Quantitative evaluation method for micron-sized visual rock core perforation channel

Abstract

The invention discloses a micron-sized visual rock core perforation channel quantitative evaluation method which comprises the following steps: step S1, coring aiming at a research block, and carrying out an experimental test before perforation to obtain first basic data of a rock core; s2, perforation testing is conducted on the rock core, and the rock core is cut out at equal intervals in the perforation channel direction after testing; s3, cutting the rock core cut in the step S2 to obtain a rock block perpendicular to the plane where the hole channel direction is located, and preparing a rock core casting body sheet by using the rock block; s4, splicing the rock core casting body sheets on the same plane to form a full-casting body sheet picture of the plane where the rock core casting body sheets are located; s5, performing image analysis on each full-casting body sheet picture to obtain second basic data in the full-casting body sheets; s6, rock core perforation channel quantitative evaluation is conducted in combination with the second basic data. According to the method provided by the invention, higher-precision and visual damage evaluation can be provided for the perforated rock core, and a foundation is laid for optimal design of a perforation technology and calculation of productivity.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and particularly relates to a micron-level visualized rock core perforation channel quantitative evaluation method. Background Art

[0002] With the continuous development of the national economy, the country's dependence on foreign oil and natural gas has continued to reach new highs, and the issue of national energy security has become increasingly prominent. With the continuous rise in international oil prices, increasing domestic oil and natural gas exploration and development is of great significance to national energy security.

[0003] With the continuous in-depth exploitation of oil and gas resources, the proportion of unconventional oil and gas resource exploration and development is increasing. However, due to the poor porosity and permeability of such unconventional reservoirs, the method of observing the perforation channels by using a ground-mounted gun through a concrete target is no longer applicable to the evaluation of the perforation channels of such reservoirs. The use of large-scale industrial CT scanning to evaluate perforation cannot accurately characterize the perforation damage and is expensive. Therefore, a more accurate and intuitive experimental method is needed to evaluate the pore and fracture characteristics, compaction zone, fracture zone and perforation range around the core channel after perforation. Summary of the invention

[0004] The present invention provides a micron-level visualized core perforation channel quantitative evaluation method, comprising the following steps:

[0005] Step S1: coring the studied block and conducting experimental tests before perforating to obtain the first basic data of the core;

[0006] Step S2: performing a perforation test on the core, and cutting the core at equal intervals along the direction of the perforation channel after the test;

[0007] Step S3: cutting a rock block in a plane perpendicular to the channel direction from the core intercepted in step S2, and using the rock block to prepare a core casting thin slice;

[0008] Step S4: splicing the core casting thin sections on the same plane to form a full casting thin section photo of the plane;

[0009] Step S5: performing image analysis on each full cast thin section photo to obtain second basic data in the full cast thin section;

[0010] Step S6: quantitatively evaluate the core perforation channels in combination with the second basic data.

[0011] Preferably, in the present invention, the experimental test in step S1 includes a porosity test, a compressive strength test, and a casting thin section analysis.

[0012] Preferably, in the present invention, the first basic data of the core in step S1 includes porosity, permeability, uniaxial compressive strength, rock grain size, pore diameter, pore area, and surface porosity.

[0013] Preferably, in step S2, 4-6 cores are cut at equal intervals for the penetration portion, and 2-3 cores are cut at equal intervals for the tail end portion of the channel.

[0014] Preferably, in the present invention, the shape of the rock block in step S3 is nearly circular, nearly semicircular or nearly fan-shaped.

[0015] Preferably, in step S4, a fully automatic microscope is used to collect images under a multi-field microscope for seamless splicing to form a photo of the entire casting thin section.

[0016] Preferably, in the present invention, the second basic data in step S5 includes pore diameter, pore area, surface area ratio and seam porosity in the casting thin slice.

[0017] Preferably, in the present invention, step S5 further comprises: taking the center of the hole as the center of the circle, dividing the circle into annular zones at regular intervals, and performing image analysis on each annular zone.

[0018] Preferably, step S6 of the present invention further comprises: quantitatively evaluating the width of the compaction zone and the fracture zone in the core perforation, the characteristics of the pores and cracks around the hole channel, and the perforation range.

[0019] On the other hand, the present invention provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that when the processor executes the computer program, the steps of the quantitative evaluation method of micron-level visual core perforation channels as described in any one of the above claims are implemented.

[0020] On the other hand, the present invention provides a computer-readable storage medium having a computer program stored thereon, characterized in that when the computer program is executed by a processor, the steps of the method for quantitative evaluation of micron-level visualized core perforation channels as described in any one of the above claims are implemented.

