IL33261A

IL33261A - Process and installation for measuring the physical characteristics of rocks during drilling

Info

Publication number: IL33261A
Application number: IL33261A
Authority: IL
Original assignee: Aquitaine Petrole
Priority date: 1968-10-30
Filing date: 1969-10-27
Publication date: 1972-12-29
Also published as: CA925848A; CH511363A; RO75744A; DE1954256A1; IL33261A0; US3626482A; OA03335A; RO75744B; DE1954256B2; DE1954256C3; JPS502841B1; ES372983A1; GB1285985A; LU59716A1; NL6916279A; BE740919A; DD77941A5

Description

Physical Process and Installation for Measuring the/Characteristics of Rocks during Drilling y>o y tyu» wsnbv τη-tp nya Tmp nonyai no»p I 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 o the rock* Experiments have previously bee 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 informationdelivered by a vibration pickup device* with the object of supplying instantaneous information relating to the characteristics of the j 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 V-- signal is capable of being used after processing as a value from which command signals can be estab- lished for automatically controllin the drilling.

Another object of the invention is to provide means with which 1* 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 rooks encountered by the tool.

The method accordin to tho. invention makes it possible to obtain, as a function of the depth at whioh the tool is operating, a value which is directly related to the physical, mechanical and stratigraphio properties of the rocks being attached by the drillin tool. , .

The method aocofdin to the, invention, oomprises collecting, at at least one. oint 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 f om the signal thus processed,, a frequency, band centered i 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 o the signal. thus, selected, the value thereo .being directly ΊΑΛted to the lithological prope ties of \ 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 frer-quencies which arises when the attacking elements of the tool act on the rock tor 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 tooli 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 pperative 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 mnmber of wheels which form the primary In addition, the number of teeth carried by each cutter wheel can fcary. There may be, for example - approximately 22) 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, thee-) suffaces 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 llthological properties of good ouality 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. / Ρ,Α. 35261/ί During the course of tests it has been P.A. 3^1 2 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 straikh gauges arranged parallel to the axis of the drilling gear and in a plane perpen-> dicular 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 b 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 & 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 P.A. 33*61/2 f table by means of which the drilling gear is driven in rotation, the gauges being inclined at 45 degrees 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 totary table, while the torsional vibrations ar^ picked up below the rotary table, the pickup devices being positioned in accordance with the nature of the vibratipns which are to be collected, as will be apparent to, anyone skilled in the art, j ' When the masuring section is disposed at a / I place near the tool, a l signals are collected below the rotary tablo and it i$ only the . different positioning of the pickup devices/ which determines the nature oi the vibrations which are/to be collected.

In tne/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 suit- • I able device such as a magnetostrietjive bar or a piezo- ,j electric crystal, or by. means of the stream of mud, the The invention is also concerned with appartus 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, mean,s for processing the said signal in such a way as to limit ii&s 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, timesthe 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 ' 'rilling tool is operating.

The apparatus used preferably comprises at least one pair of pickup devices and means for effecting the algebraic summation or the install taneous differencing of the signals obtained from each pickup device in orde ' to obtain a singiti 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 ar applicable moire particularly to use with a pair of pickup devices. A similar s stem can be used when the signal is collected by a single pickup device, without departing from the scope of the present invention.

P.A. 33261/2 The measuring appartus used at the upper part of the drilling gear will he described with reference to the following embodiments In a first embodiment, the devices for picking up longitudinal vibrations are constituted by txtfo accelerometers disposed on opposite generatrices of a sleeve interposed between the injection head and the "%¾d which drives the drilling gear in rotation, the accelerometers being placed on shoulders which are perpendicular to the axis of the sleeve and offset aaially by from 2 centimeters to 9 inetiiers, the electrical axes of the acclerometers being parallel and opposed.

In a second em odiment, the devices for picking up torsional Vibrations are constituted bjp two acceler- meters placed on diametrically opposed generatrices of the lower part of the rod which drives the drilling gear, the accelerometers being arranged on shofltlders 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 vibaations arc strain gauges arranged on a sleeve interposed between the injection head and the rod for rotating the drilling gear, the pickups being at two diametrically opposed and 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 pre-fera ly used where it is desired to observe the longitudinal vibrations, which permit obtaining a useful signal when usin£ tools operating by percussion, for example tools having cutter wheels, whereas the second and fouith 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 x*ays; A first embodiment consists in plaoing 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 accelerameter 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 s¾4ected signal and uses this amplitude to control a device for transmitting this amplitude to a detector located at the upper P.A. 1 . part of the drilling gear, the? said amplitude then being correlated with the drilling depth.

