Method for evaluating fracture development degree by utilizing fracture strength

Abstract

The invention provides a method for evaluating fracture development degree by using fracture strength. The method comprises the following steps: S1, acquiring an imaging logging result report of a target work area; s2, acquiring fracture attribute parameters according to the imaging logging result report, wherein the fracture attribute parameters at least comprise fracture density, fracture occurrence, fracture effectiveness and fracture length; s3, calculating a crack strength index and generating a crack strength graph based on the crack attribute parameters obtained in the step S2; and S4, dividing crack strength in different directions on the crack strength graph obtained in the step S3 according to different crack orientations and inclination angles, and evaluating the crack development strength in different orientations of the target work area. The crack development degree can be quantitatively evaluated, so that the problem that quantitative evaluation of the crack development degree is tedious in operation due to more information in the prior art is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field exploration and development, in particular to a method for evaluating fracture development degree by using fracture intensity. BACKGROUND

[0002] The reservoir characteristics of gas storage are the main factors affecting the safe operation of gas storage and gas storage capacity, and especially the evaluation and understanding of the development degree of natural fractures play a crucial role in the judgment of the type of storage space.

[0003] At present, the most direct and effective means for single well fracture evaluation is core observation and imaging logging, and the imaging logging can describe the fractures, including fracture development well section, fracture occurrence, density, morphological characteristics, filling degree and the like, and since more information is given, the operation is cumbersome in the quantitative evaluation of fracture development degree.

[0004] In terms of fracture intensity calculation, for example, the patent "Fracture intensity prediction method based on data body dimension reduction and discrete coefficient calculation", with publication number CN111399049A, superimposes the gather data according to the azimuth angle range and calculates the offset attribute to obtain the attribute data body, then performs dimension reduction processing, and finally calculates the discrete coefficient based on the reduced data body to obtain the fracture intensity data body, thereby improving the fracture prediction accuracy. The patent "Method for calculating fracture intensity in favorable area of target layer", with publication number CN111506861B, uses waveform classification, establishment of fracture samples, correlation coefficient analysis, and data reconstruction to accurately divide different fracture intensities within the favorable seismic facies. By classifying the waveforms of the three-dimensional post-stack seismic data, the favorable seismic facies area is determined, the reflection waveforms of the fracture samples in the target layer are established, and the correlation coefficient calculation is performed with the reflection waveforms of each grid point in the same seismic facies. Then, the correlation coefficient value and the fracture density value of the fracture samples are used for data reconstruction calculation to obtain the fracture density contour or color plane, which is used for analyzing different fracture intensities. The patent "Coal reservoir fracture prediction model construction method based on multi-source data body fusion", with publication number CN119270382A, comprehensively uses core data, conventional logging, imaging logging, CT scanning, and seismic prediction fracture data, and uses mathematical methods for analysis and fusion to construct a coal reservoir fracture prediction model. In calculating the fracture intensity, the coal sample is obtained, the number of fractures, inclination, length, filling degree, and properties of the coal sample end face are recorded, the artificial core fracture intensity is calculated, and the imaging logging data are used to generate the fracture surface intensity. The non-overlapping parts of the two are given a higher fracture intensity value to generate the coal sample fracture intensity curve. The patent "Fracture quantitative prediction method and device based on post-stack seismic data", with publication number CN113534247B, quantitatively predicts the fracture from the seismic perspective by processing and analyzing the post-stack seismic data, extracting relevant attributes, establishing a fracture prediction model, and realizing quantitative prediction of fracture intensity and other parameters. The patent "Method for fine characterization of fracture and cave attribute parameters in acid fracturing numerical simulation", with publication number CN114510808B, comprehensively uses logging data, core data, drilling emptying data, and seismic data to establish a natural fracture distribution geological model and a cave distribution geological model in the geological modeling software, and an initial fracture-cave joint distribution geological model. By obtaining the reservoir rock sample and the rock mechanics parameters obtained from laboratory experiments, the compressive strength and elastic modulus mechanics parameters of the rocks in different regions of the geological model are differentiated, thereby providing fine fracture and cave attribute parameter characterization for acid fracturing numerical simulation. The patent involves calculation and application of fracture intensity related parameters.

