Downhole instrument for real-time laser-induced breakdown spectroscopy (LIBS) analysis

Abstract

A downhole instrument for real-time laser-induced breakdown spectroscopy (LIBS) analysis of a borehole wall. The instrument includes an elongated housing having a bottom end and a top end, an optical head at the bottom end thereof, a LIBS spectrometer at the top end thereof, and a laser therebetween. The optical head includes laser delivery optics and plasma emission collection optics, the spectrometer is fiber-optically coupled to the optical head; the laser is configured to deliver pulses directly to the laser delivery optics for focusing before passing through a side window of the optical head to a sample point on the borehole wall; and the optical head is configured to collect radiation emitted from a laser-induced plasma at the sample point and transmit the emitted radiation via fiber-optic coupling to the spectrometer via the plasma emission collection optics.

Description

[0001] Related applications This application claims Convention priority to Australian Provisional Patent Application 2023903389, filed on 24 October 2023, the contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to instruments and methods for determining geological structures in the field below the borehole during mineral exploration and mining. The invention is particularly useful in drilling where depth-accurate core or cuttings samples are not recovered from the borehole, and therefore analysis of recovered materials using top-of-hole techniques is not easily achieved and / or lacks depth accuracy. Background Technology

[0003] Real-time downhole measurements promise low-cost, automated, and objective geochemical analysis that can be integrated into drilling workflows and influence "while-you-drill" decisions. Current technologies with near-real-time measurement potential exist in the form of wellhead and downhole technologies. Downhole technologies include, for example, prompt-gamma neutron activation analysis (PGNAA), which has the advantage of sensing large rock volumes but faces limitations in calibration, sample collection, and detection for certain minerals, such as gold.

[0004] Ideally, real-time downhole instruments would be able to transmit a large amount of chemical composition from the geological sample being analyzed, without requiring any specific sample preparation steps, and would be achievable through miniaturized sensors. In this regard, physical drilling characteristics and complexities (such as surface roughness, water flow, drilling mud, and other drilling aids) have proven to pose a greater challenge to accurate analysis than miniaturizing analytical hardware to allow for well deployment.

[0005] The range of analytical techniques applicable to this type of chemical analysis in laboratory settings is extensive, including X-ray photoelectron spectroscopy, electron microscopy, various types of chromatography, UV and visible light absorption spectroscopy, infrared spectroscopy, fluorescence assays and chemiluminescence, X-ray fluorescence spectroscopy, atomic absorption and flame emission spectroscopy, atomic emission spectroscopy, nuclear magnetic resonance spectroscopy, mass spectrometry, labeling methods, potentiometric methods, voltametric and coulometric methods, secondary ion mass spectrometry, and atom probe tomography.

[0006] However, most of these techniques require sample digestion or specific sample preparation. For example, thermal analysis techniques require placing a sample, contained in a suitable sample pan or crucible, in a furnace and subjecting it to certain desired temperature conditions, and most spectroscopic analysis techniques require a pre-treatment digestion step.

[0007] While numerous techniques are available for chemical analysis in laboratory settings (e.g., thermal analysis, wet chemistry, chromatography, various ICP-based techniques), only a limited number are adaptable to downhole tools and used for the analysis of geological materials outside of laboratory space. These techniques may include X-ray fluorescence (XRF) spectroscopy, alpha particle X-ray (APXS) spectroscopy, including the aforementioned Proton-Induced X-Rayemission (PGNAA), Proton-Induced X-Rayemission (PIXE), Proton-Induced Gamma Emission (PIGE), and Switchable Radioactive Neutron Sources (SRNS).

[0008] Furthermore, while some commercially available downhole measurement tools exist, they are limited to gamma-ray and neutron-based instruments rather than multi-element downhole tools. In this regard, the field use of gamma-ray and neutron technologies requires strict regulations.

[0009] Before summarizing the invention, it should be understood that various directional terms, such as up, down, upward, upright, top, bottom, etc., are used throughout this specification to provide background and clarity for the invention with reference to the normal upright use of instruments in drilling (which is typically, but not always, reasonably vertical). These terms should not be construed as limiting the invention to use only in one particular direction.

[0010] This document includes a discussion of the background of the invention to explain the context of the invention. This should not be construed as an admission that any material cited was disclosed, known, or part of the general public prior to the priority date of this application. Summary of the Invention

[0011] This invention provides a downhole instrument for real-time analysis of the borehole wall that utilizes laser-induced breakdown spectroscopy (LIBS).

[0012] In particular, the present invention provides a downhole instrument for real-time laser-induced breakdown spectroscopy (LIBS) analysis of the borehole wall, the instrument comprising an elongated housing having a bottom end and a top end, the housing containing an optical head at its bottom end, a LIBS spectrometer at its top end, and a laser located between the optical head and the LIBS spectrometer, wherein: a) The optical head includes laser delivery optics and plasma emission and collection optics; b) The spectrometer is coupled to the optical head via optical fiber; c) The laser is configured to deliver the pulse directly to the laser delivery optics for focusing before it passes through the side window of the optical head to the sample point on the borehole wall; and d) The optical head is configured to collect radiation emitted from laser-induced plasma at the sample point, and the emitted radiation is transmitted to the spectrometer via fiber optic coupling through plasma emission collecting optics.

