WO2024087965A1 - Well-ground combined mining coiled tubing directional fracturing gas extraction system and method - Google Patents

Abstract

A well-ground combined mining coiled tubing directional fracturing gas extraction system and method. The extraction method comprises the following steps: constructing at least one directional long drill hole in a determined layout layer; putting a casing pipe in the first directional long drill hole, and fixing the hole; putting a fracturing fluid delivery pipe into a ground penetrating well to extend to an opening of the directional long drill hole; completing the assembly of a well-ground combined mining coiled tubing directional fracturing gas extraction system; performing a hydraulic sand blasting perforation operation in a first fracturing segment; after completing the hydraulic sand blasting perforation operation, supplementing water to a coiled tubing, in addition, delivering a fracturing fluid into the first fracturing segment by means of the above-well fracturing fluid delivery pipe and an underground confluence pipe, so as to complete the combined operation of hydraulic fracturing on the first fracturing segment and water supplement to the coiled tubing; completing the fracturing operation in the residual fracturing segments in the first directional long drill hole; after completing segmented fracturing construction of all directional long drill holes, performing pressure maintaining and blowout operations; and after finishing the blowout operation, completing a gas extraction operation.

Description

A continuous pipe directional fracturing gas extraction system and method for combined well and ground mining Technical Field

The present invention belongs to the technical field of coal mine gas extraction, relates to a gas extraction system, and specifically to a continuous pipe directional fracturing gas extraction system and method for combined well and ground mining.

Background technique

Ground continuous pipe vehicles can be used for hydraulic fracturing, hydraulic cutting, drilling and dredging, and underground coal gasification. However, it has not yet been promoted in coal mines. The main reason is that the working conditions in coal mines are harsh and the working space is limited. The existing combined underground continuous pipe directional fracturing gas extraction system is large in size and difficult to meet the requirements of limited space operations. Secondly, the combined underground continuous pipe directional fracturing gas extraction system needs to be designed for intrinsic safety and explosion-proof, and obtain coal safety certification. The ground continuous pipe vehicle is large in size, powerful, and has a long continuous pipe length. It cannot be simply reduced and applied to underground coal mines. Thirdly, the existing ground continuous pipe injection head is large in size and cannot meet the requirements of underground coal mine working space. It is a vertical structure design and is only suitable for the injection of vertical hole continuous pipes.

In response to the demand for continuous pipe operations in mines, researchers have developed some combined underground and underground continuous pipe directional fracturing gas extraction systems. However, existing continuous pipe operation machines for coal mines have the following problems: (1) The equipment such as the drum and injection head with continuous pipes does not have the ability to move automatically, and these equipment are heavy and difficult to carry underground in coal mines; (2) The equipment such as the drum and injection head with continuous pipes mainly relies on flatbed trucks for transportation and cannot be transported to locations where no rails are laid, limiting the scope of use of the equipment; (3) Continuous pipe operation equipment requires complex assembly and installation operations underground in coal mines, and the underground working environment of coal mines is complex, which will increase the underground coal mine operation environment. Workers' work intensity; (4) According to general design standards, the roller axis diameter should be at least 40 times the outer diameter of the coiled tubing to ensure the service life of the coiled tubing. Limited by the size of the coiled tubing roller, the size of the coiled tubing operation equipment is often too high to be transported through tank cages, air gates, etc., and the capacity of the coiled tubing roller cannot be guaranteed. If the axis diameter is reduced, the coiled tubing will undergo plastic deformation, reducing the service life of the coiled tubing; (5) The existing operation method uses ground pumping of fracturing fluid to the long borehole orifice for diversion. During the annular sand fracturing stage, the diverted sand-carrying fluid carries the proppant into the coiled tubing, which will continuously wear the coiled tubing and the sandblasting perforating gun, shortening the service life of the system.

Summary of the invention

In view of the defects and shortcomings in the prior art, the present invention provides a combined underground mining continuous tubing directional fracturing gas extraction system and method to solve the technical problems of the prior art that the combined underground mining continuous tubing extraction system is inconvenient to use and has a short service life.

