A method and system for modeling spatial distribution of fractures in a reservoir

Abstract

The application discloses a method and system for simulating reservoir fracture spatial distribution, and the specific steps of the method are as follows: obtaining fracture intensity by using seismic attributes; obtaining fracture geometric parameters by using core data; obtaining single-well fracture permeability by well testing interpretation; constructing an initial discrete fracture network according to the fracture geometric parameters and the fracture intensity; calculating the calculated fracture permeability according to the initial discrete fracture network; comparing the calculated fracture permeability with the single-well fracture permeability, and reconstructing the discrete fracture network until the difference between the adjusted calculated fracture permeability and the single-well fracture permeability is within an error range, and finally obtaining a final fracture network model. The application is based on the fracture intensity, the fracture geometric parameters and the single-well fracture permeability, adjusts the fracture geometric parameters through an iterative mode, simulates the reservoir fracture spatial distribution, and finally establishes a discrete fracture network model.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas geology, and specifically relates to a method and system for simulating the spatial distribution of reservoir fractures. Background Technology

[0002] Regardless of the method used to establish a DFN model in existing technologies, it is necessary to estimate the fracture distribution, which is crucial for subsequent fracture permeability calculations. The process of calculating permeability using numerical simulation algorithms requires a continuous spatial distribution of fractures. This requirement is relatively easy to achieve within small reservoir areas, but it is challenging for large-scale underground reservoirs (often with a distribution range exceeding 100 km). 2 The algorithm fails to converge due to the uneven distribution of cracks, making it difficult to achieve the expected results.

[0003] Fracture modeling typically builds upon outcrop studies. By scanning the outcrops (with an accuracy of up to 0.2 mm), a comprehensive set of parameters for the two-dimensional fracture distribution can be established. These parameters are then used to simulate the three-dimensional fracture distribution, leading to the creation of a discrete fracture network model. However, accurately obtaining these parameters when building a discrete fracture network model of an underground reservoir is quite challenging, and the fracture distribution in the underground reservoir differs to some extent from the fracture distribution obtained from the outcrops.

[0004] Therefore, there is an urgent need to provide a method and system for simulating the spatial distribution of reservoir fractures. Summary of the Invention

[0005] To address the above-mentioned problems, one of the objectives of this invention is to provide a method for simulating the spatial distribution of reservoir fractures.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for simulating the spatial distribution of reservoir fractures, comprising the following steps:

[0008] Utilizing seismic properties to determine crack strength;

[0009] Statistical analysis of fracture geometric parameters using core data;

[0010] Single-well fracture permeability is obtained through well test interpretation;

[0011] An initial discrete crack network is constructed based on crack geometry parameters and crack strength;

[0012] The calculated fracture permeability is obtained based on the initial discrete fracture network.

[0013] By comparing the calculated fracture permeability with the single-well fracture permeability, when the difference between the calculated fracture permeability and the single-well fracture permeability is not within the allowable error range, the discrete fracture network is reconstructed until the difference between the adjusted calculated fracture permeability and the single-well fracture permeability is within the error range, thus obtaining the final fracture network model.

[0014] Preferably, the crack geometry parameters include crack length, height, extension direction, aperture, and dip angle.

[0015] Preferably, the specific process of constructing the initial discrete crack network based on crack geometry parameters and crack strength is as follows:

[0016] The study area was divided into multiple cells;

[0017] Select valid cells from multiple cells;

[0018] Select the valid cells to be calculated, and use the average crack strength as the crack density;

[0019] Using the Monte Carlo method, the distribution of crack length, height, extension direction, aperture, and dip angle is established;

[0020] Construct an initial discrete crack network within the valid cells.

