U.S. patent number 3,777,560 [Application Number 05/207,326] was granted by the patent office on 1973-12-11 for methods and apparatus for measuring the rate of penetration in well drilling.
This patent grant is currently assigned to Schlumberger Technology Corporation. Invention is credited to Jean-Hubert Guignard.
United States Patent |
3,777,560 |
Guignard |
December 11, 1973 |
METHODS AND APPARATUS FOR MEASURING THE RATE OF PENETRATION IN WELL
DRILLING
Abstract
New and improved methods and apparatus exemplifying the present
invention are disclosed herein for measuring at the surface the
changes in total elongation of a drill string due to variations in
the tensional forces acting thereon during a typical well drilling
operation, measuring the changes in the total length of the drill
string as it is moved into and out of the borehole at the surface,
and uniquely combining these measurements for producing an output
signal which is representative of the changes in the borehole depth
as well as converting the combined measurements for producing
another output signal which is representative of the actual rate of
penetration of a drill bit coupled to the drill string.
Inventors: |
Guignard; Jean-Hubert (Sainte
Mesne, FR) |
Assignee: |
Schlumberger Technology
Corporation (New York, NY)
|
Family
ID: |
9066552 |
Appl.
No.: |
05/207,326 |
Filed: |
December 13, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Dec 30, 1970 [FR] |
|
|
7047214 |
|
Current U.S.
Class: |
73/152.45;
340/853.6; 73/152.49 |
Current CPC
Class: |
E21B
45/00 (20130101) |
Current International
Class: |
E21B
45/00 (20060101); E21b 045/00 () |
Field of
Search: |
;73/151.5,151 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Myracle; Jerry W.
Claims
What is claimed is:
1. A method for determining the rate of advancement into earth
formations by a drill bit suspended from a drill string in a
borehole penetrating said earth formations and comprising the steps
of: successively measuring the downward incremental displacments of
the surface end of said drill string being moved into said borehole
while said drill bit is drilling into said earth formations for
producing a series of first electrical pulses respectively
corresponding to an incremental increase to the length of said
drill string in said borehole; successively measuring the
incremental changes in tensional forces acting on said drill string
while said drill bit is drilling into said earth formations and
converting said force changes to corresponding increments of length
of alternatively producing either a series of second electrical
pulses respectively corresponding to an incremental elongation of
said drill string or a series of third electrical pulses
respectively corresponding to an incremental contraction of said
drill string; comparing the total of said first and second
electrical pulses occurring during a time interval after the
occurrence of one of said third electrical pulses with the total of
said third electrical pulses occurring during said time interval;
once the total of said first and second electrical pulses counted
during said time interval equal the total of said third electrical
pulses counted during said time interval, successively processing
said first and second electrical pulses for producing a series of
electrical output pulses respectively corresponding to a net
incremental increase in the overall length of said drill string
until the occurrence of another one of said third electrical
pulses; and successively converting said output pulses to a signal
representative of the rate of downward advancement of said drill
bit into said earth formations during a selected time interval.
2. The method of claim 1 further including the step of: totalizing
said output pulses for providing an indication of the actual depth
of said drill bit in said borehole.
3. Apparatus adapted for determining the rate of penetration into
earth formations by a drill bit suspended from a drill string in a
borehole penetrating such formations and comprising:
displacement-responsive means adapted for producing a series of
first electrical pulses respectively corresponding to a downward
movement of an incremental length of a drill string into a borehole
during a drilling operation; elongation-responsive means adapted
for alternatively producing either a series of sound electrical
pulses respectively corresponding to an incremental elongation of
the overall length of a drill string in a borehole during a
drilling operation or a series of third electrical pulses
respectively corresponding to an incremental contraction of the
overall length of a drill string in a borehole during a drilling
operation; processing means operatively coupled to said
displacement-responsive means and to said elongation-responsive
means and adapted to respond to said electrical pulses produced
thereby for providing a series of electrical output pulses
respectively corresponding to a net incremental increase in the
overall length of a drill string in a borehole during a drilling
operation so long as the total number of said first and second
electrical pulses produced during a selected time interval exceeds
the total number of said third electrical pulses produced during
said selected time interval; and converting means operatively
coupled to said processing means and adapted to respond to said
output pulses for providing an output signal representative of the
rate of penetration into earth formations by a drill bit while
drilling a borehole during said selected time interval.
4. The apparatus of claim 3 wherein said processing means provides
said output pulses by directing said first and second electrical
pulses to said converting means whenever the total number of said
first and second electrical pulses produced during said selected
time interval exceeds the total number of said third electrical
pulses produced during said selected time interval.
5. The apparatus of claim 3 further including: totalizing means
operatively coupled to said processing means and adapted to respond
to said output pulses for providing a signal representative of the
actual depth of such a drill bit in a borehole during said selected
time interval.
6. The apparatus of claim 3 wherein said processing means include:
reversible pulse-counting means having an addition input, a
subtraction input, and an output and operatively arranged for
alternatively providing a first gate-control signal at said output
whenever pulses are received by one of said inputs and providing a
second gate-control signal at said output so long as the number of
pulses received by said one input exceeds the number of pulses
received by the other of said inputs, means adapted for coupling
said third electrical pulses to said one pulse-counting means
input, and gating means adapted to receive said first and second
electrical pulses and having a first output for directing said
first and second electrical pulses as said output pulses to said
converting means in response to said first gate-control signal and
a second output for directing said first and second electrical
pulses to said other pulse-counting means input in response to said
second gate-control signal.
