AQUIFER MONITORING DEVICE.

Abstract

AQUIFER MONITORING DEVICE. An aquifer monitoring device (10) comprises a first piezometric probe (30a) including a first pressure sensor (11) providing first pressure measurements (P1) in the aquifer, a second piezometric probe (30b) including a second pressure sensor (12) providing second pressure measurements (P2) in the aquifer, the second piezometric probe (30b) being positioned at a determined distance (D) from the first piezometric probe (30a), and a pressure measurement acquisition and processing module (20) coupled to the first and second piezometric probes (30a, 30b) and arranged to calculate differential data (P2-P1) from the first and second pressure measurements taken in a time-synchronous manner, said differential data being characteristic of an aquifer parameter. The first and second pressure sensors (11, 12) are paired.The pairing criteria are such that the first and second pressure sensors are manufactured using a collective manufacturing technology ensuring substantially identical properties, the first and second pressure sensors have identical pressure sensitivity (SP11, SP12) within 10%, and the first and second pressure sensors have identical temperature sensitivity (ST11, ST12) within 10%. See Figure 9 for abbreviations.

Description

Title of the invention: AQUIFER MONITORING DEVICE. technical field

[0001] The invention relates to an aquifer monitoring device. An aquifer is a geological formation with sufficient permeability to allow water to flow freely through it (via pores or fissures) and contains a groundwater layer, for example, a water table. The invention also relates to a piezometric probe for such an aquifer monitoring device. A piezometer is a tube drilled from the surface into the geological formation, providing access to the groundwater. Such a tube allows the piezometric level of the water to be measured using a piezometric probe equipped with a sensor to automatically record variations in the water level. Finally, the invention relates to a method for manufacturing such an aquifer monitoring device. Prior Art

[0002] Figure [Fig. 1] schematically illustrates a geological formation 1 comprising different parts, for example a watercourse 2, a water-unsaturated zone 3 forming soil, an impermeable zone 4 such as parent rock, permeable zones 5, and slightly permeable zones 6. Several boreholes forming open tubes to the surface, for example, three boreholes forming three piezometers PZ1, PZ2, and PZ3 respectively, were drilled into the formation at various locations at distances from one another. Although the boreholes are shown to have substantially identical depths, their depths may vary from one location to another.

[0003] Various technologies exist for measuring the piezometric level of water in boreholes. A water level recorder with a sensor allows for the automatic and continuous recording, or recording at defined intervals, of variations in the water level over time in a borehole (i.e., for monitoring and surveillance). For example, one technology uses a pressure sensor. Such a sensor measures the pressure exerted by the water above the sensor (i.e., in the vertical direction due to Earth's gravity) and allows the water level in the borehole to be deduced. For example, with a measurement dynamic range of approximately ten bar, the resolution of such a pressure sensor is on the order of a millibar (corresponding to 1 cm of water height), while the accuracy (or absolute error) is lower than the resolution, which is on the order of ten millibars.

[0004] Figure [Fig. 2] schematically illustrates, on the left, a borehole forming a tube open to the surface and constituting a piezometer PZi drilled in a formation 1. Two sensors, CPI and CP2, are positioned vertically at different depths in the borehole below the piezometric level of the water (horizontal line in the borehole). The first sensor, CPI, measures the pressure P1 at the first depth. The second sensor, CP2, measures the pressure P2 at the second depth. Figure [Fig. 2] also shows, on the right, the evolution of the pressures (P) P1 and P2 measured by the sensors over time (t). These measurements are affected by various disturbances, such as surface disturbances like vibrations. It can be seen that the evolution of the pressure P1 measured by the first sensor does not follow the same pattern as the evolution of the pressure P2 measured by the second sensor.A precise measurement of the pressure difference therefore seems difficult to obtain due to this disparity in response to surface disturbances.

