Mineral prospecting system and method

Abstract

A subsurface mineral exploration system in a terrestrial area includes a current generator configured to generate an injection current (Ic) comprising at least a plurality of circuits, called stages; a control circuit configured to select a group of stages, called active stages, according to a current setpoint and to activate said active stages (20.i) so as to connect the voltage sources in series; the control circuit being configured to measure the injection current (Ic) following the activation of said active stages (20.i), and to issue a fault alarm (DEF) if the measured injection current (Ic) is less than a current threshold (S) determined with respect to the current setpoint (Ic*) for a duration exceeding a predetermined monitoring duration (d1). Abstract figure: Figure 4

Description

Title of the invention: System and method of mineral prospecting technical field

[0001] The invention relates to the field of mineral exploration, in particular, by means of a mineral exploration system by injecting a current into the subsoil of a terrestrial area in order to determine the characteristics of the subsoil for the purpose of exploitation. The invention aims more specifically to improve the reliability of the exploration system.

[0002] A system for mineral prospecting of the subsoil of a terrestrial area according to the prior art is known from patent applications FR2980653A1 and FR3105446A1. The prospecting system comprises: • a current generator configured to provide an injection current • at least one pair of electrodes connected to the current generator, the electrodes being configured to be positioned in the soil of said terrestrial area so as to inject the injection current into the soil, and • a plurality of voltage sensors connected to a processing module and positioned between the electrodes.

[0003] Such a mineral exploration system makes it possible to determine the characteristics of the subsoil according to the principle of induced polarization. When the current generator is activated, an injection current flows through the subsoil between the electrodes. Each voltage sensor locally measures the voltage induced by the injection current. The processing module can then determine the characteristics of the subsoil based on the measured voltages.

[0004] More specifically, when the injection current flowing between two electrodes is abruptly interrupted, the voltage at the voltage sensors does not drop instantaneously to zero, but rather exhibits a rapid initial decrease followed by a slower decrease. If the injection current is reactivated, the voltage will initially increase at a very high rate and then increase slowly. Characterizing the voltage drop using the processing module allows the resistivity and chargeability of the subsurface to be determined, particularly for differentiating the materials constituting the subsurface (ore types, water circulation, slag heaps, etc.). This technique is primarily used to measure the surface electrical polarization of metallic minerals. For example, disseminated sulfides exhibit very good induced polarization responses.Similarly, massive sulfides, which should theoretically have weaker responses, in practice have very good responses.

[0005] By varying the distance between the two electrodes, soundings are obtained at different depths, which makes it possible to map the variability of the resistivity and loadability as a function of depth and thus determine the precise nature of the subsoil.

[0006] In practice, the current generator must supply an injection current that conforms to a setpoint current determined for the load seen by the mineral exploration system. In other words, the setpoint current is a function of the nature of the subsoil (load). Thus, the setpoint current changes over time.

[0007] In order to enable the current generator to supply an injection current equal to the setpoint current, the current generator comprises a plurality of stages, each providing a voltage step. Thus, depending on the value of the setpoint voltage, the number of voltage stages that must be activated varies. For example, to cover a setpoint voltage range between 100V and 10,000V, approximately ten voltage stages are provided. In practice, each voltage stage includes a voltage converter comprising four controlled power switches, in particular, of the IGBT type.

[0008] To enable effective mineral exploration, it is important that the injection current conforms to the setpoint current and that the injection current has a rapid increase to reach the setpoint current. In practice, the stages are activated successively to reach the setpoint current.

[0009] During the use of the mineral exploration system, malfunctions occurred during the generation of the injection current. In particular, it appeared that one of the switches could have a fault in its control.

[0010] With reference to [Fig. 1], a first curve Cia shows the emission of an injection current le of 20 A in the absence of a fault, and a second curve Clb shows the emission of an injection current Ic(defl) in the presence of a fault. On the first curve Cia, the injection current le exhibits rapid growth and stabilizes at the setpoint current value. On the second curve Clb, a first instant t1 of decrease in the injection current Ic(defl) is observed, which induces a second instant t2 of failure of a power switch. The injection current Ic(defl) is stopped at a third instant t3 by a short-circuit protection mechanism.

[0011] Such a malfunction leads to overvoltages in the current generator, which can damage numerous components of the current generator. This necessitates repairing the current generator and halting all mineral exploration. Since mineral exploration is generally carried out in remote locations, repair operations are complex, time-consuming, and very expensive. These operations must be carried out as soon as possible, given that all teams dedicated to mineral exploration (drilling, etc.) are stopped when the mineral exploration system is not operational. The costs and losses related to malfunctions of the power generator are estimated at several million USD per year.

[0012] One of the objectives of the present invention is to improve the reliability of a current generator of a mining prospecting system. PRESENTATION OF THE INVENTION

[0013] The invention relates to a mineral prospecting system for the subsoil of a terrestrial area, the mineral prospecting system comprising: • a current generator configured to generate an injection current, • at least one pair of electrodes connected to the current generator, the electrodes being configured to be positioned in the soil of said terrestrial area so as to inject the injection current into the soil, • a plurality of voltage sensors connected to a processing module and positioned between the electrodes in order to obtain characteristics of the subsoil,

[0014] The current generator comprises: • at least a plurality of circuits, called stages, • each stage comprising at least one DC voltage source isolated from the voltage sources of the other stages, a switching circuit comprising four switches arranged in a first and a second half-bridge, each formed of two switches mounted in series between a positive and a negative pole of the voltage source, • the stages being interconnected in such a way that the midpoint of the second half-bridge of each stage is connected to the midpoint of the first half-bridge of the following stage, the electrodes being respectively connected to the midpoint of the first half-bridge of a first stage, and to the midpoint of the second half-bridge of a final stage, • a control circuit configured for: • select a group of stages, called active stages, based on a current setpoint, • activate said active stages so as to connect them in series with the voltage sources,

[0015] According to the invention, the control circuit is remarkable in that it is configured to: • Measure the injection current following the activation of said active stages, • Issue a fault alarm if the measured injection current is below a current threshold determined relative to the current setpoint for a period exceeding a predetermined monitoring period.

[0016] Thanks to the invention, any abnormal drop in the injection current during a monitoring period makes it possible to detect a malfunction of the current generator early and proactively. This advantageously prevents any subsequent degradation.

[0017] The invention also relates to a method of mineral prospecting of the subsoil of a land area using a mineral prospecting system as described above, the method comprising steps consisting of: • Inject the injection current into the ground, • Measure the voltages between the electrodes to obtain characteristics of the subsoil,

[0018] The method is notable in that the current injection step comprises substeps consisting of: • Select a group of stages in the current generator, called active stages, based on a current setpoint, • Activate the said active stages, so as to connect the voltage sources in series, • Measure the injection current following the activation of said active stages, • Issue a fault alarm if the measured injection current is below a current threshold determined relative to the current setpoint for a period exceeding a predetermined monitoring period.

[0019] Depending on one aspect, the monitoring duration is between 1ms and 3ms. This allows for a reactive alarm to be triggered while avoiding false alarms in the event of a very brief power drop.

[0020] According to one aspect, the current threshold is equal to the current setpoint. The detection is thus very responsive.

[0021] According to one aspect, the current threshold is equal to the current setpoint less a constant between 1% and 10% of the current setpoint, preferably 2% of the current setpoint. Such a constant allows small variations in the injection current, which are normal, without triggering a DEF fault alarm.

[0022] According to one aspect, the mineral exploration method includes a step of inhibiting the emission of a fault alarm for a duration that begins following the activation of the active stages. Any untimely emission of a fault alarm is thus avoided.

[0023] According to one aspect, the inhibition duration is between 100ms and 500ms.

[0024] According to one aspect, the mineral prospecting method includes a substep consisting of stopping the generation of the injection current following the emission of a fault alarm.

[0025] According to one aspect, the mineral prospecting method includes a substep consisting of resetting the current generator following the emission of a fault alarm so as to restart a sequence of generating the injection current.

[0026] The invention also relates to a computer program type product, comprising at least one sequence of instructions stored and readable by a processor and which, once read by this processor, causes the execution of the steps of the method as presented above.

[0027] The invention also relates to a computer-readable medium comprising the computer program-type product as described above. PRESENTATION OF FIGURES

[0028] The invention will be better understood upon reading the following description, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0029] Fig. 1 is a schematic representation of a first curve Cia of generation of an injection current without fault and a second curve Clb of generation of an injection current with a fault.

[0030] Fig. 2 is a schematic representation of a mineral prospecting system according to the invention.

[0031] Fig. 3 is a schematic representation of a current generator comprising a plurality of stages.

[0032] Fig. 4 is a schematic representation of an example of the implementation of a step in issuing a fault alarm.

[0033] Fig. 5 is a schematic representation of an injection current emission curve with fault detection after reset.

[0034] Fig. 6 is a schematic representation of an emission curve of an injection current during a change in the current setpoint.

[0035] It should be noted that the figures set out the invention in detail to implement the invention, said figures being of course able to serve to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0036] With reference to [Fig. 2], a mineral prospecting system 1 is shown according to one embodiment of the invention. The mineral prospecting system 1 is intended to be used in a land area Z in order to determine characteristics of the subsoil SS of said land area Z such as, for example, electrical resistivity and / or chargeability values ​​in order to determine the nature of said subsoil and in particular to carry out a mapping of said subsoil SS. By "terrestrial zone Z", we mean both a zone on land and a zone under the sea.

[0037] Electrical resistivity corresponds to the ability of the materials forming the subsoil to oppose the flow of electric current. Resistivity can be analyzed from any type of current signal injected into the ground. Chargeability is the measure of the electrical expansion of the subsoil following the injection of an electric current with known properties. Chargeability is preferably analyzed from a square wave current signal injected into the ground.

[0038] Indeed, a material constituting the subsoil SS of the Z zone, particularly a rock, behaves like an electrical capacitor that stores electrical energy when a current passes through it and then releases it, when the current ceases to be injected, over a period of time that depends on its mineralogical and chemical nature. Measuring this parameter provides information that completes the electrical resistivity profile of the subsoil SS of the Z zone, particularly in terms of clay content, fracturing, and porosity.

[0039] As illustrated in [Fig.2], the mineral exploration system 1 comprises: • a current generator 2 configured to supply an injection current, • at least one pair of electrodes 3A, 3B connected to the current generator 2, electrodes 3A, 3B being configured to be positioned in the soil of said terrestrial zone Z so as to inject the injection current into the soil, and • a plurality of voltage sensors 4 connected to a processing module 5 and positioned between electrodes 3A, 3B so as to obtain characteristics of the subsoil SS.

[0040] With further reference to [Fig. 2], the mineral exploration system 1 comprises a first electrical connection line 10A and a second electrical connection line 10B connected respectively to electrodes 3A and 3B. Electrodes 3A and 3B operate in pairs and are bidirectional. Electrodes 3A and 3B are adapted to be positioned in the ground to allow the injection current generated by the current generator 2 to flow between them. Voltage sensors 4 are suitable for measuring the voltage generated by the injection current flowing in the ground between two electrodes 3A and 3B.

[0041] The processing module 5 is capable of controlling the current generator 2 via a wired or wireless communication link, for example, a Wi-Fi or Bluetooth® link. In particular, the processing module 5 is capable of controlling the current generator 2 so that said current generator 2 generates an injection current e whose intensity is, for example, on the order of a few tens or hundreds of Amperes or even a few kiloamperes and which is intended to circulate in the first electrical connection line 10A and in the second electrical connection line 10B.

[0042] The general structure of a mineral prospecting system 1 is known to a person skilled in the art and will not be presented in further detail.

[0043] As previously presented, the current generator 2 is capable of generating an injection current that can circulate in the ground between two electrodes 3A, 3B.

[0044] The current generator 2 is configured to supply a regulated, alternating polarity, high-voltage injection current to the terminals of a load. In this case, the load is the ground.

[0045] With reference to [Fig.3], the current generator 2 comprises at least a plurality of circuits, referred to as stages 20.1-20.10. When a stage is designated in general terms, it is referenced 20.1.

[0046] In this example, the current generator 2 comprises ten stages, referenced 20.1 to 20.10. As a non-limiting application example, the current generator 2 has a power output of approximately 100 kW and is designed to supply current pulses of approximately 60 A. Each stage 20.1 corresponds to a voltage level. In this example, stages 20.1 to 20.10 correspond respectively to the voltage levels 1800V, 1800V, 1800V, 1800V, 1800V, 900V, 500V, 280V, 160V, and 200V PWM, for a maximum total voltage of approximately 11 kV. The supplied voltage allows for the generation of the correct injection current value.

[0047] In this example, each switch of a 2O.i stage is chosen to be able to allow a current of an intensity of around 60 A to flow in the conducting state and to withstand a voltage of at least 2000 V in the blocked state.

[0048] In this example, a stage 20.10 is adjustable to provide a variable voltage to enable the supply of a precise injection current. Such a stage is called a "regulation stage" and is known to those skilled in the art. The general structure of a current generator 2 is known from patent applications FR2980653A1 and FR3105446A1.

[0049] Still with reference to [Fig.3], each stage 2O.i includes a DC voltage source 21 isolated from the voltage sources 21 of the other stages 2O.i, a switching circuit 22 comprising four switches Q1 - Q4 arranged in a first Q1, Q2 and a second Q3, Q4 half-bridges each formed of two switches mounted in series between a positive pole and a negative pole of the voltage source 21. In this example, as illustrated in [Fig.3], the current generator 2 includes a general voltage source 21 G, in particular a generator set, which supplies each voltage source 21 of a stage 2O.i in an isolated manner.

[0050] The 2O.i stages being interconnected with each other such that the midpoint of the second Q3, Q4 half-bridge of each 2O.i stage is connected to the midpoint of the first Q1, Q2 half-bridge of the next stage 20.i+1, electrodes 3A, 3B being respectively connected to the midpoint of the first half-bridge of a first stage 20.1, and to the midpoint of the second half-bridge of a last stage 20.10.

[0051] With further reference to [Fig. 3], the power generator 2 includes a control circuit 6 configured to control the various stages 20-i. In particular, the control circuit 6 is configured to: • select a group of stages, called active stages, according to an injection current setpoint*, • activate said active stage 2O.i so as to connect the voltage sources 21 in series,

[0052] Thus, some stages are inactive and are not taken into account depending on the injection current to be supplied.

[0053] The current generator 2 thus makes it possible to provide an injection current le which conforms to a current setpoint le*. The current setpoint le* is advantageously determined dynamically as a function of the characteristics of a load 7, i.e., the ground.

[0054] The grids of switches Q1 to Q4 are connected to the control circuit 6, in particular via an optical fiber, to generate the switching control signals of the different stages.

[0055] With reference to [Fig. 4], the invention is notable in that the control circuit 6 is configured to: • Measure the injection current following the activation of said active stages 2O.i, • Issue a fault alarm DEF if the measured injection current le is less than a current threshold S determined in relation to the current setpoint le* for a period greater than a predetermined monitoring period dl.

[0056] Thus, if the injection current le does not reach the current setpoint le* during the predetermined monitoring time dl, this means that one of the switches is defective and that there is a risk of malfunction for the current generator 2. The emission of a fault alarm DEF is thus automatic and reactive.

[0057] According to one aspect, the control circuit 6 measures the injection current from any type of current sensor.

[0058] Preferably, the monitoring duration dl is between 1 and 3 ms, preferably equal to 2 ms. This allows for a reactive alarm to be triggered while avoiding false alarms in the event of a very brief current drop.

[0059] According to one aspect, the current threshold S is equal to the current setpoint le*. Thus, any current deviation can lead to the reactive emission of a DEF fault alarm. According to another aspect, the current threshold S is equal to the current setpoint le* less a constant between 1% and 10% of the current setpoint, preferably 2% of the current setpoint. Such a constant allows for small variations in the injection current that are normal without emitting a DEF fault alarm.

[0060] With reference to [Fig. 4], the method includes a step of inhibiting a fault alarm emission DEF for an inhibition duration d2 beginning after the activation of the active stages 2O.i. Such an inhibition step advantageously allows time for the injection current le to stabilize. Any spurious emission of a fault alarm is thus avoided. Preferably, the inhibition duration d2 is between 100 ms and 500 ms, preferably on the order of 300 ms.

[0061] The emission of a DEF fault alarm allows early detection if a fault is present during the generation of the injection current.

[0062] According to one aspect, and again with reference to [Fig. 4], the control circuit 6 is configured to stop the generation of the injection current following the emission of a fault alarm DEF. This protects the current generator 2 against the occurrence of overvoltages that could destroy components of the current generator 2.

[0063] According to one aspect, the control circuit 6 is configured to reset the current generator to RAZ following the emission of a fault alarm DEF in order to restart a sequence of generating the injection current le. In practice, such a reset generally allows the injection current le to be generated without malfunction, given that the faults are mainly intermittent. An intermittent fault can therefore no longer damage the current generator 2 as in the prior art.

[0064] According to one aspect, and again with reference to [Fig. 4], the control circuit 6 is configured to display an MSG error code on a machine interface of the mining exploration system 1 following the emission of a DEF fault alarm. This allows operators to be warned of a fault related to the generation of the injection current. Preferably, the MSG error code indicates the faulty stage.

[0065] An example of the implementation of a mineral prospecting method for a subsoil SS of a land area Z will now be presented, using a mineral prospecting system 1 as previously described, the method comprising steps consisting of: • Inject an injection current into the ground, and • Measure voltages between electrodes 3A, 3B in order to obtain characteristics of the SS subsoil.

[0066] The current injection step includes a substep consisting of selecting a group of stages of the current generator 2, called active stages, according to a current setpoint le*. The current setpoint le* has been previously determined according to the load 7, i.e., the characteristics of the ground.

[0067] In this example, with reference to [Fig. 5], to reach a current setpoint le* of 60A, a plurality of stages are activated at a first instant t1. In this example, with reference to [Fig. 5], the injection current le is equal to 60A between the first instant t1 and the second instant t2.

[0068] Starting at the second instant t2, the injection current drops due to a malfunction until its value falls below the threshold S, which is 58.8 A at the third instant t3. The injection current continues to decrease during the monitoring period dl of 2 ms until the fourth instant t4. At the fourth instant t4, a fault alarm DEF is issued and the generation of the injection current le is stopped, thus protecting the integrity of the components of the current generator 2. An error code MSG is also issued to warn the operator. In this case, the fault is intermittent, and the generation of the injection current le is reset RAZ following the issuance of the fault alarm DEF. Following the reset, as shown in [Fig. 5], the injection current le increases in a controlled manner after the fault has cleared.

[0069] Thanks to the invention, any suspicious drop in the injection current is quickly stopped to avoid any damage to the current generator 2.

[0070] With reference to [Fig.6], an example of implementation is shown in which at a first instant t1, a plurality of stages are activated to reach a first current setpoint Ici* of 17A then, at a second instant t2, a plurality of stages are activated to reach a second current setpoint Ic2* of 20A.

[0071] As illustrated in [Fig. 6], the injection current le reaches the second current setpoint Ic2* at a third instant t3. Thanks to the inhibition time d2, no fault alarm DEF is issued after the second instant t2, thus allowing the injection current le time to stabilize following a setpoint change. The stabilization time t3-t2 is advantageously shorter than the inhibition time d2.

[0072] The integrity of the mineral exploration system 1 is thus guaranteed, allowing mineral exploration operations to continue without damage to the power generator 2, without repair costs and without loss of time. The economic advantage is therefore substantial.

