CN214616424U - Drilling fluid backflow system for offshore drilling without marine riser - Google Patents

Abstract

The present disclosure provides an offshore non-riser drilling fluid return system, the system comprising: the device comprises a drilling fluid volume control unit, an open water area drilling drill rod, a drilling fluid backflow pipeline, a drilling fluid backflow pump arranged on the drilling fluid backflow pipeline, and a drilling fluid treatment device. The drilling fluid volume control unit is mounted directly on the wellhead or above the riser-less blowout preventer with its top open to the sea water. The drill pipe extends from the drilling platform through the volume control unit and performs drilling operations via the interior of the volume control unit. The drilling fluid backflow pipeline is connected with the volume control unit through a hose, and the drilling fluid backflow pump is sequentially installed in one pipe section of the backflow pipeline along the axial direction and used for pumping the drilling fluid flowing into the backflow pipeline from the volume control unit back to the drilling platform and recycling the drilling fluid after being processed by the drilling fluid processing device. The system is not limited by the size of a drilling ship and the water depth, can effectively recover drilling fluid, and is suitable for full-water-depth drilling operation.

Description

Drilling fluid backflow system for offshore drilling without marine riser

Technical Field

The disclosure belongs to the technical field of offshore energy exploitation, and relates to an offshore drilling fluid backflow system without a marine riser.

Background

The drilling operation performed at sea can realize the development and utilization of seabed energy, and can be used for exploiting energy sources such as petroleum, natural gas, combustible ice and the like. In order to realize deep-water drilling and ultra-deep drilling, a non-riser drilling technology can be adopted in deep-water drilling operation. However, for ultra-deep water drilling operation, the existing large-scale drilling equipment uses a large-aperture marine riser, a high-pressure well control pipeline needs to be installed, the installation is realized underwater, the installation safety cannot be guaranteed, and meanwhile, the cost is high.

Specifically, the main function of the large bore riser is to effect the return flow of drilling fluid and the choke kill operation, which is accomplished by way of a choke kill line attached to the riser and connected between the on-board well control system and the blowout preventer. Generally, a well control line for a riser-less drilling of shallow waters is implemented by establishing a separate operational line between the drilling vessel and the blowout preventer. However, in ultra-deep water operations, it is economically undesirable to install such high-pressure well control lines, and in practice, safe installation is not possible.

At present, a deepwater non-riser drilling technology of 1000-2000 meters is mature, and is generally applied to surface layer drilling before a blowout preventer (BOP) is installed. However, the application water depth of the non-riser drilling technology has limitations, as the water depth increases, no matter when the operation water depth is increased to more than 2000 meters in a test, or a rotary control head (RCD) is installed on the top of the BOP, the backflow of the drilling fluid is limited to a certain extent, and as the hydrostatic pressure generated by a longer drilling fluid backflow line to the well bore will greatly affect the stability of the well bore, the method has obvious limitations when being used in a deeper sea area. The operation of pumping drilling fluid into the well bore during the drilling process without a riser and then returning the drilling cuttings to the drilling vessel with the drilling fluid from the nearby drilling fluid return line is not feasible by using an underwater rotary control head, and in deep sea drilling or deeper drilling scenarios where the water depth exceeds 1500 to 2000 meters, the pumping capacity of the pump is limited and drilling fluid of sufficient quantity and specific gravity cannot be pumped back to the drilling vessel.

SUMMERY OF THE UTILITY MODEL

Technical problem to be solved

The present disclosure provides an offshore drilling fluid recirculation system for drilling without a riser, which is suitable for offshore energy recovery in full-depth water areas (including deep water areas with a depth of less than 2600 m, or ultra-deep water areas with a depth of more than 2600 m) to at least partially overcome the limitations of the existing drilling fluid recovery systems in deeper sea areas.

