A method for preparing layered heterogeneous rock samples and a method for studying heterogeneity.

Abstract

This invention discloses a method for preparing layered heterogeneous rock samples and a method for studying heterogeneity. The sample preparation method includes: determining a reference plane direction based on the bedding plane extension direction of the layered heterogeneous rock sample; cutting and flattening the top and bottom surfaces of the rock sample along a direction parallel to the reference plane; cutting the side surfaces of the rock sample along a direction perpendicular to the reference plane to ensure a consistent cross-sectional shape of the rock sample parallel to the reference plane; cutting the rock sample into a first rock sample and a second rock sample along a direction perpendicular to the reference plane; obtaining XRF scans of the cut surfaces of the second rock sample; obtaining a sequence of dividing lines arranged vertically based on the data differences in the scans; and sequentially cutting the first rock sample according to the dividing line sequence to obtain multiple rock samples. This method yields a wide variety of rock samples with good heterogeneity representation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of petroleum geology and rock sample sample preparation, and particularly relates to a layered heterogeneous rock sample preparation method and a heterogeneity research method. BACKGROUND

[0002] At present, there are two requirements for core sample selection and preparation in the domestic geological industry: 1) the sample properties are as similar as possible to meet parallel testing; and 2) the sample properties are as different as possible and contain all types to meet comparative testing. Fine-grained sedimentary rocks have strong heterogeneity, so when the fine-grained sedimentary rock sample preparation is mainly for the purpose of heterogeneity research, the sample properties need to be as different as possible and contain all types. At present, the conventional technical method for rock sample selection and preparation is less, and it is difficult to meet the resolution requirements of fine-grained sedimentary rocks with particles less than 0.0625mm (more than 50%). Especially in fine-grained sedimentary rocks with strong heterogeneity, the properties of the sample usually change in millimeter-micron level. In order to finely study the heterogeneity of fine-grained sedimentary rocks, a more fine sample preparation method is urgently needed. SUMMARY

[0003] In order to at least partially solve the above technical problems existing in the prior art, the present application is made by the inventors, and through specific embodiments, a layered heterogeneous rock sample preparation method and a heterogeneity research method are provided, and the prepared rock samples are full in type and good in heterogeneity representation.

[0004] In a first aspect, an embodiment of the present application provides a layered heterogeneous rock sample preparation method, comprising:

[0005] determining a reference surface direction according to the extension direction of the bedding surface of the layered heterogeneous rock sample, cutting the top surface and the bottom surface of the rock sample along the direction parallel to the reference surface direction to be flat, and cutting the side surface of the rock sample along the direction perpendicular to the reference surface, so that the shape of the cross section of the rock sample parallel to the reference surface is consistent;

[0006] cutting the rock sample into a first rock sample and a second rock sample along the direction perpendicular to the reference surface;

[0007] obtaining an XRF scan map of the cutting surface of the second rock sample, and obtaining a sequence of segmentation lines arranged in an up-down order according to the data difference in the scan map, the segmentation lines being parallel to the reference surface direction;

[0008] cutting the first rock sample in turn according to the sequence of segmentation lines to obtain a plurality of rock samples.

[0009] In some embodiments, the reference surface direction is determined according to the extension direction of the bedding surface of the layered heterogeneous rock sample, comprising:

[0010] The direction of the bedding plane of the statistical stratified heterogeneous rock sample is determined, and the direction with the most developed bedding plane is determined as the reference plane direction; or

[0011] Based on the direction of each bedding plane of the stratified heterogeneous rock sample, the reference plane direction is obtained by cluster analysis.

[0012] In some embodiments, the volume ratio of the first rock sample to the second rock sample is greater than 10;

[0013] The width of the cutting surface of the second rock sample is 1-5 cm.

[0014] In some embodiments, the XRF scan map is a plurality of set element content distribution maps, and the sequence of segmentation lines arranged in ascending and descending order is obtained according to the data difference in the scan map, including:

[0015] Selecting the strongest representative one from the plurality of set element content distribution maps, determining a plurality of possible segmentation lines along the width direction thereof, and the content change rate of the corresponding element at the possible segmentation line is higher than a first set threshold;

[0016] For each possible segmentation line, the content change rate of other set elements at the position is determined, and the comprehensive change rate is determined by weighted average method according to the content change rate of each set element, and the possible segmentation line with the comprehensive change rate higher than a second set threshold is determined as the segmentation line, thereby obtaining the sequence of segmentation lines arranged in ascending and descending order.