[0013] The elongated housing is preferably a one-piece housing with removable bottom and top ends to allow access to the interior of the housing and, if necessary, removal of the optical head, laser, and / or spectrometer. As mentioned, the housing may also be formed from multiple housing sections or have removable access ports along its length, as required. Describing the housing as "elongated" means that the length of the housing is typically several times larger than the diameter of the housing, in order to keep the diameter of the housing close to the diameter of the borehole, while having sufficient length to accommodate the required components.

[0014] The elongated housing may also include a suitable cooling system within it, such as a circulating airflow system, operable in response to temperature readings taken around either or both of the laser and spectrometer. The operation of the laser and spectrometer in such an instrument can be adversely affected by temperature, and such a cooling system is very useful in certain situations. In this regard, the housing would ideally have internal channels allowing air to pass around its various components, these channels being in fluid communication with a suitable fan or similar device also suitably located within the housing.

[0015] LIBS spectrometers can be any suitable type of optical spectrometer capable of receiving radiation emitted from laser-induced breakdown spectra. LIBS has been found to provide an efficient and powerful method for the simultaneous multi-element analysis of materials. The elements that can be detected and theoretically quantified cover most of the periodic table, including light elements such as Li, Be, B, Na, and Mg.

[0016] In principle, LIBS is a form of atomic emission spectroscopy that relies on the characteristic spectra emitted by plasma generated by a series of high-energy laser pulses striking a sample surface. Each laser pulse results in a high-intensity plasma at a point on the sample surface, and the resulting plasma emission spectrum contains atomic emission lines from the types of atoms present in the plasma. Multiple spectra can be averaged at different sensitivities, and every element in the periodic table can be measured. LIBS data can also be collected and integrated in tandem with datasets from other analytical techniques, including hyperspectral, X-ray fluorescence, and Raman spectroscopy. LIBS analysis also causes minimal damage to the sample, with each laser pulse consuming only nanograms of sample material.

[0017] In a preferred configuration, the LIBS spectrometer will have sufficient resolution and wavelength range to allow for good resolution of the synthetic emission spectrum generated by the laser pulses. The spectrometer configuration can be either an echelle or a Czerny-Turner configuration, but a compact Czerny-Turner configuration will be preferred due to its ease of miniaturization.

[0018] In one embodiment of the invention, the instrument may include two spectrometers: an ideally registered UV spectrometer and a near-infrared (NIR) spectrometer, such that the entire laser plasma is observed from a limited field of view of the plasma emission collection optics, and transmitted to the spectrometer via the plasma emission collection optics and corresponding fiber optic coupling. The ability to capture a very narrow time slice (spectrometer integration time) of the emitted radiation within a limited time after the plasma's appearance (spectrometer delay time) is useful for determining the temperature of the plasma and the resolution and intensity of the emission spectral lines of characteristic elements. Accurate and precise characterization of the plasma infers information about laser-matter interactions and aids in the quantitative calculation of elemental abundances.

[0019] In this invention, the purpose of the laser is to ablate and thermally excite the sample, thereby generating a high-temperature plasma that emits light capable of identifying elements and their concentrations. In a preferred embodiment, the laser will be able to control the energy of each pulse and will make the pulses consistent. This consistency will include pulse length, wavelength, and intensity distribution.

[0020] In a preferred embodiment, the laser will be a single-pulse or dual-pulse laser with an excitation wavelength ranging from 200 nm to 1600 nm and a pulse length in the nanosecond or femtosecond range. Preferably, the laser will have a pulse length in the nanosecond range. For example, a Q-switched Nd-YAG laser is contemplated as a useful source of high-energy Q-switched pulses in the desired wavelength range.

[0021] As described above, the optical head includes a laser delivery optics and a plasma emission collection optics, and is configured to collect radiation emitted from laser-induced plasma at a sample point. This radiation is transmitted from the laser to the sample point via the laser delivery optics, and then transmitted via fiber optic coupling to the spectrometer via the plasma emission collection optics. In one embodiment, the optical head includes an optical component support that can be housed within an optical component housing within an elongated housing or directly within the elongated housing itself. The optical component support has mounting sections capable of receiving and holding both the laser delivery optics and the plasma emission collection optics.

[0022] Optical support brackets can be formed from multiple components as an assembly or as a one-piece component (e.g., injection-molded or 3D-printed with pre-formed mounting sections ready to receive appropriate optics). Ideally, the optical support bracket will be configured to rigidly hold the laser delivery optics and plasma collection optics to allow for precise adjustment and alignment of the optics. In this regard, as will become apparent in the following description of the laser delivery optics and plasma collection optics, such adjustment and alignment may include or relate to beam alignment, back reflection protection, collimator positioning, laser deflectors (multiple laser deflectors), and tilting optical windows (multiple tilting optical windows).

