Method and system for designing three-dimensional fracturing complex fracture network of shale oil system

Abstract

The invention provides a shale oil system three-dimensional fracturing complex fracture network design method and system, and the method comprises the steps: carrying out the rock core observation and microscopic recognition of an original three-dimensional seepage path of a reservoir rock sample, including natural fractures and pores; secondly, quantitatively characterizing and depicting the number and the form of the cracks by using CT and nuclear magnetic resonance technologies, and forming a digital characterization unit of the aperture network structure; secondly, proper fracturing processes are selected according to different original crack matching relations, and comprise the near-control and far-expansion process, the broadband expansion process, the pressurization crack expansion process and the like; and a CO2 composite pre-acid strong crack initiation process is added. And finally, establishing a fine three-dimensional geologic model, a crustal stress model and an actual well group numerical simulation model according to well group optimized and reasonable three-dimensional fracturing parameters. The three-dimensional seepage and three-dimensional fracturing fracture network design method has the advantages of high precision, comprehensive parameters, convenience, easiness in operation and the like.

Description

Technical Field

[0001] The present invention relates to the field of data supervision, and in particular to a method and system for designing a complex fracture network for three-dimensional fracturing of a shale oil system. Background Art

[0002] Shale oil reservoirs have small pores and well-developed natural fractures, and they mainly rely on horizontal well volume fracturing to connect natural fractures and form three-dimensional seepage channels. However, due to the deployment of three-dimensional development layers and well positions, the reduction of well spacing and layer spacing will lead to changes in reservoir fluid flow channels and three-dimensional seepage paths, and even cause pressure channeling and fluid heterogeneity, increasing the difficulty of future development.

[0003] In recent years, with the improvement of experimental methods and numerical simulation technology, the geological engineering integration model has gradually formed, and three-dimensional fracturing and complex fracture network design have received more and more attention. Research based on geological models and complex fracture network expansion simulation models has gradually matured, but shale reservoirs have developed natural fractures and are difficult to handle due to the influence of ground stress and complex structures. In particular, the identification and characterization of natural fractures are extremely difficult, and research on complex fracture network design based on the optimal path of three-dimensional seepage has not been reported.

[0004] In the three-dimensional development of shale oil, the design of three-dimensional complex fracture networks is crucial, which not only determines the channels for fluid flow in the reservoir, but also affects the development life of horizontal wells. At present, the horizontal well fracturing evaluation and production capacity under single-well fracture optimization have achieved good results, but the complex fracture network design based on three-dimensional development multi-well optimization has not been effectively studied and widely used. This is mainly because there is no experimental characterization and reservoir numerical simulation implementation method based on complex fracture networks, and the three-dimensional development design of this technology cannot be obtained, which limits the development of this technology and method. Summary of the invention

[0005] In view of the above problems, the present invention is proposed to provide a method and system for designing complex fracture networks for three-dimensional fracturing in a shale oil system that overcomes the above problems or at least partially solves the above problems.

[0006] According to one aspect of the present invention, a method for designing a complex fracture network for three-dimensional fracturing of a shale oil system is provided, the fracture network design method comprising:

[0007] Core observation and identification of natural fractures under microscope;

[0008] quantitatively characterizing and describing fractures based on the natural fractures;

[0009] Selecting a suitable fracturing process according to the fracture matching relationship;

[0010] Increase carbon dioxide compound preacid;

[0011] Numerical simulation determines the reasonable three-dimensional fracturing transformation mode.

[0012] Optionally, the core observation and identification of natural fractures under microscope specifically include:

[0013] Identify the original three-dimensional seepage path through core and microscope;

[0014] Multi-directionally connected multi-type and multi-scale fractures and pores.

[0015] Optionally, the original three-dimensional seepage path includes a horizontal seepage channel and a vertical seepage channel.

[0016] Optionally, the horizontal seepage channel includes: bedding fractures and grain edge fractures.

[0017] Optionally, the vertical seepage channels include: intercrystalline joints, overpressure joints, and structural joints.

[0018] Optionally, after the step of quantitatively characterizing and depicting the natural fractures, the method further comprises:

[0019] Using online CT scanning technology and pore structure change experiments, two-dimensional images were extracted and superimposed to construct a three-dimensional digital core model. The porosity, connected pore ratio and permeability were calculated using the maximum sphere method.

[0020] Optionally, the fracture complexity is divided into high gray matter lamination, medium gray matter lamination and medium gray matter lamination.

