A method for evaluating the degree of fracture development using fracture intensity

Abstract

This invention provides a method for evaluating fracture development using fracture intensity, comprising: S1. Obtaining imaging logging results for the target area; S2. Obtaining fracture attribute parameters based on the imaging logging results, including at least fracture density, fracture orientation, fracture effectiveness, and fracture length; S3. Calculating a fracture intensity index and generating a fracture intensity map based on the fracture attribute parameters obtained in step S2; S4. Dividing the fracture intensity in different directions on the fracture intensity map obtained in step S3 according to different fracture orientations and dip angles, and evaluating the fracture development intensity in different orientations of the target area. This invention can quantitatively evaluate the degree of fracture development, solving the problem of cumbersome operation in quantitatively evaluating fracture development due to the large amount of information in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field exploration and development technology, specifically to a method for evaluating the degree of fracture development using fracture strength. Background Technology

[0002] The characteristics of gas storage reservoirs are the main factors affecting the safe operation of gas storage facilities and the amount of gas stored. In particular, the evaluation and understanding of the degree of development of natural fractures plays a crucial role in determining the type of storage space.

[0003] Currently, the most direct and effective means of evaluating fractures in a single well are core observation and imaging logging. Imaging logging can describe fractures, including fracture development intervals, fracture occurrence, density, morphological characteristics, and degree of filling. However, due to the large amount of information provided, quantitatively evaluating the degree of fracture development is cumbersome.

[0004] In terms of crack intensity calculation, for example, the patent "A Crack Intensity Prediction Method Based on Data Volume Dimensionality Reduction and Discrete Coefficient Calculation" (publication number CN111399049A) improves crack prediction accuracy by superimposing and offsetting gather data according to azimuth range to obtain attribute data volume, then performing dimensionality reduction on it, and finally calculating the discrete coefficient based on the dimensionality-reduced data volume. The patent "A Crack Intensity Calculation Method in Favorable Area of ​​Target Layer" (publication number CN111506861B) uses waveform classification, crack sample establishment, correlation coefficient analysis, and data reconstruction to accurately classify different crack intensities within favorable seismic phases. By classifying waveforms of three-dimensional post-stack seismic data, favorable seismic facies regions are identified. The reflection waveform of the target layer of the fracture sample is established and its correlation coefficient is calculated with the reflection waveform of each grid point within the same seismic facies. Then, the data is reconstructed using the correlation coefficient value and the fracture density value of the fracture sample to obtain fracture density contour lines or color plane maps for analyzing different fracture intensities. The patent "A Method for Constructing a Coal Reservoir Fracture Prediction Model by Multi-Source Data Volume Fusion", publication number CN119270382A, integrates core data, conventional logging, imaging logging, CT scans, and seismic fracture prediction data, and uses mathematical methods to analyze and fuse them to construct a coal reservoir fracture prediction model. In calculating fracture strength, coal samples are obtained, and the number, dip angle, length, filling degree, and properties of fractures on the sample end face are recorded. The fracture strength of the artificially described core is calculated, and fracture surface strength is generated using imaging logging data. The non-overlapping portions of the two data are assigned a higher fracture strength value to generate a coal sample fracture strength curve. The patent "Quantitative Prediction Method and Device for Fractures Based on Post-Stack Seismic Data," publication number CN113534247B, describes a method for quantitatively predicting fractures from a seismic perspective. It processes and analyzes post-stack seismic data, extracts relevant attributes, establishes a fracture prediction model, and achieves quantitative prediction of parameters such as fracture strength. The patent... A method for fine characterization of fracture and cavity attribute parameters in numerical simulation of acid fracturing, published in CN114510808B, comprehensively utilizes well logging data, core data, drilling venting data, and seismic data to establish geological models of natural fracture distribution and karst cave distribution in geological modeling software, and establishes an initial fracture-karst cave joint distribution geological model. By obtaining reservoir rock samples and laboratory experiments, rock mechanical parameters are obtained, and the compressive strength and elastic modulus mechanical parameters of rocks in different regions of the geological model are assigned differentiated values, providing fine characterization of fracture and cavity attribute parameters for numerical simulation of acid fracturing. This involves the calculation and application of fracture strength-related parameters.

