Marine riser-free slurry circulating system and control method and operation method thereof

Abstract

The invention discloses a mud circulating system based on no marine riser and a control method and an operation method of the mud circulating system, and relates to the technical field of oil and gas drilling. The drilling device comprises a floating drilling platform, a wellhead suction device and a drill column, the upper end of the drill column which is vertically arranged is arranged on the floating drilling platform, and the lower end of the drill column penetrates through the wellhead suction device; the low-pressure slurry treatment system is arranged on the floating drilling platform; the backflow pipeline system comprises a lifting pump, a hard pipe, a first hose and a second hose, the upper end of the vertically-arranged hard pipe is arranged on the drilling ship, a lower inlet of the hard pipe is connected with an outlet of the lifting pump, and the two ends of the first hose are connected with an outlet of the wellhead suction device and an inlet of the lifting pump respectively. Two ends of the second hose are respectively connected with an upper outlet of the hard pipe and an inlet of the low-pressure slurry treatment system. The problem that an existing drilling platform cannot store too many hard pipes can be solved, and the situation that existing hard pipes are prone to distortion and breakage, interference or collision with drill column operation and recovery accidents are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas drilling, and particularly relates to a mud circulation system based on a riserless pipe, and a control method and an operation method thereof. Background Art

[0002] Compared with conventional drilling methods, the riserless mud circulation technology can well match the fracture pressure and the formation pore pressure, effectively control the annulus pressure in the wellbore, and at the same time can simplify the wellbore structure of deep water wells and avoid potential safety hazards caused by multiple layers of casing; moreover, the subsea drilling fluid lift system saves drilling time and cost, reduces pressure hazards, prevents well leakage, and is easier to control the shallow flow layer. Therefore, in oil and gas drilling operations, the riserless mud circulation technology is usually adopted.

[0003] The riserless mud circulation technology generally uses a flexible hose as the return pipeline in a shallow water environment. However, in a deep water environment, a string of rigid pipes connected together is used as the return pipeline, and the current maximum application water depth is about 1500 meters. However, there are many problems in applying to deeper water depths, resulting in the difficulty of popularizing and applying the riserless mud circulation technology in a deeper drilling environment.

[0004] Among them, these problems are mainly manifested in the following aspects: (1) Since a large number of rigid pipes need to be connected into a return pipeline, and the deck operation area of the drilling platform is limited, more rigid pipes cannot be stored. (2) The rigid pipes as the return pipeline and the drill string operate together in the moonpool area. In order to separate the subsea suction module and the subsea pump by a certain distance, the return rigid pipe needs to be obliquely inserted into the seabed at a certain angle, and at the same time, the subsea anchoring module is used to insert into the seabed, which will lead to problems such as difficulty in stably inserting the subsea anchoring module and interference between the rigid pipe and the drill string during operation. (3) When the ship's heading needs to be rotated and adjusted due to the influence of wind and waves, there are problems such as easy twisting and breaking of the return rigid pipe and collision with the drill string. (4) In case of an emergency, it is difficult to safely recover the rigid pipe and the drill string at the same time, so there is a risk of accidents. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention provides a mud circulation system based on a riserless pipe, and a control method and an operation method thereof, which can solve the problem that there is not enough space on the deck of the existing drilling platform to store too many rigid pipes, and can avoid the situations that the existing rigid pipes are prone to twisting and breaking, interference or collision with the drill string during drilling, and recovery accidents, and helps to improve the operation efficiency.

[0006] A first aspect embodiment of the present invention provides a mud circulation system based on a riserless pipe, which includes: A drilling device, which includes a floating drilling platform, a wellhead suction device, and a drill string. The drill string is vertically arranged. The upper end of the drill string is provided on the floating drilling platform, and the lower end of the drill string passes through the wellhead suction device; A drilling ship; A low-pressure mud treatment system, which is provided on the floating drilling platform; A return pipeline system, which includes a lift pump, a rigid pipe, a first hose, and a second hose. The rigid pipe is vertically arranged. The upper end of the rigid pipe is provided on the drilling ship. The lower inlet of the rigid pipe is connected to the outlet of the lift pump. One end of the first hose is connected to the outlet of the wellhead suction device, and the other end is connected to the inlet of the lift pump. One end of the second hose is connected to the upper outlet of the rigid pipe, and the other end is connected to the inlet of the low-pressure mud treatment system.

[0007] The mud circulation system based on the riserless according to the embodiment of the first aspect of the present invention has at least the following beneficial effects: The drill string and the rigid pipe are respectively arranged corresponding to the floating drilling platform and the drilling ship. The two ends of the first hose are respectively connected to the outlet of the wellhead suction device and the inlet of the lift pump. The two ends of the second hose are respectively connected to the upper outlet of the rigid pipe and the inlet of the low-pressure mud treatment system. Then, the lower inlet of the rigid pipe is connected to the outlet of the lift pump, so as to form a mud return pipeline. When the drilling device is operating, the wellhead suction device can suck and collect the mud returned from the wellbore. Then, under the action of the lift pump, the mud is promoted to flow out of the wellhead suction device and flows through the first hose, the lift pump, the rigid pipe, and the second hose in sequence, and finally flows to the low-pressure mud treatment system, so that the mud returns from the seabed to the floating drilling platform, realizing the mud circulation function without a riser.

[0008] The present invention adopts the combination of a floating drilling platform and a drilling ship to separately arrange the drill string and the rigid pipe, both of which are in a vertical state, effectively increasing the horizontal distance between the drill string and the rigid pipe. In this way, it can avoid the problems that the drill string and the rigid pipe are prone to interference and collision during the drilling operation, and it is difficult to safely recover the drill string and the rigid pipe in case of emergencies. At the same time, it can prevent the rigid pipe from being easily twisted and broken when the ship's heading needs to be adjusted due to the influence of wind and waves. Also, it solves the problem that the existing drilling platform cannot store too many rigid pipes due to the small deck operation area, thereby greatly reducing the operation risk, improving the operation efficiency, and promoting the wide use of the riserless mud circulation technology in a deeper ocean drilling environment.

[0009] In some embodiments of the present invention, the drilling ship has a high-pressure mud manifold, and the return pipeline system further includes a first control valve, a second control valve, and a three-way manifold. The three-way manifold has three pipe interfaces, and the three pipe interfaces are respectively connected to the upper outlet of the rigid pipe, the inlet of the second flexible pipe, and the outlet of the high-pressure mud manifold. The first control valve is arranged at the upper outlet of the rigid pipe, and the second control valve is arranged at the outlet of the high-pressure mud manifold.

[0010] In some embodiments of the present invention, the mud circulation system without a riser further includes a control system. The control system is electrically connected to the first control valve, the second control valve, and the lift pump respectively. The control system can control the first control valve and the lift pump to open during the mud return condition, and at the same time control the second control valve to close, and can control the second control valve to open during the supply condition, and at the same time control the first control valve and the lift pump to close.

