Method for identifying annulus under-pressure characteristics of injection-production well of gas storage

Abstract

The invention relates to a method for identifying annulus pressure characteristics of an injection-production well of a gas storage, and belongs to the technical field of oil and gas development. Comprising the following steps: step 1, establishing a characteristic curve identification chart; 2, drawing an actual pressure change curve according to the oil pressure, the A annulus pressure value and the B annulus pressure value; and 3, the actual pressure change curve is compared with the pressure change characteristics of the characteristic curve recognition plate, and then the under-pressure reason of the annulus under-pressure well is judged. The method has good operability and universality, the under-pressure reason can be judged according to the on-site oil casing pressure change trend of the gas storage under-pressure well, and a certain basis is provided for gas storage injection and production well annulus under-pressure diagnosis and treatment.

Description

Technical Field

[0001] The invention relates to a method for identifying annular pressure characteristics of an injection and production well of a gas storage reservoir, and belongs to the technical field of oil and gas development. Background Art

[0002] The construction and safe operation of gas storage groups are important guarantees for injection and production peak regulation, national gas consumption, and even the stable and controllable national energy. The operation mode of the injection and production wells in a single injection and production cycle is divided into the injection period, the balance period, and the production period. The oil pressure gradually rises to a high point during the injection period, and the oil pressure gradually decreases and stabilizes during the balance period and the production period. During the injection and production process, due to the alternating injection and production conditions, the injection and production strings, packers, and other sealing problems, poor cementing quality, etc., the injection and production wells A annulus (casing annulus) or B annulus (casing annulus) will have a certain pressure, which will affect the daily safe and stable operation of the injection and production wells to a certain extent.

[0003] Currently, there is a lack of convenient and universal identification methods for the annular pressure problem caused by various reasons in the injection and production wells of gas storage facilities. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention discloses a method for identifying the annulus pressure characteristics of gas storage injection and production wells. By summarizing and establishing a characteristic curve identification chart based on the actual on-site annulus pressure change trends at all levels, the cause of annulus pressure in the gas storage injection and production wells can be quickly determined, providing a basis for the next step of graded control.

[0005] The technical solution adopted by the present invention is: a method for identifying the annular pressure characteristics of a gas storage injection and production well, comprising the following steps:

[0006] Step 1: According to the oil pressure of the injection and production wells and the change trend of the annular pressure at all levels, establish a characteristic curve identification chart through physical logic analysis and investigation of the actual pressure-carrying causes;

[0007] Step 2: Pressure gauges are installed at the wellheads of all levels of annuli of the gas storage reservoir injection and production wells. The oil pressure, A annulus pressure, and B annulus pressure data are collected in real time during the injection and production cycle, starting from the time when the annulus is pressurized. The actual pressure change curve is drawn by computer based on the oil pressure, A annulus pressure, and B annulus pressure values.

[0008] Step 3: Compare the pressure change characteristics of the actual pressure change curve with those of the characteristic curve identification plate. According to the characteristics of the actual pressure change curve, find the characteristic curve identification plate that is most similar to the actual pressure change curve through computer graphic analysis, and then determine the cause of the pressure in the annulus pressure well.

[0009] Furthermore, the physical logic analysis in step 1 is as follows:

[0010] (1) Identification chart of the normal pressure characteristic curve of annulus A: During the injection and production process, the injection and production string expands due to the pressure and thermal effects of the gas on the injection and production string, squeezing the annulus A. According to the gas state equation, the annulus A will have a certain pressure. As the injection and production cycle progresses, the pressure and thermal effects of the gas on the injection and production string remain basically stable, and the physical properties of the fluid in the annulus A change little, so the pressure of the annulus A is basically stable or fluctuates within a small range.

[0011] (2) The wellhead casing head seal failure leads to the mutual pressure characteristic curve identification chart of the A annulus and the B annulus: The wellhead casing head is a barrier to isolate the annuli at all levels. When the wellhead casing head seal that isolates the A annulus and the B annulus fails, the A annulus and the B annulus are connected to form a pressure system. Therefore, the pressure change trends of the two are positively correlated, and the pressure values ​​are close.

