Double-coal seam dirt band crossing fracturing simulation experiment device and experiment method

Abstract

The invention provides a double-coal-seam dirt band crossing fracturing simulation experiment device and method, and the device comprises a simulation stratum which sequentially comprises a top plate, an upper coal seam, a dirt band layer, a lower coal seam and a bottom plate from top to bottom; the horizontal stress loading assembly is used for carrying out stress loading on the simulated stratum in the horizontal direction; the vertical stress loading assembly is used for carrying out stress loading on the simulated stratum in the vertical direction; one end of the fracturing mechanism extends into the simulated stratum, the other end of the fracturing mechanism is connected with an external liquid supply assembly, and the fracturing mechanism is used for injecting fracturing liquid into the simulated stratum; the sensor assemblies are distributed on the upper coal seam, the dirt band layer and the lower coal seam. By means of the scheme, the problem that in the prior art, the indirect fracturing effect and the crack crossing expansion rule controlled by the layering stress under the double-coal-seam dirt band condition cannot be accurately reflected is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal bed methane exploitation, in particular to a double coal seam interlayer crossing fracturing simulation experiment device and experiment method. BACKGROUND

[0002] In the process of coal bed methane exploitation, crossing fracturing technology is an important stimulation measure, which refers to injecting fracturing fluid into the wellbore by high pressure in the fracturing operation, so that the fracture not only extends in a single reservoir, but also penetrates the interlayer between the layers, connects multiple vertically distributed target reservoirs, forms a cross-layer fracture network, and thus releases the natural gas resources therein.

[0003] The interlayer is a thin layer of rock embedded in the coal seam in coal geology, which is embedded in the coal seam due to geological action, leading to complexification of the coal seam structure and directly affecting the coal quality and mining technology. However, the existing coal seam crossing fracturing experiment device is mostly designed for a single coal seam or coal seam roof, and less for the case of double coal seams with interlayer, which leads to the problem that the experiment device in the prior art cannot accurately reflect the indirect fracturing effect and fracture crossing extension law controlled by the layered stress under the condition of double coal seams with interlayer. SUMMARY

[0004] The present application provides a double coal seam interlayer crossing fracturing simulation experiment device and experiment method to solve the problem that the prior art cannot accurately reflect the indirect fracturing effect and fracture crossing extension law controlled by the layered stress under the condition of double coal seams with interlayer.

[0005] In order to solve the above problems, according to one aspect of the present application, a double coal seam interlayer crossing fracturing simulation experiment device is provided, comprising: a simulated formation, the simulated formation comprises, from top to bottom, a roof, an upper coal seam, an interlayer, a lower coal seam and a floor; a horizontal stress loading assembly for loading stress on the simulated formation in the horizontal direction; a vertical stress loading assembly for loading stress on the simulated formation in the vertical direction; a fracturing mechanism, one end of the fracturing mechanism extending into the interior of the simulated formation, the other end of the fracturing mechanism connected with an external liquid supply assembly, the fracturing mechanism being used for injecting fracturing fluid into the simulated formation; and a sensor assembly, distributed in the upper coal seam, the interlayer and the lower coal seam.

[0006] Further, the horizontal stress loading assembly is a plurality of groups, at least one group of horizontal stress loading assemblies is arranged in the upper coal seam, at least one group of horizontal stress loading assemblies is arranged in the interlayer, and at least one group of horizontal stress loading assemblies is arranged in the lower coal seam.

[0007] Further, the simulated formation is of a rectangular structure, one group of horizontal stress loading assemblies is arranged on each of the four sides of the upper coal seam, one group of horizontal stress loading assemblies is arranged on each of the four sides of the interlayer, and one group of horizontal stress loading assemblies is arranged on each of the four sides of the lower coal seam.

[0008] Further, the horizontal stress loading assembly comprises, from outside to inside, a first hydraulic cylinder, a first force transmission rod, a first steel plate, a first hydraulic bag and a first polytetrafluoroethylene film arranged in sequence.

[0009] Further, the vertical stress loading assembly comprises a second force transmission rod and a second hydraulic cylinder arranged above the top plate, and a second hydraulic bag and a second polytetrafluoroethylene film arranged between the top plate and the simulated stratum.

[0010] Further, the sensor assembly comprises pressure sensors respectively buried in the upper coal seam, the interburden layer and the lower coal seam, each pressure sensor being connected to the dynamic data acquisition instrument through a wire; emission sensors respectively buried in the upper coal seam, the interburden layer and the lower coal seam, each emission sensor being connected to the dynamic data acquisition instrument through a wire; and strain gauges respectively buried in the upper coal seam, the interburden layer and the lower coal seam, each strain gauge being connected to the dynamic data acquisition instrument through a wire.

