A method of cavity creation

Abstract

The application provides a cavity forming method, comprising the following steps: S1, drilling two straight wells to a target layer at a first distance range on the ground surface; S2, selecting one of the two straight wells to make a lateral horizontal well in the middle of a salt layer and towards the other straight well; S3, performing independent cavity forming operations on the straight well bare hole sections of the two straight wells; and S4, after the cavities of the two straight wells and the bare hole sections of the lateral horizontal well are connected respectively, starting a double-well convection cavity forming operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of salt cavern gas storage cavity making, and particularly relates to a cavity making method. BACKGROUND

[0002] The salt cavern gas storage is a kind of underground cavern formed by injecting fresh water into a thick salt layer or salt dome to dissolve the salt layer and then discharging the saturated or nearly saturated brine. The salt rock has the characteristics of dense structure, low porosity, low permeability, large plastic deformation capacity and damage self-healing, and is considered as the best medium for storing oil, natural gas and related products.

[0003] At present, the mainstream technology of salt cavern gas storage is single-well single-cavity construction, which is suitable for thick rock salt stratum. However, some newly built salt cavern gas storages have thin salt layers (less than 100m) and many interlayers. The traditional single straight well cavity making technology has small volume and slow speed, and is not suitable for thin salt layer cavity making. The horizontal U-shaped well is an effective way for efficient cavity making in thin salt layer, which can greatly improve the lateral extension capacity of the dissolved cavity compared with the straight well cavity making technology, form a relatively flat cavity in the thin salt layer, fully utilize the salt rock resources in the thin salt layer, and maximize the salt cavern volume.

[0004] However, the existing horizontal well design method has a large target distance, and the large section of salt rock resources before entering the target cannot be fully dissolved and utilized, which limits the cavity making volume of the horizontal well in the thin salt layer. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a cavity making method.

[0006] The technical scheme for solving the above technical problem is as follows: a cavity making method, comprising: S1, drilling two straight wells into a target layer at a first distance range on the ground surface; S2, selecting one of the two straight wells to make a sidetracking horizontal well in the middle of the salt layer towards the other straight well; S3, independently making cavities in the straight well bare hole sections of the two straight wells; and S4, after the cavities of the two straight wells and the bare hole section of the sidetracking horizontal well are connected, starting the double-well convection cavity making operation.

[0007] The beneficial effects of the technical scheme are as follows: before the target cavity of the horizontal well is entered, full utilization of large-section salt rock resources can be realized, so that the cavity volume of the horizontal U-shaped well in the thin salt layer is effectively expanded. The well structure is simple and easy to operate, and each cavity stage presents an obvious pressure prompt signal, so that the construction personnel can accurately master the progress of the cavity, thereby ensuring the accuracy and safety of the cavity. One sidetracking horizontal well and one vertical well are cooperatively operated, the vertical well bare hole section is first used for independent cavity operation, the maximum cavity volume and salt rock utilization rate are obtained in the same construction period, after the cavity of the two wells is connected with the bare hole of the sidetracking horizontal well, double-well cavity operation can be started, on the basis of fully utilizing the salt rock resources in front of the target of the vertical well, the cavity volume of the double wells is maximized. Key technical support is provided for the economic and efficient construction of the thin salt layer.

[0008] Further, the step S2 comprises: S21, drilling the vertical well section of one vertical well to the position below the salt layer top by a second value range and casing and cementing; S22, drilling to the position about 10-20m away from the salt layer bottom and bare hole completion; and S23, sidetracking a horizontal well by sidetracking technology at the position above the salt layer top by a fourth value range.

[0009] The beneficial effects of the above further technical scheme are as follows: the vertical well section of one vertical well is first drilled to the position about 10-30m below the salt layer top and casing and cementing is performed, so as to ensure the sealing property of the cavity at the casing shoe. Then, drilling is performed to the position about 10-20m away from the salt layer bottom and bare hole completion is performed; and a horizontal well is sidetracked by sidetracking technology at the position above the salt layer top by 10-20m, so as to ensure that the sealing property of the wellbore in the salt layer is not affected by the windowing.

