Experimental device and experimental method for physical simulation of segmented fracturing of coal seam roof horizontal well

Abstract

The application provides an experimental device and experimental method for physical simulation of segmented fracturing of a coal seam roof horizontal well, a rock sample preparation mold includes a fixed frame and a movable frame, the fixed frame and the movable frame are movably connected and enclose a sample preparation mold cavity with an opening, the movable frame can move relative to the fixed frame and adjust the thickness of the rock plate; a fracturing wellbore extends into the sample preparation mold from the opening and is poured into the rock plate by a sample preparation material, i.e., a mixture of similar materials, and a fracturing fluid is injected through the rock plate to fracture the multilayer rock sample, the multilayer rock sample includes a plurality of rock plates arranged in sequence along the thickness direction of the rock plate; a wellbore holder is located at the opening, the rock sample preparation mold and the fracturing wellbore are detachably connected with the wellbore holder, and the wellbore holder is used to drive the fracturing wellbore to move along the thickness direction of the rock plate. The application can realize fracturing of different lithology and different thickness combined formations at different fracturing positions, has a wider application scenario, and can ensure that the fracturing wellbore does not deviate from the center line of the sample preparation mold cavity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of horizontal well fracturing experiment, and particularly relates to an experimental device and an experimental method for physical simulation of horizontal well staged fracturing. BACKGROUND

[0002] Low-permeability and soft coal seams are widely distributed, accounting for about 60% of the total coal resources in China, with high coalbed methane content and large total resources. Therefore, the development of coalbed methane in low-permeability and soft coal seams is a research focus in domestic coalbed methane development. However, due to the low elastic modulus of coal and rock, the soft formation, and the development of natural cleat cracks, the direct hydraulic fracturing reconstruction effect of low-permeability and soft coal seams is not ideal, and a complex fracture network is easily formed. The low-permeability and soft coal has strong plasticity, and the opening degree of a single fracture is limited, forming a wide and short fracture that is prone to sand plugging, making it difficult to improve the sand ratio, and reducing the effective support rate and the length of the fracture. The structure of the low-permeability and soft coal is broken, and the fracture formed after fracturing is prone to collapse, which will cause plugging of the fracture channel and reduce the fracture conductivity. The coal and rock have strong plasticity, and are prone to inlaying with quartz sand proppant commonly used in fracturing, further reducing the fracturing reconstruction effect. However, the fracture propagation mechanism under different geological factors, stress conditions and fracturing construction parameters has not been clearly defined.

[0003] Therefore, by using the physical simulation method in the laboratory, the fracture propagation mechanism under different geological factors, stress conditions and fracturing construction parameters can be studied, which can provide a reference for the design of the staged and clustered fracturing scheme for the low-permeability and soft coal seam roof horizontal well. The existing hydraulic fracturing physical simulation experiment method is to directly perform horizontal well staged and clustered fracturing in the producing layer (CN107620585B, CN107420096B, CN107461181B, CN109162687B). The rock plate of the large-size true triaxial hydraulic fracturing physical simulation experiment is a 300x300x300mm cube. The conventional mold can only produce rock plates of one size (300x300x300mm). When studying a multilayer rock sample composed of rock plates with different lithology and thickness, the conventional mold cannot meet the requirements. Moreover, the conventional mold cannot fix the wellbore position, and during the sample preparation process, the handheld wellbore is filled with sample preparation materials, which is prone to deviation from the center of the mold. Whether the wellbore is centered will directly affect the accuracy of the hydraulic fracturing physical simulation experiment, especially the success or failure of the horizontal well fracturing simulation experiment. The existing experimental method can only simulate single-layer fracturing, and cannot study multilayer rock samples composed of rock plates with different lithology and thickness. How to make the wellbore centered during the preparation of samples with different strata combinations is a difficult problem. How to maximize the use of hydraulic energy has not been effectively solved. SUMMARY

[0004] The main purpose of the present application is to provide an experimental device and an experimental method for physical simulation of staged fracturing of a horizontal well, aiming to solve the technical problem that the prior art cannot study a multi-layer rock sample composed of rock plates with different lithology and different thickness, and how to make the wellbore in the center during the sample preparation and the sample making process.

[0005] In order to achieve the above-mentioned purpose, the present application provides an experimental device for physical simulation of staged fracturing of a horizontal well in a coal seam roof, which comprises a rock sample making mold including a fixed frame and a movable frame, the fixed frame and the movable frame are movably connected and enclose a sample making mold cavity with an opening, the movable frame can move relative to the fixed frame and adjust the thickness of the rock plate of the sample making mold cavity; a fracturing wellbore extends into the sample making mold cavity from the opening, the fracturing wellbore is used for pouring the sample making raw material filled into the rock plate and fracturing the multi-layer rock sample by injecting fracturing fluid, the multi-layer rock sample comprises a plurality of rock plates arranged in sequence along the thickness direction of the rock plate; a wellbore holder is located at the opening, the rock sample making mold and the fracturing wellbore are detachably connected with the wellbore holder, and the wellbore holder is used to drive the fracturing wellbore to move along the thickness direction of the rock plate.

[0006] In the embodiment of the present application, the fixed frame comprises: a support plate, and the movable frame is arranged opposite to the support plate along the thickness direction of the rock plate; two fixed side plates extend along the thickness direction of the rock plate and are arranged opposite to each other, the support plate extends in a direction perpendicular to the thickness of the rock plate, and the two ends of the support plate are respectively connected perpendicularly to the two fixed side plates; a bottom assembly is vertically supported at the bottom of the support plate, the fixed side plate and the movable frame, the bottom assembly comprises a transparent wear-resistant plate, a grid scale plate and a mounting plate, the mounting plate is provided with a mounting groove, and the transparent wear-resistant plate and the grid scale plate are sequentially stacked and clamped in the mounting groove, and the mounting groove is provided corresponding to the opening.

[0007] In the embodiment of the present application, the movable frame comprises: a movable flat plate, and the support plate is arranged opposite to the movable flat plate along the thickness direction of the rock plate; a vertical plate is arranged at the end of the movable flat plate and is perpendicularly connected with the movable flat plate, and the two vertical plates extend along the thickness direction of the rock plate and are used to face contact with the two fixed side plates.

[0008] In the embodiment of the present application, the experimental device for physical simulation of staged fracturing of a horizontal well in a coal seam roof further comprises: a fastening frame installed on the fixed side plate, the fastening frame is provided with a first threaded hole; a fastening rod extends along the thickness direction of the rock plate, the movable flat plate is provided with a second threaded hole corresponding to the first threaded hole, the fastening rod passes through the first threaded hole and extends into the second threaded hole, and the fastening rod is used to abut against the movable flat plate along the thickness direction of the rock plate.

[0009] In the embodiment of the present application, the fastening frame comprises a connecting rod, two ends of the connecting rod are connected with two fixing side plates respectively, the vertical plate is provided with a avoiding notch for avoiding the connecting rod, a mounting block is mounted on the connecting rod, and the size of the mounting block is larger than that of the connecting rod, and the first threaded hole is arranged in the mounting block.