[0021] The present invention has the following advantages: (1) In view of the fact that the existing evaluation methods cannot reflect the real state of the core after perforation and cannot obtain relatively accurate perforation test parameters, the present invention proposes a micron-level visualized core perforation channel quantitative evaluation method. By analyzing the thin slices of the core channel casting, the accuracy is greatly improved, up to 1-4 microns, and the pore and crack characteristics, compaction zone, fracture zone and perforation range around the core channel can be accurately obtained with high accuracy. (2) The present invention can not only clearly visualize the channel body, larger cracks and perforating bullet residues, but also clearly see the smaller cracks and pores in the rock, and have an intuitive understanding of the pore and crack characteristics, compaction zone, fracture zone and perforation range around the core channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a microscopic characteristic diagram of a sandstone casting thin section in a certain area in an embodiment of the present invention;

[0023] Figure 2 This is a sandstone grain size distribution diagram of a certain area in an embodiment of the present invention;

[0024] Figure 3 The single pore size distribution histogram of sandstone in a certain area in the embodiment of the present invention;

[0025] Figure 4 The single hole area distribution histogram of sandstone in a certain area in the embodiment of the present invention;

[0026] Figure 5 This is a thin slice cutting scheme for sandstone target casting in a certain area in an embodiment of the present invention;

[0027] Figure 6 A thin slice of a sandstone target casting in a certain region in an embodiment of the present invention;

[0028] Figure 7 This is a full-thin-section photo of a sandstone target casting in a certain area in an embodiment of the present invention;

[0029] Figure 8 Schematic diagram of the division of the ring zones of the full-sheet photo in an embodiment of the present invention;

[0030] Fig. 9 This is a diagram showing the division of the channel annular zones of a cast thin film in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with an example of combined production of natural gas hydrate and underlying gas in a certain sea area. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0032] In the existing technology, the accuracy of the core perforation test evaluation method is generally low, especially for tight reservoirs, the existing evaluation method can no longer reflect the actual state of the core after perforation. In the existing technology, CT visualization evaluation method is used to evaluate the state after perforation. However, in the large-size core CT data, only the main body of the channel, larger cracks and perforating bullet residues are visible, and smaller cracks and pore characteristics cannot be observed intuitively. Based on this, the invention provides a micron-level visualization core perforation channel quantitative evaluation method, which can provide higher accuracy and more intuitive evaluation of the core after perforation, and provide strong data support for the research and development of perforating bullets, which is of great significance to the development of oil and gas fields, especially unconventional oil and gas fields.

[0033] A micron-level visualized core perforation channel quantitative evaluation method according to the present invention comprises the following steps:

[0034] Step S1: coring the studied block and conducting experimental tests before perforating to obtain the first basic data of the core;

[0035] Specifically, the experimental tests include porosity test, compressive strength test, and casting thin section analysis;

[0036] Specifically, the first basic data of the core includes porosity, permeability, uniaxial compressive strength, rock grain size, pore diameter, pore area, and surface porosity;

[0037] In a specific embodiment, cores were taken from sandstone in a certain area, cast thin sections were made, and porosity and permeability tests, cast thin section analysis, and compressive strength tests were performed. The porosity of the sandstone in a certain area was 10.07%, and the permeability was 1.07 mD, which was a low-porosity, low-permeability, dense sandstone. By statistically analyzing the particle size characteristics of the cast thin sections, it was found that the sandstone in a certain area was mainly medium-fine-grained sandstone, and the medium (such as Figure 1 , Figure 2 As shown, Figure 1 A and B in the middle are the same field of view, in which the pores are developed, mainly intergranular pores and feldspar solution pores, and the filling materials are mainly clay minerals and iron mud; Figure 1 C and D in the middle are in the same field of view, with dense mass areas and undeveloped pores. The cement is mainly zeolite, followed by iron mud. Through the observation of cast thin sections and statistical analysis of pores, the rock is highly heterogeneous, and the rock surface rate is 0.81%, and the homogeneity of the single pore area is 338.3μm 2 The maximum pore size is 31.09 μm, and the minimum pore size is 14.70 μm, which belongs to the small-pore type dense sandstone (such as Figure 1 , Figure 3 , Figure 4 As shown). Through the uniaxial compressive strength test of sandstone, the uniaxial compressive strength of sandstone is between 43-50MPa, and the rock strength is relatively high.

[0038] Step S2: performing a perforation test on the core, and cutting the core at equal intervals along the direction of the perforation channel after the test;

[0039] Specifically, 4 to 6 cores are cut at equal intervals for the penetration portion, and 2 to 3 cores are cut at equal intervals for the tail end portion of the borehole.