[0010] Further, the step S23 comprises: S231, using a short-radius flexible drilling tool to sidetrack a horizontal well in one vertical well, and controlling the curvature radius of the build-up section to be between 20-30m; S232, casing and cementing at the position about 10-30m vertically below the salt layer top; and S233, drilling the horizontal section and performing bare hole completion.

[0011] The beneficial effects of the above further technical scheme are as follows: the sidetracked horizontal well is accurately made, and the work efficiency is improved.

[0012] Further, after the step S233, the following step S2331 is performed: S2331, setting a bridge plug or cement plug at the position close to the casing shoe in the casing of the build-up section.

[0013] The beneficial effects of the above further technical scheme are as follows: after the bare hole horizontal section is drilled, a bridge plug or cement plug is set at the position close to the casing shoe in the casing of the build-up section, so as to cut off the flow channel between one vertical well and the sidetracked horizontal well, avoid mutual interference of the cavity construction of one vertical well and the cavity construction of the double wells of one vertical well and another vertical well, and avoid the corrosion of the halogen water to the casing of the sidetracked well, thereby ensuring the sealing property of the wellbore.

[0014] Further, the second numerical range is 10-30m, the third numerical range is 10-20m, and the fourth numerical range is 10-20m.

[0015] The beneficial effect of the further technical solution is that the straight well section of a straight well is drilled to about 10-30m below the top of the salt layer to ensure the sealing of the cavity at the casing shoe. Then, the open hole completion is drilled to about 10-20m from the bottom of the salt layer; the window sidetracking horizontal well is sidetracked at 10-20m above the top of the salt layer in a straight well to ensure that the sealing of the wellbore in the salt layer is not affected by the windowing.

[0016] Further, in step S2, the dogleg range of the pre-target build-up section is 35-43° / 30m, the horizontal displacement range of the A target point is 30-40m, and the A target point and the B target point are set at a vertical depth of 30-50m from the bottom of the salt layer.

[0017] The beneficial effect of the further technical solution is that it ensures that the straight well cavity of a straight well can communicate with the horizontal open hole section, and at the same time, enough space is left for the straight well to independently form a cavity.

[0018] Further, step S1 includes: S11, drilling another straight well at the same time as the straight well at a position 30-40m from the horizontal section B point of the straight well; S12, drilling the straight well section of the other straight well to about 10-30m below the top of the salt layer to set the casing for well cementation; and S13, drilling the open hole to a position 10m from the bottom of the salt layer.

[0019] The beneficial effect of the further technical solution is that the positions and depths of the straight well and the other straight well are accurately designed, improving the accuracy.

[0020] Further, the first numerical range is 100-200m, and the depths of the two straight wells are consistent.

[0021] The beneficial effect of the further technical solution is that the positions and depths of the straight well and the other straight well are accurately designed, improving the accuracy.

[0022] Further, in step S2, the horizontal section of the straight well is sidetracked to a length of 100-200m, in step S3, after the completion of the straight well and the other straight well, the straight well cavity forming process is started at the same time, the cavity height range is 6-10m, and a cavity with a diameter range of 80-100m is built, after the completion of the slotting of the straight well and the other straight well, the reverse circulation and oil pad cavity dissolving process are continued to be used at the same time, so that the diameter of the cavity is always maintained at 80-100m, and when the top of the dissolved cavity rises to a position 2-3m from the horizontal open hole section, the thickness of the oil pad is increased.

