Cavity making method

Abstract

The invention provides a cavity construction method. The cavity construction method comprises the steps that S1, two vertical wells are drilled towards a target stratum in the position, away from the ground surface by a first numerical value range, respectively; s2, one of the two vertical wells is selected to manufacture a sidetrack horizontal well in the direction from the middle of the salt layer to the other vertical well; s3, the two vertical wells are subjected to independent cavity building operation through vertical well open hole sections; and S4, after the dissolving cavities of the two vertical wells communicate with the open hole section of the sidetrack horizontal well, double-well convection cavity construction operation is started.

Description

Technical Field

[0001] The invention relates to the technical field of cavity making in salt cavern gas storage, and in particular to a cavity making method. Background Art

[0002] Salt cavern gas storage is an underground cave formed by injecting fresh water into thick salt layers or salt domes to dissolve the salt layers through water-soluble mining, and then draining saturated or nearly saturated brine. Salt rock has the characteristics of dense structure, low porosity, low permeability, high plastic deformation capacity and self-healing of damage, and is recognized as the best medium for storing oil, natural gas and related products.

[0003] At present, the mainstream technology for salt cavern gas storage is single-well single-cavity construction, which is suitable for thicker rock salt formations. However, some newly built salt cavern gas storages have thin salt layers (less than 100m) and many interlayers. The traditional single vertical well cavity construction has a small volume and slow speed, which is not suitable for large-scale cavity construction in thin salt layers. Horizontal U-shaped wells are an effective way to efficiently create cavities in thin salt layers. Compared with vertical well cavity construction technology, it can greatly improve the lateral extension capacity of the dissolution cavity, form a relatively flat cavity in the thin salt layer, make full use of the salt rock resources in the thin salt layer, and maximize the volume of the salt cavern.

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

[0005] The technical problem to be solved by the present invention is to provide a cavity creation method in view of the deficiencies in the prior art.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: a cavity making method, comprising: S1, drilling two vertical wells respectively toward the target layer at a first numerical range of the distance from the surface; S2, selecting one of the two vertical wells to make a side-drilling horizontal well in the middle of the salt layer toward the direction of the other vertical well; S3, performing independent cavity making operations on the two vertical wells using the vertical well open hole sections; S4, when the dissolution cavities of the two vertical wells are respectively connected with the open hole sections of the side-drilling horizontal well, starting the double-well convection cavity making operation.

[0007] The beneficial effect of the technical solution of the present invention is that before the horizontal well cavity enters the target, it can realize the full dissolution utilization of large sections of salt rock resources, thereby effectively expanding the cavity volume of the horizontal U-shaped well in the thin salt layer. The wellbore 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 grasp the progress of the cavity, thereby ensuring the accuracy and safety of cavity making. A side-drilled horizontal well and a vertical well work together. The two wells first use the vertical well open hole section for independent cavity making operations to obtain the maximum cavity volume and salt rock utilization rate within the same construction period. When the two well cavities are connected to the side-drilled horizontal well open hole respectively, the double-well cavity operation can be started. On the basis of making full use of the salt rock resources before the target of a vertical well, the double-well cavity volume is maximized. Provide key technical support for the economical and efficient construction of a library in thin salt layers.

[0008] Further, step S2 includes: S21, drilling a vertical well section of a vertical well to a second numerical range below the top of the salt layer and then casing and cementing the well; S22, drilling to a third numerical range from the bottom of the salt layer and completing the open hole; S23, side-drilling a horizontal well by using the side-drilling technology at a fourth numerical range above the top of the salt layer in a vertical well.

[0009] The beneficial effect of adopting the above further technical solution is: first, a vertical well is drilled to a position about 10 to 30 meters below the top of the salt layer, and casing is installed and cemented to ensure the sealing of the cavity at the casing shoe. Then, the well is drilled to an open hole completion position about 10 to 20 meters from the bottom of the salt layer; a horizontal well is drilled by side-drilling technology at a position 10 to 20 meters above the top of the salt layer in a vertical well, so as to ensure that the sealing of the wellbore inside the salt layer is not affected by the window opening.

