Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Matter no.: A890282US
Document no. 89805 v.2
Apparatus for Receiving Downhole Acoustic Signals
FIELD OF THE INVENTION
The invention relates generally to an apparatus for receiving downhole
acoustic signals.
BACKGROUND OF THE INVENTION
Real-time collection of navigation and other relevant downhole data at a drill
bit and transmission of the data to a surface rig is a common practice in off-
shore
and land-based drilling rigs. This technology has been called "Measurement-
While-
Drilling" (MWD). Logging data may also be transmitted uphole, and if so, the
technology is referred to as Logging-While-Drilling (LWD).
Current commercialized MWD and LWD technologies include mud pulse
telemetry, in which pressure pulses are generated in the mud by periodically
constricting the flow through the drill string. However, the data transmission
rates
using mud pulse telemetry are slow (< 1 binary bit/second), which limits the
type of
data that can be usefully collected. Wireline telemetry has been used in the
industry, and provides greater data throughput than mud pulse telemetry, but
electric
cables that are used to transmit data up and down the drill string are
vulnerable to
damage and impose limitations to the operation of the drill string.
Wireless telemetry technology other than mud pulse telemetry has been
developed that avoids the physical limitations of wireline cables and has a
higher
data transmission throughput than mud-pulse telemetry. Examples of wireless
telemetry include electromagnetic telemetry, in which signals are sent as
electromagnetic waves through the Earth. Electromagnetic Telemetry is limited
to
operating in areas where the formation resistivity is in an acceptable range
to allow
transmission.
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Another type of wireless telemetry is acoustic telemetry, which involves the
transmission of data with acoustic energy through such mediums as drill pipe.
Acoustic telemetry applications include MWD, LWD, drill-stem-testing (DST),
production, downhole pump performance, smart well completions, utility
crossings
and river crossings.
Several technological challenges exist with implementing acoustic telemetry
technology in these applications. The complex wave physics associated with
this
type of data transmission require careful consideration to the design of the
components of an acoustic telemetry system, which include a downhole sensor
pack
and transmitter, and an above-surface receiver. Technical challenges exist in
ensuring that the above-surface receiver receives an acoustic signal with
measurable strength and quality, and that the components of the telemetry
system
are robust, affordable and compatible with the drilling operation.
As an example, US patent no. 6,320,820 describes an acoustic telemetry
system in which an "acoustic telemetry receiver" is coupled to a kelly to
receive
transmitted telemetry signals. The telemetry receiver in this instance is a
wired
device, and thus cannot be used while tubulars are rotating. It is also bulky,
limiting
its placement on the drillstring to locations that may not be acoustically
optimal.
Another application of acoustic telemetry technology in the drilling industry
is
above-ground acoustic monitoring of downhole acoustic signals from sources
other
than an acoustic transmitter. Monitoring applications include receiving timing
information for seismic-while-drilling (SWD), monitoring drilling dynamics,
air
hammer monitoring, fluid hammer monitoring, casing drilling, and bottom hole
assembiy (BHA) retrieval and seating confirmation.
Examples of published monitoring systems includes the Advanced Drillstring
Analysis and Measurement System (ADAMS) published in IADC/SPE paper 19998
and SPE paper 14327. The ADAMS comprises a measurement sub, a wireless
telemetry system, and an instrumented trailer laboratory. The measurement sub
must be inserted into the drillstring, to form a structural component, and is
thus
intrusive and not compatible with various drill collar connections without
additional
cross-over subs. This requires additional rig time to install, adds potential
failure
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points, adds additional wear and tear to the drill string components, and
affects rig
operations such as pumping.
It is therefore desirable to provide an acoustic telemetry system that
improves
on at least some of the deficiencies of the state of the art.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided an apparatus for
receiving downhole acoustic signals. The apparatus comprises at least one
instrument housing made of an acoustically conductive material; the housing
includes a contacting portion contactable with a rotatable above-surface
component
used in borehole applications in such a manner that acoustic signals from a
downhole source conducted through the rotatable above-surface component is
conducted through the housing. The apparatus also comprises instruments inside
the housing, such as a transducer for converting acoustic signals conducted
through
the housing into electric signals, a data acquisition circuit communicative
with the
transducer, and a wireless transmitter communicative with the data acquisition
circuit
and for transmitting the electric signals to a remote destination. The
apparatus also
includes a clamping assembly attached to the instrument housing and having
sufficient length and flexibility to enable the apparatus to surround the
perimeter of
the rotatable above-surface component; the clamping assembly includes a
fastener
configured to removably fasten the apparatus to the rotatable above-surface
component, thereby enabling the apparatus to operate while the rotatable above-
surface component is rotating.
