U.S. patent number 3,626,482 [Application Number 04/868,873] was granted by the patent office on 1971-12-07 for method and apparatus for measuring lithological characteristics of rocks.
This patent grant is currently assigned to Societe Anonyme dite: Societe Nationale des Petroles d'Aquitaine. Invention is credited to Jean Lutz, Claude Jean Quichaud, Michel H. Raynaud.
United States Patent |
3,626,482 |
Quichaud , et al. |
December 7, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
METHOD AND APPARATUS FOR MEASURING LITHOLOGICAL CHARACTERISTICS OF
ROCKS
Abstract
A method by which physical and mechanical characteristics of
rocks are measured during drilling, comprises picking up a signal
representing the vibrations of a train of rods forming part of
drilling gear, selecting the components of the said signal which,
after peak-clipping, are in a frequency band which is centered on,
and preferably is related to, a characteristic frequency of the
tool, establishing from the components thus selected, a value which
is representative of the amplitude of the vibrations, and
correlating this value with the drilling depth.
Inventors: |
Quichaud; Claude Jean (Billere,
FR), Raynaud; Michel H. (Pau, FR), Lutz;
Jean (Pau, FR) |
Assignee: |
Societe Anonyme dite: Societe
Nationale des Petroles d'Aquitaine (Coubevoie,
FR)
|
Family
ID: |
27244905 |
Appl.
No.: |
04/868,873 |
Filed: |
October 23, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Oct 30, 1968 [FR] |
|
|
6905142 |
Dec 11, 1968 [FR] |
|
|
177543 |
Feb 27, 1969 [FR] |
|
|
171873 |
|
Current U.S.
Class: |
340/853.6;
73/152.47; 175/50; 340/854.4; 340/853.8; 340/856.4 |
Current CPC
Class: |
E21B
44/00 (20130101); E21B 12/02 (20130101) |
Current International
Class: |
E21B
44/00 (20060101); E21B 12/02 (20060101); E21B
12/00 (20060101); E21b 047/00 (); E21b
049/00 () |
Field of
Search: |
;175/25,24,50
;73/151 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Leppink; James A.
Claims
We claim:
1. A method for measuring characteristics of rocks during drilling
by means of drilling gear comprising a drilling tool having at
least one set of elements for attacking rock at a depth in a drill
hole, means for driving said drilling tool at a certain frequency
of rotation, and a measuring section for monitoring the drilling
operation, said method comprising the steps of generating signals
which are representative of vibrations of said drilling gear
detected at at least one point on said measuring section,
eliminating from said signals parasitic voltages outside a range
defined by two predetermined values of opposite polarities, so as
to provide a resultant signal, selecting from said resultant signal
a signal comprising a frequency band centered on a frequency equal
to said frequency of rotation of said tool multiplied by the number
of said attacking elements in at least one of said sets, which
selected signal has an amplitude within said band which is directly
related to lithological properties of rocks being attacked by said
tool, measuring said amplitude, and correlating it with the depth
at which said tool is working.
2. A method according to claim 1, in which vibrations are detected
at at least one pair of points located on said drilling gear, said
method further comprising the step of effecting algebraic summation
of said generated signals.
3. A method according to claim 2, in which the vibrations detected
at said pair of points are detected by means of two pickup devices
arranged at points on two diametrically opposite generatrices of
said measuring section.
4. A method according to claim 3, in which said generated signals
are representative of longitudinal vibrations, and in which said
diametrically opposite points at which said pickup devices are
located are offset relatively to one another along the axis of said
drilling gear by a distance which is between 2 centimeters and 9
meters.
5. A method according to claim 1, in which said selected signal is
obtained by selecting signal components in said frequency band by
means of a band-pass filter arrangement having a mean frequency
which is controlled as a function of the instantaneous speed of
rotation of said drilling gear multiplied by the number of
attacking elements in at least one set.
6. A method according to claim 1, in which said measuring section
is situated at the upper part of said drilling gear.
7. A method according to claim 1, in which said measuring section
is situated near said tool.
8. A method according to claim 1, utilizing a tool having a number
of cutter wheels, each having inner and outer rows of cutting
teeth, in which said generated signals are representative of
longitudinal vibrations, and said selected signal is selected in a
frequency band centered on a frequency equal to said frequency of
rotation of said tool multiplied by the number of said cutter
wheels or the number of cutting teeth in said outer row of each of
said cutter wheels.
9. A method according to claim 8, in which said signals
representing longitudinal vibrations are generated by means of at
least one pair of accelerometers which are offset axially and have
electrical axes which are parallel to the axis of said drilling
gear.
10. A method according to claim 8, in which said signals represent
longitudinal stresses in said drilling gear and are generated by
means of at least one pair of strain gauges disposed parallel to
the axis of said drilling gear.
11. A method according to claim 1, in which said tool is a diamond
tool having a plurality of diamond-bearing surfaces and in which
said generated signals represent torsional vibrations, said
selected signal being selected in a frequency band centered on a
frequency which is equal to the frequency of rotation of said tool
multiplied by the number of said diamond-bearing surfaces.
12. A method according to claim 11, in which said generated signals
represent torsional accelerations which are detected by means of
accelerometers having their electrical axes located in a plane
perpendicular to the axis of said drilling gear.
13. A method according to claim 11, in which said generated signals
represent torsional stresses which are detected by means of strain
gauges located in a plane which is inclined at 45.degree. to the
axis of said drilling gear or of said measuring section.
