Note: Descriptions are shown in the official language in which they were submitted.
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1 BACKGROUND OF THE INVENTION
2 1. Field of the Invention
3 This invention relates to an improved method and apparatus for
4 performing wellbore telemetry operations. In one aspect, it relates to a
method for establishing and maintaining a communication link between a
6 subsurfac~ location in a rotary drill string and a surface location.
7 2. Description of the Prior Art
8 In the drilling of oil wells, gas wells, and similar boreholes, it
9 frequently is desirable to transmit data between subsurface and surface
locations. One application where data transmission has received considerable
11 attention in recent years is in wellbore telemetry systems designed to
12 sense, transmit, and receive information indicative of a subsurface condi-
13 tion. This operation has become known in the art as "logging while dril-
14 ling."
A major problem associated with wellbore telemetry systems has been
16 that of providing reliable means for transmitting signals between the sub-
17 surface and surface locations. This problem can best be appreciated by
18 considering the manner in which rotary drilling operations are normally
19 performed. In conventional rotary drilling, a borehole is advanced by
rotating a drill string provided with a drill bit at its lower end. Lengths
21 of drill pipe, usually about 30 feet long, are added to the drill string,
22 one-at-a-time, as the borehole is advanced in increments. In adapting a
23 telemetry system to rotary drilling equipment, the means for transmitting the
24 electric signal through the drill string must permit the connection of
additional pipe lengths to the drill string as the borehole is advanced.
26 An early approach to the problem involved the use of continuous
27 electric cable which was adapted to be lowered inside the drill string and to
28 make contact with a subsurface terminal. This technique, however, required
29 withdrawing the cable from the drill string each time a pipe length was added
to the drill string. A more recent approach involves the use of special
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1 drill pipe. Each pipe section of the special pipe is provided with an
2 electric conductor having connectors at its opposite ends. Electric con-
3 tinuity is maintained across the junction of two pipe sections by connectors
4 of one section contacting a connector on the adjacent pipe section (see U.S.
Patent Nos. 3,518,608 and 3,518,609). Disadvantages of this system include
6 the high cost of the special pipe sections, the need for a large number of
7 electric connections (one at each joint), and the difficulty of maintaining
8 insulation of the electric connectors at each joint.
9 Still another approach involves the use of cable sections mounted
in each pipe section (see U.S. Patent No. 2,748,358). The cable sections are
11 connected together as pipe sections are added to the drill string. Each
12 cable section is normally made slightly longer than its associated pipe
13 section, with the result that a small amount of slack is present in the
14 conductor string at all times.
A more recent approach involves the use of a cable maintained in
16 a looped configuration within the drill string. The looped arrangement
17 stores cable in the drill string and permits the cable to be extended as
18 the drill string is lengthened. This technique normally requires the use
19 of sheaves and other apparatus within the drill string to maintain the cable
in the looped configuration. However, this arrangement presents flow res-
21 trictions within the relatively narrow opening. Moreover, care must be
22 exercised to prevent cable entanglement, particularly for long cable loops.
23 SUMMARY OF THE INVENTION
24 The purpose of the present invention is to provide a communication
link between a subsurface location in a well and the surface.
26 Briefly the invention, in one embodiment, involves transmitting
27 data from the subsurface location via an insulated conductor extending
28 upwardly from the subsurface location and functioning as an antenna. A
29 second insulated conductor extends downwardly from the surface and, normally,
will substantially overlap the first conductor. The transmitted signal is
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1 picked up by this second conductor through electromagnetic coupling. The
2 second conductor functions as a receiving antenna and is coupled to a
3 receiver at the surface.
4 Normally, the transmitting antenna is lowered to the desired sub-
surface location when it is desired to begin telemetering operations and
6 the receiving antenna is also inserted into the well at this time. Because
7 the overlapping length of the two antennas is not critical, both antennas
8 may initially extend substantially the entire length of the wellbore. The
9 well can then be drilled to approximately twice its original depth before
the wires cease to overlap and the communication link is lost. At that
11 time, the length of the receiving antenna may be increased to reestablish
12 the overlap to resume telemetering operations.
13 A principal advantage of this invention is that the well depth
14 can be substantially increased and the communication link maintained with-
out increasing the length of either conductor.
16 Another advantage is that the interior of the drill pipe is rela-
17 tively unobstructed.
1~ BRIEF DESCRIPTION OF TH DRAWINGS
19 FIGURE 1 is a schematic view of well drilling equipment with two
electric conductors arranged within the drill string in a preferred con-
21 figuration.
22 FIGURE 2 is an enlarged fragmentary view, shown partially in
23 longitudinal section, of apparatus useful in the invention for supporting
24 the lower conductor within the drill string.
FIGURE 3 is a top plan view of the apparatus illustrated in
26 FIGURE 2.
27 FIGURES 4-6 are schematic views illustrating a preferred sequence
28 of steps for adding a length of drill pipe into the drill string.