[0023] The beneficial effects of the further technical scheme are as follows: after the completion of the completion of the one straight well and the other straight well, the straight well cavity forming process is started, the cavity height is controlled to be 6-10 m, and the cavity with a diameter of 80-100 m is built. The cavity volume and the utilization rate of salt rock are maximized in the same construction period. After the completion of the building of the groove of the one straight well and the other straight well, the reverse circulation and oil pad cavity dissolving process are continuously used, so that the cavity diameter is always kept at 80-100 m. When the top of the cavity slowly rises to a position 2-3 m away from the horizontal open hole section, the thickness of the oil pad is appropriately increased, so that the cavity can be fully and stably expanded laterally, and the cavities of the one straight well and the other straight well can be communicated with the wellbore at the horizontal open hole section, so that the flow channel is formed between the one straight well and the other straight well.

[0024] Further, in step S4, when the one straight well and the other straight well are both communicated with the horizontal open hole section, if the two straight wells need to continue to expand the cavity volume controlled by a single well, the fluid pressure in the cavities of the two straight wells is kept balanced, and then the cavity dissolving operation can be continuously performed by using the straight well cavity forming method respectively. After the completion of the cavity forming of the one straight well and the other straight well, the double-well cavity forming method with one injection and one extraction is used, the two straight wells are alternately injected with fresh water and extracted with brine, the counterflow cavity forming operation of the horizontal open hole section is carried out, the oil pad is used to control the upward dissolving of the cavity, the balanced expansion of the overall cavity shape is realized, and finally the dumbbell-shaped cavity is formed.

[0025] Further, in step S4, when the one straight well and the other straight well are both communicated with the horizontal open hole section, if the two straight wells need to continue to expand the cavity volume controlled by a single well, the fluid pressure in the cavities of the two straight wells is kept balanced, and then the cavity dissolving operation can be continuously performed by using the straight well cavity forming method respectively. After the completion of the cavity forming of the one straight well and the other straight well, the double-well cavity forming method with one injection and one extraction is used, the two straight wells are alternately injected with fresh water and extracted with brine, the counterflow cavity forming operation of the horizontal open hole section is carried out, the oil pad is used to control the upward dissolving of the cavity, the balanced expansion of the overall cavity shape is realized, and finally the dumbbell-shaped cavity is formed.

[0026] The advantages of the additional aspects of the present application will be partially given in the following description, partially will become obvious from the following description, or will be understood by the practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The schematic flow chart of the cavity forming method provided by the embodiment of the present application is shown.

[0028] Figure 2 The structural schematic diagram of the side-tracking U-shaped horizontal well body provided by the embodiment of the present application is shown.

[0029] Figure 3 The structural schematic diagram of the two-well independent groove building by using the positive circulation method provided by the embodiment of the present application is shown.

[0030] Figure 4 The structural schematic diagram of two wells provided by the embodiment of the present application is used to independently dissolve cavities and connect horizontal open hole sections by reverse circulation method.

[0031] Figure 5 The structural schematic diagram of expanding the cavity volume of a horizontal well by U-shaped well cavity forming method provided by the embodiment of the present application.

[0032] Figure 6 The structural schematic diagram of expanding the cavity volume of a horizontal well by U-shaped well cavity forming method provided by the embodiment of the present application. DETAILED DESCRIPTION

[0033] The principles and characteristics of the present application are described below in combination with the drawings, and the embodiments are only used to explain the present application and not to limit the scope of the present application.

[0034] As shown in the drawings, Figure 1 The embodiment of the present application provides a cavity forming method, which comprises the following steps: S1, drilling two straight wells to a target layer at a first distance range on the ground surface; S2, selecting one of the two straight wells to make a lateral horizontal well in the middle of a salt layer towards the other straight well; S3, independently forming cavities in the straight well open hole sections of the two straight wells; and S4, after the cavities of the two straight wells and the open hole section of the lateral horizontal well are connected, starting the double-well counterflow cavity forming operation.

