A method for identifying tectonic fractures in weathered volcanic rocks

Abstract

The present application relates to the technical field of digital image processing of geological structure, and particularly relates to a method for identifying volcanic tectonic fractures after weathering modification. The method of the present application comprehensively uses drilling, imaging logging, core and sidewall core data, combines with chart drawing and stereographic projection functions, realizes identification and statistics of volcanic tectonic fractures after weathering modification, and significantly improves the identification accuracy of volcanic tectonic fractures.

Description

Technical Field

[0001] This invention relates to the field of digital image processing technology for geological structures, and in particular to a method for identifying cracks in volcanic rock structures after weathering. Background Technology

[0002] With the continuous improvement of global oil and gas exploration, volcanic rocks have become an important area of ​​exploration, possessing enormous potential. Compared with sedimentary rocks, volcanic rocks are characterized by their density, brittleness, and low primary porosity. Tectonic fractures play a crucial role in improving the porosity and permeability of volcanic rocks. On the one hand, tectonic fractures can serve as favorable reservoir spaces in volcanic rocks, connecting previously isolated primary and secondary pores, thereby improving reservoir connectivity. On the other hand, they can also act as channels for later fluid migration, where fluids can dissolve the surrounding rocks, forming more favorable volcanic reservoirs. However, other types of fractures, such as primary fractures and weathering fractures, also develop in volcanic rocks. Weathering alters and disrupts the orientation and spatial morphology of tectonic fractures, making accurate identification of tectonic fractures a major challenge that urgently needs to be overcome.

[0003] Previous studies have primarily employed direct or indirect identification methods to investigate structural fractures in volcanic rocks. Direct identification methods typically utilize core samples and thin sections under a microscope to identify structural fractures; this method offers high accuracy but is challenging to obtain. In contrast, indirect identification methods usually utilize well logging curves and seismic reflection data to identify structural fractures in volcanic rocks; data acquisition is easier, but this method has lower reliability. Summary of the Invention

[0004] To address the above problems, this invention provides a method for identifying structural cracks in volcanic rocks after weathering, comprising the following steps:

[0005] S1 filters the depth, dip, dip angle, width, and type data of high-conductivity and high-resistance fractures from volcanic rock imaging logging data. Based on the dip, the fracture direction is obtained. Then, the scatter plot function of Excel software is used to draw scatter plots of fracture depth-fracture dip angle and width, and scatter plots of fracture depth-fracture direction.

[0006] S2 aligns the single-well columnar section with the scatter plot obtained in step 1 at depth. Based on the fracture width, dip angle, and orientation, combined with the logging curve characteristics of the single-well columnar section, and combined with the characteristics of the weathering zone and inner zone of volcanic rock, the weathering zone and inner zone of volcanic rock are identified.

[0007] S3. Import the crack data of the depth segment corresponding to the inner band identified in step S2 into the Stereonet software to draw the inner band crack pole diagram and the inner band crack density diagram.

[0008] S4 In the internal zone fracture pole diagram and isodense diagram drawn in step 3, the direction of the denser fractures is identified as its dominant development direction. These fractures are called dominant fractures. Then, the number, dip, dip angle and width of fractures in different dominant directions are statistically analyzed, and the minimum, maximum and average values ​​of the dip, dip angle and width of fractures in different dominant directions are obtained.

[0009] S5 Based on the statistical results of the dominant cracks in the inner zone, the minimum and maximum values ​​of the dip and dip angle of the dominant cracks obtained in step 4 are used as standards to determine whether the dip and dip angle of the cracks in the weathering zone meet the standards of dominant cracks, and finally the dominant cracks in the weathering zone are selected.

[0010] S6 Based on the dominant fracture data obtained in steps S4 and S5, use Stereonet software to draw the dominant fracture pole diagram and dominant fracture isodensity diagram.

