Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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REAL TIME TELEMETRY
This invention relates to a telemetry system and in particular to a telemetry
system suitable for use in the transmission of data in a borehole.
It is desirable, in the drilling of a subterranean borehole in a formation, to
be
able to transmit data along the borehole. For example, where a steerable
drilling
system is being used and downhole sensors are provided and arranged to output
signals representative of for example, the drilling direction, it is desirable
to be able
to transmit signal data representative of the drilling direction, in real
time, to an
operator located at the surface.
A number of telemetry systems are known which are capable of providing
such transmission of data. However, such systems tend to be relatively complex
and
expensive, and may not be able to transmit data in real time. There are
situations
where the amount of data to be transmitted is relatively small and the
provision of
such a telemetry system cannot be justified or, if provided, is not used to
its fullest
extent. It is an object of the invention to provide a telemetry system of
relatively
simple and convenient form, suitable for use in such applications.
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According to an aspect of the present invention, there is provided a
telemetry system for use in a drilling system, the telemetry system comprising
a
rotary valve controlling the supply of drilling fluid or mud to a bias pad
piston
arrangement of a downhole tool, the rotary valve having a rotary valve member
and
an outlet member, the rotary valve member including an opening which
selectively
communicates with a series of openings in the outlet member to enable control
over
the flow of drilling fluid or mud to the downhole tool, the system further
comprising
receiving data to be transmitted, encoding the data as a duration, and
controlling the
rotation of the rotary valve such that the rotary valve member of the rotary
valve is
rotated with respect to the outlet member for the said duration at a
predetermined
rotary speed to cause the formation of pressure fluctuations or waves in the
drilling
fluid or mud to create telemetry signals.
According to another aspect, there is provided a telemetry system for
use in a drilling system including a rotary valve controlling the supply of
drilling fluid or
mud to a downhole tool, the system comprising receiving data to be
transmitted,
encoding the data as a duration, and controlling the rotation the rotary
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valve such that the rotary valve is rotated for the said duration at a
predetermined
rotary speed to cause the formation of pressure fluctuations or waves in the
drilling
fluid or mud.
It has been found that the rotation of a rotary valve produces pressure
fluctuations or waves in the drilling fluid or mud supplied to, and through,
the rotary
valve, in use, and that these fluctuations or waves can be sensed, for
example, at the
surface. By appropriate control of the rotary valve, these pressure
fluctuations or
waves can be used to transmit signals, without requiring the provision of
additional,
complex downhole tools. Consequently, data can be transmitted in real time to
an
operator located at the surface.
Conveniently, in some embodiments, the drilling system includes at
least one downhole sensor, the output of which comprises the data to be
transmitted.
In order to increase the amount of data that can be transmitted using the
system, two or more predetermined rotary speeds may be chosen, each being
indicative of the output of a respective sensor. Alternatively, the data may
be
encoded using a look-up table, a first signal transmitted by rotating the
valve for a
first duration at a first predetermined rotary speed being used to transmit
information
relating to one coordinate of the look-up table, a second signal transmitted
by
= rotating the valve for a second duration at a second predetermined speed
being used
to transmit information relating to another coordinate of the look-up table.
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The signal transmitted using the system may be decoded by the operator
simply by monitoring for how long the pressure fluctuations or waves at the
predetermined frequency are received. This may be achieved manually or
= automatically using an appropriated controlled device.
The signals transmitted in this fashion are most readily identifiable when the
drill pipe is stationary. Conveniently, therefore, the system is used to
transmit data
shortly after the dovvnhole tool has completed its start-up sequence when the
pumps
supplying the drilling fluid or mud are switched on. However, it may be
possible to
use the system to transmit data to the surface at other times.
Embodiments of the invention will further be described, by way of
example, with reference to the accompanying drawings, in which:
Figure 1 is a diagrammatic view illustrating part of a bottom hole assembly
including a downhole tool controlled using a rotary valve;
Figure 2 is a diagrarrunatic view illustrating the rotary valve; and
Figures 3a and 3b are tables illustrating two possible encoding techniques.