[0012] (3) Characteristic curve identification chart of pressure in annulus A caused by poor sealing of injection and production string: When the injection and production string is not tightly sealed, a leakage point is generated. Under the pressure difference between the inside and outside sides, the gas in the injection and production string leaks into the annulus A through the leakage point; during the steam injection period, the oil pressure continues to rise, and the gas continuously leaks into the annulus A, causing the pressure of the annulus A to rise synchronously. When the oil pressure rises to a high point, the pressure value of the annulus A also reaches a high point. Due to the presence of protective fluid in the annulus A, the pressure value of the annulus A cannot be consistent with the oil pressure, and there will be a certain difference; during the equilibrium period and gas production period, the oil pressure slowly decreases. At this time, although there is a pressure difference between the inside and outside of the leakage point, the gas in the annulus A is trapped in the protective fluid and cannot escape, so the pressure of the annulus A remains relatively stable; entering the next injection and production cycle, when there is a pressure difference between the inside and outside of the leakage point, the gas in the injection and production string will leak into the annulus A through the leakage point again, causing the pressure of the annulus A to further increase.

[0013] (4) Identification chart of the characteristic curve of annulus A pressure caused by poor sealing of the packer: When the pressure at the lower end of the packer is greater than the pressure at the upper end, due to the pressure difference, the gas leaks into the annulus A through the leak point, causing the pressure value of the annulus A to increase; but due to the large size of the leak point caused by the poor sealing of the packer and the gravity of the annulus protection fluid, when the gas leaked into the annulus A reaches a certain level, the pressure at the upper end of the packer is greater than the pressure at the lower end. Under the action of the pressure difference, some of the protection fluid will flow out through the leak point, causing the volume of the fluid in the annulus A to decrease and the pressure value to decrease. When the pressure at the lower end of the packer is greater than the pressure at the upper end, the gas will leak into the annulus A through the leak point, causing the pressure of the annulus A to increase. Therefore, the pressure of the annulus A will fluctuate up and down, but the overall trend is to increase.

[0014] (5) Characteristic curve identification chart of B annulus pressure caused by micro cracks in cement sheath: Micro cracks are generated in cement sheath, and gas will flow up to the top of B annulus through the micro cracks in the perforation section, resulting in B annulus pressure. Since cement sheath is a solid medium with low compressibility, the formation of micro cracks is equivalent to connecting the injection and production pipe string with B annulus, so during the steam injection period, the pressure of B annulus and oil pressure remain relatively consistent, and the pressures of the two are close; during the equilibrium period and gas production period, the gas in the formation is produced through the injection and production pipe string, and the bottom hole pressure drops. When it is lower than the pressure of B annulus, the gas in B annulus will flow down to the bottom hole through the micro cracks in cement sheath, and along with the production of formation gas, the pressure of B annulus will drop rapidly.

[0015] Furthermore, the pressure variation characteristics of the characteristic curve identification plate in step 3 are:

[0016] (a) The pressure change characteristics of the characteristic curve identification chart are as follows: during multiple injection and production cycles, the oil pressure will fluctuate with the changes in the injection and production conditions, but the pressure of the A annulus does not change with the oil pressure, and is less than the oil pressure, basically maintaining at a certain pressure value or the difference between the maximum and minimum values ​​of the A annulus pressure is no more than 2MPa; this means that the A annulus is normally pressurized.

[0017] (b) The pressure change characteristics of the characteristic curve identification chart are as follows: during multiple injection and production cycles, the B annulus pressure (or A annulus pressure) changes synchronously with the A annulus pressure (or B annulus pressure), and the absolute value of the pressure difference between the B annulus pressure and the A annulus pressure is no more than 2MPa; this is due to the failure of the wellhead casing head seal, which leads to the mutual pressure between the A and B annuli.

[0018] (c) The pressure change characteristics of the characteristic curve identification chart are as follows: within a single injection and production cycle, the pressure of annulus A rises with the oil pressure during the gas injection period. When the oil pressure reaches a high point, the pressure of annulus A also reaches a high point. During the equilibrium period and gas production period, the oil pressure gradually decreases and tends to be stable, and the pressure of annulus A remains relatively stable. In the next injection and production cycle, the pressure of annulus A still changes according to this rule, and the pressure of annulus A is always less than the oil pressure. This means that the injection and production string is not tightly sealed, resulting in pressure in annulus A.