[0011] S7 In the pole plot and isodense plot drawn in step 6, the direction of denser cracks is identified as its dominant development direction. These cracks are called dominant cracks. Then, the number, dip, dip angle and width of cracks in different dominant directions are statistically analyzed. The minimum, maximum and average values ​​of the dip, dip angle and width of cracks in different dominant directions are calculated to finally reveal the structural crack development characteristics of volcanic rocks after weathering.

[0012] Based on the above scheme, the crack direction was determined using Excel software, with the formula: direction = IF(tendency>90,if(tendency>270,tendency-270,tendency-90),tendency+90).

[0013] Based on the above scheme, the specific method of step S3 is as follows: Copy the crack data of the depth segment corresponding to the inner band identified in step S2 into the txt software, then use the Import File function of the Stereonet software to import the cracks of the inner band into the Stereonet software, and then use the Poles function in the Calculations menu to draw the pole diagram of the cracks of the inner band. Each pole on the diagram represents the projection of the normal of each crack surface onto the Schottky grid; then use the Contour function in the Plot menu to generate the density diagram of the cracks of the inner band.

[0014] Based on the above scheme, when generating dense maps of the inner bands with cracks, the Inspector function in the View menu is used. An appropriate size is set in the Spacing parameter of the Contours option to highlight the density of cracks in the inner bands.

[0015] Based on the above scheme, the Spacing parameter is set as follows: by default, Interval is 2 and Significance level is 3. If there are few cracks, lower Interval to make the contour lines denser and lower Significance level to make the lines more precise. If there are many cracks, increase Interval and Significance level to make the contour lines sparser and the lines smoother.

[0016] Based on the above scheme, the specific method of step S6 is as follows: import the dominant cracks selected in steps 4 and 5 into the Stereonet software, use the Poles function in the Calculations menu to draw the dominant crack pole plot, and then use the Contour function in the Plot menu to generate the dominant crack density plot.

[0017] This invention uses an indirect method, which, based on previous research methods, identifies structural cracks and reduces the impact of weathering on the research results.

[0018] The method of this invention comprehensively utilizes drilling, imaging logging, core and wall core data, combined with chart plotting and stereographic projection functions, to achieve the identification and statistical analysis of structural cracks in weathered volcanic rocks, significantly improving the identification accuracy of structural cracks in volcanic rocks.

[0019] The method of this invention overcomes the shortcomings of existing direct methods, such as the need to identify fractures one by one in imaging logging data and core / wall core data, which takes a lot of time, is limited by the availability of data, and has a high cost of obtaining core and wall core data. At the same time, it overcomes the defects of existing traditional methods, such as the inability of data statistics to avoid the influence of weathering on fractures, and the fact that the rose diagram used only focuses on the strike and ignores the key parameter of dip angle, resulting in incomplete analysis results.

[0020] In the method of this invention, steps S1 and S2 utilize charts, which are simple to operate, effective, and easy to learn, dividing the weathering zone and the inner zone, thus increasing the reliability of the analysis. Steps S3 and S4 utilize projection, combining the orientation of dip and dip angle, resulting in clear and easy-to-understand isohyet maps, which only count the inner zone, reducing interference from non-structural fractures. Based on the above, steps S5 and S6 screen out the structural fractures within the weathering zone, laying the foundation for structural fracture analysis of the entire well section, providing a new research approach for exploring the development of volcanic rock reservoirs, and are of great significance for the exploration and development of volcanic rock oil and gas. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is the scatter plot obtained in step 1 of embodiment 2 of this application;

[0023] Figure 2 This is a corresponding diagram of the scatter plot and single-well columnar plot in step 2 of embodiment 2 of this application;

[0024] Figure 3 This is the internal fracture pole diagram drawn in step 3 of embodiment 2 of this application;

[0025] Figure 4 The inner screen with cracks and other dense patterns obtained in step 3 of embodiment 2 of this application (default parameters);

[0026] Figure 5 This is the internal diagram with cracks and other dense patterns obtained in step 3 of embodiment 2 of this application (with modified parameters);

[0027] Figure 6 This is the dominant crack pole diagram drawn in step 6 of embodiment 2 of this application;

[0028] Figure 7 The dominant crack density map obtained in step 6 of embodiment 2 of this application (default parameters);

[0029] Figure 8 This is the dominant crack density map (with modified parameters) obtained in step 6 of embodiment 2 of this application.

