A method for evaluating the heterogeneity of a conglomerate reservoir

Abstract

The present application belongs to the technical field of conglomerate oil and gas development, and discloses a method for evaluating the heterogeneity of a conglomerate reservoir. The method comprises the following steps: S1: collecting a conglomerate image of a conglomerate sample, and obtaining a structural heterogeneity index of the conglomerate according to the conglomerate image; S2: performing an indentation test on the conglomerate sample to obtain a material heterogeneity index of the conglomerate; and S3: calculating a heterogeneity index of the conglomerate reservoir according to the structural heterogeneity index of the conglomerate and the material heterogeneity index of the conglomerate, wherein the greater the heterogeneity index, the stronger the heterogeneity. The method for evaluating the heterogeneity of a conglomerate reservoir provided by the present application can be realized without special equipment and complex heterogeneity tests, and the operation method and calculation process are simple and easy to implement, the experimental period is short, and the structural heterogeneity and material heterogeneity of the conglomerate are taken into account, so that the evaluation result is more accurate and reliable.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of conglomerate oil and gas development, and particularly relates to a method for evaluating the heterogeneity of a conglomerate reservoir. BACKGROUND

[0002] Conglomerate reservoirs have great development potential and are an important field for future oil and gas exploitation. Conglomerates are composed of conglomerates and matrix, and this special structure leads to strong heterogeneity, which brings great difficulties to drilling, fracturing and development of conglomerate reservoirs, especially in the selection of drill bits in the drilling field and the evaluation of fracture morphology in the hydraulic fracturing field. The heterogeneity of conglomerate reservoirs has important reference value for engineering design.

[0003] For the evaluation of the heterogeneity of the reservoir, some methods for evaluating the heterogeneity have been proposed at home and abroad. However, these methods are mainly proposed for fine-grained sedimentary reservoirs, and the structural characteristics of conglomerate reservoirs and the essential reasons for the heterogeneity of conglomerate reservoirs are not considered. The essential reason for the heterogeneity of conglomerate reservoirs is that conglomerates are distributed in the matrix, and the mechanical properties of conglomerates and matrix are different, resulting in heterogeneity. Therefore, two problems must be clarified in evaluating the heterogeneity of conglomerate reservoirs: one is the structural characteristics of conglomerate, that is, the influence of conglomerate content on heterogeneity; the other is the material characteristics of conglomerate reservoir, that is, the influence of the mechanical properties of conglomerate and matrix on heterogeneity.

[0004] The prior art also proposes similar research methods. For example, a Chinese patent with application number CN2111327814.2 discloses a method, device, medium, equipment and program product for evaluating the heterogeneity of conglomerate, which collects conglomerate images of conglomerate samples, determines grain size heterogeneity parameters according to the conglomerate images, obtains first test data of the conglomerate samples under a preset indentation test, determines micro-domain mechanical property distribution characteristic parameters according to the first test data, obtains second test data of the conglomerate samples under a preset three-point bending experiment, determines cementation strength distribution characteristic parameters according to the second test data, and finally determines the heterogeneity coefficient of the conglomerate corresponding to the conglomerate sample according to the grain size heterogeneity parameters, the micro-domain mechanical property distribution characteristic parameters and the cementation strength distribution characteristic parameters, so as to use the heterogeneity coefficient to represent the conglomerate heterogeneity. However, the method of the patent mainly considers the influence of grain size structure, and focuses more on the material heterogeneity of conglomerate and matrix. The sample preparation of the evaluation method is difficult, many tests are required, and some test conditions are too harsh, which prolongs the experimental period.

[0005] Therefore, there is an urgent need for a simple and easy-to-use evaluation method for the heterogeneity of conglomerate reservoirs that takes into account the structural characteristics of conglomerate. SUMMARY

[0006] The present application aims at the problem of difficult evaluation of conglomerate reservoir heterogeneity in the prior art, and provides a method for evaluating conglomerate reservoir heterogeneity, which can be realized without special equipment and complex heterogeneity test, and has simple and easy operation method and calculation process, short experimental period, and consideration of conglomerate structure heterogeneity and material heterogeneity, and more accurate and reliable evaluation result.

