WO2011049573A1

WO2011049573A1 - Em telemetry gap sub

Info

Publication number: WO2011049573A1
Application number: PCT/US2009/061678
Authority: WO
Inventors: Allen Richard Young; James F. Huber; Laura Sue Fore
Original assignee: Ms Energy Services
Priority date: 2009-10-22
Filing date: 2009-10-22
Publication date: 2011-04-28
Also published as: CA2778434A1

Abstract

An insulator system for insulating a first member from a second member. The system includes a first member and a second member, wherein a first end of the first member is coupled to a second end the second member to form an attachment point. The insulator system also includes a binder disposed at the attachment point between the first member and the second member, and a plurality of insulating particles (IPs) dispersed within the binder, wherein the binder and the plurality of IPs comprise dielectric materials.

Description

EM TELEMETRY GAP SUB

TECHNICAL FIELD

[0001] The present invention relates in general to insulating a tubular assembly and more specifically to insulating a gap sub assembly.

BACKGROUND

[0002] Since the inception of Measurement While Drilling (MWD), at least two distinct means have been used to telemeter directional, stratigraphic, and/or other information measured downhole to the surface during drilling operations. One method is Mud Pulse Telemetry, a method that modulates surface pressure in the drilling mud flow as a string of digital pulses. Another method utilizes the drill pipe and Bottom Hole Assembly (BHA) as an electrical current dipole, a form of antenna for transmitting information. The pipe and BHA form a string that is made into a dipole antenna by inserting an insulating gap sub-assembly in the string to insulate one end of the string from the other end. This allows the resulting dipole antenna to be driven by a downhole transmitter circuit sending data from downhole sensors and associated microelectronics. Voltages resulting from the downhole electrical current flow may be detected and the information decoded at the surface of the ground using metal rod antennae, appropriate electronic receiver amplifiers, signal conditioning and computing equipment.

[0003] Since the inception of EM Telemetry, many methods have been used to provide robust electrical insulation while providing high mechanical strength, two requirements that are difficult to simultaneously achieve. For instance, a Gap Sub assembly may be formed by a threaded pin connected to a box. A thin layer of dielectric material may be provided to prevent electric current from passing between the pin and box. However, the dielectric material must also have high strength to withstand high torsion, compressive, bending, and other loads that may be exerted on the gap sub assembly. Accepted insulation methods, such as ceramic coating on a modified American Petroleum Institute (API) threads, may be expensive to implement. These coatings can be easily damaged during assembly and typically have a downhole lifetime of 300 hours or less.

[0004] Therefore, it is a desire to provide a low cost, high strength, and reliable dielectric material that may be utilized as an insulator in downhole tool, such as a gap sub assembly.

SUMMARY

[0005] In view of the foregoing and other considerations, the present invention relates to an improved insulator for a downhole tool.

[0006] Accordingly, an embodiment provides an insulator system for insulating a first member from a second member. The system includes a first member and a second member, wherein a first end of the first member is coupled to a second end the second member to form an attachment point. The insulator system also includes a binder disposed at the attachment point between the first member and the second member, and a plurality of insulating particles (IPs) dispersed within the binder, wherein the binder and the plurality of IPs comprise dielectric materials.

[0007] Yet another embodiment provides a method for insulating a gap sub assembly. The method includes aligning an upper sub pin and a lower sub box of the gap sub assembly, and inserting a plurality of insulating particles (IPs) into a fill hole, wherein the fill hole leads to a gap between the upper sub pin and the lower sub box, the plurality of IPs separating the upper sub pin and the lower sub box.

