Experimental device for simulating deep coal bed gas horizontal well fracturing scale

Abstract

The invention relates to an experimental device for simulating the fracturing scale of a deep coal bed gas horizontal well, which comprises an experimental groove, a simulated coal bed in the experimental groove and at least two horizontal well pipes, the two horizontal well pipes are buried in the simulated coal bed and are at the same height, the front ends of the horizontal well pipes penetrate out of the experimental groove and are used for inputting fracturing fluid, and the rear ends of the horizontal well pipes are communicated with the experimental groove. The rear ends of the horizontal well pipes are closed and located in the simulated coal seam, and the rear ends of the two horizontal well pipes are opposite and do not make contact with each other. A plurality of through holes are formed in the side face of the horizontal well pipe and allow fracturing fluid to be output from the horizontal well pipe. And a plurality of strain sensors are uniformly buried in the simulated coal seam, are connected with an analysis device outside the experimental tank through optical fibers, and are used for detecting the strain change condition of the simulated coal seam during fracturing.

Description

Technical Field

[0001] The invention belongs to the technical field of deep coalbed methane horizontal well fracturing, and in particular relates to an experimental device for simulating the scale of deep coalbed methane horizontal well fracturing. Background Art

[0002] In the field of deep coalbed methane development, as the depth of coal seams increases, the ground strain on the coal reservoir also increases, resulting in a decrease in the permeability of the coal reservoir, which is not conducive to the output of gas and water, resulting in a decrease in the production capacity of coalbed methane wells. The existing fracturing equipment and fracturing technology restrict the radius of ultra-large-scale hydraulic fracturing, resulting in the failure to effectively transform deep coal reservoirs and restricting the commercial development of deep coalbed methane. Deep coalbed methane development mostly adopts ultra-large-scale horizontal well fracturing, but there is currently little research on the impact radius of horizontal well fracturing scale and horizontal well fracturing technology, which cannot provide effective theoretical guidance for large-scale commercial applications. Summary of the invention

[0003] In view of the above problems, the present invention provides an experimental device for simulating the scale of deep coalbed methane horizontal well fracturing, comprising an experimental tank, a simulated coal seam in the experimental tank, and at least two horizontal well pipes, the two horizontal well pipes are buried in the simulated coal seam and are at the same height, the front end of the horizontal well pipe passes through the experimental tank for inputting fracturing fluid, the rear end of the horizontal well pipe is closed and is inside the simulated coal seam, the rear ends of the two horizontal well pipes are opposite and do not contact each other; a plurality of through holes are provided on the side of the horizontal well pipe to allow the fracturing fluid to be output from the horizontal well pipe;

[0004] Several strain sensors are evenly buried in the simulated coal seam. The strain sensors are connected to the analysis device outside the experimental tank through optical fibers to detect the strain changes of the simulated coal seam during fracturing.

[0005] Optionally, the experimental tank is a cube, and two adjacent side surfaces are respectively provided with oil-filled bags, and the lower surface of the top cover is provided with an oil-filled bag, which can contain hydraulic oil and is used to provide appropriate confining pressure for the simulated coal seam inside the experimental tank, so that the simulated coal seam in the experimental tank can withstand the formation pressure of a real deep underground coal reservoir.

[0006] Further optionally, the two horizontal well pipes are placed horizontally inside the experimental tank, with the front end of one horizontal well pipe passing through one side of the experimental tank, and the front end of the other horizontal well pipe passing through the opposite side of the experimental tank.

[0007] Optionally, the horizontal well pipe is a hollow cylinder, and a number of holes are evenly arranged on the side wall of the horizontal well pipe to simulate bullet holes after perforating the horizontal well; each hole is provided with a removable hole plug to simulate the perforating bullet and prevent coal slag from entering the horizontal well pipe when compacting the coal seam.

[0008] Further optionally, the holes penetrate the side wall of the horizontal well pipe and are evenly distributed in a spiral shape along the circumference and axial direction of the horizontal well pipe;

[0009] The hole plug is a cylindrical rubber plug, and the head of the hole plug is provided with an openable and closable umbrella-shaped limiting component. The center of the limiting component is inserted into the top surface of the hole plug through a fixing rod to fix and support the limiting component. The limiting component is provided with an openable and closable umbrella surface. When the hole plug is pressed toward the inside of the horizontal well pipe by the external simulated coal seam, the bottom edge of the umbrella surface abuts against the outer side surface of the horizontal well pipe. As the hole plug is pressed into the horizontal well pipe, the umbrella surface gradually opens to form resistance to prevent the hole plug from being completely pressed into the horizontal well pipe.