[0011] Further, the sensor assembly further comprises displacement meters arranged between the upper coal seam and the interburden layer, and displacement meters arranged between the interburden layer and the lower coal seam, each displacement meter being connected to the dynamic data acquisition instrument through a wire.

[0012] Further, the fracturing mechanism comprises an expansion pipe and a steel pipe installed inside the expansion pipe, the steel pipe extending to the structure inside the simulated stratum is provided with at least one first opening, the other end of the steel pipe is connected to the liquid supply assembly outside, the expansion pipe extending to the structure inside the simulated stratum is provided with at least one second opening, the second opening is aligned with the first opening, and the second opening and the first opening form a perforation hole.

[0013] Further, the double-coal-seam interburden through-layer fracturing simulation experiment device further comprises a CT scanner for scanning the cracks in the simulated stratum.

[0014] According to another aspect of the present application, the present application also provides an experimental method, the experimental method being used in the double-coal-seam interburden through-layer fracturing simulation experiment device, and the experimental method comprising the following steps:

[0015] S1: obtaining the mechanical parameters and three-directional stress values of the actual top plate, the actual upper coal seam, the actual interburden layer, the actual lower coal seam and the actual bottom plate from the ground stress measurement data of the actual stratum structure of a target mining area obtained by using the stress relief method, the hydraulic fracturing method and the acoustic emission method;

[0016] S2: constructing a simulated stratum based on the actual stratum structure, and arranging a horizontal stress loading assembly, a vertical stress loading assembly, a sensor assembly and a fracturing mechanism in the simulated stratum;

[0017] S3: loading horizontal stress and vertical stress on the simulated stratum through the horizontal stress loading assembly and the vertical stress loading assembly to simulate the stress state of the actual stratum structure;

[0018] S4, the fracturing mechanism injects fracturing fluid into the simulated stratum through the high-pressure pump, and observes the pump injection pressure change and the sensor assembly parameter change until the simulated stratum is fractured;

[0019] S5, the high-pressure pump is vented, the horizontal stress loading assembly and the vertical stress loading assembly are depressurized, and based on the visual observation, photographing and CT scanning of the simulated stratum, the fracture penetration layer and the fracture extension state are analyzed.

[0020] In the scheme, the thickness of each sublayer in the simulated stratum is set according to the actual stratum structure, providing an experimental basis for double coal seam interburden translayer fracturing simulation; the horizontal stress loading assembly and the vertical stress loading assembly respectively apply stress load in the horizontal and vertical directions of the simulated stratum to simulate the horizontal and vertical stress effects between each layer in reality; the fracturing mechanism is set, the fracturing fluid is injected into the simulated stratum by high pressure, so that the fracture spreads between the layers to form a cross-layer fracture network; the sensor assembly is set in each layer of the simulated stratum for real-time monitoring of stress dynamic data, sublayer dislocation value, fracture expansion condition and the like in the fracturing translayer of the simulated stratum, facilitating the arrangement and analysis of experimental data, realizing accurate feedback of indirect fracturing effect and fracture translayer expansion law controlled by sublayer stress under the condition of double coal seam interburden, and being beneficial to the improvement and perfection of coal seam translayer fracturing technology. BRIEF DESCRIPTION OF DRAWINGS

[0021] The drawings accompanying the specification of this application form a part thereof, serve to provide further understanding of the application, and together with the description of the exemplary embodiments of the application and the explanation thereof serve to explain the application, and do not constitute an improper limitation on the application. In the drawings:

[0022] Figure 1 A structure schematic view of the double coal seam interburden translayer fracturing simulation experimental device provided by the embodiment of the application is shown;

[0023] Figure 2 A structure schematic view of the double coal seam interburden translayer fracturing simulation experimental device provided by the embodiment of the application is shown; Figure 1 A structure schematic view of the double coal seam interburden translayer fracturing simulation experimental device provided by the embodiment of the application is shown;

[0024] Figure 3 A structure schematic view of the double coal seam interburden translayer fracturing simulation experimental device provided by the embodiment of the application is shown; Figure 1 A structure schematic view of the double coal seam interburden translayer fracturing simulation experimental device provided by the embodiment of the application is shown;

[0025] Figure 4 A structure schematic view of the double coal seam interburden translayer fracturing simulation experimental device provided by the embodiment of the application is shown; Figure 1A schematic diagram of the simulated internal structure of a coal seam with interbedded gangue in a double coal seam fracturing experimental device, showing the fracturing structure located in the interbedded gangue layer and facing the upper coal seam.

[0026] Figure 5 It shows Figure 1 A schematic diagram of the simulated internal structure of a coal seam with interbedded gangue in a double coal seam fracturing test device, where the fracturing structure is located in the lower coal seam and faces the interbedded gangue layer.

