CN117347401B - Multidimensional quantitative characterization method for damage to coal macro-micro structure by embedding propping agent - Google Patents
Multidimensional quantitative characterization method for damage to coal macro-micro structure by embedding propping agent Download PDFInfo
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- 239000003245 coal Substances 0.000 title claims abstract description 113
- 230000006378 damage Effects 0.000 title claims abstract description 77
- 239000003795 chemical substances by application Substances 0.000 title claims abstract description 63
- 238000012512 characterization method Methods 0.000 title claims abstract description 62
- 238000003384 imaging method Methods 0.000 claims abstract description 22
- 230000003287 optical effect Effects 0.000 claims abstract description 12
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- 230000008859 change Effects 0.000 claims description 21
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- 239000006004 Quartz sand Substances 0.000 claims description 10
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 10
- 238000003825 pressing Methods 0.000 claims description 10
- 238000012634 optical imaging Methods 0.000 claims description 8
- 239000002245 particle Substances 0.000 claims description 7
- 238000000576 coating method Methods 0.000 claims description 6
- 229920002379 silicone rubber Polymers 0.000 claims description 6
- 238000005530 etching Methods 0.000 claims description 5
- 238000005498 polishing Methods 0.000 claims description 4
- 239000011248 coating agent Substances 0.000 claims description 3
- 239000000470 constituent Substances 0.000 claims description 3
- 239000004447 silicone coating Substances 0.000 claims description 3
- 239000004945 silicone rubber Substances 0.000 claims description 3
- 229920001169 thermoplastic Polymers 0.000 claims description 3
- 239000004416 thermosoftening plastic Substances 0.000 claims description 3
- 239000011800 void material Substances 0.000 claims description 3
- 238000005303 weighing Methods 0.000 claims description 3
- 230000006835 compression Effects 0.000 claims 1
- 238000007906 compression Methods 0.000 claims 1
- 230000007547 defect Effects 0.000 abstract description 3
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 8
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- 239000001307 helium Substances 0.000 description 6
- 229910052734 helium Inorganic materials 0.000 description 6
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 6
- 238000010329 laser etching Methods 0.000 description 4
- 239000002390 adhesive tape Substances 0.000 description 3
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
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- 229910052799 carbon Inorganic materials 0.000 description 1
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- 238000003698 laser cutting Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
- G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
- G01N23/046—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material using tomography, e.g. computed tomography [CT]
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/088—Investigating volume, surface area, size or distribution of pores; Porosimetry
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/21—Polarisation-affecting properties
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
Abstract
The invention discloses a multidimensional quantitative characterization method for damage to a coal macro-micro structure by proppant embedding, which belongs to the technical field of proppant embedding and comprises the following steps: processing and obtaining a cylindrical coal sample; quantitatively characterizing macro-micro structural characteristics of the coal sample; cutting the coal sample to obtain a first microscopic feature of a section and a three-dimensional imaging result; carrying out proppant paving on the cut coal sample to obtain macro-micro structural characteristics; applying confining pressure to the sample, and obtaining three-dimensional macroscopic quantitative characterization after removing the confining pressure; cleaning a section of the core holder proppant sample to obtain a second microscopic feature; comparing the first microscopic feature with the second microscopic feature, and performing two-dimensional microscopic quantitative characterization; optical three-dimensional imaging is carried out on the section after cleaning, and three-dimensional microscopic quantitative characterization is obtained; and obtaining two-dimensional and three-dimensional joint characterization of the damage degree of the macro-fine structure of the coal sample based on all the characteristics. The invention makes up the defect that the prior art cannot accurately and quantitatively characterize the damage degree of propping agent to coal bodies.
Description
Technical Field
The invention belongs to the technical field of proppant embedding, and particularly relates to a multidimensional quantitative characterization method for damage of a coal macro-micro structure by proppant embedding.
Background
The main component of the coalbed methane is methane (CH) 4 ) Is mainly in the adsorption state in the coal seam. The hypotonic nature of coal reservoirs determines that reservoir reformation techniques are typically required for coalbed methane development to increase the single well yield of coalbed methane. The hydraulic fracturing technology is one of the most main reservoir reconstruction technologies at present, and by the hydraulic fracturing technology, fracturing cracks with high-efficiency diversion capability can be formed in the reservoir, so that the yield increase reconstruction of the coal-bed gas well is realized.
