Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to the field of MWD ("measurement while drilling")
technology
for the wireless telemetry logging of wells during drilling operations, and
more particularly
to an improved valve for generating "mud pulse" telemetry signals in the
drilling mud during
drilling operations.
In the drilling of deep bore holes such as oil and gas wells, it is desirable
to monitor
certain downhole conditions and to transmit information on these conditions to
the surface.
For example, information on such downhole conditions as temperature, pressure,
bore hole
orientation or deviation from the vertical, and a variety of geophysical data
relating to the
formation in which the bit is drilling are of interest to the driller. Such
variables typically are
monitored by a variety of prior art sensors with transducers which convert the
parameters
into electrical signals for transmission directly to the surface via
electrical conductors, or
which are used to command some form of wireless telemetry system for
transmitting a
surface detectable signal.
Direct or "hardwired" transmission systems present significant difFculty in
that cable
or similar conductors used for transmitting the signals are susceptible to
damage and are
awkward to manipulate during drilling. The more common approach in the
drilling industry
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219 ~'~ 22
is to utilize pressure pulses in the circulating drilling fluid ("mud") which
pulses are
propagated to the surface through the flowing column of drilling mud. The
pressure pulses
typically represent binary coded digital signals and are analogous to the
variable being
measured. The binary coded signals then are decoded by digital computers at
the surface
in order to interpret the data.
Two types of MWD mud pulse telemetry are utilized in the industry. Positive
pulse
systems use a downhole valve which restricts or briefly blocks mud flow to the
drill bit in
order to produce a surface detectable pressure increase or positive pulse.
Negative pulse
systems bypass the pressure drop across the bit by briefly opening a flow
passage to the
annulus from the drill stem interior above the bit, thus producing a surface
detectable
pressure decrease or negative pulse.
Examples of negative pulse MWD signal generators are provided, for example, in
U.S. Patents 4,386,422 issued May 31, 1983, entitled "Servo Valve for Well-
Logging
Telemetry" and 4,405,021 issued September 28, 1983, entitled "Apparatus for
Well
Logging While Drilling." A principal drawback with such negative pulse
generators is that,
if the valve fails in the bypass mode, substantial drilling fluid energy will
be lost into the
annulus, bypassing the bit, and decreasing drilling efficiency. A secondary
drawback is
that negative pulses, by their nature, are more difficult to detect and more
easily lost in the
general background noise of the flowing column of drilling mud. For these
reasons,
positive pulse generators are more widely used.
Examples of positive pulse mud signal generators are provided, for example, by
U.S. Patents 5,103,430 issued April 7, 1992, entitled "Mud Pulse Pressure
Signal
Generator;" and by U.S. Patent 4,550,382 issued October 29, 1985, and its
divisional
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219~'~2~
Patent 4,699,352 issued October 13, 1987, both entitled "Apparatus for Well
Logging
Telemetry."
A principal object in the design of MWD mud pulsing tools is to provide a
pulse
generator which can operate reliably in the hostile environment produced by
the exposure
to drilling mud a. ~d other downhole conditions. The present invention has a
unique servo
valve assembly which is designed to be more reliable than current art. Two
features which
distinguish the servo assembly from others is that it has no reciprocating
parts exposed to
the mud environment, other than the servo valve shaft, and also has no "dead
space"
cavities or chambers exposed to drilling mud which would allow solids and
debris to
accumulate.
Another principal object in the design of MWD mud pulsing tools is to provide
a
device which consumes a minimum amount of electrical power. All current
retrievable mud
pulsing tools receive their power from electrical storage batteries, which are
included as
part of the MWD string. When battery power is expended, the tools must be
retrieved from
the borehole to replace the batteries-a costly and time consuming process.
Motors or
solenoids are the primary driving means of most current art MWD tools. The
present
invention provides a MWD positive pulse generator which is more power
efficient due to
the unique servo valve design consisting of a low power consumption motor
which greatly
extends battery life. The primary unique feature of the servo assembly
operation which
contributes to this efficiency is that the servo valve is electrically powered
for only half its
cycle (opening or closing), with the other half of the cycle being spring
powered.
Therefore, timing of the cycle can be controlled electrically or mechanically
to reach an
optimum system for power consumption and reliability. Also, the assembly
utilizes a ball
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nut and lead screw preferably having a diameter to pitch
ratio of 3 to 1 or less, which is lower than other current
art. A higher diameter to pitch ratio would require a
stronger spring force to reliably close the valve. While a
stronger spring force could be provided, it would require a
more power consuming motor to provide the necessary torque
to overcome the spring means during the opening cycle.
These and other objects, advantages and features
of the invention will be apparent to those skilled in the
art from a consideration of the following specification,
including the claims and appended drawings.
