Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02629835 2008-04-24
Method and Apparatus for Mud Pulse Telemetry
BACKGROUND OF THE INVENTION
[001] Field of the Invention
[002] The present invention relates generally to mud pulse telemetry. More
particularly,
relating to mud,pulse apparatus having an uncompensated pulser and method of
operating the
apparatus in conjunction with standard drilling operation procedures, such as
connection pipe
sections to a drill string.
[003] Description of the related art.
[004] Mud pulse telemetry systems are known in the art of drilling bore holes.
The
systems transmitting measured down hole parameter information to the surface
through coded
pressure pulses. The systems are used to transmit down hole information useful
to the
operation of drilling the bore hole and information pertaining to the
formation through which
the bore hole is being drilled. Examples of mud pulse telemetry system are
described in U.S.
Patents 6,845,563; 5,774,420; 6,714,138; and 4,914,637, the entirety of which
is incorporated
herein by reference
SUMMARY OF THE INVENTION
[005] In accordance with the present invention, a method and apparatus for mud
pulse
telemetry is provided. The method and apparatus in accordance with the present
invention
provides for a low cost, unmanned, wireless survey tool for the drilling
industry.
[006] In general, in one aspect, a telemetry apparatus for transmitting
information from a
drill string positioned at a down hole location in a bore hole to a surface
location, the drill
string having a flow passage through which a drilling fluid flows is provided.
The telemetry
apparatus including a pulser positioned within the flow passage approximate
the down hole
location for generating a series of positive pressure pulses in the drilling
fluid which are
encoded to contain the information to be transmitted. The pulser comprising, a
rotor capable
-page 1 of 21-
CA 02629835 2008-04-24
of at least partially blocking the flow passage, a motor positioned within an
internal housing
defined by the pulser, the housing being filled by a gas at atmospheric
pressure, a drive shaft
extending from the drive motor to a position external of the internal housing,
the drive shaft is
connected to said rotor, and a seal positioned about the drive shaft such that
the seal seals the
internal housing.
[007] In general, in another aspect, a telemetry apparatus for transmitting
information
from a drill string positioned at a down hole location in a bore hole to a
surface location, the
drill string having a flow passage through which a drilling fluid flows is
provided. The
telemetry apparatus including a rotor capable of at least partially blocking
the flow passage, a
motor positioned within an internal housing defined by the pulser, the housing
being filled by
a gas at atmospheric pressure, a drive shaft extending from the drive motor to
a position
external of the internal housing, the drive shaft is connected to said rotor,
a seal positioned
about the drive shaft such that the seal seals the internal housing, a stator
co-axially aligned
with the rotor and having at least one flow channel through which the drilling
fluid is
directed, and the rotor being angularly rotated by said motor into a first
operative position
where the rotor at least partially blocks the at least one flow channel and
into a second
inoperative position where the drilling fluid is free to flow through the at
least one flow
channel.
[008] In general, in another aspect, a telemetry apparatus for transmitting
information
from a drill string positioned at a down hole location in a bore hole to a
surface location, the
drill string having a flow passage through which a drilling fluid flows is
provided. The
telemetry apparatus including a body for positioning in the flow passage of
the drill string
approximate the down hole location, the body directing the drilling fluid
therethrough, a rotor
capable of at least partially blocking the flow passage when rotated into a
first position and at
least partially reducing the blockage when rotated into a second position,
wherein rotation of
the rotor creates positive pressure pulses in the drilling fluid, which are
encoded to contain
the information to be transmitted, a drive motor positioned within a gas
filled internal housing
that is defined by the body, a drive shaft extending from the motor at least
partially outward
from said internal housing and connected to the rotor, and a seal received by
the body such
that the drive shaft extends axially through the seal and such that the seal
seals the internal
housing.
