Well-ground combined mining continuous pipe directional fracturing gas extraction system and method

Abstract

The application discloses a well-ground combined mining continuous pipe directional fracturing gas extraction system and method, and the extraction method comprises the following steps: constructing at least one directional long borehole in a determined laying layer; fixing the borehole after casing the first directional long borehole; lowering a fracturing fluid conveying pipeline into the well and extending to the borehole mouth of the directional long borehole; completing the assembly of the well-ground combined mining continuous pipe directional fracturing gas extraction system; performing a first fracturing section hydraulic sandblasting perforation operation; after the hydraulic sandblasting perforation operation is completed, water is supplemented to the continuous pipe, and meanwhile, fracturing fluid is conveyed into the first fracturing section by means of the fracturing fluid conveying pipeline on the well and the downhole collecting pipeline, so that the first fracturing section hydraulic fracturing and continuous pipe water supplementing combined operation is completed; the fracturing operation of the remaining fracturing sections in the first directional long borehole is completed; after the segmented fracturing construction of all the directional long boreholes is completed, pressure maintaining and blowout operations are performed; and after the blowout operation is completed, the gas extraction operation is completed.

Description

Technical Field

[0001] This invention belongs to the field of coal mine gas extraction technology, and relates to gas extraction systems, specifically to a coaxial coiled tube directional fracturing gas extraction system and method for combined mine and surface operations. Background Technology

[0002] Surface coiled tubing trucks can be used for hydraulic fracturing, hydraulic slotting, borehole clearing, and underground coal gasification. However, they have not yet been widely adopted in underground coal mines. The main reasons are: firstly, the harsh working conditions and limited space in underground coal mines mean that existing combined mine-ground and surface coiled tubing directional fracturing gas extraction systems are too large to meet the requirements of confined space operations; secondly, these systems require intrinsically safe explosion-proof design and coal mine safety certification; and thirdly, surface coiled tubing trucks are large, require high power, and have long coiled tubing, making them unsuitable for simple downsizing in underground coal mines; and fourthly, existing surface coiled tubing injection heads are too bulky to meet the space requirements of underground coal mine operations, and their vertical design limits their application to vertical borehole coiled tubing injection.

[0003] In response to the needs of continuous tubing operations in mines, researchers have developed some joint mine-ground directional fracturing gas extraction systems using continuous tubing. However, existing continuous tubing machines for coal mines have the following problems: (1) Equipment such as the drums and injection heads with continuous tubing attached do not have automatic walking capabilities, and these devices are heavy and difficult to transport underground in coal mines; (2) Equipment such as the drums and injection heads with continuous tubing attached mainly rely on flatbed trucks for transportation, which cannot be transported to locations without railway tracks, thus limiting the scope of use of the equipment; (3) Continuous tubing operation equipment requires complex assembly and installation operations underground in coal mines, and the complex working environment underground in coal mines will increase the risk of accidents. (4) According to general design standards, the diameter of the drum shaft should be at least 40 times the outer diameter of the continuous tube to ensure the service life of the continuous tube. Due to the size of the continuous tube drum, the size of the continuous tube operation equipment is often too large, making it impossible to transport by cage, damper, etc., and the capacity of the continuous tube drum cannot be guaranteed. If the shaft diameter is reduced, the continuous tube will undergo plastic deformation, reducing the service life of the continuous tube. (5) The existing operation method uses ground pumping of fracturing fluid to the long borehole opening for diversion. In the annular sand fracturing stage, the diverted sand-carrying fluid carries proppant into the continuous tube, which will continuously wear the continuous tube and sandblasting perforation gun, shortening the service life of the system. Summary of the Invention

[0004] To address the deficiencies and shortcomings of existing technologies, this invention provides a coaxial coiled tube directional fracturing gas extraction system and method for combined mine and surface operations, thereby solving the technical problems of inconvenience and short service life of existing coaxial coiled tube extraction systems for combined mine and surface operations.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A coaxial coiled tubular directional fracturing gas extraction system for mining, comprising a drum assembly, a dynamic sealing device at the orifice, and a downhole fracturing pump;

[0007] The roller device includes a first transport mechanism and a continuous tube roller mechanism disposed on the first transport mechanism. The continuous tube roller mechanism includes a roller skid and a roller body disposed inside the roller skid. A continuous tube is wound around the roller body.

[0008] The orifice dynamic sealing device includes a second transport mechanism and an injection head and a blowout preventer connected to the second transport mechanism; at least two hydraulic lifting mechanisms for adjusting the height and tilt angle of the injection head are provided below the injection head; the blowout preventer is connected to the orifice device provided at the orifice of the downhole directional long borehole; a through-flow moving space is provided in the injection head, the blowout preventer and the orifice device; the continuous tube can reciprocate back and forth in the moving space under the drive of the injection head.

