A layered water injection string

Abstract

The application discloses a layered water injection pipe column, and solves the technical problem that the pipe column of the prior art externally bound cable is prone to causing cable damage when a deformed casing is lowered. The application comprises a conventional pipe, a crossing pipe, a prefabricated pipe and a connecting assembly; the conventional pipe is externally provided with a fixing portion to bind the cable; the crossing pipe is sleeved on the conventional pipe and internally has a first cable passage; the prefabricated pipe internally has a second cable passage; the connecting assembly comprises a first connecting terminal arranged in the crossing pipe and a second connecting terminal arranged in the prefabricated pipe and electrically connected, the first connecting terminal is electrically connected with the cable in the first cable passage, the second connecting terminal is electrically connected with the cable in the second cable passage, and the cable is converted from external setting to internal setting or from internal setting to external setting; when a target well of the pipe column needs to be deformed, the conventional pipe can be lowered in a non-deformed area, and the prefabricated pipe can be lowered in a deformed area, so that the inner wall of the deformed casing is prevented from grinding through and clamping the protective layer of the cable, and the risk of pulling out the clamped well is avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cable-controlled intelligent separate layer water injection in the oil industry, and particularly relates to a separate layer water injection string. BACKGROUND

[0002] Water injection is an effective method for maintaining reservoir pressure, realizing high and stable production of oilfields and improving development effect of oilfields. About 92% of the reservoirs of oilfields in China are continental clastic rock deposits, which have strong vertical heterogeneity. During water injection development, injected water is prone to channeling along high-permeability layers, resulting in inefficient water injection. Developing separate layer water injection technology to realize effective water injection in multiple layers is an important means for continuously improving water flooding recovery at high and ultra-high water cut stages. The separate layer water injection technology uses cable and carrier wave technology to power the downhole cable-controlled intelligent water distributor and provide communication between the cable-controlled water distributor and the ground control device, so as to realize real-time acquisition of layer flow, pressure, water nozzle opening and temperature parameters and real-time adjustment of injection volume under separate layer water injection state.

[0003] The existing cable-controlled process string adopts a cable bound outside the string. During running in, various problems are often encountered. For example, for special well conditions such as casing deformation wells or sidetracking wells, when the string is run in to the casing deformation area or the sidetracking area, the deformed casing inner wall may grind through or break the protective layer of the cable, resulting in insulation failure of the cable and signal loss, which cannot meet the process requirements. SUMMARY

[0004] To solve the technical problem that the existing separate layer water injection string with externally bound cable is prone to cable damage when running in the casing deformation area, the application provides a separate layer water injection string.

[0005] In the first aspect of the application, a separate layer water injection string includes a conventional pipe, a crossing pipe, a prefabricated pipe and a connecting assembly.

[0006] The conventional pipe is externally provided with a fixing part for binding the cable.

[0007] The crossing pipe is sleeved at one end of the conventional pipe, and the inside of the crossing pipe has a first cable passage for the cable to pass through.

[0008] The prefabricated pipe has a second cable passage for the cable to pass through in the inside.

[0009] The connecting assembly includes a first connecting terminal and a second connecting terminal. The first connecting terminal is arranged in the crossing pipe and can be electrically connected with the cable in the first cable passage. The second connecting terminal is arranged in the prefabricated pipe and can be electrically connected with the cable in the second cable passage. The first connecting terminal and the second connecting terminal are electrically connected.

[0010] In some embodiments, one of the first connecting terminal and the second connecting terminal has a plug portion, and the other has a plug slot, the plug portion is inserted into the plug slot to electrically connect the first connecting terminal and the second connecting terminal.

[0011] In some embodiments, a spring is arranged in the plug slot along the plug slot axis.

[0012] In some embodiments, the first connecting terminal comprises a first fixing disc, a first current-carrying coil and a first connecting portion, the first current-carrying coil is fixed on the first fixing disc, the first connecting portion is electrically connected with the first current-carrying coil, and the first current-carrying coil is used to electrically connect with the cable.