[0023] In one form, the laser delivery optics include a focusing lens and a laser deflector. The focusing lens is used to focus a collimated laser pulse that enters longitudinally ("longitudinally" in the case of an elongated housing) and the laser deflector is used to laterally redirect the focused pulse from the laser through the side window to the sample point.

[0024] In a preferred embodiment, the focusing lens will be a single plano-convex lens assembly or multiple plano-convex lens assemblies having a damage threshold sufficient to withstand damage from the laser pulse. Corrective optics for laser alignment, astigmatism, and other focusing characteristics may also be present. Preferably, the focusing lens will be a glass plano-convex lens coated with a suitable anti-reflective coating for the laser excitation wavelength used.

[0025] Laser delivery optics may also include a beam expander that maximizes the diameter of the collimated laser beam, thereby beneficially reducing the flux on the optics and increasing the energy density at the focal point.

[0026] The laser deflector used for the incoming laser pulse will preferably be a plane mirror with a suitable reflective coating for the laser excitation wavelength and a suitable damage threshold, and will preferably be sized such that the mirror size is larger than the maximum size of the focused beam. In this respect, the size of the incident beam on the laser deflector depends on the position of the focal point relative to the instrument housing; therefore, the beam size will be minimum when the sample is close to the instrument, defining the damage threshold (maximum flux), and the beam size on the mirror will be maximum when the sample is farthest from the instrument, defining the size of the mirror.

[0027] Preferably, the laser delivery optics will also include an autofocusing device (such as an autofocusing lens), which may include a distance sensor (such as a time-of-flight laser sensor) to measure the distance from the sensor to the sample on the surface, and the output of the sensor is fed into the input of the autofocusing device to help provide rapid and automatic focusing. The autofocusing device may be positioned between the laser and the laser deflector.

[0028] With this in mind, the typically rough surface of the wellbore causes the distance between the instrument and the wellbore to vary as the instrument moves along the borehole and as it is repositioned from one location to another. The preferred configuration of the laser delivery optics described above, including the use of an autofocus device and a distance sensor, helps to avoid measurement and detection difficulties caused by the laser pulses not being at the same focal point when they reach the borehole surface.

[0029] An autofocusing device can simply provide a focused beam with a consistent convergence angle and therefore a consistent laser energy density at the focal point. In this respect, the autofocusing device can be a liquid lens, a gel lens, a deformable mirror lens, a galvano-mirror lens, or a voice coil activated lens, or can be achieved simply by physically moving a glass lens or lens combination to move the focal point relative to the instrument.

[0030] Furthermore, the distance sensor can be a time-of-flight sensor in the form of a single-area sensor or a multi-area sensor, with a transmitter, receiver, and processor located on the same integrated circuit chip. The sensor will preferably utilize a laser diode outside the spectrometer's wavelength range, ensuring the spectrum is not contaminated by other light sources. Preferably, the time-of-flight sensor will be a compact, microprocessor-controlled sensor with very low power requirements. The sensor's resolution / accuracy is preferably less than the distance the plasma will travel (i.e., the waist region). For example, although the plasma will typically form within a 5 mm range, the sensing resolution / accuracy may be + / - 2 mm.

[0031] The characteristics of laser power conditioning may also necessitate the use of adjustable (manual or remote) beamsplitters to vary the pulsed laser power reaching the sample surface. This may be necessary because most lasers are optimized to produce maximum energy efficiency and pulse stability for a limited range of laser pulse repetition rates and energies. With a beamsplitter, the laser can be operated under optimized conditions while simultaneously varying the pulse energy at the sample surface.

[0032] In another embodiment of the invention, a pulse energy measurement sensor can be used to measure the energy of the portion of the laser pulse reflected from the beam splitter. This makes it possible to characterize the transmitted pulse and determine variations in the laser pulse energy, pulse length, or optical mode structure.

[0033] Furthermore, given that the primary purpose of a beam splitter is to reduce the laser energy interacting with the sample, it may be desirable, for example, to include a suitably oriented quarter-wave plate after the beam splitter. In this configuration, any circularly polarized reflections from the focusing lens or optical window can be prevented from propagating back to the laser.

[0034] In one embodiment of the invention, the plasma emission collecting optics includes a deflector for concentrating radiation emitted laterally through a side window at a sample point, which is then returned to the instrument during operation, and for deflecting the radiation by 90 degrees to guide it substantially longitudinally toward a collimator. In this embodiment, the collimator collects the emitted radiation and converts it into a parallel (collimated) beam for transmission to an optical fiber coupled for direct delivery to a spectrometer.

[0035] The position of the collimator relative to the plasma emission deflector and fiber coupling can be determined with reference to the position of the laser plasma, and may need to be adjustable (if autofocus is not used) to change the focusing requirements as the actual sample point moves away from the optimal focus.

[0036] Ideally, the plasma emission deflector used for the emitted radiation will be a coated plane mirror or shaped mirror, the coating preferably allowing reflection of wavelengths between 180 nm and 950 nm. Preferably, the plasma emission deflector will have a parabolic shape, which will deflect the plasma emission in a manner that concentrates the light at an optical collimator. In this respect, the parabolic mirror is preferably an off-axis parabolic mirror, so that the plasma emission does not reflect back at the focal point (i.e., it reflects at an angle of 90° to the laser path). Furthermore, the deflecting lens will have an aperture of sufficient diameter to allow the excitation laser to pass through, but different optical arrangements may make this unnecessary.

