CN108226002B - Method for obtaining secondary porosity based on cutoff value of secondary porosity spectrum of scale electrography - Google Patents
Method for obtaining secondary porosity based on cutoff value of secondary porosity spectrum of scale electrography Download PDFInfo
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Abstract
The invention discloses a method for acquiring secondary porosity based on a scale electrography secondary porosity spectrum cutoff value, which comprises the following steps: s1, establishing a secondary porosity spectrum cutoff value calculation formula: the cutoff value of the secondary porosity spectrum is a x + median porosity, a is a fixed coefficient and is the porosity variance in the range of the minimum porosity and the median porosity in a selected window on the electric imaging logging image; s2, calculating the secondary porosity of the rock core by using a rock core nuclear magnetic resonance T2 spectrum; and S3, calculating the numerical value of the fixed coefficient a in the formula by using the cut-off value of the core secondary porosity scale secondary porosity spectrum calculated by the core nuclear magnetic resonance T2 spectrum to obtain the scaled secondary porosity. The method adopts the nuclear magnetic resonance T2 spectrum scale of the rock core, obtains the fixed coefficient a in the secondary porosity spectrum cutoff value calculation formula by using a successive approximation method, increases the reliability of the secondary porosity spectrum cutoff value calculation result, and further obtains the secondary porosity obtaining method with high accuracy.
Description
Technical Field
The invention relates to the technical field of acquisition of secondary porosity of carbonate reservoirs, in particular to a method for acquiring secondary porosity based on a cutoff value of a secondary porosity spectrum of scale electrical imaging.
Background
The carbonate reservoir has the reservoir characteristics of simultaneous development of matrix pores (primary pores) and secondary pores, complex pore throat structure, various reservoir spaces, strong reservoir heterogeneity and the like. Due to the influence of diagenesis and the like, primary pores are often difficult to store effectively, the pore diameters of secondary pores are usually larger than those of the primary pores, the permeability is better than that of the primary pores, and the pore diameters are main storage spaces and transportation channels of oil and gas in carbonate reservoirs, so that the research on the logging evaluation method of the secondary porosity of the carbonate reservoirs is developed, especially the secondary porosity is calculated accurately, the method has important significance for the effectiveness evaluation of the carbonate reservoirs, and theoretical basis can be provided for the formulation and adjustment of oil field development schemes and the effective improvement of recovery ratio.
Because the formation of the secondary porosity is controlled by a series of factors such as corrosion action, cementation, diagenesis, biological action and the like, the response relation between a single logging parameter and the secondary porosity is generally poor, and the secondary porosity cannot be effectively evaluated by using conventional logging information, at present, the secondary porosity is evaluated and researched by adopting electric imaging logging information at home and abroad, wherein the method for calculating the secondary porosity mainly comprises the following 3 steps:
(1) calculating a reservoir porosity spectrum by using the electrical imaging logging data: firstly, selecting an electrical imaging logging image window, converting a borehole wall washing belt conductivity value in the window into a borehole wall washing belt resistivity value, converting a borehole wall washing belt resistivity matrix into the porosity of each imaging logging pixel point by utilizing an Archie's formula, carrying out frequency statistics on the porosity within a certain depth range of a reservoir in different porosity value intervals, and drawing a frequency histogram which is the electrical imaging porosity spectrum of a stratum in a coordinate system.