[0010] In the embodiment of the present application, the coal seam roof horizontal well staged fracturing physical simulation experimental device comprises at least two spaced fastening frames, and / or the outer surface of the movable plate is provided with a reinforcing table protruding towards the fastening frame, and the second threaded hole is arranged in the reinforcing table.

[0011] In the embodiment of the present application, the fixing side plate is provided with a scale ruler away from the bottom assembly, and the scale ruler extends along the thickness direction of the rock plate.

[0012] In the embodiment of the present application, the fracturing wellbore comprises a plugging group and an outer wellbore, the outer wellbore is provided with two groups of perforating clusters, the phase angle between the two groups of perforating clusters is one hundred and twenty degrees, the perforating cluster comprises a plurality of downward perforating holes arranged at intervals along the extension direction of the outer wellbore, the plugging group comprises a plurality of expansion pipes with different lengths, the expansion pipe is used for penetrating in the outer wellbore and plugging the downward perforating hole, and / or the wellbore holder comprises a sliding rod and a guide rod, the fixed frame is provided with a sliding groove extending along the thickness direction of the rock plate, the sliding rod and the sliding groove are in sliding contact, the guide rod is provided with a guide groove for the fracturing wellbore to pass through, the guide rod and the guide groove extend along the thickness direction of the rock plate, one end of the guide rod is fixedly connected with the fixed frame, and the other end of the guide rod is movably connected with the movable frame.

[0013] The present application also provides a coal seam roof horizontal well staged fracturing physical simulation experimental method, the experimental method comprises:

[0014] The wellbore holder and the fracturing wellbore are detached from the rock sample preparation mold, the movable frame is adjusted according to the preset size, and the coal plate and the bottom plate are prepared by using the rock sample preparation mold;

[0015] The fracturing wellbore, the wellbore holder and the rock sample preparation mold are connected, the position of the fracturing wellbore is adjusted according to the preset roof thickness, the fracturing wellbore is centered, the movable frame is adjusted according to the preset roof thickness, and the roof is prepared by using the rock sample preparation mold;

[0016] The roof, the coal plate and the bottom plate are sequentially stacked from top to bottom, and a plurality of rock samples are formed.

[0017] The segmented plugging method is adopted to the fracturing well bore to segmentally fracture the multilayer rock sample, and the fracturing data and the pump injection pressure curve are recorded during the fracturing process, the experiment is stopped when the fracturing fluid in the injection pump is injected, and the fracturing data is saved, the multilayer rock sample is profiled along the fracture surface, and the fracture propagation mechanism is analyzed according to the fracturing data, the pump injection pressure curve and the fracture profile.

[0018] In the embodiment of the present application, the segmented fracturing of the multilayer rock sample by using the fracturing well bore to perform the segmented plugging method comprises:

[0019] The multilayer rock sample is placed into a sample loading cavity of a true triaxial hydraulic fracturing device, a jack for loading lateral confining pressure and a top cap of axial pressure of the top of the true triaxial hydraulic fracturing device are assembled respectively, then a main pressure chamber of the true triaxial hydraulic fracturing device is sealed and connected to an oil pressure pipeline;

[0020] Three-directional stresses of the true triaxial hydraulic fracturing device are simultaneously loaded to minimum values, the three-directional stresses include a vertical stress perpendicular to the direction of the multilayer rock sample, a minimum horizontal principal stress parallel to the direction of the fracturing well bore, and a maximum horizontal principal stress parallel to another direction of the multilayer rock sample;

[0021] The stresses that do not reach the set stress values among the minimum horizontal principal stress, the maximum horizontal stress and the vertical stress are increased to the set stress values, after the stress loading is completed, the multilayer rock sample is statically placed for a preset time length, so that the stress balance is achieved in the multilayer rock sample.

[0022] A colored dye is injected into the fracturing fluid as a tracer, the fracturing fluid is sucked by an injection pump, an injection pipe of the injection pump is connected to the fracturing well bore, and the injection pump is used to inject high-pressure fracturing fluid into the fracturing well bore.

[0023] Through the above technical solution, the experimental device for the physical simulation of the coal seam roof horizontal well segmented fracturing provided by the embodiment of the present application has the following beneficial effects:

[0024] After the specified thickness of the rock plate is determined, the movable frame is moved relative to the fixed frame according to the rock plate thickness, so that the rock plate thickness in the inner cavity of the sample preparation mold matches the specified thickness, and the sample preparation raw material is filled into the inner cavity of the sample preparation mold through the opening. In the case where the fractured wellbore is not needed to be cast in the rock plate, the wellbore holder and the fractured wellbore can be disassembled relative to the rock sample preparation mold, and in the case where the fractured wellbore is needed to be cast in the rock plate, the wellbore holder can be installed on the rock sample preparation mold and connected with the fractured wellbore. The position of the fractured wellbore relative to the rock sample preparation mold is adjusted to a specified position by moving the wellbore holder relative to the rock sample preparation mold, so that the center line of the fractured wellbore and the inner cavity of the sample preparation mold are parallel, the fractured wellbore is always kept centered and does not need to be held by hand, the situation that the fractured wellbore deviates from the center line of the inner cavity of the sample preparation mold during the filling of the sample preparation raw material into the inner cavity of the sample preparation mold is avoided, and the situation that the hydraulic fracturing physical simulation experiment fails due to the deviation of the fractured wellbore is avoided. After one layer of rock plate is prepared by using the rock sample preparation mold and the rock plate is demolded, the rock plate thickness in the inner cavity of the sample preparation mold can be matched with the specified thickness of another layer of rock plate, and after the preparation of multiple layers of rock sample is completed, multiple layers of rock sample of the composite formation can be stacked to achieve better preparation effect and simulate different fracturing positions. The present application can realize fracturing of different lithology, different thickness combination formation at different fracturing positions, has wider application scenarios, and can provide reference for fracturing scheme design of low-permeability soft coal roof horizontal well by studying crack propagation mechanism under different geological factors, stress conditions and fracturing construction parameters; and the fractured wellbore can be kept from deviating from the center line of the inner cavity of the sample preparation mold, and the experimental accuracy of the horizontal well staged fracturing physical simulation is improved.