[0013] In some embodiments, the first fixing disc has a first water passage communicating with the inside of the conventional pipe.

[0014] In some embodiments, the second connecting terminal comprises a second fixing disc, a second current-carrying coil and a second connecting portion, the second current-carrying coil is fixed on the second fixing disc, the second connecting portion is electrically connected with the second current-carrying coil, and the second current-carrying coil is used to electrically connect with the cable.

[0015] In some embodiments, part of the first cable passage is arranged outside the conventional pipe.

[0016] In some embodiments, the crossing pipe comprises a first pipe segment and a second pipe segment, the first pipe segment is sleeved on the conventional pipe, the first connecting terminal is arranged in the second pipe segment, the first cable passage comprises a first passage segment and a second passage segment connected with each other, the first passage segment is arranged in the first pipe segment, the second passage segment is arranged in the second pipe segment, and the opening area of the first passage segment is greater than that of the second passage segment.

[0017] In some embodiments, the conventional pipe or the prefabricated pipe has a drainage port, and the layered water injection string further comprises a differential pressure switch, the differential pressure switch is installed on the drainage port, and the differential pressure switch comprises a differential pressure pipe body, a connecting seat and a switch piece; the differential pressure pipe body is provided with a second water passage; the connecting seat is a rotary body and is connected to the inner wall of the differential pressure pipe body in the circumferential direction of the differential pressure pipe body, so as to divide the second water passage into two sub-passages; the connecting seat is provided with a water passage passing through the connecting seat, the water passage passes through the connecting seat and communicates with the two divided sub-passages; and the switch piece is arranged at the front end of the connecting seat along the water flow direction and can reciprocate along the axis of the differential pressure pipe body to abut or be spaced from the connecting seat, so as to disconnect or communicate the water passage and the second water passage.

[0018] The layered water injection pipe column provided by the embodiment of the present application comprises a conventional pipe, a crossing pipe, a prefabricated pipe and a connecting assembly; the conventional pipe is externally provided with a fixing part for binding a cable; the crossing pipe is sleeved at one end of the conventional pipe, and the inside of the crossing pipe has a first cable channel for the cable to pass through; the prefabricated pipe has a second cable channel for the cable to pass through in the inside; the connecting assembly comprises a first connecting terminal and a second connecting terminal, the first connecting terminal is arranged in the crossing pipe and can be electrically connected with the cable in the first cable channel, the second connecting terminal is arranged in the prefabricated pipe and can be electrically connected with the cable in the second cable channel, and the first connecting terminal and the second connecting terminal are electrically connected.

[0019] The layered water injection pipe column of the present application, because the conventional pipe is externally provided with a fixing part for binding a cable, that is, the cable is located outside the conventional pipe body; the prefabricated pipe has a second cable channel for the cable to pass through in the inside, that is, the cable is located inside the prefabricated pipe body; the crossing pipe is sleeved at one end of the conventional pipe, and the other end is connected with the prefabricated pipe through the connecting assembly, that is, the conventional pipe and the prefabricated pipe are connected through the crossing pipe, realizing the conversion of the cable from the external setting of the conventional pipe to the internal setting of the prefabricated pipe or from the internal setting of the prefabricated pipe to the external setting of the conventional pipe; when the target well where the pipe column needs to be lowered has a deformation area, for example, a casing deformation well and a sidetracking well, the conventional pipe for externally binding the cable can be lowered in the non-deformed casing area, and the prefabricated pipe for internally passing through the cable can be lowered in the deformed casing area, so as to prevent the inner wall of the deformed casing from grinding and breaking the protective layer of the cable when the pipe column is lowered into the casing deformation area or the sidetracking area, avoid the insulation failure and signal loss of the cable, protect the cable by the prefabricated pipe, and also do not need to lower a special cable protection clamp, thereby solving the tool lowering problem and avoiding the risk of pulling out the stuck well. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A structure schematic diagram of the fishing-free injection system of the embodiment of the present application is shown.

[0021] Figure 2 A schematic diagram of the prefabricated pipe in the fishing-free injection device of the embodiment of the present application is shown.

