U.S. patent number 3,872,932 [Application Number 05/408,261] was granted by the patent office on 1975-03-25 for process and apparatus for automatic drilling.
This patent grant is currently assigned to Institut Francais du Petrole des Carburants et Lubrifiants. Invention is credited to Jean-Charles Gosselin.
United States Patent |
3,872,932 |
Gosselin |
March 25, 1975 |
PROCESS AND APPARATUS FOR AUTOMATIC DRILLING
Abstract
The process comprises progressively increasing the weight on the
drill bit, determining the greatest value of the penetration rate
of the drill bit during this period, progressively decreasing the
weight on the drill bit when the penetration rate has reached a
determined value and again progressively increasing the weight on
the drill bit when the tension on the drill pipe has reached a
fixed value. The passage from a period during which this weight
decreased and vice-versa is achieved by varying the linear speed of
the drill pipe at the ground surface, whereby the tension on the
drill pipe is varied.
Inventors: |
Gosselin; Jean-Charles
(Versailles, FR) |
Assignee: |
Institut Francais du Petrole des
Carburants et Lubrifiants (Rueil-Malmaison, FR)
|
Family
ID: |
23615545 |
Appl.
No.: |
05/408,261 |
Filed: |
October 23, 1973 |
Current U.S.
Class: |
173/1; 173/6;
175/26; 175/103 |
Current CPC
Class: |
E21B
44/005 (20130101); E21B 19/22 (20130101); E21B
19/08 (20130101) |
Current International
Class: |
E21B
19/22 (20060101); E21B 19/00 (20060101); E21B
19/08 (20060101); E21B 44/00 (20060101); E21b
003/12 () |
Field of
Search: |
;173/1,4,6
;175/27,40,57 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Leppink; James A.
Attorney, Agent or Firm: Craig & Antonelli
Claims
What I claim is:
1. A process for automatically optimizing the penetration rate of a
drill bit suspended from drill pipe, said drill bit being driven in
rotation by a motor whose torque decreases with an increasing of
its rotation speed, and said drill bit having a penetration rate
which, as a function of the weight exerted on the drill bit,
reaches a maximum value for an optimum value of the weight, said
process comprising
measuring the tension on the drill pipe,
periodically determining the penetration rate of the drill bit,
automatically adjusting the linear speed of the drill pipe at the
ground surface so as to provide values of the linear speed which
are successively greater and lower than the rate of penetration of
said drill bit into the ground, the variation in linear speed
causing alternatively a decrease and an increase in the tension on
the drill pipe, thereby producing an oscillation in the value of
the weight on the drill bit about the optimum value of said weight,
wherein during each period when the linear speed at the surface is
greater than the penetration rate, said penetration rate is
periodically determined and the highest value thereof is
recorded,
effecting a transition from said period when said linear speed is
greater than the penetration rate to a second period during which
the linear speed at the surface is lower than the penetration rate
when said penetration rate has reached a preselected value, and
effecting a transition to another period wherein the linear speed
at the surface has a greater value than the penetration rate when
the tension on the drill pipe reaches a preselected limit-value,
said tension increasing to said preselected limit-value.
2. A process according to claim 1, wherein a pulsing period is
effected by an operating parameter of the drilling process, and
wherein each determined value of the penetration rate and each
measured value of the tension are average values determined over a
time interval to said pulsing period.
3. A process according to claim 2, wherein said operating parameter
is the drilling fluid pressure.
4. A process according to claim 2, making use of a substantially
rigid drill pipe, wherein said operating parameter is an angle of
rotation of the drill pipe.
5. A process according to claim 1, wherein said limit-value of the
tension on the drill pipe is determined as a function of the value
of the tensile stress in the drill pipe when the penetration rate
reaches said recorded highest value.
6. A process according to claim 1, comprising recording the value
of the tension on the drill string which corresponds to said
highest value of the penetration rate and determining said limit
value of the tension as a function of said value of the tension
corresponding to said recorded highest value of the penetration
rate.
7. A process according to claim 1, wherein the linear speed of the
drill pipe is set up at such a value that a difference exists
between said linear speed and the penetration rate of the drill
bit, this difference being selected as a function of the value of
the penetration rate and of the values of parameters which
characterize the drilling operation.
