CN110853138A - Dual-medium carbonate rock pore-fracture dual-network model construction method - Google Patents
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Abstract
The invention relates to the technical field of oil and gas development, in particular to a dual-medium carbonate rock pore-fracture dual network model construction method. 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, and extracting a space to be identified; performing morphological analysis on the space to be identified, and completing the separation of the pore space and the crack space according to the morphological analysis result; respectively constructing network models for the separated pore space and crack space by adopting a sphere filling method to obtain a pore network model and a crack network model; and adding a communicating throat between the pore network model and the fracture network model to complete the construction of the pore-fracture dual network model. The invention can accurately construct the pore network model and the crack network model when constructing the dual-medium carbonate rock network model, and simultaneously fuse 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 and gas development, in particular to a dual-medium carbonate rock pore-fracture dual network model construction method.
Background
With the increasing strength of exploration and development in China, the types of the existing oil and gas reservoirs are more and more complex, and particularly the exploratory reserves of the pore-fracture carbonate rock gas reservoirs are increased continuously. The pore-fracture type carbonate gas reservoir is different from a conventional sandstone gas reservoir, and a fracture and pore dual medium system is formed due to the existence of a large number of natural fractures in the pore-fracture type carbonate gas reservoir, so that the seepage characteristics and the fluid exchange relationship of the pore-fracture type carbonate gas reservoir are more complex, and the difficulty in formulating a development scheme is higher.
For the research on the seepage characteristics of carbonate rock with the simultaneous development of cracks and pores, the common method is to construct a crack and a rock system with a common pore medium, and to utilize a finite element method to couple the flow characteristics of fluid in different media of the pores and the cracks for solving and calculating. The method has a complex operation process and needs to construct a large enough model for a rock core sample with strong heterogeneity, so that the research period is greatly increased, and the method cannot be popularized and used in a large scale.
Since the introduction of the pore network model into the field of core analysis in the 50 th 20 th century, the pore network model has gradually become an important tool for the representation of the micro pore structure of the core and the prediction of the micro seepage characteristics. The conventional pore network model construction method is mainly used for porous media, and due to the continuity of a crack space and the wide range of three-dimensional expansion, part of information can be lost in the conventional modeling method, so that the real three-dimensional topological structure of the crack cannot be accurately captured. In addition, for the dual-medium carbonate rock with pores and cracks developing simultaneously, fluid exchange exists between the pores and the cracks, and a set of network model is used for representing the pores and the cracks simultaneously, so that certain errors obviously exist, and the influence is caused on later-stage research and analysis.
To sum up, when a dual-medium carbonate rock network model is constructed, two problems need to be solved simultaneously: firstly, the problem of accurately constructing a crack network model is solved; secondly, network models need to be respectively constructed for two mediums of the pore and the crack and then are fused into a set of pore-crack dual network models.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a dual-medium carbonate rock pore-fracture dual network model construction method, which can accurately construct a pore network model and a fracture network model when constructing a dual-medium carbonate rock network model and simultaneously fuse the pore network model and the fracture network model into the pore-fracture dual network model when being applied.
The technical scheme adopted by the invention is as follows:
the method for constructing the dual-medium carbonate rock pore-fracture dual network model comprises the following steps:
the method comprises the following steps: collecting a dual-medium carbonate rock sample, and scanning the dual-medium carbonate rock sample to obtain a lossless three-dimensional image;
step two: performing image segmentation processing on the three-dimensional image, and extracting a space to be identified containing 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 the separation of the pore space and the crack space according to the morphological analysis result;
step four: respectively constructing network models for the separated pore space and crack space by adopting a sphere filling method to obtain a pore network model and a crack network model;
step five: and adding a communicating throat between the pore network model and the fracture network model to complete the construction of the pore-fracture dual network model.
Preferably, in the first step, a CT scanner is used to perform CT scanning on the dual-medium carbonate rock sample to obtain a nondestructive three-dimensional image.
Preferably, the specific process for acquiring the three-dimensional image of the dual-medium carbonate rock sample comprises the following steps: firstly, scanning a dual-medium carbonate rock sample by utilizing 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.
