A drilling and completion string and construction method for multi-branch wells

Abstract

This invention discloses a branch well completion string, comprising, from bottom to top, a guide shoe, a screen pipe, a sealing assembly, an anchoring assembly, and a guiding assembly. The sealing assembly includes a first coupling, a central pipe, a valve head, and a sealing pipe connected sequentially by threads. The first coupling connects to the anchoring assembly, and the sealing assembly connects to the screen pipe via a second coupling. The sealing pipe contains a soluble sealing structure, and the central pipe is fitted with a rubber sleeve sealing structure. The anchoring assembly includes a lower connector, a support pipe, and a guide body connected sequentially. The lower connector is sealed to the first coupling. The lower part of the guide body is connected to an outwardly expandable anchor claw. A hydraulic cylinder sleeve is provided outside the support pipe, and a piston acting on the anchor claw is arranged between the hydraulic cylinder sleeve and the support pipe. Pressure transmission holes are arranged on the wall of the support pipe. The guiding assembly includes a reverse rod inserted into the guide body and communicating with the support pipe. The upper part of the reverse rod is threadedly connected to an upper connector. This invention also discloses a method for constructing the above-mentioned branch well completion string.

Description

Technical Field

[0001] This invention relates to the field of oil extraction, and in particular to a drilling and completion string and construction method for multi-branch wells. Background Technology

[0002] Multi-branch wells refer to the drilling of multiple branch wells into an oil and gas reservoir from a single main wellbore. The main wellbore can be a vertical, directional, or horizontal well, while the branch wells can be either directional or horizontal. For oil reservoir development, multi-branch well technology helps in formulating rational development plans, effectively developing multi-target reservoirs at a lower cost. Furthermore, each branch wellbore shares a common wellhead and upper section, significantly reducing drilling costs, land occupation, and environmental protection. It is an effective technology for achieving high production with fewer wells in oilfield development.

[0003] There are two main types of multi-branch wells: one is a new well drilled with the purpose of completing a branch well, and the other is a multi-branch well drilled sideways from an existing wellbore. Currently, most branch wells are formed by sideways drilling from existing wells. This process generally involves three methods: one is to mill a section of casing, cement a section, and then drill directionally in the milled section to form the branch wellbore; another is to run a guide tool inside the casing, use a milling taper to create a window in the casing, and then drill directionally to form the branch wellbore; the third is to run a special guide hole opener, use a small drill bit to punch or drill holes in the casing wall to create a hole, and then run a flexible hose with a water jet drill bit, using high-pressure water jets to erode the formation and guide the hose forward to form the branch wellbore. These branch well technologies are particularly suitable for tapping remaining oil in old oilfields or improving injection-production well networks, but they cannot be implemented in newly drilled open-hole wells.

[0004] In open-hole wells, sidetracking branch wells generally employs two methods: suspended sidetracking and cement plug sidetracking. Suspended sidetracking requires high well inclination of the existing well (sidetracking is difficult with inclinations below 45°), and the wellbore is prone to instability. Cement plug sidetracking requires drilling 80-100m long cement plugs in the open hole, which occupies a large length of the original wellbore, contaminates the formation with cement slurry, and has a long setting time, increasing drilling cycle and cost.

[0005] Chinese patent application CN96195731.X discloses an apparatus and method for drilling and completing multi-branch wells. It mainly relates to an apparatus and method for drilling and completing multi-branch wells using separate casings. The basic principle is to drill two small wellbores directly from the bottom of the same large-sized surface casing or technical casing. During well completion, a "pants-fork" shaped wellbore reconnection and sealing device is run in to merge the completion casings of the two small wellbores and reconnect them to the upper casing, forming a single wellhead; or the completion casings of both small wellbores can be directly reconnected to the wellhead, forming two wellheads for separate production. However, this technology has the following problems: ① Due to the size limitation of the surface casing or technical casing, a maximum of 2-3 small wellbores can be drilled in the main wellbore; ② The well completion device is complex, technically difficult, and the subsequent production or operation measures are also relatively complex; ③ This technology has long been monopolized by foreign companies, resulting in high construction costs, making it unsuitable for widespread application in domestic oilfield development.

[0006] Chinese Patent Application No. 2005101079384 discloses a novel method for drilling and completing multi-branch wells. This patented technology is the same as the technical paper "Multi-branch Well Drilling and Completion Technology Based on Expansion Tube Positioning System" published in Volume 36, Issue 6 of "Petroleum Exploration and Development". Its process principle is as follows: First, drill the main wellbore, then run casing cementing in the main wellbore, run in the expansion tube positioning device and guide pipe, open a window in the casing to side-drill branch wellbores, run casing cementing in the branch wellbores, and then run in the milling tool to mill and retrieve the cementing release tool, tail pipe overlapping section and guide pipe in the main wellbore, leaving the expansion tube positioning device in the main wellbore. Based on this principle, multiple branch wellbores can be side-drilled. The technology has the following problems: ① It requires casing cementing in the main wellbore, which increases the cost of casing and cement, and extends the drilling cycle. Cementing also pollutes the oil and gas reservoir, affects reservoir permeability, and is not conducive to later production. Furthermore, if casing cementing is used for loose sandstone reservoirs, perforation is required for sand control in the casing during later production, which increases operating costs and operating cycle. ② The technology is complex. Before drilling the side-drilling branch well, expansion tube positioning is required, followed by the installation of the guide tube. After the branch wellbore is completed, the milling tool needs to be installed to retrieve the guide tube. The construction process is complicated, and the drilling and completion cycle is long.

[0007] Chinese patent application number 2018108174419 discloses a method for open-hole completion of multi-branch wells. Its technical principle is similar to the aforementioned patented technology, but differs in that the main wellbore undergoes a three-stage open-hole completion, and each branch wellbore undergoes a two-stage open-hole completion. After each branch wellbore is completed, a drillable bridge plug is temporarily inserted for plugging. After all branch wellbores are drilled, each drillable bridge plug is removed. This open-hole completion technology avoids cement slurry contamination of the oil and gas reservoir, but it still has the following problems: the main wellbore and each branch wellbore add an extra drilling stage, significantly increasing drilling costs and extending the drilling cycle; the process of inserting and removing drillable bridge plugs is complex, also extending the drilling cycle; open-hole completion for each wellbore is only applicable to reservoirs that do not produce sand, and sand control measures cannot be implemented for sand-producing reservoirs, and the wellbore is prone to collapse.

