WO2014202618A2

WO2014202618A2 - Method for determining the configuration of a structure

Info

Publication number: WO2014202618A2
Application number: PCT/EP2014/062740
Authority: WO
Inventors: Philippe BRUNNER; Pascal Felber; Philippe Renard; Stéphane SCHILT; Thomas SÜDMEYER
Original assignee: University Of Neuchâtel
Priority date: 2013-06-17
Filing date: 2014-06-17
Publication date: 2014-12-24
Also published as: WO2014202618A3

Abstract

A method for determining the mineralogical, or geological, or chemical configuration of a structure, comprising: illuminating the structure with a broadband laser source that emits electromagnetic radiation having a plurality of wavelengths, recording an image of the surface of the structure that includes information on the spectrum of the radiation reflected or diffused by the structure.

Description

Method for determining the configuration of a structure

Field of the invention

[0001] The present invention relates, in embodiments, to methods and devices for analyzing quantitatively and chemically geological structures. Further, the present invention concerns also methods of mining, waste storage, oil field and aquifer exploiting and managing, and the like.

Description of related art

[0002] In the field of geostatistics, it is known how to employ two-point and multiple-point statistics for generating simulations in order to predict the amount of oil and gas reserves. With the same techniques, it is also known how to model the geometry and the physical parameters of the reservoirs allowing to model oil or gas flow through the reservoir and optimize its recovery, or to assess the water permeability of a geological structure, for example in a waste disposal site. Multiple-point statistics simulation techniques are recognized as the most flexible methods known so far to integrate a conceptual geological model in a statistic framework, and are widely used in the petroleum industry and in hydrogeology.

[0003] Such simulations typically use 2D or 3D models of the reservoir that includes a grid of a large number, often in excess of a million, of individual cells. These models typically represent the values of one physical property, often the underlying geological facies expressed as a discrete- valued category variable. The goal of modelling is to obtain an image of the underground reservoir that reflects the knowledge of the general geological structures present on the site, restrained by conditioning values measured at certain points, for example corresponding to wells, and, in some cases, by seismic data.

[0004] The simulated images (either in 2D or in 3D) respect the structures and morphology of a given reference training image and adhere to the conditioning data. This technique has been described, among others in International Patent Application WO2010057505, which is hereby incorporated by reference.

[0005] It is known to use hyperspectral mapping, which is a technique using spectrally qualified images, to obtain information on the

mineralogical or chemical composition of a structure. When the structure is outdoors, for example a geologic outcrop, or a large man-made structure like a bridge, such methods rely on available natural light for illuminating the structure under scrutiny. Natural illumination from the sun is affected by a number of factors, including cloud coverage, daytime, atmospheric dust, humidity, limiting the applicability and repeatability of the method, in particular in the present of shadows, or varying spatial orientation of the structure.

[0006] Laser-Induced Breakdown Spectroscopy (LIBS) is a type of atomic emission spectroscopy which uses a highly energetic laser radiation as excitation source. The laser forms a plasma on the surface of a sample, which ionizes and excites the matter, whereupon the emitted light is analysed to detect the characteristic wavelengths of different elements.

Brief summary of the invention

[0007] According to the invention, these aims are achieved by means of the method of the appended claims

Brief Description of the Drawings

[0008] The invention will be better understood with the aid of the description of an embodiment given by way of example and illustrated by the figures, in which: Figure 1 shows a schematically the method of the invention

Figure 2 illustrates schematically a hyperspectral imaging device according to one aspect of the invention Figure 3 plots the absorption spectrum of several common minerals for visible and infrared light.

Detailed Description of possible embodiments of the Invention

[0009] Figure 2 illustrates schematically a device 200 according to an aspect of the present invention that includes a first laser source 85 arranged to generate a broadband laser emission in a succession of high- intensity short peaks, for example a femtosecond laser. Preferably, the light emitted by the broadband laser source 85 is situated in the visible and/or near-infrared portion of the electromagnetic radiation, for example distributed about a central wavelength comprised between 400 and 3000 nm, for example between 1000 and 2500 nm. The source 85 is arranged to illuminate, by the interposition of a suitable optics, the surface 210 of a target that may be a wall, a geological outcrop, or a large structure, situated at a distance ranging from some metres to several hundred of metres or more from the source 85.