[0005] Figure [Fig. 3] schematically illustrates, on the left, two boreholes forming open tubes to the surface and constituting two piezometers PZi and PZi+1 drilled in a formation 1 including an aquifer. The second borehole is separated horizontally from the first borehole, for example by a distance of 1000 m. A first sensor CPI is placed at a defined depth in the first borehole below the piezometric level of the water (horizontal line in the first borehole). The first sensor CPI measures the pressure PL. A second sensor CP2 is placed at substantially the same defined depth in the second borehole below the piezometric level of the water (horizontal line in the second borehole). The second sensor CP2 measures the pressure P2. Such a configuration of the piezometers PZi and PZi+1 is intended, for example, to measure groundwater flow. Figure [Fig.Figure 3 also shows, on the right, the evolution of the pressures (P) PI and P2 measured by the sensors over time (t), as well as the evolution of the difference P1-P2 over time (t). As in the previous example, these measurements are affected by various disturbances, such as surface disturbances like temperature variations. For a 10 mm variation in the piezometric level of the aquifer, requiring a sensor measurement accuracy on the order of Imbar and a flow velocity of 0 lm / s, for example over a period of 3 hours, we observe that the evolution of the pressure PI measured by the first sensor is not affected in the same way as the evolution of the pressure P2 measured by the second sensor. Furthermore, regarding the differential measurement P1-P2 with these two sensors, the error in the differential measurement is approximately the error of each sensor. It is therefore difficult, if not impossible, to accurately measure the difference between these two sensors. to measure flow velocities over a timescale of a few hours, let alone over several days.

[0006] There is therefore a need for a solution that allows for more precise measurements that are minimally affected by disturbances. Summary of the invention

[0007] An object of the invention is to provide an aquifer monitoring device that overcomes one or more of the drawbacks or limitations of existing devices. In particular, the invention provides an aquifer monitoring device that is independent of various disruptive events.

[0008] According to one aspect, an aquifer monitoring device is proposed comprising: - a first piezometric probe including a first pressure sensor providing initial pressure measurements in the aquifer, - a second piezometric probe including a second pressure sensor providing second pressure measurements in the aquifer, the second piezometric probe being positioned at a determined distance from the first piezometric probe, - a pressure measurement acquisition and processing module coupled to the first and second piezometric probes and arranged to calculate differential data from the first and second pressure measurements taken in a time-synchronous manner, said differential data being characteristic of an aquifer parameter, the first and second pressure sensors being paired according to pairing criteria including: • The first and second pressure sensors are manufactured using a collective manufacturing technology ensuring substantially identical properties, • The first and second pressure sensors have identical pressure sensitivity to within 10%, and • The first and second pressure sensors have identical temperature sensitivity to within 10%.

[0009] The first piezometric probe and the second piezometric probe can be positioned relative to each other in a vertical arrangement at a distance of a few centimeters to a few tens of meters.

[0010] The first piezometric probe and the second piezometric probe can be positioned relative to each other in a horizontal arrangement at a distance of a few tens of meters to a few tens of kilometers.

[0011] The aquifer monitoring device may further include a first temperature sensor associated with the first pressure sensor, and a second temperature sensor associated with the second pressure sensor, the first and second sensors temperature being coupled to the pressure measurement acquisition and processing module to correct differential data based on temperature measurements synchronized with pressure measurements.

[0012] Each of the first and second pressure sensors can be made in the form of an electronic component with a MEMS microelectromechanical system.

[0013] The MEMS microelectromechanical system electronic component may include: - a supporting substrate, side walls and a sensitive membrane which define and close a watertight cavity, at least the sensitive membrane being exposed to an aquifer fluid when a pressure of said aquifer fluid is to be measured, - the cavity being either under vacuum or filled with a gas whose reference pressure is lower than the pressure of the aquifer liquid, and - a strain detection circuit arranged on the sensitive membrane to measure the compression state of the sensitive membrane which is proportional to the pressure of the aquifer liquid.

[0014] The strain detection circuit may include a transverse gauge and a longitudinal gauge, substantially positioned at the center of the sensitive membrane.

[0015] The aquifer monitoring device may include several pairs of piezometric probes forming paired piezometric probes, each pair comprising first and second paired pressure sensors.

[0016] According to another aspect, a piezometric probe of an aquifer monitoring device according to the invention is proposed, said piezometric probe being made in the form of an elongated cylindrical body with a longitudinal axis comprising: - a weight equipped with a pressure tap, the weight being positioned at a distal end of said body, - a measuring module forming a sealed housing fixed to the ingot and comprising a pressure sensor in fluidic connection with the pressure tap, a temperature sensor and an electronic module coupled to the pressure and temperature sensors, and - a waterproof connector fixed to the housing at another end of said body to couple the piezometric probe to a power, communication and deployment cable.

[0017] According to yet another aspect, a method for manufacturing an aquifer monitoring device is proposed, comprising the following steps: - to manufacture first and second pressure sensors using a collective manufacturing technology ensuring substantially identical properties - verify that the first and second pressure sensors have identical pressure sensitivity within 10%, - verify that the first and second pressure sensors have identical temperature sensitivity within 10%, - define the first pressure sensor and the second pressure sensor as paired, and - couple the first and second paired pressure sensors to a pressure measurement acquisition and processing module.

