Shale reservoir natural fracture slippage evaluation method based on fracture discrete model

Abstract

The invention relates to the technical field of oil and gas development, in particular to a shale reservoir natural fracture slippage evaluation method based on a fracture discrete model, which comprises the following steps: calculating a coherent attribute and a curvature attribute according to post-stack seismic data and geological structure form data, and performing enhancement processing on a trend, a tendency and a disconnection point to obtain an attribute enhancement body; calculating a fracture seismic facies according to the coherence attribute and the curvature attribute; performing crack automatic tracking and gridding processing according to the curvature attribute after enhancement processing, and performing discrete crack grouping according to the crack seismic facies to obtain a discrete crack model; and calculating the slip property of the natural fracture according to the calculated crustal stress data in combination with a discrete fracture model, wherein the slip property is calculated according to the Coulomb criterion. A discrete fracture model is established by calculating seismic geometric enhancement attributes and fracture seismic facies, analysis and calculation are performed by integrating crustal stress data, natural fracture slippage evaluation is completed, and unified quantitative slippage calculation on discrete fractures is realized.

Description

Technical Field

[0001] The invention relates to the technical field of natural fracture prediction, and in particular to a method for evaluating the slip properties of natural fractures in shale reservoirs based on a three-dimensional discrete model. Background Art

[0002] The exploration and development of shale gas is gradually moving towards deeper layers. In the process of deep shale gas exploration and development, the development of natural fractures in shale reservoirs has a very important impact on the production of shale gas wells. However, due to underground stress disturbance, faults and natural fractures may cause shear slip, which may lead to engineering risks. The research method of natural fault slip was based on fault interpretation and coherence body data in the early days. By calculating the angle between the fault strike and the maximum horizontal principal stress direction, the slip was roughly judged qualitatively. The existing method mainly uses the Coulomb-Moore failure criterion to calculate the fault slip based on seismic coherence body, curvature body and ground stress data.

[0003] The prior art has at least the following problems:

[0004] (1) Early methods could only make a rough judgment on the slip properties by calculating the angle between the fault strike and the direction of the maximum horizontal principal stress in fault interpretation and coherence body data, but could not make a quantitative judgment.

[0005] (2) The existing methods use the Coulomb-Moore failure criterion to calculate the fault slip properties based on the seismic coherence body, curvature body and ground stress data. The analysis scale is relatively large and the characterization accuracy needs to be further improved.

[0006] It can be seen that there is still room for improvement in the existing natural fracture prediction technology solutions. Adjustments and optimizations should be made to improve the accuracy of predictions and judgments, so as to better predict the generation and development of natural fractures and provide a reference for formulating shale gas extraction plans. Summary of the invention

[0007] In order to overcome at least one of the defects mentioned above, the present invention proposes a method for evaluating the slip properties of natural fractures in shale reservoirs based on a three-dimensional discrete model. First, the seismic geometric attributes and the seismic phases of the fractures are calculated, and a discrete fracture model is established through automatic fracture tracking, fracture gridding, and fracture grouping technology; then, based on the Coulomb-Moore criterion, the established discrete fracture model (DFN model) is analyzed and calculated with the comprehensive geostress data to complete the slip property evaluation of the natural fractures.

[0008] In order to achieve the above purpose, the evaluation method disclosed in the present invention can adopt the following technical solutions:

[0009] The natural fracture slip evaluation method of shale reservoir based on fracture discrete model includes:

[0010] According to the post-stack seismic data and geological structure morphology data, the coherence attributes and curvature attributes are calculated, and the strike, dip and disconnection points are enhanced to obtain the attribute enhancement body;

[0011] Calculate the fracture seismic phase based on coherence attributes and curvature attributes;

[0012] Automatically track and mesh the fractures according to the enhanced curvature attributes, and group the fractures into discrete groups according to the fracture seismic phases to obtain a discrete fracture model.

[0013] The slip properties of natural fractures are calculated based on the calculated geostress data and combined with the discrete fracture model. The slip properties are calculated based on the Coulomb-Moore criterion.

[0014] The above disclosed evaluation method combines post-stack seismic data and actual address structural morphology data, establishes an evaluation model after computational processing, calculates slip properties within the model, and obtains evaluation results of the slip properties of natural fractures.

