Abstract:
A tricone rock bit for horizontal wells and hard formation wells includes three head sections and three cones arranged at the lower ends of the head sections, where the supper parts of the three head sections are connected together to form one integrated drill bit body; jet nozzle bosses are arranged between the head sections on the drill bit body; jet nozzles are mounted in nozzle holes of the jet nozzle bosses; gauge cutting elements are arranged on the top rear of the OD of the head sections, forming a gauge surface on the top of the head sections; the front face of the head sections is a ruled surface, inclining backwards at an angle α, and inclining outwards at an angle β. The tricone rock bit has low lateral vibrations, high stability, good effects of bottom hole cleaning and cutting element cooling, long service life and high penetration rate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation application of International Patent Application No. PCT/CN2011/080272, filed Sep. 28, 2011, entitled “TRICONE ROCK BIT FOR HORIZONTAL WELLS AND HARD FORMATION WELLS,” by Zengyuan SHAO et al., which is hereby incorporated herein in its entirety by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to the field of geological drilling and oil drilling, and more particularly to a tricone rock bit for horizontal wells and hard formation wells. 
       BACKGROUND OF THE INVENTION 
       [0003]    The existing tricone rock bit usually includes a bit body with three head sections, a cone is rotatably mounted on bearing shaft inclined at lower ends of the head sections, the cone having steel cutting elements or cemented carbide inserts, and drilling fluid is pumped into a drill fluid course from a drill string, and then is discharged out of three nozzles. Each nozzle is mounted in a nozzle boss, and the nozzle bosses are disposed at rear sides of the head sections. The drilling fluid impacts the well bottom and then returns back up from both sides of the nozzle boss. The bit contacts the borehole wall at three points on a heel row of cutting elements of the cones, and the point of contact is on a leading side of each cone. When horizontal wells and hard formation wells are drilled, the roller cone bit has the following problems: quick lateral movement and strong impact result in deviation of the center of rotation of the bit from its geometric center and acceleration of wear and break of the cutting elements, and even lead to premature bearing failure; due to gravity, removal of drilling cuttings from the well bottom is poor, which also easily results in that the cone shell wears and cutting elements breakage or loss; the water jet orientation is unreasonable, and the cutting elements are not timely cooled accordingly, thereby accelerating the wear. Wear-resistant cutting elements are arranged above OD of the head sections (head OD) to resist lateral vibration, but they cannot adequately suppress severe lateral vibration as the cutting elements arrangement center on the OD of the head sections is usually on the axis of the head sections. 
         [0004]    U.S. Pat. No. 6,227,314 (entitled “INCLINED LEG EARTH-BORING BIT”) changes the conventional rear nozzle boss into a front nozzle boss, the upper portion of the head OD is offset circumferentially a distance relative to the lower portion, a gage point is formed on the upper portion of the head OD, the nozzle boss and the lower portion of the leg form a mud up-return channel, but the channel changes its direction on the upper portion of the leg, not helpful for smooth up-return of the mud. 
         [0005]    U.S. Pat. No. 6,688,410 (entitled “Hydro-lifter rock bit with PDC inserts”) cancels the cone gage point, but disposes the gage point on the upper portion of the head OD, the geometric centerline on the upper portion of the head OD is parallel to the centerline of the bit, and the geometric centerline on the lower portion is at an angle to the centerline of the bit. In this patent, the borehole diameter is formed by cutting action of the head OD, which can decrease drilling efficiency of the bit. 
       SUMMARY OF THE INVENTION 
       [0006]    In one aspect, the present invention relates to a tricone rock bit for horizontal wells and hard formation wells, which can reduce lateral vibration of the cone rock bit in drilling of horizontal wells and hard formation wells, and has a better bottom hole cleaning effect, thereby further improving drilling efficiency and comprehensive effects of the cone rock bit, so as to solve shortcomings existing in the prior art. 
