A method and device for detecting the sealing property of a rock salt solution cavity CO2 geological storage

Abstract

The application provides a rock salt solution cavity CO2 geological storage sealing detection method and device, after nitrogen is injected into the annulus between the production casing and the test pipe column to form gas-water two-phase distribution, temperature profile and pressure profile from the wellhead to the top of the cavity are obtained; the gas-water interface depth of the gas-water two-phase distribution is identified according to the temperature profile; the amplitude of the abnormal signal is obtained based on the pressure profile; the annulus gas column volume is calculated based on the gas-water interface depth and the wellbore size, and the leakage rate of the amount of gas material in the annulus with time and the corresponding change trend are determined in combination with the wellhead pressure and the wellhead temperature; if the above obtained parameters meet the preset sealing condition, it is determined that the sealing is qualified. The method realizes high sensitivity, high reliability and quantitative detection of the sealing performance of the casing shoe of the rock salt solution cavity CO2 geological storage system through the coupling judgment of the three parameters of the temperature profile, the pressure profile frequency domain characteristics and the gas leakage rate.

Description

Technical Field

[0001] This application relates to the field of CO2 geological storage technology, and more specifically, to a method and apparatus for detecting the sealing performance of CO2 geological storage in rock salt cavities. Background Technology

[0002] Rock salt cavities are considered ideal sites for geological carbon dioxide sequestration due to their low permeability, self-healing ability, and enormous gas storage capacity. Artificial cavities formed in deep rock salt formations through water-soluble extraction are characterized by structural stability and good sealing properties, making them suitable for long-term sequestration of industrially captured carbon dioxide. This is of great significance for achieving carbon peaking and carbon neutrality goals.

[0003] Currently, in rock salt cavity carbon dioxide sealing projects, conventional methods for testing sealing performance typically involve injecting pressurized gas or liquid into the cavity and monitoring wellhead pressure changes or using downhole acoustic or electromagnetic flaw detection tools to detect leaks in the casing and cavity walls. This method draws on testing experience from natural gas storage facilities, evaluating sealing performance through phased pressure testing and holding tests.

[0004] However, existing sealing tests cannot monitor the sealing status of the production casing shoe, a critical weak link, in real time and dynamically during the carbon dioxide injection process. In particular, they cannot quantitatively distinguish between the annular fluid thermal expansion effect, rock salt creep, and pressure and interface changes caused by actual leakage, resulting in large errors in leakage rate calculation. Summary of the Invention

[0005] The purpose of this application is to provide a method and apparatus for detecting the sealing performance of CO2 geological storage in rock salt cavities. This method uses the coupling of three parameters—temperature profile, pressure profile frequency domain characteristics, and gas leakage rate—to achieve highly sensitive and reliable quantitative detection of the sealing performance of the casing shoe in a rock salt cavity CO2 storage system.

[0006] Firstly, a method for detecting the sealing performance of CO2 geological sequestration in rock salt cavities is provided, the method including: After nitrogen is injected into the annulus between the production casing and the test string to form a gas-water two-phase distribution, temperature and pressure profiles from the wellhead to the top of the cavity are obtained. The gas-water interface depth of the gas-water two-phase distribution is identified based on the temperature profile; the frequency domain transformation is performed on the pressure change sequence at the casing shoe extracted from the pressure profile to obtain the amplitude of the abnormal signal. The volume of the annular air column is calculated based on the gas-water interface depth and wellbore dimensions. Combined with wellhead pressure and wellhead temperature, the leakage rate and corresponding trend of the amount of gaseous substances in the annulus over time are determined. When the fluctuation of the gas-water interface depth is less than a predetermined threshold, the amplitude of the abnormal signal is lower than the set statistical multiple of the background noise spectrum, and the leakage rate trend approaches zero, the seal is deemed qualified.

[0007] In one possible implementation, the method further includes, prior to the formation of a gas-water two-phase distribution by injecting nitrogen into the annulus between the production casing and the test string: Distributed fiber optic sensors are installed at equal intervals along the axial direction on the outer wall of the production casing. The installation point of each fiber optic sensor is mechanically fixed by the casing coupling, and the sensor signal transmission fiber is connected to the surface demodulator. After well completion, the test string is run in, and the annulus is formed between the production casing and the test string.

[0008] In one possible implementation, identifying the gas-water interface depth based on this temperature profile includes: Calculate the temperature gradient along the depth of the wellbore; The depth at which the calculated temperature gradient is reversed from a positive value to a negative value, or from a negative value to a positive value, is determined as the gas-water interface depth.