-page 2 of 21-
CA 02629835 2008-04-24
(009] In general, in another aspect, a telemetry apparatus for transmitting
information
from a drill string positioned at a down hole location in a bore hole to a
surface location, the
drill string having a flow passage through which a drilling fluid flows is
provided. The
telemetry apparatus including a body for positioning in the flow passage of
the drill string
approximate the down hole location, the body directing the drilling fluid
therethrough; a rotor
capable of at least partially blocking the flow passage when rotated into a
first position and at
least partially reducing the blockage when rotated into a second position,
wherein rotation of
the rotor creates positive pressure pulses in the drilling fluid, which are
encoded to contain
the information to be transmitted; a drive motor positioned within a gas
filled internal
housing that is defined by the body; a drive shaft extending from the motor at
least partially
outward from said internal housing and connected to the rotor; a seal received
by the body
such that the drive shaft extends axially through the seal and such that the
seal seals the
internal housing; a pressure sensor positioned such that the drilling fluid
within the flow
passage acts upon the sensor for measuring the drilling fluid pressure within
the flow passage;
a measurement sensor for measuring a down hole parameter; and a microprocessor
connected
to the pressure sensor, the measurement sensor and the motor for taking
drilling fluid pressure
readings, down hole parameter measurement and controlling the operation of the
motor to
rotate the rotor based upon the drilling fluid pressure and the down hole
parameter
measurement, thereby generating the positive pressure pulses within the
drilling fluid.
100101 In general, in another aspect, a method for transmitting information
from a drill
string positioned at a down hole location in a bore hole to a surface
location, the drill string
having a flow passage through which a drilling fluid flows is provided. The
method
comprising the steps of:
measuring drilling fluid pressure to detect a predetermined drop of drilling
fluid
pressure and then a subsequent predetermined rise of drilling fluid pressure;
and
generating a sequence of positive pressure pulses in the drilling fluid at a
position
approximate the down hole location that propagates in a direction towards the
surface
location, the sequence of positive pressure pulses being generated at a time
after the
predetermined rise of drilling fluid pressure is detected, the sequence of
positive pressure
pulses are encode with the information to be transmitted to the surface
location.
-page 3 of 21-
CA 02629835 2008-04-24
[0011] In general, in another aspect, a method for transmitting information
from a drill
string positioned at a down hole location in a bore hole to a surface
location, the drill string
having a flow passage through which a drilling fluid flows is provided. The
method
comprising the steps of:
directing the drilling fluid across a rotor positioned approximate the down
hole
location, the rotor capable of at least partially obstructing the flow passage
by rotating into
a first position and capable of at least partially reducing the obstruction by
rotating into a
second position, the rotation of the rotor being effected by a drive assembly
including a
motor;
measuring drilling fluid pressure to detect a predetermined drop of drilling
fluid
pressure and then a subsequent predetermined rise of drilling fluid pressure;
and
generating a sequence of positive pressure pulses in the drilling fluid at a
position
approximate the down hole location that propagates in a direction towards the
surface
location, the sequence of positive pressure pulses being generated at a time
after the
predetermined rise of drilling fluid pressure is detected, the sequence of
positive pressure
pulses are encode with the information to be transmitted to the surface
location.
[0012] There has thus been outlined, rather broadly, the more important
features of the
invention in order that the detailed description thereof that follows may be
better understood
and in order that the present contribution to the art may be better
appreciated.
[0013] Numerous objects, features and advantages of the present invention will
be readily
apparent to those of ordinary skill in the art upon a reading of the following
detailed description
of presently preferred, but nonetheless illustrative, embodiments of the
present invention when
taken in conjunction with the accompanying drawings. The invention is capable
of other
embodiments and of being practiced and carried out in various ways. Also, it
is to be
understood that the phraseology and terminology employed herein are for the
purpose of
descriptions and should not be regarded as limiting.
[0014] As such, those skilled in the art will appreciate that the conception,
upon which
this disclosure is based, may readily be utilized as a basis for the designing
of other structures,
methods and systems for carrying out the several purposes of the present
invention. It is
-page 4 of 21-
CA 02629835 2008-04-24
important, therefore, that the claims be regarded as including such equivalent
constructions
insofar as they do not depart from the spirit and scope of the present
invention.
