Drilling fluid return system for offshore riserless drilling

Abstract

The present disclosure provides a drilling fluid return system for offshore riser-free drilling, the system comprising: a drilling fluid volume control unit, an open water drilling drill pipe, a drilling fluid return pipeline, a drilling fluid return pump installed thereon, and a drilling fluid treatment device. The drilling fluid volume control unit is directly installed on the wellhead or above the riser-free blowout preventer, and its top is open to the seawater. The drill pipe extends from the drilling platform through the volume control unit, and drilling operations are performed through the inside of the volume control unit. The drilling fluid return pipeline is connected to the volume control unit through a hose, and the drilling fluid return pump is sequentially installed in a pipe section in the return pipeline along the axial direction, which is used to pump the drilling fluid flowing into the return pipeline from the volume control unit back to the drilling platform, and circulate it after being treated by the drilling fluid treatment device. The system is not limited by the size of the drilling ship and the water depth, can effectively recover the drilling fluid, and is suitable for drilling operations at full water depth.

Description

Technical Field

[0001] The present invention belongs to the technical field of offshore energy exploitation and relates to an offshore riser-free drilling drilling fluid return system. Background Art

[0002] Drilling operations carried out at sea can realize the development and utilization of seabed energy, and can be used to mine energy such as oil, natural gas and combustible ice. In order to achieve deepwater drilling and ultra-deep drilling, riser-free drilling technology can be used in deepwater drilling operations. However, for ultra-deepwater drilling operations, existing large-scale drilling equipment uses large-diameter risers, which require the installation of high-pressure well control pipelines, and are installed underwater, which cannot guarantee the safety of the installation and is also costly.

[0003] Specifically, the main function of the large-diameter riser is to realize the return of drilling fluid and throttling and well-killing operations, which is achieved through the throttling and well-killing pipeline attached to the riser and connected between the well control system and the blowout preventer on the ship. Generally speaking, the well control pipeline for riser-free drilling in shallow waters is achieved by establishing an independent operating pipeline between the drilling ship and the blowout preventer. However, in ultra-deepwater operations, the installation of such a high-pressure well control pipeline is not economically desirable and cannot be safely installed in practice.

[0004] At present, the deepwater riserless drilling technology of 1000m to 2000m is relatively mature and is generally used for surface drilling before installing blowout preventers (BOP). However, the application depth of riserless drilling technology is limited. As the water depth increases, whether it is when the operating water depth is increased to more than 2000m in testing or by installing a rotary control head (RCD) on the top of the BOP, the return of drilling fluid is subject to certain restrictions. Since the hydrostatic pressure generated by the long drilling fluid return pipeline on the wellbore will greatly affect the stability of the wellbore, there are obvious limitations in using this method in deeper waters. The method of using an underwater rotary control head to pump drilling fluid into the wellbore and then return the drill cuttings to the drillship through the nearest drilling fluid return pipeline during riserless drilling is not feasible. In deep-sea drilling with a water depth of more than 1,500 to 2,000 meters or deeper drilling scenarios, the pumping capacity of the pump is limited, and it is impossible to pump a sufficient amount and specific gravity of drilling fluid back to the drillship. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] The present disclosure provides an offshore riserless drilling fluid return system, which can be applied to offshore energy exploitation in waters of all water depths (including deep waters with a depth of less than 2,600 meters, or ultra-deep waters with a depth of more than 2,600 meters), so as to at least partially overcome the limitations of existing drilling fluid recovery systems in deeper waters.

[0007] (II) Technical solution

[0008] One aspect of the present disclosure provides a drilling fluid return system for offshore riserless drilling. The offshore riserless drilling fluid return system comprises: a drilling fluid volume control unit 212, an open water drilling drill pipe 211, a drilling fluid return pipeline 221, a drilling fluid return pump 222 installed on a pipe section of the drilling fluid return pipeline 221, and a drilling fluid processing device 206. The drilling fluid volume control unit 212 is located in the seawater and the top of the drilling fluid volume control unit 212 is open to the seawater, and the bottom of the drilling fluid volume control unit 212 is facing the drilling position. The open water drilling drill pipe 211 is used to be lowered from a floating drilling platform 201 and pass through the drilling fluid volume control unit 212 for drilling operations, and the drilling fluid is pumped from the drilling platform 201 to the wellbore 31 through the internal holes of the drill pipe 211. The drilling fluid return pipeline 221 is connected to the drilling fluid volume control unit 212 through a hose. The drilling fluid return pump 222 is used to pump the drilling fluid 50 flowing from the drilling fluid volume control unit 212 into the drilling fluid return pipeline 221 back to the drilling platform 201 and to circulate the drilling fluid after being processed by the drilling fluid processing device 206 .

[0009] According to an embodiment of the present disclosure, a differential pressure sensor 214 is installed on the drilling fluid volume control unit 212, and the differential pressure sensor 214 is used to sense the differential pressure value inside and outside the drilling fluid volume control unit 212 according to the height of the interface 32 between the drilling fluid and the seawater in the drilling fluid volume control unit 212. The above system also includes: a control unit, which is electrically and / or communicatively connected to the differential pressure sensor 214 and the drilling fluid return pump 222, and is used to control the drilling fluid return pump 222 according to the differential pressure value fed back by the differential pressure sensor 214, so that the interface 32 between the drilling fluid and the seawater in the drilling fluid volume control unit 212 is at a preset height.

[0010] According to the embodiment of the present disclosure, a drill pipe U-shaped pipe blocking valve 213 is provided on the drill pipe 211 ; and a drilling fluid return pipeline controllable U-shaped pipe blocking valve 223 is provided on the drilling fluid return pipeline 221 .

[0011] According to an embodiment of the present disclosure, the above-mentioned offshore riser-less drilling drilling fluid return system further includes: a detachable connection structure, which is arranged on one of the drilling fluid volume control unit 212 and the drilling fluid return pipeline 221 or between the two, and the above-mentioned detachable connection structure is connected to the drilling fluid volume control unit 212 and the drilling fluid return pipeline 221 through the above-mentioned hose. The above-mentioned detachable connection structure includes: a fixed part, and a separation part detachably connected to the above-mentioned fixed part, and the above-mentioned separation part is separated from the above-mentioned fixed part based on the control of an external force or an electrical control signal.

[0012] According to an embodiment of the present disclosure, the above-mentioned offshore riser-free drilling drilling fluid return system further includes: a drilling base emergency disconnection unit 232, which is arranged between the drilling fluid volume control unit 212 and the drilling fluid return pipeline 221, and is used to be installed on the drilling base 231, and is arranged at intervals from the area where the wellbore 31 is located; an emergency disconnection structure 233 detachably connected to the drilling base emergency disconnection unit 232; an umbilical cable 235 and a tensioning connector 234 used to connect between the drilling platform 201 and the emergency disconnection structure 233, and the umbilical cable 235 and the tensioning connector 234 are fixed to each other. Among them, the emergency disconnection structure 233 is controlled by the tensioning force of the tensioning connector 234, and when the tension reaches or exceeds the preset tensioning force of the tensioning connector 234, the emergency disconnection structure 233 is disconnected from the drilling base emergency disconnection unit 232. In this embodiment, the above-mentioned drilling base emergency disconnection unit 232 serves as a fixed part, and the emergency disconnection structure 233 serves as a separation part.

[0013] According to an embodiment of the present disclosure, the hose between the drilling fluid return pipeline 221 and the drilling fluid volume control unit 212 includes: a drilling fluid suction hose non-emergency disconnection pipe section 216 connected between the drilling fluid volume control unit 212 and the drilling base emergency disconnection unit 232; and a drilling fluid suction hose emergency disconnection pipe section 226 connected between the emergency disconnection structure 233 and the drilling fluid return pipeline 221. The drilling fluid suction hose non-emergency disconnection pipe section 216 and the drilling fluid suction hose emergency disconnection pipe section 226 are used to transmit the drilling fluid 50.