7. The apparatus of claim 3 wherein said processing means include:
reversible pulse-counting means having an addition input, a
subtraction input, and an output and operatively arranged for
alternatively providing a first gate-control signal at said output
for a predetermined state of said pulse-counting means and
providing a second gate-control signal at said output for another
predetermined state of said pulse-counting means, means adapted for
coupling said third electrical pulses to one of said inputs of said
pulse-counting means, and gating means adapted to receive said
first and second electrical pulses and having a first output for
directing said first and second electrical pulses as said output
pulses to said converting means in response to said first
gate-control signal and a second output for directing said first
and second electrical pulses to the other of said inputs of said
pulse-counting means in response to said second gate-control
signal.
8. The apparatus of claim 3 wherein said converting means include
circuit means adapted for determining the frequency of said output
pulses during said selected time interval to provide said output
signal.
9. The apparatus of claim 3 wherein said displacement-responsive
means are further adapted for alternatively producing a series of
fourth electrical pulses respectively corresponding to an
incremental decrease in the overall length of a drill string in a
borehole during a drilling operation; and said processing means are
adapted for providing said output pulses so long as the total
number of said first and second electrical pulses produced during
said selected time interval exceeds the total number of said third
and fourth electrical pulses produced during said selected time
interval.
10. The apparatus of claim 3 wherein said elongation-responsive
means include: tension-responsive means adapted to be coupled to a
drill string and responsive to tension variations therein for
producing electrical signals representative of increases and
decreases of the overall length of such a drill string; and
signal-differentiating means coupled to said tension-responsive
means and adapted to receive said electrical signals as well as
first and second comparison signals of selected equal magnitude for
alternatively producing said second electrical pulses only so long
as the magnitude of said electrical signals is greater than the
magnitude of said first comparison signal and producing said third
electrical pulses only so long as the magnitude of said electrical
signals is less than the magnitude of said second comparison
signal.
11. The apparatus of claim 10 wherein said electrical signals are
analog voltages and said signal-differentiating means include:
first signal-comparison means having a first input coupled to said
tension-responsive means for receiving said electrical signals
therefrom, a second input adapted for receiving feedback signals
for comparison with said electrical signals, and an output adapted
for providing output signals representative of the differences
between signals applied to said first and second inputs; second
signal-comparison means having a first signal input coupled to said
output of said first signal-comparison means for receiving said
output signals therefrom, second and third signal inputs
respectively adapted for receiving said first and second comparison
signals, a first signal output adapted for providing a first output
signal so long as signals applied to said first signal input exceed
said first comparison signal, and a second signal output adapted
for providing a second output signal so long as signals applied to
said first signal input are less than said second comparison
signal; pulse-generating means coupled to said first and second
signal outputs and responsive to said first and second output
signals for alternatively producing said second and third
electrical pulses; and feedback means coupled between said
pulse-generating means and said second input of said first
signal-comparison means and adapted for regulating said first
signal-comparison means to discontinue the production of said
second and third electrical pulses whenever either the total number
of either said second pulses or the total number of said third
pulses produced during said selected time interval equal the total
elongation or contraction during said selected time interval of a
drill string coupled to said tension-responsive means.
12. The apparatus of claim 10 wherein said electrical signals are
analog voltages and said signal-differentiating means include:
first signal-comparison means having a first input coupled to said
tension-responsive means for receiving said electrical signals
therefrom, a second input adapted for receiving feedback signals
for comparison with said electrical signals, and an output adapted
for providing output signals representative of the differences
between signals applied to said first and second inputs; second
signal-comparison means having a first signal input coupled to said
output of said first signal-comparison means for receiving said
output signals therefrom, second and third signal inputs
respectively adapted for receiving said first and second comparison
signals, a first signal output adapted for providing a first output
signal so long as signals applied to said first signal input exceed
said first comparison signal, and a second signal output adapted
for providing a second output signal so long as signals applied to
said first signal input are less than said second comparison
signal; pulse-generating means coupled to said first and second
signal outputs and responsive to said first and second output
signals for alternatively producing said second and third
electrical pulses; and feedback means coupled between said
pulse-generating means and said second input of said first
signal-comparison means and adapted for regulating said first
signal-comparison means by producing second analog voltages equal
to said first-mentioned analog voltages to discontinue the
production of said second and third electrical pulses whenever the
total number of said second pulses less the total number of said
third pulses produced during said selected time interval represents
said analog voltage.
13. A method for determining at least one function representative
of the penetration into earth formations by a drill bit suspended
from a drill string in a borehole penetrating said earth formations
and comprising the steps of: successively determining the
incremental lengths of said drill string moved into said borehole
from the surface while said drill bit is drilling into said earth
formations for deriving a first signal proportional to successive
increases in the overall length of said drill string in said
borehole; successively determining the incremental changes in the
overall length of said drill string due to variations in tensional
forces acting thereon for alternatively deriving either a second
signal proportional to successive elongational increases in the
overall length of said drill string or a third signal proportional
to successive contractional decreases in the overall length of said
drill string; and alternatively combining said first and second
signals with one another for deriving an output signal
representative of overall increases in the length of said drill
string upon further advancement of said drill bit into said earth
formations and combining said first and second signals with said
third signal upon each occurrence of said third signal for
selectively discontinuing further transmission of said output
signal and then algebraically summing said combined signals only so
long as the summation of further length increases respectively
represented by subsequently-occurring first and second signals is
less than the summation of further length decreases represented by
subsequently-occurring third signals.
14. The method of claim 13 wherein said incremental length changes
are determined by measuring incremental changes in tensional forces
imposed on said drill string, and multiplying said incremental
force changes by a co-efficient representative of the rate of
elongation and said overall length of said drill string.
15. The method of claim 13 further including the step of: averaging
said output signal over a selected time interval for determining
the rate of penetration of said drill bit during said selected time
interval.
16. The method of claim 13 further including the step of:
totalizing said output signal over a selected time interval for
determining the total downward advancement of said drill bit during
said selected time interval.
