A method and system for quantitatively describing natural fracture line density near a wellbore

Abstract

The application provides a method and system for quantitatively describing natural fracture line density near a wellbore, which comprises the following steps: according to the period data and mechanical characteristics of fractures in a reservoir to be described, calling corresponding fracture distribution characteristic data table to identify different occurrences and different orders of fractures contained in the reservoir and marking and distinguishing, then aiming at all the marked fracture zones, considering geological factors controlling fracture development, using a matching strategy to calculate fracture densities of different occurrences, and then arranging to obtain corresponding fracture density curves. The scheme comprehensively considers the multi-period, multi-group and multi-order characteristics of natural fractures in the oil and gas reservoir, combines the formation mechanism and main control factors of the fractures, can represent the fracture development state consistent with the actual fracture development characteristics, and can reliably and finely describe the natural fracture density conditions of different development characteristics in various mechanical layers of the reservoir.

Description

Technical Field

[0001] This invention relates to the field of geological research technology for oil and gas field development, and in particular to a method and system for quantitatively describing the linear density of natural fractures near wellbore. Background Technology

[0002] In oil and gas field development engineering, the fracture linear density of an oil and gas reservoir refers to the number of fractures per unit length in the direction of the fracture normal. In the process of three-dimensional geological modeling of natural fractures in oil and gas reservoirs, the single-well fracture density parameter, as hard data for establishing the spatial distribution density model of fractures, plays a key role in controlling the reliability of the fracture model. If the single-well fracture density parameter is inaccurate, the fracture model established on this basis will inevitably fail to reflect reality.

[0003] Natural fractures exhibit multiple phases, levels, and occurrences, and their distribution within reservoirs is highly heterogeneous, making the establishment of a reliable single-well fracture density model extremely challenging. Currently, single-well fracture density parameters are primarily obtained through core fracture descriptions and imaging logging fracture interpretation results. This involves counting the number of fractures in the wellbore (or wellwall) and calculating the number of fractures within different length ranges (window lengths) along the wellbore's extension direction (referred to as the window length method in this paper), thereby obtaining a single-well fracture density curve. When using the above logic to calculate fracture density results...

[0004] The following problems exist in calculating the linear density of fracture development in a certain work area with multiple phases, levels, and attitudes:

[0005] ① When fractures of different orientations are included in the calculation simultaneously, the calculation results cannot reliably reflect the actual fracture development data of the reservoir. For example, a certain area usually has natural fractures with multiple orientations and dip angles. Drilling cores or imaging logging interpretation may encounter these fractures with different orientations at the same time. If the "fracture density" is obtained by including the fractures of different orientations in the calculation based only on their quantity without considering their orientation, the degree of fracture development reflected by the result cannot indicate the fracture density of which orientation, and cannot reflect the actual fracture development in the reservoir.

[0006] ② The problem of simultaneous calculation of fractures of different levels: Since most of the fractures that can be observed by drilling cores or imaging logging are local fractures, all the fractures encountered in each well may have multiple levels at the same time. If fractures of different levels are used together to calculate their linear density, it is difficult to determine which level of fracture density the density belongs to. Using this parameter as hard data for modeling will cause the generated fractures to fail to reflect the level characteristics that match reality, resulting in model errors.

[0007] Using the traditional window length method can lead to the two problems mentioned above. It ignores the geometric characteristics of crack distribution under different orientations and orders, and the calculated crack density may differ significantly from the actual situation. Furthermore, characterizing crack development features based on this method may be problematic, thus affecting the accuracy of crack distribution prediction and modeling.

[0008] The information disclosed in the background section of this invention is intended only to enhance the understanding of the general background of this invention, and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art. Summary of the Invention

[0009] To address the aforementioned problems, this invention provides a method and system for quantitatively describing the linear density of natural fractures near the wellbore. This method primarily targets multi-stage, multi-level, and multi-occurrence natural fractures encountered during well drilling in fractured oil and gas reservoirs. It proposes a strategy capable of calculating the linear density of fractures of different levels and series. This method yields a fracture linear density that conforms to the actual fracture development status of the subsurface reservoir, laying the foundation for further three-dimensional fracture modeling and evaluation of the impact of fractures on oil and gas reservoir development. In one embodiment, the method includes:

[0010] The feature identification step involves calling the corresponding fracture distribution feature data table to identify the different occurrences and orders of fractures contained in the reservoir based on the fracture sequence data and mechanical characteristics in the reservoir to be described.

[0011] The marking and division steps involve marking the entire reservoir to be described according to the occurrence and order of fractures at different stages, thus forming multiple fracture zones.

[0012] Density calculation steps: For all fracture zones, based on the geological factors controlling fracture development, a matching calculation strategy is used to calculate the fracture density matching various orientation fractures in different rock mechanical layers.

[0013] The data processing steps and the calculated fracture density were used to plot fracture density curves for different stages, different attitudes and different grades of fracture zones along the wellbore.

[0014] Preferably, in one embodiment, the method further includes:

[0015] The feature statistics steps are as follows: Based on the formation mechanism of reservoir fractures, the mechanical characteristics and parameter distribution characteristics of fractures at different stages are statistically analyzed. Based on this, the fractures at different stages are finely divided according to their corresponding different occurrences and different levels. The division results and the corresponding fracture parameter distribution characteristics are linked and recorded to form a fracture parameter distribution characteristic data table.

[0016] As a further improvement of the present invention, the density calculation step includes:

[0017] Based on wellbore data and the orientation characteristics of rock mechanical layers, reservoir fracture-related rock mechanical layers are classified into the following categories: rock mechanical layers with a distribution direction perpendicular to the wellbore axis, and rock mechanical layers with a distribution direction oblique to the wellbore axis.

[0018] Specifically, in one embodiment, if the current fracture zone belongs to a rock mechanical layer whose distribution direction is perpendicular to the wellbore axis, the density calculation step includes the following operations:

[0019] Step A1: Determine whether a set of natural fractures perpendicular to the rock surface can be found within the rock strata through core identification or imaging logging interpretation. If yes, proceed to step A2; otherwise, proceed to step A3.

[0020] Step A2: Determine whether the average spacing of the obtained cracks is less than the core diameter. If so, calculate the corresponding crack density according to the first calculation strategy; otherwise, calculate the corresponding crack density according to the second calculation strategy.

[0021] Step A3: Determine whether a set of natural fractures obliquely intersecting the rock surface can be obtained through core identification or imaging logging interpretation. If so, calculate the corresponding fracture density according to the third calculation strategy.

[0022] Furthermore, in one embodiment, if the current fracture zone belongs to a rock mechanical layer whose distribution direction is oblique to the wellbore axis, the density calculation step includes the following operations:

[0023] If it is found through core identification or imaging logging that a set of natural fractures perpendicular to the rock surface are developed within the rock stratum, then the fracture density of the corresponding fractures is calculated according to the fourth calculation strategy.

[0024] If a set of natural fractures obliquely intersecting the rock surface is found within the rock stratum through core identification or imaging logging interpretation, the fracture density of the corresponding fractures is calculated according to the fifth calculation strategy.

