Method for approximately establishing rock attribute evolution in fracturing range by adopting distance field

Abstract

The invention discloses a method for approximately establishing rock attribute evolution in a fracturing range by adopting a distance field. The method comprises the following steps: S1, establishing a fracturing crack plane geometric model and a fracturing influence range three-dimensional geometric model; s2, by taking the fracturing fracture plane geometric model as a data source and the fracturing influence range three-dimensional geometric model as a target source, mapping fracture data into the fracturing influence range three-dimensional geometric model by adopting a generalized stretching method, and meanwhile, setting a grid search method as a nearest point form; s3, calculating a distance field d in a fracturing influence range; s4, calculating a damage coefficient D; s5, according to the relational expression of the Young modulus, the porosity and the damage coefficient, the change conditions of the Young modulus and the porosity within the influence range after fracturing are obtained through calculation, and a rock attribute evolution result within the influence range of fracturing is obtained. According to the method, the characterization method for effectively characterizing the influence of fracturing transformation on the rock related attributes is established by adopting the distance field, and relatively reliable data is provided for follow-up related research simulation.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field geology, and in particular to a method for establishing the evolution of rock properties within the fracturing range by using distance field approximation. Background Art

[0002] Unconventional energy reservoirs such as shale tight gas reservoirs have physical properties of ultra-low porosity and extremely low permeability, resulting in extremely high internal fluid flow resistance, making it difficult for natural gas to be economically and effectively developed through natural seepage in its original state. To break through this exploitation bottleneck, modern oil and gas engineering generally uses hydraulic fracturing technology to artificially transform the reservoir, ultimately constructing a seepage channel with industrial value. This technological breakthrough has not only promoted the global unconventional oil and gas revolution but also become the core engineering technology means for the commercial development of shale gas.

[0003] While the fracturing transformation constructs a seepage channel with industrial value, it also causes damage and destruction to the rock within a certain range. The appearance of the fracture and the tension and compression during the fracture growth process lead to changes in the physical properties of the rock within the range. Whether it is numerical simulation during oil and gas exploitation, enhanced recovery numerical simulation in the later stage of exploitation, or even simulation of carbon dioxide sequestration in depleted oil and gas reservoirs, relatively accurate rock physical properties are required as a basis for simulation. Therefore, the change in the physical properties of the rock within a certain range due to fracturing transformation is an indispensable consideration factor in the simulation process.

[0004] The complex fracture network system formed by hydraulic fracturing significantly changes the original seepage-mechanical coupling field of the reservoir, and the traditional homogeneous reservoir model can no longer accurately describe the heterogeneous characteristics of the transformed area. Based on the above technical background, there is an urgent need in the current field of unconventional oil and gas development to construct a method that can quantitatively characterize the evolution results of the physical properties of rocks in the fracturing transformation area. It provides a data basis for subsequent development and enhanced production simulation, and can also significantly improve the simulation reliability of caprock integrity assessment, sequestration capacity calculation, and leakage risk warning during the CO2 sequestration process, which has important engineering value for promoting the coordinated development of green and efficient unconventional oil and gas development and the carbon neutrality goal. Summary of the Invention

[0005] Aiming at the problem that the traditional homogeneous reservoir model cannot accurately describe the change in the physical properties of rocks in the fracturing transformation area, the present invention provides a method for establishing the evolution of rock properties within the fracturing range by using distance field approximation.

[0006] The present invention establishes a characterization method that can effectively characterize the influence of fracturing transformation on rock-related properties by introducing a distance field, and can approximately characterize the change in rock properties within the affected range after fracturing. This method will provide certain reference value for numerical simulation of engineering such as oil and gas reservoir exploitation and carbon dioxide sequestration.

[0007] The method for establishing the evolution of rock properties within the fracturing range by approximating the distance field provided by the present invention is as follows:

[0008] S1. Establish a planar geometric model of the fracture, and establish a three-dimensional geometric model of the fracturing influence range according to the geometric dimensions of the fracture and the influence range dimensions.

[0009] S2. Using the planar geometric model of the fracture as the data source and the three-dimensional geometric model of the fracturing influence range as the target source, establish a data mapping relationship by using the generalized stretching method, map the fracture data into the three-dimensional geometric model of the fracturing influence range, and set the grid search method in the form of the nearest point.

[0010] S3. Calculate the spatial distance field d of the fracturing influence range by using the three-dimensional distance field calculation formula, with the calculation reference being the pressure fracture geometric model; the calculation formula for the distance field d within the fracturing influence range is as follows;

[0011]

[0012] where d is the distance field, m; X, Y, and Z are the coordinates of any point within the fracturing influence range, m; A_b(x), A_b(y), and A_b(z) are the coordinates of the nearest point on the corresponding fracture of any point mapped by the generalized stretching method, m.

[0013] S4. Process the calculation result of the distance field d by using the normalization method to obtain the damage coefficient. The calculation formula for the damage coefficient D is as follows:

[0014]

[0015] The calculated damage coefficient D is distributed within the range of 0 to 1, where 0 indicates that the rock is not damaged by fracturing, and 1 indicates that the rock is completely damaged.