[0037] Furthermore, the collimator will preferably be a fixed-focus collimator with a lens having an anti-reflective coating and a coupler for fiber optic connection. The collimator will preferably have high transmission efficiency across the entire wavelength range of the spectrometer. The collimator can be a single-lens system or a multi-lens system with any of the SMA905, FC / PC, or FC / APC fiber optic couplings, but will preferably be a single-lens system with SMA905 fiber optic coupling.

[0038] In addition, the fiber optic coupling can be an SMA905, FC / PC, or FC / APC system, but the SMA905 system is preferred.

[0039] In one form of the invention, the laser delivery optics includes an air jetter having two main functions: (a) keeping the laser exit window and emission inlet window clean from debris due to plasma and other dust that may be present in the borehole; and (b) allowing air to flow over the sample surface to keep the sample surface dust-free and, if the sample surface is wet, to aid in drying. This air jetter system can be supplied with compressed air by an external borehole system or by an internal compressed air pump, but an internal compressed air pump with a filtration system is preferred. This air jetter system can also be configured to first cool the internal components of the instrument.

[0040] Regarding the deployment of the instrument according to the invention, and particularly regarding the instrument's ability to provide real-time measurement and analysis, and thus its potential to provide continuous measurement and analysis, the harsh and variable conditions in the well and the varying distances from the instrument to the well surface mean that easily controlled descents and ascents will be preferred. Therefore, the instrument of the invention is ideally contemplated to interconnect with a surface winch capable of receiving control information directly or indirectly provided by the control system, using information from the LIBS spectrometer and autofocus system, cameras, and additional sensors (if present). Ideally, additional control over the instrument's lateral position and axial rotation within the well can also be provided by active or passive stabilizers attached to the instrument.

[0041] The control information will preferably suggest the position and speed information of the instrument, which is controlled by a winch physically connected to and thus supports the instrument from above via wires and / or cables. In this respect, this physical connection between the winch and the instrument also provides opportunities for supplying power and other communications to the instrument, some of which can be enhanced or replaced by suitable wireless communication hardware and protocols (such as WiFi or 4G / 5G, if available in the specific drilling environment).

[0042] Generally speaking, and without wishing to be confined to this technical theory, it should be understood that the generation process of LIBS spectra is the same as that of optical emission spectra used in other laboratory analytical methods, such as inductively coupled plasma optical emission spectrometry (ICP-OES). Similar to ICP-OES, LIBS generates plasma from a small sample of solid material, and the atomic emission lines present in the light emitted by the plasma can be used to identify the elements present in the sample and their concentrations. In this respect, light is emitted when electrons excited to higher energy levels by energy (transmitted by a laser) fall back to lower energy levels. The energy difference between the energy levels is represented by photons, which are collected and measured.

[0043] With this in mind, while ICP methods produce continuous, stable plasmas that can be analyzed on timescales of seconds, LIBS plasmas are unstable and typically have lifetimes measured in microseconds. This introduces the complexity that the plasma observed during observation will vary in temperature and density, and even for the same material, significant shot-to-shot variation can exist in the observations. Matrix effects caused by sample characteristics (such as sample composition, primary minerals, mineral density, and grain packing density) also produce variations in plasma temperature and electron density, ensuring that identical elemental combinations will not appear at common temperatures and densities. For these reasons, understanding how the appearance of the spectrum relates to temperature and density is useful.

[0044] Regarding this complexity, at a certain moment, and after a sufficient delay following the decay of continuous radiation, the optical signal consists of emission peaks at wavelengths characterizing the emitting elements. For these emitting elements, the signal intensity at a given wavelength in the LIBS plasma can be correlated with other parameters through this idealized relationship:

[0045] In this equation, at a given wavelength ( The intensity (I) at point ( ) is related to the elemental concentration (C). The term multiplied by the concentration is determined by the atomic constant ( ). — Upper level quad degeneracy (QD) —Einstein coefficient), ( — It consists of the upper energy level (U), plasma temperature (T), and partition function U(T). This equation is solved together with another relationship that calculates the balance between different types of plasma and is also subject to conservation laws.

[0046] This is a strongly nonlinear algebraic function of plasma temperature, which results in the richness of LIBS spectroscopy, making it a preferred instrument and method for determining geological structures in-situ during mineral exploration and mining. For example, this gives LIBS spectroscopy a different character than hyperspectral spectroscopy, which is essentially a normalized representation of differences in excitation and does not exhibit the complexity of wavelength variations dependent on excitation. Furthermore, if the temperature is constant in the above relationship, it can be reduced to a simple algebraic relationship. This algebraic function applies to all elements in the periodic table, enabling in-situ determination of elemental concentrations. This contrasts with other analytical techniques that cannot detect all elements (e.g., XRF) or cannot be measured in-situ (e.g., ICP-OS).

