WO2005107395A2 - Flexible drillstring apparatus and method for manufacture - Google Patents

Abstract

A flexible drillstring and method of manufacture are disclosed. The flexible drillstring is characterized by a continuous flexibility profile cut through the wall thickness of a section of pipe to give it elastic flexibility. The method of manufacture includes drawing a section of pipe across a mandrel and cutting the continuous profile with a laser, water jet, or EDM cutter.

Description

FLEXIBLE DRILLSTRING APPARATUS AND METHOD FOR MANUFACTURE

BACKGROUND OF THE INVENTION The present invention relates to a drillstring for boring a subterranean well bore; more particularly, the present invention relates to a flexible ultra-short radius drillstring to drill subterranean formations. More particularly still, the present invention relates to a method of manufacturing the ultra-short radius drillstring. Conventional directional drilling devices rely on the flexibility that exists within of conventional drill pipe only at long lengths. Particularly, several 20-40 foot (6 - 12 m) long sections or "joints" of drill pipe are threaded together and run downhole to a desired subterranean location where the deviated hole is desired. The drill bit is then deflected away from the primary bore (using a whipstock or any other device known to one skilled in the art) and the drillstring deviates away from the "vertical" at a rate of less than 10° per joint of pipe. Over great distances, the drillstring is able to make a gradual curve from vertical to horizontal drilling. This method is feasible where a gradual change in wellbore direction is desirable or where long lengths of horizontally drilled wellbore are desired. Unfortunately, this method does not lend itself where immediate horizontal deviations from a wellbore are desired. For example, if a primary bore is drilled through a coal seam, it may be desirable to branch out in several directions at the coal seam to fully exploit the hydrocarbons trapped therein. Conventional directional drilling methods would not be effective in these circumstances because the coal seam may be of limited size and difficult to "hit" at their large bend radiuses. Presently, seams are often explored through perforating or fracturing, but this practice can often be too destructive and not maximize the production of hydrocarbons. A drillstring capable of making a short radius deviation into the formation would be well received by those in the petroleum production and exploration industries. SUMMARY OF THE INVENTION The deficiencies of the prior art are addressed by a flexible drilling apparatus comprising a drillstring characterized by an outer diameter, a thickness, and a length. The drillstring is preferably located between a drill bit and a tool joint. The drillstring thickness preferably includes a flexibility profile cut therethrough along the length, wherein the flexibility profile is configured to allow the drillstring to bend elastically along that length at a bend radius. The flexibility profile can be helical. Optionally, the flexibility profile is configured to allow torsional elasticity about an axis of the outer diameter in a first direction, and optionally resist torsional elasticity about the axis in a second direction. Optionally the bend radius can be less than three to ten times the outer diameter. Thus, the bend radius can be less than or equal to 18 inches (45.8 cm), less than or equal to 12 inches (30.5 cm), less than or equal to 8 inches (20.3 cm), or less than or equal to 6 inches (15.3 cm) depending on the type of cuts made in the drillstring pipe forming the flexibility profile. Optionally, the drill bit is a single cone nutating drill bit. Optionally, a hose delivers drilling fluids through a bore of the drillstring to the drill bit. Optionally, the flexibility profile is manufactured from a single continuous cut. Optionally, the flexibility profile is manufactured from two or more continuous cuts. Optionally, the drilling apparatus includes a wear band stabilizer proximate the drill bit. The wear band stabilizer can optionally be facilitate fluid and debris flow thereacross. The wear band stabilizer can optionally create a relatively rigid zone of the drillstring proximate the drill bit. Optionally, the wear band stabilizer can be configured to be replaceable or can include material harder than the drillstring. The flexibility profile can be manufactured by a laser machining process. The deficiencies of the prior art are also addressed by a method to manufacture a flexible drillstring including mounting a length of pipe in a laser cutting machine that includes a laser cutting head with a variable output laser. The method preferably includes positioning a mandrel within the length of pipe, wherein the mandrel is configured to guide the pipe to and past the laser cutting head. The method preferably includes energizing the laser cutting head to cut the pipe and rotating and engaging the length of pipe across the laser cutting head to create a continuous cut flexibility profile. Optionally, the rotating and engaging can be performed by a computer controlled manipulator assembly. Optionally, the method can further include a second laser cutting head, wherein the two cutting heads cut separate continuous helical paths of the flexibility profile. Optionally, the laser cutting head is stationary and only the length of pipe is moved. The deficiencies of the prior art can also be addressed by a method to manufacture a flexibility profile wherein the method includes mounting a section of pipe to be cut into the drillstring upon a mandrel of a continuous linear cutting machining. The method preferably includes energizing the linear cutting machining and rotating and engaging the section of pipe across the linear cutting machine with a computer controlled manipulator assembly to create the flexibility profile. Optionally, the continuous linear cutting machine can be a laser cutting machine, a water jet cutting machine, or a WireEDM cutting machine.