[0015] For a better understanding of the invention, its operating advantages
and the
specific objects attained by its uses, reference should be had to the
accompanying drawings
and descriptive matter in which there is illustrated preferred embodiments of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention will be better understood and objects other than those
set forth
above will become apparent when consideration is given to the following
detailed description
thereof. Such description makes reference to the annexed drawings wherein:
[0017] Figure 1 is a diagram, partially schematic, showing a drilling
operation employing
the mud pulse telemetry system in accordance with the present invention;
100181 Figure 2 is a schematic diagram of the mud pulser telemetry system in
accordance
with the present invention;
[0019] Figure 3 is a diagram, partially schematic, showing the basic
mechanical
arrangement of a pulser according to the current invention;
[0020] Figures 4-9 are consecutive portions of a longitudinal cross-section
through the
pulser and a portion of the drilling string at the bottom hole location;
[0021] Figure 10 is a diagrammatic, transverse cross-sectional view taken
along line 10-
10 in Figure 3 showing the rotor and stator in accordance with the pulser of
the present
invention;
[0022] Figure 11 is the diagrammatic transverse cross-sectional view of Figure
10
showing the rotor in a secondary position with respect to the stator;
-page 5 of 21-
CA 02629835 2008-04-24
[0023] Figure 12 is an enlarged, detailed cross-section view of a seal in
accordance with
the present invention; and
[0024] Figure 13 is a perspective, explode view of a partial section of the
seal.
[0025] The same reference numerals refer to the same parts throughout the
various
figures.
DETAILED DESCRIPTION OF THE INVENTION
[0026] With reference to Figure 1, a bore hole drilling operation including a
mud pulse
telemetry system 10 in accordance with the current invention is shown. Drill
bit 11 attached
to a down hole end of a drill string 12 drills a bore hole 14 into a formation
16. The drill
string 12 is conventional and is comprised of several sections of pipe coupled
together. The
drill string 12 can be rotated at the surface using conventional equipment to
drill the bore hole
14 or the drill string can include down hole motor 18 for rotating the drill
bit 10, thereby
drilling the bore hole. The drilling operation further includes a typical
drilling fluid or
drilling mud system having a drilling fluid pump 20 which pumps drilling fluid
22 down a
flow passage 24 of the drill string 12 where it then flows outward from the
drill bit 10 into the
annulus 26 between the outer surface of the drilling string and the bore hole
14. The drilling
fluid 22 then continues to flow upward through the annulus 26 to the surface
where it is
cleaned by a drilling fluid cleaning system (not shown) and then recirculated
back into the
flow passage 24. The mud pulse telemetry system 10 in accordance with the
current
invention is shown positioned at a down hole location 30 within the flow
passage 24 of the
drill string.
[0027] With reference to Figure 2, a basic system diagram of the mud pulse
telemetry
system 10 is shown. The telemetry system 10 includes sensor package 32 for
measuring
down hole parameters, a data encoder 34, a power supply 36, which may be a
battery or
turbine, and a pulser 38. The pulser 38 comprises a controller 40, which may
be a
microprocessor, motor driving circuitry 42, a motor 44, such as a reversible
brushless DC
motor that operates at a minimum of 1000 RMP, a reduction gear box 46 that can
provide a
speed reduction of at least about 200:1, a stator 48, a rotor 50, a drive
shaft 52 directly
-page 6 of 21-
CA 02629835 2008-04-24
coupling the output of the motor to the rotor, an angular position encoder 54,
and a drilling
fluid pressure sensor 56.
[0028] Sensor package 32 can include a single sensor or multiple sensors for
measuring
various down hole parameters such as but not limited to inclination or drift
of the drilling
string, azimuth of the drill string, pressure, temperature, voltage, and
shock. The sensor
package 32 receives or measures information 58 useful in connection with the
drilling
operation and sends output signals 60 to the data encoder 34. The data encoder
34 receives
the output signals 60 and generates a digital code 62 that is transmitted to
the controller 40.
The controller 40 processes the digital code and generates command signals 64
to the motor
driving circuitry 42. The motor driving circuitry 42 operates the motor 44 in
accordance with
the command signals to rotate the rotor 50 to generate pressure pulses 68 in
the drilling fluid
22. The pressure pulses 68 are sensed by a sensor 70 positioned at the surface
and are
decoded and processed by a data acquisition system 72. The angular position
encoder 54
suitable for high temperature applications is coupled to the output of the
motor 44. The
angular position encoder 54 sends signa155 to the controller 40 containing
information of the
angular position of the rotor 50, which may also be used by the controller in
generating
command signals 64. The drilling fluid pressure sensor 56 measures the
pressure of the
drilling fluid 22 within the flow passage 24 and transmits signa157 to the
controller 40
containing information pertaining to the pressure of the drilling fluid.
[0029] Further, the mud pulse telemetry system 10 may include a pressure pulse
generator
28 positioned at the surface for generating pulses 29 within the drilling
fluid 22. The pressure
pulse 29 may be encoded with operation information and are received by
drilling fluid
pressure sensor 56 and transmitted to the controller 40. The operation
information may be
used by the controller 40 in generating command signals 64.
