FR2674030A1 - Logging tool with transmission/reception apparatus having variable geometry - Google Patents

Abstract

In a tool body designed to be lowered into a well at the end of an electrical transmission cable (3), a variable-geometry transmission/reception apparatus is arranged which includes at least one transmission unit designed to send signals to the formations surrounding the well, and at least one unit for receiving the signals reflected by the formations. The variation in the geometry may be obtained by combining, with at least one of the said transmission and/or reception units, translation means (endless screw 13, motor 15) allowing it to be moved parallel to the axis of the well and a control assembly (16, 17) for controlling the movements of the mobile unit. It is also possible to select, by electric switching, a pair of transmission and reception units for the signals with a particular separation, from a large number of units distributed in proximity to one another along the tool body, and optionally juxtaposed. Application for acoustic logging in the scope in particular of very-high resolution micro-reflection operations or for electrical logging, for example.

Description

 The present invention relates to a logging tool with a variable geometry transceiver adapted to be moved along a well or borehole.

 Studies relating to the nature and configuration of the subsoil are often carried out by drilling through one or more wells and by dropping a well tool at the end of an electric cable. In the tool is arranged a logging device adapted to the type of investigation carried out, comprising at least one unit for transmitting signals to the formations surrounding the well and at least one unit for receiving the signals returned by these same formations. The signals received are most often adapted by an electronic assembly for acquisition in the tool before being transmitted by lines of the power-carrying cable to a control and recording device on the surface.

 The transmitting units and the receiving units are installed in the body of the tool at fixed locations thereof remote from each other.

 In sonic type tools, the transmitting and receiving units include piezoelectric or magneto-restrictive type transducers.

 With several transmitters and receivers it is possible to produce collections of sonic traces with a receiving point, transmitting point or common mirror point, similar to those carried out in seismic prospecting by refraction or reflection, and to apply to sonic data treatments similar to those carried out in the field seismic.

 The smallest distance of the order of 10 to 50 cm separating two consecutive receivers or two transmitters is usually used as vertical resolution. The depth of investigation in the formations around the well corresponds to the depth of investigation of the refracted waves (from a few tens of centimeters to 1 meter).

It is a function of the speed of sound in the training.

Long spacing tools allow good time discrimination of different arrivals, as long as
The transmitter is sufficiently powerful and that the attenuation of the terrain crossed is not too strong. The dominant transmission frequency is generally of the order of ten tens of kHz and the width of the frequency band on reception from a few hundred Hz to a few tens of kHz. The sampling steps in time of the received signals are generally a few microseconds for a listening time of a few milliseconds.

 For petroleum applications, the sonic tools are lowered into wells of small diameter (less than 0.5 m) and kept centered in the well filled with liquid (mud or water). In large diameter holes, the tool is kept off center to avoid too great dispersion of the wave in the mud.

 Axial symmetry well tools have multi-directional transmitters and receivers. The emitters generate in the fluid a compression wave which gives rise in formation to a compression wave (P wave) and / or a shear wave (S wave) at the limiting angles of refraction.

 In a vertical well, such tools make it possible to record five propagation modes, the refracted compression wave, The refracted shear wave, only in rapid formation, The fluid wave and two guided dispersive modes which are the waves pseudo-Rayleigh and Stoneley waves.

 To obtain information on S waves, tools equipped with polarized transmitters and receivers can be used. Such tools generate compression waves polarized perpendicular to the axis of the well; these compression waves create flexural modes at the wall of the well, which give rise in the formation to pseudo-shear waves propagating parallel to the axis of the well.

 Different well tools are described for example in the patents GB 2 108 668, US 4 850 450, US 4 951 267 etc.

 The relatively small number of transmitters and / or receivers of existing logging tools and their relatively large spacing has the effect of limiting their investigation capabilities.

For spacings of the order of 15 to 25 cm, which are common, we note that in some cases, the refracted modes P and S and the fluid modes (propagation along the well) for example are masked by the effects of '' spatial aliasing. When
The spacing is larger, of the order of 20 to 25 cm for example, certain reflections are practically impossible to identify.