14. In combination with drilling gear comprising a drilling tool
having at least one set of elements for attacking rock within a
drill hole, and means for driving said drilling tool at a selected
frequency of rotation, the improved apparatus for measuring rock
characteristics during drilling which comprises:
vibration responsive means including at least one vibration pickup
device positioned to detect vibrations by said tool, said vibration
responsive means being adapted to produce at its output an electric
signal representative of said vibrations,
voltage-limiting means connected to the output of said vibration
responsive means for eliminating from said signal voltages outside
a predetermined range of values,
means connected to the output of said voltage-limiting means for
selecting from said signal a frequency band centered on a frequency
equal to the frequency of rotation of said tool multiplied by the
number of attacking elements in at least one of said sets,
and means responsive to the amplitude of said signal in said
frequency band for correlating said amplitude with the depth in
said drill hole at which said drilling tool is operating.
15. The combination according to claim 14, comprising at least two
vibration pickup devices and means for effecting the algebraic
summation of signals delivered by the respective pickup devices so
as to supply a single signal to said voltage-limiting means.
16. The combination according to claim 13, in which said pickup
devices are constituted by two accelerometers for picking up
longitudinal accelerations, disposed on two opposed generatrices of
a connector situated at the lower part of said drilling gear near
said tool, said accelerometers being arranged on shoulders
perpendicular to the axis of said connector and being rigidly
attached to said shoulders.
17. The combination according to claim 42, in which said pickup
devices are constituted by two accelerometers for picking up
torsional vibrations, disposed diametrically opposite one another
on two generatrices of a connector which is inserted in the
drilling gear near said drilling tool, said accelerometers being
disposed on shoulders parallel to the axis of said connector and
the electrical axes of said accelerometers being parallel and
diametrically opposite each other.
18. The combination according to claim 15, in which said pickup
devices are constituted by strain gauges for picking up
longitudinal vibrations, disposed on a connector located at the
lower part of said drilling gear near said tool, said gauges being
disposed at two diametrically opposite points on the longitudinal
surface of said connector and the axes of said gauges being
parallel to the axis of said measuring section.
19. The combination according to claim 15, in which said pickup
devices are constituted by strain gauges for picking up torsional
vibrations, disposed on a connector located at the lower part of
said drilling gear near said tool, said gauges being disposed at
two diametrically opposite points on the longitudinal surface of
said connector, which lie in a common plane inclined at 45.degree.
to the axis of said connector.
20. The combination according to claim 15, in which said
vibration-responsive means is situated at the upper part of said
drilling gear.
21. The combination according to claim 20, in which said driving
means comprises rod means and said drilling gear includes a
drilling head and a sleeve interposed between said head and said
rod means, and said pickup devices are accelerometers for detecting
longitudinal vibrations, disposed on two opposite generatrices of
said sleeve, on shoulders which are perpendicular to the axis of
said sleeve, and offset along said axis, said accelerometers being
rigidly connected to said shoulders.
22. The combination according to claim 20, in which said drive
means comprises rod means and said pickup devices comprise two
accelerometers responsive to torsional vibrations, disposed on two
diametrically opposite generatrices of the lower part of said rod
means, said accelerometers being rigidly mounted in a common plane,
on shoulders which are parallel to the axis of said rod means and
are situated in an axial plane.
23. The combination according to claim 20, in which said drive
means comprises rod means and said drilling gear includes a
drilling head and a sleeve interposed between said head and said
rod means, and said pickup devices comprise strain gauges
responsive to longitudinal vibrations, disposed on two
diametrically opposite generatrices of said sleeve at two points
slightly offset axially of said sleeve.
24. The combination according to claim 20, in which said drive
means comprises rod means and said pickup devices comprise strain
gauges responsive to torsional vibrations, said gauges being
disposed at two diametrically opposite points at the lower part of
the longitudinal surface of said rod means, in a common plane which
is inclined at 45.degree. to the axis of said drilling gear.
25. The combination according to claim 14, in which said vibration
responsive, voltage limiting and frequency band-selecting means are
situated at the lower part of said drilling gear, and which
comprises means for transmitting to the surface the amplitude of
said selected signal.
26. The combination according to claim 25, in which said means for
transmitting the amplitude of said selected signal to the surface
comprises rod means through which said drilling tool is driven,
together with magnetostrictive means for transmitting along said
rod a signal responsive to the amplitude of said selected signal,
and a magnetostrictive receiver above the ground for detecting the
signal transmitted along said rod and transmitting it to said
correlating means.
27. The combination according to claim 48, in which said means for
transmitting the amplitude of said selected signal comprise conduit
means for the passage of a stream of mud, a valve controlling the
pressure of said stream of mud in said conduit means, and means for
operating said valve in dependence upon said selected signal,
whereby the pressure of said stream of mud is modulated in
accordance with the amplitude of said selected signal.
Description
The present invention relates to a method and apparatus for
measuring lithological characteristics of rocks as they are being
drilled and at the instant when the drilling tool acts on the
rock.
Experiments have previously been made involving correlating the
amplitude of the stresses observed in the upper part of the
drilling rod with the mechanical characteristics of the rocks. The
experiments have failed, because of the composite nature of the
signal.
One of the objects of the invention is to provide means whereby it
is possible to process the crude information delivered by a
vibration pickup device, with the object of supplying instantaneous
information relating to the characteristics of the rock as this is
actually being drilled.
Another object of the invention is to provide means which will
enable an instantaneous signal to be obtained which is
representative of the physical and mechanical properties of the
rock, as these are picked up by the drilling tool, and which signal
is capable of being used after processing as a value from which
command signals can be established for automatically controlling
the drilling.
Another object of the invention is to provide means with which it
is possible to deliver, as a function of the progress of the
drilling, a diagraph which is representative of the physical and
mechanical properties of the rocks encountered by the tool.