[0030] With reference to Figure 3, a partial schematic diagram of the
mechanical
arrangement of the pulser 38 is shown. The pulser 38 is shown positioned with
the flow
passage 24 of the drill string 12 at the down hole location 30 such that the
drilling fluid 22 is
caused to flow across the pulser. The pulser 38 can be fixedly attached to the
drilling string
12 or removably attached to the drilling string through the use of a
conventional hanger sleeve
-page 7 of 21-
CA 02629835 2008-04-24
(not shown) to facilitate wire line placement and retrieval of the pulser. A
wire line is
removable attachable to a spear point 75 forming part of the pulser 38.
[0031] The rotor 50 is preferably positioned upstream of the stator 48 and is
driven by a
drive train positioned within the pulser body 74. The rotor is connected to a
drive shaft 52
which is supported by a bearing assembly 76. The drive shaft is connected to a
reduction gear
box 46 which is coupled to the output of the motor 44. The motor 44, the
reduction gear box
46 and a portion of the drive shaft 52 is positioned within an internal
housing 78 defined by
the pulser body 74. A seal 80 is positioned about the drive shaft 52 such that
the drive shaft
extends axially through the seal and such that seal seals the internal housing
78. The internal
housing is gas filled, preferably with an inert gas and at atmospheric
pressure.
[0032] The pressure sensor 56 is received by the pulser body 74 such that the
pressure of
the drilling fluid 22 within the flow passage 24 may be measured.
Additionally, the pulser
body 74 houses the controller 40, the motor driving circuit 42, and the sensor
package 32.
100331 With reference to Figures 4-13 a preferred embodi.ment of the telemetry
system 10
is shown positioned at a down hole location 30 within a the flow passage 24 of
the drilling
string 12. The pulser 38 is of an elongated cylindrical shape of a dimension
permitting the
placement of the pulser within the flow passage 24 with out unduly restricting
the flow of
drilling fluid 22 through the flow passage 24. The pulser 38 includes a pulser
body 74 that can
be of a unitary construction or can be of a plurality of separate body members
coupled
together as shown. As previously mentioned, the pulser body 74 can be fixedly
mounted to
the drill string 12 or removably mounted to the drill string through the use
of a conventional
hanger sleeve 82 which is attached to the drill string. The pulser includes at
its upstream
most end a spear point 75 which is engagable with a wire line for placement
and retrieval of
the pulser 38.
[0034] A rotor 50 is positioned within the flow passage 24 coaxially with the
drill string
12 and preferably upstream of a stator 48. With additional reference to
Figures 10 and 11,
which are transverse cross-section views of the pulser 38 taken through the
rotor 50, the rotor
includes a plurality of lobes 100 extending radially from a center portion 102
and the stator
includes a plurality of channels 104 equal to the number of lobes 100 through
which the
-page 8 of 21-
CA 02629835 2008-04-24
drilling fluid 22 is directed. The rotor 50 is rotatable with respect to the
stator 48 such that
the lobs 100 of the rotor are positioned to at least partially block the
drilling fluid 22 from
flowing through the channels 104 of the stator as shown in Figure 11 and is
rotatable to at
least partially reduce the blockage as shown in Figure 10.
[0035] The rotor 50 is connected to a drive shaft 52 which extends axially
through the
stator 48 and the pulser body 74. The drive shaft 52 is support at an upstream
end of the
pulser body 74 by a bushing 85 and at a downstream end by a bearing 86 and is
coupled to a
reduction gear box 46, which is in turn coupled to the output of a motor 44,
as shown in
Figure 5. The motor 44, the reduction gear box 46 and a portion of the drive
shaft 52 is
positioned in an internal housing 78 defined by the pulser body 74. The
internal housing 78 is
filled with gas, such as air or preferably an inert gas and at atmospheric
pressure. A sea180,
which will be described in further detail below, is positioned about the drive
shaft 52 such
that the drive shaft extends axially through the seal and such that the seal
seals the internal
housing 78. A seal housing 83 defmed by the pulser body 74 receives the
sea180.
[0036] The pulser 38 includes a fluid pressure sensor 56 for measuring the
pressure of the
drilling fluid 22 within the flow passage 24. The fluid pressure sensor 56 can
comprises a
piston 110 received within pressurized oil filled bore 112 defined by the
pulser body 74. The
piston 110 has an outward facing surface 114 which is contactable by the
drilling fluid 22.