 The logging tool according to the invention makes it possible to avoid the drawbacks mentioned above. It comprises an elongated tool body adapted to be lowered into a well or borehole, connected to a device for maneuvering on the surface by an electro-carrying cable provided with transmission lines, and a logging device performing successive emission cycles. reception of signals comprising at least one unit for transmitting signals towards the formations crossed by the well or borehole, and at least one unit for receiving the signals.

 The logging tool according to the invention is characterized in that it comprises an arrangement for modifying the relative arrangement of the units of the logging device involved in said transmission-reception cycles, and a control assembly for obtaining a configuration. determined from the logging device by displacement of at least one mobile unit.

 According to a first embodiment The arrangement for modifying the relative arrangement of the units of the logging device involved in said transmission-reception cycles, comprises means for longitudinally moving at least one of said units relative to the others. logging unit.

 The longitudinal displacement means comprise for example at least one shuttle associated with drive means for moving said shuttle in a direction substantially parallel to the direction of elongation of the body of the tool.

The drive means of each shuttle comprise for example a worm screw arranged in a direction substantially parallel to the axis of the body, a nut driven in translation by the rotation of said screw, a motor for driving the screw in rotation , The steering assembly comprising means for counting the number of turns of the screw and preselection means allowing an operator to impose the spacing between said units and
The spacing between two positions of each mobile unit.

 The logging device can comprise at least two mobile units each associated with drive means.

 The drive means comprise, for example, motors for driving each mobile unit separately and independently of each other.

 The drive means may also include a single motor for driving said mobile units.

 According to one embodiment, the logging device comprises at least one fixed transmitter of acoustic waves and at least one mobile receiver of acoustic waves connected to the control and acquisition assembly.

 According to another embodiment, the logging device comprises at least one acoustic wave transmitter and means for making it directive.

 According to another embodiment, the transmitting or receiving unit comprises for example a plurality of electrodes fixed to an electrode holder for transmitting or receiving electrical signals and said mobile unit is a cursor element connected to an electric generator , Said cursor element being adapted to come into contact successively with a plurality of electrodes fixed to an electrode holder, by displacement of said shuttle.

 The control assembly preferably includes means for counting the number of turns of said screw, means for preselecting the spacing between said units and the pitch of movement of the tool between two successive measurements, and circuits Logics to control The displacements of each mobile unit according to their spacing values and preselected steps.

According to a second embodiment, the logging apparatus comprises a plurality of signal transmission and / or reception units distributed along the probe and a control unit for said units, the arrangement for modifying the arrangement relative units of the logging device involved in said transmission-reception cycles, in this case comprising means for selecting from all of said units, at least one stroke the transmission and reception units whose spacing is selected from a discrete set of spacing values
The selection means comprise for example a switching element electrically connected on the one hand to the control assembly and on the other hand to said transmitting and / or receiving units.

 Said transmitting and / or receiving units are for example acoustic or seismic transducers or alternatively electrodes in electrical contact with the formations through which the well passes.

 The invention also relates to a method for implementing the logging tool.

 This method includes, for example, the use of a logging device suitable for carrying out acoustic soundings, carrying out acoustic soundings to identify reflections on discontinuities in the formations surrounding the well, and Establishing sections with constant offset to follow up on the reflections previously identified.

 The method can also include the use of a logging device suitable for carrying out acoustic sounding by reflection and carrying out micro-reflection operations to locate by continuity the location of discontinuities in the formations surrounding the well.

 The use of displacement means and / or means for selecting pairs of transceivers makes possible all kinds of configurations from a transceiver assembly to one or more transmitters and / or receivers and therefore the optimum selection. the spacing parameter which can reveal discontinuities in the mid places crossed by the logging tool and in particular geological discontinuities in the terrain surrounding a well, within the framework of a use in the geophysical field. With the logging tool according to the invention, it is possible to make localized studies at very high resolution in acoustic micro reflection.

Other characteristics and advantages of the logging tool according to the invention will appear better on reading the following description of an embodiment described by way of nonlimiting example, with reference to the appended drawings where - Fig. 1 shows a logging tool lowered into a well for
take measurements; - Fig.2 schematically shows a first mode of implementation of
The invention with an assembly allowing the controlled movement of a
location of transmission and / or reception of signals by at least
a transmitting and / or receiving unit; - Fig.3 schematically shows another embodiment where
movement set changes where signals are applied
transmitted by selection of a transmission unit from a plurality
of units distributed along the body of the logging tool
applied for example to an electrical logging probe; and - Figs. 4 to 8 show different records of the same area
of a representative physical model of a well, obtained with a
acoustic logging device with two spacing receivers
variable, for decreasing spacings.

