Damper and completion structure for improving the axial isolation effect of continuous packer along the wellbore

Abstract

A resistance enhancer and completion structure that can improve the axial isolation effect of a continuous isolation body in a wellbore, wherein the resistance enhancer is an overall cylindrical structure; a central mounting hole for installing a central pipe column is provided at the axial center position of the resistance enhancer; one or more filling channels that are consistent with the axial direction of the cylinder are provided inside and / or outside of the resistance enhancer. The present invention firstly reduces the crossflow of formation produced water in the wellbore annulus by providing a resistance enhancer with a smaller flow area in the wellbore; secondly, flow guide grooves are provided at both ends of the resistance enhancer, and when multiple resistance enhancers are used in series as standard parts, multiple resistance enhancers can be installed in series on the central pipe column on site according to actual needs without aligning the filling channels of multiple resistance enhancers, which is very convenient for on-site assembly and use, and can not only improve the on-site installation efficiency, but also more accurately limit the crossflow flow of formation produced water in the wellbore.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas well exploitation, and relates to a resistance increasing device capable of improving the axial sealing effect of a continuous sealing body in a wellbore, a method capable of improving the axial sealing effect of a continuous sealing body in a wellbore, and a completion structure capable of improving the axial sealing effect of a continuous sealing body in a wellbore. Background Art

[0002] In the field of oil and gas well production technology, the wellbore of an oil and gas well generally passes through multiple sections of formations. Since the permeability of each section of the formation is usually inconsistent and the viscosity of the formation water is much lower than that of the crude oil to be produced, under the same bottom hole pressure difference, the local formation with high permeability often produces a large amount of formation water. The commonly used water control method is to control water by inserting a flow control string (or water control string) with a balanced flow rate into the wellbore. When there is a flow control string in the wellbore to control water and increase oil production, these formation waters flow along the axial direction of the wellbore annulus in the wellbore annulus, resulting in the ineffective flow control of the flow control string. By isolating the wellbore annulus, controlling the production of formation water and reducing the flow of formation water in the wellbore annulus is an effective method to improve crude oil recovery. The existing methods for isolating the wellbore annulus to achieve water control mainly include two methods: water control by an expansion packer and water control by a continuous packer.

[0003] The expansion packer has been used to a certain extent due to its simple structure and low cost. However, the device has the following shortcomings when used: First, because the diameter of the device is larger than the diameter of the central pipe string (or close to the diameter of the wellbore), the pipe string connected by multiple central pipe strings is very likely to encounter obstructions when going down the well. In order to solve the problem of obstruction when going down the well, it is necessary to reduce the number of expansion packers set on the pipe string, for example, a expansion packer is set every 50-100 meters, so as to isolate the wellbore into multiple independent separation units with a length of 50-100 meters. However, inside each separation unit, the wellbore annulus is still connected, and there is still a crossflow problem, which will cause the oil production of the unit to be unable to reach the optimal level; in extreme cases, if there are a large number of water-producing areas inside the separation unit (for example, underground water is connected through cracks), then the oil recovery rate of the separation unit will become even lower. Secondly, the expansion packer is usually a prefabricated part, which cannot perfectly adapt to complex well conditions such as inconsistent well diameters, non-centered central pipe strings, and uneven well surface, and thus cannot completely prevent the crossflow of formation water between different separation units. Thirdly, after the liquid expansion packer is fully expanded, it sticks to the well wall and cannot be pulled out. However, there is a gap between the resistance increaser and the well wall, so it can be pulled out.

[0004] Continuous packer water control is a new method of oil and gas well water control that has emerged in recent years. Referring to Chinese invention patents CN2009102507912, CN2014100135988, CN2019100846588, CN2019104892759, etc., the basic principle of this method is to fill the wellbore with packer particles to form a continuous packer. The internal microchannels of the continuous packer formed by the micropores between the packer particles have an anti-channeling effect on the produced fluid, thereby reducing the output of formation water, and can meet the actual application needs under various well conditions (such as irregular well diameter, casing leakage, deformation, cement ring channeling grooves, annulus outside the old screen pipe, annulus outside the perforated pipe, etc.). However, this method still has some shortcomings in its application: on the one hand, since there must be microchannels in the continuous packer for oil and gas to pass through, in order to ensure the smooth production of oil and gas, the resistance of the microchannel to the flow of the produced liquid should not be too small to ensure the fluidity of the produced liquid; on the other hand, because the fluidity of water is much higher than that of oil, for the scenario where the spacing between the formations is small (for example, 2-5 meters), the produced water in the local section of the wellbore that is higher than the water formation will still flow through the microchannels in the continuous packer along the wellbore annulus to the adjacent formation structure section. In other words, there is still a large cross-flow phenomenon in the produced water in the wellbore, which makes it impossible to achieve the optimal oil recovery rate.

