Coal mine nearly-horizontal coiled tubing casing drilling injection head device

Abstract

The invention is suitable for the technical field of coal mine underground extraction drilling, and provides a coal mine nearly-horizontal coiled tubing casing drilling injection head device which adopts a double-injection-head execution system composed of a coiled tubing injection head and a casing injection head and a control system based on an anti-explosion computer and a PLC. The mode that torque or current control follows speed control is adopted by the control system, the two injection heads are driven to work cooperatively, and the continuous pipe and the PVC sleeve arranged outside the continuous pipe in a sleeving mode are synchronously pushed into a drill hole. After drilling is completed, the diameter-reducing eccentric drill bit connected to the front end of the casing pipe is reduced through electric control and is separated from the casing pipe, then the continuous pipe and the drill bit are pulled out, and the casing pipe is permanently reserved in a hole to complete hole fixing. Drilling and fixing synchronous operation is achieved, the problems of hole forming and hole protecting of the continuous pipe drilling machine in the soft coal seam are effectively solved, and the drilling utilization rate, the gas extraction efficiency and the operation safety are improved.

Description

Technical Field

[0001] This invention belongs to the field of underground coal mine drilling technology, and particularly relates to a coal mine near-horizontal continuous casing drilling injection head device. Background Technology

[0002] Under the conditions of high ground stress, high gas content, and high temperature and pressure in deep coal mines, the coal mine and its surrounding rock soften due to strain, resulting in reduced formation stability. This makes it difficult to form gas drainage boreholes, leading to short gas drainage cycles, low borehole utilization, and significant safety hazards.

[0003] Compared to the single-joint segmented drill pipes commonly used in coal mines, coiled tubing can withstand higher internal pressure. This characteristic facilitates technologies such as high-pressure jets carrying drill cuttings and screw motors driving drill bits for high-speed rock cutting, giving it a unique advantage in drilling through soft coal seams. However, unlike segmented rotary drilling rigs which have relatively mature hole-holding technologies, coiled tubing near-horizontal drilling rigs are a relatively new product, and there is currently no dedicated hole-holding technology to address borehole collapse issues.

[0004] While existing drilling and screen-down technology has achieved hole-stabilizing capabilities to some extent, it struggles to reach deep holes. Subsequent developments in hole-stabilizing technologies such as screen-down completion, casing drilling, and casing drilling can ensure drilling depth, but these are only applicable to rigs using segmented rotary drilling. Therefore, there is an urgent need to develop a hole-stabilizing device suitable for near-horizontal coiled tubing drilling rigs. Summary of the Invention

[0005] The purpose of this invention is to provide a near-horizontal continuous casing drilling injection head device for coal mines, which aims to solve the technical problems of difficult drilling, difficult hole consolidation, and low drilling utilization rate in deep soft coal seams.

[0006] This invention is implemented as follows: a drilling injection head device for near-horizontal coiled tubing and casing in coal mines. The device mainly comprises two parts: an execution system and a control system. The execution system employs a dual-injection-head design, including a coiled tubing injection head and a casing injection head, used to clamp and drive the coiled tubing and casing respectively, achieving synchronous drilling and hardening. The coiled tubing injection head is located at the end furthest from the borehole opening, using a chain roller system to clamp and drive the coiled tubing for continuous drilling. It is specially designed with a constant load clamping device and a release mechanism based on the double-lever principle to provide stable clamping force and handle stuck drill bits. The casing injection head is located at the end closest to the borehole opening, used to clamp and synchronously advance the split PVC casing sleeved on the outside of the coiled tubing. The bottom end of the casing is connected to an electrically controllable, diameter-reducing eccentric drill bit via a casing shoe.

[0007] The control system is based on an explosion-proof downhole computer, which uses a PLC module to coordinate the control of the two injection heads. The system adopts a torque or current control followed by speed control mode, that is, the continuous tubing injection head drills at a set speed, while the casing injection head follows with a matching torque or current, ensuring that the two advance synchronously and avoiding mutual competition.

[0008] During drilling, the coiled tubing and casing are synchronously advanced into the hole under the drive of their respective injection heads. After drilling to the predetermined depth, an electrical control signal is sent to the drill bit at the bottom of the hole through the cable inside the coiled tubing, causing the eccentric drill bit to reduce its diameter and disconnect from the casing. Subsequently, the coiled tubing injection head reverses and withdraws the coiled tubing and drill bit, while the casing injection head remains clamped, leaving the casing intact in the borehole to form a permanent support channel and achieve hole solidification while drilling.