[0035] The beneficial effects of the technical scheme of the present application are as follows: before the target of the horizontal well cavity, the full dissolution and utilization of the large section of salt rock resources can be achieved, thereby effectively expanding the cavity volume of the horizontal U-shaped well in the thin salt layer. The well structure is simple and easy to operate, and each cavity stage will present an obvious pressure prompt signal, so that the construction personnel can accurately master the progress of the cavity, thereby ensuring the accuracy and safety of the cavity forming. One lateral horizontal well and one straight well are used for cooperative operation, two wells are used for independent cavity forming operation by using the straight well open hole section, the maximum cavity volume and salt rock utilization rate are obtained in the same construction period, when the cavities of the two wells and the open hole section of the lateral horizontal well are connected, the double-well cavity forming operation can be started, and on the basis of fully utilizing the salt rock resources in front of the target of the straight well, the maximum double-well cavity volume is obtained. The present application provides key technical support for the economic and efficient construction of a thin salt layer.

[0036] The embodiment of the present application aims at the engineering problem of low resource utilization rate of salt rock before the target of the thin salt layer horizontal well, and proposes a cavity forming method for improving the resource utilization rate before the target of the thin salt layer horizontal well (cavity forming method) in combination with the single-well single-cavity cavity forming method and the U-shaped well cavity forming method. The cavity forming method needs a sidetracking horizontal well and a straight well to be operated cooperatively. The two wells are used to independently form cavities by using the open hole section of the straight well, so that the maximum cavity volume and salt rock utilization rate are obtained in the same construction period. After the cavities of the two wells (one straight well and another straight well) are connected with the open hole of the sidetracking horizontal well respectively, the U-shaped well cavity operation can be started. On the basis of fully utilizing the salt rock resources before the target of the I well (one straight well), the cavity volume of the U-shaped well is maximized. The method can provide key technical support for the economic and efficient construction of the thin salt layer.

[0037] Further, the step S2 comprises: S21, drilling the straight well section of one straight well to the position below the salt layer top by a second value range and casing and cementing; S22, drilling to the position with a third value range from the salt layer bottom and open hole completion; and S23, sidetracking a horizontal well by sidetracking technology at the position above the salt layer top of one straight well by a fourth value range.

[0038] The beneficial effect of the above further technical solution is that the straight well section of one straight well is first drilled to the position below the salt layer top by about 10-30 m and casing and cementing is performed, so as to ensure the sealing of the cavity at the casing shoe. Then, the open hole completion is performed at the position with a distance of about 10-20 m from the salt layer bottom; and the horizontal well is sidetracked by sidetracking technology at the position above the salt layer top by 10-20 m, so as to ensure that the sealing of the wellbore in the salt layer is not affected by the window opening.

[0039] Further, the step S23 comprises: S231, using a short-radius flexible drilling tool to sidetrack a horizontal well in one straight well, and controlling the curvature radius of the build-up section to be between 20-30 m; S232, casing and cementing at the position below the salt layer top by a vertical depth of 10-30 m; and S233, open hole completion after drilling the horizontal section.

[0040] The beneficial effect of the above further technical solution is that the sidetracked horizontal well is accurately made, and the work efficiency is improved.

[0041] Further, after the step S233, S2331, a bridge plug is set or a cement plug is made at the position close to the casing shoe in the casing of the build-up section.

[0042] The beneficial effect of the above further technical solution is that after the open hole horizontal section is drilled, the bridge plug is set or the cement plug is made at the position close to the casing shoe in the casing of the build-up section, so as to cut off the flow channel between one straight well and the sidetracked horizontal well, avoid the mutual interference of the cavity forming of one straight well and the cavity forming of the two straight wells, and avoid the corrosion of the brine to the casing of the sidetracked well, so as to ensure the sealing of the wellbore.

[0043] Further, the second numerical range is 10-30m, the third numerical range is 10-20m, and the fourth numerical range is 10-20m.

[0044] The beneficial effect of the further technical solution is that the straight well section of a straight well is drilled to about 10-30m below the top of the salt layer, the casing is cemented, the sealing of the cavity at the casing shoe is ensured, then the open hole is drilled to about 10-20m from the bottom of the salt layer, and the horizontal well is sidetracked by window sidetracking technology above 10-20m from the top of the salt layer in the straight well, so as to ensure that the sealing of the wellbore in the salt layer is not affected by the window.