[0010] Further, step S23 includes: S231, using a short-radius flexible drilling tool to side-drill a horizontal well in a vertical well, and controlling the curvature radius of the deflection section to be between 20 and 30 meters; S232, side-drilling to a vertical depth of 10 to 30 meters below the top of the salt layer and casing cementing; S233, drilling the horizontal section and completing the open hole.

[0011] The beneficial effects of adopting the above further technical solution are: accurately making side-drilling horizontal wells and improving work efficiency.

[0012] Furthermore, the method after step S233 includes: S2331, setting a bridge plug or a cement plug at a position close to the casing shoe in the casing of the deflection section.

[0013] The beneficial effect of adopting the above-mentioned further technical scheme is as follows: after the horizontal section of the open hole is drilled, a bridge plug or a cement plug is set near the casing shoe in the casing of the inclined section to cut off the flow channel between a vertical well and a side-drilled horizontal well, thereby avoiding mutual interference between the cavity making of a vertical well and the cavity making of a vertical well and another vertical well, and at the same time avoiding the corrosion of brine on the side-drilling casing to ensure the sealing of the wellbore.

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

[0015] The beneficial effect of adopting the above further technical solution is: first, a vertical well is drilled to a position about 10 to 30 meters below the top of the salt layer, and casing is installed and cemented to ensure the sealing of the cavity at the casing shoe. Then, the well is drilled to an open hole completion position about 10 to 20 meters from the bottom of the salt layer; a horizontal well is drilled by side-drilling technology at a position 10 to 20 meters above the top of the salt layer in a vertical well, so as to ensure that the sealing of the wellbore inside the salt layer is not affected by the window opening.

[0016] Furthermore, in step S2, the dogleg angle of the pre-target deflection section ranges from 35 to 43° / 30m, the horizontal displacement range in front of target point A ranges from 30 to 40m, and the vertical depths of target points A and B are set between 30 and 50m from the bottom of the salt layer.

[0017] The beneficial effect of adopting the above further technical solution is: ensuring that the vertical well cavity can be connected with the horizontal open hole section, and at the same time leaving enough space for independent cavity construction of the vertical well.

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

[0019] The beneficial effect of adopting the above further technical solution is: accurately designing the position and depth of one vertical well and another vertical well to improve accuracy.

[0020] Furthermore, the first numerical range is 100-200 m, and the depths of the two vertical wells are the same.

[0021] The beneficial effect of adopting the above further technical solution is: accurately designing the position and depth of one vertical well and another vertical well to improve accuracy.

[0022] Furthermore, in step S2, the horizontal section of the side drilling of a vertical well is 100 to 200 meters long. In step S3, after the completion of one vertical well and another vertical well, the vertical well cavity making process is used to start the cavity making operation at the same time. The cavity height range is 6 to 10 meters, and the cavity with a diameter range of 80 to 100 meters is built. After the grooving of one vertical well and another vertical well is completed, the reverse circulation and oil pad cavity dissolution processes are continued to be used simultaneously, so that the cavity diameter is always maintained at 80 to 100 meters. When the top of the cavity rises to 2 to 3 meters away from the horizontal open hole section, the thickness of the oil pad is increased.

[0023] The beneficial effect of adopting the above further technical solution is that after the completion of one vertical well and another vertical well, the vertical well cavity making process is used at the same time to start the cavity making operation, the cavity height is controlled to 6 to 10 meters, and a cavity with a diameter of 80 to 100 meters is built. The cavity volume and salt rock utilization rate are maximized within the same construction period. After the troughing of one vertical well and another vertical well is completed, the reverse circulation + oil pad cavity dissolution process is continued to be used simultaneously to keep the cavity diameter at 80 to 100 meters. When the top of the cavity slowly rises to 2 to 3 meters 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, ensuring that the cavity of the first vertical well and the other vertical well can be connected to the wellbore at the horizontal open hole section, thereby forming a flow channel between the first vertical well and the other vertical well.