[0011] In some embodiments of the present invention, a plurality of first buoyancy blocks are arranged along the extending direction of the first flexible pipe; and / or, A plurality of second buoyancy blocks are arranged along the extending direction of the second flexible pipe.

[0012] In some embodiments of the present invention, the drilling ship has a drill pipe, a first derrick, and a first top drive. The drill pipe is set as the rigid pipe, the first top drive is drivingly connected to the rigid pipe, and the first top drive is slidably connected to the first derrick in the up and down direction to drive the rigid pipe to lift and lower; the drilling ship has a heave compensation system, and the heave compensation system is used to compensate for the heave movement of the rigid pipe.

[0013] In some embodiments of the present invention, a plurality of pipe fixing devices are arranged along the extending direction of the rigid pipe, and the plurality of pipe fixing devices are detachably connected to the first flexible pipe.

[0014] In some embodiments of the present invention, the pipe fixing device includes a bracket, a first pin, and a connecting rod. The bracket is U-shaped, one end of the connecting rod is hinged to one end of the bracket, and first jacks are provided at the other end of the bracket and the other end of the connecting rod. The first pin can be inserted into all the first jacks so that the connecting rod and the bracket jointly form a fixing cavity for fixing the first flexible pipe.

[0015] In some embodiments of the present invention, the pipe fixing device further includes a second pin. The connecting rod is horizontally arranged, the first pin and the second pin are vertically arranged, and second jacks are provided at one end of the bracket and one end of the connecting rod. The second pin can be inserted into all the second jacks so that one end of the connecting rod is hinged to one end of the bracket.

[0016] The second aspect of the present invention provides a control method for a mud circulation system based on a riserless system, which is applied to the mud circulation system based on a riserless system as described in the first aspect, and includes the following steps: After receiving the input command, determine the current operating condition; If the current operating condition is the mud reflux condition, control the first control valve and the lift pump to open, and control the second control valve to close; If the current operating condition is the replenishment condition, control the second control valve to open, and control the first control valve and the lift pump to close.

[0017] According to the control method for a mud circulation system based on a riserless system in the second aspect of the present invention, it has at least the following beneficial effects: According to the command input by the user, determine the current operating condition of the mud circulation system based on a riserless system; if it is determined that the mud circulation system based on a riserless system is in the mud reflux condition, ensure that the lift pump and the first control valve are in the open state, and the second control valve is in the closed state, so as to promote the mud to return from the seabed to the low-pressure mud treatment system on the floating drilling platform through the reflux pipeline system, realizing the mud circulation operation without a riser; if it is determined that the mud circulation system based on a riserless system is in the replenishment condition, ensure that the second control valve is in the open state, and the lift pump and the first control valve are in the closed state, so as to promote the replenishment liquids such as mud, cement slurry, and drilling water on the drilling ship to be transported from the high-pressure mud manifold to the low-pressure mud treatment system on the floating drilling platform through the second hose, thereby completing the replenishment work.

[0018] With such a design, it is possible to adjust the working states of the first control valve, the second control valve, and the lift pump according to the change of the operating condition, so as to promote the mud circulation system based on a riserless system to switch between the mud reflux condition and the replenishment condition.

[0019] The third aspect of the present invention provides an operation method for a mud circulation system based on a riserless system, which is applied to the mud circulation system based on a riserless system as described in the first aspect, and includes the following steps: Drive the wellhead suction device to move downward and install it on the wellhead, and drive the drill string on the floating drilling platform to drill into the wellhead suction device; Drive the drilling ship to sail a first distance in the direction close to the floating drilling platform, and drive the rigid pipe to drive the lift pump and the first hose to move downward a second distance, and connect the second hose to the low-pressure mud treatment system; After the first hose moves downward a second distance, drive the ROV to disassemble the first hose from the pipe fixing device and connect the first hose to the wellhead suction device; After the first hose and the second hose are installed, drive the drilling ship to sail a third distance away from the floating drilling platform, and drive the rigid pipe to drive the lift pump to move down a fourth distance; Turn on the heave compensation system on the drilling ship, and drive the rigid pipe to drive the lift pump to move down to the seabed; Start the lift pump to carry out the mud return operation condition.

[0020] According to the operation method of the riserless mud circulation system according to the third aspect embodiment of the present invention, it has at least the following beneficial effects: when the floating drilling platform is positioned relative to the wellhead on the sea surface, move the wellhead suction device downward from the floating drilling platform and set it at the wellhead, then move the drill string downward and screw it into the wellhead suction device, so that the drill string can carry out drilling operations at the wellhead. During this process, the wellhead suction device can suck and collect the mud returning from the wellbore; drive the drilling ship closer to the floating drilling platform to reduce the horizontal distance between the drilling ship and the floating drilling platform, so as to install the second hose on the low-pressure mud treatment system on the floating drilling platform. Moreover, after the rigid pipe drives the lift pump and the first hose to move down a second distance, use the ROV to remove the first hose from the pipe fixing device on the rigid pipe at the seabed, so as to install the first hose on the wellhead suction device. At this time, the work of connecting the return pipeline system to the wellhead suction device and the low-pressure mud treatment system respectively has been completed.

[0021] Then, drive the drilling ship away from the floating drilling platform to increase the horizontal distance between the drilling ship and the floating drilling platform to avoid interference and collision between the drill string and the rigid pipe; then, after the position of the drilling ship on the sea surface is confirmed, drive the rigid pipe to drive the lift pump to move down to an appropriate height position from the seabed, start the heave compensation system on the drilling ship, and then drive the rigid pipe to drive the lift pump to continue to move down until the lift pump is located on the seabed. At this time, through the action of the heave compensation system, the wave heave compensation function of the riserless mud circulation system can be realized, avoiding the problem of the rigid pipe being pulled and damaged in the case of strong wind and waves, and ensuring that the riserless mud circulation system can carry out drilling operations smoothly. When the return pipeline system is installed and the positions of the lift pump and the rigid pipe are set, the lift pump can be operated to carry out the mud return process during the drilling process.

[0022] Other features and advantages of the present invention will be described in the following specification, and, in part, will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained by the structures specifically pointed out in the specification, the claims, and the drawings. Brief Description of the Drawings

[0023] Figure 1It is a schematic structural diagram of a mud circulation system based on a riserless pipe when the first hose and the second hose are in a non-use state according to an embodiment of the present invention; Figure 2 It is a schematic structural diagram of a mud circulation system based on a riserless pipe when the first hose and the second hose are installed according to an embodiment of the present invention; Figure 3 It is a schematic structural diagram of a mud circulation system based on a riserless pipe when performing a mud reflux operation condition according to an embodiment of the present invention; Figure 4 It is a schematic structural diagram of a pipe fixing device from a top view angle according to an embodiment of the present invention; Figure 5 It is a specific flow schematic diagram of a control method for a mud circulation system based on a riserless pipe according to an embodiment of the present invention; Figure 6 It is a specific flow schematic diagram of an operation method for a mud circulation system based on a riserless pipe according to an embodiment of the present invention.

