CN114577673B - Pore wettability NMR characterization method of equal-particle-size pulverized coal - Google Patents
Pore wettability NMR characterization method of equal-particle-size pulverized coal Download PDFInfo
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- 239000011148 porous material Substances 0.000 title claims abstract description 108
- 239000003245 coal Substances 0.000 title claims abstract description 95
- 238000012512 characterization method Methods 0.000 title claims abstract description 19
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 108
- 239000002245 particle Substances 0.000 claims abstract description 88
- 238000002347 injection Methods 0.000 claims abstract description 42
- 239000007924 injection Substances 0.000 claims abstract description 42
- 238000009736 wetting Methods 0.000 claims abstract description 34
- 239000002817 coal dust Substances 0.000 claims abstract description 23
- 238000000034 method Methods 0.000 claims abstract description 17
- 230000014509 gene expression Effects 0.000 claims abstract description 16
- 229920006395 saturated elastomer Polymers 0.000 claims abstract description 16
- 238000012417 linear regression Methods 0.000 claims abstract description 9
- 239000000843 powder Substances 0.000 claims description 17
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- 238000005481 NMR spectroscopy Methods 0.000 description 36
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- 238000004364 calculation method Methods 0.000 description 3
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- 239000000463 material Substances 0.000 description 3
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- 238000012360 testing method Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 2
- 239000004810 polytetrafluoroethylene Substances 0.000 description 2
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- 239000011800 void material Substances 0.000 description 2
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
- G01N24/08—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects by using nuclear magnetic resonance
- G01N24/081—Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
- Y02A90/30—Assessment of water resources
Abstract
The invention provides a pore wettability NMR characterization method of equal-particle-size pulverized coal, comprising the following steps of S1, respectively dripping quantitative water into pulverized coal samples with various particle sizes, and measuring the NMR transverse relaxation time T of the pulverized coal samples with various particle sizes 2 The method comprises the steps of carrying out a first treatment on the surface of the Step S2, measuring the NMR transverse relaxation time T of the coal dust sample with each particle size in a saturated state 2 'A'; step S3, according to NMR transverse relaxation time T in saturated state 2 ' doing a linear regression graph; step S4, determining the equivalent wetting aperture R of the wetting area g The method comprises the steps of carrying out a first treatment on the surface of the And S5, drawing a linear fitting curve of the equivalent wetting aperture and the particle size of the coal dust sample, so as to determine a pore wettability expression. The method can obtain the wetting characteristic of the coal reservoir, can facilitate mutual comparison of different (or same) particle size or different (or same) pore size, has important significance in potential productivity evaluation of the reservoir and process optimization of various links of development and production, and has the significance in aspects of coal seam water injection outburst elimination, coal seam hydraulic fracturing and the like.
Description
Technical Field
The invention belongs to the technical field of coal wettability characterization research, and particularly relates to a pore wettability NMR characterization method of equal-particle-size pulverized coal.
Background
Pore wettability is specific to coal reservoir fluid migration and distribution, and CO 2 Geological sequestration, water flooding efficiency and development and utilization of coalbed methane have important roles. As a porous medium, compared with the surface wettability, the porous wettability considers the influence of complex pore structures, physicochemical properties and the like on the wetting environment more, and has a more practical guiding significance. However, the prior research on the wettability of the pores has two defects, namely, the wettability of the pores is often indirectly characterized by a traditional surface wettability characterization method (contact angle method), but the simple characterization relationship is questioned in the world; secondly, the study object of pore wettability is simplified into the contact angle characterization of a capillary glass tube, and the guiding value of the pore wettability of a real material (such as coal) is also questionable. Limitations exist in both aspects that greatly limit the guidance of pore wettability for practical engineering. In view of the prior art, it is necessary to propose a pore wettability characterization method for an actual coal material, so as to objectively reflect the wetting environment and the wetting capability of the actual material.
Accordingly, there is a need to provide an improved solution to the above-mentioned deficiencies of the prior art.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a pore wettability NMR characterization method of equal-particle-size pulverized coal.
