Patent Publication Number: US-10787886-B2

Title: Auxiliary feeding device for flexible pipe of radial horizontal well

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national stage of International Patent Application No. PCT/CN2017/084070, filed on May 12, 2017, which claims the benefit of priority under 35 U.S.C. § 119 from Chinese Patent Application No. 201611225315.1, entitled “AUXILIARY FEEDING DEVICE FOR FLEXIBLE PIPE OF HORIZONTAL WELL IN RADIAL DIRECTION” and filed on Dec. 27, 2016. The content of the foregoing applications is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to the technical field of oil exploitation, and in particular to an auxiliary feeding device for a flexible pipe of a radial horizontal well. 
     BACKGROUND ART 
     As the developments of the oil and gas fields in central and eastern China have entered the middle and late stages, the number of the old and abandoned wells increasingly rises, and it is urgent to promote the renovation of the old wells and tap the potential of the remaining oil. The developments of the old oil fields also face the problems of high water injection pressure and low edge well recovery ratio. Meanwhile, the new proved reserves are still insufficient, while most of the unutilized reserves are complex oil and gas reservoirs such as those with low permeability, thickened oil and oil sheets, as well as the fractured oil and gas reservoirs. 
     The ultra-short radius sidetrack horizontal well drilling technology (also known as the radial horizontal well drilling technology) is a new oilfield production increasing technology developed in recent decades, which means radially drilling one or more horizontal wellbores which are radially distributed in a vertical wellbore. The radial horizontal well drilling technology achieves a steering of tens of meters of high-pressure flexible pipe from a vertical direction to a horizontal direction in a casing by a steering gear within a small turning radius, realizes a continuous rock breaking drilling through a rotary jetting by a water jet bit, and finally forms micro wellbores. 
     The radial horizontal well drilling technology can be utilized to restore the dead wells, thereby greatly improving the oil well production and the oil recovery ratio, and reducing the drilling cost. Therefore, the radial horizontal well drilling technology is an effective measure to renovate the old oil fields, tap the potential of the reservoirs, and stabilize and increase the production, especially suitable for the developments of those with oil sheets, vertical fractures, thickened oil and low permeability, the water-injected “dead oil area”, and the lithological trapped reservoirs. The radial horizontal drilling technology has gradually shown many advantages in exploitations of the complex oil and gas reservoirs, gradually become an effective measure for tapping the potential of the old oilfields and stabilizing the production of the old oilfields, and also become a development direction for increasing the coal bed gas production per well. 
     In addition to protecting the oil and gas formations, the radial horizontal well drilling technology can deplug the well drilling, well cementation and fractured immediate vicinity of wellbore, communicate the micro-crack and fracture system, reduce the fluid flow resistance, and improve the oil and gas production. Further, the radial horizontal well drilling technology can effectively prevent the gas cone or water cone effect. 
     The radial horizontal well drilling technology needs to achieve a steering from the vertical direction to the horizontal direction within a turning radius of 300 mm. After the development in recent decades, the technology has evolved from the initial radial horizontal well technology that performs large diameter reaming to form an ultra-short radius, to the current radial horizontal well technology that steers within the casing. The steering gear within the casing has a small turning radius, an accurate orientation, a simple structure and a small volume, and there is no need for forging and milling the casing or reaming. 
     However, the radial horizontal well technology that steers within the casing can only take the high-pressure flexible pipe as the working line which is difficult to be continuously fed downward. In addition, the high-pressure flexible pipe has a complicated downhole stress state, and the track of the steering gear is narrow; during the downhole drilling, the high-pressure flexible pipe is easy to produce very large bending and buckling deformations when passing through the steering gear within the small turning radius, and a resistance from the narrow track is increased correspondingly, which may result in discontinuous feeding. 