[0024] Reference numerals: 110, floating drilling platform; 120, drill string; 130, wellhead suction device; 140, second derrick; 150, second top drive; 200, wellbore; 310, drilling ship; 320, first derrick; 330, first top drive; 410, rigid pipe; 420, lift pump; 430, first hose; 440, first buoyancy block; 450, pipe fixing device; 451, bracket; 452, connecting rod; 453, first pin; 454, second pin; 455, U-bolt; 456, connecting plate; 460, three-way manifold; 470, second hose; 480, second buoyancy block; 510, high-pressure mud manifold; 520, low-pressure mud treatment system. Detailed Description of the Invention

[0025] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described by referring to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0026] In the description of the present invention, it should be understood that the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0027] In the description of the present invention, it should be noted that, unless otherwise clearly specified and defined, the terms "connected" and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] Conventional drilling techniques generally adopt the single-gradient drilling method. However, during deepwater drilling, there is a problem of too narrow formation pressure gap, so a multi-layer casing system must be adopted, and the drillable water depth and well depth limit are restricted by various factors. At the same time, the large and long riser system is very complex in force under harsh marine environments, which is prone to causing drilling accidents.

[0029] The riserless mud recovery system (RMR), as a kind of dual-gradient drilling technology, does not use the conventional marine riser during drilling. Instead, it uses a subsea suction module to divert the cuttings and drilling fluid returned from the wellbore annulus, and under the action of a subsea pump, returns them to the drilling platform from the seabed through a small-diameter return pipeline, thereby realizing the riserless drilling fluid circulation.

[0030] Compared with the conventional drilling method, the riserless mud recovery system can well match the fracture pressure and the formation pore pressure, effectively control the annulus pressure in the wellbore, and at the same time can simplify the wellbore structure of deep wells and avoid the potential safety hazards brought by multi-layer casings. Moreover, the subsea drilling fluid lifting system saves the drilling time and cost, reduces the pressure risk, prevents well leakage, and is also easier to control the shallow flow layer. Therefore, the riserless mud recovery system is usually adopted in offshore oil and gas drilling operations.

[0031] The riserless mud recovery system generally uses a flexible pipe as the return pipeline in shallow water environments. However, in deepwater environments, a string of rigid pipes connected together is used as the return pipeline, and the current maximum application water depth is about 1500 meters. However, for deeper water depth applications, the riserless mud recovery system has many problems as follows, which makes it difficult to promote and apply the riserless mud recovery system in deeper offshore drilling environments.

[0032] Specifically, these problems mainly include: (1) Since a large number of rigid pipes need to be connected into a return pipeline, and the deck operation area of the drilling platform is limited, more rigid pipes cannot be stored on the drilling platform. (2) The rigid pipes serving as the return pipeline and the rigid pipes serving as the drill string operate together in the moonpool area, that is, there are two rigid pipes from the sea surface to the seabed in the moonpool area. In order to separate the subsea suction module and the subsea pump by a certain distance, generally, the return rigid pipe needs to be inserted obliquely into the seabed at a certain inclination angle, and at the same time, the subsea anchoring module is inserted into the seabed, which will lead to problems such as the subsea anchoring module being difficult to stably insert into the seabed and interference in the operation of the double-pipe string. (3) When the bow direction of the ship needs to be rotated and adjusted due to the influence of wind and waves, there are problems such as the return rigid pipe being prone to twist and break and colliding with the drill string. (4) In the event of an emergency, it is very difficult to safely recover the two pipe strings at the same time, so there is an accident risk.

[0033] Based on the above technical problems, the present invention provides a riserless mud circulation system, its control method and operation method, which can solve the problem that the deck operation area of the existing drilling platform is small and too many rigid pipes cannot be stored, and can avoid the situation that the existing rigid pipes are prone to twist and break, interfere with or collide with the drill string operation, and recovery accidents during the drilling process, which is beneficial to reducing the operation risk and improving the operation efficiency, and finally realizes that the riserless mud circulation technology can be popularized and applied in a deeper ocean drilling environment.

[0034] The following refers to Figures 1 to 6 Describe the riserless mud circulation system, its control method and operation method provided according to the embodiments of the present invention.

[0035] As Figures 1 to 4 shown, the riserless mud circulation system according to the first aspect embodiment of the present invention can be applied to work such as ocean scientific drilling, deep-sea oil and gas exploration and development, and natural gas hydrate exploitation, and perform riserless drilling fluid circulation work during the drilling process.

[0036] As Figures 1 to 3 shown, the riserless mud circulation system of this embodiment includes a drilling device, a drilling ship 310, a low-pressure mud treatment system 520, and a return pipeline system.

[0037] The drilling device includes a floating drilling platform 110, a wellhead suction device 130, and a drill string 120. Among them, the drill string 120 is arranged vertically, that is, the length of the drill string 120 extends along the up and down directions. The upper end of the drill string 120 is provided on the floating drilling platform 110. The drill string 120 can move with the floating drilling platform 110 on the sea surface, enabling the floating drilling platform 110 to drive the drill string 120 to move to an appropriate position for drilling work. The lower end of the drill string 120 penetrates through the wellhead suction device 130.

[0038] It can be understood that in one embodiment, the floating drilling platform 110 is a semi-submersible drilling platform; in another embodiment, the floating drilling platform 110 is a drillship. The wellhead suction device 130 is arranged on the floating drilling platform 110 before drilling work is carried out. It can move with the floating drilling platform 110. The wellhead suction device 130 is lowered through a winch on the floating drilling platform 110 and is correspondingly arranged at the wellhead on the seabed. The wellhead suction device 130 can be used to suck and collect the mud returning from the wellbore 200.

[0039] A second derrick 140 and a second top drive 150 are provided on the floating drilling platform 110. The second top drive 150, as a top drive drilling device, is installed in the top area of the second derrick 140 through a guide pulley assembly. The second top drive 150 is drivingly connected to the drill string 120. When the second top drive 150 is operating, it can drive the drill string 120 to rotate. The second derrick 140 can provide structural support for the second top drive 150, bearing its own weight and the load of the drill string 120. The second top drive 150 can move up and down along the guide rail provided inside the second derrick 140 to realize the lifting control of the drill string 120. The floating drilling platform 110 belongs to the prior art, while the second derrick 140, the second top drive 150, and the drill string 120 are auxiliary equipment on the floating drilling platform 110. Those skilled in the art should understand their specific structures, connection relationships, and working principles, which will not be elaborated here.