[0030] Figure 9 The images are the imaging logging data and wall core data of the corresponding area in Embodiment 2 of this application. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] This invention provides a method for identifying structural cracks in volcanic rocks after weathering, comprising the following steps:

[0034] S1 filters the depth, dip, dip angle, width, and type data of high-conductivity and high-resistance fractures from volcanic rock imaging logging data. Based on the dip, the fracture direction is calculated as follows: direction = IF(dip>90,if(dip>270,dip-270,dip-90),dip+90). Then, Excel software's scatter plot function is used to draw scatter plots of fracture depth-fracture dip angle and width, and scatter plots of fracture depth-fracture direction.

[0035] S2 aligns the single-well columnar section with the scatter plot obtained in step S1 at depth. Based on the fracture width, dip angle, and strike, combined with the logging curve characteristics of the single-well columnar section and the characteristics of the weathering zone and inner zone of the volcanic rock, the actual fracture data is compared to identify the weathering zone and inner zone of the volcanic rock.

[0036] The weathering crust of volcanic rocks refers to an assemblage of volcanic rocks formed after sedimentary discontinuity, weathering, leaching, and alteration, exhibiting differences in mineral, structural, and reservoir characteristics. It is characterized by weathered clay layers, argillaceous infill in oxidizing environments within faults, and microscopic features such as iron oxide linings in self-fractured fractures and bottom-indicating structures. The weathering crust develops a five-layer structure from top to bottom: soil layer, hydrolysis zone, dissolution zone, disintegration zone, and parent rock. The weathering crust can be viewed as a weathering zone, and the parent rock as an inner layer.

[0037] Weathering zones are typically characterized by high crack width, scattered crack dip angles and orientations, relatively high quartz and clay mineral content curves, and relatively low feldspar and calcite content curves; in contrast, enclosed zones are typically characterized by low crack width, relatively concentrated crack dip angles and orientations, relatively low quartz and clay mineral content curves, and relatively high feldspar and calcite content curves.

[0038] S3. Copy the fracture data of the depth segment corresponding to the inner band identified in step S2 to the txt software. Then, use the Import File function of the Stereonet software to import the inner band fractures into the Stereonet software. Then, use the Poles function in the Calculations menu to draw the inner band fracture pole plot. Each pole on the plot represents the projection of the normal of each fracture surface onto the Schiele net. Then, use the Contour function in the Plot menu to generate an inner band fracture isopleth map. Use the Inspector function in the View menu to set an appropriate size in the Spacing parameter in the Contours option to highlight the density of the inner band fracture orientation. The specific settings are as follows: In the default state, Interval is 2 and Significance level is 3. If there are few fractures, lower the Interval to make the contour lines denser and lower the Significance level to make the lines more precise. If there are many fractures, increase the Interval to make the contour lines sparser and increase the Significance level to make the lines smoother.

[0039] S4 In the internal zone fracture pole diagram and isodense diagram drawn in step S3, the direction of the denser fractures is identified as its dominant development direction (these fractures are called dominant fractures). Then, the number, dip, dip angle and width of fractures in different dominant directions are statistically analyzed, and the minimum, maximum and average values ​​of the dip, dip angle and width of fractures in different dominant directions are calculated.

[0040] Based on the statistical results of the dominant cracks in the inner zone, S5 uses the minimum and maximum values ​​of the dip and dip angle of the dominant cracks obtained in step S4 as standards to determine whether the dip and dip angle of the cracks in the weathering zone meet the standards of dominant cracks, and finally selects the dominant cracks in the weathering zone.