[0015] Furthermore, when the coherent attributes are calculated and processed in the present invention, the calculation and processing method is optimized and the following feasible option is proposed: the coherent attributes are obtained by calculating the eigenvalues ​​of the seismic data samples, and the seismic data sample vectors form the following matrix:

[0016]

[0017] The covariance matrix corresponding to the above matrix is ​​C a×a =D N×a T D N×a , based on the intrinsic structure coherence estimate, is determined as follows

[0018] The curvature properties are determined as follows

[0019]

[0020] Where K x represents the curvature along the x direction, d x is the apparent inclination angle.

[0021] Furthermore, the present invention optimizes the calculation method when calculating and determining the fracture seismic phase and proposes the following feasible option: the Bayesian probability clustering analysis algorithm is used when calculating the fracture seismic phase, and the following process is included:

[0022] Determine the earthquake attributes to be clustered and the number of categories to be divided;

[0023] The earthquake attributes that follow the same set distribution are classified into one category, and Π(θ) is used as the prior probability of the Bayesian formula;

[0024] Using the Euclidean distance formula Distance measurement is performed on individuals with a single attribute to determine the category;

[0025] Using Bayesian formula i=1,2…k to test clustering results;

[0026] When the test results meet the classification requirements, the calculation ends; otherwise, the clustering is recalculated and the above process is repeated.

[0027] Furthermore, the object of automatic crack tracking in the present invention is a limited object, specifically: the automatic crack tracking is to automatically track the property enhancement body after enhancement processing, and to count the length and direction of the tracked cracks; the crack gridding includes crack feature gridding, which is used to determine the topological relationship between crack lines and obtain the horizontal and vertical connection information between cracks.

[0028] Furthermore, when calculating the slip properties of natural fractures, each fracture structural surface satisfies the following relationship when it is in a critical sliding state:

[0029] σ n =0.5(σ1+σ3)+0.5(σ1-σ3)cos2β

[0030] τ=0.5(σ1-σ3)sin2β

[0031] Among them, σ n is the effective normal stress on the crack surface, τ is the shear stress, σ1 is the maximum stress, σ3 is the minimum stress, and β is the angle between the maximum stress and the normal direction of the crack surface; Characterize the slip properties of discrete fractures.

[0032] Compared with the prior art, some beneficial effects of the technical solution disclosed in the present invention include:

[0033] The present invention establishes a discrete fracture model (DFN model) by calculating seismic geometric enhancement attributes and fracture seismic phases, and based on the Coulomb-Moore criterion, analyzes and calculates comprehensive geostress data to complete the slip evaluation of natural fractures, thereby realizing a unified quantitative slip calculation of discrete fractures. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only represent some embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 A flow chart of the slip evaluation of natural fractures in shale reservoirs based on a three-dimensional discrete fracture model provided by the present invention;

[0036] Figure 2 A prediction result diagram after the curvature body attributes provided in an embodiment of the present invention are enhanced;

[0037] Figure 3 The fracture seismic phase of the Yang 101 well area provided in the embodiment of the present invention;

[0038] Figure 4 The discrete fracture model of the Yang 101 well area provided in an embodiment of the present invention;

[0039] Figure 5 The three-dimensional discrete fracture slip model of the Yang 101 well area provided in the embodiment of the present invention;

[0040] Figure 6 This is a change point analysis diagram of the three-dimensional discrete crack-slip model set of the Yang 101H3 platform provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments.

[0042] In view of the fact that the existing technology for evaluating the slip properties of cracks is insufficiently accurate, the following embodiment is optimized and a feasible option is proposed.

[0043] Example

[0044] This embodiment provides a method for evaluating the slip properties of natural fractures in shale reservoirs based on a fracture discrete model, which specifically includes the following steps:

[0045] S01: Based on post-stack seismic data and geological data (post-stack depth domain seismic data, existing structural maps, burial depth maps, etc.), calculate the coherence attributes and curvature attributes and enhance the strike, dip and disconnection points to obtain the attribute enhancement body.