The clamping assembly may further include a plurality of members each
pivotably connected to one or more of another member, the housing, and the
fastener. At least some of the members may be removable, thereby enabling the
clamping assembly length to conform to the perimeter of the rotatable above-
surface
component.
The housing contacting surface may further comprise at least one contact
tooth for providing a high pressure contact interface between the housing and
the
rotatable above-surface component. The rotatable above-surface component may
be selected from the group of a kelly and a saver sub of a drilling rig.
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The apparatus may comprise a plurality of housings, and if so, the housings
are pivotably connected to one or more of another housing, the clamping
assembly
member, and the fastener. Where a pair of housings are adjacent to each other,
each adjacent housing may have a conduit opening, and the apparatus may
further
comprise a flexible conduit connected at each end to a conduit opening, and an
electrical connector passing through the conduit and electrically connecting
the
instruments in one housing to the instruments in the adjacent housing.
The housing may further comprise an RF transparent portion, and an RF
antenna mounted inside the housing such that the antenna can receive and
transmit
RF energy through the RF transparent portion.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic elevation view of a conventional drilling rig and a safe
area monitoring station.
Fig. 2 is an isometric view of an embodiment of an apparatus for receiving
downhole acoustic signals.
Fig. 3 is a schematic top view of the apparatus of Fig. I attached to an above-
surface rotating component of a drilling rig.
Fig. 4 is a schematic top view of an embodiment of an apparatus for receiving
downhole acoustic signals having four housings and five spacer members and
mounted on a 12" diameter tubular portion of the drilling rig.
Figs. 5 & 6 are schematic top sectioned views of adjacent housings of the
apparatus and a flexible conduit interconnecting the housings.
Fig. 7a is an exploded isometric view of a housing with transparent window
and antenna.
Fig. 7b is a collapsed view of the housing of Fig 7a.
Fig. 8 is a system diagram of instruments inside the housing of the apparatus.
Fig. 9 is a schematic diagram of a safe area monitoring station for receiving
RF signals from the apparatus.
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DETAILED DESCRIPTION
Fig. 1 provides a simplified representation of a typical drilling rig 99.
Boreholes 110 are drilled into the earth with a drill string comprising a
drill bit 106
connected to the surface by multiple joints of drill pipe 107. A downhole
acoustic
transmitter and sensors 105 may be located near the bit, to provide
information
about the formation geology, fluid pressure, wellbore geometry, etc.
Additional
and/or alternative bottom hole assembly (BHA) components such as positive
displacement motors, air hammers, rotary steerable devices, and other devices
may
be present. The drill pipe 107 is threaded into a square or hexagonal section
pipe
called a kelly 104 which is driven by a rotary table 101. Typically, the kelly
104 is
attached to the swivel 100 via a saver sub 103. The swivel 100 is supported by
a
bail 102 which is carried by a hook 111, attached to traveling blocks 112. The
traveling blocks 112 are lifted and lowered by a cable assembly 113.
According to an embodiment of the invention, and referring to Fig. 2, an
apparatus 1 for receiving downhole acoustic signals is removably attachable to
an
above-surface rotating component of the drill string, below the bearing
surface of the
swivel 100, and preferably on the saver sub 103, or the top portion of the
kelly 104.
These preferred locations provide the optimum acoustic location on the
drilling rig
99; the bearing surface and the change in acoustic impedance between the drill
string and the swivel 100 act as an acoustic reflector, and thus all points
above the
swivel 100 only contains a small fraction of the acoustic energy generated
downhole.
While the description of the apparatus 1 is in the context of use on a
drilling
rig, it is to be understood that the apparatus 1 may also be attached to a
service rig,
slant rig, well head, or other surface equipment associated with boreholes in
the
earth.
