CN112362553B - Compact sandstone micro-pore structure characterization method - Google Patents
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Abstract
The invention discloses a compact sandstone microscopic pore structure characterization method, which comprises the steps of dividing a casting body slice into different pore units, extracting a picture of a pore in each unit, counting the area and the circumference of each pore, calculating a shape factor of the corresponding pore, and calculating the corresponding pore radius based on pore radius calculation formulas with different shapes. And then, combining the pore distribution in the casting body slice and the characteristics of the constant-speed mercury pressing mercury feeding curve, and simultaneously combining the throat distribution obtained by high-pressure mercury pressing with the corrected constant-speed mercury pressing throat distribution to obtain the complete throat distribution of the rock core. And finally, respectively providing the pore radius of the rock core and a distribution characterization method thereof when the pore shape distribution is stable and the pore shape distribution has larger difference based on the shape factor distribution obtained by the casting body slice. The method gets rid of the defects of the prior various methods for characterizing the micro-pore structure, and the obtained data of the size and the distribution of the pores and the throats of the compact rock are more accurate.
Description
Technical Field
The invention relates to the technical field of unconventional oil and gas exploration, in particular to a compact sandstone micro-pore structure characterization method.
Background
Compact oil is another big hot spot in the global unconventional oil and gas exploration and development field after shale, and has become one of the important energy successors in the future of China. In the exploration and development process of a compact reservoir, the obvious differences from medium and high permeability reservoirs are that rock particles of the compact reservoir are fine, the porosity and the permeability are low, the compression effect is strong in the diagenesis process, the micro-pore structure is complex, and the pore throat is mainly micro-nano-scale. Accurately representing the microscopic pore throat structure of the compact reservoir rock, and determining the size and the distribution of the pore and the throat of the compact reservoir, thereby having very important practical significance for the efficient development of the compact reservoir.
At present, the commonly used reservoir pore throat structure characterization method has two aspects of qualitative and quantitative, and for a compact reservoir, the commonly used representative technical means include cast body slices, constant-pressure mercury pressing, constant-speed mercury pressing and nuclear magnetic resonance. In all the characterization methods, the casting body slice can be directly used for observing the pore throat structure of the compact oil reservoir, and the relevant pore throat structure information in the rock core can be extracted through subsequent image processing while providing visual understanding. Injecting mercury into a sample by constant-pressure mercury pressing at constant pressure, obtaining a capillary pressure curve, and calculating by combining a Washburn equation to obtain pore throat radius distribution; the constant-speed mercury pressing is injected into the rock core at a constant and extremely low speed, the mercury feeding process is close to a quasi-static process, the change characteristics of the pore and the throat can be obtained simultaneously by analyzing the change of a pressure curve in the mercury feeding process, so that capillary curves of the pore and the throat are obtained respectively, and the pore radius distribution and the throat radius distribution can be obtained by calculation by combining with a Washburn equation. The NMR technology is a technology for detecting the pore structure of stratum by measuring the amplitude and relaxation rate of the NMR relaxation signal of hydrogen nuclei in the pore fluid of stratum rock by utilizing the self magnetism of the hydrogen nuclei and the interaction principle of the hydrogen nuclei and an external magnetic field2Related to pore size and fluid properties.
However, these current test methods suffer from the following disadvantages:
(1) although the size and the communication condition of the pores can be visually observed through the casting body slice, the reflected information is two-dimensional information, and certain errors exist in the size and the distribution of the pores of the rock core in a three-dimensional space.
(2) During the initial mercury feeding stage of the constant-speed mercury-pressing experiment, the increase of the mercury feeding amount is caused by the sticking of mercury in a non-wetting phase on pit recesses on the rough surface of the rock sample and the false mercury feeding volume caused by the sticking. With the gradual increase of the pressure, the pit is filled with mercury, and at the moment, the mercury does not really enter the pore throat system, and the pressure does not reach the displacement pressure. However, in the mercury inlet amount, if the cavity volume of the part is accumulated into the mercury inlet amount of the total pore throat system, the mercury inlet saturation degree value is larger, and the phenomenon is called the hemp skin effect. Under the influence of the existence of the hemp skin effect, the mercury saturation degree is larger, the drawn capillary curve has a distortion phenomenon, and the represented pore size and the distribution thereof have larger errors; further, the maximum mercury injection pressure for constant-rate mercury injection was 1000Psi (6.9MPa), and the lower limit of the pore throat radius was 0.12 μm, which was not characterized for pore throats of 0.12 μm or less.