The method according to the invention makes it possible to obtain,
as a function of the depth at which the tool is operating, a value
which is directly related to the physical, mechanical and
stratigraphic properties of the rocks being attacked by the
drilling tool.
The method according to the invention comprises collecting, at at
least one point located on a measuring section of drilling gear
which is provided at its lower part with a drilling tool, signals
which are representative of the vibratory state of the drilling
gear at this point, bringing the values of parasitic voltages which
are beyond two predetermined levels and are of opposite signs, to
values equal to these levels, selecting from the signal thus
processed, a frequency band centered on a frequency equal to the
product of the frequency of rotation of the tool times the number
of operative elements of the tool, measuring the amplitude of the
signal thus selected, the value thereof being directly related to
the lithological properties of the rocks attacked by the drilling
tool, and correlating this value with the depth at which the tool
is working.
During the course of the studies which led to the present
invention, an unexpected effect has been noted, residing in the
fact that the amplitude of the signal which is processed in order
to eliminate parasitic components and which is selected in a
frequency band centered on a frequency which is equal to the
product of the frequency of rotation times the number of attacking
elements of the tool, is representative of the lithological
properties of the rocks.
The characteristic emission spectrum of the drilling tool, that is
to say the spectrum of frequencies which arises when the attacking
elements of the tool act on the rock for the purpose of breaking it
down, varies with the frequency of rotation of the tool and with
the number of attacking elements carried by the said tool. However,
the spectrum of frequencies which is received is useless without
filtration, because of the composite character which arises due to
the transfer function of the rods.
On the other hand, filtration of this signal in the frequency band
referred to above, enables a useful signal to be obtained if care
is taken to eliminate parasitic signals.
According to one feature of the invention, in carrying out this
method, the numbers which are characteristic of the arrangement of
the operative elements of the tool are defined, in the case of
cutter wheel tools, by the number of cutter wheels or by the number
of teeth in one of the rows of teeth of a cutter wheel, and in the
case of diamond tools, by the number of diamond-bearing areas.
By way of example, in tools having cutter wheels, the number of
wheels which form the primary attacking elements may be two, three
or four, depending on circumstances.
In addition, the number of teeth carried by each cutter wheel can
vary. There may be, for example, approximately 20 teeth in the
outer row of teeth carried by the wheel and from eight to 10 teeth
in the intermediate row of teeth carried by the wheel.
Similarly, in diamond tools, the number of elements for attacking
the rock is determined by the number of surfaces on which the
diamonds are mounted, these surfaces being separated by
channels.
The method according to the invention can be carried into effect by
collecting a single vibratory signal and processing it by the
method referred to above.
The result thus obtained enables information to be collected
regarding the lithological properties of good quality rocks.
According to one preferred mode of carrying the invention into
effect, signals representing the vibratory state of the drilling
gear are collected at at least one pair of points diametrically
opposite one another on the drilling gear and the algebraic
summation or the instantaneous differencing of these signals is
effected.
According to a preferred mode of carrying the invention into
effect, two vibratory signals are collected by means of pickup
devices positioned on two diametrically opposed generatrices of the
drilling gear, the two pickup devices being offset axially by from
2 centimeters to 9 meters.
During the course of tests it has been found possible to effect an
improvement in the quality of the relationship between the
amplitude of the signal which is processed and the lithological
properties of the rocks, if a pair of vibratory signals is
collected.
The explanation of this phenomenon seems to reside in the more
effective elimination which is obtained by means of two opposed
pickup devices, of the nonuseful vibrations which arise from, for
example, the transfer function.
In carrying out the invention the signal may be picked up at a
measuring section, the location of which is chosen to be, according
to the circumstances, either at the upper part of the drilling gear
or at a place near the tool.
In a first mode of carrying out the method according to the
invention, there is collected at the measuring section of the
drilling gear at least one signal which is representative of the
longitudinal vibrations of the said drilling gear, when using
drilling tools comprising cutter wheels.
According to a preferred form of this first mode of carrying out
the method according to the invention, there is collected at the
upper part of the drilling gear, by means of accelerometers, at
least one signal representing the longitudinal accelerations
generated in the said gear by the operation of the drilling tool,
the bearing faces of the accelerometers being horizontal, opposed
to one another and offset axially.
In another variant of this form of the method, at least one signal
representative of the stresses existing in the drilling gear is
collected at the measuring section, by means of a plurality of
strain gauges arranged parallel to the axis of the drilling gear
and in a plane perpendicular to the said axis.
In a second mode of carrying out the method according to the
invention, a signal representative of the torsional vibrations to
which the said gear is subjected when using diamond drilling tools
is collected at the upper part of the measuring section.
In a preferred form of this second mode of carrying out the method
according to the invention, the torsional accelerations to which
the drilling gear is subjected are collected at the measuring
section, the signal being picked up by means of accelerometers
which are arranged beneath the rotary table used for driving the
drilling gear in rotation and the electrical axes of which are
located in a plane perpendicular to the axis of the drilling
gear.
According to a modification of this second mode of carrying out the
method according to the invention, the torsional stresses to which
the drilling gear is subjected are collected at a measuring section
of the said gear, the pickup of the signal again being effected by
means of strain gauges arranged beneath the rotary table by means
of which the drilling gear is driven in rotation, the gauges being
inclined at 45.degree. relatively to the drilling gear.
When the measuring section is located at the upper part of the
drilling gear the longitudinal vibrations are picked up above the
rotary table, while the torsional vibrations are picked up below
the rotary table, the pickup devices being positioned in accordance
with the nature of the vibrations which are to be collected, as
will be apparent to anyone skilled in the art.