[0022] Figure 3 A connection schematic diagram of multiple prefabricated pipes in the fishing-free injection device of the embodiment of the present application is shown.

[0023] Figure 4 A connection schematic diagram of the first connecting terminal and the second connecting terminal in the fishing-free injection device of the embodiment of the present application is shown.

[0024] Figure 5 A schematic diagram of the crossing pipe in the fishing-free injection device of the embodiment of the present application is shown.

[0025] Figure 6 An assembly schematic diagram of the prefabricated pipe and the crossing pipe in the fishing-free injection device of the embodiment of the present application is shown.

[0026] Figure 7 An assembly diagram of a conventional pipe and a crossing pipe in the fishing-free injection packer of the embodiment of the application is shown.

[0027] Figure 8 An opening diagram of a differential pressure switch in the fishing-free injection packer of the embodiment of the application is shown.

[0028] Figure 9 A closing diagram of a differential pressure switch in the fishing-free injection packer of the embodiment of the application is shown.

[0029] Explanation of reference signs:

[0030] 100, conventional pipe;

[0031] 200, crossing pipe;

[0032] 300, prefabricated pipe;

[0033] 310, first connecting terminal; 320, second connecting terminal;

[0034] 311, first fixing disc; 312, first power supply coil;

[0035] 400, differential pressure switch;

[0036] 410, upper joint; 420, connecting body; 430, lower joint; 440, connecting seat; 450, switch piece; 460, spring;

[0037] 500, packer;

[0038] 600, hanger;

[0039] 700, water distributor;

[0040] 800, cable;

[0041] 900, oil layer;

[0042] 1000, sidetracked deviated well section; 1100, straight well section. DETAILED DESCRIPTION

[0043] In order for those skilled in the art to which the present application pertains to more clearly understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without any creative work fall within the scope of protection of the present application.

[0044] The embodiment of the present application provides a layered water injection pipe column, when the pipe column is lowered into a casing deformation well or a sidetracking well, the inner wall of the deformed casing prevents the protective layer of the cable from being worn through and broken.

[0045] Please refer to Figure 1 The layered water injection pipe column provided by the embodiment of the present application comprises a conventional pipe 100, a crossing pipe 200, a prefabricated pipe 300 and a connecting assembly; the conventional pipe 100 is externally provided with a fixing part for binding a cable 800; please refer to Figure 5 The crossing pipe 200 is sleeved at one end of the conventional pipe 100, and the inside of the crossing pipe 200 has a first cable passage for the cable 800 to pass through; please refer to Figure 2 The prefabricated pipe 300 has a second cable passage for the cable 800 to pass through; please refer to Figure 6 And Figure 7 The connecting assembly comprises a first connecting terminal 310 and a second connecting terminal 320, the first connecting terminal 310 is arranged in the crossing pipe 200 and can be electrically connected with the cable 800 in the first cable passage, the second connecting terminal 320 is arranged in the prefabricated pipe 300 and can be electrically connected with the cable 800 in the second cable passage, and the first connecting terminal 310 and the second connecting terminal 320 are electrically connected.

[0046] In some embodiments, the conventional pipe 100, the prefabricated pipe 300 and the crossing pipe 200 are all provided with a water passage, and the first cable passage and the second cable passage are not communicated with the water passage; please refer to Figure 2 In some embodiments, the prefabricated pipe 300 is provided with a plurality of sub-prefabricated pipes 300, and the plurality of sub-prefabricated pipes 300 are connected through the first connecting terminal 310 and the second connecting terminal 320; in some embodiments, the cable 800 outside the conventional pipe 100 is bound, enters the inside of the crossing pipe 200 through the first cable passage, is connected with the first connecting terminal 310, and the first connecting terminal 310 is electrically connected with the second connecting terminal 320, so that the cable 800 outside the conventional pipe 100 is electrically connected with the cable 800 arranged in the prefabricated pipe 300.

