U.S. patent number 3,807,502 [Application Number 05/350,674] was granted by the patent office on 1974-04-30 for method for installing an electric conductor in a drill string.
This patent grant is currently assigned to Esso Production Research Company. Invention is credited to Joe Keith Heilhecker, Donald Bayne Wood.
United States Patent |
3,807,502 |
Heilhecker , et al. |
April 30, 1974 |
METHOD FOR INSTALLING AN ELECTRIC CONDUCTOR IN A DRILL STRING
Abstract
A method for installing an electric conductor in a drill string
during drilling operations wherein an insulated electric conductor
is lowered into the drill string and thereafter the drill string
and conductor are lengthened as the borehole is advanced by adding
lengths of pipe and conductor sections to the drill string and
conductor, respectively.
Inventors: |
Heilhecker; Joe Keith (Houston,
TX), Wood; Donald Bayne (Houston, TX) |
Assignee: |
Esso Production Research
Company (Houston, TX)
|
Family
ID: |
23377716 |
Appl.
No.: |
05/350,674 |
Filed: |
April 12, 1973 |
Current U.S.
Class: |
166/385; 174/47;
340/855.2; 166/66; 175/50 |
Current CPC
Class: |
E21B
19/00 (20130101); E21B 19/22 (20130101); E21B
47/12 (20130101); H01R 13/523 (20130101); E21B
17/003 (20130101) |
Current International
Class: |
E21B
47/12 (20060101); E21B 17/00 (20060101); E21B
19/22 (20060101); E21B 19/00 (20060101); H01R
13/523 (20060101); E21b 047/12 () |
Field of
Search: |
;166/315,65
;175/40-50,104 ;174/47 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Leppink; James A.
Attorney, Agent or Firm: Graham; Robert L.
Claims
I claim:
1. A method of establishing and maintaining electric continuity
between a subsurface terminal in a well and a surface terminal
which comprises:
a. lowering a pipe string in said well by connecting a plurality of
pipe sections together in end-to-end relation;
b. lowering a first electric conductor in said pipe string to
establish electric continuity between said subsurface terminal near
the lower end of said pipe string and said surface terminal;
c. repeatedly advancing said well by an amount sufficient to
require lengthening said pipe string;
d. for each of such advancements, adding a length of pipe to said
pipe string and a conductor section to said first electric
conductor.
2. A method as defined in claim 1 wherein said first electric
conductor is substantially free of connectors.
3. A method as defined in claim 1 wherein said first electric
conductor comprises armored cable.
4. A method as defined in claim 2 wherein each of said conductor
sections comprises insulated electric cable free of armor.
5. A method as defined in claim 2 wherein the combined length of
the conductor sections added according to step (d) is less than the
length of said first conductor.
6. A method of establishing and maintaining electric continuity
between a subsurface location within a well and the surface which
comprises:
a. lowering in said well a pipe string comprising a plurality of
pipe sections connected together in end-to-end relation;
b. lowering in said pipe string a continuous electric cable to
establish electric continuity from a subsurface terminal and a
surface terminal; and
c. advancing said well in increments of predetermined length and
for each incremental advancement, lengthening said pipe string and
said electric cable by:
threading a cable section through a length of pipe to be added to
said pipe string;
connecting said cable section to the upper end of the cable in said
drill string and said surface terminal; and
connecting said length of pipe into said pipe string.
7. A method as defined in claim 6 wherein the step of lowering said
continuous electric cable in said pipe string includes supporting
the upper end of said continuous electric cable on said pipe
string.
8. A method as defined in claim 6 wherein the total length of cable
sections added to the electric cable according to step (c) never
exceeds the length of said continuous electric cable.
9. A method of drilling a well while maintaining an electric
circuit between a subsurface location in said well and the surface
which comprises:
a. lowering a pipe string in said well, said pipe string comprising
a plurality of pipe sections;
b. lowering a first electric cable into said pipe string, said
first electric cable establishing electric circuit between a
subsurface terminal near the lower end of said pipe string and a
surface terminal;
c. repeatedly advancing said well in increments sufficient to
require lengthening said pipe string, and for each increment so
advanced, lengthening said pipe string and electric cable in said
pipe string by disconnecting said pipe string and separating
electric cable at the surface, threading an electric cable section
through a length of pipe, connecting said cable section with the
electric cable in the pipe string to reestablish the electric
circuit between said terminals, and connecting the length of pipe
into said pipe string, the total length of said cable sections
being less than the length of said first electric cable.
