Directional long drill hole hydraulic fracturing similar simulation method

Abstract

The invention discloses a directional long drill hole hydraulic fracturing similar simulation method. A similar simulation device is constructed according to a geometric similarity principle and directional long drill hole hydraulic fracturing drilling parameters; calculating and determining a stress similarity ratio alpha sigma according to a geometric similarity ratio alpha L and a density similarity ratio alpha rho of the similar simulation device; based on a coal rock sample mechanical test result and a stress similarity ratio alpha sigma, determining a material ratio of each layer of similar simulation material model; simulating a directional long drill hole hydraulic fracturing three-dimensional fracture, and determining the burying position of the prefabricated metal plate; sequentially laying a bottom plate, a coal seam, an overlying rock layer and a fracturing layer in the bottom plate, the coal seam and the overlying rock layer, and burying the prefabricated metal plate in a designated position of the fracturing layer; and a monitoring unit is arranged, the model is maintained, the prefabricated metal plate is taken out after maintenance is completed, and the working face is excavated. According to the method disclosed by the invention, the regulation and stress adjustment effects of the directional long drilling hole hydraulic fracturing on the surrounding rock structure of the stope face are determined, and a theoretical basis is provided for researching a rock burst prevention and control mechanism and fracturing layer selection optimization of the directional long drilling hole hydraulic fracturing.

Description

Technical Field

[0001] The invention relates to a directional long borehole hydraulic fracturing similarity simulation method, belonging to the technical field of coal mine rock burst prevention and control. Background Art

[0002] With the continuous increase in the depth and intensity of coal mining, underground mining space is facing unprecedented high-stress environment, complex mining layout and difficult-to-detect geological environment. Rock burst has become one of the most serious dynamic disasters threatening deep coal mining. Among them, the hard roof has a large step distance due to its high strength and good integrity. It is easy to collapse in time as the working face advances. Therefore, when it breaks, it is very easy to induce impact, which poses a great threat to the safety of the working face.

[0003] The directional long-borehole segmented hydraulic fracturing technology has the advantages of regional weakening of hard rock formations, good fracturing effect of fracture networks, and prevention and control of rock bursts at the source. In recent years, it has been widely used in coal mine rock burst prevention and control and has developed rapidly. However, the mechanism of hydraulic fracturing on rock structure regulation and stress adjustment is not clear at present, and the influence of different fracturing layers on fracturing effect is not clear, which still cannot meet the needs of guiding on-site hydraulic fracturing construction to prevent rock bursts. Summary of the invention

[0004] The present invention provides a similarity simulation method for directional long borehole hydraulic fracturing. The method can determine the effects of directional long borehole hydraulic fracturing on the surrounding rock structure regulation and stress adjustment of the mining face according to the overburden structure evolution and surrounding rock stress monitoring results, and provide a theoretical basis and guidance for studying the mechanism of directional long borehole hydraulic fracturing for preventing and controlling rock burst and optimizing the selection of fracturing layers.

[0005] In order to achieve the above object, the present invention provides a directional long borehole hydraulic fracturing similarity simulation method, comprising the following steps:

[0006] S1. Construct a similar simulation device based on the geometric similarity principle and directional long-hole hydraulic fracturing drilling parameters;

[0007] S2, according to the geometric similarity ratio α of the similar simulation device L and density similarity ratio α ρ , calculate and determine the stress similarity ratio α σ ;

[0008] S3, based on the mechanical test results of coal and rock samples and the stress similarity ratio α σ , determine the material ratio of each layer of similar simulation material model;

[0009] S4, simulating three-dimensional fractures of directional long-hole hydraulic fracturing to determine the buried position of the prefabricated metal plate;

[0010] S5, laying the bottom plate, coal seam, overlying rock layer and the fracturing layer therein in sequence, and burying the prefabricated metal plate at the designated position of the fracturing layer;

[0011] S6. After the monitoring unit system is deployed, the similar model is cured. After the model is air-dried and cured, the prefabricated metal plate is taken out and the working surface is excavated.

[0012] Furthermore, the similar simulation device in S1 includes a bottom plate, side plates and baffles, the bottom plate is provided with side plates on the left and right sides, and the bottom plate is provided with a plurality of baffles on the front and rear sides.

