STAGED WELL AND RUBBER PLUG OPERATION METHOD FOR SAID METHOD

Abstract

A well-stage operation method is disclosed, comprising the following stages: running, after performing a first well diversion operation in a well, a pipe string (100) into the well, wherein the pipe string (100) includes, from bottom to top, a floating circumference (2), a plug seat (7), a round-tip slip sleeve (3), and a fracturing slip sleeve (4); performing a cementing operation, wherein cement slurry pumped into an internal chamber of the pipe string (100) enters an annular space between the pipe string and the wellbore through the plug seat (7) and the floating circumference (2) to form a cement sleeve, wherein the cement sleeve isolates the round-tip slip sleeve (3) from the fracturing slip sleeve (4);Perform a second diversion operation to ensure that the round-tipped slip sleeve (3) of the tubing string (100) is exposed; perform a pressure test on the tubing string; and carry out staged fracturing constructions. A rubber plug (20) suitable for the well staged operation method is also disclosed.

Description

STAGED WELL AND RUBBER PLUG OPERATION METHOD FOR SAID METHOD CROSS REFERENCE TO RELATED APPLICATIONS This application claims the priorities of Chinese patent application No. 202010534849.2 entitled Staged stimulation pipe string for well cementation and method and filed on June 12, 2020, Chinese patent application No. 202010534828.0 entitled Wellbore operation preparation method for single channel well construction and filed on June 12, 2020, and Chinese patent application No. 202010596721.9 entitled Rubber plug and bumping tool for tubing cementation including the same and filed on June 28, 2020, the contents of which are incorporated herein by reference in their entirety. TECHNICAL FIELD OF THE INVENTION The present invention relates to the technical field of oil / gas field production, and in particular to a well staged operation method and a rubber plug used for the well staged operation method. TECHNICAL BACKGROUND OF THE INVENTION For existing oil / gas reservoirs, especially dense oil / gas reservoirs, staged stimulation technology is commonly used for well construction, including well cementing, well completion, fracturing, and other operational stages. One common fracturing method is long horizontal section staged fracturing, and the corresponding well completion methods primarily include casing-through staged completion and open-hole staged completion. Staged completion of casing drilling and staged completion of open-hole drilling each involve several relevant processes, requiring a variety of equipment to be lowered into the well to perform the various operations. For example, staged completion of casing drilling includes the stages of post-drilling bypass, casing cementing, sound measurement, bypass, drilling, pipe scraping, staged completion string service, mud displacement, and so on.Open-hole staged completion includes simulated bypass stages in the horizontal section after drilling, open-hole staged pressure release of the pipe string through the drill rod, mud displacement in the horizontal section, packer sealing through the ball, drop, mud displacement in the vertical section, push pressure release of the pipe string, short casing string service, etc. The conventional staged well completion process mentioned above requires numerous stages, a long operating period, and diverse equipment. This leads to high well construction costs and low development benefits for dense oil / gas reservoirs. Therefore, it is difficult for conventional well completion technology to meet production demands. BRIEF DESCRIPTION OF THE INVENTION With respect to some or all of the prior art technical problems, the present invention proposes a method of well stage operation whereby well cementing, well completion, and fracturing operations can be performed simultaneously. The method requires only a few stages and therefore has a short operating period, and can be widely used in different types of oil / gas reservoirs. The present invention further proposes a rubber plug for such a method of well stage operation. According to a first aspect of the present invention, a method of staged well operation is provided, comprising the following stages: lowering, after performing a first well diversion operation in a well, a string of pipe into the well, wherein the string of pipe includes, from bottom to top, a floating circumference, a plug seat, a round-tip slip sleeve, and a fracturing slip sleeve; performing a cementing operation, wherein cement slurry pumped into an internal chamber of the pipe string enters an annular space between the pipe string and the well through the plug seat and the floating circumference to form a cement sleeve, wherein the cement sleeve isolates the round-tip slip sleeve from the fracturing slip sleeve;Perform a second diversion operation to ensure that the round-tip slip sleeve of the pipe string is exposed; perform a pressure test on the pipe string; and perform a staged fracturing construction. In a preferred embodiment, the cementing operation step comprises: pumping a cushion fluid into the pipe string, wherein the cushion fluid enters the annular space between the pipe string and the wellbore through the plug seat and the flushing float; pumping the cement slurry into the annular space between the pipe string