[0005] Specifically, the conventional use range of packing particles is 16-100 mesh (particle size range 0.15-1.18mm), and the corresponding continuous packer permeability is 20D-300D. Compared with the permeability of the formation, even the permeability of 20D is still very high. For example, a 3-1 / 2in water control screen was run into a 6in multi-layer vertical well, and the continuous packer particles with a permeability of 40D were filled. Under the production pressure difference of 1Mpa, the crossflow of the 2-meter-long continuous packer ring (i.e., the continuous packer corresponding to the blind section between the two screens) reached 29 cubic meters / day. A 5-1 / 2in flow control screen was run into an 8-1 / 2in horizontal well, and the continuous packer particles with a permeability of 20D were filled. Under the production pressure difference of 1Mpa, the crossflow of the 2-meter-long continuous packer ring was 45 cubic meters / day. It can be seen from this that even if continuous isolation is used for water control, the interlayer axial crossflow rate in the wellbore annulus is still large, and the isolation effect needs to be further improved. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the prior art and to provide a resistance increaser and a resistance increase device which have a simple structure, convenient operation, high reliability, good effect of limiting crossflow flow, and do not affect the filling of continuous sealing body particles in the production section, and can improve the axial sealing effect of the continuous sealing body in the wellbore along the wellbore, as well as a completion structure which can improve the axial sealing effect of the continuous sealing body in the wellbore along the wellbore.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A resistance increaser that can improve the axial isolation effect of a continuous isolation body in a wellbore, the resistance increaser being in an overall cylindrical structure; a central mounting hole for mounting a central pipe column is provided at the axial center position of the resistance increaser; one or more filling channels that are consistent with the axial direction of the cylinder are provided inside and / or outside the resistance increaser, and the sum of the effective flow areas of the filling channels is 1 / 20-1 / 2 of the cross-sectional area of ​​the cylinder.

[0009] Furthermore, the resistance increaser has a plurality of filling channels, and the plurality of filling channels are distributed in a circularly symmetrical manner based on the axis of the cylinder.

[0010] Furthermore, both ends of the resistance increaser are provided with annular grooves connected to each filling channel, the annular grooves at both ends have the same size and the same position relative to the axis of the cylinder; the effective flow guide area of ​​the annular groove is not less than the flow area of ​​a single filling channel.

[0011] Furthermore, the cross-sectional shape of the filling channel inside the resistance increasing device is one or more of a circular shape, an elliptical shape, a sector shape, and a rounded sector shape.

[0012] Furthermore, the cross-sectional shape of the filling channel on the outer side of the resistance increaser is one or more of a semicircular shape, a fan shape, and a rounded / chamfered fan shape, and the outer side surface of the filling channel is connected to the annulus of the wellbore.

[0013] To achieve the above object, the present invention also provides the following technical solutions:

[0014] A resistance increasing device capable of improving the axial isolation effect of a continuous isolation body in a wellbore comprises the resistance increasing device as described above and a central pipe column, wherein the central pipe column passes through the central mounting hole of the resistance increasing device and is connected and fixed to the resistance increasing device.

[0015] Furthermore, the resistance increasing device and the central pipe column are connected and fixed by one or more of welding, bolt fixing or clamp fixing.

[0016] Further, the central pipe column is a short-jointed blind pipe;

[0017] Furthermore, flow control filter pipe strings are installed at both ends of the short-section blind pipe.

[0018] To achieve the above object, the present invention provides the following technical solutions:

[0019] A completion structure capable of improving the axial isolation effect of a continuous isolation body in a wellbore comprises a plurality of center pipe strings connected end to end in the wellbore, a continuous isolation body is arranged in the annulus between the center pipe string and the wellbore wall, and one or more of the center pipe strings are provided with a resistance enhancer as described above.