[0007] To achieve the above technical purposes, the present application adopts the following technical solutions:

[0008] A method for evaluating conglomerate reservoir heterogeneity, comprising the following steps:

[0009] Step S1: collecting a conglomerate image of a conglomerate sample, and obtaining a structure heterogeneity index of the conglomerate according to the conglomerate image;

[0010] Step S2: performing an indentation test on the conglomerate sample to obtain a material heterogeneity index of the conglomerate;

[0011] Step S3: calculating a heterogeneity index of the conglomerate reservoir according to the structure heterogeneity index and the material heterogeneity index of the conglomerate; the greater the heterogeneity index, the stronger the heterogeneity.

[0012] Further, the step S1 specifically comprises:

[0013] Step S101: preparing a sample;

[0014] Step S102: performing image acquisition on a test plane of the sample, and obtaining a conglomerate gravel content C g according to test plane image information;

[0015] Step S103: calculating a structure heterogeneity index of the conglomerate according to the conglomerate gravel content C g obtained in step S102 through the following formula:

[0016]

[0017] In the above formula, Is is the structure heterogeneity index of the conglomerate; C g is the conglomerate gravel content; C g0 is a critical conglomerate gravel content value, that is, a minimum conglomerate gravel content value when the conglomerate is completely in a gravel support mode.

[0018] Further, the critical conglomerate gravel content value Cg0 of the conglomerate is simulated according to a PFC particle discrete element theory, and C g0 = 0.7.

[0019] Further, the step S101 specifically comprises:

[0020] Select representative rock samples to prepare regular or irregular samples, and then grind and polish the test surface of the samples.

[0021] Furthermore, the test plane of the sample can be a regular or irregular plane, and the regular plane includes rectangles, squares, circles, or ellipses.

[0022] Further, in step S102, image acquisition of the test plane of the sample is performed, specifically including:

[0023] First, use a CT scanner to obtain images of the sample's end face;

[0024] Then, use Photoshop to adjust the contrast, brightness and color levels of the scanned end face image. Then use the quick pick tool in Photoshop to pick the gravel boundary and use the fill tool to fill the gravel background to complete the gravel image extraction.

[0025] Finally, ImageJ software was used to analyze the gravel images and calculate the gravel area.

[0026] Furthermore, in step S102, the gravel content C of the conglomerate... g The calculation formula is as follows:

[0027]

[0028] In the above formula, C g Gravel content; A g To measure the area of ​​gravel in the test plane, mm 2 A s For testing the area of ​​a plane, mm 2 .

[0029] Furthermore, step S2 specifically includes:

[0030] Step S201: Obtain the hardness of the gravel and matrix through indentation testing;

[0031] Step S202: Based on the hardness of the gravel and matrix obtained in step S201, calculate the material heterogeneity index of the conglomerate using the following formula:

[0032]

[0033] In the above formula, I M H represents the material heterogeneity index of conglomerate; g The peak value of the Gaussian distribution of gravel hardness, GPa, H m The value represents the peak value of the Gaussian distribution of the matrix hardness, in GPa.

[0034] Further, the step S201 specifically comprises:

[0035] The sample is tested by nanoindentation test according to the regular dot matrix;

[0036] After the test, the gravel test points and the matrix test points are screened according to the indentation test positions, and the hardness data of the test points are obtained;

[0037] The obtained gravel test point hardness data and matrix test point hardness data are respectively calculated for peak hardness according to Gaussian distribution, and the respective peak hardnesses represent the gravel hardness and the matrix hardness.

[0038] Further, in the step S201, the gravel test points and the matrix test points are respectively screened according to the indentation test positions, specifically comprising:

[0039] The test points completely falling on the gravel represent the gravel, the test points completely falling on the matrix represent the matrix, and the data close to the edge position is discarded.