BRIEF DESCRIPTION OF THE DRAWINGS For a more detailed description of the preferred embodiments of the present invention, reference will be made to the accompanying drawings, wherein: Figure 1 is a schematic profiled drawing of a flexible drillstring assembly in accordance with a preferred embodiment of the present invention. Figure 2 is a schematic profiled drawing of the flexible drillstring assembly of Figure 1 detailing a drill bit and wear band stabilizer arrangement. Figure 3 is a schematic profiled drawing of the flexible drillstring assembly of Figure 1 detailing a rotary threaded connection to the flexible drillstring. Figure 4 is an approximate scale cutting drawing for one embodiment of the flexible drillstring assembly, as shown in Figure 1. Figure 5 is an approximate scale cutting drawing for another embodiment of the flexible drillstring assembly, as shown in Figure 3. Figure 5A is a close-up of the cutting detail of Figure 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring initially to Figure 1 , a flexible drillstring assembly 100 in accordance with a preferred embodiment of the present invention is shown. Flexible drillstring assembly 100 preferably includes at least one section of flexible drill pipe 102, a wear band stabilizer 104, and a drill bit assembly 106. Flexible drill pipe section 102 is preferably constructed from a length of steel pipe that is cut using a continuous laser-cut machine. Pipe section 102 shown is preferably manufactured from a 1.80 inch (4.5 cm) outside diameter, 0.2 inch (0.5 cm) thick steel pipe, but any diameter and thickness pipe may be used. Furthermore, pipe section 102 is preferably manufactured using a laser machining process, but other continuous high-tolerance machining processes including, but not limited to, wire electron discharge machining (WireEDM) processes may be used. As sections 102 are preferably manufactured from steel pipe or tubing, adjacent sections 102 can be welded together using traditional methods to create effective sections 102 that are much longer than the current manufacturing technology would permit. Furthermore, alternative materials (titanium, aluminum, stainless steel, nickel-based superalloy) may be similarly be used. Referring now to Figures 1 and 2 simultaneously, stabilizers

