Salt-cavern gas storage cavity-building oil-water interface monitoring tool and monitoring method thereof

Abstract

The invention provides a salt-cavern gas storage cavity construction oil-water interface monitoring tool which comprises a detection device, a density adjusting device, a floating device and a timing device. The detection device is used for detecting underground pressure; the density adjusting device is connected with the detection device and is used for adjusting the initial density of the detection device to be consistent with the density at the oil-water interface; the timing device is connected with the floating device and is used for controlling the floating device to start at fixed time; and the floating device is connected with the detection device and is used for increasing the buoyancy of the floating device so as to drive the detection device to float. According to the salt cavern gas storage cavity-building oil-water interface monitoring tool, the cost input of downhole operation or optical fiber tripping-in can be reduced, high economic benefits are achieved, and large-scale application can be achieved.

Description

Technical Field

[0001] The present application relates to the field of salt cavern gas storage, and in particular to a salt cavern gas storage cavity oil-water interface monitoring tool and a monitoring method thereof. Background Art

[0002] Salt cavern gas storage uses the salt rock cavity left by water-soluble mining to store oil and natural gas. At present, the caverns of salt cavern gas storage generally adopt the solution mining method, which is to build the cavity from bottom to top, transport fresh water to the bottom of the cavity, dissolve the salt layer, discharge the brine, and then gradually dissolve upwards.

[0003] In order to ensure the shape of the cavity and control the dissolution in the cavity during the cavern making process, it is necessary to inject diesel as a dissolution inhibitor at the top of the cavity through the annular space between the outer cavity making pipe and the production casing to control the dissolution rate in the cavity. The interface depth between diesel and brine in the cavity is the cavity top depth. The control of the oil-water interface is the most important link in the entire cavity making process. If the position of the oil-water interface is out of control during the cavity making process, it will cause the cavity top plate to dissolve, the cavity shape to be uncontrolled, the cavity volume to lose, and the production casing to dissolve through, which will destroy the stability of the cavity.

[0004] At present, the interface detection of diesel and fresh water or fresh water and brine mixture is usually achieved by the following two methods:

[0005] Calculation method: Calculate the annular volume between the outer tube and the casing and the annular volume between the outer tube and the open hole section, and then calculate the oil injection volume to reach the predetermined depth to form the oil-water interface; or determine the position of the oil-water interface by the sound velocity calculation method. However, the above calculation method can only determine the approximate position of the oil-water interface, and it is difficult to accurately locate it.

[0006] Electrical measurement method: mainly uses optical fiber to monitor the oil-water interface, that is, at the beginning of the cavity creation, the optical fiber is fixed on the outer wall of the cavity creation outer tube and lowered from the ground into the well. Although optical fiber monitoring of the oil-water interface has high accuracy, it needs to be lowered into the well, which is complicated to operate and has high costs, which greatly limits its large-scale application in salt cavern gas storage. Summary of the invention

[0007] In order to reduce cost investment, this application proposes a salt cavern gas storage cavity oil-water interface monitoring tool and monitoring method, and adopts the following technical solutions:

[0008] In the first aspect, the present application discloses a salt cavern gas storage cavity oil-water interface monitoring tool, including a detection device, a density adjustment device, a floating device and a timing device;

[0009] The detection device is used to detect downhole pressure;

[0010] The density adjustment device is connected to the detection device and is used to adjust the initial density of the detection device to be consistent with the density at the oil-water interface;

[0011] The timing device is connected to the floating device and is used to control the timing start of the floating device;

[0012] The floating device is connected to the detection device and is used to increase its own buoyancy to drive the detection device to float.

[0013] Optionally, the floating device includes a gas generator and an air bag;

[0014] The airbag is connected to the detection device;

[0015] The timing device is connected to the gas generator and is used to control the timing start of the gas generator;

[0016] The gas generator is connected to the airbag and is used to supply gas into the airbag.

[0017] Optionally, the floating device further includes an airbag restraint assembly;

[0018] The airbag restraint assembly is connected to the detection device;

[0019] The airbag is arranged in the airbag restraint assembly.