[0017] In some embodiments, further comprising:

[0018] Judging whether the distance between two adjacent segmentation lines is less than a set distance threshold;

[0019] If yes, one of the segmentation lines is deleted, or the two adjacent segmentation lines with a distance less than the set distance threshold are merged according to the merging rule of cluster analysis, thereby obtaining a new segmentation line.

[0020] In some embodiments, the set distance threshold satisfies the following requirements:

[0021] The volume of the rock sample with the cross section of the cross section of the first rock sample as the cross section is not less than a set volume threshold.

[0022] In some embodiments, the set distance threshold is 0.2 mm.

[0023] In some embodiments, the first rock sample is sequentially cut according to the sequence of segmentation lines, thereby obtaining a plurality of rock samples, including:

[0024] At least one cutting direction perpendicular to the reference plane direction is determined according to the research needs, and the vertical cutting of the first rock sample is completed according to each cutting direction;

[0025] Cut the first rock sample after cutting with a set of materials, and cut the wrapped first rock sample in sequence according to the sequence of the split lines, to obtain a plurality of rock samples.

[0026] In some embodiments, the layered heterogeneous rock sample is a fine-grained sedimentary rock.

[0027] In a second aspect, the embodiments of the present application provide a method for researching the heterogeneity of a layered heterogeneous rock sample, comprising:

[0028] Cutting the layered heterogeneous rock sample according to the above method to obtain a plurality of rock samples;

[0029] Based on the obtained plurality of rock samples, the heterogeneity is researched.

[0030] The beneficial effects of the above technical solutions provided by the embodiments of the present application at least include:

[0031] (1) The method for preparing a layered heterogeneous rock sample provided by the embodiments of the present application cuts the rock sample into a first rock sample and a second rock sample along a direction perpendicular to the reference plane; obtains an XRF scan map of the cutting surface of the second rock sample, and obtains a sequence of split lines arranged in an up-down order according to the data difference in the scan map; and cuts the first rock sample in sequence according to the sequence of the split lines to obtain a plurality of rock samples. For the continuous section preparation of the micro-heterogeneity of the fine-grained sedimentary rock, the working efficiency is improved, and the sample loss rate is reduced. The types of the prepared rock samples are complete, and the heterogeneity is well represented, which provides a basis for realizing fast and high-resolution sample property judgment.

[0032] (2) The method for preparing a layered heterogeneous rock sample provided by the embodiments of the present application cuts the rock sample into a first rock sample and a second rock sample along a direction perpendicular to the reference plane; the second rock sample is not cut, but serves as a reference rock sample, and since it has the same vertical cutting surface as the first rock sample, the second rock sample can provide a physical reference for analyzing the longitudinal heterogeneity distribution characteristics of the first rock sample at any time during the cutting process of the first rock sample.

[0033] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. The objects and other advantages of the present application can be realized and achieved by the structure particularly pointed out in the written description, claims, and drawings.

[0034] The technical solutions of the present application will be further described in detail below with the help of the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of the specification, illustrate embodiments of the application and are intended to provide a further understanding of the application, and are made a part of the disclosure, but do not limit the application. In the drawings:

[0036] Figure 1 Flow chart of sample preparation method for layered heterogeneous rock sample in embodiment one of the present application;

[0037] Figure 2 Example chart of sample preparation process for layered heterogeneous rock sample in embodiment two of the present application;

[0038] Figure 3 Example chart of sample profile in embodiment two of the present application;

[0039] Figure 4 Example chart of XRF scan image in embodiment two of the present application. DETAILED DESCRIPTION

[0040] Example embodiments of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. While example embodiments of the present disclosure are shown in the drawings, it is understood that the present disclosure can be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0041] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for the purposes of the present application, ranges of values are understood to be "open-ended" ranges, unless otherwise stated. The upper and lower limits of these ranges can independently be included or excluded in the range, and are also independently includeable or excludeable in the range established by the recited limits. Thus, for example, a range of "1 to 10" is understood to include the values of 1 and 10, but to exclude the values of 0 and 11.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. All publications mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The citation of any reference is not an admission that it is prior art with respect to the present application. All documents mentioned herein are incorporated herein by reference.