[0027] Figure 6 It shows Figures 2 to 4 In the embodiment, a line graph of the average width of fractures in the upper coal seam versus time;

[0028] Figure 7 It shows Figures 2 to 4 A line graph of the average width of the fracture in the lower coal seam versus time in the embodiment;

[0029] Figure 8 It shows Figures 2 to 4 A line graph of crack length versus time in the embodiment;

[0030] Figure 9 It shows Figures 2 to 4 Line graph of maximum crack opening versus time in the embodiment;

[0031] Figure 10 It shows Figures 2 to 4 The example shows a time-location line graph of the coal seam penetration.

[0032] The above figures include the following reference numerals:

[0033] 10. Simulated strata; 11. Roof; 12. Upper coal seam; 13. Interbedded gangue layer; 14. Lower coal seam; 15. Floor;

[0034] 20. Horizontal stress loading assembly; 21. First hydraulic cylinder; 22. First force transmission rod; 23. First steel plate; 24. First hydraulic bladder; 25. First polytetrafluoroethylene film;

[0035] 30. Vertical stress loading assembly; 31. Second force transmission rod; 32. Second hydraulic cylinder; 33. Second hydraulic bladder; 34. Second polytetrafluoroethylene film;

[0036] 40. Fracturing mechanism; 41. Expansion tube; 42. Steel pipe; 43. Perforation channel; 431. First opening; 432. Second opening. Detailed Implementation

[0037] With reference to the drawings, the technical solutions in the embodiments will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. The following descriptions of the embodiments are only illustrative, rather than limiting the present application and its applications. Based on the embodiments in the present application, other embodiments obtained by those of ordinary skill in the art without creative efforts should be within the scope of the present application.

[0038] As shown in Figures 1 to 5 The embodiments of the present application provide a double coal seam sandwiching interlayer fracturing simulation experiment device, which comprises: a simulated formation 10, the simulated formation 10 comprises, from top to bottom, a roof 11, an upper coal seam 12, an interlayer 13, a lower coal seam 14 and a floor 15; a horizontal stress loading assembly 20, which loads stress on the simulated formation 10 in the horizontal direction; a vertical stress loading assembly 30, which loads stress on the simulated formation 10 in the vertical direction; a fracturing mechanism 40, one end of which extends into the interior of the simulated formation 10, and the other end of which is connected with a liquid supply assembly outside, the fracturing mechanism 40 being used for injecting fracturing fluid into the simulated formation 10; a sensor assembly, which is distributed in the upper coal seam 12, the interlayer 13 and the lower coal seam 14.

[0039] In the present scheme, the thicknesses of the respective layers in the simulated formation 10 are set according to the actual formation structure, providing an experimental basis for double coal seam sandwiching interlayer fracturing simulation; the horizontal stress loading assembly 20 and the vertical stress loading assembly 30 respectively apply stress loads on the simulated formation 10 in the horizontal and vertical directions, so as to simulate the horizontal and vertical stress effects between the respective layers in reality; the fracturing mechanism 40 is provided, high-pressure fracturing fluid is injected into the simulated formation 10 by means of the fracturing mechanism 40, so that the cracks spread between the layers, forming a cross-layer crack network; the sensor assembly is provided in each layer of the simulated formation 10, and is used for real-time monitoring of stress dynamic data, layering dislocation values, crack propagation conditions and the like of the simulated formation in fracturing interlayer, so as to facilitate the arrangement and analysis of experimental data, and to realize accurate feedback of the indirect fracturing effect and crack interlayer propagation law controlled by layering stress under the condition of double coal seam sandwiching interlayer, which is conducive to the improvement and perfection of the coal seam interlayer fracturing technology.

[0040] As shown in Figure 1 The horizontal stress loading assembly 20 is provided in multiple groups, at least one group of horizontal stress loading assemblies 20 is provided in the upper coal seam 12, at least one group of horizontal stress loading assemblies 20 is provided in the interlayer 13, and at least one group of horizontal stress loading assemblies 20 is provided in the lower coal seam 14. By providing the horizontal stress loading assembly 20 in different layer positions of the simulated formation 10, the horizontal stress of each layer can be independently controlled, the influence of the earth stress difference on coal seam fracturing is simulated, and the flexibility and accuracy of the experiment device are enhanced, which is conducive to more accurately studying the crack propagation law in the coal seam.