(II) technical scheme

One aspect of the present disclosure provides an offshore non-riser drilling fluid return system. Above-mentioned marine no marine riser drilling fluid return-flow system includes: a drilling fluid volume control unit 212, an open water drilling pipe 211, a drilling fluid return line 221, a drilling fluid return pump 222 mounted to a section of the drilling fluid return line 221, and a drilling fluid treatment device 206. The drilling fluid volume control unit 212 is located in the sea water and the top of the drilling fluid volume control unit 212 is open towards the sea water and the bottom of the drilling fluid volume control unit 212 is towards the drilling location. Open water drilling pipe 211 is used to lower from a floating rig 201 and drill through drilling fluid volume control unit 212 and drilling fluid is pumped from rig 201 through the bore hole inside pipe 211 to wellbore 31. The drilling fluid return line 221 is connected to the drilling fluid volume control unit 212 by a hose. The drilling fluid return pump 222 is used for pumping the drilling fluid 50 flowing from the drilling fluid volume control unit 212 into the drilling fluid return line 221 back to the drilling platform 201, and is recycled after being processed by the drilling fluid processing device 206.

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 configured to sense a differential pressure value inside and outside the drilling fluid volume control unit 212 according to a height of an interface 32 between the drilling fluid and the seawater in the drilling fluid volume control unit 212. The above system further comprises: and a control unit, which is electrically and/or communicatively connected with the differential pressure sensor 214 and the drilling fluid return pump 222, and is configured 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 of the drilling fluid and the seawater in the drilling fluid volume control unit 212 is at a preset height.

According to the embodiment of the disclosure, a drill pipe U-shaped pipe blocking valve 213 is arranged on the drill pipe 211; a controllable U-shaped pipe blocking valve 223 of the drilling fluid return line is arranged on the drilling fluid return line 221.

According to an embodiment of the present disclosure, the above-mentioned offshore non-riser drilling fluid return system further comprises: and the separable connecting structure is arranged on one or both of the drilling fluid volume control unit 212 and the drilling fluid return pipeline 221, and the separable connecting structure is connected with the drilling fluid volume control unit 212 and the drilling fluid return pipeline 221 through the hoses. The separable connecting structure comprises: the separation part is detachably connected with the fixing part and is separated from the fixing part under the control of an external force or an electrical control signal.

According to an embodiment of the present disclosure, the above-mentioned offshore non-riser drilling fluid return system further comprises: the drilling base plate emergency disconnection unit 232 is arranged between the drilling fluid volume control unit 212 and the drilling fluid return pipeline 221, is used for being installed on the drilling base plate 231 and is arranged at intervals with the area where the well bore 31 is located; an emergency disconnection structure 233 detachably connected to the drilling template emergency disconnection unit 232; an umbilical 235 and a tension connection 234 for connection between the drilling platform 201 and the emergency disconnect structure 233, the umbilical 235 and tension connection 234 being secured to one another. Wherein the emergency disconnection structure 233 is controlled by a tension force of the tension connector 234, and when the tension force reaches or is greater than a preset tension force of the tension connector 234, the emergency disconnection structure 233 is disconnected from the drilling template emergency disconnection unit 232. In this embodiment, the drilling template emergency disconnection unit 232 is used as a fixed part, and the emergency disconnection structure 233 is used as a separate part.

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 includes: a drilling fluid intake hose non-emergency disconnect pipe section 216 connected between the drilling fluid volume control unit 212 and the drilling template emergency disconnect unit 232; and a drilling fluid intake hose emergency disconnect pipe section 226 connected between the emergency disconnect structure 233 and the drilling fluid return line 221. Wherein the drilling fluid intake hose non-emergency disconnect section 216 and the drilling fluid intake hose emergency disconnect section 226 are used to transport the drilling fluid 50.

According to an embodiment of the present disclosure, the above-mentioned offshore non-riser drilling fluid return system further comprises: a riser-less subsea blowout preventer 218, the riser-less subsea blowout preventer 218 connected between the drilling fluid volume control unit 212 and the wellbore 31.

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 kill hose non-emergency disconnect pipe section 217 connected between the riser-less subsea blowout preventer 218 and the drilling template emergency disconnect unit 232; and a kill hose emergency disconnect pipe segment 227 connected between the emergency disconnect structure 233 and the fixed end of the kill line hot stab connection 225 attached to the drilling fluid return line 221. Wherein the kill hose non-emergency disconnect section 217 and the kill hose emergency disconnect section 227 are used to transport kill fluid that is pumped through a kill umbilical connected to the free end of the kill line hot stab connection 225.

