CN105840178A - On-line monitoring system and method for dissolution cavity of salt cavern storage - Google Patents

Abstract

The present invention provides an on-line monitoring system and method for salt cavern storage solution cavity. The device includes surface unit and downhole unit, and adopts ultra-large-scale programmable logic devices and embedded soft-core microprocessors to make downhole instruments highly integrated. At the same time, the probe-type sensor is used to overcome the bottleneck of the narrow space, solve the problem of placing the measuring device in the annular space of the small wellbore, and promote the development of the dissolution cavity process to a large extent. The probe, using the fixed reference length between the capacitor plates, dynamically detects the dielectric constant of the brine where the probe is located, realizes the automatic calibration of the capacitance sensor during the monitoring process of the dissolution cavity, and eliminates the traditional capacitance detection method due to the The influence of the dielectric constant change on the measurement results caused by the change of the degree of polarization effectively solves the problem of misjudgment of the shape of the cavity roof.

Description

An online monitoring system and method for salt cavern storage solution chamber

technical field

The invention relates to a method and device for monitoring a dissolution cavity of a salt cavern storage, in particular to online monitoring of the height of the top plate of the dissolution cavity during the process of the dissolution cavity.

Background technique

Underground salt cavern storage is an underground facility that uses water-soluble methods to form caves in underground salt layers or salt domes to store natural gas, crude oil and other media. Compared with traditional ground storage tanks, underground salt cavern storage has the advantages of large storage scale, high safety and less land occupation. Therefore, it has become the preferred storage solution for the construction of oil reserve bases. Cavity engineering technology is the longest and most complicated technology in the construction process of salt cavern storage. It includes two core issues: one is how to build a stable cavity shape; the other is how to increase the speed of salt cavern cavity building. For how to build a stable cavity shape, there are two key technologies: one is the cavity shape design, and the other is the control of the cavity shape during the cavity creation process. During the cavity dissolution process, due to gravity differentiation, the vertical upper salt layer dissolves relatively quickly, while the horizontal salt layer dissolves relatively slowly. If control measures are not taken, the top of the salt layer will be dissolved quickly. The shape required by the repository.

The purpose of the project realization is to detect the position of the cavity roof during the dissolution process and obtain a real-time curve reflecting the height of the cavity roof. Utilizing the property that the salt layer is insoluble in oil but soluble in water, diesel oil is added into the cavity as a spacer to isolate the salt layer on the upper part of the cavity from direct contact with fresh water. Therefore, through the on-line detection of the interface between diesel oil and fresh water during the cavity building process, the protection of the cavity roof is realized, thereby controlling the shape of the cavity cavity.

Since underground salt cavern storage is often built at about 1,000 meters underground, the cavity construction period is long, the annulus space of the construction wellbore is small, the monitoring device needs to be placed in the wellbore for 2-3 years, and the fluctuation range of the oil-water interface reaches tens of meters. However, the oil-water interface measurement methods used in ground storage tanks, such as floating ball type, differential pressure type, short-wave absorption type, radio frequency admittance type, etc., cannot adapt to the working environment of the dissolved cavity. In addition, in the dissolution process of salt caverns, as the dissolution process progresses, the environment changes, such as the concentration of salt in the brine gradually increases, the degree of salinity will increase, and the dielectric constant will decrease.

Contents of the invention

In order to overcome the deficiencies of the prior art, the present invention provides an online monitoring method and device for the dissolution cavity of a salt cavern storage, which solves the problems of fully automatic processing, online detection, real-time transmission and automatic calibration in the process of the storage cavity dissolution, Accurate measurement and real-time monitoring of the height of the cavity top plate are realized, thereby controlling the top shape of the cavity.