[0008] Chinese patent application number 2014101750077 discloses a method and tool for completing a synchronous multi-branch radial horizontal well. Its basic principle is as follows: during well completion, a pre-drilled casing is used for cementing. The pre-drilled holes are closed by an inner sliding sleeve. Before radial drilling, a tool is lowered in to open all the pre-drilled holes in sequence. Then, a multi-strand high-pressure hose held by a high-pressure hose holder is lowered in and aligned with the pre-drilled holes. The high-pressure hose nozzle at the front end of the high-pressure hose sprays out multiple branch wells using high-pressure water jet. Chinese patent application number 2018104056894 discloses a self-propelled multi-branch small-bore completion tool and its operation method, and Chinese patent application number 2019108565826 discloses a multi-branch hydraulic jet radial drilling string and drilling method. Both use a hose in conjunction with a hydraulic nozzle to form branch wellbores through water jets. The principle is similar to that of patent application number 2014101750077. This type of technology has the following problems: the wellbore diameter of the horizontal well formed by this jet rock breaking is small, the channel is irregular, and due to the hose, the forward trajectory of the hydraulic jet drill bit is uncontrollable, the formed wellbore trajectory is also irregular, the wellbore trajectory cannot be measured, there is a lack of applicable completion technology, sand control is not possible in sand-producing reservoirs, the wellbore is prone to collapse and closure due to lack of support, and the production declines rapidly.

[0009] Chinese Patent Application No. 2019105335273 discloses a turbine drilling multi-branch small well completion tool and its operation method. Although it adopts a method of using a turbine to drive a flexible shaft and drill bit to rotate and break rocks for drilling, it also has problems such as small well diameter, irregular channel, uncontrollable forward trajectory, inability to measure well trajectory, lack of applicable completion technology, and easy well collapse and closure. Summary of the Invention

[0010] To overcome the problems existing in the prior art, this invention provides a multi-branch well drilling and completion string and construction method, which drills multiple branch wells in a low-cost drilling method in a new wellbore, and completes them with a matching completion process, thereby expanding the application field of branch well technology and achieving the development effect of high production with fewer wells.

[0011] A branch well completion string includes, from bottom to top, a guide shoe, a screen pipe, a sealing assembly, an anchoring assembly, and a guiding assembly;

[0012] The sealing assembly includes a first coupling, a central tube, a valve head, and a sealing tube connected sequentially by threads. The first coupling is used to connect the anchoring assembly, and the sealing assembly is connected to the screen tube via a second coupling. The sealing tube is provided with a soluble sealing structure inside, and the central tube is provided with a deformable rubber sleeve sealing structure outside.

[0013] The anchoring assembly includes a lower connector, a support tube, and a guide body connected in sequence. The lower connector is sealed to the first coupling. The lower part of the guide body is connected to an anchor claw that can be extended and opened for anchoring. A hydraulic cylinder sleeve is provided outside the support tube. A piston acting on the anchor claw is arranged between the hydraulic cylinder sleeve and the support tube. A pressure transmission hole is arranged on the tube wall of the support tube.

[0014] The guide assembly includes an inverted rod inserted into the guide body and communicating with the support tube, and the upper part of the inverted rod is threadedly connected to an upper connector.

[0015] In this invention, the completion string for the branch wellbore (from bottom to top) consists of: guide shoe + screen pipe + sealing assembly + anchoring assembly + guiding assembly + drill string. The completion string for the last branch wellbore (from bottom to top) consists of: guide shoe + screen pipe + blind flange + sealing assembly + cementing assembly + casing (to wellhead).

[0016] In this invention, the screen tube can be one or more. Preferably, depending on the sand control requirements, the screen tube is a perforated screen tube, a slotted screen tube, or a composite precision sand filter tube. The sealing assembly is one set or multiple sets connected in series. The deformable rubber sleeve sealing structure is an expansion rubber sleeve sealing structure, a compression rubber sleeve sealing structure, or an oil / water-swellable rubber sleeve sealing structure. In another preferred embodiment, one or more sleeves can also be added between the screen tube and the sealing assembly.

[0017] The soluble sealing structure utilizes formation fluids to dissolve and form an oil and gas production channel during commissioning. Preferably, the soluble sealing structure includes a ball seat arranged inside a sealing tube and fixed to the sealing tube by shear pins; the ball seat has a conical sealing surface that mates with the ball to form a seal. In another embodiment, other sealing and plugging mechanisms may also be used.

[0018] Preferably, the rubber sleeve sealing structure includes an inner rubber sleeve fitted onto a central tube, support plates evenly arranged on the outer surface of the inner rubber sleeve, and an outer rubber sleeve fitted over the support plates. In this application, the support plates are preferably made of stainless steel, but other materials may also be used.

[0019] The upper end of the inner rubber cylinder is vulcanized and sealed with the adjusting ring and vulcanizing head outside the central tube, and the lower end of the inner rubber cylinder is vulcanized and sealed with the valve head and vulcanizing head; the upper and lower ends of the support plate are respectively fixed on the end rings that are threadedly connected to the adjusting ring and the valve head; the upper and lower ends of the outer rubber cylinder are also vulcanized and sealed with the end rings that are threadedly connected to the adjusting ring and the valve head and the pressure ring.

[0020] Preferably, a sealed space is formed between the adjusting ring, the inner surface of the inner rubber cylinder, the outer surface of the valve head and the central tube. The rubber cylinder assembly is expanded outward by hydraulic pressure. This sealed space is connected to the internal space of the tubing column through the liquid inlet channel inside the valve head. The liquid inlet channel is controlled by the liquid inlet valve, check valve and shut-off valve on the valve head.