[0008] The foregoing has outlined some of the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The foregoing and other features and aspects of the present invention will be best understood with reference to the following detailed description of a specific embodiment of the invention, when read in conjunction with the accompanying drawings, wherein:

[0010] Figure 1 is an illustrative embodiment of the electromagnetic telemetry system disclosed herein;

[0011] Figure 2 A is an embodiment illustrating similarly sized IPs dispersed in a binder; [0012] Figure 2B is an embodiment illustrative IPs of various sizes dispersed in a binder; [0013] Figure 2C is an embodiment illustrating small IPs dispersed in a binder to for a grit; [0014] Figure 3 is an illustrative embodiment of a gap sub assembly;

[0015] Figure 4 is a close up view of a portion of a gap sub in an embodiment utilizing single threads

[0016] Figure 5 is a close up view of a portion of a gap sub in an embodiment utilizing double threads;

[0017] Figure 6 is an embodiment illustrating gap sub combining threads and grooves;

[0018] Figure 7 is an embodiment illustrating gap sub secured utilizing IPs and grooves; and

[0019] Figure 8 is a close up view of a portion of gap sub illustrating an embodiment of face seal. DETAILED DESCRIPTION

[0020] Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views.

[0021] Telemetry may be utilized in a drilling string to provide information regarding performance of the drilling operation, which is common in operations such as measurements while drilling (MWD). Figure 1 is an illustrative embodiment of an electromagnetic (EM) telemetry system 10. One way of transmitting telemetry information from the tool string to the surface utilizes an EM signal imposed between a pin and box portion of a gap sub assembly 15. This may require electrical isolation across gap sub assembly 15 to form an electric dipole. The remainder of the dipole may be formed by a bottomhole assembly (BHA) 20 attached below gap sub 15 and a drill pipe 25 attached above gap sub 15.

[0022] The electric dipole thus formed may be driven by a transmitter circuit that drives an electric current into the downhole rock formation adjacent to gap sub 15, BHA 20 and drill pipe 25. The amplitude of the currents may diminish as distance from gap sub 15 increases. These currents flow roughly in the shape of an oblate spheroid and the voltage equipotential lines are perpendicular to the current. The voltage equipotential lines may be detected at earth's surface, which may diminish radially outward away from the wellhead.

[0023] Because these equipotential lines appear at earth's surface, receiver antennae 30 can be placed at distances varying from zero to hundreds of meters from the wellhead, with a minimum of two antennae being required to detect a voltage differential (AV). A surface device 32 may measure AV and store, display, and/or transmit the telemetry data as desired. For example, surface device 32 may include a computer system, a display, a receiver and/or transmitter, storage and the like. The voltage potentials induced by the driven gap sub 15 and received at earth's surface are modulated upon transmission to represent the varying physical parameters being measured downhole. The data represented may include measurements of borehole trajectory, natural gamma radiation intensity or electrical resistivity to determine formation lithology, and other parameters.

[0024] A durable, high strength electrical insulation between a pin and box of gap sub assembly 15 is needed given that the entire torque transmitted through drill pipe 25 must be imparted to BHA 20 through gap sub 15. Further, gap sub assembly 15 may be subject to bending during directional drilling and the like. Methods such as ceramic coating of modified American Petroleum Institute (API) threads may be expensive to implement and may be less reliable than the methods and systems discussed herein. Further, ceramic coatings may be brittle and may crack when subjected to forces exerted on the ceramic during drilling operations.