[0013] Furthermore, the geometric similarity ratio α in S2 L The calculation is done using the following formula:

[0014] α L =r / b; where b is the width of the similar material model frame and r is the directional long-hole fracturing radius;

[0015] Density similarity ratio α ρ The calculation is done using the following formula:

[0016] α ρ =ρ s / ρ g ; In the formula, ρ s is the average density of the coal-bearing stratum rock mass, ρ g is the average density of similar materials made with sand aggregate;

[0017] Stress similarity ratio α σ The calculation formula is α σ =α L ×α ρ .

[0018] Furthermore, the material ratio of each layer of the similar simulation material model in S3 is based on the bulk density and strength parameters of the coal rock, and the mechanical parameters of the prepared material are R C is the actual mechanical parameter of coal rock.

[0019] Furthermore, the prefabricated metal plate in S4 includes an embedded part, a connecting part and a fixed part connected by welding, wherein the embedded part is in a semicircular arch shape, the diameter of the semicircle is equal to the thickness of the fracturing layer, and its height is half the width of the simulation device; the connecting part is semi-elliptical, and the fixed part is rectangular.

[0020] Furthermore, the specific laying process of S5 is as follows: laying the bottom plate, coal seam, overlying rock layer and the fracturing layer inside it in sequence on a similar simulation device; when laying the fracturing layer, fixing the prefabricated metal plate at the designed position, adding corresponding similar materials, and paving and compacting.

[0021] Furthermore, the monitoring unit system in S6 includes a stress gauge and a displacement monitoring gauge.

[0022] Based on the on-site engineering situation, the present invention establishes a similar material model to simulate the construction of directional long-bore hydraulic fracturing at the engineering site, studies the effects of directional long-bore hydraulic fracturing on the structure regulation and stress adjustment of the surrounding rock of the mining face, and studies the fracturing effect analysis under different fracturing layers, which has important practical application value for guiding the selection and optimization of the on-site fracturing layer. According to the evolution of the overburden structure and the monitoring results of the surrounding rock stress, the present invention determines the effects of directional long-bore hydraulic fracturing on the structure regulation and stress adjustment of the surrounding rock of the mining face, which provides an important theoretical basis and guidance for studying the mechanism of preventing and controlling rock burst by directional long-bore hydraulic fracturing and the optimization of the selection of fracturing layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the method of the present invention;

[0024] Figure 2 This is a distribution diagram of directional long-hole hydraulic fracturing in a mine in an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of the structure of a prefabricated metal plate in an embodiment of the present invention;

[0026] Figure 4 It is a schematic diagram of the three-dimensional structure of a three-dimensional similarity simulation device in an embodiment of the present invention;

[0027] Figure 5 It is a schematic diagram of the three-dimensional structure of a three-dimensional similar simulation device with a baffle in part according to an embodiment of the present invention;

[0028] Figure 6 It is a partial cross-sectional schematic diagram of a similar simulation device in an embodiment of the present invention.

[0029] In the figure: 1. prefabricated metal plate, 2. bottom plate, 3. coal seam, 4. base, 5. side plate, 6. baffle, 7. embedded part, 8. connecting part, 9. fixed part, 10. mudstone, 11. fine sandstone, 12. siltstone, 13. coarse sandstone, 14. medium sandstone. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings.

[0031] like Figure 1 As shown, a similarity simulation method for directional long borehole hydraulic fracturing includes the following steps:

[0032] S1. Construct a similar simulation device based on the geometric similarity principle and directional long-hole hydraulic fracturing drilling parameters;

[0033] S2, according to the geometric similarity ratio α of the similar simulation deviceL and density similarity ratio α ρ , calculate and determine the stress similarity ratio α σ ;

[0034] S3, based on the mechanical test results of coal and rock samples and the stress similarity ratio α σ , determine the material ratio of each layer of similar simulation material model;

[0035] S4, simulating directional long drilling hydraulic fracturing three-dimensional cracks to determine the buried position of the prefabricated metal plate 1;

[0036] S5, laying the bottom plate 2, the coal seam 3, the overlying rock layer and the fracturing layer therein in sequence, and burying the prefabricated metal plate 1 at the designated position of the fracturing layer;

[0037] S6. After the monitoring unit system is deployed, the similar model is cured. After the model is air-dried and cured, the prefabricated metal plate is taken out and the working surface is excavated.