In order to achieve the above object, the present invention provides the following technical solutions:
a pore wettability NMR characterization method of an equiparticle size pulverized coal, comprising:
step S1, respectively dripping quantitative water into pulverized coal samples with various particle sizes to measure the NMR transverse relaxation time T of the pulverized coal samples with each particle size 2 ；
Step S2, measuring the NMR transverse relaxation time T of the coal dust sample with each particle size in a saturated state 2 '；
Step S3, according to NMR transverse relaxation time T in saturated state 2 ' Linear regression drawing and determining the surface relaxation rate rho of the coal powder sample 2 ；
Step S4, according to the surface relaxation rate ρ 2 And NMR transverse relaxation time T of pulverized coal sample of each particle size 2 Equivalent wetting aperture R together defining a wetting zone g ；
And S5, drawing a linear fitting curve of the equivalent wetting aperture and the particle size of the coal dust sample, so as to determine a pore wettability expression.
Preferably, the coal dust sample water treatment is performed by a saturation vessel comprising:
a housing, the housing being a hollow cylinder;
the lower centralizer is connected to the lower end of the shell and is provided with a plurality of lower water holes which are opposite to the inner cavity of the shell;
the upper centralizer is axially and slidably assembled in the shell along the shell, a conical groove is formed above the upper centralizer, a plurality of upper water passing holes extending along the shell axially are formed in the inner wall of the conical groove, and a coal dust sample is arranged between the upper centralizer and the lower centralizer;
the water injection pressure head is provided with a conical bottom matched with the conical groove, a water injection hole corresponding to the conical groove is formed in the conical bottom, and the water injection pressure head is correspondingly connected with a water source so as to inject water into the coal dust sample.
Preferably, the water drain hole and the water injection hole correspond to each other in an axial direction of the housing;
and the upper centralizer and the water injection pressure head are respectively provided with a central hole, and the central holes and the shell are coaxially arranged.
Preferably, the water injection pressure head is removed, quantitative water is injected into the central hole through an injector, and after quantitative water is dripped for 24 hours, the NMR transverse relaxation time T of the coal dust sample with each particle size is measured 2 。
Preferably, the NMR transverse relaxation time T of the pulverized coal sample of the particle size to be seeded 2 And after the measurement is completed, continuously injecting water into the coal powder sample through the water injection pressure head so as to enable the coal powder sample to reach a saturated state.
Preferably, in step S3, the surface relaxation rate ρ of the pulverized coal sample 2 Is the slope of the straight line of the linear regression graph made.
Preferably, in step S4, the equivalent wetting aperture R g Determined according to the following formula:
wherein: r is R i To wet the pore size, A i To wet the signal amplitude corresponding to the aperture, A total For the signal amplitude corresponding to the whole aperture range, R g Is the equivalent wetted pore size of the wetted area.
Preferably, the pore wettability expression is:
wherein: a. b is a fitting parameter; r is (r) g The particle diameter of the pulverized coal particles is r s Being the size of inter-particulate pores, α is the correlation coefficient based on the assumption of extreme packing.
Preferably, the values of a, b in the pore wettability expression are determined by plotting a linear fit curve of equivalent wetting pore size versus various particle size dimensions.
Preferably, the relationship between particle size and inter-particle pore size can be reflected by the following formula:
wherein: r is (r) s Being the size of inter-particulate pores, α is the correlation coefficient based on the assumption of extreme packing.
The beneficial effects are that: the invention provides a pore wettability NMR characterization method of equal-particle-size pulverized coal, which can obtain the wettability characteristics of a coal reservoir, can facilitate the mutual comparison of different (or same) particle size or different (or same) pore size, and has important significance in the aspects of coal seam water injection outburst elimination, coal seam hydraulic fracturing and the like, as well as the potential productivity evaluation of the reservoir and the process optimization of each link of development and production.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. Wherein:
FIG. 1 is a chart of the process of determining the wettability of the pores of an NMR-supplied pulverized coal of equal particle size in an embodiment of the invention;
FIG. 2 is a schematic view of a water container according to an embodiment of the present invention;
FIG. 3 is a chart showing the NMR transverse relaxation times T of saturated samples in terms of five particle size sizes in an embodiment of the invention 2 ' a linear fitting map;
FIG. 4 is a graph showing equivalent pore diameter distribution of a wetted area after quantitative water is dropped into each coal dust sample for 24 hours in the specific embodiment of the invention;
FIG. 5 is a graph of a linear fit of equivalent wetted pore size to various particle size dimensions in an embodiment of the invention;
FIG. 6 is a flow chart of a method of determining wettability of a void in an embodiment of the invention.
