Method of injecting gas into old well cavity to remove brine in salt cavern gas storage

Abstract

The present invention discloses a method for injecting gas and discharging brine from an old well cavity in a salt cavern gas storage. The bottoms of the first and second cavities of the old well cavity are both lower than the top of a horizontal channel. The method comprises: lowering a first injection-production pipe and a first row of brine pipes into a wellbore of the first cavity, and lowering a second injection-production pipe and a second row of brine pipes into the wellbore of the second cavity; injecting gas through the first injection-production pipe, causing brine to be discharged through the first row of brine pipes, until the gas-water interface in the first cavity drops to the depth of the top of the horizontal channel; injecting gas through the second injection-production pipe, causing brine to be discharged through the second row of brine pipes, until the gas-water interface in the second cavity drops to the depth of the lower end of the second row of brine pipes, which is lower than the depth of the top of the horizontal channel; and injecting gas again through the first injection-production pipe, causing brine to be discharged through the first row of brine pipes, until the gas-water interface in the first cavity drops to the depth of the lower end of the first row of brine pipes. The present invention can accelerate the brine discharge speed and improve the degree of brine discharge in the cavity.

Description

Technical Field

[0001] The present invention relates to the technical field of gas storage reservoirs, and in particular to a method for injecting gas and removing brine from an old well cavity in a salt cavern gas storage reservoir. Background Art

[0002] Salt cavern gas storage, the optimal facility for peak-shaving and strategic energy reserves, has become a top choice for underground energy storage. Salt mines, when mining, create old, interconnected cavities filled with saturated brine. These cavities, often unused, are saturated with brine. Discharging this brine and fully utilizing underground resources, such as salt mines, to construct gas storage facilities has become a hot topic.

[0003] Most salt rock deposits in my country are layered rock salt, containing numerous interlayers of insoluble matter and resulting in low-grade salt. This limitation leads to a large accumulation of insoluble residue at the bottom of the cavity after water-soluble salt mining, with the top surface of the residue being uneven. The cavity morphology formed by the old well is complex, often U-shaped.

[0004] The existing technology uses a "one-injection, one-drain" gas injection and brine removal method for the old well cavity. Injection and production tubing is installed in one well, while gas injection and brine removal tubing is installed in another well. Gas is injected through the annulus between the injection and production tubing of one well and the injection and production tubing and brine removal tubing of the other well, and brine is removed from the brine removal tubing. This method has a single brine removal channel and a slow brine removal rate. Furthermore, when the distance between the two wells is large, some gas in the channel between the two cavities cannot drive water. When the horizontal channel of the old well cavity is higher than the cavity bottom, the brine in the cavity cannot be fully discharged, resulting in a loss of cavity volume and a reduction in working gas volume.

[0005] Based on this, there is still room for further improvement in the existing technology. Summary of the Invention

[0006] The main purpose of the present invention is to provide a method for injecting gas into the old cavity of a salt cavern gas storage to remove brine, so as to solve the problems of the prior art such as single brine removal channel, slow brine removal speed, limitation of the distance between two wells and limited brine removal degree.

[0007] According to one aspect of the present invention, a method for injecting gas and removing brine from an old well cavity in a salt cavern gas storage is proposed. The old well cavity comprises a first cavity, a second cavity, and a horizontal channel connecting the first cavity and the second cavity. The bottoms of the first cavity and the second cavity are both lower than the top of the horizontal channel. The method comprises:

[0008] A first injection-production pipe and a first row of brine pipes are lowered into the wellbore of the first cavity, and a second injection-production pipe and a second row of brine pipes are lowered into the wellbore of the second cavity;

[0009] Injecting gas into the first cavity through the first injection and production pipe, so that the brine in the first cavity is discharged through the first row of brine pipes, until the gas-water interface in the first cavity drops to the depth of the top of the horizontal channel;

[0010] Injecting gas into the second cavity through the second injection and production pipe, so that the brine in the second cavity is discharged through the second row of brine pipes, until the gas-water interface in the second cavity drops to the depth of the lower end of the second row of brine pipes, wherein the depth of the lower end of the second row of brine pipes is lower than the depth of the top of the horizontal channel;

[0011] Gas is injected into the first cavity again through the first injection and production pipe, so that the remaining brine in the first cavity is discharged through the first row of brine pipes until the gas-water interface of the first cavity drops to the depth of the lower port of the first row of brine pipes, completing gas injection and brine discharge.