When the measuring section is disposed at a place near the tool,
all signals are collected below the rotary table and it is only the
different positioning of the pickup devices which determines the
nature of the vibrations which are to be collected.
In the case in which the measuring section is placed at the upper
part of the drilling gear, the collected signal is processed in an
electronic unit situated near the point at which the signal is
picked up and, after processing, it is correlated with the drilling
depth.
In the second case the signal is treated at the bottom of the
drill-hole and a signal representing the amplitude of the selected
signal is transmitted to the surface either by way of the train of
rods, using a suitable device such as a magnetostrictive bar or a
piezoelectric crystal, or by means of the stream of mud, the
pressure of which is modulated, by means of a valve for
example.
The invention is also concerned with apparatus enabling the
aforesaid methods to be carried into effect, and comprising at
least one vibration pickup device arranged on the measuring section
of the drilling gear and fast with the latter, and delivering an
electrical signal, means for processing the said signal in such a
way as to limit its potential to two predetermined values, means
for selecting a frequency band of the signal thus processed,
centered on a frequency equal to the product of the frequency of
rotation of the tool, times the number of operative elements of the
latter, means for establishing from this selected signal fraction a
value representing the amplitude of this signal fraction and means
for measuring this amplitude and correlating it with the depth at
which the drilling tool is operating.
The apparatus used preferably comprises at least one pair of pickup
devices and means for effecting the algebraic summation or the
instantaneous differencing of the signals obtained from each pickup
device, in order to obtain a single signal.
Since the measuring section can be placed at the upper part of the
drilling gear or at a position near the tool, the forms of
apparatus described below relate to these two modes of carrying out
the invention but they are applicable more particularly to use with
a pair of pickup devices. A similar system can be used when the
signal is collected by a single pickup device, without departing
from the scope of the present invention.
The measuring apparatus used at the upper part of the drilling gear
will be described with reference to the following embodiments:
In a first embodiment, the devices for picking up longitudinal
vibrations are constituted by two accelerometers disposed on
opposite generatrices of a sleeve interposed between the injection
head and the rod which drives the drilling gear in rotation, the
accelerometers being placed on shoulders which are perpendicular to
the axis of the sleeve and offset axially by from 2 centimeters to
9 meters, the electrical axes of the accelerometers being parallel
and opposed.
In a second embodiment, the devices for picking up torsional
vibrations are constituted by two accelerometers placed on
diametrically opposed generatrices of the lower part of the rod
which drives the drilling gear, the accelerometers being arranged
on shoulders parallel to the axis of the driving rod and located in
the axial plane, their electrical axes being parallel and opposed
and located in a single plane perpendicular to the axis of the
drilling gear.
In a third embodiment, the devices for picking up longitudinal
vibrations are strain gauges arranged on a sleeve interposed
between the injection head and the rod for rotating the drilling
gear, the pickups being placed at two diametrically opposed and
axially offset points on the surface of the said sleeve.
In a fourth embodiment, the devices for picking up torsional
vibrations are constituted by strain gauges arranged on the lower
part of the rod by which the drilling gear is driven, the gauges
being placed at two diametrically opposed points on the surface of
the said sleeve, located in the same plane.
The first and third embodiments are preferably used when it is
desired to observe the longitudinal vibrations, which permit of
obtaining a useful signal when using tools operating by percussion,
for example tools having cutter wheels, whereas the second and
fourth embodiments are preferably used when it is desired to
collect a useful signal when using tools such as diamond tools.
The apparatus which is used at a place near the drilling tool can
be constituted in one of the following ways:
A first embodiment consists in placing an accelerometer which picks
up longitudinal vibrations on a measuring connector disposed on the
drilling gear at a place near the tool, the electrical axis of the
said accelerometer being parallel to the axis of the drilling gear
and this accelerometer supplying an electrical signal to a
processing circuit which limits the potential of the signal,
selects a frequency band, determines the amplitude of the said
selected signal and uses this amplitude to control a device for
transmitting this amplitude to a detector located at the upper part
of the drilling gear, the said amplitude then being correlated with
the drilling depth.
Three other embodiments using, respectively, strain gauges for
measuring longitudinal vibrations, accelerometers for measuring
torsional vibrations, and strain gauges for measuring torsional
vibrations, can equally well be used with one pickup device or a
pair of pickup devices.
The invention will be better understood from the following
description, by way of example only and with reference to the
accompanying drawings, of various embodiments of the said means for
carrying into effect the method according to the invention. In the
drawings:
FIG. 1 is a diagrammatic view of apparatus according to the
invention mounted on a drilling installation.
FIG. 2 shows the details of the mounting of accelerometers when
these are arranged on a sleeve interposed between the injection
head and the rod by which the drilling gear is driven.
FIG. 3 is a diagram showing the mounting of stress pickup devices
arranged on a sleeve interposed between the injection head and the
square rod.
FIG. 4 is a circuit diagram of the electronic system of the
arrangement which ensures the elimination of parasitic voltages due
to shocks, in the case where accelerometers are used as pickup
devices.
FIG. 5 is the circuit diagram of a filter used for selecting a
frequency band when the frequency emitted by a cutter wheel tool
rotating at a speed of 200 r.p.m. is picked up, and when the
vibrations emitted by the external row of teeth of the cutter tool
are collected.
FIG. 6 shows two diagraphs; the diagraph 73 is an acoustic diagraph
obtained subsequently to drilling in the manner customarily in use
hitherto, while the diagraph 74 is a diagraph obtained by the
method according to the invention, concurrently with the
drilling.