[0021] Preferably, the upper part of the adjusting ring is connected to a locking ring cap by a thread, and there is an inner circular step below the internal thread of the upper part of the adjusting ring. A locking ring is installed in the step, and the locking ring is engaged with the anti-reverse thread on the central tube. The lower end face of the locking ring cap limits the locking ring to the inner circular step of the adjusting ring.

[0022] Preferably, a locking block and a release sleeve are provided that abut against the lower part of the piston. The release sleeve covers the outside of the locking block and is fixed to the locking block by shear pins. The hydraulic cylinder sleeve is located outside the release sleeve of the piston. The contact surfaces of the piston, the release sleeve, the support tube, and the hydraulic cylinder sleeve are all sealed. The support tube between the piston and the release sleeve is provided with a pressure transmission hole. The sealed space between the piston and the release sleeve is connected to the internal space of the tube column through the pressure transmission hole. The hydraulic pressure through the pressure transmission hole pushes the piston upward, causing the anchor claw to extend and open for anchoring.

[0023] To achieve better anchoring effect, preferably, there are multiple anchor claws evenly arranged circumferentially, generally at least three. The upper end of each anchor claw is connected to the guide body by a pin, and the lower end of the anchor claw is a wedge-shaped sharp corner. A straightening arm corresponding to the anchor claw is movably connected to the piston, and the upper end of the straightening arm is connected to the middle position of the anchor claw by a pin.

[0024] Preferably, the guide body is a hollow structure, with its lower part connected to the support pipe via threads; the upper part of the guide body is a guide surface that guides the drill bit. The guide surface can apply a lateral reaction force to the drill bit in the open hole. This lateral reaction force is the same as the design orientation of the branch wellbore trajectory, forcing the drill bit to drill in the design orientation of the branch wellbore trajectory and complete the branch wellbore.

[0025] This invention also provides a method for constructing a branch well completion string, comprising: completing the first or second stage of drilling, running in surface casing or technical casing for cementing, running in the next stage of drilling string after cementing, completing the second or third stage of the main wellbore, retrieving the drilling string, running in the anchoring assembly and the guide assembly, releasing them, retrieving the feed string, running in the drilling string again along the guide assembly to drill the first branch wellbore, retrieving the drilling string after completion, running in the branch wellbore completion string, the branch wellbore completion string being suspended on the open hole wall by the anchoring assembly, the upper part of the anchoring assembly being the guide assembly, running in the drilling string again, drilling the second branch wellbore along the guide assembly at the top of the first branch wellbore completion string, retrieving the drill string after completion, running in the branch wellbore completion string again, and so on, drilling upwards to form multiple branch wellbores and performing completion, and running in the final branch wellbore completion string after completion. By implementing the cementing completion process at the top of the screen pipe, and based on the TAML multi-branch well classification system standard, the technology of this invention can achieve three-stage well completion.

[0026] The beneficial effects of this invention are:

[0027] (1) Multi-branch drilling can be carried out in newly drilled open hole wells without the need for casing cementing support guides. On the one hand, cement slurry can be avoided from polluting the oil and gas reservoir. On the other hand, the cost of casing, cement and other materials can be saved. The drilling cycle such as cement setting time can also be saved. Furthermore, when drilling branch wells, there is no need to implement the window opening process in the casing, which saves the drilling cycle.

[0028] (2) Both the main wellbore and the branch wellbore can be completed by running screen pipes, and the completion string of the branch wellbore can be reconnected to the main wellbore to achieve three-stage completion. Compared with the casing cementing completion process, this completion process can avoid the contamination of oil and gas reservoirs by cementing slurry, which is conducive to improving production capacity. On the other hand, it can support the branch wellbore and prevent wellbore collapse. It can also effectively prevent sand from appearing in sand reservoirs. The inner diameter after completion is large, which is convenient for the subsequent operation tools to be run in. After the branch wellbore is completed by casing cementing, perforation operation is required, and then a small-sized sand prevention screen pipe is run in to implement the in-pipe sand prevention process. The inner diameter of the completion is small. Therefore, the technology of this invention can save the cost and operation cycle of perforation, in-pipe sand prevention and other subsequent operations compared with casing cementing completion.

[0029] (3) It can realize the integrated construction process of drilling and completion: After the first branch well is completed, directional side drilling is carried out by relying on the guide assembly at the top of the completion string. There is no need to run and retrieve the guide device separately, which simplifies the construction process and saves the drilling cycle.

[0030] (4) Water jet radial multi-branch drilling requires special equipment such as surface-mounted coiled tubing and high-pressure pump sets. In contrast, the technology of this invention can be constructed with conventional drilling equipment or overhaul equipment. The process is simple and conducive to technology promotion.

[0031] (5) The multi-branch cementing completion process requires a cementing truck unit on the ground during the cementing process of each branch well. When drilling other branch wells, the cementing truck unit needs to wait at the well site, or the cementing truck unit needs to be dispatched once after each branch well is completed. The process is not closely connected, which is labor-intensive and time-consuming. In contrast, the technology of this invention only implements the cementing process at the top of the screen pipe in the last branch well, which requires a cementing truck unit. The other branch wells can be completed using conventional drilling equipment, which has a significant effect of cost reduction and efficiency improvement. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating the working principle of the present invention;

[0033] Figure 2 This is a schematic diagram of the integrated drilling and completion tubing string of the present invention;

[0034] Figure 3 for Figure 2 Schematic diagram of the upper structure of the central sealing assembly;

[0035] Figure 4 for Figure 2 Schematic diagram of the central structure of the central sealing assembly;

[0036] Figure 5 for Figure 2 Schematic diagram of the lower structure of the central sealing assembly;

[0037] Figure 6 This is a three-dimensional structural diagram of the anchoring assembly in the drill-completion integrated tubing of the present invention in the open state. Detailed Implementation

[0038] Many specific details are set forth in the following description to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore, the invention is not limited to the specific embodiments disclosed below. The directional terms “up,” “down,” “left,” and “right” used herein are based on the corresponding drawings, and it is understood that the use of these directional terms does not limit the scope of protection of the invention.