[0040] Further, in the step S3, the formula for calculating the heterogeneity index of the conglomerate reservoir is:

[0041] I INH = I S I M

[0042] In the above formula, I INH is the heterogeneity index of the conglomerate; I S is the structural heterogeneity index of the conglomerate; and I M is the material heterogeneity index of the conglomerate.

[0043] Further, the method further comprises the following steps:

[0044] Step S4: grading evaluation of the heterogeneity of the conglomerate reservoir according to the heterogeneity index of the conglomerate reservoir.

[0045] Further, the step S4 specifically comprises:

[0046] According to the conglomerate heterogeneity index I INH obtained in the step S3, combined with the classification method of the heterogeneity of the clastic rock in the petroleum industry, the clustering analysis and the fuzzy comprehensive evaluation method are used for comprehensive classification and evaluation, so as to formulate the evaluation standard of the conglomerate heterogeneity for grading evaluation of the heterogeneity of the conglomerate reservoir.

[0047] Further, the grading evaluation standard is:

[0048] If 0≤I INH <0.05, the heterogeneity is extremely weak;

[0049] If 0.05≤I INH <0.1, the heterogeneity is: weak;

[0050] If 0.1≤I INH <0.3, the heterogeneity is: medium;

[0051] If 0.3≤I INH <0.5, the heterogeneity is: strong;

[0052] If 0.5≤I INH <1, the heterogeneity is: very strong.

[0053] Compared with the prior art, the present application has the beneficial effects that:

[0054] The method for evaluating the heterogeneity of the conglomerate reservoir considers the essential reason for the heterogeneity of the conglomerate reservoir, comprehensively calculates the heterogeneity index of the conglomerate reservoir according to the structural heterogeneity characteristics and the material heterogeneity characteristics of the conglomerate reservoir, and evaluates the heterogeneity grade of the conglomerate reservoir according to the heterogeneity index of the conglomerate reservoir; the method solves the problems of the existing test method, such as difficult sample preparation, harsh test conditions and the like, and has the following advantages:

[0055] (1) without special equipment, ordinary rock mechanics experimental device can be realized;

[0056] (2) the sample preparation consumes low amount, is easy to process, and regular cylindrical, cuboid or irregular samples can be used;

[0057] (3) the complex and harsh heterogeneity test is avoided, the test process and calculation process are simple, and easy to operate and execute;

[0058] (4) the structural heterogeneity and the material heterogeneity of the conglomerate are considered, the evaluation result is more accurate and reliable, and the test result of more than 100 groups of samples tested by the method of the present application reaches 95%. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 The flow chart of the test method of the embodiment of the present application;

[0060] Figure 2 The schematic diagram of the conglomerate area calculation of the cuboid sample in the embodiment of the present application;

[0061] Figure 3 The schematic diagram of the conglomerate and miscellaneous base hardness calculation of the cuboid sample in the embodiment of the present application. DETAILED DESCRIPTION

[0062] With reference to the accompanying drawings, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the protection scope of the present application.

[0063] Embodiment 1

[0064] The embodiments of the present application provide a method for evaluating the heterogeneity of conglomerate reservoirs, which comprises the following steps.

[0065] In combination with Figure 1 as shown in the figure, the method specifically comprises the following steps.

[0066] Step S1: collecting a conglomerate image of a conglomerate sample, and obtaining a structural heterogeneity index of the conglomerate according to the conglomerate image, specifically comprising:

[0067] Step S101: preparing a sample;

[0068] A representative rock sample is selected to prepare a cylindrical, cuboid or other regular or irregular sample. Then, a larger plane of the sample is selected as a test plane, and the test plane is ground and polished. The processed test plane can be a regular rectangle, square, circle or ellipse, or an irregular plane.

[0069] Step S102: image acquisition is performed on the test plane of the sample, and the conglomerate content of the conglomerate is obtained according to the image information of the test plane.

[0070] Specifically,

[0071] First, the end surface image of the sample is scanned by a CT scanner.