[0010] Optionally, the experimental device further includes an operating rod, the operating rod includes a first cylinder and a second cylinder arranged concentrically, the first cylinder and the second cylinder are both hollow, a spiral top pressure strip and a spiral detonating cord are provided on the side of the first cylinder, the top pressure strip and the detonating cord are arranged side by side and parallel to each other, the top pressure strip and the detonating cord are at equal intervals at any corresponding position on the left and right, and are both spirally wound around the circular side of the first cylinder;

[0011] The top pressure strip includes a plurality of top plugs, the top plug heads extend out of the first cylinder, the top plugs penetrate the side wall of the first cylinder, and the top plug heads are used to support the hole plugs inside the horizontal well pipe;

[0012] There are several pieces of fracturing explosives on the detonating cord. After the fracturing explosives are ignited, they push the corresponding hole plugs into the simulated coal seam.

[0013] Further optionally, the top plug includes a flat plate and a plug body, the back side of the flat plate is fixedly connected to the top of the plug body, and the front side of the flat plate faces the inner wall of the horizontal well pipe and can contact the tail of the hole plug, thereby supporting the hole plug;

[0014] The plug body is inserted into the corresponding through hole, and a magnetic sheet is provided on the back of the flat plate. When the top plug does not need to support the corresponding hole plug, the plug body moves toward the inside of the first cylinder, and the back of the flat plate is magnetically attracted to the outer side of the first cylinder, thereby temporarily retracting and fixing the top plug.

[0015] Further optionally, the first cylinder body is assembled in a split and detachable manner, including a number of circular segment cylinders connected in sequence, which are connected end to end to form the first cylinder body; the circular segment cylinder at the rearmost end of the first cylinder body has a sealed rear end, and an open front end and is provided with a connecting rubber ring; the circular segment cylinder at the frontmost end of the first cylinder body has both front and rear ends open, a connecting rubber ring is provided at the rear end, and no connecting rubber ring is provided at the front end; both ends of the other circular segment cylinders in the middle are open, and both ends are connected to the circular segment cylinders adjacent to the left and right through connecting rubber rings.

[0016] Optionally, the head of the second cylinder is conical and the rest is cylindrical, with an opening provided in the center of the head. The head of the second cylinder enters the first cylinder toward the rear end of the first cylinder. When pushed in, the head of the second cylinder pushes open the top plug in the first cylinder, so that the plug body of the top plug moves to the outside of the first cylinder, and the front of the flat plate can contact and resist the tail of the hole plug in the horizontal well pipe.

[0017] Further optionally, the operating rod also includes an operating rod, the front part of the operating rod is a hollow straight rod, the rear part is provided with an opening and closing portion, the push rod passes through the straight rod and can move forward and backward along the straight rod; the rear end of the push rod is hinged to two branch rods;

[0018] The opening and closing part comprises two push rods, the rear end of the straight rod is hinged to the front ends of the two push rods, and the rear end of the branch rod is fixedly connected to the side surfaces of the corresponding push rods.

[0019] Further optionally, the rear end wall of the horizontal well pipe has a certain thickness, an elastic positioning part is provided at the center of the inner wall of the rear end, the elastic positioning part is horizontally arranged and a magnetic suction sheet is provided at the front end, and the elastic positioning part can enter and exit the rear end wall of the horizontal well pipe;

[0020] The elastic positioning part has two limiting states. When the elastic positioning part extends out of the wall surface, it is in the first limiting state. When the elastic positioning part is retracted into the wall surface, it is in the second limiting state. When the elastic positioning part is in the second limiting state, the magnetic sheet at the front end is flush with the inner wall at the rear end. The elastic positioning part is used to limit the different position states of the first cylinder in the horizontal well pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of the experimental device for simulating the scale of deep coalbed methane horizontal well fracturing;

[0022] Figure 2 is a schematic diagram of a horizontal well pipe;

[0023] Figure 3 It is a schematic diagram of the cooperation between the horizontal well pipe, the first cylinder and the second cylinder;

[0024] Figure 4 is a schematic diagram of a first cylinder;

[0025] Figure 5 is a schematic diagram of a section of the first cylinder;

[0026] Figure 6 A schematic diagram of the operating lever.

[0027] In the accompanying drawings, 1-experimental tank, 2-simulated coal seam, 3-horizontal well pipe, 4-strain sensor, 5-oil filling bag, 6-eyelet, 7-hole plug, 8-limiting component, 9-first cylinder, 10-second cylinder, 11-top pressure strip, 12-detonating cord, 13-top plug, 14-fracturing explosive, 15-plate, 16-plug body, 17-circular section cylinder, 18-connecting rubber ring, 19-straight rod, 20-push rod, 21-branch rod, 22-top rod, 23-elastic positioning part, 24-top cover. DETAILED DESCRIPTION

[0028] This embodiment is an experimental device for simulating the scale of deep coalbed methane horizontal well fracturing. Figure 1-Figure 6 As shown, it includes an experimental tank 1 and a simulated coal seam 2 in the experimental tank 1, and at least two horizontal well pipes 3. The two horizontal well pipes 3 are buried in the simulated coal seam 2 and are at the same height. The front end of the horizontal well pipe 3 passes through the experimental tank 1 for inputting fracturing fluid. The rear end of the horizontal well pipe 3 is closed and is inside the simulated coal seam 2. The rear ends of the two horizontal well pipes 3 are opposite to each other and do not contact each other. A plurality of through holes are provided on the side of the horizontal well pipe 3 to allow the fracturing fluid to be output from the horizontal well pipe 3.