Referring firstly to Figure 1, illustrated diagrammatically is part of a
bottom
hole assembly 10 for use in the formation of a borehole 14 in a subsurface
formation
12. The assembly 10 comprises a drill bit 16 carried by a bias unit 20. A
control unit
18 is operable to control the operation of the bias unit 20.
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The bias unit 20 includes a housing 22 arranged to carry a series of bias pads
24. Each bias pad 24 is able to move between a retracted position and an
Mended
position, piston arrangements 26 being provided to drive each pad 24 from its
retracted position to its extended position The piston arrangements 26 are
operable
independently of one another, the supply of fluid under pressure to the piston
arrangements 26 being controlled by a rotary control valve 28 located within
the
control unit 18.
In use, the housing 22 is carried by or forms part of a drill pipe or string
which is rotated, for example from the surface or by a downhole located motor.
If
the piston arrangements 26 are supplied with fluid under pressure in turn, in
synchronism with the rotation of the housing 22, it will be appreciated that
the bias
pads 24 are rimed, in turn, to their extended positions. In their extended
positions,
the pads 24 bear against the wall of the borehole 14 and a laterally directed
traction
force is applied to the housing 22. By controlling the piston arrangements 26
in a
manner synchronised with the rotation of the housing 22, it will be
appreciated that
the reaction force acts in a substantially consistent direction. As the drill
bit 16 is
secured to the housing 22, it will be appreciated that the operation of the
bias wit in
this manner also results in the application of a laterally directed force to
the drill bit
16, thus urging the drill bit to form a curve or dogleg in the borehole 14.
The rotary control valve 28 comprises a face sealing valve of the type
illustrated, diagrammatically, in Figure 2. The valve comprises a rotary valve
member 30 of disc-like form located within a chamber 32 to which drilling
fluid or
mud is supplied, in use, under pressure through the drill pipe through an
inlet 34.
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Also located within the chamber 32 is an outlet member 36, also of disc-like
form, a
surface of the valve member 30 abutting a surface of the outlet member 36. The
outlet member 36 is formed with a series of openings 38 extending from the
surface
against which the valve member 30 bears to the opposing surface thereof each
opening communicating with a respective outlet 40. The outlets 40 communicate,
in
use., with respective ones of the piston arrangements 26. The openings 38
provided
in the outlet member 36 are located at a common radial position.
The valve member 30 is provided with an arcuate opening 42 which extends
from the surface thereof which abuts the outlet member 36 to the opposing
surface
thereof and which is provided at the same radial position as the openings 38.
A control shaft 44 extends into the chamber 32 and is connected to the valve
member 30 to drive the valve member 30 for rotation.
It will be appreciated that, in use, fluid entering the chamber 32 passes
through the arcuate opening 42 and into whichever of the openings 38 is
aligned
therewith, the fluid flowing through the respective outlet 40 to the
associated piston
arrangement 26. The selection of which, if any, of the outlets 40 to which
fluid is
supplied by the valve 28 depends upon the angular position of the valve member
30
which, in turn, is dependent upon the angular position of the control shaft
44.
The control shaft 44 may be rotated by a range of devices. For example, an
appropriately controlled electrically operated motor may be used to drive the
shaft 44
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and thereby control the operation of the valve 28. Alternatively, the control
shaft 44
could be connected to an appropriately controlled roll stabilised platform. In
either
case, the movement of the shaft 44 may be controlled in response to the output
signals from one or more downhole sensors 46, for example arranged to sense
the
inclination of the housing 22.
Systems of this type are well known and so the operation thereof will not be
described in further detail
Whilst the control shaft 44 is rotated, pressure fluctuations or waves are
formed in the drilling fluid or mud in the drill pipe as communication
commences,
and subsequently is broken, between the arcuate opening 42 and the openings
38, in
turn. The pressure fluctuations or waves so formed can be sensed at the
surface or at
other locations spaced from the valve 28, especially at times when the drill
pipe is
not being rotated.