[0040] When drilling work is carried out on the drill string 120 on the floating drilling platform 110, the wellhead suction device 130 is mainly arranged at the wellhead, and moreover, the drill string 120 penetrates through the wellhead suction device 130. At this time, the drill string 120 serves as a drilling fluid circulation channel, capable of delivering the mud to the bottom of the well. Then, the mud carrying cuttings will be purified through the wellhead suction device 130 (or called the wellhead suction module, subsea suction module). The wellhead suction module can use devices such as cyclone separation to remove impurities. Specifically, the cuttings and drilling fluid returning from the annulus of the wellbore 200 are separated, which helps to maintain the pressure balance of the drilling fluid closed-loop circulation system.

[0041] In this embodiment, the drilling ship 310 is a small drilling ship, and the drilling ship 310 is located on one side of the floating drilling platform 110 in the left-right direction. When the floating drilling platform 110 is performing offshore construction operations, the drilling ship 310 can act as a supply ship to provide escort, personnel rotation, material supply, etc. beside the floating drilling platform 110.

[0042] The low-pressure mud treatment system 520 is provided on the floating drilling platform 110. It can be understood that the low-pressure mud treatment system 520 can play roles such as waste liquid treatment and recycling purification, waste classification treatment, and well pressure control. For example, the low-pressure mud treatment system 520 can receive waste mud, drill cuttings, and waste liquid generated during drilling, and achieve barge transportation and purification treatment through a closed cycle; perform classified solid-liquid separation through equipment such as vibrating screens, desanders, and desilters to reduce the solid content and maintain the rheological properties of the mud; ensure that the treated mud can be reinjected into the drilling cycle by adjusting parameters such as density and viscosity, reducing resource waste. Another example is that the low-pressure mud treatment system 520 can adjust the density of the mud to balance the formation pressure and effectively prevent accidents such as blowouts or losses.

[0043] The low-pressure mud treatment system 520 is a prior art and is an important part of the mud circulation system in drilling operations. It can achieve the functions of mud purification, recovery, and preparation. Those skilled in the art should understand its specific structure and working principle, and will not be elaborated here.

[0044] The function of the return pipeline system is to connect the wellhead suction device 130 and the low-pressure mud treatment system 520, so that the mud at the wellhead suction device 130 can return to the low-pressure mud treatment system 520 through the return pipeline system. The return pipeline system includes a lift pump 420, a rigid pipe 410, a first hose 430, and a second hose 470.

[0045] Among them, the rigid pipe 410 is arranged vertically, that is, the length of the rigid pipe 410 extends along the up-down direction. The upper end of the rigid pipe 410 is provided on the drilling ship 310. The rigid pipe 410 can move on the sea surface following the drilling ship 310, enabling the drilling ship 310 to drive the rigid pipe 410 to move to an appropriate position so that there is an appropriate safety distance between the rigid pipe 410 and the drill string 120. The lower end of the rigid pipe 410 is fixedly connected to the lift pump 420, and the lift pump 420 can move together with the rigid pipe 410. The lower inlet of the rigid pipe 410 is connected to the outlet of the lift pump 420. The rigid pipe 410 has a pipe cavity, and the pipe cavity is communicated with the outlet of the lift pump 420, so that the mud pumped by the lift pump 420 can flow upward through the pipe cavity of the rigid pipe 410. The rigid pipe 410 can be made of, but not limited to, titanium alloy or alloy steel and other materials.

[0046] One end of the first hose 430 is connected to the outlet of the wellhead suction device 130, and the other end of the first hose 430 is connected to the inlet of the lift pump 420, such that the lumen of the first hose 430 can be respectively communicated with the outlet of the wellhead suction device 130 and the inlet of the lift pump 420. Thus, the mud at the wellhead suction device 130 can flow through the first hose 430 to the lift pump 420, and then, through the pumping action of the lift pump 420, the mud can flow upward along the extending direction of the rigid pipe 410. One end of the second hose 470 is connected to the upper outlet of the rigid pipe 410, and the other end of the second hose 470 is connected to the inlet of the low-pressure mud treatment system 520, such that the lumen of the second hose 470 can be respectively communicated with the rigid pipe 410 and the low-pressure mud treatment system 520. Therefore, the mud at the rigid pipe 410 can flow through the second hose 470 to the low-pressure mud treatment system 520, thereby enabling the mud to return from the wellhead suction device 130 to the low-pressure mud treatment system 520.

[0047] By means of the lowering method, the rigid pipe 410, the lift pump 420, and the first hose 430 are lowered to an appropriate position in the seawater, while both the low-pressure mud treatment system 520 and the upper outlet of the rigid pipe 410 are located above the sea surface. Thus, the first hose 430 is underwater and the second hose 470 is above the water surface.

[0048] The first hose 430 is detachably connected to the wellhead suction device 130, and the second hose 470 is detachably connected to the low-pressure mud treatment system 520. Therefore, after the first hose 430 and the second hose 470 are detached, the drilling ship 310 can move arbitrarily on the sea surface with the return pipeline system.

[0049] In this embodiment, a double-ship operation mode is adopted, the wellhead suction device 130 and the drill string 120 are arranged at the floating drilling platform 110, and the return pipeline system is arranged at the drilling ship 310, so as to decouple the drilling device from the return pipeline system. Therefore, it can solve the problem in the prior art that the deck operation area of the drilling platform is small and not enough rigid pipes 410 can be stored, which further leads to the inability to popularize and apply the mud circulation technology without a riser in a deeper ocean drilling environment.

[0050] Moreover, since there is a sufficient horizontal distance between the drill string 120 and the rigid pipe 410, it can solve the problems in the prior art that it is difficult for the subsea anchoring module to be stably inserted into the seabed and there is operation interference between the drill string 120 and the rigid pipe 410, and it can also solve the problems that when the ship's bow direction needs to be rotated and adjusted due to the influence of wind and waves, the rigid pipe 410 is twisted and broken or the rigid pipe 410 collides with the drill string 120. Moreover, it can also safely recover the drill string 120 and the rigid pipe 410 simultaneously in case of an emergency, avoiding a collision accident between the drill string 120 and the rigid pipe 410 during the recovery process.

[0051] Generally, the daily operating cost of the drilling ship 310 is about one-tenth of that of the drilling rig, with relatively low costs. Therefore, when the drilling rig uses the mud circulation technology without a riser for drilling operations, the drilling ship 310 can not only function as a supply ship but also serve as a carrier ship for the return pipeline system.

[0052] It can be understood that in the mud circulation system based on a riserless pipe provided in the first aspect embodiment of the present invention, the drill string 120 and the rigid pipe 410 are respectively arranged corresponding to the floating drilling platform 110 and the drilling ship 310. The two ends of the first hose 430 are respectively connected to the outlet of the wellhead suction device 130 and the inlet of the lift pump 420, and the two ends of the second hose 470 are respectively connected to the upper outlet of the rigid pipe 410 and the inlet of the low-pressure mud treatment system 520. Then, the lower inlet of the rigid pipe 410 is connected to the outlet of the lift pump 420, thereby forming a mud return pipeline. During the operation of the drilling rig, the wellhead suction device 130 can suck and collect the mud returned from the wellbore 200. Then, under the action of the lift pump 420, the mud is forced to flow out of the wellhead suction device 130 and sequentially passes through the first hose 430, the lift pump 420, the rigid pipe 410, and the second hose 470, and finally flows to the low-pressure mud treatment system 520, enabling the mud to flow back from the seabed to the floating drilling platform 110, realizing the mud circulation function without a riser.

