A new method for characterizing complex fracture systems in deep shale gas reservoirs

Abstract

The present invention provides a new method for characterizing complex fracture systems in deep shale gas reservoirs, including: dividing single wells into natural fracture single wells, artificial fracture single wells and single wells coupled with natural fractures and artificial fractures through fracture information of single wells, using Monte Carlo method combined with discrete fracture model to generate fracture network model diagram of single wells, dividing single wells into inner and outer zones based on the permeability of fractured low-porosity shale reservoirs using radial composite model, combining dual porosity medium model and discrete fracture model according to continuity and heterogeneity of reservoir fractures, and characterizing complex fracture systems of natural fractures, artificial fractures and coupled with natural fractures and artificial fractures. The present invention forms a method for characterizing complex fracture systems of single wells, which can more accurately invert reservoir parameters and fracture parameters, improve the reliability of fracture characterization, and effectively support efficient exploration and development.

Description

Technical Field

[0001] The present invention relates to the technical field of gas reservoir development, and in particular to a new method for characterizing a complex fracture system in a deep shale gas reservoir. Background Art

[0002] In recent years, unconventional natural gas has gradually become the main force in natural gas reserve increase. There are also a large number of natural fractures in unconventional natural gas reservoirs, such as structural fractures developed in shale gas reservoirs, dissolution fractures developed in tight carbonate gas reservoirs, bedding fractures and micro fractures in shale gas, and septal fractures in coalbed methane. Natural fractures can not only serve as gas storage space, but also important natural gas seepage channels, playing a pivotal role in the entire development process of gas fields.

[0003] Most fractured shale reservoirs have poor matrix permeability, well-developed natural fractures, complex seepage mechanisms, and difficulty in describing fracture dynamics. The complex fracture system formed by the coupling of naturally developed fractures and artificial fractures is even more complex, making it difficult to accurately invert reservoir parameters and fracture parameters.

[0004] At present, conventional fracture characterization methods have the following problems in analyzing complex fractured low-rock reservoirs: (1) The formation is highly heterogeneous, the seepage mechanism of natural fractures is complex, and the planar distribution varies greatly. After large-scale fracturing, it is easier to form a physical heterogeneity zone in the vicinity of the wellbore; (2) Fracturing fractures and natural fractures form a complex fracture system, and the dynamic description of fractures is difficult; (3) The simple dual-medium model is not sufficient to characterize the complexity of the development of natural fractures; (4) There is a lack of a set of methods to characterize the complex fracture system of fractured low-porosity shale reservoirs. Summary of the invention

[0005] Based on this, it is necessary to provide a new method for characterizing complex fracture systems in deep shale gas reservoirs to address the above technical issues.

[0006] A new method for characterizing complex fracture systems in deep shale gas reservoirs comprises: dividing the single wells into natural fracture wells, artificial fracture wells and natural fracture coupled with artificial fracture wells according to the fracture information of the single wells; using the Monte Carlo method in combination with a discrete fracture model to generate a fracture network model diagram of the single well; based on the permeability of the fractured low-porosity shale reservoir, using a radial composite model to divide the single well into an inner zone and an outer zone; combining a dual-porosity medium model and a discrete fracture model according to the continuity and heterogeneity of reservoir fractures to characterize the complex fracture system of natural fractures, artificial fractures and natural fracture coupled with artificial fractures.

[0007] Furthermore, when generating the fracture network model diagram of a single well, the following assumptions are made: the fracture trajectory is determined by four parameters: the two left and right endpoints, the trajectory length and the direction angle; within a given generation domain, the fracture trajectory length, center point and direction angle all obey the random distribution function; the fracture trajectory within the generation domain is a straight line segment, both endpoints are within the generation domain, and the length of the straight line segment is the fracture length.

[0008] Furthermore, the Monte Carlo method is combined with a discrete fracture model to generate a fracture network model diagram, specifically including: determining the size of the generation domain and the number of fractures; using the Monte Carlo method to determine the geometric parameters of all fractures in each group, the geometric parameters including two endpoint positions, a direction angle and a fracture trajectory length; generating fracture geometric parameters of a random discrete fracture model based on the geometric parameters of all fractures in each group; and combining the fracture geometric parameters with the discrete fracture model to form a fracture network model diagram.

