阅读说明：本技术 双井连通盐穴储气库的扩容方法 (Expansion method of double-well communicated salt cavern gas storage ) 是由 陈飞 姜海涛 李锐敏 郭凯 肖恩山 赵艳杰 王立东 于 2020-05-29 设计创作，主要内容包括：本公开提供了一种双井连通盐穴储气库的扩容方法,所述双井连通盐穴储气库包括两个盐穴和连通所述两个盐穴的连通通道,各所述盐穴均具有井,所述扩容方法包括：在所述两个盐穴的两井之间钻出与所述连通通道连通的扩容井；对所述双井连通盐穴储气库进行多次扩容作业,所述扩容作业包括：向所述两个盐穴的井内注入溶盐介质；向所述两个盐穴的井内注入驱替介质,将所述两个盐穴内的混合液从所述扩容井排出。本公开能增大双井连通盐穴储气库体积,提高双井连通盐穴储气库的利用率。(The invention provides a capacity expansion method of a double-well communicated salt cavern gas storage, wherein the double-well communicated salt cavern gas storage comprises two salt caverns and a communication channel communicated with the two salt caverns, each salt cavern is provided with a well, and the capacity expansion method comprises the following steps: drilling an expansion well communicated with the communication channel between the two wells of the two salt caverns; it is right twin-well intercommunication salt cavern gas storage carries out dilatation operation many times, the dilatation operation includes: injecting a salt dissolving medium into the wells of the two salt caverns; and injecting a displacement medium into the wells of the two salt caverns, and discharging the mixed liquor in the two salt caverns from the expansion well. The double-well communicated salt cavern gas storage volume can be increased, and the utilization rate of the double-well communicated salt cavern gas storage is improved.)

1. A capacity expansion method for a twin-well connected salt cavern gas storage, the twin-well connected salt cavern gas storage comprises two salt caverns and a communication channel for communicating the two salt caverns, each salt cavern is provided with a well, and the capacity expansion method comprises the following steps:

drilling an expansion well communicated with the communication channel between the two wells of the two salt caverns;

it is right twin-well intercommunication salt cavern gas storage carries out dilatation operation many times, the dilatation operation includes:

injecting a salt dissolving medium into the wells of the two salt caverns;

and injecting a displacement medium into the wells of the two salt caverns, and discharging mixed liquor in the two salt caverns from the expansion well, wherein the mixed liquor at least comprises a mixture of the salt dissolving medium and the salt substances in the two salt caverns.

2. The method for expanding the twin-well connected salt cavern gas storage according to claim 1, wherein before the expansion operation of the twin-well connected salt cavern gas storage for a plurality of times, the method further comprises:

and injecting the displacement medium into the wells of the two salt caverns, and discharging the original brine in the dissolving cavities of the two salt caverns from the expansion well.

3. The method of claim 2, wherein said injecting said displacement medium into said wells of said two salt caverns and discharging said raw brine from said cavities of said two salt caverns from said expanded wells comprises:

installing injection and drainage devices in the wells of the two salt caverns, wherein the injection and drainage devices extend from the well mouths of the wells of the two salt caverns to the dissolving cavities of the two salt caverns;

and injecting the displacement medium into the dissolving cavities of the two salt caverns through the injection and discharge device, so that the original brine is discharged from the expansion well until the liquid level of the original brine is not higher than the surfaces of the bottom pits of the two salt caverns.

4. The method for expanding the dual-well connected salt cavern gas storage according to claim 3, wherein the injection and drainage device comprises: the first injection-discharge pipe is coaxially sleeved on the second injection-discharge pipe, and the length of the second injection-discharge pipe is greater than that of the first injection-discharge pipe;

the injecting a salt dissolving medium into the wells of the two salt caverns comprises:

injecting said salt dissolving medium from said second injection drain tube into the dissolution chambers of said two salt caverns;

the injecting a displacement medium into the wells of the two salt caverns comprises:

and injecting the displacement medium into the dissolving cavities of the two salt cavities from the first injection and discharge pipe.

5. The method of expanding a dual well connected salt cavern gas storage as recited in claim 1, wherein drilling an expansion well in communication with said communication channel between two wells of said two salt caverns comprises:

drilling an expansion well between two wells of the two salt caverns;

installing an expansion inner pipe and an expansion outer pipe in the expansion well, wherein the expansion outer pipe is coaxially sleeved on the expansion inner pipe, and the length of the expansion inner pipe is greater than that of the expansion outer pipe;

and forming a dilatation well dissolving cavity at the bottom of the dilatation well, so that the dilatation well dissolving cavity is communicated with the communication channel.

6. The method of claim 5, wherein said draining mixed liquor from said two salt caverns from said expansion well further comprises:

and injecting the displacement medium into the expansion well from the expansion outer pipe to displace the dissolved salt medium and discharge the dissolved salt medium from the expansion inner pipe to the expansion well.

7. The method of expanding a twin-well connected salt cavern gas storage as claimed in claim 5, wherein drilling an expansion well between two wells of the two salt caverns comprises:

determining a target point on the communicating channel, and drilling towards the target point to form a hole;

installing casing within the bore to form an expanded well.