[0012] According to one embodiment of the present invention, the distance between the lower end of the first row of brine pipes and the bottom of the first cavity is 1 to 2 meters.

[0013] According to one embodiment of the present invention, the distance between the lower ends of the second row of brine pipes and the bottom of the second cavity is 1 to 2 meters.

[0014] According to one embodiment of the present invention, the lower port of the first injection and production pipe is located in the top area of ​​the first cavity.

[0015] According to one embodiment of the present invention, the lower port of the second injection and production pipe is located in the top area of ​​the second cavity.

[0016] According to one embodiment of the present invention, the distance between the first cavity and the second cavity is 200-300 m.

[0017] According to one embodiment of the present invention, the gas-water interface of the first cavity and the second cavity is monitored using neutron logging.

[0018] According to one embodiment of the present invention, the further embodiment includes:

[0019] Evaluating the original wellbore of the old wellbore;

[0020] If it is determined that the original wellbore meets the conditions for conversion into an injection-production well, the first injection-production pipe and the first row of brine pipes or the second injection-production pipe and the second row of brine pipes are lowered into the original wellbore.

[0021] According to one embodiment of the present invention, the further embodiment includes:

[0022] Evaluating the original wellbore of the old wellbore;

[0023] If it is determined that the original wellbore does not meet the conditions for conversion into an injection-production well, the original wellbore is sealed and a new well is drilled, and the first injection-production pipe and the first row of brine pipes or the second injection-production pipe and the second row of brine pipes are lowered into the new well.

[0024] According to one embodiment of the present invention, the conversion injection-production well condition is to meet one or more of the following requirements: sealing requirements, casing quality requirements, cementing quality requirements, and injection-production throughput requirements.

[0025] In the method for injecting gas and draining brine from the old cavity of a salt cavern gas storage according to an embodiment of the present invention, gas is injected and brine is drained from the first cavity and the second cavity respectively (without draining the brine from one cavity to another cavity through a horizontal channel). This can increase the brine drainage channels, speed up the brine drainage speed, and is not restricted by the distance between the two cavities. At the same time, when the top of the horizontal channel is higher than the bottom of the cavity, the brine in each cavity can be drained to the maximum extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 A schematic diagram showing a method for injecting gas into an old well cavity to remove brine in a salt cavern gas storage according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0029] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. Subsequent embodiments will not explain this one by one.

[0030] refer to Figure 1 The present invention provides a method for injecting gas and removing brine from an old well cavity in a salt cavern gas storage. The old well cavity includes a first cavity 10, a second cavity 20, and a horizontal channel 30 connecting the first cavity 10 and the second cavity 20. The bottoms of the first cavity 10 and the second cavity 20 are both lower than the top of the horizontal channel 30. The method includes the following steps:

[0031] S1, lowering the first injection and production pipe 12 and the first row of brine pipes 14 into the wellbore of the first cavity 10, and lowering the second injection and production pipe 22 and the second row of brine pipes 24 into the wellbore of the second cavity 20; the first row of brine pipes 14 can be arranged in the first injection and production pipe 12, and the second row of brine pipes 24 can be arranged in the second injection and production pipe 22;

[0032] S2, inject gas into the first cavity 10 through the first injection and production pipe 12 (for example, inject gas through the annulus between the first injection and production pipe 12 and the first brine discharge pipe 14), so that the brine in the first cavity 10 is discharged through the first brine discharge pipe 14, until the gas-water interface of the first cavity 10 drops to the depth of the top of the horizontal channel 30 ( Figure 1 At the depth of the middle dotted line A), the gas injection and brine removal from the first cavity 10 is stopped;