[0009] The continuous tubing is also connected to the surface high-pressure pump and the downhole fracturing pump, respectively.

[0010] The present invention also has the following technical features:

[0011] Specifically, the orifice device includes a connected annular blowout preventer and an orifice four-way valve, wherein the annular blowout preventer is capable of being sealed to the blowout preventer box;

[0012] The orifice four-way connector is also connected to a gas negative pressure extraction pipeline and a downhole manifold, which are respectively connected to the surface fracturing fluid delivery pipeline and the downhole water supply pipeline. A first valve is installed on the downhole manifold. A second valve for adjusting the fracturing fluid flow rate is installed on the surface fracturing fluid delivery pipeline. A third valve and a fourth valve for adjusting the water supply flow rate of the coiled tubing are also installed on the downhole water supply pipeline. A reverse circulation sand flushing pipeline is also connected to the downhole water supply pipeline, and a reverse circulation sand flushing pipeline valve is installed on the reverse circulation sand flushing pipeline.

[0013] Furthermore, the first transportation mechanism includes a first hydraulic tracked chassis and a first support plate disposed above the first hydraulic tracked chassis; the second transportation mechanism includes a second hydraulic tracked chassis and a second support plate disposed above the second hydraulic tracked chassis.

[0014] Furthermore, the drum body is rotatably mounted on the drum support, the drum support is also provided with a pipe feeder for discharging continuous pipe, and the high-pressure rotary joint is provided on the drum body.

[0015] Furthermore, a gooseneck guide is also provided on the side wall of the injection head facing the roller support.

[0016] This invention also protects a method for directional fracturing gas extraction using coiled tubing in combined mine and surface operations. This method is implemented through the aforementioned directional fracturing gas extraction system using coiled tubing in combined mine and surface operations, and includes the following steps:

[0017] Step 1: Collect exploration data and mine data of the target mining area, and determine the layout layer of the directional long boreholes to be set in the coal mine based on the collected exploration data and mine data, and construct at least one directional long borehole within the determined layout layer.

[0018] Step 2: After running the casing in the first directional long borehole, solidify the hole;

[0019] Step 3: Connect the surface well to the underground roadway of the coal mine. After cementing the surface well with casing, run a fracturing fluid delivery pipeline into the surface well and extend it to the opening of the directional long borehole.

[0020] Step 4: Select the downhole fracturing pump according to the working power of the downhole fracturing pump, adjust the height and tilt angle of the injection head to make the blowout preventer box and the annular blowout preventer seal and connect, and then complete the assembly of the well-ground combined mining coiled tube directional fracturing gas extraction system.

[0021] Step 5: Start the surface high-pressure pump, open the second and third valves, and close the first valve, the fourth valve and the reverse circulation sand flushing pipeline valve to carry out the hydraulic sand jetting perforation operation in the first fracturing stage;

[0022] Step 6: After completing the hydraulic sandblasting perforation operation, close the third valve, open the fourth valve to replenish water to the coiled tubing, and at the same time open the first valve to deliver fracturing fluid to the first fracturing section through the surface fracturing fluid delivery pipeline and the downhole manifold pipeline, thus completing the combined hydraulic fracturing and coiled tubing water replenishment operation for the first fracturing section.

[0023] Step 7: After completing the hydraulic fracturing operation of the first fracturing section, retrieve the coiled tubing to the next fracturing section and repeat steps 5 and 6 to complete the fracturing operation of the remaining fracturing sections in the first directional long borehole.

[0024] Step 8: Repeat steps 4 to 7 to carry out segmented fracturing operations on the remaining directional long boreholes in sequence or alternately. After completing the segmented fracturing operations on all directional long boreholes, carry out pressure holding and blowout release operations.

[0025] Step 9: After the gas venting operation is completed, the gas extraction operation is finished.

[0026] Furthermore, step 1, which involves determining the strata for the placement of directional long boreholes in the coal mine based on the collected exploration and mine data, includes:

[0027] For medium-hard coal seams with a hardness coefficient f > 1.0, the stratum for directional long boreholes is the coal seam.

[0028] For soft and fractured coal seams with a hardness coefficient f≤1.0, the directional long boreholes are laid out in the roof strata 0.5 to 2.0 meters away from the top surface of the coal seam.

[0029] Furthermore, in the hydraulic fracturing operation, when sand gets stuck during the lifting of the coiled tubing after the completion of a fracturing section, the third and fourth valves are closed, and the first, second, and reverse circulation sand flushing pipe valves are opened, so that the fracturing fluid entering the directional long borehole is discharged sequentially through the coiled tubing and the reverse circulation sand flushing pipe.