and the wellbore through the plug seat and the flushing float; dropping a rubber plug into the wellbore, and pumping a displacement fluid to cause the rubber plug to move downwards until it strikes the plug seat; and shutting down the well to allow pressure to build up and give the cement time. In one specific embodiment, the cushion fluid is pumped with a selected volume so that a fluid section with a length of 200-300 m is formed in the annular space. In one specific embodiment, the cement slurry is pumped with a selected volume such that a return height of the cement slurry is at least 200 m above the fracturing slip sleeve. In one specific embodiment, pressure buildup is carried out at a pressure 3-5 MPa higher than a liquid column pressure difference. In a preferred embodiment, the step of performing the second diverting operation comprises: performing a plugging operation to determine a position of the rubber plug; and judging whether the position of the rubber plug is above the round-tip sliding sleeve, and if so, further performing a plug removal operation. In one specific embodiment, the plugging operation is performed with a flexible pipe connected to a plugging string, wherein the external diameter of the flexible pipe is 20-30 mm smaller than the internal diameter of the pipe string, and the maximum external diameter of the plugging string is 3-5 mm smaller than the internal diameter of the pipe string, wherein the flexible pipe has a service velocity of 10-20 m / min. In a preferred embodiment, pressurization is repeated several times if the flexible tubing is obstructed in a position during service, and that position is the position of the rubber plug if the position where the flexible tubing is obstructed remains the same. In one specific embodiment, the plug removal operation is performed by means of a flexible pipe connected to a plug removal string, wherein a maximum external diameter of the plug removal string is 6-8 mm less than the internal diameter of the pipe string. In one specific embodiment, the rubber plug is removed by drilling to a position 10-20 m below a lower surface of the round-tipped sliding sleeve. In one specific embodiment, the rubber plug is removed by drilling with the pumping of a plug removal working fluid to move a drill bit through the plug removal string, wherein the plug removal working fluid is pumped with a displacement of 300-500 L / min. In a preferred embodiment, a plug removal working fluid displacement operation in the pipe string is performed after the plug removal operation. In a preferred embodiment, the flexible tubing is raised after coming into contact with the rubber plug in the tubing string, and a well-building working fluid is pumped to displace the plug-removal working fluid in the tubing string. In a preferred embodiment, a pumping pressure value of the well construction working fluid is gradually decreased. In a preferred embodiment, the well construction working fluid is a reaction fluid acting on the slip sleeves of the pipe string, wherein a spacer fluid is pumped prior to the well construction working fluid. According to a second aspect of the present invention, a rubber plug used in the aforementioned well stage operation method is provided, comprising: a plug core, including an insertion head, a main body, and a connecting bottom, wherein an annular mounting groove is disposed on an outer wall of the insertion head; a cup disposed on an outer wall of the connecting bottom; and a locking member disposed in the mounting groove. In a preferred embodiment, the mounting groove includes a first straight section adjacent to the main body of the plug core, and a first sloped section adjacent to the first straight section, wherein the first sloped section is configured so that the outer diameter of the rubber plug insertion head gradually increases. The locking member is configured as a C-shaped ratchet ring, an inner wall surface including a first straight mating section at its upper portion, mating with the first straight section, and a first sloped mating section at its lower portion, mating with the first sloped section; an upper end face of the C-shaped ratchet ring bears against a lower end face of the main body of the plug core. In a preferred embodiment, the plug core insertion head includes a second straight section connected to the first sloped section, a second sloped section connected to the second straight section, and a guide section connected to the second sloped section. The second sloped section is configured such that the outer diameter of the insertion head gradually decreases from top to bottom, and the guide section is configured as a spherical surface. In a preferred embodiment, an upward-facing face of the first stage, a downward-facing face of the second stage, and a sealing groove for receiving a sealing ring are formed in an outer wall of the main body of the plug core, in IVIA / I υ I where the face of the second stage is located below the face of the first stage, and where the sealing groove is arranged between the face of the first stage and the face of the second stage. In a preferred embodiment, a transit section with a relatively larger outside diameter is provided at the upper end of the main body of the plug core, wherein an outside diameter of a main body of the cup is equal to that of the transit section. BRIEF