Note: Descriptions are shown in the official language in which they were submitted.
CA 02420402 2003-02-28
ELECTRICAL ISOLATION CONNECTOR SUBASSEMBLY FOR
USE IN DIRECTIONAL DRILLING
FIELD OF THE INVENTION
This invention relates to an electrical isolation connector subassembly
for use in data telemetry in directional drilling applications.
BACKGROUND OF THE INVENTION
The transmission of electromagnetic signals from a bore-hole to the
1o earth surface is an effective method of communicating information during
various types of drilling operations, such as measuring while drilling (MWD)
and/or logging well drilling (LWD). The ability to communicate allows for the
monitoring of drilling operations, as well as the inspection and evaluation of
surrounding geology. During directional drilling operations, such as boring
holes under river beds, subways, unusual earth formations and tapping oil
reservoirs, it is particularly important at all times to know precisely the
location
of the drill bit. A significant effort has been made to develop electrical
instruments which are capable of transmitting signals at the drill face or
inspection face back to the earth's surface.
A number of systems have been developed which incorporate
electromagnetic technology for communicating to the earth surface. For
example, in U.S. 5,394,141, described is a system where the lower portion of
the drill string is used as an antenna for purposes of transmitting
electromagnetic waves carrying information.
Various types of devices which are mounted on the outside of the drill
string for monitoring surrounding conditions and/or used in communication are
described, for example, in U.S. Pat. No. 4,684,946 to Geoservices and U.S.
Pat. No. 5,467,832 to Schlumberger Technology Corporation. The problem
with mounting communication devices and sensing devices on the exterior of
the drill string is that particularly with directional drilling the exterior
devices
are damaged by striking the formations about the bore hole.
In order to enhance communication with the earth's surface, it is
preferred to electrically isolate drill string components so that
electromagnetic
signals can be developed for data telemetry. This is achieved by a
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subassembly connector which electrically isolates adjacent drill string
components so that the isolated components provide the two terminals of an
antenna to which an alternating current is applied in developing the
electromagnetic signal for transmission to the earth's surface. Examples of
such connectors are described in U.S. Pat. No. 6,050,353 to Ryan Energy,
U.S. Pat. No. 5,138,313 to Haliburton Company, U.S. Pat. No. 5,163,714 to
Geoservice and Canadian patent application 2,151,525 to McAllister
Petroleum Services, Ltd.
The various types of subassemblies provide for electrical isolation
lo which are particularly useful in bore hole inspection, but may be subject
to
failure when used, for example, in directional drilling. It has been found
that
the drill string, and in particular the subassembly connector, is subjected to
extreme torsional, compression, tension and bending moments during
directional drilling. Such extreme forces can result in connector failure,
usually
at the weakest point in the subassembly. The connectors of these patents and
patent application may fail due to overstressing and possibly break up at
their
weakest point. Furthermore, in the prior art, such as US patent 4,766,442, it
is generally accepted that to prevent short circuiting of the alternating
current
applied to the subassembly, a substantial gap spacing (i.e. 50 cm or more) is
2o necessary. These large gaps require a protective wrapping, as the abrasive
conditions during drilling can quickly damage the insulative materials used in
these gaps. However, the protective wrapping is also subject to extreme
abrasive forces and are consequently prone to frequent failure, thus
necessitating frequent replacement.
SUMMARY OF THE INVENTION
In accordance with an aspect of this invention, provided is an electrical
isolation connector subassembly for use in data telemetry in directional
drilling
applications. The electrical isolation connector subassembly of the current
invention has enhanced strength characteristics due to a more robust design,
and incorporates a considerably smaller gap region between the electrically
isolated adjacent drill string components, thereby reducing the amount of
wear to the insulative surfaces and eliminating the need for a protective
wrapping.