[0039] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0040] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0041] like Figure 1 As shown: Taking a two-section multi-branch well as an example, the drilling string is run into the surface casing 6 of the first section, and the main wellbore 10 of the second section is drilled out. Anchoring assembly 2 and directional assembly 1 are run into the bottom of the main wellbore 10. A gyroscope is run into the well to determine the normal azimuth of the guide slope of directional assembly 1 so that it is the same as the design azimuth angle of the next branch wellbore. Anchoring assembly 2 is set and anchored to the open hole wall of the main wellbore 10. After the drill string is pulled out, the drilling string is run in. Under the constraint of directional assembly 1, the first branch wellbore 11 is drilled out. The drill string is pulled out and the completion string of the branch wellbore is run in.

[0042] A branch well completion string includes, from bottom to top, a guide shoe 5, a screen pipe 4, a sealing assembly 3, an anchoring assembly 2, a guiding assembly 1, and a drill string. The screen pipe 4 can be one or more. Depending on the sand control requirements, the screen pipe 4 can be a perforated screen pipe, a slotted screen pipe, or a composite precision sand filter pipe. One or more casings 9 can also be added between the screen pipe 4 and the sealing assembly 3. The sealing assembly 3 can be one or more sets.

[0043] like Figure 2-5As shown: The sealing assembly 3 consists of a coupling (first coupling) 2.16, a central tube 3.1, a valve head 3.9, and a sealing tube 3.15 connected sequentially via sealing tube threads. The upper part of the sealing tube 3.15 has an inner circular step, within which a ball seat 3.16 is installed and fixed to the sealing tube 3.15 by shear pins 2.9. A sealing ring is provided on the upper outer circle of the ball seat 3.16, forming a seal with the sealing tube 3.15. The top inner circle of the ball seat 3.16 is designed with a conical sealing surface, which cooperates with the ball 3.14 to form a seal. A sealed space is formed inside the tube string above the ball seat 3.16. The ball 3.14 and ball seat 3.16 can also be designed as other sealing and plugging mechanisms made of soluble materials. After achieving their sealing function, they can be retained and dissolved by formation fluids to form oil during later production. Gas production channel; a vulcanizing head 3.3 and an inner rubber sleeve 3.5 are fitted onto the central tube 3.1. The lower outer circle of the vulcanizing head 3.3 is connected to the upper inner circle thread of the valve head 3.9 via a thread. The inner cylindrical surface above the upper inner circle thread of the valve head 3.9 is provided with a sawtooth structure or a rectangular tooth structure. The upper outer circle of the vulcanizing head 3.3 has a "wedge" structure, and the outer surface is also provided with a sawtooth structure. The lower end of the inner rubber sleeve 3.5 is vulcanized together with the sawtooth structure of the valve head 3.9 and the sawtooth structure of the vulcanizing head 3.3 to form a seal. A vulcanizing head 3.3 and an adjusting ring 3.2 are symmetrically fitted onto the upper part of the central tube 3.1. The vulcanizing head 3.3 is connected to the lower inner circle thread of the adjusting ring 3.2 via a thread. The inner cylindrical surface below the lower inner circle thread of the adjusting ring 3.2 is provided with a sawtooth structure or a rectangular tooth structure. The inner rubber sleeve 3.5 is equipped with a sawtooth or rectangular tooth structure. The upper end of the inner rubber sleeve 3.5 is vulcanized together with the adjusting ring 3.2 and the vulcanizing head 3.3 in the same manner, forming a seal. Stainless steel sheets 3.6 are evenly arranged on the outer surface of the inner rubber sleeve 3.5. The upper and lower ends of the stainless steel sheets 3.6 are welded to the inner circles of the two end rings 3.4, respectively. The lower end ring 3.4 is connected to the upper outer circle thread of the valve head 3.9 via an inner circle thread, and the upper end ring 3.4 is connected to the lower outer circle thread of the adjusting ring 3.2 via an inner circle thread. A wedge-shaped pressure ring 3.7 is inserted between the top inner circle step of the two end rings 3.4 and the stainless steel sheet 3.6. The conical outer circle surface of the pressure ring 3.7 has a sawtooth structure, and the top outer circle surface of the end rings 3.4 has a sawtooth or rectangular tooth structure. The structure consists of an outer rubber sleeve 3.8 fitted over a stainless steel sheet 3.6, which is vulcanized together with the toothed structures of the end rings 3.4 and pressure rings 3.7 at the upper and lower ends, forming a seal. The inner rubber sleeve 3.5, stainless steel sheet 3.6, and outer rubber sleeve 3.8 are vulcanized to form a rubber sleeve assembly. The upper inner circle of the adjusting ring 3.2 has a sealing groove to accommodate a sealing ring, forming a seal with the central tube 3.1. Thus, a sealed space is formed between the inner surface of the adjusting ring 3.2, the inner surface of the inner rubber sleeve 3.5, the valve head 3.9, and the outer surface of the central tube 3.1. The rubber sleeve assembly can be expanded outward by hydraulic pressure. This sealed space is connected to the internal space of the tubing column through the liquid inlet channel 3.10 inside the valve head 3.9. The liquid inlet channel 3.10 is connected to the liquid inlet valve 3.13, check valve 3.12, and shut-off valve 3.11. Control the liquid inlet action; the upper inner circle of the adjusting ring 3.2 is connected to the locking ring cap 2.14 via a thread. Below the internal thread on the upper part of the adjusting ring 3.2 is an inner circular step, within which a locking ring 2.13 is installed. This lock ring 2.13 engages with the anti-reverse thread 2.12 on the central tube 3.1. The lower end face of the locking ring cap 2.14 limits the locking ring 2.13 within the inner circular step of the adjusting ring 3.2, ensuring it can only move downwards and cannot retract upwards, thus ensuring the reliability of the rubber sleeve assembly's setting seal. (See attached...) Figure 2 The sealing assembly 3 is an expansion-type rubber sleeve sealing structure. The technical solution of this invention is not limited to one sealing structure; the sealing assembly 3 can also adopt a compression-type rubber sleeve sealing structure, or an oil / water-expanding rubber sleeve sealing structure. The central tube 3.1 in the sealing assembly 3 is connected to the coupling (first coupling) 2.16 via a sealing pipe thread. The coupling 2.16 is connected to the lower connector 2.15 in the anchoring assembly 2 via a sealing pipe thread. Depending on sealing requirements, multiple sealing assemblies 3 can be designed for series connection via couplings 2.16, retaining only the bottom ball seat 3.16 and ball 3.14 to form a sealed pressure space. The bottom outer circle of the adjusting ring 3.2 in the sealing assembly 3 is designed with an outwardly protruding centering block, and the middle outer circle of the valve head 3.9 is also designed with an outwardly protruding centering block, ensuring the tubing is centered and the sealing effect is achieved after the rubber sleeve assembly is seated.