In order to achieve the above object, the present invention adopts the following technical scheme:

A continuous pipe directional fracturing gas extraction system for underground combined mining, comprising a drum device, a hole dynamic sealing device and a downhole fracturing pump;

The roller device comprises a first transport mechanism and a continuous tube roller mechanism arranged on the first transport mechanism, the continuous tube roller mechanism comprises a roller skid and a roller body arranged in the roller skid, and the continuous tube is wound on the roller body;

The orifice dynamic sealing device comprises a second transport mechanism and an injection head and a blowout prevention box connected to the second transport mechanism; at least two hydraulic lifting mechanisms for adjusting the height and inclination angle of the injection head are arranged below the injection head; the blowout prevention box is connected to an orifice device arranged at the orifice of a downhole directional long drilling hole, and a front-to-back through-moving space is arranged inside the injection head, the blowout prevention box and the orifice device, and the continuous pipe can reciprocate back and forth in the moving space driven by the injection head;

The coiled tubing is also connected to an uphole high-pressure pump and a downhole fracturing pump respectively.

The present invention also has the following technical features:

Specifically, the orifice device includes an annular blowout preventer and an orifice spool that are connected and arranged, and the annular blowout preventer can be sealed and connected to the blowout preventer box;

The orifice four-way is also connected with a gas negative pressure extraction pipeline and a downhole confluence pipeline respectively, and the downhole confluence pipeline is connected with the uphole fracturing fluid delivery pipeline and the downhole water supply pipeline respectively; the downhole confluence pipeline is provided with a first valve; the uphole fracturing fluid delivery pipeline is provided with a second valve for adjusting the flow rate of fracturing fluid, the downhole water supply pipeline is also provided with a third valve and a fourth valve for adjusting the water supply flow rate of the continuous pipe, the downhole water supply pipeline is also connected with a reverse circulation sand flushing pipeline, and the reverse circulation sand flushing pipeline is provided with a reverse circulation sand flushing pipeline valve.

Furthermore, the first transport mechanism includes a first hydraulic crawler chassis and a first support plate arranged above the first hydraulic crawler chassis; the second transport mechanism includes a second hydraulic crawler chassis and a second support plate arranged above the second hydraulic crawler chassis.

Furthermore, the drum body is rotatably arranged on a drum bracket, a pipe arranging device for arranging continuous pipes is also arranged on the drum bracket, and the high-pressure rotary joint is arranged on the drum body.

Furthermore, a gooseneck guide is provided on the side wall of the injection head facing the roller bracket.

The present invention also protects a method for extracting gas by directional fracturing of a continuous pipe for combined underground and underground mining. The method is implemented by the above-mentioned continuous pipe directional fracturing gas extraction system for combined underground and underground mining, and comprises 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 borehole set in the coal mine according to the collected exploration data and mine data, and construct at least one directional long borehole in the determined layout layer. Drill holes long;

Step 2, inserting casing into the first directional long borehole and then consolidating the hole;

Step 3, constructing a ground through-hole on the ground to connect it with the underground tunnel of the coal mine, after casing and cementing the ground through-hole, a fracturing fluid delivery pipeline is lowered into the ground through-hole and extended to the opening of the directional long drilling hole;

Step 4: Select a downhole fracturing pump according to the operating power of the downhole fracturing pump, adjust the height and inclination of the injection head, make the blowout preventer box seal and the annular blowout preventer dock, and then complete the assembly of the well-ground combined mining continuous tubing directional fracturing gas extraction system;

Step 5, start the wellbore high-pressure pump, open the second valve and the third valve, and close the first valve, the fourth valve and the reverse circulation sand flushing pipeline valve to perform hydraulic sandblasting perforation operation in the first fracturing stage;

Step 6: After the hydraulic sandblasting perforation operation is completed, the third valve is closed, the fourth valve is opened to replenish water to the coiled tubing, and the first valve is opened at the same time, and the fracturing fluid is transported to the first fracturing section by means of the uphole fracturing fluid delivery pipeline and the downhole confluence pipeline, so as to complete the hydraulic fracturing of the first fracturing section and the combined operation of replenishing water to the coiled tubing;

Step 7, after completing the hydraulic fracturing operation of the first fracturing stage, recover the coiled tubing to the next fracturing stage, repeat steps 5 to 6, and complete the fracturing operation of the remaining fracturing stages in the first directional long borehole;

Step 8, repeating steps 4 to 7, performing staged fracturing construction on the remaining directional long boreholes in sequence or alternately, and performing pressure maintenance and blowdown operations after completing the staged fracturing construction of all directional long boreholes;

Step 9: After the spraying operation is completed, the gas extraction operation is completed.

Furthermore, the step 1 of determining the layout layer of the directional long borehole set in the coal mine according to the collected exploration data and mine data includes:

For medium-hard coal seams with a coal seam hardness coefficient f>1.0, the directional long drilling hole is set in the coal seam;

For broken and soft coal seams with a coal seam hardness coefficient of f≤1.0, the layout layer of the directional long drill holes is the roof rock layer 0.5 to 2.0 meters away from the top surface of the coal seam.