(2) Calculating a cutoff value in the porosity spectrum for distinguishing primary pores from secondary pores: the method for calculating the cutoff value of the porosity spectrum based on the porosity median value proposed by B.M.Newberry and the like of the Schlumberger company in 1996 and the method for calculating the cutoff value of the discriminant porosity spectrum based on the standard linear discriminant analysis proposed by T.S.Ramakrishan and the like in 1997 are mainstream calculation methods at present, both the methods for calculating the cutoff value of the porosity spectrum are mathematical calculation methods based on the porosity, the characteristics of the porosity of a reservoir can be reflected, the method is not influenced by the morphological characteristics of the porosity spectrum, the calculation precision of the cutoff value of the porosity spectrum depends on the value of a regional empirical coefficient, the applicability of the calculation method and the reliability of the calculation result are not high, and the calculation precision of the secondary porosity in the next step is directly influenced. In order to solve the problems, the Schneider and the like in China propose a calculation method of a Gaussian function fitting porosity spectrum cutoff value method based on the shape of a porosity spectrum, but the calculation precision of the method is closely related to the shape of the porosity spectrum, the method is not suitable for the situation that the bimodal interval in the porosity spectrum is large, and the application in a carbonate reservoir is limited.
(3) Reservoir secondary porosity calculation based on secondary porosity spectrum cutoff: determining a boundary of primary pores and secondary pores in the porosity spectrum according to the calculation result of the cutoff value of the porosity spectrum, integrating the area enclosed by the envelope curve of the secondary porosity spectrum at the rear side of the boundary, and obtaining the result of the integral calculation, namely the secondary porosity.
According to the method and the steps for calculating the secondary porosity of the carbonate reservoir, the problem that the secondary porosity of the carbonate reservoir cannot be calculated by conventional well logging is effectively solved by means of electric imaging well logging information. However, in the secondary porosity calculation link, or the calculation precision excessively depends on regional experience parameters, and the parameter selection lacks theoretical basis. In addition, the calculation accuracy is also affected by the porosity spectrum morphology, and the applicability of the method is limited.
Therefore, it is necessary to establish a new secondary porosity acquisition method to meet the requirement of improving the precision of the secondary porosity.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for acquiring secondary porosity based on a cut-off value of a secondary porosity spectrum of scale electrography, which improves reliability and accuracy.
The technical scheme adopted by the invention for solving the technical problems is as follows: the method for acquiring the secondary porosity based on the cutoff value of the secondary porosity spectrum of the scaled electrography comprises the following steps:
s1, establishing a secondary porosity spectrum cutoff value calculation formula:
secondary porosity spectrum cutoff value ═ a × + median porosity
Wherein a is a fixed coefficient and is a porosity variance in a range of a minimum porosity and a porosity median in a selected window on the electrical imaging log image, and the porosity median is the porosity median in the selected window;
s2, calculating the secondary porosity of the rock core by using a rock core nuclear magnetic resonance T2 spectrum;
s3, calculating the numerical value of a fixed coefficient a in the formula by using the cut-off value of the core secondary porosity scale secondary porosity spectrum calculated by the core nuclear magnetic resonance T2 spectrum:
adjusting the numerical value of a fixed coefficient a between 1 and 3 by adopting a secondary porosity spectrum cutoff value calculation formula in the step S1, controlling the calculation result of the secondary porosity spectrum cutoff value, and integrating the area enclosed by the porosity spectrum envelope line after the cutoff value to calculate the secondary porosity to obtain the secondary porosity of the porosity spectrum; and (4) carrying out error analysis on the successively calculated porosity spectrum secondary porosity and the secondary porosity obtained in the step (S2), wherein when the error is minimum, the corresponding a value is a determined value after calibration, and the corresponding porosity spectrum secondary porosity calculation result is the secondary porosity after calibration.
Preferably, in step S1, selecting a window on the electrical imaging log image, and calculating the sum of the minimum porosity and the porosity in the median porosity range in the window; calculating the percentage of the counting rate of each porosity in the range to the total counting rate, and calculating the variance of the porosity in the range of the minimum porosity and the median of the porosity according to the percentage; and setting a fixed coefficient a to multiply the variance to obtain a secondary porosity spectrum cutoff value, and obtaining a secondary porosity spectrum cutoff value calculation formula.