[0020] To achieve the above object, the present invention provides the following technical solutions:

[0021] A completion structure capable of improving the axial isolation effect of a continuous isolation body in a wellbore, comprising a plurality of center pipe strings connected end to end in the wellbore, a continuous isolation body being arranged in the annulus between the center pipe string and the wellbore wall, and one or more center pipe strings being the resistance increasing device as described above.

[0022] The present invention provides a resistance enhancer and completion structure that can improve the axial sealing effect of a continuous packer along the wellbore. First, by setting a resistance enhancer with a small flow area in the wellbore and filling it with sealing particles, the crossflow of formation produced water in the wellbore annulus can be reduced. Second, because the entire annulus is filled with a continuous packer, there is no space to store the mud and sand produced by the "worm hole", so it is impossible for "worm holes" to form at both ends of the packer, and thus it will not cause the occurrence of problems such as well wall collapse and mud migration. Third, guide grooves are provided at both ends of the resistance enhancer. When multiple resistance enhancers are used in series as standard parts, multiple resistance enhancers can be installed in series on the center pipe column on site according to actual needs without aligning the filling channels of the multiple resistance enhancers, which is very convenient for on-site assembly and use. It can not only improve the on-site installation efficiency, but also more accurately limit the crossflow flow of formation produced water in the wellbore. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a front cross-sectional view of a resistance increasing device for improving the axial isolation effect of a continuous isolation body along the wellbore in an embodiment of the present invention;

[0024] Figure 2 It is a left view of a resistance increasing device for improving the axial isolation effect of a continuous isolation body along a wellbore in an embodiment of the present invention;

[0025] Figure 3 It is a schematic diagram of the overall structure of a resistance increasing device for improving the axial isolation effect of a continuous isolation body along the wellbore in an embodiment of the present invention;

[0026] Figure 4 It is a cross-sectional view of the overall structure of a resistance increasing device for improving the axial isolation effect of a continuous isolation body along the wellbore in an embodiment of the present invention;

[0027] Figure 5 It is a front cross-sectional view of another resistance increasing device for improving the axial isolation effect of the continuous isolation body along the wellbore in an embodiment of the present invention;

[0028] Figure 6 It is a left view of another resistance increasing device for improving the axial isolation effect of the continuous isolation body along the wellbore in an embodiment of the present invention;

[0029] Figure 7 It is a schematic diagram of the overall structure of another resistance increasing device for improving the axial isolation effect of the continuous isolation body along the wellbore in an embodiment of the present invention;

[0030] Figure 8 It is a cross-sectional view of the overall structure of another resistance increasing device for improving the axial isolation effect of the continuous isolation body along the wellbore in an embodiment of the present invention;

[0031] Fig. 9 It is a schematic diagram of the overall structure of a specific application of a resistance increasing device / resistance increasing device in a wellbore for improving the axial isolation effect of a continuous isolation body along the wellbore in an embodiment of the present invention.

[0032] Fig.10 It is a schematic diagram of the overall structure of an existing injection-production system in an embodiment of the present invention;

[0033] Fig.11 It is a schematic diagram of the overall structure of an injection-production system according to an embodiment of the present invention, which uses a resistance increasing device / resistance increasing apparatus to improve the axial isolation effect of a continuous isolation body along the wellbore. DETAILED DESCRIPTION

[0034] The following is combined with Figures 1 to 9 , further illustrating a specific implementation of a resistance increasing device and a completion structure for improving the axial isolation effect of a continuous packer along the wellbore of the present invention. It should be noted that the function of the drawings in the specification is limited to more intuitively displaying the specific features of the overall or partial technical solutions disclosed in the embodiments, and their proportions or size structures are not drawn according to the actual products, so they cannot be used as a limitation on the technical solutions disclosed in the embodiments; a resistance increasing device and a completion structure for improving the axial isolation effect of a continuous packer along the wellbore of the present invention are not limited to the description of the following embodiments.

[0035] Embodiment 1:

[0036] This embodiment provides a resistance increasing device that can improve the axial isolation effect of a continuous isolation body in a wellbore.