8. An apparatus for automatically optimizing the penetration rate
of a drill bit located at the lower end of a drill pipe, said drill
bit being driven in rotation by a motor whose torque decreases with
increasing rotation speed and having a penetration rate which, as a
function of the load applied thereon, reaches a maximum value for
an optimum value of this load, this apparatus comprising means for
measuring the tension exerted on the drill pipe, means for
evaluating the successive values of the penetration rate and
control means for sequentially performing a progressive increase
and a progressive decrease of the load on the drill bit, analyzing
means connected to said means for evaluating the penetration rate
and adapted to determine and record during each period of
increasing load the highest value detected by said evaluating
means, first actuating means operatively connected to said control
means, to said evaluating means and to said analyzing means, said
first actuating means elaborating a first limit-value as a function
of said highest value recorded by said analyzing means and
initiating a decrease in the load exerted on the weight, when the
penetration rate reaches, while decreasing, said first limit value
and second actuating means operatively connected to said control
means, said second actuating means elaborating a second limit-value
and initiating an increase in the load exerted on the drill bit
when the tension on the drill pipe has reached, while increasing,
said second limit value.
9. An apparatus according to claim 8, wherein said analyzing means
comprises comparing means connected to said means for evaluating
the penetration rate, and recording means connected to said
comparating means which compares each value of the penetration rate
to the highest value which has been previously determined during
the same period of increase in the load and transfers the greatest
of said two values to said recording means where said record value
is stored.
10. An apparatus according to claim 8, comprising means for
recording the value of the tension corresponding to the highest
value of the penetration rate recorded in said analyzing means and
wherein said recording means are connected to said second actuating
means which elaborate a second limit-value as a function of said
recorded value of the tension.
11. An apparatus according to claim 8, wherein said second
actuating means are connected to said tension measuring means and
elaborate said second limit-value as a function of the tension
corresponding to the penetration rate which, while decreasing, has
reached said first limit-value.
12. An apparatus according to claim 8, comprising at the ground
surface, motor means for advancing the drill string, said motor
means being operatively associated with means for automatically
regulating the linear speed of the drill pipe, wherein said control
means comprise a device connected on the one hand to said
elaborating means which delivers a signal representative of the
penetration rate and on the other hand to said first and second
actuating means, said device delivering a resulting signal which
represents the linear speed of the drill pipe at the ground surface
and is a function of the penetration rate represented by a signal
delivered by said evaluating means, said resulting signal having a
value which is lower than the signal representing the penetration
rate, when said first actuating means generate a signal transmitted
to said device and higher than the signal representing the
penetration rate when said second actuating means deliver a signal,
and wherein said resulting signal is transmitted to said means for
automatically regulating the linear speed of the drill pipe at the
ground surface.
Description
The present invention relates to a process and an apparatus for
automatically optimizing the penetration rate of a drilling tool
driven by a motor whose torque decreases with an increasing
rotation speed.
Such relationship between the torque and the penetration rate
characterizes, in particular, the bottom or down-hole motors, such
as the drilling turbines used in the turbodrilling process, or the
series or compound electric drilling motors used in the
electrodrilling process.
As a result of the above-defined relationship, it is observed that,
when starting from a low value of the thrust load or weight applied
on the drill bit, the penetration rate begins to increase with a
progressively increasing weight on the drill bit and then decreases
with a further increasing weight on the drill bit, until stalling
of the drill bit.
It has already been proposed, in drilling operations using a motor
whose torque decreases with an increasing rotation speed, to
progressively vary the load or weight applied on the drill bit,
about its optimum value, in alternating series of phases furing
which is repectively increased and decreased the tension of the
drill pipe from which the drill bit is suspended, to measure the
slope of the tangent to the curve which represents the penetration
rate of the drill bit into the ground as a function of the weight
exerted on the drill bit and to change over from a tension
increasing phase to a tension decreasing phase and vice-versa, when
the value of said slope reaches respectively predetermined upper
and lower values.
The problem arising when carring out such a process and making use
of the corresponding apparatus are due, in particular, to the great
difficulty encountered in determining the slope of the curve at the
operating point.
The main object of the present invention is accordingly to provide
a more easily operable process and apparatus.
