METHOD FOR THE LEAK DETECTION AND LEAK-RATE MEASUREMENT IN A WELLBORE, SALT FALL DETECTION IN A CAVERN AND SYSTEM THEREOF

Abstract

 The invention relates to a method (200) for detecting and characterize a salt fall event in a cavern, and determining a depth of an anomaly or an impedance contrast in a wellbore, for example a fluid-fluid interface, a deviated pipe, a damaged tubing/casing etc.
The method (200) of the invention includes the following steps:
- measuring the brine static pressure level and converting said pressure into a numerical brine pressure data (201);
- analyzing said pressure data and monitoring the apparition of an event in the cavern (202);
- analyzing spectral characteristics of the numerical brine pressure data, and check whether the event corresponds to a salt fall;
- triggering (206) a pressure disturbance pulse, said pressure pulse propagating from a wellhead of the wellbore through a pipe and being distorted by at least one anomaly or impedance contrast;
- measuring (207) pressure variations at the wellhead and converting said pressure variations into an numerical signal data;
- analyzing (208) spectral parameters of said numerical signal data and applying statistical methods.
The invention also relates to a system to implement the above mentioned method. The system includes a hydraulic assembly and means to store and/or display the acquired signal data, salt fall detection and characterization results and/or the results of the spectral and statistical analysis.

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention belongs to the field of the underground hydrocarbon storage and salt production industry.

[0002] More particularly, the present invention belongs to the field of real-time non-intrusive downhole interface-depth or/and casing length measurement, and salt fall event detection in a storage cavern.

BACKGROUND OF THE INVENTION

[0003] The formation process of a salt cavern for hydrocarbon storage is commonly known as "leaching".

[0004] During the leaching process, as illustrated in figure 1, a tubing 101 and a surrounding annulus 102 are introduced inside a hole in the ground, said hole having three cemented casings 104a, 104b, 104c. Water is injected through the tubing 101 in a saline formation, while resulting brine 105 is withdrawn through the annulus 102 surrounding the tubing 101. A leaching realised this way is commonly known as "direct leaching".

[0005] The process can also be realised the other way around, with the water being injected through the annulus 102 and the brine 105 being withdrawn through the tubing 101, this approach being known as "reverse leaching".

[0006] The dissolution of the salt leads to the formation of the salt cavern 106, which gets filled of brine.

[0007] For the sake of clarity, it will only be considered in the present application a direct leaching process, as illustrated in figure 1, but one skilled in the art will understand that the invention is not restricted to this type of process.

[0008] The leaching process is implemented in stages. At each stage of the process, a blanket 107, consisting in an inert fluid with regard to the brine 105, is pumped-in through an outer space 103 surrounding the aforementioned annulus 102. The blanket 107 can be a liquid or a gas, such as oil or nitrogen. The blanket 107 forms an horizontal cavern roof limiting the dissolution of the saline formation by the brine in a vertical way, thus favouring the formation of wide slices of brine. At the end of a stage, the tubing 101 and the annular space 102 may be moved upwards, and the blanket level has to be consequently readjusted, to proceed to the formation of another slice of brine. Once the whole leaching process is over, the salt cavern 106 is formed by the overlaying of the created slices.

[0009] The implementation of the leaching process in stages ensures the desired shape of the salt cavern, which mainly depends on the blanket level at each stage of the process, said blanket level being defined by a depth d below ground of an interface 108 between the brine 105 and the blanket 107.

[0010] Therefore, it is crucial to have a precise control of the interface depth during this process.

[0011] Also, mechanical integrity tests (MIT) are periodically performed to test the tightness of salt caverns used for hydrocarbon storage, among others the Nitrogen Leak Test (NLT) and the Liquid-Liquid Test (LLT). The NLT consists in injecting brine 105 through a central tubing while injecting nitrogen along an annular space located between said central tubing and the at least two cemented casings, down under the last cemented casing shoe 109. The depth of the interface between the blanket and the brine is measured at least twice, at time intervals separated by 24 hours. An upward displacement of the interface is deemed to indicate a nitrogen leak.

