Abstract:
A jet drill coupled to a distal end of a flexible jet lance is lowered into a well casing and advanced through a curved passage formed in a deflection shoe oriented to direct the jet drill through an orifice milled in the well casing. The jet drill is actuated with a pressurized fluid produced by a pump on the surface that is conveyed through a high pressure hose that runs through the flexible jet lance. Force transmitted through a thrust liner of the jet lance advances the jet drill while the lateral bore is being drilled. The thrust liner comprises helical coils of steel wire providing a high elastic modulus and buckling resistance, even while passing through the curved passage. Tension cables in the jet lance maintain tension on the thrust liner and enable the assembly to be pulled from the lateral bore and well.

Description:
RELATED  APPLICATIONS 
       [0001]    This application is based on a prior copending provisional application Ser. No. 61/426,357, filed on Dec. 22, 2010, the benefit of the filing date of which is hereby claimed under 35 U.S.C. §119(e). 
     
    
     BACKGROUND 
       [0002]    Oil and gas wells commonly bypass significant productive formations that may be uneconomic to complete at the time the well was drilled. These formations may be relatively thin and low pressure so simply perforating the zone does not provide significant new production. However, lateral drilling into such thin, horizontal oil bearing formations can result in substantial new oil production. The lateral well should be drilled at an angle as close as possible to 90 degrees relative to the vertical well to ensure that the lateral drilling tools stay within the productive zone. This objective can be accomplished by feeding a flexible lance equipped with a compact rotary jet drill though a shoe incorporating a curved passage that deflects the drill at a high angle into the formation. This approach is referred to as zero-radius lateral drilling, since the angle is defined entirely within the wellbore, as opposed to drilling a curved hole in the formation. 
         [0003]    Conventional mechanical drilling requires high thrust and torque to penetrate rock. Applying high torque and thrust though a tight radius curve is extremely difficult. A rotary jet drill of the type described in U.S. Pat. No. 7,198,456 provides the ability to penetrate a range of underground formations with very low thrust load and no torque. The rotary jet drill includes a reaction-turbine jet rotor that spins a pair of forward facing jets that erode the formation. The jet drill face has a gage ring which, provided that the drill is kept pressed against the rock face, ensures drilling of a close tolerance circular section borehole. 
         [0004]    It would be desirable to provide improved method and apparatus for zero-radius lateral drilling, for example, by using the rotary jet drill in a system that can apply the required torque and thrust through the tight curve defined within a borehole. 
       SUMMARY 
       [0005]    This application specifically incorporates by reference the disclosures and drawings of each patent application and issued patent identified above. 
         [0006]    This disclosure describes a jet drilling lance assembly that is capable of providing high-pressure fluid to power a rotary jet drill while providing sufficient thrust to maintain face contact while drilling and sufficient lateral stiffness to prevent the lance from buckling and diverting from a straight lateral trajectory. The invention further discloses a method for deploying the lance and drilling the lateral. 
         [0007]    This Summary has been provided to introduce a few concepts in a simplified form that are further described in detail below in the Description. However, this Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     
    
     
       DRAWINGS 
         [0008]    Various aspects and attendant advantages of one or more exemplary embodiments and modifications thereto will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0009]      FIG. 1A  shows an overview of the lateral drilling system at the start of drilling; 
           [0010]      FIG. 1B  shows the system after a portion of the lateral has been drilled; 
           [0011]      FIG. 2  shows a rotary jet drill; 
           [0012]      FIG. 3  shows a jet lance and cable tensioner; 
           [0013]      FIG. 4  shows the internal features of the jet lance and cable tensioner; 
           [0014]      FIG. 5  shows a detailed section of the jet lance; 
           [0015]      FIG. 6  shows an axial section of the jet lance; 
           [0016]      FIG. 7  shows an axial section of the jet lance in the curved configuration; and 
           [0017]      FIGS. 8A-8C  show details of how the lance is deployed though the deflection shoe. 
       
    
    
     DESCRIPTION 
     Figures  and  Disclosed  Embodiments  Are  Not  Limiting 
       [0018]    Exemplary embodiments are illustrated in referenced Figures of the drawings. It is intended that the embodiments and Figures disclosed herein are to be considered illustrative rather than restrictive. No limitation on the scope of the technology and of the claims that follow is to be imputed to the examples shown in the drawings and discussed herein. Further, it should be understood that any feature of one embodiment disclosed herein can be combined with one or more features of any other embodiment that is disclosed, unless otherwise indicated. 