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1 DESCRIPTION OF _HE PREFERRED EMBODIMENT
2 Conventional rotary drilling equipment, as illustrated schemat-
3 ically in FIGURE 1, includes swivel 10, kelly 11, tubular drill string 12 and4 a bit 13. These components, connected in the manner illustrated, are sus-
pended from the drilling derrick 14 by means of rig hoisting equipment. The
6 kelly 11 passes through rotary table 16 and connects to the upper end of the
7 drill string 12. The term "drill string" as used herein refers to the column8 of tubular pipe between the bit 13 and kelly 11. The major portion of the
9 drill string 12 normally is composed of drill pipe with a lower portion beingcomposed of drill collars. The drill string 12 consists of individual pipe
11 sections, either drill pipe or drill collars connected together in end-to-end
12 relation. In the lower three sections of FIGURE 1, the diameters of the
13 borehole and the drill string 12 have been expanded in relation to the upper14 section to reveal further details.
The borehole 17 is advanced by rotating the drill string 12 and
16 bit 13. Drilling fluid is pumped down through the drill string 12 and up the
17 borehole annulus. The drilling fluid is delivered to swivel 10 through a
18 hose (not shown) attached to hose connection 18 and is returned to the sur-
19 face fluid system from the borehole annulus through pipe 19. A kelly bush-
ing 20 couples the rotary table 16 to the kelly 11 and provides means for
21 transmitting power from the rotary table 16 to the drill string 12 and bit 13.
22 The present invention may also be used in systems which employ a power swivel
23 in lieu of a kelly and rotary table; for purposes of illustration, however,
24 the invention will be described in connection with the kelly and rotary table
arrangement.
26 As mentioned previously, it frequently is desirable to monitor a
27 subsurface drilling condition during drilling operations. This requires
28 measuring a physical condition at the subsurface location, transmitting the
29 data signal to the surface, and reducing the signal to useful form. Typicalsituations where telemetry is applicable in drilling operations include
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1 drilling through abnormal pressure zones, drilling through zones where hole
2 deviation is likely to be a problem, directional drilling, exploratory dril-
3 ling and the like.
4 An instrument 21 capable of measuring a subsurface condition and
generating an electrical signal indicative of or representative of that
6 condition is provided within the drill string 12. A variety of devices
7 capable of sensing a physical condition are available. These include trans-
8 ducers for measuring pressure, temperature, strain, and the like; surveying
g instruments for measuring hole deviation; and logging instruments for mea-
suring resistivity or other properties of subsurface formations. The instru-
11 ment 21 may normally be powered by batteries. Alternatively, a subsurface
12 generator driven by fluid flowing through the drill string 12 may be used to
13 power instrument 21.
14 The communication link between the instrument 21, located within
the well, and the surface is established by transmitting the data from instru-
16 ment 21 to the surface via an electromagnetic link. Normally, the data will
17 be transmitted by encoding a train of electrical pulses and using these
18 encoded pulses to modulate a carrier. Phase modulation may preferably be
19 employed in the transmission link since phase modulation is relatively insen-
sitive to noise. More than one transducer or other device may be employed in
21 the instrument 21 if desired, in which case a multiplexer may be used for
22 sending the various signals over a single transmission link.
23 Instrument 21 includes a conventional transmitter. Conductor 40 is
24 coupled to the transmitter within instrument 21 so as to function as an
antenna. This conductor wire must be electrically insulated throughout its
26 entire length to prevent shorting out the electrical signal. Conductor 40 may
27 be of sufficient stiffness to be self-standing within the well. Alternatively,
28 support member 42 may be employed to support a more flexible wire.
29 As shown in FIGURES 2 and 3, support member 42 is basically a ring-
shaped device, made from stainless steel or other strong material, adapted to
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1 fit in an annular notched shoulder 50 formed in the box end of a pipe sec-
2 tion 12B. Shoulder 50 may be provided by milling the box end of the pipe
3 section in which support member 48 rests or, alternatively, may be provided
4 by a special sub. On one side of support member 42 (see FIGURE 3) there is
an extended section 46 having a slot 48. Support bracket 51 is mounted by
6 welding or other means, colinearly with slot 48. The upper end of wire 40
7 fits into the slot 48 and support bracket 51 and is restrained from lateral
8 movement by means of a bolt 52 that is mounted in holes in support bracket 519 as shown. Wire 40 has an expansion 54 at its upper end having q diameter
wider than bracket 51 to prevent townward movement of the wire and maintain
11 the wire in tension.
12 Other structures serving the same function as support member 42
13 will suggest themselves to those skilled in the art. It is desirable that
14 the drill string not be substantially obstructed.
A receiving antenna 43 extends downwardly from the top of the well
16 so that its length substantially overlaps transmitting antenna 40. It is not
17 necessary to use special antenna wire for either the receiving or trans-
18 mitting antennas. Conducting wire such as teflon coated #18 copper clad
19 steel can be employed. This conductor must also be electrically insulated
throughout its entire length.