The propping agent is paved in the fracturing process, so that the formed fracturing cracks can be continuously expanded and effectively supported, further improvement is achieved, and the diversion capacity of the fracturing cracks can be reduced due to the embedding phenomenon of the propping agent in the cracks. Meanwhile, the proppant is embedded under the condition of reservoir closing pressure to damage the coal body to a certain extent, and the flow conductivity reduction caused by the damage of the coal body also has a great influence.
Therefore, in the proppant embedding experiment, the embedding degree of the proppant after embedding can be measured at the present stage, but the damage degree of the proppant after embedding to the macro-micro structure of the coal body does not have an accurate quantitative characterization method.
Disclosure of Invention
The invention aims to solve the defects of the prior art and provides a multidimensional quantitative characterization method for damage to a coal macro-micro structure by embedding a propping agent.
In order to achieve the above object, the present invention provides the following solutions:
a multi-dimensional quantitative characterization method for damage to a coal macro-micro structure by proppant embedding, comprising the following steps:
s1: etching a massive coal sample, and processing and obtaining a cylindrical coal sample; performing X-ray CT scanning on the coal sample, and quantitatively characterizing macro-micro structural characteristics of the coal sample in a zoned manner;
s2: cutting the coal sample, polishing a cut surface, carrying out polarized light microscopic observation to obtain a first microscopic feature of the cut surface, and carrying out three-dimensional optical imaging on the cut surface to obtain a three-dimensional imaging result;
s3: performing proppant paving on the cut coal sample to obtain a core clamp proppant sample, and performing X-ray CT scanning to obtain macro-micro structural characteristics of the core clamp proppant sample;
s4: applying confining pressure to the core clamp propping agent sample, and after removing the confining pressure, performing X-ray CT scanning and three-dimensional optical imaging on the core clamp propping agent sample from which the confining pressure is removed to obtain three-dimensional macroscopic quantitative characterization of the structural damage of the coal sample caused by the embedding of propping agent;
s5: cleaning a section of the core holder proppant sample, and carrying out polarized light microscopic observation on the cleaned section to obtain a second microscopic feature; comparing the first microscopic feature with the second microscopic feature, and carrying out two-dimensional microscopic quantitative characterization on the microscopic structural damage of the coal sample caused by proppant embedding in a two-dimensional angle;
s6: optical three-dimensional imaging is carried out on the section after cleaning, and three-dimensional microscopic quantitative characterization of the structural damage of the coal sample caused by embedding of the propping agent is obtained;
s7: and obtaining a two-dimensional and three-dimensional joint representation of the damage degree of the macro-micro structure of the coal sample based on the macro-micro structure feature, the three-dimensional imaging result, the three-dimensional macro quantitative representation, the two-dimensional micro quantitative representation and the three-dimensional micro quantitative representation.
Preferably, in step S1, the macro-micro structural features include micro component distribution, fracture distribution state, porosity and fracture volume ratio of the coal sample.
Preferably, in step S2, the first microscopic feature includes a distribution state of microscopic components of the tangential plane, different contents of microscopic components, and a fracture opening.
Preferably, in step S3, the method for laying the propping agent on the cut coal sample comprises the following steps:
coating silicon rubber on the polished section;
selecting a quartz sand propping agent with a corresponding mesh number, weighing the required mass of the quartz sand propping agent according to the area of the section coated with the silicone rubber, and coating the quartz sand propping agent on the section;
and (3) aligning and fixing the two halves of the coal sample, and performing thermoplastic wrapping to finish the laying of the propping agent.
Preferably, in step S4, the three-dimensional macroscopic quantitative characterization includes proppant embedding depth, embedding range, embedding state, microcomponent occurrence state, porosity size, pore crack occurrence state, and pore volume ratio.
Preferably, in step S5, the method for performing two-dimensional microscopic quantitative characterization includes:
carrying out polarized light microscopic observation on the section after cleaning, dividing area grids by taking 5mm as a reference, and mutually conforming to an observation area for obtaining the first microscopic features to obtain damage difference caused by embedding propping agents among different microscopic components in each area grid, and dividing the embedding diameter or the embedding radius of an embedding recess and the change condition of crack opening degree caused by each propping agent based on a preset scale standard;
and carrying out data statistics on the embedding diameter or the embedding radius and the fracture opening degree change condition to finish two-dimensional microscopic quantitative characterization of the coal sample microscopic structure damage caused by the proppant embedding in a two-dimensional angle.
