A shale oil system three-dimensional fracturing complex fracture network design method and system

Abstract

This invention provides a method and system for designing complex fracture networks in three-dimensional fracturing of shale oil systems. The method includes: first, identifying the original three-dimensional seepage paths of reservoir samples, including natural fractures and pores, using core observation and microscopic identification. Then, using CT and NMR techniques, the number and morphology of fractures are quantitatively characterized and delineated, forming digital characterization units of the pore-fracture network structure. Next, appropriate fracturing processes are selected based on different original fracture matching relationships, including controlled near-to-far expansion, broadband expansion, and pressurized expansion processes. A CO2-based pre-fracturing acid initiation process is added. Finally, based on optimized and reasonable three-dimensional fracturing parameters for the well group, a refined three-dimensional geological model, a geostress model, and a numerical simulation model of the actual well group are established. This three-dimensional fracturing network design method has advantages such as high accuracy, comprehensive parameters, convenience, and ease of operation.

Description

Technical Field

[0001] This invention relates to the field of data monitoring, and in particular to a method and system for designing complex fracture networks in three-dimensional fracturing of shale oil systems. Background Technology

[0002] Shale oil reservoirs have fine pores and well-developed natural fractures, primarily relying on horizontal well volumetric fracturing to connect these natural fractures and form three-dimensional flow channels. However, the deployment of three-dimensional development layers and well locations, along with reduced well and layer spacing, can alter reservoir fluid flow channels and three-dimensional flow paths, potentially causing pressure channeling and heterogeneous fluid distribution, increasing the difficulty of future development.

[0003] In recent years, with the improvement of experimental methods and numerical simulation technology, the integrated model of geological engineering has gradually taken shape, and three-dimensional fracturing and complex fracture network design have received increasing attention. Research based on geological models and complex fracture network expansion simulation models has gradually matured. However, the development of natural fractures in shale reservoirs and their complex influence by geostress and tectonic structures make them difficult to handle. In particular, the identification and characterization of natural fractures are extremely difficult, and research on complex fracture network design based on the optimal three-dimensional seepage path has not been reported.

[0004] In the 3D development of shale oil, the design of complex fracture networks is crucial, as it not only determines the channels for fluid flow in the reservoir but also affects the development life of horizontal wells. Currently, single-well fracture optimization for horizontal well fracturing evaluation and production has achieved good results. However, the design of complex fracture networks based on multi-well optimization in 3D development has not yet been effectively studied and widely applied. This is mainly because there are no established experimental characterization methods or reservoir numerical simulation methods based on complex fracture networks, making it impossible to obtain 3D development design for this technology, thus limiting its development. 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 in three-dimensional fracturing of shale oil systems to overcome or at least partially solve the above problems.

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

[0007] Core observation and microscopic identification of natural fractures;

[0008] The natural cracks were quantitatively characterized and delineated.

[0009] Select a suitable fracturing process based on the fracture matching relationship;

[0010] Add carbon dioxide pre-acid;

[0011] Numerical simulation was used to determine a reasonable three-dimensional fracturing stimulation mode.

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

[0013] Core samples and microscopic examination were used to identify the original three-dimensional seepage path.

[0014] Multi-directional interconnected cracks and pores of various types and scales.

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

[0016] Optionally, the horizontal seepage channels include: bedding planes and grain edge planes.

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

[0018] Optionally, the step of quantitatively characterizing and delineating the cracks based on the natural cracks further includes:

[0019] Using online CT scanning technology and pore structure change experiments, two-dimensional images were extracted, superimposed, and a three-dimensional digital core model was constructed. Porosity, the proportion of connected pores, and permeability were calculated using the maximum sphere method.

[0020] Optionally, the complexity of the cracks is classified into high-gray-matrix, medium-gray-matrix, and medium-gray-matrix laminar.