[0009] Furthermore, the dual-porosity medium model is used to characterize reservoirs in which fractures are distributed in a network and are interconnected, and the discrete fracture model is used to characterize reservoirs in which some fractures are highly heterogeneous in distribution and some fractures are not interconnected.

[0010] Furthermore, when the single well is a natural fracture well, the inner zone dual porosity model, the inner zone discrete fracture model, the outer zone dual porosity model and the outer zone discrete fracture model are combined to form four complex fracture system characterization methods for the natural fracture well case.

[0011] Furthermore, when the single well is an artificial fracture well, the inner zone dual porosity model, the inner zone discrete fracture model, the outer zone dual porosity model and the outer zone discrete fracture model are combined to form four complex fracture system characterization methods in the case of an artificial fracture well.

[0012] Furthermore, when a single well is a complex fracture system coupled with artificial fractures and natural fractures, a three-dimensional numerical well test single well model is established by using a dual-medium outer zone dual-medium model of the inner zone without artificial fractures, a discrete fracture model of the inner zone without artificial fractures, a dual-medium outer zone discrete fracture model of the inner zone without artificial fractures, a discrete fracture model of the outer zone of the inner zone without artificial fractures, a dual-medium model of the outer zone of the inner zone with discrete fractures, a discrete fracture model of the outer zone of the inner zone with discrete fractures, a dual-medium model of the outer zone of the inner zone with artificial fractures, a discrete fracture model of the outer zone of the inner zone with discrete fractures, and a discrete fracture model of the outer zone of the inner zone with discrete fractures of the well with artificial fractures, combined with unstructured grid division technology, to characterize the complex fracture system.

[0013] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: through the fracture information of a single well, the single well is divided into a natural fracture single well, an artificial fracture single well and a natural fracture coupled with an artificial fracture single well; the Monte Carlo method is combined with a discrete fracture model to generate a fracture network model diagram of the single well; based on the permeability of the fractured low-porosity shale reservoir, the radial composite model is used to divide the single well into an inner zone and an outer zone; according to the continuity and heterogeneity of the reservoir fractures, the dual-porosity medium model and the discrete fracture model are combined to characterize the complex fracture system of natural fractures, artificial fractures and the natural fracture coupled with artificial fractures, thereby forming a characterization method for the complex fracture system of a single well, which can more accurately invert reservoir parameters and fracture parameters, improve the reliability of fracture characterization, and effectively support efficient exploration and development. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic flow chart of a novel method for characterizing a complex fracture system in a deep shale gas reservoir in one embodiment;

[0015] Figure 2 A schematic diagram of a single well with a natural fracture in one embodiment;

[0016] Figure 3 A schematic diagram of a representation of an artificial fracture single well in one embodiment;

[0017] Figure 4 A schematic diagram of a well test of a dual-medium model in the inner and outer regions of a natural fracture single well in one embodiment;

[0018] Figure 5 Schematic diagram of the characterization of a dual medium model of a natural fracture single well inner zone and a discrete fracture outer zone in one embodiment

[0019] Figure 6 A schematic diagram of characterizing a discrete fracture model of a dual-medium outer region in a natural fracture single well inner region in one embodiment;

[0020] Figure 7 A schematic diagram of characterizing a discrete fracture model of an inner discrete fracture area and an outer discrete fracture area of ​​a natural fracture single well in one embodiment;

[0021] Figure 8 A schematic representation of a dual-medium model of an inner region and an outer region of a single well with an artificial fracture in one embodiment;

[0022] Fig. 9 A schematic diagram of characterizing a dual medium model of an inner zone of an artificial fractured single well and an outer zone of a discrete fracture in one embodiment;

[0023] Fig.10 A schematic diagram of characterizing a discrete fracture model of a double-medium outer region in an inner region of an artificial fractured single well in one embodiment;