[0040] In a specific embodiment, Figure 5 As shown, after the core is split along the hole after perforation, the length and diameter of the hole are measured and the macroscopic characteristics of the core hole are photographed, the core is cut at equal intervals using a cutting machine (4-6 cores are cut at equal intervals in the perforated part and 2-3 cores are cut at the tail end of the hole).

[0041] Cut out the periphery of the hole in a nearly circular, semicircular or fan-shaped shape. Preferably, a circular or semicircular rock block is selected for cutting, wherein the rock block thickness is 5cm-10cm and the rock block diameter is 6.5cm-7.5cm, in preparation for making a casting thin slice;

[0042] Step S3: cutting a rock block in a plane perpendicular to the channel direction from the core intercepted in step S2, and using the rock block to prepare a core casting thin slice;

[0043] Specifically, a fully automatic microscope is used to collect images under a multi-field microscope for seamless splicing to form a whole-cast thin section photo;

[0044] In a specific embodiment, making a rock block to prepare a core casting thin slice includes the following steps: ① Put the cut circular or semicircular rock block into a glass tube, use a casting instrument to cast the epoxy resin glue added with blue pigment into the pores and cracks of the rock block, and after the epoxy resin is completely cured (generally takes 24-48 hours), gently break the glass tube and take out the rock block after the epoxy resin is cured; ② The bottom surface of the solidified rock block is subjected to coarse grinding → medium grinding → fine grinding → fine grinding with a grinding machine, until the bottom surface is very flat, in preparation for later sticking; ③ Bond a glass slide to the bottom surface of the rock block that has been ground to a very flat surface; ④ Use a small cutting machine to slowly cut the rock block (reserve a rock slice of about 1 mm on the glass slide); ⑤ Use a grinding machine to coarse grinding → medium grinding → fine grinding → fine grinding → polishing the rock slice until the interference color of the quartz under a polarizing microscope is a primary grayish white, indicating that the thickness of the rock slice is about 0.03 mm. ⑥ Use a polishing machine to polish the surface of the casting slice to remove the pitting on the surface of the mineral slice; ⑦ Cover the surface of the mineral slice with fir glue and cover the glass, and clean the casting slice after the fir glue dries; the casting slice ( Figure 6 ).

[0045] Step S4: splicing the core casting thin sections on the same plane to form a full casting thin section photo of the plane;

[0046] In a specific embodiment, 6 casting thin sections are used to collect multi-view microscope images (900-1100 images) with a 5x objective lens (magnification 50x, resolution 4 microns), and the multi-view microscope images (900-1100 images) are seamlessly spliced ​​to form a full casting thin section photo ( Figure 7 ).

[0047] Step S5: performing image analysis on each full cast thin section photo to obtain second basic data in the full cast thin section;

[0048] Specifically, the second basic data include pore diameter, pore area, surface ratio, and seam porosity in the cast thin slice.

[0049] In a specific embodiment, image analysis is performed on each full cast thin section photograph. The semicircular photograph is divided into a ring zone every 5-8 mm with the center of the hole as the center, and a total of 6 ring zones are divided ( Figure 8 , Fig. 9 ). The whole thin-section photo was cut into 6 ring-zone photos, and the photo of each ring-zone was image analyzed. All individual pores were identified, and the pore major axis, pore minor axis, pore equivalent circle diameter and pore area of ​​the individual pores were extracted. The basic data such as the pore diameter and pore area of ​​the individual pores in each ring zone were summarized and counted, and the number of pores, surface area ratio, pore area mean, maximum pore diameter mean and minimum pore diameter mean in each ring zone were calculated (the specific data are shown in Table 1-6).

[0050] Table 1 Pore image analysis table of the whole thin section photograph of No. 1 casting

[0051]

[0052] Table 2 Pore image analysis table of the whole thin section photograph of No. 2 casting

[0053]

[0054] Table 3 Pore image analysis table of the whole thin section photograph of No. 3 casting

[0055]

[0056]

[0057] Table 4 Pore image analysis table of the whole thin section photograph of No. 4 casting

[0058]

[0059] Table 5 Pore image analysis table of the whole thin section photograph of No. 5 casting

[0060]

[0061] Table 6 Pore image analysis table of the whole thin section photograph of No. 6 casting

[0062]

[0063]

[0064] Step S6: quantitatively evaluate the core perforation channels in combination with the second basic data.

[0065] Specifically, the width of the compaction zone and the broken zone in the core perforation, the characteristics of the pores and fractures around the hole channel, and the perforation range are quantitatively evaluated.

