Method and system for laterally drilling through a subterranean formation

Abstract

A method for lateral drilling into a subterranean formation whereby a shoe is positioned in a well casing, the shoe defining a passageway extending from an upper opening in the shoe through the shoe to a side opening in the shoe. A rod and casing mill assembly are inserted into the well casing and through the passageway in the shoe until a casing mill end of the casing mill assembly substantially abuts the well casing. The rod and casing mill assembly are rotated until the casing mill end substantially forms a perforation in the well casing. An internally rotating nozzle is attached to an end of a hose and is pushed through the passageway and the perforation into the subterranean formation, and fluid is ejected from tangential jets into the subterranean formation for impinging upon and eroding the subterranean formation.

Claims

1. A method for facilitating lateral drilling through a well casing into a subterranean formation, the method comprising steps of: positioning in the well casing a shoe defining a passageway extending from an upper opening in the shoe through the shoe to a side opening in the shoe; inserting a rod and casing mill assembly into the well casing and through the passageway in the shoe until a casing mill end of the casing mill assembly substantially abuts the well casing; rotating the rod and casing mill assembly until the casing mill end substantially forms a perforation in the well casing; attaching a housing of an internally rotating nozzle to a first end of a hose for facilitating fluid communication between the hose and an interior portion of the housing, the housing defining a gauge ring extending from an end thereof opposite the hose, the internally rotating nozzle including a rotor rotatably mounted within the housing so that the entire rotor is contained within the interior portion of the housing, the rotor including at least two tangential jets recessed within the gauge ring and oriented off-center to generate torque to rotate the rotor, the rotor further defining passageways for providing fluid communication between the interior portion of the housing and the jets; connecting a second end of the hose opposite the first end of the hose to tubing in fluid communication with pressure generating equipment, to thereby facilitate fluid communication between the pressure generating equipment, the hose, and the nozzle; applying force to push the internally rotating nozzle through the passageway and the perforation into the subterranean formation and to urge the gauge ring against the subterranean formation; and ejecting fluid from the at least two tangential jets into the subterranean formation for impinging upon and eroding the subterranean formation.

2. The method of claim 1 wherein the well casing is a substantially vertical well casing.

3. The method of claim 1 wherein the well casing is a substantially horizontal well casing.

4. The method of claim 1 wherein the tubing is jointed tubing.

5. The method of claim 1 wherein the tubing is coil tubing.

6. The method of claim 1 wherein the rotor further comprises a center jet interposed between the at least two tangential jets.

7. The method of claim 1 wherein the hose is circumscribed along its entire length by at least one spring, the spring having a square cross-section, and the step of extending further comprises applying force through the at least one spring to extend the internally rotating nozzle through the passageway and the perforation into the subterranean formation.

8. A method for facilitating lateral drilling through a perforation in a well casing and into a subterranean formation, the method comprising the steps of: positioning and anchoring in the well casing a shoe defining a passageway extending from an upper opening in the shoe through the shoe to a side opening in the shoe aligned with the perforation; extending through the passageway to the perforation an internally rotating nozzle having a housing attached to a first end of a hose for facilitating fluid communication between the hose and an interior portion of the housing, the housing defining a gauge ring extending from an end thereof opposite the hose, the internally rotating nozzle including a rotor rotatably mounted within the housing so that the entire rotor is contained within the interior portion of the housing, the rotor including at least two tangential jets recessed within the gauge ring and oriented off-center to generate torque to rotate the rotor, the rotor further defining passageways for providing fluid communication between the interior portion of the housing and the jets; connecting a second end of the hose opposite the first end of the hose to tubing in fluid communication with pressure generating equipment, to thereby facilitate fluid communication between the pressure generating equipment, the hose, and the nozzle; ejecting fluid from the at least two tangential jets into the subterranean formation for impinging upon and eroding the subterranean formation; and applying force to push the internally rotating nozzle through the perforation into the subterranean formation and to urge the gauge ring against the subterranean formation.