     In the prior art, the continuous drilling of the high-pressure flexible pipe is achieved by the self-feeding force generated by the self-feeding porous jet nozzle provided at an end of the high-pressure flexible pipe. In the downhole, the self-feeding jet nozzle should not only generate a self-feeding force for the forward traction of the drilling string, but also meet the requirement of the high-efficiency rock breaking. The on-way pressure loss of the drilling fluid is inversely proportional to the inner diameter of the high-pressure flexible pipe and proportional to its length. Due to the limitation of the steering size, the inner diameter and the outer diameter of the high-pressure flexible pipe are small; and usually tens of meters of high-pressure flexible pipe is required for the radial horizontal well drilling, so that limited hydraulic energy can be transmitted to the downhole, and the hydraulic energy for the high-pressure flexible pipe to perform the string traction and rock breaking is insufficient, which finally restricts the horizontal drilling distance and thus limits the overall development of the radial horizontal well technology. 
     SUMMARY OF THE INVENTION 
     In order to solve the technical problem that the flexible pipe cannot be continuously and efficiently fed in a radial horizontal well, the present invention proposes an auxiliary feeding device for a flexible pipe of a radial horizontal well, which can effectively overcome the frictional resistance and feed the flexible pipe stably, while effectively adjusting the feeding speed of the flexible pipe so that the flexible pipe can be continuously fed and the rock can be broken efficiently, and finally achieve the objective of improving the exploitation efficiency of oil and gas resources. 
     The present invention proposes an auxiliary feeding device for a flexible pipe of a radial horizontal well, comprising an oil pipe, a steering gear connected to the oil pipe at a lower opening thereof, and two impellers; 
     an upper end surface of the steering gear is provided with an accommodating groove; the steering gear is internally provided with a through steering passage in an axial direction thereof for allowing an external flexible pipe to pass through; an inlet of the steering passage is located at a bottom wall of the accommodating groove, and an outlet of the steering passage is located at a lower portion of a sidewall of the steering gear; 
     the two impellers are located at a bottom of the accommodating groove and symmetrically disposed on two sides of the inlet; each of the impellers comprises an impeller shaft fixed in the accommodating groove, a barrel body rotatably surrounding the impeller shaft, and at least three blades fixed outside the barrel body, wherein the two impeller shafts are parallel to each other, and each of the blades is provided at a top thereof with a notch; 
     during relative and synchronous rotation of the two impellers, the notches of the two impellers are in one-to-one correspondence relation at the inlet to form a holding passage that can clamp the flexible pipe; a lower end of the flexible pipe enters the steering passage through an inner cavity of the oil pipe, the holding passage, and the inlet from top to bottom in sequence, and protrudes from the outlet; fluid injected through an upper opening of the oil pipe drives the impellers to rotate downward in an axial direction of the flexible pipe, and causes the flexible pipe clamped in the holding passage to be fed downward. 
     As compared with the prior art, the present invention has the following advantageous effects: the auxiliary feeding device for the flexible pipe of the radial horizontal well according to the present invention can provide feeding power to overcome the frictional resistance when the flexible pipe in the ultra-short radius radial horizontal well passes through the steering gear to drill; meanwhile, the feeding speed of the flexible pipe can be effectively adjusted by adjusting the velocity of the fluid, so that the flexible pipe can be continuously and stably fed and the rock can be broken efficiently, which shortens the drilling cycle and improves the drilling efficiency, and finally achieves the objective of improving the exploitation efficiency of oil and gas resources. 
     In the present invention, the fluid can be injected into the oil pipe to drive the impellers to rotate, so that the static frictional force between the holding passage and the flexible pipe provides the feeding power to the flexible pipe and overcomes the frictional force, thus feeding the high-pressure flexible pipe. The porous jet nozzle is connected at a lower end of the flexible pipe, and after the fluid is injected into the flexible pipe, the porous jet nozzle generates a self-feeding force which pulls the flexible pipe forward, and which can also auxiliarily pull the flexible pipe downward. 
     When the fluid is pumped from the upper opening of the oil pipe and flows through the slope, the slope causes the flow-through gap to be wide at the top and narrow at the bottom while guiding the fluid to impact the impellers; thus, the flow-through area of the drilling fluid is reduced, and the drilling fluid is rapidly pressurized in a short period of time to impact the impellers to rotate quickly and sensitively. A large impact force is obtained by adjusting the angle for the fluid to impact the impellers, and finally large feeding power is generated for the flexible pipe. A distance between lower ends of the two slopes is smaller than a distance between the two impeller shafts, which effectively blocks or limits the fluid from impacting the blades far away from the flexible pipe, thereby avoiding the disorder of the rotation direction of the impellers. 