[0024] Further, in step S4, after one vertical well and another vertical well are connected to the horizontal open hole section, when the two vertical wells need to continue to expand the volume of the dissolution cavity controlled by the single well, the fluid pressure in the dissolution cavity of the two vertical wells is kept basically balanced, and the dissolution cavity operation can be continued by using the vertical well cavity making method respectively; after the cavity making of one vertical well and another vertical well is completed, a double-well cavity making method of one injection and one production is adopted, and the two vertical wells are alternately injected with fresh water and produced with brine, and the convection cavity making operation of the horizontal open hole section is carried out. At the same time, an oil pad is used to control the dissolution of the cavity, so as to achieve a balanced expansion of the overall shape of the cavity, and finally form a dumbbell-shaped cavity.

[0025] The beneficial effect of adopting the above further technical solution is: when one vertical well and another vertical well are connected to the horizontal open hole section, if the two wells need to further expand the volume of the cavity controlled by the single well, as long as the fluid pressure in the cavity of the two wells is basically balanced, the cavity making method of the vertical well can be continued to be used for the cavity operation. After the cavity making of one vertical well and another vertical well is completed, the double-well cavity making method of one injection and one production is adopted, and the two wells alternately inject fresh water and produce brine to carry out the convection cavity making operation of the horizontal open hole section, and at the same time, the oil pad is used to control the dissolution of the cavity to achieve the balanced expansion of the overall shape of the cavity, and finally form a dumbbell-shaped cavity.

[0026] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic flowchart of a cavity creation method provided in an embodiment of the present invention.

[0028] Figure 2 A schematic structural diagram of a side-drilling U-shaped horizontal wellbore provided in an embodiment of the present invention.

[0029] Figure 3 A schematic diagram of the structure in which two wells provided in an embodiment of the present invention are independently constructed using the positive circulation method.

[0030] Figure 4 A schematic diagram of the structure of two wells provided in an embodiment of the present invention, both of which use the reverse circulation method to have independent dissolution cavities and connect horizontal open hole sections.

[0031] Figure 5 One of the structural schematic diagrams of expanding the volume of the horizontal well cavity by using the U-shaped well cavity making method provided in an embodiment of the present invention.

[0032] Figure 6 The second structural schematic diagram of expanding the volume of the horizontal well cavity by the U-shaped well cavity making method provided in the embodiment of the present invention. DETAILED DESCRIPTION

[0033] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention but not to limit the scope of the present invention.

[0034] like Figure 1 As shown, an embodiment of the present invention provides a cavity making method, including: S1, drilling two vertical wells toward the target layer at a first numerical range of the distance from the surface; S2, selecting one of the two vertical wells to make a side-drilling horizontal well in the middle of the salt layer toward the other vertical well; S3, performing independent cavity making operations on the two vertical wells using the vertical well open hole sections; S4, when the dissolution cavities of the two vertical wells are connected to the open hole sections of the side-drilling horizontal well respectively, starting the double-well convection cavity making operation.

[0035] The beneficial effect of the technical solution of the present invention is that before the horizontal well cavity enters the target, it can realize the full dissolution utilization of large sections of salt rock resources, thereby effectively expanding the cavity volume of the horizontal U-shaped well in the thin salt layer. The wellbore 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 grasp the progress of the cavity, thereby ensuring the accuracy and safety of cavity making. A side-drilled horizontal well and a vertical well work together. The two wells first use the vertical well open hole section for independent cavity making operations to obtain the maximum cavity volume and salt rock utilization rate within the same construction period. When the two well cavities are connected to the side-drilled horizontal well open hole respectively, the double-well cavity operation can be started. On the basis of making full use of the salt rock resources before the target of a vertical well, the double-well cavity volume is maximized. Provide key technical support for the economical and efficient construction of a library in thin salt layers.