[0010] The use of broadband laser-based or laser-driven sources allows to achieve to collect hyperspectral images of large outdoors structures with a precision and a repeatability that are not possible with available natural light, and at distances far superior than those attainable with conventional light sources.

[0011] The radiation scattered or diffused by the target 210 is collected by a spectral imaging device 60 that may be a spectral, multispectral, or hyperspectral camera that is sensitive to the infrared and/or visible light emitted by the source 85 and is capable of dividing the image in a plurality of spectral bands. Preferably the imaging device 60 is a hyperspectral sensor with the ability to subdivide the image in a large number of narrow spectral bands such that it is possible to obtain a spectrum of the received light for each pixel of the image. In variants, the invention may also include static or swept linear optical sensor, that acquire the light distribution and spectrum of one row of pixels in the image at a time, and/or a point spectrometer, that can acquire a high-resolution spectrum of the light received from one point, or one region of the target.

[0012] Since different materials, minerals and ores present different absorption and light scattering spectra, a camera having an adequate spectral coverage and resolution can be used to discriminate between these, and thus generate maps of mineralogical, geological or chemical configuration of the target. Figure 3 plots the absorption spectra in the visible and infrared light of several common minerals, namely: 121 calcite, 122 dolomite, 123 gypsum, 124 biotite, 125 illite, 126 kaolinite, 127 montmorillonite, 128 quartz. It appears that many geological material exhibit specific absorption bands in the region of the spectrum above 1.5 μηη in a broad band that extends to above 2.5 μηη. It is therefore

advantageous to use a broad spectrum source that can generate an intense and well-characterised illumination at these wavelengths. [0013] In a further variant of the invention, the radiation emitted by the source 82 is given a time structure that allows to improve the detection at the receiving device 60. If the emitted radiation is suitably time-modulated, for example, the detector 60 can include a lock-in circuit, or another synchronous detection device, in order to increase the signal-to-noise ratio and reject external background light sources. Moreover, if the wavelength emitted by the source 85 can be swept repeatedly in time, spectral information can be gathered by a fast detector 60 without spectral resolution. Such sweep could be obtained, for example, by two frequency comb laser systems with a slight relative detuning in the repetition rates. [0014] According to a preferred embodiment of the invention, the source 85 is a supercontinuum source in which a radiation beam generated by a powerful pulsed laser is broadened severely by traversing a suitable nonlinear system, like for example a photonic crystal fibre or a highly nonlinear fibre. [0015] According to another variant, the broadband source 85 of the invention could include one or several Optical Parametric Amplifiers (OPA) or Optical Parametric Oscillators (OPO) arranged to generate the light of an incident laser pulse in a radiation containing a plurality of wavelengths. For example, the light from a strong pulsed laser emitting radiation of 800 nm wavelength could be converted in an OPA into a radiation comprising photons of 1 .2 μηη and 2.4 μηη. This could then be further broadened by a supercontinuum mechanism, as mentioned above.

[0016] The bandwidth of the light emitted by the broadband source 85 is preferably higher than 10 nm, more preferably in excess of 50 nm. In a preferred variant, the laser source comprises a nonlinear optical element and arranged to broaden the bandwidth of the light to more than 500 nm, more preferably to more than 1 μηη, and preferably centred in the region of the infrared spectrum between 1 μηη and 3 μηη, in order to increase the capability of discriminating different minerals and chemicals.

[0017] The optical output power of the broadband source 85 will be chosen with consideration of the distance to the target 210, but will preferably be higher than 1 W, more preferably higher than 10 W. The light is emitted in ultra-short pulses, and the peak power will be preferably more than 10 kW and more preferably higher than 100 kW.