         [0007]    The present invention provides a tricone rock bit for horizontal wells and hard formation wells, which includes three head sections and cones mounted at lower ends of the head sections. Upper portions of the three head sections are integrally connected to form a bit body, nozzle bosses are formed between the head sections on the bit body, and nozzles are mounted in orifices of the nozzle bosses. Upper rear sides of OD of the head sections (head OD) are provided with gauge cutting elements, to form a gauge surface on the upper portions of the head sections, a front side of the head sections is a ruled surface (in the present application, the ruled surface is such a surface that is formed with a straight line (the straight line may be called a generating line) moving and sweeping along an axis parallel to the straight line in a continuously gradual (without mutation) manner, which may be, for example, a plane, or a curved surface projected into a curve along the generating line, such as an arc-shaped surface), and deflects backward at an angle of α and deflects outward at an angle of β, where the value of α is 10°˜50°, the value of β is 0°˜15°; the front side of the head sections can be obtained with a plane or a curved surface sequentially rotating at angles of α and β around a horizontal axis X and a longitudinal axis Z of the bit body in an initial azimuth and then shifting, where the horizontal axis X and the longitudinal axis Z of the bit body intersect at point O; when the front side of the head sections is a plane, its initial azimuth is located in a plane XOZ defined by the horizontal axis X and the longitudinal axis Z, while when the front side of the head sections is a curved surface projected into a curve along the generating line, its initial azimuth is defined as the following azimuth where the generating line is parallel to the longitudinal axis Z, and the horizontal axis X extends to pass through two endpoints of the curve. 
         [0008]    In one embodiment, a front side of the head OD is a plane, in its initial azimuth, the plane is located in the XOZ plane, and an ultimate position of the front side of the head sections is obtained as follows: the plane is first rotated around the X axis at the angle of α, and then rotated around the Z axis at the angle of β, then the plane can be shifted and connected with other surfaces on the OD of the head sections (head OD), to ultimately form the front side of the head OD. 
         [0009]    In one embodiment, a front side of the head sections is a part of a cylindrical surface, in its initial azimuth, a generating line of the cylindrical surface is parallel to the vertical axis Z, a projection of the cylindrical surface along the vertical axis Z is a section of an arc, the horizontal axis X extends to pass through two endpoints of the arc, and an ultimate position of the front side of the head sections is obtained as follows: the cylindrical surface is first rotated around the X axis at the angle of α, and then rotated around the Z axis at the angle of β, then the cylindrical surface is shifted and connected with other surfaces on the OD of the head sections (head OD), to ultimately form the front side of the head OD. 
         [0010]    In one embodiment, rotation around the X axis is rotation along a clockwise direction when being observed along the X axis but against a positive direction of the X axis, and rotation around the Z axis is rotation along a counterclockwise direction when being observed along the Z axis but against a positive direction of the Z axis. 
         [0011]    In one embodiment, the value of the angle α declining backward is 20°˜40°; further, the value of the angle α declining backward is 20°˜30°, and the value of the angle β declining outward is 3°˜10°. 
         [0012]    In one embodiment, the upper rear sides of OD of the head sections (head OD) extend backward to a distance, and the nozzle boss is arranged in a leg portion with the upper rear sides of OD of the head sections (head OD) extending backward. 
         [0013]    In one embodiment, an upper slope and a lower slope are formed on the rear side of the leg, and the two slopes and a front side of the following leg form a mud up-return channel declining backward. 
         [0014]    In one embodiment, the shape of a radial section (that is, a section perpendicular to the generating line) of the front side of the head sections is a straight line, an arc, a parabola, or a hyperbola. 
         [0015]    In one embodiment, a jet direction of the nozzle in the nozzle boss is toward a front side of the following cone and between a heel row of cutting elements and a middle row of cutting elements. 
         [0016]    In one embodiment, 2-3 rows of gauge cutting elements are inlaid on the gauge surface on the rear sides of the upper portions of the OD of the head sections (head OD) or the leg portion extending backward, and 2-3 gauge cutting elements in each row are staggered at intervals; 2-3 rows of gauge cutting elements are further mounted on the OD of the head sections (head OD), and 4-8 gauge cutting elements in each row are staggered at intervals; tactical diameters of all the gauge cutting elements on the leg portion extending backward that the OD of the head sections (head OD) include are 0-2 mm less than the gage diameter, and the tactical diameters gradually decrease from bottom to up and from front to back; the gauge cutting elements are cemented carbide cutting elements or diamond composite cutting elements, and a crown shape of the gauge cutting elements is flat or spherical. The beneficial effects of the present invention are as follows: (1). a gage point is set on an upper portion of a rear side of the back of the leg (head OD), which enhances drilling stability of the bit and reduces lateral vibration, and the bit does not offset easily in drilling of horizontal wells, thereby increasing the effective life of the roller cone bit; (2). the front side of the head OD wholly declines backward and outward, to form a smooth mud up-return channel, and also form a lifting force for drilling cuttings at the bottom, which promotes the drilling cuttings to up return with the mud, makes the speed of the mud up-return rapid, and facilitates increasing of the drilling efficiency; (3). the jet direction of the nozzle is guided to a front side of the following cone, so that the drilling fluid could directly jet and flush the work face of the cutting elements, which enhances the bottom hole cleaning and cooling effects of the cutting elements. This type of bit achieves a good effect in actual use, and in sections of horizontal wells and hard formation wells, compared with the conventional bit, the drilling footage is increased by 40% on average, and the average service life is doubled. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a front view of a bit according to one embodiment of the present invention. 