[0019] (d) The pressure variation characteristics of the characteristic curve identification chart are as follows: during multiple injection and production cycles, the oil pressure increases during the gas injection period, decreases during the equilibrium period and the gas production period, and the pressure in the A annulus fluctuates up and down, with an overall increasing trend; this indicates that the A annulus is pressurized due to the poor sealing of the packer.

[0020] (e) The pressure variation characteristics of the characteristic curve identification chart are as follows: within a single injection-production cycle, the pressure of annulus B increases with the oil pressure during the gas injection period. When the oil pressure reaches the highest point, the pressure of annulus B also reaches the highest point. During the equilibrium period and gas production period, the oil pressure gradually decreases and tends to be stable. The pressure of annulus B drops rapidly to the lowest point. In the next injection-production cycle, the pressure of annulus B still changes according to this law. This indicates that the micro-gap in the cement sheath causes the pressure in annulus B.

[0021] The present invention discloses a method for identifying the annular pressure characteristics of gas storage injection and production wells. The method has the beneficial effect that the method has good operability and universality, and can judge the cause of the pressure according to the on-site casing pressure variation trend of the gas storage wells, thus providing a certain basis for the diagnosis and control of the annular pressure of the gas storage injection and production wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0023] Figure 1 This is a schematic diagram of the identification chart of the normal pressure characteristic curve of annulus A;

[0024] Figure 2 This is a schematic diagram of the identification of the pressure characteristic curve of the A and B annuli due to the failure of the wellhead casing head seal;

[0025] Figure 3 This is a schematic diagram of the A annulus pressure characteristic curve identification chart due to poor sealing of the injection and production string;

[0026] Figure 4 This is a schematic diagram of the A annulus pressure characteristic curve identification chart due to poor sealing of the packer;

[0027] Figure 5 This is a schematic diagram of the identification chart of the characteristic curve of the B annulus pressure caused by micro-gaps in the cement annulus.

[0028] Specific implementation methods

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In order to further understand the content of the present invention, the present invention is further described below in conjunction with specific implementation methods.

[0031] The well logging methods used in the following embodiments are conventional methods unless otherwise specified. The present invention is described in detail with reference to the accompanying drawings as follows:

[0032] Embodiment 1:

[0033] like Figures 1 to 5 As shown, it should be noted that in each figure: ① represents the gas injection period; ② represents the balance period + gas production period; A method for identifying the annular pressure characteristics of the injection and production wells of a gas storage reservoir includes the following steps:

[0034] Step 1: According to the oil pressure of the injection and production wells and the change trend of the annular pressure at all levels, establish a characteristic curve identification chart through physical logic analysis and investigation of the actual pressure-carrying causes;

[0035] Step 2: Pressure gauges are installed at the wellheads of all levels of annuli of the gas storage reservoir injection and production wells. The oil pressure, A annulus pressure, and B annulus pressure data are collected in real time during the injection and production cycle, starting from the time when the annulus is pressurized. The actual pressure change curve is drawn by computer based on the oil pressure, A annulus pressure, and B annulus pressure values.

[0036] Step 3: Compare the pressure change characteristics of the actual pressure change curve with those of the characteristic curve identification plate. According to the characteristics of the actual pressure change curve, find the characteristic curve identification plate that is most similar to the actual pressure change curve through computer graphic analysis, and then determine the cause of the pressure in the annulus pressure well.

[0037] Furthermore, the physical logic analysis in step 1 is as follows:

[0038] (1) Identification chart of the normal pressure characteristic curve of annulus A: During the injection and production process, the injection and production string expands due to the pressure and thermal effects of the gas on the injection and production string, squeezing the annulus A. According to the gas state equation, the annulus A will have a certain pressure. As the injection and production cycle progresses, the pressure and thermal effects of the gas on the injection and production string remain basically stable, and the physical properties of the fluid in the annulus A change little, so the pressure of the annulus A is basically stable or fluctuates within a small range.

[0039] (2) The wellhead casing head seal failure leads to the mutual pressure characteristic curve identification chart of the A annulus and the B annulus: The wellhead casing head is a barrier to isolate the annuli at all levels. When the wellhead casing head seal that isolates the A annulus and the B annulus fails, the A annulus and the B annulus are connected to form a pressure system. Therefore, the pressure change trends of the two are positively correlated, and the pressure values ​​are close.