[0021] Preferably, the specific process of comparing the calculated fracture permeability with the single-well fracture permeability, reconstructing the discrete fracture network, and obtaining the final fracture network model when the difference between the adjusted calculated fracture permeability and the single-well fracture permeability is within the error range is as follows:

[0022] When the difference between the calculated fracture permeability and the single-well fracture permeability is outside the allowable error range, the discrete fracture network is reconstructed by adjusting the fracture geometry parameters and using an iterative approach. The ODA algorithm is then used to calculate the fracture permeability until the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, thus obtaining the final fracture network model.

[0023] Preferably, the method further includes the following steps: comparing the calculated fracture permeability with the single-well fracture permeability; when the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, the initial fracture network model is directly obtained as the final fracture network model.

[0024] To address the aforementioned problems, a second objective of this invention is to provide a system for simulating the spatial distribution of reservoir fractures.

[0025] To achieve the above objectives, the present invention provides the following technical solution:

[0026] A system for simulating the spatial distribution of reservoir fractures, specifically comprising:

[0027] First acquisition unit: used to obtain crack strength using seismic properties;

[0028] Statistical unit: used to statistically analyze fracture geometric parameters using core data;

[0029] Second acquisition unit: used to obtain single-well fracture permeability through well test interpretation;

[0030] The first building unit is used to construct an initial discrete crack network based on crack geometry parameters and crack strength.

[0031] Calculation unit: used to calculate the fracture permeability based on the initial discrete fracture network;

[0032] The second building block is used to compare the calculated fracture permeability with the single-well fracture permeability. When the difference between the calculated fracture permeability and the single-well fracture permeability is not within the allowable error range, the discrete fracture network is reconstructed until the difference between the adjusted calculated fracture permeability and the single-well fracture permeability is within the error range, thus obtaining the final fracture network model.

[0033] Preferably, the crack geometry parameters include crack length, height, extension direction, aperture, and dip angle.

[0034] Preferably, the first building unit is specifically used for:

[0035] The study area is divided into multiple cells;

[0036] Select valid cells from multiple cells;

[0037] Select the valid cells to be calculated, and use the average crack strength as the crack density;

[0038] Using the Monte Carlo method, the distribution of crack length, height, extension direction, aperture, and dip angle is established;

[0039] Construct an initial discrete crack network within the valid cells.

[0040] Preferably, the second building unit is specifically used for:

[0041] By comparing the calculated fracture permeability with the single-well fracture permeability, if the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, the initial fracture network model is directly obtained as the final fracture network model. If the difference between the calculated fracture permeability and the single-well fracture permeability is not within the allowable error range, the discrete fracture network is reconstructed by adjusting the fracture geometry parameters and using an iterative approach. The ODA algorithm is then used to calculate the fracture permeability until the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, at which point the final fracture network model is obtained.

[0042] The beneficial effects of this invention are as follows: Based on fracture strength, fracture geometric parameters, and single-well fracture permeability, this invention adjusts fracture geometric parameters through iteration to simulate the spatial distribution of reservoir fractures and finally establishes a discrete fracture network model.

[0043] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 A schematic diagram of the fracture distribution is shown, in which well locations are marked with black circles;

[0046] Figure 2 A schematic diagram of crack length estimation is shown;

[0047] Figure 3 A diagram illustrating cell division is shown;

[0048] Figure 4 A diagram of the crack network model of the present invention is shown. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] This invention discloses a method for simulating the spatial distribution of reservoir fractures, the specific steps of which are as follows:

[0051] S1 obtains the fracture strength, preferably by statistically analyzing seismic attributes. Specifically, fracture strength is traditionally established based on discontinuity attributes such as seismic coherence, curvature, and seismic wave amplitude anomalies. However, these attributes reflect the geometric characteristics of the fracture, and directly using them as fracture strength requires support from drilling core samples and test data. Another approach is to use seismic wave attenuation attributes, which have permeability and are therefore also suitable for fracture modeling. Preferably, the fracture strength is normalized.