Furthermore, in the hydraulic fracturing operation, when sand jam occurs when the coiled tubing is lifted up after the construction of one fracturing section is completed, the third valve and the fourth valve are closed, and the first valve, the second valve and the reverse circulation sand flushing pipeline valve are opened, so that the fracturing fluid entering the directional long borehole is discharged in sequence through the coiled tubing and the reverse circulation sand flushing pipeline.

Furthermore, the operating power of the downhole fracturing pump is determined by the following formula:
P = (Δp + p _extension ) × Q

Where:

P is the operating power of the downhole fracturing pump, in W;

Δp is the friction resistance of the fracturing fluid flowing through the coiled tubing, in Pa;

p _extension is the formation fracture extension pressure, in Pa;

Q is the flow rate of water supplied to the coiled tubing by the downhole fracturing pump, m ³ /s.

Furthermore, the friction resistance of the fracturing fluid flowing through the coiled tubing is determined by the following formula:

Where:

ρ is the density of the fracturing fluid, in kg/m ³ ;

L is the winding length of the coiled tube, in meters;

d is the inner diameter of the continuous tube, in m;

Re is the Reynolds number of the fracturing fluid flowing in the coiled tubing.

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

(1) The roller device and the orifice dynamic sealing device in the system of the present invention are assembled in a split manner. The single device is small in size and easy to transport. It can be transported through a coal mine cage or an inclined shaft. Since a first transport mechanism and a second transport mechanism with automatic walking capability are provided, there is no need to rely on manpower for transportation, thereby reducing the labor intensity of workers underground in the coal mine. In addition, the device does not rely on rail transportation and can reach locations where no rails are laid for operation, thereby improving the convenience and scope of use of the device.

(2) The coiled tube drum mechanism and the first transport mechanism in the system of the present invention are detachably connected. This structure ensures that the coiled tube winding length is guaranteed and that the height limit requirement of the transport is not exceeded during the transport of the operating equipment.

(3) The system of the present invention provides a downhole fracturing pump to replenish the coiled tubing. On the one hand, it can prevent the annular fluid from squeezing the coiled tubing, which would lead to a reduction in the inner diameter of the coiled tubing, an increase in the flow friction of the fracturing fluid, an increase in the injection pressure, and even an extrusion force that exceeds the anti-external squeeze strength of the coiled tubing and destroys the coiled tubing. On the other hand, it can prevent the proppant from entering the coiled tubing during the diversion of the sand-carrying fluid and wearing out the coiled tubing and the sandblasting perforating gun, and can effectively avoid the complex control of the pressure and flow at the diversion point, thereby realizing the systematic operation of uphole perforation, uphole sand fracturing and downhole water replenishment.

(4) The system of the present invention is provided with a reverse circulation sand flushing pipeline. When the coiled tubing is pulled up and encounters sand jam, the reverse circulation well washing operation can be implemented by switching the valve, so that the coiled tubing can be lifted up after reverse circulation sand flushing and unblocking, thus solving the problem of only It can solve the problems of continuous tubing breakage, injection head pulling force exceeding limit, injection head failure, etc. caused by hard pulling of continuous tubing with the injection head.

(5) The method of the present invention pumps the fracturing fluid into the well through the surface, thus avoiding the complicated process of mixing sand in the coal mine. The addition of sand before the pump can make the proppant in the fracturing fluid obtain an initial velocity close to that of the fracturing fluid, which can increase the suspended migration distance when it migrates in the pipeline. It realizes the large-volume joint injection of the well and the well, effectively solving the problem that the existing fracturing construction displacement cannot be increased. The joint injection displacement of the well high-pressure pump and the downhole fracturing pump can exceed 7m3/min. It realizes the joint operation of orifice pressure perforating, annulus injection fracturing and continuous pipe water replenishment, and finally realizes the rapid and safe transportation of ground fracturing fluid and downhole supplementary liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the overall structure of the system of the present invention;

FIG2 is a schematic diagram of a partial structure of the present invention;

Figure 3 is a schematic diagram of the structure of the roller device;

FIG4 is a schematic structural diagram of a dynamic sealing device for an orifice;

FIG5 is a flow chart of the method of the present invention.