[0025] As a further improvement of the present invention, in step A2, the corresponding crack density is calculated according to the first calculation strategy, including:

[0026]

[0027] The corresponding crack density is calculated according to the second calculation strategy, including:

[0028] Identify the thickness of the rock mechanical layer where the crack is located H 岩心 The corresponding crack spacing index is obtained by combining the corresponding crack outcrop data. The average spacing of fractures near the wellbore is calculated based on the rock mechanical layer thickness and fracture spacing index. S 岩心:

[0029] Then, the linear density of the current fracture on the plane of rock mechanical layer distribution is calculated according to the following formula:

[0030]

[0031] In the formula, L d S represents the average linear density of fractures within the current rock mechanical layer, and S represents the average fracture spacing. S 岩心 The average spacing of cracks near the wellbore;

[0032] The crack spacing index is the ratio of the thickness of the exposed cracked rock layer to the median crack spacing within a set range.

[0033] Further, in one embodiment, in step A3, calculating the corresponding crack density according to the third calculation strategy includes:

[0034] Identify the thickness of the rock mechanical layers in which this group of oblique fractures developed. H 岩心 ;

[0035] Combined with the statistical analysis of the crack spacing index of the corresponding outcrop oblique joints I S露头 Then, based on the two, the average vertical distance between the oblique fractures developed within the rock mechanical layer on the wellbore is calculated. S 岩心 ;

[0036] Combining the angle of the natural fractures developed within the rock strata with the oblique angle of the rock surface, S 岩心 This is converted into the average spacing between the intersection lines of this set of cracks and the rock mechanical layer. S’ 岩心 ;

[0037] The linear density of fractures on the plane of rock mechanical layer distribution is calculated using the following formula:

[0038]

[0039] In the formula, L d This represents the average linear density of fractures within the current rock mechanical layer.

[0040] Furthermore, in one embodiment, the process of calculating the corresponding crack density according to the fourth calculation strategy includes:

[0041] Rock mechanical layer thickness identified from drilling data H 岩心The apparent thickness of the rock mechanical layer is used as the basis for determining the actual thickness of the rock mechanical layer by combining the oblique angle between the rock mechanical layer distribution direction and the wellbore axis. ;

[0042] The crack spacing index for this type of crack is obtained by combining the statistical data of the corresponding exposed cracks. I S露头 Based on the actual thickness of the rock mechanical layer The fracture spacing index is used to calculate the average spacing between fractures that develop along the direction of extension of the rock mechanical layer on the wellbore. ;

[0043] Then, the linear density of the cracks on the plane of rock mechanical layer distribution is calculated according to the following formula:

[0044]

[0045] In the formula, L d This represents the average linear density of fractures within the current rock mechanical layer.

[0046] In a specific embodiment, the process of calculating the corresponding crack density according to the fifth calculation strategy includes:

[0047] Rock mechanical layer thickness identified through drilling data H 岩心 The apparent thickness of the rock mechanical layer is used as the basis for determining the actual thickness of the rock mechanical layer by combining the oblique angle between the rock mechanical layer distribution direction and the wellbore axis. :

[0048] The crack spacing index for this type of crack is obtained by combining the statistical data of the corresponding exposed cracks. I S露头 The average spacing of the set of fractures developed within the rock mechanical layer on the wellbore is calculated based on the actual layer thickness and fracture spacing index of the rock mechanical layer. S 岩心 ;

[0049] The spacing of the cracks is determined based on the oblique angle between the natural cracks developed within the rock strata and the rock surface. S 岩心 Transformed into the average spacing of cracks along the plane of the rock's mechanical layer. ;

[0050] Then, the linear density of this set of cracks on the plane of rock mechanical layer distribution is obtained according to the following formula:

[0051]

[0052] In the formula, L d This represents the average linear density of fractures within the current rock mechanical layer.

[0053] Based on the application aspects of the methods described in any one or more of the above embodiments, the present invention also provides a system for quantitatively describing the linear density of natural fractures near a wellbore, the system performing the methods described in any one or more of the above embodiments.

[0054] Compared with the closest prior art, the present invention also has the following beneficial effects:

[0055] This invention provides a method and system for quantitatively describing the linear density of natural fractures near a wellbore. The method identifies and marks the different occurrences and orders of fractures in the reservoir based on the fracture phase data and mechanical characteristics of the reservoir to be described by calling the corresponding fracture distribution characteristic data table. This overcomes the problem of simultaneous calculation of fractures of different phases and occurrences in the prior art. It facilitates the formulation of matching calculation strategies, and the marked fracture distribution and density calculation data are also easy to record and apply in an orderly manner, which helps to optimize and statistically analyze fractures.

[0056] Furthermore, this invention considers the geological factors controlling fracture development and employs a matching strategy to calculate fracture densities for fractures with different occurrences, thereby obtaining corresponding fracture density curves. Based on the clear understanding of each fracture stage, occurrence, and order, it comprehensively considers the main controlling factors of natural fracture formation in oil and gas reservoirs, fracture distribution characteristics, and reservoir geological parameters. Combining the fracture formation mechanism and main controlling factors, it can characterize the fracture development state that matches the actual fracture development characteristics, reliably and accurately describe the natural fracture density of different development characteristics in various mechanical layers of the reservoir, and is more helpful in analyzing the contribution of natural fractures with different characteristics to the reservoir and their impact on development. Moreover, the three-dimensional fracture density model developed on this basis is more accurate.

[0057] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims and drawings. Attached Figure Description

[0058] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0059] Figure 1 This is a flowchart illustrating a method for quantitatively describing the linear density of natural fractures near a wellbore, according to an embodiment of the present invention.

[0060] Figure 2 This is a schematic diagram illustrating the computational principle of a method for quantitatively describing the linear density of natural fractures near a wellbore, provided in another embodiment of the present invention.

[0061] Figure 3 This is an example diagram of the fracture line density of well A1 in block P, which uses a method for quantitatively describing the linear density of natural fractures near the wellbore according to an embodiment of the present invention.

[0062] Figure 4 This is a schematic diagram of the structure of a system for quantitatively describing the linear density of natural fractures near a wellbore, provided in an embodiment of the present invention. Detailed Implementation

[0063] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples. Those skilled in the art will then fully understand how the present invention uses technical means to solve technical problems and achieve technical effects, and will be able to implement the present invention specifically based on the above-described implementation process. It should be noted that, as long as there is no conflict, the various embodiments and features of the present invention can be combined with each other, and the resulting technical solutions are all within the protection scope of the present invention.

[0064] Although the flowchart describes the operations as sequential processes, many of these operations can be performed in parallel, concurrently, or simultaneously. The order of the operations can be rearranged. A process can terminate when its operation is complete, but it may also have additional steps not included in the diagram. A process can correspond to a method, function, procedure, subroutine, subroutine, etc.

[0065] Computer equipment includes user equipment and network equipment. User equipment or clients include, but are not limited to, computers, smartphones, PDAs, etc.; network equipment includes, but is not limited to, a single network server, a server group consisting of multiple network servers, or a cloud based on cloud computing consisting of a large number of computers or network servers. Computer equipment can operate independently to implement this invention, or it can connect to a network and implement this invention through interaction with other computer equipment in the network. The network in which the computer equipment is located includes, but is not limited to, the Internet, wide area network, metropolitan area network, local area network, VPN network, etc.