Preferably, in the third step, the step of performing morphological analysis on the crack space and the crack space includes:
s31, measuring to obtain three-dimensional length and three-dimensional minimum width data of the pore space and the crack space;
s32, calculating to obtain the ratio of the three-dimensional length to the three-dimensional minimum width;
and S33, setting a threshold, comparing the calculated ratio with the threshold, and judging the crack space or the pore space according to the comparison result.
Preferably, in the fourth step, the sphere filling method comprises: a central line extraction method is adopted to describe three-dimensional space spread and a topological structure, then a central line voxel is used as a sphere center, a space boundary point is used as a tangent point to establish an inscribed sphere, finally a rod body is established to connect all continuous inscribed spheres to the center, the opening degree of the connected inscribed sphere represents the space, and the connectivity and seepage channel information of the space are represented by the connected rod body.
Preferably, the method for constructing the network model of the fracture space comprises the following specific steps:
s41, centerline extraction: extracting continuous voxel chains, wherein the voxel chains are fracture center lines of fracture spaces;
s42, determining an expandable space by using an expansion algorithm with each voxel on the central line as a basic point, identifying an inscribed sphere corresponding to the basic point by using a contraction algorithm after finding a double-medium carbonate rock skeleton voxel range closest to each voxel, and finally calculating to obtain an upper limit value and a lower limit value of the radius of the inscribed sphere;
s43, after a series of inscribed spheres taking the central line voxel as the sphere center are extracted, optimizing the extracted inscribed spheres to obtain a residual inscribed sphere set;
and S43, sequentially connecting the residual inscribed spheres through the rod bodies to form a fracture space network model.
Preferably, in step S43, the process of optimizing the extracted inscribed sphere includes: firstly, representing each voxel in a linked list mode according to the square size of the radius of an inscribed sphere corresponding to each voxel; and then 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 residual inscribed sphere set which is not included.
Preferably, in the fifth step, the specific steps of constructing the pore-fracture dual network model include:
s51, marking contact surfaces of the pore space and the crack space, finding respective maximum inscribed spheres in the pore network model and the crack network model corresponding to the contact surfaces, and numbering the maximum inscribed spheres;
s52, obtaining the throat radius and coordination number distribution relation communicated between the pore network model and the fracture network model according to the number and area of the contact surfaces and the number of the corresponding maximum inscribed sphere;
and S53, connecting the maximum inscribed spheres in the pore network model and the fracture network model corresponding to the contact surface through throats according to the distribution relation of the throat radius and the coordination number to form a pore-fracture dual network model.
The invention has the beneficial effects that:
1. the invention can accurately construct the pore network model and the crack network model when constructing the dual-medium carbonate rock network model, and simultaneously fuse the pore network model and the crack network model into a set of pore-crack dual network model.
2. The invention utilizes the method of extracting the central line and combining the maximum inscribed sphere to establish a fracture network model for finely characterizing the real fracture space topological structure in the rock, and the model can be directly used for parameter characterization and seepage characteristic simulation of the fracture space.
3. The pore-fracture dual network model constructed by the method can be considered as a quasi-static model, the fluid flow in the model is controlled by the capillary pressure, and the singular point problem caused by the fluid flow in the fracture when the physical property of the fluid changes can be ignored. By utilizing an invasion-percolation theory, seepage simulation in dual-medium carbonate rocks and prediction of relative permeability of each phase of fluid when multiphase fluid flows simultaneously during oil field development can be realized.
4. The pore-fracture dual network model constructed by the method can be considered as a quasi-static model, the calculation speed is greatly improved compared with the conventional method for solving and calculating by coupling the flow characteristics of the fluid in different media of pores and fractures by using a finite element method, and the method can be directly applied to development and production of oil and gas fields and provides mechanism recognition and data support for the design of oil and gas field development schemes.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic flow chart of the steps of the present invention;
FIG. 2 is a micron CT scan image of dual medium carbonate rock;
FIG. 3 is a diagram of a pore network model, a fracture network model and a constructed pore-fracture dual network model of a dual medium carbonate rock;
FIG. 4 is a schematic illustration of pore space and fracture space extraction from a CT image;
FIG. 5 is a schematic view of a three-dimensional length search angle in example 2;
FIG. 6 is a schematic illustration of isolated pore space and fracture space;
FIG. 7 is a schematic drawing of centerline extraction in example 3;
FIG. 8 is a schematic diagram of the maximum inscribed sphere and seepage channel division characterizing the fracture space in example 3;
FIG. 9 is a schematic diagram of a fracture network model characterization method in example 3;
FIG. 10 is a schematic illustration of the pore to fracture interface marking in example 4;
FIG. 11 is a schematic representation of the pores of example 4 prior to their communication with the fracture throat;
FIG. 12 is a schematic view of the communicating throat between the pores and the fractures in example 4.