The technical scheme adopted in the present invention is:

An on-line monitoring system for the dissolution cavity of a salt cavern storage, including a ground unit and a downhole unit, the ground unit and the downhole unit are connected by a cable winch, a pulley block and a 7-core cable, and 1# and 4# of the 7-core cable The cable core is responsible for power supply, the 2# and 5# cable cores are responsible for transmitting the commands issued by the ground unit and the measurement data uploaded by the downhole unit, the rest of the cable cores are free, and the cable sheath is grounded; the downhole unit includes:

The downhole controller is used to decode and analyze the commands issued by the surface unit and control the work of each module in the downhole unit, and at the same time analyze and process the state information in the dissolution chamber collected by the downhole unit and perform coding operations;

The mode conversion module is used to switch the self-test or measurement working modes of the downhole unit according to the control command;

The measurement and conversion module is used to measure the capacitance value and convert the capacitance value into frequency;

The sensor group includes a pressure sensor, a temperature sensor and a three-plate capacitive sensor; both the pressure sensor and the temperature sensor are electrically connected to the downhole controller for monitoring the pressure and temperature in the dissolution chamber; the three-plate capacitive sensor passes through The mode conversion module, the measurement and conversion module are electrically connected to the downhole controller, and are used to monitor the height of the oil-water interface;

The downhole Mann code conditioning circuit is electrically connected to the downhole controller, and is composed of a transformer, a differential amplifier, a hysteresis comparator and a voltage regulator circuit, and is used to send the downhole status information encoded by the downhole controller to the surface unit, and to upload the signal Conditioning is carried out to make the signal easier to transmit on the cable and overcome the influence of the cable capacitive reactance on the signal.

Preferably, the three-plate capacitive sensor is a probe-type sensor, and its three capacitive plates are set as two long and one short, and the height of the oil-water interface is judged by the difference in capacitance between the three plates.

Preferably, the downhole unit also includes two sets of descaling devices, one group corresponds to the two long plates of the three-plate capacitive sensor, and the other group corresponds to the short plates of the three-plate capacitive sensor, and the descaling device includes A stepping motor, a push rod connected to the rotating shaft of the stepping motor and a descaling scraper arranged on the three-electrode capacitive sensor plate, the stepping motor is electrically connected with the downhole controller, and the stepping motor is controlled by the processor to work , the descaling scraper is driven by the push rod to descale the pole plate.

Preferably, the ground unit includes:

The ground controller is used to decode and analyze the roof height, temperature, and pressure information uploaded by the downhole unit and send it to the remote computer, receive and encode instructions from the remote computer; at the same time, control the modules of the ground unit to complete corresponding functions;

The ground Mann code conditioning circuit is electrically connected to the ground controller, and is composed of a transformer, a differential amplifier, a hysteresis comparator and a voltage stabilizing circuit, and is used to send the coded control command issued by the ground controller to the downhole unit, and to The signal is conditioned to make the signal easier to transmit on the cable and overcome the influence of the cable capacitance;

The depth measurement module is electrically connected with the ground controller, and is used for phase discrimination of the depth pulse signal and counting of depth pulses. The ground controller reads the pulse count value and calculates the initial depth value of the downhole instrument;

The wireless communication module is electrically connected with the ground controller, and is used to realize the information interaction between the ground unit and the remote control server;

The display module is electrically connected to the surface controller, and is used to display information such as commands, initial depth of downhole instruments, measured height, temperature, pressure of the cavity roof interface, and position of the push rod, and can also facilitate system debugging;

The alarm module is electrically connected with the ground controller, and includes sound alarm and light alarm, which are used to remind the upper limit or lower limit of the cavity roof interface measurement.

Preferably, the alarm module includes 2 frequencies of sound alarms and 2 colors of light alarms, high-frequency sounds and red lights indicate that the top plate interface of the cavity exceeds the upper limit of measurement, low-frequency sounds and yellow lights indicate that the cavity The top plate interface has exceeded the lower limit of the measurement.

As a preference, the surface controller and the downhole controller use the Cyclone V series G3CX FPGA chip with embedded Nios II soft processor.

An online monitoring method for a salt cavern storage solution cavity, comprising the following steps:

Step 1, set the cable winch, move the downhole unit, and make the capacitive sensor of the three-electrode plate be fully immersed in the diesel oil;

Step 2, start the surface unit, send downhole unit self-test or measurement commands through the ground controller, and encode the control commands through the ground Mann code conditioning circuit;

Step 3: The downhole controller receives and decodes the self-test or measurement command issued by the surface unit through the downhole Mann code conditioning circuit, and the control mode conversion module connects the fixed capacitor or the three-electrode capacitive sensor to the circuit, and at the same time collects the temperature in the dissolution chamber, Pressure and descaling blade position information;

Step 4, based on the principle of equal-precision frequency measurement, the downhole unit measures the frequency or period of the input signal, and uploads the measured frequency or period data with Manchester encoding;

Step 5, the ground controller decodes the uploaded frequency or period data, calculates the height of the interface, displays the measurement data on the LCD in real time, and transmits the measurement results to the computer through the wireless communication module.