[0044] The anchoring assembly 2 consists of a lower connector 2.15, a support tube 2.3, and a guide body 1.3 connected sequentially by threads. Each threaded connection is equipped with a sealing ring 2.7. A piston 2.5 is fitted into the middle of the support tube 2.3. The piston 2.5 and the support tube 2.3 are fixed by a locking block 2.8. A square hole is provided on the lower circumference of the piston 2.5 to install the locking block 2.8. The locking block 2.8 extends inward and mates with the groove in the outer circle of the middle part of the support tube 2.3 to fix the support tube 2.3 and the piston 2.5. After the locking block 2.8 extends inward, its outer surface is flush with the outer circular step surface of the lower part of the piston 2.5. The upper inner circular step of the release sleeve 2.10 is fitted onto the outer circular step of the lower part of the piston 2.5 and covers the outer surface of the locking block 2.8 until its upper end face abuts against the upper end face of the outer circular step of the piston 2.5. The upper outer circle of the release sleeve 2.10 is designed with a shear pin hole and is fixed to the locking block 2.8 by a shear pin 2.9. A hydraulic cylinder sleeve 2.11 is fitted over the piston 2.5 and release sleeve 2.10. The upper part of the hydraulic cylinder sleeve 2.11 is connected to the outer thread of the middle part of the piston 2.5 via an internal thread. A sealing ring 2.7 is provided on both the lower inner and outer circumferences of the piston 2.5, forming a seal with the support tube 2.3 and the hydraulic cylinder sleeve 2.11 respectively. A sealing ring 2.7 is also provided on both the lower inner and outer circumferences of the release sleeve 2.10, forming a seal with the support tube 2.3 and the hydraulic cylinder sleeve 2.11 respectively. A sealed space is formed between the piston 2.5 and the release sleeve 2.10. A pressure transmission hole 2.6 is designed in the support tube 2.3 between the inner sealing rings of the piston 2.5 and the release sleeve 2.10. The sealed space between the piston 2.5 and the release sleeve 2.10 communicates with the internal space of the tubing column through the pressure transmission hole 2.6. When hydraulic pressure is applied to the internal space of the tubing column... The pressure difference between the inner and outer sealing rings 2.7 of the release sleeve 2.10 and the pressure transmission hole 2.6 acts on the pressure differential surface, pushing the release sleeve 2.10 to shear the shear pin 2.9 downwards. Simultaneously, hydraulic pressure acts on the pressure differential surface between the inner and outer sealing rings 2.7 of the piston 2.5, pushing the piston 2.5 upwards. A locking ring cap 2.14 is threadedly connected to the lower inner circle of the cylinder sleeve 2.11, and together they are fitted onto the upper outer circular step of the lower connector 2.15. Above the inner circular thread of the lower cylinder sleeve 2.11 is an inner circular step, within which a locking ring 2.13 is installed. This lock ring 2.13 mates with the anti-reverse thread 2.12 of the lower connector 2.15. The upper end face of the locking ring cap 2.14 limits the locking ring 2.13 within the inner circular step of the cylinder sleeve 2.11, ensuring it can only move upwards and cannot retract downwards, thus ensuring the reliability of the anchoring assembly 2's setting seal. (See appendix) Figure 6A limiting sleeve 2.17 is provided between the piston 2.5 and the guide body 1.3. Both the upper end of the piston 2.5 and the lower end face of the guide body 1.3 have protruding insertion seats. The anchor claw 2.2 has a connecting ear at its upper end, a wedge-shaped tip with serrations at its lower end, and a pin hole in the middle. The straightening arm 2.4 has a connecting ear at its lower end and a fork-shaped seat at its upper end, with overlapping pin holes on both sides. The connecting ear at the upper end of the anchor claw 2.2 is inserted into the insertion seat of the guide body 1.3 and connected by pin 2.1. The connecting ear at the lower end of the straightening arm 2.4 is inserted into the insertion seat of the piston 2.5 and connected by pin 2.1. The wedge-shaped tip at the lower end of the anchor claw 2.2 is inserted into the fork-shaped seat of the straightening arm 2.4 and connected by pin 2.1, forming an "umbrella frame structure." The anchor claws 2.2 and the straightening arms 2.4 are used in pairs, and at least three pairs are provided. Figure 5 The state shown is the open state of the anchor claw 2.2 when the piston 2.5 moves upward to the top dead center. During initial installation, the limiting sleeve 2.17 is fitted onto the support tube 2.3, with its upper end face abutting against the lower end face of the guide body 1.3. It can be left unfixed or fixed to the support tube 2.3 with screws. The limiting sleeve 2.17 has a vertical groove for accommodating the anchor claw 2.2 and the straightening arm 2.4. The anchor claw 2.2 and the straightening arm 2.4 can fit tightly against the outer circle of the support tube 2.3, and their outer diameter is consistent with the maximum outer diameter of the guide body 1.3, which is conducive to the smooth lowering of the tubing into the wellbore.