17. A method for determining the rate of penetration into earth
formations by a drill bit suspended from a drill string in a
borehole penetrating said earth formations and comprising the steps
of: successively determining the incremental lengths of said drill
string moved into and out of said borehole from the surface during
a selected time interval while said drill bit is drilling into said
earth formations for alternatively deriving either a first signal
proportional to successive increases in the overall length of said
drill string in said borehole during said selected time interval or
a second signal proportional to successive decreases in the overall
length in said borehole during said selected time interval;
successively determining the incremental changes in the overall
length of said drill string due to variations in tensional forces
acting thereon during said selected time interval for alternatively
deriving either a third signal proportional to successive
elongational increases in the overall length of said drill string
during said selected time interval or a fourth signal proportional
to successive contractional decreases in the overall length of said
drill string during said selected time interval; alternatively
combining said first and third signals with one another for
deriving an output signal representative of overall increases in
the length of said drill string upon further advancement of said
drill bit into said earth formations during said selected time
interval and combining said first and third signals with said
second and fourth signals upon each occurrence of either of said
second and fourth signals for selectively discontinuing
transmission of said output signal and then algebraically summing
said combined signals only so long as the summation of further
length increases respectively represented by subsequently-occurring
first and third signals is less than the summation of further
length decreases represented by subsequently-occurring second and
fourth signals; and averaging said output signal over said selected
time interval for determining the rate of penetration of said drill
bit during said selected time interval.
18. The method of claim 17 further including the step of:
totalizing said output signal over said selected time interval for
determining the total downward advancement of said drill bit during
said selected time interval.
19. A method for determining the rate of advancement into earth
formations by a drill bit suspended from a drill string in a
borehole penetrating said earth formations and comprising the steps
of: successively measuring the incremental displacements of the
surface end of said drill string in relation to said borehole for
alternatively producing either a series of first electrical pulses
respectively corresponding to an incremental increase to the length
of said drill string in said borehole or a series of second
electrical pulses respectively corresponding to an incremental
decrease in the length of said drill string; successively measuring
the incremental changes in tensional forces acting on said drill
string while said drill bit is drilling into said earth formations
and converting said force changes to corresponding increments of
length for alternatively producing either a series of third
electrical pulses respectively corresponding to an incremental
elongation of said drill string or a series of fourth electrical
pulses respectively corresponding to an incremental contraction of
said drill string; comparing the total of said first and third
electrical pulses occurring during a time interval following the
occurrence of one of said second or fourth electrical pulses with
the total of said second and fourth electrical pulses occurring
during said time interval; once the total of said first and third
electrical pulses counted during said time interval equal the total
of said second and fourth electrical pulses counted during said
time interval, producing a series of output pulses respectively
corresponding to a net incremental increase in the overall length
of said drill string until another one of said second or fourth
electrical pulses occur; and successively converting said output
pulses to a signal representative of the rate of downward
advancement of said drill bit into said earth formations during a
selected time interval.
20. The method of claim 19 further including the step of:
totalizing said output pulses for providing an indication of the
actual depth of said drill bit in said borehole.
21. Apparatus adapted for determining the rate of penetration into
earth formations by a drill bit suspended from a drill string in a
borehole penetrating such formations and comprising:
displacement-responsive means adapted for producing first signals
representative of a downward movement of an incremental length of a
drill string into a borehole during a drilling operation;
elongation-responsive means adapted for alternatively producing
either second signals representative of incremental elongations of
the overall length of a drill string in a borehole during a
drilling operation or third signals representative of incremental
contractions of the overall length of a drill string in a borehole
during a drilling operation; processing means operatively coupled
to said displacement-responsive means and to said
elongation-responsive means and adapted to respond to said signals
produced thereby for alternatively combining said first and second
signals for providing output signals representative of incremental
increases in the overall length of a drill string in a borehole
during a drilling operation in the absence of said third signals
during a selected time interval or combining said first and second
signals with said third signals upon each occurrence thereof during
said selected time interval for discontinuing further transmission
of said output signals until the algebraic summation of further
incremental length increases represented by subsequently-occurring
first and second signals equals further incremental length
decreases represented by subsequently-occurring third signals; and
converting means operatively coupled to said processing means and
adapted to respond to said output signals for providing at least
one indication representative of the rate of penetration into earth
formations by a drill bit while drilling a borehole during said
selected time interval.
22. The apparatus of claim 21 further including: totalizing means
operatively coupled to said processing means and adapted to respond
to said output signals for providing signals representative of the
actual depth of such a drill bit in a borehole during said selected
time interval.
Description
It will be appreciated by those skilled in the art that it is of
considerable importance to know the actual rate at which the drill
bit is penetrating the earth formations during the course of a
typical well drilling operation. For example, if this so-called
"rate of penetration " can be measured with reasonable accuracy,
the influence of controlled variables (such as the rotational speed
and the weight imposed on the drill bit) on the rate of penetration
can be determined thereby enabling optimum drilling rates to be
maintained. Various proposals have, of course, been advanced
heretofore for hopefully determining the actual rate of penetration
by making one or more surface measurements. For example, one common
technique is to arrange a transducer which is responsive to the
longitudinal movements of the drill string in relation to the rig
floor for producing electrical signals which are representative of
the displacement rate of the drill string at the surface.
It will be recognized, however, that the displacement rate of the
upper portion of the drill string at the surface will rarely, if
ever, simultaneously correspond to the actual rate of penetration
of the drill bit. For example, it has been found that one of the
paramount reasons why the actual rate of penetration of a drill bit
cannot be accurately determined by simply measuring the
displacement rate of the upper portion of the drill string is that
the drill string is constantly elongating or contracting in
response to the constantly-changing longitudinal or tensional
forces which are imposed on the drill string during the course of a
drilling operation.