[0040] (3) Characteristic curve identification chart of pressure in annulus A caused by poor sealing of injection and production string: When the injection and production string is not tightly sealed, a leakage point is generated. Under the pressure difference between the inside and outside sides, the gas in the injection and production string leaks into the annulus A through the leakage point; during the steam injection period, the oil pressure continues to rise, and the gas continuously leaks into the annulus A, causing the pressure of the annulus A to rise synchronously. When the oil pressure rises to a high point, the pressure value of the annulus A also reaches a high point. Due to the presence of protective fluid in the annulus A, the pressure value of the annulus A cannot be consistent with the oil pressure, and there will be a certain difference; during the equilibrium period and gas production period, the oil pressure slowly decreases. At this time, although there is a pressure difference between the inside and outside of the leakage point, the gas in the annulus A is trapped in the protective fluid and cannot escape, so the pressure of the annulus A remains relatively stable; entering the next injection and production cycle, when there is a pressure difference between the inside and outside of the leakage point, the gas in the injection and production string will leak into the annulus A through the leakage point again, causing the pressure of the annulus A to further increase.

[0041] (4) Identification chart of the characteristic curve of annulus A pressure caused by poor sealing of the packer: When the pressure at the lower end of the packer is greater than the pressure at the upper end, due to the pressure difference, the gas leaks into the annulus A through the leak point, causing the pressure value of the annulus A to increase; but due to the large size of the leak point caused by the poor sealing of the packer and the gravity of the annulus protection fluid, when the gas leaked into the annulus A reaches a certain level, the pressure at the upper end of the packer is greater than the pressure at the lower end. Under the action of the pressure difference, some of the protection fluid will flow out through the leak point, causing the volume of the fluid in the annulus A to decrease and the pressure value to decrease. When the pressure at the lower end of the packer is greater than the pressure at the upper end, the gas will leak into the annulus A through the leak point, causing the pressure of the annulus A to increase. Therefore, the pressure of the annulus A will fluctuate up and down, but the overall trend is to increase.

[0042] (5) Characteristic curve identification chart of B annulus pressure caused by micro cracks in cement sheath: Micro cracks are generated in cement sheath, and gas will flow up to the top of B annulus through the micro cracks in the perforation section, resulting in B annulus pressure. Since cement sheath is a solid medium with low compressibility, the formation of micro cracks is equivalent to connecting the injection and production pipe string with B annulus, so during the steam injection period, the pressure of B annulus and oil pressure remain relatively consistent, and the pressures of the two are close; during the equilibrium period and gas production period, the gas in the formation is produced through the injection and production pipe string, and the bottom hole pressure drops. When it is lower than the pressure of B annulus, the gas in B annulus will flow down to the bottom hole through the micro cracks in cement sheath, and along with the production of formation gas, the pressure of B annulus will drop rapidly.

[0043] Furthermore, the pressure variation characteristics of the characteristic curve identification plate in step 3 are:

[0044] (a) Identification chart of the normal pressure characteristic curve of the A annulus: During multiple injection and production cycles, the oil pressure will fluctuate with the changes in the injection and production conditions, but the pressure of the A annulus does not change with the oil pressure and is less than the oil pressure, basically maintaining at a certain pressure value or the difference between the maximum and minimum values ​​of the A annulus pressure is no more than 2MPa.

[0045] (b) Characteristic curve identification chart of the mutual pressure between the A and B annuli caused by the failure of the wellhead casing head seal: During multiple injection and production cycles, the B annulus pressure (or A annulus pressure) changes synchronously with the A annulus pressure (or B annulus pressure), and the absolute value of the pressure difference between the two is no more than 2MPa.

[0046] (c) Characteristic curve identification chart of A annulus pressure caused by poor sealing of the injection and production string: In a single injection and production cycle, the A annulus pressure increases with the oil pressure during the gas injection period. When the oil pressure reaches a high point, the A annulus pressure also reaches a high point. During the equilibrium period and gas production period, the oil pressure gradually decreases and tends to be stable, and the A annulus pressure remains relatively stable. In the next injection and production cycle, the A annulus pressure still changes according to this law, and the A annulus pressure is always less than the oil pressure.