[0041] In some embodiments, the simulated stratum 10 is a rectangular structure, and a set of horizontal stress loading assemblies 20 is arranged on each of the four sides of the upper coal seam 12, a set of horizontal stress loading assemblies 20 is arranged on each of the four sides of the parting layer 13, and a set of horizontal stress loading assemblies 20 is arranged on each of the four sides of the lower coal seam 14. By uniformly distributing the horizontal stress loading assemblies 20 on the four sides of the simulated stratum 10, the horizontal stress received by the coal seam in each direction can be simulated, so that the crack propagation law is more comprehensively studied, the experimental error is reduced, the experimental result is closer to the actual situation, the reliability of the experimental result is improved, and a solid foundation is provided for the optimization of the fracturing through-layer process.

[0042] In some embodiments, the horizontal stress loading assembly 20 comprises, from the outside to the inside, a first hydraulic cylinder 21, a first force transmission rod 22, a first steel plate 23, a first hydraulic bag 24, and a first polytetrafluoroethylene film 25 arranged in sequence. The pressure generated by the first hydraulic cylinder 21 is transmitted to the first steel plate 23 through the first force transmission rod 22, and then dispersed to the first hydraulic bag 24 by the first steel plate 23, and finally uniformly applied to the simulated stratum 10 through the first polytetrafluoroethylene film 25, realizing effective transmission of external loading stress. The first hydraulic bag 24 and the first polytetrafluoroethylene film 25 play a flexible buffering role, which makes the external loading stress uniform, ensures that each part of the simulated stratum 10 receives the same stress, improves the uniformity and stability of the stress loading, and provides a guarantee for the accuracy and reliability of the experiment.

[0043] As shown in Figure 1 The vertical stress loading assembly 30 comprises a second force transmission rod 31 and a second hydraulic cylinder 32 arranged above the roof 11, and a second hydraulic bag 33 and a second polytetrafluoroethylene film 34 arranged between the roof 11 and the simulated stratum 10. Pressure is generated by the second hydraulic cylinder 32, transmitted to the roof 11 through the second force transmission rod 31, and then uniformly distributed to the second hydraulic bag 33 by the roof 11, and finally applied to the simulated stratum 10 through the second polytetrafluoroethylene film 34, realizing effective transmission of vertical stress. The second hydraulic bag 33 and the second polytetrafluoroethylene film 34 play a flexible buffering role, which ensures that each part of the simulated stratum 10 receives the same vertical stress, improves the uniformity and stability of the stress loading, and provides a guarantee for the accuracy and reliability of the experiment.

[0044] In some embodiments, the sensor assembly includes: pressure sensors respectively embedded in the upper coal seam 12, the interbedded gangue layer 13, and the lower coal seam 14, each pressure sensor being connected to a dynamic data acquisition instrument via a wire; emission sensors respectively embedded in the upper coal seam 12, the interbedded gangue layer 13, and the lower coal seam 14, each emission sensor being connected to the dynamic data acquisition instrument via a wire; and strain gauges respectively embedded in the upper coal seam 12, the interbedded gangue layer 13, and the lower coal seam 14, each strain gauge being connected to the dynamic data acquisition instrument via a wire.

[0045] The pressure sensor is used to monitor the stress distribution inside the simulated formation 10. The emission sensor can capture the elastic wave signals emitted when cracks are generated and propagated inside the coal seam. The strain gauge can measure the strain changes on the surface of the coal seam in real time. The emission sensor and strain gauge can monitor the crack propagation of the coal seam during the fracturing process. The data from these sensors are transmitted to the dynamic data acquisition instrument through wires to record various physical quantities in the experimental process in real time, providing data support for the optimization of the fracturing process.

[0046] In some embodiments, the sensor assembly further includes: a displacement gauge disposed between the upper coal seam 12 and the interbedded gangue layer 13, and a displacement gauge disposed between the interbedded gangue layer 13 and the lower coal seam 14, each displacement gauge being connected to a dynamic data acquisition instrument via a wire. The displacement gauges can accurately measure the relative displacement between the layers within the simulated formation 10. The measured data is transmitted to the dynamic data acquisition instrument via wires, reflecting the dynamic changes of the coal seam and interbedded gangue layer during the fracturing process, providing accurate information for analyzing the fracturing effect and the fracture propagation law.

[0047] like Figures 2 to 5 As shown, the fracturing mechanism 40 includes an expansion tube 41 and a steel pipe 42 installed inside the expansion tube 41. The steel pipe 42 extends into the simulated formation 10 and has at least one first opening 431. The other end of the steel pipe 42 is connected to an external fluid supply assembly. The expansion tube 41 extends into the simulated formation 10 and has at least one second opening 432. The second opening 432 is aligned with the first opening 431, and the second opening 432 and the first opening 431 form a perforation channel 43. The expansion tube 41 protects the steel pipe 42 from being squeezed and deformed by the internal stress of the coal seam, thereby affecting the flow rate and pressure of the fracturing fluid. Utilizing the structural characteristics of the expansion tube 41 and the steel pipe 42, it can be ensured that the fracturing fluid can be accurately injected into the predetermined layer from the perforation channel 43, thereby forming the expected fracture in the simulated formation 10, improving the injection efficiency of the fracturing fluid, and facilitating a more accurate study of the fracturing effect in the coal seam.