[0045] The guide assembly 1 is composed of a guide body 1.3, a reverse locking rod 1.2, and an upper connector 1.1 connected sequentially by threads. The guide body 1.3 is a hollow structure, with its lower inner circle connected to the support tube 2.3 by threads. The lower outer circle of the reverse locking rod 1.2 has reverse threads and is inserted into the inner circle step of the guide body 1.3, connected by the reverse threads. The reverse locking rod 1.2 can be disengaged by rotating it forward, and the lower outer circle step of the reverse locking rod 1.2 extends into the through hole of the support tube 2.3. The upper outer circle of the inverted rod 1.2 is sealed by a sealing ring 2.7; the upper outer circle of the inverted rod 1.2 is fixed by a threaded connection to the upper connector 1.1, with a sealing ring 2.7 at the threaded connection. The upper part of the upper connector 1.1 is designed with a sealing pipe thread, which can be connected to the drill string. The upper part of the guide body 1.3 is a guide surface, which can apply a lateral reaction force to the drill bit in the open hole. This lateral reaction force is the same as the design orientation of the branch wellbore, forcing the drill bit to drill in the design orientation of the branch wellbore and complete the branch wellbore. The bottom outer circle of the guide body 1.3 is designed with an outwardly protruding centering block, and the outer circle of the lower connector 2.15 is also designed with an outwardly protruding centering block to center the tubing string.

[0046] Construction process: Taking a two-section multi-branch well as an example, the drilling string is run into the surface casing 6 of the first section, and the main wellbore 10 of the second section is drilled out. Anchoring assembly 2 + guide assembly 1 is run into the bottom of the main wellbore 10 using the drill string. A gyroscope is then run into the well to determine the normal azimuth of the guide plane of guide assembly 1, ensuring it matches the designed azimuth angle of the next branch wellbore. Afterwards, anchoring assembly 2 is set. Anchoring assembly 2 is located at the very bottom of the main wellbore 10, and its lower connector 2.15 is directly connected to the guide shoe 5 via a sealing pipe thread. During setting... Hydraulic pressure of 10 MPa is applied inside the tubing. This hydraulic pressure, transmitted through pressure transmission hole 2.6, acts on the pressure differential surface formed by the inner and outer sealing rings 2.7 of the release sleeve 2.10, pushing the release sleeve 2.10 to shear the shear pin 2.9 downwards until it hits the upper end face of the lower connector 2.15. Simultaneously, the locking block 2.8 loses its support from the release sleeve 2.10 and ceases its fixing function. The piston 2.5 and support tube 2.3 can then move relative to each other. The hydraulic pressure acts on the pressure differential surface formed by the inner and outer sealing rings 2.7 of the piston 2.5. The piston 2.5 is pushed upwards, and the piston 2.5, through the pin 2.1, pushes the centering arm 2.4 to extend outwards. The centering arm 2.4, through the pin 2.1, drives the anchor claw 2.2 to extend outwards and insert into the formation for anchoring. The wedge-shaped tip of the anchor claw 2.2 has a serrated structure, which helps to anchor more firmly in the formation. During the anchoring process, the piston 2.5 drives the hydraulic cylinder liner 2.11 upwards. After the anchoring assembly 2 is seated in place, the locking ring 2.13 in the lower inner circular step of the hydraulic cylinder liner 2.11 locks into the lower connector 2.1. On the anti-reverse thread 2.12 of 5, ensure its setting reliability; continue to pressurize to 15MPa and stabilize the pressure for 5 minutes to increase the upward thrust of piston 2.5, thereby increasing the anchoring force of anchor claw 2.2. After full anchoring, depressurize the tubing string and rotate it forward 30-50 times into the drill string to disengage the reverse rod 1.2 and guide body 1.3 in the guide assembly 1. Take out the drill string and bring out the upper connector 1.1 and reverse rod 1.2 out of the main wellbore 10. The guide body 1.3 and the following components remain at the bottom of the main wellbore 10.

[0047] The drilling string is lowered, and under the support and constraint of the guide surface on the upper part of the guide assembly 1 at the bottom of the well, the first branch wellbore 11 is drilled towards the designed azimuth of the branch wellbore, i.e., the normal azimuth of the guide surface. If the drilling string is a conventional drill string structure, a branch wellbore with a conventional radius of curvature can be drilled. If the drilling string is a flexible drill string structure, a branch wellbore with a short radius of curvature can also be drilled. After the first branch wellbore 11 is completed, the drilling string is pulled out, and the branch well completion string is lowered, which includes, from bottom to top, a guide shoe 5, a screen pipe 4, a sealing assembly 3, an anchoring assembly 2, a guide assembly 1, and a feed drill string. The screen pipe 4 can be one or more, and one or more sleeves 9 can be added between the screen pipe 4 and the sealing assembly 3. The sealing assembly 3 can be one or more sets. The bottom guide shoe 5 plays a guiding role to facilitate the smooth lowering of the tubing string. When the guide shoe 5 contacts the guide slope surface of the guide assembly 1 left at the bottom of the well, it enters the first branch wellbore 11 under its guidance. The sealing assembly 3 and the above part remain in the main wellbore 10 and are located above the guide assembly 1 left at the bottom of the well.