9. The method of claim 8 wherein the well casing is a substantially vertical well casing.

10. The method of claim 8 wherein the well casing is a substantially horizontal well casing.

11. The method of claim 8 wherein the tubing is jointed tubing.

12. The method of claim 8 wherein the tubing is coil tubing.

13. The method of claim 8 wherein the hose is circumscribed along its entire length by at least one spring, the spring having a square cross-section, and the step of extending further comprises applying force through the at least one spring to extend the internally rotating nozzle through the passageway and the perforation into the subterranean formation.

14. A system for facilitating lateral drilling through a well casing and into a subterranean formation, the system comprising: a shoe positioned at a selected depth in the well casing, the shoe defining a passageway extending from an upper opening in the shoe through the shoe to a side opening in the shoe; a rod connected to a casing mill assembly for insertion into and through the well casing and through the passageway in the shoe until a casing mill end of the casing mill assembly abuts the well casing; a motor coupled to the rod for rotating the rod and casing mill assembly until the casing mill end forms a perforation in the well casing; an internally rotating nozzle having a housing attached to a first end of a hose for facilitating fluid communication between the hose and an interior portion of the housing, the housing defining a gauge ring extending from an end thereof opposite the hose, the internally rotating nozzle including a rotor rotatably mounted within the housing so that the entire rotor is contained within the interior portion of the housing, the rotor including at least two tangential jets recessed within the gauge ring and oriented off-center to generate torque to rotate the rotor, the rotor further defining passageways for providing fluid communication between the interior portion of the housing and the jets, the gauge ring being adapted for being urged against the subterranean formation while the at least two tangential jets eject fluid into the subterranean formation for impinging upon and eroding the subterranean formation; and tubing in fluid communication with pressure generating equipment, the tubing being connected to a second end of the hose opposite the first end of the hose for facilitating fluid communication between the pressure generating equipment, the hose, and the nozzle.

15. The system of claim 14 wherein the well casing is a substantially vertical well casing.

16. The system of claim 14 wherein the well casing is a substantially horizontal well casing.

17. The system of claim 14, wherein the tubing is jointed tubing.

18. The system of claim 14, wherein the tubing is coil tubing.

19. The system of claim 14, further comprising at least one spring circumscribing the hose along the entire length of the hose, the spring having a square cross-section.

20. The system of claim 14 wherein the rotor further comprises a center jet interposed between the at least two tangential jets.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a cross-sectional elevation view of a well having a drilling shoe positioned therein;

(3) FIG. 2 is a cross-sectional elevation view of the well of FIG. 1 having a perforation mechanism embodying features of the present invention positioned within the drilling shoe;

(4) FIG. 3 is a cross-sectional elevation view of the well of FIG. 2 showing the well casing perforated by the perforation mechanism;

(5) FIG. 4 is a cross-sectional elevation view of the well of FIG. 3 with the perforation mechanism removed;

(6) FIG. 5 is a cross-sectional elevation view of the well of FIG. 4 showing a hydraulic drilling device extended through the casing of the well;

(7) FIG. 6 is a cross-sectional elevation view of the nozzle of FIG. 5;

(8) FIG. 7 is a elevation view taken along the line 7-7 of FIG. 6;

(9) FIG. 8 is a cross-sectional elevation view of an alternative embodiment of the nozzle of FIG. 6 with brakes;

(10) FIG. 9 is a cross-sectional elevation view taken along the line 9-9 of FIG. 8;

(11) FIG. 10 is a cross-sectional elevation view of an alternative embodiment of the nozzle of FIG. 8 that further includes a center nozzle; and

(12) FIG. 11 is an elevation view taken along the line 11-11 of FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(13) In the discussion of the FIGURES the same reference numerals will be used throughout to refer to the same or similar components. In the interest of conciseness, various other components known to the art, such as wellheads, drilling components, motors, and the like necessary for the operation of the wells, have not been shown or discussed except insofar as necessary to describe the present invention. Additionally, as used herein, the term “substantially” is to be construed as a term of approximation.