The advantages of this invention will become apparent from the
following description of an embodiment of the invention illustrated
by the accompanying drawings wherein:
FIG. 1 shows, in the case of drilling with a bottom motor, the law
of variation of the rotation speed of the drill bit, in response to
the weight exerted thereon,
FIG. 2 diagrammatically illustrates the variations of the
penetration rate and of the pressure of the drilling fluid versus
time,
FIG. 3 shows an apparatus according to the invention for use when
the drill pipe is a flexible pipe,
FIG. 3A shows the adaptation of this apparatus to a drilling
process using rigid drill pipe elements,
FIGS. 4 and 5 illustrate the operation of the device.
The curves 1 and 2 of FIG. 1 show for two different ground layers
respectively, the penetration rate V.sub.a of the drill bit in
response to the axial load or weight W exerted on this drill
bit.
On these curves the points M.sub.1 and M.sub.2 indicate the
respective operating points when the drill bit penetrates the
corresponding ground layers and the abscissa W.sub.f represents the
weight (or load) exerted on the drill bit.
It is apparent that with an increasing weight W.sub.f on the drill
bit, starting from the operating point M.sub.1 or M.sub.2, the
corresponding operating point is displaced towards the right of
FIG. 1 on either of the two curves and the penetration rate V.sub.a
of the drill bit increases and reaches a maximum value at point
S.sub.1 (or S.sub.2). The corresponding curve portion followed by
the operating point corresponds to stable operating conditions.
If the operating point moves beyond the vertex of the operating
curve the operating conditions become unstable and the penetration
rate decreases with a further increasing weight W.sub.f on the
drill bit, until stalling of the downhole motor.
FIG. 2 represents, as a function of time, the variations in the
value of the penetration rate V.sub.a and in the pressure of the
drilling mud at the ground surface.
The penetration rate V.sub.a of the drill bit undergoes
fluctuations about an average value, these variations in curve 3
being plotted versus time.
The frequency of these fluctuations depends, in particular, on the
pulsing rate of the drilling mud circulation pumps and cannot be
filtered without introducing a time constant which is incompatible
with the response time required for an automatic apparatus for
optimizing the penetration rate of the drill bit, which device must
prevent any liability of stalling of the bit.
I will indicate hereinafter how this inconvenience can be avoided
by considering the average value of the penetration rate of the
drill bit over a time interval equal to the pulsing period of the
mud circulation pumps, for example.
The instants t.sub.n.sub.-1 and t.sub.n which are the limits of
such intervals may be selected as being the instants at which the
value of the alternating component of the pressure P.sub.s of the
drilling fluid, as measured at the ground surface, passes through
the value zero (FIG. 2), the value of this pressure P.sub.s also
oscillating about an average value shown by the straight line 4, at
the same frequency as the penetration rate, but with a time lag
.phi. corresponding to the lag between the respective values of the
drilling mud pressure at the ground surface and at the hole
bottom.
The value of the average penetration rate at the hole bottom
between instants t.sub.n.sub.-1 and t.sub.n is given by the
formula: ##SPC1##
wherein ##SPC2##
is the average value of the linear speed of the drill pipe, as
measured at the surface between the two considered instants,
.alpha. the elasticity coefficient of drill pipe, T.sub.n.sub.-1
and T.sub.n the respective tensile stresses or tensions to which
the drill pipe is subjected at instant t.sub.n.sub.-1 and instant
t.sub.n respectively.
FIGS. 3 and 3A illustrate two embodiments of apparatus for carrying
out the process according to the invention:
FIG. 3 illustrates the case of use of a flexible drill pipe unwound
from a storing reel and FIG. 3A the case of use of a drill string
formed of rigid pipe elements.
In these figures, reference 5 designates the drill bit suspended
from a drill pipe 7 and driven by a downhole motor 6, which is, for
example, a drilling turbine fed with hydraulic power from the
ground surface, reference 8 indicating the bore hole.
The drill pipe 7 is lowered in the bore by means of a handling
device 9 which may comprise at least one endless caterpillar chain
carrying jaws or clamping shoes in the case of FIG. 3, and a winch
33 with a cable 34 wound thereon and supporting a pulley block in
the case of use of a drill string 7 formed by rigid drill pipe
elements (FIG. 3A).
This handling device 9 is driven by a motor 10, optionally through
an irreversible coupling device 11 which can at will be engaged or
disengaged by means of electric control signals transmitted through
control cable 12 (FIG. 3).