     When the impellers rotate, the notches close to the flexible pipe (at the middle) form a holding passage for clamping the flexible pipe, and other notches located above the impeller shafts are tightly matched with the limiting blocks, which limits the fluid from flowing away from the other notches in a direction opposite to a rotation direction of the impellers, and blocks the fluid, thereby avoiding the loss of hydraulic energy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front sectional schematic view of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention; 
         FIG. 2  is a front schematic view of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention; 
         FIG. 3  is a right schematic view of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention; 
         FIG. 4  is a top schematic view of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention; 
         FIG. 5  is a partial schematic view of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention at an accommodating groove; 
         FIG. 6  is a sectional schematic view of a first steering body of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention; 
         FIG. 7  is a right schematic view of a first steering body of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention; 
         FIG. 8  is a front schematic view of an impeller of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention; 
         FIG. 9  is a left schematic view of an impeller of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention; 
         FIG. 10  is an A-A sectional schematic view of  FIG. 8 ; 
         FIG. 11  is a top schematic view of an impeller of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention; 
         FIG. 12  is a stereo schematic view of a flow guiding and limiting body of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention; 
         FIG. 13  is a front schematic view of a flow guiding and limiting body of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention; 
         FIG. 14  is a right schematic view of a flow guiding and limiting body of an auxiliary feeding device for a flexible pipe of a radial horizontal well according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The above technical features and advantages of the present invention are clearly and completely described as follows in conjunction with the drawings. It is obvious that those described are only some, rather than all, of the embodiments of the present invention. 
     Referring to  FIGS. 1 to 4 , the present invention proposes an auxiliary feeding device for a flexible pipe of a radial horizontal well, comprising an oil pipe  10 , a steering gear  20  connected to the oil pipe  10  at a lower opening thereof, and two impellers  30 . 
     Referring to  FIGS. 1 and 5 to 7 , an upper end surface of the steering gear  20  is provided with an accommodating groove  21 ; the steering gear  20  is internally provided with a through steering passage  22  in an axial direction thereof for allowing an external flexible pipe  100  to pass through; an inlet of the steering passage  22  is located at a bottom wall of the accommodating groove  21 , and an outlet of the steering passage  22  is located at a lower portion of a sidewall of the steering gear  20 . 
     As shown in  FIG. 5 , the two impellers  30  are located at a bottom of the accommodating groove  21  and symmetrically disposed on two sides of the inlet. Referring to  FIGS. 5 and 8 , each of the impellers  30  comprises an impeller shaft  32  fixed in the accommodating groove  21 , a barrel body  34  rotatably surrounding the impeller shaft  32 , and at least three blades  36  each fixed outside the barrel body  34 , and the two impeller shafts  32  are parallel to each other. Referring to  FIGS. 9 to 11 , each of the blades  36  is provided at a top (i.e., an outer edge) thereof with a notch  362 . 
     As shown in  FIG. 1 , during relative and synchronous rotation of the two impellers  30 , the notches  362  of the two impellers  30  are located in one-to-one correspondence relation at the inlet (i.e., the notches  362  on the two sides of the inlet are in one-to-one correspondence relation) to form a holding passage that can clamp the flexible pipe  100 . A lower end of the flexible pipe  100  enters the steering passage  22  through an inner cavity of the oil pipe  10 , the holding passage and the inlet from top to bottom in sequence, and protrudes from the outlet. The fluid injected through an upper opening of the oil pipe  10  drives the impellers  30  to rotate downward in an axial direction of the flexible pipe  100 , and causes the flexible pipe  100  clamped in the holding passage to be fed downward. 