[0018] The first and second pressure sensors can also be calibrated together.

[0019] The collective manufacturing technology can be the microtechnology of manufacturing electronic components with a microelectromechanical system MEMS, the first and second pressure sensors being from the same wafer of single-crystal semiconductor material or from the same batch of several wafers of single-crystal semiconductor material.

[0020] Such an aquifer monitoring device can be used to characterize at least one aquifer parameter chosen from among a water level in the aquifer, water contamination in the aquifer, a measurement of water flow velocity in the aquifer, a measurement of water pumping in the aquifer.

[0021] With the invention, the measurements are insensitive to specific disturbing events generally coming from the surface such as, for example, temperature variations (amplitude between day and night), atmospheric pressure variations, vibrations, etc... These effects are all the more disturbing as in the applications considered, said pressure sensors and piezometric probes are located close to the surface, i.e. from a few meters to a few tens of meters, and as these effects are equivalent to the dynamic measurement range of said sensors and probes.

[0022] Other advantages will become apparent from the following description of the invention. Brief description of the drawings

[0023] The present invention is illustrated by examples and not limited to the accompanying drawings, in which similar references indicate similar elements: Figure [Fig.1] schematically illustrates a geological formation comprising several piezometers; Figure [Fig.2] schematically illustrates, on the left, a piezometer and shows, on the right, the evolution of pressures measured by two sensors arranged vertically over time; Figure [Fig.3] schematically illustrates, on the left, two piezometers and shows, on the right, the evolution of the pressures measured by two sensors arranged horizontally over time, as well as the evolution of a pressure difference over time; Figure [Fig. 4] schematically illustrates an example of a MEMS pressure sensor in cross-sectional view; and Figure [Fig.5] schematically illustrates an example of a strain sensing circuit for the MEMS pressure sensor of figure [Fig.4]; Figure [Fig.6] shows the evolution of the thermal sensitivity dVS / dT as a function of the imbalance voltage of the bridge VS of a pressure sensor of an aquifer monitoring device according to the invention; Figure [Fig.7] schematically illustrates, on the left, an aquifer monitoring device comprising a piezometer with two paired pressure sensors in a vertical configuration and shows, on the right, the evolution of the pressures measured by these two vertically arranged sensors over time; Figure [Fig.8] schematically illustrates, on the left, an aquifer monitoring device comprising two piezometers with two paired pressure sensors in a horizontal configuration and shows, on the right, the evolution of the pressures measured by these two horizontally arranged sensors over time, as well as the evolution of a pressure difference over time; Figure [Fig.9] schematically illustrates an example of the realization of a piezometric probe of an aquifer monitoring device according to the invention in a side view in cross-section along a longitudinal plane; Figure [Fig. 10] schematically illustrates the example of the realization of the piezometric probe of figure [Fig.9] according to a perspective view; Figure [Fig. 11] schematically illustrates the deployment of two piezometric probes of an aquifer monitoring device according to the invention in a borehole; and Figure [Fig. 12] schematically illustrates a method for manufacturing an aquifer monitoring device according to the invention. Detailed description

[0024] The invention will be understood from the following description, in which reference is made to the attached drawings.

[0025] In the following, the following definitions apply: - accuracy is the difference between the value measured and read by means of a sensor and the true value; - resolution is the smallest observable variation, which depends on the observation window (integration time); - In general, the resolution is smaller than the precision (for example, between 10 and 100 times); and - stability is linked to drift over time.