Summary of the Invention
According to one aspect of the present invention,
there is provided a pulser apparatus responsive to a signal
from a downhole sensor for creating a positive pressure
pulse in a column of drilling fluid being circulated through
a drill string to a drill bit, said apparatus comprising: a
wire-line retrievable assembly adapted to be received within
the bore of the drill string; seating means on the
retrievable assembly for seating the assembly in the lower
portion of the drill string, above the drill bit, in a
position substantially blocking the flow of drilling fluid
around said assembly, so that a major portion of the
drilling fluid which flows to said drill bit will flow
through an annulus between said assembly and said drill
string and through a fluid passageway in said assembly,
before being supplied to said drill bit; a main bore in the
assembly having an inlet and outlet through which a major
portion of the drilling fluid which flows to said bit may
flow, said inlet for said main bore being in communication
with said annulus and the outlet of said main bore being in
communication with said drill string below said assembly;
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main valve means in said assembly for selectively
restricting the flow of drilling fluid through said main
bore, said main valve means comprising, orifice means
defining a main orifice in said main bore, a valve tip in
said main bore above said main orifice and adjustable toward
and away from said main orifice to adjust the amount of
drilling fluid flowing through said main bore; a main valve
spring for urging said main valve tip toward said main
orifice, a main valve piston connected to said main valve
tip by a main valve stem, a cylinder in surrounding
relationship to said main valve piston and comprising an
upper chamber above said main valve piston and a lower
chamber below said main valve piston; a first fluid
passageway in said assembly having an inlet in communication
with said main bore and an outlet in communication with said
upper cylinder chamber for supplying drilling fluid at a
pressure substantially equal to the pressure in said main
bore below said main valve tip to said upper cylinder
chamber; a second fluid passageway in said assembly having
an inlet in communication with said annulus and an outlet in
communication with said upper cylinder chamber for supplying
drilling fluid at a pressure substantially equal to that of
the drilling fluid in said annulus to said upper cylinder
chamber; pilot valve means in said assembly for selectively
closing said second fluid passageway responsive to a signal
from said sensor; and a third fluid passageway having an
inlet in communication with said annulus and an outlet in
communication with said lower cylinder chamber for supplying
drilling fluid at a pressure substantially equal to the
pressure in said annulus to said lower cylinder chamber;
said main bore, said inlet to said main bore, said main
valve tip and said orifice means being so configured, and
said main valve tip being adapted to be so positioned with
respect to said orifice means, when said main valve means is
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open, that the flow of drilling fluid through said inlet to
said main bore, around said main valve tip and through said
orifice means produces a first fluid pressure in said main
bore at said inlet to said first fluid passageway, which
first fluid pressure is lower than the annulus fluid
pressure at said inlets to said second and third fluid
passageways, whereby, when said pilot valve is closed, said
first fluid pressure will be communicated through said first
fluid passageway to the said upper chamber of said cylinder
while said higher annulus fluid pressure will be
communicated through said third fluid passageway to said
lower cylinder chamber, creating a pressure differential
across the main valve piston which is sufficient to overcome
the closing effect of said main valve spring, so as to
retain said main valve open and, when said pilot valve is
opened responsive to said signal, said annulus fluid
pressure will be transmitted through said second fluid
passageway to said upper cylinder chamber, reducing the
pressure differential across said main valve piston
sufficiently to permit said main valve spring to cause said
main valve tip to move toward said main orifice, so as to
reduce the flow of drilling fluid through said main bore and
create a positive pressure pulse in said drilling fluid in
said drill string above said assembly.
According to another aspect of the present
invention, there is provided a pulser apparatus responsive
to a signal from a downhole sensor for creating a positive
pressure pulse in a column of drilling fluid being
circulated through a drill string to a drill bit, said
apparatus comprising: a wire-line retrievable assembly
adapted to be received within the bore of the drill
string;seating means on said retrievable assembly for
seating the assembly in the lower portion of the drill
-4b-
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string in predetermined relationship to an orifice means
carried by the drill string and defining a main orifice and
in such a manner that a major portion of the drilling fluid
which flows to said bit may flow through an annulus between
said assembly and the wall of said drill string and through
said orifice means in said drill string before being
supplied to said drill bit; main valve means in said
assembly for selectively restricting the flow of drilling
fluid through said main orifice in said orifice means, said
main valve means comprising, a valve tip carried by said
assembly and adjustable toward and away from said main
orifice to adjust the amount of drilling fluid flowing
through said main orifice, a main valve spring on said
assembly for urging said main valve tip towards said main
orifice, main valve piston connected to said main valve tip
by a main valve stem, a cylinder in surrounding relationship
to said main valve piston and comprising an upper chamber
above said main valve piston and a lower chamber below said
main valve piston; a first fluid passageway in said assembly
having an inlet in communication with the lower portion of
said main valve tip and an outlet in communication with said
upper cylinder chamber, for supplying drilling fluid at a
pressure substantially equal to that of the drilling fluid
immediately below said main valve tip to said upper cylinder
chamber; a second fluid passageway in said assembly having
an inlet in communication with said annulus and an outlet in
communication with said upper cylinder chamber, for
supplying drilling fluid at substantially the pressure in
said annulus to said upper cylinder chamber; pilot valve
means in said assembly for selectively closing said second
fluid passageway responsive to a signal from said sensor;
and means for operating said pilot valve means, said
operating means comprising, a DC electric motor adapted to
operate responsive to said control signal, a threaded drive
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shaft adapted to be rotated through a plurality of
revolutions about its longitudinal axis by said motor when
said motor is operated, a threaded follower on said drive
shaft and held against rotation, so that said follower will
move up or down responsive to rotation of said drive shaft
and a valve stem interconnecting said follower and said
pilot valve tip for transmitting the vertical movement of
said follower to said valve tip to open said pilot valve; a
third fluid passageway having an inlet in communication with
said annulus and an outlet in communication with said lower
cylinder chamber for supplying drilling fluid at a pressure
substantially equal to the pressure in said annulus to said
lower cylinder chamber; said orifice means and said main
valve tip being so dimensioned and configured, and said main
valve tip being adapted to be so positioned with respect to
said orifice means, when said main valve means is open, that
the flow of drilling fluid around said main valve tip and
through said orifice means produces a first fluid pressure
at the inlet to said first fluid passageway which first
fluid pressure is lower than the annulus fluid pressure at
said inlets to said second and third fluid passageways,
whereby, when said pilot valve is closed, said first fluid
pressure will be communicated through said first fluid
passageway to said upper chamber of said cylinder, while
said higher annulus fluid pressure will be communicated
through said third fluid passageway to said lower cylinder
chamber, creating a pressure differential across said main
valve piston which is sufficient to overcome the closing
effect of said main valve spring means, so as to retain said
main valve open and, when said pilot valve is opened
responsive to said signal, said annulus fluid pressure will
be transmitted through said second fluid passageway to said
upper cylinder chamber, reducing the pressure differential
across said main valve piston sufficiently to permit said
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main valve spring means to cause said main valve tip to move
towards said main orifice, so as to reduce the flow of
drilling fluid through said main orifice and create a
positive pressure pulse in said drilling fluid in said drill
string above said assembly.