[0020] Optionally, the airbag restraint assembly includes a restraint portion, and a plurality of grids are provided on the restraint portion.

[0021] Optionally, the gas generator contains one or more reactants, and the one or more reactants can react alone or with each other to generate gas to inflate the airbag.

[0022] Optionally, a pressure relief valve is provided on the airbag to relieve pressure on the airbag.

[0023] Optionally, the density adjustment device includes a density adjustment portion and a connecting pipe;

[0024] The density adjustment part is connected to the detection device through the connecting pipe;

[0025] The density adjustment part has a plurality of density adjustment materials therein.

[0026] Optionally, the floating device, the detection device and the density adjustment device are arranged in sequence from top to bottom along the vertical direction.

[0027] Optionally, a first connecting portion is provided at the bottom of the detection device, and the connecting tube is detachably connected to the first connecting portion.

[0028] Optionally, a second connecting portion is provided on the top of the detection device, and the floating device is detachably connected to the second connecting portion.

[0029] In a second aspect, the present application discloses an oil-water interface monitoring method, based on the salt cavern gas storage cavity oil-water interface monitoring tool as described in the first aspect, comprising:

[0030] Based on the depth range of the oil-water interface during the cavity creation process, the gas generator and timing device are set in advance;

[0031] Lower the tool as a whole into the cavity through the annular space between the production casing and the outer wall of the cavity-making outer tube;

[0032] When the detection device is stable at the oil-water interface, the timing device controls the floating device to start at a fixed time to increase its own buoyancy and drive the detection device to float;

[0033] Based on the data in the detection device, the pressure value at the oil-water interface is obtained;

[0034] The depth of the oil-water interface is obtained based on the pressure value at the oil-water interface, the wellhead pressure value and the diesel density.

[0035] Optionally, obtaining the oil-water interface depth based on the pressure value at the oil-water interface, the wellhead pressure value and the diesel density includes:

[0036] According to the pressure value at the oil-water interface, the wellhead pressure value and the diesel density, the oil-water interface depth is calculated based on the following formula:

[0037] h=(H1-H0) / ρg;

[0038] Among them, h is the depth of the oil-water interface, H1 is the pressure value at the oil-water interface, H0 is the pressure value at the wellhead, ρ is the diesel density, and g is the gravitational acceleration.

[0039] Based on the above technical solution, the beneficial effects of this application compared with the prior art are as follows:

[0040] The salt cavern gas storage cavity oil-water interface monitoring tool in the embodiment of the present application detects the pressure value at the oil-water interface through a detection device, and returns the detection device to the wellhead within a certain time interval, and calculates the depth of the oil-water interface through the detected pressure value at the oil-water interface, thereby monitoring the depth of the oil-water interface. It meets the requirements for oil-water interface monitoring in the cavity making process, is beneficial to protect the cavity top plate, control the cavity morphology, improve the cavity making quality, and ensure the safe operation of the salt cavern gas storage. Compared with conventional oil-water interface monitoring technology, the detection device will automatically return after each measurement to transmit the pressure value at the oil-water interface to the wellhead, which can reduce the cost investment of downhole operations or lowering optical fibers, has strong economic benefits, and can be applied on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the structure of the oil-water interface monitoring tool for the salt cavern gas storage cavity in the embodiment of the present application;

[0042] Figure 2 It is a schematic diagram of oil-water interface monitoring in the salt cavern gas storage cavity in the embodiment of the present application.

[0043] Description of reference numerals:

[0044] 1. Detection device; 11. First connection part; 12. Second connection part; 2. Floating device; 21. Gas generator; 22. Airbag; 23. Airbag restraint assembly; 231. Restraint part; 231a. Grid; 3. Timing device; 4. Density adjustment device; 41. Density adjustment part; 411. Density adjustment particles; 42. Connecting pipe; 100. Production casing; 200. External tube for cavity making; 300. Internal tube for cavity making; 400. Brine; 500. Fresh water; 600. Diesel; 700. Interface monitoring tool; 800. Cavity. DETAILED DESCRIPTION

[0045] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0046] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present disclosure. Instead, they are merely examples of devices and methods consistent with some aspects of the present disclosure as detailed in the appended claims.