[0047] This relationship is useful in the development of data analysis for the instrument of this invention, and it is part of a positive model that correlates observed spectra with material composition. Regarding data analysis ideally suited for use with the instrument of this invention, the following are some preferred analytical tools: a) Given the partition function and atomic parameters, evaluate the basic LIBS equation to create simulated spectra independent of other LIBS spectral models, as well as elemental and mineral species spectra for 204 selected mineral phases.

[0048] b) Evaluate plasma temperature and electron density using physics-based methods and by matching model-generated spectra to experimental spectra, and thus identify relevant plasma parameters to facilitate the development of calibration-free LIBS methods.

[0049] c) These physical models are applied in conjunction with engineering simulations of systems that take into account the real-world behavior of optical systems, spectrometers, and lasers. This makes the spectral models based on engineered systems, rather than physically idealized models.

[0050] d) Integration of modeling of real-world downhole environments, including contaminants and humidity, as well as statistical properties of drill hole mineralogical characteristics.

[0051] e) Physical and engineering models can be integrated with machine learning to provide data-driven modeling.

[0052] f) Data analysis can be integrated with the feedback control system to optimize instrument parameters for the borehole target in real time based on observed and available conditions and spectral quality. A multi-scan system can be implemented, where an initial coarse scan of the borehole is used to optimize the second scan.

[0053] The purpose of lasers is to ablate and thermally excite solid samples, resulting in high-temperature plasma that emits light capable of identifying elements and their concentrations. An example in engineering modeling is that key parameters of the laser are the energy of each pulse and its consistency. If it is assumed that increasing pulse energy leads to increased temperature, then the statistics of the pulse energy will be useful in the aforementioned forward modeling process.

[0054] In this regard, the following useful features have been shown: a) The operating time of the laser tends to follow a pattern where there is no increase or decrease in energy; b) The pulse energy is approximately normally distributed around the average pulse energy; and c) Outliers exist in the spectral results. These outliers can be identified and removed due to their unique spectra. Outliers are more likely to be low-energy pulses than high-energy pulses.

[0055] Knowing that laser energy can be characterized by a normal distribution means that normal statistics can be fed into the equation relating pulse energy to plasma temperature, and then into the LIBS equations to understand the lens-to-lens variations in the spectrum caused by the laser. This helps limit errors in predictive modeling and facilitates predictive modeling that is less sensitive to the source of such variations. In fact, laser energy stability tends to depend on the laser operating at a preferred power setpoint, meaning that avoiding large-scale changes in laser power may be preferable in the presence of feedback control. Attached Figure Description

[0056] The invention will now be described with reference to the accompanying drawings, figures, and tables. However, the following description does not limit the generality of the above description.

[0057] In the attached diagram: Figures 1(a) and 1(b) are schematic diagrams of an instrument according to a preferred embodiment of the present invention; Figure 2 This is a cross-sectional view of a selected configuration of the optical head of the instrument in Figure 1; Figure 3 The figure shows the spectral intensities of the emission lines of Fe - 256 nm, Ca - 393 nm, and Na - 589 nm measured from the cross sections (dashed lines) of the six test blocks below when the test blocks are dry (black) and wet (gray). Figure 4 The diagram shows: (A) the effect of borehole surface roughness and focal point; (B) the focal range where the laser intensity is high enough to cause breakdown; (C) the experimental setup; (D) the analysis direction relative to the angled surface; and (E) the experimentally determined maximum intensity region of approximately 2 mm. Detailed Implementation

[0058] Figure 1(a) illustrates a downhole instrument 10 according to a preferred embodiment of the present invention. The instrument 10 is for real-time analysis of the borehole wall and utilizes laser-induced breakdown spectroscopy (LIBS). The instrument 10 includes an elongated housing having a bottom end 14 and a top end 16. Inside the housing are an optical head 18 located at the bottom end 14, two LIBS spectrometers 20 (in this embodiment) facing the top end 16, and a laser 22 located between the optical head and the LIBS spectrometers.

[0059] Optical head 18 includes laser delivery optics and plasma emission and collection optics (as shown in Figure 1(b) and 1200). Figure 2 (as better illustrated in the figure), and the spectrometer 20 is optically coupled to the optical head 18 via fiber optic coupling 28.

[0060] Laser 22 is configured to deliver pulses directly to a laser delivery optics for focusing before they pass through a side window 30 of optical head 18 (see FIG. 1(b)) to a sample point (not shown) on the borehole wall. Optical head 18 is configured to collect radiation emitted from laser-induced plasma at the sample point and transmit the emitted radiation via fiber optic coupling 28 to spectrometer 20 (see FIG. 1(b)) via plasma emission collection optics.

[0061] The housing may be a single piece; however, in this embodiment, the housing is formed of multiple housing sections. The housing also includes a cooling system within it, in the form of a circulating airflow system (not shown), operable in response to temperature readings taken around both the laser 22 and the spectrometer 20. The housing includes internal channels (not shown) that allow air to pass around its various components, these channels being in fluid communication with a fan (not shown) also located within the housing.