[0026] Figures [Fig. 7] and [Fig. 8] schematically illustrate, on the left, an aquifer monitoring device 10 comprising one, respectively two piezometers Pz, PZi+i, each comprising two paired pressure sensors 10, 11 in a vertical configuration, respectively in a horizontal configuration. The aquifer monitoring device 10 comprises a first piezometric probe including a first pressure sensor 11 providing initial pressure measurements P1 in an aquifer, and a second piezometric probe including a second pressure sensor 12 providing second pressure measurements P2 in the aquifer. The second piezometric probe is positioned at a predetermined distance from the first piezometric probe, whether in a vertical or horizontal configuration.The aquifer monitoring device 10 further includes a pressure measurement acquisition and processing module 20 coupled to the first and second piezometric probes and arranged to calculate differential data from the first and second pressure measurements taken in a time-synchronous manner. The differential data P1-P2 are characteristic of an aquifer parameter. The first and second pressure sensors 11 and 12 are paired according to defined pairing criteria. According to a first pairing criterion, the first and second pressure sensors are manufactured using a collective manufacturing technology ensuring substantially identical properties.As an example, each of the first and second pressure sensors can be manufactured as a microelectromechanical system (MEMS) electronic component, that is, using the microtechnology of manufacturing electronic components with a MEMS (MEMS stands for MicroElectroMechanical System). This technology allows for the fabrication of multiple pressure sensors as if they were produced from the same wafer of single-crystal semiconductor material or from the same batch of several wafers of single-crystal semiconductor material. According to a second matching criterion, the first and second pressure sensors have identical pressure sensitivity to within 10%. According to a third matching criterion, the first and second pressure sensors have identical temperature sensitivity to within 10%. With such criteria, the paired first and second pressure sensors are insensitive to disruptive events. surface such as a temperature variation (e.g., variations between day and night, variations related to human activities, or variations related to light, etc.), a variation in atmospheric pressure (e.g., low pressure of a weather depression, or high pressure of an anticyclone), a vibration (e.g., shock, sound wave) "propagating" from the surface to the place of measurement.

[0027] Figure [Fig. 12] schematically illustrates a manufacturing process for such an aquifer monitoring device 10. According to a first step SI, the first and second pressure sensors 11, 12 are fabricated FAB using a collective fabrication technology. For example, the collective fabrication technology is the microtechnology for manufacturing electronic components with a microelectromechanical system (MEMS), where the first and second pressure sensors are produced from the same wafer of single-crystal semiconductor material or from the same batch of several wafers of single-crystal semiconductor material WF (known from the English term "wafer"). Such a collective fabrication technology ensures that the properties of the pressure sensors 11, 12 are substantially identical. According to a second step S2, the first and second pressure sensors 11, 12 are tested CHK SP to verify that they have identical pressure sensitivity SPn, respectively SPi2, within 10%. If this is not the case (NOK), another pair of pressure sensors is selected. Otherwise (OK), the process continues. According to a third step S3, the first and second pressure sensors 11,12 are tested CHK Tx to verify that they have sensitivity to a temperature STn, respectively ST2, identical to within 10%. If this is not the case (NOK), another pair of pressure sensors is selected. Otherwise (OK), the process continues. According to an optional fourth step S4, the first and second pressure sensors 11, 12 can be calibrated jointly using ETAL, i.e., simultaneously. The calibration can be performed at the manufacturing site or as a verification calibration carried out off-site. The calibration can take into account: - the applied pressure (i.e., the reference value of the standard), - the temperature (i.e., to correct for the thermal sensitivity of the sensor being calibrated), and - atmospheric pressure. According to a fifth step S5, the first and second pressure sensors 11,12 are then defined as paired PAIR. The identification of the paired sensors is made possible by the fact that each pressure sensor is delivered with a manufacturing certificate indicating, for example, the wafer number or the batch number of wafers of single-crystal semiconductor material, and the sensitivity data. mentioned above, and / or where applicable a calibration certificate containing the important data. According to a sixth step S6, the first and second paired pressure sensors 11, 12 are coupled CPL to a pressure measurement acquisition and processing module 20.

[0028] Figure [Fig.4] schematically illustrates an example of a sensor Pressure sensors 10 and 11 are implemented as a microelectromechanical system (MEMS) electronic component, as shown in a cross-sectional view. Figure 5 schematically illustrates an example of a strain detection circuit for such a pressure sensor. For example, such pressure sensors are marketed by OPENFIELD.

[0029] In this example, the pressure sensor 10, 11 comprises a support substrate 13, side walls 14, and a sensitive membrane 15, which define and close a sealed cavity 16 and a strain-sensing circuit 17. When a pressure Pi of the aquifer liquid is to be measured, at least the sensitive membrane 15 is exposed to the aquifer liquid. The pressure Pi exerts a force on the sensitive membrane 15, causing it to deform. Optionally, depending on the positioning of the pressure sensor, other parts such as the side walls 14 may also be subjected to the liquid pressure. The cavity 16 is either under vacuum or filled with a gas whose reference pressure is lower than the pressure of the aquifer liquid or the pressure range for which the pressure sensor is designed.A strain detection circuit 17 is arranged on the sensitive membrane 15 to measure the compression state of the sensitive membrane 15, which is proportional to the pressure Pi of the aquifer liquid.

