Concentric three-pipe layered steam flooding process pipe column

Abstract

The utility model relates to the technical field of oilfield exploitation underground process pipe columns, in particular to a concentric three-pipe layered steam flooding process pipe column. The concentric three-pipe layered steam flooding process pipe column comprises an outer pipe column body, a middle pipe column body and an inner pipe column body. The outer pipe column body comprises an outer pipe, an upper packer, a middle packer, a lower packer, an upper inserting pipe sealer and a lower inserting pipe sealer. The middle pipe column comprises a middle pipe and an upper sealing insertion pipe, and the upper sealing insertion pipe is inserted into the upper insertion pipe sealer in a sealed mode so that an annular space between the middle pipe column and the outer pipe column above the upper insertion pipe sealer can form a first steam injection channel. The inner pipe column comprises an inner pipe and a lower sealing insertion pipe, and the lower sealing insertion pipe is inserted into the lower insertion pipe sealer in a sealed mode so that the annular space between the inner pipe column and the middle pipe column and the annular space between the inner pipe column and the outer pipe column above the lower insertion pipe sealer can jointly form a second steam injection channel. The inner pipe column is provided with a third steam injection channel, and the outer pipe is connected with an upper steam injection valve, a middle steam injection valve and a lower steam injection valve. According to the utility model, three-layer accurate steam distribution and injection can be realized.

Description

Technical Field

[0001] The utility model relates to the technical field of downhole process strings for oilfield exploitation, in particular to a concentric three-tube stratified steam flooding process string. Background Art

[0002] The heavy oil in heavy oil reservoirs has high viscosity, large density and poor fluidity, making it difficult to exploit. In the early stage, steam stimulation was mainly relied on for development. However, the effect gradually deteriorated in the later stage of development. To improve the development effect of heavy oil, the method of injecting hot steam into heavy oil reservoirs is currently widely used. Due to the heterogeneity characteristics of heavy oil reservoirs, in order to adapt to the stratified steam injection process for different numbers of layers and different demand targets, a stratified steam flooding process string needs to be used in combination to inject hot steam into different production layers in the well. The Chinese utility model patent with the authorization announcement number CN202215220U discloses a concentric stratified steam flooding downhole process string. This process string includes an inner steam injection pipe and an outer steam injection pipe. The inner steam injection pipe has an inner steam injection channel. The outer steam injection pipe is sleeved outside the inner steam injection pipe, and an annular steam injection channel is formed between the outer steam injection pipe and the inner steam injection pipe. The outer steam injection pipe is sequentially connected with a telescopic pipe, a heat-insulating oil pipe, an upper packer, a concentric gas distribution device, a lower packer and a telescopic sliding seal device from top to bottom. The outer cylinder of the telescopic sliding seal device is connected to the lower packer, and the inner cylinder is connected to the inner steam injection pipe. A plurality of split seal ring groups are hermetically arranged between the outer cylinder and the inner cylinder. When it is necessary to inject steam into the lower oil layer, the hot steam can be injected into the inner steam injection channel and then into the lower oil layer through the inner steam injection channel. When it is necessary to inject steam into the upper oil layer, the hot steam can be injected into the annular steam injection channel between the inner and outer steam injection pipes and then into the upper oil layer through the annular steam injection channel, so as to achieve two-channel stratified steam injection. However, this process string can only achieve two-layer stratified steam flooding and cannot meet the requirement of three-layer stratified steam flooding. At present, there is no process string that can achieve three-layer stratified steam flooding. Summary of the Utility Model

[0003] The purpose of the utility model is to provide a concentric three-tube stratified steam flooding process string to solve the problem that the existing concentric stratified steam flooding downhole process string cannot meet the requirement of three-layer stratified steam flooding.

[0004] The concentric three-tube stratified steam flooding process string of the utility model adopts the following technical solutions:

[0005] The concentric three - pipe stratified steam flooding technology string includes an outer - pipe string, a middle - pipe string, and an inner - pipe string. The outer - pipe string includes an outer pipe, upper, middle, and lower packers, and upper and lower insertion - tube sealers. The middle - pipe string includes a middle pipe and an upper sealing insertion tube. The upper sealing insertion tube is sealingly inserted into the upper insertion - tube sealer so that an annular space between the middle - pipe string and the outer - pipe string above the upper insertion - tube sealer forms a first steam injection channel. The inner - pipe string includes an inner pipe and a lower sealing insertion tube. The lower sealing insertion tube is sealingly inserted into the lower insertion - tube sealer so that the annular space between the inner - pipe string and the middle - pipe string and the annular space between the inner - pipe string and the outer - pipe string above the lower insertion - tube sealer jointly form a second steam injection channel. The inner - pipe string has a third steam injection channel communicating with the lower inner cavity of the outer - pipe string. The outer pipe is connected with an upper steam injection valve and a middle steam injection valve respectively communicating with the first and second steam injection channels, and a lower steam injection valve communicating with the lower inner cavity of the outer - pipe string.

