CN110618158A - Method for constructing capillary pressure curve of rock core by utilizing nuclear magnetic resonance information - Google Patents
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Abstract
The invention relates to a method for constructing a capillary pressure curve of a rock core by utilizing nuclear magnetic resonance information, which firstly starts with a nuclear magnetic resonance experiment and the characteristics of a corresponding capillary pressure curve, summarizes controlled conditions that Pc and 1/T2 are in a two-section fitting relationship and a three-section fitting relationship, secondly, establishing a universal fitting relation between Pc and 1/T2, between the T2 geometric mean and the throat diameter mean, and between the T2 geometric mean and the segmentation point 1/T2, then, aiming at the rock sample only measured by the nuclear magnetic resonance experiment, the extracted T2 geometric mean value is used for obtaining the throat diameter mean value, the rock sample Pc and 1/T2 are determined to be in several sections of fitting relation according to the numerical value of the throat diameter mean value, and then, the value of the 1/T2 of the rock sample segmentation point is obtained by utilizing the geometric mean value of T2, and finally, a capillary pressure curve of the rock sample is drawn by utilizing the nuclear magnetic resonance T2 spectrum information of the rock sample, and the pore structure evaluation parameter is obtained according to the capillary pressure curve. Compared with the capillary pressure curve measured by experiments, the result constructed by the method has better inosculation and can accurately calculate the mean value of the diameter of the larynx.
Description
Technical Field
The invention relates to a method for constructing a capillary pressure curve of a rock core, in particular to a method for constructing a capillary pressure curve of the rock core by utilizing nuclear magnetic resonance information, and belongs to the technical field of reservoir pore structure evaluation.
Background
As the exploitation of oil fields enters the middle and later stages, the low-porosity and low-permeability reservoir gradually becomes the main body of increasing the storage and the production of old oil fields in the east of China. Because the reservoir has the characteristics of complex pore structure, strong heterogeneity and the like, the evaluation method of the conventional reservoir is often poor in effect when applied to the reservoir, for example, fluid interpretation is easy to misjudge, the accuracy of a calculation result of a pore permeability parameter is low, an Archie saturation formula is not suitable, and the like. In general, the calculation precision of the reservoir parameters does not meet the industry requirements, so that the well logging interpretation work is difficult. In order to improve the interpretation and evaluation precision of the reservoir stratum, the development of the evaluation of the pore structure of the reservoir stratum is a key technology for solving the problem of difficult logging evaluation of the low-porosity and low-permeability reservoir stratum.
The capillary pressure curve is an important means for quantitatively evaluating the pore structure of a reservoir and dividing the type of the reservoir. At present, the determination of the capillary pressure curve still needs to be completed in a laboratory, the core sample is limited, and discrete data points cannot be evaluated in a more detailed way in the whole well section. With the rise of nuclear magnetic resonance technology, a pore radius extracted from a nuclear magnetic resonance experiment T2 spectrum is compared with a roar channel radius extracted from a capillary pressure curve by numerous scholars, and when the nuclear magnetic resonance experiment T2 spectrum and the roar channel radius are in proportion or correlation, a nuclear magnetic resonance T2 spectrum can be converted into the capillary pressure curve, and finally a pseudo capillary pressure curve of a whole well section is obtained through the nuclear magnetic resonance logging technology, so that the purpose of continuous and quantitative evaluation of a pore structure of a reservoir is achieved. Certainly, in the process of obtaining the pseudo capillary pressure curve of the whole well section from the nuclear magnetic resonance logging, a plurality of factors such as influence of two-phase fluids (oil and water coexisting in pores) and the like need to be considered, so that the technology focuses on how to construct the core capillary pressure curve by utilizing the T2 spectrum information of the nuclear magnetic resonance experiment, and the aim of continuously and quantitatively evaluating the pore structure of the reservoir by obtaining the pseudo capillary pressure curve of the whole well section through the nuclear magnetic resonance logging technology is finally achieved.
There are several methods in the published literature for fitting a pseudo capillary pressure curve using a nuclear magnetic resonance experiment T2 spectrum:
a linear scaling method for single conversion coefficient. Referring to SPWLA 40th Annual Logging Symposium, 5.1999, Yakov Volokitin et al, Constructing Capillary Pressure in the present of hydracylinders, described by a linear scale of a single transformation coefficient in actual data, but the transformed result was very good in the large pore portion, but the non-matching bifurcation occurred in the small pore portion due to the complex and variable relationship between the pore radius and the throat radius.
And II, a step power function calibration method. In journal of the university of Jilin (the edition of Earth science) and the improvement method for evaluating the rock pore size distribution through nuclear magnetic resonance T2 distribution and the novel method for constructing the capillary pressure curve through the nuclear magnetic resonance T2 distribution in the nuclear magnetic resonance T2 distribution, researchers find that a power function relationship exists between T2 distribution and pore size distribution according to core experiment measurement, and obtain a single power function constructed capillary pressure curve of unimodal T2 distribution; the double peak T2 distribution uses the trough between two peaks as the boundary point of big and small holes, and uses different power functions to construct the capillary pressure curve by sections.
And thirdly, a two-dimensional equal-area scaling method. Referring to the journal of "logging technology" in 2 months in 2009, in the text of "application of nuclear magnetic resonance logging in reservoir pore structure evaluation", researchers first convert a measured capillary pressure curve into pore-throat radius distribution, determine a transverse conversion coefficient between a T2 spectrum of each sample and the corresponding pore-throat radius distribution by using a differential similarity principle, then determine a longitudinal conversion coefficient between a T2 spectrum of each sample and the corresponding pore-throat radius distribution by using a piecewise equal-area scaling method, and finally establish a relationship between the transverse conversion coefficient and the longitudinal conversion coefficient and rock porosity and permeability to realize a process of constructing the capillary pressure curve.
And fourthly, a matrix calibration method. In the article "matrix method for converting nuclear magnetic resonance T2 spectrum to pseudo capillary pressure curve" in journal of natural gas earth science of 12 months 2015, researchers propose a matrix method for converting the aperture radius and the throat radius on the whole based on the idea of linear conversion.
Combining the above four methods, it was found that the relationship between pore radius extracted from the T2 spectrum and the throat radius extracted from the capillary pressure curve is not simply a scale relationship. The change in the T2 distribution morphology reflects a change in porosity, and when the T2 distribution is unimodal, it does not represent the absence of macropores, but only the predominance of micropores and microporosities, and thus the first, second and fourth methods referred to herein with a single scale relationship are one-sided. When the distribution of T2 is bimodal, large, medium and small pores are developed, and the homogeneity is good, a multi-section different scale fitting relationship appears between the large, medium and small pores, and the basis of the section is a node which actually reflects the change of the pores, so that the description of the two sections provided by the second method is quite general. In addition, the trough between the two wave crests is used as a large-hole and small-hole dividing point, so that the value selection of a homogeneous reservoir is not problematic, but the reservoir with large pore structure change easily causes segmentation inaccuracy due to the value selection, and errors are generated on the constructed capillary pressure curve. The third method and the second method determine the fitting in several sections according to the form of the T2 spectrum, which is too ideal, and in addition, the method of fitting the conversion coefficient according to the rock porosity and the permeability does not have problems in the rock core data, but has problems in the actual stratum, because the pore permeability in the actual stratum is an unknown parameter, calculation is needed to obtain the fitting, under the condition of good pore permeability, the pore permeability is easy to be determined, the error of the constructed capillary pressure curve is relatively small, under the condition of pore permeability difference, the pore permeability is not easy to be determined, and the error of the constructed capillary pressure curve is large.