[0009] In one possible implementation, the pressure change sequence at the casing shoe is extracted from this pressure profile, including: In the pressure profile, the depth coordinates of the production sleeve shoe are located, and the pressure values ​​at the depth coordinates are extracted sequentially from the pressure profiles at multiple consecutive sampling times, and arranged in chronological order to form a sequence of pressure changes over time.

[0010] In one possible implementation, the amplitude of the abnormal signal is obtained by frequency domain transformation of the pressure change sequence at the casing shoe extracted from the pressure profile, including: Perform a fast Fourier transform on the pressure change sequence to obtain the pressure fluctuation spectrum; Target frequency points with frequencies higher than a set high-frequency threshold are identified from the pressure fluctuation spectrum, and the amplitude corresponding to each target frequency point is extracted. The maximum amplitude is taken as the amplitude of the abnormal signal.

[0011] In one possible implementation, the annular air column volume is calculated based on the gas-water interface depth and wellbore dimensions, including: Calculate the annular cross-sectional area based on the geometric parameters of the production casing and the test string; The volume of the annular air column is obtained by multiplying the difference between the gas-water interface depth and the wellhead reference depth by the cross-sectional area of ​​the annulus.

[0012] In one possible implementation, based on the annular air column volume, wellhead pressure, and wellhead temperature, the leakage rate and corresponding trend of the amount of gaseous material in the annulus over time are determined, including: At each sampling moment, according to the ideal gas law, the product of the wellhead pressure and the volume of the annular air column is divided by the product of the gas constant and the wellhead temperature to obtain the amount of gaseous substance in the annulus at that sampling moment. The time-difference derivative of the gaseous substance quantity sequence at multiple consecutive sampling times is used to obtain the rate of change of gaseous substance quantity, which is the leakage rate. The leakage rate is then arranged in chronological order to obtain the trend of leakage rate change over time.

[0013] Secondly, a sealing performance testing device for CO2 geological sealing in rock salt cavities is provided, the device comprising: The acquisition unit is used to acquire the temperature and pressure profiles from the wellhead to the top of the cavity after nitrogen is injected into the annulus between the production casing and the test string to form a gas-water two-phase distribution. The identification unit is used to identify the gas-water interface depth of the gas-water two-phase distribution based on the temperature profile. The acquisition unit is also used to perform frequency domain transformation on the pressure change sequence at the casing shoe extracted from the pressure profile to obtain the amplitude of the abnormal signal. The determination unit is used to calculate the volume of the annular air column based on the gas-water interface depth and wellbore size, and to determine the leakage rate and corresponding trend of the amount of gaseous substances in the annulus over time by combining the wellhead pressure and wellhead temperature; and to determine that the seal is qualified when the fluctuation of the gas-water interface depth is less than a predetermined threshold, the amplitude of the abnormal signal is lower than a set statistical multiple of the background noise spectrum, and the trend of the leakage rate tends to zero.

[0014] Thirdly, an electronic device is provided, which includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory, used to store computer programs; When a processor executes a program stored in memory, it implements any of the steps described in the first aspect above.

[0015] Fourthly, a computer-readable storage medium is provided, wherein a computer program is stored therein, and when executed by a processor, the computer program implements the steps of any of the methods described in the first aspect above.

[0016] Embodiments of the present application provide a method and apparatus for detecting the sealing performance of CO₂ geological storage in rock salt cavities. In the method, after nitrogen is injected into the annulus between the production casing and the test string to form a gas-water two-phase distribution, the temperature profile and pressure profile from the wellhead to the top of the cavity are obtained; the depth of the gas-water interface of the gas-water two-phase distribution is identified according to the temperature profile; frequency domain transformation is performed on the pressure change sequence at the casing shoe extracted from the pressure profile to obtain the amplitude of the abnormal signal; the volume of the annular gas column is calculated based on the depth of the gas-water interface and the wellbore size, and combined with the wellhead pressure and wellhead temperature, the leakage rate of the amount of gas substances in the annulus over time and the corresponding change trend are determined; when the fluctuation of the gas-water interface depth is less than a predetermined threshold, the amplitude of the abnormal signal is lower than a set statistical multiple of the background noise spectrum, and the change trend of the leakage rate tends to zero, it is determined that the sealing is qualified. The method realizes high-sensitivity and high-reliability quantitative detection of the sealing performance at the casing shoe of the carbon dioxide storage system in rock salt cavities through the coupling judgment of three parameters: temperature profile, pressure profile frequency domain characteristics and gas leakage rate. Description of Drawings

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application are briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained from these drawings without creative effort.

