CA2496170C - Gap sub assembly - Google Patents
Gap sub assembly Download PDFInfo
- Publication number
- CA2496170C CA2496170C CA002496170A CA2496170A CA2496170C CA 2496170 C CA2496170 C CA 2496170C CA 002496170 A CA002496170 A CA 002496170A CA 2496170 A CA2496170 A CA 2496170A CA 2496170 C CA2496170 C CA 2496170C
- Authority
- CA
- Canada
- Prior art keywords
- pin
- box
- gap sub
- sub assembly
- connection
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
- 239000002759 woven fabric Substances 0.000 claims abstract description 7
- 239000004744 fabric Substances 0.000 claims description 11
- 239000000919 ceramic Substances 0.000 claims description 6
- 238000005553 drilling Methods 0.000 claims description 5
- 230000000903 blocking effect Effects 0.000 claims description 3
- 239000012530 fluid Substances 0.000 claims description 3
- 239000004593 Epoxy Substances 0.000 claims description 2
- 229910000831 Steel Inorganic materials 0.000 description 3
- 230000000712 assembly Effects 0.000 description 3
- 238000000429 assembly Methods 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000010959 steel Substances 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000005755 formation reaction Methods 0.000 description 2
- 241000628997 Flos Species 0.000 description 1
- 229920000271 Kevlar® Polymers 0.000 description 1
- 230000003466 anti-cipated effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000005524 ceramic coating Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 239000003989 dielectric material Substances 0.000 description 1
- 239000012777 electrically insulating material Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000004761 kevlar Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000004848 polyfunctional curative Substances 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
- E21B17/003—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings with electrically conducting or insulating means
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
- F16L25/00—Constructive types of pipe joints not provided for in groups F16L13/00 - F16L23/00 ; Details of pipe joints not otherwise provided for, e.g. electrically conducting or insulating means
- F16L25/02—Electrically insulating joints or couplings
- F16L25/021—Electrically insulating joints or couplings for screw-threaded joints
Landscapes
- Engineering & Computer Science (AREA)
- Mining & Mineral Resources (AREA)
- Mechanical Engineering (AREA)
- Geology (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Engineering & Computer Science (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Fluid Mechanics (AREA)
- Environmental & Geological Engineering (AREA)
- Physics & Mathematics (AREA)
- Geochemistry & Mineralogy (AREA)
- Earth Drilling (AREA)
- Insulating Bodies (AREA)
- Connections By Means Of Piercing Elements, Nuts, Or Screws (AREA)
- Connections Arranged To Contact A Plurality Of Conductors (AREA)
- Multi-Conductor Connections (AREA)
Abstract
The gap sub assembly comprises a pair of electrically conductive subs. Each sub has a threaded pin and box. A pin and box are threaded together to form a connection. An electrically insulating, woven fabric overlies and conforms with the threads of the connection pin. An electrically insulating, annular washer separates the seal faces of the connection. The assembly functions to provide an electrical discontinuity when incorporated into a conductive drill string.
Description
1 "GAP SUB ASSEMBLY"
2 FIELD OF THE INVENTION
3 The present invention relates to an electrically insulating gap sub
4 assembly for use in a drill string. The gap sub assembly functions to block current flow through the drill string.
8 It is known in oilfield drilling technology to provide an assembly, at the 9 lower end of a drill string drilling a wellbore, for transmitting downhole data, measured by sensors, to a receiver at ground surface. This transmission is done 11 by means of electric signals passing upwardly through the formation penetrated 12 by the wellbore.
13 For example, it is known to measure the inclination and direction of the 14 wellbore adjacent the bit using an EMT tool. The EMT tool includes a signal generating unit spaced behind the drill bit. This unit produces alternating current 16 signals indicative of the measurements taken by downhole sensors.
17 In conjunction with the signal generating unit it is necessary to provide, in 18 the drill string, a device that will block current flow through the conductive steel 19 pipe of the drill string, to thereby induce the current flow to move upwardly to ground surface through the formations penetrated by the wellbore.