[0009] The present invention provides a drilling injection head device for near-horizontal continuous casing in coal mines, which has the following beneficial effects:

[0010] This invention employs a simultaneous casing and coiled tubing installation mode, solving the technical challenge of borehole stabilization in soft coal seams. Furthermore, the stabilization depth can extend throughout the entire borehole. Due to its continuous operation, the coiled tubing drilling rig offers higher operational efficiency than traditional segmented rotary drilling rigs. Based on the internal cable routing of the coiled tubing, its drilling-while-drilling (DWD) technology boasts greater scalability, facilitating in-situ acquisition and dynamic monitoring of geological data. Attached Figure Description

[0011] Figure 1 Schematic diagram of the continuous casing drilling injection head execution system;

[0012] Figure 2 A schematic diagram of the structure of a near-horizontal continuous casing drilling injection head device for coal mines provided by the present invention;

[0013] Figure 3 This is a schematic diagram of a split-type PVC sleeve;

[0014] Figure 4 A schematic diagram of a eccentric drill bit with a retractable diameter;

[0015] Figure 5 This is a schematic diagram of the working logic of the control system;

[0016] Figure 6 This is a block diagram of the continuous tube injection head speed feedback control.

[0017] Figure 7 Block diagram of the sleeve injection head torque / current feedback control;

[0018] Figure 8 A schematic diagram showing the range of drilling pressure and drill bit torque required for coal mine drilling;

[0019] Figure 9 This is a schematic diagram of the dynamic model of the casing drilling process;

[0020] Figure 10 A three-dimensional view of the dynamic simulation results of the casing drilling process;

[0021] Figure 11 This is a diagram showing the axial force distribution of the drill string during the casing drilling process.

[0022] In the attached diagram: 1. Double lever frame; 2. Slide rail; 3. Chain roller system; 4. Constant load clamping device; 5. Drive motor; 6. Chassis; 7. Base; 8. Double lever motor; 9. Unlocking mechanism; 10. Eccentric drill bit; 11. Casing; 12. Continuous tubing; 13. Casing shoe. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0025] In an embodiment of the present invention, the coal mine near-horizontal continuous casing drilling injection head device includes an execution system and a control system:

[0026] like Figure 1 As shown, the core of the execution system consists of two independent injection mechanisms: a coiled tubing injection head and a casing injection head. These are arranged sequentially along the drilling direction, forming a dual-injection-head system. The coiled tubing injection head is responsible for clamping and driving the coiled tubing located in the center; the casing injection head is responsible for clamping and driving the casing fitted outside the coiled tubing. This design allows the casing to provide additional tension to the bottom of the coiled tubing borehole, assisting drilling and ultimately leaving the casing inside the borehole to achieve hole solidification.

[0027] like Figure 2 As shown, the main body uses a chain roller system to clamp the continuous tube, driven by an active motor. To overcome the problem of chain tension fluctuations caused by traditional hydraulic cylinder clamping, which leads to alternating damage to the surface of the continuous tube, this invention designs a constant load clamping device. This device is independent of the chain roller drive system and is connected between the frame and the base, providing a continuous and stable clamping force for the continuous tube, effectively extending the tube's lifespan.

[0028] To address the problem of the continuous tubing being unable to rotate and unstick in horizontal drilling, two sets of unsticking mechanisms were arranged before and after the injection head. These mechanisms are mounted on a double-lever frame and driven by a double-lever motor. This mechanism utilizes the double-lever principle to amplify the thrust at the input end by tens of times, thereby driving the entire injection head to generate high-frequency axial vibration on the slide rail, thus loosening the stuck continuous tubing.

[0029] like Figure 3 As shown, the casing is made of modular PVC material, consisting of several non-perforated components assembled into an assembly with only a central through hole. PVC material has anti-static and flame-retardant properties, providing effective support for the borehole wall without affecting subsequent mining operations.