[0048] In some embodiments, the dual coal seam parting through layer fracturing simulation experiment device further comprises a CT scanner for scanning the fractures in the simulated formation 10. The CT scanner can clearly show the fracture structure inside the simulated formation 10 to accurately obtain the fracture penetration layer and the fracture extension state, thereby providing intuitive data support for the optimization of the through layer fracturing process.

[0049] Embodiments of the present application also provide an experimental method for the above-mentioned dual coal seam parting through layer fracturing simulation experiment device, which comprises the following steps:

[0050] S1: Obtain the mechanical parameters and three-directional stress values of the actual roof, actual upper coal seam, actual parting layer, actual lower coal seam and actual floor in the actual formation structure of the target mining area by using stress relief method, hydraulic fracturing method and acoustic emission method, and combine the measured data;

[0051] S2: Construct the simulated formation 10 based on the actual formation structure, and arrange the horizontal stress loading assembly 20, the vertical stress loading assembly 30, the sensor assembly and the fracturing mechanism 40 in the simulated formation 10;

[0052] S3: Load the horizontal stress and the vertical stress on the simulated formation 10 by the horizontal stress loading assembly 20 and the vertical stress loading assembly 30 to simulate the stress state of the actual formation structure;

[0053] S4: The fracturing mechanism 40 injects fracturing fluid into the simulated formation 10 by the high-pressure pump, and observes the changes of pump injection pressure and sensor assembly parameters until the simulated formation 10 is fractured;

[0054] S5: Empty the high-pressure pump, unload the horizontal stress loading assembly 20 and the vertical stress loading assembly 30, and analyze the fracture penetration layer and the fracture extension state based on the visual observation, photographing and CT scanning of the simulated formation 10.

[0055] The mechanical parameters and three-directional stress values in the actual formation structure are converted into loading parameters in the experimental device, so that the geological conditions are close to the actual conditions; the stress and fracturing simulation of the simulated formation 10 are carried out by setting the stress loading assembly and the fracturing mechanism 40, which is convenient for studying the crack propagation law, and the fracture penetration layer and the fracture extension state are analyzed by visual observation, photographing and CT scanning of the simulated formation 10, which is conducive to the optimization and improvement of the fracturing process.

[0056] As Figures 2 to 5As shown, four specific embodiments in the present application are shown, respectively, when the fracturing mechanism 40 in the double coal seam interlayer penetrating layer fracturing simulation experiment device is located in the upper coal seam 12 and the perforation hole 43 is directed to the interlayer 13, when the fracturing mechanism 40 is located in the interlayer 13 and the perforation hole 43 is directed to the lower coal seam 14, when the fracturing mechanism 40 is located in the interlayer and the perforation hole 43 is directed to the upper coal seam 12, and when the fracturing mechanism 40 is located in the lower coal seam 14 and the perforation hole 43 is directed to the interlayer 13. The specific embodiments are as follows:

[0057] Embodiment 1: When the fracturing mechanism 40 in the double coal seam interlayer penetrating layer fracturing simulation experiment device is located in the upper coal seam 12 and the perforation hole 43 is directed to the interlayer 13.

[0058] The basic situation of the coal seam in the actual well testing area is that the thickness of the upper coal seam is 2 meters, the thickness of the lower coal seam is 3 meters, and the thickness of the interlayer is 1 meter, wherein the surface depth of the upper coal seam is 400 meters.

[0059] In the double coal seam interlayer penetrating layer fracturing simulation experiment method, the three-way stress value is calculated as:

[0060] First, the in-situ stress measurement data of the stress relief method, the hydraulic fracturing method and the acoustic emission method in the well testing area is obtained.

[0061] Among them, the minimum horizontal stress is the closure pressure, that is, σ h =P s , in the formula, σ h is the minimum horizontal stress, P s is the measured average closure pressure;

[0062] The vertical stress is calculated by the weight of the overburden rock, σ v =γH, in the formula, σ v is the vertical stress, γ is the unit weight of the overburden rock, and H is the depth below the surface;

[0063] The maximum horizontal stress is calculated by the following formula: σ H =3P s -P b -P o , in the formula, σ H is the maximum horizontal stress, P s is the average closure pressure, P b is the pressure recorded when the fracture breaks, and P o is the pore pressure, which is determined by measuring the water level in the well. P o can be determined by the following formula: P o =19.8h / 10000, h is the coal seam depth.

[0064] The maximum and minimum horizontal stresses and the vertical principal stress can be determined by the above method. The relationship between the three principal stresses and the depth can be obtained by statistical plotting of multiple data and linear fitting.