(14) Referring to FIG. 1 of the drawings, the reference numeral 10 generally designates an existing well encased by a well casing 12 and cement 14. While the well 10 is depicted as a substantially vertical well, it could alternatively be a substantially horizontal well (in which case FIG. 1 would be treated similarly as a top or plan view rather than an elevation view) or it could be formed at any desirable angle. The well 10 passes through a subterranean formation 16 from which petroleum is drawn. A drilling shoe 18 is securely attached to a tubing 20 via a tapered threaded fitting 22 formed between the tubing 20 and the shoe 18. The shoe 18 and tubing 20 are defined by an outside diameter approximately equal to the inside diameter of the well casing 12 less sufficient margin to preclude jamming of the shoe 18 and tubing 20 as they are lowered through the casing 12. The shoe 18 further defines a passageway 24 which extends longitudinally through the shoe, and which includes an upper opening 26 and a lower opening 28. The passageway 24 defines a curved portion having a radius of preferably at least three inches. The upper opening 26 preferably includes a limit chamfer 27 and an angle guide chamfer 29, for receiving a casing mill, described below.

(15) As shown in FIG. 1, the shoe 18 is lowered in the well 10 to a depth suitable for tapping into a hydrocarbon deposit (not shown), and is angularly oriented in the well 10 using well-known techniques so that the opening 28 of the shoe 18 is directed toward the hydrocarbon deposit. The shoe 18 is fixed in place by an anchoring device 25, such as a conventional packer positioned proximate to a lower end 18a of the shoe 18. While the anchoring device 25 is shown in FIG. 1 as positioned proximate to the lower end 18a of the show 18, the anchoring device is preferably positioned above, or alternatively, below the shoe.

(16) FIG. 2 depicts the insertion of a rod 30 and casing mill assembly 32 as a single unit through the tubing 20 and into the passageway 24 of the shoe 18 for perforation of the well casing 12. The rod 30 preferably includes an annular collar 34 sized and positioned for seating in the chamfer 27 upon entry of the casing mill 32 in the cement 14, as described below with respect to FIG. 3. The rod 30 further preferably includes, threadingly connected at the lower end of the rod 30, a yoke adapter 37 connected to a substantially barrel-shaped (e.g., semi-spherical or semi-elliptical) yoke 36 via a substantially straight yoke 38 and two conventional block and pin assemblies 39 operative as universal joints. The barrel-shaped yoke 36 is connected to a similar substantially barrel-shaped yoke 40 via a substantially straight yoke 42 and two conventional block and pin assemblies 43 operative as universal joints. Similarly, the barrel-shaped yoke 40 is connected to a substantially barrel-shaped yoke 44 via a substantially straight yoke 46 and two conventional block and pin assemblies 47 operative as universal joints. Similarly, the barrel-shaped yoke 44 is connected to a substantially barrel-shaped “half” yoke 48 via a conventional block and pin assembly 49 operative as a universal joint. The surfaces of the yokes 36, 40, 44, and 48 are preferably barrel-shaped so that they may be axially rotated as they are passed through the passageway 24 of the shoe 18. The yoke 48 includes a casing mill end 48a preferably having, for example, a single large triangular-shaped cutting tooth (shown), a plurality of cutting teeth, or the like, effective upon axial rotation for milling through the well casing 12 and into the cement 14. The milling end 48a is preferably fabricated from a hardened, high strength, stainless steel, such as 17-4 stainless steel with tungsten carbides inserts, tungsten carbide, or the like, having a relatively high tensile strength of, for example, at least 100,000 pounds per square inch, and, preferably, at least 150,000 pounds per square inch. While four substantially barrel-shaped yokes 36, 40, 44, and 48, and three substantially straight yokes 38, 42, 46, are shown and described with respect to FIG. 2, more or fewer yokes may be used to constitute the casing mill assembly 32.

