Note: Descriptions are shown in the official language in which they were submitted.
CA 02354994 2001-08-13
ACOUSTIC FLOW PULSING APPARATUS AND METHOD
FOR DRILL STRING
Cross-Reference to Related Application
(0001] This application is related to and claims
the benefit of the filing date of Canadian patent
application No. 2, 331, 021 filed on 9 January, 2001 .
Field of the Invention
(0002] This invention relates to underground
drilling. In particular, the invention relates to
underground drilling methods which involve the
creation of acoustic pulses in drilling fluid, the
use of such pulses to operate downhole tools, and
the use of such pulses to increase drilling rates .
The invention also relates to apparatus adapted to
practice the methods of the invention.
Background
(0003] Deep wells such as oil and gas wells are
typically drilled by rotary drilling methods. Some
such methods are described in Walter, US patent No.
4,979,577. Apparatus for rotary drilling typically
comprises a suitably constructed derrick. A drill
string having a drill bit at its lower end is
gripped and turned by a kelly on a rotary table.
(0004] During the course of drilling operations,
drilling fluid, often called drilling mud, i~
pumped downwardly through the hollow drill string.
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The drilling fluid exits the drill string at the
drill bit and flows upwardly along the well bore to
the surface. The drilling fluid carries away
cuttings, such as rock chips.
(0005] The drill string is typically suspended from
a block and hook arrangement on the derrick. The
drill string, comprises a drill pipe, drill collars
and may comprise drilling tools, such as reamers
and shock tools, with the drill bit being located
at the extreme bottom end.
[0006] Drilling a deep underground well is an
extremely expensive operation. Great cost savings
can be achieved if the drilling process can be made
more rapid. A large number of factors affect the
penetration rate that can be achieved in drilling
a well.
[0007] Around the late 1940s, it was discovered
that drilling efficiency could be improved by
equipping the openings in drill bits, which allow
escape of drilling fluid with nozzles . The nozzles
provide high velocity jets of drilling fluid at the
drill bit. This innovation resulted in a dramatic
increase in achievable drilling rates. Today,
almost all drill bits are equipped with high
velocity nozzles to take advantage of this
increased efficiency. It is worthwhile to note
that between 45 - 65% of all hydraulic power output
CA 02354994 2001-08-13
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from a mud pump is typically used to accelerate the
drilling mud in the drill bit nozzles.
[0008] The flow rate of drilling fluid affects
penetration rates . Rock drill bits drill by forming
successive small craters in a rock face as
individual drill bit teeth contact the rock face.
Once a drill bit tooth has formed a crater, rock
chips must be removed from the crater. The amount
of drilling fluid necessary to effect proper chip
removal depends upon the type of rock formation
being drilled and the shape of the crater produced
by the drill bit teeth. Maintaining an appropriate
flow of drilling fluid is important for maintaining
a high penetration rate.
[0009] The weight on the drill bit also has a very
significant effect on drilling penetration rates.
If adequate cleaning of rock chips from the rock
face is effected, doubling of the drill bit weight
will roughly double the drilling penetration rate
(i.e. drilling/penetration rate is typically
directly proportional to weight on the drill bit) .
However, if inadequate cleaning takes place,
further increases in the drill bit weight do not
cause corresponding increases-in penetration rate
because rock chips not cleared away a.re being
reground, thus wasting energy. If this situation
occurs, one solution is to increase pressure and
flow of the drilling fluid in an attempt to effect
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better clearing of rock chips from the vicinity of
the drill bit.
[0010] Further information on rotary drilling and
penetration rate may be found in standard texts on
the subject, such as Preston L. Moore's Drilling
Practices Manual, published by PennWell Publishing
Company (Tulsa, Oklahoma).
[0011] Downhole vibrating tools known as mud
hammers have been developed in an effort to
increase drilling penetration rates of drill
strings. A typical mud hammer comprises a striker
hammer which is caused to repeatedly apply sharp
blows to an anvil. The sharp blows are transmitted,
through the drill bit to the teeth of the drill
bit. This has been found to increase drilling
penetration rates. Mud hammers are expensive to
operate as drill bit life is significantly reduced
by the use of a mud hammer.
