Method for analyzing compaction and pressure-solution action strength influence factors in carbonate rocks

Abstract

The invention relates to a method for analyzing influence factors of compaction and pressure-solution action strength in carbonate rock, which comprises the following steps of: S1, counting rock cores obtained by drilling a carbonate rock reservoir, and recording the number and the form of suture lines, the thickness of insoluble residues and the accumulative amplitude of each rock core; s2, samples are selected from the rock core obtained in the step S1 and the field rock outcrop of the same target layer, and each sample is prepared into a common rock slice and a casting body slice impregnated with blue epoxy resin; s3, counting the number and accumulated amplitude of suture lines in the rock slice; s4, determining component content data of different lithologic slices; s5, performing micro-area X-ray diffraction analysis on the rock powder, and measuring mineral components and proportions in different lithologic samples; and S6, integrating the data counted in the steps S1, S3, S4 and S5, and analyzing the trend of the influence of the data on the compaction strength and the crush-solution strength in the carbonate rocks.

Description

Technical Field

[0001] The present invention belongs to the technical field of testing or analyzing materials by means of measuring the chemical or physical properties of the materials, and particularly relates to an analysis method of factors affecting the intensity of compaction and pressure solution in carbonate rocks. Background Art

[0002] For deep and ultra-deep carbonate reservoirs, increasing evidence indicates that compaction and pressure dissolution have a significant impact on the porosity and permeability of carbonate reservoirs. The porosity and permeability of carbonate reservoirs, in turn, play a crucial role in their storage properties and oil well productivity. Therefore, in actual oil and gas production, it is necessary to assess the intensity of compaction and pressure dissolution in carbonate reservoirs. This helps in estimating the porosity reduction effect caused by compaction and pressure dissolution during exploration, preliminarily determining the degree of pore retention, and enabling more effective reservoir prediction. However, this research is not currently available in the art.

[0003] By analyzing the influence of sutures on the intensity of compaction and pressure dissolution of carbonate reservoirs, the present invention assists in estimating the porosity reduction effect of reservoirs in different regions caused by compaction and pressure dissolution during exploration, and can preliminarily determine the degree of reservoir pore retention. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an analysis method for factors affecting the intensity of compaction and pressure solution in carbonate rocks in response to the above-mentioned deficiencies in the prior art.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0006] A method for analyzing factors affecting the intensity of compaction and pressure solution in carbonate rocks is provided, comprising the following steps:

[0007] S1. Statistically analyze the cores obtained from drilling in carbonate reservoirs, and record the number, morphology, thickness of insoluble residue, and cumulative amplitude of each core;

[0008] S2. Samples are selected from the cores obtained in S1 and from field rock outcrops of the same target layer and numbered. Multiple relatively pure samples of a single lithology are selected from the drill core samples and field rock outcrops. Each sample is prepared into a plain rock thin section and a blue epoxy resin-impregnated cast thin section.

[0009] S3. Take photos of the ordinary rock thin sections and the blue epoxy resin-impregnated casting thin sections prepared in S2, and count the number and cumulative amplitude of the suture lines in the rock thin sections;

[0010] S4. Use image analysis to quantitatively analyze the three components of cement, particles, and matrix in the ordinary rock thin sections and the blue epoxy resin-impregnated cast thin sections prepared in S2, determine the area percentage of each component, and calculate the average value of the component content data obtained by measuring the component content data of thin sections of the same lithology to obtain the component content data of thin sections of different lithologies;

[0011] S5. Select different carbonate rock samples from the S2 core and field rock outcrops of the same target layer and prepare them into rock powder. The obtained rock powder is then subjected to micro-area X-ray diffraction analysis to measure the mineral composition and proportion of each lithologic sample;

[0012] S6. Based on the data on the number of sutures, cumulative amplitude, area percentage of different components, and mineral composition and proportion counted in steps S1, S3, S4, and S5, analyze the trend of their influence on the compaction and pressure solution strength of carbonate rocks.

[0013] According to the above scheme, in step S1, the morphology of the suture line is divided into three types: box-shaped, tooth-shaped and wavy. The thickness of the insoluble residue is the distance between the upper boundary of the suture line and the lower boundary of the suture line. The amplitude of the suture line is the distance between the two points farthest apart in the direction perpendicular to the extension of the suture line. The cumulative amplitude is the sum of the amplitudes counted on each section of the core.

[0014] According to the above scheme, the samples selected in step S2 are based on rock samples with suture lines that can be clearly identified by the naked eye as the standard, and rock samples with no suture lines are used as the observation control group.