[0053] The present invention adopts a combination of a floating drilling platform 110 and a drilling ship 310 to separately arrange the drill string 120 and the rigid pipe 410 in a vertical state, effectively increasing the horizontal distance between the drill string 120 and the rigid pipe 410. In this way, it can avoid the problems that the drill string 120 and the rigid pipe 410 are prone to interference and collision during drilling operations, and it is difficult to safely recover the drill string 120 and the rigid pipe 410 in case of emergencies. It can also prevent the rigid pipe 410 from being easily twisted and broken when the ship's heading needs to be adjusted due to the influence of wind and waves. At the same time, it also solves the problem that the existing drilling platform cannot store too many rigid pipes 410 due to the small deck working area, thereby greatly reducing the operation risk, improving the operation efficiency, and promoting the wide use of the mud circulation technology without a riser in a deeper ocean drilling environment.

[0054] In some embodiments, as Figures 1 to 3 shown, the drilling ship 310 is equipped with a high-pressure mud manifold 510. Moreover, the return pipeline system further includes a first control valve, a second control valve, and a three-way manifold 460. Among them, the three-way manifold 460 has three pipe interfaces, which are respectively connected to the upper outlet of the rigid pipe 410, the inlet of the second hose 470, and the outlet of the high-pressure mud manifold 510. The first control valve is provided at the upper outlet of the rigid pipe 410, and the second control valve is provided at the outlet of the high-pressure mud manifold 510.

[0055] It is understandable that the three-way pipe manifold 460 is fixedly installed on the upper part of the rigid pipe 410 and can move along with the rigid pipe 410. Two of the pipe interfaces of the three-way pipe manifold 460 are directly connected to the upper outlet of the rigid pipe 410 and the inlet of the second flexible pipe 470 respectively, and the other pipe interface of the three-way pipe manifold 460 is connected to the outlet of the high-pressure mud pipe manifold 510 through a flexible pipe. The high-pressure mud pipe manifold 510 can transport the supply fluids such as mud, cementing fluid, and drilling water for replenishment on the drilling ship 310 to the low-pressure mud treatment system 520 on the floating drilling platform 110 through the second flexible pipe 470.

[0056] Of course, in other embodiments, it is not excluded that two of the pipe interfaces of the three-way pipe manifold 460 are directly connected to the inlet of the second flexible pipe 470 and the outlet of the high-pressure mud pipe manifold 510 respectively, and the other pipe interface of the three-way pipe manifold 460 is connected to the upper outlet of the rigid pipe 410 through a flexible pipe.

[0057] The first control valve is used to control the opening and closing state of the upper outlet of the rigid pipe 410, and the second control valve is used to control the opening and closing state of the outlet of the high-pressure mud pipe manifold 510. The first control valve and the second control valve can be manual valves or electric valves. In this embodiment, the first control valve and the second control valve are selected as electric valves, and the on-off states of the first control valve and the second control valve can be remotely controlled to realize the switch control functions of the first control valve and the second control valve. By switching the states of the first control valve and the second control valve, the inlet of the second flexible pipe 470 can be connected to the upper outlet of the rigid pipe 410 or the outlet of the high-pressure mud pipe manifold 510, so that it is possible to select to transport the mud returned from the seabed to the drilling device for the mud reflux working condition; or select to transport the mud flowing out of the high-pressure mud pipe manifold 510 to the drilling device for the replenishment working condition.

[0058] Furthermore, the mud circulation system without a riser further includes a control system. The control system is electrically connected to the first control valve, the second control valve, and the lifting pump 420 respectively, and the control system can send control commands to the first control valve, the second control valve, and the lifting pump 420 to control their opening and closing states.

[0059] When in the mud reflux working condition, the control system can control the first control valve and the lifting pump 420 to open, and at the same time control the second control valve to close, so that the mud at the wellbore 200 flows through the wellhead suction device 130, the first flexible pipe 430, the lifting pump 420, the rigid pipe 410, the three-way pipe manifold 460, and the second flexible pipe 470 in sequence under the operation of the lifting pump 420 and the wellhead suction device 130, and finally flows to the low-pressure mud treatment system 520; during this process, since the second control valve is closed, it is possible to prevent the supply fluid at the high-pressure mud pipe manifold 510 from flowing to the low-pressure mud treatment system 520, thereby avoiding the problem of unstable mud reflux working condition.

[0060] Moreover, the control system can control the second control valve to open during the replenishment operation, and at the same time control the first control valve and the lift pump 420 to close, so as to prompt the replenishment liquid at the high-pressure mud manifold 510 to flow through the three-way manifold 460 and the second hose 470 in sequence, and finally flow to the low-pressure mud treatment system 520; during this process, since both the first control valve and the lift pump 420 are in the closed state, the replenishment operation can be prevented from being affected by the mud reflux operation.

[0061] It can be understood that the control system can be, but is not limited to, the upper computer, the central control computer of the drilling ship 310, or a handheld terminal device such as a controller. By adopting the above setting method, the real-time switching of the double-operation conditions of mud circulation and material replenishment can be realized.

[0062] In some embodiments, as Figures 1 to 3 shown, a plurality of first buoyancy blocks 440 are provided along the extending direction of the first hose 430. A plurality of second buoyancy blocks 480 are provided along the extending direction of the second hose 470.

[0063] It can be understood that the number of the first buoyancy blocks 440 and the number of the second buoyancy blocks 480 can be selected according to actual needs and are not specifically limited herein. The first buoyancy blocks 440 can be fixed on the first hose 430 by binding, and the second buoyancy blocks 480 can be fixed on the second hose 470 by binding. The materials of the first buoyancy blocks 440 and the second buoyancy blocks 480 are not limited and can be, but are not limited to, made of existing composite foam buoyancy materials or hollow glass microsphere-reinforced epoxy resin-based materials.

[0064] The setting of the first buoyancy blocks 440 can enhance the buoyancy effect of the first hose 430 underwater, so that it is easy to carry the first hose 430 by an existing ROV (Remotely Operated Vehicle) and install the first hose 430 at the outlet of the wellhead suction device 130. The setting of the second buoyancy blocks 480 can enhance the buoyancy effect of the second hose 470 on the water surface, enabling the second hose 470 to float on the sea surface and reducing the pulling forces on the low-pressure mud treatment system 520 and the three-way manifold 460 at both ends of the second hose 470.