[0041] S6. Import the dominant fractures selected in steps S4 and S5 using the Import File function of the Stereonet software. Then, use the Poles function in the Calculations menu to plot the pole plot of the dominant fractures. Next, use the Contour function in the Plot menu to generate a density plot of the dominant fractures. Use the Inspector function in the View menu to set an appropriate size in the Spacing parameter of the Contours option. Refer to step S3 for parameter settings to highlight the density of the dominant fracture orientation.

[0042] S7 In the pole plot and isodense plot drawn in step S6, the direction of denser cracks is identified as its dominant development direction (these cracks are called dominant cracks). Then, the number, direction, dip angle and width of cracks in different dominant directions are statistically analyzed. The minimum, maximum and average values ​​of the direction, dip angle and width of cracks in different dominant directions are calculated to finally reveal the structural crack development characteristics of volcanic rocks after weathering.

[0043] The method of this invention combines the chart drawing function of Excel software and the stereographic projection function of Stereonet software to achieve the identification and statistical analysis of structural cracks in weathered volcanic rocks.

[0044] Example 2

[0045] Based on the method in Example 1, this invention uses the buried hill structure fractures in the Mesozoic volcanic rocks of the Bohai Bay Basin as an example for identification and statistical analysis. The specific operation is as follows.

[0046] 1. From volcanic rock imaging logging data, select data on the depth, dip direction, dip angle, width, and type of high-conductivity and high-resistance fractures. Calculate the fracture strike based on the dip direction: strike = IF(dip direction > 90, if(dip direction > 270, dip direction - 270, dip direction - 90), dip direction + 90), as shown in Table 1 (due to the large amount of data, only the first and last 10 rows are shown in Table 1). Then, use the scatter plot function in Excel to plot scatter plots of fracture depth versus fracture dip angle and width, and fracture depth versus strike (e.g., ...). Figure 1 (As shown).

[0047] Table 1. Data selected from volcanic rock imaging logging data.

[0048]

[0049] 2. Align the single-well columnar section with the scatter plot obtained in step 1 at depth. Based on the fracture width, dip angle, and orientation, combined with the logging curve characteristics of the single-well columnar section, and considering the characteristics of the weathering zone and inner zone of the volcanic rock, compare the actual fracture data to identify the weathering zone and inner zone of the volcanic rock.

[0050] The weathering crust of volcanic rocks refers to an assemblage of volcanic rocks formed after sedimentary discontinuity, weathering, leaching, and alteration, exhibiting differences in mineral, structural, and reservoir characteristics. It is characterized by weathered clay layers, argillaceous infill in oxidizing environments within faults, and microscopic features such as iron oxide linings in self-fractured fractures and bottom-indicating structures. The weathering crust develops a five-layer structure from top to bottom: soil layer, hydrolysis zone, dissolution zone, disintegration zone, and parent rock. The weathering crust can be viewed as a weathering zone, and the parent rock as an inner layer.

[0051] Weathering zones are typically characterized by high crack width, scattered crack dip angles and orientations, relatively high quartz and clay mineral content curves, and relatively low feldspar and calcite content curves; in contrast, enclosed zones are typically characterized by low crack width, relatively concentrated crack dip angles and orientations, relatively low quartz and clay mineral content curves, and relatively high feldspar and calcite content curves.

[0052] 3. Copy the crack data corresponding to the depth segment of the inner band identified in step 2 into a txt software (as shown in Table 2). Then, use the Import File function of the Stereonet software to import the cracks of the inner band into the Stereonet software. Finally, use the Poles function in the Calculations menu to draw the pole diagram of the cracks in the inner band (as shown in Table 2). Figure 3 As shown in the figure, each pole represents the projection of the normal to each crack surface onto the Schottky grid. Then, using the Contour function in the Plot menu, a dense map of the inner crack zone is generated (e.g., Figure 4 As shown in the image, using the Inspector function in the View menu, the Spacing parameter in the Contours option is set to an appropriate size to highlight the density of the internal fracture orientation. The specific settings are as follows: By default, Interval is 2 and Significance level is 3. If the number of fractures is small, lower the Interval to make the contour lines denser and lower the Significance level for more precise lines; if the number of fractures is large, increase the Interval to make the contour lines sparser and increase the Significance level for smoother lines. Figure 4 This is the view with the default parameters (Interval: 2; Significance level: 3). Figure 5 This is the view after the parameters have been modified (Interval: 3; Significance level: 1).