[0029] A number of strain sensors 4 are evenly buried in the simulated coal seam 2. The strain sensors 4 are connected to an analysis device outside the experimental tank 1 through optical fibers to detect the strain changes of the simulated coal seam 2 during fracturing.

[0030] Optionally, the experimental tank 1 is a cube, and two adjacent sides are respectively provided with oil-filled bags 5, and the lower surface of the top cover 24 is provided with an oil-filled bag 5, and the oil-filled bag 5 can contain hydraulic oil, which is used to provide appropriate confining pressure for the simulated coal seam 2 inside the experimental tank 1, so that the simulated coal seam 2 in the experimental tank 1 can withstand the formation pressure of the real deep underground coal reservoir;

[0031] The outer side surface of the top cover is evenly provided with a plurality of buckles, which can realize the sealing connection between the top cover and the side surface and maintain the pressure inside the experimental tank 1.

[0032] The experimental tank 1 is provided with three oil-filled bags 5 to provide confining pressure in three-dimensional directions, and the other two side surfaces and the bottom surface provide reaction force, so that the six surfaces of the simulated coal seam 2 are all under confining pressure.

[0033] Further optionally, the oil port of the oil-filled bag 5 passes through the side or top cover of the corresponding test tank 1 and is connected to an external oil supply device; a sealing ring is provided at the connection between the oil port and the corresponding side or top cover to prevent air leakage there.

[0034] Further optionally, the two horizontal well pipes 3 are placed horizontally inside the test tank 1, the front end of one horizontal well pipe 3 passes through one side of the test tank 1, and the front end of the other horizontal well pipe 3 passes through the side of the opposite side of the test tank 1, one of the two sides is provided with an oil-filled bag 5, and both sides and the oil-filled bag 5 are provided with through holes to allow the horizontal well pipe 3 to pass through, and when the oil-filled bag 5 is filled with hydraulic oil, the side of the oil-filled bag 5 is tightly attached to the outer wall of the horizontal well pipe 3 and the edge of the through hole on the side of the test tank 1, playing a sealing role. The other side without the oil-filled bag 5 can place a sealing ring at its own through hole, and the sealing ring is tightly attached to the outer wall of the horizontal well pipe 3 to play a sealing role.

[0035] Optionally, the method of setting up a simulated coal seam 2 inside the experimental tank 1 is as follows: open the top cover, fill the experimental tank 1 with coal particles or coal slag, stop filling when the filling reaches the bottom of the through hole on the side, compact this part of the coal material, and initially form a whole piece of coal seam; place two horizontal well pipes 3 above the coal seam, the front ends of the horizontal well pipes 3 pass through the corresponding side walls, and the rear ends of the two horizontal well pipes 3 are a certain distance apart. In one experiment, the distance between the rear ends of the two horizontal well pipes 3 is fixed. By carrying out multiple experiments, it is possible to study Different spacings of the horizontal well pipes 3 have different fracturing effects on the coal seams in the same area; after placing the horizontal well pipes 3, continue to fill in coal particles or coal slag. After filling the experimental tank 1, apply pressure downward from the top of the coal sample to compact the coal sample to form a simulated coal seam 2; then cover and seal the top cover, and flush hydraulic oil into the three oil-filling bags 5 of the experimental tank 1. The pressure in the experimental tank 1 is detected by a pressure gauge. When the pressure reaches the real formation pressure of the simulated coal reservoir, stop filling with hydraulic oil. After the pressure in the experimental tank 1 stabilizes, the experiment can be started.

[0036] Optionally, the horizontal well pipe 3 is a hollow cylinder, and a plurality of holes 6 are evenly arranged on the side wall of the horizontal well pipe 3 to simulate bullet holes after perforating the horizontal well; each hole 6 is provided with a removable hole plug 7 to simulate the perforating bullet and prevent coal slag from entering the horizontal well pipe 3 when compacting the coal seam.

[0037] Further optionally, the holes 6 penetrate the side wall of the horizontal well pipe 3 and are evenly distributed in a spiral shape along the circumferential and axial directions of the horizontal well pipe 3. The horizontal and vertical spacings of two adjacent holes 6 can be set according to the process conditions of horizontal well perforation and fracturing to be simulated in the experiment.

[0038] The hole plug 7 is a cylindrical rubber plug, and the head of the hole plug 7 is provided with an openable and closable umbrella-shaped limiting component 8, the center of the limiting component 8 is inserted into the top surface of the hole plug 7 through a fixing rod to fix and support the limiting component 8, and the limiting component 8 is provided with an openable and closable umbrella surface, when the hole plug 7 is pressed into the horizontal well pipe 3 by the external simulated coal seam 2, the bottom edge of the umbrella surface abuts against the outer side surface of the horizontal well pipe 3, and as the hole plug 7 is pressed into the horizontal well pipe 3, the umbrella surface gradually opens to form resistance to prevent the hole plug 7 from being completely pressed into the horizontal well pipe 3. The material of the limiting component 8 is steel.