[0012] Also, during operations such as leaching process, the pipes used to inject the fluids may present plugs or may be damaged, so it is necessary to have a way to check the operational status of the wellbore.

[0013] Therefore, the real-time detection of impedance contrasts in a well, especially an interface between two fluids, is very valuable when it comes to salt cavern gas storage.

[0014] A large number of salt caverns are used for fluid hydrocarbon storage worldwide. These caverns have various sizes, with volumes ranging up to millions of barrels or millions of cubic meters. When liquid products are being stored, they are typically pumped in or out by displacement with brine. Handling of the brine normally involves hanging strings used to pump brine near the bottom of the cavern. It appears that hanging strings, regardless of the product handled, may be damaged when they extend significantly down into the cavern. Some events as salt-block fall, or also buckling due to inappropriate flowrates, can damage these hanging strings. An undetected damaged string can later on lead to some dramatic incident such as cavern overfilling.

[0015] The accumulation volumes of salt fall material can be extremely large (up to tens of millions cubic meters), indicating that only a few of the salt falls are large enough to cause significant damage.

[0016] A salt-block fall can be detected by fast pressure changes measured at wellhead during a short period of time. Nevertheless, some fast pressure variations can occur at wellhead without being due to salt falls. Therefore, the real-time detection of salt falls, their filtering to distinguish between significant and insignificant events, and their characterization by volume and by location can provide a very valuable information when operating a storage cavern, and it is helpful for an early detection of damaged strings.

[0017] At the moment, solutions are known to carry out a blanket-level measurement. Part of these solutions are based upon differences in physical characteristics of the blanket and the brine.

[0018] Grosswig et al. describe in their September 2015 "Optic Measurement System for Temperature, Automatic and Continuous Blanket Interface Monitoring in Caverns" conference paper a measurement of the blanket-brine interface depth using an optical fiber temperature sensing technology. An optical fiber sensing cable runs through the blanket into the brine and is heated up by electrical power. The differences in thermal conductivity between the blanket medium and the brine medium induce different saturation temperatures allowing a calculation of the interface depth.

[0019] The European patent number EP 0111353 discloses a capacitance-principle-based down-hole tool to measure the position of the interface. An electrode is inserted in the tubing, the tubing wall acting as a second electrode, and the difference in capacitances for blanket medium and for brine medium is used to determine the interface position upon the capacitive measuring principle.

[0020] These solutions present the disadvantage of being intrusive and may need maintenance from time to time. Furthermore, they are expensive and take time to implement. In addition, the leak controls are only made at large time intervals on the order of five years, which means that a leak appearing right after a leak control would not be detected before a long period of time.

[0021] The American patent application US 4934186 discloses an apparatus allowing continuous calculations of the depth of a fluid level within a wellbore filled with gas during a test interval. A sonic pulse is generated by an assembly located on the wellhead, travels down the annulus between the tubing and the casing of the well, and reflects off down hole discontinuities such as collars (tubing couplings) and the interface. The reflected sonic energy is sensed by a microphone. Knowing the acoustic round trip travel time and the number of collars allow the apparatus to calculate the interface depth.

[0022] This apparatus can be used for measurements in annulus filled with gas as well, but requires a substantially uniform annulus, so that the reflected signal does not contain extraneous echoes due to a substantial change in the cross section of the annulus, permitting the echoes due to the collars to be precisely identified. Therefore, such an apparatus is more adapted to hydrocarbon production wells than storage wells which often requires the use of a plurality of cemented casings having different cross-section areas impeding the measurement. Furthermore, this type of apparatus is to be used punctually during tests such as MIT, so it does not allow the detection of a leak appearing between two tests, which can be separated by a long time interval. Moreover this apparatus is compatible with a gas medium only, thus its usage is limited by a gas blanket wells.

[0023] Currently, there is no known solutions for salt fall detection and its characterization.