[0005] For example, the paper "The phenomena of rupture and flow in solids," Philosophical Transactions of the Royal Society of London, Series A, 1921, Vol. 221, No. 582-593, proposed the energy balance theory, arguing that crack propagation requires the reduction of elastic stored energy to be greater than or equal to the increase of new surface energy, laying the theoretical foundation for crack propagation in brittle materials. The paper "Analysis of stresses and strains near the end of a crack traversing a plate," Journal of Applied Mechanics, 1957, Vol. 24, No. 3, introduced the stress intensity factor (K) and proposed using the critical value of K as a criterion for crack instability and propagation, forming the core framework of linear elastic fracture mechanics. The paper "Numerical Calculation of Three-Dimensional Crack Stress Intensity Factor," Chinese Journal of Rock Mechanics and Engineering, 2006, Vol. 25, Supplement 2, used a meshless Galerkin method. The method calculates the stress intensity factor at the three-dimensional crack front and handles the isolation effect of the crack surface through a visual criterion. The results are in good agreement with traditional methods. The literature "Construction of an Intelligent Decision Support System Framework for Coal Seam Floor Water Hazard Prevention" (Coal Geology and Exploration, 2021, Vol.49, No.1) constructs an integrated "data-model-solution" framework. Through a spatial point prediction model for floor water inrush and a reliability analysis model for grouting modification projects, intelligent decision-making for coal seam floor water hazards is achieved. The literature... Fracture Intensity - Schafer's Method The proceedings of the 1980 SPE Western Regional Meeting, titled "Schafer Fracture Strength Index (SFI)," proposed a formula for predicting initial well production using formation dip logging data. Where a, b, and c are crack length parameters, and d is wellbore ellipticity; the literature "Collapse mechanisms and fragility curves based on Lumped Damage Mechanics for RC frames subjected to earthquakes", EngineeringStructures, 2024, Vol. 299, proposes a lumped damage mechanics (LDM) framework, combines incremental dynamic analysis (IDA) to construct seismic vulnerability curves for reinforced concrete frames, and quantifies the impact of crack propagation on structural collapse; the literature "Crack tip location and stress intensity factor calculation method based on digital image correlation displacement field", CSDN blog (Technical Review), 2025 online publication, reviews the application of digital image correlation (DIC) technology in crack tip location and stress intensity factor (SIF) calculation, and compares the advantages and disadvantages of methods such as displacement gradient method and J integral method; the literature "Quantitative fracture characterization in unconventional reservoirs", SPE Journal, 2009 In 2016, Vol. 14, No. 3, a multi-scale fracture modeling method was proposed, which combined core, logging and seismic data to evaluate the fracture intensity of shale oil reservoirs and optimize fracturing process parameters; the paper "A review of hydraulic fracturing monitoring technologies", Journal of Natural Gas Science and Engineering, 2016, Vol. 36, systematically summarized the application of microseismic monitoring, distributed fiber optic sensing and other technologies in real-time tracking of fracture propagation, and analyzed their accuracy and limitations; The existing technologies described above cover classical theories, numerical simulations, experimental methods, and engineering applications for crack strength calculation. From Griffith's energy balance theory to modern machine learning and real-time monitoring technologies, research has continuously deepened our understanding of crack formation and propagation mechanisms. However, none of these technologies have clearly defined the calculation of crack strength or the evaluation of crack development. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for evaluating the degree of crack development using crack strength, which can quantitatively evaluate the degree of crack development, thereby solving the problem that the existing technology has a large number of crack evaluation parameters and cannot quantitatively evaluate the degree of crack development.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: The present invention provides a method for quantitatively evaluating the degree of fracture development using fracture intensity as a single parameter, comprising the following steps: S1. Obtaining an imaging logging report of the target work area; S2. Obtaining fracture attribute parameters based on the imaging logging report, wherein the fracture attribute parameters include at least fracture density, fracture orientation, fracture effectiveness, and fracture length; S3. Calculating a fracture intensity index and generating a fracture intensity map based on the fracture attribute parameters obtained in step S2; S4. Dividing the fracture intensity in different directions on the fracture intensity map obtained in step S3 according to different fracture orientations and dip angles, and evaluating the fracture development intensity in different orientations of the target work area.

