FR3022029A1 - DEVICE FOR SPECTROSCOPIC ANALYSIS OF DRILLING CARROTS - Google Patents

Abstract

A device for the spectroscopic analysis of drill core (C), in particular drill core for oil exploration, mining or scientific exploration using a laser ablation-induced spectroscopic analysis method (LIBS), comprises a measurement unit ( 6), with optical laser illumination means, connected to a laser source (63), configured to direct at least one laser beam capable of generating at a point of the core the plasma required for the use of the LIBS method, optical means for collecting plasma light. An imaging camera makes it possible to accurately photograph the analysis area and to film the analysis (65). At least one spectrometer (93) is connected to the optical collection means. Data processing means are provided for processing the signals provided by the spectrometer (s) and the images provided by the camera. A carrot holder (7) supports the carrot on a measuring table, and to hold the carrot in a predetermined position. Means (61, 62) make it possible to make a relative displacement between the measuring assembly (6) and the core support (7), in at least the axial direction (A1) of the core, and to position the beam laser, respectively the optical axis of the optical collection means, at predetermined points of the core. Adjustment means (511) facilitates adjustment of the distance between the core holder and the measuring assembly.

Description

TECHNICAL FIELD [0001] The present invention relates to a device for the spectroscopic analysis of drill core, in particular of oil exploration, mining, or scientific drilling cores, by a method of spectroscopic analysis induced by laser ablation. , which will be referred to later as the commonly used terminology of "LIBS" for "Laser Induced Breakdown Spectroscopy". According to this technique, a high energy laser and short pulses is used to vaporize and ionize a small amount of material for its analysis. The vaporized material, or the laser-induced rupture plasma, produces a strong optical emission. Spectroscopic analysis of the optical emission gives information concerning the chemical composition of the analyzed material. STATE OF THE ART [0003] The LIBS analysis, which is a rapid analysis technique, without contact, and without sample preparation, has been proposed in various fields, and has also found application in geology. In this field, nothing beats the analysis in situ or, failing that, the remote analysis of samples collected, to really identify and quantify precisely the materials present, and thus evaluate the real interest of one or more site (s). [0004] The old-fashioned approach of the geologist traveling the field still exists. It is often supplemented by sampling for extensive laboratory testing using non-mobile instruments. The process between exploration, selection, collection, transport and analysis of samples is therefore very long and costly. For example, LIBS analysis devices are known on materials in various forms, but in laboratory versions on samples of small dimensions, as taught in particular by CN102692399 or US2009 / 0273782. Others intended for the sequential or continuous analysis of granular materials or bulk powder, such as described in particular in WO2012 / 40769 or US Pat. No. 6,771,368, comprise means such as a conveyor belt for passing the material in scrolling past the measuring set. In recent years, LIBS spectrometers have been developed in a portable version, allowing the geologist to analyze, directly in the field, a few samples of his choice. Although this technique is practically the only one that allows in-situ chemical analysis directly in the field, it is not widespread in field geology because it is long and costly to implement. It is necessary to deport a source of energy recharge, the atmospheric and exposure conditions of the rocks on the surface are not always favorable, and finally it does not allow to ensure a priori a precise positioning of the zone subjected to the analysis . However, such portable LIBS spectrometers, which may take the form of a pistol manipulated by the geologist and positioned at the right of the area to be analyzed, are interesting in a punctual exploratory context. But they are not suitable for systematic and regular analysis required for example for drill core analysis, in order to evaluate the potential of a site for possible exploitation.

The object of the invention is to propose a LIBS analysis device adapted for the analysis of the composition of a drill core, and in particular adapted for a systematic and reproducible treatment with high precision. The aim of the invention is generally to allow acquisition by LIBS-type spectroscopy of elementary geochemistry data of core cores of geological subsoils, and in particular to allow acquisition of vertical geochemical profiles, with high resolution and regular spacing, in such carrots. It also aims to allow such an analysis on a plurality of cores, to ensure a comparison and / or a more effective correlation between cores from different neighboring boreholes. It also aims to facilitate the analysis of many cores by automating the analysis procedures. GENERAL DESCRIPTION OF THE INVENTION [0010] In order to solve the above-mentioned problems and to achieve the desired objectives, the subject of the present invention is a device for the spectroscopic analysis of drill cores, particularly drill cores of oil exploration, mining, or scientific, using a method of spectroscopic analysis induced by laser ablation (LIBS). According to the invention, the device comprises: a measuring assembly, comprising an imaging camera, preferably at high resolution, which makes it possible in particular to locate and identify the measurement zone, to know its appearance, to locate measurement points, and record photographs of the analyzed areas and / or films of the analyzes. optical laser illumination means, connected to a laser source, configured to direct a laser beam (or beams) capable of generating at one or more points of the core the plasma required for use of the LIBS method; Optical means for collecting light from the plasma; at least one spectrometer receiving light from the plasma collected by the optical collection means, for example via an optical fiber. Said at least one spectrometer makes it possible to measure the intensity of the spectral lines corresponding to each of the components of the target, an analysis of several spectral bands in parallel can also be carried out by means of a demultiplexer and several spectrometers. data processing means for processing the signals / spectra provided by the spectrometer (s) and the images provided by the camera; a carrot support for supporting the core on a measuring table, preferably with its longitudinal direction orthogonal to the optical axis of the measuring assembly, and for holding the core in a predetermined position, means for