SUMMARY OF THE INVENTION

[0024] The invention addresses the issues left unsolved by the prior art, by allowing a continuous real-time detection of anomalies or/and impedance contrasts encountered in a wellbore filled with liquid and/or gas media, and by permitting especially a measurement of the depth of the blanket-brine interface.

[0025] The invention relates to a method for the detection of salt fall event in a cavern and of at least one anomaly or impedance contrast of a wellbore such as a fluid-fluid interface, including:

• a step of measuring a brine static pressure level in a brine string at a wellhead of the wellbore and converting said brine static pressure level into a numerical brine pressure data;
• a step of analyzing said pressure data and monitoring the apparition of an event in the cavern;

and, in case no event is detected during step of monitoring the apparition of an event:

• a step of triggering a pressure disturbance pulse, said pressure pulse propagating from the wellhead of the wellbore through a pipe and being distorted by at least one anomaly or impedance contrast;
• a step of measuring pressure variations at the wellhead and converting said pressure variations into a numerical signal data;

[0026] According to the invention, said method further includes a step of spectrally and statistically analyzing said numerical signal data, and, in case an event is detected during step, a step of analyzing spectral parameters of brine pressure data for checking whether the event corresponds to a salt fall event detection.

[0027] In one embodiment, the method is applied to the detection of a fluid-fluid interface.

[0028] In one embodiment, the method is applied to leak detection and leak rate measurement.

[0029] In one embodiment, the method further comprises a step of remotely storing the acquired numerical signal and static data, salt fall detection and characterization results and the results of the spectral and statistical analyses.

[0030] In one embodiment, the method further comprises a step of displaying the acquired signal data and the results of the spectral and statistical analyses.

[0031] In one embodiment, the method further comprises a step of informing the operator, when appropriate, of an unexpected event such as salt fall event.

[0032] In one embodiment, the method further comprises a step of carrying out measurements of slowly varying parameters in the wellbore, the expression "slowly varying" meaning such parameters have a period of variation exceeding a period between measurements of these parameters which is up to 5 minutes.

[0033] The invention also relates to a system for implementing the method of the invention. The system of the invention comprises means for:

• measuring a brine static pressure level in a brine string at the wellhead of the wellbore and converting said brine static pressure level into a numerical brine pressure data;
• analyzing said pressure data and monitoring the apparition of an event in the cavern;
• analyzing spectral parameters of brine pressure data for checking whether the event corresponds to a salt fall event detection
• triggering a pressure disturbance pulse from the wellhead of the wellbore through the pipe;
• measuring pressure variations at the wellhead and converting said pressure variations into an numerical signal data;
• analyzing spectrally and statistically parameters of said numerical signal data and applying statistical methods.

[0034] In one embodiment, the system of the invention includes:

• a manifold containing a hydraulic assembly comprising a fluid volume chamber, electro-valves, and a dynamic pressure transducer;
• a high-frequency data acquisition system comprising a high-frequency acquisition device such as an electronic card and a mini-PC embedding a user-friendly software program to analyze and report data;
• a brine pressure sensor.

[0035] In one embodiment, the dynamic pressure transducer is a piezoelectric or quartz pressure sensor.

[0036] In one embodiment, the static pressure sensor is a passive pressure transmitter.

[0037] In one embodiment, the brine static pressure sensor is a passive pressure transmitter.

[0038] In one embodiment, the static temperature sensor is a RTD/thermocouple element.

[0039] In one embodiment, the system of the invention comprises means for displaying the numerical signal data, brine static data and static data, and the results of the spectral and statistical analyses of said signal data, salt fall detection and characterization results.

[0040] In one embodiment, the high-frequency data acquisition system also comprises means allowing a wireless and/or cellular communication.

[0041] In one embodiment, the system also includes an alarm system.

[0042] In one embodiment, the system comprises means for carrying out measurements of static parameters in the wellbore, ambient parameters such as atmospheric pressure and temperature, hardware monitoring parameters such as voltage, temperature, battery charge level etc.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The invention will be better understood after reading the following specification and reviewing the accompanying drawings. The drawings are presented for illustration purpose only and do not restrict the invention.