[0062] The LIBS spectrometer 20 has sufficient resolution and wavelength range to resolve the synthetic emission spectrum generated by the laser 22 well. The spectrometer configuration in this embodiment is two compact Cherny-Turner spectrometers because they are easy to miniaturize; however, the LIBS spectrometer 20 could be constructed using only a single spectrometer.

[0063] Laser 22 ablates and thermally excites the sample surface, generating a high-temperature plasma 31 (see Figure 1(b)), which emits light capable of identifying elements and their concentrations. Laser 22 is also able to control the energy of each pulse and produce consistent pulses. This consistency includes pulse length, wavelength, and intensity distribution.

[0064] The laser 22 in this embodiment is a single-pulse laser or a double-pulse laser, with a laser excitation wavelength range of 200nm to 1600nm and a pulse length in the nanosecond range, and specifically a Q-switched Nd-YAG laser.

[0065] Referring now to Figure 1(b), the laser delivery optics include a focusing lens 50 and a laser deflector 54. The focusing lens 50 is used to focus a longitudinally oriented collimated laser pulse 52 (which has passed through the laser collimator 51 and wedge prisms 51a and 51b). The laser deflector 54 is used to laterally redirect the focused pulse from the laser through the side window 30 to the sample point (not shown). The focusing lens 50 is a plano-convex glass lens coated with a suitable anti-reflective coating for the laser excitation wavelength used. The laser deflector 54 is sized such that the size of the mirror is larger than the maximum size of the focused beam.

[0066] The laser delivery optics also include an autofocusing lens 53 with a beam expander located between the laser 22 and the laser deflector 54.

[0067] The plasma emission collecting optics in this embodiment include a plasma emission deflector 60, which concentrates radiation emitted laterally through a side window 30 at the sample point, which is returned to the instrument 10 during operation, and deflects the radiation by 90 degrees to guide it approximately longitudinally toward a collimator 62. The collimator 62 collects the emitted radiation and converts it into a parallel (collimated) beam for transmission to an optical fiber coupler 65, which then transmits the beam directly to the spectrometer 20 of FIG. 1(a) via optical fiber 28.

[0068] Collimator 62 is a fixed-focus collimator with a lens featuring an anti-reflective coating and a coupler for fiber optic connection. Collimator 62 exhibits high percentage transmittance across the entire wavelength range of spectrometer 20. Collimator 62 is a single-lens system with SMA905 fiber optic coupling.

[0069] The plasma emission deflector 60 is an off-axis parabolic mirror (with a through-hole) that deflects plasma emission in a manner that concentrates light at collimator 62 and allows reflection of wavelengths between 180 nm and 950 nm.

[0070] Now refer to Figure 2 In this particular embodiment, the optical head 18 includes an optical component support 40 housed within a housing. The optical component support 40 has mounting sections 42, 44, and 46 capable of receiving and holding both laser delivery optics and plasma emission and collection optics. In this embodiment, the optical component support 40 is an injection-molded or 3D-printed one-piece component with pre-formed mounting sections 42, 44, and 46 ready to receive appropriate optics.

[0071] In this embodiment, the laser delivery optics further include a focusing lens 50' and a laser deflector 54'. The focusing lens 50' is used to focus a longitudinally oriented collimated laser pulse 52', and the laser deflector 54' is used to laterally redirect the focused pulse from the laser passing through the side window 30' to the sample point (not shown). The focusing lens 50' is a glass plano-convex lens coated with a suitable anti-reflective coating appropriate for the laser excitation wavelength used. The laser deflector 54' is sized such that its size is larger than the maximum size of the focused beam.

[0072] The laser delivery optics in this embodiment will also include an autofocusing lens positioned between the laser 22 and the laser deflector 54' in FIG1(a). Figure 2 (Not shown in the image), in this embodiment, the autofocusing lens includes a distance sensor to measure the distance from the sensor to the sample on the surface, and the output of the sensor is fed to the autofocusing lens (…). Figure 2The input (not shown) helps provide fast and automatic focusing. The autofocus lens in this embodiment is an electrically tuneable liquid lens with a fast response time greater than 10 Hz.

[0073] The plasma emission collecting optics in this embodiment further includes a plasma emission deflector 60' for concentrating radiation emitted laterally through the side window 30' at the sample point, which is returned to the instrument 10 during operation, and for deflecting the radiation by 90 degrees to guide it approximately longitudinally toward the collimator 62'. The collimator 62' collects the emitted radiation and converts it into a parallel (collimated) beam for transmission to an optical fiber coupling for direct delivery to the spectrometer 20 of FIG. 1(a).

[0074] Collimator 62' is also a fixed-focus collimator, featuring a lens with an anti-reflective coating and a fiber optic coupling 65' for fiber optic connection. Collimator 62' has a high percentage transmittance across the entire wavelength range of spectrometer 20. Collimator 62' is also a single-lens system with SMA905 fiber optic coupling.

[0075] The plasma emission deflector 60' has a parabolic shape to deflect the plasma emission in a way that concentrates the light at the collimator 62' and allows reflection of wavelengths between 180 nm and 950 nm.