Preferably, the step 4 further includes that the downhole controller collects the temperature and pressure values in the downhole dissolution cavity through the temperature sensor and the pressure sensor, and uploads the encoded values.

As preferably, the format of the command frame sent by the surface unit to the downhole unit in step 2 is composed of a command header, a command control word, and a command tail; in step 4, the data frame sent by the downhole unit to the surface unit includes the measured frequency or period, Also includes temperature values, pressure values and information on the position of the descaling blades.

As a preference, in step 3, the mode conversion module connects the fixed capacitor to the circuit for system self-checking to determine whether the system status is normal; The relative position of the plate capacitance sensor and the oil-water interface is different, the difference in capacitance, and the multivibrator is used to realize the conversion from capacitance to frequency.

Compared with the prior art, the present invention has the following advantages:

The present invention replaces the top plate interface and cavity shape measurement in the process of on-site cavity dissolution in a fully automated manner, saving a lot of labor costs for the cavity dissolution work; the device adopts ultra-large-scale programmable logic devices and embedded software The nuclear microprocessor makes the downhole instrument highly integrated, and at the same time, the probe sensor overcomes the bottleneck of the narrow space, solves the problem of placing the measuring device in the annular space of the small wellbore, and promotes the development of the dissolution cavity process to a large extent ;The device adopts the way of data encoding, which enables reliable long-distance transmission of downhole instruments and surface instruments, fundamentally solves the real-time monitoring of the state of the underground salt cavern dissolution cavity on the ground, and realizes real-time online monitoring; A group of probes with unequal lengths, using the fixed reference length between the capacitor plates, dynamically detects the dielectric constant of the brine where the probes are located, realizes the automatic calibration of the capacitance sensor during the monitoring process of the dissolution cavity, and eliminates the traditional capacitance The detection method can effectively solve the problem of misjudgment of the shape of the cavity roof due to the influence of the change of the dielectric constant caused by the change of the salinity; the device has two working modes of self-test and measurement. The ground can monitor the working status of the whole device, which improves the reliability of the device; the device is equipped with a descaling scraper, and according to the descaling instructions issued by the ground, the probe can be automatically descaled under the control of the motor to eliminate It eliminates the hidden danger of the probe being scaled in brine for a long time, and ensures the long-term sensitivity of the probe; through setting, when the device is in the measurement working mode, it adopts the principle of equal-precision frequency measurement, which solves the measurement error and the measured signal in the traditional frequency measurement method. Frequency-related issues; the device uses wireless network communication and serial data communication methods to connect with the host computer, so that the data measured by the device on-site can be transmitted to the background server in real time, which largely meets the needs of digital oilfield development.

Description of drawings

Fig. 1 is a schematic structural diagram of an embodiment of the present invention.

Fig. 2 is a schematic block diagram of the ground unit design provided by the embodiment of the present invention.

Fig. 3 is a schematic block diagram of the downhole unit design provided by the embodiment of the present invention.

Fig. 4 is a flowchart of an online monitoring method provided by an embodiment of the present invention.

As shown in the figure: 1. Ground unit, 2. Downhole unit, 3. Cable winch, 4. Pulley block, 11. Ground controller, 12. Ground Mann code conditioning circuit, 13. Depth measurement module, 14. Wireless communication module, 15. Display module, 16. Alarm module, 21. Downhole controller, 22. Mode conversion module, 23. Measurement and conversion module, 24. Sensor group, 25. Downhole Mann code conditioning circuit, 26. Descaling device, 241. Pressure sensor, 242. Temperature sensor, 243. Three-electrode capacitive sensor

detailed description

In order to make the above objects, features and advantages of the present invention more comprehensible, specific implementations of the present invention will be described in detail below in conjunction with the accompanying drawings.