[0065] In some embodiments, as Figures 1 to 3 shown, the drilling ship 310 has a drill pipe, and the drill pipe is provided as a hard pipe 410. It can be understood that in this embodiment, the existing drill pipe on the drilling ship 310 is directly used as the hard pipe 410 to provide a mud return channel, without the need for separate research, development, manufacturing or purchase, thus saving costs.

[0066] Further, the drilling ship 310 is provided with a first derrick 320 and a first top drive 330. The first top drive 330 is drivingly connected to the hard pipe 410, and the first top drive 330 is slidably connected to the first derrick 320 in the vertical direction to drive the hard pipe 410 to move up and down. Specifically, the first top drive 330 can be installed in the top area of the first derrick 320 through a guide pulley assembly. The first derrick 320 can provide a supporting effect for the first top drive 330, and the first top drive 330 can move up and down along the guide rail arranged inside the first derrick 320 to realize the lifting control of the hard pipe 410.

[0067] It can be understood that the first derrick 320, the drill pipe and the first top drive 330 are auxiliary equipment of the drilling ship 310. Those skilled in the art should understand their specific structures, connection relationships and working principles, which will not be elaborated here. By directly using the existing automated processing equipment such as the power catwalk, the iron roughneck, the first derrick 320 and the first top drive 330 on the drilling ship 310, the rapid disassembly, lowering and recovery of the hard pipe 410 can be realized, greatly saving costs and improving the operation efficiency and safety.

[0068] Furthermore, the drilling ship 310 is equipped with a heave compensation system, and the function of the heave compensation system is to compensate for the heave movement of the hard pipe 410.

[0069] It can be understood that in the prior art, in order to overcome the heave effect of the sea waves, a sleeve telescopic structure design is usually adopted in the subsea anchoring module to realize simple heave compensation. However, in the case of large wind and waves and a long-lasting heave effect, the telescopic sleeve is likely to be damaged, or the heave compensation speed cannot keep up, resulting in the pulling damage of the return hard pipe 410. Based on this, in this embodiment, the existing heave compensation system on the drilling ship 310 is directly used to enable underwater equipment such as the lifting pump 420 and the hard pipe 410 to overcome the heave effect of the sea waves, and be able to stably sit on the seabed for safe operation, thereby realizing the heave compensation function of the riserless mud circulation system.

[0070] The heave compensation system is a prior art, and it can be selected as hydraulic type, active type, passive type or semi-active type. As a key equipment of the drilling ship 310, the heave compensation system can be used to block the influence of the movement of the hull under the action of waves on the hard pipe 410 and compensate for the heave of the hard pipe 410. No structural improvement is made to the heave compensation system in this embodiment, and those skilled in the art should understand its specific structure and working principle, which will not be elaborated here.

[0071] Similarly, the floating drilling platform 110 is equipped with a heave compensation device. The main function of the heave compensation device is to block the influence of the movement of the hull under the action of waves on the drill string 120, compensate for the heave of the drill string 120, reduce the wear between the drill string 120 and the blowout preventer, and ensure the safety and reliability of the drilling operation.

[0072] In some embodiments, as Figures 1 to 3 shown, along the extending direction of the rigid pipe 410, a plurality of pipe fixing devices 450 are provided. The pipe fixing devices 450 are fixedly connected to the rigid pipe 410 and can move along with the rigid pipe 410. Moreover, the plurality of pipe fixing devices 450 are detachably connected to the first flexible pipe 430.

[0073] It can be understood that the function of the pipe fixing device 450 is to firmly fix the first flexible pipe 430 on the rigid pipe 410. The first flexible pipe 430 can extend along the length direction of the rigid pipe 410, so that it can be avoided that the first flexible pipe 430 is easily affected by sea waves and swings arbitrarily during the lowering process of the rigid pipe 410, the lifting pump 420 and the first flexible pipe 430, which may cause damage to the lifting pump 420 or result in unstable states of the rigid pipe 410, the lifting pump 420 and even the drilling ship 310. Thus, the safe lowering operation of the rigid pipe 410, the lifting pump 420 and the first flexible pipe 430 can be realized. The number of the pipe fixing devices 450 can be selected according to actual requirements and is not specifically limited herein.

[0074] During the lowering, the first flexible pipe 430 is fixed on the rigid pipe 410 through the pipe fixing device 450. When it is about to be lowered to the seabed, all the pipe fixing devices 450 on the rigid pipe 410 are unlocked through the operation of the ROV to release the fixing effect of the pipe fixing device 450 on the first flexible pipe 430. Then, the ROV installs one end of the first flexible pipe 430 to the outlet of the wellhead suction device 130.

[0075] Specifically, as Figure 4 shown, the pipe fixing device 450 includes a bracket 451, a first pin 453 and a connecting rod 452. Among them, the bracket 451 is U-shaped. One end of the connecting rod 452 is hinged to one end of the bracket 451 through a hinge shaft. The connecting rod 452 can swing relative to the bracket 451. First jack holes are provided at the other end of the bracket 451 and the other end of the connecting rod 452. The first pin 453 can be inserted into all the first jack holes so that the connecting rod 452 and the bracket 451 jointly form a fixing cavity for fixing the first flexible pipe 430.

[0076] In this embodiment, a plurality of connecting devices are provided on the rigid pipe 410, and the connecting devices and the pipe fixing devices 450 are arranged in one-to-one correspondence. The connecting device includes a U-shaped bolt 455, a connecting nut and a connecting plate 456. The connecting plate 456 is provided with mounting holes for the two ends of the U-shaped bolt 455 to pass through. After the two ends of the U-shaped bolt 455 pass through the mounting holes of the connecting plate 456, they are threadedly connected to the connecting nut. At this time, the connecting device can be locked on the rigid pipe 410. Of course, it is not excluded that the pipe fixing device 450 is fixed on the rigid pipe 410 by welding, bolt connection or snap connection.

[0077] The support 451 is fixedly connected to the U-shaped bolt 455. On the drilling ship 310, by inserting the first pin 453 into all the first jacks, the pipe fixing device 450 can lock the first hose 430. When the rigid pipe 410, the lifting pump 420 and the first hose 430 are lowered to the appropriate position on the seabed, the ROV pulls out the first pin 453 and drives the connecting rod 452 to rotate to open the fixing cavity. After all the first pins 453 are pulled out and all the connecting rods 452 are rotated in place, the ROV can detach the first hose 430 from the rigid pipe 410 and install it at the wellhead suction device 130.

[0078] It can be understood that the first pin 453 can be arranged vertically, obliquely or horizontally. Of course, a torsion spring can be added at the hinge joint between the connecting rod 452 and the support 451. The torsion spring is sleeved on the hinge shaft, and the two torsion arms of the torsion spring are fixedly connected to the connecting rod 452 and the support 451 respectively. Under the action of the torsion spring, the connecting rod 452 can automatically reset so that the connecting rod 452 and the support 451 form a fixing cavity.