[0047] In the description of the present disclosure, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present disclosure. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0048] In the description of the present disclosure, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present disclosure can be understood according to specific circumstances.

[0049] In the prior art, when indirectly calculating the depth of the oil-water interface using the speed of sound calculation method, it is inevitable that it will be interfered by various impurities, resulting in a large error. When using the electrical measurement method to monitor the depth of the oil-water interface, although the optical fiber can be used to accurately transmit the depth value of the oil-water interface downhole to the ground, the operation of inserting the optical fiber downhole is difficult and the cost is high, which limits the large-scale application of the monitoring device.

[0050] The inventors have found that detecting the pressure value at the oil-water interface and then calculating to further obtain the depth of the oil-water interface is a method that can more accurately and quickly obtain the depth of the oil-water interface. However, in order to transmit the pressure value at the oil-water interface to the wellhead, it is usually necessary to set up a series of detection devices, data acquisition devices and related signal transmission devices, which further increases the cost of monitoring the depth of the oil-water interface. Therefore, how to achieve timely acquisition of the pressure value at the oil-water interface at the wellhead and at the same time reduce the cost caused by setting up optical fibers is a major problem in monitoring the oil-water interface during the current cavity making process.

[0051] Therefore, in order to solve the above-mentioned problems in the prior art and reduce the cost of oil-water interface monitoring in salt cavern gas storage, the present application embodiment provides a salt cavern gas storage cavity oil-water interface monitoring tool and monitoring method. The following is a detailed description of various specific implementation methods of the salt cavern gas storage cavity oil-water interface monitoring tool and monitoring method provided in the present disclosure embodiment.

[0052] Reference Figure 1 to Figure 2 , the embodiment of the present application is a salt cavern gas storage cavity oil-water interface monitoring tool, including a detection device 1, a density adjustment device 4, a floating device 2 and a timing device 3. The density adjustment device 4 is connected to the detection device 1, and is used to adjust the initial density of the detection device 1 to be consistent with the density at the oil-water interface. The floating device 2 is connected to the detection device 1, and is used to float the detection device 1. The timing device 3 is connected to the floating device 2, and is used to control the timing start of the floating device 2. Specifically, the time interval set by the timing device 3 should meet the detection device 1 from the wellhead down to the oil-water interface downhole, so that the detection device 1 measures the pressure at the oil-water interface, and then performs the floating recovery process.

[0053] After the monitoring tool is placed from the wellhead into the well, the detection device 1 can float up within a certain time interval, so as to obtain the oil-water interface pressure value at the wellhead. On the one hand, the oil-water interface pressure value can be obtained at the wellhead without the need to manually install the detection device 1 in the well, which reduces the difficulty of oil-water interface depth detection; on the other hand, it reduces the cost of inserting optical fiber into the well, making the oil-water interface depth detection process more economical and easy to promote.

[0054] Reference Figure 1 , the detection device 1 is specifically a storage-type downhole pressure gauge, and the detection device 1 has a first connection part 11 at the bottom and a second connection part 12 at the top, wherein the first connection part 11 is connected to the density adjustment device 4, and the second connection part 12 is connected to the floating device 2. Specifically, the density adjustment device 4 can be connected to the first connection part 11 by welding, threaded connection, clamping, riveting, etc., and correspondingly, the floating device 2 can be connected to the second connection part 12 by one of the above connection methods. That is, as long as the density adjustment device 4 can be connected to the first connection part 11, the floating device 2 can be connected to the second connection part 12. Thereby, it is convenient to divide the interface monitoring tool into three parts as a whole, and the three parts are detachable, which improves the convenience of use.