[0025J Disclosed herein are illustrative embodiments of systems and methods for insulating a first member from a second member that utilizes a binder in conjunction with insulating particles (IPs) dispersed in the binder. Various embodiments are discussed herein utilizing a gap sub assembly as an exemplary implementation. However, these embodiments are merely illustrative, and the various embodiments can be applied to any suitable systems. The binder may be a high strength, high temperature epoxy (e.g. Contronics Duralco™ 4525) capable of withstanding temperatures of 200°C, and the IPs may be a high strength, dielectric material such as ceramics or metal oxides including zirconium, yttrium oxides, or any other suitable, high strength insulation materials. Preferably, the high strength IPs will have a crush strength greater than or equal to 100,000 PSI. In preferred embodiments, IPs may be spherical in shape as discussed herein. However, alternative embodiments may utilize any suitable shapes or combination of shapes such as spheroids, cubes, substantially irregular shapes, and the like. The physical size of the IPs used may vary from approximately 0.2 mm to 4 mm, for example, depending upon the dimensions of gap sub 15, the ease of assembly and durability desired for a given purpose. In some embodiments, large 4 mm IPs might be so large that the threads and/or grooves do not physically interlock except for the tangential contact of the interstitial IPs that would form a helical stack between the threads and/or grooves. The IPs dispersed in the binder may all be approximate the same size or IPs of various sizes may be dispersed in the binder. For example, Figure 2A is an embodiment illustrating similarly sized IPs 75 dispersed in a binder 70. In this embodiment, the IPs 75 are preferably relatively large, e.g. about 4 mm. Figure 2B is an embodiment illustrating IPs 75 of various sizes dispersed in a binder 70. Small-diameter IPs 75, such as 0.2 mm particles, might be dispersed in binder 70 such that an insulating "grit" may insulate closely-spaced threads. For example, Figure 2C is an embodiment illustrating small IPs 75 dispersed in a binder 70.

[0026] The resiliency of the binder 70 and the high strength of the insulating particles 75 provide an insulator that may be less prone to cracking, while still being capable of withstanding loads exerted on it during drilling operations. The distribution of torque loads over hundreds or thousands of IPs 75 being held in place by a high strength binder 70 results in a low-cost, easily replaced insulator. In addition, while this insulator may eventually fail, the mean time between failure (MTBF) should compare favorably with other insulators. Further, failure of the insulator should be gradual enough to present visual signs of wear and fatigue sufficiently in advance of failure to allow replacement prior to failure.

[0027] Figure 3 is an illustrative embodiment of a gap sub assembly 15. Gap sub 15 may provide an upper sub pin 35 and lower sub box 40. An insulator 45 is provided between upper sub pin 35 and lower sub box 40 to prevent current flow. By placing gap sub 15 in a string, gap sub 15 may prevent current from flowing between components attached on opposite ends of gap sub 15. Pin 35 and box 40 may provide threads and/or helix shaped grooves 50 utilized to couple pin 35 and box 40 to each other. Because pin 35 and box 40 may be made of an electrically conductive material, insulator 45 is provided to prevent current flow across gap sub 15. In some embodiments, a shoulder 55 may be provided that limits the distance pin 35 is threaded into box 40. Gap sub 15 may also include an inner gap ring 60 and outer gap ring 65 separating pin 35 and box 40.

[0028] In an EM telemetry system, a BHA and drill pipe may be attached to opposite sides of gap sub 15. The BHA, drill pipe, and gap sub 15 may be made of metal in order to handle the various forces exerted on the components during drilling. Insulator 45 in gap sub 15 may prevent electric current from passing between the BHA to the drill pipe and vice versa. Insulator 45 comprises a binder 70 and IPs 75 as shown in the various embodiments in Figure 2A-2C. As shown, insulator 45 fills inner gap ring 60, shoulder 55, threads and/or grooves 50, and outer gap ring 65. This substantially prevents direct contact between pin 35 and box 40 and may provide an electrical isolation across gap sub 15. However, insulator 45 may also be subject to abrasion from drilling mud and/or contact with the borehole wall. In one embodiment, wear bands 68 may be place above and below gap sub assembly 15 to reduce abrasion to insulator 45. Abrasion from drilling mud may wear away insulator 45, such as portions of the binder. However, the IPs in insulator 45 may have enough strength to reduce the velocity (e.g. create a stagnation point) in the flow of the drilling mud and resist erosion of the IPs.