[0033] S3, injecting gas into the second cavity 20 through the second injection and production pipe 22 (for example, injecting gas through the annulus between the second injection and production pipe 22 and the second row of brine pipes 24), so that the brine in the second cavity 20 is discharged through the second row of brine pipes 24 until the gas-water interface of the second cavity 20 drops to the depth of the lower end of the second row of brine pipes 24 ( Figure 1 The depth of the middle dotted line B), at this time, the gas injection is stopped, wherein the depth of the lower port of the second row of brine pipes 24 is lower than the depth of the top of the horizontal channel 30;

[0034] S4, gas is injected into the first cavity 10 again through the first injection and production pipe 12, so that the remaining brine in the first cavity 10 is discharged through the first row of brine pipes 14, until the gas-water interface of the first cavity 10 drops to the depth of the lower end of the first row of brine pipes 14 ( Figure 1 The first row of brine pipes 14 and the second row of brine pipes 24 can then be taken out to complete the gas injection and brine removal.

[0035] In the embodiment of the present invention, step S2 makes the gas-water interface of the first cavity 10 drop to the depth of the top of the horizontal channel 30, which can prevent the gas from entering the second cavity 20 through the horizontal channel 30 and affecting the gas-water interface detection. Combined with step S3, the gas-water interface of the second cavity 20 drops to the depth of the lower port of the second row of brine pipes 24. Since the depth of the lower port of the second row of brine pipes 24 is lower than the depth of the top of the horizontal channel 30 (correspondingly, the pressure of the second cavity 20 is greater than the pressure of the first cavity 10), when the first cavity 10 is injected with gas again in step S4, the gas in the first cavity 20 is reduced. The brine in the first cavity 10 cannot enter the second cavity 20, thereby ensuring that the first cavity 10 and the second cavity 20 can be independently injected with gas to discharge brine (the brine will hardly be discharged from one cavity to another cavity through the horizontal channel 30). In this way, it is not restricted by the distance between the two cavities (a long distance will not affect the brine discharge effect); and since there is no need to use a horizontal channel to discharge brine, there is no problem of "when the horizontal channel of the old cavity of the well is higher than the bottom of the cavity, the brine in the cavity cannot be discharged to the maximum extent". In this way, the brine in each cavity can be discharged to the maximum extent even when the top of the horizontal channel is higher than the bottom of the cavity. The present invention adopts two brine discharge channels to speed up the brine discharge. In addition, injecting gas into the first cavity 10 and the second cavity 20 in sequence can avoid damage to the wellbore and related equipment caused by high gas injection pressure.

[0036] In some embodiments, the distance between the lower end of the first row of brine pipes 14 and the bottom of the first chamber 10 is 1-2 m (e.g., 1 m); the distance between the lower end of the second row of brine pipes 24 and the bottom of the second chamber 20 is 1-2 m (e.g., 1 m). Such distances can ensure smooth brine discharge.

[0037] In some embodiments, the lower end of the first injection / production pipe 12 is located at the top of the first cavity 10; the lower end of the second injection / production pipe 22 is located at the top of the second cavity 20. This ensures efficient gas injection and prevents vibration caused by excessively long injection / production pipes. The lower ends of the first and second injection / production pipes 12, 22 can be located 15 meters below the surface casing shoe.

[0038] In some embodiments, the distance between the first cavity 10 and the second cavity 20 is 200 to 300 meters. As described above, the present invention performs separate gas injection and brine removal for the first cavity 10 and the second cavity 20, and there is almost no brine discharge from the first cavity 10 to the second cavity 20 (or from the second cavity 20 to the first cavity 10) through the horizontal channel 30. In this way, the distance between the first cavity 10 and the second cavity 20 is not limited. Even if the distance is large (for example, about 300 meters), the gas injection and brine removal of the first cavity 10 and the second cavity 20 can be well achieved.

[0039] In some embodiments, in steps S2 , S3 and S4 , the gas-water interface in the first cavity 10 and the second cavity 20 is monitored using neutron logging.

[0040] In some embodiments, before step S1, the method further includes: evaluating the original wellbore of the old wellbore; determining that the original wellbore has the conditions for conversion into an injection-production well, and then lowering the first injection-production pipe 12 and the first row of brine pipes 14 or the second injection-production pipe 22 and the second row of brine pipes 24 into the original wellbore in step S1.