[0039] In actual deep coal reservoir gas production projects, a vertical well is drilled first. After the bottom of the well reaches the coal reservoir at the target depth, a horizontal well is drilled in the deep coal reservoir. The front end of the horizontal well is connected to the bottom of the vertical well, and the rear end of the horizontal well points to the direction away from the vertical well and extends in the direction away from the vertical well. After the well is completed, the perforating gun is lowered into the horizontal well through the vertical well, and holes are perforated in the horizontal well in the order from the rear end to the front end. Specifically, a distance is selected in the area close to the rear end for perforation, and then the perforating gun is fired. Pull back to the ground (at this time, other positions of the horizontal well have not been perforated), pass fracturing fluid through the vertical well and the horizontal well, fracture a section of the horizontal well near the rear end, then extract the remaining fracturing fluid, lower the bridge plug from the ground, and plug the front end of the perforated section of the horizontal well; then use the perforating gun below to perforate a section of the horizontal well facing the vertical well, then pull back the perforating gun, and then fracture, and after fracturing, lower the bridge plug to plug the newly fractured section; in this way, perform progressive perforation and fracturing along the horizontal well. However, it is difficult to simulate (restore) the above perforation and fracturing methods in the laboratory, resulting in a large gap between the experimental results and the actual project, which has always been a problem faced by technicians.

[0040] Optionally, the experimental device further includes an operating rod, which includes a first cylinder 9 and a second cylinder 10 arranged concentrically, the first cylinder 9 and the second cylinder 10 are both hollow, a spiral top pressure strip 11 and a spiral detonating cord 12 are provided on the side of the first cylinder 9, the top pressure strip 11 and the detonating cord 12 are arranged side by side and parallel to each other, the top pressure strip 11 and the detonating cord 12 are at the same distance at any corresponding position on the left and right, and are both spirally wound around the circular side of the first cylinder 9;

[0041] The top pressure strip 11 includes a plurality of top plugs 13, the heads of the top plugs 13 extend out of the first cylinder 9, the top plugs 13 penetrate the side wall of the first cylinder 9, and the heads of the top plugs 13 are used to support the hole plugs 7 inside the horizontal well pipe 3;

[0042] A plurality of fracturing explosives 14 are arranged on the detonating cord 12 . The fracturing explosives 14 correspond to the hole plugs 7 one by one and are used to push the corresponding hole plugs 7 into the simulated coal seam 2 after being ignited.

[0043] The top pressure strip 11 and the detonating cord 12 are evenly wound on the outer surface of the first cylinder 9 with the same spacing and spiral rotation direction, that is, the top pressure strip 11 and the detonating cord 12 are two identical spiral lines, but are arranged at a short distance along the length direction of the first cylinder 9. For example, the top pressure strip 11 and the detonating cord 12 are spaced 1-3 cm apart at any corresponding position on the left and right, and the blasting of the fracturing explosive 14 does not affect the top plug 13. The spiral line formed by the top pressure strip 11 and the detonating cord 12 is the same as the spiral line formed by the eyelet 6, so that the top plug 13 corresponds to the hole plug 7 in the eyelet 6 one by one. After the first cylinder 9 rotates a certain angle, the fracturing explosive 14 and the hole plug 7 also correspond to each other one by one.

[0044] Further optionally, the top pressure strip 11 is provided with a plurality of through holes, which are evenly arranged along the top pressure strip 11 , and the through holes correspond to the top plugs 13 one by one. The top plugs 13 are inserted into the corresponding through holes and can enter and exit the first cylinder 9 along the radial direction of the first cylinder 9 in the through holes.

[0045] Further optionally, the top plug 13 includes a flat plate 15 and a plug body 16, the back of the flat plate 15 is fixedly connected to the top of the plug body 16, and the front of the flat plate 15 faces the inner wall of the horizontal well pipe 3 and can contact the tail of the hole plug 7, thereby supporting the hole plug 7;

[0046] The plug body 16 is inserted into the corresponding through hole, and a magnetic attraction sheet is provided on the back of the flat plate 15. When the top plug 13 does not need to support the corresponding hole plug 7, the plug body 16 moves toward the inside of the first cylinder 9, and the back of the flat plate 15 is magnetically attracted to the outer side surface of the first cylinder 9, thereby temporarily retracting and fixing the top plug 13.

[0047] Further optionally, the first cylinder 9 is a split and detachable assembly, including a plurality of circular cylinder segments 17 connected in sequence, the circular cylinder segments 17 are connected end to end to form the first cylinder 9; the rear end of the circular cylinder segment 17 at the rearmost end of the first cylinder 9 is sealed, and the front end is open and provided with a connecting rubber ring 18; the front and rear ends of the circular cylinder segment 17 at the frontmost end of the first cylinder 9 are both open, the rear end is provided with a connecting rubber ring 18, and the front end is not provided with a connecting rubber ring 18; both ends of the other circular cylinder segments 17 in the middle are open, and both ends are connected to the circular cylinder segments 17 adjacent to the left and right through the connecting rubber rings 18.