[0008] Optionally, in the above method for evaluating the degree of crack development using crack strength, in step S2, crack attribute parameters are obtained based on the statistical analysis results of Petrel, GeoFrame, or Techlog software to provide crack quantitative parameter calculation curves and tadpole diagrams.

[0009] Optionally, in the above method for evaluating the degree of fracture development using fracture intensity, the quantitative parameters of fracture include: fracture density: the total number of fractures seen per meter of well section; fracture length: the sum of fracture lengths seen per square meter of well wall; average fracture width: the average value of fracture trajectory width; fracture hydrodynamic width: the cube root of the sum of the cubes of fracture trajectory widths; fracture porosity: the ratio of the area occupied by fractures on the well wall per meter of well section to the area of ​​the well wall covered by imaging logging.

[0010] Optionally, in the above method for evaluating the degree of crack development using crack strength, in step S3, the crack strength index is calculated using the weighted composite index method, and the calculation formula is as follows:

[0011] in, The weighting coefficient is based on the crack density. It is 1.0 when the crack density is >5 cracks / meter, and the weight decreases by 0.3 for each crack density decrease. The weighting coefficients are assigned based on the fracture orientation: 1.0 for high-angle fractures, 0.7 for oblique fractures, and 0.3 for horizontal fractures. The weighting coefficients are assigned based on the effectiveness of the cracks: 1.0 for unfilled cracks, 0.5 for partially filled cracks, and 0.2 for filled cracks. The weighting coefficient is based on the crack length. It is 1.0 when the crack length is > 1m, and the weight decreases by 0.3 for each order of magnitude decrease.

[0012] Optionally, in the above method for evaluating the degree of crack development using crack strength, in step S3, the crack strength index is calculated using a formula:

[0013] In the formula, I d N represents the crack strength at depth d. d+w / 2 and N d-w / 2 These represent the cumulative number of cracks at depths d+w / 2 and dw / 2, respectively; w is the length of the statistical window.

[0014] Optionally, in the above method for evaluating the degree of crack development using crack strength, in step S3, the statistical window length is 20m.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention relates to a method for calculating and applying a fracture strength index based on fracture attribute data provided by imaging logging. The fracture strength index is used to evaluate the degree of fracture development. Fracture strength is a multi-dimensional comprehensive index integrating fracture density, occurrence, effectiveness, and length, more closely reflecting the actual permeability of the reservoir. Based on obtaining indicators such as fracture density, occurrence, effectiveness, and length, this invention uses a weighted comprehensive index method and formula calculation method to calculate the fracture strength index; it generates fracture strength curves in different directions, enabling quantitative evaluation of the degree of fracture development. This provides exploration and development technicians with a scientific fracture strength technique, providing a basis for judging the degree of fracture development and reservoir space type. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0017] Figure 1 This is a flowchart illustrating the method for evaluating the degree of crack development using crack strength according to the present invention. Figure 2 This is a schematic diagram illustrating the quantitative calculation of crack parameters; Figure 3 The image logging curve of the network fracture development in the Jidong NP280 well is shown. Figure 4 This is a fracture strength evaluation diagram of the Jidong NP21-X2460 well; Figure 5 This is a fracture strength evaluation diagram of the Jidong NP283 well; Figure 6 This is a fracture strength evaluation diagram of the Jidong NP2-82 well; Figure 7 This is a fracture strength evaluation diagram of the Jidong NP288 well; Figure 8 This is a fracture strength evaluation diagram of the Jidong NP280 well. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0019] The present invention provides a method for evaluating fracture development using fracture intensity, comprising the following steps: S1. Obtaining imaging logging results reports for the target work area; S2. Obtaining fracture attribute parameters based on the imaging logging results reports, including at least fracture density, fracture orientation, fracture effectiveness, and fracture length; S3. Calculating a fracture intensity index and generating a fracture intensity map based on the fracture attribute parameters obtained in step S2; S4. Dividing the fracture intensity in different directions on the fracture intensity map obtained in step S3 according to different fracture orientations and dip angles, and evaluating the fracture development intensity in different orientations of the target work area. This invention utilizes imaging logging results curve data and employs a weighted composite index method or formula calculation method to calculate the fracture intensity index. Using the calculated fracture intensity index for each segment, fracture intensity curves in different directions are generated, achieving a quantitative evaluation of fracture development.