[0030] like Figure 4 As shown, the end of the casing near the bottom of the hole is fixed to a reducing-diameter eccentric drill bit via a casing shoe. During drilling, the outer diameter of the drill bit expands, pressing against the casing shoe and driving the casing forward synchronously. After drilling is completed, an electrical signal is sent to the drill bit via a cable built into the coiled tubing, triggering its internal mechanism to reduce the radial dimension of the drill bit (reducing its diameter), allowing it to disengage from the casing shoe. Subsequently, the coiled tubing, carrying the drill bit, withdraws from the center of the casing, while the casing is held in place by its injection head, permanently remaining in the borehole to complete the hole-fixing process.

[0031] The control system is a hardware and software system based on an explosion-proof downhole computer and PLC. It is responsible for receiving instructions, processing sensor data, and controlling the coordinated movement of the two injection heads, and is the key to achieving synchronous injection.

[0032] like Figure 5 As shown, the industrial control computer sends advanced instructions (such as start-up and target speed value) to the PLC. Based on these instructions, the PLC controls the frequency converters and drivers in the two injection heads, thereby driving their respective injection motors and clamping motors.

[0033] To achieve synchronization, the system employs a specific control mode:

[0034] The continuous tube injection head uses a speed control mode: such as Figure 6 As shown, the PLC calculates the control quantity based on the target speed value set by the industrial control computer and the actual value fed back by the speed sensor, ensuring that the continuous tube drills at a constant speed.

[0035] The sleeve injection head uses torque or current control follow mode: such as Figure 7 As shown, the PLC calculates the control quantity and adjusts the sleeve's propulsion force based on the target torque or current value set by the industrial control computer and the real-time value fed back by the torque or current sensor. Since force is the cause of changes in the motion state of an object, when the continuous tube injection head speed is stable, as long as the motor power is sufficient, the sleeve injection head will automatically adjust its output speed to follow the movement of the continuous tube, thereby achieving synchronization of the two propulsions and avoiding mutual struggle or tube damage caused by speed differences.

[0036] The complete working principle is as follows:

[0037] 1. Fix the device at the borehole opening position in the roadway.

[0038] 2. Connect the bottom end of the casing to the reducerable eccentric drill bit via the casing shoe.

[0039] 3. Starting device. In speed control mode, the coiled tubing injection head drives the coiled tubing and drill bit to rotate and drill; at the same time, in torque control mode, the casing injection head clamps the casing and pushes it into the hole synchronously with the coiled tubing.

[0040] 4. After drilling to the designed depth, an electrical signal is sent through the continuous inner cable to trigger the eccentric drill bit at the bottom of the hole to perform a diameter reduction action, thereby releasing the lock with the casing shoe.

[0041] 5. The coiled tubing injection head rotates in reverse, uniformly extracting the coiled tubing and the reduced-diameter drill bit from the casing. During this process, the casing injection head remains clamped, ensuring the casing remains stationary and within the entire borehole, forming a stable gas extraction channel.

[0042] Example 1:

[0043] To illustrate the technical feasibility of this invention, a method for using soft coal seams (Protodyakonov's robustness coefficient) is provided. Example of a design:

[0044] The bit-rock interaction model of Detournay and Defourny was used for estimation.

[0045] Drilling pressure From friction component and cutting components It consists of two parts, and its expression is:

[0046]

[0047] In the formula, The radius of the drill bit; The uniaxial compressive strength of coal is generally taken as 10 times the Protodyakonov coefficient, i.e. ; The number of blades in a PCD drill bit; Average wear length for each blade; This is the slope of the cutting force relative to the cutting surface, typically taken as 0.6-0.8; The inherent specific energy of the coal mine reflects the energy required to cut off a unit volume of coal. In this section, it is taken to be equal to the normal contact stress. The depth of cut per revolution for each blade can be determined by the mechanical feed rate. and drill bit speed Calculated, i.e. .

[0048] Drill bit torque Also composed of frictional components and cutting components It consists of two parts, and the expression is:

[0049]

[0050] In the formula, The spatial orientation of the blade wear plane. The coefficient of friction between coal and the drill bit is determined by the surface properties of the two objects in contact. The coefficient of friction between coal and metal is approximately 0.3-0.4.