8. The method of expanding the dual-well connected salt cavern gas storage as claimed in claim 5, wherein the forming of the expansion well cavity at the bottom of the expansion well comprises:

and carrying out water-soluble cavity construction operation at the bottom of the expansion well to form an expansion well cavity communicated with the expansion well and the communication channel.

9. The method for expanding the twin-well connected salt cavern gas storage as claimed in any one of claims 1 to 8, wherein the displacement medium is natural gas.

10. The method for expanding the dual-well interconnected salt cavern gas storage as claimed in any one of claims 1 to 8, wherein the salt dissolving medium is water.

Technical Field

The disclosure relates to the technical field of salt cavern gas storage, in particular to a capacity expansion method for a double-well communicated salt cavern gas storage.

Background

The salt cavern is an underground cavern formed after mining in a thicker underground salt layer or salt dome by a water-soluble mining mode, and has large volume and good sealing. The salt under high temperature and high pressure has the characteristic of automatically healing the seam, so that the underground salt cavern can form a good sealed storage warehouse, namely a salt cavern gas storage. The salt cavern gas storage can be used for storing petroleum and natural gas.

In the related art, a salt cavern gas storage is formed by drilling a vertical well and creating a dissolution cavity at the bottom of the vertical well. The cavity refers to a space left after underground minerals are extracted and collected by water injection dissolution, for example, a cavity formed after underground rock salt is extracted by a water dissolving method. And after the cavity building is finished, installing a gas injection pipe column and a brine discharge pipe column on the vertical shaft. Then, natural gas is injected into the well through the gas injection pipe column, brine in the dissolving cavity is pushed by the natural gas to be discharged from the brine discharge pipe column, and then the brine discharge pipe column is lifted, so that the natural gas is stored in the salt cavern gas storage.

At present, a plurality of double-well communicated salt cavern gas storages exist in China, and the double-well communicated salt cavern gas storages mean that a dissolving cavity is formed at the bottom of each of two straight wells, and the two dissolving cavities are communicated through channels formed in an ore layer to form the salt cavern gas storages.

Usually, the pit of the double-well communicated salt cavern gas storage has larger volume, and the pit is mostly filled with salt production residues. The salt mining residue contains salt bed stones, soluble salts that have not been dissolved to any extent (falling to the pit during initial salt mining, no longer dissolving due to saturation of the lower salt concentration) and brine (mainly present in the voids of the pit). Therefore, the volume of the formed salt cavern gas storage is small, the utilization value is not high, and a large number of double-well communicated salt cavern gas storages are idle.

Disclosure of Invention

The embodiment of the disclosure provides a capacity expansion method for a twin-well communicated salt cavern gas storage, which can increase the volume of the twin-well communicated salt cavern gas storage and improve the utilization rate of the twin-well communicated salt cavern gas storage. The technical scheme is as follows:

the embodiment of the disclosure provides a capacity expansion method for a twin-well communicated salt cavern gas storage, wherein the twin-well communicated salt cavern gas storage comprises two salt caverns and a communication channel communicated with the two salt caverns, each salt cavern is provided with a well, and the capacity expansion method comprises the following steps: drilling an expansion well communicated with the communication channel between the two wells of the two salt caverns; it is right twin-well intercommunication salt cavern gas storage carries out dilatation operation many times, the dilatation operation includes: injecting a salt dissolving medium into the wells of the two salt caverns; and injecting a displacement medium into the wells of the two salt caverns, and discharging mixed liquor in the two salt caverns from the expansion well, wherein the mixed liquor at least comprises a mixture of the salt dissolving medium and the salt substances in the two salt caverns.

In an implementation manner of the embodiment of the present disclosure, before performing multiple expansion operations on the twin-well connected salt cavern gas storage, the expansion method further includes: and injecting the displacement medium into the wells of the two salt caverns, and discharging the original brine in the dissolving cavities of the two salt caverns from the expansion well.

In another implementation manner of the embodiment of the present disclosure, the injecting the displacement medium into the wells of the two salt caverns, and discharging the raw brine in the cavities of the two salt caverns from the expansion well includes: installing injection and drainage devices in the wells of the two salt caverns, wherein the injection and drainage devices extend from the well mouths of the wells of the two salt caverns to the dissolving cavities of the two salt caverns; and injecting the displacement medium into the dissolving cavities of the two salt caverns through the injection and discharge device, so that the original brine is discharged from the expansion well until the liquid level of the original brine is not higher than the surfaces of the bottom pits of the two salt caverns.

In another implementation manner of the embodiment of the present disclosure, the injection and drainage device includes: the first injection-discharge pipe is coaxially sleeved on the second injection-discharge pipe, and the length of the second injection-discharge pipe is greater than that of the first injection-discharge pipe; the injecting a salt dissolving medium into the wells of the two salt caverns comprises: injecting said salt dissolving medium from said second injection drain tube into the dissolution chambers of said two salt caverns; the injecting a displacement medium into the wells of the two salt caverns comprises: and injecting the displacement medium into the dissolving cavities of the two salt cavities from the first injection and discharge pipe.