10. A method as recited in claim 9 and further comprising:
d. withdrawing said pipe string so lengthened, said first electric
cable, and said cable sections from said well;
e. lowering said pipe string withdrawn in step (a) into said well;
and
f. lowering a second electric cable into said pipe string, said
second electric cable being substantially longer than said first
electric cable and extending from a subsurface terminal near the
lower end of said pipe string to a surface terminal; and
g. repeatedly advancing said well in increments sufficient to
require lengthening said pipe string, and for each increment so
advanced lengthening said pipe string and electric cable in said
pipe string by disconnecting said pipe string and electric cable at
the surface, threading an electric cable section through a length
of pipe, connecting said cable section with electric cable in the
pipe string to reestablish the electric circuit between said
terminals, and connecting the length of pipe into said pipe string,
the total length of said cable sections being less than the length
of said second electric cable.
11. A method of maintaining an electric conductor within a pipe
string used to drill a well which comprises:
a. lowering a continuous electric cable through a pipe string which
comprises a plurality of pipe sections disposed in a well to
provide an electric conductor between a subsurface terminal near
the lower end of said pipe string and a surface terminal;
b. supporting the upper end of said cable on said pipe string;
c. repeatedly advancing said well in increments of predetermined
amount; and
d. for each of said advancements, lengthening said pipe string and
the electric conductor therein by disconnecting said pipe string
and separating electric cable contained therein at the surface,
threading flexible electric cable section free of protective armor
through a length of pipe to be inserted in the pipe string,
connecting said cable section with cable in said pipe string to
extend said conductor and thereby reestablishing electric
continuity between said subsurface and surface terminals, and
inserting said length of pipe into said pipe to lengthen said pipe
string.
12. A method as recited in claim 11 and further adjusting the
length of at least one cable section used to extend said electric
conductor in said pipe string to remove excess slack from said
cable sections.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved method for performing
wellbore telemetry operations. In one aspect it relates to a method
for installing an insulated electric conductor in a pipe string
used in rotary drilling operations.
2. Description of the Prior Art
In the drilling of oil wells, gas wells, and similar boreholes, it
frequently is desirable to transmit electric energy between
subsurface and surface locations. One application where electrical
transmission has received considerable attention in recent years is
in wellbore telemetry systems designed to sense, transmit, and
receive information indicative of a subsurface condition. This
operation has become known in the art as "logging while
drilling."
A major problem associated with wellbore telemetry systems has been
that of providing reliable means for transmitting an electric
signal between the subsurface and surface location. This problem
can best be appreciated by considering the manner in which rotary
drilling operations are normally performed. In conventional rotary
drilling, a borehole is advanced by rotating a drill string
provided with a drill bit. Lengths of drill pipe, usually about 30
feet long, are added to the drill string one at a time as the
borehole is advanced in increments. In adapting an electric
telemetry system to rotary drilling equipment, the means for
transmitting the electric signal through the drill string must be
such to permit the connection of additional pipe lengths to the
drill string as the borehole is advanced. An early approach to the
problem involved the use of continuous electric cable which was
adapted to be lowered inside the drill string and to make contact
with a subsurface terminal. This technique, however, required
withdrawing the cable from the drill string each time a pipe
section was added to the drill string. A more recent approach
involves the use of special drill pipe equipped with an electric
conductor. Each pipe section is provided with connectors which mate
with connectors of an adjacent pipe section and thereby provide an
electric circuit across the joint (see U.S. Pat. Nos. 3,518,608 and
3,518,609). Disadvantages of this system include the high cost of
the special pipe sections, the need for a large number of electric
connections (one at each joint), and the difficulty of maintaining
insulation of the electric connectors at each joint.
SUMMARY OF THE INVENTION
The purpose of the present invention is to provide an electric
circuit between a subsurface location in a well and the surface.
The invention permits the monitoring of a subsurface condition or
the actuation of a subsurface instrument as drilling operations are
in progress.
Briefly, the method involves lowering a drill string in a well by
connecting a plurality of pipe sections together in end-to-end
relation, lowering an insulated electric conductor in the drill
string to extend from a subsurface terminal therein to the surface
terminal, incrementally advancing the well a predetermined amount
by manipulating the drill string, and for each such advancement
adding a length of pipe provided with an electric conductor section
to the drill string to lengthen both the drill string and the
electric conductor.