[0066] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms “a” and “an” as used herein are also intended to include the plural. It should also be understood that the terms “comprising” and / or “including” as used herein specify the presence of the stated features, integers, steps, operations, units, and / or components, without excluding the presence or addition of one or more other features, integers, steps, operations, units, components, and / or combinations thereof.

[0067] Fracture linear density refers to the number of fractures per unit length along the fracture normal direction. In the process of three-dimensional geological modeling of natural fractures in oil and gas reservoirs, the single-well fracture density parameter serves as hard data for establishing a fracture spatial distribution density model and plays a crucial role in controlling the reliability of the fracture model. If the single-well fracture density parameter is inaccurate, the fracture model established on this basis will certainly not conform to reality.

[0068] Natural fractures are characterized by multiple phases, levels, and occurrences, and their distribution in reservoirs exhibits strong heterogeneity, making it challenging to establish a reliable single-well fracture density model. Currently, single-well fracture density parameters are mainly obtained through core fracture description and imaging logging fracture interpretation results. This involves counting the number of fractures developed in the wellbore (or wellwall) and calculating the number of fractures within different length ranges (window length) along the wellbore's extension direction (referred to as the window length method in this paper), thereby obtaining a single-well fracture density curve. Specific results can be found in: [1] Dong Shaoqun, Zeng Lianbo, Cao Han et al. Modeling method and implementation of discrete fracture network with fracture density constraint [J]. Geological Review, 2018, 64(5): 1302-1314; [2] Wei Xu, Zhang Yongping, Bo Yunhe et al. A brief analysis of the application of discrete fracture network modeling technology in mudstone fractured oil and gas reservoirs in Daqing Oilfield [J]. Oil and Gas Reservoir Evaluation and Development, 2018, 8(4): 11-16; [3] Zhou Yinbang. Multi-factor synergistic fracture modeling in Honghe 156 well area of ​​Ordos Basin [J]. Science, Technology and Engineering, 2018, 18(6): 114-118; [4] Feng Wei, Feng Yu. Reservoir fracture modeling technology based on discrete fracture network [J]. Inner Mongolia Petroleum and Chemical Industry, 2015, 2:84-85; [5] Wu Yongping, Chang Lunjie, Chen Wenlong et al. Application of fracture characterization and modeling in Dina 2 gas field [J]. Fault Block Oil and Gas Field, 2015, 22(1): 78-81; [6] Wang Lezhi, Liu Honglei, Zhang Jixi et al. Automatic identification and fracture modeling of fracture system in Puguang Dawan area [J]. Science, Technology and Engineering, 2013, 13(18): 5304-5307; [7] Lang Xiaoling, Guo Zhaojie. Fracture reservoir modeling method based on DFN discrete fracture network model [J]. Journal of Peking University (Natural Science Edition), 2013, 49(6): 964-972; [8] Xu Xingan, Yin Shiqi, Xu Yunheng. Geological modeling of fractured oil reservoir [J]. Journal of Yangtze University (Natural Science Edition), 2011, 8(11): 19-22; [9] Peng Shimi, Suo Zhonghui, Wang Xiaojie et al. Discussion on the modeling method of fractured reservoir integrating multi-scale information [J]. Journal of Xi'an Petroleum University (Natural Science Edition), 2011, 26(4): 1-7;

[10] A reservoir fracture modeling method and system based on self-similarity theory (invention patent, publication number: CN110850057A);

[11] Equivalent fracture modeling method (invention patent, publication number: CN106227957A).

[0069] In the publicly available results of calculating fracture density using the window length method, the following problems arise when calculating the linear density of fractures with multiple phases, levels, and attitudes in a specific work area: ① The problem of simultaneous calculation of fractures with different attitudes. A region typically has multiple natural fractures with different orientations and dips. Core drilling or imaging logging interpretation may simultaneously encounter these fractures with different attitudes. If the "fracture density" is calculated based solely on the quantity of fractures without considering their attitude, the resulting fracture development level cannot pinpoint the specific fracture attitude and therefore cannot reflect the true fracture development in the reservoir. ② The problem of simultaneous calculation of fractures of different levels. Most fractures observed through core drilling or imaging logging are localized. Each well may encounter multiple levels of fractures simultaneously. If different levels of fractures are included in the linear density calculation, it is difficult to determine which level of fracture density the density represents. Using this parameter as hard data for modeling will result in generated fractures that do not reflect the actual level of fractures, leading to model errors. The use of the window length method leads to the two types of problems mentioned above. It ignores the geometric characteristics of crack distribution under different orientations and levels, and the calculated crack density may differ significantly from the actual situation. Furthermore, characterizing crack development features based on this may be problematic, thus affecting the accuracy of crack distribution prediction and modeling.

[0070] To address the aforementioned issues, this invention provides a method and system for quantitatively describing the linear density of natural fractures near the wellbore. This invention proposes a method capable of calculating the linear density of fractures of different grades and groups encountered during drilling in fractured oil and gas reservoirs. This objectively achieves a quantitative characterization of the development degree of different types of natural fractures near the wellbore, laying the foundation for further establishing a reliable three-dimensional fracture density model.

[0071] The following describes the detailed flow of the method according to an embodiment of the present invention with reference to the accompanying drawings, the steps of which can be executed in a computer system containing, for example, a set of computer-executable instructions. Although the logical order of the steps is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than that shown here.

[0072] Example 1

[0073] Figure 1 This diagram illustrates a flow chart of a method for quantitatively describing the linear density of natural fractures near a wellbore, as provided in Embodiment 1 of the present invention. (Refer to...) Figure 1 As can be seen, the method includes the following steps.

[0074] Feature recognition step S110: Based on the fracture stage data and mechanical characteristics in the reservoir to be described, call the corresponding fracture distribution feature data table to identify the different occurrences and different orders of fractures contained in the reservoir.

[0075] Marking and dividing step S120: Mark the entire reservoir to be described according to the occurrence and grade of fractures of different stages, and form multiple fracture zones accordingly;

[0076] Density calculation step S130: For all fracture zones, based on the geological factors controlling fracture development, a matching calculation strategy is used to calculate the fracture density matching for various orientation fractures in different rock mechanical layers.

[0077] In the data processing step S140, based on the calculated fracture density, fracture density curves of different stages, different attitudes and different grades of fracture zones along the wellbore are plotted.

[0078] The fracture linear density referred to in this invention mainly refers to the number of fractures per unit length in the direction perpendicular to the orientation of natural fractures within a certain range along the formation plane. Utilizing outcrop fracture observation and description, core fracture parameter description, imaging logging fracture parameter interpretation, and conventional logging fracture interpretation results, and based on a clear understanding of the fracture formation mechanism and main controlling factors, fracture linear density calculations are performed for different stages, levels, and occurrences based on various wellbore data. This yields descriptive parameters that accurately reflect the degree of fracture development in the actual underground environment.