(3) Although the pore throat information given by the high-pressure mercury intrusion mainly reflects the throat distribution, the pore distribution with a small part of radius is still superposed, so that the obtained throat information is incomplete.
(4) In addition, in the conventional constant-speed mercury intrusion and high-pressure mercury intrusion data processing, the pores are equivalent to spheres, and the corresponding equivalent sphere radius is calculated by using a Washburn formula to represent the pore size and distribution of the rock, but the equivalent sphere radius is inapplicable to tight reservoir sandstone which is subjected to strong compaction and cementation and has irregular pore shape, so that the calculated value is larger.
(5) The nmr technique can obtain complete pore throat information, but cannot directly obtain pore throat radius distribution. At the same time, nuclear magnetic resonance T2When the relaxation time is converted into pore throat distribution, the pore shape of the rock core is generally regarded as a fixed value, and a characterization method of the pore radius of the rock core when the pore shape difference is large is not considered.
Disclosure of Invention
Aiming at the problems, the invention provides a compact sandstone micro-pore structure characterization method, which abandons the defects of the existing various micro-pore structure characterization methods and obtains more accurate full pores and throat sizes and distribution results of compact sandstone reservoirs.
The invention adopts the following technical scheme:
a compact sandstone micro-pore structure characterization method comprises the following steps:
s1, selecting a cylindrical core of a compact sandstone reservoir, washing oil and drying, measuring the porosity and permeability of the core, and cutting the core into four sections;
s2, performing a cast body slice experiment on the section I core: dividing the casting body slice image into different pore units, calculating the shape factor of each pore, judging the pore shape based on the size of the shape factor, classifying the pore shapes according to the shapes, calculating the inscribed circle radius and the equivalent radius of the corresponding pore shape according to the relationship between the pore shape, the areas of different pore shapes and the inscribed circle radius of the pore shapes, and drawing a radius and frequency distribution histogram of the radius;
s3, performing a constant-speed mercury pressing experiment on the second section of core to obtain corrected constant-speed mercury pressing throat distribution;
s4, performing a high-pressure mercury intrusion test on the third section of core, and acquiring the complete throat radius and distribution of the core based on the high-pressure mercury intrusion test;
and S5, acquiring the complete pore radius and distribution of the core.
Preferably, in step S2, the calculation formula of the shape factor is:
wherein G is a shape factor and is dimensionless; a is the cross-sectional area of the pores, μm2(ii) a P is the perimeter of the pore, μm.
Preferably, in step S2, the calculation formula of the inscribed circle radius corresponding to the aperture shape is:
triangle:
a quadrangle:
pentagon:
irregular polygon: rEquivalence of＝0.5L (5)
Wherein A is a cross-sectional area of the voids, μm2And L is the pore length, μm.
Preferably, in step S3, the acquiring the corrected constant-speed mercury-pressing throat distribution includes the following steps:
s31, performing a constant-speed mercury injection experiment on the second section of core to obtain a curve of mercury injection pressure and mercury injection volume; calculating an extreme pressure interval by using the pore radius and the distribution thereof obtained based on the cast body slice in the step S2, and selecting a corresponding data segment from the constant-speed mercury injection pressure and mercury injection volume curve;
s32, processing the curve into an M-shaped curve segment, identifying pressure values and volume values corresponding to the pore and the throat from the curve segment, and drawing a pore capillary pressure curve, a throat capillary pressure curve and a total capillary pressure curve after correction;
and S33, calculating to obtain the corrected capillary pressure curve, pore, throat radius and distribution thereof.