[0016] S5. Based on the damage coefficient calculated in step S4, according to the relationship formulas between Young's modulus, porosity, and the damage coefficient, calculate the changes in Young's modulus and porosity within the fracturing influence range after fracturing, that is, obtain the evolution result of the rock properties within the fracturing influence range. The relationship formula between Young's modulus and the damage coefficient is as follows:

[0017] E = E0(1 - D)

[0018] where E is Young's modulus, GPa; E0 is the initial Young's modulus, GPa.

[0019] The relationship formula between porosity and the damage coefficient is as follows:

[0020] φ = φ0(1 + D)

[0021] where φ is porosity, dimensionless; φ0 is the initial porosity, dimensionless.

[0022] Preferably, step S1 is specifically as follows: First, establish a planar geometric model of a single-stage fracture according to literature data or empirical data. Then, establish a three-dimensional geometric model of the single-stage fracture influence range representing the fracture damage range according to the geometric size and influence range size of the fracture. The three-dimensional geometric model of the single-stage fracture influence range is a rounded cuboid, and the planar geometric model is located at the center of the rounded cuboid geometric model.

[0023] More preferably, in step S1, use COMSOL software to establish a planar geometric model of a single-stage fracture and a three-dimensional geometric model of the single-stage fracture influence range. Step S2 is specifically: Add a generalized stretching variable option in COMSOL software. First, define its operator name as A_b. Second, set the mesh search method to the nearest point in the advanced settings, and set the planar geometric model of the fracture established in step S1 as the source of the generalized stretching operator.

[0024] Compared with the prior art, the advantages of the present invention are as follows:

[0025] The method for establishing the evolution of rock properties within the fracture range by using distance field approximation provided by the present invention calculates the evolution of relevant rock properties within the fracture influence range by establishing relevant geometric models, and by using the generalized stretching algorithm and the spatial distance field calculation formula. The calculation results of the present invention will provide a characterization for the numerical simulation of oil and gas reservoir development and subsequent research on the evolution of rock properties after formation fracturing, ensuring the objective accuracy of the simulation results.

[0026] Other advantages, objectives, and features of the present invention will be partially reflected by the following description, and partially will also be understood by those skilled in the art through the research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic flow chart of the method for establishing the evolution of rock properties within the fracture range by using distance field approximation of the present invention.

[0028] Figure 2 It is a schematic diagram of the planar geometric model of the fracture established in the embodiment.

[0029] Figure 3 It is a schematic diagram of the three-dimensional geometric model of the fracture influence range established in the embodiment.

[0030] Figure 4 It is a schematic diagram of the distance field calculation result in the embodiment.

[0031] Figure 5 It is a schematic diagram of the damage coefficient of the fracture influence range in the embodiment.

[0032] Figure 6Schematic diagram of the evolution result of Young's modulus after fracturing in the embodiment.

[0033] Figure 7 Schematic diagram of the evolution result of porosity after fracturing in the embodiment.

[0034] Figure 8 Schematic diagram of the geometric shape of the demonstration model for subsequent research in the embodiment.

[0035] Figure 9 Schematic diagram of the in-situ stress simulation result in the embodiment. Specific implementation manners

[0036] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0037] As Figure 1 shown, the method for establishing the evolution of rock properties within the fracturing range by using distance field approximation provided by the present invention specifically includes the following steps:

[0038] Step S1: Establish a planar geometric model of the fracture and a three-dimensional geometric model of the fracturing influence range;

[0039] Use the geometric modeling tool in COMSOL software to establish a rectangular planar model with a length of 300 m and a width of 50 m (i.e., the planar geometric model of a single-stage fracture) to represent the fracture. The model established in this embodiment is as Figure 2 shown.

[0040] Taking the established planar geometric model of the single-stage fracture as the center and within a range with a radius of 50 m, establish a three-dimensional geometric model of the fracturing influence range in the shape of a rounded cuboid. The established model is as Figure 3 shown.

[0041] Step S2: Add a generalized stretching variable option in COMSOL software. First, define its operator name as A_b, and secondly, set the mesh search method to the nearest point in the advanced settings. Set the planar geometric model of the fracture established in Step S1 as the data source and the three-dimensional geometric model of the fracturing influence range as the target source to establish a data mapping relationship.

[0042] Step S3: Introduce a distance field variable in COMSOL software, define the variable name as d, and set the variable definition range to the three-dimensional geometric model of the fracturing influence range established in Step S1. The calculation formula of the distance field variable d is as shown in the following formula:

[0043]

[0044] Among them, d is the distance field, in m; X, Y, and Z are the coordinates of any point within the fracturing influence range, in m; A_b(x), A_b(y), and A_b(z) are the coordinates of the nearest point to the corresponding fracture at any point mapped through the generalized stretching operator, in m; the calculation result of the distance field is as Figure 4 shown.

[0045] Step S4: After the calculation result of the distance field d in step S3, further perform normalization processing on the distance field d to calculate the damage coefficient D. The calculation formula is as follows:

[0046]

[0047] Among them, D is the damage coefficient, dimensionless. The result distribution of the damage coefficient D is within the range of 0 to 1, where "0" indicates that the rock is not damaged by fracturing, and "1" indicates that the rock is completely damaged. The calculation result of the damage coefficient is as Figure 5 shown.