[0079] Furthermore, in one embodiment, the method further includes:

[0080] Feature statistics step S100: Based on the formation mechanism of reservoir fractures, the mechanical characteristics and parameter distribution characteristics of fractures at different stages are statistically analyzed, and the fractures at different stages are finely divided according to their corresponding different occurrences and different levels. The division results and the corresponding fracture parameter distribution characteristics are linked and recorded to form a fracture parameter distribution characteristic data table.

[0081] In practical applications, the above-mentioned characteristic statistical steps are used to study the fracture formation mechanism, clarify the mechanical characteristics and parameter distribution characteristics of fractures of different stages, and on this basis, the natural fractures encountered in the wellbore are statistically analyzed according to different stages, different occurrences, and different levels, clarifying and recording the parameter distribution characteristics of each stage, group, and level of fractures, which provides a basis for the fracture differentiation of the reservoir to be described.

[0082] By employing the statistical logic of the above embodiments, and combining the studied crack formation mechanism, mechanical characteristics of cracks at different stages, and parameter distributions, cracks of different stages, attitudes, and orders are finely classified. This helps users clearly distinguish the geometric characteristics of crack distributions at different attitudes and orders during calculation and subsequent analysis. It also facilitates reliability verification based on the matching of calculation results with actual crack distribution based on different classifications, providing highly detailed data support for optimization and maintenance.

[0083] Furthermore, combining various geological factors controlling fracture development, and based on the rock mechanical layers controlling fracture development, the linear density of fractures at different stages, groups, and levels within different rock mechanical layers identified on the wellbore is calculated, thereby obtaining the linear density curves of fractures at different stages, groups, and levels along the wellbore. Since different rock mechanical layers may develop natural fractures with different attitudes, different strategies are used to calculate the linear density of natural fractures with different attitudes. Therefore, preferably, in one embodiment, the density calculation step includes:

[0084] Based on wellbore data and the orientation characteristics of rock mechanical layers, reservoir fracture-related rock mechanical layers are classified into the following categories: rock mechanical layers with a distribution direction perpendicular to the wellbore axis, and rock mechanical layers with a distribution direction oblique to the wellbore axis.

[0085] For all fracture zones that are marked and cover different phases, different occurrences and different grades, the distribution direction of their rock mechanical layers is identified. Fracture zones with rock mechanical layer distribution direction perpendicular to the wellbore axis and fracture zones with rock mechanical layer distribution direction oblique to the wellbore axis are treated as different calculation object groups and processed using different identification and calculation strategies.

[0086] Furthermore, in one embodiment, if the current fracture zone belongs to a rock mechanical layer whose distribution direction is perpendicular to the wellbore axis, the density calculation step includes the following operations:

[0087] Step A1: Determine whether a set of natural fractures perpendicular to the rock surface can be found within the rock strata through core identification or imaging logging interpretation. If yes, proceed to step A2; otherwise, proceed to step A3.

[0088] Step A2: Determine whether the average spacing of the obtained cracks is less than the core diameter. If so, calculate the corresponding crack density according to the first calculation strategy; otherwise, calculate the corresponding crack density according to the second calculation strategy.

[0089] Step A3: Determine whether a set of natural fractures oblique to the rock surface can be obtained through core identification or imaging logging interpretation. If so, calculate the corresponding fracture density according to the third calculation strategy.

[0090] On the other hand, if the current fracture zone belongs to a rock mechanical layer whose distribution direction is oblique to the wellbore axis, in one embodiment, the density calculation step includes the following operations:

[0091] If it is found through core identification or imaging logging that a set of natural fractures perpendicular to the rock surface are developed within the rock stratum, then the fracture density of the corresponding fractures is calculated according to the fourth calculation strategy.

[0092] If a set of natural fractures obliquely intersecting the rock surface is found within the rock stratum through core identification or imaging logging interpretation, the fracture density of the corresponding fractures is calculated according to the fifth calculation strategy.

[0093] Specifically, Figure 2 The diagram illustrates the fracture density calculation principle of the method for quantitatively describing the linear density of natural fractures near a wellbore provided by an embodiment of the present invention. In one embodiment, in step A2, the corresponding fracture density is calculated according to a first calculation strategy, including:

[0094]

[0095] The corresponding crack density is calculated according to the second calculation strategy, including:

[0096] Identify the thickness of the rock mechanical layer where the crack is located H 岩心 The corresponding crack spacing index is obtained by combining the corresponding crack outcrop data. The average spacing of fractures near the wellbore is calculated based on the rock mechanical layer thickness and fracture spacing index. S 岩心 :

[0097] Then, the linear density of the current fracture on the plane of rock mechanical layer distribution is calculated according to the following formula:

[0098]

[0099] In the formula, L d S represents the average linear density of fractures within the current rock mechanical layer, and S represents the average fracture spacing. S 岩心 The average spacing of cracks near the wellbore;

[0100] The crack spacing index is the ratio of the thickness of the exposed cracked rock layer to the median crack spacing within a set range.

[0101] Further, in step A3, in one embodiment, calculating the corresponding crack density according to the third calculation strategy includes:

[0102] Identify the thickness of the rock mechanical layers in which this group of oblique fractures developed. H岩心 ;

[0103] Combined with the statistical analysis of the crack spacing index of the corresponding outcrop oblique joints I S露头 Then, based on the two, the average vertical distance between the oblique fractures developed within the rock mechanical layer on the wellbore is calculated. S 岩心 ;

[0104] Combining the angle of the natural fractures developed within the rock strata with the oblique angle of the rock surface, S 岩心 This is converted into the average spacing between the intersection lines of this set of cracks and the rock mechanical layer. S’ 岩心 ;

[0105] The linear density of fractures on the plane of rock mechanical layer distribution is calculated using the following formula:

[0106]

[0107] In the formula, L d This represents the average linear density of fractures within the current rock mechanical layer.

[0108] Specifically, in one embodiment, the process of calculating the corresponding crack density according to the fourth calculation strategy includes:

[0109] Rock mechanical layer thickness identified from drilling data H 岩心 The apparent thickness of the rock mechanical layer is used as the basis for determining the actual thickness of the rock mechanical layer by combining the oblique angle between the rock mechanical layer distribution direction and the wellbore axis. ;

[0110] The crack spacing index for this type of crack is obtained by combining the statistical data of the corresponding exposed cracks. I S露头 Based on the actual thickness of the rock mechanical layer The fracture spacing index is used to calculate the average spacing between fractures that develop along the direction of extension of the rock mechanical layer on the wellbore. ;

[0111] Then, the linear density of the cracks on the plane of rock mechanical layer distribution is calculated according to the following formula:

[0112]

[0113] In the formula, L d This represents the average linear density of fractures within the current rock mechanical layer.