[0051] The specific parameter settings are shown in Table 1:

[0052] Table 1 Calculation parameters for drilling pressure and drill bit torque

[0053] serial number Parameter name symbol value 1 Protodextral strength coefficient of coal mine 1 2 Coefficient of friction between coal and drill bit 0.4 3 PCD drill bit radius 47.625mm 4 PCD drill bit blade count 3 5 Average wear length per blade 1.2mm 6 The slope of the cutting force relative to the cutting surface 0.8 7 Spatial orientation of the blade wear plane 1.3 8 Mechanical drilling speed 1-40m / h 9 Drill bit speed 200-500rpm

[0054] Substituting these values, we can obtain the range of drilling pressure and drill bit torque for coal mine drilling operations, as follows: Figure 8 As shown, the drilling pressure ranges from 1.75 to 5.52 kN, and the drill bit torque ranges from 22.4 to 134.6 Nm, both of which are positively correlated with the mechanical drilling speed and negatively correlated with the drill bit rotation speed.

[0055] Furthermore, to ensure that the continuous tubing does not buckle in a long horizontal bore, its sinusoidal buckling critical load needs to be verified. For a tubular string constrained within a borehole, its critical load... The calculation expression is:

[0056]

[0057] in, These represent the Young's modulus, moment of inertia, effective density, and cross-sectional area of ​​the rod, respectively. It is the acceleration due to gravity. The well inclination angle is , which is in horizontal boreholes. Subtract the camber angle. This refers to the radial clearance between the rod and the hole wall, i.e., the annular space clearance.

[0058] As shown in the above formula, the sinusoidal critical load of the coiled tubing in coal mine boreholes is independent of the length of the coiled tubing. However, it should be noted that the above formula does not consider the influence of friction between the drill string and the borehole wall. If the drilling pressure is to remain constant, the injection head at the borehole opening will need to provide a greater axial force to overcome the frictional force exerted on the drill string by the borehole wall. This results in the drill string near the borehole opening experiencing a greater compressive axial force. Therefore, strictly speaking, the sinusoidal critical load of the drill string should consider the axial force near the borehole opening, i.e., the drilling pressure plus the total friction of the drill string. From this perspective, the length of the drill string is also one of the factors affecting whether the drill string buckles; that is, longer horizontal boreholes are more prone to drill string buckling.

[0059] Furthermore, the sinusoidal critical load of coiled tubing is also influenced by many other factors. For example, friction between the coiled tubing and the borehole wall can increase the critical buckling load; the critical load of coiled tubing with a large slenderness ratio is negligibly affected by boundary conditions; the initial curvature and end torque of the coiled tubing will decrease the critical load, while a higher borehole curvature can increase the critical load. In summary, accurate predictions cannot be made solely based on formulas. This paper will use dynamic simulations for further verification after making a preliminary estimate using formulas to ensure that the selection of coiled tubing dimensions meets design requirements.

[0060] According to the double-layer pipe design of this invention, the maximum load-bearing capacity of the scheme using a PVC sleeve superimposed on a continuous steel pipe is calculated. The outer diameter and wall thickness of the sleeve are taken as 100mm and 5mm respectively, and its material density is... The elastic modulus is The outer diameter and wall thickness of the continuous tube are 1.5 in and 0.125 in, respectively. The material density is... The elastic modulus is Gravitational acceleration is taken as... The inner diameter of the hole wall is 120mm, and the inclination angle of the hole trajectory is 0, that is... Substituting the above parameters into Equation 3, the sinusoidal critical loads of the casing and continuous tube in the borehole are 5.42kN and 4.28kN, respectively. The critical load after combining the two is 9.70kN, which meets the drilling requirements for soft coal seams. By referring to the table, the corresponding drum diameter for this type and size of continuous tube is 1.52m-2.03m, meeting the underground working space requirements of coal mines. It can withstand a maximum internal pressure of 60MPa, possessing the basic capability for high-pressure jetting and high-speed cutting.

[0061] Simulation verification results:

[0062] like Figure 9 As shown, a dynamic model of the casing drilling process is established. The model simplifies the PVC casing and the steel continuous pipe into beam elements, the drill bit into a rigid body, and sets the contact between the pipe string and the borehole wall.