V '■ Three other embodiments using, espectively, strain gauge 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, bjp 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 drawingss Fig.l is a digraramatic view of apparatus according to the invention mounted on a drilling infttalla$io: Fig,2 shows the details of the mounting of accelerometer when these are arranged on a sleeve interposed between the injection head and the rod by which the drilling ^ear 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. is a circuit diagram of the electronic system of the arrangement which ensures the elimination of parasitic voltage due to shocks, in the case where accelerometers are used as pickup devices.

Fig.5 is the circuit diagram of a filter ' r . emitted bj> a cutter wheel tool rotating at a speed of 200 r.p.m, Fig, 6 shows two digraphs; the diagraph 73 is an ac^oustic 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 indention 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 wave trainsjemitted by the device of i?ig. 8, Fig. 10 shows a series of filters for adjacent frequencies which are connected as a function of the operational spge§ 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 carrying the movable pulley assembly is indicated at 4, Connected to tho said block 5 is a hook 6r which supports the injection head 7·. The upper part of this injection head 7 is fixed while tho lower part can be rotated by means of a bearing system. Indicated at 8 dLs the flexible injection pipe which is connected at one end to the injection head 7 and at the other end to the s^dge pump assembly, ngm shown in the drawing* The rod by which tho flod 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 itefsrrod to simply as the "square rod. " Thia rod 9 is driven in rotation by the ootating table 10, which itself is driven by a motor (not shown). A drill shaft is indicated diagraramatically 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 which processes the electrical values representing the vibrations is indicated at 14. This signal processing assembly is connected, in the embodiments 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/ is connected by a line 18 p o a pickup device 17 permitting the progress of the drilling to be measured. This measurement of the progress of 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 ahd a male thread at its lower part. A member 21a bears on the fixed part of the injection head 7 (S?lg. l) and thus causes the external part 22 of the arrangement shown in Fig, 2 to be* held in a fixed position. The sleeve1( 2l/| on its external surface, a shell 23 on which is fixed an insulating block 24, which la thus fast with the sleeve 21 , This block 24 carries a series of metal rings, represented a 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,2 c,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 23. The cable 28 extends out of the arrangement through a pro∞ tective 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 island 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 acceler-ometer which delivers an electric signal under the influence of an acceleration. As 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 transi3-tor' having an input impedance of several megohms and an c$£put impedance of the, order of 1 k/l, 13 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 5b, Indicated at 36 is a second accelerometer ofthe 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 acceler meter 36 is likewise connected by a cable 36a tc 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.

Pig. 3 shows another form of>ihe vibration measuring assembly or pickup device indicated at 13 in the diagrammatic assembly shown in Pig. 1. Hef rring to Pig. 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 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 9 and 50 on the other hand, are opposed to one another in^mea3«ring 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 square7 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 f>.A.33261/2 ^ 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 oomponent 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 l80°j 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 brlnge the gain of the latter to a value close to 20.

Acooss 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 whifth 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, 6l 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 the threshold voltage of this system. With two S . 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 Ϊ1.2 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 Pig, 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 toibratory signal are thus added and, at the output 72, a signal is obtained which represents the maximum P.A.33261/2 , • · V amplitude of the frequenoy band of the signal selected by the filter 67. This electrical value Is available either for being reoorded, or for use for the automatic control of the drilling. The signal is reoorded 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 purpbse of controlling the advance of the recording medium or controlling the storage of the signal.

Fig. 6 tepresetts at 73 a diagraph obtained b an acoustic method in a well drilled for the purpose of producin gas. Represented at " is a diagraph obtained by the method provided by the invention. The figures on the centerllne 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 a&e two dlagraphs is similar and thai, 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 k B obtained at the actual moment of drilling, while the acoustic diagraph 73 was obtained only after drilling was terminated, Theaacoustic diagraph 73 represents the speed' of sound in the rock. It is obtained' by means of an P. A. 33261/2 ultrasonic transmitter-receiver system, which -is displaced in the well, the depth at which the ¾easurement is being made being known, A train of vibration's 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 Jh, the amplitude of the curve represents the amplitude of the signal processed by the method according tc the invention.