Figure 1 is a section of a wellbore and a salt cavity during a leaching process.

Figures 2a-2f illustrate examples of impedance contrasts in a pipe.

Figure 3 is a block diagram illustrating the method of the invention.

Figure 4 is an example of spectral and statistical analysis.

Figure 5 is an overview of the system of the invention.

Figure 6 is a view of the manifold.

Figure 7 is a curve representing an example of wellhead pressure variations over time.

Figure 8 is a schematic representation of the interface between the system of the invention and a remote connected unit.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0044] The invention relates to a method 200 for the detection of at least one anomaly/impedance contrast of a wellbore. Such impedance contrasts or anomalies might be a fluid-fluid interface, a plug in a pipe or a damaged pipe, which are mentioned by way of example only and do not restrict the scope of the invention.

[0045] The word "pipe" is used in the description to generally designate a long hollow body meant to contain liquid or gas. Tubing, casing and annulus are examples of pipes concerned by the invention.

[0046] Examples of anomalies/impedance contrasts are illustrated in figure 2a to 2f:

• plug in a tubing/casing (figure 2a) or in an annulus (figure 2b);
• damaged tubing/casing (figure 2c);
• interface level between two fluids in a tubing/casing (figure 2d) or in an annulus (figure 2e);
• interface level between two fluids in a chimney.

[0047] In an embodiment described hereinafter, the method 200 is implemented to determine:

• a salt fall in the cavern event detection and characterization;
• a depth d from a wellhead of a brine-blanket interface 108 during a leaching process, as illustrated in figure 1.

[0048] As illustrated in figure 3, the method 200 according to the invention includes the following steps:

• measuring brine static pressure level and converting said pressure level into a numerical brine pressure data 201, in practice, the measurement is conducted permanently;
• analyzing said numerical brine pressure data and monitoring an apparition of an event 202.

In case of an event detection:

[0049] 

• analyzing spectral characteristics 203 of said numerical brine pressure data and checking whether the event is a salt fall in the cavern 203.

[0050] Then, if a salt fall in the cavern is identified:

• triggering an alarm 204 for salt fall event;
• characterizing the salt fall 205 by means of enhanced mathematical modeling and analyzing the numerical brine pressure data.

[0051] If the event is not a salt fall, the method starts again at step 201.

In case of no event detection:

[0052] 

• triggering 206 a pressure disturbance pulse in the wellbore from a wellhead;
• measuring pressure variations and static parameters at the wellhead and converting said pressure variations 207 into a numerical signal data and converting said static parameters into a static data;
• analyzing a spectral characteristics 208 of said numerical signal data;
• analyzing by means of statistical methods the signal and static data and determining 209 the depth d of the interface 108;
• displaying 210 the determined depth d.

[0053] According to the invention, the brine static pressure level is first measured during step 201 at the wellhead and then analyzed 202 for a deviation from average value. Sufficient deviation of brine pressure level from its average value signals about an event processing in the cavern and in well, workover procedure etc. A deviation shall be considered "sufficient" here when it is beyond a threshold generally comprised between 0.1 bar to 2 bars, the exact value of the threshold being determined for each cavern especially, depending on cavern properties as its type, size and average brine pressure value, on ambient conditions as background pressure noise from mechanic and other activities etc. The threshold also depends on minimal size/weight of salt block which is supposed to be detected.

[0054] Then further spectral data analysis is done 203 to define salt fall event, and enhanced mathematical analysis and modeling are performed 205 for the salt fall characterization.

[0055] If no or few static brine pressure deviation is detected, the pressure disturbance pulse is triggered 206 in the wellbore, "few" meaning that the deviation is below the threshold hereinabove mentioned. The pressure disturbance pulse can be triggered by the way of introducing either a brief depression or a brief excessive pressure, thus creating respectively an implosion or an explosion inside the wellbore. The pressure disturbance pulse propagates through the wellbore, from the wellhead through the substantially vertical wellbore, and is partially distorted by the brine-blanket interface 108.