[0065]

[0066] The three-dimensional stress of the coal seam can be obtained by substituting the depth of the fracturing borehole into the above formula. The following table is a calculation example.

[0067] Three-dimensional stress at different depths

[0068]

[0069] Judgment of macroscopic type of cracks:

[0070] The macroscopic type of cracks includes vertical cracks, horizontal cracks and inclined cracks. The macroscopic type of cracks is jointly affected by the depth of the coal seam, the size and type of the ground stress. Since the direction of the cracks is mainly towards the direction with smaller stress in the coal seam, the above three macroscopic types of cracks are extended based on the differences in the depth and the horizontal stress. The main rule is that σ v >σ H >σ h is a vertical crack, σ H >σ v >σ h is an inclined crack, σ H >σ h >σ v is a horizontal crack.

[0071] As shown in Figure 1 , a simulated stratum is constructed with a scale of 1:10. The length and width of the simulated stratum are 10 dm*5 dm. The thickness of the upper coal seam is 2 dm, the thickness of the interburden is 1 dm, and the thickness of the lower coal seam is 3 dm. The coal seam is made of raw coal with a porosity of 4% and a permeability of 0.1 mD. The interburden is made of cement mortar. A stress loading mechanism, a fracturing structure and a sensor assembly are installed.

[0072] The fracturing assembly is shown in Figure 2 . The expansion pipe 41 and the steel pipe 42 are horizontally buried in the upper coal seam, and the perforation hole is located at the horizontal center of the upper coal seam and faces the interburden.

[0073] Then, the horizontal stress loading assembly 20 and the vertical stress loading assembly 30 load the horizontal stress and the vertical stress respectively to simulate the stress state of the actual stratum. Based on the three-dimensional stress relationship and the table, when the depth of the upper coal seam is 400 meters, σ v is 10.04 MPa, when the depth is 401 meters, σ h , σH The pressures are 11.12 MPa and 16.09 MPa, respectively; when the burial depth of the interbedded gangue layer is 402.5 meters, σ h σ H The pressures are 11.14 MPa and 16.11 MPa respectively; when the lower coal seam is buried at a depth of 404.5 meters, σ h σ H The stress values ​​are 11.17 MPa and 16.14 MPa, respectively. Based on the stress values ​​calculated above, a loading stress gradient is set to achieve a three-dimensional stepped synchronous loading mode of first vertical loading and then horizontal loading. The stress loading magnitude, gradient rate and alternating loading of each layer are preset by the computer PLC control system to ensure that the absolute position of the simulated strata does not change during the loading process.

[0074] The fracturing unit injects fracturing fluid into the simulated formation using a high-pressure pump, and observes changes in pumping pressure and sensor component parameters until the simulated formation is fractured.

[0075] Finally, the high-pressure pump was vented, the horizontal stress loading components and vertical stress loading components were depressurized, the simulated formation was removed, and the fracture penetration position and fracture extension state were analyzed based on visual inspection, photography and CT scan. The average width of the fracture in the lower coal seam, the average width of the fracture in the upper coal seam, the total length of the fracture, the maximum width of the fracture and the penetration time data were obtained during the fracturing process.

[0076] Example 2: In the simulated fracturing experiment device for interbedded coal seams with gangue, the fracturing mechanism 40 is located in the interbedded gangue layer 13 and the perforation channel 43 faces the lower coal seam 14.

[0077] Compared to Example 1, the difference lies in the location of the fracturing mechanism, such as... Figure 3 As shown, the expansion pipe 41 and steel pipe 42 are horizontally embedded in the interbedded rock layer, and the perforation channel is located at the horizontal center of the interbedded rock layer, facing the lower coal seam. The same specification model is used as in Example 1. Similarly, the average width of the fracture in the lower coal seam, the average width of the fracture in the upper coal seam, the total length of the fracture, the maximum width of the fracture, and the penetration time data are obtained during the fracturing process.

[0078] Example 3: In the simulated fracturing experiment device for interbedded coal seams with gangue, the fracturing mechanism 40 is located in the interbedded gangue layer and the perforation channel 43 faces the upper coal seam 12.

[0079] Compared to Example 1, the difference lies in the location of the fracturing mechanism, such as... Figure 4 As shown, the expansion pipe 41 and steel pipe 42 are horizontally embedded in the interbedded rock layer, and the perforation channel is located at the horizontal center of the interbedded rock layer, facing the upper coal seam. The same specification model is used as in Example 1. Similarly, the average width of the lower coal seam fracture, the average width of the upper coal seam fracture, the total length of the fracture, the maximum width of the fracture, and the penetration time data are obtained during the fracturing process.