Preferably, in step S2, according to that the size of the core secondary porosity is equal to the volume of the large-aperture pore fluid discharged after centrifugation, a peak start time with the longest relaxation time in the porosity component before centrifugation is obtained according to a peak feature in the core nuclear magnetic resonance T2 spectrum distribution diagram, where the start time corresponds to a cutoff value of the secondary porosity spectrum T2, and the core secondary porosity, which is the cumulative porosity before centrifugation corresponding to the cumulative total porosity before centrifugation-the cutoff value of the secondary porosity spectrum T2, is obtained.
Preferably, the method further comprises the following steps:
s4, calculating the secondary porosity of the cast body slice;
and S5, verifying the precision of the porosity spectrum secondary porosity acquired in the step S3 by using the casting body slice secondary porosity.
Preferably, in step S4, preparing a casting slice from the reservoir corresponding to the selected window position on the electrical imaging log image in step S1;
and obtaining the type and the corresponding relative content of the secondary porosity of the casting sheet according to the identification result of the casting sheet, fitting the relation between the total surface porosity and the total porosity of the casting sheet to obtain a conversion relation between the total surface porosity and the total porosity of the casting sheet, and converting the secondary porosity into the secondary porosity of the casting sheet.
Preferably, the casting flake secondary pore types include intergranular pore, intragranular pore, matrix pore, texture erosion seam.
Preferably, in step S5, the accuracy of the obtained porosity spectrum secondary porosity is verified by calculating the mean absolute error between the secondary porosities through the casting sheet secondary porosities and the porosity spectrum.
Preferably, in step S5, the average absolute error is less than 5%
The invention provides another method for acquiring secondary porosity based on a cutoff value of a scale electrography secondary porosity spectrum, which comprises the following steps:
s1, establishing a secondary porosity spectrum cutoff value calculation formula:
secondary porosity spectrum cutoff (a + average porosity)
Wherein a is a fixed coefficient and the average porosity is an arithmetic average of all porosities in a selected window on the electrogram log image;
s2, calculating the secondary porosity of the rock core by using a rock core nuclear magnetic resonance T2 spectrum;
s3, calculating the numerical value of a fixed coefficient a in the formula by using the cut-off value of the core secondary porosity scale secondary porosity spectrum calculated by the core nuclear magnetic resonance T2 spectrum:
adjusting the numerical value of a fixed coefficient a between 1 and 3 by adopting a secondary porosity spectrum cutoff value calculation formula in the step S1, controlling the calculation result of the secondary porosity spectrum cutoff value, and integrating the area enclosed by the porosity spectrum envelope line after the cutoff value to calculate the secondary porosity to obtain the secondary porosity of the porosity spectrum; and (4) carrying out error analysis on the successively calculated porosity spectrum secondary porosity and the secondary porosity obtained in the step (S2), wherein when the error is minimum, the corresponding a value is a determined value after calibration, and the corresponding porosity spectrum secondary porosity calculation result is the secondary porosity after calibration.
Preferably, in step S2, according to that the size of the core secondary porosity is equal to the volume of the large-aperture pore fluid discharged after centrifugation, a peak start time with the longest relaxation time in the porosity component before centrifugation is obtained according to a peak feature in the core nuclear magnetic resonance T2 spectrum distribution diagram, where the start time corresponds to a cutoff value of the secondary porosity spectrum T2, and the core secondary porosity, which is the cumulative porosity before centrifugation corresponding to the cumulative total porosity before centrifugation-the cutoff value of the secondary porosity spectrum T2, is obtained.
The invention has the beneficial effects that: the core nuclear magnetic resonance T2 spectrum scale is adopted, the fixed coefficient a in the secondary porosity spectrum cutoff value calculation formula is obtained by a successive approximation method, the reliability of the secondary porosity spectrum cutoff value calculation result is greatly improved, and the secondary porosity obtaining method with high accuracy is further obtained.