Disclosure of Invention
The invention aims to overcome the defects of a method for fitting a pseudo capillary pressure curve in the prior art, and provides a method for constructing a core capillary pressure curve by using nuclear magnetic resonance information, so that the precision of constructing the capillary pressure curve can be improved, and accurate pore structure parameters can be obtained.
In order to solve the technical problems, the method for constructing the capillary pressure curve of the rock core by utilizing the nuclear magnetic resonance information sequentially comprises the following steps of: drilling a plurality of rock samples on a representative rock core in a certain area, and performing oil washing and salt washing treatment on all the rock samples; secondly, cutting each rock sample into two sections, wherein the length of each section is not less than 20mm, one section is used for nuclear magnetic resonance experiment measurement, and the other section is used for capillary pressure curve measurement; thirdly, measuring the porosity of the rock sample by using a nuclear magnetic resonance experimental instrument, performing inversion to obtain a nuclear magnetic resonance experimental T2 spectrum, and calculating to obtain the permeability; fourthly, carrying out mercury intrusion experiment on another rock sample section from the same rock sample as the third step to obtain a capillary pressure curve; fifthly, analyzing the T2 spectrum of the nuclear magnetic resonance experiment of the step three, establishing a relation graph of capillary pressure Pc and 1/T2 of the rock sample, determining whether the relation between the two can be divided into two sections or three sections in the rock sample, reading a 1/T2 value corresponding to a segmentation point of the sample, and defining each segmentation point as an end point of a large pore throat or a starting point of a small pore throat; sixthly, repeating the steps from the third step to the fifth step, and concluding a rock sample with a two-section fitting relationship and a rock sample with a three-section fitting relationship between the capillary pressure Pc and 1/T2; putting capillary pressure curves of various rock samples in an intersection graph under the same coordinate system, dividing all the capillary pressure curves into several types according to forms, and extracting a throat diameter mean value from the capillary pressure curves of each rock sample to represent the division of the several types; inducing the distribution intervals of the average values of the diameters of the throats corresponding to the rock samples with the relationship between capillary pressure Pc and 1/T2 in a two-section fitting relationship and the rock samples with a three-section fitting relationship respectively, and further establishing a general fitting relation formula I between the capillary pressure Pc and 1/T2 of each section of each type; the self-sustaining sample is characterized in that the self-sustaining sample extracts a T2 geometric mean value from a nuclear magnetic resonance experiment T2 spectrum of each rock sample, and a general fitting relational expression II between the T2 geometric mean value and the throat diameter mean value of the rock sample and a general fitting relational expression III between the T2 geometric mean value of the rock sample and a segmentation point 1/T2 are established; the method is characterized in that the corresponding capillary pressure Pc is calculated according to the general fitting relation obtained in the steps and the self-tapping step aiming at the rock sample only measuring the nuclear magnetic resonance experiment T2 spectrum in the rock core of the same region, and the capillary pressure curve of the rock sample is drawn.
Compared with the prior art, the invention has the following beneficial effects: starting from the corresponding information between the nuclear magnetic resonance T2 spectrum of a single rock sample and the capillary pressure curve, and then summarizing the regularity of the results of all experimental samples in a region, a method for sectional classification is sought, which aims to improve the precision of constructing the capillary pressure curve and lay a foundation for finally realizing the purpose of obtaining the pseudo capillary pressure curve of the whole well section through the NMR logging technology to carry out continuous and quantitative evaluation on the pore structure of the reservoir. According to the invention, in the regular summary of the nuclear magnetic resonance T2 spectrum and the capillary pressure curve of the single rock sample, the relation between the single rock sample Pc and the 1/T2 is not in a one-section fitting relation or a two-section fitting relation, but in a two-section fitting relation or a three-section fitting relation. When the invention judges that Pc and 1/T2 are in several-segment fitting relation to any rock sample, the method for finding the corresponding relation from the single-peak or double-peak form of the nuclear magnetic resonance T2 spectrum is not reliable, and the control parameter that Pc and 1/T2 are in several-segment fitting relation is found from the corresponding information between the nuclear magnetic resonance T2 spectrum and the capillary pressure curve of a single rock sample. When the 1/T2 corresponding to the segmentation points is calculated, the 1/T2 corresponding to the segmentation points is calculated through the geometric mean value of T2, and compared with the 1/T2 which takes the wave trough between two peaks of a nuclear magnetic resonance T2 spectrum as the corresponding segmentation point, the accuracy is greatly improved.
As a preferable scheme of the invention, the invention also comprises the following steps: and acquiring pore throat radius distribution of the rock sample according to the capillary pressure curve of the rock sample obtained in the step, and calculating reservoir pore structure parameters such as maximum pore throat radius, median pressure, displacement pressure, mean coefficient, sorting coefficient and the like. The obtained pore structure parameters are convenient and accurate.
As a further preferable aspect of the present invention, the step iii specifically includes the following sub-steps: (3.1) making the rock sample section for nuclear magnetic resonance experiment measurement reach 100% water saturation, performing nuclear magnetic resonance experiment measurement on the rock sample section, determining the total pore volume, and calculating the porosity psi of the rock sample section according to the volume of the rock sample section; performing centrifugal water drainage on the rock sample section to enable the rock sample section to reach a water-binding state, performing nuclear magnetic resonance experiment measurement again, wherein the echo interval time is 0.35ms, and performing attenuation inversion processing on an original nuclear magnetic resonance attenuation curve to obtain a nuclear magnetic resonance experiment T2 spectrum of the rock sample section, wherein T2 is transverse relaxation time in ms; and (3.3) adopting a coats-cutoff model to calculate the permeability K of the rock sample. The parameters of porosity and permeability obtained through nuclear magnetic resonance experiments can more effectively reflect the influence of different physical properties on the spectrum form of the nuclear magnetic resonance T2.