[0014] According to an embodiment of the present disclosure, the above-mentioned offshore riserless drilling drilling fluid return system also includes: a riserless underwater blowout preventer 218, and the riserless underwater blowout preventer 218 is connected between the drilling fluid volume control unit 212 and the wellbore 31.

[0015] According to an embodiment of the present disclosure, the hose between the drilling fluid return line 221 and the drilling fluid volume control unit 212 further includes: a non-emergency disconnection pipe section 217 of the well-killing hose connected between the riser-less underwater blowout preventer 218 and the drilling base emergency disconnection unit 232; and an emergency disconnection pipe section 227 of the well-killing hose connected between the emergency disconnection structural member 233 and the fixed end of the well-killing line hot-spur connector 225 attached to the drilling fluid return line 221. The non-emergency disconnection pipe section 217 of the well-killing hose and the emergency disconnection pipe section 227 of the well-killing hose are used to transmit the well-killing fluid, and the well-killing fluid is pumped in through the well-killing umbilical cable connected to the free end of the well-killing line hot-spur connector 225.

[0016] According to an embodiment of the present disclosure, the above-mentioned offshore riser-free drilling drilling fluid return system further includes: a counterweight unit 224 installed at the bottom of the drilling fluid return pipeline 221, in which a drilling fluid return inlet valve 228 and a well-killing fluid outlet valve 229 are installed; the above-mentioned well-killing pipeline hot stab joint 225 is fixed to the counterweight unit 224. Among them, the drilling fluid suction hose emergency disconnection pipe section 226 is connected to the drilling fluid return pipeline 221 via the drilling fluid return inlet valve 228; the well-killing hose emergency disconnection pipe section 227 is connected to the well-killing umbilical cable via the well-killing fluid outlet valve 229 and the well-killing pipeline hot stab joint 225.

[0017] According to an embodiment of the present disclosure, the subsea blowout preventer 218 without a riser includes: a gate valve assembly. The gate valve assembly includes a blowout preventer shear gate valve 2182 and a blowout preventer clamping gate valve 2183 spaced from top to bottom; the blowout preventer clamping gate valve 2183 is used to clamp the drill pipe 211 when the wellbore 31 needs to be safely closed; the blowout preventer shear gate valve 2182 is used to cut off the drill pipe 211 after the blowout preventer clamping gate valve 2183 clamps the drill pipe 211, and at the same time, the wellbore 31 is sealed.

[0018] According to an embodiment of the present disclosure, a turntable and a derrick located above the turntable are provided on the drilling platform 201, a turntable opening 208 is provided on the turntable, a hollow area is provided below the drilling center 202 of the derrick, and the hollow area is a moon pool 207; wherein, after the drilling fluid return pump 222 and the drilling fluid return pipeline 221 are assembled, they can pass through the turntable opening 208 of the drilling platform 201 and be lowered below the moon pool 207.

[0019] (III) Beneficial effects

[0020] It can be seen from the above technical solutions that the offshore riser-free drilling drilling fluid return system provided by the present disclosure has the following beneficial effects:

[0021] (1) The drilling fluid volume control unit is located in the seawater and its two ends are open to the seawater and the drilling position respectively. Based on the balance between the static pressure of the seawater, the atmospheric pressure and the drilling fluid gushing out of the wellbore, there is a certain liquid level height in the drilling fluid volume control unit. Based on the U-tube principle, the drilling fluid in the drilling fluid volume control unit enters the drilling fluid return pipeline through a hose and has a certain liquid level height. The drilling fluid return pump installed inside a pipe section of the drilling fluid volume control unit can pump the drilling fluid flowing from the drilling fluid volume control unit into the drilling fluid return pipeline to above the sea surface. When performing drilling operations, it is not limited by the size or water depth capacity of the drilling platform (such as a drill ship), and can be applied to deepwater and ultra-deepwater drilling operations. The recycling of drilling fluid can reduce the space used by the drilling platform to store drilling fluid and its chemicals, thereby reducing the cost of drilling operations; and the drilling fluid return pump does not need to be installed on the seabed, and the drilling depth is deeper than that of conventional drilling systems, and can be applied to waters of all water depths, including deepwater waters with a depth of H ≤ 2600 meters or ultra-deepwater waters with a depth of H > 2600 meters.

[0022] (2) There is no need to install heavy watertight risers and their tension systems. Since a small diameter drilling fluid return line is used to replace the traditional large-diameter watertight riser used for mud return, the drilling platform's demand for drilling fluid is reduced by 70 to 90%. In addition, the present invention allows the drilling platform to have a larger offset relative to the wellbore. Unlike the use of traditional hard watertight risers, the present invention uses a hose to achieve a flexible connection between the drilling fluid return line and the volume control unit. Since the floating drilling platform does not need to maintain a very precise positioning, the amount of fuel used is greatly reduced.

[0023] (3) Since the drilling fluid return pump is installed in a pipe section inside the drilling fluid return pipeline in axial order, the diameter of the drilling fluid return pipeline is reduced, so it can be lowered below the moon pool through a small-sized turntable opening after installation on the floating drilling platform, avoiding the difficulty and insecurity of underwater installation due to the large size of the watertight pipe system in the prior art. In addition, the drilling fluid return pipeline can be installed and deployed through the lifting device on the derrick, and this arrangement can significantly reduce the operation time of the drilling operation.

[0024] (4) Based on the setting of the subsea blowout preventer without a riser, when the floating drilling platform accidentally drifts to the predetermined position, the connection between the drill pipe and the floating drilling platform is cut off, and the wellbore is sealed to achieve effective well control. After the floating drilling platform returns to the top of the wellbore, the cut drill pipe can be quickly salvaged from the wellbore, otherwise it will be difficult to reconnect.

[0025] (5) When surface drilling begins, drilling fluid enters the wellbore through the drill pipe. When a new drill pipe section is added to the drill pipe, the static pressure gradient of the drilling fluid in the drill pipe will be higher than the static pressure gradient of the open water area outside the drill pipe. According to the U-tube principle, a large amount of heavy drilling fluid will gush out of the drill pipe from the bottom of the drill pipe. By setting a drill pipe U-tube blocking valve, part of the drilling fluid that gushes out due to the U-tube principle can be effectively prevented. At the same time, the drill pipe U-tube blocking valve also helps to avoid the entry of air caused by adding drill pipes, thereby reducing the loss of drilling fluid. By setting a controllable U-tube blocking valve for the drilling fluid return line, part of the drilling fluid that gushes out due to the U-tube principle can be prevented, thereby reducing the loss of drilling fluid.

[0026] (6) In the scheme including or not including the watertight riser-free underwater blowout preventer, by setting the drilling base emergency disconnect unit and the emergency disconnect structure, the control signal based on the umbilical cable can disconnect the pipeline connection between the drilling fluid return device and the drilling fluid volume control unit in an emergency, and reconnect after the emergency is released. The pipeline from the drilling fluid volume control unit to the emergency disconnect unit on the drilling base will not be disconnected in an emergency, which will not affect the pipeline connection of the drilling part, avoiding the repositioning of the wellbore; and the pipeline between the emergency disconnect structure and the drilling fluid return pipeline will be disconnected in an emergency as the emergency disconnect structure is separated from the drilling base emergency disconnect unit, and will be reconnected after the subsequent emergency is released, effectively avoiding the drilling fluid return pipeline from being affected by the emergency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of a drilling fluid return system for offshore riserless drilling without a riserless underwater blowout preventer according to an embodiment of the present disclosure.

[0028] Figure 2 It is a schematic diagram of the principle of realizing the backflow of drilling fluid in a drilling fluid backflow system for offshore riserless drilling according to an embodiment of the present disclosure.

[0029] Figure 3 It is a schematic structural diagram of a drilling fluid return system for offshore riserless drilling including a riserless underwater blowout preventer according to another embodiment of the present disclosure.

[0030] Figure 4 It is a schematic diagram of the main components, valves and pipelines of the drilling fluid return system for offshore riserless drilling according to an embodiment of the present disclosure.