[0045] Further, in step S2, the dogleg range of the target pre-tilting section is 35-43° / 30m, the horizontal displacement range of the A target point is 30-40m, and the A target point and the B target point are vertically arranged at a depth of 30-50m from the bottom of the salt layer.

[0046] The beneficial effect of the further technical solution is that the straight well cavity can be connected with the horizontal open hole section, and enough space is left for the straight well cavity.

[0047] Further, step S1 includes: S11, drilling another straight well at a position 30-40m from the horizontal section B point of a straight well at the same time as the straight well; S12, drilling the straight well section of another straight well to about 10-30m below the top of the salt layer, and cementing the casing; and S13, drilling the open hole to a position 10m from the bottom of the salt layer.

[0048] The beneficial effect of the further technical solution is that the positions and depths of the straight well and another straight well are accurately designed, and the accuracy is improved.

[0049] Further, the first numerical range is 100-200m, and the depths of the two straight wells are consistent.

[0050] The beneficial effect of the further technical solution is that the positions and depths of the straight well and another straight well are accurately designed, and the accuracy is improved.

[0051] Further, in step S2, the horizontal section of the straight well is sidetracked to a length of 100-200m, in step S3, the straight well and another straight well are completed at the same time, and the cavity operation is started using the straight well cavity forming process, the cavity height range is 6-10m, the cavity diameter range is 80-100m, after the trench is built in the straight well and another straight well, the reverse circulation and oil pad cavity dissolving process are continued to be used at the same time, so that the cavity diameter is always maintained at 80-100m, and when the top of the cavity rises to a position 2-3m from the horizontal open hole section, the oil pad thickness is increased.

[0052] The beneficial effects of the further technical scheme are that: after the completion of the completion of the one straight well and the other straight well, the straight well cavity forming process is started simultaneously, the cavity height is controlled to be 6-10m, and the cavity with a diameter of 80-100m is built. The cavity volume and the utilization rate of salt rock are maximized in the same construction period. After the building of the groove of the one straight well and the other straight well is completed, the reverse circulation + oil pad cavity dissolving process is continuously used simultaneously, so that the cavity diameter is always kept at 80-100m. When the top of the cavity dissolving slowly rises to 2-3m away from the horizontal open hole section, the thickness of the oil pad is appropriately increased, so that the cavity dissolving can be fully and stably expanded laterally, and the cavity of the one straight well and the other straight well can be communicated with the wellbore at the horizontal open hole section, so that the flow channel is formed between the one straight well and the other straight well.

[0053] Further, in step S4, when the one straight well and the other straight well are communicated with the horizontal open hole section, if the two straight wells need to continue to expand the cavity volume controlled by the single well, the fluid pressure in the cavities of the two straight wells is kept balanced, and then the cavity dissolving operation can be continuously carried out by using the straight well cavity forming method respectively. After the cavity forming of the one straight well and the other straight well is completed, the double well cavity forming method of one injection and one extraction is used, the two straight wells are alternately injected with fresh water and extracted with brine, the counterflow cavity forming operation of the horizontal open hole section is carried out, the oil pad is used to control the upward dissolving of the cavity, the balanced expansion of the overall shape of the cavity is realized, and finally the dumbbell-shaped cavity is formed.

[0054] The beneficial effects of the further technical scheme are that: when the one straight well and the other straight well are communicated with the horizontal open hole section, if the two straight wells need to further expand the cavity volume controlled by the single well, as long as the fluid pressure in the cavities of the two wells is balanced, the cavity dissolving operation can be continuously carried out by using the straight well cavity forming method respectively. After the cavity forming of the one straight well and the other straight well is completed, the double well cavity forming method of one injection and one extraction is used, the two straight wells are alternately injected with fresh water and extracted with brine, the counterflow cavity forming operation of the horizontal open hole section is carried out, the oil pad is used to control the upward dissolving of the cavity, the balanced expansion of the overall shape of the cavity is realized, and finally the dumbbell-shaped cavity is formed.