[0048] Further optionally, the connecting rubber ring 18 is made of rubber and is in a circular ring shape, with slots provided at both ends thereof, the slots being recessed into the connecting rubber ring 18, and the circular segment cylinders 17 on both sides of the connecting rubber ring 18 respectively clamp one end of the circular segment cylinder 17 in the corresponding slots, so that the two circular segment cylinders 17 are connected through the connecting rubber ring 18. No fracturing explosive 14 and top plug 13 are provided on the connecting rubber ring 18, so that perforation and fracturing do not affect the connecting rubber ring 18.

[0049] The length of the first cylinder 9 can be adjusted by the number of installed circular cylinder segments 17 , so that segmented perforation and fracturing can be achieved in the horizontal well pipe 3 .

[0050] Optionally, the head of the second cylinder 10 is conical and the rest is cylindrical, with an opening provided in the center of the head. The head of the second cylinder 10 enters the first cylinder 9 toward the rear end of the first cylinder 9. When pushed in, the head of the second cylinder 10 pushes open the top plug 13 in the first cylinder 9, so that the plug body 16 of the top plug 13 moves to the outside of the first cylinder 9, and the front of the flat plate 15 can contact and resist the tail of the hole plug 7 in the horizontal well pipe 3.

[0051] Further optionally, the operating rod also includes an operating rod, the front part of the operating rod is a hollow straight rod 19, the rear part is provided with an opening and closing portion, a push rod 20 passes through the straight rod 19, and can move forward and backward along the straight rod 19; the rear end of the push rod 20 is hinged with two branch rods 21;

[0052] The opening and closing part includes two push rods 22 , the rear end of the straight rod 19 is hinged to the front ends of the two push rods 22 , and the rear end of the branch rod 21 is fixedly connected to the side surface of the corresponding push rod 22 .

[0053] The operating seat rod is used to control a certain circular segment cylinder 17 to rotate to a certain angle, so that the fracturing explosive 14 on the detonating cord 12 can correspond to the hole plug 7. When in use, the rear end of the operating rod faces the rear end of the horizontal well pipe 3, the operating rod extends into the second cylinder 10, and the opening and closing part extends from the opening of the head of the second cylinder 10. At this time, there is a certain distance between the head of the second cylinder 10 and the rear end of the first cylinder 9. The circular segment cylinder 17 that needs to be rotated is the circular segment cylinder 17 after the head of the second cylinder 10. Therefore, the head opening of the second cylinder 10 can locate the object that needs to be operated for the operating rod. After the opening and closing part is completely extended out of the second cylinder 10 (that is, the front end of the push rod 22 is completely extended out of the second cylinder 10), the front end of the push rod 20 and the front end of the straight rod 19 are always outside the second cylinder 10 (that is, outside the experimental tank 1), which is convenient for holding the straight rod 19 and operating the push rod 20. Push the push rod 20 into the first cylinder 9. Since the rear ends of the two branch rods 21 are fixedly connected to the corresponding push rods 22, and the two push rods 22 are also connected to the straight rod 19, the front and rear positions of the branch rods 21 and the push rods 22 cannot be moved. The push rod 20 can only change the opening and closing angle of the branch rod 21, thereby driving the push rod 22 to change the opening and closing angle. Therefore, the two push rods 22 can be separated by pushing the branch rod 21, so that the rear end of the push rod 22 can be against the circular segment cylinder 17 that needs to be rotated. A rubber pad can be set at the rear end of the push rod 22 to increase the friction force. The operating rod is rotated outside the experimental tank 1, and the target circular segment cylinder 17 is driven to rotate to a suitable angle through the push rod 22. Then, the push rod 20 is pulled outward, the branch rod 21 and the push rod 22 are closed, and then the operating rod is pulled out of the second cylinder 10 as a whole.

[0054] The first cylinder 9, the top plug 13, the second cylinder 10 and the operating rod are all made of steel.

[0055] Further optionally, the rear end wall of the horizontal well pipe 3 has a certain thickness, and an elastic positioning portion 23 is provided at the center of the inner wall of the rear end. The elastic positioning portion 23 is horizontally arranged and a magnetic sheet is provided at the front end. The elastic positioning portion 23 can enter and exit the rear end wall of the horizontal well pipe 3;

[0056] The elastic positioning part 23 has two limiting states. When the elastic positioning part 23 extends out of the wall surface, it is in the first limiting state. When the elastic positioning part 23 is retracted into the wall surface, it is in the second limiting state. When the elastic positioning part 23 is in the second limiting state, the magnetic attraction piece at the front end is flush with the inner wall at the rear end. The elastic positioning part 23 is used to limit different position states of the first cylinder 9 in the horizontal well pipe 3.