[0030] The strain detection circuit 17 can be implemented as a Wheatstone bridge consisting of four resistors R1, R2, R3, and R4, and used as a strain gauge. The four resistors are calibrated and have very similar values. The bridge is powered by a voltage source V0 and, at equilibrium, has a zero bridge imbalance voltage VS. The pressure (arrow Pi) applied to the sensitive membrane 15 causes it to deform and the resistance values ​​to vary. A change in either resistance results in a non-zero bridge imbalance voltage VS. Two adjacent resistors act in opposite directions, and two opposite resistors act in the same direction. It is therefore possible to reduce parasitic variations (such as temperature) and achieve better accuracy.

[0031] The bridge imbalance voltage VS normalized to the supply voltage V0 is given by the formula: VS / V0 = (R2-R1) / (R2+R1) and as a first approximation by the formula: VS / V0 « (R2-R1) / 2R or VS « VO.(R2-R1) / 2R R being the average value of the resistances.

[0032] The thermal sensitivity of the bridge is given by the formula: dVS / dT "l / 2{V0.(dR2 / dT) / R-(dR1 / dT) / R] - VS.dR / dT / R The thermal sensitivity of each resistance TCR (TCR is an English acronym meaning "Temperature Coefficient of Resistance") is given by the formula: TCR = 1 / R.dR / dT

[0033] The thermal sensitivity of the ST bridge can then be given by the formula: ST = 1 / Vo.dVS / dT = * / 2(TCRl-TCR2) - VS / V0.TCR When no pressure is applied, VS = 0 and ST = 1 / 2(TCR1-TCR2) The thermal sensitivity of the ST bridge depends on the homogeneity of the deposition of the resistances RI, R2, R3, R4 of the strain detection circuit 17 on the sensitive membrane 15. In general, ST is low. When pressure is applied, the voltage VS increases with the pressure (linearly to first order). The thermal sensitivity of the ST bridge depends on VS (and therefore on the pressure sensitivity SP) and the average TCR of the resistances. An experimental example is illustrated in Figure [Fig. 6], which shows the evolution of the typical thermal sensitivity of a pressure sensor used in the invention (thermal sensitivity of the ST bridge in pV / °C as a function of the bridge imbalance voltage VS in mV).

[0034] As a first approximation, the pressure sensitivity SP of a sensor depends on: - the geometry and mechanical properties of the MEMS electronic component; and - the gauge factor of the resistances (i.e. the piezo-resistive coefficient).

[0035] As a first approximation, the temperature sensitivity ST of a sensor depends on: - the imbalance voltage VS (therefore the pressure sensitivity SP); - of the average TCR; and - the homogeneity of the resistance bridge.

[0036] Regarding temperature variations, those to be considered are not solely related to temperature variations between day and night (large amplitudes at low frequencies), as small temperature variations can also generate errors in pressure measurements. Indeed, for example, thermal sensitivity is on the order of 10³ full scale / °C, which, for a pressure sensor with a full scale of 10 bar, is approximately 10 mbar / °C, or 0.1 °C corresponding to approximately 1 mbar.

[0037] As indicated in the text, this sensitivity is virtually zero without pressure and then increases (linearly) with the load (pressure) on the sensor. This thermal effect is corrected (to a large extent) by calibration. However, some residual effects remain, which can introduce error. If the sensors are paired, these thermal errors are eliminated during differential measurements.

[0038] The drift over time dVS / dt of a sensor can be written as the thermal sensitivity dVS / dT.

[0039] The overall stability of a piezoresistive sensor therefore depends on: - sensitivity to pressure SP; - the average drift of the resistances 1 / R.dR / dt; and - the homogeneity of the resistance bridge.

[0040] If two MEMS pressure sensors have the same pressure sensitivity SP and the same temperature sensitivity ST, then they will have: - similar metrological characteristics; and - similar drifts over time dVS / dt. The accuracy of a pressure sensor includes errors (e.g., calibration errors, drift over time, non-repeatability, hysteresis, thermal effects, external disturbances, etc.). A difference between two sensors with the above properties then allows for the elimination of all common errors. When comparing two sensors (differential measurement), the measurement error results from the accuracy of each sensor. With this invention, since the common errors of each paired sensor are identical, the error in the differential measurement will be primarily controlled by the resolution. Resolution is characterized by the noise level of the pressure sensor. It can be reduced by increasing the observation window (integration time or averaging time). In theory, the resolution could be very small if the averaging time were very long. The resolution must be specified with an acquisition frequency or an averaging time. The pressure sensor according to the invention has a resolution of 1 mbar, at an acquisition frequency of 1 Hz or an averaging time of 1 s. The sensor's sensitivity to pressure determines the useful signal level it produces. The higher the sensitivity, the lower the resolution and the better the signal-to-noise ratio (SNR).