[0012] In another effort to increase drilling
penetration rates of drill strings has yielded
various downhole devices which exploit the water
hammer effect to create pulsations in the flow of
drilling mud. Such devices tend to enhance the
hydraulic action of the drilling fluid. Their use
has a positive effect on rock chip removal and,
consequently, drilling penetration rates. Another
effect of these devices is to induce vibrations in
the drill string, more specifically in the drill
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bit itself. This too has a positive effect on
drilling penetration rates. Examples of such
devices can be found in US patent No. 4, 819, 745
(Walter), US patent No. 4, 830, 122 (Walter), US
patent No. 4, 979, 577 (Walter), US patent No.
5,009, 272 (Walter) and US patent No. 5, 190, 114
(Walter) .
[0013] While the devices described in these patents
have proven to be ef f ect ive at increasing dri 11 ing
penetration rates they have a number of
disadvantages which has prevented their widespread
adoption. It is difficult to design such a tool
which will operate reliably under the constantly
changing properties of drilling mud and the
constantly changing hydrostatic pressure at
downhole locations. This problem is exacerbated by
the small space within which downhole tools must
fit . In many drilling situations the downhole tools
have an outside diameter of only 6 3/4 inches.
Space constraints impose onerous constraints on the
design of such tools. Other problems with these
devices include:
~ Downhole conditions are harsh. Operating parts
of these tools may not withstand downhole
operating conditions for extended periods of
time.
~ Operating parameters cannot be adjusted while
drilling is ongoing. This makes it difficult
to optimize the performance of these tools.
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~ It is not possible to switch these tools on or
off while drilling. This makes it difficult to
ascertain the effectiveness of the tools since
there is a significant variation in drilling
penetration rates from well-to-well even if
all drilling parameters are kept constant.
~ During drilling, these tools are only
accessible for repair when they are brought to
the surface.
[0014] Despite the significant progress that has
been made in underground drilling technology over
the past century there remains a need for drilling
methods and apparatus which provide increased
drilling penetration rates.
Summary of the Invention
[0015] This invention provides methods for
underground drilling which involve generating high
intensity pressure pulses at or near the surface
and then allowing those pulses to propagate in
drilling mud down a drill string. The pulses may
cause fluctuations in the flow of drilling mud
exiting nozzles in a drill bit.
(0016] The invention also provides apparatus for
producing high intensity pulses. The apparatus
includes a valve which can suddenly substantially
block a conduit in which drilling mud is flowing,
CA 02354994 2001-08-13
thereby creating a water hammer in the flowing
drilling mud. In one embodiment of the invention a
partial flow from the same mud pump that is used to
pump drilling mud down a drill string is diverted
into a pulse generating circuit. The pulse
generating circuit includes a conduit through which
drilling mud can flow and a flow interrupter valve
downstream in the conduit . The apparatus may direct
drilling mud exiting the flow interrupter valve may
to a mud tank or may comprise a j et pump, or other
apparatus in the main mud conduit which causes a
reduced pressure at a location in the main mud
conduit where the diverted drilling mud is
reintroduced into the main mud conduit. The
apparatus includes a valve controller which
operates the flow interrupter valve on a periodic
basis.
[0017] Another aspect of the invention provides
downhole tools that are operated by pressure pulses
propagating down a drill string according to the
invention.
[0018] Further aspects and advantages of the
invention are described below and shown in the
accompanying drawings.
CA 02354994 2001-08-13
_ _
Brief Description of Drawings
[0019] In drawings which illustrate various non
limiting embodiments of the invention: Figure
1A is a schematic view of a typical classic rotary
drilling method apparatus, with a surface acoustic
pulse generator (SAP generator) pursuant to one
embodiment of the invention;
Figure 1B is an enlarged schematic diagram of
the SAP generator of Figure 1A;
Figure 2A is a schematic view of a typical
classic rotary drilling apparatus, with an SAP
generator pursuant to an alternative embodiment of
the invention;
Figure 2B an enlarged schematic diagram of the
SAP generator of Figure 2A;
Figure 3A is a schematic view of a typical
classic rotary drilling method apparatus, with an
SAP generator pursuant to a further alternative
embodiment of the invention;
Figure 3B an enlarged schematic diagram of the
SAP generator of Figure 3A;
Figure 4 is a schematic view of a typical
classic rotary drilling method apparatus equipped
with an SAP generator pursuant to a further
alternative embodiment of the invention;
Figure 5A is a schematic view of the SAP
generator of Figure 4 and a schematic view of a
preferred interrupter valve means pursuant to the
invention;
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Figure 5B is an enlarged schematic diagram of
the pref erred interrupter valve means of Figure 5A;
Figure 5C is a detailed schematic diagram of
the preferred interrupter valve means of Figure 5A;
FIG 6 is a schematic view of drilling apparatus
including an acoustic pulse generator and a
multiple piston telescopic tool located in a drill
string above a drill bit;
FIG 7 is a longitudinal sectional view of the
down hole telescopic tool of Figure 6 shown in its
"closed" position;
FIG 8 is a longitudinal sectional view of the
down hole telescopic tool of Figure 7 shown in its
"open" position;
FIG 9 is a cross sectional view through a
splined part of the telescopic tool of Figure 8;
FIG 10 is a schematic view of a drilling
apparatus including a surface acoustic pulse
generator and a multiple piston telescopic (MPT)
tool in the drill string above one or a few drill
collars;
FIG 11 is a longitudinal sectional view of the
MPT tool in a f first position wherein the weight of
the portion of the drill string below the tool is
supported by a set of springs; and,
FIG 12 is a longitudinal~sectional view of
the MPT tool of Figure 11 in a second position
which occurs when a pressure pulse lifts the
portion of the drill string below the MPT tool.