[0006] Further, the upper insertion - tube sealer is located between the upper steam injection valve and the middle packer.

[0007] Further, the lower insertion - tube sealer is located between the middle steam injection valve and the lower packer.

[0008] Further, the inner diameters of the pipe sections of the outer pipe above the upper packer, between the upper packer and the middle packer, and below the middle packer decrease in sequence.

[0009] Further, the pipe section of the outer pipe above the upper packer is a heat - insulating oil pipe, and the pipe sections between the upper packer and the middle packer and below the middle packer are both plain - type oil pipes.

[0010] Further, a thermal compensator is also connected to the outer pipe.

[0011] Further, the thermal compensator is connected to the outer pipe near the upper pipe orifice.

[0012] Beneficial effects: The present utility model newly proposes a concentric three - pipe layered steam flooding process string. This process string includes a supporting outer - pipe string, a middle - pipe string, and an inner - pipe string. The outer - pipe string is used to be lowered into the wellbore and form an annulus with the casing. After the middle - pipe string is lowered into the outer - pipe string, it can form a sealed fit with the upper - part pipe section of the outer - pipe string, thereby forming a first steam injection channel in the annulus between the middle - pipe string and the outer - pipe string. After the inner - pipe string is lowered into the middle - pipe string, it can form a sealed fit with the lower - part pipe section of the outer - pipe string, thereby forming a second steam injection channel in the annulus between the inner - pipe string and the middle - pipe string and in the annulus between the inner - pipe string and the outer - pipe string. The inner cavity of the inner - pipe string forms a third steam injection channel, and the third steam injection channel communicates with the lower - part inner cavity of the outer - pipe string. The three steam injection channels are independent of each other. Steam injection valves are respectively arranged on the outer - pipe string corresponding to the three steam injection channels. During application, the upper, middle, and lower production layers are separated by the setting of three - stage packers on the outer - pipe string. The three - stage steam injection valves respectively correspond to the positions of the three production layers. Steam can be injected into the first, second, and third steam injection channels respectively according to the steam injection requirements of each layer. The injected medium enters the corresponding production layer after passing through the corresponding steam injection channel and steam injection valve. The three steam injection channels are independent of each other and are respectively equipped with steam injection valves, so that the injected medium and steam injection volume of each channel are independent of each other and do not affect each other. Thus, separate control, metering, and adjustment of steam injection for three layers can be realized, and precise steam injection allocation for three layers can be achieved. Description of the Drawings

[0013] Figure 1 It is the overall schematic diagram of the concentric three - pipe layered steam flooding process string of the present utility model after being lowered into the well.

[0014] In the figure: 101, outer pipe; 1011, upper pipe section; 1012, middle pipe section; 1013, lower pipe section; 102, thermal compensator; 103, upper packer; 104, upper steam injection valve; 105, upper plug - in seal; 106, middle packer; 107, middle steam injection valve; 108, lower plug - in seal; 109, lower packer; 110, lower steam injection valve; 111, plug; 201, middle pipe; 202, upper sealing plug - in; 301, inner pipe; 302, lower sealing plug - in; 4, casing; 5, large four - way steam injection port; 6, middle four - way steam injection port; 7, small four - way steam injection port; 8, upper production layer; 9, middle production layer; 10, lower production layer; 11, nitrogen injection channel; 12, first steam injection channel; 13, second steam injection channel; 14, third steam injection channel. Detailed Embodiments

[0015] The features and performance of the present utility model will be further described in detail below in combination with embodiments.

[0016] In view of the defect that the existing concentric stratified steam drive downhole process string cannot meet the requirements of three-layer stratified steam drive, the utility model proposes a concentric three-tube stratified steam drive process string to meet the requirements of three-layer stratified steam drive. The principle of the scheme of the concentric three-tube stratified steam drive process string of the utility model is as follows: The concentric three-tube stratified steam drive process string includes an outer tube string, a middle tube string and an inner tube string. With the help of the sealing and matching structure on the string, three independent steam injection channels are formed in the concentric tube string. Each steam injection channel is separately equipped with a steam injection valve. With the help of three-stage packers, the three production layers are separated. The three steam injection valves correspond to the positions of the three production layers respectively. Steam can be injected into the first, second and third steam injection channels respectively according to the steam injection requirements of each layer. The injected medium can enter the corresponding production layer through the corresponding steam injection channel and steam injection valve. The three steam injection channels are independent of each other and do not affect each other. Thus, separate control, metering and regulation of steam injection for three layers can be realized, and accurate steam injection allocation for three layers can be achieved.