[0063] A double-layered pipe consisting of a PVC casing and a steel continuous pipe was placed into a 200m horizontal borehole with an inner diameter of 120mm. A speed of 0.1m / s was applied to the continuous pipe, and a thrust of 8.3kN was applied to the casing, operating at a mechanical feed rate of 0.1m / s and a drill bit rotation speed of 500rpm. Both the casing and the continuous pipe were modeled using beam elements. Element nodes near the bottom of the borehole were connected by fixed pairs, while element nodes near the borehole opening were connected by cylindrical pairs. Furthermore, the continuous pipe beam elements were fixedly connected to the rigidly modeled drill bit. Contact detection was implemented for the entire drill string, including the continuous pipe, casing, and drill bit, with the borehole. A virtual rotation speed was set for the drill bit to simulate the cutting process at the bottom of the borehole.

[0064] The backward difference method (BDF) is used to solve the system dynamics equations in the form of differential-algebraic equations (DAEs), thereby obtaining the transient time history response of rigid and flexible multibody systems during large-scale motion processes, and thus obtaining information such as the rigid body motion trajectory and the flexible body deformation state.

[0065] The simulated drilling process described above used a drilling pressure of 6.0 kN and a drill bit torque of 114.4 Nm. The simulation results are as follows: Figure 10 As shown, the entire drill string remained stable for most of the borehole section, with only slight buckling near the borehole opening due to accumulated axial pressure, which did not affect normal operation. Figure 11 As shown, the maximum axial pressures on the coiled tubing and casing at the orifice are 8.7 kN and 8.3 kN, respectively, which represent the maximum thrust required by the two injection heads. The actual drilling pressure obtained by the drill bit from both the casing and the coiled tubing is approximately 3.0 kN, demonstrating that the thrust transmission is balanced and effective. The simulation results verify the effectiveness of the torque-following-speed control mode and the feasibility of the device design.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A coal mine horizontal continuous tubular casing drilling injector head apparatus characterised in that, The coal mine near horizontal continuous pipe casing drilling injection head device comprises an execution system and a control system, and the execution system comprises: a continuous pipe injection head for clamping a continuous pipe and a casing injection head for clamping a casing and achieving synchronous advancement of the continuous pipe and the casing in cooperation with the continuous pipe injection head; The casing is sleeved outside the continuous pipe, and one end of the casing near the drill bit is fixedly connected with the reduced-diameter eccentric drill bit through the casing shoe. The continuous pipe injection head is provided with a double-lever frame, a sliding rail for installing the continuous pipe injection head is arranged on the double-lever frame, a chain roller system is arranged in the sliding rail, and the chain roller system is driven by a driving motor. The double-lever frame is also provided with an unjamming mechanism, and the unjamming mechanism is driven by a double-lever motor. A vehicle frame is provided with a constant load clamping device, and the constant load clamping device is also connected with a base for realizing constant load clamping. An unjamming mechanism is arranged on the double-lever frame, and the unjamming mechanism is driven by a double-lever motor. The control system is used for controlling the continuous pipe injection head and the casing injection head to work in cooperation and controlling the continuous pipe and the casing to be injected synchronously.

2. The coal mine horizontal continuous tubular casing drilling injector head apparatus as claimed in claim 1, wherein, The casing is made of PVC material with holes.

3. The coal mine horizontal continuous tubular casing drilling injector head apparatus of claim 1, wherein, The working logic of the control system comprises: The industrial computer sends a control instruction to the PLC, and the PLC controls the frequency converter and the driver in the continuous pipe injection head and the casing injection head respectively; A rotation speed sensor and a torque / current sensor are connected to the injection motor of the continuous pipe injection head and the casing injection head respectively, and the measured data is returned to the PLC to complete closed-loop control; The continuous pipe injection head adopts rotation speed feedback control, and the casing injection head adopts torque / current feedback control.

4. The coal mine horizontal continuous tubular casing drilling injector head apparatus as claimed in claim 1, wherein, The reduced-diameter eccentric drill bit expands in diameter in the drilling state to limit the forward displacement of the casing shoe, and after the drilling is completed, the signal channel is provided through the built-in cable in the continuous pipe to realize electric control disconnection and complete the diameter reduction action.

5. The coal mine horizontal continuous tubular casing drilling injector head apparatus as claimed in claim 1, wherein, The casing injection head adopts a chain roller system form and performs a non-continuous pushing operation mode.

6. The coal mine horizontal continuous tubular casing drilling injector head apparatus as claimed in claim 1, wherein, The control system adopts a torque control following speed control mode to ensure the synchronous movement of the two injection heads.

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