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Detailed Description
[0020] As required, detailed embodiments of the
present invention are disclosed herein. However,
it is to be understood that the disclosed
embodiments are merely exemplary of the invention,
which may be embodied in various forms . Therefore,
specific structural and functional details
disclosed herein are not to be determined as
limiting, but merely as a basis for the claims and
a representative basis for teaching one skilled in
the art to variously employ the present invention
in virtually any appropriately detailed structure.
[0021] This invention provides methods for
generating acoustic pulses at the surface and
conveying such pulses downhole to downhole tools
and/or a drill bit . In preferred embodiments of the
invention, acoustic pulses are generated by
interrupting the flow of drilling mud in a conduit
and thereby causing water hammer in the conduit.
[0022] Figure 1A is a schematic view of a typical
rotary drilling apparatus 10 which has been
modified by the addition of a surface acoustic
pulse generator (SAP generator) 20 according to the
invention. Figure 1B is a detailed schematic view
of SAP generator 20. Rotary drilling apparatus 20
comprises a mud pump 45 which pumps drilling mud 21
from a mud tank 32 into a stand pipe 22. Pump 45
typically has a relatively high capacity and
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supplies mud 21 under significant pressure. The
hydrostatic pressure within stand pipe 22 might be,
for example, 2 , 500 psi . Stand pipe 22 delivers mud
to the drill string in any suitable way.
[0023] In the illustrated embodiment, stand pipe
2'2, is fastened to a derrick 23, located on a
surface of an area to be drilled. A flexible hose
43 (made for example of reinforced rubber) carries
the f low of dri 11 ing mud 21 f rom stand pipe 22 into
a swivel 24, which is suspended from derrick 23 by
a hook. From swivel 24, drilling mud 21 enters a
drilling pipe 27 by passing through a kelly cock 25
and then a kelly 26. Drilling mud 21 is conveyed
to a drill bit 30 by way of a number of vertically
successive drill collars 28, and a bit sub 29. The
drilling fluid exits bit 30 through a number of
openings. Drilling mud 21 then returns to the
surface through the annular well bore 31
surrounding the drill string. At the surface the
mud is collected and returned to mud tank 32. The
mud may be treated to remove cuttings etc . after it
is collected.
[0024] Kelly 26 is rotated by a rotary table 33.
The rotation of kelly 26 is imparted to drill pipe
27, successive drill collars 28, bit sub 29 and
drill bit 30. As shown in Figure 1A, SAP generator
20 is preferably installed between mud pump 45 and
stand pipe 22.
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(0025] As shown in detail in Figure 1B, some of
pressurized drilling mud 21 is diverted at a
junction 145 into a conduit 52 as indicated by
arrow 53. Conduit 52 is preferably made from heavy
wall pipe. The amount of drilling mud diverted into
conduit 52 can be adj usted by a f low control valve
48. In preferred embodiments of the invention the
proportion of drilling mud which is diverted at
junction 145 is significantly smaller than the
proportion of drilling mud in the main flow which
continues past junction 145 into stand pipe 22. In
the illustrated embodiment, flow control valve 48
comprises a needle valve. The flow in conduit 52
can be adjusted by turning valve stem 49 with knob
50. Valve stem 49 is in threaded engagement 51 with
the housing of flow control valve 48. Therefore,
rotation of valve stem 49 causes valve stem 49 to
move axially, thereby altering the degree to which
valve stem 49 restricts the flow of fluid into
conduit 52. Suitable seals are provided to prevent
leakage of mud around valve stem 49.