The apparatus 1 includes a plurality of housings 10 each linked together with
a bolt 12 and nut 13 which act as a pivot for a hinge 14 integrated into each
housing
10. The housings 10 contain instruments for receiving acoustic signals,
processing
the acoustic signals into electronic data, and transmitting the data as RF
signals to
an above-surface monitoring station 108 (as shown in Figure 1). The acoustic
signals are transmitted from the downhole acoustic transmitter 105, and
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through a transmission medium, typically the drill pipe 107, kelly 104, and
the saver
sub 103.
Referring to Fig. 8, the instruments comprise two accelerometers 3 which are
electrically communicative with conditioning circuitry 4. The accelerometers 3
measure axial accelerations associated with acoustic wave signals transmitted
from
the downhole acoustic transmitter 105. As acoustic waves pass through the
saver
sub 103, the sub 103 and the housing 10 attached to it are moved in a
oscillating
manner. Since the accelerometers are attached to the housing which is
oscillating,
they are also oscillated. The accelerometers measure the accelerations
associated
with the oscillations by producing a voltage sigal proportional to the
magnitude of the
acceleration they experience.
Signals from the accelerometers 3 are electrically transmitted to the signal
conditioning circuitry 4 for conditioning, then output of the signal
conditioning circuitry
4 is sampled by an analog-to-digital converter (ADC) 5. The sample signals are
transmitted to a processor 6, which takes these samples, and encodes them in a
suitable communication protocol, and transmits the encoded signal through an
interface 7 to a transmitting radio-frequency (RF) modem 8. A power supply 9
such
as batteries are electrically connected to the instruments to power same.
Alternatively, the accelerometers 3 can be calibrated to receive downhole
acoustic signals from sources other than the acoustic transmitter 105. In such
case,
the apparatus I serves as a monitor of downhole conditions, and for example,
can
be used to monitor the operation of a downhole air hammer (not shown) by
monitoring the acoustic signals emitted by the air hammer as a result of its
operation.
Referring now to Figs. 1, 8, and 9, RF signals are transmitted by the modem 8
via an antenna 42 and are received by a monitoring station antenna 109 in a
safe
area monitoring station 108. The received signal is transmitted from the
antenna
109 to a connected receiving RF Modem 110, where the signal is decoded and
transmitted to a connected portable computer 114 or other similar display
device.
This wireless transmission allows the apparatus I to operate continuously,
regardless of the rotation state of the drill string. It also provides the
additional
benefit of eliminating the need to run cabling around the drill rig 99 and
monitoring
station 108, which would be prone to damage or interfering with the drilling
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operation. The modem 8 and antenna 42 can also receive signals transmitted by
the
monitoring station 108, and as such serves as a wireless RF transceiver.
Referring again to Fig. 2 and 3, the housing 10 serves as a protective
enclosure for the instruments against the harsh outside environment of the
drilling rig
99. The housing 10 includes a cover 15 and an instrument bay 16 covered by the
cover 15. The instrument bay 16 has side walls and a base; two sets of hinges
14
protrude from the outside surface of the base, one set at each longitudinal
edge
thereof. The cover 15 seals against an o-ring seal (not shown) located in a
groove
(not shown) in the lip of the instrument bay side walls. In the event the
apparatus 1
is used in hazardous conditions, the seal prevents potentially explosive gases
from
entering into the housing 10 and coming in contact with a source of ignition.
The
seal also prevents rain, dust, oil, or other contaminants from entering the
housing 10,
which could damage the instruments. The instruments may be shock isolated by
an
elastomer (not shown) inside the housing 10; such isolation is especially
preferred
where the apparatus 1 operates in high shock and vibration environments.
Four housings 10 are provided to house the instruments and power supply 9;
the housings 10 are pivotably interconnected at their respective hinges 14 by
the
bolts 12 and nuts 13. At the housing 10 at one end of the line of
interconnected
housings 10, one set of hinges is pivotably connected to a spacer member 17.
The
spacer member 17 has a slab-like body with two sets of hinges, with each set
of
hinges located at each longitudinal edge of the body. The other set of hinges
of the
spacer member 17 is pivotably attached to a hook 21, which has three spaced-
apart
teeth 30.