Referring to Fig. 1, this figure is an on-line monitoring system for a salt cavern storage solution cavity provided by an embodiment of the present invention, including a surface unit 1 and a downhole unit 2, and the surface unit 1 and the downhole unit 2 pass through a cable winch 3 and a pulley block 4 It is connected with a 7-core cable, the 1# and 4# cable cores of the 7-core cable are responsible for power supply, the 2# and 5# cable cores are responsible for transmitting the commands issued by the surface unit 1 and the measurement data uploaded by the downhole unit 2, and the rest The cable core is empty, and the cable sheath is grounded; the commands sent from the ground mainly include self-inspection commands, measurement commands and descaling commands, and the data uploaded underground mainly include information such as roof height, pressure, temperature and the position of the descaling scraper.

The format of the command frame sent by the surface instrument to the downhole instrument:

0X5555 command control word 0XAAAA

Command frame format description: 0X5555 indicates the command header, 0XAAAA indicates the command tail, and the command control word in the middle indicates the specific command sent by the surface instrument to the downhole instrument. The downhole instrument performs measurement operation, the command control word is 0X0703, which indicates that the downhole instrument starts descaling operation, and the descaling scraper moves downward, and the command control word is 0X0704, indicates that the downhole instrument performs descaling return operation, and the descaling scraper moves upward.

Format of data frames sent from downhole tools to the surface:

0X0707 temperature value Pressure value roof height long putter position short putter position 0XF0F0

Data frame format description: 0X0707 indicates the data head, 0XF0F0 indicates the data tail, and the middle data respectively indicate the measured temperature value, pressure value, top plate height, long push rod position and short push rod position, the temperature value is 16 bits, and the pressure value is 16 Bit, the height of the top plate is two 32 data bits, which correspond to the count values Nx and Ns respectively. The position of the long push rod is 32 bits, and the position of the short push rod is 32 bits, which correspond to the steps of the micro stepping motor respectively.

Surface unit 1, as shown in Fig. 2, includes: ground controller 11, which uses Cyclone V series G3CX FPGA chip and uses embedded Nios II soft processor to decode and analyze the roof height, temperature and pressure information uploaded by downhole unit 2 And send to the remote computer, receive remote computer instruction and carry out coding; Control each module of ground unit 1 to finish corresponding function at the same time; Composed of a voltage regulator and a voltage stabilizing circuit, it is used to send the coded control command issued by the surface controller 21 to the downhole unit 2, and condition the signal so that the signal can be transmitted on the cable and overcome the influence of the cable capacitance; depth measurement The module 13 is electrically connected with the ground controller 11, and is used for phase discrimination of depth pulse signals and counting of depth pulses. After the ground controller 11 reads the pulse count value, it calculates the initial depth value of the downhole instrument; the wireless communication module 14 communicates with The ground controller 11 is electrically connected to realize the information interaction between the ground unit 1 and the remote control server; the display module 15 is electrically connected to the ground controller 11 and used to display commands, the initial depth of downhole instruments, and the measurement of the cavity roof interface Information such as height, temperature, pressure, and the position of the push rod can also facilitate system debugging; the alarm module 16 is electrically connected to the ground controller 11, and includes 2 kinds of frequency sound alarms and 2 kinds of color light alarms. A loud sound and a red light indicate that the cavity roof interface has exceeded the upper limit of the measurement, and a low frequency sound and a yellow light indicate that the cavity roof interface has exceeded the lower limit of the measurement.

Described downhole unit 2, as shown in Figure 3, comprises: downhole controller 21, and downhole controller selects the G3CX type FPGA chip of Cyclone V series equally, adopts embedded Nios II soft processor to decode and analyze the data sent by surface unit 1 Command and control the work of each module in the downhole unit 2, and simultaneously analyze and process the state information in the dissolution cavity collected by the downhole unit 2 and perform encoding operations; the mode conversion module 22 is used to switch the self-test or Two working modes are measured; the measurement and conversion module 23 is used to measure the capacitance value and convert the capacitance value into frequency; the sensor group 24 includes a pressure sensor 241, a temperature sensor 242 and a three-electrode capacitance sensor 243; the pressure sensor 241, temperature sensors 242 are all electrically connected with the downhole controller 21, and are used to monitor the pressure and temperature in the dissolution chamber; the three-plate capacitive sensor 243 is a probe sensor, and its three capacitive plates are set as two long and one short, The height of the oil-water interface is judged by the capacitance difference between the three plates, and the three-plate capacitive sensor 243 is electrically connected to the downhole controller 21 through the mode conversion module 22, the measurement and conversion module 23 in turn; the downhole Mann code conditioning circuit 25, and the downhole The controller 21 is electrically connected, the same as the ground Mann code conditioning circuit, and is composed of a transformer, a differential amplifier, a hysteresis comparator and a voltage stabilizing circuit, and is used to send the downhole state information encoded by the downhole controller 21 to the surface unit 1, and Condition the uploaded signal to facilitate the transmission of the signal on the cable and overcome the influence of the cable capacitance on the signal;