[0055] The cavity forming method provided by the embodiment of the application can improve the resource utilization rate of the cavity forming method of the horizontal well in the thin salt layer.

[0056] Figure 1 The relative positions of the I well and the II well, the windowing position of the I well, the bridge plug isolation position of the sidetracking well, the A target point position and the B target point position of the sidetracking horizontal well of the I well are shown in the figure. The accurate control of the wellbore trajectories of the I well and the II well and the high-quality cementing quality are the prerequisites for the successful application of the application.

[0057] Figure 2 In the figure, after the design and well building are completed, before the cavities of the two wells are communicated through the sidetracking horizontal well, the I well and the II well can independently carry out the groove building and cavity dissolving operation.

[0058] Figure 3In the method, the reverse circulation and oil cushion cavity dissolution method can be used to further expand the cavity straight well during the cavity dissolution process, to ensure that the two well cavities can intersect with the wellbore trajectory of the horizontal well, to build a communication channel between the two wells, and to realize the subsequent U-shaped well cavity forming operation.

[0059] Figure 4 and Figure 5 are both through U-shaped well cavity forming method to expand the horizontal well cavity volume, wherein Figure 4 is I injection and II production (i.e. one straight well injection and another straight well production), Figure 5 is II injection and I production, and the two wells alternate injection and production to maximize the cavity volume and realize the full use of the target front salt rock resources.

[0060] (1) The cavity forming method needs one side-drilling branch horizontal well (I well) and one straight well (II well) to cooperate. Two straight wells are drilled at a distance of 100-200 m from the surface to the target layer, and the well depth is consistent. Then one of the wells (one straight well) is selected to drill a short radius horizontal branch well (side-drilling horizontal well) in the middle of the salt layer towards the other well (another straight well). Two wells (one straight well and another straight well) first use the straight well open hole section to carry out independent cavity forming operation. When the two well cavities and the side-drilling horizontal well open hole are connected, the double well counterflow cavity forming operation can be started, which can maximize the double well cavity volume on the basis of fully utilizing the target front salt rock resources of I well.

[0061] (2) The side-drilling horizontal well first drills the I well (one straight well) straight well section to about 10-30 m below the top of the salt layer and sets the casing to ensure the sealing of the cavity at the casing shoe. Then it is drilled to about 10-20 m above the bottom of the salt layer and completed as an open hole; the side-drilling horizontal well is drilled at a distance of 10-20 m above the top of the salt layer to ensure that the sealing of the wellbore in the salt layer is not affected by the window opening (see Figure 2 ).

[0062] (3) The short radius flexible drilling tool is used to drill the I well side-drilling horizontal well, and the curvature radius of the build-up section is controlled between 20-30 m. The casing is set at a vertical depth of 10-30 m below the top of the salt layer, and then the horizontal section is drilled and completed as an open hole (see Figure 2 ).

[0063] (4) In order to ensure that the I well straight well cavity forming can be connected with the horizontal open hole section, and at the same time to leave enough space for the straight well independent cavity forming, the dogleg angle of the target front build-up section should be controlled between 35-43° / 30m, the horizontal displacement of A target point should be controlled between 30-40m, and the vertical depth of A target point and B target point should be set between 30-50m from the bottom of the salt layer (see Figure 2 ).

[0064] (5) After the horizontal section of the I well is drilled, a bridge plug or a cement plug is set in the casing near the casing shoe in the build-up section to block the flow path between the I well and the sidetracked well (sidetracked horizontal well), to avoid the interference between the I well cavity forming and the I and II well cavity forming, to avoid the corrosion of the brine to the casing of the sidetracked well, and to ensure the sealing of the wellbore (see Figure 2 ).

[0065] (6) The I well is sidetracked for 100-200 m, and the II well is drilled at the same time as the I well (one straight well) at a position 30-40 m away from the B point of the I well horizontal section. The II well is cased and cemented at a position 10-30 m below the top of the salt layer, and then the open hole is drilled to a position about 10 m above the bottom of the salt layer (see Figure 2 ).