[0056] The distorted wave travels back through the wellbore and is received at the wellhead, where the pressure variations are converted and recorded into an numerical signal data.

[0057] The spectral characteristics of the recorded numerical signal data are analyzed, statistical methods are applied to signals and static data and to derived results to determine the depth of an interface. Figure 4 shows an example of the results of spectral analysis process and statistical methods applied to a recorded numerical pressure data 410. Spectral analysis and following process consist in spectral noise minimization enhancement of frequency resolution leaps corresponding to initial depression pulse properties and impedance contrasts in the well and other irregularities. The numerical data obtained after spectral analysis and following related process are illustrated in figure 4 by a dotted line 420. Further application of statistical methods and appropriate process allow to take into account and to minimize the impact of conditions changes in the well and other unpredictable factors. It substantially increases the accuracy of the measurements in the given example, the application of statistical methods allowed to consider the temperature-variation effect which impacts spectral data and fundamental frequency value corresponding to cavern roof location. The numerical data obtained after statistical analysis and appropriate related process are illustrated in figure 4 by a dashed line 430. Thus, the corrected depth is found 9 ± 0.5 meters higher than the initial estimate without statistical analysis.

[0058] In a preferred embodiment, the method 200 also comprises a step of remotely storing the acquired signals, static data and the results of the analysis constituting data, so that said data are available to an operator from any location.

[0059] Advantageously, the method 200 also comprises a step of informing the operator, when appropriate, of a salt fall event or other unexpected event during the leaching process or storage. Said unexpected event can be for example a leakage or a bad distribution of the blanket causing a partial dissolution of the saline formation above the cavity roof.

[0060] Advantageously, measurement of static parameters such as static pressure and/or static temperature in the wellbore are also carried out, as they have an influence on the spectral characteristics of the recorded signals, and can be used further in statistic analysis of the measured data.

[0061] The invention also relates to a system 300 for the salt fall detection and the detection of at least one discontinuity of a wellbore.

[0062] As illustrated in figure 5, the system 300 according to the invention comprises a manifold 310, a high-frequency data acquisition system 320 and a static brine pressure sensor 330.

[0063] The manifold 310 is in the form of a cabinet containing a hydraulic assembly comprising a fluid volume chamber 311, electro-valves 312 and 313, and a block 314 with integrated dynamic pressure transducer, static pressure sensor, static temperature sensor, as represented in figure 6. An interface element 315 of the hydraulic assembly, for example a threaded part, passes through a side face of the block 314 and connects with the outside.

[0064] The high-frequency data acquisition system 320 (hereinafter referred to as "DAS") is in the form a glass-door box containing a high-frequency acquisition card 321 connected to a mini-PC 322 as illustrated in figure 8.

[0065] The electrovalves 312;313 and the components of the block 314 of the manifold 310 is connected to the high-frequency acquisition card of the DAS 320.

[0066] When the system is used to implement the method hereinbefore described, the manifold 310 is plugged to the wellhead through the interface element 315 which may conveniently be a threaded part, the static brine pressure sensor 330 is plugged directly to a wellhead of the brine string well. The DAS 320 may be placed in height, for example mounted on a wall or on a support, to allow an easy access to an operator.

[0067] In the case the blanket pressure is low, for example equal or less than 10 bars (150 PSI) the manifold 310 also comprises an external compressed source, for example a nitrogen cylinder. The pressure pulse is then be triggered through the wellbore by pressurizing the fluid volume chamber 311 with nitrogen from the cylinder by opening the electrovalve 313, above the blanket pressure at the wellhead, for example 30 bars (450 PSI), and then opening briefly the electro-valve 312, located between said fluid volume chamber and said wellbore, for example during a few tens of milliseconds, thereby creating a narrow overpressure pulse.

[0068] Otherwise, the pressure disturbance pulse is triggered by only opening the electro-valve, causing a short depression wave.