[0041] In some embodiments, before step S1, the method further includes: evaluating the original wellbore of the old cavity of the well; if it is determined that the original wellbore does not meet the conditions for conversion into an injection-production well, sealing the original wellbore and drilling a new well to connect with the cavity, and lowering the first injection-production pipe 12 and the first row of brine pipes 14 or the second injection-production pipe 22 and the second row of brine pipes 24 into the new well in step S1.

[0042] In some embodiments, the conversion injection-production well condition is to meet one or more of the following requirements: sealing requirements, casing quality requirements, cementing quality requirements, and injection-production throughput requirements.

[0043] In a specific embodiment, the old cavity of the existing salt mine has experienced long-term brine dissolution, and has problems such as severe casing deformation and corrosion, poor cementing quality, poor sealing conditions, and small wellbore injection and production throughput. It does not have the conditions for direct conversion into a gas injection and production well. Therefore, it needs to be sealed and a new well needs to be drilled.

[0044] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples. Within the spirit of the embodiments of the present invention, the technical features of the above embodiments or different embodiments may be combined, and there are many other variations of the different aspects of the embodiments of the present invention described above, which are not provided in detail for the sake of clarity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included within the scope of protection of the embodiments of the present invention.

Claims

1. A method for injecting gas into the old cavity of a salt cavern gas storage to remove brine, characterized in that: The well old cavity includes a first cavity, a second cavity, and a horizontal channel connecting the first cavity and the second cavity, the bottoms of the first cavity and the second cavity are both lower than the top of the horizontal channel, and the method includes: A first injection-production pipe and a first row of brine pipes are lowered into the wellbore of the first cavity, and a second injection-production pipe and a second row of brine pipes are lowered into the wellbore of the second cavity; Injecting gas into the first cavity through the first injection and production pipe, so that the brine in the first cavity is discharged through the first row of brine pipes, until the gas-water interface in the first cavity drops to the depth of the top of the horizontal channel; Injecting gas into the second cavity through the second injection and production pipe, so that the brine in the second cavity is discharged through the second row of brine pipes, until the gas-water interface in the second cavity drops to the depth of the lower end of the second row of brine pipes, wherein the depth of the lower end of the second row of brine pipes is lower than the depth of the top of the horizontal channel; Gas is injected into the first cavity again through the first injection and production pipe, so that the remaining brine in the first cavity is discharged through the first row of brine pipes until the gas-water interface of the first cavity drops to the depth of the lower port of the first row of brine pipes, completing gas injection and brine discharge.

2. The method according to claim 1, characterized in that The distance between the lower end of the first row of brine pipes and the bottom of the first cavity is 1 to 2 meters.

3. The method according to claim 1, characterized in that The distance between the lower ends of the second row of brine pipes and the bottom of the second cavity is 1 to 2 meters.

4. The method according to claim 1, wherein The lower end port of the first injection and production pipe is located in the top area of ​​the first cavity.

5. The method according to claim 1, characterized in that The lower end port of the second injection and production pipe is located in the top area of ​​the second cavity.

6. The method according to claim 1, wherein The distance between the first cavity and the second cavity is 200-300 m.

7. The method according to claim 1, characterized in that Neutron logging is used to monitor the gas-water interface of the first cavity and the second cavity.

8. The method according to claim 1, characterized in that Also includes: Evaluating the original wellbore of the old wellbore; If it is determined that the original wellbore meets the conditions for conversion into an injection-production well, the first injection-production pipe and the first row of brine pipes or the second injection-production pipe and the second row of brine pipes are lowered into the original wellbore.

9. The method according to claim 1, characterized in that Also includes: Evaluating the original wellbore of the old wellbore; If it is determined that the original wellbore does not meet the conditions for conversion into an injection-production well, the original wellbore is sealed and a new well is drilled, and the first injection-production pipe and the first row of brine pipes or the second injection-production pipe and the second row of brine pipes are lowered into the new well.

10. The method according to claim 8 or 9, characterized in that The conversion injection-production well conditions are to meet one or more of the following requirements: sealing requirements, casing quality requirements, cementing quality requirements, and injection-production throughput requirements.

Images