     As shown in  FIG. 5 , after being driven by the fluid, the impeller  30  on the left side continues to rotate in a clockwise direction, and the impeller  30  on the right side continues to rotate in a counterclockwise direction, while the notches  362  close to the flexible pipe  100  on the left and right sides form the holding passage and clamp the flexible pipe  100  from the left and right sides respectively. During the rotation of the impellers  30 , the clamped flexible pipe  100  is caused to be fed downward by a frictional resistance. 
     Preferably, the two impellers  30  have the same size, i.e., the impeller shafts  32  have the same diameter and length, the barrel bodies  34  have the same diameter and length, and the blades  36  have the same width and length. When the fluid is injected through the upper opening of the oil pipe  10 , the two impellers  30  are subjected to the same impact force from the fluid since their structures and sizes are the same, which ensures that the two impellers  30  can rotate synchronously. 
     Preferably, since the velocity of the fluid injected through the upper opening of the oil pipe  10  is relatively high and the sizes of the two impellers  30  are relatively small, the impellers  30  rotate fast after being impacted by the fluid; the fluid is usually continuously injected, which ensures that the two impellers  30  can rotate synchronously at a high speed, so that the notches  362  on the left and right sides of the flexible pipe can be in one-to-one correspondence relation, and cooperate from the left and right sides to form the holding passage. 
     The auxiliary feeding device for the flexible pipe of the radial horizontal well according to the present invention can provide feeding power to overcome the frictional resistance when the flexible pipe in the ultra-short radius radial horizontal well passes through the steering gear  20 . The present invention solves the defect that it is difficult to effectively overcome the frictional resistance and feed the high-pressure flexible pipe during the construction using the ultra-short radius radial horizontal well technology. Through the present invention, the flexible pipe  100  can be mechanically fed in the radial horizontal well, and the frictional resistance is effectively overcome, so that the flexible pipe  100  can be stably fed; meanwhile, the feeding speed of the flexible pipe  100  can be effectively adjusted by adjusting the velocity of the fluid, so that the flexible pipe  100  can be continuously and stably fed and the rock can be broken efficiently, thus finally achieving the objective of improving the exploitation efficiency of oil and gas resources. 
     In this embodiment, the fluid is a drilling fluid, and the flexible pipe  100  is a high-pressure flexible pipe capable of withstanding a high pressure. The pressure of the fluid injected through the upper opening of the oil pipe  10  is insufficient to deform the flexible pipe  100  from the outside, and during operation, the flexible pipe  100  is full of high-pressure fluid that usually has a pressure of greater than or equal to 25 MPa and less than or equal to 50 MPa. Thus, the flexible pipe  100  also applies a force to the outside and will not be extruded and deformed. 
     In the auxiliary feeding device for the flexible pipe of the radial horizontal well according to the present invention, the fluid may be injected into the oil pipe  10  to drive the impellers  30  to rotate, so that a static frictional force between the holding passage and the flexible pipe  100  can provide the feeding power for the flexible pipe  100  and overcome the frictional force, thus feeding the high-pressure flexible pipe. Preferably, a porous jet nozzle  110  is connected at a lower end (i.e., a tail end) of the flexible pipe  100 ; after fluid is injected into the flexible pipe  100 , the porous jet nozzle  110  generates a self-feeding force which pulls the flexible pipe  100  forward, and which can also auxiliarily pull the flexible pipe  100  downward. 
     Preferably, the inner diameter of the steering passage  22  is greater than the outer diameter of the flexible pipe  100 . In order to prevent the buckling deformation of the high-pressure flexible pipe in the steering passage  22 , the size of the steering passage  22  should not be too large. The drilling fluid flows through an annular space between the steering passage  22  and the flexible pipe  100  to lubricate the flexible pipe  100 , and reduce the frictional resistance to the downward feeding of the flexible pipe  100 . The auxiliary feeding device for the flexible pipe of the radial horizontal well according to the present invention has a simple and reliable structure and simple operations, and can be easily controlled. 