[0052] S2 utilizes core data to statistically analyze fracture geometric parameters, including fracture length, height, extension direction, aperture, and dip angle. Specifically, the distribution of fracture height, direction, aperture, and dip angle can be statistically established from the core data. As a preferred approach, for high-angle fractures (nearly vertical), where the length is difficult to determine, the fracture length distribution is estimated using the continuous seismic attribute directions within the grid. Figure 2 As shown.

[0053] S3 obtains the single-well fracture permeability through well test interpretation; preferably, the single-well fracture permeability obtained through well test interpretation is the test result of a tight lithological section with fracture development but surrounding rock porosity of less than 5%, and the single-well fracture permeability is considered to be mainly contributed by fractures.

[0054] S4 constructs an initial discrete crack network based on crack geometry parameters and crack strength, as follows:

[0055] (I) Cell Division and Valid Cell Selection

[0056] The study area is divided into multiple cells, and valid cells are selected from these cells.

[0057] Specifically, for large study areas with unevenly distributed cracks, cell division is necessary. The following factors are typically considered when dividing cells:

[0058] (1) The cells are divided on the XY plane (because cracks usually have high-angle characteristics), and each cell needs to have a sufficient number of cracks;

[0059] (2) Effective links can be established between cracks, and isolated cracks will be considered invalid cracks;

[0060] (3) Cracks cannot be closed; cracks that are not open will be considered invalid.

[0061] Figure 1This is a schematic diagram of the crack distribution. Cells 1, 4, 5, 7, 8, 11, 12, 15, and 16 are crack-free meshes, i.e., invalid cells, and can be ignored and not included in the model construction. Although cracks exist in cells 3, 9, and 13, they are isolated and considered invalid cracks, unable to form a crack network, and therefore do not need to be calculated. The valid cells are: 2, 6, 10, and 14, thus saving a significant amount of computation.

[0062] (ii) Select the valid cells to be calculated, and use the average crack strength as the crack density;

[0063] (iii) Using the Monte Carlo method, establish the distribution of crack length, height, extension direction, aperture, and dip angle;

[0064] (iv) Construct the initial discrete crack network within the cell.

[0065] S5 calculates the fracture permeability based on the initial discrete fracture network;

[0066] Preferably, the penetration rate of effective cells is calculated using the ODA algorithm:

[0067] This algorithm, proposed by M. ODA (1985), uses the permeability tensor to estimate the permeability distribution (ODA, 1985). Figure 1 The calculations in the grid shown (2, 6, 10, and 14) are performed independently.

[0068] S6 compares the calculated fracture permeability with the single-well fracture permeability, reconstructs the discrete fracture network, and obtains the final fracture network model when the difference between the adjusted calculated fracture permeability and the single-well fracture permeability is within the error range.

[0069] Specifically, by comparing the calculated fracture permeability with the single-well fracture permeability, if the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, the initial fracture network model is directly obtained as the final fracture network model; if the difference between the calculated fracture permeability and the single-well fracture permeability is not within the allowable error range, the discrete fracture network is reconstructed by adjusting the fracture geometric parameters and using an iterative approach. The ODA algorithm is then used to calculate the fracture permeability until the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, at which point the final fracture network model is obtained.

[0070] Specifically, if the calculated fracture permeability is greater than the single-well fracture permeability, lower the extraction thresholds for fracture aperture and length distributions, repeatedly construct the discrete fracture network model, and use the ODA algorithm to calculate the fracture permeability distribution. If the calculated fracture permeability is less than the single-well fracture permeability, increase the extraction thresholds for fracture aperture and length distributions, repeatedly construct the discrete fracture network model, and use the ODA algorithm to calculate the fracture permeability distribution. Repeat this process until the error meets the requirements.