An important advantage of the method of the present invention over
prior art techniques is that it reduces the number of connectors
required in the conductor between the subsurface and surface
terminals. The combined length of conductor sections need not
exceed the length of one bit run which normally is between about
100 and several thousand feet. This means that the portion of the
circuit comprising the conductor sections will normally constitute
only a minor fraction of the complete conductor. For most wells,
the conductor installed in accordance with the method of the
present invention will contain no more than about 30 connectors
regardless of the depth of the well. The substantial reduction in
the number of connectors increases the reliability of the electric
circuit since each connector presents a potential source of
failure. Moreover, the improved method permits the use of
conventional drill pipe, which is less expensive than a string of
pipe especially made for conducting electric energy.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of well drilling equipment provided with
an electric conductor installed within the drill string in
accordance with the present invention.
FIG. 2 is an enlarged sectional view of a portion of the drill
string shown in FIG. 1.
FIG. 3 is a transverse sectional view of the assembly shown in FIG.
2 with the cutting plane taken along line 3--3 thereof.
FIG. 4 is an enlarged exploded view, shown in longitudinal section,
of a cable clamp and connector usable in the conductor shown in
FIGS. 1 and 2.
FIG. 5 is an enlarged elevation, shown partially in section, of a
connector for joining adjacent conductor sections.
FIGS. 6 and 7 illustrate the manner in which a pipe joint provided
with a conductor section is added to the upper end of a drill
string.
FIGS. 8, 9, and 10 are schematic illustrations showing the
relationship of the continuous cable and cable sections for
successive bit runs in a drilling operation.
FIG. 11 is a longitudinal sectional view of a cable connector
capable of use in the present invention.
FIG. 12 is a side elevation of a portion of the connector shown in
FIG. 11.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Conventional rotary drilling equipment, as schematically
illustrated in FIG. 1, includes swivel 10, kelly 11, tubular drill
string 12, and bit 13. These components, connected in the manner
illustrated, are suspended from the drilling derrick 14 by means of
rig hoisting equipment. The kelly 11 passes through rotary table 16
and connects to the upper end of the drill string 12. The term
"drill string" as used herein refers to the column of tubular pipe
between the bit 13 and kelly 11; and the term "pipe string" refers
to the complete pipe column including the kelly 11. The major
portion of the drill string normally is composed of drill pipe with
a lower portion being composed of drill collars. The drill string
12 consists of individual pipe sections, either drill pipe or drill
collars, connected together in end-to-end relation.
The borehole 17 is advanced by rotating the drill string 12 and bit
13 while at the same time drilling fluid is pumped through the
drill string 12 and up the borehole annulus. The drilling fluid is
delivered to swivel 10 through a hose (not shown) attached to hose
connection 18 and is returned to the surface fluid system through
pipe 19. A kelly bushing 20 couples the rotary table 16 to the
kelly 11 and provides means for transmitting power from the rotary
table 16 to the drill string 12 and bit 13. (The use of a power
swivel eliminates the need for the kelly and rotary table. The
present invention may be used with either system; for purposes of
illustration, however, it will be described in connection with the
kelly and rotary table arrangement.)
As mentioned previously, it frequently is desirable to monitor a
subsurface drilling condition during drilling operations. This
requires measuring a physical condition at the subsurface location,
transmitting this data as an electric signal to the surface, and
reducing the signal to useful form. Typical situations where
telemetry is applicable in drilling operations include drilling
through abnormal pressure zones, drilling through zones where hole
deviation is likely to be a problem, directional drilling,
exploratory drilling, and the like.
Although the present invention may be employed in most any drilling
operation wherein an electric conductor is used in tubular pipe to
transmit electric energy between a subsurface and surface location,
it finds particularly advantageous application in a wellbore
telemetry system such as that illustrated in FIG. 1 comprising an
instrument 21, conductor 22, and receiver 23.
The instrument 21 capable of measuring a subsurface condition and
generating an electric signal indicative or representative of that
condition is mounted or adapted to be mounted in the drill string
12. A variety of devices capable of sensing a physical condition
are available. These include transducers for measuring pressure,
temperature, strain and the like; surveying instruments for
measuring hole deviation; and logging instruments for measuring
resistivity or other properties of subsurface formations. The
instrument 21 may be powered by batteries or by energy transmitted
through conductor 22. Alternatively, a subsurface generator driven
by fluid flowing through the drill string 12 may be used to power
instrument 21.