[0026] A substantial portion of the drilling mud
diverted at junction 145 eventually flows back into
mud tank 32 (the two mud tanks 32 illustrated in
each of Figures 1A and 1B may be different mud
tanks but are preferably the same mud tank). SAP
generator 20 includes a flow interrupting valve 54
operated by a valve controller 55 which causes
valve 54 to periodically at least substantially
block the flow of drilling mud 21 out of conduit
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52 . A currently preferred embodiment of interrupter
valve controller 55 according to this invention is
described below with reference to Figures 5A
through 5C.
[0027] Valve controller 55 may comprise any of a
wide variety of valve control means. By way of
example only, possible valve control means include:
~ electrically operated valve actuators driven
by electrical or electronic controllers;
~ hydraulic or pneumatic control circuits;
~ valve members in valve 54 actuated by flow of
mud through valve 54; and,
~ mechanical valve operating mechanisms
comprising cams, reciprocating members,
oscillating members, or the like which move a
valve member in a valve 54 to periodically
interrupt the flow of drilling mud through
valve 54.
[0028] When valve 54 is not blocking the flow of
dri 11 ing mud, the dri 11 ing mud f lows through valve
54 and out of port 44. By rapidly blocking the
flowing drilling mud in conduit 52, flow
interrupting valve 54 generates water hammer pulses
which propagate upstream in conduit 52.
[0029] A pulse transmission means, which is a
conduit 56 in the illustrated embodiment, has one
end connected to conduit 52 at a location upstream
from interrupter valve 54. Another end of pulse
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transmission conduit 56 joins main conduit 57,
which carries the main flow of drilling mud 21 to
stand pipe 22. In preferred embodiments of the
invention, a check valve 47 prevents drilling mud
from flowing back through pulse transmission
conduit 56 into conduit 52. Check valve 47 opens
to allow drilling mud to flow through conduit 56 in
the direction of arrow 57 only under the high
pressure water hammer pulses generated by the
sudden closing of valve 54.
[0030] Water hammer induced pressure pulses in
conduit 52 are transmitted by pulse transmission
conduit 56 into main conduit 57 where they continue
to propagate downstream into the drill string. As
the bore of the drill string is typically smaller
than the bore of conduit 57 and other conduits
through which the mud passes at the surface, the
intensity of the pulses can be increased as they
pass into the smaller diameter bore of the drill
string. The pulses may be applied at underground
locations to enhance drilling performance as
described below. Pulses may also be transmitted
upstream toward pump 45. A pulsation dampener 147
may be provided in main line 57 downstream of pump
45 and upstream of pulse transmission conduit 56 to
reduce the effect of SAP generator 20 on the
operation of pump 45.
[0031] A shut off valve 46 and check valve 47
allow users to isolate SAP generator 20 from the
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main flow of drilling mud 21 while drilling
operations are ongoing. By disconnecting SAP
generator 20, drilling/penetration rates with and
without SAP generator 20 can be compared. Further,
the operating parameters of SAP generator 20 can be
adjusted during drilling operations to optimize the
performance of the drilling rig.
(0032] During operation of the apparatus, some
drilling mud 21 flows in the direction of arrow 53
through flow control valve 48 into conduit 52
toward interrupter valve 54. Valve controller 55
causes valve 54 to repeatedly open for a time long
enough for a flow of drilling mud to be established
in conduit 52 and then close relatively suddenly.
Each time this sequence of events occurs a water
hammer pulse is generated in conduit 52. The
sudden closure of interrupter valve 54 causes
kinetic energy of the mud flowing in conduit 52 to
be converted into a high pressure acoustic pulse.
The intensity of the acoustic pulse increases in
proportion to the velocity of the mud flow in
conduit 52 approximately according to the equation:
~p - @ x Vs x V (1)
where Op= pressure increase due to water hammer;
@= specific mass of drilling mud;
Vs= velocity of sound in drilling mud; and,
V - velocity of mud flow in conduit 52.
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Further details on the mathematics and physical
effects of water hammer can be found in various
texts on fluid mechanics, including Victor L
Streeter and E. Benjamin Wylie's Fluid Mechanics
(7th edition), McGraw Hill Book Company (1979).
[0033] Water hammer pressure pulses resulting from
the sudden closures of valve 54 travel upstream
from closed valve 54, at the velocity of the speed
of sound in the drilling mud inside conduit 52.