According to still another aspect of the present
invention, there is provided an apparatus responsive to a
signal from a downhole sensor for creating a positive
pressure pulse in a column of drilling fluid being
circulated through a drill string to a drill bit, said
apparatus comprising: an orientation sub carried by the
drill string and having a central bore longitudinally
therethrough, an orientation key in said orientation sub and
extending into said central bore, and an upwardly facing
helical surface disposed around the inside diameter of said
central bore; and a wire-line retrievable mud pulser
assembly adapted to be received within the bore of the drill
string and seated on said orientation sub, said retrievable
mud pulser assembly comprising a main valve means adapted to
at least partially restrict the flow of drilling mud through
the central bore of said orientation sub responsive to said
signal from said downhole sensor, to thereby create a
positive pressure pulse in said column of drilling fluid,
and a downwardly facing helical surface on said retrievable
mud pulser assembly adapted to engage said orientation key
in said orientation sub as said retrievable assembly is
lowered into said drill string, to thereby orient said
retrievable assembly in a predetermined angular relationship
to said orientation sub and to engage said upwardly facing
helical surface in said bore of said orientation sub as said
retrievable assembly is lowered further into said drill
string, for seating said retrievable assembly in a
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predetermined longitudinal relationship to said orientation
sub.
The MWD mud pulsing tool according to the present
invention comprises a tool which can be run on a wireline
into the bore of the drill pipe, seated on a pre-run
muleshole helix seat, or the like, and later wireline
retrieved for removal or servicing. The tool preferably
inclues an electrical power source, such as a conventional
nickel cadmium electrical storage battery, and an electrical
flow switch which automatically activates the tool's
electronics when mud is flowing in the drill string and
deactivates the electronics when no mud is flowing, in order
to conserve battery power. An ironless rotor DC motor is
electrically powered to drive a planetary gear which in turn
powers a threaded drive shaft mounted in a bearing assembly
to rotate a ball nut lead screw. The rotating threaded
shaft lifts the lead screw, which is attached to the pilot
valve, so as to lift the pilot valve off of its seat. When
the pilot valve is lifted off of its seat, fluid pressures
across a main valve piston are equalized, permitting a
biasing spring to cause the main valve shaft to extend into
the main valve orifice, to substantially reduce mud flow to
the bit, creating a positive pressure pulse detectable at
the surface.
-4f-
21~5'~
Closure of the main valve also causes a decrease in pressure in those internal
parts
of the tool where the fluid pressure is communication with the downstream
portion of the
tubing (below the main valve) and an increase in the fluid pressures in those
parts of the
tool which are in fluid communication with the mud in the tubing annulus above
the main
valve. As the electrically driven pilot valve reaches the upper limit of its
movement, the
electrical motor powering the pilot valve is automatically de-energized. This
causes the
ball nut and lead screw on the threaded shaft to "free wheel" downward,
responsive to
energy stored in a metal bellows attached to the pilot valve, until the pilot
valve reseats on
the pilot valve seat. Closing the pilot valve has the effect of placing the
top part of main
valve piston in communication with the low pressure downstream mud, while the
bottom
of the piston is exposed to higher pressure upstream mud. This pressure
differential
overcomes the closing effect of the main valve spring, causing the main valve
to reopen.
The time required for a cycle (closing and reopening) of the main valve is
controlled by the
speed at which the pilot valve opens to the point that the opening motor is de-
energized,
and the speed at which pilot valve then free wheels closed under the influence
of the
closing spring bellows. The pilot valve will remain closed, and the main valve
open, until
the motor is re-energized by a signal from the well logging electronics, at
which time the
cycle will be repeated.
An alternate embodiment of the invention also is shown. The alternate
embodiment
is most useful in larger bore tubing, which can more easily tolerate a
permanent mud flow
restriction from a main valve orifice permanently in the mud flow path. In the
alternate
embodiment, the main valve orifice is provided in an orientation sub which is
made up in
the tubing string at the time the string is run into the well bore. The pulser
tool is then run
-5-
2195?2~
into the tubing string on a wire line and seated in the orientation sub, just
above the main
valve orifice. Responsive to opening of the pilot valve, as discussed above,
the main valve
extends below the bottom of the pulser tool and into the main valve orifice,
in order to
generate the positive mud pulse, and retracts out of the main valve orifice
when the pilot
valve closes:
brief Description of the Drawinos
Figure 1 is a somewhat schematic illustration of the surface and downhole
portions
of a well drilling apparatus used in connection with the MWD mud pulsing tools
of the
present invention;
Figure 2a is a view in elevation and partly in section of the upper portion of
a mud
pulser tool in accordance with the present invention, illustrated with the
pilot valve in the
closed position;
Figure 2b is a view similar to 2a, illustrating the arrangement of the same
parts of
the tool with the pilot valve in the open position;
Figure 3a is a view in elevation and partly in section, comprising a
continuation of
the lower part of the MWD mud pulser tool of Figure 2a, showing the main valve
in the
open position;
Figure 3b is a view similar to Figure 3a, illustrating the same parts of the
tool with
the main valve in its closed position;
Figure 4 is a view in elevation and partly in section of the lower portion of
the tool
of Figure 3b, and also illustrating the orientation sub and orientation key
used for seating
and orienting the pulser tool in the drill string;
-6-
21972'
Figure 5 is a fragmentary view, in elevation and partly in section,
illustrating an
alternate embodiment.of the MWD mud pulser according to the present invention
which
cooperates with a main valve orifice carried by the tubing string;
Figure 6a is a fragmentary view, in elevation and partly in section,
illustrating an
alternate embodiment of the MWD mud pulser in which the helical downwardly
facing
surface on the MWD pulser stinger cooperates with a helical upward facing
surface on the
orientation sub to provide means for seating the pulser tool in the drill
string, the parts
being shown in Figure 6a with the main valve in the closed position;
Figure 6b is a view similar to Figure 6a, illustrating the arrangement of the
same
parts of the tool with the main valve in the open position;
Figure 7 is an enlarged detail plan view of the main valve orifice plate of
Figures 6a
and 6b, illustrating the orifice arrangement of a primary center flow hole
path, surrounded
by a pattern of smaller flow holes; and
Figure 8 is a schematic illustration of optional circuitry which may be used
in
conjunction with the ironless rotor DC electrical motor in the pulser servo-
mechanism to
provide electrical means for selectively retarding the speed of the closing
portion of the
servo mechanism cycle.