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In accordance with an aspect of this invention, provided is an electrical
isolation connector subassembly for interconnecting adjacent tubular drill
rods
of a drilling system used in drilling bore holes in earth formations, said
connector comprising an electrically insulative sleeve being sandwiched
between two electrically isolated subassembly components, the sleeve
providing an exterior gap between the edges of the spaced apart electrically
isolated components, the exterior gap having a width of less than 50 cm.
In accordance with an aspect of this invention, provided is an electrical
isolation connector subassembly for interconnecting adjacent tubular drill
rods
1o of a drilling system used in drilling bore holes in earth formations, said
connector comprising:
a first electrically isolated component;
a second electrically isolated component;
a plurality of insulator sleeves;
the first electrically isolated component being adapted on one end to
connect to a first tubular drill rod;
the second electrically isolated component being adapted on one end
to connect to a second tubular drill rod;
said plurality of insulator sleeves electrically separating said first and
second electrically isolated components;
wherein at least one of said insulator sleeves is sandwiched between
the first and second electrically isolated components, providing an exterior
gap between the edges of the spaced apart first and second electrically
isolated components, the exterior gap having a width of less than 50 cm.
In accordance with a further aspect of this invention, provided is an
electrical isolation connector subassembly for interconnecting adjacent
tubular
drill rods of a drilling system used in drilling bore holes in earth
formations,
said connector comprising:
a mandrel, wherein said mandrel is adapted at one end to connect to a
first tubular drill rod;
a housing, wherein said housing is adapted at one end to connect to a
second tubular drill rod;
a conductive ring located on an external surface of said connector;
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a plurality of insulator sleeves;
said mandrel and said housing being electrically continuous;
said conductive ring being electrically isolated from said mandrel and
said housing by said insulator sleeves;
an electrode assembly that engages said conductive ring wherein said
electrode assembly is electrically isolated from said mandrel and said
housing, said electrode assembly being positioned within openings in said
mandrel wherein said openings extends perpendicular to the longitudinal axis
of the electrical isolation connector subassembly;
wherein said insulator sleeves are sandwiched between the conductive
ring and adjacent opposing faces of the subassembly, providing an exterior
gap having a width of less than 50 cm.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of an assembled electrical isolation
connector subassembly of the current invention;
Fig. 2 is a section through the electrical isolation connector
subassembly of Fig. 1;
Fig. 3 is an exploded view in perspective of the electrical isolation
connector subassembly of Fig. 1;
Fig. 4 is an enlarged sectional view of the electrical isolation connector
subassembly of Fig. 1 showing further details of the subassembly;
Fig. 5 is a perspective view of an alternate embodiment of the electrical
isolation connector subassembly, shown assembled;
Fig. 6 is a section through the electrical isolation connector
subassembly of Fig. 5;
Fig. 7 is an exploded view in perspective of the electrical isolation
connector subassembly of Fig. 5; and
Fig. 8 is an enlarged sectional view of the electrical isolation connector
subassembly of Fig. 5 showing further details of the subassembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Various aspects of the invention are described in detail where it is
appreciated that the principles of the invention, as established in the
detailed
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description of the drawings, may find application for use in data telemetry
during directional drilling operations. The purpose of the invention is to .
electrically isolate drill rod components so as to form an antenna, preferably
adjacent the location of the drill bit. The antenna transmits electromagnetic
data signals to the earth surface that are interpreted and used for various
informational purposes, such as for the inspection and evaluation of bore
holes. Quite surprisingly, applicant has found that the external gap between
the electrically isolated components can actually be less than 50 cm. This
was never thought possible as per the prior art. By virtue of this shortened
external gap the invention can provide a robust drilling subassembly. This
shortened external gap greatly facilitates manufacture and assembly of the
subassembly. Although the spacing may be less than 50 cm, the preferred
spacing is from about'/2 cm to less 50 cm, or about 1 cm to about 40 cm, or
more preferably about 2 cm to about 30 cm, or about 3 cm to about 20 cm, or
most preferably about 5 cm to about 10 cm. The most preferred range is
about 5 cm to about 10 cm, from the standpoint of machining the various
components, particularly the internal portions thereof. From the standpoint of
effectiveness of signal generation, it is appreciated as the gap is shortened,
the efficiency level decreases. However, for the preferred range of about 5
cm to 10 cm, the system is very effective in generating a signal and usually
does not improve very much in effectiveness for gap spacing greater than
about 20 cm. These conditions, of course, do vary depending upon the earth
formation characteristics.