         [0019]    Referring to  FIG. 1A , a jet drilling assembly is shown in a casing  112  of a wellbore, in the earth  100 . The jet drilling assembly is run into a guide tube  106 , which is supported by slips  108  and casing  112 . At the lower end of the guide tube, a packer  124  is removably set in the casing. In one exemplary embodiment, the packer is set in a desired position mechanically by rotation of the guide tube and is thereby locked in place within the casing by tension. The packer further supports a deflection shoe  120  that is distally disposed below the packer. The same guide tube, packer, and deflection shoe may be used to deploy a milling assembly to mill a window or orifice in the casing at the elevation where the lateral well is to be drilled, so that the lateral can be drilled by advancing the jet drill through the window so that it can drill into the surrounding formation. When the mechanical milling assembly used to mill the window is removed, the jet drilling assembly is run into the well through the guide tube without changing the position of the guide tube, or packer, so that the shoe maintains its alignment with the window. The jet drilling assembly comprises a high-pressure fluid swivel  102  on the surface, high-pressure tubing  104 , a cable tensioner assembly  114 , a flexible jet lance  116 , and a jet drill  122 . 
         [0020]    The jet drilling assembly may be lowered into and raised out of the well with a winch  126 , a cable  130 , and a block assembly  134  that is supported on a frame  132 . Pressurized fluid is supplied to the swivel from a pump  128 . The use of swivel  102  enables rotation of the jet drilling assembly, which is suspended below in the bore, to orient the drilling assembly as desired. For example, the tubing string may be rotated with a pipe wrench that is applied to the string on the surface. 
         [0021]      FIG. 1B  shows the lateral well drilled after the jet drilling assembly is lowered into the well. In an exemplary embodiment, the flexible jet lance is capable of passing though a 6-inch radius curve. For example, if the well casing diameter is 4.5-inches, the lateral well inclination is about 70 degrees from the casing axis. In wells having a larger casing, the same lance can drill a well at about 90 degrees inclination relative to the well axis. 
         [0022]    Those skilled in the art will understand that various types of weight indicators are available and well known to observe the weight of the jet drilling assembly and high-pressure tubing. The weight is commonly calculated with an accuracy of about ±100 lbf. After the jet drill passes though the shoe and window in the well casing, it will tag the rock face, and the indicated weight of the jet drilling assembly and high-pressure tubing will drop. In one exemplary embodiment, the face of the jet drill is covered with a plastic cap that mechanically protects the jet drill during deployment and prevents wellbore fluid from flowing up into the assembly. Once the face of the jet drill with the cap in place tags the formation, fluid is pumped to the tool at high pressure. The jet of high pressure fluid at the drill will remove the cap and initiate drilling into the formation. The assembly is then fed into the formation, while maintaining nominal weight to ensure that the jet drill stays in contact with the formation. 
         [0023]    In one embodiment, jet drill  122  is a rotary type, such as disclosed in U.S. Pat. No. 7,198,456, and shown in  FIGS. 2A ,  2 B, and  2 C. This jet drill is capable of drilling a circular hole with a uniform diameter. The jet drill operates on high-pressure fluid, typically water, which can be supplied though a flexible, high-pressure hose. Shown in  FIGS. 2A ,  2 B, and  2 C are a housing  200 , a gage ring  202 , a rotor  204 , and outer nozzle port  206   a  and inner nozzle port  206   b.  A hose barb  208  enables the nozzle to be attached to the end of a high-pressure hose using a crimp fitting. Nozzle port  206   a  directs a jet of fluid at an outer edge of the gage ring. The rotor rotates so that the outer jet erodes the rock at the outer circumference of the gage ring Inner nozzle port  206   b  directs a jet of fluid across the centerline of the rotor to erode the rock in the center of the hole. As disclosed in U.S. Pat. No. 7,198,456, this configuration enables drilling of a uniform diameter hole, provided that the distal edge of the gage ring is kept in contact with the rock face. Ports  210  are provided to enable rock cuttings and fluid to escape the face where the pressurized jets are drilling into the formation, for transport up the annulus between the hose lance and the borehole. The jet drill requires that a nominal thrust be applied toward the formation to overcome the thrust generated by the jets and to ensure that the face of the jet drill is kept pressed against the rock being cut. In one exemplary embodiment, the jet drill produces a 1.125-inch diameter hole using a hose lance outer diameter of about 1 inch. 