In another implementation of the embodiment of the present disclosure, the drilling an expansion well between two wells of the two salt caverns, the expansion well being in communication with the communication channel, includes: drilling an expansion well between two wells of the two salt caverns; installing an expansion inner pipe and an expansion outer pipe in the expansion well, wherein the expansion outer pipe is coaxially sleeved on the expansion inner pipe, and the length of the expansion inner pipe is greater than that of the expansion outer pipe; and forming a dilatation well dissolving cavity at the bottom of the dilatation well, so that the dilatation well dissolving cavity is communicated with the communication channel.

In another implementation manner of the embodiment of the present disclosure, the discharging the mixed liquid in the two salt caverns from the expansion well further includes: and injecting the displacement medium into the expansion well from the expansion outer pipe to displace the dissolved salt medium and discharge the dissolved salt medium from the expansion inner pipe to the expansion well.

In another implementation of the embodiment of the present disclosure, the drilling an expansion well between two wells of the two salt caverns includes: determining a target point on the communicating channel, and drilling towards the target point to form a hole; installing casing within the bore to form an expanded well.

In another implementation manner of the embodiment of the present disclosure, the forming of the expansion well cavity at the bottom of the expansion well includes: and carrying out water-soluble cavity construction operation at the bottom of the expansion well to form an expansion well cavity communicated with the expansion well and the communication channel.

In another implementation of the embodiments of the present disclosure, the displacement medium is natural gas.

In another implementation of an embodiment of the present disclosure, the salt-dissolving medium is water.

The beneficial effects brought by the technical scheme provided by the embodiment of the disclosure at least comprise:

the expansion method of the double-well communicated salt cavern gas storage provided by the embodiment of the disclosure comprises the steps of drilling an expansion well communicated with a communication channel between two wells of two salt caverns. I.e. drilling an expansion well at the position between two vertical wells of two salt caverns on the ore bed. And the drilled expansion well can be communicated with a communication channel for communicating the two salt caverns. And then, carrying out multiple expansion operations on the double-well communicated salt cavern gas storage. The capacity expansion operation comprises injecting a salt dissolving medium into the wells of the two salt cavities, and dissolving the soluble salt which is not dissolved in the solution cavity of the two salt cavities by the salt dissolving medium. The volume of the bottom pit is gradually reduced along with the gradual dissolution of the salt substances, so that more free space is reserved in the dissolving cavities of the two salt pits. Then, a displacement medium can be injected from the two wells of the two salt caverns, and the displacement medium is utilized to push the mixed liquid in the two salt caverns in the solution cavities of the two salt caverns to enter the expansion well through the communication channel. And in the process of pushing the mixed liquid in the two salt caverns to move towards the expansion well by using the displacement medium, a certain amount of brine also exists in the gap of the bottom pits of the two salt caverns, and the brine existing in the gap of the bottom pits can be displaced to the expansion well, so that the space which can be used for storing natural gas in the dissolved cavity of the salt cavern is further enlarged. And finally, discharging the mixed liquid in the two salt caverns, so that the mixed liquid in the two salt caverns cannot return to the dissolving cavities of the two salt caverns, and the expansion of the double-well communicated salt cavern gas storage can be completed.

The embodiment of the disclosure dissolves the soluble salt in the bottom pits of the two salt caverns through the salt dissolving medium to obtain the mixed solution, and discharges the mixed solution in the two salt caverns out of the solution cavities of the two salt caverns through the drilled expansion well, so that the volume of the double-well communicated salt cavern gas storage is greatly increased. Meanwhile, soluble salt in the bottom pits of the two salt caverns can be dissolved to the maximum extent through multiple times of expansion operation, so that the volume of the double-well communicated salt cavern gas storage is increased to the maximum extent. The improved capacity expansion method of the embodiment enables the idle twin-well communicated salt cavern gas storage to be reused, and improves the utilization rate of the twin-well communicated salt cavern gas storage.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present disclosure, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.

FIG. 1 is a schematic diagram of a structure of an underground salt cavern gas storage provided by the related art;

FIG. 2 is a schematic diagram of a twin-well connected salt cavern gas storage provided in the related art;

fig. 3 is a flowchart of a method for expanding a dual-well connected salt cavern gas storage according to an embodiment of the disclosure;

FIG. 4 is a flow chart of another method for expanding a dual-well connected salt cavern gas storage according to an embodiment of the disclosure;

FIG. 5 is a schematic diagram illustrating a first stage of expansion of a twin-well connected salt cavern gas storage according to an embodiment of the disclosure;

fig. 6 is a schematic diagram illustrating a second stage of expansion of a twin-well connected salt cavern gas storage according to an embodiment of the disclosure;

fig. 7 is a schematic diagram illustrating a third stage of expansion of a twin-well connected salt cavern gas storage according to an embodiment of the disclosure.

Detailed Description

To make the objects, technical solutions and advantages of the present disclosure more apparent, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

Fig. 1 is a schematic structural diagram of an underground salt cavern gas storage provided by the related art. As shown in fig. 1, the salt cavern gas storage is a single-well salt cavern gas storage, which comprises a vertical well 1 and a dissolving cavity 2 communicated with the vertical well 1. And the vertical well 1 comprises a casing 11 and a production string 12 arranged in the casing 11, a packer 13 is arranged between the casing 11 and the production string 12, and a safety valve 14 is arranged in the production string 12.