[0072] Then, the contrast, brightness and color step of the scanned end surface image are adjusted by using Photoshop software, the gravel boundary is picked up by using the quick pick-up tool in the Photoshop software, and the gravel is filled in the background by using the filling tool, so as to complete the extraction of the gravel image.

[0073] Finally, the gravel image is analyzed by using Image J software, and the gravel area is calculated.

[0074] For example, Figure 2As shown, in the embodiment of the present application, taking a rectangular test area with side length a and b as an example, there are totally 6 gravels numbered 1-6 in the test area, and the gravel content C of the conglomerate is calculated g is:

[0075]

[0076] In the above formula (1), C g is the gravel content of the conglomerate; A1-A6 are the areas of gravels 1-6; a and b are the side lengths of the rectangular test area.

[0077] Step S103: According to the gravel content C of the conglomerate obtained in step S102 g , the structural heterogeneity index of the conglomerate is calculated by the following formula (2):

[0078]

[0079] In the above formula (2), C g is the gravel content of the conglomerate; I S is the structural heterogeneity index of the conglomerate.

[0080] Since the heterogeneity of the conglomerate mainly comes from the gravel content, according to the PFC particle discrete element theory simulation, it is known that when the gravel content exceeds 70%, the conglomerate at this time is completely in the gravel support mode, and accordingly the critical gravel content value C g0 of the conglomerate is determined to be 70%, i.e. 0.7, and the structural heterogeneity index of the conglomerate is calculated by the above formula (2).

[0081] Step S2: Indentation test is performed on the conglomerate sample to obtain the material heterogeneity index of the conglomerate, specifically including:

[0082] Step S201: The hardness of gravels and matrixes is obtained by nanoindentation test method;

[0083] As Figure 3 shown, nanoindentation test is performed on the test plane of the sample according to a regular lattice;

[0084] After the test is completed, according to the indentation test position, gravel test points and matrix test points are respectively screened, and test point hardness data is obtained; wherein, the test point screening process is: test points completely falling on gravels represent gravels, test points completely falling on matrixes represent matrixes, and data close to the edge position is discarded;

[0085] The obtained gravel test point hardness data and matrix test point hardness data are respectively calculated for peak hardness according to Gaussian distribution, and the respective peak hardness represents the hardness of gravels and matrixes.

[0086] Step S202: According to the hardness of the gravel and the matrix obtained in step S201, the material heterogeneity index of the conglomerate is calculated by the following formula (3):

[0087]

[0088] wherein I M is the material heterogeneity index of the conglomerate; H g is the peak value of the Gaussian distribution of the gravel hardness, GPa, H m is the peak value of the Gaussian distribution of the matrix hardness, GPa.

[0089] Since the conglomerate is composed of two materials, the gravel and the matrix, the mechanical difference between the gravel and the matrix leads to the mechanical heterogeneity of the conglomerate, and therefore the formula (3) is used to calculate and measure the material heterogeneity index of the conglomerate.

[0090] Step S3: According to the structure heterogeneity index I S of the conglomerate obtained in step S103 and the material heterogeneity index I M of the conglomerate obtained in step S202, the overall heterogeneity of the conglomerate is comprehensively determined by considering the structure heterogeneity and the material mechanical heterogeneity, and the heterogeneity index I INH of the conglomerate is calculated by the following formula (4):

[0091] I INH = I S I M (4)

[0092] In the above formula (4), I INH is the heterogeneity index of the conglomerate.

[0093] Step S4: According to the heterogeneity index I INH of the conglomerate obtained in step S3, combined with the classification method of the heterogeneity of the clastic rock in the petroleum industry, the comprehensive classification and evaluation are carried out by using the cluster analysis and the fuzzy comprehensive evaluation method, so as to formulate the evaluation standard of the heterogeneity of the conglomerate to evaluate the heterogeneity of the conglomerate reservoir in different grades.