[0005] For example, the document “The phenomena of rupture and flow in solids”, Philosophical Transactions of the Royal Society of London. Series A, 1921, Vol. 221, No. 582-593, proposes an energy balance theory that the crack propagation needs to satisfy the condition that the decrease in elastic energy storage is greater than or equal to the increase in new surface energy, laying the theoretical foundation for crack propagation in brittle materials; the document “Analysis of stresses and strains near the end of a crack traversing a plate”, Journal of Applied Mechanics, 1957, Vol. 24, No. 3, introduces the stress intensity factor (K) and proposes to use the critical value of K as the criterion for crack unstable propagation, forming the core framework of linear elastic fracture mechanics; the document “Numerical calculation of three-dimensional crack stress intensity factor”, Rock and Soil Mechanics and Engineering, 2006, Vol. 25, Supplement 2, uses the meshless Galerkin method to calculate the stress intensity factor at the front of a three-dimensional crack, and processes the isolation effect of the crack surface through the visual criterion, the results are in good agreement with the traditional method; the document “Framework construction of intelligent decision support system for coal seam floor water hazard prevention”, Coal Geology and Prospecting, 2021, Vol. 49, No. 1, constructs an integrated framework of “data-model-scheme”, realizes intelligent decision-making of coal seam floor water hazard through floor water inrush spatial point prediction model and grouting reconstruction engineering reliability analysis model; the document “ Fracture Intensity - Schafer's Method ”, SPE Western Regional Meeting, 1980, proposes Schafer's crack intensity index (SFI) to predict the initial production of oil wells combined with formation dip logging data, the formula is where a, b, c are crack length parameters, and d is the wellbore ellipticity; the literature "Collapse mechanisms and fragility curves based on Lumped Damage Mechanics for RC frames subjected to earthquakes", Engineering Structures, 2024, Vol. 299, proposes a lumped damage mechanics (LDM) framework to construct seismic fragility curves for reinforced concrete frames, combining incremental dynamic analysis (IDA) to quantify the effect of crack propagation on structural collapse; the literature "Crack tip positioning and stress intensity factor calculation method based on digital image correlation displacement field", CSDN blog (technical review), 2025 network publication, reviews the application of digital image correlation (DIC) technology in crack tip positioning and stress intensity factor (SIF) calculation, and compares the advantages and disadvantages of displacement gradient method, J integral method and other methods; the literature "Quantitative fracture characterization in unconventional reservoirs", SPE Journal, 2009 Vol.14, No.3, proposes a multi-scale fracture modeling method to evaluate the fracture strength of shale oil reservoirs combined with core, logging and seismic data, and optimizes the fracturing process parameters; the literature "A review of hydraulic fracturing monitoring technologies", Journal of Natural Gas Science and Engineering, 2016 Vol.36, systematically summarizes the application of microseismic monitoring, distributed optical fiber sensing and other technologies in real-time tracking of crack propagation, and analyzes their precision and limitations; The above prior art covers the classical theory, numerical simulation, experimental method and engineering application of crack strength calculation. From Griffith's energy balance theory to modern machine learning and real-time monitoring technology, the research continues to deepen the understanding of the mechanism of crack formation and propagation. However, none of them explicitly calculate the crack strength and evaluate the crack development degree. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a method for evaluating the crack development degree by using crack strength, which can quantitatively evaluate the crack development degree, so as to solve the problem that the crack evaluation parameters obtained by the prior art are too many and cannot quantitatively evaluate the crack development degree.

[0007] To solve the above technical problems, the technical scheme of the present application is: The method for quantitatively evaluating the fracture development degree by using the fracture intensity as a parameter comprises the following steps: S1, obtaining an imaging logging result report of a target work area; S2, obtaining fracture attribute parameters according to the imaging logging result report, wherein the fracture attribute parameters at least include fracture density, fracture occurrence, 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; and S4, dividing the fracture intensity in different directions on the fracture intensity map obtained in step S3 according to different fracture directions and angles to evaluate the fracture development intensity in different directions of the target work area.

[0008] Optionally, in the method for evaluating the fracture development degree by using the fracture intensity, in step S2, the fracture attribute parameters are obtained according to the statistical analysis results of Petrel, GeoFrame or Techlog software to provide a fracture quantitative parameter calculation curve and a tadpole map.

