentially centering and connecting the rest inscribed sphere sets through the rod bodies to form a crack space for a network model;
step five: a communication throat is added between the pore network model and the crack network model, so that the construction of a pore-crack dual network model is completed; the specific steps for constructing the pore-crack dual network model comprise: s51, marking contact surfaces of a pore space and a crack space, finding out respective maximum inscribed spheres in a pore network model and a crack network model corresponding to the contact surfaces, and numbering the maximum inscribed spheres; s52, obtaining a throat radius and coordination number distribution relation communicated between the pore network model and the crack network model according to the number and the area of the contact surfaces and the corresponding number of the maximum inscribed sphere; and S53, connecting the largest inscribed spheres in the pore network model and the crack network model corresponding to the contact surface through the throat according to the throat radius and coordination number distribution relation to form a pore-crack dual network model.
2. The dual medium carbonate pore-fracture dual network model construction method according to claim 1, characterized in that: in the first step, a CT scanner is adopted to carry out CT scanning on a dual-medium carbonate rock sample, and a nondestructive three-dimensional image is obtained.
3. The dual medium carbonate pore-fracture dual network model construction method according to claim 2, characterized in that: the specific process for acquiring the three-dimensional image of the dual-medium carbonate sample comprises the following steps: firstly, scanning a dual-medium carbonate rock sample by using a CT scanner to obtain projection data; then, reconstructing the projection data into a core gray image by using an image reconstruction method; and finally, preprocessing the gray level image to obtain a three-dimensional image of the dual-medium carbonate rock sample.
4. The dual medium carbonate pore-fracture dual network model construction method according to claim 1, characterized in that: in step S43, the process of optimizing the extracted inscribed sphere includes: firstly, according to the square size of the radius of each voxel corresponding to the inscribed sphere, each voxel is represented in a linked list form; and searching the linked list for the inscribed sphere corresponding to the voxel with the inclusion relationship, deleting the included inscribed sphere with the inclusion relationship, and finally leaving the rest inscribed sphere set which is not included.
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