The electrical isolation connector subassembly generally comprises a
first electrically isolated component and a second electrically isolated
component, the two electrically isolated components being separated by a
insulative sleeves. As will be discussed in more detail, the subassembly
comprises at least one insulative sleeve that is sandwiched between the two
electrically isolated subassembly components, the sleeve providing an
exterior gap between the edges of the spaced apart electrically isolated
components, the exterior gap having a width of less than 50 cm. With specific
reference to Fig. 1, 2 and 3, shown is an assembled electrical isolation
connector subassembly 10, ready for installation into a drill string. The
electrical isolation connector subassembly 10 shown in these figures
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comprises a longitudinal bore 12, a first coupler 14, a mandrel 16, a gap
housing 18 and a second coupler 20, the components being of circular cross-
section, of the same outside diameter and coaxial about the longitudinal axis
21. The first coupler 14 has a first end 22 adapted to connect to a first
drill
string component, and a second end 24 adapted with inwardly tapered
outside-surface threads to threadably and conductively engage the mandrel
16, the mandrel 16 having,a corresponding inside-surface threaded mating
surface. The first coupler 14 and the mandrel 16 when assembled form the
first electrically isolated component, this joined assembly having a
continuous
lo outer surface 26. The gap housing 18 and the second coupler 20 form the
second electrically isolated component. The elongate body of the mandrel 16
has an outer surface that tapers inwardly in a stepwise manner towards an
inside end 17, in a direction towards the second coupler 20, the steps being
first step 28, second step 30 and third step 32. To prevent longitudinal axial
rotation of the gap housing 18 with reference to the mandrel 16, the interface
of these two components, that being the second step 30 and an inside surface
of a first end 33 of the gap housing 18 are configured with non-circular
mating
surfaces so that when assembled, the mandrel 16 and gap housing 18 are
maintained in a non-rotatable relationship to one another. The hexagonal
mating configuration is shown in Fig. 3.
To prevent electrical contact between the mandrel 16 and the gap
housing 18, there is positioned between the mandrel 16 and the'gap housing
18 a plurality of electrically non-conductive insulator sleeves, the insulator
sleeves being placed over-top the above mentioned steps (28, 30, 32). The
electrically non-conductive insulator sleeves are removable elements that can
be reused, thereby simplifying assembly and disassembly of the connector. It
is appreciated, however, that alternative insulators could be substituted. For
example, the insulative sleeves could be formed in place by means of a
suitable insulative material injection process for filling the space occupied
by
the sleeve. For the purpose of describing the invention. the following
assumes use of the removable/reusable insulative sleeves. Positioned over
first step 28, second step 30 and third step 32 is first insulator sleeve 34,
second insulator sleeve 36 and third insulator sleeve 38, respectively. As
mentioned above, the outer surface of second step 30 is non-circular to
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prevent longitudinal axial rotation of the gap housing 18 with reference to
the
mandrel 16. Drilling torque is thereby transmitted from the upper drill along
through the subassembly 10 to the lower drill string. Therefore, the shape of
the second insulator sleeve 36 is configured to match that of the gap housing
18 and mandrel 16. In Fig. 3, where a hexagonal mating configuration is
represented, the second insulator sleeve 36 is shown with the corresponding
hexagonal shape.