In addition, the downhole unit 2 also includes two groups of descaling devices 26, one group corresponds to two long plates of the three-electrode capacitive sensor 243, and another group corresponds to the short plates of the three-plate capacitive sensor 243, and the descaling device 26 It includes a stepper motor, a push rod connected to the stepper motor shaft and a descaling scraper arranged on the three-electrode capacitive sensor 243 pole plate. The stepper motor is electrically connected with the downhole controller 21, and the stepper motor is controlled by a processor. The motor works, and the descaling scraper is driven by the push rod to descale the pole plate.

The present invention also includes an on-line monitoring method for the dissolution cavity of salt cavern storage realized by using the above system, as shown in Figure 4, including the following steps

Step 1, set the cable winch, move the downhole unit, and make the capacitive sensor of the three-electrode plate be fully immersed in the diesel oil;

Step 2, start the surface unit, send downhole unit self-test or measurement commands through the ground controller, and encode the control commands through the ground Mann code conditioning circuit;

Step 3: The downhole controller receives and decodes the self-test or measurement command issued by the surface unit through the downhole Mann code conditioning circuit, and the control mode conversion module connects the fixed capacitor or the three-electrode capacitive sensor to the circuit, and at the same time collects the temperature in the dissolution chamber, Pressure and descaling blade position information;

Step 4. Based on the principle of equal-precision frequency measurement, the downhole unit measures the frequency or period of the input signal, and uploads the measured frequency or period data together with the pressure value and temperature value in the dissolution chamber with Manchester encoding;

Step 5, the ground controller decodes the uploaded frequency or period data, calculates the height of the interface, displays the measurement data on the LCD in real time, and transmits the measurement results to the computer through the wireless communication module.

When performing the self-test operation, the downhole instrument connects a fixed capacitor to the measurement circuit, and the capacitance value is converted into a frequency value after the circuit conversion, and the frequency measurement is performed, and the data is uploaded to the surface instrument according to the data output format, and uploaded in the self-test mode The temperature value, pressure value, and push rod position are all set to fixed values, and these values are used to detect whether each device in the system is working normally.

When the measurement operation is performed, the sensor probe is connected to the measurement circuit, and the output signal of the sensor probe reflects the height of the top plate of the dissolution chamber. After the circuit conversion, the output signal of the probe is converted into a pulse signal, and the frequency of the converted pulse signal corresponds to The height of the chamber roof. The self-inspection and measurement of the roof height share the same conversion circuit. According to different commands, the downhole controller controls the on-off of the relay to realize the switching between self-inspection and measurement. The measurement of the frequency of the pulse signal adopts the principle of equal precision measurement. The steps are that the Nios II processor outputs a synchronous control signal, uses the rising edge of the measured signal to trigger, and generates a synchronous counting enable signal. The high level is effective, which ensures The sustaining time of the count enable signal is an integer multiple of the period of the signal to be measured. Under the condition that the counting enable signal is valid, use two 32-bit counters to count the measured pulse and the standard pulse at the same time, set the measured pulse count value Nx and the standard pulse count value Ns, and the Nios II processor reads them respectively Count values Nx and Ns. Use the formula fx=(Nx*fs)/Ns to find the frequency fx of the signal to be measured, so as to measure the height information of the dissolution chamber roof. For temperature measurement, a thermal resistance temperature sensor is selected, and the temperature information is converted into a voltage signal through a DC bridge, and then collected after amplification and filtering; for pressure measurement, a piezoresistive sensor is selected, and the pressure information is converted into a voltage signal through a DC bridge. Acquisition is performed after amplification and filtering. Using the equal-precision frequency measurement method, the measurement accuracy of the frequency is greatly improved, and the problem of the frequency measurement error related to the frequency of the measured signal in the traditional frequency measurement method is solved. Based on a set of probes of unequal length, using the fixed reference length between the long probe and the short probe, the dielectric constant of the brine where the probes are located is dynamically detected, realizing the monitoring of the probe signal during the dissolution cavity monitoring process Automatic compensation eliminates the influence of the traditional capacitance detection method on the measurement results due to the change of the salinity caused by the change of the dielectric constant, and effectively solves the problem of misjudgment of the shape of the cavity roof.