104A, 104B are shown proximate to drill bit 106 of flexible drilling assembly 100. Stabilizers 104A, 104B serve two purposes, they reduce wear on the rotating drilling apparatus 100 and they help to guide and maintain bit 106 into its desired trajectory. Stabilizers 104A, 104B are preferably constructed as "full gauge" steel rings with a hardness coating applied thereupon. Hardness coating may be of any type or manufacture including, but not limited to, flame-sprayed or implanted tungsten carbide. Various other hardening schemes known to one of ordinary skill in the art may also be employed. Stabilizer rings 104A, 104B are preferably manufactured of a plain steel base so that they may be connected as by threading or welding between sections of flexible drilling assembly 100 at their desired locations. Stabilizers 104A, 104B perform their task by limiting the flexibility of drilling assembly 100 near drill bit 106, and by assuming wear from the formation so pipe section 102 do not have to. Furthermore, stabilizer rings 104A, 1014B are can be constructed as shown with grooves 108 upon their outer surfaces. These grooves enable the flow of drilling fluid in the annulus formed between the outside of the drillstring assembly 100 and inside of the borehole to flow there across. Furthermore, if desired, grooves 108 can be constructed with "turbine" profiles to facilitate the removal of drill cuttings and annular fluid from the cutting surfaces of drill bit 106. Because of the perforations and cuts made in pipe section 102 to make it flexible, traditional methods of pumping drilling mud at high pressure in the drillstring bore and returning drilling mud at low pressure through the annulus may not always be sufficient on its own to cool and remove cuttings from drill bit 106. Alternatively, a hose (not shown) can be used inside the bore of pipe section 102 to deliver "bore" drilling fluids directly to drill bit 106. As shown in Figure 2, wear bands 104A and 104B act to divide pipe section 102 of flexible drilling assembly 100 into two sub sections 102A and 102B. The sectioning of pipe section 102 into sections 102A and 102B proximate to drill bit 106 may be used to reduce the amount of bending in pipe section 102 at or near bit 106. Subsections 102A, 102B can be constructed short enough to allow drillstring 100 to flex through short radius turns and bends in the drilled formation, but not so flexible as to allow drill bit 106 to deviate too far away from a desired path. Finally, while two stabilizers 104 are shown, it should be understood that they may be omitted or substituted with another stabilizer or wear band known in the art. Drill bit 106 is preferably a single cone nutating drill bit of the type disclosed in U.S. Patent Application No. 10/709,907 (published as US 20040200640 A1 ) by Allen Kent Rives, hereby incorporated herein by reference. Drill bit 106 may be attached to flexible pipe section 102B or, may optionally be engaged within a threaded receptacle 110. Receptacle 110, if used, is preferably connected to the end of section 102B of flexible pipe 102. While drill bit 106 is preferably constructed as a nutating single cone drill bit, it should be understood by one of ordinary skill that any drill bit known in the art may be used, and that the ultimate determination on the type, size, and style for bit 106 will be dependant on the composition of the formation to be drilled. Referring briefly now to Figure 3, a rotary threaded connection