Preferably, in step S7, the two-dimensional and three-dimensional joint characterization of the damage degree of the macro-micro structure of the coal sample includes quantitatively characterizing the damage degree between different components of the coal sample from two-dimensional and three-dimensional layers and quantitatively characterizing the damage degree of the macro-micro structure of the coal sample based on the damage coefficient.
Preferably, the method for quantitatively characterizing the damage degree of the macro-micro structure of the coal sample comprises the following steps:
obtaining the press-fit radius and the press-fit depth in different micro-components based on the embedding degree of the propping agent and the proportion of the propping agent; obtaining the damage coefficient of the propping agent to the coal sample section based on the press-fit radius and the press-fit depth; wherein the press-fit radius and the press-fit depth are based on the particle size of the propping agent;
based on the destruction coefficient, the porosity change rate and the fracture volume ratio change rate, finishing quantitative characterization of the destruction degree of the macro-micro structure of the coal sample;
wherein, the formula of the destruction coefficient is as follows:
in the method, in the process of the invention,respectively the transverse and longitudinal destruction coefficients, < >>The embedding distance is respectively the transverse embedding distance and the longitudinal embedding distance with the greatest frequency, and the embedding distance is +.>Is the particle size of the selected proppants; i represents the different microcomponent constituents, i=1, 2,3 …, n;
the rate of change formula is as follows:
in the method, in the process of the invention,for porosity change rate, ++>For the rate of change of the fracture volume ratio>The volume of the coal sample before and after pressing is the volume of the coal sample before and after pressing; />The pore volume before pressing and the fracture volume before pressing are respectively; />The post-press void volume and the post-press fracture volume, respectively.
Compared with the prior art, the invention has the beneficial effects that: through processing the coal sample and embedding the proppant experiments, through polarized light microscopic observation, optical three-dimensional observation and X-ray scanning observation, the characteristic structure extraction from multidimensional and macro-micro angle realizes the accurate quantitative characterization of the proppant to the damage degree of the coal body, and overcomes the defect that the proppant cannot be accurately and quantitatively characterized to the damage degree of the coal body in the prior art.
Drawings
In order to more clearly illustrate the technical solutions of the present invention, the drawings that are needed in the embodiments are briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a multi-dimensional quantitative characterization method of the damage of a macro-micro structure of coal by proppant embedding in an embodiment of the invention;
FIG. 2 is a graph of macro-micro structural features and a graph of pore gap statistics in a coal sample according to an embodiment of the present invention; wherein, (a) is CT scanning result; (b) is an Avizo processing result; (c) a pore fracture feature statistical graph;
FIG. 3 is a view of a polarized light microscope showing a cut-away sample surface according to an embodiment of the present invention;
FIG. 4 is a graph showing the result of optical three-dimensional imaging of a section of a sample according to an embodiment of the present invention;
FIG. 5 is a graph showing the occurrence of proppant in a sample after Avizo treatment according to an embodiment of the present invention;
FIG. 6 is a graph of the results of optical three-dimensional imaging embedding after proppant embedding in accordance with an embodiment of the present invention;
FIG. 7 is a diagram of a characteristic relationship according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of a proppant pack experimental set-up according to an embodiment of the invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Example 1
In order to realize the multidimensional quantitative characterization method of the damage of the proppant embedding to the macro-micro structure of the coal, the device adopted by the invention comprises the following steps: laser etching instrument, X-ray CT scanning equipment, polarizing microscope, optical three-dimensional imaging instrument and proppant embedding experimental device;
the laser etching instrument is used for etching coal samples in a proper range on the large coal samples;
the polarized light microscope is used for carrying out microscopic observation on the coal sample to obtain microscopic characteristics, namely two-dimensional quantitative characterization;
the X-ray CT scanning device is used for carrying out X-ray CT scanning on the coal sample;
the optical three-dimensional imaging instrument is used for carrying out three-dimensional optical imaging on the coal sample;
taking structural characteristics obtained by the X-ray CT scanning equipment and an optical three-dimensional imaging instrument as three-dimensional quantitative characterization;
the proppant embedding experimental device is used for embedding the propping agent into the coal sample;
specifically, the proppant embedding experimental device comprises a computer, a control air valve, a core holder, a confining pressure sensor, a hand-operated confining pressure pump, a flowmeter and a helium (He) bottle; the connection is shown in fig. 8.