[0043] In the description of the present application, it should be noted that the terms "comprising", "including", "having", "containing", and the like, are to be construed as open-ended terms, i.e., meaning "including, but not limited to".

[0044] The embodiment of the present application aims at solving the problem of making representative samples in the process of sample experimental analysis for fine-grained sedimentary rock with strong micro-heterogeneity.

[0045] Embodiment one

[0046] The embodiment one of the present application provides a sample making method for layered heterogeneous rock sample, referring to the figure, the method comprises the following steps: Figure 1

[0047] Step S11: determining the reference surface direction according to the extension direction of the bedding surface of the layered heterogeneous rock sample, cutting the top surface and the bottom surface of the rock sample along the direction parallel to the reference surface direction, and cutting the side surface of the rock sample along the direction perpendicular to the reference surface, so that the shape of the cross section of the rock sample parallel to the reference surface is consistent.

[0048] The rock sample is usually a coring section, and the top surface and the bottom surface are two end surfaces perpendicular to the axial direction of the coring section.

[0049] In general, the research direction of heterogeneity is perpendicular to the direction of the dominant bedding surface, in which case, the reference surface direction can be determined by any of the following two ways:

[0050] (1) counting the direction of the bedding surface of the layered heterogeneous rock sample, and determining the direction with the most developed bedding surface as the reference surface direction.

[0051] (2) based on the direction of each bedding surface of the layered heterogeneous rock sample, the reference surface direction is obtained by cluster analysis method.

[0052] For example, the finally determined reference surface direction is the direction with the smallest sum of differences from each reference surface, the difference from each reference surface is determined respectively, and the direction with the smallest sum of differences is determined as the reference surface direction.

[0053] Alternatively, the research direction of heterogeneity can also not be perpendicular to the direction of the dominant bedding surface, in which case, the direction perpendicular to the research direction of heterogeneity is directly taken as the reference surface direction.

[0054] Taking the reference surface direction as P and the direction perpendicular to the reference surface as V as an example, cutting the side surface of the rock sample along the direction perpendicular to the reference surface, so that the shape of the cross section of the rock sample parallel to the reference surface is consistent, can be, taking the rock sample smallest cross-sectional area polygon parallel to P or any shape smaller than the smallest cross-sectional area polygon as the boundary, setting it as Z, cutting the rock sample polygon Z along the vector V, so that the cross-sectional area of the rock sample along the vector P direction is equal.

[0055] ​Step S12: cutting the rock sample into a first rock sample and a second rock sample along a direction perpendicular to the reference plane.

[0056] The cut section is polished to be horizontal, with a height difference of no more than 1 mm.

[0057] The first rock sample is used as a scanning and reference rock sample, and the second rock sample is used as a cut rock sample, so the volume of the first rock sample does not need to be too large, and preferably, the volume ratio of the first rock sample to the second rock sample is greater than 10.

[0058] Step S13: obtaining an XRF scan map of the cutting surface of the second rock sample, and obtaining a sequence of division lines arranged in an up-down order according to differences in data in the scan map.

[0059] The above division lines are parallel to the reference plane, i.e., the cutting direction is parallel to the reference plane.

[0060] The second rock sample is placed in a Micro-XRF instrument, and the section is adjusted to be horizontal; the section is scanned using the Micro-XRF to generate an XRF scan map (data), which is a plurality of element content distribution maps.

[0061] The XRF scanning conditions along the vector V can be: a resolution of 5 microns, a scanning width W = 1-2 cm (correspondingly, the width of the cutting surface of the second rock sample is required to be 1-5 cm), and a scanning length H, wherein H is the length within the range of the sample that needs to be studied for heterogeneity, and is preferably 1 cm-30 cm, and is not more than HMax or the upper limit of the sample bin of the XRF scanner. HMax is the maximum height of the rock sample, which is the vertical distance between the top surface and the bottom surface of the sample.