The present invention is concerned primarily with the electric
conductor 22 used to transmit electric energy between surface and
subsurface locations and a method for installing the same. The
energy may be a signal generated by the subsurface instrument 21
and transmitted to the receiver 23 at the surface. Alternatively,
the energy may be electric power transmitted from the surface to
actuate or drive a subsurface instrument or motor. Or, as mentioned
previously, energy may be transmitted down the conductor 22 to
power the instrument 21, and simultaneously intelligence may be
transmitted up the same conductor.
As applied in telemetry operations, it is preferred that the energy
being transmitted be in the form of a pulsating signal. Information
can be transmitted by varying the number, amplitude, width or
spacing of a train of electric pulses, or it can be transmitted by
modulating the frequency or amplitude of the pulsating signal. More
than one transducer or other device may be employed in the
instrument 21 if desired, in which case a multiplexer may be used
for sending the various signals over a single conductor.
The instrument 21 may be mounted directly in the drill string 12
or, as illustrated in FIG. 1, it may be a separate tool that is
lowered into the drill string 12 on the conductor 22.
The insulated conductor 22 extends from a subsurface terminal on
instrument 21 substantially through the drill string 12, and
connects to a suitable surface terminal. The surface terminal in
this preferred embodiment is provided by connector 25 of conductor
24. Conductor 24 may be embedded in the kelly 11, in which case the
conductor 22 will extend to the upper end of the drill string 12
and connect to connector 25 at that point. It is preferred,
however, that conductor 24 be disposed within kelly 11 as
illustrated in FIGS. 1, 6, and 7 and extend a short distance, e.g.,
one to three feet, below kelly 11 and have connector 25 at its
lower end.
If telemetry operations are to be performed while the kelly 11 and
drill string 12 are rotating, the upper end of conductor 24 will be
connected to a device 26 capable of transmitting electric energy
from a rotating member to a stationary member. This device may be a
rotary transformer having a rotor secured to the kelly 11 and a
stator secured to the stationary portion of the swivel 10, or it
may be a slip ring and brush assembly. Electric conductor 27 and
ground conductor 28 interconnect the stationary portion of device
26 and receiver 23. If telemetry operations are to be performed at
times when the drill string 12 and kelly 11 are stationary, the
conductors 27 and 28 may be connected directly to conductor 24
through a suitable connector. In this situation, conductors 27 and
28 will be disconnected when the kelly 11 and drill string 12 are
rotated. Other means for transmitting the signal to the receiver 23
include a wireless transmitter connected to conductor 22 and
located on a rotating member, e.g. kelly 11.
The receiver 23 is an instrument capable of receiving the signal
generated by instrument 21 and reducing it to useful form.
In one aspect, the present invention relates to a method for
establishing electric continuity between a subsurface location in a
well and maintaining electric continuity as the well is advanced.
As noted above, the method employs an insulated electric conductor
disposed internally of a drill string. The electric conductor will
normally be installed after the well has been drilled to a depth
where wellbore telemetry operations are to commence. This can be as
shallow as a few hundred feet as in the case of directional wells,
or several thousand feet deep. The initial step in the improved
method is to lower a drill string in a well by connecting a
plurality of pipe sections together in end-to-end relation. The
drill sstring may be used to drill a well as it is lengthened, or
the drill string may be simply lowered in a well already drilled.
Next, a continuous electric conductor 30 (also referred to as cable
30 below) is lowered within the drill string 12 to extend from a
subsurface terminal, e.g. instrument 21, to a surface terminal,
e.g. kelly connector 25. As described in detail below electric
continuity between the subsurface and surface terminals, is
maintained by adding conductor sections to the continuous conductor
30 as the well is advanced and as the drill string 12 is
lengthened.
The term "continuous electric conductor" or "continuous electric
cable" as used herein means a length of wire or combination of
wires suitable for carrying electric current. Preferably, the
conductor is free of connectors, (except for its terminal ends) but
as a practical matter it may be necessary to connect separate
lengths of conductors together using electric connectors. A
distinguishing characteristic of the continuous electric conductor
is that it normally includes long spans of conductor lengths free
of connectors and is electrically continuous which permits it to be
lowered in the drill string in a single operation. Preferably,
conductor 30 is provided by an armored cable. Armored cable has
sufficient strength to permit the use of several thousand feet of
cable and to support the instrument 21 during running-in
operations.