[0025] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, and are used together with the following specific embodiments to explain the present application, but do not constitute a limitation on the present application. In the drawings:

[0027] Figure 1 is a structure schematic view of an experimental device for coal seam roof horizontal well staged fracturing physical simulation according to an embodiment of the present application;

[0028] Figure 2 is a structure schematic view of a rock sample preparation mold of an experimental device for coal seam roof horizontal well staged fracturing physical simulation according to an embodiment of the present application;

[0029] Figure 3 is a structure schematic view of a wellbore holder and a fractured wellbore of an experimental device for coal seam roof horizontal well staged fracturing physical simulation according to an embodiment of the present application;

[0030] Figure 4 is a schematic diagram of a fracturing wellbore structure of an experimental device for physical simulation of staged fracturing of a coal seam roof horizontal well according to an embodiment of the present application;

[0031] Figure 5 is a schematic diagram of a fracturing wellbore structure in a staged fracturing process of an experimental device for physical simulation of staged fracturing of a coal seam roof horizontal well according to an embodiment of the present application;

[0032] Figure 6 is a schematic diagram of a rock sample preparation mold structure of an experimental device for physical simulation of staged fracturing of a coal seam roof horizontal well according to another embodiment of the present application;

[0033] Figure 7 is a schematic diagram of a rock sample preparation mold structure of an experimental device for physical simulation of staged fracturing of a coal seam roof horizontal well according to another embodiment of the present application;

[0034] Figure 8 is a schematic diagram of a structure of a multi-layer rock sample matched with a fracturing wellbore according to an embodiment of the present application;

[0035] Figure 9 is a schematic diagram of a bottom assembly structure of an experimental device for physical simulation of staged fracturing of a coal seam roof horizontal well according to an embodiment of the present application;

[0036] Figure 10 is a schematic diagram of a flow of an experimental method for physical simulation of staged fracturing of a coal seam roof horizontal well according to an embodiment of the present application.

[0037] BRIEF DESCRIPTION OF DRAWINGS

[0038] No. Name No. Name

[0039] 100 staged fracturing of a coal seam roof horizontal well 21 expansion pipe

[0040] experimental device for physical simulation of staged fracturing

[0041] device

[0042] 1 rock sample preparation mold 2 fracturing wellbore

[0043] 11 fixing frame 22 outer wellbore

[0044] 111 support plate 221 perforation cluster

[0045] 112 fixing side plate 23 flow resistance ring

[0046] 1121 sliding groove 3 wellbore holder

[0047] 1122 scale ruler 31 sliding rod

[0048] 113 bottom assembly 32 guide rod

[0049] 1131 Grid ruler plate; 321 Guide groove

[0050] 1132 Transparent abrasion-resistant plate 4 Fastening bracket

[0051] 1133 Mounting plate 41 Connecting rod

[0052] 12 movable frames 42 mounting blocks

[0053] 121 Movable Plate 5 Fastening Rod

[0054] 122 reinforced platform 200 multi-layer rock samples

[0055] 123 Vertical plate 210 Coal plate

[0056] 1231 Avoid gap 220 base plate

[0057] 13 Sample mold inner cavity 230 top plate Detailed Implementation

[0058] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0059] The experimental apparatus for physical simulation of segmented fracturing of a horizontal well in the coal seam roof according to the present invention is described below with reference to the accompanying drawings.

[0060] like Figures 1 to 7 As shown, in an embodiment of the present invention, the experimental device 100 for physical simulation of segmented fracturing of a horizontal well in the coal seam roof includes a rock sample preparation mold 1, a fracturing wellbore 2, and a wellbore holder 3. The rock sample preparation mold 1 includes a fixed frame 11 and a movable frame 12, which are movably connected and form an inner cavity 13 with an opening. The movable frame 12 can move relative to the fixed frame 11 and adjust the thickness of the rock plate in the inner cavity 13. The fracturing wellbore 2 extends into the inner cavity 13 of the sample preparation mold from the opening. The fracturing wellbore 2 is used to pour the sample preparation material into the rock plate and fracturing the multi-layer rock sample 200 by injecting fracturing fluid. The multi-layer rock sample 200 includes multiple rock plates stacked sequentially along the thickness direction of the rock plate. The wellbore holder 3 is located at the opening. The rock sample preparation mold 1 and the fracturing wellbore 2 are detachably connected to the wellbore holder 3. The wellbore holder 3 is used to drive the fracturing wellbore 2 to move along the thickness direction of the rock plate. Understandably, the experimental device 100 for physical simulation of horizontal well fracturing in the coal seam roof in this embodiment is mainly used for the preparation of multi-layer rock samples 200. The multi-layer rock sample 200 may include multiple rock plates stacked in sequence, and the multiple rock plates may be a roof plate 230, a coal plate 210 and a bottom plate 220.

[0061] When the specified thickness of the rock plate is determined, the movable frame 12 can be moved relative to the fixed frame 11 according to the thickness of the rock plate, so that the thickness of the rock plate in the sample mold cavity 13 matches the specified thickness, and the sample material is filled into the sample mold cavity 13 through the opening. In the case where the fractured wellbore 2 does not need to be poured into the rock plate, the wellbore holder 3 and the fractured wellbore 2 can be detached from the rock sample mold 1. In the case where the fractured wellbore 2 needs to be poured into the rock plate, the wellbore holder 3 can be installed on the rock sample mold 1 and connected to the fractured wellbore 2. By moving the wellbore holder 3 relative to the rock sample mold 1, the position of the fractured wellbore 2 relative to the rock sample mold 1 is adjusted to the specified fracturing position, so that the center line of the fractured wellbore 2 and the sample mold cavity 13 are parallel, the fractured wellbore 2 is always kept centered and does not need to be held by hand, and the situation that the fractured wellbore 2 deviates from the center line of the sample mold cavity 13 during the filling of the sample material into the sample mold cavity 13 is avoided, and the situation that the hydraulic fracturing physical simulation experiment fails due to the deviation of the fractured wellbore 2 is avoided. After one layer of rock plate is made by using the rock sample mold 1 and the rock plate is demolded, the thickness of the rock plate in the sample mold cavity 13 can be matched with the specified thickness according to the specified thickness of another layer of rock plate. After the multi-layer rock sample 200 is made, the multi-layer rock sample 200 of the composite formation can be stacked, the making effect is better, and different fracturing positions can be simulated. The present embodiment can realize fracturing of different lithology, different thickness combination formations at different fracturing positions, and has a wider application scene. By studying the crack propagation mechanism under different geological factors, stress conditions and fracturing construction parameters, a reference can be provided for the fracturing scheme design of the low-permeability broken soft coal plate 210 roof 230 horizontal well. Moreover, the fractured wellbore 2 can be ensured not to deviate from the center line of the sample mold cavity 13, and the experimental accuracy of the horizontal well staged fracturing physical simulation is improved.

[0062] As shown in Figure 1 , Figure 6 and Figure 7 , the fixed frame 11 includes a support plate 111, two fixed side plates 112 and a bottom assembly 113. The support plate 111 and the movable frame 12 are arranged opposite to each other along the rock plate thickness direction. The two fixed side plates 112 extend along the rock plate thickness direction and are arranged opposite to each other with a certain interval. The support plate 111 extends along a direction perpendicular to the rock plate thickness direction, and the two ends of the support plate 111 are respectively connected to the two fixed side plates 112 perpendicularly. The bottom assembly 113 is supported perpendicularly at the bottom of the support plate 111, the fixed side plates 112 and the movable frame 12. The bottom assembly 113 includes a transparent wear-resistant plate 1132, a grid scale plate 1131 and a mounting plate 1133. The mounting plate 1133 is provided with a mounting slot, and the transparent wear-resistant plate 1132 and the grid scale plate 1131 are sequentially stacked and clamped in the mounting slot. The mounting slot is provided with an opening corresponding to the opening.