DESCRIPTION OF THE DRAWINGS The following preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings: Figure 1 shows a pipe string according to one embodiment of the present invention; Figure 2 shows a pipe string according to another embodiment of the present invention; Figure 3 is a flow diagram of a well-stage operation method according to the present invention; Figure 4 is a substage flow diagram of stage S320 in Figure 3; Figure 5 is a substage flow diagram of stage S330 in Figure 3; Figure 6 shows a rubber stopper according to one embodiment of the present invention; Figure 7 shows a plug core of the rubber stopper of Figure 6; and Figure 8 shows a locking element of the rubber stopper of Figure 6. In the drawings, the same reference numbers are used to indicate the same components. The drawings are not drawn to scale. DETAILED DESCRIPTION OF THE FORMS OF REALIZATION The present invention will be described in greater detail below with reference to the accompanying drawings. In the context of the present invention, the directional terms "upstream," "upward," or similar terms refer to a direction toward the wellhead, while the directional terms "downstream," "downward," or similar terms refer to a direction away from the wellhead. Furthermore, the radial direction toward the formation is referred to as "radially outward," while the direction away from the formation is referred to as "radially inward." Figure 1 shows a pipe string 100 according to one embodiment of the present invention, which is suitable for a deviated well section. As shown in Figure 1, the pipe string 100 includes a floating shoe 1, a floating circumference 2, a plug seat 7, a round-tip slip sleeve 3, a fracturing slip sleeve 4, a pipe 5, and a centralizer 6. The floating shoe 1 is arranged at one end of the pipe string 100 to facilitate the smooth lowering of the pipe string 100 into the well. The floating circumference 2 is arranged at the upper end of the floating shoe 1 to ensure that the pipe string 100 can be run smoothly. Simultaneously, the floating circumference 2 serves as a flow passage connecting an internal chamber of the pipe string 100 to the wellbore during well cementing. It also receives a rubber plug that is lowered into the internal chamber of the pipe string 100 later, as described in detail below. In an embodiment of the present invention not shown, the pipe string 100 includes two floating circumferences 2 spaced apart along an axial direction of the pipe string to enhance operational safety and ensure smooth operations such as well cementing or similar activities. The round-tip slip sleeve 3 is arranged at the upper end of the floating circumference 2 to perform a first-stage fracturing operation after well cementing is completed. In a preferred embodiment of the present invention, the round-tip slip sleeve 3 is a differential pressure slip sleeve, which can be opened by a pressure differential. In the embodiment shown in Figure 1, two round-tip slip sleeves 3 are provided, spaced apart along the axial direction of the tubing string 100. By way of non-limiting example, the round-tip slip sleeve 3 may be the one disclosed in CN110374571A or CN209261535U. The fracturing slip sleeve 4 is arranged at the upper end of the round-tipped slip sleeve 3 to perform fracturing operations for subsequent stages after cementing is complete. Although only two fracturing slip sleeves 4 are shown schematically in Figure 1, it can be understood that the pipe string 100 according to the present invention may include a plurality of fracturing slip sleeves 4 spaced apart along the axial direction of the pipe string. Preferably, the fracturing slip sleeve 4 is a full-well slip sleeve for continuous operation. As a non-limiting example, the fracturing slip sleeve 4 may be the one disclosed in CN203603846U. iviA / i υ i Preferably, the round-tip slip sleeve 3 and the fracturing slip sleeve 4 have the same internal diameter, which is equal to that of pipe 5 of pipe string 100, to ensure smooth passage of the subsequent rubber plugs. According to the present invention, the pipe string 100 may also include a centralizer 6. The centralizer 6 can perform a centralizing function and also reduces the frictional force generated when the pipe string 100 is run into the well, ensuring that the pipe string 100 can be run smoothly. In a preferred embodiment of the present invention, a plurality of centralizers 6 may be arranged in the axial direction of the pipe string 100 in sequence. The lowest centralizer 6 is located between the floating shoe 1 and the floating circumference 2. Preferably, the distance between two adjacent centralizers 6 may be in the range of 20 to 40 m. Figure 2 shows a pipe string 100 according to another embodiment of the present invention, which is suitable for a horizontal well section. The structure of the pipe string 100 shown in Figure 2 is substantially the same as that of the pipe string shown in Figure 1, so a detailed description of the latter is omitted herein. In particular, Figure 2 shows a plurality of fracturing slip sleeves 4 arranged at intervals along the axial direction of the pipe string. Figure 3 is a flow diagram of a well-stage operation method according to the present invention, which is preferably implemented with the aforementioned 100 pipe string. First, the method begins at stage S310, where an initial