The similarity of the signals will be noted, In particular, at about 1, 3^0 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, 3^0, 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, .'rt P.A.33261/2 f ! The operation of the apparatus provided by the invention and the use of the drilling method using a" " tqpl having cutting wheels will be described as fpllows, By meaas of the accelerometers 31 and 36 shown in Fig, 1 which are carried by the sleeve 21 and are located at 13t in Fig, 1 the accelerations resultin from longitudinal vibration induced in the drilling gear by the op;» ration of the cutting wheel tool are picked up. TJre voltages delivered by these accelerometers are processed by the impedance adapters 3 an 37» The low impedance voltage resultin therefrom is transmitted by the ring-brush system to' the differential amplitude and voltage lidilter assembly shown In Pig. 4, In this way, the. [components of the . signal whose" frequency is higher, than kc/3. are' eliminated and also the amplitudes higher than about 1.2 volts, The signal leaving the arrangement shown in Fig, is applied to the input of', the filte shown in Fig. 5J which ensures the filtering in a pass band which is between 40 and 100 c.p.s. This band is centered on the frequency of 70c,/s,, corresponding to a speed of rotation of the tool of 210 r.p.m, flhich produces an excitation frequency of the drilling gear of c./s. In fact, with each rotation of the drilling gear, 20 elementary pulees are transmitted by the external row of teeth of each cutter, it was found that this transmission of pulses, accounted for by the external rot? of teeth, predominated over the transmissions accounted for by the cutters or by the teetfc formin the intermediate row carried by each cutter. However, it is P.A.332^1/2 possible, by using a different pass-band filter, to analyze 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 sigaal is recorded as a function of the advance of the tool while the latter is working at the cutting position.

This signal oan 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, aild 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 circuit is effected, In the embodiments described above, by means of wired connections. It would be possible trisfcead to achieve the connection by means of Herzian (radio) waves or by means o 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, belgg shown at 102. At 103 is ( shown an injection head which permits mud to be Introduced into the drilling. rod3 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 Che drill hole to receive inforaation 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 * P.A..33261/C Pig. 8 shows the details of . the rod.110 referred to in the description of Pig* 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 oloses against a seat 120 through which the stream of mud normally passes, thereby producing pressure pplses. Signals ooming 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 piokups 125, 126 and 127. This connector is protected from the external medium by the jacket 122a which ils fixed at one of its ends and free at the other, fluid-tightness being provided at this other. end b 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, afte passing through the space between the salve member 117 and the seat 120, flows around the modulation device ,ll8 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 pack Into the Interior of the tool-oarrler 133 by way of the tube 13 . Meanwhile the current of mud Is used to drive a turbine 135 which supplied 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 longitudlaal 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 aqmultiple 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 o itudinal ibrations or the torsional vibrations P.A. 3326I/2 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 ca 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 y the gauges or acceleration detectors is effected in the ttanner 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 eliminate*. At the output of the differential amplifier there is available 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 determiaed In advance] this can be done in the 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 multiplied, one multiplies the frequency thus obtained by a number which takes account of the number of attackin 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 trlcone 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 Deads 138, 139 to a differential amplifier l40. The output l4l of the said differential amplifier is connected to a peak-clipping device 142 whose output 143 i 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 ilter l45, then the frequency is multiplied by the frequency multiplier l46.

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 imzestigated and to eliminate the effects of parasitic vibrations and of temperature and pressure.

P*A.3326j|/2 The filtering of the signal coming rom the pickups after processin can be effected Jry a filter controlled by the speed of rotation of the drilling sea .

In a modification which is applicable whatever the position of the measuring section* a series of filters having a fixed pass-band 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 fro the pickup 127, It is filtered by the fixed filter constituted by the Inductance 1 7 and the capacitance 1 8, The filtered signal is applied to a selector 1 9 which commutates the input 150 to various outputs 151, 152, 153* IS1* each of which is oonneoted to a band-pass filter 155* 1 6, 157, 1 8.