Descrir~tion of Sr~ecific Embodiments
In the preferred embodiments of the invention, as described in detail below,
pressure pulses are transmitted through the drilling fluid in the drill string
to send
information from the lower part of the well bore to the surface as the well is
drilled. At least
one downhole condition within the well is sensed, and a signal, usually
analog, is
generated to represent the sensed condition. The signal controls the closing
of the main
_ valve in the mud pulser tool to cause a substantial interruption of mud flow
to the drill bit,
resulting in a positive pressure pulse which migrates up the column of
drilling mud as part
of a coded sequence of pressure pulses representing the downhole condition.
The
sequence of mud pulses are sensed and decoded at the surface to provide a
reading of
the sensed downhole condition.
Referring to Figure 1, a well bore 10 is drilled in the earth with a rotary
drilling rig 12
which includes the usual derrick 14, derrick floor 16, draw works 18, hook 20,
swivel 22,
kelly joint 24 and rotary table 26. A drill string 28 made up of sections of
drill pipe 30
secured to the lower end of the kelly joint 24 extends into the upper end of
one or more drill
collars 32 which carry the drill bit 34. Drilling fluid, commonly called
drilling mud, circulates
from a mud pit 36 through a mud pump 38, desurger 40, a mud supply line 42 and
into the
swivel 22. The drilling mud flows down through the kelly joint, drill string,
drill collars and
out through nozzles (not shown) in the lower face of the drill bit. The
drilling mud flows
back up through the annular space 44 between the outer diameter of the drill
string and the
well bore to the surface, where it is returned to the mud pit through a mud
return line 45.
The usual shaker screen for separating formation cuttings from the drilling
mud before it
returns to the mud pit is not shown.
A transducer 46 in the mud supply line 42 detects variations in drilling mud
pressure
at the surface. The transducer generates electrical signals responsive to the
drilling
pressure variations. These signals are transmitted by an electrical conductor
48 to a
surface electronic processing system 50 such as that described in U.S. Patent
No.
4,078,620.
_g_
~z19~~2~
A nonmagnetic drilling collar 52 may be inserted between the drill collar 32
and the
drill bit and may carry the mud pulser of the present invention.
Alternatively, the mud
pulser may be carried in a section of drill pipe above the drill collars. For
some operations,
such as horizontal drilling, a hydraulic drilling motor 54 also may be
inserted in the drill
string between tie drill collars and the bit. Such a motor, if present,
utilizes fluid pressure
from the flowing mud to rotate the drill bit.
The pulser tool 56 in accordance with the present invention comprises an
elongated
cylindrical housing 58 made up of a plurality of individual threadedly
connected tubular
sections. When in use, the tool is disposed inside the lower portion of the
drill string and
is surrounded by flowing drilling mud. As shown in Figure 4, the bottom-most
section of
the tool housing comprises a conventional muleshoe stinger 60, having a
downwardly
facing helical surface on the lower end thereof, which is adapted to cooperate
with an
orientation sub 59 and orientation key 61 in the drill string in the manner
well known to
those skilled in the art to seat and orient the tool with respect to the drill
string. A
downwardly facing shoulder 62 on the muleshoe stinger cooperates with a
corresponding
upwardly facing shoulder 63 in the orientation sub to provide a seat for the
pulser. The
orientation sub may be part of the nonmagnetic drill collar 52, or may be
inserted
elsewhere in the lower portion of the drill string. An o-ring seal 64 engages
the wall of the
orientation sub to prevent flow of drilling fluid around the pulsar tool. All
drilling fluid then
must pass down the annulus 65 between the pulsar tool and the drill string
wall and
through the pulsar tool as described hereinafter.
Referring to Figures 2a and 3a, there are illustrated details of the
construction of the
pulsar mechanism with the main valve open, so that the pulsar is not
generating a pressure
-9-
219~~2
pulse. Aligned Figures 2b and 3b illustrate the same portions of the pulser in
the positions
they would occupy with the main valve closed, substantially reducing the flow
of drilling
mud through the tool and generating a positive pressure pulse. It will be
appreciated that
the entire pulser tool 56 is contained in the drill string and surrounded by
an annulus 65,
as illustrated in Figure 4. However, in Figures 2a, 2b and 3a, 3b, the
surrounding parts of
the drill string, and the annulus between the drill string and the tool, are
omitted for
simplicity of illustration. The uppermost portion of the pulser tool also is
omitted from the
illustrations, but may comprise any desired arrangement of prior art
components such as
sensors and transducers for sensing one or more downhole parameters and
creating an
analog signal proportionate to the sensed parameter, a battery pack or other
electrical
power source and a switch for actuating the electrical power source to power
the electrical
components of the pulser when mud is flowing in the drill string and down
through the
annulus 65 between the outside diameter of the pulser tool and the inside
diameter of the
tool joint in which the tool is carried. Also not shown, at the upper end of
the tool, there will
be provided an overshot engagement means for permitting the tool to be run
into the well
bore on a wire line and retrieved in a similar manner.
Although the tool of the present invention operates on the principle of
pressure
differentials, there preferably are no protrusions into the annulus between
the outside
diameter of the tool and the inside diameter of the tubing string, such as are
used in some
prior art tools to create increased pressure drops along the length of the
pulser tool.
Near the upper end of that portion of the tool shown in Figure 2a, there is
provided
an ironless rotor DC motor 66 carried in an alignment housing 68. A planetary
type gear
70 is provided below the motor and centered by the same alignment housing 68.
The
-10-
ironless rotor DC motor preferably is a Maxon'" ironless rotor DC motor which
is a small
diameter (.970 inch outside diameter), high speed (1,000 RPM @ 20 volts), high
torque
(4.5 oz-in max) motor, that draws a maximum of 1.1 amp. When combined with the
4.4 to
1 ratio planetary gearhead, the Maxon motor can produce 7.6 ounce-inches of
continuous
torque at only .50 amps current draw. The high torque to speed ratio,
therefore, is one
distinct advantage, especially considering the minimal power consumption, and
small size.