112 is preferably provided at the end of flexible pipe section 102 opposite drill bit 10. Threaded pipe connection 112 is preferably constructed as a standard oilfield rotary threaded connection and is preferably configured to connect flexible drilling apparatus 100, to a rigid, "traditional" drillstring. While threaded connection 112 is shown in Figure 3 as a relatively long in relation to its outer diameter, it should be understood by one of ordinary skill that the length can be shortened if needed to maintain over flexibility of flexible drilling assembly 100. Referring to Figures 4, 5, and 5A, the cutting detail and method for manufacturing two embodiments of flexible drill pipe sections 102, 102A, and 102B are shown. Although the cutting details are shown in two-dimensional form, one skilled in the art should readily recognize the application of the cutting details to cylindrical objects, such as steel tubing or pipe. Referring to Figure 4, flexible drill pipe sections 102, 102A, and 102B are characterized by a laser cutting profile 120. Laser cutting profile 120 is preferably machined out of solid steel tubing (or pipe) using a computer controlled laser cut machining process. In a laser cut process, a computer guides a laser across a workpiece, in this case a length of tubing or pipe, while the laser cuts a predetermined pattern. Because the material properties of the workpiece are known, the intensity and power of the laser can be adjusted so the laser does not penetrate farther into the workpiece than desired. Therefore, with a 1.80 inch (4.5 cm) outside diameter, 0.2 inch (0.5 cm) thickness steel tubing workpiece, the laser cutter can be configured to not cut substantially deeper than the 0.2 inch (0.5 cm) wall thickness. Furthermore, to prevent scarring of the other side of the tubing, a mandrel may be located in the central bore of the tubing to be cut, whereby the tubing to be cut is drawn over and rotated about the mandrel as it is laser cut. This way, any "overage" in laser output will result in superficial cutting of the mandrel, and not the other side of the tubing. Additionally, cutting profile 120 can be similarly manufactured through a water jet cutting process, one whereby a high pressure water jet is used in place of the laser. However, the laser cutter would be preferred over the water jet for its accuracy and precision of cutting as laser light scatters much less in industrial machining applications than water. Furthermore, a WireEDM solution can be employed to cut the profile 120 of Figures 4. A WireEDM machine makes its cuts by passing an energized and coated wire against the workpiece to be cut. Referring to Figure 4, one embodiment for a general pattern of cutting profile 120 can be described. Cutting profile 120 can form interlocking rings 121 having T-shaped members 124 along the length L of a workpiece. Each ring 122 is formed from one cut around the circumference of the workpiece, where the starting point and ending point for a cut are both located at a given point 122 along a path 130. Referring particularly to Figure 4, details of cutting profile 120 can be described. While one pattern for cutting a workpiece to make flexible pipe section 102, 102A, 102B is shown, it should be understood by one of ordinary skill that numerous variations to the pattern design and proportions shown may be made without departing from the spirit of the invention. Cutting profile 120 is machined by cutting along path line 130 from the start point 122 around the circumference of the workpiece, returning to point 122. Multiple cut paths 130 are made along length L of the workpiece which can provide male threads at one end and female threads at the opposing end. Preferably, the laser (or other cutter machine) head is maintained stationary while the workpiece is rotated about its center axis and displaced as necessary along its length L by a computer numerical controlled (CNC) manipulator assembly. Because the computer manipulator is highly accurate and precise, extraordinarily fine cuts are achievable. Once profile 120 is cut along multiple path lines 130, the chips and loose cuttings are removed, leaving voids 132 and slip planes 134 behind. Slip planes 134 allow machined lips 136 to travel in the direction of workpiece center axis A when tension is applied thereacross, thereby allowing the cut workpiece to flex and bend elastically. This elastic bending allows the finished workpiece (or section 102 of Figures 1-3) to be bent into various radiuses and configurations without experiencing any "memory" following the deflection. Uncut ends 140 are threaded or otherwise manufactured to form a male or female connection 104, 108, 110, or 112. Referring briefly to Figure 5, a second embodiment for the general pattern of a cutting profile is described. Cutting profile 150 preferably includes a starting point 152, and a finishing point 154 along a length L as a workpiece 156 is displaced along its axis A. Profile 150 is preferably cut as a single helical cut throughout the entire length L to be cut, although multiple helical designs may be used without departing from the spirit of the claimed invention. Particularly, using a laser cutting machine having two or more laser cutting heads, two or more helixes may be cut simultaneously, thereby reducing the amount of time to machine workpiece 156 proportionally to the number of helixes cut. For example, a machine having two laser heads cutting a double-start helix can cut a length of a profile in half the time as a single laser machine. Referring particularly to Figure 5A, details of cutting profile 150 can be described. While one pattern for cutting workpiece 126 to make flexible pipe section 102, 102A, 102B is shown, it should be understood by one of ordinary skill that numerous variations to the pattern design and proportions shown may be made without departing from the spirit of the invention. Cutting profile 150 is machined by cutting along path line 160 from the start point 152 to the finish point 154 along length L of workpiece 156. Preferably, the laser (or other cutter machine) head is maintained stationary while the workpiece 156 is rotated about its center axis and displaced along its length L by a computer numerical controlled (CNC) manipulator assembly. Because the computer manipulator is highly accurate and precise, extraordinarily fine cuts are achievable. Once profile 150 is cut along path line 160, the chips and loose cuttings are removed, leaving voids 162 and slip planes 164 behind. Slip planes 164 allow machined lips 166 to travel in the direction of workpiece center axis A when tension is applied thereacross, thereby allowing workpiece 156 to flex and bend elastically. This elastic bending allows workpiece 156 (or section 102 of Figures 1-3) to be bent into various radiuses and configurations without experiencing any "memory" following the deflection. If workpiece 156 were not to return to its original position, it would be evidence of plastic deformation in the material of workpiece 156, thereby indicating a material weakening of the device. Furthermore, the cuts at locations 168, when combined with the angle of helical path cutting angle α, allow for a torsional "spring action" in one direction or rotation about axis A. Preferably, angle α is selected to allow slight torsional elasticity in the counterclockwise direction, but not in the clockwise direction. Because drill bit torque is typically applied in the clockwise direction, elasticity in the clockwise direction would be undesirable, however torsionally elastic behavior in the counter-clockwise, "back off direction could be effective in unsticking a stuck drilling apparatus 100. The combination of helix angle α with the thickness of cut at path 160 to produce slip and bending planes at 164 and 168 makes finished workpiece 156 very flexible, yet very strong torsionally (in the clockwise direction) and axially. The resulting spring-action drillstring can be referred to as a drill spring. The drill spring just described is formed from a single cut path along the length of the drillstring, resulting in interaction between L- shaped members along a continuous helix. Interlocking rings having L-shaped members, similar to the interlocking rings having T-shaped members could also be used. Examples Using the cutting profile 120 as shown in Figure 4, on a 1.8 inch (4.5 cm) outside diameter, 0.2 inch (0.5 cm) thickness steel pipe, a complete 90° bend is possible in as little as 8 inches (20.3 cm). That results in a bend radius less than 5 times the outer diameter of the pipe. Using the helical cutting profile 150 as shown in Figure 5, on a