Preferably, the calculation formula of the extreme pressure interval is as follows:
the calculation formula of the corrected capillary pressure curve, the corrected pore and the corrected throat radius is as follows:
in the formula, RmaxIs the maximum value of pore radius, μm, obtained on cast sheet; plbThe lower limit value of the mercury injection pressure of the constant-speed mercury pressure curve is MPa; rminFor the minimum value of the pore radius based on the cast sheet,μm；Pupthe upper limit value of the mercury injection pressure on the constant-speed mercury-pressing curve is MPa; rcpThe pore radius is the corrected pore radius of the constant-speed mercury pressing, and is mum; pcpThe corrected pore capillary pressure is MPa; rctThe diameter is the throat radius after the constant-speed mercury pressing correction, and is mum; pctThe pressure of the throat capillary is MPa.
Preferably, step S4 includes the steps of:
s41, performing a high-pressure mercury intrusion test on the third section of rock sample to obtain pore throat radius distribution based on a high-pressure mercury intrusion test;
s42, drawing the corrected radius and the distribution of the constant-speed mercury pressing throat and the radius and the distribution of the pore throat obtained by high-pressure mercury pressing in the same coordinate system;
selecting the radius and the distribution of the high-pressure mercury-pressing pore throat of the data before 0.12 mu m, and selecting the corrected radius and the distribution of the constant-speed mercury-pressing throat of the data after 0.12 mu m;
and after normalization processing, the two data are redrawn in a rectangular coordinate system to obtain the complete throat radius and the distribution of the rock sample.
Preferably, in step S5, the obtaining of the complete pore radius and the distribution of the pore radius includes the following steps:
s51, measuring nuclear magnetic resonance T of the saturated water of the IV section core under the state of the completely saturated water2A spectral curve;
and S52, judging whether the pore shape distribution of the core is stable or not based on the pore shape factor and the distribution thereof acquired in the step S2.
The invention has the beneficial effects that:
1. according to the invention, a casting body sheet is firstly divided into a plurality of pore units, the area, the perimeter and the length of each pore are obtained, the pores are divided into regular trilateral, quadrilateral, pentagonal and irregular polygons through the shape factors of the pores, the calculation expressions of the radius of an inscribed circle and the equivalent radius of the corresponding pore are deduced according to the difference of the pore shapes, and the sizes and the differences of the pores based on the casting body sheet are obtained.
2. Secondly, the pore radius distribution obtained by the casting body slice is combined with the constant-speed mercury pressing, a reasonable curve interval of the constant-speed mercury pressing is selected, errors caused by the hemp skin effect are eliminated, and the corrected pore and throat sizes and distribution are obtained. Meanwhile, throat distribution obtained by high-pressure mercury pressing is combined with corrected constant-speed mercury pressing throat distribution to obtain complete throat distribution of the core.
3. Finally, a characterization method of the pore radius and the pore distribution of the core when the pore shape distribution is stable and the pore shape distribution has large difference is provided based on the shape factor distribution obtained by the casting body slice. The method gets rid of the defects of the prior various methods for characterizing the micro-pore structure, and the obtained data of the size and the distribution of the pores and the throats of the compact rock are more accurate.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly described below, and it is apparent that the drawings in the following description only relate to some embodiments of the present invention and are not limiting on the present invention.
FIG. 1 is a schematic diagram of the T2 spectrum when fully saturated with water according to the present invention;
FIG. 2 is a schematic diagram of pore shape distribution based on cast sheet statistics according to the present invention;
FIG. 3 is a schematic diagram of pore sizes and their distribution obtained based on cast sheet according to the present invention;
FIG. 4 is a graphical representation of the constant rate mercury intrusion pore size and its distribution before and after modification in accordance with the present invention;
FIG. 5 is a schematic diagram showing the size and distribution of a constant-speed mercury-pressing throat before and after correction according to the present invention;
FIG. 6 is a schematic diagram showing the size and distribution of the high-pressure mercury injection throat according to the present invention;
figure 7 is a schematic view of the complete throat distribution of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without any inventive step, are within the scope of protection of the invention.
Unless otherwise defined, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure belongs. The use of the word "comprising" or "comprises", and the like, in this disclosure is intended to mean that the elements or items listed before that word, include the elements or items listed after that word, and their equivalents, without excluding other elements or items. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships may also be changed accordingly.
The invention is further illustrated with reference to the following figures and examples.