[0114] On the other hand, in one embodiment, the process of calculating the corresponding crack density according to the fifth calculation strategy includes:

[0115] Rock mechanical layer thickness identified from drilling data H 岩心 The apparent thickness of the rock mechanical layer is used as the basis for determining the actual thickness of the rock mechanical layer by combining the oblique angle between the rock mechanical layer distribution direction and the wellbore axis. :

[0116] The crack spacing index for this type of crack is obtained by combining the statistical data of the corresponding exposed cracks. I S露头 The average spacing of the set of fractures developed within the rock mechanical layer on the wellbore is calculated based on the actual layer thickness and fracture spacing index of the rock mechanical layer. S 岩心 ;

[0117] The spacing of the cracks is determined based on the oblique angle between the natural cracks developed within the rock strata and the rock surface. S 岩心 Transformed into the average spacing of cracks along the plane of the rock's mechanical layer. ;

[0118] Then, the linear density of this set of cracks on the plane of rock mechanical layer distribution is obtained according to the following formula:

[0119] ;

[0120] In the formula, L d This represents the average linear density of fractures within the current rock mechanical layer.

[0121] In practical applications, ① when the wellbore axis is perpendicular to the direction of rock mechanical layer distribution, and core identification or imaging logging interpretation reveals a set of natural fractures perpendicular to the rock bedding plane within the rock layer, the following two situations apply:

[0122] a. If the average crack spacing ( S Smaller than the core diameter ( D If at least one of the fractures in this group intersects the wellbore, then the average linear density of fractures within this rock mechanical layer ( L d ) is equivalent to the average crack spacing ( S The reciprocal of ), that is:

[0123] (Formula 1);

[0124] b. If the fracture spacing is greater than the diameter of the drill core, the wellbore can only encounter one fracture at most, and it is necessary to identify the thickness of the rock mechanical layer where the fracture is located. H 岩心 ), combined with the statistical analysis of similar outcrops to obtain the crack spacing index ( IS露头 The average spacing of cracks near the wellbore was obtained. S 岩心 )for:

[0125] (Formula 2);

[0126] Among them, the crack spacing index ( I S露头 ( ) refers to the thickness of fractured rock layers (i.e., the thickness of rock mechanical layers) within a limited range. H 露头 ) and the median crack spacing ( S 露头 The ratio of ).

[0127] After obtaining the average spacing of the wellbore fractures ( S 岩心 Then, the linear density of this group of cracks perpendicular to the rock strata on the rock mechanical layer distribution plane is obtained as follows:

[0128] (Formula 3);

[0129] For cracks of different groups and different grades under this condition, method ① can be used to determine the crack linear density.

[0130] ② When the wellbore axis is perpendicular to the direction of rock mechanical layer distribution, and core identification or imaging logging interpretation reveals the development of a set of rock layers with an angle of [angle missing] with the bedding plane. α When natural fractures intersecting obliquely are identified in the wellbore, the thickness of the rock mechanical layer where these oblique fractures are developed is determined. H 岩心 Afterwards, the oblique joint spacing index obtained by combining similar outcrop statistics ( I S露头 The average vertical distance between the oblique fractures developed within the rock mechanical layer on the wellbore is calculated as follows: S 岩心 )for:

[0131] (Formula 4);

[0132] Will S 岩心 The average spacing between the intersection lines of this set of cracks and the rock mechanical layer is converted into:

[0133] (Formula 5);

[0134] Then the angle between this group and the rock surface is obtained as follows: α The linear density of cracks on the plane of rock mechanical layer distribution is:

[0135] (Formula 6);

[0136] For cracks of different groups and different grades under this condition, method ② can be used to determine the crack linear density.

[0137] ③ When the wellbore axis is obliquely intersecting the direction of rock strata distribution (the angle of intersection is...) θ When core identification or imaging logging interpretation reveals a set of natural fractures perpendicular to the rock surface within the rock strata, the thickness of the rock mechanical layer identified through drilling data ( H 岩心 ) is the apparent thickness of the mechanical layer, and the actual thickness of the rock mechanical layer ( )for:

[0138] (Formula 7);

[0139] This type of crack spacing index is obtained by combining statistics of similar outcrops. I S露头 The average spacing between fractures developed along the direction of the rock mechanical layer on the wellbore was obtained. )for:

[0140] (Formula 8);

[0141] Furthermore, the linear density of the cracks perpendicular to the rock strata on the rock mechanical layer distribution plane is obtained as follows:

[0142] (Formula 9);

[0143] For cracks of different groups and different grades in this case, method ③ can be used to determine the crack linear density.

[0144] ④ When the wellbore axis is obliquely intersecting the direction of rock strata distribution (the included angle is...) β Furthermore, core identification or imaging logging interpretation revealed a set of natural fractures within the rock strata that were obliquely intersecting the rock surface (at an angle of...). γ When, the thickness of the rock mechanical layer identified through drilling data ( H 岩心 ) is the apparent thickness of the mechanical layer, and its actual layer thickness ( )for:

[0145] (Formula 10);

[0146] This type of crack spacing index is obtained by combining statistics of similar outcrops. I S露头 The average spacing of the set of fractures developed within the rock mechanical layer on the wellbore was obtained. S岩心 )for:

[0147] (Formula 11);

[0148] Further increase the crack spacing S 岩心 This is converted into the average spacing of cracks along the plane of the rock mechanical layer. ):

[0149] (Formula 12);

[0150] Then the angle between this group and the rock surface is obtained as follows: γ The linear density of cracks on the plane of rock mechanical layer distribution is:

[0151] (Formula 13);

[0152] For cracks of different groups and different grades under this condition, method ④ can be used to determine the crack linear density.

[0153] Application Cases

[0154] Taking Block P of a marine carbonate gas field in my country as an example, quantitative calculations of fracture linear density in single wells were conducted. The average porosity of the main producing layer F in Block P is less than 5%, and the average permeability is less than 10 mD. The reservoir contains NW-SE, near-EW, and NE-SW trending structural fractures. The NW-SE trending fractures intersect the rock-mechanical layers perpendicularly at 90°, the near-EW trending fractures intersect the rock-mechanical layers at approximately 60°, and the NE-SW trending fractures intersect the rock-mechanical layers at approximately 30°. Five rock-mechanical layers were identified within a segment of the target layer in well A1 of Block P, from top to bottom: rock-mechanical layer 1, rock-mechanical layer 2, rock-mechanical layer 3, rock-mechanical layer 4, and rock-mechanical layer 5, with thicknesses of 0.15 m, 1.2 m, 0.8 m, 0.1 m, and 2.1 m, respectively. Similar outcrop observations indicate that fractures are mainly distributed within the rock-mechanical layers, terminating at the rock-mechanical layer interfaces, and exhibiting different levels and scales within different rock-mechanical layers. The development characteristics of fractures of different stages, occurrences, and grades within the rock mechanical layer are generally as follows: the thinner the rock mechanical layer, the smaller the fracture spacing, the greater the fracture linear density, and the higher the drilling encounter rate; conversely, the thicker the rock mechanical layer, the larger the fracture spacing, the smaller the fracture linear density, and the lower the drilling encounter rate. The ratio of the average fracture spacing to the thickness of the rock mechanical layer in which the fracture group developed shows a quantitative relationship. Based on the fracture drilling situation of well A1 in block P, and after identifying the distribution of the rock mechanical layer, the following clarifies the practical application of the quantitative description method of fracture linear density for different stages, groups, and grades in this area. Specifically:

[0155] (1) Regarding the NW-SE trending natural fractures, based on the core description, in rock mechanics layer 1 and rock mechanics layer 4, due to the relatively thin layer thickness, the fracture spacing is small (both are smaller than the core diameter), while in other rock mechanics layers, due to the relatively large thickness, the fracture spacing is larger than the core diameter, and only one fracture was observed in each layer. Figure 1 Based on the above core and similar outcrop fracture observation and description results, the process of calculating the NW-SE trending fracture linear density in this section of well A1 is as follows:

[0156] Two cracks were observed in rock mechanics layer 1 and rock mechanics layer 4 respectively, with a crack spacing of ( S The diameters are 0.1m and 0.07m respectively, both smaller than the core diameter. D At this time, the average linear density of fractures within the rock mechanical layer ( L d ) is equivalent to the average crack spacing ( S The reciprocal of ) is:

[0157] NW-SE fracture linear density within rock mechanical layer 1:

[0158] L d-1 =1 / 0.1=10 strips / m;

[0159] Linear density of NW-SE fractures within rock mechanical layer 4:

[0160] L d-4 =1 / 0.07=14.3 items / m.