[0021] Optionally, the fracture matching relationship and selection of a suitable fracturing process specifically include:

[0022] The adaptation process for the high-gray laminae is the long-section, few-cluster, six-section fracturing and expansion process;

[0023] The adaptation process of the middle gray lamina is a broadband expansion process with dense cutting and segmentation, and multi-stage temporary plugging and expansion;

[0024] The adaptation process for the middle gray layer is a pressurized expansion process to increase displacement and pressure, and variable viscosity expansion.

[0025] Optionally, the adding of carbon dioxide to compound preacid specifically includes:

[0026] Add carbon dioxide composite pre-acid strong cracking process. Both supercritical carbon dioxide and pre-acid can reduce the Young's modulus of ash-rich shale. The composite of carbon dioxide and pre-acid can strengthen the cracking of artificial fractures.

[0027] Optionally, the numerical simulation to determine a reasonable three-dimensional fracturing transformation mode specifically includes:

[0028] Step 1: Based on the Petrel Re platform, establish a detailed three-dimensional geological model and geostress model;

[0029] Step 2, establishing a numerical simulation model of an actual well group according to the refined three-dimensional geological model and the geostress model;

[0030] Step 3: Use well logging data to identify the geological-engineering double sweet spots;

[0031] Step 4, based on steps 2 and 3, reasonably optimizing the key fracturing parameters of each well and the fracturing sequence of the well group;

[0032] Step 5: Based on step 4, ensure the best overall fracturing effect through reasonable seam arrangement.

[0033] The present invention also provides a shale oil system three-dimensional fracturing complex fracture network design system, using the above-mentioned shale oil system three-dimensional fracturing complex fracture network design method, the design system comprises:

[0034] Fracture identification module, used for core observation and identification of natural fractures under microscope;

[0035] A quantitative characterization module, used for quantitatively characterizing and describing the natural fractures;

[0036] A fracturing process selection module, used to select a suitable fracturing process according to the fracture matching relationship;

[0037] A carbon dioxide increasing module is used to increase carbon dioxide composite preacid;

[0038] Numerical simulation module, used for numerical simulation to determine reasonable three-dimensional fracturing transformation mode.

[0039] The present invention provides a method and system for designing a complex seam network for three-dimensional fracturing of a shale oil system. The seam network design method includes: core observation and microscopic identification of natural fractures; quantitative characterization and characterization of fractures according to the natural fractures; selection of a suitable fracturing process according to the fracture matching relationship; addition of carbon dioxide composite pre-acid; and numerical simulation to determine a reasonable three-dimensional fracturing transformation mode. An experimental and numerical simulation method with strong universality, low parameter requirements, easy to use, and good operation is provided. The method can quickly convert the experimental and digital core data of natural fracture identification and characterization into effective numerical data for shale oil numerical simulation, which is conducive to the rapid development of three-dimensional development complex seam network design in mine practice.

[0040] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0042] Figure 1 A flow chart of a method for designing a complex fracture network for three-dimensional fracturing in a shale oil system provided by an embodiment of the present invention;

[0043] Figure 2 is a digital core extracted after fracture identification in a specific embodiment of the present invention;

[0044] Figure 3 is a numerical simulation model of a specific embodiment of the present invention;

[0045] Figure 4 It is a simulation result of multi-cluster flow-limiting perforation of a specific embodiment of the present invention;

[0046] Figure 5 It is a pressure field diagram of numerical simulation after three-dimensional fracturing according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0047] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0048] The terms "comprises" and "having" and any variations thereof in the description embodiments, claims and drawings of the present invention are intended to cover non-exclusive inclusions, for example, including a series of steps or units.

[0049] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0050] The purpose of the present invention is to provide an experimental and numerical simulation method with strong universality, low parameter requirements, easy to use and good operation. By using this method, the experimental and digital core data of natural fracture identification and characterization can be quickly converted into effective numerical data for shale oil numerical simulation, which is conducive to the rapid development of three-dimensional development scheme design of complex fracture networks in mine practice.

[0051] A complex fracture network design method for shale oil based on the most promising path for three-dimensional seepage flow, the method includes:

[0052] Step 1: Use core observation and microscopic identification technology to accurately describe the original three-dimensional seepage path of the sample, divide different types of cracks such as bedding fractures, grain edge fractures, intercrystalline fractures, overpressure fractures, and structural fractures, and clarify their number. Step 2: Use online CT scanning technology and pore structure change experiments to extract two-dimensional images, construct a three-dimensional digital core model after superposition, and calculate key parameters such as porosity, connected pore ratio and permeability using the "maximum ball" method. Step 3: Based on the results of steps 1 and 2, select a suitable fracturing process for different fracture matching relationships. Step 4: Add a carbon dioxide composite pre-acid strong fracturing process to reduce the Young's modulus of ash-rich shale and strengthen the initiation of artificial fractures. Step 5: Based on fracture identification and digital core parameters, establish a well group numerical simulation model to optimize reasonable three-dimensional fracturing parameters.