relatively moving the measuring assembly with respect to the core support, in at least the axial direction of the core, and for positioning the optical axis of the measuring assembly at predetermined points of the core, and preferably means for adjusting the distance between the core holder and the measuring assembly. With the support and positioning means of the core, and the positioning means (relative) of the measuring assembly relative to the carrot support, the device according to the invention allows to perform LIBS analyzes of drill cores at precisely determined points of the core. It therefore makes it possible to know the composition of a drill core with great precision according to the axial direction of the core. In addition, these means make it possible to ensure good repeatability of the measurements for measurements made on various cores. The invention thus provides a device for acquisition by LIBS type spectroscopy data elemental geochemistry of drill core, and in particular an acquisition of vertical profiles (logs). The device then provides the geologist with the relative position of the measurement set with respect to the core, the corresponding LIBS measurement data, and the contextual images provided by the high resolution camera. The data of each core is used to reconstruct the vertical log. The device according to the invention also allows the control of the textural context of the sampling, on a rocky material which is not homogeneous, by the camera which allows a priori to position the sampling and to control a posteriori the effective sampling point. It will also be noted that the use of the LIBS method for analyzing oil exploration drill cores makes it possible to detect light geochemical elements such as hydrogen and lithium. The term "drill core" as used herein covers all rocky elements of oblong or cylindrical shape, natural or reconstituted, resulting from a drilling operation. In particular, the term "drill core" includes solid cores (called "full size"), as well as longitudinal sections ("SLAB") of such cores, and also reconstituted cores (in particular in resin), cores consisting of resin-encased "CUTTING" as well as longitudinal cuts thereof. Regarding drill cuttings, particularly aimed rock pieces torn by the drill bit destructive drilling - non-core - and raised to the surface by the drilling mud. These cuttings can be washed, dried, included in a resin; this solidified assembly can then be sliced which can be arranged in the present device for analysis. The skilled person may employ all kinds of appropriate mechanisms to achieve the relative displacement means between the measuring assembly and the core, opting depending on the case for a displacement of the core, the measuring assembly, or both. For reasons of compactness, it is preferable to leave the core stationary during the analysis, and to move the measuring unit. Preferably, the measuring assembly is configured to allow displacement of the measuring point on the core, without relative movement in the axial direction between the measuring assembly and the core. For this purpose, the measuring assembly may comprise means for moving the laser beam or for distributing the laser radiation in several beams, over a distance for example of one or more cm, which makes it possible to take a series of measures separated by a distance of 1 to 10 mm for example. It is thus possible to produce several separate measurement points for an axial measurement position defined by the relative position of the core / measuring assembly.

This makes it possible to evaluate more quickly the heterogeneity of the analyzed zone. The principle of acquisition of several measurement points for the same axial position is hereinafter called "matrix". Several possibilities can be envisaged to move the measurement point longitudinally and / or laterally on the core and analyze the heterogeneity of the same measurement zone. A first possibility is to move the laser by deflecting the beam by means of a pivoting mirror. This solution is the simplest and most flexible, because the number of positions and the distance can be easily programmed. In a sequential firing procedure, the discrimination of the different measurement points can be done simply in a temporal way: it is enough to record the moment of the shots, the logic of definition of the different points of measurement, and the moment of recording of the spectra to go back to the spectra of each measurement point. It is then possible to carry out successively measurements at several points of the core (determined by the different positions of the laser beam), with a single device for collection and spectral analysis (focused on each of the measurement points), and without changing position. overall aim of the analysis device on the core. Alternatively, a beam splitter, a planar optical system or based on discrete optical components or optical fibers for example, can be provided at the level of the measuring assembly, making it possible to produce several laser beams (parallel or otherwise). ). These beams emerge from the measuring assembly and follow each of the respective paths and distinct from the measuring assembly to the target, to form measuring points spaced for example from 1 to 10 mm. The collection means are configured to route the plasma light from each measurement point to the spectrometer (s). It is then possible to carry out simultaneously or successively measurements at several points (determined by the laser beams), without changing the axial position for the measuring head. To successively activate each measurement channel, the direction of the source laser beam can be chosen using an associated deflection means, for example a mirror at the input of the beam splitter, to bring it successively to each optical path of illumination of the target. The spectra of each measurement point can then be discriminated by their recording dates and the sequence of sequencing shots between the different points. A single band spectrometer can be used for eg 4 measurement points using CCD detectors. Alternatively again, one can use a collection device and spectral analysis adapted for spatial discrimination of the collected light. One possibility is to send the light of the different plasmas in an analysis zone to a group of contiguous optical fibers, each fiber finally receiving the light of a sub-region of the analysis zone comprising a single point of analysis. Take the case, for example, of 4 measuring points on which one proceeds to simultaneous shots. The collection means comprises an optical device for focusing each of the plasmas obtained on a group of 4 optical fibers (for example) on which the collected light is sent; each of the fibers therefore represents a collection path to which corresponds a sub-region of the field of view and analysis, and a measurement point. Each fiber must bring the collected light to the