[0017] An embodiment of the concentric three-tube stratified steam drive process string of the utility model:

[0018] As Figure 1 shown in, the concentric three-tube stratified steam drive process string includes an outer tube string, a middle tube string and an inner tube string. The outer tube string is used to be lowered into the wellbore to form an annulus with the casing 4. The middle tube string is used to be inserted into the outer tube string to form an annulus with the outer tube string. The inner tube string is used to be inserted into the middle tube string to form an annulus with the middle tube string. The inner tube string, the middle tube string and the outer tube string form a concentric tube string.

[0019] The outer tube string includes an outer tube 101, a thermal compensator 102 connected to the upper position of the outer tube 101, upper, middle and lower packers connected to the outer tube 101 in sequence from top to bottom, upper, middle and lower steam injection valves connected to the outer tube 101 in sequence from top to bottom, and a plug 111 connected to the bottom of the outer tube 101. The three packers are used to be set in the annular space between the outer tube string and the casing 4 to separate the upper, middle and lower production layers. The upper steam injection valve 104 is between the upper packer 103 and the middle packer 106 and corresponds to the position of the upper production layer 8. The middle steam injection valve 107 is between the middle packer 106 and the lower packer 109 and corresponds to the position of the middle production layer 9. The lower steam injection valve 110 is on the lower side of the lower packer 109 and corresponds to the position of the lower production layer 10. Upper and lower insertion pipe sealers are also connected to the outer tube 101. Among them, the upper insertion pipe sealer 105 is used to form a sealing fit with a partial pipe section of the middle tube string, and the lower insertion pipe sealer 108 is used to form a sealing fit with a partial pipe section of the inner tube string. High-temperature resistant sealing components are installed in both the upper and lower insertion pipe sealers. The upper and lower insertion pipe sealers are existing products and will not be introduced in detail here.

[0020] The middle pipe string is used to be inserted into the outer pipe string. The middle pipe string includes a middle pipe 201 and an upper sealing plug 202 connected to the lower end of the middle pipe 201. The upper sealing plug 202 is used to be hermetically inserted into an upper plug sealer 105 on the outer pipe 101 to seal the annulus between the middle pipe string and the outer pipe string, so that the annulus between the middle pipe string and the outer pipe string above the upper plug sealer 105 forms a first steam injection channel 12. An upper steam injection valve 104 connected to the outer pipe 101 is communicated with the first steam injection channel 12.

[0021] The inner pipe string is used to be inserted into the middle pipe string and extend downward out of the middle pipe string. The inner pipe string includes an inner pipe 301 and a lower sealing plug 302 connected to the lower end of the inner pipe 301. The lower sealing plug 302 is used to be inserted into a lower plug sealer 108 on the outer pipe 101 to seal the annulus between the inner pipe string and the outer pipe string, so that the annulus between the inner pipe string and the middle pipe string and the annulus between the inner pipe string and the outer pipe string above the lower plug sealer 108 jointly form a second steam injection channel 13. A middle steam injection valve 107 connected to the outer pipe 101 is communicated with the second steam injection channel 13. The inner pipe string has a third steam injection channel 14, and the third steam injection channel 14 is communicated with the lower inner cavity of the outer pipe string, that is, the inner cavity below the lower plug sealer 108 of the outer pipe string. A lower steam injection valve 110 connected to the outer pipe 101 is communicated with the lower inner cavity of the outer pipe string.

[0022] When injecting steam into the first steam injection channel 12, the injected steam can enter the upper production layer 8 through the first steam injection channel 12 and the upper steam injection valve 104; when injecting steam into the second steam injection channel 13, the injected steam can enter the middle production layer 9 through the second steam injection channel 13 and the middle steam injection valve 107; when injecting steam into the third steam injection channel 14, the injected steam can enter the lower production layer 10 through the third steam injection channel 14 and the lower steam injection valve 110.