[0030] Furthermore, the operating power of the downhole fracturing pump is determined by the following formula:

[0031] P=(Δp+p 延伸 )×Q

[0032] In the formula:

[0033] P represents the operating power of the downhole fracturing pump, measured in W.

[0034] Δp is the frictional resistance of the fracturing fluid flowing through the coiled tubing, measured in Pa.

[0035] p 延伸 This represents the pressure required to extend formation fractures, measured in Pa.

[0036] Q is the flow rate of water supplied from the downhole fracturing pump to the coiled tubing, in meters. 3 / s.

[0037] Furthermore, the frictional resistance of the fracturing fluid flowing through the coiled tubing is determined by the following formula:

[0038]

[0039] In the formula:

[0040] ρ is the density of the fracturing fluid, in kg / m³. 3 ;

[0041] L is the winding length of the continuous tube, in meters (m).

[0042] d is the inner diameter of the continuous tube, in meters (m).

[0043] Re is the Reynolds number of the fracturing fluid flowing in a coiled tube.

[0044] Compared with the prior art, the present invention has the following technical effects:

[0045] (1) The roller device and the orifice dynamic sealing device in the system of the present invention are assembled separately. The single device is small in size and easy to transport. It can be transported by coal mine cage or by inclined shaft. Since the first and second transport mechanisms with automatic walking capabilities are set up, there is no need to rely on manual handling, which reduces the labor intensity of underground coal mine workers. Moreover, it can reach the location where no rail is laid for operation without relying on rail transport, which improves the convenience and scope of use of the equipment.

[0046] (2) The continuous tube roller mechanism in the system of the present invention is detachably connected to the first transport mechanism. This structure ensures that the winding length of the continuous tube can be guaranteed, and that the height limit of the transport equipment is not exceeded during the transport process.

[0047] (3) The system of the present invention uses a downhole fracturing pump to replenish fluid to the coiled tubing. On the one hand, it can avoid the annular fluid from squeezing the coiled tubing, which would reduce the inner diameter of the coiled tubing, increase the flow friction of the fracturing fluid, increase the injection pressure, and even cause the squeezing force to exceed the external squeezing strength of the coiled tubing and destroy it. On the other hand, it can prevent the proppant from entering the coiled tubing during the diversion of the proppant-carrying fluid, which would wear down the coiled tubing and the sandblasting perforation gun. It can effectively avoid the complex control of pressure and flow at the diversion point and realize the systematic operation of surface perforation, surface sand fracturing and downhole water replenishment.

[0048] (4) The present invention has a reverse circulation sand flushing pipeline. When the continuous tube is blocked by sand, the reverse circulation well washing operation can be carried out by switching the valve. After the reverse circulation sand flushing is unblocked, the continuous tube can be lifted up. This solves the problems that may be caused by the continuous tube breaking, the injection head pulling force exceeding the limit, and the injection head failure when the continuous tube is blocked by sand.

[0049] (5) The method of the present invention avoids the complex process of mixing sand in coal mines by pumping fracturing fluid into the surface. The addition of sand before pumping can enable the proppant in the fracturing fluid to obtain an initial velocity close to that of the fracturing fluid, which can increase the suspension and migration distance when moving in the pipeline. It realizes the large-volume joint injection of surface and underground fracturing fluid, effectively solving the problem that the existing fracturing operation cannot increase the discharge capacity. The combined injection discharge capacity of the surface high-pressure pump and the underground fracturing pump can exceed 7 m3 / min. It realizes the joint operation of injection hole with injection hole at the orifice, annular injection fracturing and continuous tubing water replenishment, and finally realizes the rapid and safe transportation of surface fracturing fluid and underground replenishment fluid. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the overall structure of the system of the present invention;

[0051] Figure 2 This is a partial structural diagram of the present invention;

[0052] Figure 3This is a schematic diagram of the drum device structure;

[0053] Figure 4 This is a schematic diagram of the orifice dynamic sealing device.

[0054] Figure 5 This is a flowchart of the method of the present invention.

[0055] Meaning of the labels in the attached figures:

[0056] 1-Drum device, 2-Orifice dynamic sealing device, 3-Downhole fracturing pump, 4-Continuous tubing, 5-Orifice device, 6-Gas negative pressure extraction pipeline, 7-Downhole manifold pipeline, 8-Uphole fracturing fluid delivery pipeline, 9-Downhole water supply pipeline, 10-Reverse circulation sand flushing pipeline.

