WO2023031465A1 - Procédé d'évaluation de la teneur en uranium par spectrométrie gamma dans un forage et dispositif associé - Google Patents
Procédé d'évaluation de la teneur en uranium par spectrométrie gamma dans un forage et dispositif associé Download PDFInfo
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- WO2023031465A1 WO2023031465A1 PCT/EP2022/074644 EP2022074644W WO2023031465A1 WO 2023031465 A1 WO2023031465 A1 WO 2023031465A1 EP 2022074644 W EP2022074644 W EP 2022074644W WO 2023031465 A1 WO2023031465 A1 WO 2023031465A1
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- calibration
- region
- energy band
- uranium
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- JFALSRSLKYAFGM-UHFFFAOYSA-N uranium(0) Chemical compound [U] JFALSRSLKYAFGM-UHFFFAOYSA-N 0.000 title claims abstract description 133
- 229910052770 Uranium Inorganic materials 0.000 title claims abstract description 129
- 238000000034 method Methods 0.000 title claims abstract description 41
- 238000001730 gamma-ray spectroscopy Methods 0.000 title claims abstract description 10
- 238000001228 spectrum Methods 0.000 claims abstract description 94
- 230000005855 radiation Effects 0.000 claims abstract description 53
- 239000000523 sample Substances 0.000 claims description 17
- 238000004364 calculation method Methods 0.000 claims description 15
- 238000011156 evaluation Methods 0.000 claims description 4
- 238000005259 measurement Methods 0.000 description 13
- 230000015572 biosynthetic process Effects 0.000 description 8
- 238000005553 drilling Methods 0.000 description 8
- 238000005755 formation reaction Methods 0.000 description 8
- 230000002285 radioactive effect Effects 0.000 description 6
- 238000009434 installation Methods 0.000 description 5
- 229910052705 radium Inorganic materials 0.000 description 5
- HCWPIIXVSYCSAN-UHFFFAOYSA-N radium atom Chemical compound [Ra] HCWPIIXVSYCSAN-UHFFFAOYSA-N 0.000 description 5
- SYUHGPGVQRZVTB-UHFFFAOYSA-N radon atom Chemical compound [Rn] SYUHGPGVQRZVTB-UHFFFAOYSA-N 0.000 description 3
- FVAUCKIRQBBSSJ-UHFFFAOYSA-M sodium iodide Chemical compound [Na+].[I-] FVAUCKIRQBBSSJ-UHFFFAOYSA-M 0.000 description 3
- 229910052729 chemical element Inorganic materials 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000000605 extraction Methods 0.000 description 2
- 230000006870 function Effects 0.000 description 2
- 238000002386 leaching Methods 0.000 description 2
- 238000012417 linear regression Methods 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- HCWPIIXVSYCSAN-IGMARMGPSA-N Radium-226 Chemical compound [226Ra] HCWPIIXVSYCSAN-IGMARMGPSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000011088 calibration curve Methods 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000012625 in-situ measurement Methods 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- XKUYOJZZLGFZTC-UHFFFAOYSA-K lanthanum(iii) bromide Chemical compound Br[La](Br)Br XKUYOJZZLGFZTC-UHFFFAOYSA-K 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 229910052704 radon Inorganic materials 0.000 description 1
- 230000008521 reorganization Effects 0.000 description 1
- 235000009518 sodium iodide Nutrition 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V5/00—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity
- G01V5/04—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity specially adapted for well-logging
- G01V5/06—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity specially adapted for well-logging for detecting naturally radioactive minerals
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/24—Earth materials
Definitions
- TITLE Method for evaluating the uranium content by gamma spectrometry in a borehole and associated device
- the present invention relates first of all to a method for evaluating a uranium content of at least one region of interest of a subsoil by gamma spectrometry, the region of interest being crossed by a borehole.
- the invention also relates to a device for evaluating the uranium content of an associated region of interest.
- Uranium occurs naturally in the form of three isotopes: 238 U, 235 U and 234 U, the latter being derived from the decay chain of
- each disintegration is most often accompanied by the emission of high energy photons also called X or gamma radiation whose energy spectrum is typically between a few tens of keV and more than 2000 keV.