[0053] Table 2. Crack data for the depth segment corresponding to the inner band identified in Step 2.

[0054]

[0055] 4. The internal fracture pole diagram drawn in step 3 ( Figure 3 ) and density map ( Figure 4 In the study, the direction in which cracks are more concentrated is identified as the dominant development direction (these cracks are called dominant cracks). Then, the number, dip, angle and width of cracks in different dominant directions are statistically analyzed. The minimum, maximum and average values ​​of the dip, angle and width of cracks in different dominant directions are calculated. The results are shown in Table 3.

[0056] Table 3. Dip, dip angle, and width data of dominant fractures in the inner zone.

[0057]

[0058] 5. Based on the statistical results of the dominant cracks in the inner zone, the minimum and maximum values ​​of the dip and dip angle of the dominant cracks obtained in step 4 are used as standards to determine whether the dip and dip angle of the cracks in the weathering zone meet the criteria for dominant cracks. Finally, the dominant cracks in the weathering zone are screened out, as shown in Tables 4-6 (Tables 4-6 are selected from Table 1). This method can avoid the influence of weathering modification on the identification of dominant cracks in the weathering zone.

[0059] Table 4. Preferred NE-oriented cracks selected from Table 1

[0060]

[0061] Table 5. Preferred near-EW direction fractures selected from Table 1

[0062]

[0063] Table 6. Preferred NW-oriented fractures selected from Table 1

[0064]

[0065] 6. Use the Import File function in Stereonet software to import the dominant fractures selected in steps 4 and 5, and then use the Poles function in the Calculations menu to draw the dominant fracture pole plot (e.g., Figure 6 (As shown), then use the Contour function in the Plot menu to generate dense maps such as dominant cracks (e.g.) Figure 7 (As shown). Using the Inspector function in the View menu, set an appropriate size in the Spacing parameter of the Contours option. Refer to step 3 for parameter settings to highlight the density of the dominant fracture orientation. Figure 7 This is the view with the default parameters (Interval: 2; Significancelevel: 3). Figure 8 This is the view after the parameters have been modified (Interval: 1; Significance level: 2).

[0066] 7. The pole plot drawn in step 6 ( Figure 6 ) and density map ( Figure 7In the study, the direction in which the cracks are more concentrated was identified as the dominant development direction (these cracks are called dominant cracks). Then, the number, dip, dip angle and width of cracks in different dominant directions were statistically analyzed. The minimum, maximum and average values ​​of the dip, dip angle and width of cracks in different dominant directions were calculated. The results are shown in Table 7, which finally revealed the characteristics of crack development in volcanic rock structures after weathering.

[0067] Table 7. Data used to reveal the development characteristics of structural fractures in weathered volcanic rocks.

[0068]

[0069] For the dominant fractures and their directions obtained using the above methods, core, wall core, and imaging logging data from the area are used to directly study fractures with the same direction as the dominant fractures. Based on the fracture morphology, orientation, and other characteristics, it is verified whether the dominant fractures are tectonic fractures. Figure 9 As shown ( Figure 9 (This refers to imaging logging data and core data from the area), from Figure 9 The core data shows that this is a tectonic fracture. Furthermore, based on the depth of the core and the high-conductivity fracture table, its dip angle matches the characteristics of a NE-trending fracture. Therefore, it can be proven that the NE-trending dominant fracture direction is the tectonic fracture direction. Similarly, it can be proven that the near-EW, NW, and NE-trending dominant fracture directions are all tectonic fracture directions. Thus, it can be clearly stated that the dominant fracture direction obtained in steps 1-7 is the tectonic fracture direction of the volcanic rock, and the dominant fracture is a tectonic fracture.