To prevent ingress of drilling mud into the assembly, a compression
gasket 40 is positioned between mandrel shoulder 42 and the edge'of the first
1o insulator sleeve 34 (see Fig. 4). To maintain the insulator sieeves (34,
36, 38)
in place on the mandrel 16, a retaining nut 44 is used that threadably engages
the threads 46 of the mandrel 16, the threads 46 being located on the outside
surface of the mandrel inside end 17. By tightening the retaining nut 44, the
electrically non-conductive insulator sleeves (34, 36, 38) and the
compressioh'
gasket 40 are biased towards the respective first shoulder 42, second
shoulder 90 and third shoulder 92 machined at each step (28, 30, 32) of the
mandrel 16 so as to ensure a contiguous electrically non-conductive layer as
well as to provide a seal against the ingress of drilling mud (see Fig. 4 for
an
enlarged, more detailed view of the region containing the various insulative
sleeves, the retaining nut and other associated components).
Positioned between the third insulator sleeve 38 and the retaining nut
44 is an insulator spacer 48, wherein the insulator spacer 48 prevents
electrical contact between the retaining nut 44 and the gap housing 18. To
lock the retaining nut 44 in place, immediately adjacent the threads 46 of the
mandrel 16 and the retaining nut 44, to the side towards the second coupler
20, is positioned a retaining washer 50 and a retaining clip 52. The retaining
clip 52 is received by a circumferential box-shaped groove 54 on the outer
surface of the tapered end 55 of the mandrel 16. To prevent electrical contact
between the mandrel 16 and the second coupler 20, an aft insulator 56 is
positioned over the retaining nut 44, the aft insulator 56 having an end face
58
that abuts the insulator spacer 48. To ensure a seal between the aft insulator
56 and the mandrel 16, the inside end 17 of the mandrel 16 is adapted to
receive a plurality of o-rings 60 fitted within circumferential box-shaped
grooves 62.
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To attach the second coupler 20 to the assembly, the second coupler
20 is adapted at a first end 64 with inside-surface threads 65 to threadably
and conductively engage the gap housing 18, the gap housing 18 having a
corresponding outside-surface threaded mating surface. Upon assembly, the
second coupler and gap housing form a smooth outer surface 66. Adjacent to
the end face 68 of the aft insulator 56, is positioned a gasket 70 that is
sandwiched between the aft insulator 56 and an inside shoulder 72 of the
second coupler 20. To ensure a seal between the aft insuiator 56 and the
second coupler 20, the outer surface of the aft insulator 56 is adapted to
1o- receive a plurality of o-rings 74 fitted within circumferential box-shaped
grooves 76. To facilitate placement of the electrical isolation connector
subassembly 10 within a drill string, the second coupler 20 is adapted at a
second end 78 to engage a second drill string component (See Fig. 2). To
permit labelling of the various components of the assembly with, for example,
serial numbers, the outside surface of first coupler 14, the mandrei 16 and
the
second coupler 20 is machined with a recessed flat surface.
With the electrical isolation connector subassembly 10 assembled,
there are two electrically isolated regions being separated by the contiguous
insulative structure comprising the plurality of electrically non-conductive
insulator sleeves (34, 36, 38), the insulator spacer 48 and the aft insulator
56,
the first electrically isolated region comprising the first coupler 14 and
mandrel
16, and the second electrically isolated region comprising the gap housing 18
and second coupler 20. At the surface of the electrical isolation connector
subassembly 10, the two electrically isolated regions are separated by an
exterior gap 98 that is preferably less than 50cm, with the gap surface oeing
the exposed surface of the first insulative sleeve 34 (as shown in Fig. 4). To
each side of the gap, there are wear shoulders 100, 102, the wear shoulders
100, 102 being received in respective circumferential recesses 104, 106
machined into the mandrel 16 and gap housing 18.
In addition, with the electrical isolation connector subassembly 10
assembled, there is a continuous longitudinal bore 12 that runs through the
electrical isolation connector subassembly 10, allowing for placement of a
transmitter electrode. The transmitter electrode 80 is housed within a wear
resistant electrically insulative wash tube (not shown) that is aligned
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concentrically with the longitudinal axis 21 (see Fig.2). To facilitate
placement
of the transmitter electrode 80 on the wash tube within the longitudinal bore
12, a centering disk or spider 81 is used. The centering disk 81 is positioned
within the longitudinal bore 12 in the non-tapered region 82 of the mandrel
16.