[0055] It should be understood that, in an optional embodiment, reference Figure 1 In order to better maintain the balance and stability of the detection device 1 during the descent process, the density adjustment device 4 is connected to the first connection part 11 at the bottom of the detection device 1, and the floating device 2 is connected to the second connection part 12 at the top of the detection device 1, that is, the floating device 2, the detection device 1 and the density adjustment device 4 are arranged in sequence from top to bottom along the vertical direction, so that the tool as a whole is in a vertical state whether it is floating or descending. This is conducive to the smooth descent or floating of the tool underground, and it will not be stuck in the annular space of the outer wall of the production casing 100 and the cavity outer tube 200.

[0056] In an alternative embodiment, referring to Figure 1 The floating device 2 includes a gas generator 21 and an airbag 22. The airbag 22 is sealed and connected to the second connecting portion 12 at the upper end of the detection device 1. The timing device 3 is connected to the gas generator 21 to control the timing start of the gas generator 21. The gas generator 21 is connected to the airbag 22 to supply gas into the airbag 22. Therefore, after the timing device 3 is initially set, the timing device 3 can control the timing start of the gas generator 21 after a certain time interval. Subsequently, the gas generated in the gas generator 21 is filled into the airbag 22, and the volume of the airbag 22 increases and expands, thereby increasing its own buoyancy. When its buoyancy increases to a certain extent, it drives the detection device 1 to float. Thereby, the pressure value at the oil-water interface is transmitted to the wellhead in a low-cost manner.

[0057] In an optional embodiment, the airbag 22 and the detection device 1 can be sealed by an O-ring or other materials that can achieve sealing. The airbag 22 can be a rubber sealed bag. The shape and thickness of the airbag 22 are designed as required to meet the oil-water interface monitoring requirements of different well depths.

[0058] In an optional embodiment, the gas generator 21 may be a chemical reaction type gas generator 21, a hydrolysis electrolysis type gas generator 21, etc. In this embodiment, the gas generator 21 is a chemical reaction type gas generator 21, that is, the gas generator 21 contains one or more reactants, and the one or more reactants can react alone or with each other to produce gas to expand the airbag 22. Specifically, the chemical reaction type gas generator 21 in this embodiment is preferably a solid-liquid generation method, that is, a method of using liquid and solid to react to produce gas, without the need for additional catalysts or heating, and can react under underground conditions. Specifically, it can be calcium hypochlorite and hydrogen peroxide, or a soluble acid and sodium bicarbonate.

[0059] Of course, in other embodiments, the gas generator 21 can also be set to a solid-solid generation mode or a liquid-liquid generation mode, as long as the two reactants can contact each other and react to generate gas. Of course, the number of reactants can also be one, such as a hydrolysis electrolysis type gas generator 21, the reactant is water, hydrogen and oxygen are generated through the electrolysis reaction of water, and the amount and stability of the generated gas can be controlled by changing the voltage and current.

[0060] It should be noted that in this embodiment, the timing device 3 is preferably a timer, that is, it can start the gas generator 21 at a certain time interval to generate gas. It should be understood that in other embodiments, the timing device 3 can also be a chemical substance, such as a barrier wrapped around the reactant, which can block the reactant before the monitoring tool reaches the oil-water interface as a whole, so that it does not react. The barrier can melt by itself during the descent of the monitoring tool. When the monitoring tool reaches the oil-water interface, the barrier is completely melted, allowing the reactant to react, thereby releasing gas to expand the airbag 22, so as to increase its own buoyancy and drive the detection device 1 to float up.

[0061] It should be understood that the thickness of the airbag 22 mainly affects the pressure of the airbag 22 when it expands, that is, under the same conditions, the thicker the airbag 22, the greater the pressure when it expands to a certain volume. When selecting the airbag 22, it should be avoided that the thickness of the airbag 22 is too large, which will lead to too high expansion pressure or inability to expand downhole. However, the thickness of the airbag 22 cannot be too small, which may easily lead to its low strength and accidental leakage, causing the monitoring tool to fail to return to the wellhead as a whole. When actually selecting the airbag 22, the appropriate size and thickness of the airbag 22 can be determined experimentally based on the overall weight of the monitoring tool and the approximate range of pressure at the oil-water interface, so that the tool as a whole can float to the wellhead.