FIG. 7 shows an embodiment in which signals are collected at the
bottom of a well or drill hole.
FIG. 8 shows a detail of the embodiment of FIG. 7.
FIG. 9 shows the detection circuit located at the upper part of the
drilling gear for the purpose of detecting wavetrains emitted by
the device of FIG. 8.
FIG. 10 shows a series of filters for adjacent frequencies, which
are connected as a function of the operational speed of the
drilling gear.
In FIG. 1, a drill derrick is represented at 1, the upper part 2 of
the derrick carrying the stationary pulley assembly 3. The cable
assembly connecting the stationary pulley assembly 3 to the block 5
carrying the movable pulley assembly is indicated at 4. Connected
to the said block 5 is a hook 6, which supports the injection head
7. The upper part of this injection head 7 is fixed, while the
lower part can be rotated by means of a bearing system. Indicated
at 8 is the flexible injection pipe which is connected at one end
to the injection head 7 and at the other end to the sludge pump
assembly, not shown in the drawing. The rod by which the drilling
gear is rotated is shown at 9. This rod is frequently of square
formation and, in the remainder of the description, it will be
referred to simply as the "square rod." This rod 9 is driven in
rotation by the rotating table 10, which itself is driven by a
motor (not shown). A drill shaft is indicated diagrammatically at
11, while the drilling gear is shown at 12. This drilling gear is
provided at its lower end with a drilling tool, indicated at 20.
Interposed between the injection head 7 and the square rod 9 is a
device 13 for measuring vibrations, which will be described in
detail with reference to the following figures. The cable
connecting the vibration measuring assembly 13 to the arrangement
15 which processes the electrical values representing the
vibrations is indicated at 14. This signal processing assembly is
connected, in the embodiment shown in the drawings, to a recording
unit 16, the winding movement of the record carrier of which is
controlled by a motor 19, which motor is connected by a line 18 to
a pickup device 17 permitting the progress of the drilling to be
measured. This measurement of the progress or advance of the
drilling gives a measure of the variation in the level of the tool
20 in the drill hole 11 as a function of time.
FIG. 2 shows in greater detail the assembly 13 referred to in the
foregoing description of the general arrangement. This assembly is
made in the form of a sleeve which connects the injection head 7 to
the square rod 9. The sleeve is represented at 21, this sleeve
having a threaded female socket at its upper part and a male thread
at its lower part. A member 21a bears on the fixed part of the
injection head 7 (FIG. 1) and thus causes the external part 22 of
the arrangement shown in FIG. 2 to be held in a fixed position. The
sleeve 21 carries on its external surface, a shell 23 on which is
fixed an insulating block 24, which is thus fast with the sleeve
21. This block 24 carries a series of metal rings, represented at
25a, 25b, 25c, 25d. Facing the block 24 and carried by the fixed
part 22 is a second insulating block 26. This block 26 carries a
series of brushes 27a, 27b, 27c, 27d which are adapted to slide on
the rings 25a, 25b, 25c, 25d.
These brushes are connected to a series of electrical leads
comprising a cable indicated at 28. The cable 28 extends out of the
arrangement through a protective housing 30. Represented at 29 is a
roller bearing carried by the sleeve 21 and there is also a
stuffing box, the whole ensuring the fluid-tightness of the chamber
defined between the sleeve 21 and the external part 22. The
fluid-tightness must be relatively good, so as to avoid fouling of
the rings 25 and the brushes 27. Represented at 31 is a quartz
accelerometer which delivers an electric signal under the influence
of an acceleration. This accelerometer is rigidly mounted on a
shoulder machined in the sleeve 21. This pickup 31 is connected by
a cable 31a to an impedance coupling device 32. This impedance
coupling device, which may be for example a field effect transistor
having an input impedance of several megohms and an output
impedance of the order of 1 k.OMEGA., is connected on the one hand
to the ring 25d by means of a measuring cable, while a second input
which supplies the feed voltage of the transistor is connected by a
second cable to another ring 25b. Indicated at 36 is a second
accelerometer of the same type as the first, disposed on a
generatrix of the sleeve diametrically opposite that on which the
accelerometer 31 is positioned and at a distance of the order of a
few tens of centimeters higher than this latter. The accelerometer
36 is likewise connected by a cable 36a to an impedance coupling
device 37 having two outputs, one of which is connected to the ring
25c while the other is connected to the ring 25b. The connections
are provided by the cables 38 and 39.
FIG. 3 shows another form of the vibration measuring assembly or
pickup device indicated at 13 in the diagrammatic assembly shown in
FIG. 1. Referring to FIG. 3, a sleeve 40 has a threaded female
socket at its upper part and a male thread at its lower part.
Indicated at 41 is a member which is fast with the sleeve 40 and
which carries an insulating block 42. Represented at 43 is a
jacket, which remains stationary by virtue of the fact that it is
held fast, by means of a rod 44, with the upper part of the
injection head. This jacket or chamber 43 thus remains stationary
while the device described is being used.
The insulating block 42 carries a series of conducting rings 45a,
45b, 45c, 45d, these rings being connected by cables 46a, 46b, 46c,
46d to a series of stress gauges 47, 48, 49, 50. The gauges 47 and
48 are mounted vertically, whereas the gauges 49 and 50 which are
mounted horizontally, that is to say perpendicular to the axis of
the sleeve 40, serve as compensation gauges. The values recorded on
the gauges 47 and 48 on the one hand, and on the gauges 49 and 50
on the other hand, are opposed to one another in a measuring
bridge, taking account of the mechanical coefficients. Represented
in FIG. 3 are brushes 51a, 51b, 51c, 51d, which slide on the rings
45a, 45b, 45c, 45d. These brushes, which are carried by an
insulating block 52, are carried by the stationary jacket 43 and
are connected to electrical leads 53a, 53b, 53c, 53d which are
assembled to form a cable 54.