[0057] The present invention can simulate the progressive perforation and fracturing method of the horizontal well in the actual deep coal reservoir. Specifically, the hole plug 7 is fully inserted into the corresponding hole 6 in advance to close the side of the horizontal well pipe 3. The horizontal well pipe 3 is placed in a suitable position in the experimental tank 1. Before compacting the coal material above the horizontal well pipe 3, the rear end of the first cylinder 9 is inserted into the horizontal well pipe 3, and the top pressure strip 11 corresponds to the spiral line formed by the hole 6. A first mark can be set at the position corresponding to the hole 6 at the front end of the horizontal well pipe 3, and a second mark and a third mark are set at the position corresponding to the top pressure strip 11 and the detonating cord 12 at the front end of the first cylinder 9. When the first mark is aligned with the second mark, it means that the top pressure strip 11 corresponds to the spiral line formed by the hole 6. The first cylinder 9 is pushed into the interior of the horizontal well pipe 3. A magnet corresponding to the elastic positioning part 23 is provided at the center of the outer side surface of the rear end of the first cylinder 9. The magnet is attracted together with the magnetic suction sheet of the elastic positioning part 23. The elastic positioning part 23 is in the first limit state, which is used to position the first cylinder 9.

[0058] Then, the head of the second cylinder 10 is inserted into the first cylinder 9, and the side wall of the second cylinder 10 contacts the plug body 16, pushing out the top plug 13, and the flat plate 15 of the top plug 13 can resist the tail of the hole plug 7. At this time, all the top plugs 13 resist the corresponding hole plug 7. The coal sample is compacted from the top to the bottom to form a simulated coal seam 2, and then the oil-filled bag 5 applies confining pressure. The head of the hole plug 7 bears the pressure outside the horizontal well pipe 3, and the tail of the hole plug 7 is supported by the top plug 13 to keep the force balance of the hole plug 7. At the same time, the limit component 8 of the hole plug 7 is stretched open, which also provides support for the hole plug 7, so that the state of the hole plug 7 is stable.

[0059] Before perforating, determine in advance the length of the perforating section, that is, the length of the horizontal well pipe 3 corresponding to one perforating and fracturing operation, and then determine the number of the circular cylinders 17 that need to be rotated according to the length. For example, if 5 circular cylinders 17 need to be rotated, take the rear end of the first cylinder 9 as the starting point, count 5 circular cylinders 17 outward, and pull the second cylinder 10 out of the experimental tank 1, so that the head of the second cylinder 10 corresponds to the sixth circular cylinder 17. The outer wall of the second cylinder 10 is provided with scale lines to facilitate accurate control of the moving distance of the second cylinder 10. The top plug 13 that loses the support of the second cylinder 10 is retracted into the first cylinder 9 under the action of magnetic attraction, and the flat plate 15 is adsorbed on the outer surface of the first cylinder 9. The part of the hole plug 7 that loses the support of the top plug 13 is temporarily supported by its own limiting component 8 and the friction between the hole plug 7 and the side of the hole 6, and does not fall back into the horizontal well pipe 3. At this time, the other top plugs 13 of the first cylinder 9 are still supported by the second cylinder 10.

[0060] The opening and closing part of the operating rod is inserted into the second cylinder 10 with the opening of the head of the second cylinder 10 extending outward from the opening of the opening and closing part and extending into the first cylinder 9. According to the above method, the two push rods 22 are separated by the push rod 20, and the two push rods 22 drive the fifth circular cylinder 17 to rotate a certain angle. The circular cylinders 17 are connected by the connecting rubber ring 18, and the circular cylinders 17 can rotate along the groove of the connecting rubber ring 18 under the action of external force. The fifth circular cylinder 17 drives the four circular cylinders 17 behind to rotate together, so that the detonating cord 12 corresponds to the hole plug 7.

[0061] The operating rod and the second cylinder 10 are withdrawn, and the remaining top plugs 13 of the first cylinder 9 are also retracted into the first cylinder 9. At this time, the remaining hole plugs 7 are no longer supported by the top plugs 13, but rely on their own support. The first cylinder 9 is pushed into the horizontal well pipe 3 to compress the elastic positioning part 23 to contract, that is, it is switched to the second limit state, that is, the entire first cylinder 9 moves toward the rear end of the horizontal well pipe 3, so that the detonating cords 12 of the first five circular sections 17 completely correspond to the holes 6 of the first perforation section length of the horizontal well pipe 3, and the fracturing explosives 14 correspond one by one to the hole plugs 7 that need to be perforated.

[0062] When installing the fracturing explosive 14 in the early stage, the length of a perforation section of this experiment and the number of actual perforations in a perforation section are determined in advance. The actual number of perforations is not greater than the number of holes 6 originally in the horizontal well pipe 3 in a perforation section length. The fracturing explosive 14 is installed at the position corresponding to the detonating cord 12 corresponding to the hole 6 to be perforated. The fracturing explosive 14 in the first perforation section length is detonated from back to front in sequence, and the fracturing explosive 14 impacts the tail of the corresponding hole plug 7. At this time, the hole plug 7 simulates the perforating bullet, and the limiting component 8 on the top shrinks into a pointed steel bullet, which impacts the simulated coal seam 2 to form a trajectory, simulating the real perforation process, and the cracks formed by the perforation in the simulated coal seam 2.