[0062] In an alternative embodiment, referring to Figure 1 As shown, the floating device 2 also includes an airbag 22 constraint assembly, and the airbag 22 constraint assembly is also connected to the second connecting portion 12 at the top of the detection device 1, and the connection method can be any one of welding, clamping, threaded connection, and riveting. The airbag 22, the gas generator 21 and the timing device 3 are all arranged in the airbag 22 constraint assembly. Specifically, the airbag 22 constraint assembly includes a constraint portion 231, which is connected to the second connecting portion 12. The constraint portion 231 is specifically tubular or cylindrical, and a plurality of grids 231a are provided on the constraint portion 231. The material of the constraint portion 231 is a light-density metal with a certain strength, such as titanium alloy, aluminum alloy, etc. Specifically, in this embodiment, the constraint portion 231 is specifically a screen tube, on which several grids 231a are provided. Of course, in other embodiments, the constraint portion 231 can also be other shapes, such as spherical.

[0063] Since the detection device 1 is lowered into the annular space between the production casing 100 and the outer wall of the cavity outer tube 200, the annular space is limited. If the airbag 22 expands without restriction, it is very likely that the expansion volume of the airbag 22 is too large and encounters resistance in the annular space, making it impossible for the detection device 1 to return to the wellhead. The airbag 22 constraint assembly can ensure that the airbag 22 expands within a certain circumferential range. When the inner diameter range of the constraint part 231 is reached, the airbag 22 mainly expands axially along the constraint part 231, greatly reducing the risk of encountering resistance, so that the tool as a whole can return to the wellhead smoothly.

[0064] In an alternative embodiment, referring to Figure 1 As shown, a pressure relief valve is provided on the air bag 22. When the tool returns to the wellhead, the pressure of the air bag 22 can be actively relieved on the ground through the pressure relief valve.

[0065] In an alternative embodiment, referring to Figure 1As shown, the density adjustment device 4 includes a density adjustment part 41 and a connecting tube 42. The density adjustment part 41 is connected to the detection device 1 through the connecting tube 42. Specifically, the connecting tube 42 is in the shape of a cylindrical tube, and the top of the connecting tube 42 is connected to the first connecting part 11, and the connecting tube 42 can be threadedly connected to the first connecting part 11. The density adjustment part 41 is in the shape of an ellipsoid and extends from the bottom of the connecting tube 42. The density adjustment part 41 contains a plurality of density adjustment particles 411, and the density adjustment particles 411 can be made of ceramsite, glass, or plastic, and the overall density of the tool can be adjusted by adjusting the particle size and whether it is hollow. Furthermore, the connecting tube 42 can be hollow and connected to the density adjustment part 41, so that the density adjustment particles 411 can be passed from the top of the connecting tube 42 into the density adjustment part 41.

[0066] The density regulating part 41 may also be a substance that can react with the mixture of fresh water 500 / brine 400 and fresh water 500, such as a cationic surfactant: for example, hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), etc. These cationic surfactants form micelle structures at the oil-water interface and can adjust the density at the interface; or polymer micelles: for example, polymers such as sodium polyacrylate (PAA-Na) and polyvinyl alcohol (PVA), which form micelle structures in brine 400 or fresh water 500 and stabilize at the oil-water interface, thereby achieving density regulation; or water-soluble polymers: for example, polyvinyl alcohol (PVA), polyvinyl ketone (PVP), etc. These water-soluble polymers can dissolve in water and interact with the oil-water interface to achieve the purpose of density regulation. When used specifically, a suitable density regulator can be selected according to actual needs and conditions.

[0067] By setting the density adjustment device 4, the density of the tool as a whole is greater than the density of diesel 600 but less than the density of fresh water 500. Therefore, after the tool as a whole is put into the well, when it descends to the oil-water interface, since the oil-water interface is the junction of diesel 600 and fresh water 500 / or fresh water 500+brine 400, the density of the tool as a whole is slightly equal to the density at the oil-water interface, so it is stable at the oil-water interface. At this time, the detection device 1 stably detects the pressure at the oil-water interface.