[0024] Fig.11 It is a schematic representation of a discrete fracture model in the inner area and outer area of ​​an artificial fracture single well in one embodiment. DETAILED DESCRIPTION

[0025] Before describing the specific embodiments of the present invention, the overall concept of the present invention is described as follows:

[0026] The present invention is mainly developed based on the deep shale gas fracturing effect evaluation research process of production dynamic data interpretation. Due to the poor permeability of the fractured shale reservoir matrix, the development of natural fractures, the complex seepage mechanism, the difficulty in describing the fracture dynamics, and the poor applicability of the existing well test interpretation and evaluation technology, the interpretation parameters are difficult to reflect the authenticity of the reservoir. The well test interpretation theory and method need to be improved. It is urgent to form a new method of test interpretation and evaluation through research and development to improve the reliability of the test interpretation results and effectively support efficient exploration and development. Among them, the characterization of fractures in fractured low-porosity shales is particularly important. Fractures have an important influence on reservoir properties, recovery rate and production capacity. Characterizing the complex fracture system occasionally formed by artificial fractures and natural fractures is the key point of well test interpretation.

[0027] After analysis, the inventors proposed a new method for characterizing complex fracture systems in deep shale gas reservoirs. First, considering the fracture conditions of a single well, the single well is divided into a single well with natural fractures, a single well with artificial fractures, and a single well with artificial fractures coupled with natural fractures. Then, the Monte Carlo method is used in combination with a discrete fracture model to generate a fracture network model diagram of the single well. Secondly, based on the strong heterogeneity of the permeability of fractured low-porosity shale reservoirs, a radial composite model is used to divide the single well into an inner zone and an outer zone. Finally, according to the continuity and heterogeneity of the single well reservoir, a dual-porosity medium model and a discrete fracture model are combined to form a method for characterizing complex fracture systems of natural fractures, artificial fractures, and natural fractures coupled with artificial fractures.

[0028] After introducing the overall concept of the present invention, in order to make the present invention more clear, the present invention is further described in detail by specific implementation methods in combination with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] like Figure 1 As shown, a new method for characterizing complex fracture systems in deep shale gas reservoirs is provided, including the following steps:

[0030] Step S101, according to the fracture information of the single well, the single well is divided into a single well with natural fractures, a single well with artificial fractures, and a single well with natural fractures and artificial fractures coupled.

[0031] Specifically, according to the actual geological data and transformation conditions of the single wells in the block, the fracture information of the single wells is obtained, and the single wells are divided into single wells with natural fractures, single wells with artificial fractures, and single wells with coupled natural fractures and artificial fractures.

[0032] Among them, an artificial fracture single well is a single well with artificial fractures formed after the reservoir is fracturing.

[0033] Step S102, using the Monte Carlo method in combination with the discrete fracture model to generate a fracture network model diagram of a single well.

[0034] Specifically, since the fractures in the fractured low-porosity shale reservoir are randomly distributed, the following assumptions are made when generating the fracture network model diagram: the fracture trajectory is determined by four parameters: the left and right endpoints, the trajectory length and the direction angle; within a given generation domain, the fracture trajectory length, center point and direction angle all obey the random distribution function; the fracture trajectory within the generation domain is a straight line segment, both endpoints are within the generation domain, and the length of the straight line segment is the fracture length.

[0035] Based on the above assumptions about the random distribution and simulation of fractures, the Monte Carlo method is used to randomly generate a geometric parameter model of fractures, including the end point position, direction angle, and trajectory length, so as to determine the spatial position of each fracture in the generation domain, so that the spatial distribution of fractures satisfies the fracture information of a single well. The Monte Carlo method is used to characterize the development of natural fractures and visualize natural fractures, which is convenient for the study of fracture systems.

[0036] The generation process of random discrete cracks is as follows: determine the size of the generation domain and the crack data; use the Monte Carlo method to determine the geometric parameters of all cracks in each group, which include the positions of two endpoints, the direction angle and the length of the crack trajectory line; generate the crack geometric parameters of the random discrete crack model based on the geometric parameters of all cracks in each group; combine the crack geometry with the discrete crack model to form a crack network model diagram.

