A method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance.

Abstract

This invention provides a method for quantitative determination of the morphology and evaluation of the anti-fracture performance of columnar ceramic proppant, belonging to the technical field of fracturing proppant performance evaluation. It can significantly alleviate or solve the problem that existing evaluation standards for spherical proppants are unable to accurately characterize the geometric characteristics, stress modes, and structural failures of columnar particles. This method involves pre-pressure image acquisition and geometric parameter measurement of the sample, pressure testing, fine powder sieving, and post-pressure geometric parameter re-measurement. The aspect ratio loss rate is calculated, and a comprehensive fracture index is constructed by combining the mass loss rate. This method can simultaneously reflect fine powder formation and morphological degradation, improving the objectivity, accuracy, and comparability of the evaluation results.

Description

Technical Field

[0001] This invention belongs to the technical field of fracturing proppant performance evaluation, specifically relating to a method for quantitative determination of columnar ceramic proppant morphology and evaluation of its anti-fracture performance. Background Technology

[0002] As hydraulic fracturing technology continues to expand into deeper, ultra-deep, and complex geological reservoirs, the load-bearing capacity, fracture resistance, and long-term conductivity of proppant in fracturing fractures are receiving increasing attention. Traditional proppants such as quartz sand and spherical ceramsite have been widely used under conventional reservoir conditions. However, under high closure stress conditions, traditional spherical or near-spherical proppants are prone to breakage, embedding, and conductivity reduction, making it difficult to fully meet the application requirements of high-strength proppants for complex reservoir development. To improve propping performance under high stress conditions, non-spherical proppants with higher structural stability and fracture resistance potential have gradually become a research hotspot. Among them, columnar ceramsite proppants, due to their high aspect ratio and inter-particle mechanical interlocking potential, are considered to have the potential to reduce local point contact failure by changing the particle contact mode and force transmission path, thereby achieving better propping performance and excellent anti-backflow properties.

[0003] However, columnar ceramsite proppants differ significantly from traditional spherical proppants in terms of geometry, stress distribution, and failure mechanisms. Existing proppant evaluation systems are primarily based on spherical or near-spherical particles, making them difficult to apply accurately to columnar ceramsite proppants. Current standards typically determine particle size ranges through sieving and treat equivalent diameters as if they were spherical particles, lacking standardized measurement methods for the aspect ratio, average columnar diameter, and distribution characteristics of columnar particles. This makes it difficult to quantitatively characterize the true geometric features of columnar ceramsite proppants and establish a correlation between geometric parameters and macroscopic properties, thus impacting product development, performance optimization, and quality control.

[0004] Furthermore, existing breakage rate testing methods typically involve applying pressure to a specified mass of proppant in a steel cylindrical container and then evaluating the degree of breakage by statistically analyzing the proportion of fine powder. This method is suitable for characterizing point-contact breakage of spherical particles in a random packing state. However, for columnar ceramic proppant, the particles may be packed in different postures such as horizontal, inclined, or vertical in a pressure vessel. Their actual stress is often a mixture of bending, shearing, and compression, which deviates from the actual loading mode of columnar particles under crack conditions. At the same time, the failure of columnar particles is not only manifested in the generation of fine powder, but may also manifest as structural damage such as end splitting, transverse breakage, length shortening, and a decrease in the length-to-diameter ratio. If only the mass of fine powder is used as the evaluation criterion, it is difficult to fully reflect the true breakage resistance and morphological integrity retention ability of columnar ceramic proppant. Furthermore, standardized testing devices and evaluation methods for anisotropic proppants such as columnar and rod-shaped proppants are still lacking. Research institutions and manufacturers often use standard methods developed for spherical proppants or employ their own non-standardized testing procedures, resulting in poor comparability between different test results and hindering product grading, process screening, and engineering promotion of columnar ceramic proppants. Ultimately, the theoretical basis of existing evaluation systems, the mechanical models of testing devices, and core performance indicators are primarily based on spherical particles, which are incompatible with the anisotropic geometric characteristics and differentiated failure mechanisms of columnar ceramic proppants.

[0005] Therefore, a method for quantitative determination of columnar ceramic proppant morphology and evaluation of its anti-fracture performance is proposed. Summary of the Invention

[0006] The present invention aims to at least solve one of the technical problems existing in the prior art, and provides a method for quantitative determination of columnar ceramic proppant morphology and evaluation of its anti-fracture performance.