bypass operation is performed after drilling is completed, and then the pipe string is run into the well. This initial bypass operation can be performed with a bypass string at the bottom of the well, allowing the well to meet the pipe string's service requirements. During service, the upper end of the pipe string is permanently connected to the wellhead. In stage S320, a cementing operation is performed, where the cement slurry pumped into the inner chamber of the pipe string enters an annular space between the pipe string and the well through a plug seat and floating circumference to form a cement sleeve, which separates the round-tip slip sleeve from the fracturing slip sleeve. According to a specific embodiment of the present invention, step S320 may include a preparatory step and four substeps. In the preparatory step, a cement tank is connected to the wellhead device and pumps suitable liquids into the pipe string according to a cementing procedure established beforehand after a pressure test. This preparatory step is well known to those in the mid-level trade. In substage S3201, a cushion fluid is first pumped into the drill string so that it can enter the annular space between the drill string and the wellbore through the plug seat and the floating circumference for cleaning. For example, the cushion fluid may include a wash fluid and a spacer fluid. The wash fluid is pumped to clean mud cakes that form on the wellbore wall, allowing the drilling fluid to flow freely. The spacer fluid is pumped to isolate the wash fluid from the cement slurry that is pumped later. This prevents the cement slurry from mixing with the mud slurry formed by the wash fluid and mud cakes, thus avoiding any negative impact on cementing quality.According to a preferred embodiment of the present invention, the pumped cushion fluid can preferably form a fluid section with a length of 200-300 m in the well. In substage S3202, the cement slurry is pumped. The cement slurry being pumped is a liquid fluid composed of cement, water, and additives. During the pumping procedure, the cement slurry enters the annular space between the pipe string and the wellbore through the plug seat and the floating circumference, forming a cement sleeve. This sleeve separates the round-tip slip sleeve and the fracturing slip sleeve (the lowest one when multiple fracturing slip sleeves are present). After a sufficient amount of cement slurry has been pumped, substage S3202 is complete. In substage S3203, a rubber plug (described below with reference to Figures 6 through 8) is released into the 100-inch tubing string, and displacement fluid is then pumped to cause the rubber plug to move downward until it impacts the plug seat. The displacement fluid is then pumped to force the cement slurry into the inner chamber of the tubing string, completely filling the annular space between the tubing string and the wellbore. In substage S3204, well operation is stopped to allow time for the cement to cure. At this time, the rubber plug is pumped out with the plug seat and thus seats within it. In a preferred embodiment, the pressure built up when well operation is stopped is selected according to the pressure differential of a liquid column; that is, it should be 3–5 MPa greater than the differential pressure of the liquid column to effectively prevent backflow of the cement slurry. While the cement cures, the cement slurry outside the tubing string gradually cures, forming a cement sheath between the outer wall of the tubing string and the formation wellbore wall.The cement sleeve is located between the round-tip slip sleeve and the fracturing slip sleeve (the lowest when there are multiple fracturing slip sleeves), achieving the staged isolation effect. In a preferred embodiment, during the cementing procedure, the return height of the cement slurry is designed according to particular well conditions, but must be at least 200 m greater than the upper fracturing slip sleeve. In step S330, a second diverting operation is performed to ensure that at least one round-tipped slip sleeve of the pipe string is exposed. According to a specific embodiment of the present invention, step S330 may include the following substeps. In the second diversion operation, a plugging operation is first performed at substage S3301. In a preferred embodiment, the plugging operation can be performed using a flexible pipe connected to a plugging string. The outer diameter of the flexible pipe can be 20–30 mm smaller than the inner diameter of the pipe string, and the maximum outer diameter of the plugging string can be 3–5 mm smaller than the inner diameter of the pipe string. The lowering speed of the flexible pipe is preferably 10–20 m / min. If the flexible pipe becomes obstructed at a certain position during operation, the plugging operation can be repeated several times by applying a pressure of 3–6 tons. If the obstruction remains, it can be determined that the obstruction is the position of the rubber plug. Then, in sub-step S3302, it is judged whether the position of the rubber plug is below the round-tip sliding sleeve 3. If so (i.e., the position of the rubber plug is below the round-tip sliding sleeve 3), the method proceeds directly to the next step S340. If not (i.e., the position of the rubber plug is above the round-tip sliding sleeve 3), which means that the round-tip