[0047] (d) Identification chart of the characteristic curve of the pressure in annulus A caused by poor sealing of the packer: During multiple injection and production cycles, the oil pressure increases during the injection period and decreases during the equilibrium period and gas production period. The pressure in annulus A fluctuates up and down, with an overall increasing trend.

[0048] (e) Identification chart of the characteristic curve of B annulus pressure caused by micro-gap in cement ring: In a single injection-production cycle, the pressure of B annulus increases with the oil pressure during the gas injection period. When the oil pressure reaches the highest point, the pressure of B annulus also reaches the highest point. During the equilibrium period and gas production period, the oil pressure gradually decreases and tends to be stable. The pressure of B annulus drops rapidly to the lowest point. In the next injection-production cycle, the pressure of B annulus still changes according to this law.

[0049] Furthermore, the (e) cement ring micro-gap causes the ratio of the pressure difference between the highest point and the lowest point of the B annulus during the equilibrium period and the gas production period to the highest point pressure on the B annulus pressure characteristic curve identification chart to be greater than 50%.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for identifying the pressure characteristics of the annulus of an injection-production well, comprising the following steps: Step 1: According to the pressure change trend of casings at all levels of injection and production wells on site, establish a characteristic curve identification chart through physical logic analysis and investigation of the actual pressure causes; Step 2: Pressure gauges are installed at the wellheads of all levels of annuli of the gas storage reservoir injection and production wells. The oil pressure, A annulus pressure, and B annulus pressure data are collected in real time during the injection and production cycle, starting from the time when the annulus is pressurized. The actual pressure change curve is drawn by computer based on the oil pressure, A annulus pressure, and B annulus pressure values. Step 3: Compare the pressure change characteristics of the actual pressure change curve with those of the characteristic curve identification plate. According to the characteristics of the actual pressure change curve, find the characteristic curve identification plate that is most similar to the actual pressure change curve through computer graphic analysis, and then determine the cause of the pressure in the annulus pressure well.

2. A method for identifying annular pressure characteristics of an injection-production well according to claim 1, characterized in that: The physical logic analysis in step 1 is as follows: (1) Identification chart of the normal pressure characteristic curve of annulus A: During the injection and production process, the injection and production string expands due to the pressure and heat effects of the gas on the injection and production string, squeezing the annulus A. According to the gas state equation, the annulus A will have a certain pressure. As the injection and production cycle progresses, the pressure and heat effects of the gas on the injection and production string remain stable, and the physical properties of the fluid in the annulus A change little, so the pressure of the annulus A tends to be stable. (2) Characteristic curve identification chart of mutual pressure between annulus A and annulus B caused by failure of wellhead casing head seal: The wellhead casing head is a barrier to isolate the annuli at all levels. When the wellhead casing head seal that isolates annulus A and annulus B fails, annulus A and annulus B are connected to form a pressure system, and the pressure change trends of the two are positively correlated; (3) Characteristic curve identification chart of pressure in annulus A caused by poor sealing of injection and production string: When the injection and production string is not tightly sealed, a leakage point is generated. Under the pressure difference between the inside and outside sides, the gas in the injection and production string leaks into the annulus A through the leakage point; during the steam injection period, the oil pressure continues to rise, and the gas continuously leaks into the annulus A, causing the pressure of the annulus A to rise synchronously. When the oil pressure rises to a high point, the pressure value of the annulus A also reaches a high point. Due to the presence of protective fluid in the annulus A, the pressure value of the annulus A cannot be consistent with the oil pressure; during the equilibrium period and gas production period, the oil pressure slowly decreases. At this time, although there is a pressure difference between the inside and outside sides of the leakage point, the gas in the annulus A is trapped in the protective fluid and cannot escape, and the pressure of the annulus A remains relatively stable; when entering the next injection and production cycle, when there is a pressure difference between the inside and outside sides of the leakage point, the gas in the injection and production string will leak into the annulus A through the leakage point again, causing the pressure of the annulus A to further increase; (4) Identification chart of characteristic curve of pressure in annulus A caused by poor sealing of the packer: When the pressure at the lower end of the packer is greater than the pressure at the upper end, due to the pressure difference, gas leaks into annulus A through the leak point, causing the pressure value of annulus A to increase; however, due to the increase in the size of the leak point caused by the poor sealing of the packer and the gravity of the annulus protection fluid, when the gas leaked into annulus A reaches a certain level, the pressure at the upper end of the packer is greater than the pressure at the lower end. Under the action of the pressure difference, the annulus protection fluid will flow out through the leak point, causing the volume of fluid in annulus A to decrease and the pressure value to decrease. When the pressure at the lower end of the packer is greater than the pressure at the upper end, gas will leak into annulus A through the leak point again, causing the pressure of annulus A to increase. The pressure of annulus A fluctuates up and down, but the overall trend is to increase. (5) Characteristic curve identification chart of pressure in annulus B caused by micro-cracks in cement sheath: Micro-cracks are generated in cement sheath, and gas will flow up to the top of annulus B through the micro-cracks in the perforation section, resulting in pressure in annulus B. Since cement sheath is a solid medium with low compressibility, the formation of micro-cracks is equivalent to connecting the injection and production string with annulus B. During the steam injection period, the pressure in annulus B remains relatively consistent with the oil pressure. During the equilibrium period and gas production period, the gas in the formation is produced through the injection and production string, and the bottomhole pressure drops. When it is lower than the pressure in annulus B, the gas in annulus B will flow down to the bottomhole through the micro-cracks in cement sheath, and along with the production of formation gas, the pressure in annulus B will drop rapidly.