Meaning of reference numerals:
1- roller device, 2- orifice dynamic sealing device, 3- downhole fracturing pump, 4- continuous pipe, 5- orifice device, 6- gas negative pressure extraction pipeline, 7- downhole confluence pipeline, 8- uphole fracturing fluid delivery pipeline, 9- downhole water supply pipeline, 10- reverse circulation sand flushing pipeline;
11-first transport mechanism, 12-roller mechanism; 21-second transport mechanism, 22-injection head, 23-spray prevention box; 51-
Annular blowout preventer, 52-orifice four-way; 71-first valve, 81-second valve, 91-third valve, 92-fourth valve;
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 ways

It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

The terms "upper", "lower", "front", "back", "top", "bottom", etc. used in the present invention to indicate directions or positional relationships are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. "Inside" and "outside" refer to the inside and outside of the contour of the corresponding components, and the above terms should not be understood as limitations on the present invention.

In addition, the terms "first", "second", etc., ordinal numbers are used only for descriptive purposes and should not be understood as indicating or implying The term "first" or "second" may indicate relative importance or implicitly indicate the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features.

In the present invention, unless otherwise specified, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, or a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

Example 1

According to the above technical solution, as shown in FIG. 1 to FIG. 3 , this embodiment provides a combined underground mining continuous pipe directional fracturing gas extraction system, including a drum device 1 , a borehole dynamic sealing device 2 and a downhole fracturing pump 3 ;

The drum device 1 includes a first transport mechanism 11 and a continuous tube drum mechanism 12 disposed on the first transport mechanism 11. The continuous tube drum mechanism 12 includes a drum skid 121 and a drum body 122 disposed in the drum skid 121. The continuous tube 4 is wound around the drum body 122. The drum body 122 can realize the collection and release and pipe arrangement of the continuous tube 4. The first transport mechanism 11 is detachably connected to the continuous tube drum mechanism 12, which reduces the size and overall height of the drum device 1, and is conducive to underground transportation in coal mines.

The orifice dynamic sealing device 2 includes a second transport mechanism 21 and an orifice sealing assembly arranged on the second transport mechanism 21, and the orifice sealing assembly includes an injection head 22 and a blowout prevention box 23 which are connected and arranged; the injection head 22 is used to provide power for the retraction and extension of the coiled tube 4 to realize the pressure-drag of the coiled tube 4, and at least two hydraulic lifting mechanisms 221 for adjusting the height and inclination angle of the injection head 22 are arranged below the injection head 22; the blowout prevention box 23 is connected to the orifice device 5 arranged at the orifice, and a moving space which is connected front to back is arranged in the injection head 22, the blowout prevention box 23 and the orifice device 5, and the coiled tube 4 can reciprocate back and forth in the moving space driven by the injection head 22.

In this embodiment, the coiled tubing 4 is also connected to an on-site high-pressure pump even on the ground and a downhole fracturing pump 3 arranged in the tunnel through a high-pressure rotary joint arranged 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 add liquid, such as high-pressure water, to the coiled tubing 4 during hydraulic fracturing to avoid squeezing of the coiled tubing 4 by the liquid flow flowing through the annulus between the directional long borehole casing and the coiled tubing 4 during the hydraulic fracturing process, and also to avoid wear of the spray gun of the directional segmented fracturing tool string due to sand passing through the coiled tubing 4 during the hydraulic fracturing process, thereby extending the service life of the segmented fracturing tool string.

As a preferred solution of this embodiment, the orifice device 5 includes an annular blowout preventer 51 and an orifice spool 52 which are connected and arranged, and the annular blowout preventer 51 is sealedly connected to the blowout preventer box 23;

The orifice spool 52 is also connected to a gas negative pressure extraction pipeline 6 and an underground confluence pipeline 7. 7 can be a high-pressure hose or steel pipe. The downhole confluence pipe 7 is connected to the uphole fracturing fluid delivery pipe 8 and the downhole water supply pipe 9 respectively. The liquid flowing into the downhole confluence pipe 7 through the uphole fracturing fluid delivery pipe 8 can enter the annulus of the long borehole casing and the continuous pipe 4; then, the fluid in the downhole water supply pipe 9 can be sent to the segmented fracturing tool string through the continuous pipe 4. A first valve 71 is arranged on the downhole confluence pipe 7; a second valve 81 for adjusting the flow rate of the fracturing fluid is arranged on the uphole fracturing fluid delivery pipe 8, and a third valve 91 and a fourth valve 92 for adjusting the flow rate of the continuous pipe are also arranged on the downhole water supply pipe 9. A sand flushing pipe 10 is also connected to the downhole water supply pipe 9, and a sand flushing valve 101 is arranged on the sand flushing pipe 10. The valves in this embodiment are all remote-controlled plug valves.