[0047] Please refer to Figure 4 In some embodiments, one of the first connecting terminal 310 and the second connecting terminal 320 has a plug-in part, and the other has a plug-in slot, the plug-in part is arranged in the plug-in slot, so that the first connecting terminal 310 is electrically connected with the second connecting terminal 320, and the electrical connection of the first connecting terminal 310 and the second connecting terminal 320 is further strengthened; in some embodiments, the first connecting terminal 310 has the plug-in part, the second connecting terminal 320 has the plug-in slot, and the plug-in slot and the plug-in part are both conductive.

[0048] In some embodiments, a spring 460 is arranged in the plug-in slot along the axial direction of the plug-in slot, so as to slow down the impact force of the plug-in operation and protect the device.

[0049] Please see Figure 4 In some embodiments, the first connection terminal 310 includes a first fixing plate 311, a first energizing coil 312, and a first connecting portion. The first energizing coil 312 is fixed on the first fixing plate 311, and the first connecting portion is electrically connected to the first energizing coil 312. The first energizing coil 312 is used for electrical connection with the cable 800. In some embodiments, the first fixing plate 311 includes a body and an insulating layer coated on the body to prevent leakage. In some embodiments, the first fixing plate 311 is made of insulating material to prevent leakage. In some embodiments, the first energizing coil 312 and the first connecting portion are conductive.

[0050] In some embodiments, the first fixed plate 311 has a first water passage communicating with the interior of the conventional pipe 100.

[0051] Please see Figure 4 In some embodiments, the second connecting terminal 320 includes a second fixing plate, a second energizing coil, and a second connecting portion. The second energizing coil is fixed on the second fixing plate, and the second connecting portion is electrically connected to the second energizing coil. The second energizing coil is used for electrical connection with the cable 800. In some embodiments, the second fixing plate includes a body and an insulating layer coated on the body to prevent leakage. In some embodiments, the second fixing plate is made of insulating material to prevent leakage. In some embodiments, the second energizing coil and the second connecting portion are conductive.

[0052] In some embodiments, the first fixed plate 311 has a first water passage communicating with the interior of the conventional pipe 100.

[0053] In some embodiments, a portion of the first cable channel is disposed outside the conventional pipe 100 so that the cable 800 is connected from outside the conventional pipe 100 through the first cable channel to the first connection terminal 310 of the through pipe 200.

[0054] Please see Figure 5 In some embodiments, the through pipe 200 includes a first pipe segment and a second pipe segment. The first pipe segment is sleeved on the conventional pipe 100. The first connecting terminal 310 is disposed in the second pipe segment. The first cable channel includes a first channel segment and a second channel segment that are connected to each other. The first channel segment is disposed in the first pipe segment, and the second channel segment is disposed in the second pipe segment. The opening area of ​​the first channel segment is larger than the opening area of ​​the second channel segment to provide a basis for the cable 800 to pass through. In some embodiments, a cable 800 socket is provided in the first cable channel to provide support and guidance for the cable 800.

[0055] Please see Figure 1 , Figure 8 as well as Figure 9In some embodiments, the conventional pipe 100 or the prefabricated pipe 300 has a drainage port, and the layered water injection pipe string further comprises a differential pressure switch 400 installed on the drainage port, the differential pressure switch 400 comprising a differential pressure pipe body, a connecting seat 440 and a switch piece 450; the differential pressure pipe body is provided with a second water passage; the connecting seat 440 is a rotary body and is connected to the inner wall of the differential pressure pipe body in the circumferential direction of the differential pressure pipe body, thereby dividing the second water passage into two sub-passages; the connecting seat 440 is provided with a water passage penetrating through the connecting seat 440, and the water passage communicates the two divided sub-passages; the switch piece 450 is arranged at the front end of the connecting seat 440 in the direction of water flow and can reciprocally move in the axial direction of the differential pressure pipe body to abut or be spaced from the connecting seat 440, so as to disconnect or communicate the water passage and the second water passage; in some embodiments, the tail pipe is connected with the differential pressure switch 400; in some embodiments, the differential pressure pipe body comprises an upper joint 410, a lower joint 430 and a connecting body 420, all of which are rotary bodies; the upper joint 410 and the lower joint 430 are connected through the connecting body 420, and the upper joint 410, the lower joint 430 and the connecting body 420 are coaxial and jointly enclose the second water passage; in some embodiments, the switch piece 450 is a rotary body and is provided with a first acting part and a second acting part which are fixedly connected and angularly arranged; in some embodiments, the first acting part is a circular ring and the second acting part is a circular cylinder; in some embodiments, the inner wall of the differential pressure pipe body is provided with a boss extending in the radial direction of the differential pressure pipe body between the first acting part and the connecting seat 440; the inner wall of the differential pressure pipe body, the boss and the switch piece 450 jointly enclose a receiving cavity; the receiving cavity is provided with a spring 460 abutting against the first acting part and the boss; the extension direction of the second acting part is between the axial direction of the differential pressure pipe body and the axial direction of the water passage; the switch piece 450 reciprocally moves in the axial direction of the differential pressure pipe body, so that the second acting part abuts or is spaced from the connecting seat 440, thereby disconnecting or communicating the water passage and the second water passage; in some embodiments, the first acting part and the second acting part are angularly arranged at an angle of 90°.