[0020] like Figure 1 As shown, the method for evaluating the degree of crack development using crack strength according to the present invention includes the following steps: S1: Obtain the imaging logging (FMI) results report for the target work area; S2: Obtain fracture attribute parameters based on the imaging logging results report, including fracture density, orientation, effectiveness, fracture length, etc., typically obtained through statistical analysis using software such as Petrel, GeoFrame, and Techlog. Taking Schlumberger's GeoFrame software as an example, it mainly provides the following five quantitative fracture parameter calculation curves and tadpole plots, illustrated in the diagram below. Figure 2 Among them, the five quantitative parameters of cracks include: (1) Fracture density (FVDC): The total number of fractures seen per meter of well section; (2) Fracture Length (FVTL): The sum of fracture lengths seen per square meter of well wall; (3) Average crack width (FVA): The average width of the crack trajectory; (4) Fracture hydrodynamic width (FVAH): the cube root of the sum of the cubes of the fracture trajectory widths; (5) Fracture porosity (FVPA): The ratio of the area occupied by fractures on the well wall per meter of well section to the area of ​​the well wall covered by FMI imaging logging.

[0021] The tadpole diagram is used to quantitatively calculate the orientation or strike of effective natural fractures. The horizontal axis (or head) of the tadpole diagram usually represents the dip angle, while the direction of the line segment at the tail represents the fracture strike.

[0022] S3. Based on the crack attribute parameters obtained in step S2, calculate the crack strength index and generate crack strength maps in different directions.

[0023] In this step, preferably, the crack strength index is calculated using a weighted composite index method or a formula calculation method.

[0024] The crack strength index is calculated using the weighted composite index method, and the formula is as follows:

[0025] The weighting coefficients for each parameter are given, but not limited to, the following methods: The weighting coefficient is based on the crack density (1.0 when the crack density is >5 cracks / meter, and the weight decreases by 0.3 for each crack density decrease). The weighting coefficients are assigned based on the fracture orientation (1.0 for high-angle fractures, 0.7 for oblique fractures, and 0.3 for horizontal fractures). The weighting coefficients are assigned based on the effectiveness of the cracks (1.0 for unfilled cracks, 0.5 for semi-filled cracks, and 0.2 for filled cracks). The weighting coefficient is based on the crack length (1.0 when the crack length is > 1m, and the weight decreases by 0.3 for each order of magnitude decrease).

[0026] The crack strength index is calculated using a formula:

[0027] In the formula, I d N represents the crack strength value at depth d (i.e., the crack strength index); d+w / 2 and N d-w / 2 These represent the cumulative number of cracks at depths d+w / 2 and dw / 2, respectively; w is the length of the statistical window, preferably 20m.

[0028] S4. Based on the different crack orientations and dip angles, the crack intensity in different directions is divided on the crack intensity map obtained in step S3, and the crack development intensity in different orientations of the work area is evaluated.

[0029] This invention utilizes imaging logging data and, based on various fracture attribute data provided by imaging logging, calculates the fracture strength index using a weighted composite index method or a formula calculation method. Fracture strength is a multi-dimensional comprehensive index integrating fracture density, occurrence, effectiveness, and length, more closely reflecting the actual seepage capacity of the reservoir. Specifically, the calculated fracture strength index for each segment generates fracture strength curves in different directions, enabling a quantitative evaluation of fracture development. This provides exploration and development technicians with a scientific method for calculating fracture strength and a basis for determining reservoir space types.

[0030] Drilling in a buried hill in eastern Hebei Province has revealed that favorable reservoirs are mainly distributed within approximately 70-100 meters of the top of the buried hill, with well-developed fractures. Weathering-dissolution fractures and tectonic fractures combine to form a network of fractures, and the pores and fractures are well connected. However, the degree of reservoir development is uneven due to factors such as the lithology of the buried hill strata, its structural location, and the overlying strata. Figure 3 The imaging logging of the Jidong NP280 well shows that the reticular fractures are well-developed and the number of tadpoles is relatively large in the 3852.5-3856m and 3889-3892m sections.

