Apparatus for drilling a curved borehole

Abstract

A non-rotating drill string is formed from a plurality of independent, cylindrical sections pivotally connected together by a latch mechanism. The adjacent ends are partially beveled such that the sections can bend in a single direction. Means are disclosed for varying the effect of the beveled surfaces, thus controlling the angle of bend for a given one of the sections. A downhole mud motor (PDM) drives the drill bit through the use of a flexible drive shaft running through the center of a metal-lined, neoprene drilling fluid hose which runs through the interior of the independent cylindrical sections. The total curvature of the borehole drilled by the system equals the sum of the angles of bend between the individual sections.

What is claimed is: 
     
       1. A drill string for drilling a curved borehole, wherein said drill string has a plurality of cylindrical sections, each of said sections having a longitudinal axis and also having an upper end and a lower end, comprising: a first of said drill string sections having first and second surfaces on the said lower end of said first section; and   a second of said drill string sections having first and second surfaces on the said upper end of said second section, said first surfaces being parallel to each other and perpendicular to each said longitudinal axis and an angle being formed between said second surfaces.   
     
     
       2. A drill string for drilling a curved borehole, wherein said drill string has a plurality of cylindrical sections, each of said sections having a longitudinal axis and also having an upper end and a lower end, comprising: a first of said drill string sections having first and second surfaces on the said lower end of said first section;   a second of said drill string sections having first and second surfaces on the said upper end of said second section, wherein said first surfaces are parallel to each other and perpendicular to each said longitudinal axis and a first angle exists between said second surfaces while said drill string is being lowered vertically, and when said drill string is in the process of drilling a curved borehole, the said second surfaces are parallel and a second angle exists between said first surfaces.   
     
     
       3. The drill string according to claim 2 including, in addition thereto, means to vary said first angle. 
     
     
       4. A drill string for drilling a curved borehole, wherein said drill string has a plurality of cylindrical sections, each of said sections having a longitudinal axis and also having an upper end and a lower end, comprising: a first of said drill string sections having first and second surfaces on the said lower end of said first section;   a second of said drill string sections having first and second surfaces on the said upper end of said second section, wherein said first surfaces are parallel to each other and perpendicular to each said longitudinal axis and a first angle exists between said second surfaces while said drill string is being lowered vertically, and while said drill string is in the process of drilling a curved borehole, the said first angle is reduced and a second angle is formed between said first surfaces.   
     
     
       5. The drill string according to claim 4 including, in addition thereto, means to vary the amount the said first angle is reduced. 
     
     
       6. A drilling system for drilling a curved borehole, comprising: a drill string having a plurality of independent cylindrical sections pivotally connected together;   a PDM motor in said drill string;   a drill bit in said drill string;   a steel-lined neoprene hose for delivering drilling fluid from said motor to said drill bit; and   a flexible drive shaft connected between said motor and said drill bit, said independent sections having the ability to bend only in a single direction while said system is drilling said curved borehole.   
     
     
       7. The system according to claim 6 wherein said independent sections are pivotally connected together with pairs of latch assemblies, each of said latch assemblies comprising a metal strap enclosed within a latch box having a slightly larger width than the width of said strap, each said strap being pivotally connected to two of said plurality of sections. 
     
     
       8. A drilling system for drilling a curved borehole, comprised of a drill string having a first location and a second location, and having independent sections therebetween, a PDM motor in the first location of said drill string, and a drill bit in the second location of said drill string, a flexible pressure hose interior of said independent sections and connected between said PDM motor and said drill bit and a flexible drive shaft interior of said pressure hose connected between said PDM motor and said drill bit, said independent sections having the ability to bend in only a single direction while said system is drilling said curved borehole. .Iadd. 
     
     
       9.  A drilling system for drilling a curved borehole, comprising: a drill string including a plurality of tubular members connected together and having an interior flow path for transmitting pressurized fluid;   a fluid-driven motor having a drive shaft within the drill string;   a drill bit at an end of the drill string;   a plurality of cylindrical sections spaced within the drill string between the motor and the drill bit, the plurality of cylindrical sections pivotally connected together to bend only in a single direction while the system is drilling a curved borehole;   a flexible pressure hose interior of the plurality cylindrical sections for delivering pressurized fluid from the motor to the drill bit; and   a flexible shaft positioned within the pressure hose and mechanically interconnected the drill bit to the motor drill shaft. .Iaddend. .Iadd.10. The drilling system as defined in claim 9, wherein;   each of the plurality of cylindrical sections has a longitudinal axis, an upper end, and a lower end;   a first of the cylindrical sections having its upper end connected to the fluid driven motor and having first and second surfaces on its lower end; and   a second of the cylindrical sections having first and second surfaces on its upper end, wherein the first surfaces are parallel to each other and perpendicular to each of the longitudinal axes and a first angle exists between the second surfaces while said drill string is being lowered vertically, and when the system is drilling the curved borehole the first angle is reduced and a second angle is formed between the first surfaces. .Iaddend. .Iadd.11. The drilling system as defined in claim 10, further comprising:   adjusting means to vary the reduction of the first angle. .Iaddend.   
     
     
        .Iadd.  .  A system as defined in claim 9, wherein one of said plurality of cylindrical sections is a bearing sub, the bearing sub houses a plurality of bearings, and the plurality of bearings include radial bearings and thrust bearings. .Iaddend. .Iadd.13. A drilling system as defined in claim 12, further comprising: a flow restrictor for diverting pressurized fluid to lubricate the plurality of bearings. .Iaddend. .Iadd.14. A drilling system as defined in claim 12, further comprising:   the bearing sub is the lowermost of the plurality of cylindrical sections. .Iaddend. .Iadd.15. A drilling system as defined in claim 12, wherein a lower end of the flexible pressure hose terminates within the bearing sub at a position axially above the plurality of bearings. .Iaddend. .Iadd.16. A drilling system as defined in claim 9, further comprising:   a pair of latch assemblies for pivotably connecting the cylindrical sections together, each of the latch assemblies including a metal strap enclosed within a latch box having a slightly larger width than the width of the corresponding strap, each strap being pivotably connected to two of the plurality of cylindrical sections. .Iaddend. .Iadd.17. A drilling system as defined in claim 9, wherein the fluid-driven motor is a positive displacement mud motor. .Iaddend.