[0071] This invention also discloses a system for simulating the spatial distribution of reservoir fractures, specifically comprising:

[0072] First acquisition unit: used to obtain crack strength using seismic properties;

[0073] Statistical unit: used to statistically analyze fracture geometric parameters using core data, wherein the fracture geometric parameters include fracture length, height, extension direction, aperture, and dip angle;

[0074] Second acquisition unit: used to obtain single-well fracture permeability through well test interpretation;

[0075] The first building unit is used to construct an initial discrete crack network based on crack geometry parameters and crack strength. Specifically, the first building unit is used to: divide the study area into multiple cells; select valid cells from the multiple cells; select valid cells to be calculated, using the mean crack strength as the crack density; use the Monte Carlo method to establish the distribution of crack length, height, extension direction, aperture, and dip angle; and construct the initial discrete crack network within the cells.

[0076] Calculation unit: used to calculate fracture permeability based on the initial discrete fracture network;

[0077] The second building unit is used to compare the calculated fracture permeability with the single-well fracture permeability. When the difference between the calculated fracture permeability and the single-well fracture permeability is not within the allowable error range, the discrete fracture network is reconstructed until the difference between the adjusted calculated fracture permeability and the single-well fracture permeability is within the error range, thus obtaining the final fracture network model. Specifically, the second building unit is used to: compare the calculated fracture permeability with the single-well fracture permeability; when the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, the initial fracture network model is directly obtained as the final fracture network model; when the difference between the calculated fracture permeability and the single-well fracture permeability is not within the allowable error range, the discrete fracture network is reconstructed iteratively by adjusting the fracture geometric parameters, and the fracture permeability is calculated using the ODA algorithm until the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, thus obtaining the final fracture network model.

[0078] The method of the present invention will be further illustrated below with specific implementation examples:

[0079] There are 20 wells drilled in the study area, including 4 core wells, with a total core length of approximately 300m. Two of the wells in the middle encountered relatively large fractures. CT scan images of the study area are available and can be used to analyze the geometric parameter distribution of the fractures.

[0080] The detailed steps for implementing this case are as follows:

[0081] (1) Obtaining crack strength using seismic properties ；

[0082] (2) Statistical analysis of fracture geometric parameters using core data;

[0083] We statistically analyzed all meaningful open fractures on the core sample to obtain data on the fracture opening, dip angle, height, and extension direction.

[0084] (3) Obtain the fracture permeability of a single well through well test interpretation;

[0085] The production test data and core data from the key wells are from the same well section. The test permeability data are statistically analyzed and used for subsequent comparative calculation of fracture permeability.

[0086] (4) Construct an initial discrete crack network based on crack geometry parameters and crack strength;

[0087] Divide into unit grids

[0088] The study area is large, approximately 600 km². 2 The grid is divided into 20 x 12 = 240 cells. After limiting the grid with crack strength, there are 84 effective cells for calculating crack permeability. Figure 3 As shown, Figure 3 The cells marked with the number "1" are selected. This reduces the amount of calculation by approximately two-thirds.

[0089] Construct an initial discrete crack network by randomly selecting one valid cell;

[0090] (5) The calculated fracture permeability is obtained based on the initial discrete fracture network;

[0091] The ODA algorithm was used to calculate the fracture permeability.

[0092] (6) Compare the calculated fracture permeability with the single-well fracture permeability. If the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, the initial fracture network model is directly obtained as the final fracture network model. If the difference between the calculated fracture permeability and the single-well fracture permeability is not within the allowable error range, the discrete fracture network is reconstructed iteratively by adjusting the fracture geometric parameters. The ODA algorithm is used to calculate the fracture permeability until the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, at which point the final fracture network model is obtained. Figure 4 As shown, Figure 4 The cell marked with '1' indicates a valid cell, starting from... Figure 4 It can be seen from this:

[0093] a. The invalid cell does not contain any crack fragments;

[0094] b. Only local meshes failed to simulate crack fragments;

[0095] c. The distribution of crack fragments is consistent with the crack strength.