[0048] After the completion string for the branch well is in place, a gyroscope is lowered to determine the normal azimuth of the guide plane of the guide assembly 1, ensuring it matches the design azimuth angle of the second branch well 12. Ball 3.14 is dropped, landing on the conical sealing surface above the ball seat 3.16 to form a seal. The space above ball 3.14 is sealed. Hydraulic pressure is applied to the tubing at 5 MPa, and the inlet valve 3.13 of valve head 3.9 is opened. Drilling fluid enters the sealed space formed by the inner rubber sleeve 3.5 and the central tube 3.1 through the inlet channel 3.10, beginning to expand outwards in the rubber sleeve assembly, sealing the annular space between the completion string and the main well 10. The rubber sleeve assembly is composed of an inner rubber sleeve 3.5, a stainless steel sheet 3.6, and an outer rubber sleeve 3.8. The stainless steel sheet 3.6... The outer rubber sleeve 3.8 mainly serves to protect the inner rubber sleeve 3.5. When the rubber sleeve assembly expands outward, its axial length shortens. At this time, the upper end ring 3.4 drives the adjusting ring 3.2 downward through the thread to adjust the axial length of the rubber sleeve assembly. At the same time, the locking ring 2.13 in the upper inner circular step of the adjusting ring 3.2 locks onto the anti-reverse thread 2.12 of the central tube 3.1 to ensure the reliability of the rubber sleeve assembly setting. Continue to pressurize to 7MPa and stabilize the pressure for 5 minutes to fully expand and set the rubber sleeve assembly. The check valve 3.12 is a one-way valve to prevent the backflow of drilling fluid entering the rubber sleeve assembly. Continue to pressurize to 9MPa, close the valve 3.11 to close and permanently lock the fluid inlet channel 3.10 to ensure the reliable expansion and setting of the rubber sleeve assembly. The annulus between the completion string and the wellbore described above is sealed using an expansion sealing structure. This sealing method can also use a compression rubber sleeve structure, which seals the annulus between the completion string and the wellbore by applying hydraulic pressure and the piston squeezing and deforming the rubber sleeve. Alternatively, an oil / water swellable rubber sleeve sealing structure can be used, in which the rubber sleeve absorbs liquid and expands and deforms to seal the annulus between the completion string and the wellbore by soaking it in formation fluid.

[0049] Continue applying hydraulic pressure at 10MPa. The hydraulic pressure, through the pressure transmission hole 2.6, acts on the pressure difference surface formed by the inner and outer sealing rings 2.7 of the release sleeve 2.10, pushing the release sleeve 2.10 to shear the shear pin 2.9 downwards, releasing the locking block 2.8. Simultaneously, the hydraulic pressure acts on the pressure difference surface formed by the inner and outer sealing rings 2.7 of the piston 2.5, pushing the piston 2.5 upwards. The piston 2.5 pushes the straightening arm 2.4 outwards and drives the anchor claw 2.2 to insert into the formation for support and anchoring. At the same time, the piston 2.5 drives the hydraulic cylinder liner 2.11 upwards. After the anchoring assembly 2 is seated in place, the lock in the lower inner circular step of the hydraulic cylinder liner 2.11... Ring 2.13 is locked onto the anti-reverse thread 2.12 of the lower connector 2.15 to ensure its setting reliability; continue pressurizing to 15MPa and stabilize for 5 minutes to increase the anchoring force of the anchor claw 2.2; continue pressurizing to 18MPa, and the hydraulic pressure acts on the pressure difference surface formed by the outer sealing ring 2.7 of the ball 3.14 and the ball seat 3.16, pushing the ball seat 3.16 to shear the shear pin 2.9 downward and fall to the bottom of the tubing string to form an oil and gas production channel; the ball 3.14 and the ball seat 3.16 can also be designed as other sealing and plugging mechanisms made of soluble materials, which can be dissolved by formation fluids to form an oil and gas production channel during later production. After depressurizing the tubing string, rotate it forward 30-50 times to send the drill string in, causing the reverse rod 1.2 and the guide body 1.3 in the guide assembly 1 to disconnect. Take out the drill string and leave the guide body 1.3 and the following components in the main wellbore 10. If the target oil and gas layer does not produce sand, the screen pipe 4 entering the branch wellbore can be designed as a perforated screen pipe, mainly to support the well wall and prevent wellbore collapse. If the target oil and gas layer produces sand, the screen pipe 4 can be designed as a slotted screen pipe or a composite precision sand filter pipe, to support the well wall and block formation sand from entering the oil and gas production channel.

[0050] The drilling string is run again, and under the support and constraint of the guide assembly 1 at the top of the first branch wellbore completion string, the branch wellbore is drilled to the design azimuth of the second branch wellbore 12, i.e., the guide slope normal azimuth side of the guide assembly 1, and the branch wellbore completion string is run to complete the well.

[0051] Similarly, drilling and completion work is carried out on several other branch wells until the final branch well 13 is drilled and completed. The drilling string is pulled out and the completion string for the final branch well is run in, from bottom to top: guide shoe 5 + screen pipe 4 + blind flange 14 + sealing assembly 3 + cementing assembly 8 + casing 9 (to the wellhead). When the completion string is run to the design position, the sealing assembly 3 is positioned above the guide assembly 1 of the completion string of the previous branch well, ensuring that the sealing assembly 3 is set in the main well 10. The sealing assembly 3 adopts an expansion sealing structure. After the tubing string is in place, cement injection is carried out on the top of the screen pipe: the tubing string above the blind plate is a closed space. First, the tubing string is hydraulically expanded and set to seal the sealing assembly 3, sealing the annulus between the completion tubing string and the main wellbore 10. The pressure is further increased, and the circulation hole in the cement injection assembly 8 is opened to establish a fluid circulation channel between the completion tubing string and the annulus above the sealing assembly 3. After sufficient circulation and well washing, cement injection is carried out. Cement slurry fills the annulus between the casing 9 above the sealing assembly 3 and the main wellbore 10, as well as the annulus between the casing 9 and the surface casing 6. After setting, cement stone 7 is formed, achieving permanent isolation of the formation. Finally, the blind plate 14 is drilled through to establish an oil and gas production channel.

[0052] During later production, a lifting device is installed in casing 9 for production, or production is achieved by utilizing formation energy for self-flowing. If it is a sand-bearing oil and gas reservoir, when the oil and gas flow from the first branch wellbore 11 to the main wellbore 10, the formation sand is filtered by screen pipe 4. As the oil and gas continue to rise in the main wellbore 10, it is filtered again by screen pipe 4 in the second branch wellbore 12, and so on. The sand-bearing oil and gas flow undergoes multiple filtrations by different screen pipes 4 before entering the completion string in the final branch wellbore 13, which can significantly improve the sand control effect.