[0021] Optionally, selecting a suitable fracturing process based on the fracture matching relationship specifically includes:

[0022] The adaptation process for the high gray texture layer is a controlled near-to-far expansion process with long segments and few clusters, and a six-segment fracturing and expansion process.

[0023] The adaptation process for the medium gray texture layer is a broadband expansion process with dense cutting and segmentation, and multi-level temporary plugging and expansion.

[0024] The aforementioned medium-gray layered adaptation process is a pressurized expansion process that increases discharge volume and pressurizes, and expands the joint by varying viscosity.

[0025] Optionally, the addition of carbon dioxide pre-acid specifically includes:

[0026] The addition of carbon dioxide composite pre-acid strong fracturing process enhances the initiation of artificial fractures. Both supercritical carbon dioxide and pre-acid have the effect of reducing the Young's modulus of ash-rich shale. The combination of carbon dioxide and pre-acid strengthens the initiation of artificial fractures.

[0027] Optionally, the numerical simulation to determine a reasonable three-dimensional fracturing stimulation 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: Establish a numerical simulation model of the actual well group based on the detailed three-dimensional geological model and the geostress model;

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

[0031] Step 4: Based on steps 2 and 3, reasonably optimize 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 by properly spacing the fractures.

[0033] This invention also provides a complex fracture network design system for three-dimensional fracturing in shale oil systems, applying the aforementioned method for designing complex fracture networks for three-dimensional fracturing in shale oil systems. The design system includes:

[0034] The crack identification module is used for core observation and microscopic identification of natural cracks;

[0035] A quantitative characterization module is used to quantitatively characterize and delineate the natural cracks.

[0036] A fracturing process selection module is used to select a suitable fracturing process based on the fracture matching relationship.

[0037] The carbon dioxide increasing module is used to increase the carbon dioxide compound pre-acid;

[0038] The numerical simulation module is used to determine a reasonable three-dimensional fracturing modification mode through numerical simulation.

[0039] This invention provides a method and system for designing complex fracture networks in shale oil systems using three-dimensional fracturing. The fracture network design method includes: core observation and microscopic identification of natural fractures; quantitative characterization and delineation of the natural fractures; selection of appropriate fracturing processes based on the fracture matching relationships; addition of carbon dioxide composite pre-acid; and numerical simulation to determine a reasonable three-dimensional fracturing stimulation mode. This invention provides a universally applicable, parameter-requirement-low, easy-to-use, and easy-to-operate experimental and numerical simulation method. This method can quickly convert experimental and digital core data from natural fracture identification and characterization into effective numerical data for shale oil numerical simulation, which is beneficial for the rapid design of complex fracture networks in shale oil development in field practice.

[0040] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 A flowchart illustrating a complex fracture network design method for three-dimensional fracturing in a shale oil system, provided as an embodiment of the present invention;

[0043] Figure 2 This is a digital core sample extracted after crack identification, according to a specific embodiment of the present invention;

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

[0045] Figure 4 This is a simulation result of a multi-cluster flow-limiting jet according to a specific embodiment of the present invention;

[0046] Figure 5 This is a pressure field diagram from a three-dimensional numerical simulation of fracturing according to a specific embodiment of the present invention. Detailed Implementation

[0047] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0048] The terms "comprising" and "having," and any variations thereof, in the specification, embodiments, claims, and drawings of this invention are intended to cover non-exclusive inclusion, such as including a series of steps or units.

[0049] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0050] The purpose of this invention is to provide an experimental and numerical simulation method that is universally applicable, has low parameter requirements, is easy to learn and operate. This method can quickly convert experimental and digital core data for natural fracture identification and characterization into effective numerical data for shale oil numerical simulation, which is beneficial for the rapid design of complex fracture networks in three-dimensional development in mining practice.