[0036] The embodiment of the present invention aims at the engineering problem of low utilization rate of salt rock resources before target in the construction of horizontal wells in thin salt layers. Combining the single-well single-cavity construction method and the U-shaped well construction method, a cavity construction method (cavity construction method) for improving the utilization rate of resources before target in horizontal wells in thin salt layers is proposed. The cavity construction method requires a side-drilled horizontal well and a vertical well to work together. The two wells first use the vertical well open hole section to perform independent cavity construction operations to obtain the maximum cavity volume and salt rock utilization rate within the same construction period. When the dissolution cavities of the two wells (one vertical well and another vertical well) are connected to the side-drilled horizontal well open hole respectively, the U-shaped well dissolution cavity operation can be started. On the basis of making full use of the salt rock resources before target in the I well (a vertical well), the cavity construction volume of the U-shaped well is maximized. This method can provide key technical support for economical and efficient construction of libraries in thin salt layers.

[0037] Further, step S2 includes: S21, drilling a vertical well section of a vertical well to a second numerical range below the top of the salt layer and then casing and cementing the well; S22, drilling to a third numerical range from the bottom of the salt layer and completing the open hole; S23, side-drilling a horizontal well by using the side-drilling technology at a fourth numerical range above the top of the salt layer in a vertical well.

[0038] The beneficial effect of adopting the above further technical solution is: first, a vertical well is drilled to a position about 10 to 30 meters below the top of the salt layer, and casing is installed and cemented to ensure the sealing of the cavity at the casing shoe. Then, the well is drilled to an open hole completion position about 10 to 20 meters from the bottom of the salt layer; a horizontal well is drilled by side-drilling technology at a position 10 to 20 meters above the top of the salt layer in a vertical well, so as to ensure that the sealing of the wellbore inside the salt layer is not affected by the window opening.

[0039] Further, step S23 includes: S231, using a short-radius flexible drilling tool to side-drill a horizontal well in a vertical well, and controlling the curvature radius of the deflection section to be between 20 and 30 meters; S232, side-drilling to a vertical depth of 10 to 30 meters below the top of the salt layer and casing cementing; S233, drilling the horizontal section and completing the open hole.

[0040] The beneficial effects of adopting the above further technical solution are: accurately making side-drilling horizontal wells and improving work efficiency.

[0041] Furthermore, the method after step S233 includes: S2331, setting a bridge plug or a cement plug at a position close to the casing shoe in the casing of the deflection section.

[0042] The beneficial effect of adopting the above-mentioned further technical scheme is as follows: after the horizontal section of the open hole is drilled, a bridge plug or a cement plug is set near the casing shoe in the casing of the inclined section to cut off the flow channel between a vertical well and a side-drilled horizontal well, thereby avoiding mutual interference between the cavity making of a vertical well and the cavity making of a vertical well and another vertical well, and at the same time avoiding the corrosion of brine on the side-drilling casing to ensure the sealing of the wellbore.

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

[0044] The beneficial effect of adopting the above further technical solution is: first, a vertical well is drilled to a position about 10 to 30 meters below the top of the salt layer, and casing is installed and cemented to ensure the sealing of the cavity at the casing shoe. Then, the well is drilled to an open hole completion position about 10 to 20 meters from the bottom of the salt layer; a horizontal well is drilled by side-drilling technology at a position 10 to 20 meters above the top of the salt layer in a vertical well, so as to ensure that the sealing of the wellbore inside the salt layer is not affected by the window opening.

[0045] Furthermore, in step S2, the dogleg angle of the pre-target deflection section ranges from 35 to 43° / 30m, the horizontal displacement range in front of target point A ranges from 30 to 40m, and the vertical depths of target points A and B are set between 30 and 50m from the bottom of the salt layer.

[0046] The beneficial effect of adopting the above further technical solution is: ensuring that the vertical well cavity can be connected with the horizontal open hole section, and at the same time leaving enough space for independent cavity construction of the vertical well.

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

[0048] The beneficial effect of adopting the above further technical solution is: accurately designing the position and depth of one vertical well and another vertical well to improve accuracy.