[0038] Furthermore, the similar simulation device in S1 includes a base 4, a side panel 5 and a baffle 6. The left and right sides of the base are connected to the side panels 5, and a plurality of baffles 6 are provided on the front and rear sides of the base.

[0039] Furthermore, the geometric similarity ratio α in S2 L The calculation is done using the following formula:

[0040] α L =r / b; where b is the width of the similar material model frame and r is the directional long-hole fracturing radius;

[0041] Density similarity ratio α ρ The calculation is done using the following formula:

[0042] α ρ =ρ s / ρ g ; In the formula, ρ s is the average density of the coal-bearing stratum rock mass, ρ g is the average density of similar materials made with sand aggregate;

[0043] Stress similarity ratio α σ The calculation formula is α σ =α L ×α ρ .

[0044] Furthermore, the material ratio of each layer of the similar simulation material model in S3 is based on the bulk density and strength parameters of the coal rock, and the mechanical parameters of the prepared material are R C is the actual mechanical parameter of coal rock.

[0045] Furthermore, the prefabricated metal plate 1 in S4 includes an embedded portion 7, a connecting portion 8 and a fixed portion 9 connected by welding, wherein the embedded portion 7 is in a semicircular arch shape, the diameter of the semicircle is equal to the thickness of the fracturing layer, and its height is half the width of the simulation device; the connecting portion 8 is semi-elliptical, and the fixed portion 9 is rectangular.

[0046] Furthermore, the specific laying process of S5 is as follows: the bottom plate 2, coal seam 3, overlying rock layer and the fracturing layer therein are laid in sequence on a similar simulation device; when laying the fracturing layer, the prefabricated metal plate 1 is fixed at the designed position, and the corresponding similar materials are added, and the layers are flattened and compacted.

[0047] Furthermore, the monitoring unit system in S6 includes a stress gauge and a displacement monitoring gauge.

[0048] Embodiment: A coal mine 1802 working face adopts directional long-hole hydraulic fracturing construction. According to the on-site engineering conditions and the actual fracturing conditions, the method of the present invention is used to perform similar simulation analysis. The steps are as follows:

[0049] (1) Figure 2 As shown, the length of the 1802 working face of a mine is 240m. A total of 3 boreholes are designed in the No. 1 drilling site, and the distance between the fracturing sections is 30m. The simulation area of ​​this embodiment is the 2# borehole fracturing crack with a distance of 30m, the distance between the fracturing sections is 15m, and the simulated mining length is 180m. The model frame size of the similar simulation device is: 2.4m×0.3m×1.3m (length×width×height), and the similarity ratio α is determined L 1:200;

[0050] (2) The average density of the coal-bearing stratum rock mass on site is 2500 kg / m3, and the average density of similar materials made of sand as aggregate is 1500 kg / m3. The density similarity ratio α is obtained. ρ =2500 / 1500=1.667;

[0051] (3) According to the determined model geometric similarity ratio α L and density similarity ratio α ρ , the stress similarity ratio α is calculated σ =α L ×α ρ =200×1.667=333.3;

[0052] (4) Based on the rock mechanical parameters and stress similarity ratio α near the fracturing drilling site σ , determine the material ratio and dosage of similar material models, as shown in Table 1:

[0053] Table 1 Material ratio and dosage of similar material models

[0054]

[0055] (5) Figure 3 As shown, in this embodiment, the prefabricated metal plate 1 is semi-elliptical, with a long diameter of 3 cm and a short diameter of 1.5 cm; the fixing portion is a square with a side length of 3 cm; the fracturing layer is located at 36-51 cm of the model and the width of the front and rear baffles of the similar simulation device is 10 cm. When laying, the fixing portion is fixed at a height of 40 cm on the model frame, and the spacing is 10 cm;

[0056] (6) Arranging materials from bottom to top on a similar simulation device to form a bottom plate 2, a coal seam 3, and an overlying rock layer; installing a plurality of baffles 6 on the front and rear side facades to close the front and rear side facades of the corresponding layers;

[0057] (7) When laying the fracturing layer, first place the prefabricated metal plate 1 at the designed position and install the baffle 6 to fix it. Place the materials and flatten and compact them to complete the laying of the left part of the fracturing layer, and then complete the laying of the right part of the fracturing layer and other overlying rock layers, such as Figure 5 and Figure 6 As shown;