[0063] After perforating, the first cylinder 9 is pulled out of the horizontal well pipe 3, and fracturing fluid (the fracturing fluid is a conventional fracturing fluid, or configured according to the experimental requirements) is injected into the horizontal well pipe 3 from the front end of the horizontal well pipe 3, and the fracturing fluid is output from the perforated holes 6 to the simulated coal seam 2 outside to simulate the fracturing process. During the perforation and fracturing process, the strain change data of the coal seam is monitored in real time by the strain sensor 4 in the simulated coal seam 2, and transmitted to the external analysis device. By analyzing the strain change range of the coal seam under different fracturing transformation conditions, the optimal fracturing parameters are selected to guide the ultra-large-scale fracturing project on the site of the coalbed methane well.

[0064] During fracturing, the fracturing fluid inside the horizontal well pipe 3 also supports the unperforated plug 7 to a certain extent, so that the plug 7 continues to maintain balance. After fracturing is completed, the fracturing fluid is pumped out of the horizontal well pipe 3, and a small amount of clean water can be used to clean the inside of the horizontal well pipe 3, and a water-soluble bridge plug (which can be kept for more than 24 hours to meet the experimental requirements) is used to seal the front end of the first perforated section.

[0065] At this time, the first cylinder 9 is outside the experimental tank 1. The circular cylinder 17 corresponding to the first perforation section can be manually removed, and then the angle of the circular cylinder 17 corresponding to the second perforation section can be manually rotated, and then the first cylinder 9 is inserted into the horizontal well pipe 3. The rear end of the first cylinder 9 is against the bridge plug at this time, which means that the first cylinder 9 is inserted into place. The fracturing explosives 14 within the length of the second perforation section are detonated from back to front, and the fracturing explosives 14 impact the corresponding hole plugs 7 to perform perforation. Then withdraw the first cylinder 9, input fracturing fluid into the horizontal well pipe 3, perform fracturing, and repeat the above operation. Then, according to the above method, perform the receding perforation and fracturing experiments of the remaining perforation sections in turn. The above operations of the two horizontal well pipes 3 are performed simultaneously.

[0066] The experimental device described in the present invention can simulate ultra-large-scale fracturing of deep coalbed methane horizontal wells under different fracturing layers, different fracturing fluid displacement and types, different proppant sizes, and well spacing between two horizontal wells, and evaluate the indirect fracturing transformation effect of the top plate of deep coalbed methane wells with the help of strain sensors, thereby optimizing the well spacing between horizontal wells of deep coalbed methane wells and the scale of hydraulic fracturing. It can guide the well site deployment and fracturing technology of deep coalbed methane horizontal wells, maximize the transformation radius of deep coalbed methane horizontal wells, and improve the recovery rate of deep coalbed methane.

Claims

1. An experimental device for simulating the scale of deep coalbed methane horizontal well fracturing, characterized in that: It includes an experimental tank, a simulated coal seam in the experimental tank, and at least two horizontal well pipes. The two horizontal well pipes are buried in the simulated coal seam and are at the same height. The front end of the horizontal well pipe passes through the experimental tank for inputting fracturing fluid. The rear end of the horizontal well pipe is closed and is inside the simulated coal seam. The rear ends of the two horizontal well pipes are opposite to each other and do not contact each other. A plurality of through holes are provided on the side of the horizontal well pipe to allow the fracturing fluid to be output from the horizontal well pipe. Several strain sensors are evenly buried in the simulated coal seam. The strain sensors are connected to the analysis device outside the experimental tank through optical fibers to detect the strain changes of the simulated coal seam during fracturing.

2. The experimental device for simulating deep coalbed methane horizontal well fracturing scale according to claim 1, characterized in that: The test tank is a cube, and two adjacent sides are respectively provided with oil-filled bags, and the lower surface of the top cover is provided with an oil-filled bag, which can contain hydraulic oil and is used to provide appropriate confining pressure for the simulated coal seam inside the test tank, so that the simulated coal seam in the test tank can withstand the formation pressure of the real deep underground coal reservoir; Two horizontal well pipes are placed horizontally inside the experimental tank, with the front end of one horizontal well pipe passing through one side of the experimental tank, and the front end of the other horizontal well pipe passing through the side of the opposite side of the experimental tank.

3. The experimental device for simulating deep coalbed methane horizontal well fracturing scale according to claim 2, characterized in that: The horizontal well pipe is a hollow cylinder, and a plurality of holes are evenly arranged on the side wall of the horizontal well pipe to simulate bullet holes after perforating the horizontal well; each hole is provided with a detachable hole plug to simulate the perforating bullet and prevent coal slag from entering the horizontal well pipe when compacting the coal seam.