[0063] In the present embodiment, the rock plate thickness direction is Figure 1The opening is located at the upper end of the inner cavity 13 of the sample preparation mold, the fracturing wellbore 2 extends in the up-down direction, and the two fixed side plates 112 are oppositely arranged in the left-right direction. After the thickness of the rock plate is determined, the bottom assembly 113, the two fixed side plates 112 and the support plate 111 can be fixed by screws, then the movable frame 12 is moved to the predetermined position, and the movable frame 12 is calibrated by the scale ruler 1122 and the grid scale plate 1131. Since the size of the rock sample preparation mold 1 is usually large, the upper scale ruler 1122 and the lower grid scale 1131 are used together to calibrate the size of the rock plate, which can avoid the parallelism of the rock plate being insufficient and the difficulty in assembling the rock plate, and then the movable frame 12 is fixed relative to the fixed frame 11, the wellbore holder 3 is fixed at the opening at the top end of the rock sample preparation mold 1, and the fracturing wellbore 2 is fixed on the wellbore holder 3. As shown in Figure 9 The transparent wear-resistant plate 1132, the grid scale plate 1131 and the mounting plate 1133 are sequentially stacked in the up-down direction, and the outer surface of the transparent wear-resistant plate 1132 is flush with the slot of the mounting groove. The transparent wear-resistant plate 1132 can be made of transparent tempered glass, the grid scale plate 1131 can be made of a grid steel ruler, and the mounting plate 1133 can be made of a steel plate, which can improve the stability of the bottom assembly 113. The support plate 111 in the embodiment is a U-shaped plate, and the fixed side plate 112 is an L-shaped plate. The fixed side plate 112 includes a fixed plate and a connecting plate, which are connected perpendicularly. The connecting plate and the mounting plate 1133 are in surface contact and can be connected by screws, bolts or other connecting members.

[0064] In an embodiment, the movable frame 12 includes a movable flat plate 121 and a vertical plate 123. The movable flat plate 121 and the vertical plate 123 can be integrally formed or have a split structure. The movable flat plate 121 and the support plate 111 are oppositely arranged in the thickness direction of the rock plate. The vertical plate 123 is arranged at the end of the movable flat plate 121 and is connected perpendicularly to the movable flat plate 121. The two vertical plates 123 extend in the thickness direction of the rock plate and are used to be in surface contact with the two fixed side plates 112. The movable frame 12 and the support plate 111 in the embodiment have the same shape and size, both being U-shaped plates. The vertical plates 123 are located at the left and right ends of the movable flat plate 121. In the embodiment, the vertical plates 123 can increase the connection area of the movable frame 12 and the fixed frame 11 and ensure the perpendicularity of the inner cavity 13 of the sample preparation mold.

[0065] As shown in Figure 1As shown, the experimental device 100 for the physical simulation of the segmented fracturing of the coal seam roof horizontal well further comprises a fastening frame 4 and a fastening rod 5; the fastening frame 4 is installed on the fixed frame 11, and the fastening frame 4 is provided with a first threaded hole; the fastening rod 5 extends along the thickness direction of the rock plate, the movable plate 121 is provided with a second threaded hole corresponding to the first threaded hole, the fastening rod 5 penetrates through the first threaded hole and extends into the second threaded hole, and the fastening rod 5 is used for abutting against the movable plate 121 along the thickness direction of the rock plate. By calibrating the movable frame 12 and the fracturing wellbore 2 through the scale ruler 1122 and the grid ruler plate 1131, the fastening rod 5 can be threadedly connected with the first threaded hole and the second threaded hole by rotating the fastening rod 5, so that the fastening rod 5 relatively fixedly connects the fixed frame 11 and the movable frame 12, and the movable frame 12 is fastened to the fixed frame 11.

[0066] In the embodiment of the present application, the fastening frame 4 comprises a connecting rod 41 and a mounting block 42; the connecting rod 41 is respectively connected with two fixed side plates 112 at both ends, and the vertical plate 123 is provided with an avoiding notch 1231 avoiding the connecting rod 41; the mounting block 42 is installed on the connecting rod 41, and the size of the mounting block 42 is larger than that of the connecting rod 41, and the first threaded hole is provided in the mounting block 42. In the embodiment, the left and right ends of the connecting rod 41 can be connected with the fixed side plates 112 through screws, bolts or the like, and the size of the avoiding notch 1231 provided in the vertical plate 123 corresponding to the connecting rod 41 is larger than the cross-sectional size of the connecting rod 41, so as to facilitate the adjustment and disassembly between the fixed frame 11 and the movable frame 12. In the embodiment, the mounting block 42 is arranged at the middle part of the connecting rod 41, so as to increase the matching area between the fastening rod 5 and the fastening frame 4.

[0067] In the embodiment of the present application, the experimental device 100 for the physical simulation of the segmented fracturing of the coal seam roof horizontal well comprises at least two fastening frames 4 arranged at intervals; and the outer surface of the movable plate 121 is provided with a reinforcing table 122 protruding towards the fastening frame 4, and the second threaded hole is provided in the reinforcing table 122. Figure 1 As shown, the two fastening frames 4 in the embodiment are arranged at intervals along the up-down direction, the reinforcing table 122 is arranged corresponding to the mounting block 42, and the shape of the reinforcing table 122 matches the shape of the mounting block 42. In the embodiment, the movable frame 12 and the fixed frame 11 can be fastened by the plurality of fastening frames 4 and the fastening rod 5, so as to improve the connection stability between the movable frame 12 and the fixed frame 11.

[0068] In the embodiment of the present application, the fixed side plate 112 is provided with a scale ruler 1122 on the side away from the bottom assembly 113, and the scale ruler 1122 extends along the thickness direction of the rock plate. In the embodiment, the scale ruler 1122 is located at the upper end of the fixed side plate 112, and the grid ruler plate 1131 is located at the lower end of the fixed side plate 112. The movable frame 12 and the fracturing wellbore 2 are calibrated through the scale rulers 1122 at the upper and lower ends and the grid ruler, so as to improve the convenience and accuracy of the calibration of the movable frame 12.

[0069] As shown in Figures 2 to 5 , the fracturing wellbore 2 comprises a plugging group and an outer wellbore 22, the outer wellbore 22 is provided with two groups of perforation clusters, the phase angle between the two groups of perforation clusters is one hundred and twenty degrees, the perforation cluster comprises a plurality of perforation clusters 221 arranged at intervals along the extension direction of the outer wellbore 22, and the plugging group comprises a plurality of expansion pipes 21 with different lengths, which are used to penetrate into the outer wellbore 22 and plug the perforation clusters 221.