As shown in fig. 1 to 7, a method for characterizing a micro-pore structure of tight sandstone includes the following steps:
s1, selecting a cylindrical core of a compact sandstone reservoir, washing oil and drying, measuring the porosity and permeability of the core, and cutting the core into four sections;
s2, performing a cast body slice experiment on the section I core: dividing the casting sheet image into different pore units, and shooting pictures of all pores in each unit by using a high-power microscope; extracting corresponding pore outlines, pore sizes (pore cross sections) A, pore perimeters P and pore lengths L by using ImageJ software; the shape factor of each pore was calculated using the following formula:
wherein G is a shape factor and is dimensionless; a is the cross-sectional area of the pores, μm2(ii) a P is the perimeter of the pore, μm.
As shown in tables 1 and 2, the pore shapes are judged based on the size of the shape factor, and are classified according to the shapes, the inscribed circle radius and the equivalent radius corresponding to the pore shapes are calculated according to the relationship between the pore shapes, the areas of different pore shapes and the inscribed circle radius, and the radius and the frequency distribution histogram thereof are drawn;
| type of shape | In proportion of |
| Trilateral shape | 26％ |
| Quadrilateral shape | 63 |
| Pentagon | |
| 3％ | |
| Circular shape | 8％ |
TABLE 1 pore shape Classification statistical Table
TABLE 2 statistic table of radius distribution of inscribed circle
The calculation formula of the radius of the inscribed circle corresponding to the pore shape is as follows:
triangle:
a quadrangle:
pentagon:
irregular polygon: rEquivalence of＝0.5L (5)
Wherein A is a cross-sectional area of the voids, μm2And L is the pore length, μm.
S3, performing a constant-speed mercury pressing experiment on the second section of core to obtain corrected constant-speed mercury pressing throat distribution;
s31, performing a constant-speed mercury injection experiment on the second section of core, recording mercury injection pressure and mercury injection volume in the experiment process, calculating an extreme pressure interval by using the pore radius and the distribution thereof obtained based on the casting body slice in the step S2, and selecting a corresponding data section from a curve of the constant-speed mercury injection pressure and the mercury injection volume;
in the formula, RmaxIs the maximum value of pore radius, μm, obtained on cast sheet; plbThe lower limit value of the mercury injection pressure of the constant-speed mercury pressure curve is MPa; rminIs the minimum value of pore radius, μm, obtained on cast sheet; pupThe upper limit value of the mercury injection pressure on the constant-speed mercury-pressing curve is MPa;
s32, according to the principle of a constant-speed mercury-pressing experiment, abnormal points in the curve are removed, the curve is processed into an 'M' -shaped curve section with 'one rising and one falling', pressure values and volume values corresponding to the pore and the throat are identified from the 'M' -shaped curve section by using a bubbling sorting algorithm, and a corrected pore capillary pressure curve, a throat capillary pressure curve and a total capillary pressure curve are drawn.
S33, calculating the following formulas to obtain the corrected capillary pressure curve, pore space, throat radius and distribution thereof:
Rcpthe pore radius is the corrected pore radius of the constant-speed mercury pressing, and is mum; pcpThe corrected pore capillary pressure is MPa; rctThe diameter is the throat radius after the constant-speed mercury pressing correction, and is mum; pctThe pressure of the throat capillary is MPa.
S4, performing a high-pressure mercury intrusion test on the third section of core, and acquiring the complete throat radius and distribution of the core based on the high-pressure mercury intrusion test;
s41, performing a high-pressure mercury intrusion test on the third section of rock sample according to the national standard GB/T29171-2012 'determination of rock capillary pressure curve', and acquiring the pore throat radius distribution acquired based on the high-pressure mercury intrusion test;
s42, drawing the corrected radius and the distribution of the constant-speed mercury pressing throat and the radius and the distribution of the pore throat obtained by high-pressure mercury pressing in the same coordinate system; selecting the radius and the distribution of the high-pressure mercury-pressing pore throat according to data before 0.12 mu m by taking 0.12 mu m as a boundary, and selecting the radius and the distribution of the corrected constant-speed mercury-pressing throat according to data after 0.12 mu m; and finally, after normalization processing, the two data are redrawn in a rectangular coordinate system to obtain the complete throat radius and the distribution of the rock sample.