[0029] Figure 4 is a close up view of a portion of a gap sub 15 in an embodiment utilizing larger IPs 75 within single threads 50. Pin 35 is threaded to box 40 to couple pin 35 and box 40 in gap sub 15, but an insulator prevents electric conductivity between pin 35 and box 40. The insulator is made from a binder 70 and insulating particles (IPs) 75, which are used to block current flow through gap sub 15. IPs 75 may also hold pin 35 and box 40 spatially apart withstanding various forces exerted during drilling operations and the like. The remaining interstitial space not occupied by IPs 75 is filled by a binder 70, such as an epoxy or any other suitable material. The resiliency of binder 70 may make the insulator less likely to crack during drilling operations. Binder 70 and/or IPs 75 provide a suitable resistance across gap sub 1 (e.g. 1 ΜΩ). However, in embodiments utilizing other materials for the binder 70 and IPs 75, the resistance may vary.

[0030] In some embodiments, it may be necessary to drill one or more fill holes in gap sub 15 near the start and/or end of the threads to allow binder 70 and IPs 75 to be inserted between threads 50. In one embodiment, pin 35 and box 40 may be axially aligned for assembly. Essentially pin 35 or box 40 is suspended above the other portion of gap sub 15 so that the central axis is aligned. Prior to coupling the threads of pin 35 and box 40, IPs 75 may be inserted through fill hole 80 to fill spaces provided in between the threads of pin 35 and box 40. Proper axial alignment may allow IPs 75 to be inserted into fill hole 80 and the IPs 75 may run down the threads. In other embodiments, applying external vibration, injecting IPs 75 with compressed air, and/or rotating pin 35 or box 40 back-and-forth may be utilized to move IPs 75 into a desired position in threads 50. Once the IPs 75 are in place, pin 35 and box 40 may be torqued together causing IPs 75 to be forced into tangential contact with threads 50 of pin 35 and box 40 locking IPs 75 in place. However, in other embodiments, pin 35 and box 40 may be torqued together after binder 70 is injected.

[0031] Next, binder 70 may be injected through fill hole 80. Binder 70 may be applied in a liquid state to allow binder 70 to flow and effectively fill the voids that are not occupied by IPs 75. In some embodiments, a clam shell like mold place around pin 35 and box 40 may be utilized, and the binder 70 may be injected through a fill hole to form the insulator (i.e. injection molding). In some embodiments, binder 70 may be injected utilizing an compressed air powered gun (e.g. grease gun) or the like. In some embodiments, it may be preferable to inject binder 70 through bottom port to minimize the occurrence of air bubbles. Depending on the type of binder 70 utilized, it may be necessary to place a heater in contact with gap sub 15 to cure binder 70. While the embodiment discussed utilizes single threads, the threads for the pin 35 and box 40 do not need to be conventional in shape and type because the IPs may act as load bearing elements. The threads may be standard API threads, non-API threads, single threads, double threads, or the like. In other embodiments, methods to enhance the filling of voids, such as evacuation or even reduction of epoxy surface tension by chemical means, may be utilized. For instance, in one embodiment, a vacuum or degassing may be utilized when injecting binder 70 to prevent air gaps and air bubbles from forming. [0032] Other embodiments can include the use of multiple sizes of IPs 75 to optimize mixture strength in a fashion similar to using finely graded aggregates to strengthen concrete. For example, finely graded IPs 75 may be mixed into binder 70 to form an insulating "grit" that increase the strength of the mixture. In one embodiment, an insulating grease may be applied as well to facilitate the torque down of the threads. Further, a shoulder of additional insulating material may be applied prior to torquing the threads together to prevent damage to binder 70 and IPs 75 during coupling of the threads.

[0033] In some embodiments, the IPs 75 may have a hardness and crush strength higher than the metals comprising pin 35 and box 40. As a result, localized deformation of the metals may occur in pin 35 and box 40 reducing the contact pressure upon the IPs 75 by distributing the thread mating torque over more surface area of the IPs 75. In some embodiments, a softer metallic plating 85 could be deposited, using techniques such as electrodepositing, onto the harder base metal of pin 35 and/or box 40 to enhance force distribution. Distributing force over a greater surface area of the IPs 75 may prevent IPs 75 from being crushed prior to achieving peak loading during the thread torque-up process.