[0018] Figure 1 is a schematic flow chart of a method for detecting the sealing performance of CO₂ geological storage in a rock salt cavity provided by an embodiment of the present application; Figure 2 is a schematic structural diagram of a device for detecting the sealing performance of CO₂ geological storage in a rock salt cavity provided by an embodiment of the present application; Figure 3 is a schematic structural diagram of an electronic device provided by an embodiment of the present application. Detailed Description

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Unless otherwise defined, the technical or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art. The words "first," "second," and similar terms used in this application do not indicate any order, quantity, or importance, but are only used to distinguish different components. The words "comprising" or "including," etc., mean that the element or object preceding the word covers the element or object listed after the word and its equivalents, but do not exclude other elements or objects. The words "connected," "coupled," or "connected," etc., are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up," "down," "left," "right," etc., are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0020] The sealing test method for CO2 geological sealing in rock salt cavities provided in this application embodiment involves injecting nitrogen into the annulus between the production casing and the test tubing to form a stable gas-water two-phase distribution. Distributed fiber optic sensors are used to continuously acquire temperature and pressure profiles, thereby identifying the gas-water interface depth, analyzing the pressure fluctuation spectrum, and calculating the leakage rate and its changing trend in conjunction with the gas state equation. Finally, the sealing is determined to be qualified based on a comprehensive multi-parameter criterion.

[0021] The wellbore structure implementing the method described in this application may include: a vertically or directionally drilled wellbore, into which a production casing is run, and which is consolidated with the formation via a cement sheath. The bottom of the production casing is the production casing shoe, i.e., the lowest point of the casing. A test string is run into the production casing; the test string is used to inject or extract carbon dioxide into the rock salt cavity. The annular space between the production casing and the test string is called the annulus.

[0022] Distributed fiber optic sensors are installed at equal intervals along the axial direction on the outer wall of the production casing. These sensors function as both temperature and pressure sensors. Each sensor is mechanically secured at its mounting point using casing couplings to prevent displacement or damage during downhole operation. The sensor signal transmission fiber optic cable is led along the outer wall of the production casing to the wellhead and connected to a surface demodulator. The surface demodulator emits optical pulses, receives backscattered light signals, and demodulates and calculates the temperature and pressure values ​​at various points along the fiber, generating temperature and pressure profiles. The surface demodulator is also equipped with a data acquisition and processing unit for storing and analyzing monitoring data, performing frequency domain transformation, leakage rate calculation, and qualification determination.

[0023] The wellhead is also equipped with a nitrogen injection line connected to the annulus, featuring a pressure control valve, flow meter, and temperature sensor for injecting nitrogen into the annulus and monitoring the pressure, flow rate, and temperature at the annulus inlet in real time. The annulus outlet line is similarly equipped with a throttle valve and flow meter to regulate the discharge rate and monitor the discharge flow. The test string has independent injection and depressurization systems.

[0024] The sealing test method of this application is divided into a preparation stage and an application stage.

[0025] Preparation Phase: Before running the production casing into the well, install distributed fiber optic sensors along its outer wall and secure them with casing couplings, connecting the transmission fiber optic cable to the surface demodulator. After well completion, run the test string to form the annulus. Install the nitrogen injection and venting system and various surface instruments.

[0026] Application Phase: First, nitrogen is injected into the annulus to displace the brine, causing the gas-water interface to drop to a predetermined depth below the production casing shoe. After stabilization, a distributed fiber optic monitoring system is activated to acquire temperature and pressure profiles at a set sampling frequency. The data processing unit automatically identifies the gas-water interface depth based on the temperature profile and extracts the pressure change sequence at the casing shoe based on the pressure profile, obtaining the amplitude of abnormal signals through frequency domain transformation. Simultaneously, the annular air column volume is calculated using the gas-water interface depth and wellbore dimensions. Combined with wellhead pressure and temperature, the amount of gaseous matter in the annulus changes over time based on the gas state equation, thus obtaining the leakage rate and its trend. After continuous monitoring for a sufficient period, the gas-water interface depth fluctuation value, abnormal signal amplitude, and leakage rate trend are compared with their respective thresholds. If all meet the qualification conditions, the seal is deemed qualified.

[0027] The preferred embodiments of this application are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit this application. Furthermore, the embodiments and features in the embodiments of this application can be combined with each other without conflict.

[0028] Figure 1This is a flowchart illustrating a method for detecting the sealing performance of CO2 geological sealing in rock salt cavities, as provided in an embodiment of this application. Figure 1 As shown, the method may include: Step S110: After injecting nitrogen into the annulus between the production casing and the test string to form a gas-water two-phase distribution, obtain continuous temperature and pressure profiles from the wellhead to the top of the cavity.