By way of explanation, the usual practice in drilling a well is to
arrange one or more drill collars in the drill string just above
the drill bit for imposing a downward force on the drill bit which
is no more than the combined weight of the drill collars and to
employ a series of tandemly-coupled joints of drill pipe for the
remainder of the drill string extending to the surface. To prevent
buckling of the drill pipe in the string, an upward force or
so-called "hook load" is typically maintained on the surface end of
the drill string to assure that the drill pipe is always in
tension. By observing a so-called "weight indicator" operatively
coupled to the surface end of the drill string, this upward force
is maintained within a predetermined range which is somewhat less
than the total weight of the drill string but at least slightly
greater than the total weight of the drill pipe in the drill string
so that at least some -- if not a major portion -- of the total
weight of the drill collars will always be imposed on the drill bit
during the drilling operation to achieve a desired "weight on
bit".
A typical drilling procedure is to set the drill bit on the bottom
of the borehole after an additional joint of drill pipe has been
coupled to the upper end of the drill string, impose a selected
minimum upward force on the drill string which is within the
aforementioned range of forces, and then resume rotation of the
drill string to continue the drilling operation without
concurrently lowering the drill string. Thus, as the drill bit
successively excavates the borehole, the drill string will be
progressively elongated which concurrently reduces the downward
force acting on the drill bit (weight on bit) and increases the
upward force acting on the surface end of the drill string (hook
load). Once the surface measurements indicate that this upward
force has reached a selected maximum corresponding to a desired
minimum downwardly-acting force on the drill bit, the drill string
is lowered to again reduce the upward force on the drill string to
the aforementioned selected minimum value. It will be appreciated,
therefore, that the forces acting on the surface end of the pipe
will be successively increased from this selected minimum force to
the selected maximum force and then reduced as the cycle is
repeated.
As a result, it will be recognized that the drill string is
constantly subjected to varying tension forces which cause the
drill string to be correspondingly elongated. The degree of
elongation is, however, not at all inconsequential. For example,
with a drill string composed substantially of 10,000-feet of a
typical 4 1/2 -inch diameter drill pipe, tension forces in the
order of 140,000-lbs. are not at all uncommon. Moreover, if this
force is varied only 1,000-lbs. for a period of only 1-minute, it
can be shown that the difference between the actual rate of
penetration of the drill bit and the rate of displacement in the
drill string as measured at the surface will be in the order of
5-feet/hour. This would, of course, represent a serious error since
drilling rates are commonly as low as 2 to 3-feet/hour; and an
error of this magnitude would obviously preclude accurate control
of the drilling operation.
Accordingly, it is an object of the present invention to provide
new and improved methods for accurately determining from surface
measurements the rate of penetration of a drill bit while drilling
a borehole.
Another object of the invention is to provide new and improved
apparatus for measuring the instantaneous drilling rate of a
borehole after eliminating movements of the drill string which do
not correspond to the actual drilling through the formations.
These and other objects of the present invention are attained by
providing methods and apparatus for measuring the changes in the
elongation of the drill string in the borehole; measuring the
incremental lengths of the drill string being moved into the
borehole from the surface during a drilling operation; and, after
combining these two measurements, converting them in such a manner
as to derive information at the surface which is representative of
the actual rate of penetration of the drill bit .
The novel features of the present invention are set forth with
particularity in the appended claims. The invention, together with
further objects and advantages thereof, may be best understood by
way of the following description of exemplary apparatus and methods
employing the principles of the invention as illustrated in the
accompanying drawings, in which:
FIG. 1 shows a typical drilling rig including new and improved
apparatus according to the invention;
FIG. 2 is a block diagram of a preferred embodiment of new and
improved apparatus arranged in accordance with the present
invention and especially adapted for practicing the methods of the
invention; and
FIG. 3 depicts a portion of the unique circuit shown in FIG. 2.
Referring to FIG. 1, a typical rotary drilling rig 10 is shown with
a crown block 11 over which runs a cable 13 driven by a draw works
18 adapted for operatively controlling the upward and downward
movements of a traveling block 12. The traveling block 12 carries a
hook 14 from which is suspended a rotary swivel 15 supporting a
drill string 16 comprised of a number of tandemly-coupled joints of
drill pipe and drill collars. As is typical, the drill string 16
carries a drill bit 17 at its lower end and is dependently
supported at its upper end from a kelly joint 20 which is
rotatively driven by a rotary table 21 on the rig floor. Drilling
mud is delivered to the drill string 16 in the usual fashion by a
mud hose 23 coupled in the usual fashion to the swivel 15.
To practice the new and improved methods of the present invention
with the drilling rig 10, it will be appreciated that downward
movements of the drill bit 17 resulting in further excavation of
the borehole are substantially achieved by moving the surface end
of the drill string 16 downwardly as by lowering the traveling
block 12. As previously described, however, the drill string 16 is
constantly subjected to significant tensional forces which
continuously vary during the course of a drilling operation. Since
these tensional forces are typically of substantial magnitude and
the drill string 16 usually has a considerable length, it has been
found that the accurate determination of the actual rate of
penetration of the drill bit 17 requires that the resulting
variations in the overall length of the drill string caused by its
elongation and contraction under these changing tensional forces be
taken into account.
Measurements of the vertical displacement of the drill string 16
are, of course, best measured at the surface. Various techniques
for making these measurements are known to those skilled in the
art. To determine the changes in the overall length of the drill
string 16 caused by variations in the tensional forces acting on
the drill string, these varying forces can be measured at any place
in the drill string such as, for example, by conventional strain
gages. It should also be noted that since the total weight of the
drill string 16 is equal to the summation of the aforementioned
"hook load" (typically measured at the surface) and the
aforementioned "weight on bit" (typically measured downhole), a
change in either of these two forces will be representative of a
change in the tensional forces acting on the drill string.