- Fig.9 schematically shows a second mode of implementation
of the invention by selecting a pair of transceiver
signals among a large set of transmitters and receivers
distributed along the body of the tool; and - Fig.10 shows an application similar to that of Fig.3 where
Electrode selection means are used in the case of
electrical logs.

 The well tool 1 shown in FIG. 1 is lowered into a well or borehole 2 at the end of an electrically-carrying cable 3 connected to a support structure 4 disposed on the surface. The cable is wound on a storage reel 5 placed on a truck 6. The cable 3 generally used, comprises a plurality of transmission lines allowing exchanges of control signals between the apparatuses in the tool 1 and a control station 7 on the surface, and also a transfer to it and the data collected.

 According to the embodiment of FIG. 2, the transceiver apparatus comprises a first fixed unit 8 for transmitting or receiving signals arranged on a first fixed support 9 and a second unit 10 movable relative to the first. This second unit is fixed on a second support or shuttle 11 secured to a nut 12 locked in rotation. The nut 12 is engaged on an endless screw 13 held towards its opposite ends by two guide boxes with bearings 14a and 14b. The worm 13 is rotated by an electric motor 15. The rotation of the screw 13 has the effect of longitudinally displacing the nut 12 and the associated shuttle 11 and therefore varying the spacing e between the first unit 8 and the second 10.

 According to one embodiment, the logging tool comprises a fixed wave transmitter, a first fixed receiver carried by the fixed support 9 and a second receiver carried by the mobile shuttle 11. With this arrangement the first fixed receiver can be used by example to calibrate by comparison the signals received by the mobile receiver.

 The logging tool also includes a first control module 16 in the body of the tool and a second surface module 17 connected to each other by lines included in the electrically-carrying cable 3, to control the displacement and positioning of the units in relation to each other. The rotation of the screw 13 which conditions the movement of the second unit 10 is measured by a tachometer 18. After shaping by an element 19, the pulses produced by the tachometer 18 are applied to a counter- down counter 20 and a counter 21 operating as a down counter. The up-down counter 20 is connected to a display 22 in the second module 17, which indicates the value of the spacing e.

In this same surface module, a preselection element with coding wheels 23 is arranged, allowing the operator to set a set value for the spacing e. This setpoint is transmitted by the cable 3 to a comparator 24 in the bottom module 16, arranged to compare the setpoint and the current value in the counter 20. The comparator 24 is connected to a logic control circuit 25 An electrical supply assembly 26 in the surface module 17 is connected by lines of the electrically-carrying cable 3, to a circuit 27 for controlling the motor 15 and to an assembly G for supplying the various elements of the module bottom 16. The motor control circuit 27 is interposed between the latter and the logic circuit 25. Any inequality detected by the comparator 24 causes the motor 15 to rotate in one direction or in the opposite direction, depending on the sign of this inequality . Upon detection of EQUALITY, the control logic circuit cuts the power to motor 15.

The device also includes means for preselecting the value of the pitch of displacement of the well tool between two successive measurements, consisting of coding wheels 28 in the surface module 17, connected by a line of the cable 3 to a preselection input. of the counter 21. A control input of the counter 21 is connected to the output of a door 29. The output of the counter 21 is connected to a control pulse generator 30. This pulse is applied to a control input of the gate 29 and via a shaping element 31, to a device for transmitting and receiving logging signals 32. A logic control circuit 33 has a first input connected to the output of the counter 24, a second input 34 for the initialization of the positioning of or each mobile element and a third input 35 for selecting the fixed or mobile operating mode. A first output of the control logic circuit 33 is connected to the Control logic circuit 25. A second output is connected to the control input of door 29. A third output is connected, via a line of cable 3, with the control 36 of the winch 5 on the surface (Fig.1)
The operator has the possibility to select a particular spacing e for a whole series of log measurements between a minimum value and a maximum value, and he can do it by
The intermediary of the coding wheels 15. He can also choose, during the same series of log measurements, to vary in steps
The spacing e and in this case, it activates the coding wheels 28 for the selection of the pitch. When the Logic circuit 34 detects that the shuttle 11 is at the end of its travel, it commands by 36, the winch 5 on the surface, to bring the transmission-reception means opposite in the next well interval.