[0034] Figure 5 is a close up view of a portion of a gap sub 15 in an embodiment utilizing double threads 50. Pin 35 and box 40 may be coupled together utilizing double threads. In an embodiment utilizing double threads, some threads may only have binder 70 disposed in the thread instead of IPs 75. Binder 70 may provide shouldering similar to the shouldering that would be provided if the threads were in contact. As with the single thread embodiment, IPs 75 may be inserted prior to injection of binder 70. Once binder 70 hardens, gap sub 15 is ready to withstand forces that may be exerted on it during drilling operations. Binder 70 and IPs 75 may also be subject to abrasion by flow from drilling mud and/or borehole contact. While a small portion of the binder 70 and IPs 75 may be removed by abrasion, electric isolation may still remain across gap sub 15.

[0035] Figure 6 is an embodiment illustrating gap sub 15 combining threads 105 and grooves 1 10. Pin 35 may be coupled to box 40 utilizing threads 110. In addition to threads 1 10, pin 35 and box 40 may also provide grooves 105 following the same tapered helical axis. Grooves 105 form a channel when pin 35 and box 40 are coupled together that provides space for IPs 75 to fill. Fill hole 80 provides an opening for IPs 75 to be inserted into the channel formed by grooves 105. Once IPs 75 are in a desired position in grooves 105, a binder may be injected through fill hole 80 to fill the remaining space.

[0036] Figure 7 is an embodiment illustrating gap sub 15 secured utilizing IPs 75 and grooves 1 10. Both pin 35 and box 40 provide grooves 105 to house IPs 75. When grooves 105 of pin 35 and box 40 are properly aligned, a helical channel is provided for IPs 75. Because threads are not utilized in this embodiment, it should be noted that pin 35 can be vertically inserted into and take out of box 40 without requiring rotation of pin 35 or box 40.

[0037] As IPs 75 are inserted into fill hole 80, the IPs 75 may roll down the channel formed by grooves 105. As discussed previously, a variety of additional techniques can be utilized to ensure that IPs 75 fill grooves 105 including compressed air injection, vibration, rotating pin35 or box 40 back-and-forth, and the like. Once IPs 75 are within grooves 105, pin 35 cannot be separated from box 40 without rotation of pin 35 or box 40. Additionally, a ring of IPs 75 may be place between pin 35 and box 40 to form a face seal as discussed in detail below.

[0038] Figure 8 is a close up view of a portion of gap sub 15 illustrating an embodiment of face seal 1 15. Pin 35 is coupled to box 40 utilizing IPs 75 placed within grooves 105 through fill hole 80. Groove rings 120 are cut into pin 35 and box 40 so that a ring of IPs 75 may be place between pin 35 and ring 40. IPs 75 isolate the upper face of pin 35 from the lower face of box 40 and act in a similar manner as ball bearings in a thrust bearing. When a binder is injected to fill grooves 105, the binder may also fill the gap created by IPs 75 of face seal 1 15. While several of the embodiments discussed herein may discuss a combination of specific features, it should be noted that many of the features are interchangeable within a variety of the embodiments. For instance, while a face seal is discussed in an embodiment utilizing grooves, it can be utilized in embodiments utilizing threads. Further, while many of the figures illustrate embodiments utilizing large IPs, other embodiments utilizing a variety of different IPs sizes can be utilized as desired. The various embodiments discussed herein are provided for illustrative purposes only, and any suitable combinations of features discussed herein can be implemented.