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

[0010] Optionally, in the method for evaluating the fracture development degree by using the fracture intensity, in step S3, the fracture intensity index is calculated by using a weighted comprehensive index method, and the calculation formula is as follows: wherein, is a weight coefficient based on the fracture density, and when the fracture density is greater than 5, the weight coefficient is 1.0, and the weight coefficient decreases by 0.3 for each decrease of one fracture; is a weight coefficient based on the fracture occurrence, and when the fracture occurrence is a high-angle fracture, the weight coefficient is 1.0, when the fracture occurrence is a cross fracture, the weight coefficient is 0.7, and when the fracture occurrence is a horizontal fracture, the weight coefficient is 0.3; is a weight coefficient based on the fracture effectiveness, and when the fracture effectiveness is an unfilled fracture, the weight coefficient is 1.0, when the fracture effectiveness is a semi-filled fracture, the weight coefficient is 0.5, and when the fracture effectiveness is a filled fracture, the weight coefficient is 0.2; is a weight coefficient based on the fracture length, and when the fracture length is greater than 1 m, the weight coefficient is 1.0, and the weight coefficient decreases by 0.3 for each decrease of one order of magnitude.

[0011] Optionally, in the method for evaluating the fracture development degree by using the fracture intensity, in step S3, the fracture intensity index is calculated by using a formula calculation method, and the formula is as follows: In the formula, I d is the fracture intensity value at depth d; N d+w / 2 and N d-w / 2 are the fracture cumulative numbers at depths d+w / 2 and d-w / 2, respectively; and w is the length of the statistical window.

[0012] Optionally, in the method for evaluating the fracture development degree by using the fracture intensity described above, the length of the statistical window in step S3 is 20 m.

[0013] Compared with the prior art, the method has the following beneficial effects: The method is based on the fracture property data provided by the imaging logging, and calculates the fracture intensity index and the method of application. The fracture development degree is evaluated by using the fracture intensity index. The fracture intensity is a multi-dimensional comprehensive index that integrates the fracture density, occurrence, effectiveness and length, and is closer to the actual seepage capacity of the reservoir. Based on the indexes of the fracture density, occurrence, effectiveness and length, the fracture intensity index is calculated by using the weighted comprehensive index method and the formula calculation method. The fracture intensity curve graphs in different directions are generated, the quantitative evaluation of the fracture development degree can be realized, a scientific fracture intensity technical means is provided for the exploration and development technical personnel, and the basis is provided for the judgment of the fracture development degree and the reservoir space type. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the specific embodiments or the prior art description will be briefly introduced.

[0015] Figure 1 is a flowchart of the method for evaluating the fracture development degree by using the fracture intensity of the present application; Figure 2 is a schematic diagram of the quantitative calculation of the fracture parameters; Figure 3 shows the netted fracture development curve graph of the imaging logging of Jidong NP280 well; Figure 4 is the fracture intensity evaluation graph of Jidong NP21-X2460 well; Figure 5 is the fracture intensity evaluation graph of Jidong NP283 well; Figure 6 is the fracture intensity evaluation graph of Jidong NP2-82 well; Figure 7 is the fracture intensity evaluation graph of Jidong NP288 well; Figure 8 is the fracture intensity evaluation graph of Jidong NP280 well. DETAILED DESCRIPTION

[0016] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application.

[0017] The method for evaluating the fracture development degree by using the fracture intensity of the present application comprises the following steps: S1. obtaining the imaging logging result report of a target work area; S2. obtaining the fracture attribute parameters according to the imaging logging result report, the fracture attribute parameters at least including the fracture density, fracture occurrence, fracture effectiveness and fracture length; S3. calculating the fracture intensity index and generating the fracture intensity map based on the fracture attribute parameters obtained in step S2; and 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 to evaluate the fracture development intensity in different orientations of the target work area. The fracture intensity index is calculated by using the imaging logging result curve data and by using the weighted comprehensive index method or the formula calculation method, and the fracture intensity curve map in different directions is generated by using the calculated fracture intensity index of each section, so that the fracture development degree is quantitatively evaluated.