[0057] 11-First transport mechanism; 12-Roller mechanism; 21-Second transport mechanism; 22-Injection head; 23-Blowout preventer box; 51-Annular blowout preventer; 52-Orifice four-way valve; 71-First valve; 81-Second valve; 91-Third valve; 92-Fourth valve;

[0058] 101-Reverse circulation sand flushing pipeline valve; 111-First hydraulic crawler chassis; 112-First support plate; 121-Roller skid; 122-Roller body; 123-Roller bracket; 124-Pipe arranger; 211-Second hydraulic crawler chassis; 212-Second support plate; 221-Hydraulic lifting mechanism; 222-Gooseneck guide. Detailed Implementation

[0059] It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0060] The terms “upper,” “lower,” “front,” “rear,” “top,” and “bottom” used in this invention refer to orientations or positional relationships only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. “Inner” and “outer” refer to the inner and outer contours of the corresponding components, and the above terms should not be construed as limitations on the invention.

[0061] Furthermore, the terms "first," "second," and other ordinal numbers are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0062] In this invention, unless otherwise stated, the terms "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0063] Example 1

[0064] Following the above technical solutions, such as Figures 1 to 3 As shown, this embodiment provides a coaxial coiled tubing directional fracturing gas extraction system for mining, including a drum device 1, an orifice dynamic sealing device 2, and a downhole fracturing pump 3;

[0065] The roller device 1 includes a first transport mechanism 11 and a continuous tube roller mechanism 12 mounted on the first transport mechanism 11. The continuous tube roller mechanism 12 includes a roller skid 121 and a roller body 122 mounted inside the roller skid 121. A continuous tube 4 is wound around the roller body 122. The roller body 122 can realize the loading, unloading, and arrangement of the continuous tube 4. The first transport mechanism 11 and the continuous tube roller mechanism 12 are detachably connected, which reduces the size and overall height of the roller device 1 and is beneficial for underground transportation in coal mines.

[0066] The orifice dynamic sealing device 2 includes a second transport mechanism 21 and an orifice sealing assembly mounted on the second transport mechanism 21. The orifice sealing assembly includes an injection head 22 and a blowout preventer 23 connected together. The injection head 22 provides power for the extension and retraction of the continuous tube 4 to enable pressurized dragging of the continuous tube 4. At least two hydraulic lifting mechanisms 221 are provided below the injection head 22 for adjusting the height and tilt angle of the injection head 22. The blowout preventer 23 is connected to the orifice device 5 mounted at the orifice. A through-flow moving space is provided in the injection head 22, the blowout preventer 23, and the orifice device 5. The continuous tube 4 can reciprocate back and forth in the moving space under the drive of the injection head 22.

[0067] In this embodiment, the coiled tube 4 is also connected to a surface high-pressure pump and a downhole fracturing pump 3 located in the roadway via a high-pressure rotary joint mounted on the drum body 122 and a high-pressure hose connected to the high-pressure rotary joint. The downhole fracturing pump 3 is used to replenish the coiled tube 4 with liquid, such as high-pressure water, during hydraulic fracturing to avoid the fluid flow from the annulus between the directional long borehole casing and the coiled tube 4 causing compression of the coiled tube 4 during hydraulic fracturing. It also avoids the wear of the spray gun of the directional segmented fracturing tool string caused by sand passing through the coiled tube 4 during hydraulic fracturing, thus extending the service life of the segmented fracturing tool string.

[0068] As a preferred embodiment, the orifice device 5 includes an annular blowout preventer 51 and an orifice four-way valve 52 connected together, and the annular blowout preventer 51 is sealed to the blowout preventer box 23.

[0069] The orifice four-way valve 52 is also connected to a gas negative pressure extraction pipeline 6 and a downhole manifold 7. The downhole manifold 7 can be a high-pressure hose or a steel pipe. The downhole manifold 7 is connected to the surface fracturing fluid delivery pipeline 8 and the downhole water supply pipeline 9. The fluid flowing into the downhole manifold 7 from the surface fracturing fluid delivery pipeline 8 can enter the annulus of the long borehole casing and coiled tubing 4. Then, the fluid from the downhole water supply pipeline 9 can be sent into the segmented fracturing tool string through the coiled tubing 4. The downhole manifold 7 is equipped with a first valve 71; the surface fracturing fluid delivery pipeline 8 is equipped with a second valve 81 to regulate the fracturing fluid flow rate; the downhole water supply pipeline 9 is also equipped with a third valve 91 and a fourth valve 92 for regulating the water supply flow rate of the coiled tubing; the downhole water supply pipeline 9 is also connected to a sand flushing pipeline 10, which is equipped with a sand flushing valve 101. In this embodiment, all valves are remotely controlled plug valves.