 According to another embodiment (not shown), there is a second shuttle on the side of the first fixed support opposite the first shuttle. It is also associated with a worm and a drive motor to vary its spacing relative to the first fixed support. The drive motor of this second screw can be separate from the motor driving the first screw.

 According to a variant of the previous embodiment, one can fix one to the other two worms with opposite winding direction threads, drive them in rotation by a single motor and in this case, their rotation has the effect of moving the two mobile shuttles away or closer together from the fixed support.

In Figs. 4 to 8, we can see the incidence of
The separation of an acoustic receiver from a fixed transmitter, on recordings obtained in a model representative of a well. The DX spacing varies from 25cm for Fig. 4 to 5cm for Fig. 8 in 5cm steps. For spacings of 25 to 15 cm (Fig. 4 to 6), we note that the refracted modes in P and S waves are affected by
The effect of spatial aliasing or aliasing. For spacings of 20 and 25cm (fig. 4, 5), we also see that the reflections are practically impossible to identify. In the example shown in
Fig. 8 for example, we see, on the other hand, that the different wave trains are correctly sampled spatially and that it is possible to identify different waves which, in a well, correspond to diffractions on fault planes for example.

 The device according to the invention can also be used in the context of electrical logging operations. According to this embodiment, the mobile support 11 is used to move longitudinally a cursor or brush 37 (Fig. 3) connected to an electric generator (not shown) in order to bring it successively in electrical contact with a series of electrodes 38 fixed to an electrode holder 39 and brought into contact with the wall of the well. By displacement of the cursor 37 caused likewise by the rotation of the screw 13, the point of application of an electric current to the wall of the well can thus be moved in steps.

 According to another embodiment of the invention, the production of a transmission-reception apparatus with variable geometry is obtained by positioning along the body 1 of the tool a large number of transmission units and / or reception regularly spaced and by selecting among them, at least once the transmission-reception. Along the body, there is for example a set of n reception units R1, R2, ... Rp, ... Rn with a determined distribution. The interval between them can be fixed and reduced for example to the minimum spacing compatible with their transmission and / or reception section. The most appropriate spacing in this case is a multiple of the elementary spacing separating two successive units.

 It is also possible to vary the interval between the units R1 to Rn according to their position of installation along the body.

The selection of at least once the transmission and reception units is carried out by means of a switching member 40 connected on the one hand to all the receivers R1 to Rn and on the other hand to a set of control 41. This is adapted to actuate the transmitter E, to control the switch 40 so as to select one of the receivers
Rk having with the transmitter E a spacing Lk suitable for the operation carried out.

 According to a variant of the previous embodiment, it is also possible to associate the switching device 40 with a plurality of transmitters and operate by associating a selected transmitter with a single receiver.

 One can also possibly operate from a combined structure by having a set of transmission units E and a set of reception units R, each associated with a switching device and select a transmission unit and a unit. reception among these two sets whose spacing is suitable for a specific application.

According to another embodiment similar to that of the
Fig. 3, it is also possible to associate the selection switch 40 (FIG. 10) with a plurality of electrodes S1, S2, ... Sn brought into contact with the wall of the well, and thereby select the distance separating a transmitting electrode or receiver and a complementary receiver or transmitter electrode.

 It would not go beyond the scope of the invention, by using in a seismic or acoustic application, a directional transmitter and / or receiver or by providing at least one transmitter or receiver of the logging device, with an absorbent element arranged so as to make the directivity diagram of this transmitter or receiver asymmetrical so as to favor the waves emitted towards one side of the probe or else the waves received in a certain direction as described in French patent application No. 90 / 17029.