Wherein, the dissolving cavity in the single-well salt cavern gas storage is formed by a water dissolving method. The concrete process is that clear water is injected into the bottom of the vertical well from the production pipe column of the vertical well, so that the clear water dissolves soluble salt in the ore bed to form brine 21, solid substances in the ore bed are gradually reduced, and a cavity communicated with the vertical well, namely a dissolving cavity 2, is formed in the ore bed. Impurities and stones are not easy to dissolve in the dissolving cavity, and the impurities and the stones cannot be discharged out of the dissolving cavity along with the brine 21 in the cavity manufacturing process, so that the impurities and the stones are accumulated at the bottom of the cavity to finally form a pit 22.

As shown in fig. 1, if the soluble salt content in the deposit is high, a larger cavern can be formed, and the pit occupies only a small part of the volume of the cavern. And if the soluble salt content in the ore bed is less, the bottom pit in the formed cavity occupies most of the volume, so that the formed cavity has smaller volume.

Fig. 2 is a schematic structural diagram of a twin-well connected salt cavern gas storage provided in the related art. As shown in fig. 2, the twin well salt cavern gas reservoir comprises: two salt caves, two salt caves all have vertical well 1, two straight well 1 and the soluble cavity 2 that communicates with two vertical well 1 respectively, and communicate through communicating channel 3 between two soluble cavities 2, and two salt caves communicate through communicating channel 3 promptly. The two vertical wells 1 are respectively provided with a production pipe column 12 for injecting or discharging natural gas or brine.

As shown in figure 2, the salt content of the ore bed in the double-well communicated salt cavern gas storage is low, so that the size of a dissolving cavity 2 formed at the bottom hole positions of two straight wells 1 is small. That is, the formed pit 22 is closer to the bottom position of the vertical well 1, and the piled stones and impurities with different sizes in the pit 22 are overlapped and supported with each other, so that the formed pit contains a large amount of gaps, and the gaps are filled with brine, so that the pit 22 occupies more than 50% of the total volume of the molten cavity 2. In addition, the upper part of the bottom pit 22 in the cavity 2 is also filled with brine 21, which is inconvenient for storing substances such as petroleum, natural gas and the like. Therefore, the existing large quantity of double-well communicated salt cavern gas storage is in an idle state.

In order to improve the utilization rate of the twin-well communicated salt cavern gas storage, the embodiment of the disclosure provides a capacity expansion method of the twin-well communicated salt cavern gas storage. Fig. 3 is a flowchart of a method for expanding a dual-well connected salt cavern gas storage according to an embodiment of the disclosure. As shown in fig. 3, the capacity expansion method includes:

step 101: and drilling an expansion well communicated with the communication channel between the two wells of the two salt caverns.

Wherein, make the dilatation well can communicate with the intercommunication of the dissolved cavity of two mouths of well to the dissolved cavity of two mouths of well that will expand the dilatation well and twin-well intercommunication salt cavern gas storage also communicates.

Step 102: and carrying out multiple expansion operations on the double-well communicated salt cavern gas storage.

Wherein, the dilatation operation includes:

in the first step, a salt dissolving medium is injected into the wells of the two salt caverns.

Salt dissolving medium is injected into two wells of the two salt cavities to dissolve salt substances in the dissolving cavities of the two salt cavities. Namely dissolving salt substances into a salt dissolving medium to form a mixture, and obtaining the mixture which is the brine.

And secondly, injecting a displacement medium into the wells of the two salt caverns, and discharging the mixed solution in the two salt caverns from the expansion well.

Wherein the mixed solution at least comprises a mixture of a salt dissolving medium and salt substances in the two salt holes. I.e. the mixed liquor may comprise a mixture of the salt species in the two salt caverns dissolved in the dissolved salt medium and the brine present in the two salt caverns themselves, e.g. in the interstices of the pit of the salt cavern.

The displacement medium is insoluble in brine and does not react with brine. Therefore, the displacement medium is injected into the two wells of the two salt caverns, so that the brine in the dissolving cavities of the two salt caverns can be pushed to move to the expansion well through the communication channel, and finally the brine is displaced to the expansion well.