[0029] Specifically, after well completion, the annulus is filled with the original brine. At the start of monitoring, high-purity nitrogen is injected into the annulus through the nitrogen injection line at the wellhead, while the annulus outlet choke valve is opened to control the discharge flow. Nitrogen is less dense than brine and gradually accumulates upwards during injection, displacing the brine downwards. By controlling the injection and discharge rates, the gas-water interface slowly descends. When the interface logging tool or fiber optic monitoring system shows that the gas-water interface depth has reached a predetermined depth below the production casing shoe (e.g., 5 to 10 meters, the specific value is set according to well conditions and is not a limitation of this invention), discharge is stopped, and the nitrogen pressure is kept constant to stabilize the interface at that depth. At this point, a stable two-phase distribution with gas above and water below is formed in the annulus: a nitrogen column above the interface and a brine column below the interface.

[0030] In some embodiments, the temperature and pressure profiles are acquired by distributed fiber optic sensors pre-embedded axially along the outer wall of the production casing. These distributed fiber optic sensors possess both temperature and pressure sensing functions; the acquisition method involves sequentially collecting temperature and pressure signals at a set sampling frequency, and then demodulating them using a ground-based demodulator to generate synchronized temperature and pressure profiles.

[0031] In practice, the ground demodulator transmits optical pulses into the optical fiber and receives the Raman scattered light (sensitive to temperature) and Brillouin scattered light (sensitive to temperature and strain, which can be converted into pressure) returning along the fiber. The temperature and pressure values ​​at various depths along the wellbore are then calculated. A temperature profile is formed by using depth as the x-axis and temperature as the y-axis; a pressure profile is formed by using depth as the x-axis and pressure as the y-axis.

[0032] As a preferred embodiment, the sampling frequency can be adjusted between once per minute and once every ten minutes. More preferably, the sampling frequency can be adaptively adjusted according to the real-time fluctuation amplitude of the gas-water interface depth. When the ground demodulator detects an increase in the amplitude of gas-water interface depth fluctuations (indicating a possible significant change in the system), the system automatically increases the sampling frequency to capture rapidly changing dynamic processes; conversely, when the amplitude of gas-water interface depth fluctuations decreases, the system automatically decreases the sampling frequency to reduce data redundancy and power consumption. This adaptive sampling strategy optimizes data acquisition efficiency while ensuring detection accuracy.

[0033] Step S120: Identify the gas-water interface depth of the gas-water two-phase distribution based on the temperature profile; obtain the amplitude of the abnormal signal by frequency domain transformation of the pressure change sequence at the casing shoe extracted from the pressure profile.

[0034] (1) Identify the depth of the gas-water interface based on the temperature profile After obtaining the temperature profile, the depth of the gas-water interface is identified based on the characteristics of temperature profile changes. The physical principle is as follows: In a stable gas-water two-phase distribution state, the area above the interface is the gas phase distribution zone (nitrogen column). Due to the good compressibility of gas, the gas pressure exhibits an adiabatic gradient with depth, and the temperature is affected by compression or expansion; its temperature gradient with depth is related to the adiabatic process. Below the interface is the water phase distribution zone (brine column). The liquid is almost incompressible, and the pressure exhibits a hydrostatic pressure gradient with depth. The temperature is mainly controlled by the geothermal gradient of the formation, and the change is gradual. Therefore, the temperature gradient with depth in the gas column segment and the water column segment have opposite signs. The specific identification method includes the following sub-steps: The first step is to calculate the temperature gradient along the depth of the wellbore. The surface demodulator represents the temperature profile as a set of discrete depth-temperature data points, and performs differential calculations on adjacent depth points to obtain the temperature gradient value within each depth interval.

[0035] The second step involves searching downwards along the depth direction from the wellhead for the point where the sign of the temperature gradient reverses. When the temperature gradient reverses from a positive to a negative value, or vice versa, the depth at which this reversal point is located is determined as the gas-water interface depth. The gas column exhibits an adiabatic gradient due to the adiabatic expansion or compression of the gas, while the water column exhibits a geothermal gradient due to formation heat conduction. Since the signs of these gradients are opposite, the gradient reversal characteristic at the interface is very obvious, resulting in high identification accuracy.

[0036] This identification method does not rely on absolute temperature values, but only utilizes the relative changes in gradients. Therefore, it is not affected by the measurement error of the absolute temperature value inside the wellbore, and has strong robustness.

[0037] (2) Extract the pressure change sequence at the casing shoe and perform frequency domain transformation to obtain the amplitude of the abnormal signal. The pressure profile provided by the distributed fiber optic sensors includes pressure distribution information at various depths along the wellbore. This step focuses on the production casing shoe, a critical weak point, and analyzes its dynamic pressure variation characteristics over time.