spectrometer (s) and must be associated with a specific area of the detector, typically a CCD matrix, to discriminate the spectra relative to each point. The spectrometers are preferably remote from the measuring head, the different fibers can be combined into a single cable (fiber bundle) for the transmission of signals to the spectral analysis area. The signals from each measuring point are then separated again at the level of the spectral analysis zone by suitable optical devices. The cable brings the 4 signals (for example) to the single spectrometer, or respectively to a demultiplexer to separate the different spectral bands of each point, and then inject them into another cable which brings them to the spectrometers. Each spectrometer (one per spectral band) finally analyzes, on its CCD detector, the 4 rearranged beams to be aligned along the entrance slit. The discrimination is done by the area of the CCD covered by each of the beams, taking care to avoid the mixing of the signals. Finally, spectrally separated collection and spectral analysis channels can be envisaged, configured to associate a (single) collection channel and independent spectral analysis with a measurement point (and thus with a laser beam). This ensures better isolation of the signals from each other but weighs down the collection and spectral analysis devices compared to previous solutions, making the system less compact and more complex. In all cases, the different measurement points must all be in the field of view of the camera and the collection means must maximize the collection of each plasma. Thanks to the means for adjusting the distance between the core support and the measuring assembly, the device can adapt to transverse dimensions, and therefore a very wide variety of core diameters, to ensure that the position of the assembly is preset. measurement with respect to the core, a finer adjustment of the laser firing parameters and the image taking that can be made by own settings of the measurement set. Preferably, the carrot support comprises a conveyor, typically motorized rollers, for carrying the core to be analyzed and move axially to bring it to the required position facing the assembly 20 of measurement. An axial stop may be provided to define the same axial position of the different cores to be analyzed. According to a first embodiment, the conveyor comprises a plurality of fixed rollers in position on the measuring table, the rollers being arranged with their inclined axes to form a centering vee of the core, and at least some of the rollers being motorized to move the core axially. According to a second embodiment, the conveyor comprises a support and centering chute on which the core is immobilized, and said chute is movable on the measuring table, guided in translation 30 in the axial direction of the core. , so as to ensure a positional match between the core and the measuring assembly, regardless of their relative position in said axial direction. According to a preferred arrangement, the device comprises successively a carrot feed table, the aforesaid measuring table, carrying the measuring assembly and the carrot support, and a core removal table, the three aforementioned tables forming a modular assembly in which the tables can be assembled, then separated and reassembled easily. Such a modular embodiment greatly facilitates the use of the device which can thus, particularly during mineral exploration cores, oil or scientific, be easily mounted near a coring site, and then disassembled and moved to be used on another site. The feed table and the discharge table each comprise a plurality of carrot conveying means, movable in a direction transverse to the longitudinal direction of the carrot support of the measuring table to be aligned with said support of carrot, each of these conveying means comprising carrot translation means, for moving a carrot carried by a conveying means of the feed table to the carrot support of the measuring table, or moving a carrot carried by said carrot support to a conveying means of the evacuation table. According to the embodiment chosen, it will be the only carrot that will be moved from the supply table to the carrot support of the measurement table, and then from the latter to the evacuation table, or this will be the carrot carried by a support chute. Whatever the embodiment, the conveying means allow to load several cores on the feed table, waiting to perform the analysis successively on each core. Similarly, the conveying means of the evacuation table can store several cores analyzed before evacuating them in groups. Thus, all the conveyor and carrot placement operations on the measuring table in the analysis position, as well as their evacuation on the evacuation table, can be easily automated. The carrot support of the measurement table is preferably located in a closed analysis chamber, forming a box. This box comprises a frame, side walls, a retractable entrance door on the side of the supply table, a retractable exit door on the side of the discharge table, and an upper cover having a longitudinal opening for communication between the measuring assembly and the core placed inside the analysis chamber, during the displacement of the measurement unit over the entire length of the core. The measuring chamber is closed to ensure the confinement of the laser radiation, to prevent the disturbance, by environmental lights, of radiation emitted during the ablation of core material by the laser and spectrum collection devices and of images, and also to provide if necessary a cooling and desiccation of the chamber of analysis. To close the longitudinal opening, it will be possible to use deformable closure means of flexible strips, during the passage of the measuring assembly, to allow said communication between the measuring assembly and the interior of the chamber analysis, and then returning to the closed position. Advantageously, the measuring assembly carried by the measuring table is guided in translation, in the longitudinal direction of the carrot support, on the integral frame of the measuring table, and translation means are provided by example a screw-nut system, actuated by a motor for precise positioning of the measuring assembly with respect to the core analyzed. The laser source can be deported to limit / lighten the mass of the measuring assembly, the laser beam being conveyed thereto by an optical transmission system, for example based on optical fiber. The positioning of the measurement unit may be automatic, by an automation of the translation and positioning means, for example incremental from an original position, for example every 2 to 20 cm from one end of the carrot. It will still be appreciated that the presence of the camera allows an observation of the texture of the carrot, which is not possible to the naked eye by a geologist using just for example a manual version gun-LIBS type. In