This pressure pulse also propagates into conduit
56. Check valve 47 opens and allows the pressure
pulse to propagate into main flow conduit 57. The
pressure pulses travel at the speed of sound in the
drilling mud through stand pipe 22 and down through
the drill string to drill bit 30. The pressure
pulses cause oscillations in the flow of drilling
mud exiting through the nozzles of drill bit 30.
This enhances cleaning of the bottom of well bore
34 and helps to achieve improved drilling
penetration rates.
[0034] Figure 2A is a schematic view of a drill
rig according to an alternative embodiment of the
invention comprising an alternative SAP generator
35. In this embodiment, drilling mud exiting from
SAP generator 35 is returned to the main flow of
drilling mud in conduit 57 . The construction of SAP
generator 35 is shown in detail in Figure 2B. A
venturi 37 is provided in main conduit 57. Venturi
37 acts as a jet pump. The hydrostatic pressure
CA 02354994 2001-08-13
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within main conduit 57 is reduced at point 59,
which is in a volume adjacent to venturi 37. The
volume may comprise an annular region surrounding
venturi 37 . Mud exiting from down stream port 44 of,
interrupter valve 54 is returned to main partial
flow of drilling mud 53 at point 59. The pressure
difference between junction 145 at which drilling
mud f lows into SAP generator 35 and point 59 drives
the flow of drilling mud through SAP generator 35.
SAP generator 35 functions otherwise in the same
manner as the SAP generator 20 described above.
High intensity acoustic pulses are delivered into
main conduit 57 at point 40. A valve 58 is
provided to facilitate isolating SAP generator 35
from main conduit 57. It should be noted that entry
of the acoustic pulse can be also incorporated down
stream into the venturi arrangement 37.
[0035] SAP generator 35 provides the advantages
that it permits better monitoring of the drilling
mud flow and of mud loss in the well bore. It
further allows more flexibility in terms of
installation. It should be noted that SAP generator
35 may be constructed so that the acoustic pulses
are coupled to main conduit 57 at a point in the
venturi arrangement down stream from venturi 37.
[0036] Figures 3A and 3B show an alternative SAP
generator 41 pursuant to an alternative embodiment
of this invention. SAP generating circuit 41 is
incorporated into a tool 42 , which is placed below
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swivel 24. Tool 42 is preferably placed above kelly
cock 25 and kelly 26. SAP generator 41 operates
similarly to SAP generator 35, but introduces
pulses directly into the drill string. The pulses
do not need to travel through flexible hose 43 . All
other things being equal, SAP generator 41 should
produces pulses of higher intensity at drill bit 30
than the embodiments described above. Venturi
arrangement 37 is incorporated into a lower tool
body 64. A top tool sub 65 has a conduit 60 that
allows a portion of the main flow of drilling mud
21 to enter SAP generator 41. Interrupter valve 54
can be a self regulating valve operated by the
water hammer itself as is described in US patent
No. 5, 549, 255 (Walter), at Figures 8 and 9 which
is incorporated herein by reference.
[0037] The main advantage of SAP generator 41 is
that generated acoustic pulses are inserted
directly into the drill string and do not have to
travel through rubber hose 43, which may tend to
somewhat attenuate the pulses. The main
disadvantage is that it is not as easily accessible
for servicing and adjustment as SAP 20 or SAP 35.
[0038] Figure 4 shows an alternative SAP generator
135 pursuant to an alternative embodiment of this
invention. SAP generator 135 is similar to SAP
generator 20, save for the fact that it lacks a
pulse transmission conduit 56 and check valve 47.
Pressure pulses generated by the sudden closure of
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interrupter valve 54 travel upstream from valve
54 and enter main conduit 75 at junction 145.
[0039] SAP generator 135 has an additional flow
control valve 148 located between down stream port
44 of interrupter valve 54 and mud tank 32 . Second
flow control valve 148 allows valve 54 to be
isolated for servicing. Second flow control valve
148 also allows the back pressure on valve 54 to be
adj usted . Depending upon the construction of valve
54, the performance of valve 54 may be adjusted by
altering the back pressure.
[0040] The SAP generator 135 of Figure 4 has the
advantage of simplicity. Further it does not
require the placement of equipment on the drill rig
floor which is already crowded in a typical
drilling operation. Flow control valves 48 and 148
can be adjusted so that just enough drilling mud
flows through SAP generator 135 when valve 54 is
open to slightly reduce the flow and pressure in
main conduit 57 downstream from junction 45.