If sand is stuck during the process of lifting 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 liquid flows into the annulus through the tool string into 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, finally realizing reverse circulation well washing.

As a preferred solution of this embodiment, the first transport mechanism 11 includes a first hydraulic crawler chassis 111 and a first support plate 112 arranged above the first hydraulic crawler chassis 111; the second transport mechanism 21 includes a second hydraulic crawler chassis 211 and a second support plate 212 arranged above the second hydraulic crawler chassis 211.

As a preferred solution of this embodiment, the drum body 122 is rotatably arranged on the drum bracket 123, and the rolling bracket 123 is also provided with a pipe discharger 124 for discharging the continuous pipe 4. A high-pressure rotary joint is arranged on the drum body 122, and a high-pressure hose is connected to the high-pressure rotary joint. The high-pressure hose is respectively connected to the uphole high-pressure pump and the downhole fracturing pump through a tee, that is, the high-pressure hose is respectively connected to the downhole water supply pipeline 9 and the uphole fracturing fluid delivery pipeline 8 through the tee.

As a preferred solution of this embodiment, a gooseneck guide 222 is further provided on the side wall of the outer shell 221 facing the roller bracket 123, and the gooseneck guide 222 is used for guiding the continuous tube transportation.

The process of using this system is as follows:

After the orifice spool is installed, the drum device 1, the orifice dynamic sealing device 2 and the downhole fracturing pump 3 are assembled on site in the underground coal mine tunnel, and the continuous pipe 4 wound on the drum body 122 and connected to the tool string at the head end is sent into the orifice through the pipe arranger 124, the gooseneck guide 222, the injection head 22 and the blowout preventer box 23.

During hydraulic perforation: the jet liquid is sent from the ground along the pipeline into the coiled tubing 4 to start the perforation operation. After the perforation operation is completed, the sand-added fracturing fluid is sent into the annulus in the directional long borehole through the pipeline through valve switching to perform hydraulic fracturing. While the hydraulic fracturing is being performed, the downhole fracturing pump 3 replenishes liquid into the coiled tubing 4 to prevent the coiled tubing 4 from being squeezed and deformed by the liquid flow in the annulus, resulting in a smaller liquid flow channel in the coiled tubing 4.

Example 2

This embodiment discloses a method for extracting gas by directional fracturing of a continuous pipe for underground combined mining. The method is implemented by the system for extracting gas by directional fracturing of a continuous pipe for underground combined mining disclosed in Example 1. The method is applied to a coal mine in Huaibei. The target coal seam in this mine is a high-gas outburst coal seam. In order to improve the efficiency of gas extraction, a joint well-ground operation mode is used to achieve efficient regional gas control.

The specific steps include:

Step 1, collecting exploration data and mine data of the target mining area, and determining the layout layer of the directional long drill hole set in the coal mine according to the collected exploration data and mine data, and constructing at least one directional long drill hole in the determined layout layer;

For medium-hard coal seams with a coal seam hardness coefficient f>1.0, the directional long drilling hole is set in the coal seam;

For broken and soft coal seams with a coal seam hardness coefficient of f≤1.0, the layout layer of the directional long drill holes is the roof rock layer 0.5 to 2.0 meters away from the top surface of the coal seam.

In this embodiment, the drilling field is expanded on one side of the tunnel, and the drilling field depth is 4.0m. Then, a directional long borehole is constructed from the coal seam floor tunnel to the coal seam roof, and the drilling trajectory is controlled in the rock layer of the coal seam roof. The final hole depth of the directional long borehole is 300m, and the vertical distance between the directional long borehole and the coal seam top is 1 to 1.5m.

During the drilling process of directional long boreholes, the borehole inclination angle is controlled to be less than 10° and the deflection intensity is not greater than 0.1°/m.

Step 2, inserting casing into the first directional long borehole to fix the hole;

Conventional mud was used to displace cement to the hole mouth and waited for 48 hours. Then the sonic logging instrument was pushed by the drilling rig to evaluate the quality of the horizontal section cementing.

Step 3, constructing a ground through-hole on the ground to connect it with the underground tunnel of the coal mine, after casing and cementing the ground through-hole, a fracturing fluid delivery pipeline is lowered into the ground through-hole and extended to the opening of the directional long drilling hole;

In actual operation, the ground through well can use the existing cable holes or hydrological observation holes in the coal mine; the well location of the ground through well should avoid the collapse area, and the ground through well can use vertical wells or directional wells. The ground through well can use casing as the liquid passage, or a fracturing fluid delivery pipeline can be lowered into the wellbore as the liquid passage.