As a further preferable aspect of the present invention, the step fourth specifically includes the following sub-steps: drying the rock sample, placing the rock sample in a rock sample pressure-bearing chamber of a mercury porosimeter, and sealing and vacuumizing; pressing mercury into the pores of the rock sample section from a certain lower constant pressure, and recording the volume of mercury entering the rock sample under each constant pressure, wherein the mercury squeezing pressure is equivalent to capillary pressure Pc of the rock sample and has a unit of MPa; increasing the mercury squeezing pressure in sequence and repeating the measuring process until the set maximum mercury injection pressure is reached; and (4.4) calculating the mercury saturation of the rock sample section according to the corresponding mercury injection volume, so as to obtain a capillary pressure curve of the rock sample section. The capillary pressure curve is obtained by adopting a mercury pressing method, so that convenience is realized, and the experimental period can be saved.
As a further preferable scheme of the invention, the step fifthly specifically comprises the following substeps: reversely accumulating the ordinate porosity component of the rock sample from the maximum value to the minimum value according to the transverse relaxation time T2 to obtain a reversely accumulated porosity component curve, and dividing the reversely accumulated porosity component curve by the porosity of the rock sample to obtain a T2 spectrum accumulated curve which is similar to the capillary pressure curve in physical significance and form; from the spectrum accumulation curve of T2, 1/T2 corresponding to a value equivalent to the mercury saturation in the capillary pressure curve of step four is found; and (5.3) establishing a relation graph of capillary pressure Pc and 1/T2 of the rock sample, determining whether the relation between the capillary pressure Pc and the 1/T2 can be divided into two or three sections in the rock sample, and reading a 1/T2 value corresponding to a section point of the sample. The porosity component reverse accumulation is carried out from the maximum value to the minimum value according to the transverse relaxation time T2, namely the large pore is reversely accumulated to the small pore, which is consistent with the capillary pressure change from the large pore throat to the small pore throat reflected by the capillary pressure curve, so that the rule summarization is carried out by starting from the corresponding information between the single nuclear magnetic resonance T2 spectrum and the capillary pressure curve.
As a further preferable aspect of the present invention, in the step (5.2), if a value equivalent to the mercury saturation in the capillary pressure curve of the step (fourth) cannot be directly found from the T2 spectrum accumulation curve, linear interpolation is performed from upper and lower sections of adjacent mercury saturations. The corresponding data points are obtained through linear interpolation, and the method is convenient, quick, reliable and accurate.
As a further preferred version of the present invention, said step advantageously comprises the following sub-steps: extracting a T2 geometric mean value from a nuclear magnetic resonance experiment T2 spectrum, calculating according to the general fitting relation II of the step of the self-care, and determining whether the relation between the capillary pressure Pc of the rock sample and 1/T2 is in a two-segment fitting relation or a three-segment fitting relation; calculating 1/T2 corresponding to the segmentation point according to a general fitting relational expression of step self-care through a geometric mean value T2; respectively calculating capillary pressure Pc according to different sections by using the first general fitting relation in the step (10.3) as an ordinate of a capillary pressure curve; and (10.4) converting the porosity component of the rock sample nuclear magnetic resonance experiment T2 spectrum into approximate mercury saturation, and drawing a capillary pressure curve of the rock sample as an abscissa of the capillary pressure curve. By summarizing the rule of the corresponding relation between the nuclear magnetic resonance T2 spectrum and the capillary pressure curve of the single rock sample, the obtained rule is applied to the rock sample only measuring the nuclear magnetic resonance experiment T2 spectrum in the rock core of the same region. The geometric mean value of T2 is extracted through a nuclear magnetic resonance experiment T2 spectrum, the mean value of the throat diameter is obtained through fitting, the method is used for judging whether any rock sample Pc and 1/T2 are in a two-section fitting relation or a three-section fitting relation, and compared with a method for judging by using single-peak and double-peak forms of a nuclear magnetic resonance T2 spectrum, the method is greatly improved in accuracy.
Drawings
The invention will be described in further detail with reference to the following drawings and detailed description, which are provided for reference and illustration purposes only and are not intended to limit the invention.
FIG. 1 is a diagram of the nuclear magnetic resonance T2 spectrum of a sample of No. 41 sandstone reservoir in gold lake in the northeast China basin.
FIG. 2 is a diagram of the nuclear magnetic resonance T2 spectrum of a sample of a depressed sandstone reservoir 46 from gold lake in the North Suzhou basin in China.
FIG. 3 is a schematic diagram of capillary pressure curves of samples of No. 41 sandstone reservoir sunk in gold lake in the northeast of China.
FIG. 4 is a schematic representation of the capillary pressure curve of a sample number 46 of a depressed sandstone reservoir from gold lake in the North and China basin.
FIG. 5 is a schematic diagram showing the conversion relationship between Pc and 1/T2 of samples of the number 41 sandstone reservoir in the gold lake in the northeast China basin.
FIG. 6 is a schematic diagram showing two-stage conversion relationship between Pc and 1/T2 of samples of a depressed sandstone reservoir No. 46 in gold lake in the North and China basin.
FIG. 7 is a schematic diagram of three-stage conversion relationship between Pc and 1/T2 of samples of the depressed sandstone reservoir No. 46 of the gold lake in the North and China basin.
FIG. 8 is a schematic diagram of comparison between a capillary pressure curve and an actually measured capillary pressure curve respectively constructed by a two-stage conversion relation and a three-stage conversion relation between Pc and 1/T2 of samples of a depressed sandstone reservoir 46 of gold lake in the North and China basin.
Fig. 9 is a schematic diagram of capillary pressure curves of samples No. 41 and No. 48 of a sandstone reservoir sunk in gold lake in the northeast of China.
FIG. 10 is a schematic diagram of three-stage conversion relationship between Pc and 1/T2 of a sample of No. 48 of a sandstone reservoir sunk in gold lake in the North and China basin.
FIG. 11 is a schematic diagram of the relationship between the geometric mean value of T2 and 1/T2 of a sandstone reservoir sunk in gold lake in the North and China basin.
FIG. 12 is a diagram of the classification results of capillary pressure curve morphology of a sandstone reservoir sunken in gold lake in the northeast of China.
FIG. 13 is a cross plot of the mean value of geometric time versus the mean value of throat diameter of a sandstone reservoir T2 sunk in gold lake in the North Suzhou basin in China.
Fig. 14 is a schematic diagram of a comparison of a capillary pressure curve measured on samples of a number 22 sandstone reservoir sunk in gold lake in the northeast of China with a constructed capillary pressure curve.
Fig. 15 is a schematic diagram of the comparison of the actual measured capillary pressure curve of a sample of a depressed sandstone reservoir 57 number from gold lake in the northeast of China with the constructed capillary pressure curve.
FIG. 16 is a cross plot of mean calculated values of throat diameters of depressed sandstone reservoirs in gold lake in the North Suzhou basin in China and the results of laboratory analysis.
Detailed Description
The technical scheme of the invention is described below by taking the rock sample of a sandstone reservoir sunk in gold lake in the northwest basin of China as an example, but the invention is not limited by the scheme.