[0039] While several embodiments are discussed with reference to measurements while drilling (MWD) applications, other embodiments can be applied to other needs such as galvanic isolation of pipe to prevent corrosion or any other suitable application that requires or is enhanced by the insulation of one tubular metallic element from another. The combination of the binder and IPs in the insulator for the gap sub assembly provides the resiliency of the binder and the compressive strength of the IPs. While IPs may be crushed by forces exerted during drilling operations, the binder is less brittle than the IPs and less likely to crack. Further, while portions of the binder and IPs may be worn away by abrasion, the wear is visible on the exterior of the gap sub assembly and may allow the insulator to be replaced prior to failure.

[0040] From the foregoing detailed description of specific embodiments of the invention, it should be apparent that a system for providing a high strength insulation for a gap sub assembly that is novel has been disclosed. Although specific embodiments of the invention have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects of the invention, and is not intended to be limiting with respect to the scope of the invention. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope of the invention as defined by the appended claims which follow.

Claims

WHAT IS CLAIMED IS:

1. An insulator system for insulating a first member from a second member, the system comprising: a first member; a second member, wherein a first end of the first member is coupled to a second end the second member to form an attachment point; a binder disposed at the attachment point between the first member and the second

member; and a plurality of insulating particles (IPs) dispersed within the binder, wherein the binder and the plurality of IPs comprise dielectric materials.

2. The system of claim 1, wherein the binder is an epoxy resin.

3. The system of claim 2, wherein the plurality of IPs have a crush strength greater than about 100,000 PSI.

4. The system of claim 1 , wherein the plurality of IPs comprise a ceramic material or a metal oxide.

5. The system of claim 4, wherein the plurality of IPs comprise a material selected from the group consisting of zirconia, zirconium oxide, and yttrium oxides.

6. The system of claim 1 , wherein the plurality of IPs are spheres, elliptical spheres, or spheroids.

7. The system of claim 1 , wherein the plurality of IPs are substantially identical in size and shape.

8. The system of claim 1, wherein the plurality IPs are substantially different sizes and shapes.

9. The system of claim 1, wherein sizes of the plurality of IPs range from approximately 0.2 to 4 mm.

10. The system of claim 1 , wherein the first member and the second member include API standard threads, non-standard threads, double threads, or single threads.

.

1 1. The system of claim 1 , wherein the first end of the first member and the second end of the second member provide grooves, the grooves forming a helical channel when the first end of the first member is aligned with the second end of the second member.

12. The system of claim 1 , wherein a layer of metallic plating is formed between the

attachment point, the layer of metallic plating having hardness lower than the IPs.

13. The system of claim 1, wherein the first member is a lower sub box and the second member is an upper sub pin, and the lower sub box and the upper sub pin form a gap sub assembly when coupled together.

14. The system of claim 13 further comprising: a ring of IPs disposed between an upper face of the upper sub pin and a lower face of the lower sub box, wherein the ring of IPs prevents contact between the upper face and the lower face.

15. A method for insulating a gap sub assembly, the method comprising: aligning an upper sub pin and a lower sub box of the gap sub assembly; and inserting a plurality of insulating particles (IPs) into a fill hole, wherein the fill hole leads to a gap between the upper sub pin and the lower sub box, the plurality of IPs separating the upper sub pin and the lower sub box.

16. The method of claim 15 further comprising: injecting a binder into the fill hole, wherein the binder fills space remaining in the gap between the upper sub pin and the lower sub box; and torquing the upper sub pin and the lower sub box together, wherein the torquing causes the plurality of IPs to come in contact with the upper sub pin and the lower sub box.

17. The method of claim 16, wherein the binder is injected utilizing a compressed air gun.

18. The method of claim 16 further comprising: attaching a vacuum to the gap sub assembly, wherein the vacuum prevents air bubbles and air gaps from forming in the binder.

19. The method of claim 16, wherein upper sub pin and the lower sub box are coupled together with enough force to cause local deformation in the upper sub pin and the lower sub box from contact with the IPs.

20. The method of claim 15 further comprising: placing a ring of IPs between an upper face of the upper sub pin and a lower face of the lower sub box, wherein the ring of IPs prevents contact between the upper face and the lower face.