[0070] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for identifying tectonic fractures of weathered volcanic rocks, characterized by, Comprising the following steps: S1 screen the depth, tendency, dip angle, width and type data of high conductive and high resistive fractures from the volcanic rock imaging logging data, get the fracture strike according to the tendency, then draw the scatter plot of fracture depth-dip angle and width, fracture depth-fracture strike by using the scatter plot function of Excel software; S2 align the single well columnar chart with the scatter plot obtained in step 1 in depth, identify the weathering zone and inner zone of volcanic rock according to the fracture width, dip angle and strike, combined with the logging curve characteristics of single well columnar chart, combined with the characteristics of volcanic rock weathering zone and inner zone; S3 import the fracture data of the depth section corresponding to the inner zone identified in step S2 into Stereonet software to draw the inner zone fracture pole point graph and inner zone fracture contour map; S4 identify the relatively dense direction of the fractures as the dominant development direction in the inner zone fracture pole point graph and contour map drawn in step 3, these fractures are called dominant fractures, then count the number, tendency, dip angle and width of the fractures in different dominant directions, and get the minimum value, maximum value and average value of the tendency, dip angle and width of the fractures in different dominant directions; S5 based on the statistical results of the dominant fractures in the inner zone, use the minimum and maximum values of the tendency and dip angle of the dominant fractures obtained in step 4 as the standard to determine whether the fracture tendency and dip angle in the weathering zone meet the standard of the dominant fractures, and finally screen out the dominant fractures in the weathering zone; S6 draw the dominant fracture pole point graph and dominant fracture contour map by using Stereonet software according to the data of the dominant fractures obtained in steps S4 and S5; S7 identify the relatively dense direction of the fractures as the dominant development direction in the pole point graph and contour map drawn in step 6, these fractures are called dominant fractures, then count the number, strike, dip angle and width of the fractures in different dominant directions, and finally get the structural fracture development characteristics data of the weathering-reformed volcanic rock, including the minimum value, maximum value and average value of the strike, dip angle and width of the fractures in different dominant directions.

2. The method for identifying tectonic fractures of weathered volcanic rocks according to claim 1, characterized in that, When getting the fracture strike according to the tendency, it is carried out in Excel software, strike = IF(tendency>90,if(tendency>270,tendency-270,tendency-90),tendency+90).

3. The method for identifying tectonic fractures of weathered volcanic rocks according to claim 1, characterized in that, The specific method of step S3 is as follows: copy the fracture data of the depth section corresponding to the inner zone identified in step S2 to txt software, then import the inner zone fractures into Stereonet software by using the Import File function of Stereonet software, and draw the inner zone fracture pole point graph by using the Poles function in the Calculations menu, each pole point on the graph represents the projection of the normal line of each fracture surface on the Schmidt net; then generate the inner zone fracture contour map by using the Contour function in the Plot menu.

4. The method for identifying tectonic fractures of weathered volcanic rocks according to claim 3, characterized in that, When generating the inner zone fracture contour map, use the Inspector function in the View menu to set the size in the Spacing parameter in the Contours option to highlight the density of the inner zone fracture occurrence.

5. The method for identifying tectonic fractures of weathered volcanic rocks according to claim 4, characterized in that, The setting method of the spacing parameter is as follows: in the default state, the interval is 2, and the significance level is 3, and the contour distribution of the equal-density diagram in the default state is adjusted; the interval is adjusted to be higher to make the contour lines more sparse, and to be lower to make the contour lines more dense; the significance level is adjusted to be higher to make the contour lines smoother, and to be lower to make the contour lines more accurate.

6. The method for identifying tectonic fractures of weathered volcanic rocks according to claim 1, characterized in that, The specific method of step S6 is as follows: the dominant crack screened out in steps 4 and 5 is imported into the Stereonet software, the pole point diagram of the dominant crack is drawn through the Poles function in the Calculations menu, and then the Contour function in the Plot menu is used to generate the equal-density diagram of the dominant crack.

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