[0015] According to the above scheme, the ordinary rock slices and the blue epoxy resin impregnated casting slices in step S2 have the same size, with a length not exceeding 30 mm, a width not exceeding 25 mm, and a thickness of 0.03 mm.

[0016] According to the above protocol, the number and amplitude of stylolites in the rock thin sections in step S3 were measured using ImageJ software.

[0017] According to the above scheme, in step S4, the image analysis method is used to quantitatively analyze the different components in the ordinary rock thin sections and the blue epoxy resin-impregnated cast thin sections prepared in S2. The specific method is: after taking pictures with a microscope, Photoshop software is used to determine the area percentage of each component based on the ratio of the pixel value of the area occupied by the selected cement, particle or matrix to the total pixel value.

[0018] According to the above scheme, the particle size of the rock powder in step S5 is less than 10 μm.

[0019] The present invention conducts statistics on sutures at the core scale (meter scale) and rock thin section scale (micrometer scale) for carbonate rock types such as mud-powder crystal dolomite, powder crystal dolomite, and granular dolomite during the WW formation deposition period. The method also uses image analysis methods to test the area percentage of the three components of cement, particles, and matrix in the core, thereby determining the influence of different components on the degree of suture development and morphology. The mineral composition of the rock samples is accurately determined through micro-area X-ray diffraction analysis, thereby statistically analyzing the changes in suture density and morphology under different rock mineral composition combinations. Finally, a comprehensive analysis is conducted from the aspects of structural components, mineral composition combinations, lithology and lithofacies, and the influencing factors of suture conditions on the intensity of compaction and pressure solution are more comprehensively revealed from multiple perspectives. The porosity reduction effect of deep to ultra-deep carbonate reservoirs in the XX formation can be estimated.

[0020] The beneficial effects of the present invention are as follows: the present invention provides an analysis method for factors affecting the intensity of compaction and pressure dissolution in carbonate rocks, determines the influence of core suture conditions on different types of carbonate reservoirs through experiments and test analysis, provides a certain evaluation basis for the pore evolution of deep and ultra-deep carbonate reservoirs, can evaluate the pore reduction effect caused by compaction and pressure dissolution of carbonate reservoirs, preliminarily judge the degree of reservoir pore retention, and make more favorable reservoir predictions, which is of great significance in the research and evaluation of Lower Paleozoic carbonate reservoirs in the XX area. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the morphology of different sutures in Example 1 of the present invention;

[0022] Figure 2 These are photos of rock thin sections and core samples from Example 1;

[0023] Figure 3 This is a schematic diagram of the measurement of the percentage of structural components in a rock slice using Photoshop software in Example 1;

[0024] Figure 4 This is the density distribution histogram of different dolomite sutures in the XX formation obtained in Example 1;

[0025] Figure 5 The dolomite content and suture density distribution histogram of the XX formation dolomite obtained in Example 1;

[0026] Figure 6 This is a histogram of the distribution of structural component content and suture density of the XX formation dolomite obtained in Example 1. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0029] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0030] Example 1

[0031] Taking carbonate rock samples as an example, we statistically analyzed the development of sutures and analyzed the intensity of compaction-pressure solution and its relationship with the structural components of carbonate rocks. The specific steps are as follows:

[0032] S1. Observation and collection of rock samples

[0033] The cores collected in this example are from three wells: Well A, Well B, and Well C, all from carbonate rocks deposited during the XX formation period in the outcrop section of the XX region. Rock samples were collected primarily from the aforementioned well locations and sections. To ensure the production of later rock thin sections, the collected rock samples had a minimum length and width of 3 cm × 4 cm. 30 samples were collected from Well A, 60 from Well B, and 30 from Well C. The core samples were numbered and named using the "well number - core section number - number of samples" format. The total length of the core samples was 150 m. In addition, 60 samples were collected from the outcrop section of the XX region, and the numbering and naming used was "profile name - layer section number - number of samples."

[0034] The collected cores were observed with the naked eye and a magnifying glass, and the number of sutures in each core was counted. The suture density is the number of sutures developed per meter of core. The morphology of each suture was divided into three types: box-shaped, tooth-shaped, and wavy. The morphology diagram of the suture is shown in the figure below. Figure 1 As shown, a is a wavy suture line, b is a box-shaped suture line, and c is a spike-shaped suture line. The insoluble residue thickness and the cumulative amplitude of each suture line are measured and recorded. The insoluble residue thickness is the distance between the upper boundary and the lower boundary of the suture line, and the cumulative amplitude of the suture line is the distance between the two points that are farthest apart in the direction perpendicular to the extension of the suture line.