The invention relates to a method for constructing a capillary pressure curve of a rock core by utilizing nuclear magnetic resonance information, which sequentially comprises the following steps of:
the rock core analysis method includes drilling a plurality of rock samples with the diameter of 25.4mm and the length of 45mm ~ 65mm on a representative rock core of a sandstone sunk in gold lake of the North Suzhou basin, performing oil and salt washing treatment on all the rock samples, and meeting the requirements of the rock core conventional analysis method standard in SY/T5336 + 1996.
Secondly, each rock sample is cut into two sections respectively, two ends of each section are ground flat respectively, the length of each section after being ground flat is not less than 20mm, one section is used for nuclear magnetic resonance experiment measurement, and the other section is used for measuring a capillary pressure curve.
Thirdly, measuring the porosity of the rock sample by using a nuclear magnetic resonance experimental instrument according to the standard of SY/T6490-2000, performing inversion to obtain a nuclear magnetic resonance experimental T2 spectrum, and calculating to obtain the permeability. The NMR T2 spectrum of sample No. 41 is shown in FIG. 1, and the porosity of sample No. 41 is 8.9%, and the permeability is 0.02 × 10-3μm2FIG. 2 shows a NMR T2 spectrum of sample No. 46, corresponding to sample No. 46 having a porosity of 15.3% and a permeability of 21.5X 10-3μm2It can be seen that when the corresponding physical properties of the two samples are different, the T2 spectrum morphology is obviously different, the physical properties of the No. 41 sample are poor, the T2 spectrum morphology presents a single peak characteristic, the physical properties of the No. 46 sample are relatively good, and the T2 spectrum morphology presents a double peak characteristic.
The step three specifically comprises the following substeps: (3.1) making the rock sample section for nuclear magnetic resonance experiment measurement reach 100% water saturation, performing nuclear magnetic resonance experiment measurement on the rock sample section, determining the total pore volume, and calculating the porosity psi of the rock sample section according to the volume of the rock sample section; performing centrifugal water drainage on the rock sample section to enable the rock sample section to reach a water-binding state, performing nuclear magnetic resonance experiment measurement again, wherein the echo interval time is 0.35ms, and performing attenuation inversion processing on an original nuclear magnetic resonance attenuation curve to obtain a nuclear magnetic resonance experiment T2 spectrum of the rock sample section, wherein T2 is transverse relaxation time in ms; and (3.3) adopting a coats-cutoff model to calculate the permeability K of the rock sample.
And fourthly, performing mercury injection experiment on another rock sample section from the same rock sample as the third step according to the standard of SY/T/5346-2005 to obtain a capillary pressure curve.
Step four specifically includes the following substeps: drying the rock sample, placing the rock sample in a rock sample pressure-bearing chamber of a mercury porosimeter, and sealing and vacuumizing; pressing mercury into the pores of the rock sample section from a certain lower constant pressure, and recording the volume of mercury entering the rock sample under each constant pressure, wherein the mercury squeezing pressure is equivalent to capillary pressure Pc of the rock sample and has a unit of MPa; increasing the mercury squeezing pressure in sequence and repeating the measuring process until the set maximum mercury injection pressure is reached; and (4.4) calculating the mercury saturation of the rock sample section according to the corresponding mercury injection volume, so as to obtain a capillary pressure curve of the rock sample section.
Wherein the capillary pressure curve of sample No. 41 is shown in FIG. 3, and the porosity of sample No. 41 is 8.9%, and the permeability is 0.02 × 10-3μm2FIG. 4 shows a capillary pressure curve of sample No. 46, which corresponds to sample No. 46 having a porosity of 15.3% and a permeability of 21.5X 10-3μm2The physical properties of the capillary pressure curve are different, the capillary pressure curve is different in form, the physical properties of the No. 41 sample are poor, the capillary pressure curve is wholly deviated to the upper right corner of a cross graph, the maximum mercury saturation degree is low correspondingly, the reflection pore structure is poor, the mercury feeding amount in the sample is small, the physical properties of the No. 46 sample are good, the capillary pressure curve is wholly arranged in the middle of the cross graph, the maximum mercury saturation degree is large correspondingly, the reflection pore structure is good, and the mercury feeding amount in the sample is large.
Fifthly, analyzing the T2 spectrum of the nuclear magnetic resonance experiment of the step three, establishing a relation graph of capillary pressure Pc and 1/T2 of the rock sample, determining whether the relation between the two is specifically divided into two sections or three sections in the rock sample from the graph, reading a 1/T2 value corresponding to the segmentation point of the sample, and defining each segmentation point as the end point of the large pore throat or the starting point of the small pore throat.
Step fifthly specifically comprises the following substeps: and (5.1) reversely accumulating the ordinate porosity component of the rock sample from the maximum value to the minimum value according to the transverse relaxation time T2 to obtain a reversely accumulated porosity component curve, and dividing the reversely accumulated porosity component curve by the porosity of the rock sample to obtain a T2 spectrum accumulation curve which is similar to the capillary pressure curve in physical significance and form and converts the reversely accumulated porosity component into an approximate mercury saturation component.
From the spectrum accumulation curve of T2, 1/T2 corresponding to a value equivalent to the mercury saturation in the capillary pressure curve of step four is found; if the value identical to the mercury saturation in the capillary pressure curve in the step four cannot be directly found from the T2 spectrum accumulation curve, linear interpolation is conducted from the upper interval and the lower interval of the adjacent mercury saturation;
and (5.3) establishing a relation graph of capillary pressure Pc and 1/T2 of the rock sample, determining whether the relation between the capillary pressure Pc and the 1/T2 can be divided into two or three sections in the rock sample, and reading a 1/T2 value corresponding to a section point of the sample.
Wherein, the schematic diagram of the conversion relationship between Pc and 1/T2 of sample No. 41 is shown in FIG. 5, which shows a clear two-segment fitting relationship; a schematic diagram of the two-segment transformation relationship between Pc and 1/T2 of sample No. 46 is shown in fig. 6, the two-segment fitting relationship cannot describe the whole process well, after encryption interpolation processing, the fitting relationship between Pc and 1/T2 of sample No. 46 is shown in three segments in fig. 7, a schematic diagram comparing a capillary pressure curve constructed by the two-segment transformation relationship and the three-segment transformation relationship between Pc and 1/T2 of sample No. 46 with an actually measured capillary pressure curve is shown in fig. 8, which illustrates that the three-segment transformation relationship between Pc and 1/T2 of sample No. 46 can describe the whole process better than the two-segment transformation relationship between Pc and 1/T2. The capillary pressure curves of samples No. 41 and No. 48 are schematically shown in FIG. 9, the capillary pressure curves are more deviated to the upper right corner of the intersection, the relationship between Pc and 1/T2 is more two sections, the capillary pressure curves are more deviated to the middle of the intersection, the relationship between Pc and 1/T2 is more three sections, the three-section conversion relationship between Pc and 1/T2 of the sample No. 48 is schematically shown in FIG. 10, which is exactly consistent with the change characteristics of the capillary pressure curves of FIG. 9, while 1/T2 exactly corresponds to the size of the throat, the smaller 1/T2 is, the larger the throat is, the larger 1/T2 is, the smaller the throat is, as shown in FIG. 10 by two segmentation points, according to the description of the change of the whole capillary pressure curve, 1/T2 corresponding to A point can be defined as the ending point of the large throat, and 1/T2 corresponding to B point can be defined as the starting point of.