[0062] In some embodiments, the sequence of division lines can be obtained by: selecting a representative strongest one from the plurality of element content distribution maps, which can be the one with the highest resolution or the most obvious bedding boundary; determining a plurality of possible division lines along the width direction (parallel to the reference plane); determining the content change rate of the corresponding element at each possible division line, and determining the content change rate of other set elements at each possible division line; determining a comprehensive change rate by weighted average method according to the content change rate of each set element; and determining the possible division line with a comprehensive change rate higher than a second set threshold as a division line to obtain a sequence of division lines arranged in an up-down order.

[0063] The first set threshold and the second set threshold can be the same or different; preferably, the first set threshold is smaller than the second set threshold, because the first set threshold is used for preliminary selection (which can be understood as rough selection), and the second set threshold is used for final selection (which can be understood as fine selection); and the specific values thereof are flexibly set according to actual research needs.

[0064] In some embodiments, the determination of the segmentation line can also not be performed in two steps, but directly determine a plurality of analysis positions (each analysis position is parallel to the width direction) at a set interval; for each analysis position, determine the content change rate of each set element at the position, and according to the content change rate of each set element, determine the comprehensive change rate by weighted average method, and determine the analysis position with the comprehensive change rate higher than the set threshold as the segmentation line, to obtain the sequence of segmentation lines arranged in an up-down order.

[0065] The layered heterogeneous rock sample studied in the embodiments of the present application is mainly aimed at fine-grained sedimentary rock. The specific definition of fine-grained sedimentary rock can refer to the definition in geology and sedimentology. In general, the sedimentary rock with more than 50% of particles less than 0.0625 mm is defined as fine-grained sedimentary rock.

[0066] Based on the research precision requirement of the heterogeneity of fine-grained sedimentary rock, it is usually necessary to prepare a rock sample with a thickness of not less than 0.2 mm.

[0067] Therefore, after obtaining the sequence of segmentation lines by the image method, it can further include judging whether the distance between two adjacent segmentation lines is less than a set distance threshold; if yes, deleting one of the two segmentation lines, or merging the two adjacent segmentation lines with a distance less than the set distance threshold according to the merging rule of cluster analysis, to obtain a new segmentation line.

[0068] The set distance threshold is usually set to 0.2 mm.

[0069] For example, TOC monitoring requires grinding the rock sample into powder, so the rock sample prepared needs to meet certain volume requirements to ensure that the volume meets the research needs. Therefore, in some embodiments, the set distance threshold meets the following requirements:

[0070] The volume of the rock sample with the cross section of the cross section of the first rock sample as the cross section is not less than the set volume threshold.

[0071] Step S14: sequentially cutting the first rock sample according to the sequence of segmentation lines to obtain a plurality of rock samples.

[0072] The cutting of the first rock sample according to the sequence of segmentation lines can be realized by using a diamond wire cutting instrument.

[0073] In the same vertical direction, a plurality of rock samples can be cut according to the research needs, so in some embodiments, it can include determining at least one cutting direction perpendicular to the reference surface direction according to the research needs, and completing the vertical cutting of the first rock sample according to each cutting direction; wrapping the cut first rock sample with a set material (which can be wrapped with industrial wax), and sequentially cutting the wrapped first rock sample according to the sequence of segmentation lines to obtain a plurality of rock samples.

[0074] The method for preparing a layered heterogeneous rock sample provided by the embodiment one of the present application cuts the rock sample into a first rock sample and a second rock sample along a direction perpendicular to the reference plane; obtains an XRF scan map of the cutting surface of the second rock sample, and obtains a sequence of segmentation lines arranged in an up-down order according to the data difference in the scan map; and cuts the first rock sample according to the sequence of segmentation lines to obtain a plurality of rock samples. The method improves the work efficiency and reduces the sample loss rate for the continuous slicing preparation of the microscopic heterogeneity of fine-grained sedimentary rocks, and the obtained rock samples are of various types and have good heterogeneity representation, thereby providing a basis for realizing rapid and high-resolution sample property judgment.