sliding sleeve cannot be opened smoothly, an additional sub-step S3303 is required. In substage S3303, a plug removal operation is performed to expose the round-tip slip sleeve 3. This allows the round-tip slip sleeve 3 to be gently opened, ensuring that the first fracturing stage can be carried out smoothly. In a preferred embodiment, the plug removal operation can be performed with the existing coiled tubing connected to a plug removal string. The maximum external diameter of the plug removal string can be 6–8 mm smaller than the internal diameter of the tubing string. This arrangement ensures that the cement waste generated by the plug removal operation can pass through the area between the plug removal string and the tubing string without difficulty, facilitating the smooth backflow of cement waste.Typically, the plug removal operation involves removing the rubber plug by drilling, which can be done at a position 10-20 m below the lower surface of the round-tip slip sleeve 3. This operation can ensure the smooth opening of the round-tip slip sleeve 3, which is beneficial for meeting the staged fracturing and gas testing requirements later on. In one specific embodiment, the internal diameter of the tubing is 88.3 mm. The assembly of the coiled tubing and plug removal string includes, from top to bottom, a coiled tubing with a diameter of 50.8 mm, a rivet joint with a diameter of 73 mm, a check valve with a diameter of 73 mm, a release tool with a diameter of 73 mm, a screw shaft with a diameter of 73 mm, and a drill bit with a diameter of 80 mm. During the plug removal operation, the pumping device pumps working fluid from the coiled tubing, which drives the screw shaft to rotate the drill bit and remove the rubber plug by drilling. The pumped working fluid can return to the ground through the space between the coiled tubing and the tubing string, and the cement waste generated by the plug removal operation can return to the ground via the working fluid.During plug removal, the working fluid displacement can be 300-500 L / min to better control the plug removal speed. This ensures not only efficient plug removal but also prevents cement residue from becoming lodged in the space between the flexible tubing and the pipe string. In substage S3304, the plug removal working fluid is displaced in the tubing string to prevent the mud plug removal working fluid from entering and contaminating the formation, thus ensuring the smooth implementation of subsequent production operations. In one specific embodiment, coiled tubing may be lowered in the tubing string and then raised a certain distance after contacting the rubber plug surface. Following this, well-construction working fluid is pumped at a certain displacement to displace the plug removal working fluid in the tubing string. The aforementioned rise distance and well-construction working fluid pumping displacement must be selected so that the working fluids do not mix with each other during the replacement of the plug removal working fluid with the well-construction working fluid.In a specific example, the lift distance is, for example, 2 m, and the pumping displacement of the well construction working fluid is, for example, 250-350 L / min. Preferably, the pumping pressure of the well-construction working fluid is gradually reduced, ensuring that the working fluid in the drill string can displace the plug removal working fluid normally and that the fluid backflow can be achieved smoothly. It should be noted that, depending on the requirements, the well-construction working fluid can have different properties, such as clean water. In some other cases, it is necessary to pump an acidic reaction fluid into the inner chamber of the drill string during fracturing to dissolve the slip sleeve or a slip sleeve opening tool released in the well.In this case, a certain amount of spacer fluid must be pumped before the acid reaction fluid to prevent or reduce the mixing of the acid reaction fluid with the fluids injected into the pipe string. Consequently, the effectiveness of the acid reaction fluid can be ensured to guarantee the dissolution of the slip sleeve or the loosened slip sleeve opening tool. The amount of spacer fluid and acid reaction fluid pumped can be adjusted according to different wells. In one specific embodiment, the internal diameter of the pipe is 88.3 mm. The well construction working fluid includes the spacer fluid, reaction fluid, and clean water, which are pumped sequentially. The reaction fluid contains 2–7% solvent, or 8–20% hydrochloric acid and 2–7% solvent.Six cubic meters of reaction fluid are pumped after one cubic meter of spacer fluid, and then clean water is supplied until the plug removal working fluid in the well is completely displaced. During the pumping procedure, the displacement rate can be 0.33 m³ / min, and the pumping pressure gradually decreases from an initial value of 36.0 MPa to 30.0 MPa. In stage S340, a complete well pressure test is performed. For example, clean water is injected into the 100-inch tubing string from a gas recovery tree at the wellhead using a pump truck to complete the well pressure test. The test can be performed in a staged pressurization manner until the pressure reaches a predetermined maximum strength. For example, the tubing string has a strength rating of 100 MPa, and the predetermined maximum