In this embodiment, the ground through well adopts a three-opening wellbore structure, with a first-opening drill bit of Φ444.5mm, a surface casing of Φ339.7mm, a second-opening drill bit of Φ311.1mm, a technical casing of Φ244.5mm, and a third-opening drill bit of 215.9mm, without casing. A fracturing fluid delivery pipeline is lowered into the ground through well.

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

Step 4: select a downhole fracturing pump according to the operating power of the downhole fracturing pump, adjust the height and inclination of the injection head 22, make the blowout preventer box 23 seal and dock with the annular blowout preventer 51, and then complete the assembly of the underground combined mine continuous pipe directional fracturing gas extraction system; specifically, the tool string is assembled underground in the coal mine, and is manually sent into the orifice, and the continuous pipe is connected. The front end of the extension pipe is connected to the tail end of the tool string; the height and inclination of the injection head 22 are adjusted using the hydraulic lifting mechanism 221, and the blowout preventer box at the head end of the injection head 22 is tightly docked with the end of the annular blowout preventer 51 to complete the equipment assembly.

For water replenishment operation, the density of water is 1000kg/m ³ , the displacement is 0.8m ³ /min, i.e. 0.0133m ³ /s, the length of the coiled tube 4 wound on the drum body 122 is 300m, the outer diameter of the coiled tube 4 is 38.1mm, and the inner diameter is 32.1mm. The friction resistance of water flowing through the wound coiled tube is calculated to be 44.17MPa. The formation fracture extension pressure is 13.5MPa, and the power of the required pump for replenishment is calculated to be: 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, so in this embodiment, a underground fracturing pump with a power of 800KW is selected.

The operating power of the downhole fracturing pump 3 determines the ability of the downhole fracturing pump to replenish water into the coiled pipe 4, which can avoid the problem of not being able to achieve the designed water replenishment displacement or insufficient water replenishment pressure due to the inability of the downhole fracturing pump 3 to meet the needs during the construction process. If the water replenishment displacement is insufficient, the fracturing construction cannot reach the designed total displacement, affecting the final fracturing construction effect. If the water replenishment pressure is insufficient, the coiled pipe will be subjected to external squeezing force from the annular fracturing fluid. On the one hand, there is a risk of reducing the service life of the coiled pipe and squeezing and destroying the coiled pipe. On the other hand, during use, the coiled pipe is squeezed by the external liquid and the internal diameter is reduced, which will further increase the friction resistance of the fracturing fluid flow, and it is easy to cause overpressure danger, which is not conducive to safe construction operations.

Step 5: Start the wellbore 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 perform hydraulic sandblasting perforation operation in the first fracturing stage;

Step 6: After the hydraulic sandblasting perforation operation is completed, the third valve 91 is closed, the fourth valve 92 is opened to replenish water to the coiled tubing 4, and the first valve 71 is opened at the same time, and the fracturing fluid is transported to the first fracturing section by means of the uphole fracturing fluid delivery pipeline 8 and the downhole confluence pipeline 7, so as to complete the hydraulic fracturing of the first fracturing section and the combined operation of replenishing water to the coiled tubing;

The displacement during the coiled tubing water replenishment operation is 0.8m ³ /min, without adding sand; the hydraulic fracturing displacement of the first fracturing stage is 7m ³ /min, and the sand ratio is 6% to 13%.

Step 7, after completing the hydraulic fracturing operation of the first fracturing section, recycle the coiled tubing 4 to the next fracturing section, repeat steps 3 to 4, and complete the fracturing operation of the remaining fracturing sections in the first directional long borehole;

Step 8, repeating steps 2 to 7, performing staged fracturing construction on the remaining directional long boreholes in sequence or alternately, and performing pressure maintenance and blowdown operations after completing the staged fracturing construction of all directional long boreholes;

In the above hydraulic fracturing operation, when the fracturing of the previous section is completed and the packer is released to lift the coiled tubing for fracturing the next section, sand jam may occur and the coiled tubing cannot be lifted. If the injection head 22 is used to pull the coiled tubing hard, the coiled tubing may be broken, the injection head tension exceeds the limit, the injection head fails, and other problems may occur.