The surface equipment for lowering the cable 30 in the drill string
12 can be similar to conventional cable handling equipment used in
well logging operations. Such equipment normally includes a power
winch having a cable wound thereon and a sheave suspended from the
rig drawworks for guiding the cable into or out of the drill string
12.
With the instrument 21 properly located at the desired subsurface
location -- preferably in a suitable sub immediately above the
drill bit 13 -- the cable 30 extends internally through the drill
string 12 and terminates in a connector 31 at its upper end.
In one embodiment of the invention (illustrated in FIGS. 1-7), the
upper end of the continuous cable 30 is supported on a spider 32 or
similar support secured to the drill string 12. After the
continuous cable 30 has been lowered in the drill string 12, its
upper terminal end provided with connector 31 is supported on the
drill string 12 by means of spider 32. As described in detail
below, spider 32 may be mounted in the box of a pipe section, e.g.
pipe section 33, of the drill string 12 (see FIG. 2). Initially,
connector 31 of cable 30 is mated with companion connector 25 of
kelly conductor 24 completing the electric circuit between
instrument 21 and receiver 23. The kelly 11 is then attached to the
drill string 12 placing equipment in condition for commencing
drilling operations and permitting wellbore monitoring, if desired.
If a cable 30 of fixed length is used, it is possible that the
connector 31 will not be located exactly opposite a box end of the
top pipe section with the cable 30 properly positioned within the
drill string 12. However, the length of drill string 12 can be made
equal to the length of cable 30 by adding short pipe sections at
the upper end of the drill string 12.
While drilling operations are in progress, the next pipe section,
e.g. pipe section 34 shown in FIGS. 6 and 7, to be added to the
drill string 12 is placed in a shallow borehole 35 (commonly
referred to as "mouse hole") below the derrick floor. A length of
conductor section, preferably a cable section 36, is threaded
through pipe section 34. Cable section 36 normally will be slightly
longer than pipe section 34 and is provided with connectors 37 and
38 at its opposite ends.
When the drilling has proceeded to the point that it becomes
necessary to insert another pipe section in the drill string 12,
the kelly 11 and drill string are elevated, the drill string 12 is
supported in the rotary table 16, and the kelly 12 separated from
the drill string 12. Connectors 25 and 31 are manually separated
and the kelly 11 is swung over into alignment with pipe section 34.
Connector 25 is mated with the upper exposed connector 37 of cable
section 36 and kelly 11 is screwed into the box of pipe section 34
(See FIG. 7); this assembly is then elevated above the drill string
12. The length of the cable section 36 is such that it extends a
short distance, e.g. about one to three feet, below the lower end
of pipe section 34, exposing connector 38. This connector is
manually mated with connector 31 which again completes the circuit
between the subsurface instrument 21 and the receiver 23. The pin
of pipe section 34 is then screwed into the box of the top pipe
section 33 of the drill string 12. This operation lengthens both
the drill string 12 and the conductor 22 which now comprises cable
30 and cable section 36.
Drilling operations are resumed and the subsurface condition
monitored as desired. The individual sections of drill pipe can be
added in the manner described above and illustrated in FIGS. 6 and
7 for each incremental advance of predetermined length of the
borehole 17. It should be noted that a spider 32 need not be
provided to support the upper end of each cable section. However, a
temporary support plate may be employed to facilitate connecting
the cable sections together. Such a plate provided with a radial
slot can rest on the box shoulder and be adapted to support a
connector thereon. After the connectors of adjacent cable sections
are mated, the plate is removed.
Drilling operations will continue with the individual pipe sections
34 being added for each incremental advance of the borehole 17 in
the manner described above. After drilling has progressed and a
number of pipe sections and cable sections have been added to the
system, the lower portion of conductor 22 will be provided by the
continuous cable 30 and the upper portion by a plurality of cable
sections 36 joined in end-to-end relation. This arrangement is
illustrated in FIG. 1. Normally, drilling operations will continue
in this manner until it becomes necessary to change the drill bit
13. The number of pipe sections and the number of cable sections 36
added during a particular bit run will thus normally be determined
by the length of borehole the bit is capable of drilling. This
varies within wide limits, but normally ranges from about 100 feet
for hard formations to several thousand feet for soft
formations.
There are a number of cables commercially available that can serve
as cable 30 and cable sections 36 in the present invention. A
particularly suitable cable is a single conductor, three-sixteenths
inch armored cable manufactured by Vector Cable Company and sold as
type I-18P. This cable is sufficiently strong to support long
lengths; it has protective armor which guards against damage; and
it is sufficiently flexible to facilitate installation.