In the preferred manner of practicing the present invention during
the course of a drilling operation, a series of measurements are
continuously obtained for successively producing a series of first
signals which are representative of the incremental vertical
displacements of the surface end of the drill string 16.
Simultaneously therewith, another series of measurements are
continuously obtained which are representative of incremental
changes in tensional forces acting on the drill string 16. These
latter measurements are successively converted by a predetermined
factor which is functionally related to the total length of the
drill string 16 and its coefficient of elongation for successively
producing a series of second signals which are representative of
the incremental elongational changes in the overall length of the
drill string. Thereafter, the first and second signals are combined
to obtain a series of successive third signals which are
representative of the net downward incremental distances traveled
by the drill bit 17 during the measuring period. By determining the
rate of these successive combined signals, indications of the
actual rates of penetration of the drill bit 17 are continuously
provided at the surface. Moreover, by continuously totaling these
combined third signals, indications of the total distance traveled
by the drill bit 17 into the formations during the measured period
are also presented at the surface.
In keeping with the objects of the present invention, apparatus is
provided for producing a series of first signals which are
representative of the direction as well as incremental vertical
displacements of the drill string 16 during the course of a
drilling operation with the drilling rig 10. Accordingly, in the
preferred embodiment of the present invention,
displacement-responsive transducer means 24 are placed on top of
the drilling rig 10 and operatively associated with one of the
pulleys in the crown block 11 to respond to the rotation of the
pulley for successively producing a series of first electrical
signals which are representative of the direction as well as the
incremental distances traveled by the surface end of the drill
string 16. As will be subsequently explained, the output signals
from the displacement transducer 24 are transmitted by means such
as a suitable electrical cable 25 to a new and improved signal
processing and recording unit 26. Furthermore, in the preferred
embodiment of the present invention, elongation-responsive means
including a force-responsive transducer 27 coupled between the
swivel 15 and the kelly 20 are operatively arranged for
successively producing a series of second electrical signals which
are representative of incremental changes in the length of the
drill string 16.
Turning now to FIG. 2 showing the preferred embodiment of the
present invention, the displacment-responsive transducing means 24
are illustrated as including a lamp 31 directed toward one side of
a rotatable disk 32 having a series of either peripheral notches or
alternately transparent and opaque zones spaced around the rim of
the disk. When the disk 32 is rotatively driven by the crown block
pulley 11, the light from the lamp 31 periodically strikes a
photodiode 33 arranged on the other side of the disk for producing,
at an output X, a train of successive pulses at a frequency or
pulse rate which is proportional to the rotational speed of the
disk. In a similar fashion, a second photodiode 34 is arranged on
the other side of the disk 32 for producing, at an output Y, a
second train of pulses having the same frequency or pulse rate as
the first train but which are phase-shifted 90.degree. in relation
thereto. it will be appreciated, therefore, that the second pulse
train either leads or lags the first pulse train depending upon the
rotational direction of the disk 32.
The photodiodes 33 and 34 are linked via the cable 25 to a typical
directional logic circuit 35 which is included in the processing
and recording unit 26. This circuit 25, which may include a shaping
input circuit, is well known by those skilled in the art and is
cooperatively arranged for generating a series of positive pulses,
+V.sub.s, when the disk 32 rotates in one selected direction and a
series of negative pulses, -V.sub.s, when the disk 32 rotates in
the other direction. Thus, as a matter of choice, the circuit 35 is
arranged so that a downward movement of the drill string 16 will
produce a corresponding series of positive pulses, +V.sub.s, and an
upward movement of the string will conversely produce a
corresponding series of negative pulses, -V.sub.s, with each pulse
being representative of a selected increment of length. It will be
seen, therefore, that the signals, +V.sub.s and -V.sub.s, are
alternative output signals from the logic circuit 35, with the
number of these pulses being representative of the total distance
traveled by the upper portion of the drill string 16 and their
frequency or pulse rate being respectively proportional to the rate
of travel or vertical displacement of the drill string at the
surface. The polarity of these pulses will, of course, indicate the
direction of travel.
In the preferred embodiment of the present invention, the
transducer 27 coupled to the upper part of the drill string 16 is
comprised of a strain gage bridge 38 whose opposite ends are
connected to the input of an amplifier 36. The bridge 38 is
thermally compensated to minimize its residual drift thereby making
it possible to accurately measure small variations in the tension
forces acting on the drill string 16. In the preferred embodiment
of the transducer 27, the bridge 38 is arranged so that the maximum
drift will be in the order of only 10-kilograms/minute. With a
minimal drift of this order, weight variations of only about
33-kilograms over a period of 1-minute can be sensed by the bridge
38 to provide an accuracy of about 0.1-meters/hour in measuring the
rate of penetration of the drill bit 17.
The output signal, W, of the amplifier 36 is coupled by the cable
28 to a weighting circuit 37 comprised, for example, of a variable
resistor 40 for multiplying the output signal, W, of the amplifier
36 by a selected coefficient, K, which is a function of the
elasticity of the drill pipe in the drill string 16.
By virtue of Hooke's Law, it will be recognized that the
coefficient, K, is determined by dividing the total length of the
drill pipe in the drill string by the product of the transverse
cross-sectional metal area and the modulus of elasticity of this
drill pipe. Thus, by multiplying the force, W, sensed by the
transducer 27 by the coefficient, K, the variations in the
resulting signal, KW, will be representative of the changes in the
elongation of the drill string 16 which are produced by variations
in the tension force, W. It will, of course, be realized that
should different types of drill pipe be coupled into the drill
string 16, the coefficient, K, will be determined by simply adding
the individual coefficients calculated for each type of drill pipe
included in the string 16 so as to provide an overall or a
composite value for the coefficient, K, for producing the signal,
KW. It should also be noted that since only a minor portion of the
overall length of the drill collars in the drill string 16 will be
in tension and since these drill collars are also relatively stiff
in relation to the drill pipe in the string, the coefficient, K,
may be safely determined without considering the drill collars.