A helium (He) bottle for holding helium, and introducing helium after the core sample is pressed and embedded to determine the variation degree of the sample permeability;
the control air valve is used for controlling the circulation of the displacement gas helium;
the rock core holder is used for placing the prepared coal sample and applying confining pressure to carry out a press-fit experiment;
the confining pressure sensor is used for monitoring the magnitude of confining pressure applied to the sample in the pressure embedding process;
the hand-operated confining pressure pump is used for pumping liquid into the confining pressure cavity through the hand-operated pressurizing pump to apply confining pressure to the sample;
a flow meter for recording the magnitude of helium flow through the core holder;
and the computer is used for controlling the device and performing software operation.
Example two
As shown in fig. 1, a multi-dimensional quantitative characterization method for the damage of a macro-micro structure of coal by proppant embedding comprises the following steps:
s1: etching a massive coal sample, and processing and obtaining a cylindrical coal sample; carrying out X-ray CT scanning on the coal sample, and quantitatively characterizing macro-micro structural characteristics of the coal sample in a zoned manner;
a further embodiment is that,
and (3) etching a sample in a proper range on a large coal sample by using a laser etching instrument, enabling two circular surfaces of the sample to be parallel to the layering direction and the side surfaces of the sample to be perpendicular to the layering direction, and then processing the sample into a cylindrical sample with the diameter of 2.5cm and the height of 5cm by using a linear cutting machine.
As shown in fig. 2, wherein (a) is a CT scan result; (b) is an Avizo processing result; (c) a pore fracture feature statistical graph; and (3) carrying out X-ray CT scanning imaging on the processed sample, describing a macro-micro structure of the coal sample by using Avizo software after scanning, sharpening by using Media Filter filtering, selecting the whole sample by using Interactive Thresholding algorithm and establishing a template mask, selecting corresponding gray values according to different sample characteristics by using Top-Hat threshold algorithm to carry out threshold segmentation on the macro-micro structure, and quantitatively analyzing the characteristics of fracture volume, porosity and the like by using volume fraction module after extracting the macro-micro structure. Dividing the extraction process into a plurality of regions by regional grids, quantitatively describing macro-micro structural features in each region by taking 5mm as a reference,
in step S1, macro-micro structural features include micro component distribution, pore crack distribution state, porosity and crack volume ratio of the coal sample.
S2: cutting a coal sample, polishing a cut surface, carrying out polarized light microscopic observation to obtain a first microscopic feature of the cut surface, and carrying out three-dimensional optical imaging on the cut surface to obtain a three-dimensional imaging result; as shown in fig. 3-4.
A further embodiment is that in step S2, the first microfeatures comprise the distribution of the microcomponents of the cut surface, the different microcomponents content and the fracture opening.
Cutting the marked sample by using a laser cutting machine perpendicular to a layering surface, polishing a cut surface, dividing the cut surface into a plurality of areas by using a laser etching instrument with each 5mm as a reference, observing the characteristics of microscopic component distribution states, different microscopic component contents, crack opening and the like in grids of each area under a polarizing microscope, and imaging the surface of the cut surface by adopting optical three-dimensional imaging for marking and expressing.
S3: as shown in fig. 5, a propping agent is paved on a cut coal sample to obtain a core clamping propping agent sample, an X-ray CT scan is performed, an Avizo software is used for processing and extracting a macro-micro structure, and the propping agent occurrence state and the section surface state in an artificial joint are clarified after the sample is paved and before confining pressure is applied, so that macro-micro structure characteristics (propping agent occurrence state and section surface state) of the core clamping propping agent sample are obtained;
in a further embodiment, in step S3, the method for laying the propping agent on the cut coal sample comprises the following steps:
coating silicon rubber on the polished section;
selecting a quartz sand propping agent with a corresponding mesh number, weighing the required mass of the quartz sand propping agent according to the area of the section coated with the silicone rubber, and coating the quartz sand propping agent on the section;
and (3) aligning and placing the two halves of coal samples, fixing the two halves of coal samples by using transparent adhesive tapes, cutting the range of the adhesive tapes beyond the side surfaces, and wrapping the two halves of coal samples by using a hot air gun to finish the laying of the propping agent.