[0035] S2. Preparation of rock thin sections

[0036] Samples of various lithologies were selected from core and outcrop samples from S1. Rock samples with clearly identifiable stylolites and relatively pure single lithologies served as the standard. Rock samples with no sutures and relatively pure single lithologies served as the control group. A total of 108 rock samples were collected, including 75 core samples and 34 field outcrop samples. Both ordinary thin sections and blue epoxy resin-impregnated cast thin sections were prepared for each sample. Because blue epoxy resin-impregnated cast thin sections primarily fill pores, thin sections were not prepared for lithologies with poorly developed pores.

[0037] The specific preparation methods of ordinary rock slices and blue epoxy resin impregnated cast slices are as follows: the rock sample (the preparation of the blue epoxy resin impregnated cast slice requires that the relatively flat surface of the rock sample be drip-infiltrated with blue casting glue before cutting) is cut into rock slices with a length and width of 3 to 5 cm using a slicer according to the required orientation. The cut rock slices are rinsed with water and placed on the iron grinding wheel of a grinding machine. After coarse grinding, medium grinding, and fine grinding are performed to a thickness of 0.1 mm, and then fine grinding is performed with ultra-fine diamond powder (No. 800) to a thickness of about 0.03 mm. Then polish it to make the polished surface very smooth and complete, then rinse it with clean water and bake it in an oven at 47°C for 12 hours. Stick the polished surface on a glass slide with Canada gum. After solidification, continue to grind the other side of the rock slice until it is translucent. Finally, press and rub it with the finest corundum (No. 800) to a thickness of about 0.03mm. Wash and dry the slice, put a small amount of gum on the cover glass, heat it, and cover it on the slice. Be careful to expel all the internal bubbles and dry it in a drying oven to finally obtain a rock slice.

[0038] The same sample was made into ordinary rock thin sections and blue epoxy resin impregnated cast thin sections, respectively. A total of 144 rock thin sections of four lithologies (mud-powder crystal dolomite, argillaceous dolomite, psammitic dolomite, and micritic psammitic dolomite) were made. The lithology and number of thin sections are shown in Table 1 below.

[0039] Table 1

[0040]

[0041] S3. Rock thin section observation and recording

[0042] The prepared rock slices were placed under a polarizing microscope for observation. A fixed 10x eyepiece and adjustable 2x, 5x, and 10x objective lenses were used to observe the rock slices. The number and amplitude of the suture lines under each rock slice were counted.

[0043] The thin-section photos under the microscope were taken using image analysis software. The thin-section photos and core photos of different types of dolomite in the XX formation are shown in the attached figure. Figure 2As shown, the main materials are muddy mud-powder crystal dolomite, mud-powder crystal dolomite, micritic psammitic dolomite and psammitic dolomite containing sutures. Image processing software was used to measure the amplitude of the photographed sutures and the thickness of the insoluble residue of the sutures. The number was measured in "strips / thin slices". The amplitude was based on the distance between the two points farthest apart in the direction perpendicular to the extension of the suture. The thickness of the insoluble residue was based on the average of the maximum and minimum thicknesses of a single suture.

[0044] S4. Rock thin section composition statistics

[0045] Image processing software was used to analyze and count the photos of the rock slices taken above. The selection function was used to measure the overall size of the photo field and the size of the portion occupied by the same component, and the ratio was calculated as the proportion data of the component. The main statistics were the area percentage content of the two components of cement, particles and matrix, and pores in the same field of view in a single rock slice. The statistical diagram of different components of XX formation dolomite is shown in the attached figure. Figure 3 As shown, the areas of different components are circled, where red represents cement, blue represents pores, and yellow represents particles;

[0046] A total of 80 photos of cast rock thin sections were selected for statistical analysis of structural components, including 48 photos of rock thin sections with sutures and 32 photos of rock thin sections without sutures. The measurement data were summarized in an Excel spreadsheet, and the proportions of different structural components were calculated (see Table 2).

[0047] Table 2 Proportions of different structural components in different lithologies

[0048]

[0049] S5. Micro-area X-ray diffraction analysis of rock mineral components

[0050] 120 carbonate rock samples of different lithologies (mud-powder crystal dolomite, argillaceous dolomite, psammitic dolomite, and micritic psammitic dolomite) were selected from the core and outcrop samples of S1. They were ground into powder using a trace powder sample preparation method and sieved to a particle size between 0.1 μm and 10 μm. The samples were required to have sufficient grains in the volume exposed to X-rays to ensure random orientation of the sample particles exposed to X-rays, thereby minimizing the influence of orientation as much as possible and thus enabling better comparison with standard materials.