[0049] Furthermore, the first numerical range is 100-200 m, and the depths of the two vertical wells are the same.

[0050] The beneficial effect of adopting the above further technical solution is: accurately designing the position and depth of one vertical well and another vertical well to improve accuracy.

[0051] Furthermore, in step S2, the horizontal section of the side drilling of a vertical well is 100 to 200 meters long. In step S3, after the completion of one vertical well and another vertical well, the vertical well cavity making process is used to start the cavity making operation at the same time. The cavity height range is 6 to 10 meters, and the cavity with a diameter range of 80 to 100 meters is built. After the grooving of one vertical well and another vertical well is completed, the reverse circulation and oil pad cavity dissolution processes are continued to be used simultaneously, so that the cavity diameter is always maintained at 80 to 100 meters. When the top of the cavity rises to 2 to 3 meters away from the horizontal open hole section, the thickness of the oil pad is increased.

[0052] The beneficial effect of adopting the above further technical solution is that after the completion of one vertical well and another vertical well, the vertical well cavity making process is used at the same time to start the cavity making operation, the cavity height is controlled to 6 to 10 meters, and a cavity with a diameter of 80 to 100 meters is built. The cavity volume and salt rock utilization rate are maximized within the same construction period. After the troughing of one vertical well and another vertical well is completed, the reverse circulation + oil pad cavity dissolution process is continued to be used simultaneously to keep the cavity diameter at 80 to 100 meters. When the top of the cavity slowly rises to 2 to 3 meters 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, ensuring that the cavity of the first vertical well and the other vertical well can be connected to the wellbore at the horizontal open hole section, thereby forming a flow channel between the first vertical well and the other vertical well.

[0053] Further, in step S4, after one vertical well and another vertical well are connected to the horizontal open hole section, when the two vertical wells need to continue to expand the volume of the dissolution cavity controlled by the single well, the fluid pressure in the dissolution cavity of the two vertical wells is kept basically balanced, and the dissolution cavity operation can be continued by using the vertical well cavity making method respectively; after the cavity making of one vertical well and another vertical well is completed, a double-well cavity making method of one injection and one production is adopted, and the two vertical wells are alternately injected with fresh water and produced with brine, and the convection cavity making operation of the horizontal open hole section is carried out. At the same time, an oil pad is used to control the dissolution of the cavity, so as to achieve a balanced expansion of the overall shape of the cavity, and finally form a dumbbell-shaped cavity.

[0054] The beneficial effect of adopting the above further technical solution is: when one vertical well and another vertical well are connected to the horizontal open hole section, if the two wells need to further expand the volume of the cavity controlled by the single well, as long as the fluid pressure in the cavity of the two wells is basically balanced, the cavity making method of the vertical well can be continued to be used for the cavity operation. After the cavity making of one vertical well and another vertical well is completed, the double-well cavity making method of one injection and one production is adopted, and the two wells alternately inject fresh water and produce brine to carry out the convection cavity making operation of the horizontal open hole section, and at the same time, the oil pad is used to control the dissolution of the cavity to achieve the balanced expansion of the overall shape of the cavity, and finally form a dumbbell-shaped cavity.

[0055] A cavity making method provided in an embodiment of the present invention can be used as a cavity making method for improving the pre-target resource utilization rate of a horizontal well in a thin salt layer:

[0056] Figure 1 The relative positions of wells I and II, the window position of well I, the isolation position of the bridge plug of the side-drilled well, and the target positions of A and B of the side-drilled horizontal well of well I are shown in the figure. Precise control of the wellbore trajectories of wells I and II and high-quality cementing quality are the prerequisites for the successful application of the present invention.

[0057] Figure 2 In the process, after the well construction is completed according to the design, before the dissolution cavities of the two wells are connected through the side-drilled horizontal well, wells I and II can carry out independent trough construction and dissolution cavity operations.