In the figure: 202. a water injection pressure head; 2021. a water injection hole; 2022. a water injection pipe; 204. a syringe; 206. a housing; 208. an upper centralizer; 2081. a central bore; 2082. a water passing hole is formed; 210. a coal dust sample; 212. a lower centralizer; 2121. and draining the water hole.
Detailed Description
The following description of the technical solutions in the embodiments of the present invention will be clear and complete, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which are derived by a person skilled in the art based on the embodiments of the invention, fall within the scope of protection of the invention.
In the description of the present invention, the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", etc. refer to the orientation or positional relationship based on that shown in the drawings, merely for convenience of description of the present invention and do not require that the present invention must be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention. The terms "coupled" and "connected" as used herein are to be construed broadly and may be, for example, fixedly coupled or detachably coupled; either directly or indirectly through intermediate components, the specific meaning of the terms being understood by those of ordinary skill in the art as the case may be.
The invention will be described in detail below with reference to the drawings in connection with embodiments. It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
As shown in fig. 1-6, a pore wettability NMR characterization method of a pulverized coal with equal particle diameter is a characterization method based on calculation based on nuclear magnetic resonance transverse relaxation time, and specifically includes: step S1, respectively dripping quantitative water into pulverized coal samples with various particle sizes, and measuring the transverse relaxation time T of the pulverized coal samples with various particle sizes after a certain time 2 The method comprises the steps of carrying out a first treatment on the surface of the Step S2, measuring the coal dust sample with each particle sizeNMR transverse relaxation time T of product in saturation 2 'A'; step S3, according to NMR transverse relaxation time T in saturated state 2 ' Linear regression drawing and determining the surface relaxation rate rho of the coal powder sample 2 The method comprises the steps of carrying out a first treatment on the surface of the Step S4, according to the surface relaxation rate ρ 2 And NMR transverse relaxation time T of pulverized coal sample of each particle size 2 Equivalent wetting aperture R together defining a wetting zone g The method comprises the steps of carrying out a first treatment on the surface of the And S5, drawing a linear fitting curve of the equivalent wetting aperture and the particle size of the coal dust sample, so as to determine a pore wettability expression. The wettability characteristic of the coal reservoir can be obtained through the pore wettability expression, so that the mutual comparison of different (or the same) particle size or different (or the same) pore size can be facilitated, and the method has important significance in the aspects of coal seam water injection outburst elimination, coal seam hydraulic fracturing and the like for potential productivity evaluation of the reservoir and process optimization of various links of development and production. In this example, the quantitative water plain water, the specific volume or weight of which is determined according to the actual test needs.