Sixthly, repeating the steps from the third step to the fifth step, and concluding a rock sample with a two-section fitting relationship and a rock sample with a three-section fitting relationship between the capillary pressure Pc and 1/T2.
According to the method of pages 209 to 233 in oil reservoir physics published by 2004 oil industry publishers (publication number ISBN 978-7-5021-4678-8, Yangtze and the like of authors), capillary pressure curves of various rock samples are placed in a cross-plot under the same coordinate system, all the capillary pressure curves are divided into several types according to forms, and the mean value of the throat diameter is extracted from the capillary pressure curves of each rock sample to represent the division of the types.
The graphical representation of the classification results of capillary pressure curves of the reservoir in the example region is shown in fig. 11, and the classification can be divided into five categories, wherein the classification is mainly based on two points, namely, a flat section exists in each capillary pressure curve (which can be defined as a relative flat section entering other pore throats from the maximum pore throat radius), and the flat section is classified in a way of being located at the upper position or the lower position in the intersection graph; and secondly, when each capillary pressure curve has no flat section, the whole section of capillary pressure curve is classified according to the tendency characteristics.
And inducing the distribution intervals of the average values of the diameters of the throats corresponding to the rock samples with the relationship between capillary pressure Pc and 1/T2 in a two-section fitting relationship and the rock samples with a three-section fitting relationship respectively, and further establishing a general fitting relation expression I between the capillary pressure Pc and 1/T2 of each section of each type.
The self-sustaining sample is obtained by extracting a T2 geometric mean value from a nuclear magnetic resonance experiment T2 spectrum of each rock sample, and establishing a general fitting relational expression II between the T2 geometric mean value and the throat diameter mean value of the rock sample, as shown in figure 12; and a third general fitting relation between the geometric mean of T2 of the rock sample and the segmentation point 1/T2, as shown in FIG. 13.
The method is characterized in that the corresponding capillary pressure Pc is calculated according to the general fitting relation obtained in the steps and the self-tapping step aiming at the rock sample only measuring the nuclear magnetic resonance experiment T2 spectrum in the rock core of the same region, and the capillary pressure curve of the rock sample is drawn.
The step (ii) comprises the following sub-steps: extracting a T2 geometric mean value from a nuclear magnetic resonance experiment T2 spectrum, calculating according to the general fitting relation II of the step of the self-care, and determining whether the relation between the capillary pressure Pc of the rock sample and 1/T2 is in a two-segment fitting relation or a three-segment fitting relation;
calculating 1/T2 corresponding to the segmentation point according to a general fitting relational expression of step self-care through a geometric mean value T2;
respectively calculating capillary pressure Pc according to different sections by using the first general fitting relation in the step (10.3) as an ordinate of a capillary pressure curve;
and (10.4) converting the porosity component of the rock sample nuclear magnetic resonance experiment T2 spectrum into approximate mercury saturation, and drawing a capillary pressure curve of the rock sample as an abscissa of the capillary pressure curve.
The schematic diagram of the comparison between the actual capillary pressure curve of the sample No. 22 and the constructed capillary pressure curve is shown in FIG. 14, the schematic diagram of the comparison between the actual capillary pressure curve of the sample No. 57 and the constructed capillary pressure curve is shown in FIG. 15, the sample No. 22 and the sample No. 57 do not participate in method modeling, and are used for checking the accuracy of the method.
According to the method from pages 209 to 233 in oil reservoir physics published by oil industry publishers (publication number ISBN 978-7-5021 and 4678-8, the winner of the author, and the like) in 2004, the pore throat radius distribution of the rock sample is obtained according to the capillary pressure curve of the rock sample, and the parameters of the pore structure of the reservoir layer, such as the maximum pore throat radius, the median pressure, the displacement pressure, the mean coefficient, the sorting coefficient, and the like, are obtained according to the steps. An intersection graph of the calculated throat diameter mean values of the 6 samples and the laboratory analysis result is shown in fig. 15, and it can be seen that the calculated throat diameter mean values and the laboratory analysis result are mostly on a diagonal line of 45 degrees, which shows that the method can accurately calculate the throat diameter mean values, and further evaluate the pore characteristics of the reservoir.
Referring to fig. 1, a schematic diagram of the measurement of sample number 41 in the nmr experiment is shown, wherein the abscissa represents the transverse relaxation time in ms; the ordinate is the porosity component in%. Sample No. 41 had a porosity of 8.9% and a permeability of 0.02X 10-3μm2The nuclear magnetic resonance experiment T2 spectrum measurement result is a single peak, and the pore structure is relatively poor and is consistent with the pore permeation measurement result.
Referring to fig. 2, a schematic diagram of the measurement of the sample number 46 in the nmr experiment is shown, wherein the abscissa represents the transverse relaxation time in ms; the ordinate is the porosity component in%. Sample No. 46 had a porosity of 15.3% and a permeability of 21.5X 10-3μm2The nuclear magnetic resonance experiment T2 spectrum measurement result is bimodal, and the pore structure is better and is consistent with the pore permeation measurement result.
Referring to fig. 3, a schematic diagram of capillary pressure curve measurement of sample No. 41 is shown, wherein the abscissa is mercury saturation, and the unit is%; the ordinate is capillary pressure in MPa. The capillary pressure curve of sample No. 41 is deviated towards the upper right corner of the intersection graph, which shows that a certain amount of mercury can enter pores only by needing large mercury inlet pressure, when the mercury inlet pressure reaches more than 20MPa, more mercury can hardly enter the pores, and the mercury saturation degree in the pores is about 40 percent, which shows that the pore structure is poor and pores and micropores develop.
Referring to fig. 4, a schematic diagram of the capillary pressure curve measurement of a sample No. 46 is shown, wherein the abscissa represents mercury saturation in%; the ordinate is capillary pressure in MPa. The capillary pressure curve of sample No. 46 is wholly in the middle of the intersection graph, and as the mercury inlet pressure is increased, the mercury inlet amount is increased for the sample with a better pore structure, and the corresponding mercury saturation is higher.
FIG. 5 is a diagram showing the conversion relationship between sample No. 41 Pc and 1/T2. Wherein, the abscissa is the reciprocal of the transverse relaxation time, and the unit is 1/ms; the ordinate is capillary pressure in MPa. The sample No. 41 is shown in FIG. 1, which corresponds to a single peak in the T2 spectrum of the nuclear magnetic resonance experiment with 100% water saturation, and the relationship between Pc and 1/T2 is in power exponent, which is consistent with the relationship mentioned in the prior art, which is a nonlinear power function conversion scale, but the conversion relationship is two-stage, which is different from the prior art that the single peak characteristic of the T2 spectrum of the nuclear magnetic resonance experiment is considered as one-stage. Where the 1/T2 corresponding to the segmentation point was 0.162, when the sample 1/T2 ≧ 0.162, it was noted that mercury began to push toward the small pore throat as the pressure increased.