[0075] The method for preparing a layered heterogeneous rock sample provided by the embodiment one of the present application cuts the rock sample into a first rock sample and a second rock sample along a direction perpendicular to the reference plane; the second rock sample is not cut but used as a reference rock sample, and since the second rock sample has the same vertical cutting surface as the first rock sample, the second rock sample can provide a physical reference for analyzing the longitudinal heterogeneity distribution characteristics of the first rock sample at any time during the cutting process of the first rock sample.

[0076] Embodiment two

[0077] The embodiment two of the present application provides a specific implementation process of a method for preparing a layered heterogeneous rock sample, as shown in Figure 2 for the illustration of the implementation process, the specific implementation process can include the following steps:

[0078] (1) taking the dominant bedding plane in the sample sedimentary structure bedding plane as a reference plane, and setting it as P.

[0079] (2) cutting the sample at both ends parallel to the reference plane P to take a plane, and setting the vertical vector from the top surface to the bottom surface as V.

[0080] (3) taking the boundary of the smallest cross-sectional polygon of the sample parallel to the reference plane P as the boundary, setting it as Z, and cutting the sample polygon Z along the vector V to make the cross-sectional area of the sample along the vector P direction equal.

[0081] (4) cutting the sample into two parts along the vector V, and setting the two parts as A and A', respectively; the volume ratio of A to A' is greater than 10, and the cut section in A' is polished to be horizontal, with a height difference of not more than 1mm.

[0082] Preferably, the width of the section of A' is between 1cm and 5cm, too wide XRF scanning speed is slow, and too narrow information is less.

[0083] (5) placing the sample A' into a Micro-XRF (micro area X-ray fluorescence spectrometer) instrument, adjusting the section to be horizontal; using the Micro-XRF to scan the section to generate an image and data.

[0084] Preferably, the conditions for XRF scanning along the vector V for the profile of sample A' are: resolution of 5 microns, scanning width W = 2 cm, and scanning length H of 20 cm.

[0085] Referring to Figure 3 Fig. 1 shows an example of a profile of a sample; and Figure 4 Fig. 2 shows an example of the obtained XRF scanning image, from left to right, the content distribution diagrams of Al, Fe, K, S and Si elements, respectively.

[0086] Figure 4 Fig. 3 shows the 10 determined segmentation line positions in Fig. 1.

[0087] (6) Taking the segmentation line at the place where the image difference is large or the data is obviously changed, the sample is marked as D1, D2,..., Dn, and the first-stage sampling is completed.

[0088] (7) The distance between adjacent segmentation lines in the first-stage sampling is calculated, and the distance less than 0.2 mm is merged, and the merging rule is performed according to the principle of cluster analysis, the second-stage sampling is completed, and the sample is marked as S1, S2, S3,..., Sn.

[0089] (8) According to the second-stage sampling mark result, the sample A is cut and separated, and the diamond wire cutting instrument is used to cut the sample A parallel to the reference plane P.

[0090] Preferably, before cutting the sample A, the sample A is cut into several parts (the number and position are determined according to the research needs) along the vector V, and then the industrial wax is used for wrapping and cutting, so that each small section is corresponding to the same position.

[0091] Preferably, before cutting the sample A, the volume of the prepared sample is estimated according to the area and thickness of the second-stage sample, so as to meet the sample amount demand of subsequent test, and if the sample demand is large, the test project needs to be combined again, so as to ensure the sample amount.

[0092] It should be understood that the specific order or hierarchy of steps in the disclosed processes is an example of an example order or hierarchy of steps. Based on design preference, it should be understood that the specific order or hierarchy of steps in the processes can be rearranged without departing from the scope of protection of the disclosure. The appended method claims recite the elements of various steps in an example order, and are not intended to be limited to the specific order or hierarchy described.

[0093] In the detailed description above, various features are grouped together in single embodiments for the purpose of streamlining the disclosure. This method of disclosure, however, is not to be interpreted as reflecting a necessity that the claimed subject matter requires more features than are explicitly recited in each claim. Rather, as the following claims reflect, inventive subject matter can lie in fewer than all features of a single disclosed embodiment. Thus, the following claims are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate preferred embodiment.