(17) The rod 30 is preferably connected at the well-head of the well 10 to a rotating device, such as a motor 51, effective for generating and transmitting torque to the rod 30 to thereby impart rotation to the rod. The torque transmitted to the rod 30 is, by way of example, from about 25 to about 1000 foot-pounds of torque and, typically, from about 100 to about 500 foot-pounds of torque and, preferably, is about 200 to about 400 foot-pounds of torque. The casing mill assembly 32 is preferably effective for transmitting the torque and rotation from the rod 30 through the passageway 24 to the casing mill end 48.

(18) In operation, the tubing 20 and shoe 18 are lowered into the well casing 12 and secured in position by an anchoring device 25, as described above. The rod 30 and casing mill assembly 32 are then preferably lowered as a single unit through the tubing 20 and guided via the angle guide chamfer 29 into the shoe 18. The motor 51 is then coupled at the well-head to the rod 30 for generating and transmitting preferably from about 100 to about 400 foot-pounds of torque to the rod 30, causing the rod 30 to rotate. As the rod 30 rotates, it imparts torque and rotation to and through the casing mill assembly 32 to rotate the casing mill end 48.

(19) The weight of the rod 30 also exerts downward axial force in the direction of the arrow 50, and the axial force is transmitted through the casing mill assembly 32 to the casing mill end 48. The amount of weight transmitted through the casing mill assembly 32 to the casing mill end 48 may optionally be more carefully controlled to maintain substantially constant weight on the casing mill end 48 by using weight bars and bumper subs (not shown). As axial force is applied to move the casing mill end 48 into the well casing 12 and cement 14, and torque is applied to rotate the casing mill end 48, the well casing 12 is perforated, and the cement 14 is penetrated, as depicted in FIG. 3. The weight bars are thus suitably sized for efficiently perforating the well casing 12 and penetrating the cement 14 and, to that end, may, by way of example, be sized at 150 pounds each, it being understood that other weights may be preferable depending on the well. Weight bars and bumper subs, and the sizing thereof, are considered to be well known in the art and, therefore, will not be discussed in further detail herein.

(20) As the casing mill end 48 penetrates the cement 14, the collar 34 seats in the chamfer 27, and the perforation of the well casing is terminated. The rod 30 and casing mill assembly 32 are then withdrawn from the shoe 18, leaving a perforation 52, which remains in the well casing 12, as depicted in FIG. 4. Notably, the cement 14 is preferably not completely penetrated. To obtain fluid communication with the petroleum reservoir/deposit of interest, a horizontal extension of the perforation 52 is used, as discussed below with respect to FIG. 5.

(21) FIG. 5 depicts a horizontal extension technique that may be implemented for extending the perforation 52 (FIG. 4) laterally into the formation 16 in accordance with present invention. The shoe 18 and tubing 20 are maintained in place. A flexible hose 62, having a nozzle 64 affixed to a lower end thereof, is extended through the tubing 20, the guide chamfer 29 and passageway 24 of the shoe 18, and the perforation 52 into the cement 14 and subterranean formation 16. The hose 62 is preferably only used in a lower portion of the well 10 as necessary for passing through the shoe 18 and into the formation 16, and high-pressure jointed tubing or coil tubing (not shown) is preferably used in an upper portion of the well for coupling the hose 62 to equipment 67 at the surface of the well, as discussed below. The flexible hose 62 is preferably a high-pressure (e.g., tested for a capacity of 20,000 PSI or more) flexible hose, such as a Polymide 2400 Series hose, preferably capable of passing through a curve having a radius of three inches. The hose 62 is preferably circumscribed by a spring 66 preferably comprising spiral wire having a square cross-section which abuts the nozzle 64 at a first or lower end of the hose and the tubing (e.g., a ring at a lower end of the tubing, not shown) at a second or upper end of the hose for facilitating “pushing” the hose 62 downwardly through the tubing 20. The spring 66 may alternatively comprise spiral wire having a round cross-section. The nozzle 64 is a high-pressure rotating nozzle, as described in further detail below with respect to FIGS. 6-10. A plurality of annular guides, referred to herein as centralizers, 68 are preferably positioned about the spring 66 and suitably spaced apart for inhibiting bending and kinking of the hose 62 within the tubing 20. Each centralizer 68 has a diameter that is substantially equal to or less than the inside diameter of the tubing 20, and preferably also defines a plurality of slots and/or holes 68a for facilitating the flow of fluid through the tubing 20. The centralizers 68 are preferably also configured to slide along the spring 66 and rest and accumulate at the top of the shoe 18 as the hose 62 is pushed through the passageway 24 and perforation 52 into the formation 16.