[0056] The use process of the layered water injection pipe string of the present application will be described in detail as follows:

[0057] Step 1, connect the differential pressure switch 400 and the tail pipe, and then connect the prefabricated pipe 300 and the conventional pipe 100 according to the well conditions, and set down by the injection traction device, set down the prefabricated pipe 300 in the casing deformation area and set down the conventional pipe 100 in the casing non-deformation area, connect the conventional pipe 100 and the prefabricated pipe 300 through the crossing pipe 200, and reciprocally set down to the position where the hanger is located at the wellhead; the cable 800 is set down to the position of the water distributor 700 together with the conventional pipe 100 or the prefabricated pipe 300, and is connected with the water distributor 700;

[0058] Step 2, connect the cable 800 with the integrated control cabinet and calibrate the depth; after the cable 800 is pulled out, it is sealed by a proper method;

[0059] Step 3, pressurize the differential pressure switch 400 to make the switch part 450 abut against the connecting seat 440 to disconnect the water passage from the second water passage, and the packer 500 is set;

[0060] Step 4, check the sealing and channeling;

[0061] Step 5, connect the water injection pipeline for normal production.

[0062] The layered water injection string of the present application has at least the following advantages:

[0063] (1) The layered water injection string of the present application, because the conventional pipe is externally provided with a fixing part for binding the cable, i.e. the cable is located outside the conventional pipe body; the precast pipe is internally provided with a second cable passage for the cable to pass through, i.e. the cable is located inside the precast pipe body; the crossing pipe is sleeved at one end of the conventional pipe and connected at the other end to the precast pipe through the connecting assembly, i.e. the conventional pipe and the precast pipe are connected through the crossing pipe, realizing the conversion of the cable from the external setting of the conventional pipe to the internal setting of the precast pipe or from the internal setting of the precast pipe to the external setting of the conventional pipe; when the target well where the string is to be set has a deformation area, for example, a casing deformation well and a sidetracking well, the conventional pipe externally binding the cable can be set in the area of the undeformed casing, and the precast pipe internally passing through the cable can be set in the area of the deformed casing, so that the precast pipe protects the cable to prevent the inner wall of the deformed casing from grinding through or breaking the protective layer of the cable when the string is set in the casing deformation area or the sidetracking area, avoiding the insulation failure and signal loss of the cable, and also avoiding the need to lower a special cable protection clamp, solving the problem of tool lowering and avoiding the risk of pulling out the stuck well.

[0064] (2) The layered water injection string of the present application, because the spring is axially arranged in the insertion slot, the insertion operation between the insertion part and the insertion slot can be buffered, and the device is protected.