The potentiometer 40 is, of course, selected to provide the maximum
anticipated value of the coefficient, K, when the movable contact
is at the ungrounded end of the resistance element. Thus, for
lesser values of K, the movable contact will be selectively set at
an appropriate intermediate portion on the resistance element of
the potentiometer 40. Although the potentiometer 40 theoretically
requires repositioning each time an additional joint of drill pipe
is coupled into the string 16, it has been found that as a
practical matter sufficiently-accurate measurements are obtained in
the practice of the present invention by readjusting the
potentiometer at only infrequent intervals. For example, when the
drill bit 17 is drilling in hard formations, adjustments of the
potentiometer 40 may be made only once every 12 to 24-hours since
drilling speeds are typically so low in such formations that the
overall length of the drill string 16 is not significantly
increased in such a time interval.
The output of the weighting circuit 37 is coupled to the input of a
quantized differentiating circuit 41 which, as will subsequently be
described in more detail in relation to FIG. 3, is operatively
arranged for producing a series of output signals which are
proportional to incremental changes in the overall length of the
drill string 16 caused by the elongation and contraction of the
drill string. In the preferred embodiment of the present invention,
this is accomplished by comparing the signals, KW, with two
comparison signals, +S and -S, of opposite polarity and
respectively having a selected magnitude of an equal value. The
magnitude of these comparison signals is selected so that the
differentiating circuit 41 will produce alternative series of
output pulses, +V.sub.a or -V.sub.a, having a pulse rate or
frequency which is representative of the rate of change in
elongation of the drill string, with each pulse being
representative of a selected incremental unit of change in length
of the drill string 16. In this manner, the positive output pulses,
+V.sub.a, from the differentiating circuit 41 will be successively
produced in response to incremental elongations of the drill string
16 and the negative output pulses, -V.sub.a, will be successively
produced in response to incremental contractions of the drill
string.
Accordingly, as described to this point, it will be appreciated
that the new and improved apparatus of the present invention
includes displacement-responsive means (as exemplified by the
transducer 24 and the logic circuit 35) operatively arranged for
producing a first series of output pulses, either +V.sub.s or
-V.sub.s, which are respectively related to a selected incremental
length of the drill string 16 which has been moved either
downwardly or upwardly in relation to the rig floor. The frequency
or pulse rate of the first series of pulses, +V.sub.s and -V.sub.s,
will be proportional to the rate of travel of the drill string 16
and the polarity of the pulses will indicate the direction of the
movement. Moreover, the elongation-responsive means of the present
invention (as exemplified by the circuit 42) are adapted for
producing a second series of output pulses, either +V.sub.a or
-V.sub.a, which are respectively related to incremental
elongational changes in the overall length of the drill string 16.
The frequency or pulse rate of these second pulses will be
proportional to the rate of the change of the overall length of the
drill string 16; and their polarity will indicate whether the
overall length of the string has been increased or decreased.
It will be recognized that the drill bit 17 will be penetrating an
earth formation only upon downward movements of the drill bit
whether these movements are caused by further elongation of the
drill string 26, an actual downward movement or displacement of the
drill string at the surface, or a combination of these two
movements. Moreover, it should be appreciated that the actual
displacement movements of the drill string 16 are independent of
the elongational changes of the drill string. For example, as
previously explained, the usual drilling practice is to
periodically retain the upper end of the drill string 16 at a
selected position in relation to the rig floor and allow it to
further elongate as the drill bit 17 continues to deepen the
borehole. Conversely, as the drill string 16 is periodically
lowered to increase the weight imposed on the drill bit 17, the
drill string will be contracted as the tensional forces acting
thereon are correspondingly reduced. In this latter situation, it
will be recognized that the downward travel of the drill string 16
will be partially offset by the attendant relaxation of the drill
string so that during this time the actual rate of penetration of
the drill bit 17 will be correspondingly less than the rate of
downward travel of the surface end of the drill string.
In keeping with the objects of the present invention, therefore,
the new and improved apparatus disclosed in FIG. 2 is further
arranged for combining the aforementioned signals, V.sub.s and
V.sub.a, and then converting the combined signals for providing
accurate indications at the surface which are representative of the
actual rate of penetration of the drill bit 17. To accomplish this,
the positive signal outputs of the displacement-responsive means
and the elongation-responsive means are respectively coupled to the
inputs of an OR gate 48 for producing a series of positive output
pulses, +V.sub.d, in response to the generation of either positive
displacement pulses, +V.sub.s, or positive elongation pulses,
+V.sub.a, or both. Similarly, the negative signal outputs of the
displacement-responsive means and the elongation-responsive means
are respectively coupled to the inputs of an OR gate 49 for
producing a corresponding series of negative output pulses,
-V.sub.d, in response to the generation of either or both of the
negative pulses, -V.sub.s and -V.sub.a.
To prevent the displacement-responsive pulses, +V.sub.s or
-V.sub.s, from being masked by the elongation-responsive pulses,
+V.sub.a or -V.sub.a, the circuits supplying these pulses to the
gates 48 and 49 are respectively designed to generate very short
pulses thereby reducing the probability that two of these pulses
may appear simultaneously at the inputs of the gates 48 and 49.
Thus, in the preferred embodiment of the present invention, shaping
circuits such as monostable multivibrators or one shots 43 and 44
are added to the outputs of the logic circuit 35 to minimize the
duration of the pulses, +V.sub.s and -V.sub.s. It will also be
noted that instead of being alternative signals as are the signals,
+V.sub.s and -V.sub.s or +V.sub.a and -V.sub.a, the combined
signals, +V.sub.d and -V.sub.d, may simultaneously appear at the
outputs of the OR gates 48 and 49.