The secondary porosity of the casting body sheet is used for verifying the result of the secondary porosity of the porosity spectrum, and the accuracy of the result of the secondary porosity is effectively guaranteed.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a schematic flow chart of a method for obtaining secondary porosity based on a graduated electrographic secondary porosity spectrum cutoff according to a first embodiment of the present invention;
FIG. 2 is a nuclear magnetic resonance T2 spectrum distribution diagram of a carbonate reservoir core in the invention;
FIG. 3 is a graph of the fit of the total porosity of the cast sheet to the total porosity of the cast sheet of the present invention.
Detailed Description
Referring to fig. 1, the method for obtaining secondary porosity based on scaled electrographic secondary porosity spectrum cut-off of the first embodiment of the invention comprises the following steps:
s1, establishing a secondary porosity spectrum cutoff value calculation formula:
secondary porosity spectrum cutoff value ═ a × + median porosity
Wherein a is a fixed coefficient; a porosity variance within a range of a minimum porosity and a median porosity in a selected window on the electrographic log; the median porosity is the median porosity in the selected window, and the physical meaning of the porosity is that the porosity is greater than 50% of the porosity and less than 50% of the porosity corresponding to a cumulative percentage of porosity distribution of 50%.
Specifically, in step S1, a window is selected on the electrical imaging log image, and the sum of the minimum porosity in the window and the porosity in the porosity median range is calculated; calculating the percentage of the counting rate of each porosity in the minimum porosity and porosity median range in the window to the total counting rate, and calculating the porosity variance in the minimum porosity and porosity median range according to the percentage; and setting a fixed coefficient a to multiply the variance to obtain a secondary porosity spectrum cutoff value, and obtaining a secondary porosity spectrum cutoff value calculation formula.
And S2, calculating the secondary porosity of the core by using the nuclear magnetic resonance T2 spectrum of the core.
Specifically, according to the fact that the size of the secondary porosity of the core is equal to (or approximately equal to) the volume of the large-aperture pore fluid discharged after centrifugation, the peak start time with the longest relaxation time in the porosity component before centrifugation is obtained according to the peak characteristics in the nuclear magnetic resonance T2 spectrum distribution diagram of the core, the start time corresponds to the cutoff value of the secondary porosity spectrum T2, and the cumulative porosity before centrifugation corresponding to the cumulative total porosity before centrifugation-the cutoff value of the secondary porosity spectrum T2 of the core is obtained.
S3, calculating the numerical value of the fixed coefficient a in the formula by using the cut-off value of the nuclear magnetic resonance secondary porosity scale secondary porosity spectrum of the rock core:
adjusting the numerical value of a fixed coefficient a between 1 and 3 by adopting a secondary porosity spectrum cutoff value calculation formula in the step S1, controlling the calculation result of the secondary porosity spectrum cutoff value, and integrating the area enclosed by the porosity spectrum envelope line after the cutoff value to calculate the secondary porosity to obtain the secondary porosity of the porosity spectrum; and (4) carrying out error analysis on the successively calculated porosity spectrum secondary porosity and the secondary porosity obtained in the step (S2), wherein when the error is minimum, the corresponding a value is a determined value after calibration, and the corresponding porosity spectrum secondary porosity calculation result is the secondary porosity after calibration.
Further, the method for obtaining secondary porosity based on scaled electrographic secondary porosity spectrum cut-off value according to the first embodiment of the present invention further comprises the following steps:
and S4, calculating the secondary porosity of the casting body slice.
Wherein the cast sheet is prepared corresponding to the selected window on the electrographic log image of step S1.
And obtaining the type and the relative content of the secondary porosity of the casting sheet according to the identification result of the casting sheet, fitting the relation between the total surface porosity and the total porosity of the casting sheet to obtain a conversion relation between the total surface porosity and the total porosity of the casting sheet, and converting the secondary porosity into the secondary porosity of the casting sheet. The casting body flake secondary pore types comprise inter-granular dissolving pores, intra-granular dissolving pores, matrix dissolving pores and structural dissolving seams. The total areal porosity of the cast sheet includes the total areal porosity of the cellular and slot-like cells in the cast sheet.