21 One known device in use for this purpose is commonly referred to as a 22 'gap sub assembly'.
1 The gap sub assembly comprises a pair of tubular pipe subs threadably 2 connected end to end by a pin and box connection. A'sub' is industry 3 terminology for a short length of pipe having threaded pin and box ends. A
pin 4 and box are threaded together to form a 'connection' joining the two subs end to end. The sub also usually has a shoulder, at the pin root, forming an annular 6 face. In such a case, the box used forms an annular end face . These faces are 7 provided to press together and seal when the connection is 'made up', thereby 8 preventing the egress of drilling fluid into the well annulus.
9 Heretofore, commercially used gap sub assemblies have usually involved applying a coating of dielectric material, such as ceramic or the material identified 11 by the trade-mark TEFLONTM, and bonding it onto the threads of the pin and the 12 end faces of the connection. In this way an electrically insulated gap is provided.
13 When the gap sub assembly is incorporated into the electrically conductive drill 14 string, the gap serves to block current flow along the string.
However, these known gap sub assemblies have shortcomings. The 16 assemblies are subject to severe compressive and tensile stresses in use.
The 17 brittle ceramic coatings tend to crack and chip, thereby leading to loss of the 18 electric discontinuity. And the TeflonTM coating may extrude during use, leading 19 to the same result.
There therefore exists a need for a durable and relatively 21 inexpensive gap sub assembly.
2 In accordance with one preferred embodiment of the invention, an 3 electrically insulating gap sub assembly is provided, comprising:
4 = a pair of tubular steel subs, each sub having a threaded pin and box at its ends, each pin and box preferably having a seal face;
6 = the pin of one sub being threaded into the box of the other sub to 7 form a connection which joins the subs end to end;
8 = a layer of electrically insulating, woven fabric wrapping and 9 conforming with the threads of the connection pin; and = an annular washer of electrically insulating material, positioned 11 between the seal faces.
12 Preferably, the woven fabric is formed of poly (p-13 phenyleneterephtalamide), a material which is sold commercially under the 14 registered trade-mark KEVLARTM. Such fabric has been shown to be capable of withstanding the make-up torque applied when threading together the two 16 subs. It also has been shown to withstand the tensional and compressive 17 stresses which arise when incorporated into an operational drill string.
And 18 finally, it is effective to provide electrical discontinuity.
19 In the preferred case where the sub connection pin and box have annular seal faces, an electrically insulating washer may be provided between 21 the faces. The washer, preferably formed of ceramic, is adapted to withstand 22 compressive loading applied by the two seal faces when the gap sub 23 assembly is made up and incorporated into the operational drill string.
1 In one embodiment, the invention is directed to an electrically insulating 2 gap sub assembly for use in a drill string, comprising: tubular first and second 3 subs, each sub having a threaded pin and box, the subs being connected end to 4 end by a pin and box connection; and a layer of electrically insulating, woven fabric wrapping and conforming with the threads of the connection pin, so that 6 the fabric layer electrically isolates one sub from the other by blocking current 7 flow therebetween.
Figure 1 is a perspective exploded view of a gap sub assembly in 11 accordance with the preferred embodiment;
12 Figure 2 is a side sectional view showing the connection of the gap sub 13 assembly of Figure 1, in a made up condition; and 14 Figure 3 is an expanded view of the circled portion of Figure 2.
17 Having reference to the Figures, there is provided a gap sub assembly 1 18 comprising a pair of tubular, steel pipe subs 2,3. Each sub 2,3 has a threaded 19 pin 4 and box 5 at its ends. When assembled, the pin 4 of one sub 2 is threadably connected with the box 5 of the other sub 3 to form a connection 6 21 joining the subs end to end. At the connection 6, the sub 2 has a shoulder 22 forming an annular face 8 and the box 5 of the sub 3 has an annular end face 9.