[0037] Step S103: Based on the permeability of the fractured low-porosity shale reservoir, a radial composite model is used to divide the single well into an inner zone and an outer zone.

[0038] Specifically, since the permeability of fractured low-porosity shale reservoirs is highly heterogeneous, a single well can be divided into inner and outer zones according to the permeability. The high permeability zone is divided into the inner zone through the radial composite model, and the low permeability zone is divided into the outer zone through the radial composite model. There is an obvious difference in permeability between the inner and outer zones, which can be determined based on the actual permeability of the single well.

[0039] Step S104, according to the continuity and heterogeneity of reservoir fractures, the dual-porosity medium model and the discrete fracture model are combined to characterize the complex fracture system of natural fractures, artificial fractures and the coupling of natural fractures and artificial fractures.

[0040] Among them, the dual-porosity medium model is suitable for reservoirs where fractures are distributed in a network and interconnected, and the discrete fracture model is suitable for reservoirs where some fractures are unevenly distributed and some fractures are not interconnected.

[0041] Specifically, when the fracture distribution is highly heterogeneous, the energy storage described by the discrete fracture model is closer to the actual reservoir. Combined with the degree of development of fractures in the actual reservoir, the dual-porosity medium model and the discrete fracture model are combined, and the continuity and heterogeneity of the reservoir are comprehensively considered to form a fracture characterization method for natural fractures, artificial fractures, and complex fracture systems coupled with natural fractures and artificial fractures.

[0042] Among them, Figure 2 As shown in the figure, when considering the degree of development of natural fractures, the dual porosity medium model and the discrete fracture model are used to describe the reservoir, that is, the model includes a combination of the inner zone dual porosity model, the inner zone discrete fracture model, the outer zone dual porosity model and the outer zone discrete fracture model, forming four complex fracture system characterization methods in the case of natural fractures in a single well.

[0043] Among them, Figure 3 As shown in the figure, for a single well with artificial fractures, artificial fractures are formed in the reservoir after fracturing, and a complex seepage process is formed between the artificial fractures and the natural fractures. Considering the dual influence of artificial fractures and natural fractures, the model is divided into an inner zone dual porosity model, an inner zone discrete fracture model, an outer zone dual porosity model and an outer zone discrete fracture model, and they are combined to form four complex fracture system characterization methods in the case of a single well with artificial fractures, which solves the problem that it is difficult to characterize complex fractures in fractured low-porosity shale.

[0044] Among them, Figures 4 to 11 As shown in the figure, based on the complex fracture system coupled with artificial fractures and natural fractures, eight characterization methods are established based on the dual-porosity medium model and the discrete fracture model, including the dual-medium outer zone dual-medium model of the inner zone without artificial fractures, the discrete fracture model of the outer zone of the inner zone without artificial fractures, the dual-medium model of the outer zone of the inner zone without artificial fractures, the discrete fracture model of the outer zone of the inner zone without artificial fractures, the discrete fracture model of the outer zone of the inner zone without artificial fractures, the dual-medium outer zone dual-medium model of the inner zone with artificial fractures, the discrete fracture model of the outer zone of the inner zone with artificial fractures, the dual-medium model of the outer zone of the inner zone with artificial fractures, the discrete fracture model of the outer zone of the inner zone with artificial fractures, and the discrete fracture model of the outer zone of the inner zone with artificial fractures. A three-dimensional numerical well testing single well model is established according to the unstructured grid division technology.

[0045] In this embodiment, the single well is divided into a natural fracture well, an artificial fracture well and a natural fracture coupled with an artificial fracture well through the fracture information of the single well. The Monte Carlo method is combined with a discrete fracture model to generate a fracture network model diagram of the single well. Based on the permeability of the fractured low-porosity shale reservoir, the radial composite model is used to divide the single well into an inner zone and an outer zone. According to the continuity and heterogeneity of the reservoir fractures, the dual-porosity medium model and the discrete fracture model are combined to characterize the complex fracture system of natural fractures, artificial fractures and the natural fracture coupled with artificial fractures. A characterization method for the complex fracture system of a single well is formed, which can more accurately invert reservoir parameters and fracture parameters, improve the reliability of fracture characterization, and effectively support efficient exploration and development.