[0068] Reference Figure 2As shown, during the cavern making process of the salt cavern gas storage, fresh water 500 is transported to the bottom of the cavity along the annular space between the outer cavity making pipe 200 and the inner cavity making pipe 300 at the top of the cavity 800, and the brine 400 is discharged after dissolving the salt layer, and then gradually dissolved upward. At the same time, diesel 600 is injected as a dissolving agent through the annular space between the outer cavity making pipe 200 and the production casing 100 at the top of the cavity 800. When monitoring the oil-water interface of the salt cavern gas storage cavity, the interface monitoring tool 700 is lowered from the annular space of the outer wall of the production casing 100 and the outer cavity making pipe 200. Due to its own gravity, the interface monitoring tool 700 will continue to descend along the annular space until it reaches the depth where the diesel 600 and fresh water 500 / fresh water 500 and brine 400 are mixed, that is, the oil-water interface. Under the action of the density adjustment device 4, the interface monitoring tool 700 is stabilized at the oil-water interface until the timing device 3 controls the gas generator 21 to start generating gas, thereby expanding the airbag 22, increasing the buoyancy of the interface monitoring tool 700 as a whole, and floating up to the wellhead. The detection device 1 records the pressure value from the beginning of entering the well until it returns to the wellhead. The data of the detection device 1 is processed and analyzed at the wellhead, and the pressure value with the longest stable time is the pressure at the oil-water interface.

[0069] In a second aspect, the present application discloses an oil-water interface monitoring method, based on the salt cavern gas storage cavity oil-water interface monitoring tool as described in the first aspect, comprising:

[0070] Based on the depth range of the oil-water interface during the cavity making process, the gas generator 21 and the timing device 3 are set in advance;

[0071] The tool is lowered into the cavity 800 through the annular space between the outer wall of the production casing 100 and the outer cavity tube 200;

[0072] When the detection device 1 is stable at the oil-water interface, the timing device 3 controls the floating device 2 to start at a fixed time to increase its own buoyancy and drive the detection device 1 to float;

[0073] Based on the data in the detection device 1, the pressure value at the oil-water interface is obtained;

[0074] The depth of the oil-water interface is obtained based on the pressure value at the oil-water interface, the wellhead pressure value and the diesel 600 density.

[0075] Specifically, before placing the tool, it is necessary to first estimate the depth of the oil-water interface, and then set the gas generation amount of the gas generator 21 and the time interval to be set by the timer in advance according to the estimated value. The gas generation amount is based on the fact that the tool as a whole can return to the wellhead, and the time interval is based on the fact that the detection tool can be lowered from the wellhead to the oil-water interface.

[0076] It should be noted that the detection device 1 is specifically a storage-type downhole pressure gauge, which is in a detection state throughout the entire process of descending from the wellhead along the annular space, that is, the data obtained from the returned storage-type downhole pressure gauge should include multiple continuous pressure values. Among them, since the detection device 1 will be stable for a period of time at the oil-water interface, the pressure value with the longest stable time is the pressure at the oil-water interface.

[0077] Specifically, after obtaining the pressure value at the oil-water interface, the oil-water interface depth is calculated based on the following formula according to the pressure value at the oil-water interface, the wellhead pressure value and the density of diesel 600:

[0078] h=(H1-H0) / ρg;

[0079] Among them, h is the depth of the oil-water interface, H1 is the pressure value at the oil-water interface, H0 is the pressure value at the wellhead, ρ is the density of diesel 600, and g is the acceleration of gravity.

[0080] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is covered in a manner similar to the term "including", as explained by "including" used as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or".

Claims

1. A salt cavern gas storage cavity oil-water interface monitoring tool, characterized in that: It comprises a detection device (1), a floating device (2), a timing device (3) and a density adjustment device (4); The detection device (1) is used to detect downhole pressure; The density adjustment device (4) is connected to the detection device (1) and is used to adjust the initial density of the detection device (1) to be consistent with the density at the oil-water interface; The timing device (3) is connected to the floating device (2) and is used to control the timing start of the floating device (2); The floating device (2) is connected to the detection device (1) and is used to increase its own buoyancy to drive the detection device (1) to float upward.