As previously mentioned, the actual rate of penetration of the
drill bit 17 is decreased by contractions of the drill string 16 in
response to decreases of the tensional forces acting thereon as
well as by any upward movements of the drill string. Conversely,
the actual rate of penetration of the drill bit 17 is increased
both by downward movements as well as by further elongations of the
drill string 16. Accordingly, the output signals, +V.sub.d and
-V.sub.d, from the OR gates 48 and 49 are respectively supplied to
the addition and subtraction inputs of a typical reversible counter
46 such as shown in French Pat. No. 1,541,771. For reasons that
will subsequently be explained, the outputs of the OR gates 48 and
49 are respectively coupled to the counter 46 by way of AND gates
47 and 45 which, as far as is necessary for understanding the
present invention to this point, are both always operatively
enabled so that as long as the drilling operation is actually
progressing the V.sub.d signal will be applied to the counter for
algebraic summation.
As illustrated in FIG. 2, the +V.sub.d signals from the AND gate 47
are simultaneously supplied to one input of an AND gate 50 having
its output coupled to the addition input of the counter 46 as well
as to one input of an AND gate 51. The output stages of the counter
46 are connected to an OR gate 52 whose output is connected, on the
one hand, to the other input of the AND gate 50, on the other hand,
to an inverter 53. The output of the inverter 53 is connected to
the second input of the AND gate 51. When the counter 46 is in a
"zero" state, the output signal of the OR gate 52 is a zero signal
which inhibits the AND gate 50 and enables the AND gate 51. For all
other states of the counter 46, the AND gate 51 is inhibited, the
pulses +V.sub.d then being applied to the input of the counter for
summation.
It will be seen, therefore, that the circuit 54 including the
counter 46, the operatively-arranged gates 50-52, and the inverter
53 is responsive to the displacement signals, +V.sub.d and
-V.sub.d, for providing a third signal, V.sub.p, only when there is
a downward advancement of the drill bit 17 during a drilling
operation as a result of either downward displacement of the drill
string 16 at the surface or an elongation or increase in the
overall length of the drill string. On the other hand, the circuit
54 is cooperatively arranged so that an upward displacement of the
drill string 16 will discontinue the production of further output
pulses, V.sub.p , until the drill bit 17 is again at its previous
lowermost depth to continue further excavation of the borehole.
By way of explanation, it will be appreciated that each time there
is either an incremental upward movement of the drill string 16 at
the surface (-V.sub.s) or an incremental shortening of the drill
string (-V.sub.a), the OR gate 49 will always supply a negative
pulse, -V.sub.d, directly to the subtracting input of the counter
46. Similarly, each time the OR gate 48 supplies a positive pulse,
+V.sub.d, representative of either an incremental downward movement
or an incremental lengthening of the drill string 16, the OR gate
52 is selectively responsive to the present state of the counter 46
for either directing the positive pulse to the adding input of the
counter or for producing a pulse, V.sub.p, at the output of the
gate 51. For example, assume that the drill bit 17 has been
steadily moving downwardly so that the output of the OR gate 52 is
a zero signal signifying that the counter 46 is in a "zero" state.
The OR gate 52 will, therefore, inhibit the AND gate 50 and enable
the AND gate 51 so that each positive pulse, +V.sub.d, at the input
of the circuit 54 will simultaneously produce an output pulse,
V.sub.p, at the output of the circuit 54. Under this situation, a
continuation of positive input pulses, +V.sub.d, will produce a
corresponding series of output pulses, V.sub.p, having the same
pulse rate.
A single negative input pulse, -V.sub.d, signifying either a
shortening of the drill string 16 or an upward movement of the
drill string at the surface will, however, be applied to the
subtracting input of the counter 46 to produce an output signal
from the OR gate 52 which is representative of the counter being in
a negative or "non-zero" state. The OR gate 52 then inhibits the
AND gate 51 to discontinue further production of the output
signals, V.sub.p, until the counter 46 is again in a "zero" state
and concurrently enables the AND gate 50 to direct subsequent
positive input pulses, +V.sub.d, to the adding input of the
counter.
It will be appreciated, therefore, that the continuation of
negative input pulses, -V.sub.d, will maintain the condition of the
circuit 54 and no output signals, V.sub.p, will be produced which
is, of course, representative of no advancement of the drill bit 17
and a zero rate of penetration. On the other hand, assume that this
situation was in response to either a momentary elevation of the
drill string 16 at the surface or a brief reduction in the tension
load sensed by the strain gage 38 causing the drill string to
shorten, once either a downward movement or a lengthening of the
drill string occurs to produce a positive input pulse, +V.sub.d,
this positive pulse will be directed to the counter 46 to place it
into a less-negative state. Thus, once the number of positive
pulses, +V.sub.d, which are directed by the AND gate 50 to the
counter 46 equals the number of negative pulses, -V.sub.d,
previously stored in the counter, the counter is again placed in a
"zero" state and the AND gates 50 and 51 are again respectively
inhibited and enabled by the zero output signal of the OR gate 52.
It should be noted that the delay of this circuitry will prevent
the final positive pulse, +V.sub.d, re-enabling the AND gate 51
from producing an output pulse, V.sub.p. Once the counter 46 is
restored to its "zero" state, the output pulses, V.sub.p, will
again be produced by the circuit 54 in response to the subsequent
input pulses, +V.sub.d.
It should be noted that the counter 46 needs only to have a
sufficient number of stages for storing a displacement equal to the
vertical distance over which the traveling block 12 is capable of
moving in relation to the floor of the rig 10 since it is not
necessary to totalize movments of the drill string 16 over any
greater distance above the bottom of the borehole. A manual reset
55 is provided for resetting the counter 46 when drilling is to be
resumed such as, for example, after a trip for changing the drill
bit 17 or when the system 26 is to be energized.