In another alternative embodiment, the water treatment of the pulverized coal sample is performed by a saturation vessel, whereby the NMR transverse relaxation time T of the pulverized coal sample of each particle size is performed 2 Measurement and measurement of NMR transverse relaxation time T of pulverized coal sample of each particle size in saturated state 2 'A'; specifically, the saturation vessel includes: the shell 206, the shell 206 is a hollow cylinder, and the inner columnar cavity is used for holding a pulverized coal sample for water treatment; the lower centralizer is a circular plate body or a cover body matched with the bottom of the shell 206, can be detachably connected to the lower end of the shell 206 in a threaded connection or sleeving manner or is integrally formed with the shell 206, and is provided with a plurality of water passing holes facing to the inner cavity of the shell 206; the upper centralizer 208 is of a columnar structure, the upper centralizer 208 is axially and slidably assembled inside the shell 206 along the shell 206, and the upper centralizer 208 has a certain weight and can compact and stabilize a pulverized coal sample by self weight; a conical groove is arranged above the upper centralizer 208, a plurality of water passing holes extending along the axial direction of the shell 206 are arranged on the inner wall of the conical groove, and a coal dust sample is arranged between the upper centralizer 208 and the lower centralizer; water injection ram 202 is also provided withThe sum of the mass of the water injection pressure head 202 and the mass of the upper centralizer 208 is 200g, and the loaded pulverized coal sample is restrained by the upper centralizer 208 and the lower centralizer, so that the particle position of the pulverized coal sample is kept from moving; the main body of the water injection pressure head 202 is a columnar cavity matched with the inner cavity of the shell and is provided with a conical bottom matched with the conical groove, the conical bottom is provided with a water injection hole 2021 corresponding to the conical groove, and the water injection pressure head 202 is correspondingly connected with a water source through a water injection pipe 2022 so as to inject water into the coal seam.
In this embodiment, the housing 206 is made of Polytetrafluoroethylene (PTFE) and has an inner cavity diameter of 40mm.
In another alternative embodiment, the plurality of the water drain holes 2082 and the water injection holes 2021 are all corresponding to each other in the axial direction of the housing 206; a central bore 2081 is provided in each of the lower centralizer, the upper centralizer 208, and the water injection head, the central bore 2081 being coaxially disposed with the housing 206. The aperture of the central aperture 2081 is greater than the surrounding water apertures, the aperture of a particular central aperture 2081 being 4mm, and the apertures of the lower water aperture, the upper water aperture 2082 and the water injection aperture 2021 being 2mm. On the lower centralizer, the lower water holes are uniformly distributed circumferentially and radially about the central hole 2081, on the upper centralizer 208, the upper water holes 2082 are uniformly distributed circumferentially and radially about the central hole 2081, and on the water injection head, the water injection holes 2021 are uniformly distributed circumferentially and radially about the central hole 2081.
In an alternative embodiment, the NMR transverse relaxation time T of the pulverized coal sample is measured for each particle size 2 During measurement, the water injection pressure head 202 is not needed, after the pulverized coal sample is compacted through the water injection pressure head 202 and the upper centralizer 208, the water injection pressure head 202 is taken down, quantitative water is injected into the central hole 2081 of the upper centralizer 208 through the injector 204, after the quantitative water is dripped for 24 hours, the NMR transverse relaxation time T of the pulverized coal sample with each particle size is measured 2 . The volume of specific quantitative water was 1.5ml.
NMR transverse relaxation time T of pulverized coal sample of to-be-seeded particle size 2 And after the measurement is completed, continuous water injection is carried out on the coal seam through the water injection pressure head 202 so as to enable the coal dust sample to reach a saturated state. Specifically, the lower centralizer, upper centralizer 208 and water flooding are performedThe water holes on the pressure head 202 are aligned, a water source is opened, water is injected through the water injection pressure head 202 for 10min, the water injection pressure head 202 is taken down, and the water of the upper centralizer 208 and the lower centralizer is wiped dry by utilizing water absorption paper, so that the water saturation treatment of the coal dust sample is completed.
In another alternative embodiment of the present application, in step S3, the surface relaxation rate ρ of the pulverized coal sample 2 Is the slope of the straight line of the linear regression graph made.
In step S4, equivalent wetting aperture R g Determined according to the following formula:
wherein: r is R i To wet the pore size, A i To wet the signal amplitude corresponding to the aperture, A total For the signal amplitude corresponding to the whole aperture range, R g Is the equivalent wetted pore size of the wetted area.
The pore wettability expression is:
wherein: a. b is a fitting parameter; r is (r) g The particle diameter of the pulverized coal particles is r s Being the size of inter-particulate pores, α is the correlation coefficient based on the assumption of extreme packing.
In the pore wettability expression, the values of a, b in the pore wettability expression are determined by plotting a linear fit curve of equivalent wetting pore diameter versus particle size. The relationship between particle size and inter-particle pore size can be reflected by the following equation:
wherein: r is (r) s Being the size of inter-particulate pores, α is the correlation coefficient based on the assumption of extreme packing.