Since the combined length of the cable sections 36 will normally be
short, these sections in the preferred embodiment of the present
invention need not be provided with protective armor. Suitable
cable types include a single conductor, 12 AWG, neoprene jacket
conductor sold as B-5025 by Vector Cable Company. The length of
each cable section 36 normally will be longer than the average
length of pipe section used in the drill string to compensate for
variations in the length of pipe sections. The excess length of
each cable section also permits the cable to be twisted as pipe
sections are screwed together. Moreover, the flexibility of this
cable permits cable sections to be overlapped and clamped at the
surface or otherwise adjusted to match the length of the pipe
sections through which they extend.
As shown in FIGS. 2 and 3, the spider 32 for supporting the upper
end of the cable 30 is sized to fit into a box end 40 of pipe
section 33. Radial arms 41 rest on internal shoulder 42 of the box
40 and an opening 43 through the axial center of the spider 32
receives the upper end of cable 30. The spider 32 should be
designed to minimize the flow restriction through box 40,
particularly if internal upset drill pipe is used. A cable clamp 44
comprising sleeves 45 and 46 anchors the armor of cable 30 as shown
in FIG. 4. The cable 30 passes through the center opening of clamp
44. Wire strands 47 stripped from the armor pass around the upper
sleeve 45, through suitable axial openings, and between clamping
surfaces of sleeves 45 and 46. Tightening the lower sleeve 46 on
upper sleeve 45 thus firmly secures the wire strands. In the
installed position, the clamp 44 is supported on the upper surface
of spider 32.
The primary function of the spider 32 is to support the upper end
of the cable 30 at a fixed location in the drill string 12. This
permits the use of unarmored, flexible cable sections in the drill
string above the spider 32.
In the embodiment of the invention described above, the connectors,
e.g. connectors 37 and 38, employed to join adjacent cable section
36 are preferably plug type connectors. Such connectors are easily
installed, provide water-tight connections, and provide adequate
strength. Connector 31 (cable 30), connectors 37 and 38 (cable
sections 36), and connector 25 (kelly) may include identical female
connectors such as those illustrated in FIG. 4. A double contact
plug 50 which is detachable from both female connectors but may be
considered a part of either provides electric continuity through
each connection. As shown in FIG. 5, the connection comprising
connectors 37 and 38 for joining adjacent cable sections 36 also
includes a double contact plug 53. For these connections, it is
preferred that a locking sleeve comprising a pair of threaded metal
halves 51 and 52 be employed. The locking sleeve adds strength to
the connection. In this regard, it should be noted that the
connection for joining a cable section 36 to cable 30 does not
include a locking sleeve. Thus, the cable sections 36 joined by
connections with locking sleeves can be retrieved as a unit by
pulling up on the top cable section 36. Connector 38 will pull free
of connector 31 permitting the cable sections 36 to be withdrawn
from the drill string in a single operation.
The conductor 22 described above is provided with a single
conductor. In such a design, the electric ground circuit may be
provided by the armor if armored cable is used to the surface, by
the drill pipe itself, or by a combination of cable armor and drill
pipe. Alternatively, the cable 30 and cable sections 36 and
connectors may be provided with a plurality of conductors and
contacts.
In describing the operation of the embodiment of the invention
described above, it will be assumed that the borehole 17 has been
drilled to a certain depth using conventional techniques and at
this depth it is desired to commence drilling while logging
operations. The drill string 12 with bit 13 is lowered into the
borehole 17 in the usual manner. The instrument 21 is then lowered
on cable 30 and located at the proper depth within the drill string
12. The upper end of the cable 30 is provided with the cable clamp
44 and connector 31. The spider 32 is inserted on the cable 30
immediately below the cable clamp 44. This assembly is then seated
in the box end 40 of the top section of drill pipe, e.g. pipe
section 33. After the kelly connector 25 is mated with connector
31, the kelly 11 is screwed into the box end 40 placing the
assembly in condition for drilling and logging. The borehole 17 is
advanced in increments of predetermined length -- about equal to
length of pipe to be added to the drill string. Lengths of pipe
provided with cable sections 36 are added after each incremental
advancement of the borehole in the manner described previously with
reference to FIGS. 6 and 7. The cable 30 and drill string 12 are
thus lengthened together as the borehole is advanced using
conventional drill pipe.