The expansion method of the double-well communicated salt cavern gas storage provided by the embodiment of the disclosure comprises the steps of drilling an expansion well communicated with a communication channel between two wells of two salt caverns. Namely, the expansion well is drilled at the position between two vertical wells on the ore bed, wherein the two vertical wells are communicated with the salt cavern gas storage. And the drilled expansion well can be communicated with a communication channel for communicating the two salt caverns. And then, carrying out multiple expansion operations on the double-well communicated salt cavern gas storage. The capacity expansion operation comprises injecting a salt dissolving medium into the wells of the two salt holes, and dissolving soluble salt (namely salt substances) which is not dissolved in the dissolving cavity of the two salt holes of the double-well communicated salt hole gas storage. The salt substance is mostly filled in the salt layer interlayer stones of the solution cavities of the two salt holes, so that a bottom pit is formed together with the salt layer interlayer stones and most of the volume of the double-well communicated salt hole gas storage is filled. The pit volume of two salt pits of the double-well communicated salt pit gas storage is larger. At the moment, salt dissolving media are injected into the dissolving cavities of the two salt cavities, so that salt substances in the salt layer included stones in the dissolving cavities of the two salt cavities can be dissolved to form brine. Because the salt substance can become liquid brine after being dissolved, and the volume of the bottom pit is gradually reduced along with the gradual dissolution of the salt substance, more free space is reserved in the dissolving cavities of the two salt pits. And after dissolving most salt matter, can pour into the displacement medium into from two mouths of two wells of two salt caves, this displacement medium is insoluble in brine and can not react with brine, dissolve the displacement medium that the intracavity was poured into along with two salt caves and increase gradually, the whole chamber of dissolving of two salt caves can progressively be filled to the displacement medium, and promote the brine of dissolving the intracavity of two salt caves, from the space in the salt layer double-well intercommunication salt cave gas storage reservoir rock to more depths removal, and finally push away the brine of dissolving the intracavity of two salt caves to the dilatation well through the intercommunication passageway. Even if the free space in the dissolving cavities of the two salt caverns is more, the volume of the double-well communicated salt cavern gas storage is expanded. And in the process of pushing the mixed liquid in the two salt caverns to move towards the expansion well by using the displacement medium, a certain amount of brine also exists in the gap of the bottom pits of the two salt caverns, and the brine existing in the gap of the bottom pits can be displaced to the expansion well, so that the space which can be used for storing natural gas in the dissolved cavity of the salt cavern is further enlarged. And finally, discharging the brine in the expansion well, so that the brine cannot return to the dissolved cavity of the double-well communicated salt cavern gas storage, and the expansion of the double-well communicated salt cavern gas storage can be completed. The soluble salt in the bottom pit of two salt caves is dissolved, and the formed brine is discharged from the dissolved cavities of the two salt caves through the drilled expansion well, so that the volume of the double-well communicated salt cave gas storage is greatly increased, the idle double-well communicated salt cave gas storage can be reused, and the utilization rate of the double-well communicated salt cave gas storage is improved. According to the embodiment of the invention, the soluble salt in the bottom pits of the two salt caverns can be dissolved to the maximum extent through multiple expansion operations, so that the volume of the double-well communicated salt cavern gas storage is increased to the maximum extent.

Fig. 4 is a flowchart of another expansion method for a twin-well connected salt cavern gas storage according to an embodiment of the disclosure. As shown in fig. 4, the capacity expansion method includes:

step 201: and drilling an expansion well communicated with the communication channel between the two wells of the two salt caverns.

Fig. 5 is a schematic diagram of a first stage of expansion of a twin-well connected salt cavern gas storage according to an embodiment of the disclosure. As shown in fig. 5, the first stage of expansion is to drill an expansion well 4 at a position between two vertical wells 1. The specific process of drilling the expansion well 4 may include the following three steps:

in the first step, an expansion well is drilled between the two wells of the two salt caverns.

The specific process of drilling the expansion well may be:

selecting one point on the communicating channel 3 as a target point, and drilling a hole in the ore bed by drilling a drilling tool to the target point after setting the target point; then, a sleeve is installed in the hole along the axial direction of the hole and fixed to form an expansion shaft, so that the expansion well is obtained. The expansion well 4 thus formed may communicate with the communication passage 3 at a target point.

Illustratively, as shown in fig. 5, the expansion wellbore 41 may be disposed at a position between two vertical wells 1 of two salt caverns on the mineral seam. After the expansion shaft 41 is drilled, the bottom part of the expansion shaft 41 is communicated with the communication channel 3 between the two dissolving cavities 2 of the two wells (namely, the expansion shaft 41 is communicated with the communication channel 3 for communicating the two salt cavities), so that the purpose that the expansion shaft 4 is simultaneously communicated with the two dissolving cavities 2 of the two wells of the two salt cavities is realized.

Due to the scouring effect of brine in the communicating channel 3, the diameter of the communicating channel 3 is increased to a certain extent when being formed compared with that when a horizontal drill is adopted in the salt mine exploitation process, but the diameter of the communicating channel 3 is far smaller than that of the main body part of a salt cavern, the shape of the communicating channel cannot be accurately measured by a common geophysical logging method, the shape change of a salt cavity can be reversed according to the volume of the salt cavern, the content of insoluble substances and the underground operation record, the shape of the communicating channel is predicted, and the target point can be conveniently determined by combining the shape of the communicating channel.

And secondly, installing an expansion inner pipe and an expansion outer pipe in the expansion well, wherein the expansion outer pipe is coaxially sleeved on the expansion inner pipe, and the length of the expansion inner pipe is greater than that of the expansion outer pipe.

Illustratively, as shown in FIG. 5, an expanded inner tube 42 and an expanded outer tube 43 are installed coaxially spaced-apart and nested within an expanded wellbore 41. The expansion inner pipe 42 and the expansion outer pipe 43 both extend from the well head position of the expansion well as the starting point to the bottom of the expansion well. And the length of the expansion inner pipe 42 is greater than that of the expansion outer pipe 43, i.e. the expansion outer pipe 43 is closer to the bottom of the expansion well than the expansion inner pipe 42.