[0051] A complex fracture network design method for shale oil based on the optimal path of three-dimensional seepage, which includes:

[0052] Step 1: Using core observation and microscopic identification techniques, the original three-dimensional seepage path of the sample is precisely described, and different types of fractures, such as bedding fractures, grain edge fractures, intergranular fractures, overpressure fractures, and tectonic fractures, are classified, and their numbers are determined. Step 2: Using online CT scanning technology and pore structure change experiments, two-dimensional images are extracted, superimposed, and a three-dimensional digital core model is constructed. Key parameters such as porosity, the proportion of connected pores, and permeability are calculated using the "maximum sphere" method. Step 3: Based on the results of Steps 1 and 2, appropriate fracturing techniques are selected for different fracture matching relationships. Step 4: A carbon dioxide composite pre-acid strong fracturing process is added to reduce the Young's modulus of the ash-rich shale and enhance the initiation of artificial fractures. Step 5: Based on fracture identification and digital core parameters, a well group numerical simulation model is established, and reasonable three-dimensional fracturing parameters are optimized.

[0053] The shale oil complex fracture network design method based on the optimal three-dimensional seepage path in this invention is highly practical, convenient, quick, and easy to apply, with 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 the development of natural fractures is observed intuitively and quantitatively described using core observation and microscopic identification methods.

[0055] In step 102, based on step 101 and step 1, using online CT scanning technology and pore structure change experiments, two-dimensional images are extracted from the core after layer-by-layer scanning. Pixels are extracted using MATLAB software, and the images are then superimposed to construct a three-dimensional digital core model. Key parameters such as porosity, the proportion of connected pores, and permeability are calculated using the "maximum sphere" method. The digital core obtained after fracture identification is shown below. Figure 2 As shown.

[0056] The maximum sphere radius uses a range of radii instead of a single radius value, and calculates the square of the radius:

[0057]

[0058] In step 103, based on steps 101 and 102, the fitted digital core model is used to derive fracture and pore parameters. Different fracturing modes are selected according to different fracture combination matching relationships, providing a reference for the numerical simulation in step 105. A schematic diagram of the numerical simulation model is shown below. Figure 3 As shown.

[0059] In step 104, based on the parameter characteristics of 102 and 103, it is selected whether to add a process of supercritical carbon dioxide and pre-acid. Generally, carbon dioxide composite pre-acid is chosen for ultra-dense shale reservoirs to reduce the difficulty of fracture initiation. The simulation results of multi-cluster confined perforations are as follows: Figure 4 As shown.

[0060] In step 105, based on step 104, a refined geological model and a reservoir numerical simulation model are established. The three-dimensional well network is imported into the model, and a comprehensive fracturing simulation of the well group is performed. Considering the fracturing processes of steps 103 and 104, numerical simulation calculations are conducted, and the optimal three-dimensional fracturing design scheme based on three-dimensional seepage is obtained. This has certain guiding significance for field applications. The pressure field diagram after three-dimensional fracturing numerical simulation is shown below. Figure 5 As shown.

[0061] Core samples and microscopic examination revealed the original three-dimensional seepage pathways, including horizontal seepage channels such as bedding fractures and grain edge fractures, and vertical seepage channels such as intergranular fractures, overpressure fractures, and tectonic fractures, as well as multi-directional, 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, superimposed, and a three-dimensional digital core model was constructed. Key parameters such as porosity, proportion of connected pores, and permeability were calculated using the "maximum sphere" method.

[0065] To select appropriate fracturing processes for different fracture matching relationships, this patent specifies that the complexity of fractures is divided into high-gray-textured laminae, medium-gray-textured laminae, and medium-gray-textured laminae based on the development of natural fractures, as shown in Table 2.

[0066] Table 2

[0067]

[0068]

[0069] The addition of carbon dioxide composite pre-acid strong fracturing process enhances the initiation of artificial fractures. Both supercritical carbon dioxide and pre-acid have the effect of reducing the Young's modulus of ash-rich shale. The combination of carbon dioxide and pre-acid strengthens the initiation of artificial fractures.