[0037] like Figure 1-8As shown, the resistance increaser 1 is a cylindrical structure or a nearly cylindrical structure as a whole. The purpose of setting it into this shape is to facilitate the assembly of the resistance increaser 1 as a sleeve structure with the center pipe column and then lower it into the wellbore 2. The axial center position of the resistance increaser 1 is provided with a center mounting hole 11 for mounting the center pipe column (that is, the center center mounting hole 11 of the sleeve structure), and the inside and / or outside of the resistance increaser 1 are provided with one or more filling channels 12 consistent with the axial direction; the sum of the effective flow areas of the filling channels 12 is 1 / 20-1 / 2 of the cross-sectional area of ​​the cylinder. The effective flow area of ​​the filling channel 12 refers to the cross-sectional area of ​​the filling channel 12. Specifically, during the filling and isolation particle stage, the filling fluid carrying the isolation particles mainly flows through the filling channel 12 and the outer annulus of the resistance increaser 1, transports the filling particles to the deep part of the wellbore 2, and gradually accumulates from the deep part of the wellbore 2 to the shallow part to form a continuous isolation body; during the production stage, the production fluid in the annulus of the wellbore 2 also mainly flows through the outer annulus of the resistance increaser 1 and the filling channel 12 of the resistance increaser 1.

[0038] Specifically, the filling channel 12 is at least one, or may be multiple. When the resistance increaser 1 has multiple filling channels 12, the multiple filling channels 12 are symmetrically distributed around the cylinder axis. The resistance increaser 1 may only have an internal filling channel 12 or an external filling channel 12, or may have both of the above filling channels 12.

[0039] like Figure 1-4 As shown, the filling channel 12 of the resistance increaser 1 is arranged inside, and the cross-sectional shape is one or more of circular, elliptical, fan-shaped, and rounded fan-shaped; of course, it can also be other similar shapes, but the use of a circular or fan-shaped structure is not only easy to process, but also has less resistance to the filling liquid.

[0040] like Figure 5-8 As shown, the filling channel 12 of the resistance increaser 1 is arranged on the outside, and the cross-sectional shape is one or more of a semicircular, a fan-shaped, a rounded / chamfered fan-shaped, and the outer side surface of the filling channel 12 is connected with the annulus of the wellbore 2. The rounded / chamfered fan-shaped means that the two corners of the fan-shaped close to the axis are rounded, and the two corners away from the axis are chamfered. The purpose is that the two inner rounded corners can reduce the resistance to the filling fluid, and the outer chamfer is an arc surface to reduce the probability of blockage when going down the well. The "connected" means that the outer side surface of the filling channel 12 is an open structure, which is connected to the annulus of the wellbore 2 as a whole. After the filling is completed, it can form an integrated continuous isolation body.

[0041] Preferably, both ends of the resistance increaser 1 are provided with an annular groove 13 connected with each filling channel 12, and the annular grooves 13 at both ends are consistent in size (including the diameter of the ring, the width and depth of the groove), and consistent in position relative to the axis of the cylinder (the center of the ring falls on the axis). The purpose of providing the annular groove 13 is that when the prefabricated resistance increaser 1 is used as a standard part, the corresponding number of resistance increasers 1 can be selected on site for use in series according to the resistance value to be generated. When two or more resistance increasers 1 are used in series, if the annular groove 13 is not provided, the filling channels 12 of the resistance increasers 1 need to be completely aligned before use, otherwise the filling channels 12 are blocked and the filling liquid cannot be injected into the wellbore 2. By providing the annular groove 13, the annular grooves 13 of two adjacent resistance increasers 1 can form a guide groove, thereby realizing the connection of the filling channels 12 of two adjacent resistance increasers 1. In order to ensure the connectivity effect, the effective flow guide area of ​​the annular groove 13 should not be less than the flow area of ​​a single filling channel 12. Specifically, the number of the annular grooves 13 can be one or more, depending on the number and arrangement of the filling channels 12. If the filling channels 12 are arranged in two circles, two annular grooves 13 with different diameters need to be set. By setting the annular groove 13, when the user installs multiple resistance increasers 1 on the central pipe column (such as a blind pipe), there is no need to consider the alignment of the flow guide channel, thereby improving work efficiency; at the same time, through the free combination of multiple resistance increasers 1, the additional resistance value for the crossflow of the production fluid in the wellbore 2 after production can also be flexibly and accurately set.