As the drill string is lengthened and as cable sections 36 are
added, excess lengths of cable will be introduced into the drill
string since each cable section 36 will normally be slightly longer
than its companion pipe section. Slack can be periodically removed
from the conductor by pulling excess cable from the drill string at
the surface, overlapping excess lengths, and clamping the
overlapped cable in that configuration. Alternatively, spiders can
be provided in certain pipe sections to prevent excess cable from
accumulating and snarling within the drill string 12.
When it is desired to interrupt drilling operations, as for example
when it is necessary to change the bit 13, the upper portion of the
conductor 22 comprising a plurality of cable sections 36 may be
retrieved by first disconnecting kelly 11 from the drill string 12,
then separating kelly connector 25 from cable connector 37 of the
top cable section, and finally reeling in the string of cable
sections 36. Connector 38 secured to connector 31 of cable 30 pulls
free separating the string of cable sections 36 from cable 30. The
drill string 12 then can be withdrawn in the usual manner until the
pipe section, e.g., section 33, containing the spider 32 is
reached. The continuous cable 30 is then withdrawn by reeling it on
a suitable drum. The remainder of the drill string 12 is then
withdrawn in the conventional manner.
The drill string that was withdrawn from the borehole is provided
with a new bit and rerun into the borehole. A second continuous
cable 30 with instrument 21 attached to its lower end is then
lowered through the drill string 12 to the instrument setting
depth. The second continuous cable may be longer than the previous
one by an amount about equal to the advancement of the borehole
made by the previous bit run. A new cable may be employed for this
purpose or a length of cable about equal to the advancement of the
borehole may be attached to the first continuous cable 30. The
equipment is assembled in the manner described above, and drilling
and telemetry operations resumed. The cable sections 36 withdrawn
from the drill string may be reused as individual lengths of pipe
are added to the drill string 12.
An important feature of the invention is that the number of
connectors required to maintain electric continuity from the
subsurface terminal to the surface terminal need be employed only
in a minor fraction of the total conductor. This is schematically
illustrated in FIGS. 8-10. For purposes of illustration, let it be
assumed that the well is about 5,000 feet where wellbore telemetry
operations are to commerce; further, each bit is capable of
drilling about 500 feet. During the initial bit run at this depth,
the borehole is advanced from 5,000 to 5,500 feet. This advancement
will be in increments about equal to the length of a pipe section,
e.g. about 30 feet. The drill string 12 and conductor 22 are
lengthened for each incremental advance in the manner described
previously. At the end of the first bit run (see FIG. 8), the
continuous cable 30 extends from about 500 to about 5,500 feet and
the cable sections 36 connected in end-to-end relation by about 17
connectors (assuming 30-feet joints of drill pipe are used) extend
from the top of the drill string 12 to about 500 feet. The drill
string 12, and conductor 22, are withdrawn from the borehole and
the operations repeated for a second bit run.
At the end of the second bit run (see FIG. 9), the second
continuous cable 30 extends from about 500 feet to about 6,000
feet, or 500 feet more than the length of the first continuous
cable; and the length of the cable sections 36 remains about the
same, extending from the upper end of the drill string 12 to about
500 feet.
The operations are repeated for a third bit run which is
illustrated in FIG. 10, showing the third continuous cable 30 now
extending from about 500 feet to about 6,500 feet and the cable
sections 36 extending from the upper end of the drill string to
about 500 feet.
These operations may be repeated several times over; or wellbore
telemetry operations may be interrupted for several bit runs and
resumed at a later time. Of course it will be understood that there
will be variations in the footage that each bit is capable of
drilling; that is, some bit runs may be as low as 100 feet or may
be as long as 1,000 feet and even longer. It also will be
understood that the method is not limited to the drilling
capability of the bit. For example, wellbore telemetry operations
may be interrupted for reasons other than withdrawing the drill
string or replacing the bit. In this regard, it should be noted
that the apparatus disclosed in this preferred embodiment permits
the cable sections 36 to be withdrawn from the drill string 12
enabling drilling operations to continue in the conventional
manner.
A comparison of FIGS. 8-10 reveals that lengths of the cable
sections 36 remain about the same whereas the continuous cable 30
is lengthened for each bit run. Note that the combined length of
cable sections 36 never exceeds the length of the continuous cable
30. This method thus permits a substantial reduction in connections
required in the conductor over that required in many prior art
techniques. In the above example, only 18 connectors were required
in each of the three operations. If the cable 30 is lengthened
after each bit run by adding a length of cable section equal to the
length drilled by that bit run, one additional connector will be
required for each successive bit run.