     The present invention mechanically enables the flexible pipe  100  to overcome the resistance upon passing through the steering gear  20 , and provides stable power for feeding the flexible pipe  100  downward, thereby ensuring continuous and efficient drilling, shortening the drilling cycle, and improving the drilling efficiency. When the displacement of the ground drilling fluid is increased or decreased, the rotation speed of the impeller  30  about the impeller shaft  32  is increased or decreased accordingly. Due to the clamping effect of the holding passage on the flexible pipe  100 , the feeding speed of the flexible pipe  100  is correspondingly increased or decreased under the effect of the static frictional force. In addition, the rock breaking capacity of the porous jet nozzle  110  connected to the lower end of the flexible pipe  100  also varies with the displacement of the drilling fluid, thereby achieving the consistency between the feeding speed of the flexible pipe  100  and the rock breaking speed of the porous jet nozzle  110 . 
     Further, as shown in  FIGS. 4 and 5 , the auxiliary feeding device for the flexible pipe of the radial horizontal well further comprises two flow guiding and limiting bodies  40  which are symmetrically disposed on two sides of the inlet to form a flow-through gap  41  therebetween. 
     Each of the flow guiding and limiting bodies  40  is fixed in the accommodating groove  21 , and disposed above the corresponding impeller  30 . The fluid injected through the upper opening of the oil pipe  10  passes through the flow-through gap  41 , applies a force to the two blades  36  forming the holding passage, and drives the impellers  30  to rotate downward in the axial direction of the flexible pipe  100 . 
     The fluid is guided by the flow guiding and limiting bodies  40  to impact the impellers  30  to rotate; while the impellers  30  are rotating, the static frictional force generated between the holding passage and the flexible pipe  100  serves as the power to overcome the frictional resistance to the flexible pipe  100  in the steering gear  20 , thereby gradually feeding the flexible pipe  100  downward. 
     Further, referring to  FIGS. 12 to 14 , each of the flow guiding and limiting bodies  40  at least comprises a flow guiding body  42 , one side of which abuts against a sidewall of the accommodating groove  21 , and an opposite side of which is provided with a slope  422 . As shown in  FIG. 5 , the flow-through gap  41  is located between two slopes  422  and has a truncated cone shape that is reduced from top to bottom. 
     After the pumping is started on the ground, the fluid (e.g., the drilling fluid) is pumped in from the upper opening of the oil pipe  10 . When the fluid flows through the slope  422 , since the slope  422  is at an angle with the vertical direction, the slope  422  causes the flow-through gap  41  to be wide at the top and narrow at the bottom while guiding the fluid to impact the impellers  30 ; thus, the flow-through area of the drilling fluid is reduced, and the drilling fluid is rapidly pressurized in a short period of time to impact the impeller  30  to rotate quickly and sensitively. 
     Preferably, the angle between the slope  422  and the vertical direction can be adjusted based on actual needs, so as to adjust the angle for the fluid to impact the impeller  30  to obtain a large impact force, thereby increasing the rotation speed of the impeller  30 , and finally generating the large feeding power for the flexible pipe  100 . 
     Further, each of the flow guiding and limiting bodies  40  further comprises a limiting block  44  that is fixed to a bottom of the fluid guiding body  42 . Each of the limiting blocks  44  is extended in a rotation direction of the corresponding blade  36 , and a cross-sectional shape of the limiting block  44  is matched with a shape of the notch  362 . 
     In order to prevent the fluid from flowing away in a direction opposite to a rotation direction of the impellers  30  after the fluid passes through the flow-through gap  41 , the limiting block  44  matching the notch  362  in shape and size is designed by simulating the rotation trajectory of the notch  362 . As shown in  FIG. 5 , when the impellers  30  rotate, the notches  362  close to the flexible pipe  100  (at the middle) form the holding passage for clamping the flexible pipe  100 , and other notches  362  located above the impeller shafts  32  are tightly matched with the limiting blocks  44 . That is, the limiting blocks  44  are tightly fitted into other notches  362  located above the impeller shafts  32 , so as to limit the fluid from flowing away from the other notches  362  in the direction opposite to the rotation direction of the impellers  30 , and block the fluid, thereby avoiding the loss of hydraulic energy. 