S5, verifying the precision of the porosity spectrum secondary porosity acquired in the step S3 by using the casting sheet secondary porosity:
and calculating the average absolute error between the secondary porosities through the casting sheet secondary porosities and the porosity spectrum, and verifying the accuracy (namely precision) of the obtained porosity spectrum secondary porosities.
If the verification result meets the precision of the relevant requirement, outputting a secondary porosity obtaining result; if not, returning to the step S3 to determine the secondary porosity spectrum cutoff value again until the acquisition precision is met.
The method for acquiring the secondary porosity based on the secondary porosity spectrum cutoff value of the scaled electrography in the second embodiment of the invention comprises the following steps:
s1, establishing a secondary porosity spectrum cutoff value calculation formula:
secondary porosity spectrum cutoff (a + average porosity)
Where a is a fixed coefficient and the average porosity is the arithmetic average of all porosities in a selected window on the electrogram log image.
And S2, calculating the secondary porosity of the core by using the nuclear magnetic resonance T2 spectrum of the core.
Specifically, according to the fact that the size of the secondary porosity of the core is equal to (or approximately equal to) the volume of the large-aperture pore fluid discharged after centrifugation, the peak start time with the longest relaxation time in the porosity component before centrifugation is obtained according to the peak characteristics in the nuclear magnetic resonance T2 spectrum distribution diagram of the core, the start time corresponds to the cutoff value of the secondary porosity spectrum T2, and the cumulative porosity before centrifugation corresponding to the cumulative total porosity before centrifugation-the cutoff value of the secondary porosity spectrum T2 of the core is obtained.
S3, calculating the numerical value of a fixed coefficient a in the formula by using the cut-off value of the core secondary porosity scale secondary porosity spectrum calculated by the core nuclear magnetic resonance T2 spectrum:
adjusting the numerical value of a fixed coefficient a between 1 and 3 by adopting a secondary porosity spectrum cutoff value calculation formula in the step S1, controlling the calculation result of the secondary porosity spectrum cutoff value, and integrating the area enclosed by the porosity spectrum envelope line after the cutoff value to calculate the secondary porosity to obtain the secondary porosity of the porosity spectrum; and (4) carrying out error analysis on the successively calculated porosity spectrum secondary porosity and the secondary porosity obtained in the step (S2), wherein when the error is minimum, the corresponding a value is a determined value after calibration, and the corresponding porosity spectrum secondary porosity calculation result is the secondary porosity after calibration.
Further, the method for obtaining secondary porosity based on scaled electrographic secondary porosity spectrum cut-off value according to the second embodiment of the present invention further comprises the following steps:
and S4, calculating the secondary porosity of the casting body slice.
And S5, verifying the precision of the porosity spectrum secondary porosity acquired in the step S3 by using the casting body slice secondary porosity.
The specific operations of steps S4 and S5 can be referred to the above description of the first embodiment.
The invention is explained in detail by taking an 11-1 biological reef limestone oil field which flows through a basin at the mouth of a Zhujiang river as an example and taking LH11-1-D5P1 wells as an example for obtaining the secondary porosity of a target interval:
secondary porosity spectrum cutoff value ═ a × + median porosity
In the formula: -a variance of the minimum porosity to a median porosity range;
a, fixing a coefficient, wherein the coefficient determines the calculation precision of a secondary porosity spectrum cut-off value.
The secondary porosity is approximately equal in magnitude to the volume of large pore fluid discharged after centrifugation. And finding the third peak starting time with the longest relaxation time in the porosity component before centrifugation, wherein the time corresponds to a cut-off value of the secondary porosity spectrum T2, and the accumulated porosity before centrifugation corresponding to the cumulative total porosity before centrifugation minus the cut-off value of the secondary porosity spectrum T2 is the secondary porosity.