2. The salt cavern gas storage cavity oil-water interface monitoring tool according to claim 1 is characterized by: The floating device (2) comprises a gas generator (21) and an air bag (22); The airbag (22) is connected to the detection device (1); The timing device (3) is connected to the gas generator (21) and is used to control the timing start of the gas generator (21); The gas generator (21) is connected to the airbag (22) and is used to supply gas into the airbag (22).

3. The salt cavern gas storage cavity oil-water interface monitoring tool according to claim 2 is characterized by: The floating device (2) also includes an air bag (22) restraint component; The airbag (22) restraint assembly is connected to the detection device (1); The airbag (22) is arranged in the airbag (22) restraint component.

4. The salt cavern gas storage cavity oil-water interface monitoring tool according to claim 3 is characterized by: The airbag (22) restraint assembly comprises a restraint portion (231), and a plurality of grids (231a) are provided on the restraint portion (231).

5. The salt cavern gas storage cavity oil-water interface monitoring tool according to any one of claims 2 to 4, characterized in that: The gas generator (21) contains one or more reactants, and the one or more reactants can react alone or with each other to generate gas to expand the airbag (22).

6. The salt cavern gas storage cavity oil-water interface monitoring tool according to any one of claims 2 to 4, characterized in that: The airbag (22) is provided with a pressure relief valve for relieving pressure from the airbag (22).

7. The salt cavern gas storage cavitation oil-water interface monitoring tool according to claim 1 is characterized by: The density adjustment device (4) comprises a density adjustment portion (41) and a connecting pipe (42); The density adjustment part (41) is connected to the detection device (1) via the connecting pipe (42); The density adjustment portion (41) contains a plurality of density adjustment materials.

8. The salt cavern gas storage cavitation oil-water interface monitoring tool according to claim 1 is characterized by: The floating device (2), the detection device (1) and the density adjustment device (4) are arranged in sequence from top to bottom along the vertical direction.

9. The salt cavern gas storage cavitation oil-water interface monitoring tool according to claim 7, characterized in that: The bottom of the detection device (1) is provided with a first connecting portion (11), and the connecting pipe (42) is detachably connected to the first connecting portion (11).

10. The salt cavern gas storage cavitation oil-water interface monitoring tool according to claim 1, characterized in that: The top of the detection device (1) is provided with a second connecting portion (12), and the floating device (2) is detachably connected to the second connecting portion (12).

11. A method for monitoring an oil-water interface, based on the salt cavern gas storage cavity oil-water interface monitoring tool according to any one of claims 1 to 10, characterized in that: include: Based on the depth range of the oil-water interface during the cavity making process, a gas generator (21) and a timing device (3) are set in advance; Lowering the entire tool into the cavity (800) through the annular space between the outer walls of the production casing (100) and the cavity-making outer tube (200); When the detection device (1) is stabilized at the oil-water interface, the timing device (3) controls the floating device (2) to start at a fixed time, so as to increase its own buoyancy and drive the detection device (1) to float upward; Based on the data in the detection device (1), the pressure value at the oil-water interface is obtained; The depth of the oil-water interface is obtained based on the pressure value at the oil-water interface, the wellhead pressure value and the density of diesel (600).

12. The oil-water interface monitoring method according to claim 11, characterized in that: The step of obtaining the depth of the oil-water interface based on the pressure value at the oil-water interface, the wellhead pressure value and the density of the diesel (600) comprises: According to the pressure value at the oil-water interface, the wellhead pressure value and the density of diesel (600), the depth of the oil-water interface is calculated based on the following formula: h=(H1-H0) / ρg; Where, h is the depth of the oil-water interface, H1 is the pressure at the oil-water interface, H0 is the pressure at the wellhead, ρ is the density of diesel (600), and g is the acceleration of gravity.

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