A real time digital computer 13 receives a signal, such as an
electric signal representing the measuring value of the tensile
stress T applied to the drill string 7. This signal is transmitted
through line 14 and can be supplied, in the case of the embodiment
of FIG. 3, by a device 15 comprising at least one strain gauge at
the lower part of the drill string 7 (FIG. 3) or at a location 35,
on the dead end of a pulley block 31 at the surface, in the
embodiment illustrated by FIG. 3A.
A device 16 is used for measuring the length L of the drill pipe
suspended from the ground surface by means of the handling device
9.
This device comprises, for example, a roller in contact with the
drill string 7, driven in rotation by the linear displacement of
the later, this roller in turn driving in rotation the emitter 16
of a synchromechanism known in the art as a "Selsyn", whose
receiver 17, to which it is electrically connected through a cable
18, actuates a revolution counter device, providing, in the form of
a series of electric pulses, a digital measurement of length L,
which is supplied to the computer 13 through cable 19.
The feed rate V.sub.d of the drill string, at the ground surface,
can be measured by devices 20 and 21 which are respectively similar
to devices 16 and 17, the digital value of said feed rate being
supplied to the digital computer 13 through cable 22.
For this measurement of V.sub.d, it is preferred to use devices
separate from those used for measuring the length L, so as to
determine with a sufficient accuracy the linear speed V.sub.d of
the drill string.
The value of the elasticity coefficient .alpha. of the drill string
7 is set up at 23 in the computer 13 which also receives, through
conductor 24, a signal representing the digital value of the
alternating component of the pressure P.sub.s of the drilling mud
at the gound surface, this pressure being measured by any suitable
pressure sensor (not shown in the figure) placed in the drilling
mud circuit and producing a measuring signal which is filtered by a
device 25 so as to keep only its alternating component which is
supplied to the computer 13.
The digital value of .alpha. set up at 23 will preferably be a
value measured in situ. For this purpose, the average value of the
coefficient .alpha. corresponding to the reached depth may be
periodically determined in manner stated below.
This measurement can be performed by raising the drill bit over a
few meters and then lowering it again so that it rests on the well
bottom without drilling.
By observing during this lowering of the drill bit the variation in
the tensile stress T on the drill pipe, in the linear speed V.sub.d
of this drill pipe at the ground surface, and in the penetration
rate V.sub.a, it can be seen that the tensile stress T
progressively decreases from instant t.sub.A when the bit reaches
the bottom of the bore hole, in proportion to the elastic
shortening of the drill string.
This shortening is discontinued at the instant t.sub.B when the
feed rate V.sub.d of the ground surface becomes zero.
The relationship: ##SPC3##
shows that, between instants t + t.sub.A and t + t.sub.B, the value
of V.sub.a given by the computer 13 will be different from zero if
the value of .alpha. which is used is not the proper one.
More precisely the value of V.sub.a will be kept positive between
instant t.sub.A and instant t.sub.B when the value of which is used
in the computer 13 is too low since, in such a case, the absolute
value of the negative term
.alpha. L [T.sub.n - T.sub.n.sub.-1 ]/(t.sub.n -
t.sub.n.sub.-1)
will be too low for the right-hand side of the equation (1), the
value of ##SPC4##
thus being the greater in that right-hand side and resulting in a
positive value of ##SPC5##
On the contrary, if the value selected for .alpha. is too high, the
absolute value of the negative term
.alpha. L (T.sub.n - T.sub.n.sub.-1)/(t.sub.n - t.sub.n.sub.-1)
will be greater than that of ##SPC6##
and will accordingly result in a negative value of ##SPC7##
as determined by the computer 13. The exact value of .alpha.,
measured in situ for the drilled depth, may be determined by the
computer 13, by following relationship: ##SPC8##
in which t.sub.k and t.sub.k.sub.-1 indicate two instants within
the time interval between t.sub.A and t.sub.B, L is the drill pipe
length supported from the surface, and T.sub.k.sub.-1 and T.sub.k
are the respective tensile stresses applied to the drill pipe at
instants t.sub.k.sub.-1 and t.sub.k.