At this time, 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 pipeline valve 101 are opened, so that the fracturing fluid entering the directional long borehole passes through the coiled tubing 4 and the reverse circulation sand flushing pipeline valve 101 in sequence. After the blocked sand is flushed out, the injection head 22 can normally lift the coiled tubing 4, which solves the problems in the prior art that the coiled tubing 4 can only be pulled hard by the injection head 22 when sand is stuck, which may cause the coiled tubing 4 to break, the injection head 22 to exceed the pulling force limit, and the injection head 22 to fail.

Step 9: After the spraying operation is completed, the gas extraction operation is completed.

The method of the present invention avoids the complicated process of sand mixing in coal mines by pumping fracturing fluid on the ground, and the addition of sand before the pump can make the fracturing fluid proppant obtain an initial velocity close to that of the fracturing fluid, and can increase the suspended migration distance when migrating in the pipeline, effectively solving the technical problem that the displacement of the fracturing fluid cannot be increased in the existing fracturing construction operation, and realizes the large displacement joint injection of the well and the well. Through the joint injection of the well high-pressure pump and the downhole fracturing pump, the injection displacement can exceed ^7m3 /min; the joint operation of orifice pressure perforation, annulus injection fracturing and continuous pipe water replenishment is realized, and finally the rapid and safe transportation of the ground fracturing fluid and the downhole supplementary liquid is realized.

The above implementation process is only an example for clearly explaining the present application, and is not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the scope of protection of this application.

Claims (10)

1. A continuous pipe directional fracturing gas extraction system for underground combined mining, comprising a drum device (1), characterized in that it also comprises a borehole dynamic sealing device (2) and a downhole fracturing pump (3);

   The roller device (1) comprises a first transport mechanism (11) and a continuous tube roller mechanism (12) arranged on the first transport mechanism (11); the continuous tube roller mechanism (12) comprises a roller skid (121) and a roller body (122) arranged in the roller skid (121); a continuous tube (4) is wound around the roller body (122);

   The orifice dynamic sealing device (2) comprises a second transport mechanism (21) and an orifice dynamic sealing assembly arranged on the second transport mechanism (21), the orifice dynamic sealing assembly comprising an injection head (22) and a blowout prevention box (23) which are connected and arranged; at least two hydraulic lifting mechanisms (221) for adjusting the height and inclination angle of the injection head (22) are arranged below the injection head (22); the blowout prevention box (23) is connected to an orifice device (5) arranged at the orifice of a downhole directional long borehole, and a front-to-back through-moving space is arranged inside the injection head (22), the blowout prevention box (23) and the orifice device (5), and the continuous pipe (4) can make a front-to-back reciprocating motion in the moving space under the drive of the injection head (22);

   The coiled tubing (4) is also connected to an uphole high-pressure pump and a downhole fracturing pump (3) respectively.
2. The continuous tubing directional fracturing gas extraction system for underground combined mining as claimed in claim 1 is characterized in that the orifice device (5) comprises an annular blowout preventer (51) and an orifice spool (52) connected and arranged, and the annular blowout preventer (51) can be sealed and connected to the blowout preventer box (23);

   The orifice spool (52) is also connected to a gas negative pressure extraction pipeline (6) and a downhole confluence pipeline (7), respectively. The downhole confluence pipeline (7) is connected to an uphole fracturing fluid delivery pipeline (8) and a downhole water supply pipeline (9), respectively. The downhole confluence pipeline (7) is provided with a first valve (71). The uphole fracturing fluid delivery pipeline (8) is provided with a second valve (81) for adjusting the flow rate of the fracturing fluid. The downhole water supply pipeline (9) is also provided with a third valve (91) and a fourth valve (92) for adjusting the flow rate of the continuous pipe water supply. The downhole water supply pipeline (9) is also connected to a reverse circulation sand flushing pipeline (10), and the reverse circulation sand flushing pipeline (10) is provided with a reverse circulation sand flushing pipeline valve (101).
3. The continuous tubing directional fracturing gas extraction system for combined underground and underground mining as described in claim 1 is characterized in that the first transport mechanism (11) includes a first hydraulic crawler chassis (111) and a first support plate (112) arranged above the first hydraulic crawler chassis (111); the second transport mechanism (21) includes a second hydraulic crawler chassis (211) and a second support plate (212) arranged above the second hydraulic crawler chassis (211).
4. The continuous pipe directional fracturing gas extraction system for combined well and ground mining as claimed in claim 1 is characterized in that the drum body (122) is rotatably arranged on a drum support (123), and a pipe loader (124) for discharging the continuous pipe (4) is also arranged on the drum support (123), and the high Press swivel joint.
5. The continuous pipe directional fracturing gas extraction system for underground combined mining as described in claim 1 is characterized in that a gooseneck guide (222) is also provided at one end of the injection head (22) facing the roller bracket (123).
6. A method for extracting gas by directional fracturing of a continuous pipe for combined underground mining, characterized in that the method is implemented by the continuous pipe directional fracturing gas extraction system for combined underground mining as claimed in any one of claims 1 to 5, comprising the following steps:

   Step 1, collecting exploration data and mine data of the target mining area, and determining the layout layer of the directional long drill hole set in the coal mine according to the collected exploration data and mine data, and constructing at least one directional long drill hole in the determined layout layer;

   Step 2, inserting casing into the first directional long borehole and then consolidating the hole;

   Step 3, constructing a ground through-hole on the ground to connect it with the underground tunnel of the coal mine, after casing and cementing the ground through-hole, a fracturing fluid delivery pipeline is lowered into the ground through-hole and extended to the opening of the directional long drilling hole;

   Step 4: select a downhole fracturing pump according to the operating power of the downhole fracturing pump, adjust the height and inclination of the injection head (22), make the blowout preventer box (23) and the annular blowout preventer (51) seal and dock, and then complete the assembly of the well-ground combined mining continuous pipe directional fracturing gas extraction system;

   Step 5: start the wellbore 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), and perform hydraulic sandblasting perforation operation in the first fracturing stage;

   Step 6: After the hydraulic sandblasting and perforating operation is completed, the third valve (91) is closed, and the fourth valve (92) is opened to replenish water into the coiled tubing (4). At the same time, the first valve (71) is opened to transport the fracturing fluid into the first fracturing section via the uphole fracturing fluid delivery pipeline (8) and the downhole confluence pipeline (7), thereby completing the combined operation of hydraulic fracturing and coiled tubing water replenishment for the first fracturing section.

   Step 7, after completing the hydraulic fracturing operation of the first fracturing section, retrieving the coiled tubing (4) to the next fracturing section, repeating steps 5 to 6, and completing the fracturing operation of the remaining fracturing sections in the first directional long borehole;

   Step 8, repeating steps 4 to 7, performing staged fracturing construction on the remaining directional long boreholes in sequence or alternately, and performing pressure maintenance and blowdown operations after completing the staged fracturing construction of all directional long boreholes;

   Step 9: After the spraying operation is completed, the gas extraction operation is completed.
7. The method for gas extraction by directional fracturing of continuous pipe for underground combined mining as claimed in claim 6 is characterized in that the step 1 of determining the layout layer of the directional long borehole set in the underground coal mine according to the collected exploration data and mine data comprises:

   For medium-hard coal seams with a coal seam hardness coefficient f>1.0, the directional long drilling hole is set in the coal seam;

   For broken and soft coal seams with a coal seam hardness coefficient of f≤1.0, the layout layer of the directional long drill holes is the roof rock layer 0.5 to 2.0 meters away from the top surface of the coal seam.
8. The method for gas extraction by directional fracturing of continuous tubing for combined well-ground mining as described in claim 6 is characterized in that, during the hydraulic fracturing operation, when sand jam occurs when the continuous tubing is lifted 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 pipeline valve (101) are opened, so that the fracturing fluid entering the directional long borehole is discharged in sequence through the continuous tubing (4) and the reverse circulation sand flushing pipeline (10).
9. The method for gas extraction by directional fracturing of continuous pipe for underground combined mining according to claim 6 is characterized in that the operating power of the underground fracturing pump is determined by the following formula:
   P = (Δp + p _extension ) × Q

   Where:

   P is the operating power of the downhole fracturing pump, in W;

   Δp is the friction resistance of the fracturing fluid flowing through the coiled tubing, in Pa;

   p _extension is the formation fracture extension pressure, in Pa;

   Q is the flow rate of water supplied to the coiled tubing by the downhole fracturing pump, m ³ /s.
10. The method for gas extraction by directional fracturing of continuous pipe for underground combined mining as claimed in claim 9 is characterized in that the friction resistance of the fracturing fluid flowing through the continuous pipe is determined by the following formula:
    

    Where:

    ρ is the density of the fracturing fluid, in kg/m ³ ;

    L is the winding length of the coiled tube, in meters;

    d is the inner diameter of the continuous tube, in m;

    Re is the Reynolds number of the fracturing fluid flowing in the coiled tubing.