(22) Drilling fluid is then pumped at high pressure preferably via jointed tubing or coil tubing (not shown) through the hose 62 to the nozzle 64 using conventional pressure generating equipment 67 (e.g., a compressor, a pump, and/or the like) at the surface of the well 10. The drilling fluid used may be any of a number of different fluids effective for eroding subterranean formation, such fluids comprising liquids, solids, and/or gases including, by way of example but not limitation, one or a mixture of two or more of fresh water, produced water, polymers, water with silica polymer additives, surfactants, carbon dioxide, gas, light oil, methane, methanol, diesel, nitrogen, acid, and the like, which fluids may be volatile or non-volatile, compressible or non-compressible, and/or optionally may be utilized at supercritical temperatures and pressures. The drilling fluid is preferably injected through the hose 62 and ejected from the nozzle 64, as indicated schematically by the arrows 66, to impinge subterranean formation material. The drilling fluid loosens, dissolves, and erodes portions of the earth's subterranean formation 16 around the nozzle 64. The excess drilling fluid flows into and up the well casing 12 and tubing 20, and may be continually pumped away and stored. As the earth 16 is eroded away from the frontal proximity of the nozzle 64, a tunnel (also referred to as an opening or hole) 70 is created, and the hose 62 is extended into the tunnel. The tunnel 70 may generally be extended laterally 200 feet or more to insure that a passageway extends and facilitates fluid communication between the well 10 and the desired petroleum formation in the earth's formation 16.

(23) After a sufficient tunnel 70 has been created, additional tunnels may optionally be created, fanning out in different directions at substantially the same level as the tunnel 70 and/or different levels. If no additional tunnels need to be created, then the flexible hose 62 is withdrawn upwardly from the shoe 18 and tubing 20. The tubing 20 is then pulled upwardly from the well 10 and, with it, the shoe 18. Excess drilling fluid is then pumped from the well 10, after which petroleum product may be pumped from the formation.

(24) FIG. 6 depicts one preferred embodiment of the nozzle 64 in greater detail positioned in the tunnel 70, the tunnel having an aft portion 70a and a fore portion 70b. As shown therein, the nozzle 64 includes a hose fitting 72 configured for being received by the hose 62. In a preferred embodiment, the hose fitting 72 also includes circumferential barbs 72a and a conventional band 73 clamped about the periphery of the hose 62 for securing the hose 62 onto the hose fitting 72 and barbs 72a.

(25) The hose fitting 72 is threadingly secured to a housing 74 of the nozzle 64 via threads 75, and defines a passageway 72b for providing fluid communication between the hose 62 and the interior of the housing 74. A seal 76, such as an O-ring seal, is positioned between the hose fitting 72 and the housing 74 to secure the housing 74 against leakage of fluid received from the hose 62 via the hose fitting 72. The housing 74 is preferably fabricated from a stainless steel, and preferably includes a first section 74a having a first diameter, and a second section 74b, also referred to as a gauge ring, having a second diameter of about 2-20% larger than the first diameter, and preferably about 10% larger than the first diameter. While the actual first and second diameters of the housing 74 are scalable, by way of example and not limitation, in one preferred embodiment, the second diameter is about 1-1.5 inches in diameter, and preferably about 1.2 inches in diameter. About eight drain holes 74c are preferably defined between the first and second sections 74a and 74b of the housing 74, for facilitating fluid communication between the aft portion 70a and the fore portion 70b of the tunnel 70. The number of drain holes 74c may vary from eight, and accordingly may be more or less than eight drain holes.