[0079] Furthermore, as Figure 4 shown, the pipe fixing device 450 further includes a second pin 454. Among them, the connecting rod 452 is arranged horizontally, the first pin 453 and the second pin 454 are arranged vertically, and second jacks are provided at one end of the support 451 and one end of the connecting rod 452. The second pin 454 can be inserted into all the second jacks so that one end of the connecting rod 452 is hinged to one end of the support 451. At this time, both the first pin 453 and the second pin 454 serve as the hinge shafts between the support 451 and the connecting rod 452. When it is difficult to pull out one of the first pin 453 and the second pin 454, the ROV can pull out the other.

[0080] As Figures 1 to 5 shown, according to the control method of the mud circulation system based on the riserless of the second aspect embodiment of the present invention, it is applied to the mud circulation system based on the riserless of the first aspect embodiment. Specifically, the control method includes the following steps: Step S11: After receiving the input instruction, judge the current working condition.

[0081] Step S12: If the current working condition is the mud reflux condition, control the first control valve and the lifting pump 420 to open, and control the second control valve to close.

[0082] Step S13: If the current working condition is the replenishment condition, control the second control valve to open, and control the first control valve and the lifting pump 420 to close.

[0083] The control system can execute step S11, step S12, and step S13. The control system can, according to the instructions input by the user, determine the current operating condition of the riserless mud circulation system, and know that the current operating condition is the mud return condition, or the replenishment condition, or the shutdown condition, so that the control system can issue corresponding response instructions.

[0084] If it is determined that the riserless mud circulation system is in the mud return condition, then through the instructions issued by the control system, ensure that the lift pump 420 and the first control valve are in the open state, and the second control valve is in the closed state, thus prompting the mud to return from the seabed to the low-pressure mud treatment system 520 on the floating drilling platform 110 through the return pipeline system, realizing the riserless mud circulation operation.

[0085] If it is determined that the riserless mud circulation system is in the replenishment condition, then through the instructions sent by the control system, ensure that the second control valve is in the open state, and the lift pump 420 and the first control valve are in the closed state, thus prompting the replenishment fluids such as mud, cementing fluid, and drilling water on the drilling ship 310 to be transported from the high-pressure mud manifold 510 to the low-pressure mud treatment system 520 on the floating drilling platform 110 through the second hose 470, thereby completing the replenishment work.

[0086] If it is determined that the riserless mud circulation system is in the shutdown condition, then the control system can control the first control valve, the second control valve, and the lift pump 420 to close, so that both the mud return work and the replenishment fluid transportation work are in a stopped state.

[0087] With such a design, the working states of the first control valve, the second control valve, and the lift pump 420 can be adjusted according to the change of the operating condition, prompting the riserless mud circulation system to be able to switch between the mud return condition and the replenishment condition.

[0088] As Figures 1 to 4 、 Figure 6 shown, the operation method of the riserless mud circulation system according to the third aspect embodiment of the present invention is applied to the riserless mud circulation system as in the first aspect embodiment. Specifically, the operation method includes the following steps: Step S21: Drive the wellhead suction device 130 to move downward and install it on the wellhead, and drive the drill string 120 on the floating drilling platform 110 to drill into the wellhead suction device 130.

[0089] Step S22: Drive the drilling ship 310 to sail a first distance in the direction close to the floating drilling platform 110, and drive the rigid pipe 410 to drive the lift pump 420 and the first hose 430 to move downward a second distance, and connect the second hose 470 to the low-pressure mud treatment system 520.

[0090] Step S23: After the first hose 430 is lowered by a second distance, drive the ROV to disassemble the first hose 430 from the pipe fixing device 450 and connect the first hose 430 to the wellhead suction device 130.

[0091] Step S24: After the first hose 430 and the second hose 470 are installed, drive the drilling ship 310 to sail a third distance away from the floating drilling platform 110, and drive the rigid pipe 410 to drive the lift pump 420 to move down by a fourth distance.

[0092] Step S25: Turn on the heave compensation system on the drilling ship 310, and drive the rigid pipe 410 to drive the lift pump 420 to move down to the seabed.

[0093] Step S26: Start the lift pump 420 to carry out the mud return operation mode.

[0094] It can be understood that the specific values of the first distance, the second distance, the third distance, and the fourth distance are not limited and can be set according to the actual situation.

[0095] Before step S21, when the mud circulation operation without a riser needs to be carried out, the floating drilling platform 110 and the drilling ship 310 can operate in parallel. The floating drilling platform 110 and the drilling ship 310 can both turn on their own dynamic positioning functions, so that a certain horizontal distance, such as 100 meters, is separated between the floating drilling platform 110 and the drilling ship 310.

[0096] In step S21, after the floating drilling platform 110 completes the positioning relative to the wellhead on the sea surface, with the help of the winch on the floating drilling platform 110, lower the wellhead suction device 130 from the floating drilling platform 110 and set it at the wellhead on the seabed mud line. Then, use the second derrick 140 and the second top drive 150 to move the drill string 120 down and screw it into the wellhead suction device 130, so that the drill string 120 can carry out the drilling operation at the wellhead. During this process, the wellhead suction device 130 can suck and collect the mud returning from the wellbore 200.

[0097] In step S22, the existing automated processing equipment such as the power catwalk, iron roughneck, the first derrick 320, and the first top drive 330 on the drilling ship 310 can be used to connect components such as the first hose 430 tied with the first buoyancy block 440, the lift pump 420, the rigid pipe 410, and the three-way manifold 460, and lower them. By moving down by a second distance, the height position of the lift pump 420 is 10 meters away from the seabed mud line.

[0098] Before or after lowering the rigid pipe 410, the drilling ship 310 is driven closer to the floating drilling platform 110 to reduce the horizontal distance between the drilling ship 310 and the floating drilling platform 110, so as to install the second hose 470 on the low-pressure mud treatment system 520 on the floating drilling platform 110. Specifically, the drilling ship 310 is slowly driven a first distance to move the drilling ship 310 to a position at a certain distance, such as 10 meters, from the floating drilling platform 110. Then, the drilling ship 310 activates its dynamic positioning function to keep the drilling ship 310 in a stable state. At this time, the second hose 470 can be installed at the inlet of the low-pressure mud treatment system 520.

[0099] In step S23, when the rigid pipe 410 drives the lift pump 420 and the first hose 430 to move down a second distance and the drilling ship 310 moves a first distance, the ROV is activated to let the ROV run to a position near the rigid pipe 410. The pipe fixing devices 450 are sequentially opened from top to bottom on the seabed by means of the ROV to remove the first hose 430 from the pipe fixing device 450 on the rigid pipe 410 and lower the first hose 430 to the seabed. Then, one end of the first hose 430 is driven by the ROV to connect the first hose 430 to the outlet of the wellhead suction device 130. At this time, the work of connecting the return pipeline system to the wellhead suction device 130 and the low-pressure mud treatment system 520 respectively has been completed.