And S5, acquiring the complete pore radius and distribution of the core.
S51, measuring the dry weight of the fourth section of core, vacuumizing the core to 133Pa, pressurizing and saturating the simulated formation water under the pressure of 20MPa for 48 hours, measuring the weight of the saturated core, calculating the effective porosity of the core, completing the saturation of the rock sample when the relative error between the effective porosity of the rock sample and the gas porosity is less than 2%, namely satisfying the formula 8, and otherwise, repeating the steps to saturate again until the core is completely saturated; measurement of nuclear magnetic resonance T in the fully saturated Water State2Spectral curves.
S5.2, judging whether the pore shape distribution of the rock core is stable or not (namely, the pore shape in the rock core is mainly in a certain shape) based on the pore shape factor and the pore shape distribution obtained in the S2;
s521, when the distribution quantity of pores in a certain shape in the core is more than 60%, determining that the core is stable: the corrected constant-speed mercury intrusion pore size and distribution and the nuclear magnetic resonance T obtained in the step S32Combining spectral curves to combine pore maxima with NMR T2The maximum value of time corresponds to the maximum value of time, and the modified constant-speed mercury-pressing pore distribution and the nuclear magnetic resonance T are adopted2Obtaining NMR T by using equation 9 with the shape of the spectral curve as a reference2Conversion coefficient between time and throat radius, thereby converting nuclear magnetic resonance T2The spectra are converted to corresponding pore throat distribution curves.
T2＝CRNMR (9)
Wherein C is a conversion coefficient, ms/mum; t is2Is nuclear magnetic resonance T2Time, ms; rNMRThe pore throat radius after nuclear magnetic resonance conversion is mum;
drawing a pore throat cumulative distribution curve according to the converted nuclear magnetic resonance pore throat distribution curve; meanwhile, the complete throat distribution obtained in the step S4 is drawn as an accumulated distribution curve, the two accumulated distribution curves are drawn in the same coordinate system, and the two accumulated distribution curves are subtracted and redrawn to obtain the complete pore size and distribution of the core.
When the shape distribution of the pores in the core varies widely (i.e., the number of pores of no one shape is more than 60%):
first, the complete throat distribution and the nuclear magnetic resonance T obtained in the step S42The spectral curves are drawn under the same coordinate system; according to T in equation 102Functional relationship between time and pore throat radius using nuclear magnetic resonance T2Calibrating the left front of a spectral curve to obtain the relaxation rate (wherein the shape factor is 2, the shape of the throat is mainly long cylindrical), and carrying out nuclear magnetism sharingVibrating T2Converting the spectral curve into a pore throat distribution curve;
in the formula, ρ2Surface relaxation rate, μm/ms; fsPore shape factor (long cylinder 2, sphere 3); rNMRThe pore throat radius after nuclear magnetic resonance conversion is mum;
secondly, according to the converted nuclear magnetic resonance pore throat distribution curve, an accumulated pore throat distribution curve and an accumulated throat distribution curve are drawn in the same way, and the two accumulated distribution curves are subtracted and re-sampled to obtain the size and the distribution of the long cylindrical pores;
thirdly, according to the ratio (2/3) of the long cylindrical shape factors and the spherical shape factors, converting the size and the distribution of the long cylindrical pores into the size and the distribution of equivalent spherical pores;
fourthly, respectively obtaining the radiuses and the distribution of the inscribed spheres in different shapes according to the relation (formula 11-13) between the inscribed spheres and the equivalent spheres in different cross-sectional shapes, and obtaining the average pore radius R of the rock core by using a weighted average method based on the pore shape factor and the distribution thereof obtained in the step S2EBAnd the distribution thereof.