[0069] When the pressure disturbance pulse has travelled back to the wellhead after being distorted by the brine-blanket interface 108, the dynamic pressure transducer in the block 314 of the manifold 310 detects the pressure variations and convert it into electric variations, which are transmitted to the high-frequency card 321 of the DAS 320 and registered as numerical signal data.

[0070] Various transducers may be used, such as piezoelectric sensors, for example a quartz sensor. In any case, the used transducers may advantageously present a wide bandwidth, allowing for example the measurement of pressure variations up to 100 000 Hz. Such a bandwidth allows the sensor to be used for different type of operations such as the measurement of an interface depth or the detection of a damaged pipe.

[0071] The converted pressure variations transmitted to the high-frequency card 321 is then transmitted to and analyzed on the mini-PC 322.

[0072] The recording time of the pressure variations depends on the well parameters and operating conditions. Figure 7 shows an example of a signal data 400 recorded and displayed on a screen of the mini-PC 322, while monitoring the brine-blanket interface depth d during a leaching process. The signal data 400 in this figure represents the evolution in time of the wellhead pressure variations. In this example the duration of the recorded signal data is of 40s.

[0073] Advantageously, pressure disturbances are triggered periodically in automatic mode, so a real-time monitoring is carried out.

[0074] Preferably, each one of the recorded signal datasets can be displayed independently at any time on a screen 326 connected to the mini-PC 322 so that the operating staff on place can observe displayed results and manually trigger supplementary tests or extra measurements through the glass door of the data acquisition box.

[0075] Advantageously, the system 300 also comprises means to measure static parameters inside the wellbore, such as static pressure and/or static temperature of the blanket. Once the numerical signal data is transmitted to the mini-PC 322, a software embedded in the mini-PC 322 proceeds to a spectral analysis of said signal data and further statistical analysis of a set of signal and static data, and registered data on atmospheric conditions as well.

[0076] As explained hereinbefore, the type of analysis depends on the conducted operation: depth measurement, damaged pipe detection...

[0077] In a preferred embodiment, the DAS 320 also comprises a router 323 and a USB modem 324, such as a 3G/4G router and a 3G/4G key, to provide said DAS with the Internet. In this embodiment, the DAS 320 also comprises a switch 325 to interconnect the high-frequency acquisition card 321, the router and the mini-PC 322. A router 323, a USB modem 324 and a switch 325 are all separated devices or a all-in-one device like a 3G/4G Wi-Fi router for example.

[0078] Copies of the data constituted by the acquired numerical signal data, static data and the results of its analysis are made and transmitted to an online storage space / computing resources 502 (Cloud) through a secured connection 501 a, for example a public/private-key-encrypted channel, so the enhanced processing can be performed and operator can have access to this data from a computer or a mobile device via secured Internet connection 501 b.

[0079] Advantageously, the cloud part 502 has an alarm system to, when appropriate, give the operator notice of an unexpected event during the leaching process as mentioned above. For example, the cloud software can automatically notify the authorized person via an email and/or a SMS and/or other message type.

[0080] The power supply of the system 300 can be an electric outlet or a solar panel for example.

[0081] Advantageously, the system embeds a battery so it is autonomous in case of a power cut.

[0082] The system and the method described herein before are not limited to the salt fall event detection and measurement of an interface depth, and one skilled in the art will understand that it can be applied for the detection of other type of anomalies, such as plugs in pipes, damaged or deviated pipes.

[0083] Depending on the information sought, the system and / or the method shall be adapted. In particular, the duration of the recorded signal data may vary, as well as the conducted spectral and statistical analyses.

[0084] Also, though the invention is described for the detection of only one type of an event in a cavern, one type of discontinuity, it will be understood by one skilled in the art that the invention can be used to detect simultaneously several events and impedance contrasts in a wellbore, in a cavern, or in other type of underground storage.