According to an embodiment of the present disclosure, the above-mentioned offshore non-riser drilling fluid return system further comprises: a weight unit 224 installed at the bottom of the drilling fluid return line 221, wherein a drilling fluid return inlet valve 228 and a well killing fluid outlet valve 229 are installed in the weight unit 224; the kill line hot stab 225 is secured to the counterweight unit 224. Wherein the drilling fluid intake hose emergency disconnect pipe section 226 is in communication with the drilling fluid return line 221 via a drilling fluid return inlet valve 228; kill hose emergency disconnect pipe segment 227 communicates with the kill umbilical via kill fluid outlet valve 229 and kill line hot stab connection 225.

According to an embodiment of the present disclosure, the riser-less subsea blowout preventer 218 includes: a gate valve set. The gate valve group comprises a blowout preventer shear gate valve 2182 and a blowout preventer clamping gate valve 2183 which are arranged from top to bottom at intervals; the blowout preventer clamp ram valve 2183 is used to clamp the drill pipe 211 when it is desired to safely close the wellbore 31; blowout preventer shear ram valve 2182 is used to sever drill pipe 211 while allowing wellbore 31 to be sealed after blowout preventer clamp ram valve 2183 clamps drill pipe 211.

According to the embodiment of the disclosure, a rotary table and a derrick located above the rotary table are arranged on a drilling platform 201, a rotary table opening 208 is arranged on the rotary table, a hollow area is arranged below a drilling center 202 of the derrick, and the hollow area is a moon pool 207; wherein the drilling fluid return pump 222, when assembled with the drilling fluid return line 221, can be lowered through the rotary table opening 208 of the drilling platform 201 to below the moon pool 207.

(III) advantageous effects

According to the technical scheme, the offshore drilling fluid backflow system without the marine riser has the following beneficial effects:

(1) the drilling fluid volume control unit is positioned in seawater, two ends of the drilling fluid volume control unit are respectively opened towards seawater and a drilling position, a certain liquid level height is formed in the drilling fluid volume control unit based on the balance among seawater static pressure, atmospheric pressure and drilling fluid gushed from a well hole, the drilling fluid in the drilling fluid volume control unit enters a drilling fluid backflow pipeline through a hose and has a certain liquid level height based on a U-shaped pipe principle, and a drilling fluid backflow pump installed inside one pipe section of the drilling fluid volume control unit can pump the drilling fluid flowing into the drilling fluid backflow pipeline from the drilling fluid volume control unit to the position above the sea surface. When the drilling operation is carried out, the method is not limited by the size or the water depth capacity of a drilling platform (such as a drilling ship), and can be suitable for the drilling operation of deep water and ultra-deep water; the drilling fluid return pump does not need to be installed on the seabed, is deeper than the drilling depth of a conventional drilling system, and can be applied to full-depth water areas, including deep water areas with the water depth H less than or equal to 2600 meters or ultra-deep water areas with the water depth H more than 2600 meters.

(2) Heavy marine risers and tension systems thereof do not need to be installed, and the requirement of the drilling platform on the demand of drilling fluid is reduced by 70-90% because the traditional large-aperture marine riser for mud backflow is replaced by a small-diameter drilling fluid backflow pipeline; in addition, the present disclosure allows for a greater offset of the drilling platform relative to the wellbore, unlike the use of conventional hard risers, which utilize flexible connections between the drilling fluid return line and the volume control unit, since a floating drilling platform is not required to maintain a very precise positioning, the amount of fuel used is greatly reduced.

(3) Because the drilling fluid return pump is installed in the pipe section in the drilling fluid return pipeline along the axial sequence, the diameter size of the drilling fluid return pipeline is reduced, and therefore the floating drilling platform can pass through a small-sized turntable opening and is placed below a moon pool after being installed, and the difficulty and the insecurity that in the prior art, the drilling fluid return pump only can be installed underwater due to the fact that the drilling fluid return pump comprises a marine riser system with large size are avoided. In addition, the drilling fluid return pipeline can be installed and deployed through a hoisting device on the derrick, and the arrangement can remarkably reduce the operation time of drilling operation.

(4) Based on the arrangement of the underwater blowout preventer without the marine riser, when the floating type drilling platform is accidentally drifted to a preset position, the connection between the drill rod and the floating type drilling platform is cut off, a well hole is sealed, and effective well control is realized. The pinched-off drill pipe can be quickly fished out of the wellbore after the floating rig is returned directly above the wellbore, otherwise reconnection would be difficult.