And (3) performing error analysis on the porosity spectrum secondary porosity calculated by the interval of the LH11-1-D5P1 well target step and the nuclear magnetic resonance T2 spectrum, and when a is 1.01, minimizing the error between the calculated secondary porosity and the nuclear magnetic resonance T2 spectrum calculated secondary porosity, thereby determining that the fixed coefficient a in a cutoff value formula of the secondary porosity spectrum is 1.01 and completing the calibration of the secondary porosity.
Fig. 3 is a graph of the fit of the total porosity of the cast slab to the total porosity, from which an example of the transformation of the total porosity to the cast slab porosity is found, y being 0.61x +6.75, and the secondary porosity is converted to the secondary porosity of the cast slab.
TABLE 1 Secondary porosity accuracy analysis
The secondary porosity obtained by a casting body slice and a nuclear magnetic resonance method is compared, and the secondary porosity obtained by a porosity spectrum is well in consistent relation with the secondary porosity of the casting body slice and the secondary porosity calculated by a nuclear magnetic resonance T2 spectrum.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (7)
1. A method for obtaining secondary porosity based on a cut-off value of a secondary porosity spectrum of scale electrography is characterized by comprising the following steps:
s1, establishing a secondary porosity spectrum cutoff value calculation formula:
secondary porosity spectrum cutoff = a × + median porosity
Wherein a is a fixed coefficient and is a porosity variance in a range of a minimum porosity and a porosity median in a selected window on the electrical imaging log image, and the porosity median is the porosity median in the selected window;
s2, calculating the secondary porosity of the rock core by using a rock core nuclear magnetic resonance T2 spectrum;
s3, calculating the numerical value of a fixed coefficient a in the formula by using the cut-off value of the core secondary porosity scale secondary porosity spectrum calculated by the core nuclear magnetic resonance T2 spectrum:
adjusting the numerical value of a fixed coefficient a between 1 and 3 by adopting a secondary porosity spectrum cutoff value calculation formula in the step S1, controlling the calculation result of the secondary porosity spectrum cutoff value, and integrating the area enclosed by the porosity spectrum envelope line after the cutoff value to calculate the secondary porosity to obtain the secondary porosity of the porosity spectrum; performing error analysis on the successively calculated porosity spectrum secondary porosity and the secondary porosity obtained in the step S2, wherein when the error is minimum, the corresponding a value is a determined value after calibration, and the corresponding porosity spectrum secondary porosity calculation result is the secondary porosity after calibration;
s4, calculating the secondary porosity of the casting body slice: taking the reservoir corresponding to the position of the selected window on the electrical imaging logging image in the step S1, and preparing a casting body slice; obtaining the type and the corresponding relative content of the secondary porosity of the casting sheet according to the identification result of the casting sheet, fitting the relation between the total surface porosity and the total porosity of the casting sheet to obtain a conversion relation between the total surface porosity and the total porosity of the casting sheet, and converting the secondary porosity into the secondary porosity of the casting sheet;
s5, verifying the precision of the porosity spectrum secondary porosity acquired in the step S3 by using the casting sheet secondary porosity: and calculating the average absolute error between the secondary porosities through the casting sheet secondary porosities and the porosity spectrum, and verifying the accuracy of the obtained porosity spectrum secondary porosities.
2. The method for obtaining secondary porosity based on the graduated electrical imaging secondary porosity spectrum cutoff value according to claim 1, wherein in step S1, a window is selected on the electrical imaging log image, and the sum of the minimum porosity in the window and the porosity in the porosity median range is calculated; calculating the percentage of the counting rate of each porosity in the range to the total counting rate, and calculating the variance of the porosity in the range of the minimum porosity and the median of the porosity according to the percentage; and setting a fixed coefficient a to multiply the variance to obtain a secondary porosity spectrum cutoff value, and obtaining a secondary porosity spectrum cutoff value calculation formula.