[0070] The fracturing wellbore 2 in the prior art is mostly spiral perforation fracturing wellbore 2 or directional perforation fracturing wellbore 2, and the fracturing effect is poor; the phase angle between the two groups of perforation clusters is one hundred and twenty degrees, and the 120° phase angle double lateral downhole perforation hole 221 can not only save hydraulic energy and operation cost, but also effectively form fractures, and effectively avoid the fracturing failure caused by the generation and migration of coal powder, and effectively reform a large volume and good fracture extension. The expansion pipe 21 in the embodiment can use an oil expansion pipe 21, which has high strength, high elongation rate and low rebound, and is widely used and has good effect. A large amount of raw materials is saved. By referring to the widely used and good effect expansion pipe 21 technology in workover, the fracturing wellbore 2 in the embodiment uses the expansion pipe 21 to plug the downhole perforation hole 221 of the non-fracturing well section, so as to realize the purpose of staged fracturing. The plugging group is an expansion pipe 21 with different lengths, and the plugging method cooperates with the outer wellbore 22 to realize staged fracturing. When fracturing a certain section, the diameter of the expansion pipe 21 is increased by hydraulic pressure, so as to fix the expansion pipe 21 on the inner wall of the outer wellbore 22, close the perforation cluster 221 of other sections, and make the fracturing fluid pass through the perforation cluster of the current fracturing section along the perforation cluster to the rock plate for fracturing. As shown in Figure 5 , in an embodiment, the fracturing wellbore 2 cross section schematic diagram when fracturing the first section, the second section and the third section, the first section, the second section and the third section are arranged from the bottom of the fracturing wellbore 2 to the wellhead, and the first section, the second section and the third section are sequentially fractured by expansion pipes 2 with different lengths.

[0071] As shown in Figure 4As shown, the 120° phase angle double lateral downhole perforation hole 221 is adopted, the outer wellbore 22 is cut from the 45# steel pipe, the outer diameter is 14 mm, and the inner diameter is 10 mm. The outer wellbore 22 is composed of a wellhead circular pipe located at the wellhead and a downhole hollow circular pipe connected to the lower end of the wellhead circular pipe. The wellhead circular pipe is 30 mm long, and the downhole hollow circular pipe is 250 mm long. The wellhead circular pipe is divided into two sections. One section has an outer diameter of 18 mm and a thickness of 20 mm, and the two sides are cut flat, with a length of 16 mm, which serves as the force point for tightening the wrench. The other section has an outer diameter of 14 mm and a thickness of 10 mm, and the outer wall is threaded for connecting the liquid injection pipe. The downhole hollow circular pipe is composed of three horizontal well sections, each 80 mm long, and a bottom seal block 10 mm long. The flow resistance ring 23 on the fracturing wellbore 2 is designed in sections. The flow resistance ring 23 is a steel disc with an outer diameter of 18 mm and a thickness of 10 mm. The flow resistance ring 23 can help with staged fracturing, prevent fracturing fluid from flowing, and avoid interference between stages. Six perforation clusters 221 with a diameter of 2 mm are evenly distributed on the outer wellbore 22 at a 120° phase angle. The distance between any two adjacent perforation clusters 221 is 40 mm. The perforation cluster 221 is 2 mm long and is made of a paper tube wrapped around a thin iron wire and inserted into the outer wellbore 22.

[0072] Furthermore, the wellbore holder 3 in the present embodiment includes a sliding rod 31 and a guide rod 32. The fixed frame 11 is provided with a sliding groove 1121 extending along the thickness direction of the rock plate. The sliding rod 31 and the sliding groove 1121 are in sliding contact. The guide rod 32 is provided with a guide groove 321 through which the fracturing wellbore 2 passes. The guide rod 32 and the guide groove 321 both extend along the thickness direction of the rock plate. One end of the guide rod 32 is fixedly connected to the fixed frame 11, and the other end of the guide rod 32 is movably connected to the movable frame 12.

[0073] The top of the fixed side plate 112 is provided with a movable sliding groove 1121. The sliding rod 31 cooperates with a screw to drive the sliding of the fracturing wellbore 2. The support plate 111 and the top of the movable frame 12 are provided with threaded holes to fix the wellbore holder 3.

[0074] The wellbore holder 3 in the present embodiment is in the shape of a "cross". It can be connected to the top of the fracturing wellbore 2 through a nut and a gasket to fix the fracturing wellbore 2. The "cross" shaped wellbore holder 3 is connected to the rock sample preparation mold 1 through a screw. The guide rod 32 parallel to the direction of the tightening rod 5 can be a steel bar. A 300 mm long guide groove 321 is dug in the middle of the steel bar. The two ends of the sliding rod 31 are connected to the sliding grooves 1121 of the rock sample preparation mold 1 through screws. The sliding rod 31 can move in the sliding grooves 1121 at the top of the left and right fixed side plates 112 of the rock sample preparation mold 1 to drive the sliding of the fracturing wellbore 2 in the guide groove 321.

[0075] In an embodiment, the rock sample preparation mold 1 is composed of five steel plates, the edges of each plate are threaded, and the plates are fixed by screws to form a 300*300*300mm sample preparation mold cavity 13. The rock sample preparation mold 1 is provided with a shaft holder 3 at the top. When making rock plates, the support plate 111 at the front end of the rock sample preparation mold 1 is fixed with screws, and a threaded hole is provided at the top center of the movable frame 12, which is connected with the movable screw on the shaft holder 3. The top of the two fixed side plates 112 on the left and right of the rock sample preparation mold 1 is pasted with a 300mm steel ruler, and the scale range is flush with the mold cavity; the central part of the bottom assembly 113 has a grid scale plate 1131.

[0076] As shown in Figure 4 , Figure 8 and Figure 10 , the present application also provides an experimental method for segmental fracturing physical simulation of a coal seam roof horizontal well, the experimental method comprising:

[0077] Step S1, the shaft holder 3 and the fracturing wellbore 2 are detached from the rock sample preparation mold 1, the movable frame 12 is adjusted according to the preset size, and the coal plate 210 and the floor plate 220 are made by using the rock sample preparation mold 1;

[0078] Step S2, the fracturing wellbore 2, the shaft holder 3 and the rock sample preparation mold 1 are connected, the position of the fracturing wellbore 2 is adjusted according to the preset position of the fracturing wellbore 2, the fracturing wellbore 2 is centered, the movable frame 12 is adjusted according to the preset roof thickness, and the roof 230 is made by using the rock sample preparation mold 1;

[0079] Step S3, the roof 230, the coal plate 210 and the floor plate 220 are sequentially stacked from top to bottom, and a multilayer rock sample 200 is formed;

[0080] Step S4, the multilayer rock sample 200 is segmentally fractured by using the fracturing wellbore 2 for segmental plugging, and the first segment, the second segment and the third segment are sequentially fractured by using the expansion pipes 21 of different lengths. During the fracturing process, the fracturing data and the pump injection pressure curve are recorded, the experiment is stopped when the fracturing fluid in the injection pump is injected, and the fracturing data is saved, the multilayer rock sample 200 is cut along the crack surface, and the crack propagation mechanism is analyzed according to the fracturing data, the pump injection pressure curve and the crack profile.