In another alternative embodiment, in each step, the prepared particle size is not less than three, the particle size range is between 0.075 and 3mm, specifically, five particle size coal powder samples are prepared, the particle size is divided into 10-12 meshes, 18-20 meshes, 30-35 meshes, 60-80 meshes and 100-200 meshes, and before the test, the equal particle size coal powder is screened by sieving.
In step S2, NMR transverse relaxation times T are respectively carried out on the coal dust samples with 5 particle sizes in the saturated state 2 ' make measurements and record;
in step S3, NMR transverse relaxation time T in saturated state 2 ' do linear regression curve, see FIG. 3; wherein X is an amount related to the particle size of the pulverized coal, and points in the figure represent data corresponding to particle sizes of 10 to 12 mesh, 18 to 20 mesh, 30 to 35 mesh, 60 to 80 mesh and 100 to 200 mesh, respectively. Y is the NMR transverse relaxation time T of the saturated coal sample 2 'transverse relaxation rate after geometric averaging'. The data of each particle size can be drawn into a linear fitting straight line with zero intercept, and the slope of the obtained linear fitting straight line is the surface relaxation rate rho 2 (＝196μm/s)。
In the step S4, combining the surface relaxation rate and the transverse relaxation time T after quantitative water is dripped into each coal dust sample for 24 hours 2 Determination of the equivalent pore diameter R of the wetted area g See fig. 4: the data points in fig. 4 were obtained by laboratory experiments. The horizontal axis of the image represents the pore size, the vertical axis represents the signal amplitude, the curve in the figure is a wetting pore size distribution diagram of 1.5ml of water drop into coal dust for 24 hours, and the wetting pore size distribution under each particle size can be obtained by a formula (4).
In step S5, the values a and b in the formula (6) are determined by drawing a linear fit curve of the equivalent wet pore diameter and the particle size, and referring to fig. 5, the data points 502, 504, 506, 508, 510 in fig. 5 can be obtained through experiments, and the linear fit curve 512 of the equivalent wet pore diameter and the particle size is obtained through the above data point fitting. In fig. 5, the horizontal axis of the image represents the particle size, the vertical axis represents the equivalent wetting aperture, a fitting curve 512 is drawn based on the data distribution of fig. 5, and the best estimated values of the fitting parameters a, b in the present embodiment are obtained based on the fitting curve, and in this example, a is determined to be 0.017 and b is determined to be 0.002 by the fitting curve. Thus, in the example shown, pore wettability at different pore scales can be expressed as:
thus, the expression of pore wettability can be carried out for different types of coal, and mutual comparison under different (or same) particle size or different (or same) pore size can be facilitated.
In this example, steps S1-S5 may be repeated to determine pore wettability expressions for different types of coal, facilitating comparison of pore wettability at different or the same pore sizes.
In the above embodiments, the calculation and characterization is based on the nuclear magnetic resonance NMR transversal relaxation time, which can be defined by the following formula:
wherein ρ is 2 For the surface relaxation rate, S is the sample surface area and V is the sample pore volume. NMR transverse relaxation time T in saturation 2 ' acquisition and NMR transverse relaxation time T 2 The same applies.
NMR transverse relaxation time T 2 Also associated with the bulk relaxation and diffusion relaxation times, both are often negligible based on the conditions of smaller pore size and low magnetic field strength. In this embodiment, the pore shape of the porous medium is often divided into a columnar shape and a spherical shape, so that the pore wettability characterization method provided by the invention is suitable for spherical pore assumption, and based on the pore size and the NMR transverse relaxation time T under the wetting range 2 The relationship of (2) can be calculated by the following formula:
wherein: r is pore radius, F s Is a geometric form factor (in the formula, the value of the pores of the spherical porous medium takes 3); c is called the conversion factor.