The computer 13 determines, from signals representing the values of
V.sub.d, .alpha., L and T, the different successive values of
(V.sub.a) which are transmitted through a conductor 28 to an
apparatus 27 capable of processing such date, in the manner
indicated in the following description of the operation of the
apparatus.
simultaneously, the value of (V.sub.a) is transmitted to a device
26 through a conducor 30. This device 30 delivers a signal which is
a function of the value of V.sub.a and is supplied to one of the
input terminals of the comparator 36 which is a part of the circuit
controlling the rotation speed of the motor 10, which circuit will
not be described in detail.
The devices 27 and 26, which have been illustrated separately in
order to facilitate a better understanding of the operation, can be
combined with the computer 13.
The operation of the apparatus will now be described, with
reference to FIG. 4.
At the instant t.sub.o, the computer determines the value of the
penetration rate Va.sub.o which corresponds to the operating point
M.sub.o in FIG. 4.
The value of the weight on the drill bit is then W.sub.o, the
tension in the drill string is T.sub.o, (.DELTA.T.sub.o +
.DELTA.W.sub.o = 0) and Vd.sub.o is the value of the linear speed
of the drill pipe at the ground surface.
The value Va.sub.o is set up in the device 27 and optionally also
the corresponding tension T.sub.o.
The conductor 30 supplies to circuit 26 a signal representing the
value Va.sub.o, this circuit delivering a signal which is, for
example, proportional to the value 2Va.sub.o which is supplied to
one input terminal of the comparator 36, said comparator 36
receiving on another input terminal signal representing the
revolution speed of the motor. The comparator 36 delivers a signal
which is a function of the difference of the received signals and
actuates the control circuit which maintains the speed of the motor
10, at any time, at
V.sub.d = 2 V.sub.a
At the instant t.sub.o the clutch 11 is engaged.
At this instant Vd.sub.o > Va.sub.o and the weight on the drill
bit increases (while the tension on the flexible drill pipe is
decreasing).
Therefrom results a displacement of the operating point M.sub.o
towards the right of FIG. 4.
At the instant t.sub.1 = t.sub.o + .DELTA.t, the operating point is
M.sub.1 and the computer 13 determines the new value of the
penetration rate Va.sub.1.
This value is transmitted as hereinabove indicated to the means for
controlling the linear speed of the drill pipe. This value is also
supplied to the device 27 which compares it to the previously
recorded value Va.sub.o, for example by, determining the difference
(Va.sub.1) - (Va.sub.o). When this difference is positive the
circuit 27 substitutes in the memory the value Va.sub.1, for the
value Va.sub.o and optionally substitutes the value T.sub.1 for the
value T.sub.o.
This procedure is continued and at the instant
t.sub.2 = t.sub.1 + .DELTA.t = t.sub.o + 2 .DELTA.t
the same operation is effected
At the instant t.sub.m = t.sub.o + m .DELTA. t, the operating point
M.sub.m is substantially at the vertex of the curve. The device 27
thus records a value Va.sub.m which is substantially equal to the
maximum penetration rate together with the corresponding tension of
the drill string.
At the instant t.sub.(m.sub.+1) = t.sub.m + .DELTA.t = t.sub.o + (m
+1) .DELTA.t the operating point reaches the position
M.sub.(m.sub.+1), i.e. the portion of the curve which corresponds
to a decrease of the penetration rate as the weight on the tool
increases. The corresponding value V.sub.a(m.sub.+1) is accordingly
not recorded, since the difference V.sub.a(m.sub.+1) - V.sub.am is
negative.
The weight on the drill bit is still increased until the instant
t.sub.x when the operating point M.sub.x has reached a position
defined by the relationship: ##SPC9##
wherein Y represents a set-up value, which is for example supplied
to the computer 13 through the conductor 29. At this instant, the
computer 13 delivers a control pulse which disengages the device 11
and, since the device 9 is no longer actuated, the advance of the
drill pipe is stopped, thereby resulting in an increase of the
tension on the drill pipe and consequently a decrease in the weight
on the drill bit.
The operating point is then displaced towards the right of the
figure.