FIG. 6 is a diagram showing a two-segment fitting relationship between sample No. 46 Pc and 1/T2. Wherein, the abscissa is the reciprocal of the transverse relaxation time, and the unit is 1/ms; the ordinate is capillary pressure in MPa. The sample No. 46 has better physical properties than the sample No. 41, the porosity is 15.3 percent, and the permeability is 21.5 multiplied by 10-3μm2Referring to fig. 3, the T2 spectrum for a 100% saturated water nmr experiment corresponds to a double peak. It is clear that in the transformation relationship between Pc and 1/T2 in FIG. 6, the two-stage establishment of the power exponent relationship between Pc and 1/T2 is obviously inappropriate from the viewpoint of Haidan et al, 1/T2<At 0.100, the Pc and 1/T2 data points are more likely to be subdivided into two segments. Therefore, the capillary pressure curve corresponding to sample No. 46 corresponds to 1/T2<At 0.100, linear interpolation is performed again for Pc and mercury saturation.
FIG. 7 is a diagram showing the three-segment fitting relationship between sample No. 46 Pc and 1/T2. Wherein, the abscissa is the reciprocal of the transverse relaxation time, and the unit is 1/ms; the ordinate is capillary pressure in MPa. After treatment, the fitting relation between the sample No. 46 Pc and 1/T2 presents three segments, and the whole process of the relation between Pc and 1/T2 can be more depicted than the two segments in FIG. 6. The sample has two segmentation points which respectively correspond to 1/T2 values of 0.006 and 0.127, when 1/T2 is less than or equal to 0.006, the relationship between Pc and 1/T2 shows a linear relationship, when 0.006 is less than 1/T2 is less than 0.127, mercury enters the medium pore throat along with the increase of pressure (0.1MPa is less than PC and less than 1MPa), the relationship between Pc and 1/T2 shows a power exponential relationship, when 1/T2 is more than or equal to 0.127, the relationship between Pc and 1/T2 shows a power exponential relationship, and mercury starts to advance to the small pore throat along with the increase of pressure.
Referring to fig. 8, a schematic diagram of comparison between a capillary pressure curve and a measured capillary pressure curve respectively constructed by a two-stage fitting relationship and a three-stage fitting relationship between sample number 46 Pc and 1/T2 is shown. Wherein, the abscissa is mercury saturation, and the unit is%; the ordinate is capillary pressure in MPa. The result constructed by three sections on the whole is more consistent with the actually measured capillary pressure curve and is obviously superior to the capillary pressure curve constructed by two sections.
From all the experimental rock samples, the fitting relation between Pc and 1/T2 of the single rock sample of the local research object is only two-stage and three-stage, and no one-stage conversion relation exists. In what case, the fitting relation between Pc and 1/T2 is two-stage or three-stage, and a distinguishing relation needs to be found from the capillary pressure curve.
From the capillary pressure curve, when the pore structure is better, the position of the whole section of capillary pressure curve in an intersection graph is lower, see No. 48 sample in FIG. 9, three-section change characteristics are presented in the whole mercury inlet process, the first section is an initial stage when mercury enters a rock core, and the mercury enters the throat of a large pore along with the increase of the capillary pressure; the second section is a middle gentle section of the capillary pressure curve, which shows that mercury gradually occupies the medium pore throat in the pressure interval, and the mercury saturation increases rapidly and the corresponding capillary pressure changes little in the process; the third section is the final steep-tilted section of the capillary pressure curve, which shows that mercury is gradually pushed to the small-pore throat, the capillary pressure is sharply increased, and the mercury feeding amount is relatively small. Referring to the three-segment fitting relationship between Pc and 1/T2 in the No. 48 sample in FIG. 10, it can be seen that the variation characteristics of the capillary pressure curve are exactly consistent, while 1/T2 corresponds to the size of the throat, and the smaller the 1/T2, the larger the throat, and the larger the 1/T2, the smaller the throat. Therefore, for the sample with better pore structure, the more Pc and 1/T2 show a three-segment fitting relationship, wherein referring to the two segmentation points in FIG. 10, according to the description of the change of the whole capillary pressure curve, 1/T2 corresponding to A point can be defined as the ending point of large pore throat, and 1/T2 corresponding to B point can be defined as the starting point of small pore throat.
Similarly, when the pore structure is poor, the whole section of capillary pressure curve is located on the upper side in the intersection graph, referring to sample No. 41 in FIG. 9, two-section change characteristics are presented in the whole mercury inlet process, the first section is that when mercury enters the core in the initial stage, mercury enters the pore throat along with the increase of capillary pressure, in the process, the proportion of the large pore throat and the medium pore throat is small, so that the capillary pressure value is increased, and the mercury inlet amount is small; the second section is a steep tilting section of a capillary pressure curve, mercury is gradually pushed towards the small pore throats along with the rise of the capillary pressure, and the mercury solution cannot displace water in the small pore throats, so that the capillary pressure is increased, and the mercury saturation is not changed any more. This is consistent with the relationship of sample number 41 Pc and 1/T2 in FIG. 5 being a two-step fit, so for samples with poorer pore structure, the relationship of Pc and 1/T2 is a two-step fit, and the intersection of the two steps in FIG. 5 can be defined as the starting point of the pore throat.
Fig. 11 is a schematic diagram showing the classification results of sandstone reservoir capillary pressure curve morphology method in a region sunken in gold lake in the northeast of China. The basis of the division is mainly based on two points, namely that a flat section exists in each capillary pressure curve (which can be defined as a relative flat section entering other pore throats from the maximum pore throat radius), and the flat section is divided into types by being located at the upper position or the lower position in a cross plot; and secondly, when each capillary pressure curve has no flat section, the whole section of capillary pressure curve is classified according to the tendency characteristics. The 5 types marked by the capillary pressure curve form method are used, and because the number of samples is large, only a few representative capillary pressure curves are selected for displaying in each type of the graph.
See table 1, which shows several statistical tables corresponding to the porosity, permeability, throat diameter mean, T2 spectrum form and the fitting relationship between Pc and 1/T2 in the classification of capillary pressure curve morphology of samples in the sandstone reservoir stratum part in a depressed area of gold lake in the northeast of China.
TABLE 1
It can be seen from table 1 that (only a part of samples corresponding to the same sample are selected, which both measure the T2 spectrum of the nmr experiment and the capillary pressure curve), there is an obvious correspondence according to the fitting relationship between the five types divided by the capillary pressure curve and Pc and 1/T2, wherein the fitting relationship between Pc and 1/T2 of the types i and ii is two-stage, and the fitting relationship between Pc and 1/T2 of the types iii, iv and v is three-stage.