NMR transverse relaxation time T 2 The response of this wetting process is sensitive to quantitative water dripping into the coal fines, and the coal pore walls have an effect of promoting the magnetic relaxation of the fluid, the extent of which depends on the wetting characteristics of the coal pore walls in contact with the fluid, the coal pore size distribution characteristics, the coal pore connectivity and its complexity, etc. Thus, the pore size distribution in the wet range is primarily determined by the strength of the fluid-coal porous medium interactions.
The precondition for realizing the calculation of the interaction strength of the fluid-coal porous medium is the surface relaxation rate rho of the coal 2 Is determined by the above-described method. The following formula shows the NMR transverse relaxation time T under consideration of various particle sizes 2 And the surface relaxation rate ρ 2 Relationship between:
wherein:is the water saturation porosity of the coal powder sample, r g Is the particle size of pulverized coal particles. Based on various particle size (three or more) tests, the transverse relaxation time T can be determined by NMR 2 With the particle diameter r of the pulverized coal g Is used for determining the surface relaxation rate rho by a linear regression method of (1) 2 Is of a size of (a) and (b).
Based on NMR transverse relaxation time T 2 The relationship with the pore size of the wetted area after the quantitative water is dripped into a certain volume of coal powder can reflect the degree or capacity (the interaction strength of the fluid-coal porous medium) of pore wetting of the quantitative water in the coal powder, namely the pore wettability, by characterizing the pore size distribution of the wetted area after a certain time.
For hydrophobic coal powder, the capillary force has repulsive force on water, so that the diffusion of water in coal powder particles is hindered, the wetting area is smaller, and the contact is madeThe smaller pores are less likely to be touched and are difficult to access even when encountered, and the measured NMR transverse relaxation time T 2 The size is larger; for hydrophilic coal fines, the capillary forces promote the wetted diffusion of water, which is larger in the wetted area, contacts more smaller pores and preferentially selects smaller pore aggregates, resulting in a measured NMR transverse relaxation time T 2 Smaller. Thus, the wetted area pore distribution characteristics can be visually reflected by the following formula:
wherein: r is R i To wet the pore size, A i To wet the signal amplitude corresponding to the aperture, A total For the signal amplitude corresponding to the whole aperture range, R g The size of the equivalent wetted pore size of the wetted area after 24 hours.
In practice, the size of the particle size substantially reflects the size of the inter-particle voids, and based on the assumption of simple cubes and tetrahedral ultimate packing of the particles, the relationship between particle size and inter-particle void size can be reflected by the following formula:
wherein: r is (r) s Being the size of inter-particulate pores, α is the correlation coefficient based on the assumption of extreme packing. In addition, R corresponding to multiple pulverized coal with different particle sizes g Unlike, and the equivalent wetted pore size is essentially the size of the inter-particulate pore wetted region, the relationship of equivalent wetted pore size to particle size tends to be linearly related.
This relationship can be expressed as:
wherein: a, b are fitting parameters, which are determined by drawing linear fitting graphs of equivalent wetting pore diameters and various particle diameter sizes, data of different particle diameter sizes obtained in a laboratory and corresponding equivalent wetting pore diameters are input into the fitting graphs, as shown in fig. 5, the horizontal axis of the image represents the particle diameter size, the vertical axis represents the equivalent wetting pore diameter, and then the values a and b in the embodiment are obtained through the fitting graphs.