- the unit of measurement of radiation is expressed in counts per unit of time, for example in counts per second.
- the total gamma radiation is measured over the entire energy spectrum, in the form of a total count, all along the drilling by moving a scintillator detector.
- the scintillator detector comprises, for example, a crystal of sodium iodide (Nal).
- Na sodium iodide
- This method works relatively well when there is a balance between the different chains of uranium parentage.
- the total gamma radiation is roughly proportional to the uranium content of the formation.
- a calibration coefficient, specific to the gamma radiation detector links the total radiation measured and the uranium content of the formation. The coefficient of calibration is obtained by simulation or even experimentally from standard samples.
- the disadvantage of this method is that the measurement carried out does not make it possible to characterize the whole of the mineralized zone (typically several tens of meters) but only the extracted core. As a result, the true grade of the deposit may be biased. In addition, the extraction of the core, then its measurement in situ or even its sending to a laboratory make the measurement longer and more expensive than a measurement in a borehole.
- the measurement of the 1001 keV line characteristic of uranium alone requires several hours of acquisition in the event of a low uranium content (less than 1000 ppm) and the measurement of the 234 Th line (top of the chain), faster, may however be subject to significant attenuation phenomena in the case of a uranium nugget.
- Patent FR 3 088 445 presents a method for quantifying the imbalance and the uranium content of a sample by measuring two specific energy bands on a gamma radiation energy spectrum.
- the first energy band includes a signal characteristic of uranium and radium, the second energy band being almost exclusively characteristic of radium.
- the object of the invention is to overcome these drawbacks, by proposing a method for evaluating the uranium content of at least one region of interest of a subsoil traversed by a borehole which makes it possible to obtain values of precise uranium content, even when the latter are low and the radioactive imbalance of uranium is important.
- the invention relates to a method for evaluating a uranium content of at least one region of interest of a subsoil by gamma spectrometry, the region of interest being crossed by a borehole, the method comprising the following steps: a) acquiring at least one energy spectrum of gamma radiation associated with the region of interest, the energy spectrum comprising at least a low energy band, a high energy band, a contribution of the auto phenomenon -attenuation of uranium in the low energy band being greater than a contribution of the self-attenuation phenomenon of uranium in the high energy band, b) evaluating the uranium content of the region of interest using the area of the low energy band, the area of the high energy band of the energy spectrum acquired in the region of interest and at least two calibration coefficients.
- the method according to the invention makes it possible to reliably evaluate low uranium contents in the formations of the subsoil during drilling, in particular in the presence of strong radioactive imbalances of uranium, typically much less than 1, and including for low uranium contents.
- the method comprises one or more of the following characteristics, taken in isolation or according to all technically possible combinations:
- the low-energy band comprises a lower limit and an upper limit, the lower limit being greater than 98 keV to avoid a contribution from uranium fluorescence X-radiation in the low-energy band;
- the low energy band is substantially between 120 keV and 170 keV and the high energy band is substantially between 960 keV and 1046 keV;
- the method comprises a step of determining the calibration coefficients by modeling or using calibration blocks; - the method comprises a step of determining the calibration coefficients in the borehole, the subsoil comprising at least a first calibration region and a second calibration region traversed by the borehole, said determination step comprising:
- each of the calibration energy spectra comprising at least a low energy band, a high energy band, and a energy centered on an energy line at 1001 keV of 234m Pa,
- the invention also relates to a device for evaluating a uranium content of a region of interest of a subsoil by gamma spectrometry, the region of interest being crossed by a borehole, the device comprising:
- spectrometric probe comprising a scintillator detector
- an acquisition module connected to the spectrometric probe, the acquisition module being configured to acquire at least one energy spectrum of gamma radiation associated with the region of interest, the energy spectrum comprising at least one low energy band, one high energy band, a contribution of the self-attenuation phenomenon of uranium in the low energy band being greater than a contribution of the self-attenuation phenomenon of uranium in the high energy band,
- a uranium content evaluation module configured to evaluate the uranium content of the region of interest using the area of the low energy band, the area of the high energy band of the energy spectrum acquired in the region of interest and at least two calibration coefficients.