this context, the operator who has identified with the eye certain areas of the core may operate a firing sequence on an area of his choice, possibly deviating from the main axis of the core. To do this, the device may also include complementary displacement means for moving the measuring assembly transversely to the longitudinal direction of the core, to perform analyzes on either side of the generator located in the plane. vertical passing through the axis of the carrot. The means for adjusting the distance between the carrot support and the measuring assembly may in particular be formed of motors acting on the height of the armature. The device according to the invention will also preferably comprise means for automating the control of the displacement motors of the measurement unit, the control of the laser and the camera, and the acquisition of the results of the analysis. LIBS, this automation allowing a regular and controlled sampling step, and therefore a more relevant subsequent treatment of the data and a more efficient comparison / correlation between two boreholes. The automation means may also include an image processing module, for example by graphic segmentation, to automatically identify areas of different appearance and perform analyzes. It will also be noted that the LIBS analysis associated with the ablation of material by the laser makes it possible to detect and overcome surface contaminations. In particular, the present device allows repeated irradiation of the core 30 on the same measurement point as required, so as to reach a certain depth of measurement. In practice, the number of laser shots made at a measuring point may, for example, vary from a few tens to several hundreds, to reach a penetration depth of up to about 1 mm. It is also possible to envisage longer sequences and greater depths of penetration, but on the one hand it is linked to the material analyzed, and on the other hand the measurement may possibly be disturbed by fallout of material from the surface. in the crater formed. Finally, the stability of the line of sight can be a limiting factor if the number of consecutive shots increases and according to the rate of the laser beam. It remains to note that the present device can be configured to integrate in addition a Raman measurement at half the wavelength of that used for the LIBS. The Raman measurement can be done by the illumination and collection channels used for the LIBS, adapting them to carry both wavelengths. Alternatively, an additional illumination path can be provided at the measuring head, forming a collection point in the field of view and analysis, i.e. collection means and the camera. According to the configurations, as explained above, the Raman measurement can be done simultaneously or sequentially with respect to the LIBS measurements. Very simply, if one works in LIBS at 1064 nm, one can easily obtain a laser source adapted to the Raman with a doubler of frequency, the Raman radiation thus prepared being injected on an independent illumination path for a matrix measurement. In another aspect, the present invention also relates to a drill core analysis method according to the LIBS technique as described below.

BRIEF DESCRIPTION OF THE DRAWINGS [0042] Other features and characteristics of the invention will become apparent from the description of at least one embodiment presented below, by way of illustration, with reference to the accompanying drawings. These show: Fig. 1: a side view of the entire device according to a first embodiment: FIG. 2: a top view of the entire device of Fig.1; Fig. 3: a view in a cross section of the device of Fig.1, also showing the electronic equipment associated with the measuring assembly; Fig. 4: a diagram illustrating a carrot measurement protocol; Fig. 5-6: images of carrots analyzed according to the LIBS technique; Fig. 7: a cross-sectional view of a second variant of the present device; Fig. 8: a view along the longitudinal axis of the core of a third variant of measuring assembly used in the present device; Fig. 9: a) a view along the longitudinal axis of the core of a fourth variant of measuring assembly used in the present device, and b) a view of the measuring points obtained.

DESCRIPTION OF A PREFERRED EMBODIMENT [0043] A first variant of the present invention is illustrated in FIGS. 1 to 3. The analysis device represented successively comprises a feed table 1, a measurement table 2 and an evacuation table. 3. These tables are dismountably assembled. They are supplemented by accessory tables, such as a control and signal processing table 41, supporting an electronic control unit 91 for digital processors, for controlling the laser, the various motors and the camera, between other, as well as a demultiplexer 92, and one or more spectrometer (s) 93 for processing the light signals coming from the measuring assembly, and a table 42 carrying for example a digital block 94 for calculation and wireless retransmission by An antenna 95. The measuring table 2 carries a box 5, of suitable dimensions to contain a drill core C and thus having an elongate shape in an axial direction Al of such a core. The casing 5 comprises a frame 51, side walls 52, an entry door 53 and an outlet door 54, made for example in the form of guillotine doors. The casing 5 also comprises a cover 55 in which is formed a longitudinal opening 551 closed by flexible deformable flaps 552. The measuring assembly 6 is carried by the armature 51 of the casing 5, guided in translation on said armature , the displacement of the measuring assembly 6 being for example made by a threaded rod 61 cooperating with a tube 62, forming a screw nut system actuated by a position control motor of the measuring assembly, not shown. This motor-driven screw / nut system thus constitutes a means of axial displacement of the measurement assembly with respect to the core, which remains in position in the measurement chamber. In a typical measurement protocol, the measurement set is moved along the core to take measurements along the core, preferably advancing at a constant pitch. It is thus easy to take measurements reliably and reproducibly on drill core, which allows to build the vertical profile of the rock corresponding to drilling with good accuracy along the axis of drilling. The armature 51 also advantageously comprises 511 engines for modifying the altitude of the measurement assembly with respect to the measurement table 2 and thus to adapt this altitude as a function of the diameter of the core C. height adjustment can be done manually by the operator, or automatically, by detecting the distance between the measuring assembly and the core, which can for example be done either by dedicated detector or for example by an autofocus system of the measuring set. The measuring assembly 6 generally comprises: laser optical illumination (or irradiation) means connected to a laser source 63 (which