The pore wettability expression is determined according to a linear fitting straight line of the equivalent wettability pore diameter and the particle size, the equivalent wettability pore diameter under different inter-particle pore sizes can be obtained through the formula (6), and the size of the equivalent wettability pore diameter is the determined pore wettability expression R g (r)。
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Claims (6)
1. A pore wettability NMR characterization method of an equal particle size pulverized coal, comprising:
step S1, respectively dripping quantitative water into pulverized coal samples with various particle sizes to measure the NMR transverse relaxation time of the pulverized coal samples with each particle sizeT 2 ；
Step S2, carrying out water treatment on the sample to enable the coal powder sample to reach a saturated state, and measuring the NMR transverse relaxation time of the coal powder sample with each particle size under the saturated stateT 2 '；
Step S3, according to NMR transverse relaxation time in saturated stateT 2 ' Linear regression drawing and determining the surface relaxation rate of coal powder sample；
Step S4, according to the surface relaxation rateAnd NMR transverse relaxation time of pulverized coal sample of each particle sizeT 2 Co-defining wetting zones etcEffective wetting pore diameter R g ；
S5, drawing a linear fitting curve of the equivalent wetting aperture and the particle size of the coal dust sample, so as to determine a pore wettability expression;
carrying out water treatment on coal dust samples through a saturation vessel, wherein the saturation vessel comprises:
a housing, the housing being a hollow cylinder;
the lower centralizer is connected to the lower end of the shell and is provided with a plurality of lower water holes which are opposite to the inner cavity of the shell;
the upper centralizer is of a columnar structure, is axially and slidably assembled inside the shell along the shell, has a certain weight and can compact and stabilize a coal dust sample by means of dead weight; a conical groove is formed above the upper centralizer, a plurality of upper water passing holes extending along the axial direction of the shell are formed in the inner wall of the conical groove, and a coal powder sample is arranged between the upper centralizer and the lower centralizer;
the water injection pressure head is provided with a conical bottom matched with the conical groove, the main body of the water injection pressure head is a columnar cavity matched with the inner cavity of the shell, the conical bottom is provided with a water injection hole corresponding to the conical groove, and the water injection pressure head is correspondingly connected with a water source through a water injection pipe so as to inject water into the coal dust sample;
the sum of the mass of the water injection pressure head and the mass of the upper centralizer is 200g, and the loaded pulverized coal sample is restrained by the upper centralizer 208 and the lower centralizer, so that the particle position of the pulverized coal sample is kept from moving; the lower water passing hole, the upper water passing hole and the water injection hole are mutually corresponding in the axial direction of the shell;
the upper centralizer and the water injection pressure head are provided with central holes, and the central holes and the shell are coaxially arranged;
the aperture of the central hole is larger than that of the surrounding water passing holes, the lower water passing holes are uniformly distributed in the circumferential direction and the radial direction of the central hole on the lower centralizer, the upper water passing holes are uniformly distributed in the circumferential direction and the radial direction of the central hole on the upper centralizer, and the water injection holes are uniformly distributed in the circumferential direction and the radial direction of the central hole on the water injection pressure head; taking down the water injectionA pressure head, injecting quantitative water into the central hole through an injector, dripping the quantitative water for 24 hours, and measuring to obtain the NMR transverse relaxation time of the pulverized coal sample with each particle sizeT 2 The method comprises the steps of carrying out a first treatment on the surface of the NMR transverse relaxation time of coal dust sample of to-be-seeded particle sizeT 2 And after the measurement is completed, continuously injecting water into the coal powder sample through the water injection pressure head so as to enable the coal powder sample to reach a saturated state.
2. The method for pore wettability NMR characterization of a pulverized coal of equal particle size according to claim 1, wherein in step S3, the surface relaxation rate of the pulverized coal sample isIs the slope of the straight line of the linear regression graph made.
3. The method for pore wettability NMR characterization of uniform particle size pulverized coal according to claim 1, wherein in step S4, the equivalent wetting pore diameter R g Determined according to the following formula:
，
wherein:to moisten the size of the pore size, +.>For the signal amplitude corresponding to the wetting aperture, +.>Signal amplitude corresponding to the full aperture range, < >>Is the equivalent wetted pore size of the wetted area.
4. The method for characterizing pore wettability NMR of an equal particle size pulverized coal according to claim 1, wherein the pore wettability expression is:
，
wherein: a. b is a fitting parameter;is pulverized coal particle size>Is the size of inter-granular pores>Is a correlation coefficient based on the extreme stacking assumption.
5. The method for characterizing pore wettability NMR of a pulverized coal of equal particle size according to claim 4, wherein the values of a and b in the pore wettability expression are determined by plotting a linear fit curve of equivalent wetting pore diameter and various particle size.
6. The method of claim 4, wherein the relationship between particle size and inter-particle pore size is reflected by the following equation:
，
wherein:is the size of inter-granular pores>Is a correlation coefficient based on the extreme stacking assumption.
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