[0041] Figure 5A shows a drill rig including a SAP
generator 135 in which valve 54 and valve
controller 55 are provided by an interrupter
mechanism 120. Interrupter mechanism 120 can be
used to advantage in any of the SAP generators
described above. Figures 5B and 5C are more
detailed views of interrupter mechanism 120.
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[0042] Interrupter mechanism 120 comprises a
valve member 127 which bears against a valve seat
127A. Valve member is biassed into a closed
position by a spring 128. An air bladder 129
contains compressed air (which can be supplied
through a port 130) . Air bladder 129 applies forces
to valve member 127 which tend to move valve member
127 into an open position wherein drilling mud can
flow from an inlet chamber 122 between valve member
127 and valve seat 127A into an outlet chamber 123 .
Drilling mud can enter inlet chamber 122 through
inlet passage 121. Drilling mud can leave outlet
chamber 123 through outlet passage 124.
[0043] In operation, compressed air is admitted
into bladder 129 until valve member 127 is moved
into its open position against the force exerted by
spring 128. As soon as this occurs, drilling mud
begins to flow from inlet chamber 122 to outlet
chamber 123. As drilling mud begins to flow through
downstream choke valve 148 a back-pressure is
developed. This back pressure, combined with the
forces exerted on valve member 127 by f lowing fluid
cause valve member 127 to move into its closed
position. The closure of valve member 127 causes a
water hammer pulse to propagate upstream from input
chamber 121. Valve member 127 is maintained in its
closed position by the pressure pulse. When the
pressure pulse reaches main conduit 57, or another
place where fluid can flow to relieve pressure, a
negative pulse propagates back toward interrupter
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mechanism 120. Upon arrival of the negative pulse,
valve member 127 is pulled open and the cycle
repeats itself.
[0044] An advantage of interrupter mechanism 120
is that it can be constructed in a robust manner
and the frequency of generated pulses can be easily
and continuously changed. The operation of
mechanism 120 can be adjusted by varying the air
pressure in bladder 129 and varying the setting of
downstream choke valve 148.
[0045] An accumulator may be provided upstream
from interrupter mechanism 120 to increase the
duration of acoustic pulses . In general this is not
required and has the disadvantage of reducing the
intensity of the acoustic pulses propagated down
the drill string.
[0046] In the foregoing embodiments of the
invention, intense acoustic pulses are generated at
the surface by a SAP generator. The pulses are
introduced into the drilling mud which is flowing
down the drill string. The pulses propagate down
the drill string to the bit . At the bit the pulses
cause variations in the mud flow which can increase
the efficiency of the drilling operation. The
intense acoustic pulses can also be used to actuate
downhole tools. The tools can be of simple robust
construction. One class of tools that may be
actuated by acoustic pulses according to the
CA 02354994 2001-08-13
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invention includes tools which impart mechanical
vibration to the drill bit . Such tools may suddenly
force the drill bit downwardly upon the arrival of
a pulse at the tool. In the alternative, such tools
may lift a lower portion of the drill string
slightly in response to the arrival of a pulse and
then drop the lower portion of the drill string
after the pulse has passed. Other types of tools
such as drilling jars may also be actuated by the
acoustic pulses of the invention.
[0047] Figure 6 is a schematic view of a rotary
drilling apparatus which includes a multiple piston
telescopic tool 66 mounted in the drill string
above drill bit 30. Pulses generated by SAP
generator 35 are conveyed down through the drill
string as described above. When the pulses reach
multiple piston telescopic tool 66 the tool extends
slightly, thereby accelerating' the drill bit into
the formation being drilled. This embodiment of the
invention can significantly vibrate the entire
drill string 67, thus reducing friction between
drill string 67 and well bore 68. The vibration of
drill bit 30 also enhance percussive action of
drill bit 30 at the bottom of hole 34, resulting in
faster drilling and lower torque requirements.
[0048] Figures 7 and 8 show a longitudinal
sectional view of a multiple piston telescopic tool
66 in normal and extended positions respectively.