(5) When surface layer drilling begins, drilling fluid enters a borehole through a drill rod, when a new drill rod part is added on the drill rod, the static pressure gradient of the drilling fluid in the drill rod is higher than that of an open water area outside the drill rod, according to the U-shaped pipe principle, a large amount of heavy drilling fluid can gush out of the drill rod from the bottom of the drill rod, and through the arrangement of the drill rod U-shaped pipe blocking valve, part of the drilling fluid gushed out due to the U-shaped pipe principle can be effectively prevented, meanwhile, the drill rod U-shaped pipe blocking valve is also beneficial to avoiding air entering caused when the drill rod is added, and the loss of the drilling fluid is reduced; through setting up the controllable U-shaped pipe of drilling fluid return line and blocking the valve, can prevent because of the partial drilling fluid that U type pipe principle was gushed, reduce the loss of drilling fluid.

(6) In the scheme that the underwater blowout preventer without the marine riser is included or not, the drilling base plate emergency disconnection unit and the emergency disconnection structural member are arranged, the pipeline connection between the drilling fluid backflow device and the drilling fluid volume control unit can be disconnected based on a control signal of an umbilical cable in an emergency, and the reconnection is carried out after the emergency is removed, the pipeline between the drilling fluid volume control unit and the emergency disconnection unit on the drilling base plate is not disconnected in the emergency, the pipeline connection of a drilling part cannot be influenced, and the well hole is prevented from being relocated; and the pipeline between the emergency disconnection structural member and the drilling fluid return line can be disconnected along with the separation of the emergency disconnection structural member from the drilling base plate emergency disconnection unit under the emergency condition, and is reconnected after the subsequent emergency is relieved, so that the drilling fluid return line is effectively prevented from being influenced under the emergency condition.

Drawings

FIG. 1 is a schematic block diagram of an offshore non-riser drilling fluid return system without a non-riser subsea blowout preventer, according to an embodiment of the present disclosure.

Fig. 2 is a schematic diagram illustrating a principle of drilling fluid return flow implementation of an offshore non-riser drilling fluid return flow system according to an embodiment of the present disclosure.

FIG. 3 is a schematic block diagram of an offshore non-riser drilling fluid return system including a non-riser subsea blowout preventer according to another embodiment of the present disclosure.

FIG. 4 is a schematic diagram of the main components, valves and piping of an offshore non-riser drilling fluid return system according to an embodiment of the present disclosure.

FIG. 5 is a schematic diagram of a structure of a riser-less subsea blowout preventer and a drilling fluid volume control unit according to an embodiment of the present disclosure.

Fig. 6 is a flow chart of an assembly method of an offshore non-riser drilling fluid return system according to an embodiment of the present disclosure.

Fig. 7 is a schematic diagram of a process of passing a drilling fluid return line and a drilling fluid return pump through a small bore turntable opening and suspending the drilling fluid return line on a gimbal hanger in a moonpool vehicle according to an embodiment of the present disclosure.

Fig. 8 is a flow chart of a drilling fluid recovery method based on an offshore non-riser drilling fluid return system according to an embodiment of the present disclosure.

[ notation ] to show

11-sea level; 12-the seabed;

13-seawater;

201-floating drilling platform; 202-well center;

203-a lifting device; 204-moon pool vehicle;

205-universal suspension; 206-drilling fluid treatment means;

207-moon pool; 208-a turntable opening;

211-a drill rod;

212-drilling fluid volume control unit;

2121-suction line connection operable by an ROV;

2122-ROV auxiliary control panel;

2123-blowout preventer control fluid accumulator; 2124-accumulator liquid-replenishing pipe;

213-drill pipe U-shaped pipe blocking valve; 214-differential pressure sensor;

216-drilling fluid suction hose non-emergency disconnect pipe section;

217-the kill hose is not an emergency disconnect pipe section;

218-riser-less subsea blowout preventer;

2181-a kill hose access connection; 2182-shearing a gate valve of the blowout preventer;

2183-the blowout preventer clamps the gate valve; 2184-kill valve on;

2185-a well-depressing valve; 2186-wellhead connector;

221-drilling fluid return line; 222-drilling fluid return pump;

223-a controllable U-shaped pipe blocking valve of a drilling fluid return line;

224-a counterweight unit;

225-kill line hot stab sub;

226-emergency disconnection of the pipe section of the drilling fluid suction hose;