[0094] The above description includes examples of one or more embodiments. Of course, not all possible combinations of components or methods described above will be described, but one of ordinary skill in the art will recognize that further combinations and permutations of various embodiments are possible. Accordingly, the embodiments described herein are intended to embrace all such alterations, modifications, and variations going to the full scope of the appended claims. Additionally, the term "comprising" as used in the specification and in the claims is to be construed as meaning "including", "consisting of", or "consisting essentially of", as the case can be, in accordance with the interpretation of such terms in the patent law. Furthermore, any use of the term "or" in the description or claims is to be interpreted as "inclusive OR", in the sense that it is intended to mean "either or both". Also, the use of "first", "second", etc. is to be interpreted as descriptive, not as an indication of importance.

Claims

1. A method of preparing a sample of a layered, heterogeneous rock sample, characterized by, The method comprises the following steps: determining a reference surface direction according to the extension direction of the bedding plane of a layered heterogeneous rock sample, cutting the top surface and the bottom surface of the rock sample along a direction parallel to the reference surface direction, and cutting the side surface of the rock sample along a direction perpendicular to the reference surface direction, so that the shape of the cross section of the rock sample parallel to the reference surface is consistent; cutting the rock sample along a direction perpendicular to the reference surface into a first rock sample and a second rock sample; obtaining an XRF scan map of the cutting surface of the second rock sample, the XRF scan map being a plurality of element content distribution maps, selecting a representative strongest one from the plurality of element content distribution maps, determining a plurality of possible division lines along the width direction of the strongest one, the content variation rate of the corresponding element at the possible division line being higher than a first set threshold, for each possible division line, determining the content variation rate of other set elements there, and determining a comprehensive variation rate by weighted average method according to the content variation rate of each set element, determining the possible division line with a comprehensive variation rate higher than a second set threshold as a division line, and obtaining a division line sequence arranged in an up-down order, the division line being parallel to the reference surface direction; cutting the first rock sample in sequence according to the division line sequence to obtain a plurality of rock samples.

2. The method of claim 1, wherein, The method for determining the reference surface direction according to the extension direction of the bedding plane of a layered heterogeneous rock sample comprises the following steps: counting the direction of the bedding plane of the layered heterogeneous rock sample, and determining the direction with the most developed bedding plane as the reference surface direction; or obtaining the reference surface direction by cluster analysis based on the direction of the bedding plane of the layered heterogeneous rock sample.

3. The method of claim 1, wherein, The volume ratio of the first rock sample to the second rock sample is greater than 10. The width of the cutting surface of the second rock sample is 1-5 cm.

4. The method of claim 1, wherein, The method further comprises the following steps: judging whether the distance between two adjacent division lines is less than a set distance threshold; if yes, deleting one of the two adjacent division lines, or merging the two adjacent division lines with a distance less than the set distance threshold according to the merging rule of the cluster analysis principle to obtain a new division line.

5. The method of claim 4, wherein, The set distance threshold satisfies the following requirement: the volume of a rock sample with a cross section of the cross section of the first rock sample and a thickness of the set distance threshold is not less than a set volume threshold.

6. The method of claim 4, wherein, The set distance threshold is 0.2 mm.

7. The method of claim 1, wherein, The method for cutting the first rock sample in sequence according to the division line sequence to obtain a plurality of rock samples comprises the following steps: determining at least one cutting direction perpendicular to the reference surface direction according to research needs, and completing the vertical cutting of the first rock sample according to each cutting direction; wrapping the cut first rock sample with a set material, and cutting the wrapped first rock sample in sequence according to the division line sequence to obtain a plurality of rock samples.

8. The method according to any one of claims 1 to 7, characterized in that The layered heterogeneous rock sample is a fine-grained sedimentary rock.

9. A method for investigating the heterogeneity of a layered heterogeneous rock sample, characterized in that, The method comprises the following steps: cutting a layered heterogeneous rock sample according to the method in any one of claims 1-8 to obtain a plurality of rock samples; conducting a heterogeneity study based on the obtained plurality of rock samples.

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