           [0018]      FIG. 2  is a bottom view of a bit according to one embodiment of the present invention. 
           [0019]      FIG. 3  is a front view of a partial sectional view of a bit with a nozzle boss according to one embodiment of the present invention. 
           [0020]      FIG. 4  is a front view of a bit according to another embodiment of the present invention. 
           [0021]      FIG. 5  is a front view of a bit according to a third embodiment of the present invention. 
           [0022]      FIGS. 6   a - 6   c  are schematic views showing how to obtain an ultimate azimuth from an initial azimuth when a front side of the head OD is a plane. 
           [0023]      FIGS. 7   a - 7   c  are schematic views showing how to obtain an ultimate azimuth from an initial azimuth when the front side of the head OD is a part of a cylindrical surface. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The description will be made as to the embodiments of the present invention in conjunction with the accompanying drawings. 
         [0025]    The first embodiment of the tricone rock bit is shown in  FIGS. 1-3 , which includes three head sections  3  and cones  4  mounted at lower ends of the head sections. Upper portions of the three head sections are integrally connected to form a bit body by welding, an upper portion of the bit body is provided with taper threads  1 , for connecting a drilling string; upper rear sides of OD of the head sections (head OD) extend backward to a distance, to form a leg portion extending backward, gauge cutting elements are mounted on a portion of the head OD extending backward, the gauge cutting elements are inlaid on the head OD, 2-3 rows may be arranged at front and rear, 2-3 gauge cutting elements in each row may be staggered at intervals, the gauge cutting elements are diamond composite cutting elements or cemented carbide cutting elements, to form a gauge surface on the upper portions of the head sections, and 2-3 rows of gauge cutting elements may be further inlaid on the OD of the head sections (head OD), 4-8 gauge cutting elements in each row may be staggered at intervals; tactical diameters of all the gauge cutting elements on the OD of the head sections (head OD) are 0-1 mm less than the gage diameter, and the tactical diameters gradually decrease from bottom to up and from front to back; after the gauge cutting elements are inlaid on the gauge surface on the upper portions of the head sections, the diameter of this portion is 1 mm less than the gage diameter of the roller cone bit, and lateral stability of the bit is enhanced. 
         [0026]    A front side of the head sections is a ruled surface, the ruled surface is at an angle of a (declining backward) to an axis of the bit, and is at an angle of β (declining outward) to a horizontal reference axis (X axis), where the value of α is 10°˜50°, for example, 20°˜30°, the value of β is 0°˜15°, for example, 8°˜10′; in the present application, the ruled surface is such a surface that is formed with a straight line (the straight line may be called a generating line) moving and sweeping along an axis parallel to the straight line in a continuously graded (without mutation) manner, which may be, for example, a plane, or a curved surface projected into a curve along the generating line, such as an arc-shaped surface. 
         [0027]    An upper slope and a lower slope are formed on the rear side of the leg, and the two slopes and a front side of the following leg form a mud up-return channel wide at the bottom and narrow at the top and declining backward, which forms a great lifting force for drilling cuttings at the bottom, and promotes the drilling cuttings to up return with the mud. A nozzle boss  8  is disposed in a leg portion with the upper rear sides of OD of the head sections (head OD) of the bit body extending backward, a fluid course is disposed in the bit body and communicates with an orifice of the nozzle boss, a nozzle  7  is mounted in the orifice of the nozzle boss, a jet direction  6  of the nozzle  7  is toward a front side of the following cone and between an outer row of cutting elements and a middle row of cutting elements, a minimum distance between a nozzle potential core of jet and the following cone cutting elements is 0, so that cutting elements  5  are effectively cooled when entering the work face and during operation. 
         [0028]    The second embodiment of the present invention is shown in  FIG. 4 , and is different from the previous embodiment in that a front side  2  of the head sections is not inclined outward, and an angle β formed between the front side  2  and the central plane of the bit is equal to 0. 