When performing descaling and starting operation, the downhole controller outputs 2 sets of control pulses to the micro stepping motor according to the stroke of the push rod. One set of pulses corresponds to the long probe, and one set corresponds to the short probe. The motor rotates clockwise to drive the The rod moves down, and the push rod moves to drive the descaling blade to move down. When performing descaling and return operations, the downhole controller outputs 2 sets of control pulses to the micro-stepping motor according to the stroke of the push rod. One set of pulses corresponds to the long probe, and one set corresponds to the section probe. The rod moves upward, and the movement of the push rod drives the descaling scraper to move upward, and the descaling scraper is retracted.

The parts not described in the description are prior art or common knowledge. This embodiment is only used to illustrate the invention, but not to limit the scope of the invention. Any modifications such as equivalent replacements made by those skilled in the art to the present invention are considered to fall within the protection scope of the claims of the invention.

Claims (10)

1. An on-line monitoring system for the dissolution cavity of a salt cavern storage, comprising a ground unit (1) and a downhole unit (2). ) and a 7-core cable, in which 1# and 4# cable cores are responsible for power supply, and 2# and 5# cable cores are responsible for transmitting commands issued by the ground unit (1) and uploaded by the downhole unit (2) measurement data, the remaining cable cores are free, and the cable sheath is grounded; it is characterized in that: the downhole unit (2) includes The downhole controller (21) is used to decode and analyze the commands issued by the surface unit (1) to control the work of each module in the downhole unit (2), and at the same time analyze and process the state information in the dissolution chamber collected by the downhole unit (2) And perform encoding operations; A mode switching module (22), used for switching the downhole unit (2) between two working modes of self-inspection or measurement according to the control command; The measurement and conversion module (23) is used to measure the capacitance value and convert the capacitance value into frequency; The sensor group (24) comprises a pressure sensor (241), a temperature sensor (242) and a three-electrode capacitive sensor (243); the pressure sensor (241), the temperature sensor (242) are all connected with the downhole controller (21) Electrically connected, used to monitor the pressure and temperature in the dissolution chamber; the three-plate capacitive sensor (243) is electrically connected to the downhole controller (21) through the mode conversion module (22), measurement and conversion module (23) in turn, used for Monitor the height of the oil-water interface; The downhole Mann code conditioning circuit (25), electrically connected with the downhole controller (21), is composed of a transformer, a differential amplifier, a hysteresis comparator and a voltage stabilizing circuit, and is used to send the downhole controller (21) to the surface unit (1). ) coded downhole status information, and conditioning the uploaded signal to facilitate the transmission of the signal on the cable and overcome the influence of the cable capacitance on the signal. 2. according to claim 1, a kind of on-line monitoring system facing salt cavern storage solution cavity, it is characterized in that: described three-plate capacitive sensor (243) is a probe type sensor, and its three capacitive plates are set to Two long and one short, the height of the oil-water interface is judged by the capacitance difference between the three plates. 3. According to claim 1, an online monitoring system facing salt cavern storage solution cavity, characterized in that: the downhole unit (2) also includes two sets of descaling devices (26), one set corresponding to the three-electrode plate Two long plates of the capacitive sensor (243), another group of corresponding short plates of the three-plate capacitive sensor (243), the descaling device (26) includes a stepper motor, a pusher that is connected with the stepper motor shaft Rod and the descaling scraper that is arranged on the pole plate of three-electrode capacitive sensor (243), described stepping motor is electrically connected with downhole controller (21), is controlled by processor to work stepping motor, drives descaling by push rod. Scale scraper to descale the plate. 