[0031] Figure 5 It is a schematic structural diagram of a riser-less underwater blowout preventer and a drilling fluid volume control unit according to an embodiment of the present disclosure.

[0032] Figure 6The present invention is a flow chart of an assembly method of a drilling fluid return system for offshore riserless drilling according to an embodiment of the present disclosure.

[0033] Figure 7 The present invention is a schematic diagram of a process of passing a drilling fluid return pipeline and a drilling fluid return pump through a small-diameter turntable opening and a process of suspending the drilling fluid return pipeline on a universal hanger in a moon pool vehicle according to an embodiment of the present invention.

[0034] Figure 8 The present invention is a flow chart of a drilling fluid recovery method based on a drilling fluid return system for offshore riserless drilling according to an embodiment of the present disclosure.

[0035]

Explanation of symbols

[0036] 11- sea surface; 12- sea bed;

[0037] 13- Sea water;

[0038] 201- floating drilling platform; 202- drilling center;

[0039] 203-lifting device; 204-moon pool car;

[0040] 205-universal hanger; 206-drilling fluid treatment device;

[0041] 207-moon pool; 208-turntable opening;

[0042] 211-drill pipe;

[0043] 212-drilling fluid volume control unit;

[0044] 2121 - Suction line connector operable by ROV;

[0045] 2122-ROV auxiliary control panel;

[0046] 2123-BOP control fluid accumulator; 2124-Accumulator refill pipe;

[0047] 213-drill pipe U-tube blocking valve; 214-differential pressure sensor;

[0048] 216-Non-emergency disconnection section of drilling fluid suction hose;

[0049] 217-Non-emergency disconnection section of well killing hose;

[0050] 218-Underwater BOP without Riser;

[0051] 2181-well killing hose access connector; 2182-blowout preventer shear gate valve;

[0052] 2183-BOP clamping gate valve; 2184-upper well kill valve;

[0053] 2185-downwell valve; 2186-wellhead connector;

[0054] 221-drilling fluid return pipeline; 222-drilling fluid return pump;

[0055] 223-Controllable U-shaped pipe blocking valve for drilling fluid return pipeline;

[0056] 224- counterweight unit;

[0057] 225-hot-spur joint for well-killing pipeline;

[0058] 226-Emergency disconnect section of drilling fluid suction hose;

[0059] 227- Emergency disconnection section of well killing hose; 228- Drilling fluid return inlet valve;

[0060] 229-killing fluid outlet valve;

[0061] 231-drilling base; 232-drilling base emergency disconnect unit;

[0062] 233- Emergency disconnection structure; 234- Tensioning connector;

[0063] 235-umbilical cable; 236-umbilical cable fixing piece;

[0064] 31-wellbore; 32-interface between drilling fluid and seawater;

[0065] 41- atmospheric pressure; 131- seawater static pressure gradient;

[0066] 50-drilling fluid;

[0067] 51-static pressure gradient of the drilling fluid in the volume control unit;

[0068] 61-static pressure gradient of drilling fluid in return line;

[0069] 71- Reflux pump inlet pressure; 72- Reflux pump outlet pressure;

[0070] 73-Reflux pump outlet flow. DETAILED DESCRIPTION

[0071] The present disclosure provides an offshore riserless drilling drilling fluid return system for offshore drilling operations, which can return drilling fluid from the wellbore to the drilling platform without using a traditional offshore platform riser. The offshore riserless drilling drilling fluid return system described in the present disclosure is not limited by the size or water depth capacity of the drilling ship when performing drilling operations, so a relatively small floating drilling platform (such as a drilling ship or other offshore drilling equipment) can be used, greatly improving economic benefits. The offshore riserless drilling drilling fluid return system disclosed in the present disclosure can be applied to deepwater drilling or ultra-deepwater drilling of underwater substrates or sedimentary formations.

[0072] The offshore riser-free drilling drilling fluid return system provided by the present disclosure includes: a drilling fluid volume control unit, an open water drilling drill pipe, a drilling fluid return pipeline, a drilling fluid return pump installed on a pipe section of the drilling fluid return pipeline, and a drilling fluid processing device. The drilling fluid volume control unit is located in the seawater and the top of the drilling fluid volume control unit is open to the seawater, and the bottom of the drilling fluid volume control unit is facing the drilling position. The open water drilling drill pipe is used to be lowered from the drilling platform and pass through the drilling fluid volume control unit for drilling operations, and the drilling fluid is pumped from the drilling platform to the wellbore through the internal holes of the drill pipe. The drilling fluid return pipeline is connected to the drilling fluid volume control unit by a hose. The drilling fluid return pump is used to pump the drilling fluid that flows from the drilling fluid volume control unit into the drilling fluid return pipeline back to the drilling platform, and it is recycled after being treated by the drilling fluid processing device.

[0073] The offshore riserless drilling drilling fluid return system provided by the present disclosure may further include at least one of the following structures: a riserless underwater blowout preventer, an emergency disconnect structure including a drilling base emergency disconnect unit and an emergency disconnect structural member.

[0074] The offshore riserless drilling fluid return system with a drilling fluid volume control unit and a drilling fluid return pipeline disclosed in the present invention can work under two working conditions. The first working condition is a scenario where the drilling fluid volume control unit is not equipped with a riserless underwater blowout preventer. The drilling fluid volume control unit with a wellhead head can be fixed on the drilling base plate to implement drilling operations at a well-positioned wellbore position, thereby realizing the return of drilling fluid during wellbore drilling. The second working condition is a scenario where the drilling fluid volume control unit is equipped with a riserless underwater blowout preventer. A riserless underwater blowout preventer is installed between the drilling fluid volume control unit and the wellbore. In addition to realizing the function of returning drilling fluid in conventional drilling operations, the underwater blowout preventer can also cut off the connection between the drill pipe and the floating drilling platform and seal the wellbore when the floating drilling platform accidentally drifts to a predetermined position, thereby realizing effective well control.

[0075] The offshore riser-free drilling drilling fluid return system disclosed in the present invention can be applied to waters of all water depths, including deepwater waters with a depth of H≤2600 meters or ultra-deepwater waters with a depth of H>2600 meters, breaking the limitations of current deepwater drilling.

[0076] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0077] An exemplary embodiment of the present disclosure provides an offshore riser-less drilling fluid return system capable of recovering drilling fluid.

[0078] Figure 1 It is a schematic structural diagram of a drilling fluid return system for offshore riserless drilling without a riserless underwater blowout preventer according to an embodiment of the present disclosure. Figure 2 It is a schematic diagram of the principle of realizing the backflow of drilling fluid in a drilling fluid backflow system for offshore riserless drilling according to an embodiment of the present disclosure. Figure 3 It is a schematic structural diagram of a drilling fluid return system for offshore riserless drilling including a riserless underwater blowout preventer according to another embodiment of the present disclosure.

[0079] Figure 1 and Figure 3 The sea surface 1 and the seabed 12 are indicated in the figure, the sea water is indicated by a long and a short double line, and the sea water 13 is indicated by a black dot.

[0080] Reference Figure 1 and Figure 3 As shown, the offshore riserless drilling drilling fluid return system disclosed in the present invention includes: a drilling fluid volume control unit 212, an open water drilling drill pipe 211, a drilling fluid return pipeline 221 spaced apart from the drilling fluid volume control unit 212, a drilling fluid return pump 222 installed in a pipe section of the drilling fluid return pipeline 221, and a drilling fluid processing device 206.

[0081] The drilling fluid volume control unit 212 is located in the seawater and the top of the drilling fluid volume control unit 212 is open to the seawater, and the bottom of the drilling fluid volume control unit 212 is toward the drilling position. The open water drilling drill pipe 211 is used to be lowered from a floating drilling platform 201 and pass through the drilling fluid volume control unit 212 for drilling operations, and the drilling fluid is pumped from the drilling platform 201 to the wellbore 31 through the internal holes of the drill pipe 211. The drilling fluid return pipeline 221 is connected to the drilling fluid volume control unit 212 through a hose. The drilling fluid return pump 222 is used to pump the drilling fluid 50 flowing from the drilling fluid volume control unit 212 into the drilling fluid return pipeline 221 back to the drilling platform 201, and after being treated by the drilling fluid treatment device 206, it is recycled.