[0046] The above contents are further detailed descriptions of the present invention in combination with specific implementation methods, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A new method for characterizing complex fracture systems in deep shale gas reservoirs, characterized in that: The following steps are involved: According to the fracture information of single wells, single wells are divided into single wells with natural fractures, single wells with artificial fractures, and single wells with natural fractures and artificial fractures coupled. The Monte Carlo method is combined with a discrete fracture model to generate a fracture network model diagram of a single well; Based on the permeability of fractured low-porosity shale reservoirs, a radial composite model is used to divide a single well into inner and outer zones. According to the continuity and heterogeneity of reservoir fractures, the dual-porosity medium model and the discrete fracture model are combined to characterize the complex fracture system of natural fractures, artificial fractures and the coupling of natural fractures and artificial fractures.

2. A new method for characterizing complex fracture systems in deep shale gas reservoirs according to claim 1, characterized in that: When generating the fracture network model diagram of a single well, the following assumptions are made: The crack trajectory is determined by four parameters: the left and right endpoints, the trajectory length, and the direction angle; In a given generation domain, the length, center point and direction angle of the crack trajectory all obey the random distribution function; The crack trajectory lines in the generation domain are all straight line segments, with both endpoints within the generation domain, and the length of the straight line segment is the crack length.

3. A new method for characterizing complex fracture systems in deep shale gas reservoirs according to claim 2, characterized in that: The Monte Carlo method is combined with a discrete fracture model to generate a fracture network model diagram, specifically including: Determine the size of the generated domain and the number of cracks; Using the Monte Carlo method, the geometric parameters of all the cracks in each group are determined, wherein the geometric parameters include two end point positions, a direction angle, and a crack trajectory length; Generate the fracture geometric parameters of the random discrete fracture model according to the geometric parameters of all fractures in each group; The fracture geometric parameters are combined with the discrete fracture model to form a fracture network model diagram.

4. A new method for characterizing complex fracture systems in deep shale gas reservoirs according to claim 1, characterized in that: The dual-porosity medium model is used to characterize reservoirs in which fractures are distributed in a network and are interconnected, and the discrete fracture model is used to characterize reservoirs in which some fractures are highly heterogeneous in distribution and some fractures are not interconnected.

5. A new method for characterizing complex fracture systems in deep shale gas reservoirs according to claim 1, characterized in that: When the single well is a natural fracture well, the inner zone dual porosity model, the inner zone discrete fracture model, the outer zone dual porosity model and the outer zone discrete fracture model are combined to form four complex fracture system characterization methods for the natural fracture single well case.

6. A new method for characterizing complex fracture systems in deep shale gas reservoirs according to claim 1, characterized in that: When the single well is an artificial fracture well, the inner zone dual porosity model, the inner zone discrete fracture model, the outer zone dual porosity model and the outer zone discrete fracture model are combined to form four complex fracture system characterization methods in the case of an artificial fracture well.

7. A new method for characterizing complex fracture systems in deep shale gas reservoirs according to claim 1, characterized in that: When a single well is a complex fracture system coupled with artificial fractures and natural fractures, a three-dimensional numerical well test single well model is established by combining unstructured grid division technology with a dual-medium outer zone dual-medium model of the inner area and the outer area of ​​the well without artificial fractures, a discrete fracture model of the inner area and the outer area of ​​the well without artificial fractures, a dual-medium model of the inner area and the outer area of ​​the well without artificial fractures, a discrete fracture model of the inner area and the outer area of ​​the well without artificial fractures, a dual-medium model of the inner area and the outer area of ​​the well with artificial fractures, a discrete fracture model of the inner area and the outer area of ​​the well with artificial fractures, and a discrete fracture model of the inner area and the outer area of ​​the well with artificial fractures.

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