Another distinct feature of this motor is that it is operationally power
efficient. The motor
uses only as much current as torque requirements dictate. The lower the torque
required,
the lower the current draw, while the motor attempts to maintain a constant
speed,
determined by the set voltage. A preferred model of the Maxon motor is model
number
2322.982-11.225-200. The preferred Maxon gearhead model number is GP022A023-
04.4A1AOOA. The motor is provided with electrical power from an electrical
storage battery
(not shown) provided elsewhere in the tool and connected to the motor by
electrical
conductors (not shown). A shaft 72 is rotatedly driven by the DC motor and
planetary gear.
An attached alignment sleeve 74 rotates with the shaft and is journaled in
needle roller
bearings 76 and thrust bearings 78. Alternatively, other bearing types, such
as radial
bearings, could be used. An enlarged diameter lower portion of the shaft 72 is
threaded
to provide a threaded drive shaft 80. The drive shaft 80 engages mating
threads on a ball
nut 82. Torque shaft 84 is attached to and rotates with the ball nut 82 and is
centered for
rotation by bearings 86. An antirotation pin 88 engaging an antirotation
bushing 90 retains
the torque shaft and ball nut against rotation, so that as the threaded drive
shaft is turned
by the DC motor, the bail nut and torque shaft will move longitudinally upward
with respect
to the housing 58. Pilot valve stem 91 transmits the linear movement to the
pilot valve tip
-11-
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92, which is adapted to engage the pilot valve seat 94 carried in pilot valve
housing 96.
A metal bellows assembly 95 extends between the upper part of the pilot valve
tip and the
bearings 86, in surrounding relationship to the pilot valve stem 91. As
explained below,
the metal bellows serves as a resilient means, providing spring energy to
reseat the pilot
valve automatic3l!y at the end of the pulse cycle.
Below the pilot valve housing 9fi is the main valve piston 98, adapted to move
vertically within the inside diameter of the tool housing 58. The main valve
stem 100,
guided by the housing 58 and by centralizer bushing 102, transmits linear
movement of the
main valve piston to the main valve tip 104. Compression spring 106 confined
between
the centralizer bushing 100 and a shoulder on the main valve tip, urges the
main valve tip
toward the main valve seat or orifice plate 108 and into the main valve
orifice 109.
It will be appreciated by those skilled in the art that providing the main
valve orifice
in the tool, rather than in the tubing string as do prior art tools, produces
several
advantages. First, the orifice and valve tip can be retrieved by wire line,
along with the toot,
so that the orifice and valve tip sizes can be changed as desired to adjusted
the strength
of the pressure pulse created when the main valve is closed Secondly, by
including the
main valve orifice in the body of the tool, the orifice is removed when the
tool is removed,
so that the tubing string is free of a permanent obstruction and the resulting
pressure drop
which otherwise would result from leaving the orifice plate in the tubing
string.
With the parts in the position shown in Figures 2a-3a, the pilot valve is
closed and
the main valve is open. All drilling mud passing down the annulus 65 between
the pulser
tool and the inside diameter of the drill pipe enters the main mud orifices
110; flows
-12-
21~~?2~
downward through the bore of the main valve orifice 109, the bore of the
muleshoe stinger
60, and on to the drill bit.
Pilot bore 112 formed through the main valve tip, main valve stem and main
valve
piston communicates, through horizontal pilot passages 114 with the upper main
piston
chamber 118 tc permit drilling mud pressure to be exerted on the top of the
main valve
piston 98. Orifices 118 through tool housing 58 communicate with lower main
piston
chamber 120, to permit annulus drilling mud pressure to be exerted on the
bottom of the
main valve piston. Upper orifices 122 admit drilling mud from the annulus to
the pilot valve
chamber 124 above the pilot valve 92; however, since the pilot valve is
closed, the mud
in pilot valve chamber 124 is not in communication with that in the upper main
piston
chamber 116. The area 126 inside the metal bellows assembly 95 and in
surrounding
relationship to pilot valve stem 92 is filled with lubricating oil, which
serves to lubricate the
threaded drive shaft 80 and ball nut assembly 82. Pressure compensator
membrane 128
is exposed to the pressure of drilling mud in annulus through pressure
compensator
orifices 130 and serves to equalize the pressure of the lubricating oil with
that of the drilling
mud.
The size, shape and positions of the main mud orifices 109, main valve orifice
108
and main valve tip 104 are such that a Venturi effect is created as the
drilling mud flows
past the bottom of the main valve tip, through main valve orifice 109 and into
the bore of
the muleshoe stinger 60. The pressure at this point, denominated P1, is
somewhat lower
than the pressure of mud flowing through the annulus. Since the pilot valve is
closed, a
pressure of P1 will act on the top of the main valve piston. The somAwhat
higher fluid
pressure from the annulus, denominated P2, will act on the bottom of the main
valve piston
-13-
21~~'~2~'
through orifices 118 and cavity 120. The pressure differential thus created is
sufficient to
overcome the closing force of main valve spring 106, as well as the entraining
force of the
mud flowing past the main valve tip, so that the main valve is biased toward
the open
position shown in Figure 3a.
When it is r~esired to create a mud pulse for MWD telemetry purposes, the
sensor
transducer components carried in the upper part of the tool (not shown)
actuate the
ironless rotor DC motor 66. This causes the pilot valve 92 to lift off the
valve seat 94 and
permits drilling mud from the pilot orifices 122 and pilot chamber 124 to
communicate
through pilot bore 112 to the top of the main valve piston 98. Since this will
be at
substantially the same pressure, P2, as the mud acting on the bottom of the
main valve
piston, the pressure across the main valve piston will be substantially
equalized. The main
valve spring 106, together with the entraining force of drilling fluid flowing
around the main
valve tip 104, will cause the main valve tip to enter the main valve orifice
108, substantially
reducing the flow of drilling mud to bit. To reduce wear, it is preferred that
the main valve
tip be slightly smaller in outside diameter than the inside diameter of the
main valve orifice,
so that a minor amount of mud may continue to flow around the main valve tip.