[0023] The function of the upper plug sealer 105 on the outer pipe 101 is to form a sealing fit with the middle pipe string to form a first steam injection channel 12 in the annulus between the outer pipe string and the middle pipe string. The upper steam injection valve 104 is communicated with the first steam injection channel 12, and the middle steam injection valve 107 is communicated with the second steam injection channel 13. Therefore, the connection position of the upper plug sealer 105 on the outer pipe 101 must be on the lower side of the upper steam injection valve 104 and at the same time on the upper side of the middle steam injection valve 107. Preferably, the upper plug sealer 105 is located between the upper steam injection valve 104 and the middle packer 106, as Figure 1 shown in the figure. In this way, the upper plug sealer 105 can be as close as possible to the upper steam injection valve 104, thereby shortening the length of the first steam injection channel 12, minimizing the heat loss of steam injection as much as possible, enabling the injected steam to enter the upper production layer 8 as soon as possible, improving the steam injection effect, and reducing the steam injection cost. Of course, in other embodiments, the upper plug sealer 105 can also be located between the middle packer 106 and the middle steam injection valve 107.

[0024] The function of the lower insertion tube seal 108 on the outer tube 101 is to form a sealing fit with the inner tube string, thereby forming a second steam injection channel 13 in the annulus between the outer tube string and the inner tube string. The middle steam injection valve 107 is connected to the second steam injection channel 13, and the lower steam injection valve 110 is connected to the third steam injection channel 14. Therefore, the connection position of the lower insertion tube seal 108 on the outer tube 101 must be below the middle steam injection valve 107 and above the lower steam injection valve 110 at the same time. Preferably, the lower insertion tube seal 108 is located between the middle steam injection valve 107 and the lower packer 109, as Figure 1 shown in the figure. This can make the lower insertion tube seal 108 as close as possible to the middle steam injection valve 107, thereby shortening the length of the second steam injection channel 13, minimizing the heat loss of the injected steam as much as possible, enabling the injected steam to enter the middle production layer 9 as soon as possible, improving the steam injection effect, and reducing the steam injection cost. Of course, in other embodiments, the lower insertion tube seal 108 can also be located between the lower packer 109 and the lower steam injection valve 110.

[0025] The outer tube 101 includes multiple pipe sections. The pipe section of the outer tube 101 above the upper packer 103 is defined as the upper pipe section 1011, the pipe section between the upper packer 103 and the middle packer 106 is defined as the middle pipe section 1012, and the pipe section below the middle packer 106 is defined as the lower pipe section 1013. The inner diameters of the upper pipe section 1011, the middle pipe section 1012, and the lower pipe section 1013 decrease in sequence. Among them, the upper pipe section 1011 is a Φ139.5mm heat-insulating tubing, the middle pipe section 1012 is a Φ114.3mm flush tubing, and the lower pipe section 1013 is a Φ73mm flush tubing. The middle tube string and the inner tube string need to be sleeved inside the upper pipe section 1011, so the inner diameter is relatively large; the middle tube string and the inner tube string need to be sleeved inside the middle pipe section 1012, and the upper insertion tube seal 105 needs to be connected to this pipe section, so the inner diameter of this pipe section is slightly smaller than that of the upper pipe section 1011; only the inner tube string needs to be sleeved inside the lower pipe section 1013, and the outer diameter of the inner tube string is smaller, so the inner diameter of the lower pipe section 1013 is relatively small. Such a setting of the outer tube 101 can minimize the cost of the pipe string as much as possible while meeting the usage requirements and make the pipe string assembly more convenient.

[0026] The upper pipe section 1011 of the outer pipe 101 is set as a heat-insulated oil pipe, and the middle pipe section 1012 and the lower pipe section 1013 are both set as plain oil pipes. This is because the upper pipe section 1011 is closer to the wellhead, and heat loss is likely to occur easily after steam is injected from the wellhead. Therefore, the upper pipe section 1011 is set as a heat-insulated oil pipe to minimize heat loss as much as possible. While the middle pipe section 1012 and the lower pipe section 1013 have penetrated deep into the well, and the degree of heat loss is relatively low, so they are set as plain oil pipes. Plain oil pipes have a lower cost compared to heat-insulated oil pipes, which can reduce the cost of the pipe string on the basis of reducing steam heat loss. Of course, in other embodiments, it is also feasible to set all pipe sections of the outer pipe 101 as heat-insulated oil pipes, which has a better effect of reducing steam heat loss but a relatively higher cost.