1 The pin 4 and box 5 of each sub 2,3 are machined to form tapered threads 2 10, such as Hughes H-90T"" threads, having crests 11 and trough 12. The 3 connection pin 4 is machined to standard dimensions. The connection box 5 is 4 machined slightly oversize to allow room for the layer 13 of KEVLARTM woven fabric. Cutting the connection box threads .007" deeper for a .005" thick fabric 6 layer 13, is suitable.
7 The fabric layer 13 is dimensioned to completely cover the connection pin 8 threads 10 with minimal overlap. The fabric layer 13 is sized to extend onto the 9 pin root 14. A cord 15, such as dental floss or fishing line, is secured around the fabric layer 13, so as to cause the latter to conform snugly with the thread crests 11 11 and troughs 12.
12 An annular, electrically insulating ceramic washer 16, available from 13 Dynamic Ceramic, Calgary, under the trade-mark TECHNOXTM, is positioned so 14 as to contact and separate the connection pin face 8 and connection box end face 9. The washer 16 has a thickness of .070".
16 A coating 17 of a sealing compound, such as SCOTCH WELDT"" epoxy 17 and hardener, available from 3M, is applied over the fabric layer 13 and washer 18 16, to prevent intrusion of drilling fluid between the threads 10.
19 The subs 2,3 are screwed together and chain tongs are used to apply about 500 ft-lbs of torque. The two sub faces 8,9 should come to within about 21 1/8" of facing up if the threads 10 are properly cut.
22 The electrical resistance across the gap 18 is then tested using an ohm-23 meter. It should read at least 1 Mohm.
8 It is known in oilfield drilling technology to provide an assembly, at the 9 lower end of a drill string drilling a wellbore, for transmitting downhole data, measured by sensors, to a receiver at ground surface. This transmission is done 11 by means of electric signals passing upwardly through the formation penetrated 12 by the wellbore.
13 For example, it is known to measure the inclination and direction of the 14 wellbore adjacent the bit using an EMT tool. The EMT tool includes a signal generating unit spaced behind the drill bit. This unit produces alternating current 16 signals indicative of the measurements taken by downhole sensors.
17 In conjunction with the signal generating unit it is necessary to provide, in 18 the drill string, a device that will block current flow through the conductive steel 19 pipe of the drill string, to thereby induce the current flow to move upwardly to ground surface through the formations penetrated by the wellbore.
21 One known device in use for this purpose is commonly referred to as a 22 'gap sub assembly'.
1 The gap sub assembly comprises a pair of tubular pipe subs threadably 2 connected end to end by a pin and box connection. A'sub' is industry 3 terminology for a short length of pipe having threaded pin and box ends. A
pin 4 and box are threaded together to form a 'connection' joining the two subs end to end. The sub also usually has a shoulder, at the pin root, forming an annular 6 face. In such a case, the box used forms an annular end face . These faces are 7 provided to press together and seal when the connection is 'made up', thereby 8 preventing the egress of drilling fluid into the well annulus.
9 Heretofore, commercially used gap sub assemblies have usually involved applying a coating of dielectric material, such as ceramic or the material identified 11 by the trade-mark TEFLONTM, and bonding it onto the threads of the pin and the 12 end faces of the connection. In this way an electrically insulated gap is provided.
13 When the gap sub assembly is incorporated into the electrically conductive drill 14 string, the gap serves to block current flow along the string.
However, these known gap sub assemblies have shortcomings. The 16 assemblies are subject to severe compressive and tensile stresses in use.
The 17 brittle ceramic coatings tend to crack and chip, thereby leading to loss of the 18 electric discontinuity. And the TeflonTM coating may extrude during use, leading 19 to the same result.
There therefore exists a need for a durable and relatively 21 inexpensive gap sub assembly.
2 In accordance with one preferred embodiment of the invention, an 3 electrically insulating gap sub assembly is provided, comprising:
4 = a pair of tubular steel subs, each sub having a threaded pin and box at its ends, each pin and box preferably having a seal face;
6 = the pin of one sub being threaded into the box of the other sub to 7 form a connection which joins the subs end to end;
8 = a layer of electrically insulating, woven fabric wrapping and 9 conforming with the threads of the connection pin; and = an annular washer of electrically insulating material, positioned 11 between the seal faces.