strength during operation is 80 MPa, based on calculations. During the pressure test, a fluid is initially pumped at 30 MPa, which is then gradually pressurized to, for example, 40 MPa, 50 MPa, 60 MPa, 70 MPa, 75 MPa, 78 MPa, and 80 MPa in sequence. In stage S350, a staged fracturing operation is performed. First, pressurized fluid is pumped into the inner chamber of the pipe string to a predetermined pressure, achieved by the pump truck through pressurization, in order to open a corresponding round-tipped slip sleeve. Once the slip sleeve is opened, the pressurized fluid forces the cement liner to rupture at this location, establishing a flow channel between the pipe string and the formation. The first stage of fracturing then proceeds according to the fracturing design. Subsequently, based on the structure of the fracturing slip sleeve, the slip sleeve opening tool is deployed into the pipe string.After the slip sleeve opening tool reaches position, the lower fracturing slip sleeve is opened by the buildup of pressure, crushing the cement sheath located there. The second stage of fracturing construction can then be carried out. Fracturing constructions for all subsequent stages can be performed sequentially. Once the fracturing operation is complete, the fracturing equipment is removed from the well site. The well is then opened to drain the fluids, and production is tested. Finally, the tubing string can be put directly into production as a production string. Those in the mid-level trade are familiar with these procedures. According to the well-stage operation method of the present invention, well cementing and well completion operations can be performed by running the work string 100 in a single stroke. In particular, according to the present invention, the cement sleeve formed during well cementing is used as a spacer to perform staged stimulation for subsequent well completion. According to the well-stage operation method of the present invention, staged fracturing can be implemented immediately after well cementing, simplifying the well cementing and well completion operations of the prior art and improving work efficiency.At the same time, the 100-pipe string according to the present invention has a simple structure and can complete well cementing and completion operations without devices such as drilling guns, packers, or the like, resulting in significant savings in equipment resources and effectively reducing well construction costs. In the well-stage operation method according to the present invention, the stage of lowering the rubber plug to provide pumping pressure with the plug seat is a critical step. If the rubber plug cannot create an effective pump and seal, subsequent stages will be severely affected. Therefore, according to another aspect of the present invention, a rubber plug suitable for the well-stage operation method according to the present invention is provided. The rubber stopper 20 according to the present invention will be described in detail below with reference to Figures 6 to 8. As shown in Figure 6, the rubber stopper 20 mainly includes a stopper core 30, a cup 40, and a locking member 50. As shown in Figure 7, the plug core 30 is roughly rod-shaped and acts as a supporting skeleton. From bottom to top, the plug core 30 has an insertion head 32, a main body 35, and a connecting bottom 38, which are fixedly connected to each other in sequence. An annular mounting groove 25 is provided on an outer wall of the insertion head 30 for mounting the locking member 50. The cup 40 is arranged around an outer wall of the connecting bottom 38 to scrape the cement grout when it comes into contact with an inner wall of the pipe during the displacement procedure. According to the present invention, the mounting groove 25, in which the locking member 50 is disposed, is provided on the outer wall of the insertion head 32 of the plug core 30. Once the cement slurry has been injected, the rubber plug 20 is run down the tubing according to the present invention. When the rubber plug 20 moves into the plug seat 7, the locking member 50 forms a locking fit with a coupling locking member on the plug seat 7. Since the locking member 50 is restricted in the mounting groove 25, the plug core 30 is fixed relative to the locking member 50, which defines the position of the rubber plug 20. In this way, backflow of the cement slurry can be effectively prevented, improving the quality of the tubing cementation. Therefore, the quality of the well into which subsequent completion tools are run can be ensured. In one embodiment, as shown in Figure 7, the mounting groove 25 includes a first straight section 26 adjacent to the main body 35 of the plug core 30, and a first sloped section 21 adjacent to the first straight section 26. From top to bottom, the first sloped section 21 is configured so that an outer diameter of the insertion head 32 gradually increases. In one embodiment, as shown in Figure 8, the locking member 50 is configured as a C-shaped ratchet ring. An inner wall surface of the C-shaped ratchet ring includes a first straight coupling section 51 on its upper portion, to cooperate with the first straight section 26. In addition, the inner wall surface of the C-shaped ratchet ring further includes a first slope coupling section 52 on its lower portion, to cooperate with the first slope section 21. After