[0085] The method and system of the invention have the following advantages:

• the system is non-intrusive and can easily and quickly be plugged to the wellhead through the interface element;
• they are non-interruptive as measurement can be made while there is an active flow in the well;
• permanent monitoring is made possible without intervention for days or weeks or months;
• the system can be of low power consumption as solar panel may be used as power supply;
• the system can be controlled remotely as soon as a mobile communication network is available, and data can be displayed at real time on authorized computers and/or mobile phones, allowing a 24 hour /7 days alarm triggering through email and/or message/notification when a problem is detected;
• unlike some existing intrusive tools, there is no limitation related to depths;
• leaks and damages in highly deviated (even horizontally deviated) pipes can be detected and measured.

Claims

1. A method (200) for the detection of salt fall event in a cavern and of at least one anomaly or impedance contrast of a wellbore such as a fluid-fluid interface, including:

- a step of measuring a brine static pressure level in a brine string at a wellhead of the wellbore and converting said brine static pressure level into a numerical brine pressure data (201);

- a step of analyzing said pressure data and monitoring the apparition of an event in the cavern (202);

and, in case no event is detected during step of monitoring the apparition of an event:

- a step of triggering (206) a pressure disturbance pulse, said pressure pulse propagating from the wellhead of the wellbore through a pipe and being distorted by at least one anomaly or impedance contrast;

- a step of measuring (207) pressure variations at the wellhead and converting said pressure variations into a numerical signal data;

characterized in that said method further includes a step of spectrally and statistically analyzing (208) said numerical signal data, and, in case an event is detected during step (202), a step of analyzing (203) spectral parameters of brine pressure data for checking whether the event corresponds to a salt fall event detection.

2. The method according to claim 1 wherein said method is applied to the detection of a fluid-fluid interface.

3. The method according to claim 1 wherein said method is applied to leak detection and leak rate measurement.

4. The method according to any of the preceding claims characterized in that said method further comprises a step of remotely storing the acquired numerical signal and static data, salt fall detection and characterization results and the results of the spectral and statistical analyses.

5. The method according to any of the preceding claims characterized in that said method further comprises a step of displaying the acquired signal data and the results of the spectral and statistical analyses.

6. The method according to any of the preceding claims characterized in that said method further comprises a step of informing the operator, when appropriate, of an unexpected event such as salt fall event.

7. The method according to any of the preceding claims characterized in that said method further comprises a step of carrying out measurements of slowly varying parameters in the wellbore.

8. A system (300) for implementing the method (200) according to any of the preceding claims, characterized in that it comprises means for:

- measuring a brine static pressure level in a brine string at the wellhead of the wellbore and converting said brine static pressure level into a numerical brine pressure data;

- analyzing said pressure data and monitoring the apparition of an event in the cavern;

- analyzing spectral parameters of brine pressure data for checking whether the event corresponds to a salt fall event detection

- triggering a pressure disturbance pulse from the wellhead of the wellbore through the pipe;

- measuring pressure variations at the wellhead and converting said pressure variations into an numerical signal data;

- analyzing spectrally and statistically parameters of said numerical signal data and applying statistical methods.

9. The system according to claim 8 characterized in that it includes:

- a manifold (310) containing a hydraulic assembly comprising a fluid volume chamber (311), electro-valves (312; 313), and a dynamic pressure transducer (314);

- a high-frequency data acquisition system (320) comprising a high-frequency acquisition device such as an electronic card (321) and a mini-PC (322) embedding a user-friendly software program to analyze and report data;

- a brine pressure sensor (330).

10. The system according to claim 8 or claim 9 characterized in that the dynamic pressure transducer (314) is a piezoelectric or quartz pressure sensor.

11. The system according to any of claims 8 to 10 characterized in that the system (300) comprises means for displaying the numerical signal data, brine static data and static data, and the results of the spectral and statistical analyses of said signal data, salt fall detection and characterization results.

12. The system according to any of claims 8 to 11 characterized in that the high-frequency data acquisition system (320) also comprises means allowing a wireless and/or cellular communication.

13. The system according to any of claims 8 to 12 characterized in that the system (300) also includes an alarm system.

14. The system according to any of claims 8 to 13 characterized in that the system (300) comprises means for carrying out measurements of static parameters in the wellbore.

Drawing