Detailed Description
The invention is further described with reference to the following figures and specific embodiments. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. Specific structural and functional details disclosed herein are merely illustrative 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 understood that the terms first, second, etc. are used merely for distinguishing between descriptions and are not intended to indicate or imply 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. 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" herein is merely one type of association relationship that describes an associated object, meaning that three relationships may exist, e.g., a and/or B may mean: a exists alone, B exists alone, and A and B exist at the same time, and the term "/and" is used herein to describe another association object relationship, which means that two relationships may exist, for example, A/and B, may mean: a alone, and both a and B alone, and further, the character "/" in this document generally means that the former and latter associated objects are in an "or" relationship.
It is to be understood that in the description of the present invention, the terms "upper", "vertical", "inside", "outside", and the like, refer to an orientation or positional relationship that is conventionally used for placing the product of the present invention, or that is conventionally understood by those skilled in the art, and are used merely for convenience in describing and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and therefore should not be considered 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 adjacent" or "directly coupled" to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between … …" versus "directly between … …", "adjacent" versus "directly adjacent", etc.).
In the description of the present invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "disposed," "mounted," and "connected" are to be construed broadly, e.g., as meaning fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled 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 otherwise. It will be further understood that the terms "comprises," "comprising," "includes," and/or "including," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but 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 facilitate 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, systems may be shown in block diagrams in order not to obscure the examples in unnecessary detail. In other instances, well-known processes, structures and techniques may be shown without unnecessary detail in order to avoid obscuring example embodiments.
Example 1:
the embodiment provides a dual medium carbonate rock pore-fracture dual network model construction method, as shown in fig. 1:
the method comprises the following steps:
the method comprises the following steps: and carrying out CT scanning on the double-medium carbonate rock sample by using micron CT to obtain a nondestructive real sample three-dimensional image.
Step two: and (3) extracting pore and crack spaces from the three-dimensional image obtained in the step one by using an image segmentation technology. At this time, the pores and the cracks are extracted as the same phase, and the pores and the cracks need to be further separated, so that the purpose of respectively constructing the network models is realized.
Step three: and D, performing morphological analysis on the pore space and the fracture space extracted in the step two, calculating the three-dimensional length and three-dimensional minimum width information of each pore/fracture, and dividing the pores and the fractures according to the ratio of the two.
Step four: the three-dimensional spatial distribution and the topological structure of the crack are really depicted by utilizing a center line extraction method for the crack space separated in the third step, then the crack boundary is ascertained by using each center line voxel as a sphere center and a method of continuous expansion search, the real opening degree of the crack is represented by mutually connected spheres, the rod-shaped construction among the connected spheres is used for representing the connectivity and seepage channel information of the crack; and meanwhile, constructing a network model for the pore space separated in the third step by using the sphere filling method to obtain a pore network model.
Step five: and after the pore network model and the fracture network model are respectively obtained according to the fourth step and the fifth step, a communicating throat is added between the largest spheres representing pores and fractures, so that the pore-fracture dual network model is constructed.
As shown in fig. 2, is an original micrometer CT scan image of the dual medium carbonate rock, and as shown in fig. 3, is a pore network model, a fracture network model and a final pore-fracture dual network model obtained by the method.
The method for establishing the digital core by utilizing the gray level image obtained by micron CT scanning mainly comprises the following three steps: 1. scanning the processed rock sample by utilizing CT equipment to obtain projection data of the rock sample; 2. reconstructing the acquired 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 image, the pore space and the crack space in the gray image are separated from the rock skeleton by using an image segmentation method, as shown in part b in fig. 4.