The piston 110 is caused to displaced inward or outward depending upon the
drilling fluid
pressure exerted upon the outward facing surface. The inward and outward
displacement of
the piston 110 is related to the pressure differential between the pressure of
the drilling fluid
22 and the pressure of the oil within the bore 112. An inward displacement of
the piston 110
compresses the oil and increases the pressure within the bore 112. Similarly,
an outward
displacement of the piston 110 decompresses the oil and decreases the pressure
within the
bore 112. The pressure within the bore is measured by a transducer 116 that
generates a
pressure signa157 and transmits the pressure signal to a controller 40.
[0037] An angular position encoder 54 suitable for high temperature
applications is
coupled to the output of the gear box 46. The angular position of the rotor
attached to the
shaft 52 is defined by the angular position encoder 54, and the hall sensors
built into the
motor 44 which sends signa155 to the controller 40 containing information of
the angular
-page 9 of 21-
CA 02629835 2008-04-24
position of the rotor 50, which may also be used by the controller in
generating command
signals 64. . The angular position encoder can be that of a hall effect sensor
94 positioned
about the drive shaft 52 and a magnet 96 secured to the drive shaft. The
angular position
encoder 54 defines a known angular point of the draft shaft 52 which in turn
results in a
known position of the rotor 50 attached to the drive shaft. The telemetry
system 10 uses this
point as a start reference, the drive shaft 52 is rotated x number of counts
in a direction to at
least partially block or at least partially reduce the blockage the flow
passage 24 by counting
the pulses generated by the angular position encoder.
[0038] As shown in Figure 6 the pulser body 74 defines an electronics housing
90 which
is positioned therein the various electronic assemblies of the telemetry
system 10, such as but
not limited to the controller 40, a motor driving circuit 42, and a sensor
package 32. The
sensor package 32 can include various sensors such as but not limited to a
drift or inclination
sensor, an azimuth sensor, a temperature sensor, a pressure sensor and a shock
sensor.
[0039] The pulser 38 further includes a mid centralizer 92 an end view thereof
is shown
in Figure 7a and a longitudinal cross-section is shown in Figure 7b. The mid
centralizer
includes a plurality of centralizing blades 94 which extend from the body 96
thereof. The
centralizing blades 94 contact the inner surface of the drill string 12 and
centralize the pulser
body 74 within the flow passage 24. A power supply 36, such as a battery back,
is also
provided and is shown in Figure 8. Further, a bottom centralizer 98, shown in
Figures 9a and
9b, is included and acts to centralize the bottom of the pulser 38 within the
flow passage 24.
As in the mid-centralizer 92, the bottom centralizer 98 includes a plurality
of centralizing
blades 99 which contact the inner surface of the drill string 12.
[0040] Now with reference to Figures 12 and 13, a detailed discussion of the
seal 80 will
be had. Figure 12 is an enlarged longitudinal cross section of the seal 80 and
Figure 13 is a
partial explode view of the seal. The sea180 provides an uncompensated drive
train for the
pulser 38 which simplifies and reduces manufacturing and maintenance costs of
the pulser.
Heretofore, pulsers have had a compensated drive train where all or at least
part of the drive
train is positioned within pressurized oil filled housing. This was required
to eliminate a high
pressure differential across a seal where a driving shaft of the drive train
would exit the
housing into the drilling fluid to create either a rotating action or a
reciprocating action to
-page 10 of 21-
CA 02629835 2008-04-24
drive an actuator such as a rotor or a hydraulic valve. Without the
compensation and under a
high pressure differential there is a high amount of friction or seal drag
across the seal
requiring a large torque to drive the shaft making battery operated devices
undesirable.
Further under a high pressure differential, when the shaft has been broken
free to move it is
very prone to leakage.