Wherein, the annular space between dilatation inner tube 42 and the dilatation outer tube 43 and dilatation inner tube 42 all can regard as the passageway of transport medium, and the dilatation inner tube 42 and the dilatation outer tube 43 through setting up coaxial setting are convenient for the injection and the discharge of material in the dilatation well like this.

In the embodiment of the present disclosure, in order to prevent the annular space between the expansion outer tube 43 and the expansion wellbore from affecting the injection and discharge of the substances in the expansion well, a packer is arranged between the expansion outer tube 43 and the expansion wellbore to block the annular space between the expansion outer tube 43 and the expansion wellbore, thereby preventing the injection and discharge of the substances in the expansion well.

Meanwhile, a safety valve can be arranged in the expansion inner tube 42, when the ground or the underground is abnormal, the expansion inner tube 42 can be cut off in time through a ground control system, and the injected substances in the expansion well or the substances in the expansion well are prevented from being discharged outwards, so that the operation safety is ensured.

And thirdly, injecting a salt dissolving medium into the bottom of the expansion shaft through the expansion inner pipe 42 to form an expansion well dissolving cavity 44 at the bottom of the expansion well 4.

The specific steps of forming the expansion well molten cavity 44 at the bottom of the expansion well 4 may include: after the formation of the expansion well 4, a water-soluble cavity-making operation is performed at the bottom of the expansion well 4 to form an expansion well dissolution chamber 44 communicating the expansion well 4 and the communication passage 3.

As shown in fig. 5, the expansion well 4 communicates with the communication passage 3 through the expansion well relief 44. Because the stratum inclination angle and the lithology change, there will be the error with the target spot usually in the in-process of boring and establishing dilatation well 4 for do not link to each other between dilatation well 4 and the intercommunication passageway 3, consequently after forming dilatation well 4, through water-soluble chamber-building operation, can form dilatation well dissolving chamber 44, make dilatation well dissolving chamber 44 and intercommunication passageway 3 communicate, thereby make dilatation well 4 can link to each other with intercommunication passageway 3.

When the cavity is formed by water, the following method can be specifically adopted:

an initial cavity is formed at the bottom of the expansion well 4 through water cavity-making operation. Then, water injection operation is carried out to the bottom of the two expansion wells 4 through the expansion inner pipes 42 of the expansion wells 4, and when brine is discharged from the well mouths of the expansion wells 4, the water injection is stopped. When no brine is discharged from the well mouth of the expansion well 4, the water-soluble cavity construction operation and the water injection operation are repeated until brine is discharged from the well mouth of the expansion well 4. The water-soluble cavity-making operation is performed by gradually injecting water so that the diameter of the initial cavity is gradually increased to obtain an expanded well cavity 44 (see fig. 5) which is finally communicated with the communication channel 3. Namely, clear water is injected into the bottom position of the dilatation shaft through the dilatation inner tube 42, and soluble salt in the ore bed is dissolved by the clear water, so that an dilatation well dissolving cavity 44 communicated with the communication channel 3 is formed in the ore bed, and the dilatation well communicated with the communication channel 3 is obtained.

Alternatively, the soluble salt in the deposit may form brine after dissolving in the clear water, and a displacement medium, such as natural gas, may be injected into the expansion well dissolution chamber 44 of the expansion well from the expansion outer tube 43. So as to drive the brine in the dissolved cavity of the expansion well to be discharged from the expansion inner pipe 42, so that more cavities are formed in the dissolved cavity 44 of the expansion well, and the brine displaced from the dissolved cavity of the double-well communicated salt cavern gas storage can be conveniently and subsequently absorbed.

In the implementation mode, the expansion well dissolution cavity is formed at the bottom of the expansion well, so that the expansion well can conveniently absorb brine displaced from the dissolution cavity of the double-well communicated salt cavern gas storage in the subsequent flow. Simultaneously, the expansion well solution cavity also increases the contact area between the expansion well and the communication channel, so that brine can more easily enter the expansion well from the solution cavity of the double-well communicated salt cavern gas storage.

Step 202: and injecting a displacement medium into the wells of the two salt caverns, and discharging the original brine in the dissolving cavities of the two salt caverns from the expansion well.

Wherein the original brine is originally existed in the dissolving cavities of the two salt caverns. That is, it is present in the caverns of both salt caverns prior to performing the method of expanding the volume of the twin well connected salt cavern gas reservoir of the present disclosure.

Fig. 6 is a schematic diagram of a second stage of expansion of a twin-well connected salt cavern gas storage according to an embodiment of the disclosure. As shown in fig. 6, the second stage of the expansion is to displace the original brine 51 in the two vertical wells 1 in the two-well connected salt cavern gas storage to the expansion well 4. And the specific displacement process may include the following two steps:

firstly, installing injection and discharge devices in two wells of a double-well communicated salt cavern gas storage, wherein the injection and discharge devices extend to the dissolving cavities of the two salt caverns from the well mouths of the two wells of the two salt caverns.

Wherein, notes drain device can include: the device comprises a first injection and discharge pipe 15 and a second injection and discharge pipe 16, wherein the first injection and discharge pipe 15 is coaxially sleeved on the second injection and discharge pipe 16, and the length of the second injection and discharge pipe 16 is greater than that of the first injection and discharge pipe 15.