         [0029]    The third embodiment of the present invention is shown in  FIG. 5 , and is different from the first embodiment in that the shape of a radial surface (that is, a section perpendicular to the generating line) of a front side  2  of the head sections is an inwardly concave arc, to form a front side of the leg inclined outwards and being an inwardly concave arc surface. 
         [0030]    Alternatively, the shape of the radial surface (that is, a section perpendicular to the generating line) of the front side of the head sections is a parabola or a hyperbola. 
         [0031]    In one embodiment, the front side of the head sections can be obtained by sequentially rotating at angles of α and β around a horizontal axis X and a longitudinal axis Z of the bit body in an initial azimuth and then shifting, where the horizontal axis X and the longitudinal axis Z of the bit body intersect at point O; when the front side of the head sections is a plane, its initial azimuth is located in a plane XOZ defined by the horizontal axis X and the longitudinal axis Z, while when the front side of the head sections is a curved surface projected into a curve along the generating line, its initial azimuth is defined as the following azimuth where the generating line is parallel to the longitudinal axis Z, and the horizontal axis X extends to pass through two endpoints of the curve. 
         [0032]    In one embodiment, when a front side of the head OD is a plane, in its initial azimuth, the plane is located in the XOZ plane, and an ultimate position of the front side of the head sections is obtained as follows: the plane is first rotated around the X axis at the angle of α, and then rotated around the Z axis at the angle of β, then the plane can be shifted and connected with other surfaces on the OD of the head sections (head OD), to ultimately form the front side of the head OD. 
         [0033]    According to another aspect of the present invention, when a front side of the head OD is a part of a cylindrical surface, in its initial azimuth, a generating line of the cylindrical surface is parallel to the vertical axis Z, a projection of the cylindrical surface along the vertical axis Z is a section of an arc, the horizontal axis X extends to pass through two endpoints of the arc, and an ultimate position of the cylindrical surface of the head sections is obtained as follows: the cylindrical surface is first rotated around the X axis at the angle of α, and then rotated around the Z axis at the angle of β, then the cylindrical surface can be shifted and connected with other surfaces on the OD of the head sections (head OD), to ultimately form the front side of the head OD. 
         [0034]      FIGS. 6   a - 6   c  exemplarily show a process of forming an ultimate azimuth from an initial azimuth when a front side of the head sections is a plane. 
         [0035]    As shown in  FIGS. 6   a - 6   c,  when a front side of the head OD is a plane, in its initial azimuth, the plane is located in the XOZ plane. For ease of description without limitations, vertical edges of a rectangle shown to represent a plane coincide with the Z axis or are parallel to the Z axis, and horizontal edges of the rectangle coincide with the X axis (refer to  FIG. 6   a ). In this way, the plane is first rotated around the X axis (for example, rotated clockwise when being observed along the X axis but against a positive direction of the X axis) at the angle of α (refer to  FIG. 6   b ), rotated around the Z axis (for example, rotated counterclockwise when being observed along the Z axis but against a positive direction of the Z axis) at the angle of β (refer to  FIG. 6   c ), and then is shifted and connected with other surfaces on the OD of the head sections (head OD), and finally the front side of the head OD is formed through cutting. In other words, the front side of the head OD can be obtained with a plane sequentially rotating at angles of α and β around a horizontal axis X and a longitudinal axis Z of the bit body from an initial azimuth and then shifting. 
         [0036]      FIGS. 7   a - 7   c  exemplarily show a process of forming an ultimate azimuth from an initial azimuth when a front side of the head sections is a part of a cylindrical surface. When a front side of the head sections is a curved surface of a part of a cylindrical surface, in its initial azimuth, as shown in  FIG. 7   a , the generating line of the cylindrical surface is parallel to the longitudinal axis Z, and the horizontal axis X extends to pass through two endpoints of the arc of the cylindrical surface projected along the longitudinal axis Z. In this way, the cylindrical surface is first rotated around the X axis (for example, rotated clockwise when being observed along the X axis but against a positive direction of the X axis) at the angle of α (refer to  FIG. 7   b ), and then is rotated around the Z axis (for example, rotated counterclockwise when being observed along the Z axis but against a positive direction of the Z axis) at the angle of β (refer to  FIG. 7   c ), then the cylindrical surface is shifted and connected with other surfaces on the OD of the head sections (head OD), and finally the front side of the head OD is formed through cutting. In other words, the front side of the head OD can be obtained with a cylindrical surface sequentially rotating at angles of α and β around a horizontal axis X and a longitudinal axis Z of the bit body from an initial azimuth and then shifting.