[0038] First, the pressure change sequence at the casing shoe is extracted from the pressure profile. Specifically, the design depth coordinates for the manufactured casing shoe are pre-stored in the ground demodulator. At each sampling moment, the pressure profile is acquired at that depth coordinate, and the pressure value at that depth is read. Since the distributed fiber optic sensor continuously updates the pressure profile across multiple sampling moments, the pressure values ​​corresponding to the casing shoe depth coordinates at each sampling moment are extracted sequentially and arranged chronologically to form a one-dimensional pressure-time change sequence, denoted as... ,in For the first Each sampling time, This represents the pressure value at the corresponding moment at the cannula shoe.

[0039] The aforementioned pressure change sequence contains rich information about the sealing status. When the system is completely sealed, pressure fluctuations at the casing shoe mainly originate from environmental noise (such as ground equipment vibration, fluid disturbances, etc.), and its spectral characteristics are a single, stable signal with a dominant frequency. When a small leak exists, turbulence, bubble bursting, or pressure pulses generated by the fluid (nitrogen or brine) passing through the narrow gap will superimpose multiple discrete high-frequency components into the pressure signal. Therefore, these high-frequency anomalous signals can be separated from the background noise through frequency domain transformation.

[0040] The specific frequency domain transformation and abnormal signal extraction steps are as follows: Perform a Fast Fourier Transform on the above pressure change sequence. Let the length of the pressure change sequence be... The sampling time interval is The Fast Fourier Transform converts the time-domain signal into a frequency-domain representation, yielding the pressure fluctuation spectrum with a frequency resolution of [value missing]. The transformation result gives the amplitude corresponding to each frequency component.

[0041] Target frequencies higher than a set high-frequency threshold are identified from the pressure fluctuation spectrum. The high-frequency threshold can be set empirically, for example, 2 to 3 times the system's natural vibration frequency, or the upper limit of the dominant bandwidth of the background noise spectrum. After identifying these target frequencies, the amplitude corresponding to each target frequency is extracted, and the maximum amplitude is taken as the amplitude of the abnormal signal, denoted as . This amplitude reflects the intensity of high-frequency pressure fluctuations caused by the leak; a larger amplitude indicates a more severe leak.

[0042] Compared to directly observing the raw pressure signal, frequency domain transformation can extract weak, periodic, or quasi-periodic leakage characteristics from a strong noise background, greatly improving the detection sensitivity of minute leaks.

[0043] Step S130: Calculate the annular air column volume based on the gas-water interface depth and wellbore dimensions, and determine the leakage rate and corresponding trend of the amount of gaseous material in the annulus over time based on the annular air column volume, wellhead pressure and wellhead temperature.

[0044] (1) Calculate the volume of the annular air column First, calculate the annular cross-sectional area based on the geometric parameters of the production casing and the test string. Let the inner radius of the production casing be... The outer radius of the test tube is Then the cross-sectional area of ​​the annulus Calculate using the following formula: ;in, and The unit is meters. The unit is square meters. These geometric parameters are known values ​​in the well completion design.

[0045] Then, determine the difference between the gas-water interface depth and the wellhead reference depth. Let the wellhead reference depth (usually taken as the surface or rotary table surface) be... The depth of the gas-water interface identified is The difference between the two (Positive for downward) represents the height of the air column segment. Multiplying the annular cross-sectional area by the height of the air column segment yields the annular air column volume: In the formula, The unit is cubic meters. This volume represents the total volume of space occupied by nitrogen gas within the annulus. Because the gas-water interface may experience slight fluctuations during monitoring, the gas column volume needs to be updated in real time based on the interface depth at each sampling moment.

[0046] (2) Determine the leakage rate and trend of the amount of gaseous substances in the annulus over time. At each sampling time, the amount of nitrogen in the annulus is calculated using the ideal gas law. The ideal gas law is: ;in: The absolute pressure of the gas is expressed in Pascals. In this method, the pressure measured by the wellhead pressure sensor is used. Because the wellhead is connected to the annular air column, and the pressure distribution within the gas column is determined by the static gas column pressure gradient, but to simplify calculations and considering the limited height of the gas column, the error introduced by directly using the wellhead pressure to represent the average gas column pressure is acceptable. Alternatively, the average pressure at the midpoint of the gas column can be used. As a preferred implementation method, the wellhead pressure is used. The volume of the gas, i.e., the volume of the annular air column. The unit is cubic meters. This represents the amount of substance of a gas, expressed in moles. Let be the ideal gas constant, then we can take . . This is the absolute temperature of the gas, measured in Kelvin. The temperature is taken from the wellhead temperature sensor reading. Similarly, wellhead temperature is used as an approximation of the average gas column temperature.