[0046] Preferably, in this embodiment, when calculating and processing the coherent attributes, the calculation and processing method is optimized and the following feasible options are adopted: the coherent attributes are obtained by calculating the eigenvalues ​​of the seismic data samples, and the seismic data sample vectors form the following matrix:

[0047]

[0048] In the above matrix, d ij is the seismic sampling point, i is the horizontal sampling number, j is the vertical sampling number, D N×a is the matrix of seismic data sample points. The covariance matrix corresponding to the matrix is ​​C a×a =DN×a T D N×a , the coherence estimate based on the eigenstructure is determined as follows

[0049] λ max is the matrix D N×a The maximum eigenvalue of C nn Representative D n×n The covariance matrix of n C nn The coherence estimation based on the intrinsic structure has higher lateral resolution and stronger noise resistance than the previous methods.

[0050] The curvature properties are determined as follows

[0051]

[0052] Where K x represents the curvature along the x direction, d x is the apparent inclination angle.

[0053] S02: Calculate the fracture seismic phase based on the coherence attribute and curvature attribute.

[0054] Preferably, in this embodiment, when calculating and determining the fracture seismic phase, the calculation method is optimized and the following feasible options are adopted: when calculating the fracture seismic phase, a Bayesian probability clustering analysis algorithm is adopted, and the following process is included:

[0055] Determine the earthquake attributes to be clustered and the number of categories to be divided;

[0056] Assume that the existing earthquake attributes are first classified into one category, namely Π(θ0), which is also used as the prior probability of the Bayesian formula;

[0057] Using the Euclidean distance formula Distance measurement is performed on individuals with a single attribute to determine the category (in the Euclidean distance formula, x ik is the k-th coordinate of the ith point, x jk is the k-th dimension coordinate of the j-th point, d ij is the distance between the i-th point and the j-th point in the k-dimensional space. In general, k = 2 or 3 represents two-dimensional space and three-dimensional space respectively);

[0058] Using Bayesian formula Test clustering results (in the Bayesian formula, Π(θ i ) is the prior distribution of the attribute, representing the seismic attribute sample θ i The knowledge that is classified as category x, p(x|θ i ) is the sample θ iThe probability of being distributed in category x, p(θ i |x) is the existing sample θ i The probability of classifying the earthquake into x under the condition of (x), p(x) represents the probability of the latest earthquake attribute category);

[0059] When the test results meet the classification requirements, the calculation ends; otherwise, the clustering is recalculated and the above process is repeated.

[0060] S03: Automatically track and mesh the fractures according to the enhanced curvature attributes, and group the fractures into discrete groups according to the fracture seismic phases to obtain a discrete fracture model.

[0061] The object of automatic crack tracking in this embodiment is a limited object, specifically: the automatic crack tracking is to automatically track the property enhancement body after enhancement processing, and to count the length and direction of the tracked cracks; the crack gridding includes crack feature gridding, which is used to determine the topological relationship between crack lines and obtain the horizontal and vertical connection information between cracks.

[0062] S04: Based on the calculated geostress data, the slip properties of natural fractures are calculated in combination with a discrete fracture model, and the slip properties are calculated based on the Coulomb-Moore criterion.

[0063] When calculating the slip properties of natural fractures, each fracture structural surface satisfies the following relationship when it is in a critical sliding state:

[0064] σ n =0.5(σ1+σ3)+0.5(σ1-σ3)cos2β

[0065] τ=0.5(σ1-σ3)sin2β

[0066] Among them, σ n is the effective normal stress on the crack surface, τ is the shear stress, σ1 is the maximum stress, σ3 is the minimum stress, and β is the angle between the maximum stress and the normal direction of the crack surface; Characterizes the slip property of discrete fractures. The larger the value, the higher the slip property.

[0067] The above disclosed evaluation method combines post-stack seismic data and actual address structural morphology data, establishes an evaluation model after computational processing, calculates slip properties within the model, and obtains evaluation results of the slip properties of natural fractures.

[0068] According to the above embodiment, an example is given here for illustration:

[0069] See also Figure 1 The embodiment of the present invention provides a method for evaluating the slip properties of natural fractures in shale reservoirs based on a fracture discrete model, which is performed in the following steps:

[0070] Step 101, firstly, analyzing the post-stack seismic data and the geological structure morphology, calculating the coherence attribute and the curvature attribute and performing attribute enhancement processing;

[0071] Step 102, calculating the fracture seismic phase using the Bayesian probability clustering analysis algorithm for the calculated coherence attributes and curvature attributes;

[0072] Step 103, firstly, the curvature enhancement attribute calculated in step 101 is subjected to automatic fracture tracking and fracture meshing, and then discrete fracture grouping is performed with reference to the fracture seismic phase calculated in step 102, and finally a discrete fracture model is obtained;

[0073] Step 104, using the calculated geostress data to calculate the slip properties of natural fractures according to the Coulomb-Moore criterion, to complete the slip property assessment.