3. A method for identifying annular pressure characteristics of an injection-production well according to claim 1, characterized in that: The pressure variation characteristics of the characteristic curve identification plate in step 3: (a) Identification chart of the normal pressure characteristic curve of annulus A: During multiple injection-production cycles, the oil pressure will fluctuate with the changes in injection-production conditions, but the pressure of annulus A does not change with the oil pressure and is less than the oil pressure; (b) Characteristic curve identification chart of A and B annulus pressure crossover caused by wellhead casing head sealing failure: During multiple injection and production cycles, the B annulus pressure (or A annulus pressure) changes synchronously with the A annulus pressure (or B annulus pressure), and the absolute value of the pressure difference between the B annulus pressure and the A annulus pressure is no more than 2MPa; (c) Characteristic curve identification chart of A annulus pressure caused by poor sealing of injection and production string: In a single injection and production cycle, the pressure of A annulus rises with the increase of oil pressure during the gas injection period. When the oil pressure reaches a high point, the pressure of A annulus also reaches a high point. During the equilibrium period and gas production period, the oil pressure gradually decreases and tends to be stable. The pressure of A annulus remains relatively stable. In the next injection and production cycle, the pressure of A annulus still changes according to this law, and the pressure of A annulus is always less than the oil pressure. (d) Characteristic curve identification chart of A annulus pressure caused by poor sealing of the packer: During multiple injection and production cycles, the oil pressure rises during the injection period and decreases during the equilibrium period and the production period. The pressure of A annulus fluctuates up and down, with an overall increasing trend. (e) Identification chart of the characteristic curve of B annulus pressure caused by micro-gap in cement ring: In a single injection-production cycle, the pressure of B annulus increases with the oil pressure during the gas injection period. When the oil pressure reaches the highest point, the pressure of B annulus also reaches the highest point. During the equilibrium period and gas production period, the oil pressure gradually decreases and tends to be stable. The pressure of B annulus drops rapidly to the lowest point. In the next injection-production cycle, the pressure of B annulus still changes according to this law.

4. A method for identifying annular pressure characteristics of an injection-production well according to claim 3, characterized in that: (a) Identification chart of the normal pressure characteristic curve of annulus A: During multiple injection and production cycles, the oil pressure will fluctuate with the changes in injection and production conditions, but the pressure of annulus A does not change with the oil pressure and is less than the oil pressure. The difference between the maximum and minimum values ​​of the pressure of annulus A is no more than 2MPa.

5. A method for identifying annular pressure characteristics of an injection-production well according to claim 3, characterized in that: (e) The ratio of the pressure difference between the highest and lowest points of the B annulus and the pressure at the highest point in the equilibrium period and gas production period of the B annulus pressure characteristic curve identification chart caused by the micro-gap in the cement annulus is greater than 50%.

Images