Illustratively, as shown in fig. 6, a first injection-discharge pipe 15 and a second injection-discharge pipe 16 are coaxially and alternately sleeved in two wells of two salt caverns. The first injection-discharge pipe 15 and the second injection-discharge pipe 16 both extend from the well head positions of the two wells of the two salt caverns as starting points to the well bottoms of the two wells of the two salt caverns. And the length of the second injection and discharge pipe 16 is greater than that of the first injection and discharge pipe 15, that is, the first injection and discharge pipe 15 is closer to the bottoms of two wells of two salt holes compared with the second injection and discharge pipe 16.

The annulus between the first injection and discharge pipe 15 and the second injection and discharge pipe 16 can be used as a channel for conveying media, so that the first injection and discharge pipe 15 and the second injection and discharge pipe 16 which are coaxially arranged are convenient for injecting and discharging substances in two wells of two salt holes.

In the embodiment of the present disclosure, in order to avoid that the annular space between the first pipe 15 and the second pipe 16 will affect the injection and discharge of the substances in the two wells of the two salt cavities, a packer is disposed between the first pipe 15 and the second pipe 16 to isolate the annular space between the first pipe 15 and the second pipe 16, thereby preventing the injection and discharge of the substances in the two wells of the two salt cavities.

And secondly, injecting a displacement medium into the dissolving cavities of the two salt caverns through an injection and discharge device, so that the liquid level of the original brine is not higher than the surfaces of the bottom pits of the two salt caverns.

Wherein, the bottom pit is formed by that no soluble salt which can be dissolved in the salt pit falls to the bottom of the salt pit and is accumulated at the initial stage of the salt pit construction.

The real-time liquid level height of the original brine can be obtained by modeling and calculating the wellhead pressure of the wells for detecting the two salt caverns and the density of the original brine. The specific calculation process can be found in the related art. The surface positions of the pits of the two salt caverns can be measured by sonar to determine the depth positions of the pits of the two salt caverns, and the surface of the pits of the two salt caverns is determined by the depth positions.

In combination with the above-described structure of the injection and drainage device, the second step may include: a displacement medium, for example natural gas, is injected into the cavities of the two salt caverns through a first injection-discharge pipe 15. Along with the natural gas 6 that injects increases gradually, the whole dissolving cavity 2 of two salt caves can be filled gradually to natural gas 6 to promote the original brine 51 in the dissolving cavity 2 of two salt caves, follow the clearance in the salt layer double stone of twin-well intercommunication salt cave gas storage and move to deeper, and finally push original brine 51 in the dissolving cavity 2 of two mouths of well of two salt caves to in the dilatation well 4.

As shown in fig. 6, at this stage, the raw brine 51 is approximately level with the surface of the bottom pit 22 of the two salt caverns. That is, most of the original brine 51 in the two salt caverns enters the gaps between the salt layers of the two salt caverns and is displaced into the expansion well dissolution cavity 44 of the expansion well 4 through the communication channel 3. The raw brine 51 will therefore be at a level no higher than the surface of the pit 22 in both salt caverns, so that the two salt caverns have more space to fill with natural gas.

Combining the dilatation inner tube 42 and the dilatation outer tube 43 that set up in the above-mentioned dilatation well, discharging the original brine in the dissolving cavity of two salt caverns from the dilatation well in step 202 can include: by injecting a displacement medium, such as natural gas 6, from the outer expansion tube 43 into the expansion well dissolution chamber 44 of the expansion well. To drive the raw brine 51 in the expanded well cavity 44 of the expanded well 4 out of the expanded inner pipe 42.

Step 203: and carrying out multiple expansion operations on the double-well communicated salt cavern gas storage.

Because the dissolved salt substances in the pit can be dissolved by one expansion operation per cycle, the expanded volume of the double-well communicated salt cavern gas storage is limited. Therefore, the soluble salt in the bottom pits of the two salt caverns can be dissolved to the maximum extent through repeated circulating expansion operation, so that the volume of the double-well communicated salt cavern gas storage is increased to the maximum extent.

The specific time when to stop the loop expansion operation in step 203 can be determined in the following two ways.

First, the volume of the salt cavern may be surveyed after a certain number of cycles of expansion (e.g., 3 to 5). Stopping the expansion operation when the volume of the salt cavern reaches the expected volume; if the volume of the salt cavern does not reach the expected volume, the cyclic expansion operation is continued until the volume of the salt cavern reaches the expected volume.

Second, the concentration of brine discharged from the expansion well may be detected, with lower concentrations of brine discharged indicating less undissolved salt in the salt cavern, at which time the space available for expansion in the salt cavern is smaller.

For example, if the concentration of brine discharged from the expansion well is not higher than the expected concentration (e.g., 5% to 10%), the expansion operation may be stopped; and if the concentration of the brine discharged from the expansion well exceeds the expected concentration, continuing to circulate the expansion operation until the concentration of the discharged brine is not higher than the expected concentration.

Wherein, the dilatation operation includes:

in the first step, a salt dissolving medium is injected into the wells of the two salt caverns.

In the first step, a salt dissolving medium is injected into two wells of two salt caverns to dissolve salt substances in a dissolving cavity of the two salt caverns. Namely dissolving salt substances into a salt dissolving medium to form a mixture, and obtaining the mixture which is the brine.