[0047] Therefore, in the first At each sampling time, the amount of nitrogen in the annular atmosphere for: ; Among them, subscript Indicates the first Each sampling time. It is calculated from the gas-water interface depth at that moment.

[0048] A sequence of gaseous quantities at multiple consecutive sampling times By performing time-difference differentiation, the rate of change of the amount of gaseous substance is obtained. Let the sampling time interval be... Then the first The instantaneous rate of change at each moment is approximately: Alternatively, backward difference can be used: The physical meaning of this rate of change is the decrease (if leakage occurs) or increase (if refilling occurs) in the amount of nitrogen in the annulus per unit time. In a closed annulus without active refilling, if leakage occurs from the annulus to the formation or to the cavity, the amount of nitrogen decreases, and the rate of change is negative; its absolute value is the leakage rate (unit: moles per second). For ease of engineering application, the leakage rate can be converted to standard state volumetric flow rate or mass flow rate. The absolute value of the rate of change of the amount of gas is defined as the leakage rate. , The leakage rate at any given time is: ; Arranging the leakage rates in chronological order yields the trend of leakage rates over time. The trend curve reflects the development of leakage behavior: if the leakage is a brief release caused by initial pressure disturbance or temperature equilibrium, the leakage rate will decrease rapidly; if there is a structural leakage path, the leakage rate may remain at a high level or change slowly; if the rock salt has self-healing ability, the leakage rate may gradually decrease and tend to zero.

[0049] Step S140: Based on the fluctuation of the gas-water interface depth over time, the amplitude of the abnormal signal, and the trend of the leakage rate, the seal is deemed qualified.

[0050] Based on the fluctuations in the gas-water interface depth over time, the amplitude of abnormal signals, and the trend of leakage rate changes, a comprehensive judgment is made regarding whether the seal is qualified. The judgment criteria include: First, the fluctuation in the gas-water interface depth is less than a predetermined threshold. During continuous monitoring, the gas-water interface depth is recorded at each sampling time, such as the gas-water interface depth at the i-th sampling time. , calculating the difference between its maximum value and minimum value, that is the fluctuation range . The predetermined threshold can be set according to the wellbore size and allowable leakage, for example, one meter or less. A small fluctuation range of the gas-water interface indicates that no large-scale fluid exchange has occurred, and the two-phase distribution in the annulus remains stable.

[0051] Second, the amplitude of the discrete high-frequency abnormal signal extracted from the pressure fluctuation spectrum is lower than the set statistical multiple of the background noise spectrum. The background noise spectrum can be obtained at the initial stage of detection (a short window confirming no leakage) or through statistics of historical working condition data without leakage. The mean square deviation of the amplitude of each frequency component in the background noise spectrum can be calculated . The set statistical multiple is usually 3 times the mean square deviation (i.e., 3σ criterion), and can also be 2 times or 4 times. If the amplitude of the abnormal signal (where k is the set statistical multiple), it is considered that no significant high-frequency leakage characteristic signal is detected.

[0052] Third, the change trend of leakage rate tends to zero. A continuous monitoring duration is preset, for example, 48 hours, 72 hours or 96 hours. Within this monitoring duration, the change trend of leakage rate over time is observed . If the leakage rate presents the characteristic of gradually decreasing first and then entering a stable stage, the fluctuation range of the leakage rate in the stable stage is less than the set stability threshold (for example, 10% of the initial leakage rate or a very small absolute threshold), and at the same time the average value of the leakage rate in the stable stage approaches zero (for example, less than 0.01 mole per second), then this condition is satisfied. Further, as an extended judgment criterion, when the change trend of the leakage rate satisfies that the increment of leakage rate every 6 hours in the last 24 hours is less than 5% of the initial leakage rate, and the final leakage rate value is lower than the lower limit of the detection instrument error, the qualification can be judged more strictly.

[0053] When all the above three conditions are satisfied at the same time, that is, the depth fluctuation of the gas-water interface is less than the predetermined threshold, the amplitude of the abnormal signal is lower than the set statistical multiple of the background noise spectrum, and the change trend of the leakage rate decreases and tends to a stable zero value, then the sealing performance of the rock salt cavity and the wellbore is judged to be qualified. On the contrary, if any condition is not satisfied, the sealing performance is judged to be unqualified, and cement injection plugging, casing repair or other repair measures are required.