[0048] Step S5: After obtaining the damage coefficient within the fracturing influence range in step S4, according to the relationship formula between Young's modulus, porosity, and the damage coefficient, calculate the changes in Young's modulus and porosity within the fracturing influence range, that is, obtain the rock property evolution result within the fracturing influence range. Among them, the calculation formula for Young's modulus is:

[0049] E = E0(1 - D)

[0050] The calculation formula for porosity is:

[0051] φ = φ0(1 + D)

[0052] Among them, E is Young's modulus, in GPa; E0 is the initial Young's modulus, in GPa; φ is porosity, dimensionless; φ0 is the initial porosity, dimensionless.

[0053] The calculation results of Young's modulus and porosity within the fracturing influence range are as Figure 6 and Figure 7 shown. Therefore, through the operations of the above steps S1 to S5, the evolution of Young's modulus and porosity within the fracturing influence range can be obtained.

[0054] Based on the established model of the fracturing influence range, an application research example of the research results of this method is carried out using the solid mechanics module in COMSOL software. The model uses a model of 500×500×350 m for demonstration, and the model schematic diagram is as Figure 8 shown. Among them, the relevant parameter settings are shown in Table 1.

[0055] Table 1 Relevant parameters of the demonstration model

[0056]

[0057]

[0058] The demonstration results of the method based on the present invention are as Figure 9 shown. The left figure is a side view, and the right figure is a front view. It can be seen from the figure that due to the influence of fracturing, the change of rock properties in this range has caused a certain degree of change in the stress distribution in this area. Thus, it can be seen that whether to consider the change of rock properties within the fracturing range will have a great impact on the subsequent research, which also proves the necessity of the method of the present invention.

[0059] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the equivalent embodiments with equivalent changes by using the above-disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for establishing the evolution of rock properties within the fracturing range by using distance field approximation, characterized in that, It includes the following steps: S1. Establish a planar geometric model of the fracture and a three-dimensional geometric model of the fracturing influence range according to the geometric dimensions of the fracture and the dimensions of the influence range; S2. Using the planar geometric model of the fracture as the data source and the three-dimensional geometric model of the fracturing influence range as the target source, establish a data mapping relationship by the generalized stretching method, map the fracture data into the three-dimensional geometric model of the fracturing influence range, and set the grid search method in the form of the nearest point; S3. Calculate the distance field d within the fracturing influence range, and the calculation formula is as follows; where d is the distance field, m; X, Y, and Z are the coordinates of any point within the fracturing influence range, m; A_b(x), A_b(y), and A_b(z) are the coordinates of the nearest point of the corresponding fracture of any point mapped by the generalized stretching method, m; S4. Calculate the damage coefficient D according to the distance field d: The calculated damage coefficient D is distributed in the range of 0 to 1, where 0 indicates that the rock is not damaged by fracturing, and 1 indicates that the rock is completely damaged; S5. Based on the damage coefficient calculated in step S4, according to the relationship between Young's modulus, porosity and the damage coefficient, calculate the changes in Young's modulus and porosity within the influence range after fracturing, that is, obtain the evolution result of the rock properties within the fracturing influence range.

2. The method for establishing the evolution of rock properties within the fracturing range by using distance field approximation according to claim 1, characterized in that, In step S5, the relationship between Young's modulus and the damage coefficient is as follows: E = E0(1 - D) where E is Young's modulus, GPa; E0 is the initial Young's modulus, GPa.

3. The method for establishing the evolution of rock properties within the fracturing range by using distance field approximation as described in claim 1, characterized in that, In step S5, the relationship between porosity and the damage coefficient is as follows: φ = φ0(1 + D) where φ is porosity, dimensionless; φ0 is the initial porosity, dimensionless.

4. The method for establishing the evolution of rock properties within the fracturing range by using distance field approximation as described in claim 1, wherein Specifically, step S1 is: establish a planar geometric model of a single-stage fracture according to literature data or empirical data. At the same time, establish a three-dimensional geometric model of a single-stage fracturing influence range representing the fracturing damage range according to the geometric dimensions of the fracture and the dimensions of the influence range. The three-dimensional geometric model of the single-stage fracturing influence range is a rounded cuboid, and the planar geometric model is located at the center of the rounded cuboid geometric model.

5. The method for establishing the evolution of rock properties within the fracturing range by using distance field approximation as claimed in claim 4, wherein In step S1, use COMSOL software to establish a planar geometric model of a single-stage fracture and a three-dimensional geometric model of a single-stage fracturing influence range.

6. The method for establishing the evolution of rock properties within the fracturing range by using distance field approximation as described in claim 5, characterized in that, Specifically, step S2 is: add a generalized stretching variable option in COMSOL software. First, define its operator name as A_b. Second, set the grid search method to the nearest point in the advanced settings, and set the planar geometric model of the fracture established in step S1 as the source of the generalized stretching operator.

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