[0058] (8) Figure 4 As shown, the overlying rock layers are mudstone 10, fine sandstone 11, siltstone 12, coarse sandstone 13, medium sandstone 14, fine sandstone 11, coarse sandstone 13, medium sandstone 14, and fine sandstone 11 from bottom to top;

[0059] (9) After the model is naturally air-dried for 20 days, the front and rear baffles 6 are removed, and the prefabricated metal plate 1 is taken out using tools such as pliers to complete the laying of the hydraulic fracturing similar simulation three-dimensional model;

[0060] (10) Excavate tunnels and install monitoring systems such as stress gauges and displacement monitoring meters around the tunnels;

[0061] (11) Simulated working face mining. The average daily advance of the 1802 working face was 4 m, and the simulated mining length was 180 m. Therefore, each excavation was 2 cm, with a total of 45 cycles, 3 cycles per hour, and 15 cycles per day. It is expected that the simulated excavation and mining will be completed in 3 days.

[0062] The above embodiments show that the method of hydraulic fracturing similarity simulation of the present invention has important theoretical significance and practical application value for studying the evolution law of overburden in the mining area after hydraulic fracturing, the action mechanism of surrounding rock stress in the tunnel and the optimal design of fracturing layer.

Claims

1. A similarity simulation method for directional long borehole hydraulic fracturing, characterized in that: The steps include: S1. Construct a similar simulation device based on the geometric similarity principle and directional long-hole hydraulic fracturing drilling parameters; S2, according to the geometric similarity ratio α of the similar simulation device L and density similarity ratio α ρ , calculate and determine the stress similarity ratio α σ ; S3, based on the mechanical test results of coal and rock samples and the stress similarity ratio α σ , determine the material ratio of each layer of similar simulation material model; S4, simulating three-dimensional fractures of directional long-hole hydraulic fracturing to determine the buried position of the prefabricated metal plate; S5, laying the bottom plate, coal seam, overlying rock layer and the fracturing layer therein in sequence, and burying the prefabricated metal plate at the designated position of the fracturing layer; S6. After the monitoring unit system is deployed, the similar model is cured. After the model is air-dried and cured, the prefabricated metal plate is taken out and the working surface is excavated.

2. The directional long borehole hydraulic fracturing similarity simulation method according to claim 1, characterized in that: The similar simulation device in S1 includes a bottom plate, side plates and baffles. The left and right sides of the bottom plate are provided with side plates, and the front and rear sides of the bottom plate are provided with a plurality of baffles.

3. The directional long borehole hydraulic fracturing similarity simulation method according to claim 1, characterized in that: The geometric similarity ratio α in S2 L The calculation is done using the following formula: α L =r / / b; where bb is the width of the similar material model frame, and r is the directional long drilling fracturing radius; Density similarity ratio α ρ The calculation is done using the following formula: α ρ =ρ s / ρ g ; In the formula, ρ s is the average density of the coal-bearing stratum rock mass, ρ g is the average density of similar materials made with sand aggregate; Stress similarity ratio α σ The calculation formula is α σ =α L ×α ρ .

4. The directional long borehole hydraulic fracturing similarity simulation method according to claim 3, characterized in that: The material ratio of each layer of the similar simulation material model in S3 is based on the bulk density and strength parameters of coal rock, and the mechanical parameters of the prepared materials are R C is the actual mechanical parameter of coal rock.

5. The directional long borehole hydraulic fracturing similarity simulation method according to claim 1, characterized in that: The prefabricated metal plate in S4 includes an embedded part, a connecting part and a fixed part connected by welding, wherein the embedded part is in a semicircular arch shape, the diameter of the semicircle is equal to the thickness of the fracturing layer, and its height is half the width of the simulation device; the connecting part is semi-elliptical, and the fixed part is rectangular.

6. The directional long borehole hydraulic fracturing similarity simulation method according to claim 1, characterized in that: The specific laying process of the S5 is as follows: laying the bottom plate, coal seam, overlying rock layer and the fracturing layer inside it in sequence on a similar simulation device; when laying the fracturing layer, fixing the prefabricated metal plate at the designed position, adding corresponding similar materials, and paving and compacting.

7. The directional long borehole hydraulic fracturing similarity simulation method according to claim 1, characterized in that: The monitoring unit system in S6 includes a stress gauge and a displacement monitoring gauge.

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