installation, an upper end face of the C-shaped ratchet ring rests against a lower end face of the main body 35 of the plug core 30.Thus, after the locking element 50 engages to form a lock with the coupling locking element in the plug seat 7, the C-shaped ratchet ring can be effectively prevented from falling out due to the restraint of the lower end face of the main body 35 on the upper end face of the C-shaped ratchet ring and the cooperation between the first slope coupling section 52 and the first slope section 21, even if the cement grout subjects the plug core 30 to an upward force. Consequently, the safety and stability of the rubber plug 20 lock can be ensured. As shown in Figure 7, the insertion head 32 of the plug core 30 includes a second straight section 23 connected to the first sloped section 21. Below the second straight section 23, a second sloped section 27 and a guide section 29 are arranged sequentially. The second sloped section 27 is configured so that the outer diameter of the insertion head 32 gradually decreases from top to bottom. Preferably, the guide section 29 is configured as part of a spherical surface. With the above arrangement, the insertion head 32 has its largest outer diameter in the area where the second straight section 23 is located. That is, the insertion head 32 is configured to have a large outer diameter in the middle and a small outer diameter at both ends, giving it a shape similar to a date pit.In addition to ensuring the stability of the locking coupling, this structure also provides good guidance, ensures a smooth descent of the rubber plug 20 and prevents jamming on any stage face of the pipe string. According to the present invention, at least one sealing groove 33 is formed on the outer wall of the main body 35 to mount the sealing ring 22, in order to generate the sealing effect of the cementation. With this arrangement, the sealing ring 22 is positioned above the locking member 50, so that the locking member 50 does not pass through the sealing groove 33 during assembly. Consequently, the locking member 50 will not come into contact with the sealing ring 22 and damage the sealing surface. Preferably, an upward-facing face of the first stage 34 is formed on the outer wall of the main body 35, and a downward-facing face of the second stage 36, axially separated from the face of the first stage 34, is also formed on the outer wall of the main body 35, wherein the face of the second stage 36 is located below the face of the first stage 34.With this arrangement, a protruding part is formed that projects radially outwards on the outer wall of the main body 35. In one embodiment, the sealing groove 33 is located between the face of the first stage 34 and the face of the second stage 36. Therefore, the sealing groove 33 is located on the protruding part of the main body 35. On one hand, this arrangement makes the external diameter of the main body 35 below the face of the second stage 36 relatively small, which is convenient for lowering it. On the other hand, the axial size of the main body 35 between the face of the first stage 34 and the face of the second stage 36 is relatively small, thereby preventing excessive wear of the sealing ring 22. Preferably, the angle between the face of the first stage 34 and the axial direction of the plug core 30 is 130-140 degrees, such as 135 degrees, while the angle between the face of the second stage 36 and the axial direction of the plug core 30 is 145-155 degrees, such as 150 degrees. Preferably, a transit section 37 with a larger outer diameter is provided at the upper end of the main body 35. Once the cup 40 is placed on the connection bottom 38 of the plug core 30, the outer diameter of the main body of the cup 40 is equal to that of the transit section 37. Furthermore, the plug core 30 is formed as a single piece, with the rubber cup 40 attached to the outer wall of the connection bottom 38 of the plug core 30 by vulcanization. This arrangement ensures the overall strength of the plug core 30, eliminating any weak points in the rubber plug 20, thus improving safety. Simultaneously, this arrangement guarantees a stable connection between the cup 40 and the plug core 30, ensuring smooth operation. According to a preferred embodiment, the C-shaped ratchet ring is made of 42CrMo alloy steel, which enhances its ability to withstand pressure differentials. This allows such a C-shaped ratchet ring to be used in wells with more severe conditions and higher pressure differentials during well cementing (e.g., a pressure differential of 60–70 MPa). To ensure wear resistance and temperature resistance of the 40 cup, it can be made of compounds such as nitrile rubber, fluororubber, natural rubber, or similar materials. The proportions of the components of the 40 cup can also be adjusted according to the actual conditions to meet the relevant requirements. Although the present invention has been described above with reference to exemplary embodiments, various modifications may be made and components may be replaced by equivalents thereof without departing from the scope of the present invention. In particular, provided there is no structural conflict, each technical feature mentioned in each embodiment may be combined in any manner. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions that are within the scope of the claims.