Two modifications of the arrangements described in connection with
FIGS. 2 and 3 are possible. The vibration pickups, where these are
accelerometers or stress gauges, can be positioned at some other
point of the drilling gear, such that these pickups are situated
beneath the rotary table at the time of drilling. Two longitudinal
grooves are then formed in the square rod 9, permitting the passage
of wires which connect the pickup devices to the collector system
constituted by the rings and brushes. The accelerometers are
mounted in recesses formed at the base of the square rod, so that
the operative faces are parallel to the axis of the square rod and
are fixed relatively to shoulders on the said rod, the operative
faces of the two accelerometers being disposed in the same plane on
either side of the axis of the square rod.
FIG. 4 shows the amplifier-filter assembly which effects the
algebraic sum of the two signals and eliminates the parasitic
component of the signal, which is due to shocks. In the case of
FIG. 2, the signals provided by the accelerometers give signals
which are out of phase by 180.degree.; these are applied to the two
inputs 56a and 56b of a differential amplifier 56 with a gain of
about 20, which thus gives, in effect, the algebraic sum of the two
signals. The differential amplifier 56 has a gain of 50,000 in open
loop. Connected between the two inputs 56a and 56b of the
differential amplifier 56 is a diode, represented at 57. Connected
to the output 56c of the differential amplifier is a variable
resistance 58, so that this resistance produces a feedback to the
differential amplifier and brings the gain of the latter to a value
close to 20.
Across the negative input 56a of the differential amplifier and the
output 56c is connected a series of capacitances 59a, 59b, 59c,
forming a filter network which very strongly attenuates the signals
which are beyond a predetermined frequency value; in a particular
case, this value may be of the order of 5 kc./s, for example.
A number of pairs of diodes 60, 61 are connected between the
terminals 56a and 56c, so as to provide two series of diodes. The
diodes 60 of the first series are connected so that conduction is
allowed in the direction from 56a towards 56c, while the diodes of
the second series are connected so that conduction is allowed in
the direction from 56c towards 56a. The number of these diodes
defines the threshold voltage of this system. With two pairs of
diodes providing two series each containing two diodes, a
peak-clipping threshold of the order of 1.2 volts is obtained, that
is to say, a variable voltage of a maximum of .+-.1.2 volts is
available between the reference line 62 and the output terminal
56c. This makes it possible to eliminate the random signals of high
amplitude which originate from phenomena foreign to the vibrations
induced by the drilling tool.
FIG. 5 illustrates a frequency selection arrangement. The output
signal from across the terminals 56c and 62 of the system shown in
FIG. 4 is received at the input 63. It is applied through two
transistors 64 and 65, which serve as impedance adapters or
couplers, to a total feedback differential amplifier 66, and then
to a frequency selector device 67 formed by a series of
capacitances, resistances and self-inductances. This filter is
designed to act as a pass-band filter having a constant response
coefficient in its narrow passband and an attenuation on either
side of this band of about 50 decibels per octave. The filtered
signal is applied to the input of a second differential amplifier
68, in the output circuit of which two diodes 69 and 70 are
connected to be effective in opposite directions. These diodes
rectify the alternations of the vibratory signal and the rectified
signals are applied to the respective inputs of a third
differential amplifier 71. The amplitudes of the positive and
negative portions of the vibratory signal are thus added and, at
the output 72, a signal is obtained which represents the maximum
amplitude of the frequency band of the signal selected by the
filter 67. This electrical value is available either for being
recorded, or for use for the automatic control of the drilling. The
signal is recorded or stored as a function of the depth at which
the tool is working, using a pickup device by means of which it is
possible to know the depth of the tool at any given time, for the
purpose of controlling the advance of the recording medium or
controlling the storage of the signal.
FIG. 6 represents at 73 a diagraph obtained by an acoustic method
in a well drilled for the purpose of producing gas. Represented at
74 is a diagraph obtained by the method provided by the invention.
The figures on the centerline of FIG. 6 represent the depths in
meters at which are found the rocks whose properties are studied by
the two methods. It will be seen that the general shape of the
curves forming the two diagraphs is similar and that, in
particular, the zones in which the speed of sound is high in the
acoustic diagraph correspond to zones in which the amplitude of the
vibratory signal observed by the method according to the invention
has high values.
It must be pointed out that the mechanical diagraph 74 was obtained
at the actual moment of drilling, while the acoustic diagraph 73
was obtained only after drilling was terminated.
The acoustic diagraph 73 represents the speed of sound in the rock.
It is obtained by means of an ultrasonic transmitter-receiver
system, which is displaced in the well, the depth at which the
measurement is being made being known. A train of vibrations is
transmitted by the transmitter and then received by the receiver.
Measurement of the transit time enables the speed of sound in the
rock to be determined by the relationship
T=VL, where T is the transit time,
V is the speed of sound,
L is the transmitter-receiver distance.
On the other hand, in the diagraph 74, the amplitude of the curve
represents the amplitude of the signal processed by the method
according to the invention.
The similarity of the signals will be noted. In particular, at
about 1,340 meters, two peaks coincide. Between 1,375 and 1,390
meters, there is coincidence between a series of signal peaks.
Moreover, between 1,335 and 1,340, the same tendency is observed
for the two signals.
This coincidence of tendency is found between 1,370 and 1,380
meters. Similarly, a tendency to decrease is found in the region of
1,390 meters.