- the device further comprises a module for determining the calibration coefficients configured to determine the coefficients calibration, the subsoil comprising at least a first calibration region and a second calibration region crossed by the borehole, the acquisition module being configured to acquire at least a first energy spectrum of calibration gamma radiation associated with the first calibration region, a second calibration spectrum associated with the second calibration region and a gamma radiation energy spectrum associated with the region of interest comprising at least a low energy band and a high energy band, each of the calibration spectra comprising at least the low energy band, the high energy band, and an energy band centered on an energy line at 1001 keV of 234 m Pa, the module for determining the calibration coefficients comprising:
- a first calculation sub-module for calculating a first uranium content of the first calibration region and a second uranium content of the second calibration region using respectively the energy band centered on the energy line at 1001 keV of 234 m Pa the first calibration gamma radiation energy spectrum and the second calibration gamma radiation energy spectrum,
- a second calculation sub-module for calculating at least a first ratio and a second ratio between the area of the low energy band and the area of the high energy band respectively of the first calibration energy spectrum and of the second spectrum calibration energy
- a third calculation sub-module for calculating the calibration coefficients from the at least first and second uranium contents and from the at least first ratio and second ratio.
- Figure 1 is a schematic representation of a borehole and a device according to a first embodiment of the invention
- Figure 2 is an example of a gamma radiation spectrum acquired by the acquisition module of the device in Figure 1,
- Figure 3 is a schematic representation of a method according to a first embodiment of the invention.
- Figure 4 represents the relationship between the C BE /C HE ratio and the uranium content for different imbalances and an enlargement is inserted for contents between 0 and 3000 ppm.
- mass content In the rest of the description, the terms “mass content”, “mass concentration”, and “content” are considered to be synonyms. Likewise, the terms “line”, “energy line”, “peak”, “energy peak” are also considered synonyms.
- a device 100 for evaluating the uranium content of at least one region of interest 10 of a subsoil 11 traversed by a borehole 12 according to a first embodiment is represented schematically in FIG.
- the borehole 12 is represented in FIG. 1 vertically, that is to say with a dip equal to 90°.
- the borehole 12 is not vertical and has any dip and azimuth.
- the drilling 12 is carried out through a plurality of geological formations 14. For example, the drilling 12 is carried out for exploration purposes to search for a possible deposit of uranium 16. Alternatively, the drilling 12 is carried out at purposes of developing an identified deposit. The information collected in borehole 12 is then used to estimate the uranium reserves of deposit 16.
- the borehole 12 notably passes through at least a first region 18, called the first calibration region, and a second region 20, called the second calibration region.
- Borehole 12 also passes through at least one reference region 21, for example located above first calibration region 18.
- the reference region 21 is an unmineralized region. “Non-mineralized region” means a region in which the uranium content is low, below a reference threshold.
- the reference threshold is for example between 10 ppm and 50 ppm.
- the first calibration region 18 has a first uranium content Cm U1 .
- the second calibration region 20 has a second uranium content Cm U2 .
- the first calibration region 18 and the second calibration region 20 are mineralized regions.
- mineralized region is meant a region in which the uranium content is greater than the reference threshold, preferably greater than a multiple of the reference threshold.
- the multiple is for example equal to 2, 3, 4 or 5.
- the device 100 comprises a spectrometric probe 102 arranged to be inserted into the borehole 12 and a surface installation 104 making it possible to move the spectrometric probe 102 along the borehole 12 upwards and downwards according to the direction of the borehole.
- the surface installation 104 comprises a winch 106 and a device 108 adapted to know the position of the spectrometric probe inside the borehole 12, for example an encoder wheel.
- the spectrometric probe 102 is connected by a cable 110 to the surface installation 104.
- the cable 110 allows both the displacement of the spectrometric probe 102 inside the borehole 12, the power supply of the spectrometric probe 102 and the transfer of the measurements made by the spectrometric probe 102.