[0051] The obtained rock powder was analyzed by micro-X-ray diffraction to measure the mineral composition of different lithology samples:

[0052] Under the conditions of operating voltage of XX kV and current of XX mA, the component content analysis was performed using the XX system, with a theoretical analysis accuracy of 1%. The instrument configuration and test conditions for the micro-area X-ray diffraction test are shown in Table 3 below:

[0053] Table 3

[0054]

[0055] The measurement results show that the mineral compositions of the four types of rock types, namely mud-powder crystal dolomite, mudstone dolomite, psammitic dolomite and mud-crystal psammitic dolomite, are mainly composed of two carbonate minerals, calcite and dolomite. Among them, the dolomite content of mud-powder crystal dolomite is 64% to 82%, the dolomite content of mudstone dolomite is 51% to 77%, the dolomite content of psammitic dolomite is 86% to 97%, and the dolomite content of mud-crystal psammitic dolomite is 83% to 94%.

[0056] S6. Comprehensive Analysis

[0057] The density distribution histogram of stylolites in different dolostone formations in XX stratum is obtained by combining the number, morphology, thickness of insoluble residues and cumulative amplitude of stylolites in the cores counted in S1, the number and amplitude of stylolites in the rock slices counted in S3, the percentage content of different rock components (cement, particles and matrix) counted in S4, and the mineral composition combination of different lithologic samples measured in S5. Figure 4 , Figure 4 A1, B2, C1, and NCSQ represent well A1, well B2, and well C1, respectively, and field outcrops in the XX region. Histogram of dolomite content and stylolite density in the XX formation ( Figure 5 ) and the histogram of XX formation suture density and different structural components ( Figure 6 ).

[0058] By comparing the differences between lithologies with developed sutures and those without, as well as the relationship between the proportion of different components and the development of sutures, the compaction and pressure solution strength in carbonate rocks can be analyzed.

[0059] 1. Relationship between compaction, pressure solution strength and lithology and lithofacies

[0060] Observation of cores from Wells A, B, and C shows that the average stylolite density is 19.9 lines / m in the mud-powder crystal dolomite, 4.9 lines / m in the psammitic dolomite, 7.8 lines / m in the micritic psammitic dolomite, 22.4 lines / m in the micritic dolomite, and 24.7 lines / m in the argillaceous dolomite.

[0061] In terms of the thickness of insoluble residue, the average thickness of the micritic dolomite is 0.72 cm, the average thickness of the psammic dolomite is 0.13 cm, the average thickness of the micritic psammic dolomite is 0.38 cm, the average thickness of the micritic dolomite is 0.71 cm, and the average thickness of the argillaceous dolomite is 0.78 cm.

[0062] Figure 4 The figure is a histogram of the distribution density of stylolites in different dolomite formations in the XX formation. According to the statistical data from the field outcrops in A1 well, B2 well, C1 well and XX area, the stylolites in the four lithologies are muddy mud-powder crystal dolomite, mud-powder crystal dolomite, mud-crystal psammitic dolomite and psammitic dolomite. It is obvious that the stylolite density of the first two lithologies is much higher than that of the latter two lithologies. The density of stylolites in argillaceous dolomite (argillaceous mud-powder crystal dolomite, mud-powder crystal dolomite) is 2-4 times that of dolomite grainstone (mud-crystal psammitic dolomite and psammitic dolomite), indicating that grainstone dolomite has strong resistance to pressure dissolution, while argillaceous dolomite and mud-powder crystal dolomite are more susceptible to compaction and pressure dissolution. The grain content of mud-crystal psammitic dolomite is less than that of psammitic dolomite, and the degree of development of its stylolites is also higher. This shows that with the increase of grain content, the ability of rock to resist compaction and pressure dissolution increases under the grain support structure.

[0063] 2. Relationship between compaction, pressure solution strength and structural components

[0064] from Figure 6 A histogram of suture density and structural components shows that suture density decreases and then increases with increasing particle content. A low point appears at particle content of 50-70%, indicating that rocks with 50-70% particle content have strong resistance to pressure dissolution. The suture density decreases and then increases with increasing cement content. A low point appears at cement content of 25-30%, indicating that rocks with 25-30% cement content have strong resistance to pressure dissolution. Higher matrix content reduces resistance to pressure dissolution. In summary, the presence of particles increases the rock's resistance to compaction and pressure dissolution, while an increase in matrix content reduces the rock's resistance to pressure dissolution.