[0096] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for simulating the spatial distribution of reservoir fractures, characterized in that: The specific steps are as follows: Utilizing seismic properties to determine crack strength; Statistical analysis of fracture geometric parameters using core data; Single-well fracture permeability is obtained through well test interpretation; An initial discrete crack network is constructed based on crack geometry parameters and crack strength; The crack geometry parameters include crack length, height, extension direction, aperture, and dip angle; The specific process of constructing the initial discrete crack network based on crack geometry parameters and crack strength is as follows: The study area was divided into multiple cells; Select valid cells from multiple cells; Select the valid cells to be calculated, and use the average crack strength as the crack density; Using the Monte Carlo method, the distribution of crack length, height, extension direction, aperture, and dip angle is established; Construct an initial discrete crack network within the valid cells; The calculated fracture permeability is obtained based on the initial discrete fracture network. By comparing the calculated fracture permeability with the single-well fracture permeability, when the difference between the calculated fracture permeability and the single-well fracture permeability is not within the allowable error range, the discrete fracture network is reconstructed until the difference between the adjusted calculated fracture permeability and the single-well fracture permeability is within the error range, thus obtaining the final fracture network model.

2. The method for simulating the spatial distribution of reservoir fractures according to claim 1, characterized in that: The process of comparing and calculating fracture permeability with single-well fracture permeability, and then reconstructing the discrete fracture network when the difference between the calculated fracture permeability and the single-well fracture permeability is outside the allowable error range, continues until the difference between the adjusted calculated fracture permeability and the single-well fracture permeability is within the error range. The specific steps to obtain the final fracture network model are as follows: When the difference between the calculated fracture permeability and the single-well fracture permeability is outside the allowable error range, the discrete fracture network is reconstructed by adjusting the fracture geometry parameters and using an iterative approach. The ODA algorithm is then used to calculate the fracture permeability until the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, thus obtaining the final fracture network model.

3. The method for simulating the spatial distribution of reservoir fractures according to claim 2, characterized in that: It also includes the following steps: comparing the calculated fracture permeability with the single-well fracture permeability. When the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, the initial fracture network model is directly obtained as the final fracture network model.

4. A system for simulating the spatial distribution of reservoir fractures, characterized in that: Specifically, it includes: First acquisition unit: used to obtain crack strength using seismic properties; Statistical unit: used to statistically analyze fracture geometric parameters using core data; Second acquisition unit: used to obtain single-well fracture permeability through well test interpretation; The first building unit is used to construct an initial discrete crack network based on crack geometry parameters and crack strength. The crack geometry parameters include crack length, height, extension direction, aperture, and dip angle; The first building unit is specifically used for: The study area is divided into multiple cells; Select valid cells from multiple cells; Select the valid cells to be calculated, and use the average crack strength as the crack density; Using the Monte Carlo method, the distribution of crack length, height, extension direction, aperture, and dip angle is established; Construct an initial discrete crack network within the valid cells; Calculation unit: used to calculate the fracture permeability based on the initial discrete fracture network; The second building block is used to compare the calculated fracture permeability with the single-well fracture permeability. When the difference between the calculated fracture permeability and the single-well fracture permeability is not within the allowable error range, the discrete fracture network is reconstructed until the difference between the adjusted calculated fracture permeability and the single-well fracture permeability is within the error range, thus obtaining the final fracture network model.

5. The system for simulating the spatial distribution of reservoir fractures according to claim 4, characterized in that: The second building unit is specifically used for: When the difference between the calculated fracture permeability and the single-well fracture permeability is outside the allowable error range, the discrete fracture network is reconstructed by adjusting the fracture geometry parameters and using an iterative approach. The ODA algorithm is then used to calculate the fracture permeability until the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, thus obtaining the final fracture network model.

6. The system for simulating the spatial distribution of reservoir fractures according to claim 5, characterized in that: The second building unit is also used to: compare the calculated fracture permeability with the single-well fracture permeability, and when the difference between the calculated fracture permeability and the single-well fracture permeability is within the allowable error range, directly obtain the initial fracture network model as the final fracture network model.

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