Inasmuch as the frequency or pulse rate of the pulses, V.sub.p, is
proportional to the actual rate of penetration, circuit means 56
are provided for converting the frequency of these pulses to an
indication or record of the rate of penetration of the drill bit 17
during the course of a drilling operation. In the preferred manner
of accomplishing this, the circuit means 56 include a
frequency-to-voltage converter which is comprised of a monostable
or one-shot circuit 57 followed by a low-pass filter 60 designed to
cover the anticipated frequency or pulse rate output range of the
pulses, V.sub.p. It will, of course, be appreciated that the
low-pass filter 60 will cooperate to provide an output signal which
is the average of the instantaneous drilling speed. Thus, for
providing a record of the rate of penetration of the drill bit 17
as a function of time, the output of the frequency-to-voltage
converter 56 is coupled to a time recorder 64. To provide a record
of total depth as a function of time, the output pulses, V.sub.p,
are also coupled to the time recorder 64 by means such as a pulse
divider 61 for printing a mark on the recording medium each time
the drill bit 17 has drilled an incremental depth corresponding to
the predetermined distance assigned to each pulse.
It will also be recognized that the summation of the number of
output pulses, V.sub.p, is also representative of the total depth
of the borehole as drilled at that time. Accordingly, to provide
visual indications or a continuous record of the rate of
penetration versus depth during the course of a drilling operation
with the drill rig 10, the output pulses, V.sub.p, are also
employed for operating a stepping motor 62 which drives a recorder
63 to which the output of the converter 56 is coupled. If a rate of
penetration indicator, as at 65, is desired, it can also be coupled
to the output of the converter 56 for providing an instantaneous
indication at some convenient location on the surface of the
present application rate of the drill bit 17.
It will be recognized that when another joint of pipe is added to
the drill string 16, the kelly 20 is temporarily disconnected and
the drill string is suspended by slips placed in the rotary table
21. Various movements of the traveling block 12 are, of course,
then employed in adding another joint of pipe to the drill string
16. Accordingly, to temporarily block the counter 46, a comparator
66 is coupled to the inputs of the AND gates 45 and 47. The inputs
of the comparator 66 are respectively connected to a reference
voltage source 67 and to the output of the amplifier 36. Thus, when
the weight sensed by the elongation-responsive means 27 is less
than a predetermined value, the comparator 66 then functions to
inhibit the AND gates 45 and 47 for temporarily blocking the
counter 46. The reference voltage is preferably chosen so that this
blocking occurs at the moment when the tension measurement of the
bridge 38 indicates that the drill string 16 has been placed on the
slips. When the drill string 16 is again suspended from the
traveling block 12, the AND gates 45 and 47 are re-enabled and the
counter 46 then resumes its operation.
Referring to FIG. 3, a preferred embodiment of the quantized
differentiating circuit 41 is shown in greater detail. The output
signal, KW, of the weighting circuit 37 is applied to one input of
a differential amplifier 70 having its output connected to one of
the inputs of each of two comparators 71 and 72. As will
subsequently be explained, equal voltages, +S and -S, of opposite
polarity are each coupled to the other of the inputs of the two
comparators 71 and 72 and the outputs of the comparators are
respectively connected to the "set" and "reset" terminals of a
bistable multivibrator 73 consisting, for example, of two
operatively-interconnected NAND gates 74 and 75. The outputs of the
comparators 71 and 72 are also coupled to a NAND gate 76 which is
connected to the control terminal of a multivibrator 77. The
multivibrator 77 is connected to one of the inputs of each of the
two AND gates 80 and 81 having their other inputs respectively
coupled to the forward and reverse outputs of the bistable
multivibrator 73. The outputs of the AND gates 80 and 81 which
supply the output pulses, +V.sub.a and -V.sub.a, of the
differentiator 41, are respectively coupled to the adding and
subtracting terminals of a reversible counter 82 whose output
states are in turn connected to a binary-to-analog converter 83
which operatively supplies a control or feedback signal to the
second input of the differential amplifier 70.
In operation, an increase in the input signal, KW, greater than the
+S signal is detected by the comparator 71 which is operative for
triggering the multivibrator 77 as well as setting the bistable
multivibrator 73 for enabling the AND gate 80 and inhibiting the
AND gate 81. A series of output pulses, +V.sub.a, are generated by
the multivibrator 77 and supplied to the addition input of the
counter 82, with each pulse being representative of an incremental
increase in length of the drill string 16 as established by the
conversion factor of the D/A converter 83. As the contents of the
counter 82 increase and are transformed into corresponding analog
signals by the D/A converter 83, the proportionally-decreasing
output signal of the differential amplifier finally becomes less
than the +S signal, and the comparator 71 is then operative for
inhibiting the multivibrator 77 to discontinue further production
of the output pulses, +V.sub.a. The operation of the circuit 41 is
similar for a decrease in the amplitude of the input signals, KW,
except that -V.sub.a output pulses will appear at the subtraction
input of the counter 82.
Accordingly, it will be appreciated that the present invention has
provided new and improved methods and apparatus for providing
surface measurements of the actual rate of penetration of a
drilling bit during the course of a drilling operation. As
previously described, these new and improved methods and apparatus
are uniquely arranged for accurately determining the distance
traveled downwardly by the drill string and the increases in its
overall length. By combining and then converting the combined
measurements, instantaneous indications are provided at the surface
which are representative of the true rate of penetration of the
drill bit.
While only a particular embodiment of the present invention and one
mode of practicing the invention have been shown and described, it
is apparent that changes and modifications may be made without
departing from this invention in its broader aspects; and,
therefore, the aim in the appended claims is to cover all such
changes and modifications as fall within the true spirit and scope
of this invention.
* * * * *