         [0024]    The jet drill is coupled to a distal end of flexible jet lance  116 , which is coupled to a distal end of tensioner assembly  114 , as shown in  FIG. 3 . Referring to  FIG. 5 , the flexible jet lance includes an inner high-pressure hose  500  through which pressurized fluid is supplied to the jet drill, spacers  502 , tension cables  400 , and a thrust liner  300 . 
         [0025]    High-pressure hose  500  can be of a multilayer wire-wrap or wire mesh reinforcement wrapped around an impermeable inner liner. Those skilled in the art will recognize that these types of hoses are capable of withstanding high pressure, while maintaining flexibility, without significant changes in diameter or length due to the applied fluid pressure. In one exemplary embodiment, a 6-layer hose capable of withstanding continuous operation at 20,000 psi is used. 
         [0026]    Spacers  502  are arc shaped and are disposed between the high-pressure hose and the outer thrust liner  300  to form a slip fit. In one exemplary embodiment, four spacers are provided and disposed so that they are equally spaced apart around the hose. Alternate arrangements with more or fewer spacer segments can instead be used. The spacer can be constructed of a high-shear-strength polymer, such as nylon or acrylonitrile-butadiene-styrene (ABS), which is capable of withstanding immersion in water and oil and heating to temperatures of 100° C. or more. Longitudinally reinforced polymer with transverse flexibility, but high transverse shear strength, may also be used for the spacers. 
         [0027]    Thrust liner  300  can be fabricated from heavy gage steel wire with a quadrilateral cross section, i.e., wire having a roughly square or rectangular cross section, which is wound as a helical spring having coils in solid contact. The winding pitch can be small, and adjacent surfaces of the wire coils should be in solid and continuous contact along the longitudinal axis of the thrust liner when the hose is straight. The square wire section can thus support a high compression load. As long as the helical spring of thrust liner  300  is straight and in compression as shown in  FIG. 6 , it will have an elastic modulus and buckling resistance comparable to a steel tube. This relatively high stiffness enables the assembly to be delivered into a long horizontal hole without buckling. 
         [0028]    As shown in  FIG. 7 , when the flexible jet lance assembly is forced to bend in a curve when passing though the curved deflection shoe, the adjacent surfaces of the wire segments comprising the helical coil of thrust liner  300  separate slightly along the outer radius of the curve, but maintain contact along the inner radius. Any tendency of the hose to shear due to transverse sliding of the wire segments comprising the helical coil is resisted by spacer segments  502  and pressurized hose  500 , which is flexible, but very stiff in the radial direction. 
         [0029]    In an exemplary embodiment, the thrust liner has an outer diameter of 1-inch and is capable of withstanding 2000 lbf of thrust, without buckling or shearing. In this example, the jet drill has a gage diameter of about 1.125 inches and can drill a hole that is about 1.13-inches in diameter. The flexible jet lance in this example is 50-feet long. Those skilled in the art will recognize that maintaining a relatively low ratio between the hole diameter and the thrust enables the application of high thrust before the column becomes elastically unstable. 
         [0030]    Tension cables  400  are disposed in gaps between the spacers, within the annulus between thrust liner  300  and pressurized hose  500 . The spacers prevent the cables from all slipping to one side of the annulus and causing the lance to become asymmetric and unstable with respect to compressive or tensile loading. These tension cables are constructed of multi-wire steel, providing high flexibility and tensile strength. Further, the cables have sufficient tensile elasticity to accommodate relative changes in length as the lance assembly is bent though a radius, as shown in  FIG. 4  and as is required, to pass though deflection shoe  120 . 
         [0031]    As shown in  FIG. 4 , tension cables  400  are attached to a hose fitting  302 , which is disposed at the end of the flexible jet lance and to a retainer  402   a  inside cable tensioner assembly  114  (see  FIG. 1A ). Retainer  402   a  is free to move axially inside housing  304 . A retainer support  402   b  is threadably engaged by a tensioner  404 . Unthreading tensioner  404  applies tension to cables  400  and thrust to thrust liner  300 . An end cap  406  is affixed to a distal end of housing  304 . Pulling on tension assembly  114  stretches cables  400  so that tensioner  404  comes into contact with end cap  406 , and the pulling force is transferred to the cables though tensioner  404 , retainer support  402   b,  and retainer  402   a.  The cable pull force is applied through hose fitting  302  so that pulling on the tensioner assembly pushes thrust liner  300  upwards. This configuration makes it possible to pull flexible jet lance  116  and the attached jet drill out of the lateral borehole and out through the deflection shoe. In one exemplary embodiment, there are eight cables  400  for providing a tensile pull capacity of 4000 lbf. This load capacity enables the operator to observe variations in pull load, which can be an indication of hole instability. 