[0042] If only the filling channel 12 is provided on the outside, as a simplified structure, the annular groove 13 may not be provided, and the annular space outside the resistance increasing device 1 is used as a flow guide channel. This implementation mode should be considered as an equivalent technical solution of the present embodiment.

[0043] Embodiment 2:

[0044] This embodiment provides a resistance increasing device that can improve the axial isolation effect of the continuous isolation body in the wellbore 2.

[0045] The resistance increasing device includes the resistance increasing device 1 and a central pipe column as described in Example 1, and the central pipe column passes through the central mounting hole 11 of the resistance increasing device 1 and is connected and fixed to the resistance increasing device 1. Specifically, the resistance increasing device 1 and the central pipe column are connected and fixed by one or more of welding, bolt fixing or clamp fixing. As an optional embodiment, the central pipe column is a short-section blind pipe; of course, the central pipe column can also be a screen tube or other types of pipe columns, for example, the resistance increasing device 1 is arranged at one end or both ends of the screen tube.

[0046] The purpose of the technical solution described in this embodiment is to make the resistance increasing device 1 and the central pipe column into standard parts to make them a standardized resistance increasing device. When in use, it can be directly used as a central pipe column with resistance increasing function for downhole construction without the need for on-site assembly, which is more convenient for construction operations.

[0047] Embodiment 3:

[0048] This embodiment provides a specific application method of the resistance increasing device / resistance increasing apparatus described in Embodiment 1 or 2.

[0049] (1) The resistance increasing device 1 is spliced ​​with the central pipe column to form a resistance increasing device, or a prefabricated resistance increasing device is directly used, and is assembled into a pipe string with other central pipe columns such as the screen pipe 3 according to a predetermined number and position, and lowered into the wellbore 2;

[0050] (2) filling the wellbore 2 with a filling fluid carrying sealing particles through the wellbore 2 annulus; Fig. 9 As shown, the packing fluid carries the packing particles and gradually accumulates from the inside to the outside in the annulus of the wellbore 2 to form a continuous packing body 4; the continuous packing body 4 simultaneously fills the filling channel 12 of the resistance increaser / resistance increaser device and the outer annulus area of ​​the resistance increaser / resistance increaser device;

[0051] (3) Production: The produced fluid and produced water in the annulus of the wellbore 2 flow in the annulus. When passing through the area where the resistance increaser / resistance increaser is located, the effective flow area of ​​the filling channel 12 is small, and the resistance encountered is larger than that of the area in the annulus where the resistance increaser / resistance increaser is not installed, so the flow rate is small.

[0052] For example, a 5-1 / 2-in flow control screen was run into a 8-1 / 2-in horizontal well, and continuous packer particles with a permeability of 20D were filled. Under a production pressure difference of 1 MPa, the continuous packer crossflow corresponding to the blind section between the two screens was 45 cubic meters per day. After the resistance increaser of the present invention was applied to the adjacent well of the 8-1 / 2-in horizontal well, the continuous packer crossflow corresponding to the blind section between the two screens was 15 cubic meters per day.

[0053] Embodiment 4:

[0054] This embodiment provides another specific application of the resistance increasing device / resistance increasing apparatus described in Embodiment 1 or 2.

[0055] like Fig.10As shown in the figure, it is an injection and production system including a water injection well M1 and an oil production well M2. As can be seen from the figure, due to the high permeability of the formation at C in the figure, more driving fluid (usually formation water, represented by thick black lines in the figure) injected into the water injection well M1 enters the oil production well M2 through the formation at C. First, it leads to a high water content in the production fluid of the oil production well M2. Second, due to the crossflow of the driving fluid in the wellbore, part of the driving fluid at A, B, D, and E in the wellbore crossflows to C, resulting in a low driving fluid pressure in the formations at A, B, D, and E, and low oil production efficiency. Therefore, it is impossible to achieve the optimal working efficiency of this injection and production system.