     Further, as shown in  FIG. 5 , a distance between lower ends of the two slopes  422  is smaller than a distance between the two impeller shafts  32 . 
     As shown in  FIG. 5 , taking the impeller  30  at the left side as an example, when the fluid impacts the blade  36  at the right side of the impeller shaft  32 , a part of the fluid causes the impeller  36  to rotate clockwise, thereby forming a mechanical driving force to drive the flexible pipe  100  to be fed. Due to the existence of the slopes  422 , particularly since the distance between lower ends of the two slopes  422  is smaller than the distance between the two impeller shafts  32 , the fluid is effectively blocked or limited from impacting the blade  36  at the left side of the impeller shaft  32  (far away from the flexible pipe  100 ), thereby avoiding the disorder of the rotation direction of the impellers  30 . 
     However, each of the blades  36  has a notch  362 , and when the fluid impacts the blade  36  at the right side of the impeller shaft  32 , a part of the fluid may flow away from the notch  362  of the impeller  30  at the left side of the impeller shaft  32 , which causes the loss of hydraulic energy. In order to avoid the loss of hydraulic energy, the part of the fluid should be limited from flowing away (counterclockwise) from the above of the impeller  30 . Thus, the flow guiding and limiting body  40  is designed with the limiting block  44 . 
     The design process of the limiting block  44  is as follows: the notch  362  rotates by a certain angle to form a curved surface, and a space enclosed by the curved surface and the bottom of the fluid guiding body  42  is the shape of the limiting block  44 . The rotation angle of the notch  362  is not limited, as long as the formed shape of the limiting block  44  is sufficient to limit the fluid from flowing away from the notch  362  of the blade  36  at the left side of the impeller shaft  32 . 
     In this embodiment, the rotation angle of the notch  362  is 90 degrees. Since the curved surface of the limiting block  44  is obtained by the rotation of the notch  362 , it can be tightly matched with the notch  362 . The notch  362  rotated to the limiting block  44  is tightly fitted with the curved surface of the limiting block  44 , so as to effectively limit the fluid from flowing away in the direction opposite to the rotation direction of the impeller  30 . 
     Taking the slope  422  of the flow guiding and limiting body  40  at the left side as an example, under the condition that the height of the slope  422  is constant, the angle between the slope  422  and the vertical direction is acute. The angle should ensure that the fluid does not directly impact the blade  36  located at the left side of the impeller shaft  32  of the impeller  30  corresponding to a lower portion of the slope so as to cause the disordered rotation of the impeller. Thus, the fluid directly impacts the blade  36  located at the right side of the impeller shaft  32  of the impeller  30  corresponding to the lower portion of the slope so as to form a driving force that drives the flexible pipe  100  to be fed downward. Preferably, the angle between the slope  422  and the vertical direction is 30 degrees to 45 degrees. 
     Further, each of the flow guiding and limiting bodies  40  further comprises at least one fixing block  46  that is fixed to the sidewall of the flow guiding body  42 . As shown in  FIG. 6 , the accommodating groove  21  is provided on the sidewall thereof with assembly chutes  24  which are slidably matched with the fixing blocks  46  respectively, and the fixing blocks  46  can be fixed in the assembly chutes  24 . 
     As shown in  FIG. 13 , the flow guiding body  42  is a trapezoidal column having a trapezoidal longitudinal section, wherein a straight sidewall at the left side abuts against the sidewall of the accommodating groove  21 , and an opposite inclined sidewall at the right side is the slope  422 . In this embodiment, the fixing blocks  46  are respectively disposed on the straight sidewalls at the front side and the rear side of the flow guiding body  42 ; correspondingly, four assembly chutes  24  are provided on the sidewall of the accommodating groove  21 . 
     Further, each of the impeller shafts  32  is horizontally disposed, and two ends of each of the impeller shafts  32  are fixed in the assembly chute  24 , respectively. 