[0074] Below, the specific implementation of the example is further described in detail to support the technical problem to be solved by the present invention.

[0075] 1. The embodiment of the present invention selects the Ordovician Wufeng Formation in the Yang 101 well area of ​​the South Sichuan shale gas block in the Southwest Oil and Gas Field, and the reservoir is a marine shale reservoir.

[0076] 2. The coherence volume is obtained by calculating the eigenvalues ​​of seismic data samples. The seismic data sample vectors form a matrix:

[0077]

[0078] The covariance matrix corresponding to this matrix is ​​C a×a =D N×a T D N×a , then the intrinsic structure-based coherence estimation can be defined as

[0079] Curvature is an indicator that characterizes the geometric characteristics of the formation. The calculation formula is as follows:

[0080]

[0081] Where K x represents the curvature along the x direction, d x is the apparent inclination angle.

[0082] Attribute enhancement processing refers to enhancing the direction, tendency and disconnection points of the attributes on the basis of the original attributes to obtain an attribute enhancement body.

[0083] Figure 2 This is the prediction result diagram after the curvature body attribute is enhanced. The black curvature body enhancement attribute and the colored one are the curvature body attributes.

[0084] 3. Calculate fracture seismic phases using the Bayesian probability clustering analysis algorithm through the following steps: (1) Determine the seismic attributes to be clustered and the number of categories to be divided; (2) Assume that the seismic attributes clustered into one category follow a certain distribution, and use Π(θ) as the prior probability of the Bayesian formula; (3) Use the Euclidean distance formula Distance measurement is performed on individuals with a single attribute to determine the category; (4) Using the Bayesian formula Check the clustering results; (5) If they meet the classification requirements, the algorithm ends; otherwise, recalculate the clustering and repeat (2)-(5).

[0085] Figure 3 This is the fracture seismic phase of the Yang 101 well area. From the figure, we can see that different colors represent fracture phase belts. The fracture seismic phase of the Yang 101 well area is divided into four phase belts: faults and micro-faults, large and medium-scale discrete fractures, small-scale fractures, micro-fracture belts and matrix.

[0086] Figure 4 This is the discrete fracture model of the Yang 101 well area. From the figure, we can see the distribution position and direction of the discrete fracture zone.

[0087] 4. Calculate the slip property based on the Coulomb-Moore criterion. According to the Coulomb-Moore criterion, each crack structural surface satisfies the following relationship when it is in a critical sliding state:

[0088] σ n =0.5(σ1+σ3)+0.5(σ1-σ3)cos2β

[0089] τ=0.5(σ1-σ3)sin2β

[0090] Among them, σ n is the effective normal stress on the crack surface, μ is the shear stress, σ1 is the maximum stress, σ3 is the minimum stress, and β is the angle between the maximum stress and the normal direction of the crack surface.

[0091] Last passed It is used to characterize the slip properties of discrete faults, which affect the sliding of the fracture surface. It is not only a parameter reflecting the sliding of the fracture structure surface, but also a parameter that characterizes the fracture permeability and flow properties of the fluid.

[0092] Figure 5 This is the three-dimensional discrete fracture slip model of the Yang 101 well area. From the figure, we can see the distribution position and direction of the discrete fracture zone. The warm and cold colors represent the strength of fracture slip. The warmer the color, the greater the slip value, and vice versa.

[0093] 5. The spatial position of the casing change point of a single platform in the Yang 101 well area and the three-dimensional fracture slip model of the Yang 101 well area are comprehensively analyzed to further analyze and evaluate the fracture distribution, direction and slip properties.

[0094] Figure 6 This is the analysis diagram of the change point of the three-dimensional crack-slip model of the Yang 101H3 platform. From the figure, we can see that some of the change points fall in the discrete crack zone with large slip.

[0095] The above are the implementation methods listed in this embodiment, but this embodiment is not limited to the above optional implementation methods. Those skilled in the art can arbitrarily combine the above methods to obtain other various implementation methods. Anyone can derive other various implementation methods under the inspiration of this embodiment. The above specific implementation methods should not be understood as limiting the protection scope of this embodiment. The protection scope of this embodiment should be based on the definition in the claims.