[0041] Figure [Fig. 7] schematically illustrates, on the left, an aquifer monitoring device 10 comprising a borehole forming a tube open to the surface and constituting a piezometer PZi drilled into a formation 1, and having two paired pressure sensors 11, 12. The two paired pressure sensors 11, 12 are arranged vertically (vertical configuration) at different depths in the borehole below the piezometric level of the water (horizontal line in the borehole). The first paired pressure sensor 11 measures the pressure P1 at the first depth. The second paired pressure sensor 12 measures the pressure P2 at the second depth. Figure [Fig. 7] also shows, on the right, the evolution of the pressures (P) P1 and P2 measured by the sensors over time (t). It can be observed that the evolution of the PI pressure measured by the first twin pressure sensor 11 evolves identically to the evolution of the P2 pressure measured by the second twin pressure sensor 12, regardless of surface disturbances such as vibrations, temperature changes (diurnal / nocturnal variation), or atmospheric pressure, etc. These identical evolutions are made possible by the synchronization of the two twin pressure sensors and their identical sensitivities. This allows for highly accurate density measurements in this vertical configuration: - density measurement (usi) on a 1m H column; - density xgx H = 1000 x 10 x 1 = lO.OOOPa ~ lOOmbar; And - a density measurement to 1% therefore requires a measurement of the difference P1-P2 with a precision greater than Imbar.

[0042] Figure [Fig. 8] schematically illustrates, on the left, an aquifer monitoring device 10 comprising two boreholes forming open tubes to the surface and constituting two piezometers PZi, respectively PZi+1 drilled in a formation 1, each having a twin pressure sensor 11, respectively 12. The second borehole is separated horizontally by a distance D from the first borehole, for example D = 1000 m. The first twin pressure sensor 11 is located at a defined depth in the first borehole below the piezometric level of the water (horizontal line in the first borehole). The first twin pressure sensor 11 measures the pressure PL. The second twin pressure sensor 12 is located at substantially the same defined depth in the second borehole below the piezometric level of the water (horizontal line in the second borehole).The second twin pressure sensor 12 measures the pressure P2. Figure [Fig. 8] also shows, on the right, the evolution of the pressures (P) PI and P2 measured by the sensors over time (t), as well as the evolution of the difference P1-P2 over time (t). In the example shown, groundwater flow occurs in a generally horizontal direction, with a 10 mm change in the groundwater level flowing from the first piezometer PZi to the second piezometer PZi+1 at a velocity of 0 lm / s (the flow is represented by the horizontal arrow). First, it is observed that the evolution of the pressure PI measured by the first twin pressure sensor 11 is affected in the same way as the evolution of the pressure P2 measured by the second twin pressure sensor 12, with a time lag (the slopes of the evolution of the pressures PI and P2 represented by the dashed lines are parallel).These two measures are insensitive to surface disturbances such as vibrations, changes in temperature or atmospheric pressure, etc... Furthermore, with regard to the . In the differential measurement P1-P2, the error in the differential measurement of the two paired sensors cancels out, and the plateau represents the time required for the propagation of a 10 mm level change from the first piezometer PZi to the second piezometer PZi+1. In the example, it took 3 hours for the flow to travel the distance D of 1000 m between the two piezometers PZi and PZi+1. It is therefore possible to measure the flow velocity over a timescale of a few hours. This would also be the case for a flow occurring over several days. In such a configuration of piezometers PZi and PZi+1, it is therefore possible to measure groundwater flow with high accuracy.

[0043] Differential measurement with twin pressure sensors offers the following advantages: - synchronization allowing for the suppression of high-frequency noise; - identical deviations; and - identical sensitivities to pressure and temperature.

[0044] Figures [Fig. 9] and [Fig. 10] schematically illustrate an example of the embodiment of a piezometric probe 30 of an aquifer monitoring device 10. Figure [Fig. 9] shows the piezometric probe 30 in a side view in cross-section along a longitudinal plane. Figure [Fig. 10] shows the piezometric probe 30 in a perspective view.