[0058] Figure 3In the process of cavity dissolution, the reverse circulation + oil pad dissolution method is used in wells I and II to further expand the cavity vertical well during the cavity dissolution process, ensure that the dissolution cavities of the two wells can intersect with the wellbore trajectory of the side-drilled horizontal well, build a connecting channel between the two wells, and realize the subsequent U-shaped well cavity construction operation.

[0059] Figure 4 and Figure 5 Both methods use the U-shaped well cavity creation method to expand the volume of the horizontal well cavity. Figure 4 I injection II production (i.e. one vertical well for injection and another vertical well for production), Figure 5 For II injection and I production, alternating injection and production in two wells can maximize the cavity volume and achieve full utilization of pre-target salt rock resources.

[0060] (1) This cavity making method requires the coordinated operation of a side-drilled horizontal well (well I) and a vertical well (well II). Two vertical wells are drilled towards the target layer at a distance of 100 to 200 m from the surface, with the same well depth. Then one of the wells (a vertical well) is selected to side-drill a short-radius horizontal branch well (a side-drilled horizontal well) in the middle of the salt layer toward the other well (another vertical well). The two wells (a vertical well and another vertical well) first use the vertical well open hole section for independent cavity making operations. When the two wells' cavities are connected to the open hole of the side-drilled horizontal well, the dual-well convection cavity making operation can be started. On the basis of making full use of the salt rock resources in front of the target of well I, the cavity making volume of the dual wells is maximized.

[0061] (2) The side-drilling horizontal well is firstly to drill the vertical well section of Well I (a vertical well) to about 10 to 30 m below the top of the salt layer, and to install casing and cement the well to ensure the sealing of the cavity at the casing shoe. Then, the well is drilled to about 10 to 20 m from the bottom of the salt layer and the open hole is completed; the side-drilling technology is used to open a window 10 to 20 m above the top of the salt layer in Well I to ensure that the sealing of the wellbore inside the salt layer is not affected by the window opening (see Figure 2 ).

[0062] (3) A short-radius flexible drilling tool was used to side-drill a horizontal well in Well I, and the curvature radius of the deflection section was controlled to be between 20 and 30 m. The well was side-drilled to a vertical depth of 10 to 30 m below the top of the salt layer, and casing was installed for cementing. After that, the horizontal section was drilled and the well was completed in an open hole (see Figure 2 ).

[0063] (4) To ensure that the vertical wellbore cavity of Well I can be connected with the horizontal open hole section and to leave enough space for the independent cavity of the vertical well, the dogleg angle of the inclination section before the target should be controlled between 35° and 43° / 30m, the horizontal displacement in front of target point A should be controlled between 30 and 40m, and the vertical depth of target points A and B should be set between 30 and 50m from the bottom of the salt layer (see Figure 2 ).

[0064] (5) After the horizontal section of the open hole is drilled, a bridge plug or cement plug is set near the casing shoe in the casing of the deflection section to cut off the flow channel between the vertical well I and the side-drilled well (side-drilled horizontal well), avoid mutual interference between the two operation stages of the vertical well I (a vertical well) and the double-well well I and II, and avoid the corrosion of brine on the side-drilled casing to ensure the sealing of the wellbore (see Figure 2 ).

[0065] (6) The horizontal section of Well I is 100 to 200 m long. Vertical Well II (another vertical well) is drilled at the same time as Well I (a vertical well) at a position 30 to 40 m away from Point B of the horizontal section of Well I. The vertical section of Well II is drilled to a position 10 to 30 m below the top of the salt layer, and then casing is installed and cemented. After that, the open hole is drilled to a position about 10 m from the bottom of the salt layer (see Figure 2 ).

[0066] (7) In order to maximize the cavity volume and salt rock utilization within the same construction period, after the completion of Wells I and II, the vertical well cavity construction technology was used to start the cavity construction operation. The cavity height was controlled to 6 to 10 m, and a cavity with a diameter of 80 to 100 m was built (see Figure 3 ).