1.8 inch (4.5 cm) outside diameter, 0.2 inch (0.5 cm) thickness steel pipe, a complete 90° bend is possible in as little as 12 inches (3.5 cm). That results in a bend radius less than 6 times the outer diameter of the pipe. In contrast, with the flexibility of "regular" rigid drill pipe, most 20-40 foot (6 - 12 m) long joints of drill pipe are only deflectable from 0 to 10 degrees. Thus, a rigid drill pipe can take more than 200 feet to make a complete 90 bend. The flexible drillstring of the present invention results in a bend radius which is but a fraction of the distance required by a rigid drill string. The smaller bend radius can allow drilling operations to take advantage of coalbed seams of limited size, as well as minimizing the uncertainty that the drilling operation will "hit" the intended drilling target. As illustrated by the above description and examples, design parameters affecting the resulting bend radius of the flexible drillstring of the present invention include pipe thickness, pipe diameter, the cut path design (such as number of interlocking members per circumference), cut path thickness, and angle α. Approriate changes in the design parameters of the flexible drillstring can result in bend radiuses less than 5 times the outer diameter of the pipe. By cutting the flexible drillstring in either of the manners described above, the drillstring after going around the ultrashort radius then locks in a straight line thereby providing a straight hole from the bend forward unlike prior art flexible drillstrings commonly referred to as "baseball stitch articulated drillstrings" which provided flexible but uncontrollable drillstrings. Numerous embodiments and alternatives thereof have been disclosed. While the above disclosure includes the best mode belief in carrying out the invention as contemplated by the named inventors, not all possible alternatives have been disclosed. For that reason, the scope and limitation of the present invention is not to be restricted to the above disclosure, but is instead to be defined and construed by the appended claims. Finally, reference has been made to a "rigid" versus a "flexible" drillstring. It should be understood by one of ordinary skill in the art that all drillstrings are somewhat "flexible" at long lengths and the terms rigid and flexible are intended to be relative, not absolute terms. The flexible drillstring of the present invention is intended to be capable of much smaller radiuses of flexure that a typical (or standard) rigid drillstring.

Claims

CLAIMS What is claimed is:

1. A flexible drilling apparatus comprising: a drillstring, said drillstring located between a drill bit and a tool joint; said drillstring characterized by an outer diameter, a thickness, and a length, wherein said thickness includes a flexibility profile cut therethrough along said length; said flexibility profile is configured to allow said drillstring to bend elastically along said length at a bend radius.