12 Preferably, the woven fabric is formed of poly (p-13 phenyleneterephtalamide), a material which is sold commercially under the 14 registered trade-mark KEVLARTM. Such fabric has been shown to be capable of withstanding the make-up torque applied when threading together the two 16 subs. It also has been shown to withstand the tensional and compressive 17 stresses which arise when incorporated into an operational drill string.
And 18 finally, it is effective to provide electrical discontinuity.
19 In the preferred case where the sub connection pin and box have annular seal faces, an electrically insulating washer may be provided between 21 the faces. The washer, preferably formed of ceramic, is adapted to withstand 22 compressive loading applied by the two seal faces when the gap sub 23 assembly is made up and incorporated into the operational drill string.
1 In one embodiment, the invention is directed to an electrically insulating 2 gap sub assembly for use in a drill string, comprising: tubular first and second 3 subs, each sub having a threaded pin and box, the subs being connected end to 4 end by a pin and box connection; and a layer of electrically insulating, woven fabric wrapping and conforming with the threads of the connection pin, so that 6 the fabric layer electrically isolates one sub from the other by blocking current 7 flow therebetween.
Figure 1 is a perspective exploded view of a gap sub assembly in 11 accordance with the preferred embodiment;
12 Figure 2 is a side sectional view showing the connection of the gap sub 13 assembly of Figure 1, in a made up condition; and 14 Figure 3 is an expanded view of the circled portion of Figure 2.
17 Having reference to the Figures, there is provided a gap sub assembly 1 18 comprising a pair of tubular, steel pipe subs 2,3. Each sub 2,3 has a threaded 19 pin 4 and box 5 at its ends. When assembled, the pin 4 of one sub 2 is threadably connected with the box 5 of the other sub 3 to form a connection 6 21 joining the subs end to end. At the connection 6, the sub 2 has a shoulder 22 forming an annular face 8 and the box 5 of the sub 3 has an annular end face 9.
1 The pin 4 and box 5 of each sub 2,3 are machined to form tapered threads 2 10, such as Hughes H-90T"" threads, having crests 11 and trough 12. The 3 connection pin 4 is machined to standard dimensions. The connection box 5 is 4 machined slightly oversize to allow room for the layer 13 of KEVLARTM woven fabric. Cutting the connection box threads .007" deeper for a .005" thick fabric 6 layer 13, is suitable.
7 The fabric layer 13 is dimensioned to completely cover the connection pin 8 threads 10 with minimal overlap. The fabric layer 13 is sized to extend onto the 9 pin root 14. A cord 15, such as dental floss or fishing line, is secured around the fabric layer 13, so as to cause the latter to conform snugly with the thread crests 11 11 and troughs 12.
12 An annular, electrically insulating ceramic washer 16, available from 13 Dynamic Ceramic, Calgary, under the trade-mark TECHNOXTM, is positioned so 14 as to contact and separate the connection pin face 8 and connection box end face 9. The washer 16 has a thickness of .070".
16 A coating 17 of a sealing compound, such as SCOTCH WELDT"" epoxy 17 and hardener, available from 3M, is applied over the fabric layer 13 and washer 18 16, to prevent intrusion of drilling fluid between the threads 10.
19 The subs 2,3 are screwed together and chain tongs are used to apply about 500 ft-lbs of torque. The two sub faces 8,9 should come to within about 21 1/8" of facing up if the threads 10 are properly cut.
22 The electrical resistance across the gap 18 is then tested using an ohm-23 meter. It should read at least 1 Mohm.
5 1 The subs 2,3 are then screwed further together, to apply about 5000 ft-lbs 2 of torque in the case of 3-3/4" diameter subs. At about 2000 ft-lbs, the 3 connection components should face together. The assembly 1 should then again 4 be tested for resistance across the gap 18. The ohm-meter should read more than 1 Mohm.