There are a number of arrangements capable of providing the
conductor sections in the upper portion of the drill string 12. The
conductor sections may be permanently mounted in the drill pipe
joints such as those described in U.S. Pat. Nos. 3,518,608 and
3,518,609. Preferably, however, the conductor sections are provided
by a cable section which can be threaded through each length of
pipe to be added to the drill string.
The present invention also contemplates that the upper cable
sections 36 may be provided by armored cable, in which case the
connectors for joining adjacent cable sections must be adapted to
anchor the armor as well as provide electric continuity across the
connection. The use of armored cable joined by suitable connectors
permits the entire conductor to be supported on the kelly cable 24,
assuming, of course, that this cable is also armored and that
connector 25 has sufficient mechanical strength to bear the weight
of the entire conductor string 22.
One embodiment of an armored cable connector suitable for use in
this second embodiment is shown in FIGS. 11 and 12. The connector
assembly designated generally as 55 includes a lower body section
56 and an upper body section 57, each having an axial passage
formed therein for receiving the conductor and connectors. A lower
cable section 36 which in this embodiment will be provided by
armored cable extends upward into the lower end of the body section
56 and terminates in a female connector 62. Strands stripped from
the cable section 36 pass through axial openings 58 formed in a
clamping sleeve 60. The strands are anchored by means of nut 59
threadedly connected to collar 60. The anchoring assembly is
maintained to the lower body section 56 by collar 61.
A bulkhead connector 63 is threadedly connected to the interior of
the lower body section 56. The pin (not shown) of the bulkhead
connector 63 extends downwardly and mates with the female connector
62. An O-ring 64 positioned at the base of the bulkhead connector
provides a fluid tight seal between the connector 63 and body
section 56. A second bulkhead connector 65 is also threadedly
connected to the interior of the lower body section 56 and is
provided with an upwardly extending pin (not shown). This connector
is also provided with an O-ring 66 at its base. An insulated
conductor 67 interconnects the interior contacts of bulkhead
connectors 63 and 65.
A second, upper armored cable also illustrated as 36 in FIG. 11
extends downwardly into the upper body section 57 and is similarly
provided with a cable anchor comprising sleeve 68, nut 69, and
collar 70. The conductor wire of cable 36 extends through the upper
body section 57 terminating in the female connector 71. Connector
71 is maintained in place by bushing 72.
The lower and upper body sections 56 and 57 are separable and are
adapted to be joined by coupling 73. Coupling 73 is mounted on the
upper body section 57 for relative rotation thereon, and it is
provided with internal threads adapted to mate with external
threads formed on the lower body section 56. A spring-loaded
locking sleeve 74 is also provided to insure that the parts are
maintained in assembled relation. The locking sleeve 74 includes a
lug 75 adapted to fit snugly into a complementary shaped recess 76
formed in the lower edge of coupling 73 (See FIG. 12). The locking
sleeve 74 is mounted for relative axial movement on the body
section 56. The connection between the locking sleeve 74 and body
56 may be splined or grooved so as to prevent relative rotational
movement.
The female connectors 62 and 71 may be similar to those illustrated
in FIG. 4.
During drilling operations, the cable sections 36 may be joined in
the manner described previously with reference to FIGS. 6 and 7.
With the upper cable section 36 positioned above an adjacent cable
section (each cable section being provided with complementary
halves of the connector assembly 55) the connector 71 is mated with
the pin of bulkhead connector 65. The coupling 73 is then screwed
onto the lower body section 56, and finally the locking sleeve 74
which has been maintained in a retracted position, is moved
upwardly until the lug 75 enters the recess 76 formed in the lower
edge of collar 73. As cable sections 36 are added to the conductor
22, it may be necessary to remove slack from the conductor. This
may be achieved by periodically overlapping a portion of a cable
section to remove slack from the conductor and securing the
overlapped portions; or by using spiders as described above.
Although the present invention has been described with reference to
conventional rotary drilling operations, it can also be used with
other types of drilling equipment including turbo drills and
positive displacement hydraulic motors. These devices normally
include a motor or turbine mounted on the lower end of the drill
string and adapted to connect to and drive a bit. The motor or
turbine powered by the drilling fluid drives the drill bit while
the drill string remains stationary. When this type subsurface
drilling device is used in directional drilling operations, the
present invention provides a highly useful means for transmitting
directional data to the surface.
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