Tool 66 is coupled to a bottom end of a section of
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one drill collar 28 via a coupling which, for
example comprises a conventional threaded coupling
95. Tool 66 includes a ram 69 which is coupled to
drill bit 30 at a connection 70. Connection 70 may
be a conventional threaded coupling. Ram 69 bears
splines 96 and is received within a female-splined
member 89 as shown in Figures 8 and 9. Splines
96 provide a torque coupl ing between f emale spl fined
member 89 and ram 69. Ram 69 can therefore slide
longitudinally within the body of tool 66 without
interrupting the transmission of rotational motion
to drill bit 30. A top end of ram 69 is coupled to
a pair of pistons 72, 74. Ram 69 and pistons 72 and
74 can move longitudinally in tool 66 as a unit.
The arrival at tool 66 of a pressure pulse
propagating through the drilling mud in bore 79
forces pistons 72 and 74 downwardly. This, in turn,
causes ram 69 to move from the normal position
shown in Figure 7 to the extended position shown in
Figure 8.
[0049] In the illustrated tool 66 each of pistons
72 and 74 is slidably disposed within a housing.
Piston 72 is disposed within housing 90. Piston 74
is disposed within a housing 91. Housing 90 is
coupled to housing 91 by a suitable coupling, such
as threaded coupling 92. Housing 91 is coupled to
a top sub 93 at a suitable coupling, such as
threaded coupling 94. Housing 91 is coupled to
female-splined member 89 which receives ram 69 by
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a suitable coupling such as a threaded coupling
91A.
[0050] Each piston is located between a pair of
cavities . Cavities 77 and 78 are upwardly adj acent
to pistons 72 and 74 respectively. Cavities 77 and
78 are each in fluid communication with bore 79 . In
the illustrated embodiment apertures 81 and 82 are
provided for this purpose. Cavities 83 and 84 are
downwardly adjacent to pistons 72 and 74
respectively. Cavities 83 and 84 are each in fluid
communication with the well bore 31 outside of tool
66. In the illustrated embodiment apertures 85 and
86 are provided for this purpose.
[0051] A cavity 76 is also defined between the
upper end of ram 69 and housing 90. This cavity is
in fluid communication with bore 79, for example by
way of apertures 80. Shaft seals 87 and piston
seals 88 seal cavities 76 , 77 and 78.
[0052]The number of pistons may be varied. One or
more pistons may be used. Preferably two or more
pistons are provided. An additional piston may be
added simply by coupling a piston like piston 72
between pistons 72 and 74 and a housing like
housing 91 between housings 91 and 92.
[0053] Figure 7 shows multiple piston telescopic
tool 66 when no acoustic pressure pulse is present
and tool 66 is in its position. When a pressure
CA 02354994 2001-08-13
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pulse propagating down bore 79 reaches area 97, the
pressure of drilling mud in area 97 is suddenly
increased. This causes drilling mud to be forced
into cavities 76, 77 and 78 via apertures 80, 81
and 82 respectively. The increased pressure within
cavities 76, 77 and 78 acting on projected piston
areas results in an axial force on ram 69. This
force drives ram 69, and drill bit 30, into the
bottom of hole surface 34. For example, a pressure
pulse of 1,500 psi acting on total area of 80 in2
will produce an axial force of 120,000 lbs. This
axial force will cause drill bit 30 to be thrust
against the bottom of hole 34, while reaction to
this axial force will lift the part of the drill
string situated above multiple piston telescopic
tool 66. Relative telescopic movement is indicated
by "E" on Figure 8. When the pressure pulse has
passed the weight of the drill string above
multiple piston telescopic tool 66 will cause tool
66 to collapse back into its normal position and
thereby closing gap E. The dropping drill string
will also deliver additional impact forces applied
to drill bit 30.
[0054] Figure 10 is a schematic view of a drilling
rig according to an alternative embodiment of this
invention. In the apparatus of Figure 10, high
pressure pulses generated at SAP generator 35 are
conveyed down the drill string through a multiple
piston telescopic tool 98, mounted above one or
more lower drill collars 99, and attendant bit sub
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29 and drill bit 30. This embodiment provides for
vigorous axial vibration of the bottom part of the
drill string, allowing in some instances to drill
percussively without need for a classical drill bit
30.
[0055] Figures 11 and 12 show a longitudinal
sectional view of a multiple piston telescopic tool
98. A bottom part of tool 98, identified by "L",
is similar to the multiple piston telescopic tool
66 shown in Figures 7 and 8, except that:
~ bottom part L is adapted to be coupled to a
top section of a lower drill collar 99. In the
illustrated embodiment, ram 69A in bottom part
L comprises a male thread 100, which can be
screwed to drill collar 99.