[0082] According to the embodiments of the present disclosure, referring to Figure 1 and Figure 3 As shown, when the riserless subsea blowout preventer 218 is not installed, the drilling fluid volume control unit 212 is arranged toward the drilling position, for example, it can be installed on the wellbore head of the drilling base plate 231; when the drilling fluid volume control unit 212 is installed with the riserless subsea blowout preventer 218, the drilling fluid volume control unit 212 is installed above the riserless subsea blowout preventer 218. In either case, the top of the drilling fluid volume control unit 212 is open toward the seawater, and the bottom faces the drilling position. Figure 1 Although the kill hose emergency disconnect pipe section 227 is illustrated in the figure, in fact, in a system that does not include the riserless subsea blowout preventer 218, the kill hose emergency disconnect pipe section 227 may not be installed. In the process of drilling a wellbore at a drilling location during surface drilling, it is not necessary to install the riserless subsea blowout preventer 218. In deep sea drilling, the riserless subsea blowout preventer 218 may be installed as needed.

[0083] The floating drilling platform 201 is a carrier and control platform for offshore drilling operations and can be a drilling ship, for example Figure 1 The bottom of the semi-submersible drilling vessel in the example shown is located in the seawater. The floating drilling platform 201 has two operation centers, namely the drilling center 202 and the drilling fluid return pipeline center. The drilling center 202 corresponds to the axis of the drill pipe 221, and the drilling fluid return pipeline center can be shown with reference to the axis of the drilling fluid return pipeline 221. There is a certain distance between the drilling center 202 and the axis of the drilling fluid return pipeline 221 to prevent the drill pipe 221 and the drilling fluid return pipeline 221 from interfering with each other during operation.

[0084] According to the embodiments of the present disclosure, referring to Figure 1 As shown, a differential pressure sensor 214 is provided on the drilling fluid volume control unit 212. The differential pressure sensor 214 is used to sense the differential pressure value inside and outside the drilling fluid volume control unit 212 according to the height of the interface 32 between the drilling fluid and the seawater in the drilling fluid volume control unit 212. The floating drilling system also includes: a controller. The controller is electrically and / or communicatively connected to the differential pressure sensor 214 and the drilling fluid return pump 222, respectively, and is used to control the drilling fluid return pump 222 according to the differential pressure value fed back by the differential pressure sensor 214, so that the interface 32 between the drilling fluid and the seawater in the drilling fluid volume control unit 212 is at a preset height. In the present disclosure, "A and / or B" means only A, only B, or both A and B. In this embodiment, the controller can be located on the drilling platform 201, and transmit the control signal to the pressure difference sensor 214 and the drilling fluid return pump 222 via the umbilical cable, or a wireless communication module is installed on the pressure difference sensor 214 and the drilling fluid return pump 222 to achieve communication connection with the controller, or the above situations are included simultaneously.

[0085] Reference Figure 1 As shown, in the drilling fluid return system of the riser-free drilling, the wellbore is open to the seawater, so that the drilling fluid in the wellbore will directly contact the seawater in the drilling fluid volume control unit 212, and form the interface 32 between the drilling fluid and the seawater. One or more differential pressure sensors 214 installed on the drilling fluid volume control unit 212 can monitor the interface 32 in real time, and transmit the liquid level signal to the controller in real time, so as to control the real-time flow rate of the drilling fluid return pump 222 in the drilling fluid return pipeline 221, so that the height of the interface 32 between the drilling fluid and the seawater can be controlled in real time and accurately. The above controller can be a main controller arranged on the floating drilling platform 201, and the main controller can adjust the rotation speed of the drilling fluid return pump in real time according to the real-time change of the height of the interface 32 between the drilling fluid and the seawater in the drilling fluid volume control unit 212, so as to achieve the purpose of real-time control of the height of the interface 32 between the drilling fluid and the seawater.

[0086] Reference Figure 1 and Figure 2 As shown, the drilling fluid volume control unit 212 is located in the seawater and its two ends are open toward the seawater and the drilling position (after the wellbore 31 is drilled out by the drill pipe 211 at the drilling position, the drilling position corresponds to the wellbore 31). Based on the balance between the static pressure of the seawater, the atmospheric pressure and the drilling fluid 50 gushing out of the wellbore 31, there is a certain liquid level in the drilling fluid volume control unit 212. Figure 2 The figure shows the static pressure gradient 131 of seawater, the atmospheric pressure 41, and the static pressure gradient 51 of the drilling fluid in the volume control unit caused by the drilling fluid 50. Based on the U-tube principle, the drilling fluid 50 in the drilling fluid volume control unit 212 enters the drilling fluid return pipeline 221 through a hose and has a certain liquid level. In order to distinguish and describe that the drilling fluid entering the drilling fluid return pipeline is a balance achieved by the combined action of the static pressure of seawater, the atmospheric pressure, and the drilling fluid 50 gushing out of the wellbore 31, the reference numeral 61 is used to illustrate the static pressure gradient of the drilling fluid in the drilling fluid return pipeline. The static pressure gradient 61 of the drilling fluid in the drilling fluid return pipeline is the balance of the static pressure gradient 131 of seawater, the atmospheric pressure 41, and the static pressure gradient 51 of the drilling fluid in the volume control unit. Figure 2 The reflux pump inlet pressure 71, reflux pump outlet pressure 72 and reflux pump outlet flow rate 73 are also illustrated. The drilling fluid reflux pump 222 is slightly lower than the liquid level of the drilling fluid 50 entering the drilling fluid reflux pipeline 221 through the hose, and pumps the drilling fluid 50 flowing from the drilling fluid volume control unit 212 into the drilling fluid reflux pipeline 221 to above the sea surface.

[0087] The drilling fluid return pump 222 is axially installed on a pipe section of the drilling fluid return pipeline 221. For example, there may be one or more drilling fluid return pumps 222, and multiple drilling fluid return pumps 222 are sequentially arranged in the axial direction on a pipe section of the drilling fluid return pipeline 221. The position of the drilling fluid return pump 222 is lower than the liquid level of the drilling fluid 50 in the drilling fluid return pipeline 221, and the liquid level is determined by the static pressure balance of atmospheric pressure, seawater and drilling fluid. The setting position of the drilling fluid return pump can be set according to the number of drilling fluid return pumps, pumping capacity, diameter of the drilling fluid return pipeline and pumping requirements.

[0088] According to the embodiments of the present disclosure, referring to Figure 1 As shown, the drilling fluid treatment device 206 in the above-mentioned offshore riserless drilling drilling fluid return system is used to be arranged on the floating drilling platform 201. The drilling fluid treatment device 206 is connected to the drilling fluid return pipeline 221. The drilling fluid return pump 222 pumps the drilling fluid 50 in the drilling fluid return pipeline 221 to the drilling fluid treatment device 206, and the drilling fluid treatment device 206 is used to treat the drilling fluid 50 so as to recycle the treated drilling fluid 50.

[0089] The drilling fluid treated by the drilling fluid treatment device 206 will be sent to the wellbore 31 again through the drilling pipe 211 in the open water for drilling operations.

[0090] The disclosed offshore riser-free drilling drilling fluid return system is not limited by the size or water depth of the drilling vessel when performing drilling operations, and can be applied to deepwater and ultra-deepwater drilling operations. In addition, the drilling fluid return pump does not need to be installed on the seabed, and the drilling depth is deeper than that of conventional drilling systems, and can be applied to waters of all water depths, breaking through the limitation of traditional technologies for recovering drilling fluid in deep sea waters.

[0091] In deep sea scientific drilling operations, the offshore riserless drilling drilling fluid return system disclosed in the present invention has considerable economic value because it enables the drilling fluid used in the drilling operation to be recycled, rather than discarding the drilling fluid in the seawater as in previous drilling operations without the installation of this system. The recycling of drilling fluid can reduce the space used to store drilling fluid and its chemicals on the drilling platform, thereby reducing the cost of drilling operations.