2. The flexible drilling apparatus of claim 1 wherein said flexibility profile cut is a series of lateral interlocking cuts.

3. The flexible drilling apparatus of claim 2 wherein the series of lateral interlocking cuts form a continuous chain of interlocking rings having T-shaped members.

4. The flexible drilling apparatus of claim 1 wherein said flexibility profile is helical.

5. The drilling apparatus of claim 4 wherein said flexibility profile is configured to allow torsional elasticity about an axis of said outer diameter in a first direction.

6. The drilling apparatus of claim 5 wherein said flexibility profile is configured to resist torsional elasticity about said axis in a second direction.

7. The drilling apparatus of claim 1 wherein said bend radius is less than said outer diameter multiplied by 10.

8. The drilling apparatus of claim 1 wherein said bend radius is less than said outer diameter multiplied by 7.

9. The drilling apparatus of claim 1 wherein said bend radius is less than said outer diameter multiplied by 5.

10. The drilling apparatus of claim 1 wherein said bend radius for a 1.8 inch (4.5 cm) diameter drillstring is 12 inches (30.5 cm) or less.

11. The drilling apparatus of claim 1 wherein said bend radius for a 1.8 inch (4.5 cm) diameter drillstring is 8 inches or less (20.3 cm or less).

12. The drilling apparatus of claim 1 wherein said drill bit is a single cone nutating drill bit.

13. The drilling apparatus of claim 1 further comprising a hose to deliver drilling fluids through a bore of said drillstring to said drill bit.

14. The drilling apparatus of claim 1 wherein said flexibility profile is manufactured from a single continuous cut.

15. The drilling apparatus of claim 1 wherein said flexibility profile is manufactured from two or more continuous cuts.

16. The drilling apparatus of claim 1 further comprising a wear band stabilizer upon said drillstring proximate to said drill bit.

17. The drilling apparatus of claim 16 wherein said wear band stabilizer is profiled to facilitate flow of fluids and debris thereacross.

18. The drilling apparatus of claim 16 wherein said wear band stabilizer creates a relatively rigid zone of said drillstring proximate said drill bit.

19. The drilling apparatus of claim 16 wherein said wear band stabilizer is configured to be replaceable.

20. The drilling apparatus of claim 16 wherein said wear band stabilizer comprises a material harder than said drillstring.

21. The drilling apparatus of claim 1 wherein said flexibility profile is manufactured from a laser machining process.

22. A method to manufacture a flexible drillstring, the method comprising: mounting a length of pipe into a laser cutting machine, wherein the laser cutting machine includes a laser cutting head with a variable output laser; positioning a mandrel within the length of pipe, the mandrel configured to guide the length of pipe to and past the laser cutting head; energizing the laser cutting head to cut the length of pipe; and rotating and engaging the length of pipe across the laser cutting head to create a continuous cut flexibility profile.

23. the method of claim 22 wherein the rotating and engaging is performed by a computer controlled manipulator assembly.

24. The method of claim 22 further comprising a second laser cutting head, wherein the two laser cutting heads cut separate continuous helical paths of the flexibility profile.

25. The method of claim 22 wherein the laser cutting head is stationary and only the length of pipe is moved.

26. A method to manufacture a helical flexibility profile of claim 1 , the method comprising: mounting a section of pipe to be cut into the drillstring upon a mandrel of a continuous linear cutting machine; energizing the linear cutting machine; and rotating and engaging the section of pipe across the linear cutting machine with a computer controlled manipulator assembly to create the flexibility profile.

27. The method of claim 26 wherein the continuous linear cutting machine is a laser cutting machine.

28. The method of claim 26 wherein the continuous linear cutting machine is a water jet cutting machine.

29. The method of claim 26 wherein the continuous linear cutting machine is a WireEDM machine.