Example 2:
as optimization of the above embodiment, the separation of the pore space and the fracture space can be performed by calculating the three-dimensional length and the three-dimensional minimum width ratio of the pore and the fracture, and selecting an appropriate threshold value to perform effective separation. The three-dimensional length measurement is to place each pore/crack in a coordinate system as shown in fig. 5, search from 0 degree to 162 degrees in a step of 18 degrees in the theta and phi directions respectively, and record the distance between the head and tail end points 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 edge of the pore/crack 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 fracture is in a flat shape, the ratio of the three-dimensional length to the minimum width of the fracture is far larger than that of the pore, so that the fracture and the pore can be distinguished by the ratio. Fig. 6 shows the result of distinguishing the pores and cracks in fig. 4 using the three-dimensional length and the minimum width ratio.
Example 3:
as optimization of the above embodiment, when the network model is constructed for the fracture space separated in step three, the following operations are sequentially adopted to obtain the fracture network model:
1. extracting a center 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 possible search space is first determined using a dilation algorithm. After finding the skeleton voxel range closest to each voxel, adopting a contraction algorithm to identify an inscribed sphere corresponding to the central 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 voxel are extracted, the extracted inscribed spheres need to be optimized since some of the spheres are a subset of other spheres. The optimization method represents each voxel in a form of a linked list according to the square size of the corresponding inscribed sphere radius of the voxel. When the loop calculation is performed until R2 becomes 0, the operation is stopped. For an inscribed sphere with a radius of R0 and a sphere center of p0 ═ x0, y0, and z0, the generated linked list is searched for an inscribed sphere corresponding to a voxel p satisfying the condition of dist2(p, p0) < R02, and it is determined whether there is an inclusion relationship with the specified sphere. And deleting the found inscribed sphere with the inclusion relationship from the linked list, and finally, leaving the maximum inscribed sphere set which is not contained by other spheres in the linked list.
4. Further, the maximum inscribed sphere set is converted into interconnected clusters, as shown in fig. 8, the main sphere in each cluster defines the size of the fracture space in the region where the cluster is located, the nodes connected between different clusters define the size of the seepage channel of the fracture space, when a seepage channel is found, links of the channel to the two main spheres respectively can be obtained, and the links are composed of the seepage channel and all inscribed spheres between the leading main spheres. As shown in fig. 9, these links also actually form the skeleton of the entire fracture network model.
Example 4:
as an optimization of 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 communicating throat is added between the largest inscribed spheres representing pores and fractures, so that the construction of the pore-fracture dual network model is realized:
1. after the pore space and the fracture space are obtained, as shown in fig. 10, the contact surfaces where the pore space and the fracture space are in contact with each other are marked, and the largest inscribed sphere number in the pore network model and the fracture network model corresponding to the contact surfaces is found.
2. And establishing a throat radius and coordination number distribution relation communicated between the pores and the cracks according to the number N and the area S of each contact surface and the number I of the corresponding maximum inscribed sphere.
3. As shown in fig. 11 to 12, according to the distribution relationship between the throat radius and the coordination number, the throat with the appropriate radius and number is selected for connecting the largest sphere of the pore and the largest sphere of the fracture corresponding to the contact surface, so as to construct a pore-fracture dual network model.
The method accurately describes the three-dimensional topological structure of the crack by a method of extracting the central line and adding the maximum inscribed sphere, finely represents the information of the spatial distribution, the opening size, the connectivity and the like of the crack, and solves the problem of accurately constructing a crack network model when a dual-medium carbonate rock network model is constructed; in addition, the method builds a communication throat between the pores and the cracks based on the real communication surface and the communication relation of the pores and the cracks, and solves the problem that two mediums of the pores and the cracks are fused into a set of pore-crack dual network model after network models are respectively built.
The present invention is not limited to the above-described alternative embodiments, and various other forms of products can be obtained by anyone in light of the present invention. The above detailed description should not be taken as limiting the scope of the invention, which is defined in the claims, and which the description is intended to be interpreted accordingly.