21 The installation of the apparatus and performance of the method of22 the present invention is as follows. After drilling has progressed to the
23 point where it is desired to commence wellbore telemetry operations, drilling
24 operations are interrupted and package 21 is lowered into the drill string
using conventional techniques with antenna 40 connected to the transmitter
26 antenna terminal thereon. For this operation, a sheave disposed above the
27 derrick floor is normally employed to guide the antenna wire 40 into the
28 wellbore as it is unreeled from a drum. When the instrument 21 is properly
29 seated in the lower end of the drill string 12, preferably in a locking sub
immediately above bit 13, the support member 42, if used, is inserted into
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1 the annular notched shoulder in the box end of the pipe section as shown in
2 FIGURE 2, and the top of antenna 40 is attached to the support member in the
3 manner described above. Receiving antenna 43 is also run into the well to
4 the desired length, which may preferably be nearly the entire length of the
well. A weight may preferably be attached to the lower end of antenna 43
6 to maintain the wire in tension. The two wires, 40 and 43, may be initially
7 lowered into the well simultaneously. Alternatively, instrument package 21
8 may be positioned within the drill string when drilling commences, or some
9 tlme later, and conducting wire 40 lowered with a conventional stabbing
connector 14 at the lower end thereof for connecting to instrument package 21
11 when it is desired to begin telemetering operations.
12 In order to facilitate the addition of pipe sections to the drill
13 string 12 it is preferred that a conductor 43A, comprising the upper portion14 of the receiving antenna, extend through the interior of kelly 11 as illus-
trated in FIGURE 1 and connect to the upper end of conductor 43.
16 If telemetry operations are to be performed while the kelly 11 and17 drilling string 12 are rotating, the upper end of conductor 43A terminates
18 at a device 26 near the upper end of the kelly, capable of conducting the
19 received signal from the rotating member to a stationary member. Device 26
may be a slip ring and brush assembly. Device 26 and electric conductor 27
21 provide means for transferring signals from the receiving antenna within the22 drill string and kelly to receiver 28. If telemetry operations are to be
23 performed only at times when the drill string 12 and kelly 11 are stationary,
24 device 26 will not be needed and the conductor 27 may be connected directly
to conductor 43A through a suitable connector. In this situation, conductor 27
26 will be disconnected from conductor 43A when the kelly 11 and drill string 12
27 are rotated. Other possibilities include connecting a receiving unit to
28 conductor 43A and positioning the receiver on a rotating member; e.g., the
29 kelly 11.
Normally, the wellbore is advanced in increments substantially
31 equal to one length of drill string. The procedure for lengthening the drill
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1 string will be described with reference to FIGURES 4 through 6. A length of
2 drill pipe 31, to be added to the drill string 12 is shown disposed in a
3 shallow hole 32 ("mouse hole") below the derrick floor.
4 In order to insert the new pipe section, the drill string is
initially eleva~ed and suspended on the rotary table 16 and the kelly 11
6 disconnected from the drill string as shown in FIGURE 4. Conductor 43 will
7 normally be connected to conductor 43A by means of connectors 36 and 35 at
8 a distance below the top of the drill string slightly greater than one
9 drill pipe section. The wire must be retracted so that the mated connec-
tors 36 and 35 are above the upper end of drill string 12. A support
11 plate 38 or spider is inserted between the upper end of the drill string
12 and connector 36 and serves to support conductor 43 within the drill string.13 Connectors 36 and 35 are then separated. FIGURE 4 illustrates the position
14 of the equipment at this juncture in the procedure. As shown in FIGURE 5,
the kelly 11 is then swung over into alignment with pipe length 31 and the
16 length of conductor suspended beneath the kelly is inserted through the new
17 length of drill pipe 31. The kelly 11 is then screwed into the pipe sec-
18 tion 31. This assembly is then elevated above the drill string 12 and
19 exposed connector 35 is reconnected with connector 36. After the support
plate 38 is removed, the lower end of pipe length 31 is screwed into the
21 drill string 12 and becomes a part thereof. The equipment is then returned
22 to the drilling position and drilling operations resumed.
23 As drilling operations proceed, pipe sections are added which
24 lengthen the pipe string. As the well is drilled deeper, the transmitting
antenna, which retains its original length, will follow the drilling bit
26 down into the well. This means that as the well is drilled deeper, the
27 length of overlap of the transmitting and receiving antennas will diminish.
28 When they cease to overlap the communication link may be broken, and to
29 retain the communication link, it will be necessary to lengthen the receiv-
ing antenna to reestablish the overlap. This can be accomplished by retract-
31 ing the entire receiving antenna 43 and inserting a new longer wire; or
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1 more preferably, at a time when a new drill pipe section is being added, a
2 new section of wire having a connector that mates with connector 36 will be
3 connected to the existing receiving antenna and the old section of antenna
4 wire, with the new section attached, lowered into the well to reestablish
the desired overlap between the transmitting and receiving antenna.
6 This invention has been successfully tested in a test well. Good
7 coupling between the two antennas was observed, with a gradual reduction in
8 coupling as the overlap decreased. The tests were conducted with two
9 teflon-insulated, 18-gauge wires inside a drill pipe filled with water,
with no attempt to hold the wires together or apart.
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