4. The experimental device for simulating deep coalbed methane horizontal well fracturing scale according to claim 3, characterized in that: The holes penetrate the side wall of the horizontal well pipe and are evenly distributed in a spiral shape along the circumference and axial direction of the horizontal well pipe; The hole plug is a cylindrical rubber plug, and the head of the hole plug is provided with an openable and closable umbrella-shaped limiting component. The center of the limiting component is inserted into the top surface of the hole plug through a fixing rod to fix and support the limiting component. The limiting component is provided with an openable and closable umbrella surface. When the hole plug is pressed toward the inside of the horizontal well pipe by the external simulated coal seam, the bottom edge of the umbrella surface abuts against the outer side surface of the horizontal well pipe. As the hole plug is pressed into the horizontal well pipe, the umbrella surface gradually opens to form resistance to prevent the hole plug from being completely pressed into the horizontal well pipe.

5. The experimental device for simulating deep coalbed methane horizontal well fracturing scale according to claim 4, characterized in that: The experimental device also includes an operating rod, which includes a first cylinder and a second cylinder arranged concentrically, the first cylinder and the second cylinder are both hollow, a spiral top pressure strip and a spiral detonating cord are arranged on the side of the first cylinder, the top pressure strip and the detonating cord are arranged side by side and parallel to each other, the top pressure strip and the detonating cord are at equal intervals at any corresponding position on the left and right, and are both spirally wound around the circular side of the first cylinder; The top pressure strip includes a plurality of top plugs, the top plug heads extend out of the first cylinder, the top plugs penetrate the side wall of the first cylinder, and the top plug heads are used to support the hole plugs inside the horizontal well pipe; There are several pieces of fracturing explosives on the detonating cord. After the fracturing explosives are ignited, they push the corresponding hole plugs into the simulated coal seam.

6. The experimental device for simulating deep coalbed methane horizontal well fracturing scale according to claim 5, characterized in that: The top plug includes a flat plate and a plug body, the back of the flat plate is fixedly connected to the top of the plug body, and the front of the flat plate faces the inner wall of the horizontal well pipe and can contact the tail of the hole plug, thereby supporting the hole plug; The plug body is inserted into the corresponding through hole, and a magnetic sheet is provided on the back of the flat plate. When the top plug does not need to support the corresponding hole plug, the plug body moves toward the inside of the first cylinder, and the back of the flat plate is magnetically attracted to the outer side of the first cylinder, thereby temporarily retracting and fixing the top plug.

7. The experimental device for simulating deep coalbed methane horizontal well fracturing scale according to claim 6, characterized in that: The first cylinder body is split and detachably assembled, and includes a number of circular cylinder segments connected in sequence, which are connected end to end to form the first cylinder body; the circular cylinder segment at the rear end of the first cylinder body has a sealed rear end, and an open front end and is provided with a connecting rubber ring; the circular cylinder segment at the front end of the first cylinder body has both front and rear ends open, a connecting rubber ring is provided at the rear end, and no connecting rubber ring is provided at the front end; both ends of the other circular cylinder segments in the middle are open, and both ends are connected to the circular cylinder segments adjacent to the left and right through connecting rubber rings.

8. The experimental device for simulating deep coalbed methane horizontal well fracturing scale according to claim 7, characterized in that: The head of the second cylinder is conical, and the rest is cylindrical. An opening is provided in the center of the head. The head of the second cylinder enters the first cylinder toward the rear end of the first cylinder. When pushed in, the head of the second cylinder pushes open the top plug in the first cylinder, so that the plug body of the top plug moves to the outside of the first cylinder, and the front of the flat plate can contact and resist the tail of the hole plug in the horizontal well pipe.

9. The experimental device for simulating deep coalbed methane horizontal well fracturing scale according to claim 8, characterized in that: The operating rod also includes an operating rod, the front part of the operating rod is a hollow straight rod, the rear part is provided with an opening and closing part, the push rod passes through the straight rod and can move forward and backward along the straight rod; the rear end of the push rod is hinged with two branch rods; The opening and closing part comprises two push rods, the rear end of the straight rod is hinged to the front ends of the two push rods, and the rear end of the branch rod is fixedly connected to the side surfaces of the corresponding push rods.

10. The experimental device for simulating deep coalbed methane horizontal well fracturing scale according to claim 1, characterized in that: The rear end wall of the horizontal well pipe has a certain thickness, and an elastic positioning part is provided at the center of the inner wall of the rear end. The elastic positioning part is arranged horizontally and a magnetic suction sheet is provided at the front end. The elastic positioning part can enter and exit the rear end wall of the horizontal well pipe; The elastic positioning part has two limit states. When the elastic positioning part extends out of the wall surface, it is in the first limit state. When the elastic positioning part is retracted into the wall surface, it is in the second limit state. When the elastic positioning part is in the second limit state, the magnetic attraction piece at its front end is flush with the inner wall at the rear end.

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