[0080] Embodiment 4: The fracturing mechanism 40 is located in the lower coal seam 14 and the perforation hole 43 is directed to the interlayer 13 in the simulation experiment device of the double coal seam interlayer fracturing.

[0081] Compared with Embodiment 1, the difference lies in the location of the fracturing mechanism, as shown in the figure, the expansion pipe 41 and the steel pipe 42 are horizontally buried in the lower coal seam, and the perforation hole is located at the horizontal center of the lower coal seam and directed to the interlayer. The same specification model as in Embodiment 1 is used, and the average width of the fracture in the lower coal seam, the average width of the fracture in the upper coal seam, the total length of the fracture, the maximum width of the fracture and the penetration time data during the fracturing interlayer process are obtained. Figure 5

[0082] In summary, the average width of the fracture in the lower coal seam, the average width of the fracture in the upper coal seam, the total length of the fracture, the maximum width of the fracture and the penetration time data during the fracturing interlayer process obtained by the above four embodiments are shown in the figure, wherein the 1# coal seam is the upper coal seam and the 2# coal seam is the lower coal seam. Figures 6 to 10

[0083] Result analysis:

[0084] Generally speaking, the wider the fracture width, the longer the length, the greater the fracture opening degree, the better the effect, and the shorter the time of penetrating the coal seam, the smaller the filtration loss of the fracturing fluid, the smaller the energy loss of the fracturing fluid, and the relatively better the effect. From Figures 6 to 10 and the above basis, in Embodiment 2, the perforation hole is designed in the center of the interlayer and directed to the lower coal seam, which has the best effect.

[0085] The above only describes some embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various changes and modifications to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

[0086] The technical features of the above-described embodiments can be combined in any way. In order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as the combination of these technical features does not exist contradictory, it should be considered as the scope of the present application.

[0087] ​​It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0088] The relative arrangement of components and steps, numerical expressions, and numerical values set forth in the examples are not intended to limit the scope of the present application unless otherwise specifically stated. It is to be understood that the drawings are not necessarily to scale of the actual proportions used in the fabrication, assembly, and operation of the example embodiments. Techniques, methods, and apparatus known to those of ordinary skill can not be discussed in detail herein, but should be considered as part of the description unless otherwise stated. In all examples shown and discussed herein, any specific values are to be interpreted as being exemplary only and not as a limitation on the scope of the example embodiments. Thus, other examples of the example embodiments can have different values. It is to be noted that like reference numerals and letters refer to like items in the drawings, and, once an item is defined in one drawing, it need not be discussed further in subsequent drawings.

[0089] In the description of the present application, it is to be understood that the orientation or positional relationships indicated by orientation words such as "front, back, upper, lower, left, right", "horizontal, vertical, perpendicular, horizontal", and "top, bottom" are generally based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description. Without the opposite indication, these orientation words do not indicate and imply that the indicated device or element must have a particular orientation or be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the scope of protection of the present application. The orientation words "inner, outer" refer to the inner and outer relative to the contour of the components themselves.

[0090] For purposes of the description hereinafter, the terms "upper", "lower", "right", "left", "rear", "front", "vertical", "horizontal", and derivatives thereof shall relate to the application as oriented in the drawing figures. However, it is to be understood that the application can assume various alternative orientations and, accordingly, such terms are not to be taken as limitations of the present application or any application specifically disclosed herein.

[0091] In addition, it should be noted that the terms "first", "second", and so on, used to describe various components, are only intended to distinguish one component from another, and are not otherwise intended to refer to a particular order or order of use. Unless otherwise stated, the above terms do not have special meanings. Therefore, they cannot be understood as limiting the scope of protection of the present application.

Claims

1. A simulation experimental device for cross-layer fracturing in a double coal seam with interbedded gangue, characterized in that, include: The simulated strata (10) includes, from top to bottom, a roof (11), an upper coal seam (12), a gangue layer (13), a lower coal seam (14), and a floor (15). A horizontal stress loading assembly (20) applies stress to the simulated formation (10) in the horizontal direction; The vertical stress loading assembly (30) applies stress to the simulated formation (10) in the vertical direction; A fracturing mechanism (40) has one end extending into the interior of the simulated formation (10) and the other end connected to an external fluid supply assembly. The fracturing mechanism (40) is used to inject fracturing fluid into the simulated formation (10). Sensor components are distributed in the upper coal seam (12), the interbedded gangue layer (13), and the lower coal seam (14).

2. The simulated experimental device for cross-layer fracturing of two coal seams with interbedded gangue as described in claim 1, characterized in that, The horizontal stress loading component (20) is in multiple sets. The upper coal seam (12) is provided with at least one set of the horizontal stress loading component (20), the interbedded gangue layer (13) is provided with at least one set of the horizontal stress loading component (20), and the lower coal seam (14) is provided with at least one set of the horizontal stress loading component (20).