[0066] (7) To maximize the cavity volume and the utilization rate of the salt rock in the same construction period, the I and II wells are simultaneously cased and cemented after completion, and then the cavity forming process is started. The cavity height is controlled to be 6-10 m, and a cavity with a diameter of 80-100 m is formed (see Figure 3 ).

[0067] (8) After the I and II wells are cased, the reverse circulation + oil pad cavity dissolving process is continued to keep the cavity diameter at 80-100 m. When the top of the cavity slowly rises to a position 2-3 m above the horizontal open hole section, the oil pad thickness is appropriately increased to ensure that the cavity can expand laterally and that the cavity of the I and II wells can be connected to the wellbore at the horizontal open hole section, thereby forming a flow path between the I and II wells (see Figure 4 ).

[0068] (9) When the I and II wells are connected to the horizontal open hole section, if the cavity volume controlled by each well needs to be further expanded, as long as the fluid pressure in the cavities of the two wells is basically balanced, the cavity forming operation can be continued by using the straight well cavity forming method, and the influence of the open hole path between the two wells on the cavity forming can be ignored (see Figure 4 ).

[0069] (10) After the I and II wells are cased, the one-injection-one-extraction cavity forming method is used, and the two wells are alternately injected with fresh water and brine to carry out the counterflow cavity forming operation in the horizontal open hole section. At the same time, the oil pad is used to control the upward dissolution of the cavity, to achieve the balanced expansion of the overall cavity shape, and finally to form a dumbbell-shaped cavity (see Figure 5 and Figure 6 ).

[0070] The cavity forming method can realize full utilization of large section of salt rock resources before the cavity in the horizontal well reaches the target, thereby effectively expanding the cavity volume of the horizontal U-shaped well in the thin salt layer. The method has the advantages of simple well structure, easy operation, and obvious pressure prompt signal in each cavity dissolution stage, so that the operator can accurately control the cavity dissolution process, thereby ensuring the accuracy and safety of cavity forming. The method is particularly suitable for efficient construction of new salt cavern storage in the thin salt layer. The thin salt layer is often difficult to effectively utilize due to insufficient thickness, but the cavity forming method can overcome this problem and make the thin salt layer play its due storage value. In addition, due to the high efficiency of the method, the construction cost can be significantly reduced, and the economic benefit can be improved, which has important significance for promoting the rapid development of salt cavern gas storage. In summary, the cavity forming method has not only advanced technology, but also great potential and value in practical application.

[0071] Specific implementation process: (1) the thickness of the salt layer is 70m, the wellhead position of I well is selected on the ground, and the wellhead position of II well is arranged at a distance of about 200m from I well along the minimum horizontal stress direction of the target layer;

[0072] (2) two wells are drilled to about 10m below the top of the salt layer, cased and cemented, and then drilled to about 10m above the bottom of the salt layer; I well is sidetracked horizontally along the direction of II well using short radius flexible drilling tools above 10-20m above the top of the salt layer, the horizontal section A target point is 40m away from the wellhead in horizontal displacement, the A target point is 30m away from the bottom of the salt layer, the length of the horizontal section between A and B target points is 130m, and the designed closure distance is 170m;

[0073] (3) the casing is cemented at 20m into the salt layer after the sidetracked horizontal well, then the drilling, deflecting and horizontal section are completed, and the open hole is completed;

[0074] (4) the intermediate pipe and the central pipe are lowered into I well and II well, and the positive circulation method is used to build slots independently, the slot depth is 8m, and the diameter is 80m;

[0075] (5) after the slot building of I well and II well is completed, the pipe string is lifted, and the reverse circulation + oil pad method is used to carry out independent cavity dissolution operation, when the top surface of the cavity is 2-3m away from A and B target points, the oil pad is appropriately thickened to further expand the cavity diameter to more than 90m, and it is ensured that the cavities of I well and II well can intersect with the horizontal open hole section;

[0076] (6) after the cavity of I well and II well establishes a flow channel through the horizontal well, the U-shaped well cavity forming method is used, I injection II production and II injection I production are alternately carried out, the oil pad is used to control the upper dissolution of the cavity, the balanced expansion of the overall shape of the cavity is realized, and after the cavity volume reaches the design requirement, the operation is stopped, and gas injection and halogen removal are started.