[0094] The grading evaluation standard is shown in Table 1 as follows:

[0095] Table 1 Evaluation standard of the heterogeneity of the conglomerate

[0096] I INH ]] [0，0.05) [0.05，0.1) [0.1，0.3) [0.3，0.5) [0.5，1) Heterogeneity Very weak Weak Moderate Strong Very strong

[0097] Example 2

[0098] The method in example 1 is applied to engineering practice to verify the method in example 1 of the present application, and the method includes the following steps:

[0099] Step S1: Collecting the conglomerate image of the conglomerate sample, and obtaining the structural heterogeneity index of the conglomerate according to the conglomerate image.

[0100] In combination with Table 2 shown below, five experimental core samples are selected near 3396.4m of XX well group, and the conglomerate content C of the five experimental core samples is measured by CT scanner scanning reconstruction calculation g respectively: 35.26%, 46.99%, 56.23%, 61.26%, 63.62%, and the corresponding structural heterogeneity indexes Is are 0.6526, 0.7699, 0.8623, 0.9126, and 0.9362 respectively.

[0101] Step S2: Indentation test is performed on the conglomerate sample to obtain the material heterogeneity index of the conglomerate.

[0102] The Gaussian distribution peak values of the conglomerate hardness of the five experimental core samples are 41.55GPa, 37.59GPa, 35.69GPa, 43.21GPa, and 38.9GPa respectively, and the Gaussian distribution peak values of the matrix hardness are 13.19GPa, 12.5GPa, 14.5GPa, 15.42GPa, and 11.65GPa respectively, and the Gaussian distribution peak values of the conglomerate hardness of the experimental core samples are used to represent the conglomerate hardness, and the Gaussian distribution peak values of the matrix hardness are used to represent the matrix hardness.

[0103] According to the obtained conglomerate and matrix hardness of the five experimental core samples, the corresponding material heterogeneity indexes I M of the conglomerate are calculated respectively as 0.68, 0.67, 0.59, 0.64, and 0.70.

[0104] Step S3: According to the structural heterogeneity index I S of the conglomerate and the material heterogeneity index I M of the conglomerate, the heterogeneity index I INH of the conglomerate is calculated. INH The heterogeneity indexes I INH of the conglomerate of the five experimental core samples are calculated as 0.44, 0.52, 0.51, 0.58, and 0.66 respectively.

[0105] Step S4: According to the obtained conglomerate heterogeneity index I INH , the conglomerate reservoir heterogeneity is evaluated, and the heterogeneity grades of the conglomerate reservoir corresponding to the five experimental core samples are strong, extremely strong, extremely strong, extremely strong, and extremely strong respectively.

[0106] From the calculated conglomerate heterogeneity index I INH , it is consistent with the actual measurement that the conglomerate property becomes worse with the increase of the conglomerate content.

[0107] Table 2 Gravel heterogeneity evaluation result data of experimental core samples

[0108]

[0109]

[0110] In addition, more than 100 groups of samples are tested by using the method of the above embodiment of the present application, and the conformity of the final test results reaches 95%, which further verifies the effectiveness of the method of the present application.

[0111] The above only describes the embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the scope of the present application should be included in the protection scope of the present application.

Claims

1. A method of evaluating the heterogeneity of a conglomerate reservoir, characterized in that, The method comprises the following steps: Step S1: collecting a conglomerate image of a conglomerate sample, and obtaining a structure heterogeneity index of the conglomerate according to the conglomerate image; Step S2: performing an indentation test on the conglomerate sample to obtain a material heterogeneity index of the conglomerate; Step S3: calculating a heterogeneity index of a conglomerate reservoir according to the structure heterogeneity index and the material heterogeneity index of the conglomerate; the greater the heterogeneity index, the stronger the heterogeneity; The step S1 specifically comprises: Step S101: preparing a sample; Step S102: image acquisition is performed on the test plane of the sample, and the gravel content of the conglomerate is obtained according to the test plane image information C g ; Step S103: Calculate the structure heterogeneity index of the conglomerate according to the conglomerate content of the conglomerate obtained in step S102 C g The structure heterogeneity index of the conglomerate is calculated by the following formula: In the above formula, is the structural heterogeneity index of the conglomerate; is the gravel content of the conglomerate; is the critical gravel content value of the conglomerate, i.e. the minimum gravel content value at which the conglomerate is completely supported by the gravel.