[0018] As shown in Figure 1 The method for evaluating the fracture development degree by using the fracture intensity of the present application comprises the following steps: S1: obtaining the imaging logging (FMI) result report of a target work area; S2: obtaining the fracture attribute parameters according to the imaging logging result report, including the fracture density, occurrence, effectiveness, fracture length and other indexes, which are usually obtained according to the statistical analysis results of Petrel, GeoFrame, Techlog and other software. Taking the GeoFrame software of Schlumberger Company as an example, the following five kinds of fracture quantitative parameter calculation curves and tadpole maps are mainly provided, and the schematic diagram is shown in Figure 2 Among the five fracture quantitative parameters, the following are included: (1) Fracture density (FVDC): the total number of fractures seen per meter of well section; (2) Fracture length (FVTL): the sum of the lengths of fractures seen per square meter of well wall; (3) Fracture average width (FVA): the average value of the fracture trace width; (4) Fracture hydrodynamic width (FVAH): the sum of the cube of the fracture trace width; (5) Fracture porosity (FVPA): the ratio of the area occupied by the fracture on the well wall per meter of well section to the area of the FMI imaging logging covering the well wall.

[0019] The effective natural fracture occurrence or strike is quantitatively calculated on the tadpole map. The “head” abscissa (or horizontal axis) of the tadpole map usually represents the dip angle, and the direction of the “tail” line segment of the tadpole map represents the fracture strike.

[0020] S3. Calculate fracture intensity index and generate fracture intensity map of different directions based on the fracture attribute parameters obtained in step S2.

[0021] In this step, preferably, the fracture intensity index is calculated by using the weighted comprehensive index method or formula calculation method.

[0022] The fracture intensity index is calculated by using the weighted comprehensive index method, and the formula is: The weight coefficients of each parameter are given but not limited to the following methods: The weight coefficient based on fracture density (1.0 when the fracture density is greater than 5 per meter, and the weight decreases by 0.3 for each decrease of one); The weight coefficient based on fracture occurrence (1.0 for high-angle fractures, 0.7 for oblique fractures, and 0.3 for horizontal fractures); The weight coefficient based on fracture effectiveness (1.0 for unfilled fractures, 0.5 for half-filled fractures, and 0.2 for filled fractures); The weight coefficient based on fracture length (1.0 when the fracture length is greater than 1 m, and the weight decreases by 0.3 for each decrease of one order of magnitude).

[0023] The fracture intensity index is calculated by using the formula calculation method, and the formula is: In the formula, I d is the fracture intensity value (i.e., the fracture intensity index) at depth d; N d+w / 2 and N d-w / 2 are the cumulative number of fractures at depths d+w / 2 and d-w / 2, respectively; and w is the statistical window length, which is preferably 20 m.

[0024] S4. Divide the fracture intensity of different directions on the fracture intensity map obtained in step S3 according to different fracture orientations and dip angles, and evaluate the fracture development intensity of different directions in the work area.

[0025] The method of the present application uses the imaging logging result curve data, and calculates the fracture intensity index based on the fracture attribute data provided by the imaging logging by using the weighted comprehensive index method or formula calculation method. The fracture intensity is a multi-dimensional comprehensive index that integrates fracture density, occurrence, effectiveness, and length, and is closer to the actual seepage capacity of the reservoir. Specifically, the fracture intensity index of each section is calculated, and a fracture intensity curve map of different directions is generated, thereby realizing quantitative evaluation of the fracture development degree and providing a scientific fracture intensity calculation method for exploration and development technical personnel and a basis for judging the type of reservoir space.

[0026] The drilled well in the buried hill of Jidong shows that the favorable reservoirs are mainly distributed in the top of the buried hill within 70m-100m, the fractures are developed, and the weathering-dissolution fractures and structural fractures form a network fracture, and the pore and fracture are well connected. However, the development degree of the reservoir is uneven due to the influence of the lithology of the buried hill, the structural position, the overlying strata and other factors. Figure 3 The imaging logging of 3852.5-3856m and 3889-3892m sections of NP280 well in Jidong shows that the network fractures are developed, and the tadpoles are more.