[0092] The offshore riserless drilling drilling fluid return system disclosed in the present invention adopts the drilling structure of riserless drilling, and there is no need to install heavy risers and their tension systems. Since a small-diameter drilling fluid return pipeline is used to replace the traditional large-diameter riser used for mud return, the drilling platform's demand for drilling fluid is reduced by 70-90%. In addition, the present invention allows the floating drilling platform to have a larger offset relative to the wellbore. In addition, the present invention allows the drilling platform to have a larger offset relative to the wellbore. Unlike the use of traditional hard risers, the present invention uses a hose to achieve a flexible connection between the drilling fluid return pipeline and the volume control unit. Since the floating drilling platform does not need to maintain a very precise positioning, the amount of fuel used is greatly reduced.

[0093] In the case where the pressure control of the wellbore is not required, the drilling fluid volume control unit 212 does not need to be installed with a riserless subsea blowout preventer, and a drilling fluid volume control unit with a wellbore head can be fixed on the drilling base plate to perform drilling operations at the wellbore position, thereby realizing the return of drilling fluid during wellbore drilling. In another embodiment described later, the drilling fluid volume control unit 212 can also be installed above the riserless subsea blowout preventer to achieve pressure control of the wellbore based on the riserless subsea blowout preventer.

[0094] According to the embodiments of the present disclosure, referring to Figure 1 As shown, a drill pipe U-shaped pipe blocking valve 213 is provided on the drill pipe 211 ; and a drilling fluid return pipeline controllable U-shaped pipe blocking valve 223 is provided on the drilling fluid return pipeline 221 .

[0095] At the beginning of surface drilling, drilling fluid enters the wellbore through the drill pipe 211. When a new drill pipe section is added to the drill pipe, the static pressure gradient of the drilling fluid in the drill pipe will be higher than the static pressure gradient of the open water area outside the drill pipe. According to the U-tube principle, a large amount of heavy drilling fluid will gush out of the drill pipe from the bottom of the drill pipe. By setting a drill pipe U-tube blocking valve installed on the drill pipe, part of the drilling fluid that gushes out due to the U-tube principle can be effectively prevented. At the same time, the drill pipe U-tube blocking valve also helps to avoid the entry of air caused by adding drill pipes, thereby reducing the loss of drilling fluid. By setting a controllable U-tube blocking valve for the drilling fluid return pipeline, part of the drilling fluid that gushes out due to the U-tube principle can be prevented, thereby reducing the loss of drilling fluid.

[0096] According to the embodiments of the present disclosure, in order to further achieve optimization in emergency situations, refer to Figure 1 and Figure 3As shown, the above-mentioned offshore riserless drilling drilling fluid return system without or including the riserless underwater blowout preventer 218 also includes: a detachable connection structure, which is arranged on one of the drilling fluid volume control unit 212 and the drilling fluid return pipeline 221 or between the two, and the detachable connection structure and the drilling fluid volume control unit 212 and the drilling fluid return pipeline 221 are connected through the above-mentioned hose, and the detachable connection structure includes: a fixed part, and a separation part detachably connected to the above-mentioned fixed part, and the method of controlling the separation part to achieve separation includes: external force or electrical control signal. For example, the form of the electrical control signal can be, for example, the controller sends a disconnection control signal to the separation part based on the umbilical cable 235 to the emergency disconnection structure 233, and the separation part changes its structure under the control of the disconnection control signal to achieve separation from the fixed part. The control method of the external force can refer to the tension control method based on the tensioning connector 234 described later.

[0097] In one embodiment, the detachable connection structure includes: a drilling base emergency disconnection unit 232, which is arranged between the drilling fluid volume control unit 212 and the drilling fluid return pipeline 221, and is used to be installed on the drilling base 231, and is arranged at a distance from the area where the wellbore 31 is located; an emergency disconnection structure 233 detachably connected to the drilling base emergency disconnection unit 232; an umbilical cable 235 and a tensioning connector 234 connected between the floating drilling platform 201 and the emergency disconnection structure 233, and the umbilical cable 235 and the tensioning connector 234 are fixed to each other. Among them, the emergency disconnection structure 233 is controlled by the tensioning force of the tensioning connector 234, and when the pulling force reaches or exceeds the preset tensioning force of the tensioning connector 234, the emergency disconnection structure 233 is disconnected from the drilling base emergency disconnection unit 232.

[0098] For example, the umbilical cable 235 and the tension connector 234 are fixed by the umbilical cable fixing member 236. In one embodiment, the tension connector 234 may be a tensioning wire rope. The tension connector 234 of the present disclosure may be a connector with certain mechanical strength and flexibility that can provide tension, and is not limited to a wire rope.

[0099] The drilling base emergency disconnection unit 232 is used to be fixedly arranged on the drilling base 231, and the drilling base 231 is used to be fixed to the seabed 12, and a part of the drilling base 231 is located above the wellbore 31. The drilling base emergency disconnection unit 232 is spaced apart from the area where the wellbore 31 is located. When the tension force applied to the tensioning connector 234 reaches or exceeds the preset tension force of the tensioning connector 234, the emergency disconnection structural member 233 is detached from the drilling base emergency disconnection unit 232.

[0100] In an offshore riserless drilling drilling fluid return system that includes or does not include a riserless underwater blowout preventer, by providing a drilling base emergency disconnect unit and an emergency disconnect structure, the control signal based on the umbilical cable can disconnect the pipeline connection between the drilling fluid return device and the drilling fluid volume control unit in an emergency, and reconnect after the emergency is released. The pipeline from the drilling fluid volume control unit to the emergency disconnect unit on the drilling base is not disconnected in an emergency, which will not affect the pipeline connection of the drilling part and avoid repositioning the wellbore; and the pipeline between the emergency disconnect structure and the drilling fluid return pipeline will be disconnected in an emergency as the emergency disconnect structure is separated from the drilling base emergency disconnect unit, and will be reconnected after the subsequent emergency is released, effectively avoiding the drilling fluid return pipeline from being affected by the emergency.

[0101] The disconnection and reconnection functions disclosed in the present invention are realized based on the structural setting of the emergency disconnection unit and the emergency disconnection structural member of the drilling base plate in the above-mentioned example, and any detachable connection structure installed between the drilling fluid volume control unit and the drilling fluid return pipeline is within the protection scope of the present invention. In other embodiments, the detachable connection structure can be placed at the bottom of the drilling fluid return pipeline, or on the drilling fluid volume control unit, or on the subsea blowout preventer without a watertight riser.

[0102] According to the embodiments of the present disclosure, referring to Figure 1 As shown, in the offshore riserless drilling drilling fluid return system that does not include a riserless underwater blowout preventer 218, the above-mentioned hose connected between the drilling fluid return pipeline 221 and the drilling fluid volume control unit 212 includes: a drilling fluid suction hose non-emergency disconnection pipe section 216 connected between the drilling fluid volume control unit 212 and the drilling base emergency disconnection unit 232; and a drilling fluid suction hose emergency disconnection pipe section 226 connected between the emergency disconnection structure 233 and the drilling fluid return pipeline 221. In this embodiment, the drilling fluid suction hose non-emergency disconnection pipe section 216 and the drilling fluid suction hose emergency disconnection pipe section 226 are used to transmit drilling fluid 50.

[0103] According to an embodiment of the present disclosure, in an offshore riserless drilling drilling fluid return system including or not including a riserless underwater blowout preventer, referring to Figure 1 and Figure 3 As shown, the hose between the drilling fluid return pipeline 221 and the drilling fluid volume control unit 212 includes: a drilling fluid suction hose non-emergency disconnection pipe section 216 connected between the drilling fluid volume control unit 212 and the drilling base emergency disconnection unit 232; and a drilling fluid suction hose emergency disconnection pipe section 226 connected between the emergency disconnection structure 233 and the drilling fluid return pipeline 221. The drilling fluid suction hose non-emergency disconnection pipe section 216 and the drilling fluid suction hose emergency disconnection pipe section 226 are used to transmit the drilling fluid 50.