S4: applying confining pressure to the core clamp propping agent sample, after removing the confining pressure, performing X-ray CT scanning and three-dimensional optical imaging on the core clamp propping agent sample from which the confining pressure is removed, and obtaining three-dimensional macroscopic quantitative characterization of the structural damage of the coal sample caused by proppant embedding; as shown in fig. 6.
A further embodiment is that in step S4, the three-dimensional macroscopic quantitative characterization includes proppant embedding depth, embedding range, embedding state, microcomponent occurrence state, porosity size, pore crack occurrence state, and pore volume ratio.
Specifically, the prepared sample is placed in a core holder, the front end and the rear end are fixed, a hand-operated confining pressure pump is connected with confining pressure, confining pressure is applied according to preset closing pressure, and the sample is kept for a certain time t until the proppant is stopped being embedded. After the proppant is stopped to be embedded, the confining pressure is removed, the cylindrical model is taken out of the core holder, the original state of the cylindrical model is kept to be rapidly subjected to X-ray CT scanning in order to avoid the change of the embedding state along with time, the macro-micro structure is extracted and processed by using Avizo software after the scanning, the area is also divided into grids in the processing process, the proppant embedding effect of a sample section after each area is embedded in a macroscopic angle is clarified, and the characteristic of embedding depth, embedding range, proppant embedding state, microscopic component occurrence state, porosity size, pore crack occurrence state, pore volume ratio and the like of the proppant is included, and the macroscopic damage of a coal body caused by the proppant embedding is quantitatively characterized in a three-dimensional aspect.
S5: cleaning a section of the core clamping propping agent sample, and carrying out polarized light microscopic observation on the cleaned section to obtain a second microscopic feature; comparing the first microscopic feature with the second microscopic feature, and carrying out two-dimensional microscopic quantitative characterization on the microscopic structural damage of the coal sample caused by proppant embedding in a two-dimensional angle;
and taking down the thermoplastic film on the surface of the sample after the extraction treatment, using a blade to scratch the transparent adhesive tape wrapped on the surface of the sample, exposing the section paved with the propping agent, flushing the surface paved with the propping agent with clean water, and slightly wiping until all quartz sand is washed off.
In a further embodiment, in step S5, the method for performing two-dimensional microscopic quantitative characterization is as follows:
carrying out polarized light microscopic observation on the section after cleaning, dividing area grids by taking 5mm as a reference, and mutually conforming to an observation area for obtaining first microscopic features to obtain damage difference caused by embedding propping agents among different microscopic components in each area grid, and dividing the embedding diameter or embedding radius of an embedding recess and the change condition of crack opening degree caused by each propping agent based on a preset scale standard;
and (3) importing the variation condition of the embedded diameter or the embedded radius and the fracture opening into Origin software for data statistics, and completing the two-dimensional microscopic quantitative characterization of the coal sample microscopic structural damage caused by the proppant embedding in a two-dimensional angle.
S6: optical three-dimensional imaging is carried out on the section after cleaning, and three-dimensional microscopic quantitative characterization of the structural damage of the coal sample caused by embedding of the propping agent is obtained;
specifically, the observed sample is placed in an optical three-dimensional imaging instrument, region grid division is carried out on the basis of 5mm to form a plurality of regions, three-dimensional imaging is carried out on embedded pits caused by propping agents every 1mm in each region, shooting errors generated by edges are eliminated, the embedded pits in the middle of each photo are selected, 2-3 pits are selected in each photo, and therefore the damage degree of propping agents to coal bodies in the transverse direction and the vertical direction in each region is obtained on a mesoscopic layer.
S7: based on macro-micro structural features, three-dimensional imaging results, three-dimensional macro quantitative characterization, two-dimensional micro quantitative characterization and three-dimensional micro quantitative characterization, the two-dimensional and three-dimensional combined characterization of the damage degree of the macro-micro structure of the coal sample is obtained.
A further embodiment is that in step S7, the two-dimensional and three-dimensional joint characterization of the degree of damage of the macro-micro structure of the coal sample includes quantitative characterization of the degree of damage between different components of the coal sample from two-dimensional and three-dimensional levels and quantitative characterization of the degree of damage of the macro-micro structure of the coal sample based on the damage coefficient. As shown in fig. 7.
In particular, regarding the characterization of the damage degree of the coal sample, the two-dimensional quantitative characterization is obtained by the observation of a polarized light microscope, and the three-dimensional quantitative characterization is obtained by the three-dimensional optical imaging and the X-ray CT scanning.