4. According to claim 1, an on-line monitoring system facing the dissolution cavity of salt cavern storage, characterized in that: the ground unit (1) comprises: The ground controller (11) is used to decode and analyze the roof height, temperature, and pressure information uploaded by the downhole unit (2) and send them to a remote computer, and receive and encode instructions from the remote computer; at the same time, it controls the modules of the ground unit (1) to complete corresponding Features; The ground Mann code conditioning circuit (12), electrically connected with the ground controller (11), is composed of a transformer, a differential amplifier, a hysteresis comparator and a voltage stabilizing circuit, and is used to send the ground controller (21) to the downhole unit (2). ) the coded control command issued, and the signal is adjusted to make the signal easier to transmit on the cable and overcome the influence of the cable capacitance; The depth measurement module (13) is electrically connected with the ground controller (11), and is used for phase discrimination of the depth pulse signal and counting of depth pulses. The ground controller (11) calculates the initial depth of the downhole instrument after reading the pulse count value value; The wireless communication module (14) is electrically connected with the ground controller (11), and is used to realize the information interaction between the ground unit (1) and the remote control server; The display module (15) is electrically connected with the surface controller (11), and is used to display information such as commands, initial depth of downhole instruments, measured height, temperature, pressure of the cavity roof interface, and the position of the push rod, and can also facilitate System debugging; The alarm module (16), electrically connected to the ground controller (11), includes an audible alarm and a light alarm, which are used to remind the upper limit or lower limit of the measurement of the cavity roof interface. 5. According to claim 4, a kind of online monitoring system facing salt cavern storage solution cavity, it is characterized in that: said alarm module (16) includes 2 kinds of frequency sound alarm and 2 kinds of color light alarm, high frequency A loud sound and a red light indicate that the cavity roof interface has exceeded the upper limit of the measurement, and a low frequency sound and a yellow light indicate that the cavity roof interface has exceeded the lower limit of the measurement. 6. According to claim 4, a kind of on-line monitoring system facing salt cavern storage solution cavity, it is characterized in that: said ground controller (11) and downhole controller (21) select the G3CX type FPGA chip of Cyclone V series , using an embedded Nios II soft processor. 7. An on-line monitoring method for a salt cavern storage solution cavity, characterized in that: comprising the following steps: Step 1, set the cable winch, move the downhole unit, and make the capacitive sensor of the three-electrode plate be fully immersed in the diesel oil; Step 2, start the surface unit, send downhole unit self-test or measurement commands through the ground controller, and encode the control commands through the ground Mann code conditioning circuit; Step 3: The downhole controller receives and decodes the self-test or measurement command issued by the surface unit through the downhole Mann code conditioning circuit, and the control mode conversion module connects the fixed capacitor or the three-electrode capacitive sensor to the circuit, and at the same time collects the temperature in the dissolution chamber, Pressure and descaling blade position information; Step 4, based on the principle of equal-precision frequency measurement, the downhole unit measures the frequency or period of the input signal, and uploads the measured frequency or period data with Manchester encoding; Step 5, the ground controller decodes the uploaded frequency or period data, calculates the height of the interface, displays the measurement data on the LCD in real time, and transmits the measurement results to the computer through the wireless communication module. 8. An online monitoring method for salt cavern storage dissolution cavities according to claim 7, characterized in that: said step 4 also includes that the downhole controller collects the temperature value in the downhole dissolution cavity through temperature sensors and pressure sensors and pressure values, and upload them after encoding. 9. A kind of on-line monitoring method facing salt cavern storage dissolution cavity according to claim 7 or 8, characterized in that: in step 2, the command frame format sent by the ground unit to the downhole unit consists of command header, command control word, Composition of the command tail; in step 4, the data frame sent from the downhole unit to the surface unit includes not only the measured frequency or period, but also temperature value, pressure value and position information of the descaling blade. 10. An online monitoring method for salt cavern storage solution cavity according to claim 6, characterized in that: in step 3, the mode switching module connects the fixed capacitor to the circuit for system self-checking to determine the system status Is it normal? The mode conversion module connects the three-plate capacitive sensor to the circuit for oil-water interface measurement mode. According to the difference in the relative position between the three-plate capacitive sensor and the oil-water interface and the difference in capacitance, the multivibrator is used to realize the conversion from capacitance to frequency. .