[0104] According to the embodiments of the present disclosure, referring to Figure 3 As shown, in the offshore riserless drilling drilling fluid return system including the riserless subsea blowout preventer 218 , the riserless subsea blowout preventer 218 is connected between the drilling fluid volume control unit 212 and the wellbore 31 .

[0105] Reference Figure 3 As shown, in the offshore riserless drilling drilling fluid return system including the riserless underwater blowout preventer 218, the hose between the drilling fluid return pipeline 221 and the drilling fluid volume control unit 212 includes, in addition to the drilling fluid suction hose non-emergency disconnection section 216 and the drilling fluid suction hose emergency disconnection section 226, the following further includes: a well-killing hose non-emergency disconnection section 217 connected between the riserless underwater blowout preventer 218 and the drilling base emergency disconnection unit 232; and a well-killing hose emergency disconnection section 227 connected between the emergency disconnection structure 233 and the fixed end of the well-killing pipeline hot-spur connector 225 attached to the drilling fluid return pipeline 221. The well-killing hose non-emergency disconnection section 217 and the well-killing hose emergency disconnection section 227 are used to transmit well-killing fluid, and the well-killing fluid is pumped in through the well-killing umbilical cable connected to the free end of the well-killing pipeline hot-spur connector 225.

[0106] Figure 4 Schematic diagram of main components, valves and pipelines of offshore riser-less drilling fluid return system according to one embodiment of the present disclosure. Figure 4 A system including a riserless subsea blowout preventer is illustrated, and the same component details are also applicable to a system without a riserless subsea blowout preventer.

[0107] Reference Figure 1 , Figure 3 and Figure 4 As shown, in the offshore riserless drilling drilling fluid return system including or not including the riserless underwater blowout preventer 218, it also includes: a counterweight unit 224 installed at the bottom of the drilling fluid return pipeline 221. The counterweight unit 224 is installed with a drilling fluid return inlet valve 228 and a well-killing fluid outlet valve 229. The well-killing pipeline hot stab connector 225 is fixed to the counterweight unit 224. Among them, the drilling fluid suction hose emergency disconnection pipe section 226 is connected to the drilling fluid return pipeline 221 via the drilling fluid return inlet valve 228; the well-killing hose emergency disconnection pipe section 227 is connected to the well-killing umbilical cable via the well-killing fluid outlet valve 229 and the well-killing pipeline hot stab connector 225.

[0108] According to the embodiments of the present disclosure, referring to Figure 4As shown, the subsea BOP 218 without a riser includes: a gate valve assembly. The gate valve assembly includes a BOP shear gate valve 2182 and a BOP clamping gate valve 2183 spaced from top to bottom. The BOP clamping gate valve 2183 is used to clamp the drill pipe 211 when the wellbore 31 needs to be safely closed. The BOP shear gate valve 2182 is used to cut off the drill pipe 211 after the BOP clamping gate valve 2183 clamps the drill pipe 211, and at the same time, the wellbore 31 is sealed.

[0109] Figure 5 It is a schematic structural diagram of a riser-less underwater blowout preventer and a drilling fluid volume control unit according to an embodiment of the present disclosure.

[0110] Reference Figure 5 As shown, the drilling fluid volume control unit 212 is provided with a suction line connector 2121 operable by ROV, an ROV auxiliary control panel 2122, a blowout preventer control fluid accumulator 2123, and an accumulator refill pipe 2124 connected to the blowout preventer control fluid accumulator 2123. The suction line connector 2121 operable by ROV is used to connect with the non-emergency disconnect pipe section 216 of the drilling fluid suction hose.

[0111] Based on the setting of the riser-free underwater blowout preventer 218, when the floating drilling platform accidentally drifts to the predetermined position, the connection between the drill pipe 211 and the floating drilling platform 201 can be cut off, and the wellbore 31 can be sealed to achieve effective well control. After the floating drilling platform 201 returns to the top of the wellbore 31, the cut drill pipe 211 can be quickly salvaged from the wellbore 31, otherwise it will be difficult to reconnect.

[0112] In one example, referring to Figure 5 As shown, the above-mentioned offshore riserless drilling drilling fluid return system including the riserless subsea blowout preventer 218 also includes: a main controller and an ROV auxiliary control panel 2122. The main controller is arranged on the floating drilling platform 201, and is electrically connected and / or communicatively connected to the riserless subsea blowout preventer 218. The ROV auxiliary control panel 2122 is arranged on the drilling fluid volume control unit 212, and is electrically connected to the riserless subsea blowout preventer 218. The ROV auxiliary control panel 2122 is electrically connected and / or communicatively connected to the main controller. Figure 5 The ROV auxiliary control panel 2122 is illustrated, and the ROV auxiliary control panel 2122 can control an underwater robot (ROV) to achieve the installation of underwater pipelines.

[0113] The valve of the subsea BOP 218 without a riser can be controlled by voice, electricity or hydraulics, and is controlled by the controller of the floating drilling platform 201 and / or the ROV auxiliary control panel 2122. The control fluid of the ROV auxiliary control panel 2122 is provided by the BOP control fluid accumulator 2123. When the control fluid stored in the BOP control fluid accumulator 2123 is insufficient, the fluid can be replenished through the accumulator replenishment pipe 2124.

[0114] Reference Figure 4 and Figure 5 As shown, the riser-free underwater blowout preventer 218 further includes: an upper kill valve 2184 connected to the blowout preventer shear gate valve 2182, a lower kill valve 2185 connected to the blowout preventer clamping gate valve 2183, and a kill hose access joint 2181 connected to both the upper kill valve 2184 and the lower kill valve 2185. The kill hose access joint 2181 is used to connect to the kill hose non-emergency disconnection pipe section 217. The riser-free underwater blowout preventer 218 can control the well-killing fluid in the well-killing hose non-emergency disconnection pipe section 217 connected from the kill hose access joint 2181 to be sent to the wellbore 31 by opening and closing the upper kill valve 2184 and the lower kill valve 2185, and then close the blowout preventer clamping gate valve 2183, and at the same time cut off the drill pipe 211, regulate the pressure in the wellbore 31 based on the kill fluid, thereby further ensuring the safety of the drilling operation.

[0115] The riserless underwater blowout preventer 218 is equipped with a well-killing hose access connector 2181. The well-killing pipeline is connected to the well-killing hose access connector 2181 of the riserless underwater blowout preventer 218 through a remote control device. For example, an underwater robot or other well-killing pipeline access methods can be used to implement the connection operation.

[0116] Reference Figure 5 As shown, the riserless subsea blowout preventer 218 further includes a wellhead connector 2186 for connecting with the wellbore 31. In one embodiment, the well killing pipeline can be a flexible well killing umbilical cable, and a well killing valve is arranged on the well killing pipeline.

[0117] According to the embodiment of the present disclosure, a rotating table and a derrick located above the rotating table are provided on the floating drilling platform 201, a rotating table opening 208 is provided on the rotating table, a hollow area is provided below the drilling center 202 of the derrick, the hollow area is a moon pool 207, and the moon pool vehicle 204 moves around the moon pool 207; a lifting device 203 is provided on the derrick. Among them, after the drilling fluid return pipeline 221 and the drilling fluid return pump 222 are assembled, they can be lowered to below the moon pool 207 through the rotating table opening 208 based on the lifting device 203. The drilling fluid return pipeline 221 and the drilling fluid return pump 222 are suspended and fixed in the universal hanger 205 of the moon pool vehicle 204 and can move with the moon pool vehicle 204 to vacate the position of the drilling center 202 for the drill pipe 211 to operate. By installing the drilling fluid return pump 222 axially on the pipe section of the drilling fluid return pipeline 221 , the diameter of the drilling fluid return pipeline is reduced, and the drilling fluid return pipeline can be lowered and recovered through a smaller-sized turntable opening.