Additional
mud flow to the bit occurs through the pilot orifices 122 and pilot bore 112;
however, the
total mud flow from the annulus through the pulser tool is substantially
reduced when the
main valve closes, with the effect that a pressure wave is created in the mud
flowing in the
annulus, which wave is transmitted through the mud up to the surface for
decoding and
interpretation as discussed above.
The pulser tool is shown with the main valve closed and pilot valve open in
Figures
3a-3b. So long as the pilot valve remains open, the main valve will remain
closed.
-14-
219722
However, the length of the pulse may be accurately controlled by the timing
means 69
which will interrupt electrical power to the motor 66 at a preselected
interval after the motor
is energized. The interval selected is such that it will terminate the upward
movement of
the pilot valve before ball nut 82 engages the housing for bearing 76, or any
other
obstruction, sincq this would cause an increase in torque on the motor and a
concomitant
increase in power usage. When it is not energized, the rotor of the DC motor
66 is free
wheeling, subject only to frictional losses. Once the motor is de-energized,
the downward
force exerted on ball nut 82 by the metal bellows 95, which was cocked during
the opening
of the pilot valve, will exert a reverse torque on the threaded shaft. This
will cause the
shaft to reverse direction, permitting the ball nut, torque shaft and pilot
valve to move
downward to return the pilot valve to its seat.
As will be apparent to those skilled in the art, the metal bellows 95 serves
both the
function of providing a spring means for returning the pilot valve to its seat
and providing
a diaphragm separating mud flowing around the outside of the spring bellows
from
lubricating oil contained inside the metal bellows. If preferred, these
functions can be
separated by replacing the metal bellows 95 with a flexible diaphragm of
rubber or another
suitable polymer to insulate the lubricating oil from the mud and positioning
a conventional
coil spring in surrounding relationship to the lower portion of the valve stem
91, to provide
the desired pilot valve spring means for returning the pilot valve to its
seat.
With this arrangement, it is apparent that the duration of a mud pulse cycle
can be
controlled by the timing means 69. The timing means controls the duration of
the opening
stroke, and the length which the ball nut 82 travels up the threaded shaft 80
while the
motor is energized, controls the timing of the closing stroke, responsive to
spring means
-15-
~19~'~2~
95. The duration of the pulse may therefore be controlled automatically by the
electronics
in the pulser tool by adjusting the timing means 69. For example, different
sensor
transducers may utilize different intervals for the pressure pulses in order
to identify the
sensor or may vary the length of pulses in order to convey additional binary
coded
information to the surface computer. Additional control for the duration of
the pulse cycle,
if desired, may be provided using the optional circuitry of Figure 8 in
conjunction with the
DC motor 66, as described in greater detail below.
An important feature of the design of the apparatus is the diameter to pitch
ratio of
the mating threads on the shaft 80 and ball nut 82, since this controls the
amount of torque
required to reverse direction of the shaft 80. The maximum preferred ratio of
OD of the
male threads on shaft 80 to the pitch between adjacent threads is from about
2.5 to 1 to
3 to 1. For a one-fourth inch diameter shaft this would require a minimum
pitch between
adjacent threads of from 0.1 to 0.083 inches. This ratio, together with
frictional losses.,
controls the force required to automatically close the valve after the motor
is de-energized.
A higher diameter to pitch ratio would require more torque to close the valve
which, in turn,
would require a stronger spring force from the metal bellows 95. While a
stronger spring
force could be provided, this would consume more power during the opening
cycle of the
valve in order to cock the spring to provide the required closing force.
Once the pilot valve re-seats, mud flow through the pilot bore 112 will be
interrupted
and the much lower pressure from below the closed main valve will be
communicated
through pilot bore 112 to the upper cavity 116 and will act on the top of the
main valve
piston 98. This low pressure will be offset by the much higher annulus
pressure of the mud
flow in the annulus operating on the bottom of the piston through orifices 118
and lower
-16-
219~7~~
cavity 120. The resulting pressure imbalance will cause the main piston valve
to move
upward, against the force of main valve spring 106, to return the main valve
to its open
position. This arrangement has the advantage of requiring power for the pilot
valve only
on the opening stroke, with power then being cut off and the pilot valve
closing
automatically.
The speed of closure of the pilot valve also is controlled by rotation of the
ball nut
82 to prevent "snap-closure" which could cause excessive stress and wear on
the pilot
valve parts.
Referring now to Figure 5, there is illustrated an alternate embodiment of the
MWD
mud pulser according to the present invention. Unlike the embodiment of
Figures 2-4, the
Figure 5 embodiment utilizes a flow obstruction in the form of an orifice
fixed permanently
in the mud flow path, even if the pulser tool is removed. Accordingly, it is
most desirable
for use with larger diameter tubing strings (typically 4'/ OD tubing or
larger) which can
tolerate such a permanent restriction without substantially affecting
efficiency of mud flow
to the bit when the pulser is not in place.
In the Figure 5 embodiment, the orientation sub 500 in which the pulser tool
is to be
seated includes an orientation sleeve 502 fixed in the orientation sub and an
orientation
key 504 attached to the sleeve. A muleshoe stinger 506, having a downwardly
facing
helical surface on the lower end thereof, is carried on the elongated body 508
of the pulser
tool and engages the orientation key and orientation sleeve to position and
orient the
pulser tool as it is run into orientation sub. The orientation sleeve 502 also
carries a main
orifice plate 510 which defines the main orifice 512. One or more ports 514 in
the wall of
the orientation sleeve 502 permit mud flow from the annulus 516 through the
orifice 512
-17-
2195?2~
and then to the drill bit at the bottom of the tool string. A main valve tip
518 and main valve
stem 520 extend below the bottom of the pulser tool housing 508 to cooperate
with the
main orifice 512. A main valve spring 522 confined between the main valve tip
and the
bottom of the valve housing urges the main valve tip toward a closed position.