It is thus seen that the measurement obtained by the method
according to the invention is proportional to the speed of sound in
the rock and this is correlated to the hardness of the rocks and
their degree of compactness or density.
Similar correlations are obtained with the gamma-ray-neutron
diagraph or the rock density diagraph.
The operation of the apparatus provided by the invention and the
use of the drilling method using a tool having cutter wheels will
now be described as follows.
By means of the accelerometers 31 and 36 kc./s in FIG. 2, which are
carried by the sleeve 21 and are located at 13 in FIG. 1, the
accelerations resulting from longitudinal vibrations induced in the
drilling gear by the operation of the cutter wheel tool are picked
up. The voltages delivered by these accelerometers are processed by
the impedance adapters 32 and 37. The low impedance voltage
resulting therefrom is transmitted by the ring-brush system to the
differential amplifier and voltage limiter assembly shown in FIG.
4. In this way, the components of the signal whose frequency is
higher than 5 kc./s. are eliminated and also the amplitudes higher
than about 1.2 volts.
The signal leaving the arrangement shown in FIG. 4 is applied to
the input of the filter shown in FIG. 5, which ensures the
filtering in a pass band which is between 40 and 100 c./s. This
band is centered on the frequency of 70 c./s, corresponding to a
speed of rotation of the tool of 210 r.p.m. which produces an
excitation frequency of the drilling gear of 70 c./s. In fact, with
each rotation of the drilling gear, 20 elementary pulses are
transmitted by the external row of teeth on each cutter. It was
found that this transmission of pulses, accounted for by the
external row of teeth, predominated over the transmissions
accounted for by the cutters or by the teeth forming the
intermediate row carried by each cutter. However, it is possible,
by using a different pass-band filter, to analyse the vibrations
generated by the cutters or by the intermediate row of teeth. It is
also possible to control an adjustable pass-band filter by means of
a signal obtained from the frequency of rotation of the drilling
gear, for example from the instantaneous speed of rotation.
The amplitude of the filtered signal is recorded as a function of
the advance of the tool while the latter is working at the cutting
position.
This signal can be used as an input value in an arrangement by
means of which it is possible to establish, from this signal,
control values serving for the automatic control of the drilling by
acting on the brake of the winch of the drilling gear, so as to
increase or decrease the weight bearing on the tool, and on the
power supply to the motor, so as to vary the speed of rotation
and/or the rate of delivery of the mud. The transmission of the
signals between the pickup devices and the processing circuits is
effected, in the embodiments described above, by means of wired
connections. It would be possible instead to achieve this
connection by means of Herzian (radio) waves or by means of
acoustic waves, for example ultrasonic waves.
In FIG. 7 a drilling derrick is shown at 101, a suspension cable
assembly which supports a train of drilling rods 108, being shown
at 102. At 103 is shown an injection head which permits mud to be
introduced into the drilling rods and a detection connector 104
receives information by way of the stream of mud, processes this
information and transmits it to a memory store. The rod which
drives the drilling gear is shown at 105 while the rotary table is
shown at 106. At 107 is shown the ground formation in which a well
or drill hole has been bored by means of the train of rods 108,
which supports a train of boring rods 109. In the train of rods 109
there is incorporated a special measuring rod 110 serving for the
transmission of signals from the bottom of the drill hole to the
surface and which constitutes a part of the device according to the
invention.
To this special rod 110 there is connected a tool-carrying device
111 fitted with a tool 112 which directly attacks the rock. A
receiver 113 is disposed at a certain distance from the drill hole
to receive information passing by way of the connector 104 and
permits one to obtain, as a function of the depth, a magnitude
which is characteristic of the mechanical properties of the rocks,
which magnitude can either be recorded or can be used for the
automatic control of drilling.
In order to achieve this transmission, the connector 104 is
provided with a radio transmitter having an antenna 114. The device
113 has a receiving antenna 115.
FIG. 8 shows the details of the rod 110 referred to in the
description of FIG. 7. It comprises a body 116. Inside this body
there is disposed firstly an assembly 117 for modulating the
pressure of the mud, constituted by a valve, the opening and
closing of which are controlled sequentially by a circuit unit 118
receiving control signals from an electronic circuit 119 situated
in the lower part of the body. The valve member 117 closes against
a seat 120 through which the stream of mud normally passes, thereby
producing pressure pulses. Signals coming from the electronic
circuit 119 are transmitted to the pressure modulator by a
connection 121. Between the pressure modulator and the electronic
circuit 119 there is disposed the measuring connector 122 which is
a rigid steel connector on which are mounted series of strain
gauges 123 and 124 and/or acceleration pickups 125, 126 and 127.
This connector is protected from the external medium by the jacket
122a which is fixed at one of its ends and free at the other,
fluid-tightness being provided at this other end by means of a
toroidal washer.
The various pickups are connected by cables which pass through a
tube 128 which connects the chamber defined between the connector
and the jacket to the electronic assembly 119.
The stream of mud, after passing through the space between the
valve member 117 and the seat 120, flows around the modulation
device 118 and passes into the interior 129 of the measuring
connector. A recess 130 allows the stream of mud to pass into the
annular space 131 surrounding the electronic assembly 119. Recesses
132 allow the current of mud to pass back into the interior of the
tool-carrier 133 by way of the tube 134. Meanwhile the current of
mud is used to drive a turbine 135 which supplies the electrical
energy necessary for the operation of the electronic assembly
119.
Acceleration detectors 126 are placed on the two opposite
generatrices of the connector in such a way that their axis is
parallel to the axis of the connector.
The acceleration detectors 125 are arranged on the opposite
generatrices at the same height, their axis being perpendicular to
the axis of the connector.