can also be deported and connected by optical fiber), configured to directing a laser beam capable of generating at a point in the core the plasma required for the use of the LIBS method, or respectively configured to generate a plurality of different laser beams to form a plurality of spatially distinct measurement points on the core; optical means for collecting (60) the light of the plasma (s); and an imaging camera 65, in particular for taking high resolution color images and videos. In the present variant, the measuring unit 6 preferably comprises an optical assembly, called telescope 60, which can be for example constructed in the manner of the telescope of the ChemCam instrumental suite equipping the Martian Curiosity Rover of NASA (mission Mars Science Laboratory), see in particular the article published in the periodical Space Science Reviews, no. 170, 2012: The ChemCam Instrument suite on the Mars Science Laboratory (MSL) Rover: Science Objectives and Mast Unit by Maurice, S., Wiens, R., Saccoccio, M., or adapted from it. This optical assembly, called telescope 60, is designed to focus the laser beam (s) (and thus create a (respectively) plasma (s)) and capture the light of the plasma (s) and the image of the context, along the same optical axis. The telescope 60 thus comprises one or more optical or optoelectronic subassemblies arranged to: focus the laser beam on a point on the surface of the analyzed core, for example by means of a movable mirror providing the function of auto-focus. It is also possible to provide an automatic focusing system comprising an automatic device for collecting and measuring the signal returned by the analysis zone to a sensor, a criterion defining the best focusing position, and a retro-active loop for automatically selecting the position of the focus control device. - collect the spectral emissions of the generated plasma. This is done by focusing the light captured by the telescope on a transmission means spectral analysis of light. Thus, at the rear of the telescope, most of the light captured is refocused on the end 64 of an optical fiber 641 (or a set of optical fibers). A dichroic plate 66 makes it possible to differentiate between the emission (laser) and collection (plasma) paths borrowed by the signals through the telescope. obtain by the camera 65 an image of the zone encompassing the point of impact of the laser, before and after the action of the laser. To do this, one can for example use a dichroic blade to send a fraction of the light collected by the telescope towards the camera, which may include a Charge Transfer Device (CCD sensor). In the present variant, the laser source 63 is directly mounted on the measuring assembly 6 and connected to the telescope 60. It can be offset outside of it, on a fixed part of the device, in order to limit the mass of the moving part. In this case, the connection between the laser source and the measuring assembly can be preferably done by optical fiber. The collected light is transmitted by the optical fiber 641 to the demultiplexer 92 which sends the light signals to one or more spectrometers 93, their charge coupling devices (CCD), and their associated electronics (not shown). The spectrometric unit is preferably selected to cover the 204 - 800 nm range. The images of the camera 65 are transmitted to the electronic control unit 91. The carrot holder 7, located in the measurement box 5 resting on the measurement table 2, comprises a plurality of motorized rollers 25 71 inclined by in order to form a support and centering V of the core C. [0054] The feed tables 1 and evacuation 3 each comprise several conveyors 11, 31, provided with motorized rollers 12, 32, able to support a carrot and moving the core in its axial direction. The feed table 1 comprises several conveyors 11 30 movable in the direction of the arrows Fl, transversely to the axial direction Al of the core, so that each conveyor 11, on which the cores C have been previously deposited, can be placed in alignment with the carrot holder 7 of the measuring table 2, and so that the core carried by the conveyor thus aligned can be translated according to the arrows F2 on the carrot support 7, after having opened the door of inlet 53 of the casing 5. Similarly, the discharge table 3 comprises several conveyors 31 movable transversely to the axial direction A1, so that each conveyor 31 can be placed in alignment with the carrot support 7, for receive a carrot translated from the carrot holder 7, after opening the exit door 54. It will be noted that the measuring instrument, respectively the optic set e of the telescope 60, is advantageously designed to allow the laser beam to be displaced on the surface of the core over a short distance, typically of the order of 1 to 2 cm. It is thus possible to take on the core a series of close measuring points, without relative displacement between the measuring unit 6 and the core C, respectively its support / the measuring table. An advantage of the present device is its transportability. The design of the device is advantageously made to form several cooperating modules to facilitate the assembly / disassembly of the device: - Module 1: Measuring instrument 6 = 60 + 65 camera + autofocus if necessary + optionally the laser 63 (if not deported) - Module 2: armature 55 - Module 3: Spectrometers + demultiplexer + electronic block - Module 4: Digital block + antenna [0059] A preferred measurement protocol will now be described with reference to FIG. step 100 the core is placed in position on the core support in the measuring chamber 5. The doors are closed and the height adjustment is performed (step 102), so as to bring the measuring assembly 6 to a predetermined distance from the core, which corresponds approximately to the focal length of the collection optics. In step 104, the device is initialized for measurement, and in particular the position counters (axial position and matrix position) are initialized. The axial position counter, denoted A, indicates the axial position of the measurement (relative position of the measurement unit 6 with respect to the core), whereas the counter R is a series of points meter, which indicates the measurements. neighbors obtained at the same point A, without relative displacement measuring unit / core. After the initialization phase, the measurement assembly is positioned / moved to the first measurement point (step 106) which corresponds to the values A = 1 and R = 1, ie P (1,1). The steps are then successively: - 108: image acquisition and / or high resolution color video before shooting - this step is optional, but the image makes it possible to know what the beam (s) (x) has (have) hit (hole, inclusion ...), and the recording of the analysis sequence can help a possible diagnosis in case of difficulty or aberration during an analysis. 110: the firing step in fact encompasses the laser firing sub-step, that is to say the emission of the radiation focused on the desired measurement point on the core, corresponding to P (A, R), and the next sub-step of the acquisition of plasma light generated by laser ablation, in accordance with the LIBS principle. Classically, the acquisition is slightly offset in time due to the associated physics. These sub-stages of laser firing and laser light acquisition are in practice repeated a number of times, for example a few tens or hundreds of times (gunshots generating a spectrum per shot). The collected light is sent to the spectrometers and processing means for analysis. In the steps described here, each laser shot provides a spectrum. But, alternatively, several shots can lead to an integrated or averaged spectral acquisition. At the end of step 110, a high resolution color image of the core at the zone including the measurement point is acquired. An alternative or another mode of operation to predict, if it is deemed useful for the intended application, is to film the laser shots and the creation of the plasma. In the "matrix" mode, several neighboring measurements are performed at the axial position A = 1. For example, a series of 5 measuring points may be spaced regularly (eg from 1 to 5 mm) and aligned along the axis of the core. Means for adjusting the position of the measurement point associated with the measuring instrument are therefore used to move the measuring point from the point P (1,1) to the point P (1,2), then P ( 1,3), without axial displacement core / measuring set. This can be done by deflecting optical elements. It is also possible to generate a matrix of laser beams (a plurality of laser beams, parallel or otherwise, along different paths), where the different beams are lit at the same time or successively. The collection, separate or common, and the spatial or temporal discrimination of the spectra from the different measurement points, then gives access to the heterogeneity of the analyzed zone. Thus after the measurement P (1,1), the measurement is made for the second point of the axial position A = 1, which is noted P (1, 2). Steps 106 to 108 are therefore repeated for each point of the matrix sequence. At the end, the measuring assembly is moved along the axis of the core to prepare it for measurement at the second axial point A = 2, which is several centimeters, for example 5 to 20 cm from the first point. P (1,1). And we reproduce the measurement steps (106 to 112) for the different points of the matrix mode at this position A = 2. The measurement steps are therefore repeated along the core, by incrementing the axial counter A to the end of the core, where it can be discharged (step 122). The process can then be stopped, or restarted with another carrot. The electronic control unit (91) can easily be configured to implement the measuring protocol described above in relation to FIG. 4. Fig.5 illustrates the measurement principle described above, and in particular the difference in pitch between the counters A and R on a core. Measuring points on the surface of the core are indicated by the black circles. The measurement starts at the top (with respect to Fig.5) of the core, the first measurement point being at the position 1, therefore P (1,1). Then the displacement of the beam (without displacement of the measurement unit) allows the acquisition of a series of 4 other points P (1,2) to P (1,5). Then the measuring set is moved to the 2nd axial position, for the acquisition of the series P (2.1) to P (2.5). Then the measuring set is moved to the 3rd axial position, for the measurement of P (3.1) to P (3.5). And so on the length of the carrot. The interest of post-firing imagery, which allows to know the exact position of the point (s) of measurement on the surface of the core, and therefore the context of the geological texture, is obvious on the Figures 5 and 6. Indeed, the contextual image allows the recognition of the analyzed area and the interpretation of LIBS data. In the case of a fine-grained matrix (typically particle size <256 μm), as for the examples of Figures 5 and 6, the laser beam has a size comparable to or greater than that of the grains, and the ablated zone by the laser will encompass grains and the matrix, giving the bulk composition of the rock ("bulk composition"). On the other hand, if the grain is large, the laser beam can fall in the middle of a grain, and the measurement will not reveal the nature of the adjacent matrix or cement, but will allow a specific analysis of the grains or inclusions analyzed. The contextual image makes it possible to see this and to interpret the results accordingly. In Figure 6, there is also shown the possibility to achieve in addition to the measurements P (A, R), along the generatrix included in the vertical plane passing through the axis of the core, transverse measurements, noted T, or offset with respect to the axis, noted D. [0069] Note that in the example shown in Figures 1 to 3, it is the motorized rollersl2, 32 and 71 which provide direct drive cores C, by contact with the surface of the carrots. It would also be possible to use chutes in which the cores are arranged and centered in a fixed manner, said chutes being mobilized by motorized rollers in a manner similar to that described above, or comprising other drive means. Such a variant with handling chute is illustrated in Fig.7, in which the measuring instrument is also simplified. In FIG. 7, the measuring table 2 is recognized with the box 5 and the frame 55, as well as the conveyor 7. It will be noted that the core is here placed in a handling chute 78, or more simply "chute", having a V-shaped section. Such a chute 78 makes it possible to rigidly support fragile (eg friable) cores, which are thus immobilized and centered in the chute, and are not subjected to direct contact with the motorized rollers 71. Alternatively, instead of the motor roller conveyor 71, other types of conveying and aligning mechanisms may be employed. For example the non-motorized rollers support the chute, whose training is performed by a lateral drive mechanism. In the present variant, the measuring assembly is simplified and compact. The reference sign 6 'designates the measuring assembly which comprises: optical laser illumination means, connected to the laser source 63, configured to direct a laser beam 80 capable of generating at a point of the core the plasma required for the use of the LIBS method. The laser source 63 is preferably not carried by the measuring assembly 6 ', and can therefore be placed on the casing 5, the measurement table 2 or offset elsewhere. The transmission of the laser radiation to the measuring assembly is done simply by optical fiber (s). At the level of the measuring assembly 6 ', the optical fiber is associated with an optical block 84 comprising alignment and focusing elements of the laser beam on the core. Optical collection means are provided for collecting / collecting the plasma light generated by the incident laser beam 80 on the surface of the core, the measurement point being in the field of view 86 of the optical collection means . The optical collection means, symbolized 88, may be formed by the end of an optical fiber, associated with optical focusing elements (not shown). As in the variant of FIG. 3, the optical collection means are connected by optical fibers 641 to the analysis instruments 92, 93. [0074] the high resolution color imaging camera 65 for the shooting of the analyzed area, before and / or after shooting, or video shots during firing, or for the selection of the area to be analyzed. The optical means of illumination 84 and collection 88, and the camera 65, are here incorporated into a common box 90, which is more compact than the telescope 60 of Fig.3. To allow the measurement point to move without moving the measuring assembly, the laser beam at the fiber exit is directed towards a beam deflection element 92, which may be for example a pivoting mirror. It will also be noted that the measuring assembly, in all the variants presented, preferably comprises a window or a porthole (not shown) which separates the optical elements from the measurement chamber. This avoids damaging the optics and other mechanisms of the telescope interior or the measuring instrument, in particular by protecting them against dust, spatter, gas and other potentially corrosive products emitted by laser ablation of the material. cored (with hydrocarbons, etc.). The control of the device according to this variant can be done by means of the electronic control unit 91, as for the variant of Fig.1, or as Fig.8 / 9 below. Here also, it can be programmed to implement the method described above in relation to FIG. In the variant of FIG. 7, the matrix mode, i.e. acquisition of several spatially separated measuring points for the same axial position measuring head / core, is achieved with a single laser beam deflected by a mirror. In the variant of FIG. 8, the measurement unit is initially designed to emit several separated laser beams towards the core, so as to form at least two spatially separated analysis points on the sample, according to a predefined pattern. Specifically, in the case presented here, the measurement set is designed to generate and direct three distinct and spatially separated laser beams to the sample, to form 3 spatially separated analysis points on the sample. The 3 measuring points, indicated 81, are aligned along the generatrix located in the vertical plane passing through the axis A of the core, which corresponds for example to the points P (1,1), P (1,2) and P (1,3) of the carrot of FIG. Each of the 3 laser beams 81 is routed to the sample via a clean optical path by optical laser illumination means contained in the measurement assembly. For example, the laser radiation coming from the source 63 through the optical fiber 82 at the measuring assembly 6 "can be redistributed, by means of a suitable coupler (not shown), on 3 optical fibers 85, defining 3 independent internal optical paths, each associated with a focusing optics (not shown) for the emission of the respective laser beam 80 'The 3 measuring points 81 are in the field of view 86' of the optical collection means 88 'The camera 85 also has a field of view encompassing the 3 measuring points [0082] As for the variant of Fig.4, the optical collection means 88' may be constituted by the end of a lenticular optical fiber (with focal length and appropriate working distance), forming a single collection path provided that this does not disturb the laser illumination pathway If the absence of disturbance is not guaranteed, it is preferable to proceed to measures sequentially, that is to say alternately at each measurement point 81, so as to generate / collect / analyze the plasmas independently for each measurement point. Moreover, with suitable optical collection means, that is to say capable of spatially discriminating the light collected, simultaneous firing can be carried out on the three measurement points 85. For this purpose, the optical means of collection may comprise a set of centrally positioned optical fibers (such as 88 '), or several distinct collection channels, each having a field of view limited to a given measurement point, and being connected to a spectrometer (or one spectral band ). A fourth variant is illustrated in FIG. 9, in which the measuring assembly 206 is designed to form 4 spatially separated analysis points on the sample, according to a predefined matrix pattern, for example placed at the four corners. of a parallelepiped. Each of the 4 laser beams 280 is conveyed to the sample via a clean optical path, by optical transmission and focusing means contained in the measuring assembly 206. As for FIG. 8, the laser radiation arriving from the source 263 by the optical fiber 282 at the measuring assembly 206 can be redistributed, by means of a suitable coupler (not shown), on 4 optical fibers 285, defining 4 independent internal optical paths, each associated with a focusing optics (not shown) for the emission of the respective laser beam 280. Here the four optical fibers are placed at the corners of a square, only two fibers 285 and two laser beams 280 being shown in Fig.9 a) for reasons of clarity. The 4 measurement points 281 obtained, shown in Fig.9 b), are arranged at the four corners of a square (this could also be a rectangle) centered relative to the generator located in the vertical plane passing through the axis A of the carrot. At the center of the 4 fibers 285 is the high resolution 240 color camera, which encompasses the square of the analysis area. The collection means comprise as many collection channels as there are illumination channels. A collection fiber 250 is therefore associated with each illumination path. In the representation of Fig.9, the end of each fiber 250 is represented with an angle, which symbolizes the focusing optics receiving the plasma light created by the associated laser beam, reflected by a dichroic plate 252. Note that in this configuration the collection channels 250 are independent and therefore allow simultaneous analysis on the four points without interference. The 4 optical fibers 250 (note that only two are represented, as for the illumination channels) meet at the rear of the measuring assembly 206 to form a bundle fiber 256 connected to the demultiplexer. The camera 240 is connected to the processing means. According to yet another embodiment, the 2x4 optical devices of FIG. 9 can be replaced by only 1, capable of focusing 4 laser beams and collecting 4 plasmas without mixing them, with a single dichroic plate on the signal path (1 path for laser wavelength -1064 nm, the other for ultraviolet to very near infrared light for plasma). [0086]

Claims (20)

REVENDICATIONS1. Apparatus for the spectroscopic analysis of drill core (C), in particular of oil exploration, mining or scientific exploration cores implementing a laser ablation induced spectroscopic analysis method (LIBS), comprising: a measuring unit (6), comprising: - optical laser illumination means, connected to a laser source (63), configured to direct at least one laser beam capable of generating in at least one point of the core the plasma required for use the LIBS method; - optical means for collecting plasma light; - an imaging camera making it possible to accurately photograph the analysis zone and / or to film the analysis (65); at least one spectrometer (93) connected to the optical collection means; data processing means for processing the signals supplied by the spectrometer (s) and the images provided by the camera; - a carrot holder (7) for supporting the core on a measuring table (2), and for holding the core in a predetermined position, - means (61, 62) for operating a relative displacement between the measurement unit (6) and the core support (7), in at least the axial direction (A1) of the core, and for positioning the laser beam, respectively the optical axis of the optical collection means, at predetermined points of the core - Preferably, adjusting means (511) for adjusting the distance between the core holder and the measuring assembly. 2. Device according to claim 1, wherein the carrot holder comprises a conveyor (7, 71), to carry the core to be analyzed and the axle to bring it to the required position in front of the measuring assembly. 3. Device according to claim 2, wherein the conveyor comprises a plurality of rollers (71) fixed in position on the measuring table, the rollers being arranged with their inclined axes to form a centering vee of the core, and some at less rollers being motorized. 4. Device according to claim 2, wherein the conveyor comprises a support and centering chute on which the core is immobilized, and said chute is movable on the measuring table, guided in translation in the axial direction of the core. 5. Device according to any one of the preceding claims, wherein the device comprises successively a core feed table (1), the measuring table (2), carrying the measuring assembly and the carrot holder, and an evacuation table (3) of the cores, the three aforementioned tables forming a modular assembly; and the feed table (1) and the discharge table (3) preferably each comprise a plurality of carrot conveying means (11, 31) movable in a direction transverse to the longitudinal direction (A1) of the support of carrot (7) of the measuring table. 6. Device according to claim 5, wherein each of the conveying means (11, 31) comprises carrot translation means (12, 32), in particular motorized transport rollers (12, 32), for moving a carrot. carried by means of conveying the feed table to the carrot support of the measuring table or moving a core carried by said core support to a means of conveying the discharge table. 7. Device according to any one of the preceding claims, comprising a closed box forming an analysis chamber in which the carrot support of the measuring table is placed. 8. Device according to claim 7, wherein the box comprises a frame, side walls, a retractable entrance door on the side of the feed table and a retractable outlet door on the side of the discharge table, and an upper cover having a longitudinal opening with the deformable closure means, allowing communication between the measuring assembly and the inside of the analysis chamber, during the displacement of the measuring assembly, over the entire length of the the carrot.. 9. Device according to any one of the preceding claims, wherein the measuring assembly (6) carried by the measuring table is guided in translation, in the longitudinal direction of the core carrier, on a frame (55) integral with the measuring table, and preferably comprising means of translation of the measuring assembly, actuated by a motor for precise positioning of the measuring assembly with respect to the core analyzed. 10. Device according to any one of the preceding claims, comprising complementary displacement means for moving the measuring assembly transversely to the longitudinal direction of the core. 11. Device according to any one of the preceding claims, wherein the measuring assembly comprises an assembly of optical elements for directing and focusing the laser beam on the core, so as to create a plasma, capture the plasma light. , especially in a fiberoptic, and capture the context around the measuring point by means of the imaging camera. The device according to any of the preceding claims, wherein the measurement assembly is configured such that laser focusing and light collection are performed along the same optical axis. 13. Device according to any one of the preceding claims, wherein: the optical illumination means are capable of directing at least two separate laser beams to the core, so as to form at least two spatially separated analysis points on the screen. sample, according to a predefined pattern; the optical collection means have a field of view in which are located said at least two measuring points. 14. Device according to claim 13, wherein the optical collection means are designed to allow spatial discrimination of plasmas from said at least two measurement points, respectively an independent collection of plasmas by separate collection channels, especially in case of simultaneous shooting of the at least two laser beams. 15. Device according to any one of the preceding claims, comprising means for adjusting the laser beam associated with the measuring assembly, for moving the measuring point without relative movement between the core, respectively its support, and the set of measurement, to achieve a matrix of non-simultaneous measurement points. 16. Device according to the preceding claim, wherein the directional adjustment of the laser beam on the core is performed by an optical element of the measuring assembly, in particular a pivoting mirror. 17. Device according to any one of the preceding claims, wherein the drill core is a solid core, a reconstituted carrot, carrot reconstituted drill cuttings, or a longitudinal section of such a core. Device according to any one of the preceding claims, in which the measuring assembly comprises focusing means, in particular autofocusing, on the optical path for laser illumination and / or for collecting the plasma light. 19. Apparatus according to any one of the preceding claims, comprising an electronic control unit (91) for controlling the device and operating in an automated way the handling of the cores and / or the acquisition of data with the measurement unit. Apparatus according to any one of the preceding claims, wherein the measuring assembly comprises an additional illumination path receiving laser radiation at a wavelength suitable for Raman analysis so as to generate a laser beam forming on the carrot a measuring point in the field of vision of the collection means.