2. The method of claim 1, wherein, The critical gravel content value of the conglomerate is simulated according to the PFC particle discrete element theory, = 0.

7.

3. The method of claim 1, wherein, The step S101 specifically comprises: A representative rock sample is selected to prepare a regular or irregular sample, and then the test plane of the sample is ground and polished.

4. The method of claim 3, wherein, The test plane of the sample is a regular or irregular plane, and the regular plane includes a rectangle, a square, a circle or an ellipse.

5. The method of claim 1, wherein, In the step S102, the test plane of the sample is subjected to image acquisition, specifically comprising: First, an end surface image of the sample is acquired by scanning with a CT scanner; Then, the contrast, brightness and color step of the acquired end surface image are adjusted using Photoshop software, the gravel boundary is picked up using a quick pick-up tool in the Photoshop software, and the gravel is background-filled using a filling tool to complete gravel image extraction; Finally, gravel image analysis is performed using Image J software to calculate the gravel area.

6. The method of claim 5, wherein, In the step S102, the gravel content of the conglomerate C g The calculation formula is as follows: In the above formula, is the gravel content; is the gravel area in the test plane, mm 2 ; is the test plane area, mm 2 .

7. The method of claim 6, wherein, The step S2 specifically comprises: Step S201: obtaining the hardness of the gravel and the matrix through indentation testing; Step S202: calculating the material heterogeneity index of the conglomerate according to the hardness of the gravel and the matrix obtained in step S201 by the following formula: In the above formula, is the non-homogeneity index of the material that is the conglomerate; is the Gaussian distribution peak value of the conglomerate hardness, GPa, is the Gaussian distribution peak value of the heteroatom hardness, GPa.

8. The method of claim 7, wherein, The step S201 specifically comprises: Nanoindentation testing is performed on the test plane of the sample according to a regular dot matrix; After the test is completed, the gravel test points and the matrix test points are respectively screened according to the indentation test positions, and the hardness data of the test points are obtained; The hardness data of the gravel test points and the hardness data of the matrix test points are respectively calculated according to the Gaussian distribution to obtain the peak hardness, and the respective peak hardness represents the hardness of the gravel and the hardness of the matrix.

9. The method of claim 7, wherein, In the step S201, the gravel test points and the matrix test points are respectively screened according to the indentation test positions, specifically comprising: The test points completely falling on the gravel represent the gravel, and the test points completely falling on the matrix represent the matrix, and the data close to the edge position is discarded.

10. The method of claim 8, wherein, In the step S3, the formula for calculating the heterogeneity index of the conglomerate reservoir is: In the above formula, is the index of the heterogeneity of the conglomerate; is the index of the structural heterogeneity of the conglomerate; is the index of the material heterogeneity of the conglomerate.

11. The method according to any one of claims 1 to 10, characterized in that, Further comprising the following steps: Step S4: grading the heterogeneity of the conglomerate reservoir according to the heterogeneity index of the conglomerate reservoir.

12. The method of claim 11, wherein, The step S4 specifically comprises: The conglomerate heterogeneity index obtained according to step S3 , combined with the classification method of the heterogeneity of clastic rocks in the oil industry, the comprehensive classification and evaluation are carried out by using clustering analysis and fuzzy comprehensive evaluation method, so as to formulate the evaluation standard of conglomerate heterogeneity to evaluate the heterogeneity of conglomerate reservoirs.

13. The method of claim 12, wherein, The grading evaluation standard is: If , the heterogeneity is: very weak; If , the heterogeneity is: weaker; If , the heterogeneity is: medium; If , the heterogeneity is: stronger; If , the heterogeneity is: very strong.

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