[0007] This invention provides a method for quantitative determination of the morphology and evaluation of the anti-fracture performance of columnar ceramsite proppant, comprising the following steps: S1: Obtain the columnar ceramsite proppant sample to be tested, and perform image acquisition and image analysis on the columnar ceramsite proppant sample to obtain the geometric parameters of each effective particle in the columnar ceramsite proppant sample to be tested. S2: Based on the obtained geometric parameters, determine the columnar diameter and aspect ratio of each effective particle in the sample before pressure bearing, and statistically obtain the average aspect ratio of the sample before pressure bearing. S3: Obtain the total mass of the columnar ceramsite proppant sample to be tested, place the columnar ceramsite proppant sample to be tested into a pressure mold, apply a target closing pressure, and maintain the pressure under the target closing pressure for a preset time; S4: Recover all materials after pressure is applied and sieve them according to the preset fine powder sieving rules to obtain fine powder quality and residual particle samples; S5: Perform image acquisition and image analysis on the remaining particle sample to obtain the geometric parameters of each effective particle in the sample after pressure bearing, and determine the average aspect ratio of the sample after pressure bearing accordingly. S6: Calculate the aspect ratio loss rate of the columnar ceramsite proppant based on the average aspect ratio of the sample before pressure, the average aspect ratio of the sample after pressure, the total mass, and the mass of the fine powder, and use the aspect ratio loss rate as the evaluation index of the anti-breakage performance of the columnar ceramsite proppant.

[0008] Furthermore, in steps S1 and S5, the image acquisition is performed using an image acquisition unit consisting of an industrial camera, a telecentric lens, an LED parallel light source, and a stage; before the image acquisition is performed, the image acquisition unit is calibrated using a standard length calibration plate to establish the conversion relationship between the pixel length and the actual length of the particles in the acquired image.

[0009] Specifically, in steps S1 and S5, the image analysis includes: performing noise reduction, contrast enhancement, threshold segmentation, morphological processing, and connected component recognition on the acquired particle image in sequence to extract the single particle contour; and removing particles whose particle projection contours intersect with the edge of the image acquisition area, particles that overlap or adhere to each other and cannot be reliably segmented, and particles with abnormal postures to obtain effective particles.

[0010] Specifically, in steps S1 and S5, the geometric parameters include at least the projected area of ​​a single particle and the length of the major axis of a single particle; wherein, the length of the major axis of a single particle is the length of the long side of the minimum bounding rectangle of the two-dimensional projected profile of a single particle; the columnar diameter is calculated based on the projected area of ​​a single particle and the length of the major axis of a single particle, and the aspect ratio is calculated based on the length of the major axis of a single particle and the columnar diameter.

[0011] Preferably, the average aspect ratio of the sample before pressure is the average aspect ratio of the individual effective particles included in the statistics of the sample before pressure; the average aspect ratio of the sample after pressure is the average aspect ratio of the individual effective particles included in the statistics of the sample after pressure.

[0012] Specifically, in step S6, the aspect ratio loss rate Calculate using the following formula:

[0013] in, The average length-to-diameter ratio of the sample before pressure is applied. The average length-to-diameter ratio of the sample after being subjected to pressure. The total mass of the columnar ceramic proppant sample to be tested is [missing information]. For fine powder quality.

[0014] Furthermore, step S6 also includes calculating the mass loss rate. And based on the said quality loss rate and the aspect ratio loss rate Calculate the comprehensive crushing index ; The mass loss rate Calculate using the following formula:

[0015] The comprehensive crushing index I f Calculate using the following formula:

[0016] in, and These are the weighting coefficients.

[0017] Furthermore, the weighting coefficients and satisfy + =1, and 0≤ ≤1, 0≤ ≤1; and, according to the comprehensive crushing index When evaluating columnar ceramsite proppant, the following conditions must be met: ≤10% is considered excellent, and 10% < ≤20% is considered qualified, meeting the requirements. A percentage greater than 20% is considered unqualified.

[0018] Furthermore, in step S3, the pressure-bearing mold includes a mold body and a detachable base. The inner wall of the mold body is polished to reduce the frictional impact between the particles and the sidewall. The mold body is provided with a replaceable inner liner. By adjusting the specifications of the inner liner, the lateral dimension of the receiving cavity can be changed to adapt to the stress evaluation requirements of columnar ceramic proppant under different crack width conditions.

[0019] Specifically, in step S4, the preset fine powder sieving rule is as follows: When the columnar ceramsite proppant sample to be tested has a nominal particle size classification range, the lower limit of the nominal particle size classification range is used as a benchmark. In the predetermined standard sieve sequence, the first sieve with a pore size value not greater than the lower limit of the nominal particle size classification range and closest to it is selected first. Then, the second sieve with a pore size smaller than the first sieve and adjacent to the first sieve in the predetermined standard sieve sequence is selected as the sieve for fine powder sieving. When the columnar ceramic proppant sample to be tested does not have a nominal particle size grading range, the 10th percentile value of the effective columnar particle diameter data included in the statistics before pressure is taken as the lower limit of the particle size range, and a sieve for fine powder screening is selected in the manner described above; and the particle mass passing through the sieve for fine powder screening is recorded as the fine powder mass.

[0020] The beneficial effects of this invention are as follows: This invention establishes a closed-loop evaluation process for the anti-fracture performance of columnar ceramic proppant by measuring its geometric parameters before pressure bearing, conducting pressure tests, screening fine powder, and re-measuring its geometric parameters after pressure bearing. This process simultaneously reflects the degree of complete particle breakage into fine powder and the degree of deterioration in particle geometry. Compared with existing methods that evaluate fracture performance solely based on fine powder quality, this invention, by introducing the aspect ratio loss rate, can more accurately characterize the structural damage of columnar ceramic proppant after pressure bearing. Furthermore, by using image acquisition and analysis to quantitatively characterize the columnar geometric features, it improves the objectivity, repeatability, and comparability of the evaluation results. Moreover, by constructing a comprehensive fracture index, the focus on fine powder blockage and morphological integrity can be flexibly adjusted according to different reservoir conditions, thus providing a more reliable evaluation basis for the product development, quality control, and engineering application of columnar ceramic proppant. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the steps of a method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance, according to a specific embodiment of the present invention. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1 As shown in the figure, a method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance, provided by a specific embodiment of the present invention, includes the following steps: S1: Use a box-type sampler to obtain a representative sample of the columnar ceramic proppant to be tested, and perform image acquisition and image analysis on the sample to obtain the geometric parameters of each effective particle in the sample. S2: Based on the obtained geometric parameters, determine the columnar diameter and aspect ratio of each effective particle in the sample before pressure bearing, and statistically obtain the average aspect ratio of the sample before pressure bearing. S3: Obtain the total mass of the columnar ceramsite proppant sample to be tested, place the columnar ceramsite proppant sample to be tested into a pressure mold, apply a target closing pressure, and maintain the pressure under the target closing pressure for a preset time; S4: Recover all materials after pressure is applied and sieve them according to the preset fine powder sieving rules to obtain fine powder quality and residual particle samples; S5: Perform image acquisition and image analysis on the remaining particle sample to obtain the geometric parameters of each effective particle in the sample after pressure bearing, and determine the average aspect ratio of the sample after pressure bearing accordingly. S6: Calculate the aspect ratio loss rate of the columnar ceramsite proppant based on the average aspect ratio of the sample before pressure, the average aspect ratio of the sample after pressure, the total mass, and the mass of the fine powder, and use the aspect ratio loss rate as the evaluation index of the anti-breakage performance of the columnar ceramsite proppant.

[0024] In one embodiment, the columnar ceramic proppant sample to be tested is a representative sample from the same batch of columnar ceramic proppant. Measurements before pressure bearing, pressure bearing tests, and measurements after pressure bearing are all performed on the same batch of samples to improve the comparability of the measurement results. Since the single particle size of columnar proppant is small, each 1g sample usually contains about 500 to 600 particles. Therefore, the sample mass used for geometric parameter measurement is small, accounting for only a small part of the overall sample, and this part of the sample is not the same sample as the sample participating in the compressive strength test. To ensure that the test results represent the true level of the overall sample before and after compression, in step S1, a representative sample of approximately 2g to 3g is first taken from the overall sample using a sampler to measure the geometric parameters before compression. In step S3, another representative sample with a bulk volume of 50mL or 50cm³ is taken from the overall sample using a sampler and weighed. The resulting sample mass is typically approximately 50g to 70g and is used for the pressure test. After the pressure test, another representative sample of approximately 2g to 3g is taken from the compressed sample using a sampler to measure the geometric parameters after compression. Further, the 50mL or 50cm³ refers to the bulk volume of the columnar proppant sample, which is obtained by measuring with a graduated cylinder. When measuring the 50mL or 50cm³ sample, the sample is compacted. When transferring the sample to the crushing chamber, the sample is compacted again and leveled to improve the consistency of the sample packing state, thereby improving the repeatability of the pressure test results and the reliability of the comparison results of the geometric parameters before and after compression.

[0025] Preferably, the columnar ceramic proppant sample to be tested is obtained by random sampling using a sampler, and the number of particles included in the statistics is not less than 500.

[0026] Furthermore, image acquisition, pressure testing, and sieving are performed sequentially. First, the geometric parameters of the sample before pressure testing are obtained, then pressure testing and sieving are performed, and finally the geometric parameters of the remaining particle sample after pressure testing are obtained to establish the correspondence between the changes in geometric morphology before and after pressure testing and the anti-breakage performance.

[0027] Based on the above basic implementation method, in steps S1 and S5, image acquisition is performed using an image acquisition unit consisting of an industrial camera, a telecentric lens, an LED parallel light source, and a stage. Before image acquisition, the image acquisition unit is calibrated using a standard length calibration plate to establish the conversion relationship between pixel length and actual particle length in the acquired image.

[0028] Furthermore, the industrial camera has a resolution of no less than 5 million pixels, and the number of particles in a single image acquisition is no less than 100. The LED parallel light source adopts a uniform illumination method to make the particle edges clear and reduce the influence of shadows on the contour extraction results.

[0029] In one implementation, image analysis is performed by image analysis software to extract the projected area of ​​a single particle, the length of the major axis of a single particle, and the columnar diameter and aspect ratio calculated therefrom based on the particle projection profile.

[0030] In one specific implementation, in steps S1 and S5, the image analysis includes: performing noise reduction, contrast enhancement, threshold segmentation, morphological processing, and connected component recognition on the acquired particle image in sequence to extract the single particle contour; and removing particles whose particle projection contour intersects with the edge of the image acquisition area, particles that overlap or adhere to each other and cannot be reliably segmented, and particles with abnormal postures to obtain effective particles.

[0031] In this embodiment, by removing particles whose particle projection contours are truncated by the edge of the image acquisition area, particles that overlap or stick together, and particles with abnormal postures, the interference of abnormal particles on the statistical results of geometric parameters can be reduced, thereby improving the accuracy of subsequent calculation results of column diameter and aspect ratio.

[0032] Furthermore, particles with abnormal postures include particles with their end faces facing upwards, particles that are placed at an angle causing their two-dimensional projection to deviate significantly from their stable lateral projection shape, or particles whose two-dimensional projection cannot reflect the relationship between the particle's length direction and its lateral dimension.

[0033] In another specific embodiment, in steps S1 and S5, the geometric parameters include at least the projected area of ​​a single particle and the length of the major axis of a single particle; wherein, the length of the major axis of a single particle is the length of the long side of the minimum bounding rectangle of the two-dimensional projected profile of a single particle; the columnar diameter is calculated based on the projected area of ​​a single particle and the length of the major axis of a single particle, and the aspect ratio is calculated based on the length of the major axis of a single particle and the columnar diameter.

[0034] In this embodiment, the projected area of ​​a single particle is used to characterize the two-dimensional projected size of the particle, and the length of the major axis of the single particle is used to characterize the dimensional features of the particle along its length direction.

[0035] Specifically, the columnar diameter is determined by the ratio of the projected area of ​​a single particle to the length of its major axis, so as to utilize the feature that the columnar particle projection is approximately rectangular to characterize its lateral size.

[0036] Furthermore, the caliber of both the samples before and after the pressure test was calculated using the same geometric parameters to ensure consistency and comparability of the measurement results.

[0037] In another specific embodiment, the average aspect ratio of the sample before pressure is the average of the aspect ratios of individual effective particles included in the statistics of the sample before pressure; the average aspect ratio of the sample after pressure is the average of the aspect ratios of individual effective particles included in the statistics of the sample after pressure. Effective particles refer to particle objects that are retained for geometric parameter statistics and aspect ratio calculation after screening during image acquisition and image analysis. Specifically, after denoising, contrast enhancement, threshold segmentation, morphological processing, and connected component recognition of the acquired particle images, clear, complete, and independently identifiable single particle contours can be formed. Among them, particles whose projected contours intersect with the edge of the image acquisition area, particles that overlap or adhere to each other and cannot be reliably separated, and particles with abnormal postures are not included in the statistical scope. The particles remaining after removing the above particles are the effective particles. Using effective particles for geometric parameter statistics helps to reduce the impact of abnormal contours, boundary truncation, and particle adhesion on the calculation results of columnar diameter, major axis length, and aspect ratio, thereby improving the accuracy and comparability of measurement results before and after pressure.

[0038] Furthermore, the average aspect ratio of the sample before pressure is used to characterize the initial geometric morphology of the columnar ceramsite proppant sample to be tested, while the average aspect ratio of the sample after pressure is used to characterize the remaining geometric morphology of the columnar ceramsite proppant sample after pressure.

[0039] Specifically, by statistically averaging the aspect ratio of individual valid particles included in the statistics, the impact of individual abnormal particles on the evaluation results can be reduced, thereby improving the stability of the anti-breakage performance evaluation results.

[0040] In another specific embodiment, in step S6, the aspect ratio loss rate Calculate using the following formula:

[0041] in, The average length-to-diameter ratio of the sample before pressure is applied. The average length-to-diameter ratio of the sample after being subjected to pressure. The total mass of the columnar ceramic proppant sample to be tested is [missing information]. For fine powder quality.

[0042] Furthermore, the aspect ratio loss rate is used to characterize the change in the geometric integrity of columnar ceramic proppant before and after pressure bearing. A larger aspect ratio loss rate indicates a more significant decrease in particle length dimension and more severe structural damage. The aspect ratio parameter is incorporated into the evaluation system when constructing the comprehensive breakage index. This is because the particle shape characteristics of columnar proppant have a significant impact on particle packing state, force transmission mode, and pressure bearing capacity. Generally, as the aspect ratio increases, the compactness of particle packing decreases, the packing density decreases, and the stability of inter-particle force support decreases, thus reducing the pressure bearing capacity. Simultaneously, the pore space formed between particles increases, improving the overall porosity of the sample, which in turn enhances conductivity. Therefore, a larger or smaller aspect ratio is not necessarily better; it needs to be controlled within an appropriate range to balance the pressure bearing capacity and conductivity of the columnar proppant, enabling it to meet downhole closure pressure conditions while improving fracture conductivity and production enhancement. Based on this, the aspect ratio can be used as one of the important geometric parameters for evaluating the quality level of columnar proppant. Furthermore, in the setting of the comprehensive breakage index, mass loss is used to characterize the portion that undergoes significant breakage after pressure and forms fine powder or debris that can pass through a sieve; aspect ratio loss is used to characterize the portion that, although not transformed into fine powder that can pass through a sieve after pressure, has undergone significant deterioration in particle morphology. This portion of particles may still remain on the sieve; therefore, evaluation based solely on mass loss cannot fully reflect the impact of particle morphology deterioration on pressure-bearing performance. By simultaneously introducing mass loss and aspect ratio loss, the explicit breakage loss and morphological performance loss of the columnar proppant during pressure bearing can be reflected respectively, thus providing a more comprehensive evaluation of the changes in the contribution of particles to the overall support capacity and conductivity after pressure bearing; among which... Part of the significance lies in the fact that, since a portion of the aspect ratio loss results in fine powder passing through the sieve and being included in the mass loss, the multiplication factor in the formula is... This is to remove the portion that has already been calculated in the mass loss within the aspect ratio loss.

[0043] Specifically, for particles that are not completely broken into fine powder but have split ends, broken in the middle, or shortened in length, the aspect ratio loss rate can reflect the degree of structural failure that is difficult to reflect by traditional fine powder quality indicators.

[0044] In another specific embodiment, step S6 further includes calculating the mass loss rate. And based on the quality loss rate and aspect ratio loss rate Calculate the comprehensive crushing index ; Quality loss rate Calculate using the following formula:

[0045] Comprehensive Breakage Index I f Calculate using the following formula:

[0046] in, and These are the weighting coefficients.

[0047] Furthermore, the mass loss rate is used to reflect the degree to which the columnar ceramsite proppant is completely broken into fine powder, and the comprehensive breakage index is used to comprehensively characterize the combined effect of fine powder formation and structural failure on the resistance to breakage performance.

[0048] Furthermore, by adjusting the weighting coefficients and It can adjust the evaluation focus of columnar ceramic proppant anti-fracture performance based on the differences in the sensitivity of different reservoirs to fine powder blockage and the requirements for particle morphology integrity.

[0049] In one specific implementation, the weighting coefficient and satisfy + =1, and 0≤ ≤1, 0≤ ≤1; and, according to the comprehensive breakage index When evaluating columnar ceramsite proppant, the following conditions must be met: ≤10% is considered excellent, and 10% < ≤20% is considered qualified, meeting the requirements. A percentage greater than 20% is considered unqualified.

[0050] Specifically, when the target reservoir is more sensitive to fine powder blockage, the weighting coefficient corresponding to the mass loss rate is increased; when the target reservoir has higher requirements for particle morphology integrity, the weighting coefficient corresponding to the aspect ratio loss rate is increased.

[0051] Furthermore, the grading criteria of excellent, qualified, and unqualified are used to quickly compare and screen the anti-fracture performance of columnar ceramsite proppant from different batches or specifications.

[0052] In one specific embodiment, in step S3, the pressure-bearing mold includes a mold body and a detachable base. The inner wall of the mold body is polished to reduce the frictional impact between the particles and the sidewall. The mold body is provided with a replaceable inner liner. By adjusting the specifications of the inner liner, the lateral dimension of the receiving cavity can be changed to adapt to the stress evaluation requirements of columnar ceramic proppant under different crack widths. Furthermore, to ensure the comparability of measurement results before and after pressure bearing, the image acquisition magnification, illumination mode, image processing parameters, and effective particle screening rules in steps S1 and S5 are kept consistent.

[0053] In this embodiment, after the inner wall of the mold is polished, the additional friction between the particles and the sidewall can be reduced, thereby reducing the influence of the sidewall constraint on the particle orientation and stress state.

[0054] Specifically, after replacing the inner liner with one of different specifications, the lateral dimension of the pressure mold cavity is changed accordingly to adapt to the stress evaluation requirements of columnar ceramic proppant under different crack width conditions.

[0055] In one specific implementation, in step S4, the preset fine powder sieving rule is as follows: When the columnar ceramsite proppant sample to be tested has a nominal particle size grading range, the lower limit of the nominal particle size grading range is used as the benchmark. In the predetermined standard sieve sequence, the first sieve with an aperture value not greater than the lower limit of the nominal particle size grading range and closest to it is selected first. Then, the second sieve in the predetermined standard sieve sequence with an aperture smaller than the first sieve and adjacent to the first sieve is selected as the sieve for fine powder sieving. When the columnar ceramsite proppant sample to be tested does not have a nominal particle size grading range, the 10th percentile value of the effective columnar diameter data of particles included in the statistics before pressure is used as the lower limit of the particle size range, and the sieve for fine powder sieving is selected in the above manner. The mass of particles passing through the sieve for fine powder sieving is recorded as the mass of fine powder. The nominal particle size grading range refers to the particle size grade range corresponding to the columnar ceramsite proppant to be tested in the process of product preparation, sieving and grading, quality inspection or product labeling. It is used to characterize the original size grading range of the batch of columnar ceramsite proppant. The nominal particle size grading range includes at least the lower limit of the nominal particle size grading range. The nominal particle size classification range is typically defined by both an upper and lower limit particle size. The lower limit of the nominal particle size classification range serves as one of the sieving benchmarks in the fine powder sieving rules. When the columnar ceramsite proppant sample to be tested has a clearly defined nominal particle size classification range, the lower limit of this range is used as the benchmark to determine the sieve for fine powder sieving in the standard sieve sequence. When the columnar ceramsite proppant sample to be tested does not have a clearly defined nominal particle size classification range, the 10th percentile of the effective columnar diameter data of particles included in the statistics before pressure is used as an alternative lower limit of the particle size range. By introducing a nominal particle size classification range, the fine powder sieving threshold can be matched with the original size class of the sample to be tested, thereby improving the rationality of distinguishing between completely crushed fine powder and remaining particles.

[0056] In this embodiment, by determining the sieve for fine powder sieving based on the lower limit of the nominal particle size grading range or the 10th percentile value of the column diameter data, the fine powder judgment threshold can be matched with the original size characteristics of the sample to be tested.

[0057] Specifically, after being sieved by a fine powder screening screen, the particles that pass through the fine powder screening screen mainly correspond to the fine powder formed by complete crushing, while the particles that do not pass through the fine powder screening screen mainly correspond to intact particles and remaining particles that are partially crushed but still retain their particle shape, so as to facilitate subsequent measurement of geometric parameters after pressure.

[0058] In one specific implementation, columnar ceramic proppant from the same batch is selected as the test sample. The test sample has a nominal particle size range, with the lower limit of the nominal particle size range being 425 μm. First, a representative sample of approximately 2g to 3g is separated from the whole sample using a sample divider, ensuring that at least 500 particles are included in the geometric parameter statistics. Firstly, the geometric parameters of the test sample are measured before pressure testing. The sample is dispersed in a single layer on a high-contrast sample carrier plate, ensuring that the particles do not contact or overlap. Image acquisition is performed using an image acquisition unit consisting of an industrial camera, a telecentric lens, an LED parallel light source, and a stage. Before image acquisition, the image acquisition unit is calibrated using a standard length calibration plate to establish the conversion relationship between pixel length and actual particle length in the acquired image. The industrial camera has a resolution of 5 megapixels, and each image contains at least 100 particles. During image analysis, the acquired particle images are sequentially subjected to denoising, contrast enhancement, threshold segmentation, morphological processing, and connected component recognition to extract single particle contours. Particles whose projected contours intersect with the edge of the image acquisition area, particles that overlap or adhere to each other and cannot be reliably segmented, and particles with abnormal postures are removed to obtain effective particles. The particle size specification of the columnar proppant is characterized by the diameter of the columnar particles, and common nominal particle size ranges include 850–425 μm, 600–300 μm, 425–212 μm, and 212–106 μm.

[0059] Furthermore, since standard sieve sizes used for particle size classification typically include 850μm (20 mesh), 710μm (25 mesh), 600μm (30 mesh), 500μm (35 mesh), 425μm (40 mesh), 355μm (45 mesh), 300μm (50 mesh), 250μm (60 mesh), 212μm (70 mesh), 180μm (80 mesh), 150μm (100 mesh), 125μm (120 mesh), and 106μm (140 mesh), therefore, in When performing fine powder sieving or sieving of crushed products after compression, the second sieve in the standard sieve sequence with an aperture value no greater than the lower limit of the nominal particle size range corresponding to the columnar ceramsite proppant is selected as the sieve for fine powder sieving. Alternatively, the lower limit of the particle size range is set to no greater than the 10th percentile of the sample columnar diameter data, and the second sieve in the standard sieve sequence with an aperture value smaller than the first sieve is selected as the sieve for fine powder sieving. This sieve selection method ensures that the sieving test matches the actual particle size specifications of the columnar proppant, improving the uniformity and comparability of the sieving results.

[0060] In this embodiment, a total of 820 effective particles were obtained. The projected area and major axis length of each effective particle were extracted. The major axis length is the length of the longest side of the minimum bounding rectangle of the particle's two-dimensional projected profile. The columnar diameter was calculated based on the projected area and major axis length of each particle, and the aspect ratio was calculated based on the major axis length and columnar diameter. Statistically, the average major axis length of the samples before pressure was 1705 μm, the average columnar diameter was 621 μm, and the average aspect ratio was 2.76. Subsequently, the samples were randomly divided using a sample divider, with 50 cm³ samples taken as the test objects. The total mass of the samples was... The sample of columnar ceramsite proppant, weighing 62.50g, was subjected to a pressure test before the pressure test. The pressure mold includes a mold body and a detachable base. The inner wall of the mold body is polished. The mold body is equipped with a replaceable inner liner. In this embodiment, an inner liner corresponding to the target stress evaluation conditions is selected to maintain the lateral dimension of the pressure-bearing cavity at a predetermined value. The sample to be tested is placed in the pressure mold, and a target closing pressure is applied at a loading rate of 13.8MPa / min on a fully automatic pressure testing machine. The target closing pressure is set to 69MPa, and the pressure is maintained at 69MPa for 2 minutes. After the pressure test is completed, all materials in the pressure mold are removed without damage and sieved according to the preset fine powder sieving rules. Since the sample to be tested in this embodiment has a nominal particle size range, and the lower limit of the nominal particle size range is 425 μm, in the predetermined standard sieve sequence, a first sieve with an aperture value not greater than 425 μm is selected, and then a second sieve with an aperture smaller than the first sieve and adjacent to the first sieve in the predetermined standard sieve sequence is selected as the sieve for fine powder sieving. In this embodiment, a 45-mesh sieve is selected as the sieve for fine powder sieving. After gentle sieving, the mass of particles passing through the fine powder sieve is recorded as the fine powder mass. In this embodiment The weight is 4.38g. The remaining particles on the sieve are used as the sample of remaining particles after pressure testing for subsequent geometric parameter re-measurement; wherein, the mild sieving is a sieving operation performed without introducing secondary crushing of the sample, and the sieving process is based on the principle of allowing fine powder to pass through the sieve while maintaining the original shape of the remaining particles as much as possible.