[0031] Fracture density, occurrence, effectiveness, and length were obtained from imaging logging data (i.e., imaging logging (FMI) results reports). Fracture strength curves for four groups of fractures in wells NP280, NP283, NP288, NP21-X2460, and NP2-82 in this buried hill reservoir were calculated using a formula-based method. The calculation results are as follows: Figures 4-8 As shown in the figure, strength groups 0, 1, 2, and 3 represent the fracture strength curve values ​​of the four fracture groups. Specifically, the fracture strength curve values ​​for fracture group 0 in well NP283 range from 0 to 3.79, for group 1 from 0 to 4.23, for group 2 from 0 to 1.15, and for group 3 from 0 to 0.49. The main development depths of fractures in groups 0 and 1 are 3855–3875 m and 3925–3930 m, respectively; the most developed depths of fractures in groups 2 and 3 are 3870–3875 m (see...). Figure 5 The fracture strength curves of the four fracture groups in well NP21-X2460 range from 0 to 2.25, 0 to 2.47, 0 to 0.71, and 0 to 0.27, respectively. The depths of the most developed sections of the four fracture groups are similar, mainly between 3835 and 3843 m (see...). Figure 4 The fracture strength curve values ​​of the four fracture groups in well NP2-82 range from 0.6 to 5.77, 0.08 to 6.43, 0 to 1.59, and 0 to 1.15, respectively (see...). Figure 6 The fracture strength curve values ​​of the four fracture groups in well NP288 are distributed as follows: 0–1.15, 0–1.37, 0–0.27, and 0–0.27, respectively (see...). Figure 7 The distribution of fracture strength curve values ​​shows that the most developed fracture depth is in the 3850-3950m section. The fracture strength curve values ​​of the four groups in well NP280 are: 0~1.1, 0~1.32, 0~0.22, and 0~0.22 respectively (see...). Figure 8 ).

[0032] The above embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and are not intended to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or improve the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in the present invention; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for evaluating the degree of crack development using crack strength, characterized in that, Includes the following steps: S1. Obtain the imaging logging results report for the target work area; S2. Obtain fracture attribute parameters based on the imaging logging results report. The fracture attribute parameters include at least fracture density, fracture orientation, fracture effectiveness, and fracture length. S3. Based on the crack attribute parameters obtained in step S2, calculate the crack strength index and generate a crack strength map; S4. Based on the different crack orientations and dip angles, the crack intensity in different directions is divided on the crack intensity map obtained in step S3, and the crack development intensity in different orientations of the target work area is evaluated.

2. In the method for evaluating the degree of crack development using crack strength according to claim 1, in step S2, the crack attribute parameters are obtained based on the statistical analysis results of Petrel, GeoFrame or Techlog software to provide a crack quantitative parameter calculation curve and tadpole diagram.

3. The method for evaluating the degree of crack development using crack strength according to claim 2, wherein, The quantitative parameters of the crack include: Fracture density: The total number of fractures observed per meter of well section; Crack length: The sum of crack lengths visible per square meter of well wall; Average crack width: The average width of the crack trajectory; Crack hydrodynamic width: the cube root of the sum of the cubes of the crack trajectory widths; Fracture porosity: The ratio of the area occupied by fractures on the well wall per meter of well section to the area of ​​the well wall covered by imaging logging.

4. The method for evaluating crack development degree using crack strength according to claim 1, in step S3, the crack strength index is calculated using the weighted composite index method, and the calculation formula is: in, The weighting coefficient is based on the crack density. It is 1.0 when the crack density is >5 cracks / meter, and the weight decreases by 0.3 for each crack density decrease. The weighting coefficients are assigned based on the fracture orientation: 1.0 for high-angle fractures, 0.7 for oblique fractures, and 0.3 for horizontal fractures. The weighting coefficients are assigned based on the effectiveness of the cracks: 1.0 for unfilled cracks, 0.5 for partially filled cracks, and 0.2 for filled cracks. The weighting coefficient is based on the crack length. It is 1.0 when the crack length is > 1m, and the weight decreases by 0.3 for each order of magnitude decrease.

5. The method for evaluating the degree of crack development using crack strength according to claim 1, in step S3, the crack strength index is calculated using a formula calculation method, the formula being: In the formula, I d N represents the crack strength at depth d. d+w / 2 and N d-w / 2 These represent the cumulative number of cracks at depths d+w / 2 and dw / 2, respectively; w is the length of the statistical window.

6. In the method for evaluating the degree of crack development using crack strength according to claim 1, in step S3, the length of the statistical window is 20m.

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