[0045] The piezometric probe 30 is made in the form of an elongated cylindrical body with longitudinal axis LL'. The piezometric probe 30 mainly comprises a weight 31, a measuring module 35 and a watertight connector 39 for a cable 40.

[0046] The weight 31 is disposed at a distal end of the body of the piezometric probe 30. The weight 31 forms a mass intended to pull the piezometric probe 30 downwards in the direction of gravity, i.e., towards the bottom of the piezometer borehole. The weight is provided with at least one pressure tap 32, for example, two pressure taps 32 and 32a. The pressure tap(s) 32 and / or 32a open on one side to the outside in contact with the liquid whose pressure is to be measured, and on the other side into an internal cavity 33. The internal cavity has a means for attaching the weight 31 to the measuring module 35, for example, a tapped hole or thread 34, and brings a sensitive element of the pressure sensor 11 into contact with the liquid pressure.

[0047] The measuring module 35 forms a sealed housing 36 fixed to the ingot and comprising the pressure sensor 11 in fluidic connection with the pressure tap 32, 32a. The measuring module 35 also comprises a temperature sensor 37 and an electronic module 38 coupled to the pressure sensor 11 and the temperature sensor 37.

[0048] The waterproof connector 39 is fixed to the waterproof housing 36 of the measuring module 35 at another end of the body to couple the piezometric probe 30 to the cable 40. The Cable 40 provides power, communication, and deployment for the piezometric probe 30. The waterproof connector 39 includes a cable clamp 41 for securely attaching the piezometric probe 30 to the cable 40, specifically to the outer sheath 42 of the cable. The waterproof connector 39 has a waterproof feedthrough 44 coupled on one side to the cable clamp 41 and on the other side to the waterproof housing 36 of the measuring module 35. The waterproof feedthrough 42 is hollow and allows the internal routing of the power and communication wires 45 within the cable 40. The power and communication wires 45 are connected to the electronic module 38. The waterproof connector 39 can be equipped with a quick-connect / disconnection means 46 for the waterproof housing 36 of the measuring module 35.

[0049] Figure [Fig. 11] schematically illustrates the deployment, in a borehole (vertical with axis ZZ') of a piezometer PZi, of two piezometric probes 30a, respectively 30b according to the embodiment shown in Figures [Fig. 10] and [Fig. 11] connected to a pressure measurement acquisition and processing module 20 via two cables 40a, respectively 40b. This assembly constitutes an aquifer monitoring device 10.

[0050] With the aquifer monitoring device of the invention, it is possible to perform, in particular: - water level measurements; - water contamination measures, for example, advances of salt water into groundwater; - measurements of water flow velocity; - pumping measures. These measurements require highly accurate and stable detection methods to determine minute variations over time periods ranging from milliseconds (e.g., to characterize pumping) to several decades (e.g., to characterize climate change). This is made possible by differential measurements between paired pressure sensors. The invention eliminates all common errors in paired pressure sensors, thereby improving their metrological performance when mounted in a network of paired pressure sensors.

[0051] It should be noted that the examples of aquifer monitoring devices according to the present invention are not limited to examples showing two paired pressure sensors; they are non-limiting examples, the invention also being applicable to several paired pressure sensors distributed in several boreholes over an area sized to cover the area of ​​interest to be monitored according to a suitable grid. Furthermore, the monitoring device of the invention is not limited to an application for aquifer monitoring, but can be easily adapted to various Other applications such as water propagation measurements in oil or gas wells (i.e. not necessarily linked to an aquifer or groundwater), or flow density measurements (twin pressure sensors used on either side of a Venturi-type device to perform differential measurements).

Claims

Demands

1. An aquifer monitoring device (10) comprising: - a first piezometric probe (30, 30a) including a first pressure sensor (11) providing first pressure measurements (PI) in the aquifer, and - a second piezometric probe (30, 30b) including a second pressure sensor (12) providing second pressure measurements (P2) in the aquifer, the second piezometric probe being positioned at a determined distance from the first piezometric probe, the aquifer monitoring device (10) is characterized in that it further comprises: - a pressure measurement acquisition and processing module (20) coupled to the first and second piezometric probes (30, 30a, 30b) and arranged to calculate differential data (P2-P1) from the first and second pressure measurements taken in a time-synchronous manner,said differential data (P2-P1) being characteristic of an aquifer parameter, and in that the first and second pressure sensors (11, 12) are paired according to pairing criteria including: • the first and second pressure sensors are manufactured using a collective manufacturing technology ensuring substantially identical properties, • the first and second pressure sensors have a pressure sensitivity (SPn, SPi2) identical to within 10%, and • the first and second pressure sensors have a temperature sensitivity (STn, STi2) identical to within 10%.