[0027] Since the middle pipe string is inserted into the outer pipe string and the inner pipe string is inserted into the middle pipe string, on the basis of already ensuring the heat-insulating effect of the outer pipe string, ordinary plain oil pipes can be used for the middle pipe string and the inner pipe string. In this embodiment, the middle pipe string uses a Φ73mm plain oil pipe, and the inner pipe string uses a Φ48.3mm plain oil pipe.

[0028] Considering that the hot steam will cause thermal stress deformation of the pipe string, in this embodiment, a thermal compensator 102 is also connected to the outer pipe 101 to provide a certain compensation for the thermal stress deformation and prevent the pipe string from being damaged under thermal stress deformation. Preferably, the thermal compensator 102 is connected near the upper pipe orifice of the outer pipe 101, so that the thermal compensator 102 has a larger deformation compensation space to fully ensure the thermal stress compensation effect. Of course, the thermal compensator can also be connected to other positions on the outer pipe, such as the position between the upper pipe orifice of the outer pipe and the upper packer.

[0029] Before the concentric three-tube layered steam flooding technology string of the utility model is lowered into the well, it is necessary to first transform the wellhead and install a large four-way, a medium four-way and a small four-way at the wellhead. When lowering the string, first lower the outer pipe string to the designed position in the casing 4, so that the upper packer 103 is located above the upper production layer 8, the middle packer 106 is located between the upper and middle production layers, and the lower packer 109 is located between the middle and lower production layers. The upper, middle and lower steam injection valves correspond to the positions of the upper, middle and lower production layers respectively, and then set the wellhead. Then lower the middle pipe string into the outer pipe string to make the middle pipe string and the outer pipe string concentrically arranged. When the middle pipe string approaches the upper insertion pipe seal 105, slowly lower it and insert the upper sealing insertion pipe 202 into the upper insertion pipe seal 105. Continue to lower the string. After the hook load decreases by 40-60 KN, slowly lift the string by 1.5 m and set the wellhead to make the upper sealing insertion pipe 202 and the upper insertion pipe seal 105 form a sealing fit. Finally, lower the inner pipe string into the middle pipe string to make the inner pipe string and the middle pipe string concentrically arranged. When the inner pipe string approaches the lower insertion pipe seal 108, slowly lower it and insert the lower sealing insertion pipe 302 into the lower insertion pipe seal 108. Continue to lower the string. After the hook load decreases by 40-60 KN, slowly lift the string by 1.5 m and set the wellhead to make the lower sealing insertion pipe 302 and the lower insertion pipe seal 108 form a sealing fit.

[0030] After the string is lowered, an annular space between the outer pipe string and the casing 4 forms a nitrogen injection channel 11, an annular space between the middle pipe string and the outer pipe string above the upper insertion pipe seal 105 forms a first steam injection channel 12, an annular space between the inner pipe string and the middle pipe string and an annular space between the inner pipe string and the outer pipe string above the lower insertion pipe seal 108 together form a second steam injection channel 13, and the inner cavity of the inner pipe string forms a third steam injection channel 14. The nitrogen injection channel 11, the first steam injection channel 12 and the second steam injection channel 13 are respectively connected to the large four-way steam injection port 5, the medium four-way steam injection port 6 and the small four-way steam injection port 7 at the wellhead, and the upper end pipe orifice of the inner pipe string is the steam injection port of the third steam injection channel 14.

[0031] After the tubing string is lowered, first inject nitrogen through the large four-way steam injection port 5 at the wellhead to displace the well fluid in the annulus between the outer tubing string and the casing 4 into the formation. Of course, other displacement gases can also be used in addition to nitrogen. The function of this step is to displace the well fluid in the annulus between the outer tubing string and the casing 4 into the formation in advance, so as to ensure that when injecting steam in subsequent operations, the injected steam can carry heat directly into the production layer, rather than mainly using the heat to heat the annulus well fluid, thereby avoiding steam heat loss and maximizing the steam injection effect. Then, apply hydraulic pressure to set the lowest-stage packer, i.e., the lower packer 109, from the upper end nozzle of the inner tubing string. After the lower packer 109 is set, continue to increase the pressure to open the lower steam injection valve 110. Then, apply hydraulic pressure to set the middle packer 106 from the small four-way steam injection port 7 at the wellhead. After the middle packer 106 is set, continue to increase the pressure to open the middle steam injection valve 107. Finally, apply hydraulic pressure to set the upper packer 103 from the middle four-way steam injection port 6 at the wellhead. After the upper packer 103 is set, continue to increase the pressure to open the upper steam injection valve 104.

