A deep water shallow well drilling structure and method

Abstract

This invention discloses a deep-water shallow drilling structure and method, comprising: a working platform, a casing string structure, and a drill string structure. The casing string structure is disposed on the working platform and includes a first casing abutting against the wellbore and a second casing connected within the first casing. The drill string structure is disposed within the second casing and movably connected to the working platform. The drill string structure includes a drill string assembly, a first limiting structure, and a drilling structure connected in sequence. The drilling structure includes a first reaming structure, a second reaming structure, and a downhole motor. The first reaming structure is connected to the second reaming structure, and the two ends of the downhole motor are respectively connected to the second reaming structure and the first limiting structure. When the second reaming structure is in the retracted state, its outer diameter is less than or equal to that of the first reaming structure, and the wellbore and the drill string structure, together with the second casing, form a first flow channel and a second flow channel, respectively. This application effectively improves the stability of the wellbore and the safety and economy of the drilling structure.

Description

Technical Field

[0001] This invention relates to the field of marine oil and gas drilling engineering technology, and in particular to a deep-water shallow drilling structure and a drilling method using the drilling structure. Background Technology

[0002] Natural gas hydrates, as a potential energy source, are characterized by their wide distribution, large resource volume, shallow burial, high energy density, and cleanliness. They are internationally recognized as the most commercially promising new clean energy source and the most ideal alternative to oil and natural gas.

[0003] Currently, open-circuit drilling is the most common method for natural gas hydrate exploration. This method is prone to wellbore instability, drill bit jamming, and abnormal pressure in the hydrate reservoir can lead to well blowouts and large amounts of mud discharge into the sea during the extraction process, affecting the marine environment. In addition, the drilling structure is not easy to recover after construction, which can result in high extraction costs for natural gas hydrates. Summary of the Invention

[0004] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, the objective of the present invention is to provide a deep-water shallow drilling structure that improves the wellbore stability in the upper shallow layer, enhances the bearing capacity of the drilling structure, improves the safety and environmental friendliness of shallow open-circuit drilling, and enhances the economic efficiency of the drilling structure.

[0005] The present invention also provides a drilling method using the above-described drilling structure.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A deep-water shallow drilling structure, comprising: Operating platform; A casing string structure is used to support a wellbore. The casing string structure is installed on the working platform. The casing string structure includes a first casing and a second casing for support. The first casing abuts against the wellbore, and the second casing is connected inside the first casing. A drill string structure is disposed within the second casing and movably connected to the working platform. The drill string structure is used for drilling into the surface. The drill string structure includes a drill string assembly, a drilling structure, and a first limiting structure, which are connected in sequence. The drilling structure includes a first reaming structure, a retractable second reaming structure, and a downhole motor for providing power. The first reaming structure is connected to the second reaming structure, and the two ends of the downhole motor are respectively connected to the second reaming structure and the first limiting structure. Wherein, along the width direction of the wellbore, the outer diameter of the second excavation structure when it is in the retracted state is less than or equal to the outer diameter of the first excavation structure, and the second casing and the wellbore form a first flow channel for drainage, and the drill string structure and the second casing form a second flow channel.

[0007] The beneficial effects of this invention are as follows: The casing string structure of this application is a double-layer casing design. The first casing is installed on the working platform, and then the second casing is connected inside the first casing. The drill string structure is then placed inside the second casing, so that the second casing and the wellbore form a first flow channel for drainage, and the drill string structure and the second casing form a second flow channel. The first casing and the second casing respectively embed and seal the first flow channel. Thus, efficient drainage can be achieved through the double flow channel, and sealing can be achieved through the double casing. This provides structural support for reducing the risk of blowout during the next reservoir drilling. Furthermore, by placing the double casing in the surface layer, it is beneficial to improve the wellbore stability in the upper shallow layer. First, it enhances the load-bearing capacity of the drilling structure. Second, the embedded structure design of the double casing provides a basis for the application of riserless mud circulation (RMR) systems. The application of RMR helps reduce the impact of mud discharge into the ocean on the marine environment and improves the safety and environmental friendliness of shallow open-path drilling. Third, setting the drill string structure inside the second casing allows the drill string structure to be lowered into or removed from the deep sea relative to the second casing, facilitating subsequent recovery of the drill string structure. At the same time, by controlling the discharge rate and drilling pressure of the drilling structure, the insertion resistance and load-bearing capacity of the double casing can be controlled, facilitating subsequent recovery of the double casing and effectively improving the economic efficiency of the drilling structure.

[0008] In the deep-water shallow drilling structure described above, along the depth direction of the wellbore, the length of the second casing is greater than that of the first casing. The first casing and the second casing are respectively used to seal the first flow channel. The second casing is provided with a first pipe section, a second pipe section, and a reducing joint for changing diameter connection. The first pipe section and the second pipe section are connected opposite to each other on both sides of the reducing joint. Along the width direction of the wellbore, the outer diameter of the second pipe section is greater than that of the first pipe section.

[0009] In the deep-water shallow drilling structure described above, the outer diameter of the first excavation structure is smaller than the inner diameter of the first pipe section, and the outer diameter of the first limiting structure is smaller than the inner diameter of the first pipe section.

[0010] As described above, in a deep-water shallow drilling structure, along the depth direction of the wellbore, the drill string assembly includes a drill pipe assembly and a drill collar assembly for providing pressure. The drill collar assembly is connected to the first limiting structure, and the outer diameter of both the drill pipe assembly and the drill collar assembly is smaller than the inner diameter of the first pipe section. One end of the drill pipe assembly is connected to the drill collar assembly, and the other end is movably connected to the working platform.

[0011] As described above, in a deep-water shallow drilling structure, the drill pipe assembly includes a first drill pipe and a second drill pipe, and the drill collar assembly includes a first drill collar, a second drill collar, and a second connector for variable diameter connection. The first drill collar and the second drill collar are connected opposite to each other on both sides of the second connector. The outer diameter of the first drill collar is larger than the outer diameter of the second drill collar. The first drill pipe is connected to the second drill collar, and the second drill pipe is connected to the first drill pipe. The first drill pipe is movably connected to the working platform.

[0012] As described above, in a deep-water shallow drilling structure, along the depth direction of the wellbore, the casing string structure further includes a feeding structure for feeding the drill string assembly. The feeding structure is connected to the opening of the second casing. The feeding structure is provided with a plurality of first drainage holes for communicating with the second flow channel and a first connecting portion for connecting the drill string assembly. The plurality of first drainage holes are arranged around the outside of the first connecting portion. The first drill pipe and the second drill collar are respectively connected to both ends of the first connecting portion.

[0013] As described above, in a deep-water shallow drilling structure, the drill string assembly, the feed structure, the first limiting structure, the downhole motor, the second enlargement structure, and the internal connection of the first enlargement structure form a third flow channel.

[0014] As described above, in a deep-water shallow drilling structure, the working platform is provided with a top drive and a wellhead, the drill string assembly is movably connected to the top drive, and the first casing is movably connected to the wellhead.

[0015] The present invention also provides a drilling method, employing a deep-water shallow drilling structure as described above, comprising the following steps: The first sleeve is abutted against the working platform; A first chuck for limiting is set at the opening of the first sleeve, the second sleeve is lowered through the first chuck, and the second sleeve is connected to the first sleeve; A second chuck for limiting is set at the opening of the second casing, and the drilling structure and the first limiting structure are lowered in through the second chuck; Remove the second chuck, lower the drill string structure, then test the drilling structure by observing it with an underwater ROV, and continue lowering the drill string structure until the second excavation structure is opened before the first excavation structure contacts the mud. Drill the preset wellbore depth by adjusting the seawater discharge rate in stages; After drilling the wellbore is completed, the casing string structure and the drill string structure are retrieved.

[0016] The beneficial effects of using the drilling method provided by this invention are at least as follows: First, compared with the traditional jet drilling structure, this application uses a controllable hydraulic expansion manipulator to control the wellbore size, thereby reducing the insertion resistance of the casing string structure and allowing the drill string structure to be inserted deeper.

[0017] Second, this application reduces the discharge rate through the third flow channel to obtain a wellbore smaller than the first pipe section, so that the first pipe section is squeezed with the formation to form a preliminary seal. At the same time, the reducing joint forms a second-stage seal with the larger wellbore, and the first casing forms a third seal with the top of the wellbore. This three-layer sealing structure provides a foundation for the next reservoir drilling, which is more efficient and reliable than conventional cementing sealing structures.

[0018] Third, the casing string structure is composed of two connected casing layers, enabling one-time insertion, which is more efficient and convenient than the separate insertion of two casing layers in conventional drilling structures.

[0019] Fourth, this application controls the insertion of the casing string structure based on the weight of the integrated casing string, and controls the bearing capacity of the drill string structure by adjusting the seawater discharge in stages. The corresponding recovery pull force is also known, which is conducive to the recovery of the casing string structure and the drill string structure, so as to save mining costs and improve environmental protection.

[0020] In the drilling method described above, the staged adjustment of seawater discharge is divided into a first stage discharge, a second stage discharge, and a third stage discharge. The first stage discharge ranges from 3300 L / min to 4000 L / min, the second stage discharge ranges from 2400 L / min to 3200 L / min, and the third stage discharge ranges from 1000 L / min to 2000 L / min. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the drill string structure connected to the feed structure according to an embodiment of the present invention; Figure 2 For the corresponding Figure 1 Enlarged view of the A-section structure; Figure 3 This is a schematic diagram of the casing column structure installed on the working platform according to an embodiment of the present invention; Figure 4 For the corresponding Figure 3 Enlarged view of the structure of section B; Figure 5 This is a schematic diagram of the drilling structure of the present invention when drilling the first wellbore. Figure 6 For the corresponding Figure 5 Enlarged view of the C-section structure; Figure 7This is a schematic diagram of the drilling structure of the present invention when drilling into the second wellbore size according to an embodiment of the present invention; Figure 8 For the corresponding Figure 7 Enlarged view of the structure of part D; Figure 9 This is a schematic diagram of the drilling structure of the present invention when drilling to the third wellbore dimension; Figure 10 For the corresponding Figure 9 Enlarged view of the E-section structure; Figure 11 For the corresponding Figure 10 Enlarged view of the G-section structure; Figure 12 For the corresponding Figure 9 Enlarged view of the F-section structure.

[0022] Reference numerals: 100-Working platform, 110-Top drive, 120-Drilling wellhead; 200-Casing string structure, 210-First casing, 220-Second casing, 221-First pipe section, 222-Second pipe section, 223-Reducing connector, 230-Feeding structure, 231-First drainage hole, 232-First connecting part; 311-Drill pipe assembly, 3111-First drill pipe, 3112-Second drill pipe, 312-Drill collar assembly, 3121-First drill collar, 3122-Second drill collar, 3123-Second connecting head, 320-Drilling structure, 321-First enlargement structure, 322-Second enlargement structure, 323-Downhole motor, 330-First limiting structure; 410-First flow channel, 420-Second flow channel, 430-Third flow channel. Detailed Implementation

[0023] The embodiments of this application are described in detail below. Examples of these embodiments are shown 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 are only used to explain this application, and should not be construed as limiting this application.

[0024] In the description of this application, it should be understood that if directional descriptions are involved, such as up, down, front, back, left, right, etc., indicating the directional or positional relationship based on the directional or positional relationship shown in the accompanying drawings, it is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0025] In the description of this application, if words such as several, greater than, less than, exceeding, above, below, or within appear, "several" means one or more, "more than" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the number itself, and "above," "below," "within," etc. are understood to include the number itself.

[0026] In the description of this application, the use of terms such as "first" and "second" is for the purpose of distinguishing technical features only, and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the order of the technical features indicated.

[0027] In the description of this application, unless otherwise expressly defined, terms such as "setup," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this application in conjunction with the specific content of the technical solution.

[0028] like Figures 1-12 As shown in the figure, an embodiment of the present invention provides a deep-water shallow drilling structure, comprising: The system comprises a working platform 100, a casing string structure 200, and a drill string structure. The casing string structure 200 supports the wellbore and is mounted on the working platform 100. It is lowered into the wellbore along with the drilling structure to support the wellbore and enhance its stability. The casing string structure 200 includes a first casing 210 and a second casing 220 for support. The first casing 210 abuts against the wellbore, and the second casing 220 is connected inside the first casing 210. The drill string structure is used for drilling to the surface. It is mounted inside the second casing 220 and movably connected to the working platform 100, allowing it to drill to a preset wellbore depth. The drill string structure includes a drill string assembly, a drilling structure 320, and a first limiting structure 330. The drill string assembly, the first limiting structure 330, and the drilling structure 320 are connected in sequence. The drilling structure 320 includes a first reaming structure 321, a retractable second reaming structure 322, and a downhole motor 323 for providing power. The first reaming structure 321 is connected to the second reaming structure 322, and the two ends of the downhole motor 323 are respectively connected to the second reaming structure 322 and the first limiting structure 330. In the width direction of the wellbore, the outer diameter of the second reaming structure 322 when it is in the retracted state is less than or equal to the outer diameter of the first reaming structure 321, and the second casing 220 and the wellbore form a first flow channel 410 for drainage. The drill string structure and the second casing 220 form a second flow channel 420.

[0029] In this embodiment of the invention, the casing string structure 200 is a double-casing design. A first casing 210 is installed on the work platform 100, and a second casing 220 is connected inside the first casing 210. The drill string structure is then placed inside the second casing 220, so that the second casing 220 and the wellbore form a first flow channel 410 for drainage. The drill string structure and the second casing 220 form a second flow channel 420. The first casing 210 and the second casing 220 respectively provide embedded sealing to the first flow channel 410. This dual-flow channel enables efficient drainage and sealing through the double-casing design, providing structural support to reduce the risk of blowouts during subsequent reservoir drilling. Furthermore, by placing a double-casing structure on the surface, [the following is also mentioned:] First, it improves the stability of the wellbore in the upper shallow layer and enhances the bearing capacity of the drilling structure. Second, the embedded structure design of the double casing provides a basis for the application of the riserless mud circulation system (RMR). The application of RMR helps reduce the impact of mud discharge into the ocean on the marine environment and improves the safety and environmental protection of the shallow open-path drilling process. Third, setting the drill string structure inside the second casing 220 allows the drill string structure to be lowered into or removed from the deep sea relative to the second casing 220, facilitating the subsequent recovery of the drill string structure. At the same time, by controlling the displacement and drilling pressure of the drilling structure, the insertion resistance and bearing capacity of the double casing can be controlled, facilitating the subsequent recovery of the double casing and effectively improving the economy of the drilling structure.

[0030] In this embodiment of the invention, the downhole motor 323 is directly connected between the second enlargement structure 322 and the first limiting structure 330, so that the rotational power of the first enlargement structure 321 and the second enlargement structure 322 comes from downhole, instead of relying on the entire drill string structure to be driven from the work platform 100. This avoids rotational friction between the drill string assembly and the second casing 220, reduces fatigue damage to the drill string assembly, and extends the service life of the drill string assembly and the second casing 220.

[0031] Preferably, in this embodiment of the invention, the first reaming structure 321 is a drill bit, and the second reaming structure 322 is a hydraulic telescopic reamer. The hydraulic telescopic reamer is equipped with a retractable and expandable blade assembly, which allows adjustment of the outer diameter of the blade assembly in the retracted state and the outer diameter in the expanded state by adjusting the seawater discharge. When the hydraulic telescopic reamer is in the expanded state, it ensures that the drill string structure drills a large wellbore, which facilitates reducing the insertion resistance of the second casing 220, thereby enabling deeper insertion of the casing string structure 200. Secondly, this application adopts a "drill first" approach. The "post-drilling" method reduces the instantaneous rock breaking volume of the drilling structure 320, reduces the torque and vibration of the drill string structure, and allows the drilling structure to drill out a regular large wellbore more smoothly. Third, this application adopts a structural design in which the outer diameter of the second excavation structure 322 when it is in the retracted state is less than or equal to the outer diameter of the first excavation structure 321. This facilitates the recycling of the first excavation structure 321 within the casing string structure 200 along with the drilling structure 320 after construction, thereby reducing the extraction cost of natural gas hydrates and improving the economic efficiency of the drilling structure.

[0032] like Figure 1 , Figures 3-6 , Figures 9-12 As shown, specifically, along the depth direction of the wellbore, the length of the second casing 220 is greater than that of the first casing 210. The first casing 210 and the second casing 220 are used to seal the first flow channel 410, respectively. The second casing 220 is provided with a first pipe section 221, a second pipe section 222, and a reducing joint 233 for changing diameter connection. The first pipe section 221 and the second pipe section 222 are connected to each other on both sides of the reducing joint 233. Along the width direction of the wellbore, the outer diameter of the second pipe section 222 is greater than that of the first pipe section 221.

[0033] In this embodiment of the invention, the second casing 220 adopts a variable diameter structure design. By designing the second pipe section 222 at the upper part of the wellbore depth direction, and the outer diameter of the second pipe section 222 being larger than the outer diameter of the first pipe section 221, and the length of the second casing 220 being larger than the length of the first casing 210, it is ensured that during the process of the second casing 220 being lowered into the wellbore depth direction, the first pipe section 221 first performs preliminary sealing of the wellbore, followed by a second sealing step performed by the variable diameter joint 233, thereby reducing the annular space gap between the second casing 220 and the wellbore; finally, the first casing 210 further seals the wellbore. The third step is sealing, which allows the second casing 220 to work with the first casing 210 to form a double mechanical seal structure, enhancing the reliability of the closed-loop circulation of mud generated during drilling and the stability of the wellbore. At the same time, along the depth direction of the wellbore, the annular space gap between the second casing 220 and the wellbore decreases, which can effectively increase the upward return speed between the drilling structure 320 and the second casing 220. This helps to assist the first enlargement structure 321 in breaking up the rock cuttings at the bottom of the wellbore and carrying them away from the bottom of the wellbore in a timely manner, preventing the first enlargement structure 321 from getting stuck due to sand accumulation, significantly improving the rock clearing efficiency of the drilling structure and enhancing the stability of the drilling structure in use.

[0034] like Figures 9-10 As shown, further, the outer diameter of the first excavation structure 321 is smaller than the inner diameter of the first pipe section 221, and the outer diameter of the first limiting structure 330 is smaller than the inner diameter of the first pipe section 221.

[0035] In this embodiment of the invention, the outer diameter of the first enlargement structure 321 is smaller than the inner diameter of the first pipe section 221, so that there is no gap between the wellbore generated by the drilling of the first enlargement structure 321 and the outer wall of the first pipe section 221, thereby forming a preliminary seal and enhancing the sealing performance; at the same time, the first limiting structure 330 is a centralizer, and the outer diameter of the first limiting structure 330 is smaller than the inner diameter of the first pipe section 221, so that the drilling structure 320 is connected to the first limiting structure 330 to improve the stability of the drill string structure during the drilling process; In this embodiment of the invention, the cutter wing assembly needs to open during wellbore enlargement. If the drill string structure swings violently during the opening of the cutter wing assembly, the cutter wing assembly of the second enlargement structure 322 will experience uneven stress, making it prone to breakage or necking. The design of the centralizer can enhance the stability of the second enlargement structure 322 during drilling. like Figure 1 , Figure 9As shown, further, along the depth direction of the wellbore, the drill string assembly includes a drill pipe assembly 311 and a drill collar assembly 312 for providing pressure. The drill collar assembly 312 is connected to the first limiting structure 330, and the outer diameter of both the drill pipe assembly 311 and the drill collar assembly 312 is smaller than the inner diameter of the first pipe section 221. One end of the drill pipe assembly 311 is connected to the drill collar assembly 312, and the other end is movably connected to the working platform 100.

[0036] In this embodiment of the invention, the drill pipe assembly 311 and the drill collar assembly 312 are designed to be non-rotating, so that the drill pipe assembly 311 and the drill collar assembly 312 mainly bear static tensile force and static counter-torsional force, rather than high-speed rotation. This effectively reduces the bending stress of the drill string assembly caused by seawater, reduces the risk of twisting or falling off leading to complex downhole accidents, and improves the safety of the drilling structure.

[0037] In this embodiment of the invention, along the depth direction of the wellbore, the drill collar assembly 312 is connected above the first limiting structure 330. Due to the large wall thickness and heavy weight per unit length of the drill collar assembly 312, it provides continuous and stable drilling pressure for the first enlargement structure 321. By accurately calculating the number and length of the drill collar assembly 312, it can be ensured that during the drilling process, the neutralization point (i.e., the dividing point where the drill string structure changes from tension to compression) always falls on the drill collar assembly 312 with high stiffness, thereby protecting the drill pipe assembly 311 connected to the upper part of the drill collar assembly 312 from damage by alternating compressive stress and effectively preventing the occurrence of fatigue fracture accidents of the first enlargement structure 321. At the same time, the high stiffness of the drill collar assembly 312 helps to maintain the stability of the drilling structure 320, suppress wellbore tilt, and improve the accuracy of wellbore drilling.

[0038] like Figure 1 , Figure 9 As shown, further, the drill rod assembly 311 includes a first drill rod 3111 and a second drill rod 3112, and the drill collar assembly 312 includes a first drill collar 3121, a second drill collar 3122 and a second connector 3123 for variable diameter connection. The first drill collar 3121 and the second drill collar 3122 are connected opposite to each other on both sides of the second connector 3123. The outer diameter of the first drill collar 3121 is larger than the outer diameter of the second drill collar 3122. The first drill collar 3121 is connected to the first limiting structure 330. The first drill rod 3111 is connected to the second drill collar 3122. The second drill rod 3112 is connected to the first drill rod 3111. The first drill rod 3111 is movably connected to the working platform 100.

[0039] In this embodiment of the invention, the connection between the drill rod assembly 311 and the drill collar assembly 312, the connection between the first drill rod 3111 and the second drill rod 3112, and the connection between the first drill collar 3121 and the first limiting structure 330 are all made using a connector to improve the stability of the drill string structure connection.

[0040] In this embodiment of the invention, the first drill collar 3121 with a larger outer diameter is connected to the first limiting structure 330. Its large mass characteristic provides a stable and continuous downward drilling pressure for the drilling structure 320, making the drilling pressure transmission more stable and improving the drilling stability of the drilling structure.

[0041] like Figures 1-2 , Figure 9 As shown, further along the depth direction of the wellbore, the casing string structure 200 also includes a feeding structure 230 for feeding the drill string assembly. The feeding structure 230 is connected to the opening of the second casing 220. The feeding structure 230 is provided with a plurality of first drainage holes 231 for connecting the second flow channel 420 and a first connecting part 232 for connecting the drill string assembly. The plurality of first drainage holes 231 are arranged around the outside of the first connecting part 232. The first drill rod 3111 and the second drill collar 3122 are respectively connected to the two ends of the first connecting part 232.

[0042] In this embodiment of the invention, the first drill pipe 3111 and the second drill collar 3122 are respectively connected to both ends of the first connecting part 232 to improve the sealing performance of the third flow channel 430; the feeding structure 230 is embeddedly connected to the opening of the second casing 220 along the wellbore depth direction. Through the sealing ring provided on the feeding structure 230, the feeding structure 230 can be embedded in the opening of the second casing 220, thereby improving the stability of the connection; multiple first drainage holes 231 are arranged around the outside of the first connecting part 232, that is, close to the pipe wall of the second casing 220, so that the circulating mud can be discharged evenly and dispersedly, avoiding excessive disturbance to the seabed environment caused by concentrated mud injection, and enhancing the environmental friendliness of the drilling structure.

[0043] like Figures 1-2 , Figure 9 As shown, the drill string assembly, the feeding structure 230, the first limiting structure 330, the downhole motor 323, the second excavation structure 322, and the first excavation structure 321 are internally connected and form a third flow channel 430.

[0044] In this embodiment of the invention, the third flow channel 430 penetrates the entire interior of the drill string structure, forming a continuous hydraulic channel from the working platform 100 directly to the first enlargement structure 321. This allows seawater to be pumped in by the pump on the working platform 100 and flow sequentially through the drill string assembly, the feed structure 230, the first limiting structure 330, the downhole motor 323, and the second enlargement structure 322. Finally, it is ejected from the nozzle of the first enlargement structure 321, forming a high-speed jet that directly impacts the bottom of the wellbore to help break the rock and ensure the closed-loop circulation of mud in the drilling structure.

[0045] like Figures 3-4 , Figure 9As shown, the work platform 100 is further provided with a top drive 110 and a drilling wellhead 120, the drill string assembly is movably connected to the top drive 110, and the first casing 210 is movably connected to the drilling wellhead 120.

[0046] In this embodiment of the invention, the working platform 100 can be a ship hull, a mobile drilling platform, or a fixed drilling platform, preferably a ship hull, to improve the flexibility of the drilling structure; the top drive 110 is set on the deck of the ship hull, and the wellhead 120 is set in the moon pool at the bottom of the ship hull, which runs through the ship hull from top to bottom, providing a vertical passage for drilling operations; wherein, the casing string structure 200 can completely pass through the wellhead 120 and be lowered into the deep sea mud surface to support the wellbore; the top drive 110 is a crane that can pull the casing string structure 200 and the drill string structure to lower the casing string structure 200 and the drill string structure, so that the drilling structure can drill to a preset depth and realize the recovery of the casing string structure 200 and the drill string structure, thereby reducing the mining cost.

[0047] like Figures 1-12 As shown in the figure, an embodiment of the present invention provides a drilling method using the above-mentioned deep-water shallow drilling structure, comprising the following steps: S1. Connect the first casing 210 to the top drive 110, so that the first casing 210 abuts against the wellhead 120 on the working platform 100.

[0048] S2. Along the depth direction of the wellbore, the first chuck for limiting is set at the pipe opening on the upper part of the first casing 210. The first pipe section 221 of the second casing 220 is lowered through the first installation position on the first chuck. Then, the reducing connector 233 is connected to the first pipe section 221. Next, the second pipe section 222 is connected to the first pipe section 221 through the reducing connector 233. Finally, the second pipe section 222 is connected to the first casing 210.

[0049] Specifically, the connection between the first sleeve 210 and the second sleeve 220 is fastened by a first locking structure. The inner wall of the first sleeve 210 is provided with a first fastening part, and the outer wall of the second sleeve 220 is provided with a first connecting part. By connecting the first connecting part to the first fastening part, the second sleeve 220 is fastened inside the first sleeve 210, thereby enhancing the convenience of structural connection.

[0050] S3. The second chuck for limiting is set at the opening of the second casing 220. The drilling structure 320 is lowered through the second mounting position of the second chuck. The first step is to connect the third connector to the drilling structure 320. The second step is to connect the first limiting structure 330 to the drilling structure 320 through the third connector and lower the first limiting structure 330. The third step is to connect the drill collar assembly 312 to the first limiting structure 330 through the fourth connector and lower the drill collar assembly 312. The fourth step is to connect the drill rod assembly 311 to the drill collar assembly 312 through the fifth connector and connect the drill rod assembly 311 to the top drive 110 and lower the drill rod assembly 311.

[0051] S4. Remove the second chuck, lower the drill string structure, and then test the drilling structure 320 by observing it with an underwater ROV. Continue lowering the drill string assembly until the first reaming structure 321 contacts the mud and the second reaming structure 322 opens, so that the cutter wings of the second reaming structure 322 open to the preset wellbore size. Then continue lowering the drill string structure.

[0052] Specifically, underwater ROV observation involves deploying an unmanned remotely operated vehicle (ROV) into the water, operated by staff, to inspect and assist in the deployment and drilling of underwater drill strings, replacing divers or human eyes.

[0053] Specifically, the drilling pressure can be adjusted by the weight of the drill string structure and casing string structure 200 lowered by the top drive 110, and the maximum drilling pressure shall not exceed the sum of the weights of the drill string structure and casing string structure 200 (referred to as the integrated string weight).

[0054] S5. Adjust the seawater discharge in stages to drill the preset wellbore size; Specifically, the weight of the entire drill string structure needs to be gradually applied by the top drive 110 in a gravity release manner (the drilling pressure does not exceed the sum of the weights of the drill string structure and the casing string structure 200), and the downward pressure weight of the drill string structure needs to be controlled between the weight of the casing string structure 200 and the weight of the integrated tubing string. The height of the end of the first enlargement structure 321 from the bottom mud surface of the wellbore should be maintained within the range of 2 meters to 5 meters to ensure that the drilling structure 320 is stable and controllable during the lowering process.

[0055] Specifically, the preset wellbore size is divided into three drilling sizes: the first wellbore size, the second wellbore size, and the third wellbore size. The first wellbore size, the second wellbore size, and the third wellbore size correspond to the seawater discharge rates of the first stage, the second stage, and the third stage, respectively.

[0056] First wellbore size: For drilling a pre-set wellbore section of approximately 28 meters, a high displacement of 3300L / min to 4000L / min is used, preferably 3800L / min. This ensures that the seawater ejected from the nozzle of the first enlargement structure 321 achieves an extremely high jetting velocity, which not only has a strong hydraulic erosion effect on unconsolidated mud and sand formations in shallow deep water, but also allows for a wellbore size slightly larger than that of the second enlargement structure 322, facilitating the insertion of the second pipe section 222. Simultaneously, it allows for direct utilization of hydraulic energy to break up the formation, achieving "jet drilling" and significantly improving drilling efficiency. The mechanical drilling rate for the first wellbore size is maintained; simultaneously, high-volume seawater drilling is employed, allowing the cutter wings of the first limiting structure 330 to fully open and enlarge the wellbore. The large wellbore, combined with the high-volume seawater drilling, generates a sufficiently high upward flow velocity. The main circulation of mud is achieved through the first flow channel 410, with a small portion circulating through the second flow channel 420. This ensures that large pieces of rock cuttings (especially clay clumps commonly found in shallow soft formations) can be carried out of the wellbore in a timely manner, preventing them from being repeatedly broken up or accumulating at the bottom of the wellbore to form a "cuttings bed," thus improving the cleaning efficiency of the wellbore.

[0057] Second wellbore size: For the section approximately 10 meters before reaching the preset wellbore size, drilling is carried out at a medium displacement of 2400L / min to 3200L / min, preferably 2800L / min, to provide sufficient driving pressure differential. This ensures that the cutter wings of the second enlargement structure 322 remain fully open during the drilling of the second wellbore size, allowing for the acquisition of the wellbore size of the second enlargement structure 322. This facilitates the smooth insertion of the first pipe section 221, and the displacement is adjusted appropriately within the medium displacement range based on the insertion resistance of the first pipe section 221. Simultaneously, drilling is carried out at a medium displacement using seawater. As the insertion depth of the casing string structure 200 increases, the circulation channel mainly relies on the second flow channel 420 for internal mud circulation, with a small portion relying on the first flow channel 410 for external mud circulation. This ensures that the seawater can effectively carry rock cuttings without generating excessive turbulence that erodes the well wall, enhancing the stability of the drilling structure during the drilling process.

[0058] Third wellbore size: To reach the preset wellbore size, drilling will be carried out at a low flow rate of 1000L / min to 2000L / min, preferably 1900L / min. This allows the second enlargement structure 322 to be completely recovered using low-flow seawater. Simultaneously, the weight of the drill string structure under pressure will be controlled to not exceed the weight of the integrated casing string. If excessive resistance is encountered during drilling, the drill string structure will be moved up and down by the top drive 110 to continue drilling. Specifically, along the depth direction of the wellbore, when the weight of the drill string structure under pressure exceeds the weight of the casing string structure 200, the height of the top of the casing string structure 200 from the bottom mud surface should be optimally maintained within 2 to 3 meters, with a maximum not exceeding 5 meters, to prevent overload from causing the casing string structure 200 to sink into the mud surface later. Simultaneously, the first casing 210 is embedded in the mud surface to seal the first flow channel 410, and drilling is carried out using low-flow seawater. The second enlargement structure 322 is in a fully retracted state, and the size of the wellbore is smaller than the outer diameter of the second casing 220, so that the second casing 220 is completely attached to the inner wall of the wellbore. At this time, the mud circulation is mainly carried out through the second flow channel 420, and the circulation of the outer flow channel of the first flow channel 410 is closed, realizing the complete isolation between the wellbore and the second casing 220, providing a safety barrier for the next reservoir drilling.

[0059] S6. After drilling to the preset wellbore size, the casing string structure 200 and drill string structure are recovered by the top drive 110 to reduce mining costs.

[0060] The beneficial effects of using a drilling method provided in this embodiment of the invention are at least as follows: First, compared with the traditional jet drilling structure, this application uses a controllable hydraulic telescoping reamer to control the wellbore size, so as to reduce the insertion resistance of the casing string structure 200 and allow the drill string structure to be inserted deeper.

[0061] Second, this application reduces the discharge rate through the third flow channel 430 to obtain a wellbore smaller than the first pipe section 221, so that the first pipe section 221 is squeezed with the formation to form a preliminary seal. At the same time, the reducing joint 233 forms a second-stage seal with the larger wellbore, and the first casing 210 forms a third seal with the top of the wellbore. This three-layer sealing structure provides a foundation for the next reservoir drilling, which is more efficient and reliable than conventional cementing sealing structures.

[0062] Third, the casing string structure 200 is composed of two connected casing layers, which enables one-time insertion, making it more efficient and convenient than the separate insertion of two casing layers in conventional drilling structures.

[0063] Fourth, this application controls the insertion of the casing string structure 200 based on the weight of the integrated tubing string, and controls the bearing capacity of the drill string structure by adjusting the seawater discharge in stages. The corresponding recovery pull force is also known, which is conducive to the recovery of the casing string structure 200 and the drill string structure, so as to save mining costs and improve environmental protection.

[0064] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A deep-water shallow drilling structure, characterized in that, include: Operating platform; A casing string structure is used to support a wellbore. The casing string structure is installed on the working platform. The casing string structure includes a first casing and a second casing for support. The first casing abuts against the wellbore, and the second casing is connected inside the first casing. A drill string structure is disposed within the second casing and movably connected to the working platform. The drill string structure is used for drilling into the surface. The drill string structure includes a drill string assembly, a drilling structure, and a first limiting structure, which are connected in sequence. The drilling structure includes a first reaming structure, a retractable second reaming structure, and a downhole motor for providing power. The first reaming structure is connected to the second reaming structure, and the two ends of the downhole motor are respectively connected to the second reaming structure and the first limiting structure. Wherein, along the width direction of the wellbore, the outer diameter of the second excavation structure when it is in the retracted state is less than or equal to the outer diameter of the first excavation structure, and the second casing and the wellbore form a first flow channel for drainage, and the drill string structure and the second casing form a second flow channel.

2. The deep-water shallow drilling structure according to claim 1, characterized in that, Along the depth direction of the wellbore, the length of the second casing is greater than that of the first casing. The first casing and the second casing are used to seal the first flow channel. The second casing is provided with a first pipe section, a second pipe section, and a reducing joint for changing diameter connection. The first pipe section and the second pipe section are connected to each other on both sides of the reducing joint. Along the width direction of the wellbore, the outer diameter of the second pipe section is greater than that of the first pipe section.

3. The deep-water shallow drilling structure according to claim 2, characterized in that, The outer diameter of the first excavation structure is smaller than the inner diameter of the first pipe section, and the outer diameter of the first limiting structure is smaller than the inner diameter of the first pipe section.

4. The deep-water shallow drilling structure according to claim 2, characterized in that, Along the depth direction of the wellbore, the drill string assembly includes a drill pipe assembly and a drill collar assembly for providing pressure. The drill collar assembly is connected to the first limiting structure, and the outer diameter of both the drill pipe assembly and the drill collar assembly is smaller than the inner diameter of the first pipe section. One end of the drill pipe assembly is connected to the drill collar assembly, and the other end is movably connected to the working platform.

5. The deep-water shallow drilling structure according to claim 4, characterized in that, The drill pipe assembly includes a first drill pipe and a second drill pipe. The drill collar assembly includes a first drill collar, a second drill collar, and a second connector for variable diameter connection. The first drill collar and the second drill collar are connected opposite to each other on both sides of the second connector. The outer diameter of the first drill collar is larger than the outer diameter of the second drill collar. The first drill pipe is connected to the second drill collar, and the second drill pipe is connected to the first drill pipe. The first drill pipe is movably connected to the working platform.

6. The deep-water shallow drilling structure according to claim 5, characterized in that, Along the depth direction of the wellbore, the casing string structure also includes a feeding structure for feeding the drill string assembly. The feeding structure is connected to the opening of the second casing. The feeding structure is provided with a plurality of first drainage holes for communicating with the second flow channel and a first connecting part for connecting the drill string assembly. The plurality of first drainage holes are arranged around the outside of the first connecting part. The first drill pipe and the second drill collar are respectively connected to the two ends of the first connecting part.

7. A deep-water shallow drilling structure according to claim 6, characterized in that, The drill string assembly, the feeding structure, the first limiting structure, the downhole motor, the second excavation structure, and the internal connection of the first excavation structure form a third flow channel.

8. The deep-water shallow drilling structure according to claim 1, characterized in that, The working platform is equipped with a top drive and a drilling wellhead, the drill string assembly is movably connected to the top drive, and the first casing is movably connected to the drilling wellhead.

9. A drilling method, employing a deep-water shallow drilling structure as described in any one of claims 1-8, characterized in that, Includes the following steps: The first sleeve is abutted against the working platform; A first chuck for limiting is set at the opening of the first sleeve, the second sleeve is lowered through the first chuck, and the second sleeve is connected to the first sleeve; A second chuck for limiting is set at the opening of the second casing, and the drilling structure and the first limiting structure are lowered in through the second chuck; Remove the second chuck, lower the drill string structure, then test the drilling structure by observing it with an underwater ROV, and continue lowering the drill string structure until the second excavation structure is opened before the first excavation structure contacts the mud. Drill the preset wellbore depth by adjusting the seawater discharge rate in stages; After drilling the wellbore is completed, the casing string structure and the drill string structure are retrieved.

10. A drilling method according to claim 9, characterized in that, The phased adjustment of seawater discharge is divided into a first-stage discharge, a second-stage discharge, and a third-stage discharge. The first-stage discharge range is 3300L / min to 4000L / min, the second-stage discharge range is 2400L / min to 3200L / min, and the third-stage discharge range is 1000L / min to 2000L / min.

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