The central frequency of the various filters is different. The frequencies are distributed in sucj* 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.

P.A.

. In the cawe 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 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 b the device 113 which, after appropriate processing, supplies an electrical value which can either be reoorded or can be aaed as a control value for controlling the input of a oomputer which controls drilling.

I is within the scope of the invention to replace the device for modulating the pressure of the mud by a eagnetostrictive transmitter coupled to the train pf 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 slgaal which is thus transmitted to the processing apparatus is transformed into a value which can either be recorded or used for P.A.33261/2 ^ 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 pressure detector which,is responsive to variations in the: pressure of the mud. .

In this case the differential amplifier .is . replaced b an, ordinary..amplifier connected with a frequency filter and a level: limiter. The/6ther. parts of the measurin 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 olalms.

Claims

P.A.33261/2 , WHAT IS CLAIMED IS: r

1. , A method for. measuring characteristics of rocks during drilling by means. of drilling gear comprising a drillin tool haying at least one se of elements for attackin rock at depth In drill hole-, means fo driving said drilling tool at a certai frequenoy 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 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 frequenoy equal to said frequenoy of rotation of said tool multiplied by the number of said attacking elements In. at least one of said sejggi?' which selected signal has an amplitude within said band which is directly, related to lithologlcal properties of rocks being attacked b 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 P. A.33261/2 7 two pickup devices arranged at points on two diamet ically opposite genera rices of said measuring section,

4. A method according to Claim 3, in hich said., generated signals are representative of longitudinal vi bratlona, end 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 eiethod according to Claimil, in which said selected signal is obtained by selecting signal components in said frequency band by means of a band½aes filter arrangement haying a mean frequency whioh 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 Aituated at the upper part o said drilling gear.

7. A method according to Claim 1, in which said measuring section is situated near sai tool*

8. A method accordigg to Claim 1, utilizing a tool having a number of cutter wheels, each having inner and outer rows of cutting teeth, in whioh said generated signals are representative of longitudinal vibrations, and said selected. signal is selected ina a frequency band centered o a frequency equal to said frequency of rotation of said tool multiplied by the number of said cutter wheels or the number P. A.33261/2 of cuttingsteeth 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 o aocelero-meters whioh are offset axialiy and &ave 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. F A method aocordlng 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 beingaselected 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 wMch 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 generatedijsiggals represent torsional stresses which are detected by means of strain gauges located In a plane which is incllded at 5° to the axis of said drillin

14. P.A.33261/2 gear of said measuring section, 1 . 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, sai<9 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, •eans 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 vo tage-limiting means.

16. The combination according to Claim 1 on shoulders perpendicular to the axis of said connec- ' tor and being rigidly attached to said shoulders,

17. The combination according to Claim 15> in which said pickup devices are constituted by two aocelerometers 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 aocelerometers being disposed on shoulders parallel to th axi of said connector and the electrical axis of said aocelerometers 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 , pickftng 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 sed&on.

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 Ρ,Α, 33261^ to the axis of said connector.

20. Th 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 mean comprises rod means and said drilling gear includes a drilling head and sleeve Interposed between said, head and said rod means> and said pickup devices are accelerometer3 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 aooelerometers 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 vibrationsj disposed on two diametrioally 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 P.A.33261/2.. y generatrices of said sleeve at two points slightly offset axlally of said sleeve.

24. The combination according to Claim 20» in whioh said drive means comprises rod means and s id 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, i a common plane which is inclined at 5° to the axis of said drilling gear.

25. The combination acoording to Claim 1 , in which said vibration responsive, voltage limiting and frequency bandaselecting 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 acoording 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 magneto-strlctlve means for transmitting along said rod a signal responsive to the amplitude of said selected signal, and a magnetostrictiee 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 21 , 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 P.A, 33261/2 7 4 of said stream of mud in said conduit means, and means for; operating said valve in dependence upon said selected signal, whereby the pressure o said stream- of mud is modulated in accordance . with the amplitude of said selected signal, COHEN ZEDEK So SFISBACH P.O. BOX 33116? TEL AVIV ATTORNEYS FOR APPLICANT