[0066] In order to comprehensively analyze the image analysis data of each ring of all casting thin sections in the core, and compare the image analysis data of each ring with the porosity test, compressive strength test, and casting thin section analysis data completed in step S1, the changes in the pore diameter, pore area, and surface ratio in each ring after perforation are analyzed, and the compaction zone width, broken zone width, pore fracture characteristics around the channel, and perforation sweep range in the core perforation are quantitatively evaluated according to the changes in these parameters, so as to provide basic parameters for product research and development.

[0067] Among them, some parameters are explained as follows:

[0068] Annular band width D: Divide the duct center outward into Annular bands of the same width for data statistics, generally 5-8mm can be selected;

[0069] The affected edge ring zone X: the outermost ring with a surface porosity greater than 1-1.1 times the original surface porosity, and a pore diameter and pore area close to the original rock;

[0070] Compacted ring zone Y: The surface porosity of the pore edge is 1-1.1 times smaller than the original surface porosity, and the pore diameter and pore area are smaller than the original rock;

[0071] Broken ring zone Y: the face rate is 1-1.1 times greater than the original face rate;

[0072] Compacted belt width = compacted belt Y × belt width D – channel radius R;

[0073] Crushing zone width = crushing ring zone Y × ring zone width D-channel radius R;

[0074] The width of the affected range = the affected edge ring X × the width of the ring D - the radius of the channel R.

[0075] In a specific embodiment, the pore image analysis data of six casting thin sections of sandstone targets in a certain area are summarized and analyzed, and compared with the porosity test, compressive strength test, and casting thin section analysis data of the original rock, and the changes in the pore diameter, pore area, and surface ratio in each ring zone after perforation are analyzed. According to the changes in these parameters, the compaction zone width, the broken zone width, the pore characteristics around the channel, and the perforation range (such as Fig. 9 , as shown in Table 7 and Table 8). No obvious compression phenomenon was observed in the sample. The influence of the rupture varied greatly from the inside to the outside. The rupture influence of the ring zone 1-2 was the most significant, and the rupture influence of the ring zone 3 gradually decreased. The influence of the ring zone 4-6 was basically stable. According to the estimated rupture center, the width of the annular rupture zone gradually decreased from the hole mouth to the end of the hole.

[0076] Table 7 Comparison of full slice pore image analysis

[0077]

[0078]

[0079] Table 8 Quantitative evaluation table of sandstone target perforation channels in a certain area

[0080]

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A micron-level visualized core perforation channel quantitative evaluation method, comprising the following steps: Step S1: coring the studied block and conducting experimental tests before perforating to obtain the first basic data of the core; Step S2: performing a perforation test on the core, and cutting the core at equal intervals along the direction of the perforation channel after the test; Step S3: cutting a rock block in a plane perpendicular to the channel direction from the core intercepted in step S2, and using the rock block to prepare a core casting thin slice; Step S4: splicing the core casting thin sections on the same plane to form a full casting thin section photo of the plane; Step S5: performing image analysis on each full cast thin section photo to obtain second basic data in the full cast thin section; Step S6: quantitatively evaluate the core perforation channels in combination with the second basic data.

2. According to the micron-level visualized core perforation channel quantitative evaluation method of claim 1, the experimental test in step S1 includes porosity test, compressive strength test, and casting thin section analysis.

3. According to the micron-level visualized core perforation channel quantitative evaluation method described in claim 1, the first basic data of the core in step S1 includes porosity, permeability, uniaxial compressive strength, rock grain size, pore diameter, pore area, and surface porosity.

4. According to the quantitative evaluation method of micron-level visualized core perforation channels according to claim 1, in step S2, 4-6 cores are cut at equal intervals for the perforated part, and 2-3 cores are cut at equal intervals for the tail end of the channel.

5. According to the micron-level visualized core perforation channel quantitative evaluation method of claim 1, the shape of the rock block in step S3 is nearly circular, nearly semicircular or nearly fan-shaped.

6. According to the method for quantitative evaluation of micron-level visualized core perforation channels according to claim 1, in step S4, a fully automatic microscope is used to collect images under a multi-field microscope for seamless splicing to form a full-cast thin section photo.

7. The micron-level visualized core perforation channel quantitative evaluation method according to claim 1, wherein the second basic data in step S5 includes pore diameter, pore area, surface porosity, and fracture porosity in the casting thin section.

8. The method for quantitatively evaluating micron-level visualized core perforation channels according to claim 1, wherein step S5 further comprises: The center of the hole is taken as the center of the circle, and each ring zone is divided into a ring zone at a certain interval, and image analysis is performed on each ring zone.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that: When the processor executes the computer program, the steps of the method for quantitatively evaluating micron-level visualized core perforation channels according to any one of claims 1 to 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for quantitatively evaluating micron-level visualized core perforation channels according to any one of claims 1 to 8 are implemented.

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