Claims (8)
1. The method for constructing the dual-medium carbonate rock pore-fracture dual network model is characterized by comprising the following steps of:
the method comprises the following steps: collecting a dual-medium carbonate rock sample, and scanning the dual-medium carbonate rock sample to obtain a lossless three-dimensional image;
step two: performing image segmentation processing on the three-dimensional image, and extracting a space to be identified containing 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 the separation of the pore space and the crack space according to the morphological analysis result;
step four: respectively constructing network models for the separated pore space and crack space by adopting a sphere filling method to obtain a pore network model and a crack network model;
step five: and adding a communicating throat between the pore network model and the fracture network model to complete the construction of the pore-fracture dual network model.
2. The dual medium carbonate rock pore-fracture dual network model building method according to claim 1, characterized in that: in the first step, a CT scanner is adopted to carry out CT scanning on the double-medium carbonate rock sample, and a nondestructive three-dimensional image is obtained.
3. The dual medium carbonate rock pore-fracture dual network model building method according to claim 2, characterized in that: the specific process for acquiring the three-dimensional image of the dual-medium carbonate rock sample comprises the following steps: firstly, scanning a dual-medium carbonate rock sample by utilizing 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 rock pore-fracture dual network model building method according to claim 1, characterized in that: in step three, the process of performing morphological analysis on the crack space and the crack space comprises the following steps:
s31, measuring to obtain three-dimensional length and three-dimensional minimum width data of the pore space and the crack space;
s32, calculating to obtain the ratio of the three-dimensional length to the three-dimensional minimum width;
and S33, setting a threshold, comparing the calculated ratio with the threshold, and judging the crack space or the pore space according to the comparison result.
5. The dual medium carbonate rock pore-fracture dual network model building method according to claim 1, characterized in that: in step four, the sphere filling method comprises the following steps: a central line extraction method is adopted to describe three-dimensional space spread and a topological structure, then a central line voxel is used as a sphere center, a space boundary point is used as a tangent point to establish an inscribed sphere, finally a rod body is established to connect all continuous inscribed spheres to the center, the opening degree of the connected inscribed sphere represents the space, and the connectivity and seepage channel information of the space are represented by the connected rod body.
6. The dual medium carbonate rock pore-fracture dual network model building method according to claim 5, characterized in that: the specific steps of constructing the network model for the crack space are as follows:
s41, centerline extraction: extracting continuous voxel chains, wherein the voxel chains are fracture center lines of fracture spaces;
s42, determining an expandable space by using an expansion algorithm with each voxel on the central line as a basic point, identifying an inscribed sphere corresponding to the basic point by using a contraction algorithm after finding a double-medium carbonate rock skeleton voxel range closest to each voxel, and finally calculating to obtain an upper limit value and a lower limit value of the radius of the inscribed sphere;
s43, after a series of inscribed spheres taking the central line voxel as the sphere center are extracted, optimizing the extracted inscribed spheres to obtain a residual inscribed sphere set;
and S43, sequentially connecting the residual inscribed spheres through the rod bodies to form a fracture space network model.
7. The dual medium carbonate rock pore-fracture dual network model building method according to claim 6, characterized in that: in step S43, the process of optimizing the extracted inscribed sphere includes: firstly, representing each voxel in a linked list mode according to the square size of the radius of an inscribed sphere corresponding to each voxel; and then 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 residual inscribed sphere set which is not included.
8. The dual medium carbonate rock pore-fracture dual network model building method according to claim 5, characterized in that: in the fifth step, the concrete steps of constructing the pore-fracture dual network model comprise:
s51, marking contact surfaces of the pore space and the crack space, finding respective maximum inscribed spheres in the pore network model and the crack network model corresponding to the contact surfaces, and numbering the maximum inscribed spheres;
s52, obtaining the throat radius and coordination number distribution relation communicated between the pore network model and the fracture network model according to the number and area of the contact surfaces and the number of the corresponding maximum inscribed sphere;
and S53, connecting the maximum inscribed spheres in the pore network model and the fracture network model corresponding to the contact surface through throats according to the distribution relation of the throat radius and the coordination number to form a pore-fracture dual network model.
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