     After the impeller shaft  32  is inserted into the center hole of the barrel body  34  to complete the assembly, the impeller  30  is placed in the accommodating groove  21 , and both ends of the impeller shaft  32  are slid into the assembly chute  24  to limit the position of the impeller  30 . Next, the two fixing blocks  46  of the flow guiding and limiting body  40  are slid into the assembly chute  24 , so that the flow guiding and limiting body  40  is fixed in the accommodating groove  21 . Preferably, the fixing block  46  is in an interference fit with the assembly chute  24  to form a reliable connection. 
     Further, as shown in  FIG. 6 , the assembly chute  24  comprises a slide-in section  242  and a clamping section  244  which are sequentially disposed from top to bottom. The width of the clamping section  244  (i.e., the dimension in the horizontal direction) is smaller than the width of the slide-in section  242  (i.e., the dimension in the horizontal direction). The two ends of each of the impeller shafts  32  are fixed in corresponding clamping sections  244 , respectively. 
     That is, the assembly chute  24  is wide at the top and narrow at the bottom. After being inserted into the assembly chute  24  from a wider portion at the upper end (i.e., the slide-in section  242 ) and sliding along the assembly chute  24 , each of the impeller shafts  32  goes to the narrower portion at the lower end (i.e., the clamping section  244 ), and is fixed and clamped by gravity. In this embodiment, the width of the fixing block  46  is larger than the diameter of the impeller shaft  32 , so that the fixing block  46  is clamped in the slide-in section  242 . 
     Further, as shown in  FIGS. 8 and 9 , the blades  36  are tabulate, extended in an axial direction of the corresponding impeller shaft  32 , and evenly arranged in a circumferential direction of the corresponding impeller shaft  32 . 
     Preferably, the number of the blades  36  of each of the impellers  30  can be adjusted based on actual needs, so that the maximum feeding power can be obtained when the injected drilling fluid impacts the blade  36 . In this embodiment, the number of the blades  36  of each of the impellers  30  is six. 
     Preferably, the number of the blades  36  of each of the impellers  30  is at least six, that is, the blades  36  are set densely; during relative rotations of the two impellers  30 , the frequency at which the blades  36  contact the flexible pipe  100  is increased, so that the notches  362  at the left and right sides of the inlet can be in one-to-one correspondence relation accurately, thereby reliably forming the holding passage. 
     Further, as shown in  FIG. 10 , the notch  362  is semi-circular, and accordingly, the formed holding passage is circular, wherein an inner diameter of the holding passage is smaller than an outer diameter of the flexible pipe  100 . Preferably, the inner diameter of the holding passage is 1 mm to 2 mm smaller than the outer diameter of the flexible pipe  100 , so that the flexible pipe  100  can be effectively clamped. 
     According to the outer diameter of the flexible pipe  100 , the barrel body  34  and the notches  362  are sized to ensure that the notches  362  can hold the flexible pipe  100  during operation. As a result, during rotation of the impeller  30 , a sufficient static frictional force can be generated between the impeller  30  and the flexible pipe  100 , and finally the flexible pipe  100  is stably and continuously fed. 
     Further, as shown in  FIGS. 2 and 3 , the steering gear  20  comprises a first steering body  25  and a second steering body  26 . As shown in  FIGS. 6 and 7 , the accommodating groove  21  is disposed on an upper end surface of the first steering body  25 , and a lower portion of the first steering body  25  has a first machined surface which is vertically disposed; the second steering body  26  has a second machined surface that is vertically disposed and is fixedly attached to the first machined surface. A first groove is provided on the first machined surface, and a second groove is provided on the second machined surface, wherein the first groove and the second groove are aligned and snap-fitted to form the steering passage  22 . 
     The steering gear  20  is disposed as left and right parts, i.e., the first steering body  25  and the second steering body  26 , that are aligned and snap-fitted. When the steering passage  22  is machined, grooves may be formed on the first machined surface and the second machined surface (i.e., the first groove and the second groove), respectively; next, the first steering body  25  is fixedly connected to the second steering body  26  by bolts; and the machining and assembly of the steering gear  20  are more convenient and precise, under the premise of ensuring that the overall structure is simple and reliable. 