(26) A rotor 84 is rotatably mounted within the interior of the housing 74 so that the entire rotor is contained within the interior of the housing, and includes a substantially conical portion 84a and a cylindrical portion 84b. The conical portion 84a includes a vertex 84a′ directed toward the hose fitting 72. The cylindrical portion 84b includes an outside diameter approximately equal to the inside diameter of the housing 74 less a margin sufficient to avoid any substantial friction between the rotor 84 and the housing 74. The cylindrical portion 84b abuts a bearing 78, preferably configured as a thrust bearing, and race 88, which seat against an end of the housing 74 opposed to the hose fitting 72. The thrust bearing 78 is preferably a carbide ball bearing, and the race 88 is preferably fabricated from carbide as well. A radial clearance seal (not shown) may optionally be positioned between the rotor 84 and the bearing race 88 to minimize fluid leakage through the bearing 78. A center extension portion 84c of the rotor 84 extends from the cylindrical portion 84b through the thrust bearings 78 and race 88, and two tangential jets 84d are formed on the rotor center extension portion 84c and recessed within the gauge ring 74b. Each jet 84d is configured to generate a jet stream having a diameter of about 0.025 to 0.075 inches, and preferably about 0.050″. Passageways 84e are defined in the rotor 84 for facilitating fluid communication between the interior of the housing 74 and the jets 84d.

(27) As shown most clearly in FIG. 7, the tangential jets 84d are offset from a center point 84f and are directed in substantially opposing directions, radially spaced from, and tangential to, the center point 84f. Referring back to FIG. 6, the jets 84d are preferably further directed at an angle 91 of about 45° from a centerline 84g extending through the rotor 84 from the vertex 84a through the center point 84f.

(28) Further to the operation described above with respect to FIGS. 1-5, and with reference to FIGS. 6 and 7, fluid is pumped down and through the hose 62 at a flow rate of about 15 to 25 gallons per minute (GPM), preferably about 20 GPM, and a pressure of about 10,000 to 20,000 pounds per square inch (PSI), preferably about 15,000 PSI. The fluid passes through the passageway 72b into the interior of the housing 74. The fluid then passes into and through the passageways 84e to the jets 84d, and is ejected as a coherent jet stream of fluid 90 from the jets 84c at an angle 91 from the centerline 84g. The jet stream of fluid 90 impinges and erodes earth in the fore portion 70b of the tunnel 70. A tangential component of the stream of fluid 90 (FIG. 7) causes the rotor 84 to rotate in the direction of an arrow 85 at a speed of about 40,000 to 60,000 revolutions per minute (RPM), though a lower RPM are generally preferred, as discussed in further detail below with respect to FIGS. 8-11. As the rotor 84 rotates, the stream of fluid 90 rotates, further impinging and eroding a cylindrical portion of earth in the fore portion 70b of the tunnel 70, thereby extending longitudinally the tunnel 70. As earth is eroded, it mixes with the fluid, drains away through the holes 74c, passes through the aft portion 70a of the tunnel 70, and then flows upwardly through and out of the well 10. The nozzle 64 is then urged via the hose 62 toward the fore portion 70b of the tunnel 70 to extend the tunnel 70 as a substantially horizontal portion of the well 10.