Mud
pressures acting on the main valve piston 524 through pilot passageway 526 and
through
ports 528 in the tool housing control the operation of the main valve piston.
The position
of the pilot valve (not shown in Figure 5) in turn controls the mud pressure
acting on the
top of the main valve piston as discussed above in connection with the
embodiment of
Figures 2a, 2b, 3a, 3b. The remainder of the pulser, not shown in Figure 5,
corresponds
to the embodiment disclosed above in connection with Figures 2a, 2b and 3a,
3b.
In both versions of the MWD pulser illustrated in Figures 2a, 2b, 3a, 3b, 4
and 5, the
muleshoe stinger at the lower end of the pulser cooperates with an orientation
sub for
orienting the pulser in the well bore. However, the seating of the MWD tool on
the
orientation sub occurs at opposed inclined annular shoulders on the pulser
tool and the
orientation sub. For example, in the Figures 3a/3b, the downwardly facing
shoulder 62 on
the muleshoe stinger cooperates with a corresponding upwardly facing shoulder
63 on the
orientation sub to provide a seat for the pulser. In the larger diameter
version, as illustrated
in Figure 5, a downwardly facing shoulder 530 on the MWD tool stinger
cooperates with
an upwardly facing shoulder 532 on the orientation sub to provide a seat for
the pulser.
A drawback with this arrangement is that the upwardly facing seating surface
or shoulder
on the orientation sub, which is near the stop of the orientation sub, is
subject to periodic
impacts from the lower end of the muleshoe stinger on the pulser and to wear
from
-18-
219722
w vibration, etc., during the use of the pulser. This can require frequent
repair or replacement
of the orientation subs used with the pulser.
Referring to Figures 6a/6b there is shown an alternate embodiment of the
pulser
stinger and orientation sub in which this problem is eliminated by utilizing
the helical
surface of the M~l~!D stinger for both orientation and seating of the pulser
on the sub.
Referring to Figure 6a, there is illustrated a modified version of the MWD mud
pulser
which, like the Figure 5 embodiment, utilizes a flow obstruction in the form
of a orifice fixed
permanently in the flow path, even when the pulser is removed. In the Figure
6a
embodiment, the orientation sub 600 includes an orientation sleeve 602 and an
orientation
key 604 attached to the sleeve. A muleshoe stinger 606 is carried on the
elongated body
608 of the pulser tool and engages the orientation key and orientation sleeve
to position
and orient the pulser tool as it is run into the orientation sub. The
orientation sub 600
would be carried by the tubing string in the same manner shown in Figure 5.
However, in
Figures 6a and 6b, the tubing string is not shown, so that the remaining parts
may be
shown enlarged and in greater detail.
The orientation sub 600 includes on the interior thereof a replaceable hard
metal
insert 610 which provides an upwardly facing helical shoulder 612 which is
adapted to
cooperate with the downwardly facing helical surface 614 at the bottom of the
MWD stinger
606. Since, as shown in Figure 6a and 6b, the upwardly facing helical shoulder
612 in the
orientation sub and the downwardly facing helix 614 at the bottom of the MWD
stinger are
mated, they are illustrated in phantom lines. The replaceable insert 610 also
engages, and
is held against rotation by, the key 604.
-19-
219~'~2~
The MWD stinger, orientation sleeve and replaceable insert 610 preferably are
so
dimensioned and configured that the opposed upwardly and downwardly facing
helical
surfaces 612 and 614 act as the seating surface for the MWD tool in the
orientation sub,
when the MWD stinger 606 is fully inserted into the orientation sub. An o-ring
616 carried
by the MWD stinger 606 provides a fluid seal between the outside diameter of
the MWD
stinger and the inside diameter of the orientation sleeve. Two larger diameter
o-rings 618,
619 carried by the MWD stinger 606 are compressed against an upwardly facing
shoulder
620 on the orientation sub to provide resilient means between the MWD pulser
and the
orientation sub for avoiding shock loading and for absorbing vibration between
the MWD
tool and the orientation sub during operation of the MWD pulser. A plurality
of openings
622 provided radially through the body of the orientation sub between the
fluid seal o-ring
616 and the shock absorbing o-rings 618, 619 permit fluid communication to
prevent
pressure locking of the parts which otherwise could occur if the parts were
assembled
without the openings and then subjected to high pressure.
The orientation sub 600 preferably is assembled into the tubing string and run
into
the well bore as part of the tubing string. When it is desired to mount the
MWD pulser in
the orientation sub, it is run into the well on a wire line until the MWD
stinger 606 enters the
central bore of the orientation sub. As the tool is lowered further, the
downwardly facing
helical surface 612 on the bottom of the MWD stinger engages the orientation
key 604,
causing the MWD tool to rotate about its longitudinal axis until the key way
605 on the
MWD stinger is aligned with the key 604, at which point the MWD pulser and
stinger will
then drop down relative to the orientation sub until the downwardly facing
helical surface
614 on the bottom of the MWD stinger engages the upwardly facing helical
shoulder 612
-20-
219~72~
on the replaceable insert 610 in the orientation sub, at which point further
downward
movement of the MWD pulser relative to the orientation sub is arrested. A
small space 624
is provided at the bottom of the helical surface on insert 610 for
accommodating the point
or tip of the MWD stinger, so that the tip of the stinger does not carry the
loading weight
of the MWD pulser. This will bring the parts into the relative positions shown
in Figures 6a,
6b with the MWD tool fully seated on the orientation sub.
The orientation sleeve 602 also carries a main orifice plate 626 which varies
from
the construction of the main valve orifice plates of Figures 3a/3b, 4 and 5.
In the
constructions of Figures 3a/3b, 4 and 5, the main valve orifice plate contains
a single
central opening or main valve orifice which preferably is of slightly larger
inside diameter
than the outside diameter of the main valve tip, so as to allow continued
circulation of some
portion of the drilling mud around the main valve tip and through the main
valve orifice,
even when the main valve tip extends into the orifice as to reduce the flow
area and
increase pressure so as to create a positive pulse in the mud stream.