Claims

1. A method for evaluating the slip properties of natural fractures in shale reservoirs based on a fracture discrete model, characterized in that: include: According to the post-stack seismic data and geological structure morphology data, the coherence attributes and curvature attributes are calculated, and the strike, dip and disconnection points are enhanced to obtain the attribute enhancement body; Calculate the fracture seismic phase based on coherence attributes and curvature attributes; Automatically track and mesh the fractures according to the enhanced curvature attributes, and group the fractures into discrete groups according to the fracture seismic phases to obtain a discrete fracture model. The slip properties of natural fractures are calculated based on the calculated geostress data and combined with the discrete fracture model.

2. The method for evaluating the slip properties of natural fractures in shale reservoirs based on a fracture discrete model according to claim 1, characterized in that: The coherence attributes are obtained by calculating the eigenvalues ​​of seismic data samples. The seismic data sample vectors form the following matrix: In the above matrix, d ij is the seismic sampling point, i is the horizontal sampling number, j is the vertical sampling number, D N×a is the matrix of seismic data sample points composed of; the covariance matrix corresponding to the matrix is ​​C a×a =D N×a T D N×a .

3. The method for evaluating the slip properties of natural fractures in shale reservoirs based on a fracture discrete model according to claim 2, characterized in that: Based on the intrinsic structure coherence estimation, it is determined as follows Among them, λ max is the matrix D N×a The maximum eigenvalue of C nn Representative D n×n The covariance matrix of n C nn The characteristic value of .

4. The method for evaluating the slip properties of natural fractures in shale reservoirs based on a fracture discrete model according to claim 1, characterized in that: The curvature properties are determined as follows Where K x represents the curvature along the x direction, d x is the apparent inclination angle.

5. The method for evaluating the slip properties of natural fractures in shale reservoirs based on a fracture discrete model according to claim 1, characterized in that: The Bayesian probability clustering analysis algorithm is used to calculate the fracture seismic phase, and includes the following process: Determine the earthquake attributes to be clustered and the number of categories to be divided; The earthquake attributes that follow the same set distribution are classified into one category, and Π(θ) is used as the prior probability of the Bayesian formula; Distance measurement is performed on individuals with a single attribute to determine the category; Test clustering results; When the test results meet the classification requirements, the calculation ends; otherwise, the clustering is recalculated and the above process is repeated.

6. The method for evaluating the slip properties of natural fractures in shale reservoirs based on a fracture discrete model according to claim 5, characterized in that: Using the Euclidean distance formula Distance measurement is performed on individuals with a single attribute to determine the category, where x ik is the k-th coordinate of the ith point, x jk is the k-th dimension coordinate of the j-th point, d ij is the distance between the i-th point and the j-th point in the k-dimensional space; Using Bayesian formula Test the clustering results, where Π(θ i ) is the prior distribution of the attribute, representing the seismic attribute sample θ i The knowledge that is classified as category x, p(x|θ i ) is the sample θ i The probability of being distributed in category x, p(θ i |x) is the existing sample θ i The probability of classifying the earthquake into category x under the condition of , p(x) represents the probability of the latest earthquake attribute category.

7. The method for evaluating the slip properties of natural fractures in shale reservoirs based on a fracture discrete model according to claim 1, characterized in that: The automatic crack tracking is to automatically track the enhanced property body after enhancement processing, and to count the length and direction of the tracked cracks; the crack gridding includes crack feature gridding to determine the topological relationship between crack lines and obtain the horizontal and vertical connection information between cracks.

8. The method for evaluating the slip properties of natural fractures in shale reservoirs based on a fracture discrete model according to claim 1, characterized in that: When calculating the slip properties of natural fractures, each fracture structural surface satisfies the following relationship when it is in a critical sliding state: s n =0.5(σ1+σ3)+0.5(σ1-σ3)cos2β τ=0.5(σ1-σ3)sin2β Among them, σ n is the effective normal stress on the crack surface, τ is the shear stress, σ1 is the maximum stress, σ3 is the minimum stress, and β is the angle between the maximum stress and the normal direction of the crack surface; Characterize the slip properties of discrete fractures.

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