[0065] (3) The layered water injection string of the present application is provided with a differential pressure switch, which remains in the normally open state under the action of the spring when not pressurized, and when pressurized, the switch part of the differential pressure switch moves towards the connecting seat through water flow pressurization to isolate the water passage from the second water passage, realizing the closing of the differential pressure switch to complete the pressurization operation; when used for a sidetracking well, because the sidetracking well has a windowing inflection point, the inner diameter of the hanger is small, and the inclination of the sidetracking section is large, the existing technology has a large error in ball setting for pressurization by ball seat, compared with the existing technology, the reliable pressure switch of the differential pressure switch of the present application replaces gravity, avoiding the problem of being unable to pressurize due to the large angle of the small-diameter sidetracking well, and having good practicability and high pressurization success rate.

[0066] (4) The layered water injection string of the present application connects the prefabricated pipe with the prefabricated pipe and the prefabricated pipe with the crossing pipe through the first connecting terminal and the second connecting terminal, the first connecting terminal and the second connecting terminal are respectively provided with the first fixing disc and the second fixing disc, and the first fixing disc and the second fixing disc are made of insulating material, which can prevent the device from electric leakage and affect the use effect.

[0067] In the present application, unless specifically defined and limited otherwise, the first feature is "on" or "under" the second feature, which can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the first feature "on", "above" and "over" the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature "under", "below" and "under" the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0068] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" indicate the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0069] In the present application, unless specifically defined and limited otherwise, the terms "connection", "fixing" and the like should be understood broadly, for example, "fixing" can be fixed connection, or detachable connection, or integral; can be mechanical connection, or electrical connection; can be directly connected, or indirectly connected through intermediate medium; can be internal communication of two elements or interaction relationship of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0070] In addition, in the present application, the description such as "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more features. In the description of the present application, the meaning of "multiple" is two or more, unless specifically defined and limited otherwise.

[0071] While the embodiments of the present application have been shown and described, it is to be understood that the embodiments can be varied, modified, substituted and changed by those skilled in the art without departing from the principles and spirit of the present application, the scope of which is defined by the claims and their equivalents.

Claims

1. A layered water injection string, characterized by The utility model relates to a layered water injection pipe column, which comprises a conventional pipe, a crossing pipe, a prefabricated pipe, a connecting assembly, a differential pressure switch and a drainage port. The utility model relates to a layered water injection pipe column, which comprises a conventional pipe, a crossing pipe, a prefabricated pipe, a connecting assembly, a differential pressure switch and a drainage port. One of the first connecting terminal and the second connecting terminal has a plug-in part, and the other has a plug-in slot, the plug-in part is inserted into the plug-in slot to electrically connect the first connecting terminal and the second connecting terminal. A spring is arranged in the plug-in slot along the axial direction of the plug-in slot. The first connecting terminal comprises a first fixed disc, a first electrically-conductive ring and a first connecting part, the first electrically-conductive ring is fixed on the first fixed disc, the first connecting part is electrically connected with the first electrically-conductive ring, and the first electrically-conductive ring is used for electrically connecting with the cable. The first fixed disc has a first water passage that is in communication with the inside of the conventional pipe.

2. The layered water injection string of claim 1, wherein, The second connecting terminal comprises a second fixed disc, a second electrically-conductive ring and a second connecting part, the second electrically-conductive ring is fixed on the second fixed disc, the second connecting part is electrically connected with the second electrically-conductive ring, and the second electrically-conductive ring is used for electrically connecting with the cable.

3. The layered water injection string of claim 2, wherein, Part of the first cable passage is arranged outside the conventional pipe.

4. The layered water injection string of claim 1, wherein, The crossing pipe comprises a first pipe segment and a second pipe segment, the first pipe segment is sleeved on the conventional pipe, the first connecting terminal is arranged in the second pipe segment, the first cable passage comprises a first passage segment and a second passage segment which are connected with each other, the first passage segment is arranged in the first pipe segment, the second passage segment is arranged in the second pipe segment, and the opening area of the first passage segment is greater than that of the second passage segment.

5. The layered water injection string of claim 4, wherein, ​ 6. The layered water injection string of claim 1, wherein, ​ 7. The layered water injection string of claim 1, wherein, ​ 8. The layered water injection string of claim 1, wherein, ​

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