Wherein, the specific damage degree characterization comprises micro component damage characteristics, pore damage characteristics, fracture damage characteristics and embedded concave characteristics;
the microcomponent disruption features include: average diameter and depth of mirror coal + bright coal single pit embedding, average diameter and depth of dark coal + wire carbon single pit embedding and average diameter and depth of area different microcomponents embedding;
the pore disruption features include: the differences of pore and pore throat number, pore throat and throat distribution, pore and Kong Hou volume ratio/surface area;
the fracture failure feature includes: region, overall fracture spread difference, region, overall fracture opening difference, fracture volume/surface area difference;
the embedded recessed features include: the average diameter and average depth of the whole embedding, the average diameter and average depth of the region embedding, and the ratio of the particle diameters of the region embedding.
The method is characterized in that after imaging of all areas is finished, photoshop software is used, the diameter and depth of the embedded recess of the propping agent are measured by taking the scale as a standard, after the measurement is finished, all the data of the embedded diameter and the embedded depth in the sample are imported into Origin software for data statistics and analysis, the two-dimensional measurement result under a polarizing microscope is combined, the data of each microscopic component are classified by taking the microscopic component as a reference, the data of each microscopic component are subjected to frequency analysis, so that differences of embedding degrees of the propping agent among different microscopic components are observed and compared, and the damage degree among different components of a coal body is quantitatively represented from the two-dimensional layer and the three-dimensional layer.
A further embodiment is that the method for quantitatively characterizing the damage degree of the macro-micro structure of the coal sample comprises the following steps:
obtaining the press-fit radius and the press-fit depth in different micro-components based on the embedding degree of the propping agent and the proportion of the propping agent; based on the press-fit radius and the press-fit depth, obtaining the damage coefficient of the propping agent to the coal sample section; wherein, the press-fit radius and the press-fit depth are based on the particle size of the propping agent;
based on the destruction coefficient, the porosity change rate and the fracture volume ratio change rate, the quantitative characterization of the destruction degree of the macro-micro structure of the coal sample is completed;
wherein, the formula of the destruction coefficient is as follows:
in the method, in the process of the invention,respectively the transverse and longitudinal destruction coefficients; />The horizontal embedding distance and the longitudinal embedding distance with the largest frequency are respectively; />Particle size for the proppant selected; i is the number representing the different microcomponent constituents, i=1, 2,3 …, n;
the rate of change formula is as follows:
in the method, in the process of the invention,for porosity change rate, ++>Is the fracture volume ratioRate of change (I/O)>The volume of the coal sample before and after pressing is the volume of the coal sample before and after pressing; />The pore volume before pressing and the fracture volume before pressing are respectively; />The post-press void volume and the post-press fracture volume, respectively.
The above embodiments are merely illustrative of the preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but various modifications and improvements made by those skilled in the art to which the present invention pertains are made without departing from the spirit of the present invention, and all modifications and improvements fall within the scope of the present invention as defined in the appended claims.
Claims (5)
1. A multi-dimensional quantitative characterization method for damage to a coal macro-micro structure by proppant embedding, which is characterized by comprising the following steps:
s1: etching a massive coal sample, and processing and obtaining a cylindrical coal sample; performing X-ray CT scanning on the coal sample, and quantitatively characterizing macro-micro structural characteristics of the coal sample in a zoned manner;
s2: cutting the coal sample, polishing a cut surface, carrying out polarized light microscopic observation to obtain a first microscopic feature of the cut surface, and carrying out three-dimensional optical imaging on the cut surface to obtain a three-dimensional imaging result;
s3: performing proppant paving on the cut coal sample to obtain a core clamp proppant sample, and performing X-ray CT scanning to obtain macro-micro structural characteristics of the core clamp proppant sample;
s4: applying confining pressure to the core clamp propping agent sample, and after removing the confining pressure, performing X-ray CT scanning and three-dimensional optical imaging on the core clamp propping agent sample from which the confining pressure is removed to obtain three-dimensional macroscopic quantitative characterization of the structural damage of the coal sample caused by the embedding of propping agent;
s5: cleaning a section of the core holder proppant sample, and carrying out polarized light microscopic observation on the cleaned section to obtain a second microscopic feature; comparing the first microscopic feature with the second microscopic feature, and carrying out two-dimensional microscopic quantitative characterization on the microscopic structural damage of the coal sample caused by proppant embedding in a two-dimensional angle;
in step S5, the method for performing two-dimensional microscopic quantitative characterization includes:
carrying out polarized light microscopic observation on the section after cleaning, dividing area grids by taking 5mm as a reference, and mutually conforming to an observation area for obtaining the first microscopic features to obtain damage difference caused by embedding propping agents among different microscopic components in each area grid, and dividing the embedding diameter or the embedding radius of an embedding recess and the change condition of crack opening degree caused by each propping agent based on a preset scale standard;
carrying out data statistics on the embedding diameter or the embedding radius and the fracture opening degree change condition to finish two-dimensional microscopic quantitative characterization of the coal sample microscopic structure damage caused by the proppant embedding in a two-dimensional angle;
s6: optical three-dimensional imaging is carried out on the section after cleaning, and three-dimensional microscopic quantitative characterization of the structural damage of the coal sample caused by embedding of the propping agent is obtained;
s7: based on the macro-micro structural features, the three-dimensional imaging results, the three-dimensional macro quantitative characterization, the two-dimensional micro quantitative characterization and the three-dimensional micro quantitative characterization, obtaining a two-dimensional and three-dimensional joint characterization of the damage degree of the macro-micro structure of the coal sample;
in the step S7, the two-dimensional and three-dimensional combined characterization of the damage degree of the macro-micro structure of the coal sample comprises the quantitative characterization of the damage degree between different components of the coal sample from the two-dimensional and three-dimensional layers and the quantitative characterization of the damage degree of the macro-micro structure of the coal sample based on the damage coefficient;
the method for quantitatively characterizing the damage degree of the macro-micro structure of the coal sample comprises the following steps:
obtaining the press-fit radius and the press-fit depth in different micro-components based on the embedding degree of the propping agent and the proportion of the propping agent; obtaining the damage coefficient of the propping agent to the coal sample section based on the press-fit radius and the press-fit depth; wherein the press-fit radius and the press-fit depth are based on the particle size of the propping agent;
based on the destruction coefficient, the porosity change rate and the fracture volume ratio change rate, finishing quantitative characterization of the destruction degree of the macro-micro structure of the coal sample;
wherein, the formula of the destruction coefficient is as follows:
in (1) the->Respectively the transverse and longitudinal destruction coefficients, < >>The embedding distance is respectively the transverse embedding distance and the longitudinal embedding distance with the greatest frequency, and the embedding distance is +.>Is the particle size of the selected proppants; i represents the different microcomponent constituents, i=1, 2,3 …, n;
the rate of change formula is as follows:
in (1) the->For porosity change rate, ++>For the rate of change of the fracture volume ratio>The volume of the coal sample before and after pressing is the volume of the coal sample before and after pressing; />Respectively is a pore before pressingVolume and fracture volume before compression; />The post-press void volume and the post-press fracture volume, respectively.
2. The method of multi-dimensional quantitative characterization of the damage to the macro-micro structure of coal by proppant embedment according to claim 1, wherein in step S1, the macro-micro structural features include micro component distribution, pore fracture distribution state, porosity and fracture volume ratio of the coal sample.
3. The method of multi-dimensional quantitative characterization of the damage to the macro-micro structure of coal by proppant embedment according to claim 1, wherein in step S2, the first microfeatures comprise the distribution state of the microcomponents of the tangential plane, the different microcomponents content and the fracture opening.
4. The method for multi-dimensional quantitative characterization of the damage to the macro-micro structure of coal by the proppant embedding according to claim 1, wherein in the step S3, the method for laying the propping agent on the cut coal sample is as follows:
coating silicon rubber on the polished section;
selecting a quartz sand propping agent with a corresponding mesh number, weighing the required mass of the quartz sand propping agent according to the area of the section coated with the silicone rubber, and coating the quartz sand propping agent on the section;
and (3) aligning and fixing the two halves of the coal sample, and performing thermoplastic wrapping to finish the laying of the propping agent.
5. The method of multi-dimensional quantitative characterization of the damage to the macro-micro structure of coal by proppant embedding according to claim 1, wherein in step S4, the three-dimensional macro-quantitative characterization comprises proppant embedding depth, embedding range, embedding state, microcomponent occurrence state, porosity size, pore crack occurrence state and pore volume ratio.
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