[0032] As described above, when applying, the packers are set stage by stage and the steam injection valves are opened stage by stage. The advantage of this is that the opening of each stage of steam injection valve and the setting of the packer are completed in one hydraulic pressure application process, which is convenient for pressure application and improves the construction efficiency. When applying hydraulic pressure to set the packer, it is required that the pressure in the steam injection channel is greater than the pressure in the annulus between the outer tubing string and the casing to achieve setting. The packers of each stage are set in sequence from bottom to top. When it is necessary to apply hydraulic pressure to set the upper-stage packer, the lower-stage packer has been set in the annulus between the outer tubing string and the casing and seals off the annulus from its position. In this way, when setting the upper-stage packer, the requirement for hydraulic pressure can be minimized, which is more convenient for setting the packer and reduces the setting cost. Of course, in specific applications, there is no strict restriction on the setting sequence of the packers of each stage. It is also possible to set the packers of each stage in sequence from top to bottom and open the steam injection valves of each stage one by one. It is also possible to set two of the packers simultaneously, etc.

[0033] When it is necessary to inject steam into the upper production layer 8, inject it through the middle four-way steam injection port 6 at the wellhead. The injected medium enters the upper production layer 8 through the first steam injection channel 12 and the upper steam injection valve 104. When it is necessary to inject steam into the middle production layer 9, inject it through the small four-way steam injection port 7 at the wellhead. The injected medium enters the middle production layer 9 through the second steam injection channel 13 and the middle steam injection valve 107. When it is necessary to inject steam into the lower production layer 10, inject it from the upper end nozzle of the inner tubing string. The injected medium enters the lower production layer 10 through the third steam injection channel 14 and the lower steam injection valve 110. The three steam injection channels are independent of each other and do not affect each other.

[0034] The injected medium can be steam, nitrogen, profile control agent, etc., to meet the needs of injecting different media in layers and quantitatively as required. Modify the surface pipeline and install a high-temperature flowmeter. The three layers can be individually metered, controlled, and adjusted, so as to achieve precise steam injection allocation for the three layers.

[0035] The above are only the preferred embodiments of the present utility model, and are not intended to limit the present utility model. The scope of patent protection of the present utility model is subject to the claims. Any equivalent structural changes made by using the content of the specification and drawings of the present utility model shall equally be included in the protection scope of the present utility model.

Claims

1. Concentric three-tube stratified steam flooding technology string, characterized in that: It includes an outer pipe string, a middle pipe string and an inner pipe string. The outer pipe string includes an outer pipe, upper, middle and lower packers, and upper and lower insertion pipe sealers; the middle pipe string includes a middle pipe and an upper sealing insertion pipe, and the upper sealing insertion pipe is sealingly inserted into the upper insertion pipe sealer so that an annular space between the middle pipe string and the outer pipe string above the upper insertion pipe sealer forms a first steam injection channel; the inner pipe string includes an inner pipe and a lower sealing insertion pipe, and the lower sealing insertion pipe is sealingly inserted into the lower insertion pipe sealer so that the annular space between the inner pipe string and the middle pipe string and the annular space between the inner pipe string and the outer pipe string above the lower insertion pipe sealer jointly form a second steam injection channel; the inner pipe string has a third steam injection channel communicating with the lower inner cavity of the outer pipe string, and the outer pipe is connected with an upper steam injection valve and a middle steam injection valve respectively communicating with the first and second steam injection channels and a lower steam injection valve communicating with the lower inner cavity of the outer pipe string.

2. The concentric three-tube stratified steam flooding process string according to claim 1, wherein: The upper insertion pipe sealer is located between the upper steam injection valve and the middle packer.

3. The concentric three-tube stratified steam flooding process string according to claim 1, wherein: The lower insertion pipe sealer is located between the middle steam injection valve and the lower packer.

4. The concentric three-tube layered steam flooding process string according to claim 1 or 2 or 3, characterized in that: The inner diameters of the pipe sections of the outer pipe above the upper packer, between the upper packer and the middle packer, and below the middle packer decrease in sequence.

5. The concentric three-tube layered steam flooding process string according to claim 1 or 2 or 3, characterized in that: The pipe section of the outer pipe above the upper packer is a heat-insulating oil pipe, and the pipe sections between the upper packer and the middle packer and below the middle packer are both plain-end oil pipes.

6. The concentric three-tube layered steam flooding process string according to claim 1 or 2 or 3, characterized in that: A thermal compensator is also connected to the outer pipe.

7. The concentric three-tube stratified steam flooding process string according to claim 6, characterized in that: The thermal compensator is connected to the outer pipe near the upper pipe orifice.

Images