[0076] Initial tests were performed using instrument 10 on the dry surfaces of a series of six test blocks (split borehole cores), which were stacked vertically and the instrument was lowered at a rate of 50 mm / min. Figure 3 The samples were measured on their flat (cut) surfaces. These samples exhibit well-defined and visually apparent inter-sample compositional differences perpendicular to the drilling direction, as well as mineralogical variability on the cm scale perpendicular to the drilling direction, thus allowing for visual validation of the raw data in the context of the expected spatial distribution of geochemistry without requiring complex data analysis.

[0077] These tests show that major elements such as iron (Fe), sodium (Na) and calcium (Ca) can be detected and correlated with the expected spatial distribution in each test block, extracting the peak area of ​​the strongest peak along the analysis cross section for a given element.

[0078] Figure 3The region of high Ca, low Fe, and Na at the top of the cross section is clearly shown, corresponding to the Ca-rich gypsum at the top of the first core. The highest observed Fe signal is found when the measured cross section intersects with Fe-rich sulfide minerals in the second and third cores. The raw intensity data presented here are unprocessed except for adjustments to the x-axis (depth) to align the individual wet and dry runs with the image.

[0079] To test the effect of wet drilling on LIBS spectra, test blocks were sprayed with a solution of water and household cleaning agent, and measurements were immediately taken using instrument 10. The results showed that although there was a slight attenuation in the overall signal intensity for some elements, this was not consistent across all blocks, and the expected downhole distributions of Fe, Ca, and Na remained distinguishable. Figure 3 Air jets of the type generally described above were used, but no additional measures to enhance the signal were employed (such as burnout pulses used to evaporate any surface water, but which would be expected to increase signal strength). It should also be noted that, through extensive laboratory measurements, the Fe, Ca, and Na contents of these samples ranged from <100 ppm to >20% (wt%).

[0080] about Figure 4 As mentioned above, the roughness of the borehole wall surface in any drilling environment makes the distance between the instrument and the sample surface variable. The effect of varying the distance from the instrument to the sample surface between 10mm and 20mm on the sample position relative to the instrument was studied, and the effect of the focal length was tested using edge material of the test block. The experimental setup is as follows: Figure 4 As shown, the maximum intensity area measured at the same time was approximately 2 mm.

[0081] To further test this, a homogeneous sample surface (terracotta) was tilted and moved in front of the instrument using a motorized platform. Terracotta was used because it is homogeneous at the LIBS scale, with a matrix and composition similar to rock (compared to metallic targets), and the surface shape can be modified to simulate the rough surfaces within a borehole. Initial testing involved smooth terracotta bricks mounted at an angle, such that the surface moved across the instrument's focal length range as the sample was moved. The sample was moved at a constant speed of 50 mm / min with a laser repetition rate of 4 Hz. This equates to an analysis interval of 0.2 mm between locations, utilizing a sample that is in focus at the first location but out of focus at the final location.

[0082] As the sample moves out of focus from the first position to the final position, a decrease in plasma intensity is observed. The observed plasma forms in the air in front of the sample surface, and two spectrometers (located within the instrument) observe the plasma within a narrow envelope of overlapping circles (via a Y-shaped fiber connected to a single collimator). Therefore, as the sample moves out of focus, the plasma moves out of the envelope observed by the two spectrometers, which is addressed by optimizing the collimator position. Alternatively, this can be achieved by including an autofocusing lens and an off-axis parabolic mirror, thus providing co-aligned laser beams and plasma observation optics.

[0083] Regarding the potential roughness of the sample surface, terracotta bricks simulating rough surfaces are prepared using a mold that binds graded gravel into blocks, allowing this morphology to be replicated for analysis under different focusing conditions. In this respect, homogeneous composition means that any variations in the results are due to the morphology. The practicality of the variable focal length system has also been demonstrated.

[0084] Finally, it should be understood that other variations and modifications of the above content may also fall within the scope of this invention.

Claims

1. A downhole instrument for real-time laser-induced breakdown spectroscopy (LIBS) analysis of the borehole wall, the instrument comprising an elongated housing having a bottom end and a top end, the housing including, inside which are an optical head located at the bottom end of the housing, a LIBS spectrometer located at the top end of the housing, and a laser located between the optical head and the LIBS spectrometer, wherein: a) The optical head includes laser delivery optics and plasma emission and collection optics; b) The spectrometer is optically coupled to the optical head; c) The laser is configured to deliver pulses directly to the laser delivery optics for focusing before they pass through the side window of the optical head to the sample point on the borehole wall; as well as d) The optical head is configured to collect radiation emitted from laser-induced plasma at the sample point, and the emitted radiation is transmitted via optical fiber coupling to the at least one spectrometer via the plasma emission collection optics.

2. The instrument according to claim 1, wherein, The elongated housing is a one-piece housing with a removable bottom and top end to allow access to the interior of the housing and to allow removal of the optical head, the laser, and / or the spectrometer.

3. The instrument according to claim 1, wherein, The elongated housing is formed by multiple housing components or has a removable access port along the length of the elongated housing.

4. The instrument according to any one of claims 1 to 3, wherein, The elongated housing includes a circulating airflow system that operates in response to temperature readings taken around either or both of the laser and the spectrometer. The housing also includes internal channels that allow air to pass around either or both of the laser and the spectrometer.

5. The instrument according to claim 4, wherein, The circulating airflow system includes an air jet that allows air to flow through the laser exit window and the emission entrance window, and also over the sample surface.

6. The instrument according to any one of claims 1 to 5, wherein, The LIBS spectrometer has sufficient resolution and wavelength range to ensure that the emitted radiation is well resolved. The LIBS spectrometer is preferably constructed as a medium echelle grating / Cherney-Turner LIBS spectrometer.

7. The instrument according to any one of claims 1 to 6, wherein, The instrument comprises two LIBS spectrometers, one for UV and one for visible light, preferably both being echelle grating / Cherney-Turner (optical) spectrometers, and the two LIBS spectrometers are registered to observe the same sample points.

8. The instrument according to any one of claims 1 to 7, wherein, The laser is a single-pulse laser or a double-pulse laser, wherein the single-pulse laser or double-pulse laser has a laser excitation wavelength range between 200nm and 1600nm, and has a pulse length in the range of nanoseconds or femtoseconds, preferably in the range of nanoseconds.

9. The instrument according to claim 8, wherein, The laser is a Q-switched Nd-YAG laser.

10. The instrument according to any one of claims 1 to 9, wherein, The optical head includes an optical device support, which can be accommodated within the optical device housing inside the elongated housing or directly within the elongated housing.

11. The instrument according to claim 10, wherein, The optical device support includes a mounting section capable of receiving and holding the laser delivery optics and the plasma emission and collection optics.

12. The instrument according to any one of claims 1 to 11, wherein, The laser delivery optics include a focusing lens and a laser deflector. The focusing lens is used to focus a longitudinally oriented parallel laser pulse, and the laser deflector is used to laterally redirect the focused pulse from the laser through the side window to the sample point.

13. The instrument according to claim 12, wherein, The focusing lens is a single plano-convex lens device or multiple plano-convex lens devices having a damage threshold sufficient to withstand damage from laser pulses.

14. The instrument according to claim 13, wherein, The focusing lens is a glass plano-convex lens, which is coated with an anti-reflective coating suitable for the laser excitation wavelength used.

15. The instrument according to any one of claims 12 to 14, wherein, The laser deflector for the incident laser pulse is a plane mirror with an anti-reflective coating suitable for the laser excitation wavelength used, the plane mirror having a damage threshold sufficient to withstand damage from the laser pulse, and the plane mirror being sized such that the size of the mirror is greater than the maximum size of the focused beam.

16. The instrument according to any one of claims 1 to 15, wherein, The laser delivery optics include an autofocusing lens positioned between a deflector and a side window. The autofocusing lens includes a distance sensor for measuring the distance from the sensor to a sample on the surface, and the output of the distance sensor is fed into the input of the autofocusing lens.

17. The instrument according to claim 16, wherein, The autofocusing lens is a liquid lens, gel lens, deformable mirror lens, current mirror lens, or voice coil activated lens, or autofocus is achieved by moving a glass lens or lens combination to move the focal point relative to the instrument.

18. The instrument according to claim 16 or 17, wherein, The distance sensor is a single-area sensor or a multi-area sensor with a transmitter, receiver and processor located on an integrated circuit chip, wherein the distance sensor utilizes a laser diode outside the wavelength range of the spectrometer so that the spectrum is not contaminated by other light sources.

19. The instrument according to claim 18, wherein, The distance sensor is a compact, microprocessor-controlled sensor with low power requirements.

20. The instrument according to any one of claims 1 to 19, the instrument comprising an adjustable beam splitter to change the pulsed laser power to the sample surface.

21. The instrument according to any one of claims 1 to 20, wherein, The plasma emission collecting optics includes a plasma emission deflector for concentrating radiation emitted laterally through the side window at the sample point back to the instrument during operation, and for deflecting the radiation by 90 degrees to guide the radiation generally longitudinally toward the collimator.

22. The instrument according to claim 21, wherein, The collimator collects the emitted radiation and converts it into a parallel beam to transmit the beam to an optical fiber coupler for direct delivery to the LIBS spectrometer.

23. The instrument according to claim 21 or 22, wherein, The plasma emission deflector used for the emitted radiation is a coated or shaped mirror that allows reflection of wavelengths between 180 nm and 950 nm.

24. The instrument according to claim 23, wherein, The plasma emission deflector has a parabolic shape that deflects the plasma emission to concentrate light at the collimator.

25. The instrument according to any one of claims 21 to 24, wherein, The collimator is a lens with an anti-reflective coating and a fixed-focus collimator for fiber optic connection coupling.

26. The instrument according to claim 25, wherein, The collimator has a high percentage transmittance across the entire wavelength range of the spectrometer.

27. The instrument according to any one of claims 1 to 26, wherein, The instrument is interconnected with a ground winch capable of receiving control information directly or indirectly provided by the control system, using information from at least the LIBS spectrometer.

28. The instrument according to claim 27, wherein, The control information includes position and speed information for the instrument, and the position and speed control of the instrument is provided by the winch above the instrument.

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