[0061] Specifically, after the pressure test, approximately 2g to 3g of representative sample was taken from the self-pressurized sample using a sampler. Image acquisition and analysis were then performed on this representative sample. To ensure the comparability of the measurement results before and after the pressure test, the image acquisition magnification, illumination method, image processing parameters, and effective particle selection rules used in the post-pressure test remained consistent with those used in the pre-pressure test. Statistically, in this embodiment, a total of 701 effective particles were obtained from the remaining particle sample after the pressure test. The average major axis length of the post-pressure test sample was 1235μm, the average columnar diameter was 594μm, and the average aspect ratio of the post-pressure test sample was [not specified]. It is 2.08; Based on the average length-to-diameter ratio of the sample before pressure application Average length-to-diameter ratio of the sample after pressure application Total mass and fine powder quality Calculate aspect ratio loss rate The aspect ratio loss rate Calculate according to the following formula:

[0062] Will =2.75 =2.08 =62.50g Substituting 4.38g into the above formula, we get: ≈22.65%; Calculate the mass loss rate and comprehensive crushing index The aforementioned quality loss rate Calculate according to the following formula:

[0063] Will =4.38g Substituting 62.50g, we get: ≈7.01%.

[0064] The comprehensive crushing index Calculate according to the following formula:

[0065] In this embodiment, the weighting coefficient is taken. =0.6, =0.4, substituting the above parameters, we get: ≈13.27%; According to the evaluation criteria of the comprehensive crushing index, when A score of ≤10% is considered excellent, while a score of <10% is considered good. ≤20% is considered acceptable. A loss rate greater than 20% is considered unqualified. Therefore, the anti-fracture performance evaluation result of this batch of columnar ceramsite proppant in this embodiment is qualified. Meanwhile, the calculation results show that although the mass loss rate... Only 7.01%, but the aspect ratio loss rate The ratio reached 22.65%, indicating that this batch of columnar ceramsite proppant, in addition to producing some fine powder after being subjected to pressure, also exhibited significant damage in the length direction and deterioration of its structural morphology. Therefore, this invention, by introducing the aspect ratio loss rate, can reveal structural failure information that is difficult to fully reflect using only the fine powder quality, thus providing a more comprehensive evaluation of the fracture resistance of columnar ceramsite proppant.

[0066] In summary, this embodiment has at least the following technical effects: The invention addresses the differences between columnar ceramsite proppant and spherical proppant in terms of geometric shape, stress mode, and failure mechanism. It constructs an anti-fracture performance evaluation process consisting of geometric parameter measurement before pressure bearing, pressure bearing test, fine powder sieving, and geometric parameter re-measurement after pressure bearing. This process can form a closed-loop evaluation system applicable to columnar ceramsite proppant, thereby making up for the shortcomings of existing spherical proppant evaluation methods that are difficult to accurately apply to columnar particles. By introducing a geometric parameter statistical method based on image acquisition and image analysis, the columnar diameter, aspect ratio, and changes before and after pressure of columnar ceramic proppant can be quantitatively characterized, which improves the objectivity, accuracy, and repeatability of the evaluation process and helps to improve the comparability of evaluation results between different batches of samples. By defining the relative change in the average length-to-diameter ratio before and after pressure as the length-to-diameter ratio loss rate, it can not only reflect the situation where the particles are completely crushed into fine powder, but also reflect the failure modes of incomplete pulverization but structural damage, such as end splitting, middle breakage, and length shortening. This breaks through the limitation of traditional methods that only evaluate crushing performance based on the quality of fine powder, and more comprehensively characterizes the crushing resistance of columnar ceramic proppant. By constructing a comprehensive fragmentation index by weighting the mass loss rate and the aspect ratio loss rate, it is possible to simultaneously take into account the degree of fine powder generation and the degree of change in particle morphology integrity. Furthermore, it is possible to adjust the evaluation focus according to the differences in the sensitivity of different reservoirs to fine powder blockage and the requirements for particle morphology integrity, thereby improving the adaptability of the evaluation results to different engineering application scenarios.