[0067] (8) After the construction of wells I and II, the reverse circulation + oil pad dissolution process is continued to be used simultaneously to keep the cavity diameter at 80-100 m. When the top of the dissolution cavity slowly rises to 2-3 m away from the horizontal open hole section, the thickness of the oil pad is appropriately increased to allow the dissolution cavity to fully and stably expand laterally, ensuring that the cavity of wells I and II can be connected to the wellbore at the horizontal open hole section, thereby forming a flow channel between wells I and II (see Figure 4 ).

[0068] (9) After both wells I and II are connected to the horizontal open hole section, if the two wells need to further expand the volume of the cavity controlled by a single well, as long as the fluid pressure in the cavity of the two wells is basically balanced, the cavity construction method of the vertical well can be continued to be used for cavity construction. The influence of the open hole channel between the two wells on their cavity construction can be ignored (see Figure 4 ).

[0069] (10) After the vertical well cavitation of Wells I and II was completed, the dual-well cavitation method of one injection and one production was adopted. The two wells alternately injected fresh water and produced brine to carry out convection cavitation operations in the horizontal open hole section. At the same time, oil pads were used to control the dissolution of the cavity to achieve balanced expansion of the overall shape of the cavity, and finally formed a dumbbell-shaped cavity (see Figure 5 and Figure 6 ).

[0070] The cavity making method proposed in the present invention can realize the full dissolution and utilization of large sections of salt rock resources before the horizontal well cavity enters the target, thereby effectively expanding the cavity making volume of the horizontal U-shaped well in the thin salt layer. The uniqueness of this method is that its well body 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 grasp the progress of the cavity, thereby ensuring the accuracy and safety of cavity making. The present invention is particularly suitable for the efficient construction of new salt cavern storage in thin salt layers. Thin salt layers are often difficult to effectively utilize due to insufficient thickness of the salt layer, and the cavity making method of the present invention can overcome this problem, so that the thin salt layer can also play its due storage value. In addition, due to the high efficiency of this method, it can also significantly reduce the cost of building a library and improve economic benefits, which is of great significance for promoting the rapid development of salt cavern gas storage. In summary, the cavity making method proposed in the present invention is not only technologically advanced, but also shows great potential and value in practical applications.

[0071] Specific implementation process: (1) The thickness of the developed salt layer is 70m. The wellhead position of Well I is selected on the ground, and the wellhead position of Well II is set about 200m away from Well I along the direction of minimum horizontal ground stress of the target layer;

[0072] (2) The first well was drilled to a point about 10 m below the top of the salt layer and casing was installed for cementing. The second well was drilled to a point about 10 m from the bottom of the salt layer. A short-radius flexible drilling tool was used to drill a horizontal well in the direction of Well II at a point 10 to 20 m above the top of the salt layer. The horizontal section target point A was 40 m away from the wellhead and 30 m away from the bottom of the salt layer. The horizontal section between target points A and B was 130 m long and the designed closing distance was 170 m.

[0073] (3) After the side-drilled horizontal well enters the salt layer, casing is installed and cemented 20 m away, followed by drilling the inclination, inclination stabilization and horizontal sections, and then completing the well in open hole;

[0074] (4) Intermediate pipes and central pipes were run into wells I and II, and the trenches were independently constructed using the positive circulation method. The trench depth was 8 m and the diameter was 80 m.

[0075] (5) After the trenching of Wells I and II is completed, the tubing string is lifted and the independent cavity operation is carried out using the reverse circulation + oil pad method. When the top surface of the cavity is 2 to 3 m away from the target points A and B, the oil pad is appropriately thickened to further expand the cavity diameter to more than 90 m to ensure that the cavity of Wells I and II can intersect with the horizontal open hole section;

[0076] (6) After the flow channels of well cavities I and II were established through horizontal wells, the U-shaped well cavity making method was adopted, and I injection and II production and II injection and I production were carried out alternately. At the same time, oil pads were used to control the dissolution of the cavity to achieve a balanced expansion of the overall shape of the cavity. After the cavity volume reached the design requirements, the operation was stopped and gas injection and brine removal were started.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cavity creation method, characterized in that: include: S1, drilling two vertical wells towards the target layer at the first numerical range of the surface distance; S2, selecting one of the two vertical wells to drill a sidetrack horizontal well in the middle of the salt layer toward the direction of the other vertical well; S3, independently perform cavity making operations on two vertical wells using the vertical well open hole sections; S4. After the dissolution cavities of the two vertical wells are connected to the open hole sections of the side-drilled horizontal well, the double-well convection cavity making operation is started.