~ cavities 76, 77 and 78 are in fluid
communication with outside well bore 31
instead of bore 79. In the illustrated
embodiment, holes 101 are provided for this
purpose.
~ cavities 83 and 84 are in fluid communication
with inside bore 79 instead of outside well
bore 31. In the illustrated embodiment, holes
103 are provided for this purpose.
[0056] A top part of tool 98 comprises a spring
housing 104, which is coupled to a third piston
housing 114 via threaded connection 105. Piston 74
comprises a piston mandrel extension 106 which
extends into spring housing 104. A spring is
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connected between spring housing 104 and mandrel
extension 106. The spring has a very large spring
constant. The spring is compressed whenever the
piston mandrel extension 106 moves longitudinally
upwardly inside spring housing 104. In the
illustrated embodiment, a stack of disk springs 107
is on mandrel extension 106 between washers 109A
and 109B. Washer 109A abuts a step in the outside
of mandrel extension 106. Washer 109B abuts the
bottom of a top sub 111 which is coupled to spring
housing 104 via threaded connection 112.
[0057] Ram 69A and other parts of the drill string
below tool 98 are supported by a safety nut 108.
Safety nut 108 is locked in place by a screw 110.
Tool 98 is coupled to the drill string at its top
end via a threaded connection 113.
[0058] Figure 12 shows multiple piston telescopic
tool 98 when the pressure within bore 102 is at its
low or zero value . Figure 13 shows multiple piston
telescopic tool 98 when a high pressure pulse has
propagated down the drill string and is passing
through bore 102 of tool 98. The pressure pulse
increases the pressure of drilling mud in bore 102
and causes drilling mud to be forced into cavities
83 and 84. This causes a force to act on pistons
72 and 74 so as to drive the pistons upwardly. When
the pistons move upwardly the portion of the drill
string located below tool 98 is also lifted
upwardly and spring 107 is compressed. After the
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effect of the pressure pulse has dissipated, loaded
stack of disk springs 107 will dynamically return
bottom part L of tool 98 to its initial position,
thus resulting in a significant percussive blow to
bottom hole 34.
[0059] For example, a pressure pulse of 1, 500 psi
multiplied by a combined piston area of 60 in2 will
produce an axial lifting force of 90,000 lbs. In
a typical drilling apparatus the weight of lower
drill collars 99, and other elements (such as drill
bit 30) located below multiple piston telescopic
tool 98, is approximately 3, 000 - 6, 000 lbs. Spring
107 will therefore elastically absorb the resultant
axial force and return bottom end of the drill
string with such a force so as to produce extreme
percussive blows to bottom hole 34. These
percussive blows can enhance drilling penetration
rates, particularly when the formation being
drilled is hard.
[0060] Figure 13 illustrates schematically
another simple tool which may be used to impart
vibration to a drill bit. Tool 200 comprises a
splined ram 202 which is slidably disposed within
a female-splined part 204. Ram 202 is coupled to a
drill bit. Female splined part 204 is coupled to
the upper portion of the drill string. A diameter
of bore 79 is reduced at or in ram 202. Ram 202
thereby presents an upwardly facing surface 208.
When a pressure pulse propagating down bore 79
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increases the hydrostatic pressure acting on
surface 208 ram 202 (and the drill bit) are
hammered downwardly.
L0061~ As will be apparent to those skilled in the
art in the light of the foregoing disclosure, many
alterations and modifications are possible in the
practice of this invention without departing from
the spirit or scope thereof. For example:
~ while the foregoing description details the
generation of high intensity pulses by
interrupting the flow of the drilling mud
pressurized by mud pump 45 a separate pump
could be used to provide flowing drilling mud
for use in generating high pressure pulses.
~ While the flowing fluid medium which is used
to generate high pressure pulses is described
above as being drilling mud, a separate
circuit in which high pressure pulses are
developed by creating water hammers in a
dif f erent f luid medium, such as water, could
be used to generate high pressure pulses which
are then coupled into the drilling mud being
pumped down drill string.
~ Other techniques could be used for generating
high pressure pulses which are propagated down
through the drill string. For example, a
piston capable of being very suddenly
accelerated could be located to transmit high
intensity pulses into the flowing drilling mud
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57. The piston could be on a very high energy
electromechanical transducer, for example.
~ Other types of tool such as drilling jars may
be constructed so as to be operable by high
intensity pulses propagated from the surface
according to the invention.
[0062] Accordingly, the scope of the invention is
to be construed in accordance with the substance
defined by the following claims.