[0081] The similar material of the coal plate 210 is proportioned and optimized according to the physical property analysis and the rock mechanics parameter test results, wherein the elastic modulus of the crushed coal is 7 GPa, and the Poisson's ratio is 0.33; the elastic modulus of the sandstone roof and floor 220 is 53 GPa, and the Poisson's ratio is 0.24; the elastic modulus of the mudstone roof and floor 220 is 21 GPa, and the Poisson's ratio is 0.3. The sample preparation raw material and the sample preparation raw material proportion of the coal plate 210 are as follows: crushed coal, cement, quartz sand and water are 4:3:1:1.6. The sample preparation raw material and the sample preparation raw material proportion of the sandstone roof and floor 220 are as follows: cement, quartz sand and water are 1:1:0.45. The sample preparation raw material and the sample preparation raw material proportion of the mudstone roof and floor 220 are as follows: cement, quartz sand, clay and water are 1:3:0.08:0.8. The cement is 325 cement, the quartz sand is 40-80 mesh quartz sand, and the clay is mixed by kaolinite and montmorillonite at a ratio of 1:1.

[0082] The embodiment fractures the adjacent layer roof 230 of the coal plate 210, so that the fracture extends vertically into the coal plate 210, thereby indirectly fracturing and reforming the coal plate 210. Most of the existing experimental methods simulate single-layer fracturing, and the embodiment can simulate the fracturing of multi-layer composite strata. The indirect fracturing of the roof 230 can avoid many problems of direct fracturing in the low-permeability crushed soft coal plate 210. The coal plate 210 has a large reforming volume and good fracture extension effect. The fracturing construction pressure is reduced, and the safety is improved. During the later drainage and mining period, the coal powder output is reduced, the continuity of drainage and mining is ensured, and the yield is obviously increased.

[0083] The manufacturing process of the coal plate 210 is as follows:

[0084] ①Coal sample preparation. Crush the tectonic coal and sieve it with a 3 cm sieve. The coal particles with a particle size of <3 cm are used to simulate crushed coal. The coal particles with a particle size of <3 cm are placed in a container for use;

[0085] ②Measurement. According to the determined proportion of each rock plate, weigh each material with an electronic scale;

[0086] ③Mix well. Pour the materials into a mixer and stir until uniform;

[0087] ④Mold preparation. Assemble the rock sample mold 1 according to the preset size, clean it, and smear a layer of oil on the surface of the mold cavity 13 to facilitate the separation of the coal plate and the mold;

[0088] ⑤Filler forming. Put the mixed material into the mold cavity 13 and smooth the surface with a spatula;

[0089] ⑥Curing for 3 days. Mark the test piece number and manufacturing date, and place it in a dry and ventilated place to wait for the test sample to solidify. Pour a small amount of water every day to prevent the test sample from cracking.

[0090] ⑦Demoulding. The sample is taken out of the mould.

[0091] ⑧Curing for 4 weeks. The removed sample is placed in a dry and ventilated place to wait for the mechanical parameters of the test piece to tend to be stable, and a small amount of water is poured every day to prevent the test piece from cracking into joints.

[0092] Similarly, the top plate 230 and the bottom plate 220 are manufactured according to the above operation steps, and the fractured wellbore 2 needs to be poured into the top plate 230 when the top plate 230 is manufactured.

[0093] Among them, the top plate 230 is manufactured:

[0094] ①Material preparation. Prepare quartz sand, cement, clay, or prepare kaolinite and montmorillonite according to the manufacturing requirements of the top plate 230;

[0095] ②Measurement. According to the determined ratio, weigh various materials with an electronic scale;

[0096] ③Mix well. Pour the materials into the mixer and stir until uniform;

[0097] ④Cut the hard iron wire into small pieces with a length of 2 cm with pliers, and cut the A4 paper into paper strips with a width of 2 cm with scissors, and use the paper strips to wind the small iron wires into paper tubes to simulate the downward perforating hole 221, and insert the paper tube into the perforating hole of the outer wellbore 22.

[0098] ⑤Mould preparation. Assemble the rock sample mould 1 according to the designed size of the rock plate, fix the prepared fractured wellbore 2 on the wellbore holder 3, install the wellbore holder 3, fix the fractured wellbore 2 at the preset position, clean the rock sample mould 1, and smear a layer of oil on the surface of the inner cavity 13 of the mould to make the top plate 230 and the mould easier to separate;

[0099] ⑥Filler forming. Pour the mixed material into the mould, and then flatten the surface with a shovel;

[0100] ⑦Curing for 3 days. Mark the test piece number and manufacturing date, and place it in a dry and ventilated place to wait for the test sample to solidify, and pour a small amount of water every day to prevent the test sample from cracking into joints.

[0101] ⑧Demoulding. The sample is taken out of the mould.

[0102] ⑨Curing for 4 weeks. The removed sample is placed in a dry and ventilated place to wait for the mechanical parameters of the test piece to tend to be stable, and a small amount of water is poured every day to prevent the test piece from cracking into joints.

[0103] The top plate 230, the coal plate 210 and the bottom plate 220 are sequentially stacked and connected from top to bottom, and the manufacturing process of the multi-layer rock sample 200 is formed.

[0104] 1. Mix epoxy resin glue. Weigh epoxy resin glue A and B according to the weight ratio of 3:1 using an electronic balance, stir them evenly with a stirring rod, and place them in a small beaker for later use;

[0105] 2. Prepare rock plates. Combine the dry maintenance top plate 230, coal plate 210, and bottom plate 220, and measure the size with a steel ruler. The total size is 295 mm.

[0106] 3. Apply glue. Apply the prepared epoxy resin glue evenly to the junction of the top plate 230 and the coal rock using a spatula, then place the rock plates in turn for bonding, press them with a weight, and measure the size again with a steel ruler. The height is 300 mm.

[0107] In this embodiment, the multi-layer rock sample 200 is made by the rock sample mold 1, and the fracturing wellbore 2 is poured into the top plate 230, which can perform indirect staged fracturing, fracturing in the adjacent layer of the producing layer, and vertical expansion of the fracture into the coal plate 210, thereby indirectly fracturing and reforming the coal plate 210. The hydraulic energy can be fully utilized, and the fracture propagation mechanism can be accurately studied according to the fracturing data, pump injection pressure curve, and fracture profile for different lithology and different thickness of the multi-layer rock sample 200 composed of rock plate combinations.

[0108] The staged fracturing of the multi-layer rock sample 200 is performed by the fracturing wellbore 2 using the staged plugging method, which includes:

[0109] The multi-layer rock sample 200 is placed into the sample loading cavity of the true triaxial hydraulic fracturing equipment, the side loading jacks of the true triaxial hydraulic fracturing equipment and the top axial pressure cover are assembled, then the main pressure chamber of the true triaxial hydraulic fracturing equipment is sealed and connected to the oil pressure pipeline;

[0110] The three-directional stress of the true triaxial hydraulic fracturing equipment is simultaneously loaded to the minimum three-directional stress, which includes the vertical stress perpendicular to the multi-layer rock sample 200, the minimum horizontal principal stress parallel to the fracturing wellbore 2, and the maximum horizontal principal stress parallel to the other direction of the multi-layer rock sample 200. The minimum three-directional stress is set by comparing the stress values of the vertical stress, the minimum horizontal principal stress, and the maximum horizontal principal stress, and the minimum stress value is set as the minimum three-directional stress.