Claims

1. A well-stage operation method comprising the following stages: lowering, after performing a first well diversion operation in a well, a string of pipe down the well, wherein the pipe string includes, from bottom to top, a floating circumference, a plug seat, a round-tip slip sleeve, and a fracturing slip sleeve; performing a cementing operation, wherein cement slurry pumped into an internal chamber of the pipe string enters an annular space between the pipe string and the wellbore through the plug seat and the floating circumference to form a cement sleeve, wherein the cement sleeve isolates the round-tip slip sleeve from the fracturing slip sleeve; performing a second diversion operation to ensure that the round-tip slip sleeve of the pipe string is exposed;Perform a pressure test on the pipe string; and carry out a phased fracturing construction.

2. The method according to claim 1, wherein the step of performing the cementing operation comprises: pumping a cushion fluid into the pipe string, wherein the cushion fluid enters the annular space between the pipe string and the wellbore through the plug seat and the floating flushing circumference; pumping the cement slurry into the annular space between the pipe string and the wellbore through the plug seat and the floating circumference; dropping a rubber plug into the wellbore, and pumping a displacement fluid to cause the rubber plug to move downwards until it strikes the plug seat; and shutting down the well operation to allow pressure to build up and give the cement time.

3. The method according to claim 2, wherein the cushion fluid is pumped with a selected volume so that a fluid section with a length of 200-300 m is formed in the annular space.

4. The method according to claim 2 or 3, wherein the cement slurry is pumped with a volume selected such that a return height of the cement slurry is at least 200 m above the fracturing slip sleeve.

5. The method according to any of claims 2 to 4, wherein the pressure build-up is carried out at a pressure 3-5 MPa higher than a liquid column pressure difference.

6. The method according to any of claims 2 to 5, wherein the step of performing the second deflection operation comprises: performing a plugging operation to determine a position of the rubber plug; and judging whether the position of the rubber plug is above the round-tipped sliding sleeve, and if so, further performing a plug removal operation.

7. The method according to claim 6, wherein the plugging operation is performed with a flexible pipe connected to a plugging string, wherein an external diameter of the flexible pipe is 20-30 mm smaller than an internal diameter of the pipe string, and a maximum external diameter of the plugging string is 3-5 mm smaller than the internal diameter of the pipe string, wherein the flexible pipe has a service velocity of 10-20 m / min.

8. The method according to claim 7, wherein the pressurization is repeated several times if the flexible tubing is obstructed in a position during service, and said position is the position of the rubber plug if the position where the flexible tubing is obstructed remains the same.

9. The method according to any of claims 6 to 8, wherein the plug removal operation is performed by means of a flexible pipe connected to a plug removal string, wherein a maximum external diameter of the plug removal string is 6-8 mm less than the internal diameter of the pipe string.

10. The method according to claim 9, wherein, in the plug removal operation, the rubber plug is removed by drilling to a position 10-20 m below a lower surface of the round-tipped sliding sleeve.

11. The method according to claim 9 or 10, wherein the rubber plug is removed by drilling with the pumping of a plug removal working fluid to move a drill bit through the plug removal string, wherein the plug removal working fluid is pumped with a displacement of 300-500 L / min.

12. The method according to any of claims 6 to 11, wherein a plug removal working fluid displacement operation in the pipe string is performed after the plug removal operation.

13. The method according to claim 12, wherein the flexible tubing is raised after coming into contact with the rubber plug in the tubing string, and a well construction working fluid is pumped to displace the plug removal working fluid in the tubing string.

14. The method according to claim 13, wherein a pumping pressure value of the well construction working fluid is gradually decreased.

15. The method according to claim 13 or 14, wherein the well construction working fluid is a reaction fluid acting on the slip sleeves of the pipe string, and wherein a spacer fluid is pumped before the well construction working fluid.

16. A rubber plug used in the well-stage operation method according to any of claims 1 to 15, comprising: a plug core, including an insertion head, a main body and a connecting bottom, wherein an annular mounting groove is disposed on an outer wall of the insertion head; a cup disposed on an outer wall of the connecting bottom; and a locking member disposed in the mounting groove.

17. The rubber plug according to claim 16, wherein the mounting groove includes a first straight section adjacent to the main body of the plug core, and a first sloped section adjacent to the first straight section, wherein the first sloped section is configured so that an external diameter of the insertion head of the rubber plug gradually increases; and the locking member is configured as a C-shaped ratchet ring, an inner wall surface including a first straight coupling section in an upper portion thereof engaging with the first straight section, and a first sloped coupling section in a lower portion thereof engaging with the first sloped section; wherein an upper end face of the C-shaped ratchet ring bears against a lower end face of the main body of the plug core.

18. The rubber stopper according to claim 17, wherein the insertion head of the stopper core includes a second straight section connected to the first slope section, a second slope section connected to the second straight section, and a guide section connected to the second slope section, and wherein the second slope section is configured so that an external diameter of the insertion head gradually decreases from top to bottom, and the guide section is configured as a spherical surface.

19. The rubber stopper according to any of claims 16 to 18, wherein an upward-facing first-stage face, a downward-facing second-stage face, and a sealing groove for receiving a sealing ring are formed in an outer wall 5 of the main body of the stopper core, wherein the second-stage face is located below the first-stage face, and wherein the sealing groove is arranged between the first-stage face and the second-stage face.

20. The rubber stopper according to any of claims 16 to 19, wherein a transit section is provided with a relatively larger external diameter at the upper end of the main body of the stopper core, wherein an external diameter of a main body of the cup is equal to that of the transit section

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