[0027] According to the imaging logging data (i.e. the imaging logging (FMI) result report), the fracture density, occurrence, effectiveness, length and other indexes are obtained. According to the formula calculation method, the fracture intensity curves of four groups of fractures in NP280 well, NP283 well, NP288 well, NP21-X2460 well and NP2-82 well in the buried hill reservoir are calculated, and the calculation results are shown in Figures 4-8 . The intensity 0 group, the intensity grade 1 group, the intensity grade 2 group and the intensity grade 3 group respectively represent the fracture intensity curve values of the four groups of divided fractures. The fracture intensity curve values of fracture 0 group of NP283 well are 0-3.79, the fracture intensity curve values of fracture 1 group are 0-4.23, the fracture intensity curve values of fracture 2 group are 0-1.15, and the fracture intensity curve values of fracture 3 group are 0-0.49; the main development depth sections of fracture 0 group and fracture 1 group are 3855-3875m and 3925-3930m; the most developed depth sections of fracture 2 group and fracture 3 group are 3870-3875m (see Figure 5 ). The fracture intensity curve value distribution ranges of four groups of fractures of NP21-X2460 well are 0-2.25, 0-2.47, 0-0.71 and 0-0.27 respectively, and the most developed sections of the four groups of fractures are similar, mainly in 3835-3843m (see Figure 4 ). The fracture intensity curve value distribution ranges of four groups of fractures of NP2-82 well are 0.6-5.77, 0.08-6.43, 0-1.59 and 0-1.15 respectively (see Figure 6 ). The fracture intensity curve value distribution ranges of four groups of fractures of NP288 well are 0-1.15, 0-1.37, 0-0.27 and 0-0.27 respectively (see Figure 7 ), and it can be seen from the distribution of the fracture intensity curve values that the most developed depth section is in the 3850-3950m section. The fracture intensity curve value ranges of four groups of fractures of NP280 well are 0-1.1, 0-1.32, 0-0.22 and 0-0.22 respectively (see Figure 8 ).

[0028] The above examples are only specific embodiments of the present application, used to illustrate the technical solutions of the present application, but not limit the present application, the protection scope of the present application is not limited to this, although the present application is described in detail with reference to the foregoing examples, those skilled in the art should understand that any person skilled in the art within the technical range disclosed by the present application, still can modify or improve the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, all should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for evaluating the degree of fracture development using fracture intensity, characterized by, The method comprises the following steps: S1. Obtain an imaging logging result report of a target work area; S2. Obtain fracture attribute parameters from the imaging logging result report, the fracture attribute parameters including at least fracture density, fracture occurrence, fracture effectiveness, and fracture length; S3. Calculate a fracture intensity index and generate a fracture intensity map based on the fracture attribute parameters obtained in step S2; S4. Divide fracture intensity in different directions on the fracture intensity map obtained in step S3 according to different fracture orientations and dip angles, and evaluate fracture development intensity in different orientations of the target work area.

2. The method for evaluating fracture development degree by using fracture intensity according to claim 1, wherein in step S2, the fracture attribute parameters are obtained according to statistical analysis results of Petrel, GeoFrame or Techlog software to provide fracture quantitative parameter calculation curves and tadpole maps.

3. The method for evaluating the degree of fracture development using fracture intensity according to claim 2, wherein, The fracture quantitative parameters include: Fracture density: total number of fractures observed per meter of well section; Fracture length: sum of fracture lengths observed per square meter of well wall; Fracture average width: average value of fracture track width; Fracture hydrodynamic width: cube root of the sum of cube of fracture track width; Fracture porosity: ratio of area occupied by fractures on well wall per meter of well section to area covered by imaging logging on well wall.

4. The method for evaluating fracture development degree by using fracture intensity according to claim 1, wherein in step S3, the fracture intensity index is calculated by using a weighted comprehensive index method, and the calculation formula is: wherein The weight coefficient based on the crack density is 1.0 when the crack density is greater than 5 cracks per meter, and the weight decreases by 0.3 for each crack reduction. The weight coefficient based on the fracture occurrence is 1.0 for high-angle fractures, 0.7 for diagonal fractures, and 0.3 for horizontal fractures. For the weight factor assigned based on fracture effectiveness, the un-filled fracture is 1.0, the half-filled fracture is 0.5, and the filled fracture is 0.2; The weight coefficient based on the crack length is 1.0 when the crack length is > 1 m, and the weight decreases by 0.3 for each order of magnitude.

5. The method for evaluating fracture development degree by using fracture intensity according to claim 1, wherein in step S3, the fracture intensity index is calculated by using a formula calculation method, and the formula is: In the formula, I d is the crack intensity value at depth d; N d+w / 2 and N d-w / 2 are the crack cumulative numbers at depths d+w / 2 and d-w / 2, respectively; w is the statistical window length.

6. The method for evaluating fracture development degree by using fracture intensity according to claim 1, wherein in step S3, the statistical window length is 20 m.

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