The detectors 125 permit torsional vibrations to be selected while
the detectors 126 permit longitudinal vibrations to be
selected.
The detector 127 is arranged parallel to the detector 125, this
single detector permitting a sinusoidal oscillation to be obtained
whose period is directly related to the speed of rotation. This
detector enables the basic frequency to be defined, upon a multiple
of which basic frequency the filtering of the vibrations is
centered. The frequency upon which the frequency is centered is a
multiple of the speed of rotation.
The gauges 123 and 124 permit either the longitudinal vibrations or
the torsional vibrations to be selected. For this purpose the
gauges are arranged in a half-bridge in a direction which is
related to the type of vibration which one wishes to measure.
Although the assemblies of acceleration detectors and deformation
gauges have been shown in the same figure, one of these assemblies
can be used on its own in order to select one or the other mode of
vibrations, according to whichever may appear more
representative.
The processing of the electrical values supplied by the gauges or
acceleration detectors is effected in the manner which will be
described below.
When acceleration detectors are used they are disposed on two
opposite generatrices of the measuring connector and the electrical
signals supplied by these detectors are opposed to one another in a
differential amplifier. In this way the signals representing the
vibratory state which is being investigated are added while all the
signals representing parasitic vibrations are eliminated. At the
output of the differential amplifier there is available a single
signal whose amplitude is substantially double the effective signal
supplied by one of the detectors. This signal is then processed. In
a first stage the amplitude is limited to a value which is
determined in advance; this can be done in a saturation amplifier
whose maximum amplitude is determined by the inverse potential of
the diodes. The signal thus treated is applied to a band-pass
filter whose mean frequency is a multiple of the speed of
rotation.
For this purpose the accelerometer 127 delivers a sinusoidal
potential which can be selectively amplified in the band from 0.2
to 5 Hz. Then by means of a frequency multiplier, one multiplies
the frequency thus obtained by a number which takes account of the
number of attacking elements of the tool. For example, when one
uses the preponderant mode of the vibrations delivered by the outer
row of teeth carried by the wheels of a tricone tool, the
multiplication factor is about 20.
The circuit described above is shown in FIG. 9 in which the
acceleration detectors 136, 137 are shown connected by leads 138,
139 to a differential amplifier 140. The output 141 of the said
differential amplifier is connected to a peak-clipping device 142
whose output 143 is connected to a band-pass filter 144 controlled
by a frequency which is a multiple of the speed of rotation
measured by the accelerometer 127 in FIG. 8. The sinusoidal
potential supplied by this accelerometer 127 is filtered by a
filter 145, then the frequency is multiplied by the frequency
multiplier 146.
The signals supplied by strain gauges are processed in a similar
manner. The signal is obtained directly due to the arrangement of
the deformation gauges in the form of a whole bridge, the
compensation gauges being arranged to measure the vibrations being
investigated and to eliminate the effects of parasitic vibrations
and of temperature and pressure.
The filtering of the signal coming from the pickups after
processing can be effected by a filter controlled by the speed of
rotation of the drilling gear.
In a modification which is applicable whatever the position of the
measuring section, a series of filters having a fixed passband and
a fixed mean frequency can be used. The signal obtained from the
pickups is supplied to the filter whose mean frequency corresponds
to the desired frequency of filtering.
This is shown in FIG. 10. The signal which gives a measure of the
speed of rotation is obtained from the pickup 127. It is filtered
by the fixed filter constituted by the inductance 147 and the
capacitance 148. The filtered signal is applied to a selector 149
which commutates the input 150 to various outputs 151, 152, 153,
154 each of which is connected to a band-pass filter 155, 156, 157,
158.
The central frequency of the various filters is different. The
frequencies are distributed in such a way that the upper cutoff
frequency of each filter is substantially equal to the lower cutoff
frequency of the following filter. The frequency of commutation is
related to the frequency of the filters.
The signals from the various filters are collected by a single
output element 159 and the resulting signal is coded and then
transmitted to the device which modulates the pressure of the
mud.
In the case where the measuring section is in the vicinity of the
tool and the signal representing the amplitude is transmitted by
modulating the pressure of the stream of mud, the pressure
variations are detected by a pressure detector disposed inside the
connector 104 described with reference to FIG. 7. This detector
influences the modulating action of a transmitter of electronic
waves which is arranged in the same connector 104. The resulting
transmission is received by the device 113 which, after appropriate
processing, supplies an electrical value which can either be
recorded or can be used as a control value for controlling the
input of a computer which controls drilling.
It is within the scope of the invention to replace the device for
modulating the pressure of the mud by a magnetostrictive
transmitter coupled to the train of rods. In this case the coded
signal is used either for direct control or to control the
modulation of the magnetostrictive transmitter. A receiver of the
same kind, that is to say a magnetostrictive receiver for example,
is arranged in the connector which is situated above the drive rod.
It enables the signals transmitted by the train of rods to be
detected and applied to the Herzian transmitter associated
therewith. The signal which is thus transmitted to the processing
apparatus is transformed into a value which can either be recorded
or used for controlling drilling.
Another mode of carrying the invention into effect consists in
using only a single detector, for example a single accelerometer or
a single pair of strain gauges (one operative and the other serving
for compensation) or a pressure detector which is responsive to
variations in the pressure of the mud.
In this case the differential amplifier is replaced by an ordinary
amplifier connected with a frequency filter and a level limiter.
The other parts of the measuring circuit are unchanged.
It will be apparent that the invention can be carried into effect
using modifications of the system described but based on the same
basic principle, without departing from the scope of the invention
as defined by the appended claims.
* * * * *