[0065] 3. Relationship between compaction, pressure solution strength and mineral composition

[0066] The results of micro-area X-ray diffraction analysis show that the dolomite content of the rock sample is 52% to 100%. The histogram of dolomite content and stylolite density of XX formation dolomite ( Figure 5 ) shows that the degree of suture development in granular dolomite increases gradually from 50% to 80%, reaching a peak at 70-80%, and then decreases. When the dolomite content is between 80% and 100%, the resistance to compaction and pressure dissolution is stronger.

[0067] Based on the above analysis, granular dolomite has the strongest resistance to compaction and pressure dissolution among carbonate rocks. The dolomite content is between 80% and 100%, the particle content is between 50% and 70%, the matrix content is less than 10%, and the cement content is between 25% and 30%. The rock has the lowest degree of suture development and the strongest resistance to compaction and pressure dissolution. That is, when the stratum is gradually buried and subjected to compaction and pressure dissolution, the granular dolomite has the highest porosity preservation compared with other lithologies. In actual application, for the prediction of favorable deep and ultra-deep reservoirs, granular dolomite should be used as the most favorable reservoir lithology to ensure that the reservoir has good porosity and pore structure.

Claims

1. A method for analyzing factors affecting the intensity of compaction and pressure solution in carbonate rocks, characterized in that: The following steps are involved: S1. Statistically analyze the cores obtained from drilling in carbonate reservoirs, and record the number, morphology, thickness of insoluble residue, and cumulative amplitude of each core; S2. Select and number samples from the cores obtained in S1 and the field rock outcrops of the same target layer. Select multiple relatively pure samples of a single lithology from the drill core samples and the field rock outcrops. Prepare ordinary rock thin sections and blue cast thin sections for each sample. S3. Take photos of the ordinary rock thin sections and blue cast thin sections prepared in S2, and count the number and cumulative amplitude of the suture lines in the rock thin sections; S4. Use image analysis to quantitatively analyze the three components of cement, particles, and matrix in the ordinary rock thin sections and blue cast thin sections prepared in S2, determine the area percentage of each component, and calculate the average value of the component content data obtained by measuring the component content data of the same thin sections to obtain the component content data of different rock thin sections; S5. Select different carbonate rock samples from the S2 core and field rock outcrops of the same target layer and prepare them into rock powder. The obtained rock powder is then subjected to micro-area X-ray diffraction analysis to measure the mineral composition and proportion of different lithologic samples. S6. Based on the data on the number of sutures, cumulative amplitude, area percentage of different components, and mineral composition and proportion counted in steps S1, S3, S4, and S5, analyze their impact trends on the compaction and pressure solution strength of carbonate rocks.

2. The method for analyzing factors affecting the intensity of compaction and pressure solution in carbonate rocks according to claim 1, characterized in that: In step S1, the morphology of the suture is divided into three types: box-shaped, tooth-shaped and wavy. The thickness of the insoluble residue is the distance between the upper boundary of the suture and the lower boundary of the suture. The amplitude of the suture is the distance between the two points farthest apart in the direction perpendicular to the extension of the suture. The cumulative amplitude is the sum of the amplitudes counted on each core segment.

3. The method for analyzing factors affecting the intensity of compaction and pressure solution in carbonate rocks according to claim 1, characterized in that: In step S2, the samples selected are based on rock samples with suture lines that can be identified by the naked eye as the standard, and rock samples with no suture lines are used as the observation control group.

4. The method for analyzing factors affecting the intensity of compaction and pressure solution in carbonate rocks according to claim 1, characterized in that: The ordinary rock slices and the blue cast slices in step S2 have the same size, and are no longer than 30 mm, no wider than 25 mm, and 0.03 mm thick.

5. The method for analyzing factors affecting the intensity of compaction and pressure solution in carbonate rocks according to claim 1, characterized in that: The measurement of the number and amplitude of stylolites in the rock thin section in step S3 is performed using image processing software.

6. The method for analyzing factors affecting the intensity of compaction and pressure solution in carbonate rocks according to claim 1, characterized in that: In step S4, image analysis is used to quantitatively analyze the different components in the ordinary rock thin sections and blue cast thin sections prepared in S2. The specific method is: after taking pictures under a microscope, image processing software is used to determine the area percentage of each component based on the ratio of the pixel value occupied by the selected object to the total pixel value.

7. The method for analyzing factors affecting the intensity of compaction and pressure solution in carbonate rocks according to claim 1, characterized in that: The diameter of the rock powder in step S5 needs to be less than 10 μm.

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