[0018] Several ultrafast lasers can be used in the frame of the invention including, but not limited to, fibre lasers, and thin-disk lasers. Other devices that could usefully be employed in the frame of the invention are

Yb:CALGO Lasers and ultrafast semiconductor lasers, which can be particularly compact and cost-efficient. Especially VECSELs and MIXSELs are well suited to generate average power levels in the watt regime in ultrashort femtosecond or picosecond pulses.

[0019] The technique described above allows the collection of a large amount of hyperspectral data remotely, and thus permits the access to structures like geological outcrops, dams and bridges that are difficult to reach with conventional prospection and measurement methods. Where the application demands it, the device 200 can be mounted on an airborne vehicle, for example for geological prospection, or on a robotic platform, for unattended operation in deep mines or in other environments where human intervention is not practical or possible.

[0020] According to another aspect of the invention, the device 200 is equipped with a LIBS radiation source 75 arranged for generating high- intensity pulses that deposit a sufficient amount of energy to generate a spot of plasma on the surface of the target 210, and thus allow remote determination of its chemical composition by atomic spectroscopy, for example. The LIBS analysis can be carried out by the same spectral detector 60. Preferably, however, since the wavelength of the atomic emission spectra that are relevant for the LIBS analysis and those of the broadband laser source 85 are rather different, and LIBS analysis requires in general a higher resolution, a dedicated spectrometer will be employed.

[0021] It was found that LIBS source 75 that generates ultrashort pulses of radiation provides both a higher efficiency in ionizing the target and has better propagation to long distances. Preferably the LIBS source 75 will emit light pulses shorter than one picoseconds, more preferably shorter than 500 femtoseconds or 200 femtoseconds.

[0022] The above described technique is capable of generating a vast amount of data that carry information on the chemical or petrographic or geological configuration of the visible surface of the target 210. In order to complete this information to the interior, or to parts of the target that are covered by vegetation or sediments, the data thus collected can be used as conditioning input in a geostatistic model 360, as shown in figure 1 .

Preferably the model combines the surface data 155, 160 obtained by hyperspectral imaging and LIBS with other data 120, 130 carrying

information on the deep structure of the target, like for example borehole or seismic data.

[0023] The geostatistic modelling software allows the generation of statistic models 290 resulting in probability maps for the geological structure (which allows to predict water flow, stability, materials,

composition, security leaks for pollutants, ...) in the structure in examination. Given the large amount of information that can be

generated by the hyperspectral imagers, the statistical modelling should preferably be capable of dealing with large simulation grids. The methods disclosed in International Patent Application WO2010057505 are therefore particularly advantageous.

[0024] The models obtained by the method and system of the invention can be exploited in a multitude of application including, but not limited to, mining, natural resources exploitation, safe waste and nuclear waste deposition, exploitation of oil and geothermal fields, C0₂ sequestration, deep oil storage, analysis of artificial structures like dams, bridges, tunnel and buildings, surveillance, law enforcement, military, vegetation mapping in forestry and agriculture, and so on.

[0025] Since a camera image will provide only a 2D characterization of a site, and an incomplete one in which some area cannot be univocally classified on the basis of the camera image alone, and need to be filled up.

[0026] For many applications (oil industry, mining, nuclear waste repository safety, groundwater hydrology), the two dimensional

characterization obtained with the methods described above will be insufficient and a fully three-dimensional characterization is required, the step of geostatistic simulation is instrumental in obtaining a complete, exploitable 3D model. To achieve this final goal, the method of the invention generates 3D stochastic fields that will combine all the available measurements (multispectral images, fs-LIBS, local property measurements, and borehole information). [0027] More precisely we will rely on multiple-points statistics

techniques that enable to account for complex 3D spatial patterns and complex relations between variables. As those methods are

computationally demanding and as the imaging detector is capable to generate extremely large data sets, the invention may benefit from distributed storage, calculation and processing techniques. [0028] Upscaling from small to large regions will require the

combination of the two systems components:

[0029] A new system solution enables progressing from large amounts of microscopic data to real predictions on a tera-scale. For our key applications, this corresponds to the progress from μηη-mm size rock measurement data to overall predictions on migration in a km-scale 3D grid.

[0030] Novel multiple-point statistics algorithms embedded in a Bayesian framework to integrate a wide range of data sources (not yet existing in Bayesian but will be done). This will enable uncertainty assessment and 3D modeling in multiple new areas, which are highly relevant to understand and predict systems relying on large amounts of data with complex patterns.

Claims

1. A method for determining the mineralogical, or geological, or chemical configuration of a structure, comprising: illuminating the structure with a broadband laser-based source that emits electromagnetic radiation having a plurality of wavelengths, recording an image of the surface of the structure that includes information on the spectrum of the radiation scattered, reflected or diffused by the structure.

2. The method of the preceding claim, comprising the extraction of a distribution of mineralogical, or geological, or chemical composition from said image.

3. The method of any of the preceding claims, comprising using the image or part of the image, or data derived from the image as input in a geostatistic simulation model.

4. The method of any of the claims from 2 to 3, further comprising: obtaining data relative to the structure by Remote Laser Induced

Breakdown Spectroscopy (LIBS), using data obtained by LIBS as input in the geostatistic simulation model.

5. The method of any of the claims from 2 to 4, further comprising: obtaining data extending below the surface of the structure by boreholes, seismic techniques, or other methods, using data extending below the surface of the structure as input in the geostatistic simulation model. The method of the preceding claim, comprising the generation of a 3D model

6. The method of any of the previous claims, wherein the structure is a mine or part of a mine, or a geological formation, or an oil field, or a man- made structure like a tunnel, a dam, a building, or a site for waste disposal.

7. The method of any of the preceding claims, in which the broadband laser-based source comprises a pulsed laser source whose output is broadened in bandwidth by a nonlinear medium.

8. The method of any of preceding claims, wherein a radiation emitted by the broadband laser-based source has a bandwidth of more than 500 nm centred in the region of the infrared spectrum between 1 μηη and 3 μηη.

9. The method of any of the preceding claims, wherein a luminous power of the broadband laser-based source is higher than 1 W and its luminous peak power is higher than 10 kW.

10. A method of exploiting a mine or an oil field or a waste disposal site comprising the generation of a geostatistic model according to one of claims from 2 to 10.

1 1 .A method of assessing the integrity of a building, dam, bridge or man- made structure, comprising the generation of a geostatistic model according to one of claims from 2 to 10.

12. Device for determining the mineralogical, or geological, or chemical configuration of a structure, comprising: a broadband laser source emitting electromagnetic radiation having a plurality of wavelengths, for illuminating the surface of the structure; an imaging and spectrum capturing device for recording an image of the surface of the structure that includes information on the spectrum of the radiation reflected or diffused by the structure.

13. The device of the previous claim, comprising computing means arranged for deriving a distribution of mineralogical, or geological, or chemical composition from said image.

14. The device of any of claims 12 to 13, in which the broadband laser-based source comprises a pulsed laser source whose output is broadened in bandwidth by a nonlinear medium.

1 5. The method of any of any of claims 12 to 14, wherein a radiation of emitted by the broadband laser-based source has a bandwidth of more than 500 nm centred in the region of the infrared spectrum between 1 μηη and 3 μηη.

16. The method of any of any of claims 12 to 1 5, wherein a luminous power of the broadband laser-based source is higher than 1 W and its luminous peak power is higher than 10 kW.

17. The device of any of claims 12 to 16, comprising computing means programmed for generating a geostatistic simulation model using the image, or part of the image, or data derived from the image as Input.

18. The device of any of claims 12 to 17, further comprising a laser source arranged for generating remotely a plasma on the surface of the structure, and a spectrum analyzer for detecting the radiation emitted by elements composing the structure.

19. The device of the previous claim, wherein the spectrum analyser is the same as the imaging and spectrum capturing device, or a spectrometer separated from the imaging and capturing device.