6 The foregoing description is directed to one specific preferred embodiment
7 of the invention. It is anticipated that other suitable, electrically insulating, woven
8 fabrics may be identified by one skilled in the art and substituted for the KEVLAR
9 fabric. Furthermore, another suitable, electrically insulating, compression-resistant material may be identified and substituted for the ceramic washer.
It is 11 intended that the scope of the invention is defined by the appended claims.
It is 11 intended that the scope of the invention is defined by the appended claims.
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrically insulating gap sub assembly for use in a drill string, comprising:
tubular first and second subs, each having a threaded pin and box, the subs being connected end to end by a pin and box connection; and a layer of electrically insulating, woven fabric wrapping and conforming with the threads of the connection pin, so that the fabric layer electrically isolates one sub from the other by blocking current flow therebetween.
tubular first and second subs, each having a threaded pin and box, the subs being connected end to end by a pin and box connection; and a layer of electrically insulating, woven fabric wrapping and conforming with the threads of the connection pin, so that the fabric layer electrically isolates one sub from the other by blocking current flow therebetween.
2. The gap sub assembly as set forth in claim 1 wherein:
the connection pin and box each have an annular seal face; and comprising:
an electrically insulating annular washer positioned between the seal faces for blocking current flow therebetween and being adapted to withstand the compressive loading experienced when used in an operational drill string.
the connection pin and box each have an annular seal face; and comprising:
an electrically insulating annular washer positioned between the seal faces for blocking current flow therebetween and being adapted to withstand the compressive loading experienced when used in an operational drill string.
3. The gap sub assembly as set forth in claim 1 or 2 wherein:
the woven fabric is formed of poly-p-phenyleneterephtalamide.
the woven fabric is formed of poly-p-phenyleneterephtalamide.
4. The gap sub assembly as set forth in claim 2 or 3 wherein:
the washer is formed of ceramic.
the washer is formed of ceramic.
5. The gap sub assembly as set forth in claim 2, 3 or 4 wherein:
the fabric layer and washer are coated with epoxy to seal against drilling fluid ingress.
the fabric layer and washer are coated with epoxy to seal against drilling fluid ingress.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002496170A CA2496170C (en) | 2005-02-08 | 2005-02-08 | Gap sub assembly |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002496170A CA2496170C (en) | 2005-02-08 | 2005-02-08 | Gap sub assembly |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2496170A1 CA2496170A1 (en) | 2006-08-08 |
| CA2496170C true CA2496170C (en) | 2008-12-30 |
Family
ID=36791458
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002496170A Active CA2496170C (en) | 2005-02-08 | 2005-02-08 | Gap sub assembly |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2496170C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102767363A (en) * | 2012-07-11 | 2012-11-07 | 中国地质大学（武汉） | Electric communication drill rod and method for increasing transmission distance of electromagnetic wave measurement while drilling signal |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2544457C (en) | 2006-04-21 | 2009-07-07 | Mostar Directional Technologies Inc. | System and method for downhole telemetry |
| US8069931B2 (en) | 2009-04-09 | 2011-12-06 | Phoenix Technology Services Lp | System, method and apparatus for downhole system having integrated measurement while operating components |
| CA2795478C (en) * | 2009-04-23 | 2014-05-27 | Kjell Haugvaldstad | A drill bit assembly having aligned features |
| US9109403B2 (en) | 2009-04-23 | 2015-08-18 | Schlumberger Technology Corporation | Drill bit assembly having electrically isolated gap joint for electromagnetic telemetry |
-
2005
- 2005-02-08 CA CA002496170A patent/CA2496170C/en active Active
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102767363A (en) * | 2012-07-11 | 2012-11-07 | 中国地质大学（武汉） | Electric communication drill rod and method for increasing transmission distance of electromagnetic wave measurement while drilling signal |
| CN102767363B (en) * | 2012-07-11 | 2015-03-04 | 中国地质大学（武汉） | Electric communication drill rod and method for increasing transmission distance of electromagnetic wave measurement while drilling signal |
Also Published As
| Publication number | Publication date |
|---|---|
| CA2496170A1 (en) | 2006-08-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request |