[0118] Based on the above, the drilling fluid return pump is installed on the drilling fluid return pipeline along the axial direction, which reduces the diameter of the drilling fluid return pipeline. After installation on the floating drilling platform, it can be lowered below the moon pool through the small-sized turntable opening, avoiding the difficulty and insecurity of underwater installation due to the large size of the watertight pipe system in the prior art. In addition, the drilling fluid return pipeline can be installed and deployed through the lifting device of the derrick, and this arrangement can significantly reduce the operation time of the drilling operation.

[0119] A second exemplary embodiment of the present disclosure provides a method for assembling a floating drilling system. The floating drilling system of this embodiment may be a floating drilling system without or with a riserless subsea blowout preventer 218 .

[0120] Figure 6 The present invention is a flow chart of an assembly method of a drilling fluid return system for offshore riserless drilling according to an embodiment of the present disclosure. Figure 7 The present invention is a schematic diagram of a process of passing a drilling fluid return pipeline and a drilling fluid return pump through a small-diameter turntable opening and a process of suspending the drilling fluid return pipeline on a universal hanger in a moon pool vehicle according to an embodiment of the present invention.

[0121] Reference Figure 6 As shown, the assembly method of this embodiment includes the following operations: S21, S22, S23, S24, S25 and S26. The implementation process of the above operations S22, S23, S24 and S26 can refer to Figure 7 shown.

[0122] In operation S21 , a drilling fluid return pipeline 221 and a drilling fluid return pump 222 are assembled on the floating drilling platform 201 .

[0123] In operation S22, the assembled drilling fluid return pipeline 221 and the drilling fluid return pump 222 are lowered to below the moon pool 207 through the turntable opening 208 based on the lifting device 203. Figure 7 shown.

[0124] The turntable opening 208 here is a small-sized turntable opening, which is used for lowering and recovering the drill pipe. Since the drilling fluid return pump is installed axially on a pipe section of the drilling fluid return pipeline, the diameter of the drilling fluid return pipeline is reduced, so that the drilling fluid return pipeline 221 and the drilling fluid return pump 222 in the drilling fluid return device are first assembled on the floating drilling platform 201, and then lowered to below the moon pool 207 through the small-sized turntable opening 208. Compared with the prior art where the return system with a watertight pipe cannot pass through the small-sized turntable opening and can only be installed underwater, the installation difficulty is greatly reduced, the efficiency of the arrangement and installation of various equipment / devices is improved, the operation time of the drilling operation is saved, and the installation accuracy is also improved.

[0125] In operation S23, the lowered drilling fluid return pipeline 221 and the drilling fluid return pump 222 are suspended and fixed in the universal hanger 205 of the moon pool car 204. Figure 7 shown.

[0126] In operation S24, the moon pool vehicle 204 is moved to clear the location of the drilling center 202. Figure 6 The double-headed arrow in the figure indicates the direction of the moon pool car's position change.

[0127] In operation S25, the drill pipe 211 and the drilling fluid volume control unit 212 are assembled on the floating drilling platform 201. The operation S25 and the operation S21 can be performed in parallel or sequentially, and the execution order of the two is not limited.

[0128] In operation S26, the drilling center 202 lowers the assembled drill pipe 211 and the drilling fluid volume control unit 212 through the turntable opening 208 to below the moon pool 207 based on the lifting device 203, so that the drilling fluid volume control unit 212 is connected to the wellbore 31. The drilling fluid volume control unit 212 is located in the seawater and its two ends are open to the seawater and the wellbore 31 respectively. Figure 7 shown.

[0129] After the drilling fluid return pipeline 221 and the drilling fluid return pump 222 are installed, they can be suspended on the moon pool vehicle 204 around the moon pool 207. The moon pool vehicle 204 will bear the weight of the pipeline and pump in the drilling fluid return device, and transfer the drilling fluid return device to the edge of the moon pool to free up the position of the drilling center 202, so that the execution of open water drilling operations is not affected.

[0130] This embodiment is described by way of example using a floating drilling system that does not include a riserless subsea blowout preventer 218. It should be noted that, in a floating drilling system that includes a riserless subsea blowout preventer 218, the above operation S25 also requires the assembly of the riserless subsea blowout preventer 218, the drill pipe 211 and the drilling fluid volume control unit 212.

[0131] The assembly method further includes: assembling a detachable connection structure, and connecting the detachable connection structure to the volume control unit and the drilling fluid return pipeline respectively. The assembly of other detailed structures will not be introduced one by one. According to the content described in the first embodiment, an underwater robot can be used to assemble the underwater pipeline.

[0132] Figure 8 The present invention is a flow chart of a drilling fluid recovery method based on a drilling fluid return system for offshore riserless drilling according to an embodiment of the present disclosure.

[0133] Reference Figure 8 , Figure 1 and Figure 2 As shown, the drilling fluid recovery method of this embodiment includes the following operations: S31, S32 and S33.

[0134] In operation S31 , the height of the interface 32 between the drilling fluid and seawater in the drilling fluid volume control unit 212 is obtained.

[0135] In operation S32 , the real-time rotation speed of the drilling fluid return pump 222 is determined according to the height of the interface 32 between the drilling fluid and the seawater.

[0136] In operation S33, the real-time rotation speed of the drilling fluid return pump 222 is adjusted to control the flow rate of the drilling fluid 50 flowing into the drilling fluid return pipeline 221, so as to recover the drilling fluid 50 and make the interface 32 between the drilling fluid and seawater at a preset height.

[0137] For a floating drilling system including a detachable connection structure and including or not including a riser-free underwater blowout preventer, during the drilling fluid recovery process, in response to an emergency, a controller (e.g., a main controller) controls whether the emergency disconnection structure 233 is detached from the drilling base emergency disconnection unit 232 based on the tension of the tensioning connector 234, so that the detachable connection structure disconnects the connection between the drilling fluid volume control unit and the drilling fluid return pipeline in an emergency. At this time, the pipeline between the drilling fluid volume control unit and the drilling base emergency disconnection unit, such as the first pipeline 216 and the second pipeline 217, is not disconnected in an emergency, which will not affect the pipeline connection of the drilling part and avoid repositioning the wellbore. The pipeline between the emergency disconnection structure and the drilling fluid return pipeline, such as the third pipeline 226 and the fourth pipeline 227, will be disconnected in an emergency as the emergency disconnection structure is separated from the drilling base emergency disconnection unit. After the emergency is released, the emergency disconnection structure 233 is reconnected to the drilling base emergency disconnection unit 232, which effectively prevents the drilling fluid return pipeline from being affected by the emergency situation and protects the drilling fluid return pipeline.

[0138] In summary, the embodiments of the present disclosure provide an offshore riser-free drilling drilling fluid return system and an assembly method thereof. There is no need to install a heavy riser and its tension system, and the recovery and recycling of drilling fluid are realized. It can be applied to deepwater and ultra-deepwater drilling operations, so that the drilling platform's demand for drilling fluid is reduced by 70-90%; and the drilling platform is allowed to have a larger offset relative to the wellbore. By using a flexible connection in the connection between the drilling fluid return pipeline and the drilling fluid volume control unit, the floating drilling platform does not need to maintain a very precise positioning, so that the amount of fuel used is greatly reduced. The drilling fluid return pump is installed along the axial direction on a pipe section of the drilling fluid return pipeline, which reduces the diameter size of the drilling fluid return pipeline. The drilling fluid return pipeline can be installed and deployed through a lifting device. This arrangement can significantly reduce the operation time of the drilling operation. Based on the setting of the riser-free underwater blowout preventer, when the floating drilling platform accidentally drifts to the predetermined position, the connection between the drill pipe and the floating drilling platform is cut off, and the wellbore is sealed to achieve effective well control. By setting up a detachable connection structure, the control signal based on the umbilical cable can disconnect the connection between the drilling fluid return pipeline and the drilling fluid volume control unit in an emergency, and reconnect after the emergency is released. The pipeline between the drilling rig and the emergency disconnect unit of the drilling base will not be disconnected in an emergency, will not affect the pipeline connection of the drilling part, and avoid repositioning the wellbore; and the pipeline between the emergency disconnect structure and the drilling fluid return pipeline will be disconnected in an emergency as the emergency disconnect structure is separated from the emergency disconnect unit of the drilling base, and will be reconnected after the subsequent emergency is released, effectively avoiding the drilling fluid return pipeline from being affected by the emergency.