Fig. 7 is a schematic diagram illustrating a third stage of expansion of a twin-well connected salt cavern gas storage according to an embodiment of the disclosure. As shown in fig. 7, the third stage of expansion is a process of injecting a salt-dissolving medium into two straight wells of two salt caverns to form brine, and displacing the salt-dissolving medium with dissolved salt into the expansion well 4. Wherein, the process of injecting the salt dissolving medium is as follows:

as can be seen from the above structure of the injection and discharge device, as shown in fig. 7, the first step of injecting the salt-dissolving medium may include: the salt dissolving medium is injected into the dissolving cavities 2 of the two salt caverns from the second injection and discharge pipe 16.

The salt dissolving medium can be water, and the original brine in the dissolving cavities of the two salt pits is all displaced into the gaps and the expansion wells in the salt layer stones of the two salt pits, so that water is injected again, the contact area between the water and the pit can be increased, the clear water can be fully contacted with the undissolved soluble salt in the pit, and the soluble salt is dissolved in the clear water to form brine.

In the first step of the capacity expansion operation, salt substances in the salt layer stones in the salt layer dissolving cavities of the two salt cavities can be dissolved to form brine by injecting water into the dissolving cavities of the two salt cavities. Because the salt substance is mixed with the liquid salt dissolving medium to form brine after being dissolved, and the volume of the pit 22 is gradually reduced along with the gradual dissolution of the salt substance, more free space is reserved in the dissolving cavities 2 of the two salt cavities.

And secondly, injecting a displacement medium into the wells of the two salt caverns, and discharging the mixed solution in the two salt caverns from the expansion well.

Wherein the mixed liquor at least comprises the mixture of the salt dissolving medium and the salt substances in the two salt holes. I.e. the mixed liquor may comprise a mixture of the salt species in the two salt caverns dissolved in the dissolved salt medium and the brine present in the two salt caverns themselves, e.g. in the interstices of the pit of the salt cavern.

The displacement medium injected in the second step is insoluble in the brine and does not react with the brine. Therefore, by injecting the displacement medium into the two wells of the two salt caverns, the brine (dissolved salt medium dissolved with soluble salt) in the dissolved cavities of the two salt caverns can be pushed to move to the expansion well through the communication channel, and finally the dissolved salt medium is displaced to the expansion well.

In combination with the structure of the injection and discharge device, as shown in fig. 7, the process of injecting the displacement medium in the second step of the expansion operation may include: and injecting a displacement medium into the dissolving cavity 2 of the double-well communicated salt cavern gas storage from the first injection and discharge pipe 15.

Wherein, as shown in fig. 7, the displacement medium may be natural gas 6, because natural gas 6 is insoluble in brine and does not react with brine, the natural gas 6 injected into the dissolving cavity 2 along with the two salt caverns is gradually increased, the natural gas 6 gradually fills the whole dissolving cavity 2 of the two salt caverns, and pushes the brine (the dissolved salt medium 52 in which soluble salt is dissolved) in the dissolving cavity 2 of the two salt caverns, and moves from the gap in the salt layer interlayer of the two salt caverns to a deeper position, and finally pushes the dissolved salt medium 52 in which soluble salt is dissolved in the dissolving cavity 2 of the two wells of the two salt caverns into the expansion well 4.

Combining the dilatation inner tube 42 and the dilatation outer tube 43 that set up in the above-mentioned dilatation well, the mixed liquid in two salt caverns is followed in the second step of dilatation operation the dilatation well is discharged and can be included: a displacement medium, such as natural gas 6, is injected from the expansion outer tube 43 into the expansion well relief 44 of the expansion well. To drive the dissolved salt medium 52 with dissolved soluble salt in the expansion well molten cavity 44 of the expansion well out of the expansion well from the expansion inner tube 42.

In the process of discharging the dissolved salt medium, the displacement medium is injected into both the wells of the two salt caverns simultaneously, so that the displacement medium injected into the expansion well 4 and the dissolved salt medium 52 in the expansion well dissolution cavity 44 of the expansion well 4 are pressurized together, and the dissolved salt medium 52 in the expansion well dissolution cavity 44 of the expansion well 4 is driven to be discharged out of the expansion well 4 from the expansion inner tube 42.

The soluble salt in the pit of this disclosed embodiment through dissolving twin-well intercommunication salt cave gas storage to the expansion well that will form discharges the dissolved chamber of twin-well intercommunication salt cave gas storage through drilling out, make the volume of twin-well intercommunication salt cave gas storage greatly increased, and, utilize the natural gas to promote the in-process that the soluble salt medium that has dissolved the soluble salt in two salt caves removed to the expansion well, a certain amount of brine also exists in the space of the pit of two salt caves itself, this brine that exists in the space of pit also can be displaced to the expansion well, thereby can be used to the space of storage natural gas in the dissolved chamber of further expanding the salt cave, the volume of increase twin-well intercommunication salt cave gas storage promptly. The idle twin-well communicated salt cavern gas storage can be reused, and the utilization rate of the twin-well communicated salt cavern gas storage is improved.

Although the present disclosure has been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure.