Mining exploration system and method

Abstract

The invention relates to a system for mining exploration of a subsurface of a land area, comprising a current generator configured to generate an injection current (Ic) comprising at least a plurality of circuits, referred to as stages, a control circuit configured to select a group of stages, referred to as active stages, on the basis of a current setpoint and to activate the 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 the active stages (20.i), and to emit a fault alarm (DEF) if the measured injection current (Ic) is less than a current threshold (S) determined in relation to the current setpoint (Ic*) for a period longer than a predetermined monitoring period (d1).

Description

Mineral prospecting system and method

[0001] The invention relates to the field of mineral exploration, in particular, to a mineral exploration system that injects a current into the subsoil of a land area to determine its characteristics for exploitation. More specifically, the invention aims to improve the reliability of the exploration system.

[0002] A system for prospecting 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 determines subsurface characteristics based on the principle of induced polarization. When the current generator is activated, an injection current flows through the subsurface between the electrodes. Each voltage sensor locally measures the voltage induced by the injection current. The processing module can then determine subsurface characteristics 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 decay. If the injection current is reactivated, the voltage will initially rise very rapidly and then increase slowly. Characterizing the voltage drop using the processing module allows for the determination of the subsurface resistivity and chargeability, 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 resistivity and chargeability 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 depends on the nature of the subsoil (load). Thus, the setpoint current changes over time.

[0007] To enable the current generator to provide an injection current equal to the setpoint current, the current generator comprises multiple stages, each providing a voltage step. Thus, depending on the setpoint voltage value, 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 required. In practice, each voltage stage includes a voltage converter comprising four controlled power switches, typically of the IGBT type.

[0008] To enable effective mineral exploration, it is important that the injection current matches the setpoint current and that the injection current increases rapidly to reach the setpoint current. In practice, the stages are activated sequentially to achieve the setpoint current.

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

[0010] With reference to the diagram, the first curve, C1a, represents the emission of an injection current Ic of 20A in the absence of a fault, and the second curve, C1b, represents the emission of an injection current Ic(def1) in the presence of a fault. On the first curve, C1a, the injection current Ic increases rapidly and stabilizes at the setpoint current value. On the second curve, C1b, we observe an initial decrease in the injection current Ic(def1) at time t1, which induces a second failure time t2 of a power switch. The injection current Ic(def1) is stopped at a third time t3 by a short-circuit protection mechanism.

[0011] Such a malfunction leads to voltage surges in the power generator, which can damage numerous components. This necessitates repairing the power generator and halting all mining operations. Since mining operations are typically conducted in remote locations, repairs are complex, time-consuming, and very expensive. These repairs must be carried out as soon as possible, as all mining exploration teams (drilling, etc.) are suspended when the mining system is not operational. The costs and losses associated with power generator malfunctions are estimated at several million USD annually.

[0012] One of the objectives of the present invention is to improve the reliability of a current generator in 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 so as to obtain characteristics of the subsoil,

[0014] The current generator comprises: at least a plurality of circuits, called stages, each stage having 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 connected in series between a positive and a negative pole of the voltage source; the stages being interconnected such 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 last stage; a control circuit configured to: select a group of stages, called active stages, according to 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 less than a current threshold determined in relation to the current setpoint for a period greater than a predetermined monitoring period.

[0016] Thanks to the invention, any abnormal drop in injection current during a monitoring period allows for the early and reactive detection of a malfunction in the current generator. This advantageously prevents any subsequent degradation.

[0017] The invention also relates to a method of mineral prospecting of the subsoil of a terrestrial area using a mineral prospecting system as described above, the method comprising steps consisting of: injecting the injection current into the ground, measuring voltages between the electrodes in order to obtain characteristics of the subsoil,

[0018] The method is notable in that the current injection step includes sub-steps consisting of: Selecting a group of current generator stages, called active stages, according to a current setpoint, Activating said active stages, so as to put the voltage sources in series, Measuring the injection current following the activation of said active stages, Issuing a fault alarm if the measured injection current is less than a current threshold determined in relation to the current setpoint for a period greater than a predetermined monitoring period.

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

[0020] In one respect, the current threshold is equal to the current setpoint. Detection is therefore very responsive.

[0021] In one aspect, the current threshold is equal to the current setpoint minus 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 triggering a DEF fault alarm.

[0022] In one aspect, the mineral exploration method includes a step to inhibit the emission of a fault alarm for a duration that begins after the activation of the active stages. This prevents any false fault alarm emission.

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

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

[0025] According to one aspect, the mineral exploration method includes a sub-step of resetting the current generator following the emission of a fault alarm in order 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 containing the computer program-type product as previously described. PRESENTATION OF THE 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] This is a schematic representation of a first curve C1a of generation of an injection current without fault and a second curve C1b of generation of an injection current with a fault.

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

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

[0032] This is a schematic representation of an example of implementing a step in issuing a fault alarm.

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

[0034] This 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 explain the invention in detail for implementing 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 the figure, a mineral exploration system 1 is shown according to one embodiment of the invention. The mineral exploration system 1 is intended for use in a terrestrial area Z in order to determine characteristics of the subsoil SS of said terrestrial 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 create a map of said subsoil SS. "Territory area Z" is understood to mean both an area on land and an area under the sea.

[0037] Electrical resistivity is the ability of subsurface materials to impede the flow of electric current. Resistivity can be analyzed using any type of current signal injected into the ground. Chargeability is a measure of the electrical expansion of the subsurface (SS) following the injection of an electric current with known properties. Chargeability is preferably analyzed using a square wave signal injected into the ground.

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

[0039] As illustrated in Figure 1, the mineral exploration system 1 comprises: a current generator 2 configured to provide an injection current Ic, 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 ground zone Z so as to inject the injection current Ic into the soil, and a plurality of voltage sensors 4 connected to a processing module 5 and positioned between the electrodes 3A, 3B so as to obtain subsurface characteristics SS.

[0040] Referring to the previous section, the mining 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 designed to be positioned in the ground to allow the injection current Ic, generated by the current generator 2, to flow between them. Voltage sensors 4 are capable of measuring the voltage generated by the injection current Ic flowing through 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, via a Wi-Fi or Bluetooth® connection. Specifically, the processing module 5 is capable of controlling the current generator 2 so that said current generator 2 generates an injection current Ic with an intensity, for example, on the order of tens or hundreds of Amperes, or even a few kiloamperes, which is intended to flow 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 the 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 Ic that can flow 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 Ic to the terminals of a load. In this case, the load is the ground.

[0045] With reference to the, the current generator 2 comprises at least a plurality of circuits, called stages 20.1-20.10. When a stage is designated in general terms, it is referenced 20.i.

[0046] In this example, the current generator 2 comprises ten stages, labeled 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 to the voltage levels 1800V, 1800V, 1800V, 1800V, 1800V, 900V, 500V, 280V, 160V, and 200V PWM, respectively, for a maximum total voltage of approximately 11 kV. The supplied voltage allows for the generation of the correct injection current, Ic.

[0047] In this example, each switch in a 20.i stage is chosen to be able to allow a current of approximately 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, thus enabling the delivery 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] With further reference to the, each stage 20.i includes a DC voltage source 21 isolated from the voltage sources 21 of the other stages 20.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 and a negative pole of the voltage source 21. In this example, as illustrated in the, the current generator 2 includes a general voltage source 21G, in particular a generator set, which supplies each voltage source 21 of a stage 20.i in an isolated manner.

[0050] The stages 20.i being interconnected with each other in such a way that the midpoint of the second Q3, Q4 half-bridge of each stage 20.i is connected to the midpoint of the first Q1, Q2 half-bridge of the following stage 20.i+1, the 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 the, 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 Ic*, activate said active stage 20.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 Ic to be supplied.

[0053] The current generator 2 thus makes it possible to provide an injection current Ic which conforms to a current setpoint Ic*. The current setpoint Ic* is advantageously determined dynamically according to 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 the, the invention is remarkable in that the control circuit 6 is configured to: Measure the injection current Ic following the activation of said active stages 20.i, 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 greater than a predetermined monitoring duration d1.

[0056] Thus, if the injection current Ic fails to reach the current setpoint Ic* during the predetermined monitoring time d1, this means that one of the switches is defective and there is a risk of malfunction for the current generator 2. The emission of a fault alarm DEF is therefore automatic and reactive.

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

[0058] Preferably, the monitoring duration d1 is between 1 and 3 ms, preferably equal to 2 ms. This allows for a reactive alarm while avoiding false alarms in the event of a very brief power drop.

[0059] In one view, the current threshold S is equal to the current setpoint Ic*. Thus, any current deviation can lead to the reactive emission of a DEF fault alarm. In another view, the current threshold S is equal to the current setpoint Ic* minus 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, which are normal, without triggering a DEF fault alarm.

[0060] With reference to the method, it includes a step of inhibiting a fault alarm emission DEF for an inhibition duration d2, which begins after the activation of the active stages 20.i. This inhibition step advantageously allows time for the injection current Ic to stabilize. This prevents any spurious fault alarm emission. 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 for early detection if a fault is present during the generation of the injection current Ic.

[0062] According to one aspect, and again referring to the control circuit 6, the control circuit 6 is configured to stop the generation of the injection current Ic 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 (RAZ) following the emission of a fault alarm (DEF) in order to restart a sequence of generating the injection current (Ic). In practice, such a reset generally allows the injection current (Ic) to be generated without malfunction, since faults are primarily 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 referring to the previous one, control circuit 6 is configured to display an MSG error code on a machine interface of the mining exploration system 1 following the issuance of a DEF fault alarm. This alerts operators to a fault related to the generation of the injection current Ic. Preferably, the MSG error code indicates the faulty stage.

[0065] An example of the implementation of a mineral prospecting method of a subsoil SS of a terrestrial zone Z will now be presented using a mineral prospecting system 1 as previously presented, the method comprising steps consisting of: Injecting an injection current Ic into the soil, and Measuring voltages between electrodes 3A, 3B in order to obtain characteristics of the subsoil SS.

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

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

[0068] Starting at time t2, the injection current Ic drops due to a malfunction until its value falls below the threshold S, which is 58.8 A at time t3. The injection current Ic continues to decrease during the monitoring period d1 of 2 ms until time t4. At time t4, a fault alarm DEF is issued, and the generation of the injection current Ic is stopped, thus protecting the integrity of the components of 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 Ic is reset (RAZ) following the issuance of the fault alarm DEF. Following the reset, the injection current Ic increases in a controlled manner after the fault has cleared.

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

[0070] With reference to the, 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 Ic1* 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 Figure 1, the injection current Ic reaches the second current setpoint Ic2* at a third time t3. Thanks to the inhibition time d2, no fault alarm DEF is issued after the second time t2, thus allowing the injection current Ic 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 mining exploration system 1 is thus guaranteed, allowing mining exploration operations to continue without damage to the power generator 2, without repair costs, and without loss of time. The economic advantage is therefore significant.

Claims

Mineral prospecting system (1) of a subsoil (SS) of a land area (Z), the mineral prospecting system (1) comprising: a current generator (2) configured to generate an injection current (Ic), 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 land area (Z) so as to inject the injection current (Ic) 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 characteristics of the subsoil (SS), the current generator (2) comprising: at least a plurality of circuits, called stages (20.1-20.10), each stage (20.1) comprising at least one DC voltage source (21) isolated from the voltage sources (21) of the other stages (20.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 and a negative pole of the voltage source (21), the stages (20.i) being interconnected with each other such that the midpoint of the second (Q3, Q4) half-bridge of each stage (20.i) is connected to the midpoint of the first (Q1, Q2) half-bridge of the following stage (20.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 to: select a group of stages, called active stages, according to a current setpoint (Ic*), activate said active stages (20.i) so as to put the voltage sources (21) in series, the control circuit (6) is characterized in that it is configured to: Measure the injection current (Ic) following the activation of said active stages (20.i), 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 greater than a predetermined monitoring duration (d1). A method for mineral prospecting of a subsoil (SS) of a land area (Z) using a mineral prospecting system (1) according to claim 1, the method comprising steps of: Injecting the injection current (Ic) 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 of: Selecting a group of stages of the current generator (2), called active stages, according to a current setpoint (Ic*), Activating said active stages (20.i), so as to connect the voltage sources (21) in series, Measuring the injection current (Ic) following the activation of said active stages (20.i) Issue a fault alarm (DEF) if the measured injection current (Ic) is below a current threshold (S) determined in relation to the current setpoint (Ic*) for a period exceeding a predetermined monitoring period (d1). Mineral prospecting method according to claim 2, wherein the monitoring time (d1) is between 1ms and 3ms. Mineral prospecting method according to any one of claims 2 to 3, wherein the current threshold (S) is equal to the current setpoint (Ic*). Mineral prospecting method according to any one of claims 2 to 3, wherein the current threshold (S) is equal to the current setpoint (Ic*) less a constant between 1% and 10% of the current setpoint (Ic*). 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. Mineral prospecting method according to claim 6, wherein the inhibition time (d2) is between 100ms and 500ms. 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 (Ic) following the emission of a fault alarm (DEF). Mineral prospecting method according to any one of claims 2 to 8, wherein the current injection step includes a substep consisting 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 (Ic). 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. Computer-readable medium containing the computer program product according to claim 10.

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