[0139] It should also be noted that, although the present disclosure is described in conjunction with the accompanying drawings, the embodiments disclosed in the accompanying drawings are intended to exemplify the preferred embodiments of the present disclosure and should not be construed as a limitation on the present disclosure. The dimensional ratios in the accompanying drawings are merely schematic and should not be construed as limitations on the present disclosure. Directional terms mentioned in the embodiments, such as "up", "down", "front", "back", "left", "right", etc., are only references to the directions of the accompanying drawings and are not intended to limit the scope of protection of the present disclosure. Throughout the accompanying drawings, the same elements are represented by the same or similar figure marks. Conventional structures or constructions will be omitted when they may cause confusion in the understanding of the present disclosure.

[0140] Moreover, the shapes and sizes of the components in the figures do not reflect the real size and proportion, but only illustrate the contents of the embodiments of the present disclosure. In addition, in the claims, any reference symbols between brackets shall not be constructed as limiting the claims.

[0141] The ordinal numbers used in the specification and claims, such as "first", "second", "third", etc., to modify the corresponding elements, do not themselves mean that the elements have any ordinal numbers, nor do they represent the order of one element and another element, or the order in the manufacturing method. The use of these ordinal numbers is only used to clearly distinguish a component with a certain name from another component with the same name.

[0142] Furthermore, the word "comprising" or "including" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

[0143] Unless there are technical obstacles or contradictions, the above-mentioned various embodiments of the present disclosure can be freely combined to form additional embodiments, and these additional embodiments are all within the protection scope of the present disclosure.

[0144] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. An offshore riser-less drilling drilling fluid return system, characterized in that: include: A drilling fluid volume control unit (212), located in the seawater, with the top of the drilling fluid volume control unit (212) open toward the seawater, and the bottom of the drilling fluid volume control unit (212) facing the drilling position; An open water drilling drill pipe (211) is used to be lowered from a floating drilling platform (201) and pass through the drilling fluid volume control unit (212) to perform drilling operations, and the drilling fluid is pumped from the drilling platform (201) through the internal holes of the drill pipe (211) to the wellbore (31); and A drilling fluid return pipeline (221) is connected to the drilling fluid volume control unit (212) via a hose, and a drilling fluid return pump (222) is installed in a pipe section of the drilling fluid return pipeline (221) and is used to pump the drilling fluid (50) flowing from the drilling fluid volume control unit (212) into the drilling fluid return pipeline (221) back to the drilling platform (201) and to circulate the drilling fluid after being processed by a drilling fluid processing device (206); in, A differential pressure sensor (214) is installed on the drilling fluid volume control unit (212), and the differential pressure sensor (214) is used to sense the differential pressure value inside and outside the drilling fluid volume control unit (212) according to the height of the interface (32) between the drilling fluid and seawater in the drilling fluid volume control unit (212); The system further comprises: a control unit, the control unit being electrically and / or communicatively connected to the pressure difference sensor (214) and the drilling fluid return pump (222), and being used for controlling the drilling fluid return pump (222) according to the pressure difference value fed back by the pressure difference sensor (214), so that the interface (32) between the drilling fluid and the seawater in the drilling fluid volume control unit (212) is at a preset height; in, The drill rod (211) is provided with a drill rod U-shaped tube blocking valve (213); The drilling fluid return pipeline (221) is provided with a controllable U-shaped pipe blocking valve (223) for the drilling fluid return pipeline.

2. The offshore riserless drilling drilling fluid return system according to claim 1, characterized in that: Also includes: A drilling base emergency disconnect unit (232), arranged between the drilling fluid volume control unit (212) and the drilling fluid return pipeline (221), used for being installed on the drilling base (231), and spaced apart from the area where the wellbore (31) is located; An emergency disconnection structure (233) detachably connected to the drilling base emergency disconnection unit (232); An umbilical cable (235) and a tensioning connector (234) used to be connected between the drilling platform (201) and the emergency disconnection structure (233), the umbilical cable (235) and the tensioning connector (234) being fixed to each other; The emergency disconnection structure (233) is controlled by the tensioning force of the tensioning connection (234); when the tension reaches or exceeds the preset tensioning force of the tensioning connection (234), the emergency disconnection structure (233) is disconnected from the drilling base emergency disconnection unit (232).

3. The offshore riserless drilling drilling fluid return system according to claim 2, characterized in that: The hose comprises: a drilling fluid suction hose non-emergency disconnection pipe section (216) connected between the drilling fluid volume control unit (212) and the drilling template emergency disconnection unit (232); and A drilling fluid suction hose emergency disconnect pipe section (226) connected between the emergency disconnect structure (233) and the drilling fluid return pipeline (221); The drilling fluid suction hose non-emergency disconnection pipe section (216) and the drilling fluid suction hose emergency disconnection pipe section (226) are used to transmit the drilling fluid (50).

4. The offshore riserless drilling drilling fluid return system according to claim 3, characterized in that: Also includes: A riserless underwater blowout preventer (218), wherein the riserless underwater blowout preventer (218) is connected between the drilling fluid volume control unit (212) and the wellbore (31).

5. The offshore riserless drilling drilling fluid return system according to claim 4, characterized in that: The hose also includes: a non-emergency disconnection pipe section (217) of a well-killing hose connected between the riser-less underwater blowout preventer (218) and the drilling template emergency disconnection unit (232); and A well-killing hose emergency disconnection pipe section (227) connected between the emergency disconnection structural member (233) and the fixed end of the well-killing pipeline hot-spur connector (225) attached to the drilling fluid return pipeline (221); The non-emergency disconnect pipe section (217) of the well-killing hose and the emergency disconnect pipe section (227) of the well-killing hose are used to transmit well-killing fluid, and the well-killing fluid is pumped in through the well-killing umbilical cable connected to the free end of the well-killing pipeline hot-spur connector (225).

6. The offshore riserless drilling drilling fluid return system according to claim 5, characterized in that: Also includes: A counterweight unit (224) installed at the bottom of the drilling fluid return pipeline (221), wherein a drilling fluid return inlet valve (228) and a well-killing fluid outlet valve (229) are installed in the counterweight unit (224); The well-killing pipeline hot-spur joint (225) is fixed to the counterweight unit (224); The drilling fluid suction hose emergency disconnect pipe section (226) is connected to the drilling fluid return pipeline (221) via the drilling fluid return inlet valve (228); and the well killing hose emergency disconnect pipe section (227) is connected to the well killing umbilical cable via the well killing fluid outlet valve (229) and the well killing pipeline hot stab joint (225).

7. The offshore riserless drilling drilling fluid return system according to any one of claims 4 to 6, characterized in that: The riserless underwater blowout preventer (218) comprises: The gate valve assembly comprises a blowout preventer shear gate valve (2182) and a blowout preventer clamping gate valve (2183) which are arranged at intervals from top to bottom; the blowout preventer clamping gate valve (2183) is used to clamp the drill pipe (211) when the wellbore (31) needs to be safely closed; the blowout preventer shear gate valve (2182) is used to cut off the drill pipe (211) after the blowout preventer clamping gate valve (2183) clamps the drill pipe (211), and at the same time, the wellbore (31) is sealed.

8. The offshore riserless drilling drilling fluid return system according to claim 1, characterized in that: The drilling platform (201) is provided with a turntable and a derrick located above the turntable, the turntable is provided with a turntable opening (208), and a hollow area is opened below the drilling center (202) of the derrick, and the hollow area is a moon pool (207); After being assembled with the drilling fluid return pipeline (221), the drilling fluid return pump (222) can be lowered through the turntable opening (208) of the drilling platform (201) to below the moon pool (207).

Images