[0053] This multi-branch well drilling and completion string and construction method has significant application effects, mainly reflected in three aspects: ① It enables multi-branch well drilling in open holes without the need for full-well casing cementing or side-drilling with windows in the casing, saving materials, costs, and construction time; ② All branch wells adopt open-hole sand control completion, avoiding cement slurry cementing from polluting the oil and gas reservoir; ③ The completion operations of each branch well and the drilling operations of the next branch well are closely connected, eliminating the need for repeated guide vane setting and retrieval operations, which can greatly improve drilling and completion efficiency and save construction time and costs.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A completion string for branched wellbore, characterized in that, It includes, from bottom to top, a guide shoe, a screen tube, a sealing assembly, an anchoring assembly, and a guide assembly; The sealing assembly includes a first coupling, a central tube, a valve head, and a sealing tube connected sequentially by threads. The first coupling is used to connect the anchoring assembly, and the sealing assembly is connected to the screen tube via a second coupling. The sealing tube is provided with a soluble sealing structure inside, and the central tube is provided with a deformable rubber sleeve sealing structure outside. The rubber sleeve sealing structure includes an inner rubber sleeve fitted on a central tube, support plates evenly arranged on the outer surface of the inner rubber sleeve, and an outer rubber sleeve fitted outside the support plates. The anchoring assembly includes a lower connector, a support tube, and a guide body connected in sequence. The lower connector is sealed to the first coupling. The lower part of the guide body is connected to an anchor claw that can be extended and opened for anchoring. A hydraulic cylinder sleeve is provided outside the support tube. A piston acting on the anchor claw is arranged between the hydraulic cylinder sleeve and the support tube. A pressure transmission hole is arranged on the tube wall of the support tube. The guide assembly includes an inverted rod inserted into the guide body and communicating with the support tube, and the upper part of the inverted rod is threadedly connected to an upper connector.

2. The branch well completion string according to claim 1, characterized in that, The screen tube is a perforated screen tube, a slotted screen tube, or a composite precision sand filter tube. The sealing assembly is a group or multiple groups connected in series; The deformable rubber sleeve sealing structure is an expansion rubber sleeve sealing structure, a compression rubber sleeve sealing structure, or an oil / water-swellable rubber sleeve sealing structure.

3. The branch well completion string according to claim 1, characterized in that, The soluble sealing structure includes a ball seat arranged inside the sealing tube and fixed to the sealing tube by a shear pin; the ball seat has a conical sealing surface that cooperates with the ball to form a seal.

4. The branch well completion string according to claim 2, characterized in that, The upper end of the inner rubber cylinder is vulcanized and sealed with the adjusting ring and vulcanizing head outside the central tube, and the lower end of the inner rubber cylinder is vulcanized and sealed with the valve head and vulcanizing head; the upper and lower ends of the support plate are respectively fixed on the end rings that are threadedly connected to the adjusting ring and the valve head; the upper and lower ends of the outer rubber cylinder are also vulcanized and sealed with the end rings that are threadedly connected to the adjusting ring and the valve head.

5. The branch well completion string according to claim 4, characterized in that, A sealed space is formed between the adjusting ring, the inner surface of the inner rubber cylinder, the valve head, and the outer surface of the central tube. The rubber cylinder assembly is expanded outward by hydraulic pressure. This sealed space is connected to the internal space of the tubing column through the liquid inlet channel inside the valve head. The liquid inlet channel is controlled by the liquid inlet valve, check valve, and shut-off valve on the valve head.

6. The branch well completion string according to claim 5, characterized in that, The upper part of the adjusting ring is connected to a locking ring cap by a thread. There is an inner circular step below the internal thread of the upper part of the adjusting ring. A locking ring is installed in the step. The locking ring is engaged with the anti-reverse thread on the central tube. The lower end face of the locking ring cap limits the locking ring to the inner circular step of the adjusting ring.

7. The branch well completion string according to claim 1, characterized in that, A locking block and a release sleeve are provided to abut against the lower part of the piston. The release sleeve covers the outside of the locking block and is fixed to the locking block by shear pins. The hydraulic cylinder sleeve is located outside the release sleeve of the piston. The contact surfaces of the piston, the release sleeve, the support tube, and the hydraulic cylinder sleeve are all sealed. The support tube between the piston and the release sleeve is provided with a pressure transmission hole. The sealed space between the piston and the release sleeve is connected to the internal space of the tube column through the pressure transmission hole. The hydraulic pressure through the pressure transmission hole pushes the piston upward, causing the anchor claw to extend and open for anchoring.

8. The branch well completion string according to claim 7, characterized in that, The anchor claws are a plurality of those evenly arranged circumferentially. The upper end of each anchor claw is connected to the guide body by a pin, and the lower end of the anchor claw is a wedge-shaped sharp corner. A straightening arm corresponding to the anchor claw is movably connected to the piston. The upper end of the straightening arm is connected to the middle position of the anchor claw by a pin.

9. The branch well completion string according to claim 1, characterized in that, The guide body has a hollow structure, with its lower part connected to the support pipe via threads; the upper part of the guide body is a guide surface that guides the drill bit in the correct direction.

10. A method for constructing a branch wellbore completion string, using the branch wellbore completion string as described in any one of claims 1-9, characterized in that, include: After the first or second drilling is completed, the surface casing or technical casing is run in for cementing. After cementing, the drilling string for the next drilling operation is run in. After the second or third main wellbore is completed, the drilling string is pulled out, and the anchoring assembly and directional assembly are run in. The string is released and the feed string is pulled out. The drilling string is run in again and drilled along the directional assembly to drill the first branch wellbore. After completion, the drilling string is pulled out, and the branch wellbore completion string is run in. The branch wellbore completion string is suspended on the open hole wall by the anchoring assembly. The directional assembly is located above the anchoring assembly. The drilling string is run in again, and the second branch wellbore is drilled along the directional assembly at the top of the first branch wellbore completion string. After completion, the drill string is pulled out, and the branch wellbore completion string is run in again. This process is repeated, drilling upwards to form multiple branch wellbores and completing them. After the last branch wellbore is completed, the last branch wellbore completion string is run in.

Images