[0100] In step S24, after the installation work of the first hose 430 and the second hose 470 is completed, the drilling ship 310 needs to be driven away from the floating drilling platform 110 to increase the horizontal distance between the drilling ship 310 and the floating drilling platform 110 to avoid interference and collision between the drill string 120 and the rigid pipe 410. Specifically, the drilling ship 310 is slowly driven a third distance to move the drilling ship 310 to a position at a certain distance, such as 50 meters, from the floating drilling platform 110. Then, the dynamic positioning function on the drilling ship 310 is activated to keep the drilling ship 310 in a stable state on the sea surface.

[0101] After the position of the drilling ship 310 on the sea surface is confirmed, the rigid pipe 410 is driven to drive the lift pump 420 to slowly move down a fourth distance through the existing automated processing equipment such as the power catwalk, iron roughneck, first derrick 320, and first top drive 330 on the drilling ship 310 until the height position of the lift pump 420 is 2 meters from the seabed.

[0102] In step S25, first start the heave compensation system on the drilling ship 310, and then drive the hard pipe 410 to drive the lift pump 420 to continue to slowly move downward until the lift pump 420 lands on the seabed. At this time, through the dynamic positioning function of the drilling ship 310 and the role of the heave compensation system, the heave compensation function of the mud circulation system based on the riserless can be realized, avoiding the problem of pulling damage of the hard pipe 410 in the case of large wind and waves, and ensuring that the mud circulation system based on the riserless can carry out the drilling operation smoothly.

[0103] In step S26, after the return pipeline system is installed and the positions of the lift pump 420 and the hard pipe 410 are set, the mud return process can be carried out during the drilling process through the coordinated operation of the drill string 120, the wellhead suction device 130, the lift pump 420, etc.

[0104] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0105] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and purposes of the present invention, and the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A mud circulation system based on a riserless pipe, characterized in that, Comprising: A drilling device, which includes a floating drilling platform, a wellhead suction device, and a drill string. The drill string is vertically arranged. The upper end of the drill string is provided on the floating drilling platform, and the lower end of the drill string passes through the wellhead suction device. A drilling ship; A low-pressure mud treatment system, which is provided on the floating drilling platform; A return pipeline system, which includes a lifting pump, a rigid pipe, a first hose, and a second hose. The rigid pipe is vertically arranged. The upper end of the rigid pipe is provided on the drilling ship. The lower inlet of the rigid pipe is connected to the outlet of the lifting pump. One end of the first hose is connected to the outlet of the wellhead suction device, and the other end is connected to the inlet of the lifting pump. One end of the second hose is connected to the upper outlet of the rigid pipe, and the other end is connected to the inlet of the low-pressure mud treatment system.

2. The mud circulation system based on a riserless pipe according to claim 1, characterized in that, The drilling ship has a high-pressure mud manifold. The return pipeline system further includes a first control valve, a second control valve, and a three-way manifold. The three-way manifold has three pipe interfaces, and the three pipe interfaces are respectively connected to the upper outlet of the rigid pipe, the inlet of the second hose, and the outlet of the high-pressure mud manifold. The first control valve is provided at the upper outlet of the rigid pipe, and the second control valve is provided at the outlet of the high-pressure mud manifold.

3. The mud circulation system based on a riserless pipe according to claim 2, wherein It further includes a control system, which is electrically connected to the first control valve, the second control valve, and the lifting pump respectively. The control system can control the first control valve and the lifting pump to open during the mud return working condition, and at the same time control the second control valve to close, and can control the second control valve to open during the supply working condition, and at the same time control the first control valve and the lifting pump to close.

4. The mud circulation system based on a riserless pipe according to claim 1, characterized in that, The first hose is provided with a plurality of first buoyancy blocks along its extending direction; and / or, The second hose is provided with a plurality of second buoyancy blocks along its extending direction.

5. The mud circulation system based on a riserless pipe according to any one of claims 1 to 4, characterized in that The drilling ship has a drill pipe, a first derrick, and a first top drive. The drill pipe is set as the rigid pipe. The first top drive is drivingly connected to the rigid pipe, and the first top drive is slidably connected to the first derrick in the up and down direction to drive the rigid pipe to lift and lower; the drilling ship has a heave compensation system, and the heave compensation system is used to compensate for the heave movement of the rigid pipe.

6. The mud circulation system based on a riserless pipe according to claim 5, characterized in that, The rigid pipe is provided with a plurality of pipe fixing devices along its extending direction, and the plurality of pipe fixing devices are detachably connected to the first hose.

7. The mud circulation system based on a riserless pipe according to claim 6, characterized in that, The pipe fixing device includes a bracket, a first pin, and a connecting rod. The bracket is U-shaped. One end of the connecting rod is hinged to one end of the bracket. The other end of the bracket and the other end of the connecting rod are both provided with first insertion holes, and the first pin can be inserted into all the first insertion holes to enable the connecting rod and the bracket to jointly form a fixing cavity for fixing the first hose.

8. The mud circulation system based on a riserless pipe according to claim 7, wherein The pipe fixing device further includes a second pin. The connecting rod is horizontally arranged. The first pin and the second pin are vertically arranged. One end of the bracket and one end of the connecting rod are both provided with second insertion holes, and the second pin can be inserted into all the second insertion holes to enable one end of the connecting rod to be hinged to one end of the bracket.

9. A control method for a mud circulation system based on a riserless system, which is applied to the mud circulation system based on a riserless system as described in claim 3, characterized in that, Including the following steps: After receiving the input instruction, judge the current working condition; If the current operation condition is the mud reflux condition, control the first control valve and the lift pump to open, and control the second control valve to close; If the current operation condition is the replenishment condition, control the second control valve to open, and control the first control valve and the lift pump to close.

10. A method for operating a mud circulation system based on a riserless pipe, which is applied to the mud circulation system based on a riserless pipe according to any one of claims 6 to 8, characterized in that, It includes the following steps: Drive the wellhead suction device to move downward and install it on the wellhead, and drive the drill string on the floating drilling platform to drill into the wellhead suction device; Drive the drilling ship to sail a first distance in the direction close to the floating drilling platform, drive the rigid pipe to drive the lift pump and the first hose to move downward a second distance, and connect the second hose to the low-pressure mud treatment system; After the first hose moves downward a second distance, drive the ROV to disassemble the first hose from the pipe fixing device and connect the first hose to the wellhead suction device; After the first hose and the second hose are installed, drive the drilling ship to sail a third distance in the direction away from the floating drilling platform, and drive the rigid pipe to drive the lift pump to move downward a fourth distance; Turn on the heave compensation system on the drilling ship, and drive the rigid pipe to drive the lift pump to move downward to the seabed; Start the lift pump to carry out the mud reflux condition.

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