3. The method for obtaining the secondary porosity based on the graduated electrical imaging secondary porosity spectrum cutoff value as claimed in claim 1, wherein in step S2, according to the fact that the size of the secondary porosity of the core is equal to the volume of the large-aperture pore fluid discharged after centrifugation, the peak start time with the longest relaxation time in the porosity component before centrifugation is obtained according to the peak characteristics in the nuclear magnetic resonance T2 spectrum distribution diagram of the core, and the start time corresponds to the secondary porosity spectrum T2 cutoff value, so that the secondary porosity of the core = the cumulative total porosity before centrifugation-the cumulative porosity before centrifugation corresponding to the secondary porosity spectrum T2 cutoff value is obtained.
4. The method for obtaining secondary porosity based on scaled electrographic secondary porosity spectrum cutoff of claim 1, wherein the casting sheet secondary porosity types comprise intergranular porosity, intragranular porosity, matrix porosity, texture erosion seams.
5. The method for obtaining secondary porosity based on graduated electromyographic secondary porosity spectral cutoffs of claim 1, wherein in step S5, the mean absolute error is less than 5%.
6. A method for obtaining secondary porosity based on a cut-off value of a secondary porosity spectrum of scale electrography is characterized by comprising the following steps:
s1, establishing a secondary porosity spectrum cutoff value calculation formula:
secondary porosity spectrum cutoff = a + average porosity
Wherein a is a fixed coefficient and the average porosity is an arithmetic average of all porosities in a selected window on the electrogram log image;
s2, calculating the secondary porosity of the rock core by using a rock core nuclear magnetic resonance T2 spectrum;
s3, calculating the numerical value of a fixed coefficient a in the formula by using the cut-off value of the core secondary porosity scale secondary porosity spectrum calculated by the core nuclear magnetic resonance T2 spectrum:
adjusting the numerical value of a fixed coefficient a between 1 and 3 by adopting a secondary porosity spectrum cutoff value calculation formula in the step S1, controlling the calculation result of the secondary porosity spectrum cutoff value, and integrating the area enclosed by the porosity spectrum envelope line after the cutoff value to calculate the secondary porosity to obtain the secondary porosity of the porosity spectrum; performing error analysis on the successively calculated porosity spectrum secondary porosity and the secondary porosity obtained in the step S2, wherein when the error is minimum, the corresponding a value is a determined value after calibration, and the corresponding porosity spectrum secondary porosity calculation result is the secondary porosity after calibration;
s4, calculating the secondary porosity of the casting body slice: taking the reservoir corresponding to the position of the selected window on the electrical imaging logging image in the step S1, and preparing a casting body slice; obtaining the type and the corresponding relative content of the secondary porosity of the casting sheet according to the identification result of the casting sheet, fitting the relation between the total surface porosity and the total porosity of the casting sheet to obtain a conversion relation between the total surface porosity and the total porosity of the casting sheet, and converting the secondary porosity into the secondary porosity of the casting sheet;
s5, verifying the precision of the porosity spectrum secondary porosity acquired in the step S3 by using the casting sheet secondary porosity: and calculating the average absolute error between the secondary porosities through the casting sheet secondary porosities and the porosity spectrum, and verifying the accuracy of the obtained porosity spectrum secondary porosities.
7. The method for obtaining the secondary porosity based on the graduated electrical imaging secondary porosity spectrum cutoff value as claimed in claim 6, wherein in step S2, according to the fact that the size of the secondary porosity of the core is equal to the volume of the large-aperture pore fluid discharged after centrifugation, the peak start time with the longest relaxation time in the porosity component before centrifugation is obtained according to the peak characteristics in the nuclear magnetic resonance T2 spectrum distribution diagram of the core, the start time corresponds to the cutoff value of the secondary porosity spectrum T2, and the cumulative porosity before centrifugation corresponding to the cumulative total porosity before centrifugation-the cutoff value of the secondary porosity spectrum T2 of the core is obtained.
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