In accordance with the invention, the formation of these pressure fluctuations
or waves is harnessed to enable the transmission of data from the bottom hole
assembly, fur example to the surface For example, where the sensor 461$
arranged
to output a signal representative of the inclination of the bias wit housing
22, the
output signal from the sensor 46 is encoded, for example using the table shown
in
Figure 3a to derive a duration representative of the sensed inclination. The
rotary
valve 28 is then driven for rotation at a predetermined rotary speed for the
derived
duration, thus =omitting a series of pressure fluctuations or waves through
the
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drilling fluid or mud at a frequency related to the speed of rotation of the
rotary valve
for the derived duration. Surface located equipment sensitive to the pressure
fluctuations or waves in the fluid can be used to enable an operator to
measure for
how long the pressure fluctuations or waves were transmitted at the
predetermined
frequency. The duration can then be decoded to provide the operator with real
time
information representative of the inclination of the housing 22.
For example, if the sensor 46 output indicates that the housing 22 is inclined
at an angle of 2.5 degrees, using the technique described hereinbefore with
reference
to Figure 31k the rotary valve 28 is rotated for a period of 30 seconds at the
predetermined rotary speed, for example at a speed causing pressure
fluctuations or
waves to be ftansmitted at a frequency of 6Hz The operator, upon measuring
that a
61iz signal has been received for 30 seconds can ascertain, in real time, that
the
inclination of the housing 22 is in the range 2 ¨ 3 degrees. It will be
appreciated that
other rotary speeds of the valve 28 may be used to transmit signals, and that
the
durations and ranges of inclination angles, and relationships therebetween,
may be
selected to suit the application in which the invention is used.
Wyse two or niore sensors are provided, data representative of the outputs of
the sensors may be transmitted, in turn, for example with the rotary valve
being
rotated at different rotary speeds so as to provide an indication of for which
parameter data is being transmitted.
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Figure 3b illustrates an alternative encoding technique which may be used to
transmit larger quantities of data using the system of the invention. In this
arrangement the output signals from the sensors are encoded using a look-up
table.
For example, if it is determined that the toolface angle is 90 degrees and the
.
deviation is 60%, then using the look-up table shown in Figure 3b it can be
seen that
this combination of parameter values occurs in column 3, row 7 of the look-up
table
In this example, the column data is transmitted by rotating the valve 28 at a
rotary
speed to generate pressure fluctuations or waves at a frequency of 4Hz, and
row data
is transmitted by rotating the valve 28 to cause pressure fluctuations or
waves at a
frequency of 6Hz.. Thus, in order to transmit the data, the valve is rotated
to cause a
4Hz signal to be transmitted for 3 units of time, for example 30 seconds, the
valve
subsequently being rotated to transmit a 6Hz signal for 7 units of time, for
example
70 seconds. Upon receiving these signals, the operator can decode the signals
using
the same look-up table to obtain, in real time, the toolface and deviation
data.
If desired, the look-up table could be used to transmit tool status codes or
words to the operator.
As mentioned hereinbefore, this information is best transmitted when the drill
string is not being rotated, and may conveniently be transmitted shortly after
the
downhole tool has completed its startup procedure when the drilling fluid
pumps are
activated after recycling. However, it may be possible to successfully
transmit and
receive data using the system at other times.
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The signal received at the surface may be measured simply by the operator
determining for how long a signal at a predetermined frequency has been
transmitted,
which he then decodes. Alternatively, surface located equipment may be used to
sense the transmission of signals at the predetermined frequency or
frequencies, to
measure for how long the signals are transmitted, to decode the signals and to
produce an appropriate output for the operator.
The ability to transmit data in real time in accordance with the invention is
advantageous in that, compared to conventional arrangements, data can be
transmitted in a relatively simple, quick and convenient manner. Data can thus
be
transmitted more frequently and cost effectively than is possible with
conventional
arrangements. The real time transmission of data also enables an operator to
ascertain that the downhole equipment is operating correctly, that
communications
links with the downhole equipment are functioning, and may allow greater
control
over the downhole equipment as, for example, deviations from a desired path
may be
sensed and corrected more quickly. The system does not require the provision
of
additional downhole tools or equipment, but rather may be implemented simply
by
appropriate m3dification of the control system of a standard downhole tooL
It will be appreciated that a range of modifications and alterations may be
made to the invention described hereinbefore without departing from the scope
of the
invention