Claims

1. Demands Mineral exploration system (1) of a subsoil (SS) of a land area (Z), the mineral exploration system (1) comprising: • a current generator (2) configured to generate an injection current (the), • at least one pair of electrodes (3A, 3B) connected to the current generator (2), the electrodes (3A, 3B) being configured to be positioned in the soil of said terrestrial zone (Z) so as to inject the injection current (le) into the soil, • a plurality of voltage sensors (4) connected to a processing module (5) and positioned between the electrodes (3A, 3B) so as to obtain subsoil characteristics (SS), • the current generator (2) comprising: • at least a plurality of circuits, called stages (20.1-20.10), • each stage (2O.i) comprising at least one DC voltage source (21) isolated from the voltage sources (21) of the other stages (2O.i), a switching circuit (22) comprising four switches (Q1 - Q4) arranged in a first (Q1, Q2) and a second (Q3, Q4) half-bridges each formed of two switches mounted in series between a positive pole and a negative pole of the voltage source (21), • the stages (2O.i) being interconnected with each other such that the midpoint of the second (Q3, Q4) half-bridge of each stage (2O.i) is connected to the midpoint of the first (Q1, Q2) half-bridge of the following stage (2O.i+1), the electrodes (3A, 3B) being respectively connected to the midpoint of the first half-bridge of a first stage, and to the midpoint of the second half-bridge of a last stage, • a control circuit (6) configured for: • select a group of stages, called active stages, according to a current setpoint (the*), • activate said active stages (2O.i) so as to put them in series with the voltage sources (21), • the control circuit (6) is characterized in that it is configured to: • Measure the injection current (le) following the activation of said active stages (2O.i), • Issue a fault alarm (DEF) if the measured injection current (le) is less than a current threshold (S) determined with respect to the current setpoint (le*) for a duration greater than a predetermined monitoring duration (dl).

2. A method for mineral prospecting of a subsoil (SS) of a land area (Z) by means of a mineral prospecting system (1) according to claim 1, the method comprising steps consisting of: • Injecting the injection current (the) into the ground, • Measuring voltages (4) between the electrodes (3A, 3B) so as to obtain characteristics of the subsoil (SS), • A method characterized in that the current injection step comprises substeps consisting of: • Selecting a group of stages of the current generator (2), called active stages, according to a current setpoint (the*), • Activating said active stages (2O.i), so as to put the voltage sources (21) in series, • Measuring the injection current (the) following the activation of said active stages (2O.i).i), • Issue a fault alarm (DEF) if the measured injection current (le) is less than a current threshold (S) determined in relation to the current setpoint (le*) for a period exceeding a predetermined monitoring period (dl).

3. Mineral prospecting method according to claim 2, wherein the monitoring time (dl) is between 1ms and 3ms.

4. Mineral prospecting method according to any one of claims 2 to 3, wherein the current threshold (S) is equal to the current setpoint (le*).

5. Mineral prospecting method according to any one of claims 2 to 3, wherein the current threshold (S) is equal to the current setpoint (le*) less a constant between 1% and 10% of the current setpoint (le*).

6. Mineral prospecting method according to any one of claims 2 to 5, comprising a step of inhibiting a fault alarm emission (DEF) for an inhibition time (d2) beginning following the activation of the active stages.

7. Mineral prospecting method according to claim 6, wherein the inhibition time (d2) is between 100ms and 500ms.

8. Mineral prospecting method according to any one of claims 2 to 7, wherein the current injection step includes a substep of stopping (STOP) the generation of the injection current (the) following the emission of a fault alarm (DEF).

9. Mineral prospecting method according to any one of claims 2 to 8, wherein the current injection step includes a substep of resetting (RAZ) the current generator (2) following the emission of a fault alarm (DEF) so as to restart a sequence of generating the injection current (the).

10. A computer program-type product, comprising at least one sequence of instructions stored and readable by a processor and which, once read by that processor, causes the execution of the steps of the method as presented according to any one of claims 2 to 9.

11. Computer-readable medium containing the computer program product according to claim 10.

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