[0070] If sand gets stuck during the process of raising the coiled tubing 4, the reverse circulation sand flushing pipeline valve 101 is opened to connect the reverse circulation sand flushing pipeline 10. That is, the fluid enters the annulus, passes through the tool string, enters the coiled tubing 4, enters the downhole water supply pipeline 9 through the high-pressure hose, and then flows out through the reverse circulation sand flushing pipeline 10, ultimately achieving reverse circulation well washing.

[0071] As a preferred embodiment, the first transport mechanism 11 includes a first hydraulic tracked chassis 111 and a first support plate 112 disposed above the first hydraulic tracked chassis 111; the second transport mechanism 21 includes a second hydraulic tracked chassis 211 and a second support plate 212 disposed above the second hydraulic tracked chassis 211.

[0072] As a preferred embodiment, the drum body 122 is rotatably mounted on the drum support 123. The drum support 123 is also provided with a pipe feeder 124 for discharging the continuous pipe 4. A high-pressure rotary joint is provided on the drum body 122. A high-pressure hose is connected to the high-pressure rotary joint. The high-pressure hose is connected to the surface high-pressure pump and the downhole fracturing pump via a tee. That is, the high-pressure hose is connected to the downhole water supply pipeline 9 and the surface fracturing fluid delivery pipeline 8 via the tee.

[0073] As a preferred embodiment, a gooseneck guide 222 is also provided on the side wall of the outer shell 221 facing the roller support 123. The gooseneck guide 222 is used for guiding the continuous tube conveying.

[0074] The usage process of this system is as follows:

[0075] After installing the orifice four-way connector, the drum device 1, the orifice dynamic sealing device 2 and the underground fracturing pump 3 are assembled on-site in the underground roadway of the coal mine. The continuous pipe 4, which is wound around the drum body 122 and has a tool string connected to its head end, is sent into the orifice through the pipe laying device 124, the gooseneck guide 222, the injection head 22 and the blowout preventer 23.

[0076] During hydraulic perforation: the jet fluid is sent from the surface along the pipeline into the coiled tube 4 to start the perforation operation. After the perforation operation is completed, the fracturing fluid is sent through the pipeline into the annulus of the directional long borehole by switching the valve to carry out hydraulic fracturing operation. At the same time as hydraulic fracturing, the downhole fracturing pump 3 replenishes the coiled tube 4 with fluid to avoid deformation of the coiled tube 4 due to the compression of the fluid flow in the annulus, which would cause the fluid flow channel in the coiled tube 4 to become smaller.

[0077] Example 2

[0078] This embodiment discloses a method for directional fracturing gas extraction using continuous coiled tubing in a mine, which is implemented using the directional fracturing gas extraction system for continuous coiled tubing in a mine disclosed in Embodiment 1. This method is applied to a coal mine in Huaibei, where the target coal seam is a high-gas outburst coal seam. In order to improve the gas extraction efficiency, the method utilizes a joint operation mode between the mine and the mine to achieve efficient regional gas control.

[0079] Specifically, the following steps are included:

[0080] Step 1: Collect exploration data and mine data of the target mining area, and determine the layout layer of the directional long boreholes to be set in the coal mine based on the collected exploration data and mine data, and construct at least one directional long borehole within the determined layout layer.

[0081] For medium-hard coal seams with a hardness coefficient f > 1.0, the stratum for directional long boreholes is the coal seam.

[0082] For soft and fractured coal seams with a hardness coefficient f≤1.0, the directional long boreholes are laid out in the roof strata 0.5 to 2.0 meters away from the top surface of the coal seam.

[0083] In this embodiment, the drilling site is expanded on one side of the roadway to a depth of 4.0m. Then, a directional long borehole is drilled from the bottom roadway of the coal seam to the top of the coal seam. The drilling trajectory is controlled in the rock strata of the top of the coal seam. The final depth of the directional long borehole is 300m, and the vertical distance between the directional long borehole and the top surface of the coal seam is 1 to 1.5m.

[0084] During the drilling process of directional long boreholes, the borehole inclination angle variation should be controlled to be less than 10°, and the directional drilling intensity should not exceed 0.1° / m.

[0085] Step 2: Install casing in the first directional long borehole to solidify the hole;

[0086] Conventional drilling mud was used to replace cement at the wellhead, and the well was allowed to set for 48 hours. Then, an acoustic logging tool was lowered using the drilling rig to evaluate the cementing quality of the horizontal section.

[0087] Step 3: Connect the surface well to the underground roadway of the coal mine. After cementing the surface well with casing, run a fracturing fluid delivery pipeline into the surface well and extend it to the opening of the directional long borehole.