[0056] like Fig.11 As shown, a completion structure is formed in the water injection well M1 according to the method described in Example 3. After production, since the driving fluid injected into the water injection well M1 through the central pipe string in the annulus of the wellbore 2 is reduced, the driving fluid in the annulus at A, B, D, and E cannot (or is less) cross-flow to the annulus area at C, and thus cannot enter the formation at C. As a result, the water content in the formation production fluid at C in the oil production well M2 is reduced, and the driving fluid pressure at the formations at A, B, D, and E is increased, thereby enhancing the oil displacement effect and increasing the oil production of the corresponding formation, thereby optimizing the oil recovery rate of the injection-production system.

[0057] Embodiment 5:

[0058] This embodiment provides a completion structure that can improve the axial isolation effect of a continuous isolation body in a wellbore, including a plurality of center pipe strings connected end to end in the wellbore, with flow control filter strings installed at both ends of the center pipe string 4. A continuous isolation body is provided in the annulus between the center pipe string and the wellbore wall. The difference from the prior art is that in the completion structure, one or more of the center pipe strings are provided with a resistance increasing device as described in Example 1; or, one or more of the center pipe strings are the resistance increasing devices as described in Example 2. It should be noted that the completion structure provided in this embodiment is not only applicable to oil production wells, but also to water injection wells.

[0059] In this embodiment, by providing a resistance increaser / resistance increase device with a smaller flow area, the resistance to the flow of produced fluid in the wellbore annulus can be increased, thereby reducing the flow of produced water from the producing formation in the wellbore annulus and improving the overall oil recovery rate of the oil well.

[0060] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A resistance increasing device capable of improving the axial isolation effect of a continuous isolation body in a wellbore, characterized in that: The resistance increasing device is in a cylindrical structure as a whole; a central mounting hole for mounting a central column is provided at the axial center of the resistance increasing device; one or more filling channels which are consistent with the axial direction of the cylinder are provided inside and / or outside the resistance increasing device, and the sum of the effective flow areas of the filling channels is 1 / 20-1 / 2 of the cross-sectional area of ​​the cylinder; Wherein, the resistance increasing device is applied to the wellbore annulus filled with sealing particles; Among them, both ends of the resistance increaser are provided with annular grooves connected to each filling channel, the annular grooves at both ends have the same size and the same position relative to the axis of the cylinder; the effective guide area of ​​the annular groove is not less than the flow area of ​​a single filling channel.

2. The resistance increasing device capable of improving the axial isolation effect of the continuous isolation body in the wellbore according to claim 1, characterized in that: The resistance increaser has a plurality of filling channels, and the plurality of filling channels are distributed in a circumferentially symmetrical manner based on the axis of the cylinder.

3. The resistance increasing device capable of improving the axial isolation effect of the continuous isolation body in the wellbore according to claim 1, characterized in that: The cross-sectional shape of the filling channel inside the resistance increasing device is one or more of a circular shape, an elliptical shape, a sector shape, and a rounded sector shape.

4. The resistance increasing device capable of improving the axial isolation effect of the continuous isolation body in the wellbore according to claim 1, characterized in that: The cross-sectional shape of the filling channel outside the resistance increaser is one or more of a semicircular shape, a fan shape, a rounded / chamfered fan shape, and the outer side surface of the filling channel is connected to the annulus of the wellbore.

5. A resistance increasing device capable of improving the axial isolation effect of a continuous isolation body in a wellbore, characterized in that: It comprises the resistance increasing device and a central tube column as claimed in any one of claims 1 to 4, wherein the central tube column passes through the central mounting hole of the resistance increasing device and is connected and fixed to the resistance increasing device.

6. The resistance increasing device capable of improving the axial isolation effect of the continuous isolation body in the wellbore according to claim 5, characterized in that: The resistance increasing device and the central pipe column are connected and fixed by one or more of welding, bolt fixing or clamp fixing.

7. The resistance increasing device capable of improving the axial isolation effect of the continuous isolation body in the wellbore according to claim 5, characterized in that: The central pipe column is a short-jointed blind pipe.

8. A completion structure capable of improving the axial isolation effect of a continuous packer in a wellbore, comprising a plurality of central pipe strings connected end to end in the wellbore, wherein a continuous packer is arranged in the annulus between the central pipe string and the wellbore wall, characterized in that: One or more of the central pipe columns are provided with a resistance increasing device as claimed in any one of claims 1 to 4.

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