2. The aquifer monitoring device (10) according to claim 1, wherein the first piezometric probe (30, 30a) and the second piezometric probe (30, 30b) are positioned relative to each other at the other according to a vertical arrangement at a distance (D) of the order of a few centimeters to a few tens of meters.

3. The aquifer monitoring device (10) according to claim 1, wherein the first piezometric probe (30, 30a) and the second piezometric probe (30, 30a) are positioned relative to each other in a horizontal arrangement at a distance (D) of the order of a few tens of meters to a few tens of kilometers.

4. The aquifer monitoring device (10) according to any one of claims 1 to 3, further comprising a first temperature sensor (37) associated with the first pressure sensor (11), and a second temperature sensor (37) associated with the second pressure sensor (12), the first and second temperature sensors being coupled to the pressure measurement acquisition and processing module (20) to correct differential data on the basis of temperature measurements (T) synchronized with pressure measurements (Pi, PI, P2).

5. The aquifer monitoring device (10) according to any one of claims 1 to 4, wherein each of the first and second pressure sensors (11, 12) is made in the form of an electronic component with a MEMS microelectromechanical system.

6. The aquifer monitoring device (10) according to the preceding claim, wherein the electronic component with a microelectromechanical system MEMS comprises: - a support substrate (13), side walls (14) and a sensitive membrane (15) which define and close a sealed cavity (16), at least the sensitive membrane (15) being exposed to an aquifer liquid when a pressure (Pi, PI, P2) of said aquifer liquid is to be measured, - the cavity (16) being either under vacuum or filled with a gas whose reference pressure is lower than the pressure of the aquifer liquid, and - a strain sensing circuit (17) disposed on the sensitive membrane to measure the state of compression of the sensitive membrane (15) which is proportional to the pressure (Pi, PI, P2) of the aquifer liquid.

7. The aquifer monitoring device (10) according to the preceding claim, wherein the strain detection circuit (17) comprises a transverse gauge and a longitudinal gauge, substantially positioned at the center of the sensitive membrane (16).

8. The aquifer monitoring device (10) according to any one of claims 1 to 7, comprising several pairs of piezometric probes forming paired piezometric probes (30, 30a, 30b), each pair comprising first and second paired pressure sensors (11, 12).

9. The aquifer monitoring device (10) according to any one of claims 1 to 8, wherein said piezometric probe (30, 30a, 30b) is made in the form of an elongated cylindrical body with longitudinal axis (LL') comprising: - a weight (31) provided with a pressure tap (32, 32a), the weight (31) being disposed at a distal end of said body, - a measuring module (35) forming a sealed housing (36) fixed on the weight (31) and comprising a pressure sensor (11, 12) in fluidic connection with the pressure tap (32, 32a), a temperature sensor (37) and an electronic module (38) coupled to the pressure and temperature sensors, and - a sealed connector (39) fixed to the housing (36) at another end of said body for coupling the piezometric probe to a power, communication and deployment cable (40).

10. A method for manufacturing an aquifer monitoring device (10) according to any one of claims 1 to 8, characterized in that it comprises the steps: - manufacture (S1) first and second pressure sensors using a collective manufacturing technology ensuring substantially identical properties, - verify (S2) that the first and second pressure sensors have identical pressure sensitivity within 10%, - verify (S3) that the first and second pressure sensors have identical temperature sensitivity within 10%, - define (S5) the first pressure sensor and the second pressure sensor as paired, and - couple (S6) the paired first and second pressure sensors to a pressure measurement acquisition and processing module.

11. The method of manufacturing an aquifer monitoring device (10) according to the preceding claim, wherein the first and second pressure sensors are calibrated together (S4).

12. The method of manufacturing an aquifer monitoring device (10) according to claim 10 or 11, wherein the collective manufacturing technology is the microtechnology of manufacturing electronic components with a microelectromechanical system MEMS, the first and second pressure sensors being derived from the same wafer of single-crystal semiconductor material or from the same batch of several wafers of single-crystal semiconductor material.

13. Use of an aquifer monitoring device (10) according to any one of claims 1 to 8 to characterize at least one aquifer parameter selected from a water level in the aquifer, water contamination in the aquifer, a measurement of water flow velocity in the aquifer, a measurement of water pumping in the aquifer.

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