[0053] The complex fracture network design method for shale oil based on the optimal path of three-dimensional seepage in the present invention is highly practical, convenient and fast, simple to apply, has good operability, and effectively realizes the numerical simulation of three-dimensional fracturing optimization design.

[0054] like Figure 1 As shown, in step 101, high-quality rock samples are selected, and core observation and microscopic identification methods are used to visually observe the development of natural fractures and make quantitative descriptions.

[0055] In step 102, based on step 101 and step 1, the core is scanned layer by layer using online CT scanning technology and pore structure change experiments to extract two-dimensional images, and the pixels are extracted using matlab software. After superposition, a three-dimensional digital core model is constructed, and key parameters such as porosity, connected pore ratio and permeability are calculated using the "largest sphere" method. The digital core extracted after fracture identification is as follows: Figure 2 shown.

[0056] The maximum sphere radius is calculated by using a radius range instead of a single radius value, and calculating the square of the radius:

[0057]

[0058] In step 103, based on steps 101 and 102, the digital core model obtained by fitting is used to derive fracture and pore parameters, and different fracturing modes are selected according to different fracture combination matching relationships to provide a reference for the numerical simulation in step 105. The schematic diagram of the numerical simulation model is shown in FIG. Figure 3 shown.

[0059] In step 104, according to the parameter characteristics of 102 and 103, it is selected whether to add supercritical carbon dioxide and pre-acid process. Generally, carbon dioxide composite pre-acid is selected for ultra-dense shale reservoirs to reduce the difficulty of fracture initiation. Figure 4 shown.

[0060] In step 105, based on step 104, a fine geological model and a reservoir numerical simulation model are established, the three-dimensional well network is imported into the model, the well group is simulated for overall fracturing, and the fracturing process of steps 103 and 104 is considered, and numerical simulation calculations are performed to obtain the optimal three-dimensional fracturing design scheme based on three-dimensional seepage, which has certain guiding significance for guiding mine application. The pressure field diagram of the numerical simulation after three-dimensional fracturing is shown in FIG. Figure 5 shown.

[0061] The original three-dimensional seepage paths were identified by core and microscope, including horizontal seepage channels such as bedding fractures and grain edge fractures, vertical seepage channels such as intercrystalline fractures, overpressure fractures, and structural fractures, and multi-directionally connected multi-type and multi-scale fractures and pores. See Table 1

[0062] Table 1

[0063]

[0064] Using online CT scanning technology and pore structure change experiments, two-dimensional images were extracted and superimposed to construct a three-dimensional digital core model. The key parameters such as porosity, connected pore ratio and permeability were calculated using the "largest sphere" method.

[0065] The appropriate fracturing process is selected according to different fracture matching relationships. According to the development of natural fractures, this patent stipulates that the fracture complexity is divided into high gray lamination, medium gray lamination and medium gray lamination, see Table 2.

[0066] Table 2

[0067]

[0068]

[0069] Add carbon dioxide composite pre-acid strong cracking process. Both supercritical carbon dioxide and pre-acid can reduce the Young's modulus of ash-rich shale. The composite of carbon dioxide and pre-acid can strengthen the cracking of artificial fractures.

[0070] According to the reasonable three-dimensional fracturing parameters optimized by the well group, a numerical simulation optimization method for the key process of three-dimensional well group fracturing is formed, including:

[0071] Step 1: Based on the Petrel Re platform, establish a detailed three-dimensional geological model and geostress model;

[0072] Step 2, based on step 1, establishing a numerical simulation model of the actual well group;

[0073] Step 3: Use well logging curves and other data to identify the geological-engineering "double sweet spots";

[0074] Step 4, based on steps 2 and 3, reasonably optimizing the key fracturing parameters of each well and the fracturing sequence of the well group;

[0075] Step 5: Based on step 4, reasonable seam layout is used to avoid or reduce the interconnection of inter-well fractures, increase the complexity of the seam network, and ensure the optimal overall fracturing effect.