[0161] The following calculation of the NW-SE trend fracture linear density within rock mechanical layers 2, 3, and 5 begins with determining the NW-SE trend fracture spacing index based on observations of similar outcrops. I S露头(NW-SE) =1.4, further we have:

[0162] NW-SE fracture linear density within rock mechanical layer 2 L d-2 =1.4 / 1.2=1.17 strips / m;

[0163] NW-SE fracture linear density within rock mechanical layer 3 L d-3 =1.4 / 0.8=1.75 strips / m;

[0164] NW-SE fracture linear density within rock mechanical layer 5 L d-5 =1.4 / 2.1=0.67 strips / m.

[0165] (2) Regarding the near-EW trending natural fractures, based on the core description, it can be seen that only 2, 1, and 2 natural fractures were observed in rock mechanics layers 1, 3, and 4, respectively. The vertical spacing of the fractures in rock mechanics layers 1 and 4 is 0.11 m and 0.08 m, respectively. The process for calculating the near-EW trending fracture linear density in this layer of well A1 is as follows: Figure 1 ):

[0166] For rock mechanical layers 1 and 4, since the vertical spacing parameter of the cracks is directly available, it can be directly converted into the average spacing of cracks along the plane of the rock mechanical layer, and then the crack linear density can be calculated, as follows:

[0167] Rock mechanics layer 1: The spacing between the intersection of this group of fractures and the bedding plane. S ' 岩心-1 for:

[0168] S ' 岩心-1 =0.11 / sin60°=0.13m;

[0169] The linear density of this set of cracks on the plane of rock mechanical layer 1 is then calculated as follows:

[0170] L d-1 =1 / 0.13=7.69 strips / m;

[0171] Similarly, the near-EW fracture linear density within rock mechanical layer 4 is:

[0172] L d-4 =sin60° / 0.08=10.83 strips / m;

[0173] For rock mechanics layer 3, the near-EW fracture spacing index is first obtained by combining similar outcrop statistics:

[0174] I S露头(近E-W) =1.36;

[0175] The average vertical distance between these fractures within the rock mechanical layer on the wellbore is then calculated as follows:

[0176] S 岩心-3 =0.8 / 1.36=0.59m;

[0177] Will S 岩心-3 This is converted into the average spacing between the intersection lines of this set of cracks and the rock mechanical plane. S ' 岩心-3 :

[0178] S ' 岩心-3 =0.59 / sin60°=0.68m;

[0179] Furthermore, the linear density of this group of cracks on the plane of rock mechanical layer 3 is obtained as follows:

[0180] L d-3 =1 / 0.68=1.47 strips / m;

[0181] (3) Regarding the NE-SW trending natural fractures, based on the core description, it can be seen that only 2 and 1 natural fractures were observed in rock mechanics layers 1 and 4, respectively, with the vertical spacing of the fractures in rock mechanics layer 1 being 0.1 m. The process for calculating the NE-SW trending fracture linear density in this section of well A1 is as follows: Figure 1 ):

[0182] For rock mechanical layer 1, since the vertical spacing parameter of the cracks is directly available, it can be directly converted into the average spacing of cracks along the plane of crack propagation along the rock mechanical layer, and then the crack linear density can be calculated as follows:

[0183] Rock mechanics layer 1: The spacing between the intersection of this group of fractures and the bedding plane. S ' 岩心-1 for:

[0184] S ' 岩心-1 =0.1 / sin30°=0.2m;

[0185] The linear density of this set of cracks on the plane of rock mechanical layer 1 is then calculated as follows:

[0186] L d-1 =1 / 0.2=5 strips / m;

[0187] For rock mechanics layer 4, the NE-SW fracture spacing index is first obtained by combining similar outcrop statistics:

[0188] I S露头(NE-SW) =1;

[0189] The average vertical distance between these fractures within the rock mechanical layer on the wellbore is then calculated as follows:

[0190] S 岩心-4 =0.1 / 1=0.1m;

[0191] Will S 岩心-4 This is converted into the average spacing between the intersection lines of this set of cracks and the rock mechanical plane. S ' 岩心-4:

[0192] S ' 岩心-4 =0.1 / sin30°=0.2m;

[0193] Furthermore, the linear density of this group of cracks on the plane of rock mechanical layer 4 is obtained as follows:

[0194] L d-4 =1 / 0.2=5 strips / m;

[0195] The fracture linear density data for different formations, grades, and occurrences in well A1 of block P are shown in the attached figure. Figure 3 As shown.

[0196] For the foregoing method embodiments, in order to simplify the description, they are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0197] This invention comprehensively considers the multi-stage, multi-group, and multi-level characteristics of natural fractures in oil and gas reservoirs. Combining the formation mechanism and main controlling factors of fractures, it proposes a method for accurately calculating the density of natural fractures at each stage, group, and level. Ultimately, it can obtain evaluation parameters reflecting the degree of fracture development that are consistent with the actual underground fracture development characteristics. The advantages of this method are that it can quantitatively describe natural fractures with different development characteristics in the reservoir separately, which is more reliable and can more accurately describe the contribution of natural fractures with different characteristics to the reservoir and their impact on development. Furthermore, the three-dimensional fracture density modeling carried out on this basis is more precise and reliable.

[0198] This invention enables a quantitative evaluation of the development level of natural fractures near wellbores in accordance with geological realities. It can be widely applied to reservoir evaluation, favorable development zone selection, and three-dimensional fracture modeling in fractured oil and gas fields in my country, providing technical support for the efficient development of oil and gas fields in my country.

[0199] It should be noted that, in other embodiments of the present invention, the method can also combine one or more of the above embodiments to obtain a new method for quantitatively describing the linear density of natural fractures near the wellbore, so as to achieve a fine description of fractures with different development characteristics.

[0200] It should be noted that, based on the methods in any one or more embodiments of the present invention described above, the present invention also provides a storage medium storing program code that can implement the methods described in any one or more embodiments, and when the code is executed by the operating system, it can implement the method described above for quantitatively describing the linear density of natural fractures near the wellbore.