[0111] The stress values of the minimum horizontal principal stress, the maximum horizontal stress, and the vertical stress that do not reach the set stress value are increased to the set stress value, and after the stress loading is completed, the multi-layer rock sample 200 is left for a predetermined period of time to achieve stress balance inside the multi-layer rock sample 200.

[0112] A colored dye is injected into the fracturing fluid as a tracer, the fracturing fluid is pumped into the fracturing wellbore 2 using a liquid injection pump, the liquid injection pipe of the liquid injection pump is connected to the fracturing wellbore 2, and the liquid injection pump is used to inject high-pressure fracturing fluid into the fracturing wellbore 2, and the first, second, and third sections of the fracturing wellbore 2 are fractured in turn.

[0113] The multilayer rock sample 200 in the embodiment is a three-layer rock plate. Specifically, the three-layer rock plate is placed in a sample loading cavity of a true triaxial hydraulic fracturing device, jacks for loading lateral pressure on the side of the true triaxial hydraulic fracturing device and a top cap for loading axial pressure on the top of the true triaxial hydraulic fracturing device are assembled, then the main pressure chamber of the true triaxial hydraulic fracturing device is sealed with bolts, and an oil pressure pipeline is connected.

[0114] When simulating three-directional stress, a vertical stress is applied in a direction perpendicular to the three-layer rock plate, a minimum horizontal principal stress is applied in a direction parallel to the fracturing wellbore 2, and a maximum horizontal principal stress is applied in another direction parallel to the rock plate.

[0115] To avoid unbalanced stress loading, the three-directional stress is first loaded to a minimum value, and then the stress that does not reach the set stress value among the minimum horizontal principal stress, the maximum horizontal stress, and the vertical stress is increased to the set stress value, to complete the three-directional stress loading. After the stress loading is completed, the sample is left for 30 minutes to allow the internal stress to balance.

[0116] To better observe the hydraulic fracture extension law, a certain amount of green dye is added to the fracturing fluid as a tracer. The fracturing fluid is sucked into the pump by using a fluid injection pump, the fluid injection pipe is connected to the fracturing wellbore 2, and the fluid injection pump is provided with a pump pressure. The computer hydraulic servo pump injection system is used to pump high-pressure liquid into the simulated fracturing wellbore 2.

[0117] The fracturing of the first section, the second section, and the third section of the fracturing wellbore 2 is sequentially performed. Before fracturing the first section, the downward perforation hole 221 of the first section of the fracturing wellbore 2 is kept open by the expansion pipe 21, and the downward perforation holes 221 of the second section and the third section are sealed.

[0118] After preparation, the displacement is set on the control page and run, the liquid injection fracturing is performed at a constant displacement as designed, the multi-layer rock sample is started to be fractured, and the fracturing data is recorded, the pump injection pressure curve is observed, and the experiment is stopped when the liquid in the fluid injection pump is about to be injected, and the fracturing data is saved.

[0119] Before fracturing the second section, the downward perforation hole 221 of the second section of the fracturing wellbore 2 is kept open by the expansion pipe 21, and the downward perforation holes 221 of the first section and the third section are sealed, and the fracturing is performed according to the above experimental method.

[0120] Before fracturing the third section, the downward perforation hole 221 of the third section of the fracturing wellbore 2 is kept open by the expansion pipe 21, and the downward perforation holes 221 of the first section and the second section are sealed, and the fracturing is performed according to the above experimental method.

[0121] After the three-section fracturing is completed, the pump pressure is first emptied, and then the confining pressure is slowly removed, the fracturing device is disassembled, and the sample is taken out. The multi-layer rock sample is cut along the fracture surface, the fracture morphology and tracer distribution are observed, and the fracture propagation law is analyzed.

[0122] In one embodiment, the fracturing wellbore 2 is 25mm from the interface between the roof 230 and the coal bed 210. A rock sample mold 1 is used to make a sandstone roof 230 with a thickness of 175mm, a coal bed 210 with a thickness of 75mm and a sandstone floor 220 with a thickness of 45mm, with 5mm reserved as the thickness of the upper and lower strata interface after the glue solidifies.

[0123] In another embodiment, the fracturing wellbore 2 is near the interface between the roof 230 and the coal bed 210, and the fracturing wellbore 2 uses a 120° phase angle double lateral downhole perforation hole 221. A mudstone roof 230 with a thickness of 145mm, a coal bed 210 with a thickness of 75mm and a mudstone floor 220 with a thickness of 70mm are made, with 5mm reserved as the thickness of the upper and lower strata interface after the glue solidifies.

[0124] In the description of the present application, it should be understood that the terms "first", "second" are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise specifically limited.

[0125] In the present application, unless otherwise specifically defined and limited, the terms "mounting", "connection", "connection", "fixing" and other terms should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected or communicate with each other; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise specifically limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0126] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in the present application and the features of the different embodiments or examples without contradiction.

[0127] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and that variations, modifications, substitutions and changes can be made by those skilled in the art without departing from the scope of the present application.

Claims

1. An experimental device for physical simulation of staged fracturing of a coal seam roof horizontal well, characterized in that, The experimental device (100) for the physical simulation of the segmented fracturing of the coal seam roof horizontal well comprises: A rock sample preparation mold (1) comprising a fixed frame (11) and a movable frame (12), the fixed frame (11) and the movable frame (12) are movably connected and surround a sample preparation mold cavity (13) with an opening, the movable frame (12) can move relative to the fixed frame (11) and adjust the thickness of the rock plate of the sample preparation mold cavity (13); A fracturing wellbore (2) extending into the sample preparation mold cavity (13) from the opening, the fracturing wellbore (2) is used for pouring the filled sample preparation material into the rock plate and fracturing the multilayer rock sample (200) by injecting fracturing fluid, the multilayer rock sample (200) comprises a plurality of rock plates arranged in sequence along the thickness direction of the rock plate; A wellbore holder (3) located at the opening, the rock sample preparation mold (1) and the fracturing wellbore (2) are detachably connected with the wellbore holder (3), and the wellbore holder (3) is used to drive the fracturing wellbore (2) to move along the thickness direction of the rock plate; The multilayer rock sample comprises a roof (230), a coal plate (210) and a bottom plate (220), the fracturing wellbore (2) is arranged in the roof (230), the fracturing wellbore (2) comprises a plugging group and an outer wellbore (22), the outer wellbore (22) is provided with two groups of perforating clusters, the phase angle between the two groups of perforating clusters is one hundred and twenty degrees, the perforating cluster comprises a plurality of downward perforating holes (221) arranged at intervals along the extension direction of the outer wellbore (22), and the plugging group comprises a plurality of expansion pipes (21) with different lengths, the expansion pipes (21) are used to penetrate into the outer wellbore (22) and plug the downward perforating holes (221).