3. The simulated experimental device for cross-layer fracturing of two coal seams with interbedded gangue as described in claim 2, characterized in that, The simulated strata (10) is a rectangular structure. A set of horizontal stress loading components (20) is set on each of the four sides of the upper coal seam (12), a set of horizontal stress loading components (20) is set on each of the four sides of the interbedded gangue layer (13), and a set of horizontal stress loading components (20) is set on each of the four sides of the lower coal seam (14).

4. The simulated experimental device for cross-layer fracturing of two coal seams with interbedded gangue as described in claim 1, characterized in that, The horizontal stress loading assembly (20) includes, from the outside to the inside, a first hydraulic cylinder (21), a first force transmission rod (22), a first steel plate (23), a first hydraulic bladder (24), and a first polytetrafluoroethylene film (25), arranged sequentially.

5. The simulated experimental apparatus for cross-layer fracturing of two coal seams interbedded with gangue according to claim 1, characterized in that, The vertical stress loading assembly (30) includes: a second force transmission rod (31) and a second hydraulic cylinder (32) disposed above the top plate (11), and a second hydraulic bladder (33) and a second polytetrafluoroethylene film (34) disposed below the top plate (11) and between the simulated strata (10).

6. The experimental apparatus for simulating cross-layer fracturing of two coal seams with interbedded gangue as described in claim 1, characterized in that, The sensor assembly includes: Pressure sensors are respectively buried in the upper coal seam (12), the interbedded gangue layer (13), and the lower coal seam (14), and each pressure sensor is connected to a dynamic data acquisition instrument via a wire; The transmitting sensors are respectively buried in the upper coal seam (12), the interbedded gangue layer (13), and the lower coal seam (14), and each transmitting sensor is connected to the dynamic data acquisition instrument via a wire; Strain gauges are respectively embedded in the upper coal seam (12), the interbedded gangue layer (13), and the lower coal seam (14), and each strain gauge is connected to the dynamic data acquisition instrument via a wire.

7. The experimental apparatus for simulating cross-layer fracturing of two coal seams with interbedded gangue as described in claim 6, characterized in that, The sensor assembly also includes: Displacement gauges are installed between the upper coal seam (12) and the interbedded gangue layer (13), and displacement gauges are installed between the interbedded gangue layer (13) and the lower coal seam (14). Each displacement gauge is connected to the dynamic data acquisition instrument via a wire.

8. The simulated experimental apparatus for cross-layer fracturing of two coal seams interbedded with gangue according to claim 1, characterized in that, The fracturing mechanism (40) includes an expansion tube (41) and a steel pipe (42) installed inside the expansion tube (41). The steel pipe (42) extends into the structure inside the simulated formation (10) and has at least one first opening (431). The other end of the steel pipe (42) is connected to an external fluid supply assembly. The expansion tube (41) extends into the structure inside the simulated formation (10) and has at least one second opening (432). The second opening (432) is aligned with the first opening (431), and the second opening (432) and the first opening (431) form a perforation channel (43).

9. The simulated experimental apparatus for cross-layer fracturing of two coal seams interbedded with gangue according to claim 1, characterized in that, The simulated fracturing experimental device for interbedded coal seams and gangue also includes a CT scanner, which is used to scan the fractures in the simulated formation (10).

10. An experimental method, characterized in that, The experimental method is used in the simulated fracturing experimental apparatus for inter-coal seam rockfill as described in any one of claims 1 to 9, and the experimental method includes the following steps: S1: Obtain geostress measurement data of the actual geological structure of the target mining area using stress relief method, hydraulic fracturing method and acoustic emission method, and combine the measurement data to obtain the mechanical parameters and triaxial stress values ​​of the actual roof, actual upper coal seam, actual interbedded gangue layer, actual lower coal seam and actual floor. S2: Construct the simulated formation (10) based on the actual formation structure, and arrange the horizontal stress loading component (20), the vertical stress loading component (30), the sensor component and the fracturing mechanism (40) in the simulated formation (10). S3: Apply horizontal and vertical stresses to the simulated formation (10) using the horizontal stress loading component (20) and the vertical stress loading component (30) to simulate the stress state of the actual formation structure; S4. The fracturing mechanism (40) injects fracturing fluid into the simulated formation (10) through a high-pressure pump, observes the changes in pumping pressure and the changes in the parameters of the sensor assembly, until the simulated formation (10) is fractured. S5. Release the pressure of the high-pressure pump, depressurize the horizontal stress loading component (20) and the vertical stress loading component (30), and analyze the fracture penetration layer and fracture extension state based on visual inspection, photography and CT scan of the simulated stratum (10).

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