[0201] Example 2

[0202] The methods described in detail in the above-disclosed embodiments of the present invention can be implemented using various forms of devices or systems. Therefore, based on other aspects of the methods described in any one or more of the above embodiments, the present invention also provides a system for quantitatively describing the linear density of natural fractures near a wellbore. This system is used to perform the method for quantitatively describing the linear density of natural fractures near a wellbore as described in any one or more of the above embodiments. Specific embodiments are given below for detailed description.

[0203] Specifically, Figure 4 The diagram shows a schematic representation of the structure of a system for quantitatively describing the linear density of natural fractures near a wellbore, as provided in an embodiment of the present invention. Figure 4 As shown, the system includes:

[0204] The feature recognition module 41 is configured to call the corresponding fracture distribution feature data table to identify the different occurrences and different orders of fractures contained in the reservoir based on the fracture stage data and mechanical characteristics in the reservoir to be described.

[0205] The marking and division module 43 is configured to mark the entire reservoir to be described according to the occurrence and grade of fractures of different stages, thereby forming multiple fracture zones.

[0206] The density calculation module 45 is configured to calculate the fracture density of various orientation fractures in different rock mechanical layers by using a matching calculation strategy based on the geological factors that control fracture development for all fracture zones.

[0207] The data processing module 47 is configured to plot fracture density curves for fracture zones of different stages, different attitudes, and different grades along the wellbore based on the calculated fracture density.

[0208] Furthermore, in one embodiment, the system further includes:

[0209] The feature statistics module 40 is configured to statistically analyze the mechanical characteristics and parameter distribution characteristics of fractures at different stages based on the formation mechanism of reservoir fractures, and to finely classify fractures at different stages according to their corresponding different occurrences and different levels, and to associate and record the classification results and the corresponding fracture parameter distribution characteristics to form a fracture parameter distribution characteristic data table.

[0210] In practical applications, in one embodiment, the density calculation module is specifically configured as follows:

[0211] Based on wellbore data and the orientation characteristics of rock mechanical layers, reservoir fracture-related rock mechanical layers are classified into the following categories: rock mechanical layers with a distribution direction perpendicular to the wellbore axis, and rock mechanical layers with a distribution direction oblique to the wellbore axis.

[0212] Furthermore, in one embodiment, if the current fracture zone belongs to a rock mechanical layer whose distribution direction is perpendicular to the wellbore axis, the density calculation module performs the following operations:

[0213] Step A1: Determine whether a set of natural fractures perpendicular to the rock surface can be found within the rock strata through core identification or imaging logging interpretation. If yes, proceed to step A2; otherwise, proceed to step A3.

[0214] Step A2: Determine whether the average spacing of the obtained cracks is less than the core diameter. If so, calculate the corresponding crack density according to the first calculation strategy; otherwise, calculate the corresponding crack density according to the second calculation strategy.

[0215] Step A3: Determine whether a set of natural fractures oblique to the rock surface can be obtained through core identification or imaging logging interpretation. If so, calculate the corresponding fracture density according to the third calculation strategy.

[0216] On the other hand, if the current fracture zone belongs to a rock mechanical layer whose distribution direction is oblique to the wellbore axis, the density calculation module performs the following operations:

[0217] If it is found through core identification or imaging logging that a set of natural fractures perpendicular to the rock surface are developed within the rock stratum, then the fracture density of the corresponding fractures is calculated according to the fourth calculation strategy.

[0218] If a set of natural fractures obliquely intersecting the rock surface is found within the rock stratum through core identification or imaging logging interpretation, the fracture density of the corresponding fractures is calculated according to the fifth calculation strategy.

[0219] In one embodiment, when the density calculation module performs step A2, it calculates the corresponding crack density according to the first calculation strategy, including:

[0220]

[0221] The corresponding crack density is calculated according to the second calculation strategy, including:

[0222] Identify the thickness of the rock mechanical layer where the crack is located H 岩心 The corresponding crack spacing index is obtained by combining the corresponding crack outcrop data. I S露头The average spacing of fractures near the wellbore is calculated based on the rock mechanical layer thickness and fracture spacing index. S 岩心 :

[0223] Then, the linear density of the current fracture on the plane of rock mechanical layer distribution is calculated according to the following formula:

[0224]

[0225] In the formula, L d S represents the average linear density of fractures within the current rock mechanical layer, and S represents the average fracture spacing. S 岩心 The average spacing of cracks near the wellbore;

[0226] The crack spacing index is the ratio of the thickness of the exposed cracked rock layer to the median crack spacing within a set range.

[0227] Further, in one embodiment, when the density calculation module performs step A3, it calculates the corresponding crack density according to the third calculation strategy, including:

[0228] Identify the thickness of the rock mechanical layers in which this group of oblique fractures developed. H 岩心 ;

[0229] Combined with the statistical analysis of the crack spacing index of the corresponding outcrop oblique joints I S露头 Then, based on the two, the average vertical distance between the oblique fractures developed within the rock mechanical layer on the wellbore is calculated. S 岩心 ;

[0230] Combining the angle of the natural fractures developed within the rock strata with the oblique angle of the rock surface, S 岩心 This is converted into the average spacing between the intersection lines of this set of cracks and the rock mechanical plane. S’ 岩心 ;

[0231] The linear density of fractures on the plane of rock mechanical layer distribution is calculated using the following formula:

[0232]

[0233] In the formula, L d This represents the average linear density of fractures within the current rock mechanical layer.

[0234] Specifically, in one embodiment, the process by which the density calculation module calculates the corresponding crack density according to the fourth calculation strategy includes:

[0235] Rock mechanical layer thickness identified through drilling data H 岩心 The apparent thickness of the rock mechanical layer is used as the basis for determining the actual thickness of the rock mechanical layer by combining the oblique angle between the rock mechanical layer distribution direction and the wellbore axis. ;

[0236] The crack spacing index for this type of crack is obtained by combining the statistical data of the corresponding exposed cracks. I S露头 Based on the actual thickness of the rock mechanical layer The fracture spacing index is used to calculate the average spacing between fractures that develop along the direction of extension of the rock mechanical layer on the wellbore. ;

[0237] Then, the linear density of the cracks on the plane of rock mechanical layer distribution is calculated according to the following formula:

[0238]

[0239] In the formula, L d This represents the average linear density of fractures within the current rock mechanical layer.

[0240] In one embodiment, the process by which the density calculation module calculates the corresponding crack density according to the fifth calculation strategy includes:

[0241] Rock mechanical layer thickness identified through drilling data H 岩心 The apparent thickness of the rock mechanical layer is used as the basis for determining the actual thickness of the rock mechanical layer by combining the oblique angle between the rock mechanical layer distribution direction and the wellbore axis. :

[0242] The crack spacing index for this type of crack is obtained by combining the statistical data of the corresponding exposed cracks. The average spacing of the set of fractures developed within the rock mechanical layer on the wellbore is calculated based on the actual layer thickness and fracture spacing index of the rock mechanical layer. S 岩心 ;

[0243] The spacing of the cracks is determined based on the oblique angle between the natural cracks developed within the rock strata and the rock surface. S 岩心 Transformed into the average spacing of cracks along the plane of the rock's mechanical layer. ;

[0244] Then, the linear density of this set of cracks on the plane of rock mechanical layer distribution is obtained according to the following formula:

[0245]

[0246] In the formula, Ld This represents the average linear density of fractures within the current rock mechanical layer.