[0076] Beneficial effects: The present invention provides an experimental and numerical simulation method with strong universality, low parameter requirements, easy use and good operation. This method can quickly convert the experimental and digital core data of natural fracture identification and characterization into effective numerical data for shale oil numerical simulation, which is conducive to the rapid development of three-dimensional development scheme design of complex fracture networks in mining practice.

[0077] The above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for designing a complex fracture network for three-dimensional fracturing of a shale oil system, characterized in that: The seam network design method comprises: Core observation and identification of natural fractures under microscope; quantitatively characterizing and describing fractures based on the natural fractures; Selecting a suitable fracturing process according to the fracture matching relationship; Increase carbon dioxide compound preacid; Numerical simulation determines the reasonable three-dimensional fracturing transformation mode.

2. A method for designing a complex fracture network for three-dimensional fracturing of a shale oil system according to claim 1, characterized in that: The core observation and identification of natural fractures under the microscope specifically include: Identify the original three-dimensional seepage path through core and microscope; Multi-directionally connected multi-type and multi-scale fractures and pores.

3. A method for designing a complex fracture network for three-dimensional fracturing of a shale oil system according to claim 2, characterized in that: The original three-dimensional seepage path includes a horizontal seepage channel and a vertical seepage channel.

4. A method for designing a complex fracture network for three-dimensional fracturing of a shale oil system according to claim 3, characterized in that: The horizontal seepage channels include: bedding fractures and grain edge fractures.

5. A method for designing a complex fracture network for three-dimensional fracturing of a shale oil system according to claim 3, characterized in that: The vertical seepage channels include: intercrystalline joints, overpressure joints, and structural joints.

6. A method for designing a complex fracture network for three-dimensional fracturing of a shale oil system according to claim 1, characterized in that: After the step of quantitatively characterizing and depicting the natural fractures, the following steps are further included: Using online CT scanning technology and pore structure change experiments, two-dimensional images were extracted and superimposed to construct a three-dimensional digital core model. The porosity, connected pore ratio and permeability were calculated using the maximum sphere method.

7. A method for designing a complex fracture network for three-dimensional fracturing of a shale oil system according to claim 1, characterized in that: The fracture complexity is divided into high gray matter lamination, medium gray matter lamination and medium gray matter lamination.

8. A method for designing a complex fracture network for three-dimensional fracturing of a shale oil system according to claim 7, characterized in that: The fracture matching relationship for selecting a suitable fracturing process specifically includes: The adaptation process for the high-gray laminae is the long-section, few-cluster, six-section fracturing and expansion process; The adaptation process of the middle gray lamina is a broadband expansion process with dense cutting and segmentation, and multi-stage temporary plugging and expansion; The adaptation process for the middle gray layer is a pressurized expansion process to increase displacement and pressure, and variable viscosity expansion.

9. A method for designing a complex fracture network for three-dimensional fracturing of a shale oil system according to claim 1, characterized in that: The method of adding carbon dioxide composite preacid specifically includes: Add carbon dioxide composite pre-acid strong cracking process. Both supercritical carbon dioxide and pre-acid can reduce the Young's modulus of ash-rich shale. The composite of carbon dioxide and pre-acid can strengthen the cracking of artificial fractures.

10. A method for designing a complex fracture network for three-dimensional fracturing of a shale oil system according to claim 1, characterized in that: The numerical simulation to determine a reasonable three-dimensional fracturing transformation mode specifically includes: Step 1: Based on the PetrelRe platform, establish a detailed three-dimensional geological model and geostress model; Step 2, establishing a numerical simulation model of an actual well group according to the refined three-dimensional geological model and the geostress model; Step 3: Use well logging data to identify the geological-engineering double sweet spots; Step 4, based on steps 2 and 3, reasonably optimizing the key fracturing parameters of each well and the fracturing sequence of the well group; Step 5: Based on step 4, ensure the best overall fracturing effect through reasonable seam arrangement.

11. A shale oil system three-dimensional fracturing complex fracture network design system, using a shale oil system three-dimensional fracturing complex fracture network design method according to any one of claims 1 to 10, characterized in that: The design system includes: Fracture identification module, used for core observation and identification of natural fractures under microscope; A quantitative characterization module, used for quantitatively characterizing and describing the natural fractures; A fracturing process selection module, used to select a suitable fracturing process according to the fracture matching relationship; A carbon dioxide increasing module is used to increase carbon dioxide composite preacid; Numerical simulation module, used for numerical simulation to determine reasonable three-dimensional fracturing transformation mode.

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