[0054] Corresponding to the above method, the embodiment of the present application also provides a sealing detection device for CO₂ geological storage in rock salt cavities, as shown in Figure 2 , the device includes: an acquiring unit 210, configured to acquire a temperature profile and a pressure profile from the wellhead to the top of the cavity after nitrogen is injected into the annulus between the production casing and the test string to form a gas-water two-phase distribution; an identifying unit 220, configured to identify the gas-water interface depth of the gas-water two-phase distribution according to the temperature profile; The acquisition unit 210 is also used to perform frequency domain transformation on the pressure change sequence at the casing shoe extracted from the pressure profile to obtain the amplitude of the abnormal signal. The determination unit 230 is used to calculate the volume of the annular air column based on the gas-water interface depth and wellbore size, and to determine the leakage rate and corresponding trend of the amount of gaseous substances in the annulus over time in combination with the wellhead pressure and wellhead temperature; and to determine that the seal is qualified when the fluctuation of the gas-water interface depth is less than a predetermined threshold, the amplitude of the abnormal signal is lower than a set statistical multiple of the background noise spectrum, and the trend of the leakage rate tends to zero.

[0055] The functions of each unit in the sealing detection device for CO2 geological sealing in rock salt cavities provided in the above embodiments of this application can be realized through the above-described method steps. Therefore, the specific working process and beneficial effects of each unit in the sealing detection device for CO2 geological sealing in rock salt cavities provided in the embodiments of this application will not be repeated here.

[0056] This application also provides an electronic device, such as... Figure 3 As shown, it includes a processor 310, a communication interface 320, a memory 330, and a communication bus 340, wherein the processor 310, the communication interface 320, and the memory 330 communicate with each other through the communication bus 340.

[0057] Memory 330 is used to store computer programs; When the processor 310 executes the program stored in the memory 330, it performs the following steps: After nitrogen is injected into the annulus between the production casing and the test string to form a gas-water two-phase distribution, temperature and pressure profiles from the wellhead to the top of the cavity are obtained. The gas-water interface depth is identified based on this temperature profile. The frequency domain transformation of the pressure change sequence at the casing shoe extracted from the pressure profile was performed to obtain the amplitude of the abnormal signal. The volume of the annular air column is calculated based on the gas-water interface depth and wellbore dimensions. Combined with wellhead pressure and wellhead temperature, the leakage rate and corresponding trend of the amount of gaseous substances in the annulus over time are determined. When the fluctuation of the gas-water interface depth is less than a predetermined threshold, the amplitude of the abnormal signal is lower than the set statistical multiple of the background noise spectrum, and the leakage rate trend approaches zero, the seal is deemed qualified.

[0058] The communication bus mentioned above can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. This communication bus can be divided into address bus, data bus, control bus, etc. For ease of illustration, only one thick line is used to represent it in the diagram, but this does not mean that there is only one bus or one type of bus.

[0059] The communication interface is used for communication between the aforementioned electronic devices and other devices.

[0060] The memory may include random access memory (RAM) or non-volatile memory (NVM), such as at least one disk storage device. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor.

[0061] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0062] The implementation methods and beneficial effects of the various components of the electronic device in the above embodiments for solving the problem can be found in [reference needed]. Figure 1 The steps in the illustrated embodiments are used to implement the electronic device. Therefore, the specific working process and beneficial effects of the electronic device provided in this application will not be repeated here.

[0063] In another embodiment provided in this application, a computer-readable storage medium is also provided, which stores instructions that, when executed on a computer, cause the computer to perform the sealing detection method for CO2 geological sealing in rock salt cavities as described in any of the above embodiments.

[0064] In another embodiment provided in this application, a computer program product containing instructions is also provided, which, when run on a computer, causes the computer to execute the sealing detection method for CO2 geological sealing in rock salt cavities as described in any of the above embodiments.

[0065] Those skilled in the art will understand that the embodiments in this application can be provided as methods, systems, or computer program products. Therefore, the embodiments in this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the embodiments in this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0066] This application describes embodiments of methods, apparatus (systems), and computer program products according to embodiments of this application with reference to flowchart illustrations and / or block diagrams. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0067] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0068] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0069] Although preferred embodiments have been described in this application, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of this application.

[0070] Obviously, those skilled in the art can make various modifications and variations to the embodiments of this application without departing from the spirit and scope of the embodiments of this application. Therefore, if these modifications and variations to the embodiments of this application fall within the scope of the claims in this application and their equivalents, then this application also intends to include these modifications and variations.