The hook 21 is one component of a fastening assembly 28. The fastening
assembly 28 also includes a pair of rod end eyebolts 19 pivotably attached at
their
proximal end to the housing 10 at the other end of the interconnected housings
10.
The eyebolts 19 are spaced apart and generally parallel to each other, and
extend
perpendicularly from the pivot bolt 12. A bolt bar 20 has a pair of holes
extending
transversely through its body, that are configured to allow the eyebolts 19 to
slide
through the bolt bar 20. The eyebolts 19 are threaded near their distal ends,
and
tightening nuts 18 are used to secure the bolt bar 20 to the eyebolts 19.
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The fastening assembly 28 engages by hooking the hook 21 onto the bolt bar
20 such that the eyebolts 19 extend between the spaces between the hook teeth
30.
Referring to Fig. 3, the apparatus 1 can be wrapped around a tubular portion
(e.g.
the saver sub 103) and secured in place by tightening the nuts 18 against the
eyebolts 19. Contact teeth 22 are provided to enhance the physical attachment
of
the apparatus I to the tubular portion. The teeth 22 also serve to enhance
acoustic
conduction between the rotating component and the housing 10, by providing a
high
pressure contact interface. The teeth 22 protrude from base of the instrument
bay
16; in this embodiment, the teeth are an integral part of the protruding
hinges 14, but
the teeth 22 may also separately protrude from the instrument bay 16 base.
Referring to Fig. 4, additional spacer members 17 (b), 17(c), 17(c), 17(d),
and
17(e) may be added to the first spacer member (now referred to as 17(a)) to
enable
the apparatus 1 to surround larger diameters tubes such as the 12" section
shown in
Figure 4 , or to other larger perimeter components. Also, the number of
housings 10
may be increased or decreased depending on the number of instruments needed.
Multiple housings 10 in the apparatus 1 are desirable to enable the
diametrical
profile (the height of the side walls) of the housings 10 to be minimized.
This
enables the apparatus 1 to be attached to and rotate with an above-surface
rotating
component without coming into contact with non-rotating parts of the drilling
rig 99.
Referring now to Figures 5 and 6, a flexible hydraulic hose 23 may be used to
provide a protected conduit between adjacent housings 10, for electrical
connectors
(not shown) to interconnect instruments in the adjacent housings 10. A drilled
hole
is provided in each adjacent housing 10, and each end of the hose 23 has a
hollow barbed fitting 24 that secures each end of hose 23 in the hole 25 of
each
25 housing 10. The barbed fitting 24 expands the hydraulic hose in the drilled
hole 25,
thereby forming a secure sealed connection. External tapered ridges (barbs) 26
are
provided on the fitting 24 prevent the fitting 24 from coming out of the hole
25 due to
flexure or vibration. The hydraulic hose 23 protects the electrical connectors
from
moisture or contact with rig equipment that may otherwise damage it.
During rotary drilling, the apparatus 1 will rotate with the drill string, but
must
still be able to communicate with a display device, typically a portable
computer
located in a safe area, and thus a hardwired communication means is not
possible.
The current invention uses a RF modem to provide this communication link.
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Referring now to Fig. 7a & b, the RF antenna 42 is enclosed in the instrument
bay 16
of one of the housings 10. This housing 10 has a RF-transparent cover 41, and
retaining plate 40 for the cover 41. An o-ring (not shown) located in a groove
43
machined in the instrument bay 16 to form a seal against the RF-transparent
cover
41. The RF-transparent cover 41 is preferably made from an impact-resistant
plastic, such as polycarbonate, compatible with the temperature extremes found
on
drilling locations. Although the RF transmission occurs substantially
perpendicular to
the plane of the RF transparent cover 41, the reflections in the rig structure
provide
what is known to those skilled in the art as a multi-path environment. In
effect,
multiple reflections provide a substantially continuous RF path between
transmitter
and receiver pair, thereby enabling continuous data transmission. This effect
is
particularly important as the transmitter may be rotating due to the operation
of the
drill string.
Optionally, the apparatus 1 may be configured to send as well as receive
acoustic signals from the downhole acoustic transmitter 105.
While the present invention has been described herein by the preferred
embodiments, it will be understood by those skilled in the art that various
changes
may be made and added to the invention. The changes and alternatives are
considered to be within the spirit and scope of the present invention.
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