         [0032]    A hose spacer  414  is threadably engaged with liner  408  to accommodate variability in the length of hose protruding from thrust liner  300 . A crimped hose fitting  410  connects the hose to an inlet adaptor  306  of the tensioner assembly with a nut  412 . 
         [0033]    To summarize, flexible jet lance assembly  116  and tensioner assembly  114  provide a number of functions required for drilling a zero radius lateral bore, including: (1) transmitting high pressure fluid to the jet drill; (2) transmitting thrust to push the flexible jet lance assembly though the deflection shoe and to react the thrust of jet drilling and contact forces without shearing or buckling; (3) transmitting tension to pull the flexible jet lance out from the borehole; and, (4) providing sufficient transverse flexibility to pass though the deflection shoe passage as shown, with minimal thrust. 
         [0034]    Referring to  FIGS. 8A ,  8 B, and  8 C, deflection shoe  120  is held fixed in the borehole by a packer  124 , which is shown schematically. The packer may be mechanically set in the wellbore using a guide string  802 . The packer and deflection shoe have previously been used to guide a flexible milling assembly, which is described in a commonly assigned provisional patent application Ser. No. 61/426,345 “Method and Apparatus for Milling a Zero Radius Window In Casing” and a corresponding utility patent application Ser. No. 13/328,111, which claims priority in that provisional application. The milling assembly disclosed in these two applications can be employed to mill a window or orifice through the well casing that is aligned with the deflection shoe exit. 
         [0035]    Jet drill  122  is shown approaching the deflection shoe in  FIG. 8A . At this point in the procedure, the jet drill is capped with a plastic cap  800 , which is designed to ease the entry of the tool into the lateral direction through a curved passage  804  of the deflection shoe. A centralizer  118  is configured to slide on jet lance  116  and includes friction grips (not separately identified) on its outer surface that ensure the centralizer stays fixed in place, centrally disposed within casing  112 , while the jet lance and jet drill are tripping into and out of the well. 
         [0036]    A curved passage through deflection shoe  120  is smaller in diameter than the centralizer, so that the centralizer stops at a point immediately proximal to deflection shoe, as shown in  FIGS. 1A and 8B . The jet lance advances through the shoe and the casing window until it tags the surrounding formation. When the flexible jet lance reaches this point, the weight indicator on the surface shows that the jet drill is in contact with the formation. Fluid is then pumped to the jet drill, which actuates the drill. The rotating high pressure jets on the jet drill erode through cap  800 , enabling the drill to start drilling the lateral through the formation around the well casing. Thrust is continually applied to the jet drill so that it drills a gage hole into the formation as shown in  FIG. 8C . 
         [0037]    Those skilled in the art will recognize that the weight (or applied thrust) on the jet drill may be monitored by a sensor (not shown) on the surface and maintained as the assembly is fed into the well. In one exemplary method, lengths of high-pressure tubing  104  are added so that a block assembly  134  is at the top of its travel when initiating jet drilling as shown in  FIG. 1A . The weight is maintained at a relatively constant level throughout the drilling process until the block assembly has moved to the bottom of its travel and the lateral is complete as shown in  FIG. 1B . The lateral is thus completed in a single pass so that the gage diameter of the borehole is maintained at the minimum diameter required to accommodate the gage ring of the jet drill. A typical workover rig capable of providing this service can accommodate 60-feet of high pressure tubing and this length of tubing is the upper limit on the length of a lateral bore that may be drilled in a single pass. This procedure provides a uniform, minimum diameter hole. The buckling stability of the lance is inversely related to the clearance between the lance and the hole. Small increases in gage diameter will significantly reduce the resistance of the lance to buckling. Stopping to pull the jet drill out of the well can enlarge the lateral bore and reduce buckling stability. Accordingly, it may be preferable in this procedure to reduce the flow rate of fluid to the jet drill to the point where jet drilling stops before the jet drill and flexible jet lance are withdrawn from the lateral bore hole. 
         [0038]    Although the concepts disclosed herein have been described in connection with the preferred form of practicing them and modifications thereto, those of ordinary skill in the art will understand that many other modifications can be made thereto within the scope of the claims that follow. Accordingly, it is not intended that the scope of these concepts in any way be limited by the above description, but instead be determined entirely by reference to the claims that follow.