Secondly, the nuclear magnetic resonance experiment T2 spectrum of the research area shows that the structure is a unimodal structure or a bimodal structure. As can be seen from Table 1, the fitting relationship between the morphology of the T2 spectrum and Pc and 1/T2 in the NMR experiment is not as good as the corresponding relationship between the morphology of the capillary pressure curve, the single-peak morphology of the T2 spectrum in the NMR experiment does not necessarily correspond to the case that the fitting relationship between Pc and 1/T2 is two-stage, or may be three-stage, and the double-peak morphology of the T2 spectrum in the NMR experiment does not necessarily correspond to the case that the fitting relationship between Pc and 1/T2 is three-stage, so that the insensitive morphology of the T2 spectrum in the NMR experiment is two-stage or three-stage for distinguishing the fitting relationship between Pc and 1/T2.
Finally, from comparing the effects of the two methods, although the capillary pressure curve morphology method is most sensitive to whether the conversion relationship between Pc and 1/T2 is two-stage or three-stage, the capillary pressure curve is the final result to be constructed, and it is found from various parameters extracted from the capillary pressure curve that the mean value of the throat diameter can be divided into five types of capillary pressure curves (see table 1). According to the five classes divided by the embodiment, all sample points are fitted with a universal fitting relation between Pc and 1/T2 in each segment of each class, so that a more accurate capillary pressure curve can be better constructed. A model of a capillary pressure curve of the whole region is established in a classifying and segmenting mode based on a nuclear magnetic resonance experiment T2 spectrum, and the model comprises the following steps:
for class I (mean throat diameter less than 0.2 μm) and class II (mean throat diameter greater than 0.2 μm and less than 0.3 μm),Pcand1/ T 2 the transformation relations of (1) are two-stage, and the stage form is as follows:
for class III (mean throat diameter greater than 0.3 μm and less than 0.9 μm), class IV (throat diameter)Diameter mean greater than 0.9 μm and less than 2 μm) and class v (throat diameter mean greater than 2 μm),Pcand1/T 2 the transformation relations of (1) are all three-section type, and the section form is as follows:
since the mean value of the throat diameter is a parameter reflecting the pore structure, and the T2 spectrum of the nuclear magnetic resonance experiment can also reflect the point, in other words, the two can establish a corresponding relation, thereby solving the classification problem of distinguishing the relation between Pc and 1/T2 as two-segment fitting or three-segment fitting.
From nuclear magnetic resonance experimentsT 2 Extracted from the spectrumT 2 The geometric mean value is calculated by the following method:
referring to FIG. 12T 2 Intersection plot of geometric mean and throat diameter mean. The two have two relations, when the physical index is synthesizedAbove 0.25, the pore structure is relatively good,T 2 the mean value of the geometric time and the mean value of the throat diameter are in a linear relationship, and the comprehensive physical property indexLess than 0.25, the pore structure is relatively poor,T 2 the geometric mean value and the throat diameter mean value are in a quadratic function relationship.
The classification problem of distinguishing whether the relation between the Pc and the 1/T2 is two-segment fitting or three-segment fitting is solved, and the next step is to determine the appropriate relation between the Pc and the 1/T2 at which segmentation point 1/T2 is selected, so that a capillary pressure curve with high precision is constructed.
Referring to FIG. 13, a graph showing the relationship between the geometric mean value of all samples T2 of sandstone reservoirs in a certain area of the gold lake depression in the North Suo basin in China and 1/T2 is shown. Wherein the abscissa is a geometric mean value of T2, and the unit is ms; the ordinate is the reciprocal of the transverse relaxation time in units of 1/ms. Since the segmentation points reflect the pore throat change, the geometric mean of T2 extracted from the T2 spectrum of the nuclear magnetic resonance experiment can also represent the change, and the correlation between the geometric mean of T2 and the ending point 1/T2 of the large pore throat and the starting point 1/T2 of the small pore throat can be established.
And finally, drawing a capillary pressure curve of the rock sample according to the provided nuclear magnetic resonance experiment T2 spectrum of any rock sample. Extracting a T2 geometric mean value from a given rock sample nuclear magnetic resonance experiment T2 spectrum, calculating a throat diameter mean value by utilizing the T2 geometric mean value, determining whether the relation between the rock sample Pc and 1/T2 is a two-section fitting relation or a three-section fitting relation, calculating 1/T2 corresponding to a segmentation point by utilizing the T2 geometric mean value, calculating corresponding capillary pressure Pc according to a general relation formula of different sections Pc and 1/T2 of different types by utilizing 1/T2 corresponding to the rock sample nuclear magnetic resonance experiment T2 spectrum as a vertical coordinate, converting the porosity component of the rock sample nuclear magnetic resonance experiment T2 spectrum into approximate mercury saturation, and drawing a capillary pressure curve of the rock sample as a horizontal coordinate of the capillary pressure curve.
The method is used for carrying out effect inspection on 6 samples of the sandstone reservoirs in the depressed certain area of the gold lake in the northwest basin in China, which do not participate in modeling analysis. Referring to fig. 14, a schematic diagram of the comparison of the measured capillary pressure curve and the constructed capillary pressure curve for sample No. 22 is shown. Referring to fig. 15, a schematic diagram of the comparison of the measured capillary pressure curve and the constructed capillary pressure curve for sample No. 57 is shown. The constructed capillary pressure curve is basically consistent with the actually measured capillary pressure curve, which shows that the capillary pressure curve characteristic of the embodiment area can be completely represented by a model of the capillary pressure curve established by classifying and segmenting the spectrum T2 spectrum of the nuclear magnetic resonance experiment.
And acquiring pore throat radius distribution by using the constructed capillary pressure curve, and calculating reservoir pore structure parameters such as maximum pore throat radius, median pressure, displacement pressure, mean coefficient, sorting coefficient and the like for quantitatively evaluating the reservoir pore structure.
In addition, the effect analysis is also performed on the pore structure calculation parameters, table 2 shows that the calculated values are very close to the experimental values by comparing the pore structure parameters obtained by the experiment with the calculated pore structure parameters, and fig. 15 shows an intersection graph of the calculated value of the mean value of the throat diameter and the results of the laboratory analysis. The calculated value of the mean value of the throat diameter and the result of laboratory analysis are mostly on a diagonal line of 45 degrees, which shows that the mean value of the throat diameter can be accurately calculated by the method, and further the pore characteristics of the reservoir stratum can be evaluated.