[0077] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for creating a cavity, characterized in that, include: S1. Drill two vertical wells into the target layer at a distance of the first numerical range from the surface; S2. Select one of the two vertical wells and drill a horizontal side-drilled well in the middle of the salt layer towards the other vertical well; S3. Independent cavity-making operations were carried out on the two vertical wells using the open hole section of the vertical well. S4. After the cavities of the two vertical wells are connected to the open hole section of the side-drilled horizontal well, the dual-well convection cavity creation operation is started. Step S2 includes: S21. Drill the vertical section of a vertical well to the second numerical range below the top of the salt layer and then run the casing for cementing. S22. Drill to the third numerical range from the bottom of the salt layer and complete the well with an open hole. S23. Horizontal well drilling with a window opening technique at the fourth numerical range above the top of the salt layer in a vertical well; Step S23 includes: S231. Use a short-radius flexible drilling tool to drill a horizontal well on the side of a vertical well, and control the curvature radius of the build-up section to be between 20 and 30 m. S232, Side-drill to a vertical depth of 10-30m below the top of the salt layer and run casing for cementing; S233, Open hole completion after drilling of the horizontal section; Step S233 is followed by: S2331, setting a bridge plug or installing a cement plug in the casing near the casing shoe in the inclined section.

2. The cavity creation method according to claim 1, characterized in that, The second value range is 10~30m, the third value range is 10~20m, and the fourth value range is 10~20m.

3. The cavity creation method according to claim 1, characterized in that, In step S2, the dogleg angle of the inclinometer section in front of the target is 35~43° / 30m, the horizontal displacement in front of target point A is 30~40m, and the vertical depth of target points A and B is set between 30~50m from the bottom of the salt layer.

4. The cavity creation method according to claim 1, characterized in that, Step S1 includes: S11, drilling another vertical well simultaneously with a vertical well at a position 30-40m away from point B of the horizontal section of a vertical well; S12, another vertical well section was drilled to a depth of 10-30m below the top of the salt layer and then the casing was run and cemented; S13. Drill with naked eyes to a position 10m from the bottom of the salt layer.

5. The cavity creation method according to claim 1, characterized in that, The first value range is 100~200m, and the two vertical wells have the same depth.

6. The cavity creation method according to claim 1, characterized in that, In step S2, the horizontal section of a vertical well is 100-200m long. In step S3, after the completion of one vertical well and another vertical well, the vertical well cavity-making process is used simultaneously to start cavity-making operations. The cavity height ranges from 6 to 10m, and the cavity diameter ranges from 80 to 100m. After the trenching of one vertical well and another vertical well is completed, the reverse circulation and oil pad cavity-making processes are used simultaneously to keep the cavity diameter at 80-100m. When the top of the cavity rises to 2-3m away from the horizontal open hole section, the thickness of the oil pad is increased.

7. The cavity creation method according to claim 1, characterized in that, In step S4, after both vertical wells are connected to the horizontal open hole section, when the two vertical wells need to continue to expand the cavity volume controlled by a single well, the fluid pressure in the cavity of the two vertical wells is kept basically balanced, and the cavity construction method can be used to continue the cavity construction operation. After the cavity construction of one vertical well and the other vertical well is completed, the dual-well cavity construction method of injection and production is adopted. The two vertical wells alternately inject fresh water and produce brine to carry out the convection cavity construction operation in the horizontal open hole section. At the same time, oil pads are used to control the cavity dissolution, so as to achieve the balanced expansion of the overall shape of the cavity and finally form a dumbbell-shaped cavity.

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