Claims (17)

 1) Logging tool comprising an elongated tool body (1) adapted to be lowered into a well or borehole (2), connected to a surface operating device (4, 5) by an electrically-carrying cable (3) provided with transmission lines, and a logging device performing successive signal transmission-reception cycles, comprising at least one unit for transmitting signals towards the formations crossed by the well or borehole, at least one reception unit signals and a control and data acquisition assembly (32), characterized in that it comprises an arrangement for modifying the relative arrangement of the units of the logging device involved in said transmission-reception cycles, and a control assembly for obtaining a determined configuration of the logging device by moving at least one mobile unit.  2) Logging tool according to claim 1, characterized in that the arrangement for modifying the relative arrangement of the units of the logging device involved in said transmission-reception cycles, means for moving longitudinally One at least said units relative to the other units of the logging apparatus.  3) Logging tool according to claim 2, characterized in that the longitudinal displacement means comprise at least one shuttle (11) associated with drive means for moving said shuttle in a direction substantially parallel to the direction of elongation of the body (1) of the tool.  4) Logging tool according to claim 3, characterized in that said drive means of each shuttle comprise an endless screw (13) arranged in a direction substantially parallel to the axis of the body, a nut (12) driven in translation by the rotation of said screw, a motor (15) for driving the screw in rotation, the control assembly comprising means (18-21) for counting the number of turns of the screw and means (23, 28) preselection allowing an operator to impose the spacing (e) between said units and the spacing between two positions of each mobile unit (10).  5) Logging tool according to one of the preceding claims 2 or 3, characterized in that the logging device comprises at least two mobile units each associated with drive means  6) Logging tool according to claim 5, characterized in that said drive means comprise motors for driving separately and independently from each other each mobile unit.  7) Logging tool according to claim 5, characterized in that said drive means comprise a single motor for driving said mobile units.  8) Logging tool according to one of the preceding claims, characterized in that the logging device comprises at least one fixed transmitter (8) of acoustic waves and at least one mobile receiver (10) of acoustic waves connected to the control and acquisition assembly (32).  9) Logging tool according to one of the preceding claims, characterized in that the logging device comprises at least one transmitter of acoustic waves and means for making it directive.  10) Logging tool according to one of claims 2 to 9, characterized in that the transmission or reception unit comprises a plurality of electrodes (38) fixed to an electrode holder (39) for transmitting and receiving electrical signals and said mobile unit is a cursor element (37) connected to an electric generator, said element being adapted to come into contact successively with said electrodes (38) by displacement of said shuttle.  11) Logging tool according to one of the preceding claims, characterized in that the control assembly comprises means (18-21) for counting the number of turns of said screw (13), means (23, 28) for preselecting the spacing between said units (8, 10) and the tool displacement pitch between two successive measurements and logic circuits (25, 33) for controlling the displacements of each mobile unit as a function of values spacing and preselected steps.  12) Logging tool according to claim 1, characterized in that the logging apparatus comprises a plurality of signal transmission and / or reception units distributed along the probe and a control unit for said units, L arrangement for modifying the relative arrangement of the units of the logging device involved in said transmission-reception cycles, comprising means (40) for selecting from all of said units, at least one pair (El, Rk) of units transmission and reception whose spacing (Lk) is selected from a discrete set of spacing values.  13) Logging tool according to claim 12, characterized in that the means for selecting from among all of said units, at least one shot of transmission and reception units, the spacing of which is chosen from a discrete set of values spacer, comprise a switching element (40) electrically connected on the one hand to a control assembly (41) and on the other hand to said transmitting and / or receiving units.  14) Logging tool according to claim 13, characterized in that said transmission and / or reception units are acoustic or seismic transducers.  15) Logging tool according to claim 13, characterized in that said emission and / or reception units are electrodes in electrical contact with the formations through which the well passes.  16) Method for implementing the logging tool according to one of the preceding claims, characterized in that a logging device suitable for carrying out acoustic surveys is used, acoustic surveys are carried out to identify reflections on discontinuities in the formations surrounding the well, and sections with constant offset are established to follow the reflections previously identified in continuity.  17) Method for the implementation of the logging tool according to one of claims 1 to 15, characterized in that one uses a logging device suitable for carrying out acoustic probes by reflection and one performs micro-reflection operations to locate the location of discontinuities in the formations surrounding the well by continuity.