The centering disk 81 is configured with an outside diameter that corresponds
to the inside diameter of the non-tapered region 82 of the longitudinal bore
12
and is positioned having a face 84 abutting an interior shoulder 86 of the
mandrel 16 to aid in maintaining it in a fixed position relative to the
mandrel
inside surface. The centering disk 81 has an aperture 94 coaxially aligned
with the longitudinal axis 21 through which the transmitter electrode is
positioned and further comprises a plurality of apertures 96 to facilitate the
passage of drill fluid or medium.
To operate, an alternating signal is applied to the electrically isolated
regions for transmitting an electromagnetic signal back to the surface, for
example, in the manner described in U.S. Pat Nos. 5,138,313 and 5,163,714.
Shown in Figs.5, 6 and 7 are alternate embodiments of the present
invention, an electrical isolation connector subassembly 110, shown
assembled and ready for installation into a drill string, The electrical
isolation
connector subassembly 110 comprises a longitudinal bore 112, a mandrel
114, a housing 116, a conductive ring 118 and an electrode assembly 120.
As will be described in more detail, the conductive ring 118 is electrically
isolated from the electrically continuous mandrel 114 and housing 116 by a
plurality of insulator sleeves. The mandrel 114 has a first end 122 adapted to
connect to a first drill string component, and a second end 124 adapted with
outside-surface threads 126 to threadably and conductively engage the
housing 116, the housing 116 having a corresponding inside-surface threaded
mating surface 128. The drilling torque is transmitted through the .
subassembly by the threaded connections at 126/128. The mandrel 114, the
housing 116 and the conductive ring 118 each have the same outside
diameter and are coaxially aligned with the longitudinal axis 130.. When
assembled, the second end 124 of the mandrel 114 abuts an inside shoulder
137 of the housing 116.
To electrically isolate the conductive -ring from the mandrel 11.4 and
housing 116, electrically non-conductive insulator sleeves are used, those
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being a first ring conductor insulator 132 and a second ring conductor
insulator 134. As mentioned in the previous embodiment, the insulator
sleeves are removable and reusable. It is appreciated, however, that the
removable/reusable insulator sleeves could be substituted with a formed-in-
place insulator using a suitable insulative material injection process. The
removable/reusable insulator sleeves are used in the following discussion.
The ring conductor insulators (132, 134) are "L" shaped, oriented such that
the outer sides (138, 140) ofthe short portions (142, 144) separates the
conductive ring from the adjacent structure (the mandrel 114 in the case of
the first ring conductor insulator 132 and the housing 116 in the case of the
second ring conductor insulator 134), and with the long portion 146 separating
the underside 148 of the conductive ring 118 from the mandrel 114. To,
accommodate placement of the ring conductor insulators 132, 134, the
mandrel 114 outside diameter steps circumferentially inwards, defining a
smaller diameter region 149 of the mandrel 114, the step forming shoulder
150. An opposing shoulder 152 is formed by an end face 154 of the housing
116. This smaller diameter portion 149 of the mandrel 114 permits the
positioning of the ring conductor insulators (132, 134) such that when
assembled, exterior gap 156, 158 of the ring conductor insulators 132, 134
remain slightly recessed in comparison to the remainder-of the assembly, and
maintain an exterior gap that is less than 50 cm in width.