TABLE 2
。
Claims (7)
1. A method for constructing a capillary pressure curve of a rock core by utilizing nuclear magnetic resonance information is characterized by comprising the following steps: the method sequentially comprises the following steps: drilling a plurality of rock samples on a representative rock core in a certain area, and performing oil washing and salt washing treatment on all the rock samples; secondly, cutting each rock sample into two sections, wherein the length of each section is not less than 20mm, one section is used for nuclear magnetic resonance experiment measurement, and the other section is used for capillary pressure curve measurement; thirdly, measuring the porosity of the rock sample by using a nuclear magnetic resonance experimental instrument, performing inversion to obtain a nuclear magnetic resonance experimental T2 spectrum, and calculating to obtain the permeability; fourthly, carrying out mercury intrusion experiment on another rock sample section from the same rock sample as the third step to obtain a capillary pressure curve; fifthly, analyzing the T2 spectrum of the nuclear magnetic resonance experiment of the step three, establishing a relation graph of capillary pressure Pc and 1/T2 of the rock sample, determining whether the relation between the two can be divided into two sections or three sections in the rock sample, reading a 1/T2 value corresponding to a segmentation point of the sample, and defining each segmentation point as an end point of a large pore throat or a starting point of a small pore throat; sixthly, repeating the steps from the third step to the fifth step, and concluding a rock sample with a two-section fitting relationship and a rock sample with a three-section fitting relationship between the capillary pressure Pc and 1/T2; putting capillary pressure curves of various rock samples in an intersection graph under the same coordinate system, dividing all the capillary pressure curves into several types according to forms, and extracting a throat diameter mean value from the capillary pressure curves of each rock sample to represent the division of the several types; inducing the distribution intervals of the average values of the diameters of the throats corresponding to the rock samples with the relationship between capillary pressure Pc and 1/T2 in a two-section fitting relationship and the rock samples with a three-section fitting relationship respectively, and further establishing a general fitting relation formula I between the capillary pressure Pc and 1/T2 of each section of each type; the self-sustaining sample is characterized in that the self-sustaining sample extracts a T2 geometric mean value from a nuclear magnetic resonance experiment T2 spectrum of each rock sample, and a general fitting relational expression II between the T2 geometric mean value and the throat diameter mean value of the rock sample and a general fitting relational expression III between the T2 geometric mean value of the rock sample and a segmentation point 1/T2 are established; the method is characterized in that the corresponding capillary pressure Pc is calculated according to the general fitting relation obtained in the steps and the self-tapping step aiming at the rock sample only measuring the nuclear magnetic resonance experiment T2 spectrum in the rock core of the same region, and the capillary pressure curve of the rock sample is drawn.
2. The method for constructing the capillary pressure curve of the core by using the nuclear magnetic resonance information as claimed in claim 1, further comprising the following steps: and acquiring pore throat radius distribution of the rock sample according to the capillary pressure curve of the rock sample obtained in the step, and calculating reservoir pore structure parameters such as maximum pore throat radius, median pressure, displacement pressure, mean coefficient, sorting coefficient and the like.
3. The method for constructing the capillary pressure curve of the core by using the nuclear magnetic resonance information as claimed in claim 1, wherein the step three specifically comprises the following sub-steps: (3.1) making the rock sample section for nuclear magnetic resonance experiment measurement reach 100% water saturation, performing nuclear magnetic resonance experiment measurement on the rock sample section, determining the total pore volume, and calculating the porosity psi of the rock sample section according to the volume of the rock sample section; performing centrifugal water drainage on the rock sample section to enable the rock sample section to reach a water-binding state, performing nuclear magnetic resonance experiment measurement again, wherein the echo interval time is 0.35ms, and performing attenuation inversion processing on an original nuclear magnetic resonance attenuation curve to obtain a nuclear magnetic resonance experiment T2 spectrum of the rock sample section, wherein T2 is transverse relaxation time in ms; and (3.3) adopting a coats-cutoff model to calculate the permeability K of the rock sample.
4. The method for building a pressure curve of a rock core capillary by using nuclear magnetic resonance information according to claim 1, wherein the step four specifically comprises the following sub-steps: drying the rock sample, placing the rock sample in a rock sample pressure-bearing chamber of a mercury porosimeter, and sealing and vacuumizing; pressing mercury into the pores of the rock sample section from a certain lower constant pressure, and recording the volume of mercury entering the rock sample under each constant pressure, wherein the mercury squeezing pressure is equivalent to capillary pressure Pc of the rock sample and has a unit of MPa; increasing the mercury squeezing pressure in sequence and repeating the measuring process until the set maximum mercury injection pressure is reached; and (4.4) calculating the mercury saturation of the rock sample section according to the corresponding mercury injection volume, so as to obtain a capillary pressure curve of the rock sample section.
5. The method for constructing the pressure curve of the capillary of the rock core by using the nuclear magnetic resonance information as claimed in claim 1, characterized in that the step fifthly specifically comprises the following substeps: reversely accumulating the ordinate porosity component of the rock sample from the maximum value to the minimum value according to the transverse relaxation time T2 to obtain a reversely accumulated porosity component curve, and dividing the reversely accumulated porosity component curve by the porosity of the rock sample to obtain a T2 spectrum accumulated curve which is similar to the capillary pressure curve in physical significance and form; from the spectrum accumulation curve of T2, 1/T2 corresponding to a value equivalent to the mercury saturation in the capillary pressure curve of step four is found; and (5.3) establishing a relation graph of capillary pressure Pc and 1/T2 of the rock sample, determining whether the relation between the capillary pressure Pc and the 1/T2 can be divided into two or three sections in the rock sample, and reading a 1/T2 value corresponding to a section point of the sample.
6. The method for constructing a rock core capillary pressure curve by using nuclear magnetic resonance information as claimed in claim 5, wherein in step (5.2), if a value equal to the mercury saturation in the capillary pressure curve in step (fourth) cannot be directly found from the T2 spectrum accumulation curve, linear interpolation is performed from the upper and lower intervals of adjacent mercury saturations.
7. The method for constructing a capillary pressure curve of a core by using nuclear magnetic resonance information as claimed in claim 1, wherein the steps are preferably as follows: extracting a T2 geometric mean value from a nuclear magnetic resonance experiment T2 spectrum, calculating according to the general fitting relation II of the step of the self-care, and determining whether the relation between the capillary pressure Pc of the rock sample and 1/T2 is in a two-segment fitting relation or a three-segment fitting relation; calculating 1/T2 corresponding to the segmentation point according to a general fitting relational expression of step self-care through a geometric mean value T2; respectively calculating capillary pressure Pc according to different sections by using the first general fitting relation in the step (10.3) as an ordinate of a capillary pressure curve; and (10.4) converting the porosity component of the rock sample nuclear magnetic resonance experiment T2 spectrum into approximate mercury saturation, and drawing a capillary pressure curve of the rock sample as an abscissa of the capillary pressure curve.
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| CN116226623A (en) * | 2023-02-21 | 2023-06-06 | 北京金阳普泰石油技术股份有限公司 | Mark layer division method and device based on SegNet segmentation model and computer equipment |
| CN116226623B (en) * | 2023-02-21 | 2023-11-21 | 北京金阳普泰石油技术股份有限公司 | Mark layer division method and device based on SegNet segmentation model and computer equipment |
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