2. A cavity creation method according to claim 1, characterized in that: Step S2 includes: S21, drilling a vertical well section of a vertical well to a position within a second numerical range below the top of the salt layer, casing and cementing the well; S22, drilling to the open hole completion at the third numerical range from the bottom of the salt layer; S23. A horizontal well is side-drilled by using the side-drilling technology to drill a window at the fourth numerical range above the top of the salt layer in a vertical well.

3. A cavity creation method according to claim 2, characterized in that: Step S23 includes: S231, use short radius flexible drilling tools to side-drill a horizontal well in a vertical well, and control the curvature radius of the deflection section to be between 20 and 30 m; S232, side drilling to a vertical depth of 10 to 30 m below the top of the salt layer, casing and cementing; S233, drill the horizontal section and complete the open hole.

4. A cavity creation method according to claim 3, characterized in that: The process after step S233 includes: S2331, setting a bridge plug or driving a cement plug at a position close to the casing shoe in the casing of the deflection section.

5. A cavity creation method according to claim 2, characterized in that: The second numerical range is 10 to 30 m, the third numerical range is 10 to 20 m, and the fourth numerical range is 10 to 20 m.

6. A cavity creation method according to claim 1, characterized in that: In step S2, the dogleg angle of the pre-target deflection section ranges from 35 to 43° / 30m, the horizontal displacement range in front of target point A ranges from 30 to 40m, and the vertical depths of target points A and B are set between 30 and 50m from the bottom of the salt layer.

7. A cavity creation method according to claim 1, characterized in that: Step S1 includes: S11, drilling another vertical well at a position 30 to 40 m away from point B of the horizontal section of a vertical well at the same time as the vertical well; S12, another vertical well is drilled to a point 10 to 30 m below the top of the salt layer, casing is installed and cemented; S13, open hole drilling to a position 10m from the bottom of the salt layer.

8. A cavity creation method according to claim 1, characterized in that: The first numerical range is 100-200 m, and the depths of the two vertical wells are the same.

9. A cavity creation method according to claim 1, characterized in that: In step S2, the horizontal section of the side drilling of a vertical well is 100 to 200 meters long. In step S3, after the completion of one vertical well and another vertical well, the vertical well cavity making process is used to start the cavity making operation. The cavity height range is 6 to 10 meters, and the cavity with a diameter range of 80 to 100 meters is built. After the trough construction of one vertical well and another vertical well is completed, the reverse circulation and oil pad cavity dissolution process are continued to be used simultaneously, so that the cavity diameter is always maintained at 80 to 100 meters. When the top of the cavity rises to 2 to 3 meters away from the horizontal open hole section, the oil pad thickness is increased.

10. A cavity creation method according to claim 1, characterized in that: In step S4, after one vertical well and another vertical well are connected to the horizontal open hole section, when the two vertical wells need to continue to expand the volume of the dissolution cavity controlled by the single well, the fluid pressure in the dissolution cavity of the two vertical wells is kept basically balanced, and the dissolution cavity operation can be continued by using the vertical well cavity making method respectively; after the cavity making of one vertical well and another vertical well is completed, a double-well cavity making method of one injection and one production is adopted, and the two vertical wells are alternately injected with fresh water and produced with brine, and the convection cavity making operation of the horizontal open hole section is carried out. At the same time, an oil pad is used to control the dissolution of the cavity, so as to achieve a balanced expansion of the overall shape of the cavity, and finally form a dumbbell-shaped cavity.

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