Claims

1. A method for detecting the airtightness of CO2 geological sealing in rock salt cavities, characterized in that, The method includes: After nitrogen is injected into the annulus between the production casing and the test string to form a gas-water two-phase distribution, temperature and pressure profiles from the wellhead to the top of the cavity are obtained. The gas-water interface depth of the gas-water two-phase distribution is identified based on the temperature profile; the frequency domain transformation is performed on the pressure change sequence at the casing shoe extracted from the pressure profile to obtain the amplitude of the abnormal signal. The volume of the annular air column is calculated based on the gas-water interface depth and wellbore dimensions. Combined with wellhead pressure and wellhead temperature, the leakage rate and corresponding trend of the amount of gaseous substances in the annulus over time are determined. When the fluctuation of the gas-water interface depth is less than a predetermined threshold, the amplitude of the abnormal signal is lower than the set statistical multiple of the background noise spectrum, and the leakage rate trend approaches zero, the seal is deemed qualified.

2. The method as described in claim 1, characterized in that, Before nitrogen is injected into the annulus between the production casing and the test string to form a gas-water two-phase distribution, the method further includes: Distributed fiber optic sensors are installed at equal intervals along the axial direction on the outer wall of the production casing. The installation point of each fiber optic sensor is mechanically fixed by the casing coupling, and the sensor signal transmission fiber is connected to the surface demodulator. After well completion, the test string is run in, and the annulus is formed between the production casing and the test string.

3. The method as described in claim 1, characterized in that, The depth of the gas-water interface is identified based on this temperature profile, including: Calculate the temperature gradient along the depth of the wellbore; The depth at which the calculated temperature gradient is reversed from a positive value to a negative value, or from a negative value to a positive value, is determined as the gas-water interface depth.

4. The method as described in claim 1, characterized in that, The pressure change sequence at the casing shoe was extracted from this pressure profile, including: In the pressure profile, the depth coordinates of the production sleeve shoe are located, and the pressure values ​​at the depth coordinates are extracted sequentially from the pressure profiles at multiple consecutive sampling times, and arranged in chronological order to form a sequence of pressure changes over time.

5. The method as described in claim 3, characterized in that, The amplitude of the abnormal signal is obtained by frequency domain transformation of the pressure change sequence at the casing shoe extracted from the pressure profile, including: Perform a fast Fourier transform on the pressure change sequence to obtain the pressure fluctuation spectrum; Target frequency points with frequencies higher than a set high-frequency threshold are identified from the pressure fluctuation spectrum, and the amplitude corresponding to each target frequency point is extracted. The maximum amplitude is taken as the amplitude of the abnormal signal.

6. The method as described in claim 1, characterized in that, The annular air column volume is calculated based on the gas-water interface depth and wellbore dimensions, including: Calculate the annular cross-sectional area based on the geometric parameters of the production casing and the test string; The volume of the annular air column is obtained by multiplying the difference between the gas-water interface depth and the wellhead reference depth by the cross-sectional area of ​​the annulus.

7. The method as described in claim 1, characterized in that, Based on the annular air column volume, wellhead pressure, and wellhead temperature, determine the leakage rate and corresponding trend of the amount of gaseous material in the annulus over time, including: At each sampling moment, according to the ideal gas law, the product of the wellhead pressure and the volume of the annular air column is divided by the product of the gas constant and the wellhead temperature to obtain the amount of gaseous substance in the annulus at that sampling moment. The time-difference derivative of the gaseous substance quantity sequence at multiple consecutive sampling times is used to obtain the rate of change of gaseous substance quantity, which is the leakage rate. The leakage rate is then arranged in chronological order to obtain the trend of leakage rate change over time.

8. A sealing performance testing device for CO2 geological sealing in rock salt cavities, characterized in that, The device includes: The acquisition unit is used to acquire the temperature and pressure profiles from the wellhead to the top of the cavity after nitrogen is injected into the annulus between the production casing and the test string to form a gas-water two-phase distribution. The identification unit is used to identify the gas-water interface depth of the gas-water two-phase distribution based on the temperature profile. The acquisition unit is also used to perform frequency domain transformation on the pressure change sequence at the casing shoe extracted from the pressure profile to obtain the amplitude of the abnormal signal. The determination unit is used to calculate the volume of the annular air column based on the gas-water interface depth and wellbore size, and to determine the leakage rate and corresponding trend of the amount of gaseous substances in the annulus over time by combining the wellhead pressure and wellhead temperature; and to determine that the seal is qualified when the fluctuation of the gas-water interface depth is less than a predetermined threshold, the amplitude of the abnormal signal is lower than a set statistical multiple of the background noise spectrum, and the trend of the leakage rate tends to zero.

9. An electronic device, characterized in that, The electronic device includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory, used to store computer programs; A processor, when executing a program stored in memory, implements the method of any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method described in any one of claims 1-7.

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