Drilling system for ultra-deep water and ultra-shallow reservoirs

Abstract

This application provides a drilling system for ultra-deepwater and ultra-shallow reservoirs. The drilling system includes a derrick, a suction frame, a blowout preventer (BOP) assembly, and a pressure regulating assembly. Casing is connected to the derrick, and drill string is located at the front end of the casing. The suction frame includes a suction platform and multiple suction piles. The suction piles of the suction frame fix the suction platform above the seabed mud layer. The suction frame provides support for the casing and lateral forces applied by the drill string, enabling the drill string to pre-adjust its direction before entering the wellhead and reaching the seabed mud layer. This achieves accurate directional drilling in ultra-deepwater and ultra-shallow reservoirs. The BOP assembly prevents blowouts, and the pressure regulating assembly regulates the drilling fluid pressure discharged from the annulus, enabling dual-gradient drilling and solving the technical problem of a narrow drilling fluid safety density window.

Description

Technical Field

[0001] This application relates to the field of oil and gas engineering drilling, and in particular to a drilling system for ultra-deepwater and ultra-shallow reservoirs. Background Technology

[0002] The seabed contains abundant oil and gas resources. In related technologies, the development of marine reservoirs usually adopts a combination of casing drilling and directional drilling. The casing is directly run from the offshore platform to below the mudline on the seabed. The casing section below the mudline is then skewed using a directional drilling device to create a directional well. Drilling fluid flows from the casing string through the drill string to the bottom of the well, and then is returned to the offshore platform from the annulus between the casing's waterstop and the casing string.

[0003] Oil and gas reservoirs located below 1500 meters above sea level are called ultra-deepwater reservoirs, while those within 200 meters of the mud line are called ultra-shallow reservoirs. Reservoirs that fall under both ultra-deepwater and ultra-shallow categories are called ultra-deepwater-ultra-shallow reservoirs. Due to their shallow burial depth, low compaction, poor lithology, and weak cementation, ultra-shallow reservoirs have a narrow drilling fluid safety density window. Furthermore, the lack of stable marker layers in the weakly cemented geology makes directional drilling difficult, hindering precise drilling. Ultra-deepwater reservoirs necessitate longer risers for casing drilling compared to other reservoirs. To balance the immense hydrostatic pressure generated by the riser fluid column and maintain wellbore stability, the baseline density of the drilling fluid needs to be increased. However, for ultra-deepwater-ultra-shallow reservoirs, this increased baseline density further narrows the already limited drilling fluid safety density window. Summary of the Invention

[0004] This application provides a drilling system for ultra-deepwater and ultra-shallow reservoirs to address the shortcomings of existing drilling processes in developing ultra-deepwater and ultra-shallow reservoirs, such as a narrow drilling fluid safety density window and the inability to accurately achieve directional drilling.

[0005] This application provides a drilling system for ultra-deepwater and ultra-shallow reservoirs, including:

[0006] A derrick, fixed on the sea surface, with a casing connected to the derrick and a drilling tool at the front end of the casing;

[0007] The suction frame includes a suction platform and multiple suction piles. The multiple suction piles are fixed in the seabed mud layer by the pressure difference between the inside and outside of the suction piles. The suction platform is fixed above the multiple suction piles. The casing extends into the seabed through the suction platform. The suction frame is configured to provide support to the casing and apply lateral force to the drill bit so that the movement path of the drill bit forms an inclined angle with the vertical direction, thereby enabling the drill bit to achieve a preset build-up rate. An annulus is formed between the casing and the wall of the formed wellbore.

[0008] A blowout preventer assembly is connected to the outlet end of the annulus and fixed to the suction platform;

[0009] The pressure regulating component is connected to the annulus via the blowout preventer component, and the pressure regulating component is used to regulate the drilling fluid pressure discharged from the annulus.

[0010] Optionally, the suction base is configured to apply a lateral thrust or a lateral pull to the drill bit.

[0011] Optionally, the system may also include a guide member disposed on the drill bit and configured to guide the drill bit to increase the lateral cutting force of the drill bit so that the drill bit moves along a preset deflection angle.

[0012] Optionally, the guide includes a guide motor.

[0013] Optionally, the lateral force Fc provided by the suction base frame to the drill string satisfies the following formula:

[0014]

[0015] in:

[0016] η is the force transmission efficiency;

[0017] F a This represents the maximum anchoring force of the suction base frame;

[0018] A z The area of ​​the bottom of the suction pile;

[0019] σ c This refers to the pressure of the overlying strata.

[0020] H z The embedment depth of the suction pile;

[0021] D is the effective diameter of the suction pile;

[0022] c u It represents the shear strength of the stratum.

[0023] Optionally, the build-up rate K during drilling by the drilling tool satisfies the following formula:

[0024]

[0025] Where: L is the length of the casing below the wellhead of the suction frame;

[0026] EI is the bending stiffness of the casing;

[0027] F c It is a lateral force;

[0028] C is the overall correction factor;

[0029] K g The inherent slope of the guiding unit.

[0030] Optionally, the blowout preventer assembly includes a blowout preventer group and a rotary blowout preventer. One end of the blowout preventer group is installed at the outlet end of the annulus, and the other end of the blowout preventer group is connected to the rotary blowout preventer via a connecting flange. The rotary blowout preventer is sealed to the outer peripheral wall of the casing, and the pressure regulating assembly is connected to the rotary blowout preventer.

[0031] Optionally, the drill string includes a guide, a drive, and a drill bit connected sequentially from the rear end to the front end of the casing. The head of the guide is connected to the casing, and the drive is configured to provide rotational power to the drill bit.

[0032] Optionally, the pressure regulating assembly includes a subsea pump and a flowback line. The inlet of the subsea pump is connected to the annulus through the blowout preventer assembly, and the outlet of the subsea pump is connected to the flowback line. The subsea pump is configured to pump drilling fluid from the annulus into the flowback line.

[0033] Optionally, the pressure regulating assembly includes a throttling manifold, the inlet of which is connected to the annulus via the blowout preventer assembly.

[0034] The drilling system for ultra-deepwater and ultra-shallow reservoirs provided in this application uses suction piles on a suction frame to fix the suction platform above the seabed mud layer, raising the wellhead above the mud layer. The suction frame provides support for the casing and lateral forces applied by the drill string, allowing the drill string to tilt rapidly under the lateral forces before reaching the seabed mud layer and entering the wellhead, thus achieving pre-inclination. This enables the construction of the required wellbore (such as a horizontal well) in ultra-deepwater and ultra-shallow reservoirs, achieving accurate directional drilling in these reservoirs. Furthermore, by installing a blowout preventer (BOP) assembly on the suction platform, well sealing and blowout prevention are achieved. Simultaneously, a pressure regulating assembly adjusts the drilling fluid pressure discharged from the annulus, ensuring that the pressure discharged from the annulus is lower than the pressure inside the annulus. This results in a pressure gradient between the sea surface and the wellhead that is less than the pressure gradient between the wellhead and the bottom of the well, achieving dual-gradient drilling. Because the pressure regulating component can regulate the drilling fluid pressure discharged from the annulus, the entire drilling system does not require the use of a riser, thus avoiding the technical problem of a narrow drilling fluid installation density window caused by the use of a riser. Attached Figure Description

[0035] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0036] Figure 1 A schematic diagram of a system structure for a drilling system for ultra-deepwater and ultra-shallow reservoirs provided in this application;

[0037] Figure 2 A schematic diagram of the system structure of a drilling system for ultra-deepwater and ultra-shallow reservoirs when the pressure regulating component provided in this application is a subsea pump;

[0038] Figure 3 A schematic diagram of the system structure of a drilling system for ultra-deepwater and ultra-shallow reservoirs when the pressure regulating component provided in this application is a choke manifold;

[0039] Figure 4 This is a schematic diagram of the internal structure of the subsea pump provided in this application;

[0040] Figure 5 This is a schematic diagram of the structure of the blowout preventer assembly provided in this application.

[0041] Figure label:

[0042] 100-Offshore platform; 110-Derrick; 120-Casing; 121-Casing string; 122-Casing shoe; 123-Casing connector; 130-Drilling tool; 131-Guide component; 132-Drive component; 133-Drill bit;

[0043] 200 - Suction base frame; 210 - Suction platform; 220 - Suction pile;

[0044] 300 - Wellbore; 310 - Guide pipe; 320 - Annulus;

[0045] 400-Blowout Preventer Assembly; 410-Blowout Preventer Group; 420-Rotating Blowout Preventer; 421-Second Housing; 422-Seal; 423-Bearing; 424-Hydraulic Cylinder; 425-Circulating Pump; 426-Locking Ring; 427-Hydraulic Fluid Passage; 428-Coolant Passage; 430-Connecting Flange;

[0046] 500-Pressure regulating assembly; 510-Subsea pump; 511-Pump body; 512-Drive module; 513-Control unit; 514-Outlet pressure sensor; 515-Inlet pressure sensor; 516-Communication module; 517-First housing; 518-Sealing system; 519-Anchor block; 520-Return pipeline; 530-Throttling manifold; 540-Mud pit; 550-Inlet pipeline.

[0047] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0048] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0049] In related technologies, ultra-deepwater and ultra-shallow reservoirs possess characteristics of both ultra-deepwater and ultra-shallow reservoirs. Ultra-shallow reservoirs are characterized by poor lithology and weak cementation. Poor lithology results in formation pore pressure that is typically lower than hydrostatic pressure, while weak cementation leads to fracture pressure that is almost equal to, or even nearly equal to, pore pressure. This results in a very narrow drilling fluid safety density window. Furthermore, if cemented geology lacks stable marker beds, and directional drilling requires these marker beds as a basis for change of direction, directional drilling within ultra-shallow reservoir formations becomes extremely difficult. Consequently, existing drilling techniques cannot accurately drill directional wells to the target location of ultra-shallow reservoirs, such as horizontal wells.

[0050] The riser connects the subsea wellhead to the offshore platform, therefore, ultra-deepwater reservoirs require a longer riser than shallower reservoirs. The fluid column formed within the riser in ultra-deepwater reservoirs is longer, generating greater hydrostatic pressure. To balance this immense hydrostatic pressure and maintain wellbore stability, drilling systems employing risers require ultra-deepwater reservoirs to use drilling fluids with a higher density than those used in other reservoirs, i.e., increasing the baseline density of the drilling fluid.

[0051] For ultra-deepwater and ultra-shallow reservoirs, the pore pressure and fracturing pressure are both raised to very high absolute values ​​by the enormous hydrostatic pressure. This causes the already narrow drilling fluid density window in ultra-shallow reservoirs to become even wider and narrower under the influence of ultra-deepwater conditions. Furthermore, due to the high hydrostatic pressure in ultra-deepwater reservoirs, thicker casing is required, which reduces the maximum curvature of the casing, making directional drilling more difficult.

[0052] In view of this, this application provides a drilling system for ultra-deepwater and ultra-shallow reservoirs to solve the defects of existing casing drilling technology in drilling ultra-deepwater and ultra-shallow reservoirs, such as a narrow drilling fluid safety density window and the inability to accurately achieve directional drilling.

[0053] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0054] like Figures 1 to 5 As shown in the embodiment of this application, the drilling system for ultra-deepwater and ultra-shallow reservoirs includes a derrick 110, a suction base 200, a blowout preventer assembly 400, and a pressure regulating assembly 500.

[0055] The derrick 110 is fixed on the sea surface, and a casing 120 is connected to the derrick 110. The front end of the casing 120 has a drill string 130.

[0056] The suction base frame 200 includes a suction platform 210 and multiple suction piles 220. The multiple suction piles 220 are fixed in the seabed mud layer by the pressure difference inside and outside the suction piles 220. The suction platform 210 is fixed above the multiple suction piles 220. The casing 120 extends into the seabed through the suction platform 210. The suction base frame 200 is configured to provide support to the casing 120 and apply lateral force to the drill string 130 so that the movement path of the drill string 130 forms an inclined angle with the vertical direction, thereby enabling the drill string 130 to reach a preset build-up rate. An annulus 320 is formed between the casing 120 and the wall of the formed wellbore 300.

[0057] The blowout preventer assembly 400 is connected to the outlet end of the annulus 320 and fixed to the suction platform 210;

[0058] The pressure regulating component 500 is connected to the annulus 320 via the blowout preventer component 400, and the pressure regulating component 500 is used to regulate the drilling fluid pressure discharged from the annulus 320.

[0059] In the above technical solution, the derrick 110 can be fixed on the sea surface by the offshore platform 100, and the derrick 110 provides an installation foundation for the casing 120. The suction platform 210 is fixed above the seabed mud layer by the suction piles 220 of the suction base 200, raising the wellhead above the seabed mud layer. The suction base 200 provides support for the casing 120 and lateral force applied by the drill string 130, allowing the drill string 130 to tilt under the action of lateral force and quickly reach the preset build-up rate before entering the wellhead and reaching the seabed mud layer. This enables the construction of the required wellbore (such as a horizontal well) in ultra-deepwater and ultra-shallow reservoirs. Furthermore, by installing a blowout preventer assembly 400 on the suction platform 210, well sealing and blowout prevention are achieved. Simultaneously, by setting up a pressure regulating component 500 to adjust the drilling fluid pressure discharged from the annulus 320, the pressure of the drilling fluid discharged from the annulus 320 is made lower than the pressure of the drilling fluid inside the annulus 320. This results in a pressure gradient between the sea surface and the wellhead being less than the pressure gradient between the wellhead and the bottom of the well, achieving dual-gradient drilling. Furthermore, because the pressure regulating component 500 can regulate the drilling fluid pressure discharged from the annulus 320, the entire drilling system does not require a riser, avoiding the technical problem of a narrow drilling fluid installation density window caused by the use of a riser.

[0060] It should be noted that the surface of the seabed mud layer 10 is the mudline of the seabed. The derrick 110 can control the lowering of the casing 120. If necessary, the derrick 110 can also control the rotation of the casing. For example, a top drive is installed on the derrick 110, and the casing 120 is connected to the top drive. The top drive controls the lowering of the casing 120 to the seabed, so that the lower end of the casing 120 passes through the blowout preventer assembly 400 and the suction platform in sequence, and then into the seabed mud layer. At the same time, the top drive can also control the rotation of the casing 120. Figures 1 to 3 The arrows in the diagram indicate the direction of drilling fluid flow.

[0061] Before installing the suction base frame 200, the casing 120 can be lowered via the derrick 110, and a pilot hole can be drilled using the drill string 130 to form the initial wellbore and obtain the geological data of the initial wellbore. Once the geological data is evaluated and the geological conditions are confirmed to be suitable, the suction base frame 200 can be installed.

[0062] The suction pile 220 is a rigid short pile that uses water pressure to press the pile body into the soil. Its basic structural form is a cylinder that is closed at the top and open at the bottom. When installing the suction base 200, the seawater inside the cylinder is pumped out by a suction pump to reduce the pressure inside the cylinder. This makes the pressure inside the cylinder less than the pressure outside the cylinder. The pressure difference between the pressure inside and outside the cylinder is used to sink the suction pile 220 into the seabed and form a stable anchor.

[0063] The wellhead on the seabed is located on the suction platform 210, which has a guide pipe 310. After the suction pile 220 is anchored in the seabed strata, the guide pipe 310 is connected to the initial wellbore. After the casing 120 passes through the suction platform 210, it enters the initial wellbore through the guide pipe 310. The angle and direction of the guide pipe 310 are precisely calculated to present a preset tilt position (start point), preset tilt direction (azimuth), and preset tilt angle (well inclination angle). The start point is located above the seabed mud layer. When the casing 120 enters the guide pipe 310, the guide pipe 310 provides support for the casing 120. When the drill string 130 at the front end of the casing 120 passes through the guide pipe 310, it will move along the preset tilt position, preset tilt direction, and preset tilt angle of the casing 120, thereby realizing the pre-start of the casing 120. Furthermore, the guide tube 310 on the suction platform 210 provides an external support for the drill string 130, reducing drill string drift and frictional resistance and ensuring directional drilling accuracy. In scenarios prone to wellbore instability, such as deep water and soft formations, the suction base 200 enhances trajectory control. By stabilizing the external support, it reduces the risk of sudden changes in local curvature and improves wellbore quality.

[0064] Furthermore, the pressure regulating component 500 controls the drilling fluid pressure discharged from the annulus 320 by adjusting the flow rate of the drilling fluid discharged from the annulus 320. Specifically, the greater the flow rate of the drilling fluid discharged from the annulus 320, the greater the pressure of the discharged drilling fluid. Since the drilling system of this embodiment does not require the use of a riser, the load on the suction pile 220 can be reduced, and the long-term stability of the suction pile 220 can be improved. For example, if a riser is used, it needs to be connected between the blowout preventer assembly 400 and the offshore platform 100. As the seawater depth increases, the riser becomes longer and heavier. Furthermore, the riser is exposed to seawater and is subjected to periodic lateral forces from wind, waves, and currents. These forces can cause the riser to vibrate and bend. The weight of the riser and the forces it receives are applied to the subsea wellhead through the blowout preventer assembly 400 and transmitted to the suction pile 220. The weight of the riser increases the load on the suction pile 220. The forces on the riser, after being transmitted to the suction pile 220, will generate dynamic bending moments and shear forces, increasing the fatigue risk of the suction pile 220 and thus affecting its long-term stability.

[0065] In some alternative embodiments, an inlet line 550 is provided between the pressure regulating assembly 500 and the blowout preventer assembly 400. By providing the inlet line 550, the position of the pressure regulating assembly 500 can be easily adjusted.

[0066] In some embodiments, the suction base 200 is configured to apply a lateral thrust or a lateral pull to the drill string 130.

[0067] It is understandable that applying lateral thrust or lateral tension to the drill string 130 can change the direction of the drill string 130 and achieve pre-angle preparation of the casing 120.

[0068] In some embodiments, the drilling system for ultra-deepwater and ultra-shallow reservoirs further includes a guide member 131 disposed on the drill string 130. The guide member 131 is configured to guide the drill string 130 to increase the lateral cutting force of the drill string 130 so that the drill string 130 moves along a preset deflection angle.

[0069] By setting the guide member 131, an angle greater than 0 can be made between the axis of the drill string 130 and the axis of the casing 120 (i.e., the axis of the drill string 130 and the axis of the casing 120 do not coincide). In this way, when the drill string 130 rotates, its sidewall faces the guide tube 310 and exerts continuous pressure on it. This causes the guide tube 310 to provide a reaction force of this pressure to the drill string 130 (i.e., the suction base 200 provides a greater lateral thrust to the drill string 130), thereby increasing the lateral cutting force of the drill string 130.

[0070] In some embodiments, the guide 131 includes a guide motor.

[0071] It is understandable that the guide motor has a fixed bending angle. When the guide motor drives the drill string 130 to rotate, the bending angle of the guide motor will cause there to be an angle greater than 0 between the axis of the drill string 130 and the axis of the casing 120.

[0072] In some embodiments, a rotary steerable system (RSS) can also be provided on the drill string 130. The rotary steerable system has a set of controllable push arms inside. When the casing 120 rotates continuously, the push arms of the rotary steerable system will extend rapidly when it rotates to a specific position according to the command, and push against the high side of the guide tube 310, so that the guide tube 310 provides a lateral reaction force to the drill string 130 (that is, the suction base 200 applies a greater lateral pulling force to the drill string 130), thereby causing the drill string 130 to deflect towards the low side of the guide tube 310.

[0073] In some embodiments, the lateral force F provided by the suction base 200 to the drill string 130c Satisfy the following formula:

[0074]

[0075] in:

[0076] η is the force transmission efficiency; the force transmission efficiency is affected by the frictional resistance of the connecting mechanism and the well inclination angle; the force transmission efficiency η takes the value of: 0.65≤η≤0.85;

[0077] F a This represents the maximum anchoring force of the suction base frame;

[0078] A z The area of ​​the bottom of the suction pile;

[0079] σ c This refers to the pressure of the overlying strata.

[0080] H z The embedment depth of the suction pile;

[0081] D is the effective diameter of the suction pile;

[0082] c u It represents the shear strength of the stratum.

[0083] It is understandable that by optimizing the size of the suction base 200, the preset tilt position, preset tilt direction and preset tilt position of the guide tube 310, and the bending angle of the guide member 131 of the drill string 130, precise pre-inclination can be achieved, which is suitable for trajectory control of deep-water large-displacement wells.

[0084] In some embodiments, the build-up rate K during drilling with drill string 130 satisfies the following formula:

[0085]

[0086] in:

[0087] L represents the length of the suction base frame (200mm) and the casing (120mm) below the wellhead.

[0088] EI represents the bending stiffness of the casing at 120mm.

[0089] F c It is a lateral force; determined by the anchoring force of the suction base 200 and the tension of the sleeve 120.

[0090] C is the comprehensive correction coefficient; it is related to formation drillability and wellbore cleanliness. The comprehensive correction coefficient is obtained by inversion based on adjacent well data and the build-up rate model. The value of the comprehensive correction coefficient C is: 0.3≤C≤0.7.

[0091] K g The inherent slope of guide component 131.

[0092] like Figure 5 As shown, in some embodiments, the blowout preventer assembly 400 includes a blowout preventer group 410 and a rotary blowout preventer 420. One end of the blowout preventer group 410 is installed at the outlet end of the annulus 320, and the other end of the blowout preventer group 410 is connected to the rotary blowout preventer 420 through a connecting flange 430. The rotary blowout preventer 420 is sealed to the outer peripheral wall of the sleeve 120, and the pressure regulating assembly 500 is connected to the rotary blowout preventer 420.

[0093] It is understood that the rotary blowout preventer 420 is sealed to the outer peripheral wall of the casing 120, ensuring that the sealed connection between the rotary blowout preventer 420 and the casing 120 is maintained during drilling operations, including both lifting and rotating movements of the casing 120, thereby achieving dynamic sealing of the annulus 320. After the blowout preventer assembly 410 is installed at the outlet end (i.e., the wellhead) of the annulus 320, it can seal the subsea wellhead and prevent blowouts. When abnormally high pressure is detected, the rotary blowout preventer 420 and the blowout preventer assembly 410 work together to quickly close the wellhead, achieving complete sealing and ensuring drilling safety.

[0094] It should be noted that the rotary blowout preventer 420 has a bypass port that connects to the connecting flange 430, and the pressure regulating component 500 is connected to the bypass port, thereby realizing the connection between the pressure regulating component 500 and the annulus.

[0095] In some embodiments, the rotary blowout preventer 420 includes a second housing 421 and a main shaft, a bearing 423, a seal 422, and a hydraulic system disposed within the second housing 421. The bearing 423 is fixed to the second housing 421. One end of the main shaft is detachably connected to the sleeve 120, and the other end of the main shaft is fixed within the bearing 423, allowing the main shaft to rotate relative to the second housing via the bearing 423. The seal 422 is sleeved around the circumference of the sleeve 120. The hydraulic system provides clamping force to the seal 422, enabling the seal 422 to clamp the sleeve 120 and achieve a seal between the rotary blowout preventer 420 and the sleeve 120. A bypass port communicates with one end of the main shaft connected to the bearing 423.

[0096] It is understood that the seal 422 has a through hole at its center, through which the casing 120 can pass. When the casing 120 rotates and is connected to the spindle of the rotating blowout preventer 420, the seal 422 is tightly pressed against the casing 120 under hydraulic pressure, forming an annular seal. The well pressure (including drilling fluid column pressure and formation pressure) acts on the back of the seal 422, enhancing its fit with the casing 120 and achieving a dynamic seal.

[0097] Optionally, the seal 422 can be a rubber core to achieve a rubber core seal.

[0098] like Figure 3As shown, optionally, the hydraulic system includes a circulating pump 425, a hydraulic fluid passage 427, a coolant passage 428, and a hydraulic cylinder 424. The hydraulic pump is used to pump hydraulic oil to the hydraulic cylinder 424 so that the hydraulic cylinder 424 clamps the seal 422, thereby enabling the seal 422 to clamp and seal the bearing 423.

[0099] Optionally, the rotary blowout preventer 420 also includes a cooling and lubrication system that injects coolant and grease into the circulating coolant channel 428 to reduce the temperature of the sealing area, reduce wear on the bearing 423, and thus extend the life of the seal 422.

[0100] Optionally, the rotary blowout preventer 420 also includes a locking ring 426 for securing the rubber core to reduce axial displacement of the rubber core in a high-pressure environment.

[0101] like Figure 1 As shown, in some embodiments, the drill string 130 includes a guide 131, a drive 132, and a drill bit 133 connected sequentially from the rear end to the front end of the casing. The guide 131 is connected to the casing 120, and the drive 132 is configured to provide rotational power to the drill bit 133.

[0102] It is understood that the drive unit 132 can drive the drill bit 133 to rotate, so that the drill bit 133 can break rocks and extend the length of the wellbore.

[0103] In some embodiments, the drill string 130 is also provided with a measurement while drilling tool.

[0104] Measurement while drilling (MSWL) tools monitor wellbore trajectory and formation parameters in real time. This allows for adjustments to the angle of the guide vane 131 and the drilling pressure based on the monitoring data, ensuring the wellbore trajectory meets design requirements.

[0105] In some embodiments, the casing 120 includes a casing string 121, a casing shoe 122, and a casing connector 123, and the drill string 130 is connected to the casing string 121 through the casing connector 123. The casing shoe 122 is disposed at the front end of the casing string 121 and is used to guide the drill string 130 into the wellbore 300.

[0106] like Figure 2 and Figure 4 As shown, in some embodiments, the pressure regulating assembly 500 includes a subsea pump 510 and a flowback line 520. The inlet of the subsea pump 510 is connected to the annulus 320 through the blowout preventer assembly 400, and the outlet of the subsea pump 510 is connected to the flowback line 520. The subsea pump 510 is configured to pump drilling fluid from the annulus 320 into the flowback line 520.

[0107] It is understandable that the subsea pump 510 can actively draw drilling fluid from the annulus 320 and discharge the drawn drilling fluid into the return line 520, from which the drilling fluid is returned to the offshore platform 100. Since the return line 520 is filled with fluid, and the pressure within the return line 520 is determined by the rotational speed and displacement of the subsea pump 510, rather than by the hydrostatic pressure of the fluid column, the pressure at the wellhead can be controlled to a level equivalent to the hydrostatic pressure of seawater by controlling the rotational speed and displacement of the subsea pump 510. This creates a low pressure gradient, making the drilling fluid pressure in the return line 520 lower than the drilling fluid pressure in the annulus 320, thus forming a dual-gradient pressure control.

[0108] like Figure 4 As shown, in some embodiments, the subsea pump 510 includes a pump body 511, a drive module 512, a control unit 513, an outlet pressure sensor 514, and an inlet pressure sensor 515. The inlet pressure sensor 515 is located at the inlet of the pump body 511 and is used to measure the pressure of the drilling fluid in the annulus 320. The outlet pressure sensor 514 is located at the outlet of the pump body 511 and is used to measure the pressure of the drilling fluid in the flowback line 520. The inlet of the pump body 511 is connected to the annulus, and the outlet of the pump body 511 is connected to the flowback line. The drive module 512 is connected to the shaft of the pump body 511, and the control unit 513 is electrically connected to the drive module 512, the inlet pressure sensor 515, and the outlet pressure sensor.

[0109] It can be understood that the inlet of pump body 511 constitutes the inlet of subsea pump 510, the inlet of subsea pump 510 is connected to the aforementioned annulus 320, and the outlet of pump body 511 constitutes the outlet of subsea pump 510. Control unit 513 can receive pressure data obtained from inlet pressure sensor 515 and outlet pressure sensor 514, and issue control commands to drive module 512 based on the obtained pressure data. Drive module 512 controls the rotational speed of pump body 511, thereby adjusting the discharge capacity of pump body 511 and realizing the function of controlling the drilling fluid pressure in return pipeline 520.

[0110] Specifically, assuming the drilling fluid pressure system within the annulus 320 and casing 120 is in a steady-state or static state, the displacement Q of the subsea pump 510 directly affects the hydrostatic pressure P by replacing part of the drilling fluid in the annulus 320 with seawater. Assume the cross-sectional area of ​​the annulus 320 is A. h The drilling fluid density is ρm, and the seawater density is ρ sw The total vertical well depth is H t If the acceleration due to gravity is g, then the relationship between the hydrostatic pressure P and the displacement Q is:

[0111]

[0112] In the formula:

[0113] P0 represents the hydrostatic pressure of the pure drilling fluid when Q=0 is not used (without the use of the subsea pump 510);

[0114] P t This reflects the pressure adjustment caused by the displacement Q of the 510 subsea pump;

[0115] Q represents the displacement of the 510 subsea pump (unit: m³ / s).

[0116] A h The cross-sectional area of ​​the annulus is 320° (unit: m²).

[0117] ρ m ρ is the density of the drilling fluid (unit: kg / m³). sw Seawater density (unit: kg / m³).

[0118] Therefore, it can be seen that the larger the displacement of the pump body 511, the more drilling fluid is replaced, and the greater the decrease in hydrostatic pressure. The rate of decrease in hydrostatic pressure is related to the density difference between the drilling fluid and seawater and the cross-sectional area of ​​the annulus 320.

[0119] It should be noted that the drive module 512 can be a hydraulic motor or an electric motor. The hydraulic oil required by the hydraulic motor or the electricity required by the electric motor can be transmitted from the offshore platform 100 through pipelines. In this embodiment, the drive module 512 is a hydraulic motor.

[0120] In some embodiments, the subsea pump 510 further includes a first housing 517, and a sealing system 518 is provided inside the first housing 517. The pump body 511, drive module 512, control unit 513, inlet pressure sensor 515 and outlet pressure sensor 514 are all sealed inside the first housing 517 by the sealing system 518. The first housing 517 has an inlet and an outlet. The inlet on the first housing 517 is connected to the inlet of the pump body 511, and the outlet on the first housing 517 is connected to the outlet of the pump body 511.

[0121] It should be noted that the sealing system 518 is used to achieve dynamic pressure balance within the first housing 517 to ensure zero liquid leakage. By setting up the first housing 517 and the sealing system 518, the interior of the first housing 517 can be sealed, preventing seawater, silt, etc. from seeping into the interior of the first housing 517 and causing malfunctions in the subsea pump 510.

[0122] In an optional embodiment, the subsea pump further includes a communication module 516, which is electrically connected to the control unit 513. The communication module 516 is used to communicate with the control system installed on the ground or offshore platform 100 to transmit the operating data of the subsea pump 510, such as speed and displacement, to the control system, thereby realizing remote monitoring and control of the subsea pump 510.

[0123] In this embodiment, the communication module 516 communicates via a cable. The cable connects the subsea pump 510 and the offshore platform 100.

[0124] like Figure 2 As shown, in some embodiments, the subsea pump 510 is connected to an anchor block 519. By inserting the anchor block 519 into the seabed mudline, the subsea pump 510 can be fixed to the seabed, preventing the subsea pump 510 from moving significantly and causing the connection between the subsea pump 510 and the blowout preventer assembly 400 to detach, thereby improving the stability of the subsea pump 510.

[0125] Optionally, the anchor block 519 can be attached to the first housing 517 of the subsea pump 510.

[0126] like Figure 3 As shown, in some embodiments, the pressure regulating assembly 500 includes a throttling manifold 530, the inlet of which is connected to the annulus 320 via the blowout preventer assembly 400.

[0127] It is understood that the choke manifold 530 has a choke valve. By adjusting the opening of the choke valve, the flow rate of drilling fluid from the annulus 320 to the choke manifold 530 can be controlled, thereby controlling the pressure of the drilling fluid discharged from the annulus 320 and regulating the bottom hole pressure so that the pressure of the drilling fluid entering the choke manifold 530 is less than the pressure of the drilling fluid in the annulus 320, thus forming a dual-gradient pressure control.

[0128] It should be noted that when the blowout preventer assembly 400 includes a rotary blowout preventer 420, the throttle manifold 530 is connected to the rotary blowout preventer 420.

[0129] In this embodiment, the bottom hole pressure (BHP) satisfies the following formula:

[0130]

[0131] In the formula:

[0132] ΔP a The flow friction pressure in the annulus 320 (unit: Pa);

[0133] ΔP c The back pressure applied to the throttle valve (unit: Pa).

[0134] The back pressure ΔP applied by the throttle valve c It is inversely proportional to the opening A (flow area) of the throttle valve, and satisfies the following formula:

[0135]

[0136] In the formula:

[0137] Q is the flow rate (m³ / s) of the throttling manifold 530.

[0138] C d This is the flow coefficient (related to valve type and fluid characteristics).

[0139] A represents the flow area (m²) corresponding to the throttle valve opening degree.

[0140] Based on the specific operating conditions (such as air intrusion), analyze the corresponding changes in annular flow friction pressure, and adjust the throttle valve opening using a PID control algorithm (decreasing the opening A will increase ΔP). c Increasing the opening A will decrease ΔP. c This keeps the bottom hole pressure (BHP) within a safe density window.

[0141] In some embodiments, to better adjust the opening of the throttle valve, multiple throttle valves connected in series and parallel (series pressure divider, parallel flow divider) are typically provided to form a throttle manifold, which reduces the impact of the opening of a single throttle valve on the overall back pressure and increases the adjustable range of the throttle valve.

[0142] In some embodiments, the drilling system further includes a mud pit 540, which is disposed on the offshore platform 100, and one end of the mud pit 540 is connected to the outlet of the choke manifold 530.

[0143] It is understandable that the drilling fluid in the annulus contains cuttings and impurities. By setting up a mud pit 540, the flowback drilling fluid can be filtered and purified to remove cuttings and impurities. The filtered and purified drilling fluid can then re-enter the well through the casing 120 inlet to achieve drilling fluid recycling.

[0144] It should be noted that the embodiments referred to in the specification, such as "one embodiment," "embodiment," "exemplary embodiment," and "some embodiments," may include specific features, structures, or characteristics, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not, is within the knowledge scope of those skilled in the art.

[0145] Generally speaking, terms should be understood at least in part by their use in context. For example, the term “one or more” as used in the text can be used, at least in part, to describe any feature, structure, or characteristic of the meaning of the singular, or a combination of features, structures, or characteristics of the meaning of the plural, depending on the context.

[0146] It should be readily understood that the terms “on,” “above,” and “on top of” in this application should be interpreted in the broadest possible sense, such that “on” means not only “directly on something” but also “on something” with an intermediate feature or layer therebetween, and that “above” or “on top of” means not only “on something” but also “on something” without an intermediate feature or layer therebetween (i.e., directly on something).

[0147] Furthermore, for ease of explanation, spatially relative terms such as "below," "below," "under," "above," and "above" may be used to describe the relationship of one element or feature relative to other elements or features as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation other than those shown in the figures. The device may have other orientations (rotated 90° or in other orientations), and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0148] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A drilling system for ultra-deepwater and ultra-shallow reservoirs, characterized in that, include: A derrick (110) is fixed on the sea surface, and a casing (120) is connected to the derrick (110). The front end of the casing (120) has a drill string (130). The suction frame (200) includes a suction platform (210) and multiple suction piles (220). The multiple suction piles (220) are fixed in the seabed mud layer by the pressure difference between the inside and outside of the suction piles (220). The suction platform (210) is fixed above the multiple suction piles (220) so that the seabed wellhead is raised above the seabed mud layer. The casing (120) extends into the seabed through the guide pipe (310) on the suction platform (210). The suction frame (200) is configured to provide support to the casing (120) and apply lateral force to the drill string (130) so that the movement path of the drill string (130) forms an inclined angle with the vertical direction, so that the drill string (130) reaches a preset build-up rate before entering the wellhead and reaching the seabed mud layer. An annulus (320) is formed between the casing (120) and the wall of the formed wellbore (300). A blowout preventer assembly (400) is connected to the outlet end of the annulus (320) and fixed to the suction platform (210); The pressure regulating assembly (500) is connected to the annulus (320) through the blowout preventer assembly (400). The pressure regulating assembly (500) is used to regulate the drilling fluid pressure discharged from the annulus (320) so that the drilling fluid pressure discharged from the annulus (320) is less than the drilling fluid pressure inside the annulus (320). It also includes a guide (131) disposed on the drill bit (130) and the guide (131) is configured to guide the drill bit (130) to increase the lateral cutting force of the drill bit (130) so that the drill bit (130) moves along a preset deflection angle.

2. The drilling system for ultra-deepwater and ultra-shallow reservoirs according to claim 1, characterized in that, The suction base (200) is configured to apply a lateral thrust or a lateral pull to the drill bit (130).

3. The drilling system for ultra-deepwater and ultra-shallow reservoirs according to claim 1, characterized in that, The guide (131) includes a guide motor.

4. The drilling system for ultra-deepwater and ultra-shallow reservoirs according to claim 1, characterized in that, The lateral force Fc provided by the suction base (200) to the drill string (130) satisfies the following formula: in: η is the force transmission efficiency; F a This represents the maximum anchoring force of the suction base frame (200); A z The area of ​​the bottom of the suction pile (220); σ c This refers to the pressure of the overlying strata. H z The embedment depth of the suction pile (220); D is the effective diameter of the suction pile (220); c u It represents the shear strength of the stratum.

5. The drilling system for ultra-deepwater and ultra-shallow reservoirs according to claim 4, characterized in that, The build-up rate K during drilling by the drill string (130) satisfies the following formula: in: L is the length of the casing below the wellhead of the suction base (200); EI is the bending stiffness of the sleeve (120); F c It is a lateral force; C is the overall correction factor; K g The inherent slope of the guide member (131).

6. The drilling system for ultra-deepwater and ultra-shallow reservoirs according to claim 1, characterized in that, The blowout preventer assembly (400) includes a blowout preventer group (410) and a rotary blowout preventer (420). One end of the blowout preventer group (410) is installed at the outlet end of the annulus (320), and the other end of the blowout preventer group (410) is connected to the rotary blowout preventer (420) through a connecting flange (430). The rotary blowout preventer (420) is sealed to the outer peripheral wall of the sleeve (120), and the pressure regulating assembly (500) is connected to the rotary blowout preventer (420).

7. The drilling system for ultra-deepwater and ultra-shallow reservoirs according to claim 1, characterized in that, The drill bit (130) includes a guide (131), a drive (132) and a drill bit (133) connected sequentially from the rear end to the front end of the casing (120). The guide (131) is connected to the casing (120), and the drive (132) is configured to provide rotational power to the drill bit (133).

8. The drilling system for ultra-deepwater and ultra-shallow reservoirs according to any one of claims 1-7, characterized in that, The pressure regulating assembly (500) includes a subsea pump (510) and a flowback line (520). The inlet of the subsea pump (510) is connected to the annulus (320) through the blowout preventer assembly (400), and the outlet of the subsea pump (510) is connected to the flowback line (520). The subsea pump (510) is configured to pump drilling fluid from the annulus (320) into the flowback line (520).

9. The drilling system for ultra-deepwater and ultra-shallow reservoirs according to any one of claims 1-7, characterized in that, The pressure regulating assembly (500) includes a throttling manifold (530), the inlet of which is connected to the annulus (320) via the blowout preventer assembly (400).

Images