With the alternate main valve orifice plate 626, there is a primary central
opening
or main valve orifice 628 surrounded by a plurality of smaller openings or
secondary
orifices 630. The main valve tip 632 is dimensioned to seat upon and fully
close the central
orifice 628, redirecting the remaining flow of the mud through the plurality
of smaller
secondary orfices 630. With this arrangement, the sudden complete closure of
the primary
flow path through the central opening 628, and resulting redirection of mud
flow to other
paths, creates a more rapid rise in the mud pressure upstream of the main
valve orifice
plate, which in turn creates a more easily detectible pressure pulse in the
mud stream.
This permits the orifice plate to be designed with a larger overall flow area
(the total area
-21-
219 ~'~ ~~
of the main and secondary orifices) than is possible with the single orifice
plate, so as to
improve mud flow to the bit and reduce mud flow pressure drop due to the
orifice plate,
without sacrificing clarity and detectability of the mud pulses at the
surface.
Additionally, with the orifice plate as illustrated in Figures 3a/3b, 4 and 5,
even when
the main vale i~ in an open position, fluid velocities of mud flowing around
the bottom of
the main valve shaft and tip toward the large central opening in the orifice
tends to create
a suction effect which could exert sufficient downward force on the main valve
stem to
move the main valve stem and tip slightly closer to the orifice opening,
thereby partially
closing the gap befinreen the main valve tip and the orifice and resulting in
a higher
pressure loss across the main valve while in the open position. The alternate
design for
the orifice plate of Figures 6a/6b and 7 reduces this effect by directing a
portion of the mud
flow radially outwardly into the plurality of side openings 630, which tends
to reduce the
suction effect on the main valve tip 632.
The remainder of the pulser, not show in Figures 6a16b and 7, corresponds to
embodiment discussed in connection with Figures 5 and 2a/2b, 3a/3b and 4.
As will be apparent to those skilled in the art, although the modified main
valve
orifice plate 626 is shown in connection with an MWD pulser embodiment in
which the
orifice plate is carried by the orientation sub, a similar modification could
be made in the
design of the main valve orifice plate 108 and main valve tip 104 to permit
the advantages
of that design to be used in the smaller diameter version of the MWD pulser as
illustrated
in Figures 2a, 2b, 3a, 3b and 4 in which the main valve orifice plate is
carried in the body
of the MWD pulser. Similarly, the advantages of the orientation sub 600
including a
replaceable insert 610 providing an upwardly facing helical shoulder adapted
to be
-22-
219~~2~
-- engaged by the helical surface on the bottom of the MWD stinger for seating
the pulser on
the sub could be utilized in conjunction with the version of the pulser shown
in Figures
2a12b, 3a/3b and 4.
In Figure 8 there is shown optional additional circuitry which may be used in
connection with the ironless rotor DC motor 66 to provide electrical means for
selectively
retarding the speed of the closing portion of the pilot valve cycle. In Figure
8, coil 800
represents the electrical winding of the ironless rotor or 66. Coil 800
selectively is
energized by electrical power flowing from a positive DC voltage source 202,
through
electrical connector 804, to the coil 800 and from the coil 800 through
electrical connector
806 to the ground 808, whenever DC motor 66 is powered to operate the pilot
valve
means.
As described above, as the pilot valve means nears the upper limit of its
opening
cycle, timer means are actuated to disconnect power from the DC motor 66. Once
the
motor is deenergized, the downward force exerted on ball nut 82 by the spring
means 95,
which was cocked during the opening of the pilot valve cycle, will exert a
reverse torque
on the threaded shaft. This will cause the shaft to reverse direction,
permitting the ball nut,
torque shaft and pilot valve to move downward to return the pilot valve to its
seat. During
this closing portion of the pilot valve cycle, the rotor in the DC motor will
free-wheel. Since
there are no loads to be overcome during the closing portion of the pilot
valve cycle, except
for frictional forces, the closing portion of the cycle can occur very
quickly. It is desirable,
in order to increase control over the duration of the full cycle, as well as
to avoid damage
to the pilot valve and pilot valve seat from too-rapid closing, to selectively
retard the 'speed
-23-
219~'~2~
of the pilot valve on its closing cycle. This may be done utilizing the
optional additional
circuitry of Figure 8.
As is well known to those skilled in the art, when a DC electric motor is run
backwards against a load, it operates as a generator. By providing an
electrical diode 810,
or other electrical resistance means, in parallel with the coil 800 of the DC
motor 66, and
electrically connected to the coil 800 through connectors 814 and 816, the
flow of current
generated by the DC motor during the pilot valve return step is substantially
impeded,
thereby forcing the motor 66 to operate as a generator and to dissipate
generated heat via
the motor coil 800. The rate at which generated heat can be dissipated
effectively by the
coil 800 controls the speed at which the motor turns, thereby selectively
retarding the
closing speed of the pilot valve responsive to the metal spring means 95.
Diode 810
electrically connected in parallel with the motor coil 800 therefore provides
electrical means
for selectively retarding the speed of the closing portion of the pilot valve
cycle.
One or more in-line diodes 818 also may be provided in electrical connector
804 in
order to prevent reversed polarity and to protect the other electrical
components of the
system from the DC current generated by the motor 66 during closing of the
pilot valve.
If desired, an electrical storage means, such as the storage cell 820, or
other battery
or capacitor, may be electrically connected, as by connector 822, into the
circuitry so as
to absorb and store a portion of the electrical energy generated by the coil
800 as the DC
electric motor 66 is operated in reverse against a load during the closing
cycle of the pilot
valve. The electrical energy thus recovered and stored in the electrical
storage means
then would be available for use in powering other operations of the tool, such
as providing
-24-
219 ~? 2'~
a portion of the electrical power needed for operating the DC electric motor
66 to open the
pilot valve on the next pulse cycle.
The foregoing disclosure and description of the invention are illustrative
thereof, and
various embodiments of the tool may be made through changes in the size,
shape,
arrangement of parts and materials of construction, without departing from the
spirit of the
invention, which is measured solely by the appended claims.
-25-