[0247] In the system for quantitatively describing the linear density of natural fractures near the wellbore provided in this embodiment of the invention, each module or unit structure can operate independently or in combination according to actual description and calculation requirements to achieve the corresponding technical effects.

[0248] It should be understood that the embodiments disclosed herein are not limited to the specific structures, processing steps, or materials disclosed herein, but should be extended to equivalent substitutions of these features as understood by those skilled in the art. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0249] The phrase "an embodiment" in the specification means that a specific feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Therefore, the phrase "an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0250] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for quantitatively describing the linear density of natural fractures near a wellbore, characterized in that, The method includes: The feature identification step involves calling the corresponding fracture distribution feature data table to identify the different occurrences and orders of fractures contained in the reservoir based on the fracture sequence data and mechanical characteristics in the reservoir to be described. The marking and division steps involve marking the entire reservoir to be described according to the occurrence and order of fractures at different stages, thus forming multiple fracture zones. Density calculation steps: For all fracture zones, based on the geological factors controlling fracture development, a matching calculation strategy is used to calculate the fracture density matching various orientation fractures in different rock mechanical layers. The data processing steps and the calculated fracture density were used to plot fracture density curves for different stages, different attitudes and different grades of fracture zones along the wellbore. If the current fracture zone belongs to a rock mechanical layer whose distribution direction is perpendicular to the wellbore axis, the density calculation step includes the following operations: Step A1: Determine whether a set of natural fractures perpendicular to the rock surface can be found within the rock strata through core identification or imaging logging interpretation. If yes, proceed to step A2; otherwise, proceed to step A3. Step A2: Determine whether the average spacing of the obtained cracks is less than the core diameter. If so, calculate the corresponding crack density according to calculation strategy a1; otherwise, calculate the corresponding crack density according to calculation strategy a2. Step A3: Determine whether a set of natural fractures oblique to the rock surface can be obtained through core identification or imaging logging interpretation. If so, calculate the corresponding fracture density according to calculation strategy a3. In step A2, the corresponding crack density is calculated according to calculation strategy a1, including: The corresponding crack density is calculated according to calculation strategy a2, including: Identify the thickness of the rock mechanical layer where the crack is located H 岩心 The corresponding crack spacing index is obtained by combining the corresponding crack outcrop data. I S露头 The average spacing of fractures near the wellbore is calculated based on the rock mechanical layer thickness and fracture spacing index. S 岩心 : Then, the linear density of the current fracture on the plane of rock mechanical layer distribution is calculated according to the following formula: In the formula, L d S represents the average linear density of fractures within the current rock mechanical layer, and S represents the average fracture spacing. S 岩心 The average spacing of cracks near the wellbore; Among them, the crack spacing index I S露头 The ratio of the thickness of the outcrop fractured rock layer to the median spacing of the outcrop fractures within a specified range is adopted. In step A3, the corresponding crack density is calculated according to calculation strategy a3, including: Identify the thickness of the rock mechanical layers in which this group of oblique fractures developed. H 岩心 ; Combined with the statistical analysis of the crack spacing index of the corresponding outcrop oblique joints I S露头 Then, based on the two, the average vertical distance between the oblique fractures developed within the rock mechanical layer on the wellbore is calculated. S 岩心 ; Combining the oblique angle between the natural fractures developed within the rock strata and the rock surface, S 岩心 This is converted into the average spacing between the intersection lines of this set of cracks and the rock mechanical layer. S’ 岩心 ; The linear density of fractures on the plane of rock mechanical layer distribution is calculated using the following formula: In the formula, L d This represents the average linear density of fractures within the current rock mechanical layer.

2. The method as described in claim 1, characterized in that, The method further includes: The feature statistics steps involve statistically analyzing the mechanical characteristics and parameter distribution characteristics of fractures at different stages based on the formation mechanism of reservoir fractures, and then finely classifying the fractures at different stages according to their corresponding different occurrences and levels. The classification results and the corresponding fracture parameter distribution characteristics are then linked and recorded to form a fracture parameter distribution characteristic data table.

3. The method as described in claim 1, characterized in that, The density calculation step includes: Based on wellbore data and the orientation characteristics of rock mechanical layers, reservoir fracture-related rock mechanical layers are classified into the following categories: rock mechanical layers with a distribution direction perpendicular to the wellbore axis, and rock mechanical layers with a distribution direction oblique to the wellbore axis.

4. The method as described in claim 1, characterized in that, If the current fracture zone belongs to a rock mechanical layer whose distribution direction is oblique to the wellbore axis, the density calculation step includes the following operations: If a set of natural fractures perpendicular to the rock surface can be found within the rock stratum by core identification or imaging logging, then the fracture density of the corresponding fractures is calculated according to calculation strategy b1. If a set of natural fractures obliquely intersecting the rock surface is found within the rock stratum through core identification or imaging logging interpretation, the fracture density of the corresponding fractures is calculated according to calculation strategy b2.

5. The method as described in claim 4, characterized in that, The process of calculating the corresponding crack density according to calculation strategy b1 includes: Rock mechanical layer thickness identified through drilling data H 岩心 The apparent thickness of the rock mechanical layer is used as the basis for determining the actual thickness of the rock mechanical layer by combining the oblique angle between the rock mechanical layer distribution direction and the wellbore axis. ; The crack spacing index for this type of crack is obtained by combining the statistical data of the corresponding exposed cracks. I S露头 Based on the actual thickness of the rock mechanical layer The fracture spacing index is used to calculate the average spacing between fractures that develop along the direction of extension of the rock mechanical layer on the wellbore. ; Then, the linear density of the cracks on the plane of rock mechanical layer distribution is calculated according to the following formula: In the formula, L d This represents the average linear density of fractures within the current rock mechanical layer.

6. The method as described in claim 4, characterized in that, The process of calculating the corresponding crack density according to calculation strategy b2 includes: Rock mechanical layer thickness identified through drilling data H 岩心 The apparent thickness of the rock mechanical layer is used as the basis for determining the actual thickness of the rock mechanical layer by combining the oblique angle between the rock mechanical layer distribution direction and the wellbore axis. : The crack spacing index for this type of crack is obtained by combining the statistical data of the corresponding exposed cracks. I S露头 The average spacing of the set of fractures developed within the rock mechanical layer on the wellbore is calculated based on the actual layer thickness and fracture spacing index of the rock mechanical layer. S 岩心 ; The spacing of the cracks is determined based on the oblique angle between the natural cracks developed within the rock strata and the rock surface. S 岩心 Transformed into the average spacing of cracks along the plane of the rock's mechanical layer. ; Then, the linear density of this set of cracks on the plane of rock mechanical layer distribution is obtained according to the following formula: In the formula, L d This represents the average linear density of fractures within the current rock mechanical layer.

7. A system for quantitatively describing the linear density of natural fractures near a wellbore, characterized in that, The system performs the method as described in any one of claims 1 to 6.

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