[0088] In actual operation, existing cable holes or hydrological observation holes in the coal mine can be used for surface breakthrough wells. The location of the surface breakthrough well should avoid subsidence areas, and it can be a vertical well or a directional well. The surface breakthrough well can use casing as a fluid passage, or a fracturing fluid delivery pipeline can be installed in the wellbore as a fluid passage.

[0089] In this embodiment, the surface breakthrough well adopts a three-section wellbore structure. The first section has a drill bit of Φ444.5mm and a surface casing of Φ339.7mm; the second section has a drill bit of Φ311.1mm and a technical casing of Φ244.5mm; and the third section has a drill bit of 215.9mm, without casing. A fracturing fluid delivery pipeline is installed in the surface breakthrough well.

[0090] Then, from the bottom of the surface-penetrating well, a steel pipe or high-pressure hose is used as a fracturing fluid delivery pipeline to connect to the orifice of the directional long borehole. The inner diameter of the fracturing fluid delivery pipeline is 76mm to 100mm.

[0091] Step 4: Select the downhole fracturing pump according to its operating power, adjust the height and inclination angle of the injection head 22 to seal the blowout preventer 23 with the annular blowout preventer 51, and then complete the assembly of the mine-ground integrated continuous tubing directional fracturing gas extraction system; specifically, this includes: first assembling the tool string in the coal mine and manually sending it into the orifice, connecting the front end of the continuous tubing to the rear end of the tool string; using the hydraulic lifting mechanism 221 to adjust the height and inclination angle of the injection head 22, and tightly connecting the blowout preventer at the head end of the injection head 22 with the end of the annular blowout preventer 51 to complete the equipment assembly.

[0092] For water replenishment operations, the density of water is 1000 kg / m³. 3 The displacement is 0.8m. 3 / min, which is 0.0133m 3The continuous tube 4 wound on the drum body 122 has a length of 300m, an outer diameter of 38.1mm, and an inner diameter of 32.1mm. The calculated frictional resistance of water flowing through the wound continuous tube is 44.17MPa. The formation fracture extension pressure is 13.5MPa. Therefore, the required power of the replenishment pump is calculated as: P = (44.17 + 13.50) × 1000000 × 0.0133 = 768.95KW. The power of the underground fracturing pump in the coal mine should be ≥768.95KW. Therefore, in this embodiment, an 800KW underground fracturing pump is selected.

[0093] The operating power of the downhole fracturing pump 3 determines its ability to replenish water into the coiled tubing 4. This prevents problems such as insufficient water replenishment volume or pressure during operation due to the downhole fracturing pump 3's inability to meet requirements. Insufficient water replenishment volume will prevent the fracturing operation from achieving the designed total volume, affecting the final fracturing effect. Insufficient water replenishment pressure will cause the coiled tubing to be subjected to external extrusion force from the annular fracturing fluid. This poses a risk of reducing the service life of the coiled tubing and even causing it to break. Furthermore, the reduced inner diameter of the coiled tubing due to external fluid compression during operation will further increase the flow friction of the fracturing fluid, increasing the risk of overpressure and compromising safe operation.

[0094] Step 5: Start the surface high-pressure pump, open the second valve 81 and the third valve 91, and close the first valve 71, the fourth valve 92 and the reverse circulation sand flushing pipeline valve 101 to carry out the hydraulic sand jetting perforation operation in the first fracturing stage.

[0095] Step 6: After completing the hydraulic sandblasting perforation operation, close the third valve 91, open the fourth valve 92 to replenish water to the coiled tubing 4, and at the same time open the first valve 71 to deliver fracturing fluid to the first fracturing section through the surface fracturing fluid delivery pipeline 8 and the downhole manifold 7, thus completing the combined hydraulic fracturing and coiled tubing water replenishment operation of the first fracturing section.

[0096] The discharge rate during continuous pipe makeup water operation is 0.8 m³. 3 / min, without sand addition; the hydraulic fracturing discharge rate for the first fracturing stage is 7m³ / min. 3 / min, sand ratio is 6% to 13%.

[0097] Step 7: After completing the hydraulic fracturing operation of the first fracturing section, retrieve the coiled tubing 4 to the next fracturing section, and repeat steps 3 to 4 to complete the fracturing operation of the remaining fracturing sections in the first directional long borehole.

[0098] Step 8: Repeat steps 2 to 7 to carry out segmented fracturing construction on the remaining directional long boreholes in sequence or alternately. After completing the segmented fracturing construction of all directional long boreholes, carry out pressure holding and blowout release operations.

[0099] In the aforementioned hydraulic fracturing operations, when the previous fracturing stage is completed and the packer is released to lift the coiled tubing for the next stage of fracturing, sand jamming may occur, preventing the coiled tubing from being lifted. If the injection head 22 is used to forcefully pull the coiled tubing, it may cause problems such as coiled tubing breakage, excessive injection head pulling force, or injection head malfunction.