[0041] The seal 80 in accordance with the present invention provides the
pulser 38 with
an uncompensated drive train that overcomes all of the drawbacks of a
compensated drive
train and which efficiently operates under a high pressure differential. The
sea180 is received
within a seal housing 83 defmed by the pulser body 74 as shown. The sea180
encompasses
the drive shaft 52 which extends axially through the seal. The sea180
comprises of a unique
stacked array of a plurality of seal elements 82 held by a plurality of seal
holders 84 and seal
washers 86 positioned intermediate of adjacent seal holders 84. Preferably,
the seal elements
are of a polypack or a poly-O type seal. The seal elements 82 are positioned
about the drive
shaft 52 and retained in position by the seal holders 84. Each seal holder 84
positions and
retains two seal elements 82, one of the seal elements 82a being retained
juxtaposed the
surface of the drive shaft 52 and the second of the seal elements 82b being
retained
juxtaposed the surface of the seal housing 83. The first seal element 82a is
of a diameter less
than that of the second seal element 82b. Each seal holder 84 is generally
cylindrical in shape
and includes first shoulder 86 of a first diameter, a first lip 88 extending
upwardly from the
outer circumference of the first shoulder, a second shoulder 89 of a second
diameter that is
greater then the diameter of the first shoulder, and a second lip 90 extending
from the inner
circumference of the second shoulder in a direction opposite of the first lip.
100421 In a preferred arrangement, the seal holders 84 each retaining two seal
elements 82
are positioned about the drive shaft 52 such that seal elements 82a and 82b
are arranged in an
alternating pattern. As shown, three seal holders 84 each retaining two seal
elements 82 for a
total of six seal elements are positioned about the drive shaft 52 and within
the seal housing
83 in a stacked arrangement. A seal washer 86 is positioned between the first
and second seal
holders, a second seal washer is positioned between the second and third seal
holders, and a
third seal washer is positioned between the third seal holder and a bottom
edge 92 of the seal
housing. A bushing 85 retained by the pulser body 74 is positioned above the
sea180 and
retains the seal within the seal housing 83.
-page 11 of 21-
CA 02629835 2008-04-24
[0043] It can know be understood, in operation, the mud pulse telemetry system
10 is
designed to function in agreement with a process know as "making a connection"
in a drilling
operation. The process of making a connection involves the coupling of an
additional pipe
section to the drilling string as a bore hole is drilled deeper into a
formation. To facilitate the
coupling of an additional pipe section, the drilling is stopped and the
drilling fluid pump 20 is
turned off to stop pumping drilling fluid 12 through the drill string 12 and
to reduce drilling
fluid pressure within the drilling string to a static pressure which is less
then the pressure of
the drilling fluid during pump on operation. The mud pulse telemetry system 10
makes use of
this intermittent cessation of drilling to take measurements of down hole
parameters which
are useful for the drilling operation. The cessation of drilling is detected
by measuring the
pressure of the drilling fluid 22 within the flow passage 24. Once a
predetermined drop of
drilling fluid pressure, the telemetry system 10 determines it is time to take
down hole
measurements at a time after the pressure drop is detection. Upon a detection
of a
predetermined rise of drilling fluid pressure, the telemetry system 10 begins
to operate the
pulser 38 at a time after the pressure rise is detected to generate encoded
pressure pulses
within the drilling fluid.
[0044] In one aspect, the telemetry system 10 can operate in either a short
survey mode
and a long survey mode. In the short survey mode one only down hole parameter
information, such as inclination, is be transmitted to the surface. In the
long survey mode
multiple sets of information pertaining to various down hole parameters, such
as inclination,
azimuth, temperature, shock, pressure or battery voltage, is transmitted to
the surface. The
telemetry system 10 may also operate in a combined short and long survey mode
where the
telemetry system operates in the short survey mode and then in the long survey
mode. The
telemetry system 10 may operate in the short survey mode for a number of
information
transmission and then switch to the long survey mode of another number of
information
transmission and then back to the short survey mode.
[0045] The pressure pulses 68 are sensed by a sensor 70 positioned at the
surface and are
decoded and processed by a data acquisition system 72. The data acquisition
system 72
displays pressure data in a time vs. pressure chart and automatically decodes
the survey data
and displays the drift (inclination of the drill string) corresponding to time
and date in a table.
-page 12 of 21-
CA 02629835 2008-04-24
The drill operator then can enter the depth of the drilling string if reading
is acceptable. Each
time a depth is entered corresponding to a drift measurement, a point is
plotted on a depth vs.
drift graph which is displayed to the drill operator to use in making any
necessary drilling
changes.
[0046] A number of embodiments of the present invention have been described.
Nevertheless, it will be understood that various modifications may be made
without departing
from the spirit and scope of the invention. Accordingly, other embodiments are
within the
scope of the following claims.
-page 13 of 21-