The mandrel 114, the housing 116 and the conductive ring 118, in the
areas immediately adjacent the exterior gap 156, 158 of the ring conductor
insulators 132, 134, are slightly recessed 160 to accommodate placement of
an abrasion resistant wrapping (not shown), the recess being sufficiently deep
to align with the exterior gap 156, 158 of the ring conductor insulators 132,
134. In addition to the two ring conductor insulators 132, 134, there is
positioned adjacent the two long portions 146 of the ring conductor
insulators132, 134, between the conductive ring 118 and the mandrel 114, a
central
insulator 161. This central insulator 161 is machined with apertures, to allow
passage of a conductor cap 162 of the electrode assembly 120. To prevent
the ingress of drilling mud, a plurality of seals are incorporated into the
assembly (See Fig. 8 for identification of seal structures). At the surface, a
compression gasket 151 is sandwiched between the first ring conductor .
CA 02420402 2003-02-28
insulator 132 and the shoulder 150 of the mandrel 114. Internally, the
underside of the conductive ring 118, the outer surface of the smaller
diameter portion of the mandrel 114 and the outer surface of the second end
124 of the mandrel 114 are fitted with o-rings 164, received by
circumferential
box-shaped grooves 166.
The electrode assembly 120, as shown in Figures 7 and 8, is the
means by which a signal is delivered to the conductive ring 118 and is
positioned within an electrode aperture 167 machined in the mandrel 114,
wherein said aperture extends perpendicular to the longitudinal axis. The
1o electrode assembly 120 is comprised of a conductor base 168, a spring 170,
and a conductor cap 162, with the spring 170 being positioned against the
conductor base 168 and biased to impart pressure against the conductor cap
162 thereby causing contact between the conductor cap 162 and the
conductive ring 118. The electrode assembly 120 is electrically isolated from
the mandrel 114 by an electrically non-conductive transverse insulator 174
that lines the electrode aperture 167 in the mandrel .114.
Positioned within the longitudinal bore 112 of the electrical isolation
connector subassembly 110, is a first wash pipe 176 and a second wash pipe
178, each wash pipe 176, 178 being- manufactured. of electrically non-
conductive material and situated having partial overlap with the transverse
insulator 174 such that the central wash pipe coupler 180 is electrically
insulated from the mandrel 114. The central wash pipe coupler 180 maintains
the transmitter electrode 182 in a coaxial alignment with the longitudinal
axis
130 of the assembly by means of a central aperture 184. Additional apertures
186 are machined into the central wash pipe coupler 180 to permit passage of
drill mud and material. At the end 187 opposite the central wash pipe coupler
180, the first wash pipe 176 is maintained in position by an upper wash pipe
cup 188. The upper wash pipe cup 188 is fixed within the longitudinal bore
112 of the assembly by having chamfered shoulder 190 positioned up against.
3o a corresponding chamfered shoulder 192 machined into the inside surface of
the mandrel 114. Similarly, the second wash pipe 178 is held in position, up
against the central wash pipe coupler 180 by means of a lower wash pipe cup
194. The lower wash pipe cup 194 is maintained in position by a snap ring
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196, the snap ring 196 being received by a circumferential box-shaped groove
198 on the inside surface 200 of the mandrel 114.
To ensure that drilling mud flows through the wash pipes 176, 178 and
not around it, a plurality of seals are incorporated into the assembly. Each
wash pipe cup 188, 194 has two sets of o-rings, sitting within circumferential
box-shaped grooves, the first set of o-rings 202 ensuring a seal between the
wash pipe cups 188, 194 and the wash pipes 176, 178, and a second set of
o-rings 204 ensuring a seal between the wash pipe cups 188, 194 and the
mandrel 114. Additional o-rings 206 are located on the central wash pipe
coupler 180, held within circumferential box-shaped grooves 208, positioned
between the central wash pipe coupler 180 and the wash pipes 176, 178.
As was mentioned above for the first embodiment, to send a signal
from the subassembly, an alternating signal is applied to the electrically
isolated regions for transmitting an electromagnetic signal back to the
surface,
for example, in the manner described in U.S. Pat Nos. 5,138,313 and
5,163,714.
Although preferred embodiments of the invention have been described
herein in detail, it will be understood by those skilled in the art that
variations
may be made thereto without departing from the spirit of the invention or the
scope of the appended claims.
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