[0100] At this point, the third valve 91 and the fourth valve 92 are closed, while the first valve 71, the second valve 81, and the reverse circulation sand flushing pipe valve 101 are opened. This allows the fracturing fluid entering the directional long borehole to be discharged sequentially through the coiled tubing 4 and the reverse circulation sand flushing pipe 10, achieving reverse circulation sand flushing to remove the blockage. After flushing out the blocked sand, the injection head 22 can normally lift the coiled tubing 4, solving the problems in the prior art where relying solely on the injection head 22 to forcefully pull the coiled tubing 4 when sand blockage occurs may cause the coiled tubing 4 to break, the injection head 22 to exceed its pulling limit, or the injection head 22 to malfunction.

[0101] Step 9: After the gas venting operation is completed, the gas extraction operation is finished.

[0102] This invention avoids the complex process of mixing fracturing fluid with sand underground in coal mines by pumping fracturing fluid into the surface. Furthermore, adding sand before the pump allows the fracturing fluid proppant to achieve an initial velocity close to that of the fracturing fluid, increasing its suspension and migration distance in the pipeline. This effectively solves the technical problem of limited fracturing fluid flow rate in existing fracturing operations, enabling combined injection of large flow rates both above and below ground. Through the combined injection of a surface high-pressure pump and an underground fracturing pump, the injection flow rate can exceed 7m³. 3 / min; it realized the combined operation of perforation injection, annular injection fracturing and coiled tubing water replenishment, and ultimately achieved rapid and safe delivery of fracturing fluid on the surface and replenishment fluid downhole.

[0103] The above-described implementation process is merely an example to clearly illustrate this application and is not intended to limit the implementation methods. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementation methods here. However, obvious variations or modifications derived therefrom are still within the protection scope of this application.

Claims

1. A coaxial coiled tubing directional fracturing gas extraction system for combined well and surface mining, comprising a drum device (1), characterized in that, It also includes a dynamic sealing device at the orifice (2) and a downhole fracturing pump (3); The roller device (1) includes a first transport mechanism (11) and a continuous tube roller mechanism (12) disposed on the first transport mechanism (11). The continuous tube roller mechanism (12) includes a roller skid (121) and a roller body (122) disposed in the roller skid (121). A continuous tube (4) is wound around the roller body (122). The orifice dynamic sealing device (2) includes a second transport mechanism (21) and an orifice dynamic sealing assembly disposed on the second transport mechanism (21). The orifice dynamic sealing assembly includes an injection head (22) and a blowout preventer (23) connected together. At least two hydraulic lifting mechanisms (221) for adjusting the height and tilt angle of the injection head (22) are disposed below the injection head (22). The blowout preventer (23) is connected to the orifice device (5) disposed at the orifice of the downhole directional long borehole. The injection head (22), the blowout preventer (23) and the orifice device (5) are provided with a through-flow space. The continuous tube (4) can reciprocate back and forth in the through-flow space under the drive of the injection head (22). The continuous tubing (4) is also connected to the surface high-pressure pump and the downhole fracturing pump (3), respectively; The orifice device (5) includes a ring blowout preventer (51) and an orifice four-way (52) connected together. The ring blowout preventer (51) can be sealed to the blowout preventer box (23). The orifice cross (52) is also connected to a gas negative pressure extraction pipeline (6) and a downhole manifold (7). The downhole manifold (7) is connected to the surface fracturing fluid delivery pipeline (8) and the downhole water supply pipeline (9). The downhole manifold (7) is equipped with a first valve (71). The surface fracturing fluid delivery pipeline (8) is equipped with a second valve (81) for adjusting the fracturing fluid flow rate. The downhole water supply pipeline (9) is also equipped with a third valve (91) and a fourth valve (92) for adjusting the continuous tubing water supply flow rate. The downhole water supply pipeline (9) is also connected to a reverse circulation sand flushing pipeline (10). The reverse circulation sand flushing pipeline (10) is equipped with a reverse circulation sand flushing pipeline valve (101).

2. The well-ground combined mining coiled tubing directional fracturing gas extraction system as described in claim 1, characterized in that, The first transport mechanism (11) includes a first hydraulic tracked chassis (111) and a first support plate (112) disposed above the first hydraulic tracked chassis (111); the second transport mechanism (21) includes a second hydraulic tracked chassis (211) and a second support plate (212) disposed above the second hydraulic tracked chassis (211).