Triangle:
a quadrangle:
pentagon:
although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (7)
1. A compact sandstone micro-pore structure characterization method is characterized by comprising the following steps:
s1, selecting a cylindrical core of a compact sandstone reservoir, washing oil and drying, measuring the porosity and permeability of the core, and cutting the core into four sections;
s2, performing a cast body slice experiment on the section I core: dividing the casting body slice image into different pore units, calculating the shape factor of each pore, judging the pore shape based on the size of the shape factor, classifying the pore shapes according to the shapes, calculating the inscribed circle radius and the equivalent radius of the corresponding pore shape according to the relationship between the pore shape, the areas of different pore shapes and the inscribed circle radius of the pore shapes, and drawing a radius and frequency distribution histogram of the radius;
s3, performing a constant-speed mercury pressing experiment on the second section of core to obtain corrected constant-speed mercury pressing throat distribution;
s4, performing a high-pressure mercury intrusion test on the third section of core, and acquiring the complete throat radius and distribution of the core based on the high-pressure mercury intrusion test;
and S5, acquiring the complete pore radius and distribution of the core.
2. The method for characterizing the micro-pore structure of tight sandstone according to claim 1, wherein in step S2, the calculation formula of the shape factor is as follows:
wherein G is a form factor, noneDimension; a is the cross-sectional area of the pores, μm2(ii) a P is the perimeter of the pore, μm.
3. The method for characterizing the microstructure of tight sandstone according to claim 2, wherein in step S2, the formula for calculating the radius of the inscribed circle corresponding to the pore shape is as follows:
triangle:
a quadrangle:
pentagon:
irregular polygon: rEquivalence of＝0.5L (5)
Wherein A is a cross-sectional area of the voids, μm2And L is the pore length, μm.
4. The method for characterizing the microstructure of tight sandstone according to claim 1, wherein in step S3, the step of obtaining the modified constant-speed mercury intrusion throat distribution comprises the following steps:
s31, performing a constant-speed mercury injection experiment on the second section of core to obtain a curve of mercury injection pressure and mercury injection volume; calculating an extreme pressure interval by using the pore radius and the distribution thereof obtained based on the cast body slice in the step S2, and selecting a corresponding data segment from the constant-speed mercury injection pressure and mercury injection volume curve;
s32, processing the curve into an M-shaped curve segment, identifying pressure values and volume values corresponding to the pore and the throat from the curve segment, and drawing a pore capillary pressure curve, a throat capillary pressure curve and a total capillary pressure curve after correction;
and S33, calculating to obtain the corrected capillary pressure curve, pore, throat radius and distribution thereof.
5. The method for characterizing the microstructure of tight sandstone according to claim 4, wherein the calculation formula of the extreme pressure interval is as follows:
the calculation formula of the corrected capillary pressure curve, the corrected pore and the corrected throat radius is as follows:
in the formula, RmaxIs the maximum value of pore radius, μm, obtained on cast sheet; plbThe lower limit value of the mercury injection pressure of the constant-speed mercury pressure curve is MPa; rminIs the minimum value of pore radius, μm, obtained on cast sheet; pupThe upper limit value of the mercury injection pressure on the constant-speed mercury-pressing curve is MPa; rcpThe pore radius is the corrected pore radius of the constant-speed mercury pressing, and is mum; pcpThe corrected pore capillary pressure is MPa; rctThe diameter is the throat radius after the constant-speed mercury pressing correction, and is mum; pctThe pressure of the throat capillary is MPa.
6. The tight sandstone micro-pore structure characterization method of claim 1, wherein the step S4 comprises the following steps:
s41, performing a high-pressure mercury intrusion test on the third section of rock sample to obtain pore throat radius distribution based on a high-pressure mercury intrusion test;
s42, drawing the corrected radius and the distribution of the constant-speed mercury pressing throat and the radius and the distribution of the pore throat obtained by high-pressure mercury pressing in the same coordinate system;
selecting the radius and the distribution of the high-pressure mercury-pressing pore throat of the data before 0.12 mu m, and selecting the corrected radius and the distribution of the constant-speed mercury-pressing throat of the data after 0.12 mu m;
and after normalization processing, the two data are redrawn in a rectangular coordinate system to obtain the complete throat radius and the distribution of the rock sample.
7. The method for characterizing the microstructure of tight sandstone according to claim 1, wherein in step S5, the step of obtaining the complete pore radius and the distribution of the pore radius of the core comprises the following steps:
s51, measuring nuclear magnetic resonance T of the saturated water of the IV section core under the state of the completely saturated water2A spectral curve;
and S52, judging whether the pore shape distribution of the core is stable or not based on the pore shape factor and the distribution thereof acquired in the step S2.
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