- the spectrometric probe 102 comprises a scintillator detector suitable for acquiring an energy spectrum as represented in FIG. 2.
- the scintillator detector comprises for example a lanthanum bromide (LaBr 3 ) crystal.
- the device 100 comprises a computer 112 for evaluating the uranium content of the region of interest 10 of the borehole 12, a display unit 114 connected to the computer 112 to display the results provided by the computer and a man-machine interface 116 to control device 100.
- the computer 112 includes for example a database 118.
- the database 118 is intended for example to record the results provided by the computer 112.
- the computer comprises a processor 120 and a memory 122 receiving software modules.
- the processor 120 is capable of executing the software modules received in the memory 122 to calculate the uranium content of the region of interest 10.
- the memory includes a 124 acquisition module and a uranium 132 content evaluation module.
- the memory 122 further comprises a module 125 for determining the calibration coefficients.
- Said module 125 comprises a first calculation sub-module 126, a second calculation sub-module 128 and a third sub-module calculation 130.
- the acquisition module 124 is configured to acquire at least a first radiation energy spectrum. More particularly, by using the surface installation 104, the acquisition module 124 makes it possible to acquire a radiation energy spectrum of the region of interest 10 of the borehole 12. In the first embodiment, the acquisition module 124 is further configured to acquire a radiation energy spectrum of the first calibration region 18 and of the second calibration region 20 .
- the spectrometric probe 102 is connected to the acquisition module 124 by the cable 110.
- FIG. 2 presents an example of an energy spectrum 200 acquired by the acquisition module 124.
- the energy spectrum 200 represents the gamma count as a function of the energy of the radiation.
- Gamma counting is usually expressed in counts per second.
- Radiation energy is usually expressed in kilo-electron-volts (keV).
- Each energy spectrum 200 includes at least a low energy band 202 and a high energy band 204.
- the low energy band 202 is a band strongly impacted by the self-attenuation phenomenon of uranium unlike the high energy band 204 which is little or not impacted by the self-attenuation phenomenon. In other words, the contribution of the self-attenuation phenomenon of uranium in the low energy band 202 is greater than the contribution of the self-attenuation phenomenon of uranium in the high energy band 204.
- the phenomenon of self-attenuation of uranium of interest for the present invention occurs when a photon emitted by uranium or one of its descendants interacts by Compton scattering in the own matrix of the material by which it is emitted then is absorbed by the photoelectric effect. The photon interacts with the atoms that are in its path. The scattered photon is then absorbed even before reaching the scintillator detector.
- the low energy band 202 is chosen so that the contribution of the self-attenuation phenomenon of uranium in the considered energy band is the main contribution.
- the contribution of the uranium self-attenuation phenomenon in the second high energy band 204 is substantially zero.
- substantially zero is meant preferably less than 1%, for example less than 0.2%.
- the low energy band 202 includes a lower bound and an upper bound.
- the lower limit is greater than 98 keV to avoid a contribution from uranium fluorescence X-rays in the low energy band 202 which would compensate for the uranium self-absorption phenomenon described above.
- Fluorescence X-radiation from uranium corresponds to the emission of a fluorescence photon which occurs as a result of a reorganization of the electronic procession of an atom when the latter completely absorbs an incident photon.
- the energy ranges of the low energy 202 and high energy 204 bands are chosen so that the ratio between the area of the low energy band C BE and the area of the high energy band HE , called the indicator K APC is as independent as possible of the uranium imbalance.
- radioactive imbalance of uranium refers to the average imbalance observed on the one hand between radon 222 Rn and uranium 238 U due to the volatility of radon, and on the other hand between radium 226 Ra (father of radon 222 Rn) and uranium 238 U due to differential leaching between uranium and radium.
- the low energy band 202 is substantially between 120 keV and 170 keV and the high energy band 204 is substantially between 960 keV and 1046 keV.
- substantially it is meant that the lower and upper limits of the energy bands 202, 204 can vary according to the resolution of the scintillator detector which influences the width at mid-height of the peaks. The variation is for example +/- 1 keV.
- the K APC indicator is defined as follows:
- C BE is the area of the low energy band 202.
- CHE is the area of the high energy band 204.
- the areas of the low energy band C BE and of the high energy band C HE correspond to the raw areas without correction of the continuous Compton background.
- At least the energy spectrum of radiation in the first region 18 of calibration, and the energy spectrum of radiation in the second region 20 of calibration comprise an energy band 206 centered on an energy line at 1001 keV of 234 m Pa.
- each energy spectrum, including the radiation spectrum of the region of interest 10 comprises the energy band 206 centered on the energy line at 1001 keV of 234 m Pa.
- This line at 1001 keV has the advantage of being located at the top of the chain of 238 U, and therefore to be independent of the imbalance of the chain. Nevertheless, the emission intensity of this radiation is 0.83%, which, in the case of U/Ra imbalance and low uranium content, may require a long counting time, eg several tens of minutes or a few hours, in order to be detected.
- the uranium-132 content evaluation module is configured to evaluate the uranium content of the region of interest 10 using the area C BE of the low energy band 202, the area C HE of the high energy 204 of the spectrum acquired in the region of interest and at least two calibration coefficients, as we will see later in the description.
- the module for determining the calibration coefficients 125 is configured to determine the calibration coefficients.
- the first calculation sub-module 126 is configured to calculate a first uranium content Cm U1 of the first calibration region 18 and a second uranium content Cm U2 of the second calibration region 20 by using the energy band 206 centered on the energy line at 1001 keV of 234 m Pa of the first calibration gamma radiation energy spectrum and of the second calibration gamma radiation energy spectrum respectively.
- the second calculation sub-module 128 is configured to calculate at least a first ratio C BE1 /C HE1 and a second ratio C BE2 /C HE2 between the area of the low energy band C BE1 , C BE2 and the area of the high energy band C HE1 , C HE2 respectively of the first calibration energy spectrum and of the second calibration energy spectrum.
- the third calculation sub-module 130 is configured to calculate a first coefficient a and a second coefficient ⁇ from the at least first and second uranium contents Cm U1 , Cm U2 and from the at least first ratio C BE1 /C HE1 and second ratio
- the modules and sub-modules 124, 125, 126, 128, 130, 132 are programmed to implement the method according to the invention, described below.
- FIG. 3 presents the steps of a method 300 for evaluating the uranium content of at least one region of interest 10 of a subsoil 11 by a borehole 12 according to a first embodiment of the invention .
- the method 300 includes a step 350 of acquiring at least one energy spectrum of gamma radiation associated with the region of interest 10.
- the energy spectrum includes at least the low energy band 202 and the high energy band 204.
- the low energy 202 and high energy 204 bands are chosen as explained above.
- method 300 includes acquiring 350 a plurality of gamma radiation energy spectra along borehole 12.
- method 300 includes acquiring an energy spectrum in a plurality of regions of interest 10 spaced by a predetermined pitch.
- the predetermined pitch is for example between 50 cm and 2 m.
- the method then comprises a step of evaluating 360 the uranium content of the region of interest 10 using the area of the low energy band 202, the area of the band of high energy 204 of the energy spectrum acquired in the region of interest 10 and at least two calibration coefficients.
- the method 300 includes a step 370 of determining the calibration coefficients.
- the step of determining the coefficients 370 is carried out before the step of acquiring 350 the energy spectrum in the region of interest 10.
- the step of determining the coefficients 370 can be performed after the step 350 of acquiring the energy spectrum in the region of interest 10.
- the step of determining the calibration coefficients 370 is performed in the borehole and in particular in the borehole 12 crossing the region of interest 10.
- the step of determining the calibration coefficients 370 comprises first of all a step of acquisition 310 using the installation 104 and the acquisition module 124 of at least a first and a second spectra energetic calibration gamma radiation respectively in the first and second calibration regions 18, 20 of the borehole 12.
- Each of the first and second energy spectra of calibration gamma radiation comprises at least the low energy band 202, the high energy band 204, and the energy band 206 centered on the energy line at 1001 keV, as represented for example on the figure 2.
- the low energy 202 and high energy 204 bands are chosen as explained above.
- the acquisition time of the first and second energy spectra is between a few tens of minutes and several hours, for example, depending on the uranium content and the time required to detect the line at 1001 keV.
- the first and second calibration regions 18, 20 are identified during a preliminary step of identifying the first and second calibration regions 18, 20.
- the method 300 includes a preliminary step of identification by measuring the total count of gamma radiation along the borehole 12. To do this, a radiometric probe for measuring by total counting of the gamma radiation is moved in the borehole 12.
- this preliminary step comprises the identification of a non-mineralized reference region 21 having a uranium content lower than the reference threshold.
- Reference region 21 has a reference gamma count.
- the first calibration region 18 and the second calibration region 20 are then identified as regions having a gamma count rate significantly higher than the reference gamma count, that is to say higher than a multiple of the reference gamma count.
- the first calibration region 18 and the second calibration region 20 are preferably chosen so that they have a different indicator K APC , that is to say a different ratio between the area C BE of the band low energy 202 and the area C HE of the high energy band 204.
- the step of determining the coefficients then comprises a step 320 of calculating a first uranium content Cm U1 of the first calibration region 18 and a second uranium content Cm U2 of the second calibration region 20 using the energy band centered 206 on the energy line at 1001 keV of 234 m Pa of the first energy spectrum of calibration gamma radiation and of the second energy spectrum of calibration gamma radiation acquired respectively in the first and second calibration regions 18, 20.
- the uranium content denoted Cm U
- S 1001 the net area of the line at 1001 keV
- K 1001 is a calibration coefficient allowing to go from a net air value at 1001 keV to the uranium content. It depends in particular on the scintillator detector and is obtained by digital simulation, experimentally using standard blocks or in reference wells.
- ⁇ a is Avogadro's constant.
- E ⁇ 1001keV is the efficiency of the scintillator detector at 1001 keV. is the emission intensity of 234m Pa at 1001 keV.
- Tc is the counting time.
- M ech is the mass of the sample.
- the net areas are obtained after subtraction of the continuous Compton background, for example carried out using software for processing energy spectra.
- the step of determining the calibration coefficients 370 then comprises the calculation 330 of at least a first ratio C BE1 /C HE1 and a second ratio C BE2 /C HE2 between the area C BE1 , C BE2 of the low energy band 202 and the area C HE1 , C HE2 of the high energy band 204 respectively of the first calibration energy spectrum and of the second calibration energy spectrum.
- Figure 4 shows a model of the variation of the C BE /C HE ratio as a function of the uranium content Cm U , and for different imbalances. It can be seen that the ratio is independent of the imbalance. Consequently, for uranium contents lower than 5000 ppm, the uranium content is related to the ratio between the area of the low energy band and the area of the high energy band by a polynomial equation of the first degree of the following form: ⁇ and ⁇ are two calibration coefficients.
- the step of determining the calibration coefficients 370 consists, on the basis of the areas C BE and C HE of each of the first and second energy spectra and of the corresponding uranium contents Cm U1 and Cm U2 calculated previously, in calculating 340 the values of the coefficients ⁇ and ⁇ .
- the uranium content Cm U in the region of interest 10 is calculated using the area C BE of the low energy band 202 and the area C HE of the high energy band 204 of the energy spectrum acquired in the region d interest 10, the first and second calculated coefficients ⁇ , ⁇ .
- the uranium content Cm B is calculated in particular with the equation: with
- the method 300 comprises the acquisition of a third energy spectrum of gamma radiation in a third calibration region 22 of the borehole 12.
- the third calibration region 22 is a mineralized region distinct from the first calibration region 18 and from the second calibration region 20 .
- the third calibration region 22 is preferably selected similarly to the first calibration region 18 and to the second calibration region 20 .
- the first calibration region 18 is located above the second calibration region 20 along the direction of the borehole 12.
- the third calibration region 22 is located below the second calibration region 20 .
- the method 300 then comprises the acquisition of a third energy spectrum of gamma radiation in the third region 22 of calibration and the calculation of the uranium content Cm U3 in this third region 22 by using the net area of the energy band 206 centered on the 1001 keV energy line of the 234 m Pa spectrum, as explained above.
- the method 300 then also includes the calculation of at least a third ratio C BE3 /C HE3 between the area C BE3 of the low energy band 202 and the area C HE3 of the high energy band 204 of the third energy spectrum calibration.
- the coefficients ⁇ and ⁇ are calculated.
- the first coefficient ⁇ and the second coefficient ⁇ are calculated by linear regression of the at least first, second and third calculated ratios C BE1 / C HE1 , C BE2 / C HE2 , C BE3 / C HE3 and of the at least first, second and third calculated uranium contents Cm U1 , Cm U2 , Cm U3 .
- the method 300 includes acquiring calibration energy spectra in any number of calibration regions.
- a plurality of calibration energy spectra are acquired and steps 320 and 330 are performed on each of said calibration spectra.
- C BE /C HE ⁇ ' x C mU 2 - ⁇ ' x C mU + ⁇ '.
- a deviation from linearity is observed which can be modeled by a quadratic equation.
- the calibration coefficients ⁇ ', ⁇ ' and ⁇ ' are for example determined from energy spectra acquired in at least three calibration regions 18, 20, 22 and by polynomial regression.
- the step of determining the calibration coefficients 370 is carried out by modeling using for example a code modeling the interactions between matter and different radiation.
- the code used is for example the Monte-Carlo N-Particle (MCNP) code [MCNP6TM, User’s manual - Version 1.0 - LA-CP-13-00634, Rev. 0 - May 2013 - Denise B. Pelowitz, editor Los Alamos National Laboratory],
- the step of determining the calibration coefficients 370 is carried out using calibration blocks.
- Calibration blocks are blocks, for example concrete blocks, whose uranium content is known.
- the spectrometric probe 102 is inserted into different calibration blocks, at least one energy spectrum of gamma radiation is acquired in each of the calibration blocks and the calibration coefficients are determined in a manner similar to what is made in the first embodiment.
- the method 300 according to the invention makes it possible to reliably evaluate low uranium contents in the formations of the subsoil while drilling, in particular in the presence of strong U/Ra radioactive imbalances of the uranium, typically much lower than 1.
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FR2109325A FR3126791B1 (fr) | 2021-09-06 | 2021-09-06 | Procédé d’évaluation de la teneur en uranium par spectrométrie gamma dans un forage et dispositif associé |
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FR3088445A1 (fr) | 2018-11-14 | 2020-05-15 | Orano Mining | Procede d'evaluation de la concentration massique en uranium d'un echantillon par spectrometrie gamma et dispositif associe |
WO2021122772A1 (fr) * | 2019-12-17 | 2021-06-24 | Orano Mining | Procédé d'évaluation de la teneur en uranium par spectrométrie gamma dans un puits de forage et dispositif associé |
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Patent Citations (2)
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FR3088445A1 (fr) | 2018-11-14 | 2020-05-15 | Orano Mining | Procede d'evaluation de la concentration massique en uranium d'un echantillon par spectrometrie gamma et dispositif associe |
WO2021122772A1 (fr) * | 2019-12-17 | 2021-06-24 | Orano Mining | Procédé d'évaluation de la teneur en uranium par spectrométrie gamma dans un puits de forage et dispositif associé |
Non-Patent Citations (2)
Title |
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MARCHAIS THOMAS: "Optimisation des mesures de spectrométrie gamma pour la prospection de l'uranium", HAL OPEN SCIENCE, 16 November 2019 (2019-11-16), pages 1 - 205, XP055915158, Retrieved from the Internet <URL:https://tel.archives-ouvertes.fr/tel-02366534/document> * |
MONTE-CARLO: "N-Particle (MCNP) [MCNP6TM, User's manual", vol. 13, May 2013, LOS ALAMOS NATIONAL LABORATORY, pages: 00634 |
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