2. The experimental apparatus for physical simulation of staged fracturing of a coal seam roof horizontal well according to claim 1, characterized in that, The fixed frame (11) comprises: A support plate (111) arranged opposite to the movable frame (12) along the thickness direction of the rock plate; Two fixed side plates (112) extending along the thickness direction of the rock plate and arranged opposite at intervals, the support plate (111) extends perpendicular to the thickness direction of the rock plate, and the two ends of the support plate (111) are respectively connected perpendicularly to the two fixed side plates (112); A bottom assembly (113) vertically supported at the bottom of the support plate (111), the fixed side plates (112) and the movable frame (12), the bottom assembly (113) comprises a transparent wear-resistant plate (1132), a grid scale plate (1131) and a mounting plate (1133), the mounting plate (1133) is provided with a mounting groove, the transparent wear-resistant plate (1132) and the grid scale plate (1131) are sequentially and laminatedly clamped in the mounting groove, and the mounting groove is provided corresponding to the opening.

3. The experimental apparatus for physical simulation of staged fracturing of a coalbed roof horizontal well according to claim 2, characterized in that, The movable frame (12) comprises: A movable flat plate (121) arranged opposite to the support plate (111) along the thickness direction of the rock plate; Two vertical plates (123) are arranged at the ends of the movable plate (121) and are connected perpendicularly to the movable plate (121), and the two vertical plates (123) extend along the thickness direction of the rock plate and are used to be in surface contact with the two fixed side plates (112).

4. The experimental apparatus for physical modeling of staged fracturing of a coalbed roof horizontal well according to claim 3, characterized in that, The experimental device (100) for the physical simulation of the segmented fracturing of the coal seam roof horizontal well further comprises: A fastening frame (4) is arranged on the fixed side plate (112), and the fastening frame (4) is provided with a first threaded hole; A fastening rod (5) extends along the thickness direction of the rock plate, the movable plate (121) is provided with a second threaded hole corresponding to the first threaded hole, the fastening rod (5) passes through the first threaded hole and extends into the second threaded hole, and the fastening rod (5) is used to abut against the movable plate (121) along the thickness direction of the rock plate.

5. The experimental apparatus for physical modeling of staged fracturing of coal seam roof horizontal well according to claim 4, characterized in that, The fastening frame (4) comprises: A connecting rod (41) is connected to the two fixed side plates (112) at both ends, and the vertical plate (123) is provided with a avoiding gap (1231) for avoiding the connecting rod (41); An installation block (42) is arranged on the connecting rod (41), and the size of the installation block (42) is greater than that of the connecting rod (41), and the first threaded hole is arranged in the installation block (42).

6. The experimental apparatus for physical modeling of the staged fracturing of a coalbed roof horizontal well according to claim 4, characterized in that, The experimental device (100) for the physical simulation of the segmented fracturing of the coal seam roof horizontal well comprises at least two fastening frames (4) arranged at intervals; And / or, The outer surface of the movable plate (121) is provided with a reinforcing table (122) protruding towards the fastening frame (4), and the second threaded hole is arranged in the reinforcing table (122).

7. The experimental apparatus for physical simulation of the staged fracturing of a coalbed roof horizontal well according to any one of claims 2 to 6, characterized in that, A scale ruler (1122) is arranged on the side of the fixed side plate (112) away from the bottom assembly (113), and the scale ruler (1122) extends along the thickness direction of the rock plate.

8. The experimental apparatus for physical simulation of staged fracturing of a coalbed roof horizontal well according to any one of claims 1 to 6, characterized in that, The wellbore holder (3) comprises a sliding rod (31) and a guide rod (32), the fixed frame (11) is provided with a sliding groove (1121) extending along the thickness direction of the rock plate, the sliding rod (31) and the sliding groove (1121) are in sliding contact, the guide rod (32) is provided with a guide groove (321) for the fracturing wellbore (2) to pass through, the guide rod (32) and the guide groove (321) both extend along the thickness direction of the rock plate, one end of the guide rod (32) is fixedly connected to the fixed frame (11), and the other end of the guide rod (32) is movably connected to the movable frame (12).

9. An experimental method for coal seam roof horizontal well staged fracturing physical simulation applied to the experimental device for coal seam roof horizontal well staged fracturing physical simulation according to any one of claims 1 to 8, characterized in that, The experimental method comprises: The wellbore holder (3) and the fracturing wellbore (2) are detached from the rock sample preparation mold (1), the movable frame (12) is adjusted according to a preset size, and the coal plate (210) and the bottom plate (220) are prepared by using the rock sample preparation mold (1). The fracturing wellbore (2), the wellbore holder (3) and the rock sample preparation mold (1) are connected, the position of the fracturing wellbore (2) is adjusted according to the preset roof thickness, the fracturing wellbore (2) is centered, the movable frame (12) is adjusted according to the preset roof thickness, and the rock sample preparation mold (1) is used to make a roof (230); The roof (230), the coal plate (210) and the floor (220) are sequentially connected from top to bottom, and a multilayer rock sample (200) is formed; The fracturing wellbore (2) is used for segmented plugging, the multilayer rock sample (200) is fractured in segments, and the fracturing data and the pump injection pressure curve are recorded during the fracturing process; the experiment is stopped when the fracturing fluid in the injection pump is injected, and the fracturing data is saved; the multilayer rock sample (200) is cut along the crack surface, and the crack propagation mechanism is analyzed according to the fracturing data, the pump injection pressure curve and the crack profile.

10. The experimental method of physical modeling of the staged fracturing of a coal bed roof horizontal well according to claim 9, characterized in that, The fracturing wellbore (2) is used for segmented plugging, the multilayer rock sample (200) is fractured in segments, and the fracturing data and the pump injection pressure curve are recorded during the fracturing process; the experiment is stopped when the fracturing fluid in the injection pump is injected, and the fracturing data is saved; the multilayer rock sample (200) is cut along the crack surface, and the crack propagation mechanism is analyzed according to the fracturing data, the pump injection pressure curve and the crack profile. The multilayer rock sample (200) is placed into a sample loading cavity of a true triaxial hydraulic fracturing device, a jack for side loading confining pressure and a shaft pressure top cover at the top of the true triaxial hydraulic fracturing device are assembled respectively, then a main pressure chamber of the true triaxial hydraulic fracturing device is sealed and connected with an oil pressure pipeline; Three-directional stresses of the true triaxial hydraulic fracturing device are simultaneously loaded to the minimum values, the three-directional stresses include a vertical stress perpendicular to the multilayer rock sample (200), a minimum horizontal principal stress parallel to the fracturing wellbore (2), and a maximum horizontal principal stress parallel to another direction of the multilayer rock sample (200); The stresses that do not reach the set stress values among the minimum horizontal principal stress, the maximum horizontal principal stress and the vertical stress are increased to the set stress values, after the stress loading is completed, the multilayer rock sample (200) is statically placed for a preset time length, so that the inside of the multilayer rock sample (200) reaches stress balance; A colored dye is injected into the fracturing fluid as a tracer, the fracturing fluid is sucked by an injection pump, an injection pipe of the injection pump is connected with the fracturing wellbore (2), and the injection pump is used to inject high-pressure fracturing fluid into the fracturing wellbore (2).

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