(29) FIGS. 8 and 9 depict the details of a nozzle 100 according to an alternate embodiment of the present invention. Since the nozzle 100 contains many components that are identical to those of the previous embodiment (FIGS. 6-7), these components are referred to by the same reference numerals, and will not be described in any further detail. According to the embodiment of FIGS. 8 and 9, a brake lining 102 extends along, and is substantially affixed to, the interior peripheral surface of the housing 74. The brake lining 102 is preferably fabricated from a relatively hard material, such as hardened carbide steel. Two or more brake pads 104, likewise fabricated from a relatively hard material, such as hardened carbide steel, are positioned within mating pockets defined between the rotor 84 and the brake lining 102, wherein the pockets are sized for matingly retaining the brake pads 104 proximate to the brake lining 102 so that, in response to centrifugal force, the brake pads 104 are urged and moved radially outwardly to frictionally engage the brake lining 102 as the rotor 64 rotates.

(30) Operation of the nozzle 100 is similar to the operation of the nozzle 64, but for a braking effect imparted by the brake lining 102 and brake pads 104. More specifically, as the rotor 84 rotates, centrifugal force is generated which is applied onto the brake pads 104, urging and pushing the brake pads 104 outwardly until they frictionally engage the brake lining 102. It should be appreciated that as the rotor 84 rotates at an increasing speed, or RPM, the centrifugal force exerted on the brake pads 104 increases in proportion to the square of the RPM, and resistance to the rotation thus increases exponentially, thereby limiting the maximum speed of the rotor 84, without significantly impeding rotation at lower RPM's. Accordingly, in a preferred embodiment, the maximum speed of the rotor will be limited to the range of about 1,000 RPM to about 50,000 RPM, and preferably closer to 1,000 RPM (or even lower) than to 50,000 RPM. It is understood that the centrifugal force generated is, more specifically, a function of the product of the RPM squared, the mass of the brake pads, and radial distance of the brake pads from the centerline 84g. The braking effect that the brake pads 104 exert on the brake lining 102 is a function of the centrifugal force and the friction between the brake pads 104 and the brake lining 102, and, furthermore, is considered to be well known in the art and, therefore, will not be discussed in further detail herein.

(31) FIG. 10 depicts the details of a nozzle 110 according to an alternate embodiment of the present invention. Since the nozzle 110 contains many components that are identical to those of the previous embodiments (FIGS. 6-9), these components are referred to by the same reference numerals, and will not be described in any further detail. According to the embodiment of FIG. 10, and with reference also to FIG. 11, an additional center jet 84h, preferably smaller than (e.g., half the diameter of) the tangential jets 84d, is configured in the center extension portion 84c of the rotor 84, interposed between the two tangential jets 84d for ejecting a jet stream 112 of fluid along the centerline 84g.

(32) Operation of the nozzle 110 is similar to the operation of the nozzle 100, but for providing an additional jet stream of fluid from the center jet 84h, effective for cutting the center of the tunnel 70.

(33) By the use of the present invention, a tunnel may be cut in a subterranean formation in a shorter radius than is possible using conventional drilling techniques, such as a slim hole drilling system, a coiled tube drilling system, or a rotary guided short radius lateral drilling system. Even compared to ultra-short radius lateral drilling systems, namely, conventional water jet systems, the present invention generates a jet stream which is more coherent and effective for cutting a tunnel in a subterranean formation. Furthermore, by utilizing bearings, the present invention also has less pressure drop in the fluid than is possible using conventional water jet systems.

(34) It is understood that the present invention may take many forms and embodiments. Accordingly, several variations may be made in the foregoing without departing from the spirit or the scope of the invention. For example, the conical portion 84a of the rotor 84, or a portion thereof, may be inverted to more efficiently capture fluid from the hose 62. The brake pads 104 (FIG. 9) may be tapered to reduce resistance from, and turbulence by, fluid in the interior of the housing 74 as the rotor 84 is rotated. The thrust bearing 78 may comprise types of bearings other than ball bearings, such as fluid bearings.

(35) Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.