[0067] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance, characterized in that, Includes the following steps: S1: Obtain the columnar ceramsite proppant sample to be tested, and perform image acquisition and image analysis on the columnar ceramsite proppant sample to obtain the geometric parameters of each effective particle in the columnar ceramsite proppant sample to be tested. S2: Based on the obtained geometric parameters, determine the columnar diameter and aspect ratio of each effective particle in the sample before pressure bearing, and statistically obtain the average aspect ratio of the sample before pressure bearing. S3: Obtain the total mass of the columnar ceramsite proppant sample to be tested, place the columnar ceramsite proppant sample to be tested into a pressure mold, apply a target closing pressure, and maintain the pressure under the target closing pressure for a preset time; S4: Recover all materials after pressure is applied and sieve them according to the preset fine powder sieving rules to obtain fine powder quality and residual particle samples; S5: Perform image acquisition and image analysis on the remaining particle sample to obtain the geometric parameters of each effective particle in the sample after pressure bearing, and determine the average aspect ratio of the sample after pressure bearing accordingly. S6: Calculate the aspect ratio loss rate of the columnar ceramsite proppant based on the average aspect ratio of the sample before pressure, the average aspect ratio of the sample after pressure, the total mass, and the mass of the fine powder, and use the aspect ratio loss rate as the evaluation index of the anti-breakage performance of the columnar ceramsite proppant.

2. The method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance according to claim 1, characterized in that, In steps S1 and S5, the image acquisition is performed using an image acquisition unit consisting of an industrial camera, a telecentric lens, an LED parallel light source, and a stage. Before the image acquisition is performed, the image acquisition unit is calibrated using a standard length calibration plate to establish the conversion relationship between the pixel length and the actual length of the particles in the acquired image.

3. The method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance according to claim 1, characterized in that, In steps S1 and S5, the image analysis includes: performing noise reduction, contrast enhancement, threshold segmentation, morphological processing, and connected component recognition on the acquired particle image in sequence to extract the single particle contour; and removing particles whose particle projection contour intersects with the edge of the image acquisition area, particles that overlap or adhere to each other and cannot be reliably segmented, and particles with abnormal postures to obtain effective particles.

4. The method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance according to claim 1, characterized in that, In steps S1 and S5, the geometric parameters include at least the projected area of ​​a single particle and the length of the major axis of a single particle; wherein, the length of the major axis of a single particle is the length of the long side of the minimum bounding rectangle of the two-dimensional projected profile of a single particle; the columnar diameter is calculated based on the projected area of ​​a single particle and the length of the major axis of a single particle, and the aspect ratio is calculated based on the length of the major axis of a single particle and the columnar diameter.

5. The method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance according to claim 1, characterized in that, The average aspect ratio of the sample before pressure is the average aspect ratio of the individual effective particles included in the statistics of the sample before pressure; the average aspect ratio of the sample after pressure is the average aspect ratio of the individual effective particles included in the statistics of the sample after pressure.

6. The method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance according to claim 1, characterized in that, In step S6, the aspect ratio loss rate Calculate using the following formula: in, The average length-to-diameter ratio of the sample before pressure is applied. The average length-to-diameter ratio of the sample after being subjected to pressure. The total mass of the columnar ceramic proppant sample to be tested is [missing information]. For fine powder quality.

7. The method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance according to claim 6, characterized in that, Step S6 also includes calculating the mass loss rate. And based on the said quality loss rate and the aspect ratio loss rate Calculate the comprehensive crushing index ; The mass loss rate Calculate using the following formula: The comprehensive crushing index I f Calculate using the following formula: in, and These are the weighting coefficients.

8. The method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance according to claim 7, characterized in that, The weighting coefficient and satisfy + =1, and 0≤ ≤1, 0≤ ≤1; and, according to the comprehensive crushing index When evaluating columnar ceramsite proppant, the following conditions must be met: ≤10% is considered excellent, and 10% < ≤20% is considered qualified, meeting the requirements. A percentage greater than 20% is considered unqualified.

9. The method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance according to claim 1, characterized in that, In step S3, the pressure-bearing mold includes a mold body and a detachable base. The inner wall of the mold body is polished to reduce the frictional impact between the particles and the sidewall. The mold body is provided with a replaceable inner liner. By adjusting the specifications of the inner liner, the lateral dimension of the mold body cavity can be changed to adapt to the stress evaluation requirements of columnar ceramic proppant under different crack width conditions.

10. The method for quantitative determination of columnar ceramsite proppant morphology and evaluation of its anti-fracture performance according to any one of claims 1 to 9, characterized in that, In step S4, the preset fine powder sieving rule is as follows: When the columnar ceramsite proppant sample to be tested has a nominal particle size classification range, the lower limit of the nominal particle size classification range is used as a benchmark. In the predetermined standard sieve sequence, the first sieve with a pore size value not greater than the lower limit of the nominal particle size classification range and closest to it is selected first. Then, the second sieve with a pore size smaller than the first sieve and adjacent to the first sieve in the predetermined standard sieve sequence is selected as the sieve for fine powder sieving. When the columnar ceramic proppant sample to be tested does not have a nominal particle size grading range, the 10th percentile value of the effective columnar particle diameter data included in the statistics before pressure is taken as the lower limit of the particle size range, and a sieve for fine powder screening is selected in the manner described above; and the particle mass passing through the sieve for fine powder screening is recorded as the fine powder mass.

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