The weight on the drill bit decreases and the tension on the drill
pipe increases until, at the instant t', the tension on the drill
pipe being equal to T', the following relationship is obtained:
T' - T.sub.x = .DELTA.T
.DELTA.T being a positive set-up value transmitted to the computer
13 through the conductor 37. At the instant t' the computer 13
delivers a pulse which controls the engagement of the device 11,
which actuates again the advance of the drill pipe at the ground
surface and consequently results in a decrease of the tension on
the drill pipe. The values V.sub.a ' and T' are recorded in the
device 27 and the above-described procedure is repeated, i.e. a new
value for v.sub.a is determined at the instant ' + .DELTA.t etc. .
.
As is apparent from the foregoing, the computer 13 provides for a
determination of the penetration rate (V.sub.a) only during the
period when the weight on the drill bit increases (which
corresponds to a decrease of the drill string tension).
The above-described process is unaffected by the fluctuations of
the value of V.sub.a caused by parasitic phenomena. Obviously, the
value .DELTA.T will be so selected that the operating point M
follows that part of the curve which corresponds to variations in
the same direction of the speed V.sub.a and of the weight W.
According to an alternative embodiment, the values of the tension
corresponding to the values of the penetration rate V.sub.a
recorded in the device 27 are simultaneously recorded and the
computer 13 delivers a pulse which controls the engagement of the
device 11 for the value of T' defined by the relationship:
T'= T.sub.m + .DELTA.'T,
.DELTA.'t being the set-up value transmitted through conductor 32
(FIG. 3).
It will then be possible instead of directly setting up reference
values .DELTA.T (or .DELTA.'T) and Y, to adjust the computer 13 so
that it elaborates itself the values .DELTA.T (or .DELTA.'T) and Y
as a function of T.sub.x (or T.sub.m) and of V.sub.a.sbsb.x or of
V.sub.a.sbsb.m :
Thus, for example, .DELTA.T or .DELTA.'T may be a fixed percentage
of T.sub.x (or of T.sub.m) and in the same way Y may represent a
fraction of V.sub.a.sbsb.m.
The rate of variation of the weight exerted on the drill bit
depends upon the difference between the value of the linear speed
(V.sub.d) of the drill pipe at the ground surface and the value of
the penetration rate (V.sub.a).
In order to achieve an efficient scanning of the curve V.sub.a =
f(W) by the computer 13, this scanning must be performed over a
sufficient time interval; in other words, the variations of the
weight on the drill bit must not be too rapid.
To this end the device 11 is omitted and there is used a device 26
which delivers a signal representing the value of V.sub.d which
should be obtained and is a function of V.sub.a, as shown in FIG.
5.
In this figure, curve A represents, by way of example, the function
V.sub.d = V.sub.a, curve B represents a function V.sub.d
=F(V.sub.a) such that V.sub.d is always greater than V.sub.a and
curve C represents a function V.sub.d = G(V.sub.a), such that
V.sub.d has a value always smaller than V.sub.a.
During the scanning period, when the weight on the drill bit
increases, the device 33 delivers a signal represented by curve B
[V.sub.d = F(V.sub.a)]. When the scanning period of the penetration
rate is ended, the computer 13 delivers a pulse transmitted to the
device 33 which is triggered and delivers a signal represented by
the curve C [V.sub.d = G (V.sub.a)].
The functions F and G can be selected by those skilled in the art.
In the example of FIG. 5 and for values of the penetration rate
V.sub.a greater than a determined limit value:
F (V.sub.a) = V.sub.a + X and G (V.sub.a) = V.sub.a - Z
wherein X and Z are positive constant values expressed by the same
units as V.sub.a.
It will thus be possible to adjust the period during which the
weight on the tool increases (while the tension on the drill pipe
decreases, by modifying the value of X.
In order to increase this period it suffices to select smaller
values for X.
In order to decrease the period during whicht the weight on the
drill tool decreases (while the tension on the drill pipe
increases), it suffices to select higher values for Z.
In order to obtain a soft and regular operation for small values of
V.sub.a together with scanning periods of sufficient duration, the
following values will preferably be selected for F and G.
F = 2 V.sub.a , G = 0
Thus the linear speed of the drill pipe is easily controlled
through conventional control means, and the clutch means 11 of
FIGS. 3 and 3A can be omitted.
Obviously the method and apparatus can be used at any time when in
the course of drilling operations the relationship between
penetration rate of the drill bit and the weight exerted on this
drill bit is of the type of the relationship illustrated by FIG.
1.
* * * * *