3. The well-ground combined mining coiled tubing directional fracturing gas extraction system as described in claim 1, characterized in that, The drum body (122) is rotatably mounted on the drum support (123), and the drum support (123) is also provided with a pipe discharger (124) for discharging the continuous pipe (4). The drum body (122) is provided with a high-pressure rotary joint.

4. The well-ground combined mining coiled tubing directional fracturing gas extraction system as described in claim 1, characterized in that, The injection head (22) is also provided with a gooseneck guide (222) at one end facing the roller support (123).

5. A method for directional fracturing gas extraction using coiled tubing in combined mine and surface operations, characterized in that, This method is implemented using the well-ground combined mining coiled tube directional fracturing gas extraction system as described in any one of claims 1 to 4, and includes the following steps: Step 1: Collect exploration data and mine data of the target mining area, and determine the layout layer of the directional long boreholes to be set in the coal mine based on the collected exploration data and mine data, and construct at least one directional long borehole within the determined layout layer. Step 2: After running the casing in the first directional long borehole, solidify the hole; Step 3: Connect the surface well to the underground roadway of the coal mine. After cementing the surface well with casing, run a fracturing fluid delivery pipeline into the surface well and extend it to the opening of the directional long borehole. Step 4: Select the downhole fracturing pump according to the working power of the downhole fracturing pump, adjust the height and tilt angle of the injection head (22) to make the blowout preventer box (23) and the annular blowout preventer (51) seal and connect, and then complete the assembly of the well-ground joint mining continuous tube directional fracturing gas extraction system. Step 5: Start the high-pressure pump on the well, open the second valve (81) and the third valve (91), and close the first valve (71), the fourth valve (92) and the reverse circulation sand flushing pipeline valve (101) to carry out the hydraulic sand blasting perforation operation in the first fracturing section; Step 6: After completing the hydraulic sandblasting perforation operation, close the third valve (91), open the fourth valve (92) to replenish water to the coiled tubing (4), and at the same time open the first valve (71) to deliver fracturing fluid to the first fracturing section through the surface fracturing fluid delivery pipeline (8) and the downhole manifold pipeline (7), thus completing the combined hydraulic fracturing and coiled tubing water replenishment operation of the first fracturing section. Step 7: After completing the hydraulic fracturing operation of the first fracturing section, retrieve the coiled tubing (4) to the next fracturing section, and repeat steps 5 to 6 to complete the fracturing operation of the remaining fracturing section in the first directional long borehole. Step 8: Repeat steps 4 to 7 to carry out segmented fracturing operations on the remaining directional long boreholes in sequence or alternately. After completing the segmented fracturing operations on all directional long boreholes, carry out pressure holding and blowout release operations. Step 9: After the gas venting operation is completed, the gas extraction operation is finished.

6. The method for directional fracturing gas extraction using coiled tubing in combined well and surface mining as described in claim 5, characterized in that, Step 1, which involves determining the strata for directional long boreholes in the coal mine based on collected exploration and mine data, includes: For medium-hard coal seams with a hardness coefficient f > 1.0, the stratum for directional long boreholes is the coal seam. For soft and fractured coal seams with a hardness coefficient f≤1.0, the directional long boreholes are laid out in the roof strata 0.5~2.0 meters away from the top surface of the coal seam.

7. The method for directional fracturing gas extraction using coiled tubing in combined well and surface mining as described in claim 5, characterized in that, In the hydraulic fracturing operation, when sand gets stuck when the coiled tubing is pulled up after the construction of a fracturing section is completed, the third valve (91) and the fourth valve (92) are closed, and the first valve (71), the second valve (81) and the reverse circulation sand flushing pipe valve (101) are opened, so that the fracturing fluid entering the directional long borehole is discharged sequentially through the coiled tubing (4) and the reverse circulation sand flushing pipe (10).

8. The method for directional fracturing gas extraction using continuous tubing in mines as described in claim 5, characterized in that, The operating power of the downhole fracturing pump is determined by the following formula: In the formula: The power output of the downhole fracturing pump is expressed in watts (W). Frictional resistance of fracturing fluid flowing through the coiled tubing, measured in Pa; This represents the pressure required to extend formation fractures, measured in Pa. The flow rate of water supplied by the downhole fracturing pump to the coiled tubing is expressed in m³ / s.

9. The method for directional fracturing gas extraction using coiled tubing in combined well and surface mining as described in claim 8, characterized in that, The frictional resistance of the fracturing fluid flowing through the coiled tubing is determined by the following formula: In the formula: This refers to the density of the fracturing fluid, expressed in kg / m³. 3 ; The winding length of the continuous tube is expressed in meters (m). This is the inner diameter of the continuous tube, in meters (m). This is the Reynolds number of the fracturing fluid flowing in the coil.

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