     As another implementable embodiment, the steering gear  20  can be designed into three parts: a barrel body, a first lower split body, and a second lower split body, wherein an upwardly opening accommodating groove  21  is provided on the barrel body  21 , the first lower split body and the second lower split body are connected side by side below the barrel body, and one side of the first lower split body and one side of the second lower split body are respectively provided with a first groove and a second groove which are aligned and snap-fitted to form the steering passage  22 . The bottom of the accommodating groove  21  is provided with a through hole that is in communication with the inlet of the steering passage  22 . 
     The internal structure of the steering gear  20  is complex and other parts need to be mounted. Other combined mounting manners may also be adopted for the steering gear  20 , and are not enumerated herein. 
     Preferably, the cross sections of the first groove and the second groove are both semicircular, and after the first steering body  25  is matched and fixed with the second steering body  26 , the cross section of the steering passage  22  is circular. After the assembly of the first steering body  25  and the second steering body  26  is completed, the first steering body  25  is connected to the lower end of the oil pipe  10 , the accommodating groove  21  of the first steering body  25  is in communication with the lower opening of the oil pipe  10 , and the steering gear  20  is anchored after being fed into the well for a predetermined depth by the oil pipe  10 . 
     In this embodiment, after other internal parts of the steering gear  20  are assembled, the first steering body  25  and the second steering body  26  are tightly connected to each other by the cooperation between nine bolts on the second steering body  26  and the bolt holes on the first steering body  25 , thereby completing the assembly. 
     Further, as shown in  FIG. 6 , the steering passage  22  comprises a vertical line segment  222 , an oblique line segment  224 , and an arc segment  226  which are sequentially connected from top to bottom. The inlet is located at an upper end of the straight line segment  222 , the outlet is located at a tail end of the arc segment  226 , and a tangential direction of a tail end of the arc segment  226  is horizontal, so that the flexible pipe  100  is extended horizontally outward from the outlet of the steering passage  22  in the radial direction of the steering gear  20 . Through a reasonable track design, the frictional resistance to the flexible pipe  100  caused by the shape of the steering passage  22  is sufficiently reduced. 
     The usage process of the auxiliary feeding device for the flexible pipe of the radial horizontal well according to the present invention is as follows: after each of the impeller shafts  32  is inserted into a central hole of the barrel body  34  and rotatably matched therewith, each of the impeller shafts  32  is slid into the clamping section  244  of corresponding assembly chute  24  and then fixed therein. Next, the two fixing blocks  46  of each of the flow guiding and limiting bodies  40  are slid into corresponding assembly chute  24  and then fixed therein. The first steering body  25  is fixedly connected to the second steering body  26  by bolts, the first steering body  25  is connected to the lower end of the oil pipe  10 , and the entire tool string is fed into the well. 
     The steering gear  20  is anchored after reaching a predetermined depth downhole, and then the flexible pipe  100  is put in through the upper opening of the oil pipe  10 . After the oil pipe  10  is fed to the predetermined depth, the porous jet nozzle  110  and the flexible pipe  100  enter the steering passage  22  through the holding passage. At this time, the holding passage holds the high-pressure flexible pipe  100 . 
     Pumping is started on the ground to pump the fluid (e.g., the drilling fluid). After flowing through the annular space between the oil pipe  10  and the flexible pipe  100 , the flow-through area of the drilling fluid is reduced by the two slopes  422  when flowing through the flow-through gap  41  at the flow guiding and limiting body  40 , thereby being pressurized to impact and drive the impellers  30  to rotate. Under the dual effects of the mechanical feeding force for the flexible pipe  100  generated by the holding passage formed at the impeller  30  and the self-feeding force generated by the porous jet nozzle  110 , the flexible pipe  100  overcomes the frictional resistance, and smoothly passes through the steering passage  22  so that rock-breaking drilling is performed stably and continuously. 
     The above specific embodiments further explain the objectives, technical solutions and advantageous effects of the present invention in details. It should be understood that those described are just specific embodiments of the present invention, rather than limitations to the protection scope of the present invention. It should be particularly pointed out that any modification, equivalent replacement, improvement, etc., made within the spirit and scope of the present invention should be covered by the protection scope of the present invention.