[0070] Based on the optimized and reasonable three-dimensional fracturing parameters for well groups, a numerical simulation optimization method for key three-dimensional well group fracturing processes is developed, 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, establish a numerical simulation model of the actual well group;

[0073] Step 3: Using well logging curves and other data, identify the geological-engineering "double sweet spot";

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

[0075] Step 5: Based on step 4, by rationally distributing fractures, the interconnection of fractures between wells is avoided or reduced, the complexity of the fracture network is increased, and the overall fracturing effect is ensured to be optimal.

[0076] Beneficial effects: This invention provides an experimental and numerical simulation method that is universally applicable, has low parameter requirements, is easy to learn and operate. Using this method, experimental and digital core data for natural fracture identification and characterization can be quickly converted into effective numerical data for shale oil numerical simulation, which is beneficial for the rapid development of complex fracture networks in mining practice.

[0077] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments 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 within the scope of protection of the present invention.

Claims

1. A method for designing complex fracture network of a shale oil system three-dimensional fracturing, characterized in that, The mesh design method includes: Core observation and microscopic identification of natural fractures; The natural cracks were quantitatively characterized and delineated. Select the appropriate fracturing process based on the fracture matching relationship; Numerical simulation was used to determine a reasonable three-dimensional fracturing stimulation mode, including: Step 1: Based on the Petrel Re platform, establish a detailed three-dimensional geological model and geostress model; Step 2: Establish a numerical simulation model of the actual well group based on the detailed three-dimensional geological model and the geostress model; Step 3: Use well logging data to identify the geological-engineering double sweet spot; Step 4: Based on steps 2 and 3, reasonably optimize 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 by properly spacing the fractures. The complexity of cracks is classified into high-gray-quality laminae, medium-gray-quality laminae, and medium-gray-quality laminae. The selection of a suitable fracturing process based on the fracture matching relationship specifically includes: The adaptation process for the high-gray strata is a segmented process with long sections and few clusters, and a six-segment hydraulic fracturing and expansion process; a carbon dioxide composite pre-acid strong fracturing process is adopted, in which both supercritical carbon dioxide and pre-acid have the effect of reducing the Young's modulus of the gray shale, and the combination of carbon dioxide and pre-acid is used to strengthen the fracturing of artificial fractures. The adaptation process for the medium gray texture layer is a broadband expansion process with dense cutting and segmentation, and multi-level temporary plugging and expansion. The aforementioned medium-gray layered adaptation process is a pressurized expansion process that increases discharge volume and pressurizes, and expands the joint by varying viscosity.

2. The method for designing complex fracture networks in three-dimensional fracturing of shale oil systems according to claim 1, characterized in that, The core observation and microscopic identification of natural fractures specifically include: Core samples and microscopic examination were used to identify the original three-dimensional seepage path. Multi-directional interconnected cracks and pores of various types and scales.

3. The method for designing complex fracture networks in three-dimensional fracturing of shale oil systems according to claim 2, characterized in that, The original three-dimensional seepage path includes horizontal seepage channels and vertical seepage channels.

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

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

6. The method for designing complex fracture networks in three-dimensional fracturing of shale oil systems according to claim 1, characterized in that, The step of quantitatively characterizing and delineating the cracks based on the natural cracks also includes: Using online CT scanning technology and pore structure change experiments, two-dimensional images were extracted, superimposed, and a three-dimensional digital core model was constructed. Porosity, the proportion of connected pores, and permeability were calculated using the maximum sphere method.

7. A complex fracture network design system for three-dimensional fracturing of shale oil systems, employing the complex fracture network design method for three-dimensional fracturing of shale oil systems as described in any one of claims 1-6, characterized in that, The design system includes: The crack identification module is used for core observation and microscopic identification of natural cracks; A quantitative characterization module is used to quantitatively characterize and delineate the natural cracks. A fracturing process selection module is used to select a suitable fracturing process based on the fracture matching relationship. The numerical simulation module is used to determine a reasonable three-dimensional fracturing modification mode through numerical simulation.

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