227-emergency disconnection of the pipe section by a kill hose; 228-drilling fluid return inlet valve;

229-a kill fluid outlet valve;

231-drilling template; 232-drilling base plate emergency disconnection unit;

233-emergency disconnection structure; 234-tension connection;

235-an umbilical; 236-umbilical cord fixation;

31-a borehole; 32-interface of drilling fluid with seawater;

41-atmospheric pressure; 131-hydrostatic pressure gradient;

50-drilling fluid;

51-hydrostatic pressure gradient of drilling fluid in volume control unit;

61-hydrostatic pressure gradient of drilling fluid in return line;

71-reflux pump inlet pressure; 72-reflux pump outlet pressure;

73-reflux pump outlet flow.

Detailed Description

The present disclosure provides an offshore non-riser drilling fluid return system for offshore drilling operations that returns drilling fluid from a wellbore to a drilling platform without the use of a conventional offshore platform riser. The set of offshore non-riser drilling fluid return systems described in this disclosure are not limited by the size or water depth capability of the drill ship when performing drilling operations, and therefore a relatively small floating drilling platform (e.g., drill ship or other offshore drilling equipment) may be used, greatly increasing economic benefits. The offshore non-riser drilling fluid return system of the present disclosure may be applied to deep water drilling or ultra deep water drilling of an underwater substrate or sedimentary earth formation.

The present disclosure provides an offshore non-riser drilling fluid return system comprising: the device comprises a drilling fluid volume control unit, an open water area drilling drill rod, a drilling fluid backflow pipeline, a drilling fluid backflow pump arranged on one pipe section of the drilling fluid backflow pipeline, and a drilling fluid treatment device. The drilling fluid volume control unit is located in the seawater and the top of the drilling fluid volume control unit is open towards the seawater and the bottom of the drilling fluid volume control unit is towards the drilling location. The open water drilling pipe is used for lowering from the drilling platform and passes through the drilling fluid volume control unit to carry out drilling operation, and the drilling fluid is pumped to a borehole from the drilling platform through a hole in the drilling pipe. The drilling fluid return line is connected with the drilling fluid volume control unit through a hose. The drilling fluid return pump is used for pumping the drilling fluid flowing into the drilling fluid return pipeline from the drilling fluid volume control unit back to the drilling platform, and recycling the drilling fluid after being processed by the drilling fluid processing device.

The offshore non-riser drilling fluid return system provided by the present disclosure may further comprise at least one of the following structures: a marine riser-free underwater blowout preventer comprises a drilling template emergency disconnection unit and an emergency disconnection structure of an emergency disconnection structural member.

The marine riser-free drilling fluid backflow system with the drilling fluid volume control unit and the drilling fluid backflow pipeline can work under two working conditions, the first working condition is a scene that the drilling fluid volume control unit is not provided with a riser-free underwater blowout preventer, and the drilling fluid volume control unit with the wellhead can be fixed on a drilling base plate to implement drilling operation at a well-positioned well position, so that backflow of the drilling fluid during well drilling is realized. The second working condition is a scene that the drilling fluid volume control unit is provided with the underwater blowout preventer without the marine riser, the underwater blowout preventer without the marine riser is arranged between the drilling fluid volume control unit and the borehole, and the connection between the drill rod and the floating drilling platform can be cut off when the floating drilling platform accidently drifts to a preset position based on the underwater blowout preventer besides the function of refluxing the drilling fluid in the conventional drilling operation, and the borehole is sealed, so that the effective well control is realized.

The offshore drilling fluid backflow system without the marine riser can be applied to full-depth water areas, including deep water areas with the water depth H being less than or equal to 2600 meters or ultra-deep water areas with the water depth H being more than 2600 meters, and breaks the limitation of current deep water drilling.

For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.

An exemplary embodiment of the present disclosure provides an offshore non-riser drilling fluid return system with drilling fluid retrievable.

FIG. 1 is a schematic block diagram of an offshore non-riser drilling fluid return system without a non-riser subsea blowout preventer, according to an embodiment of the present disclosure. Fig. 2 is a schematic diagram illustrating a principle of drilling fluid return flow implementation of an offshore non-riser drilling fluid return flow system according to an embodiment of the present disclosure. FIG. 3 is a schematic block diagram of an offshore non-riser drilling fluid return system including a non-riser subsea blowout preventer according to another embodiment of the present disclosure.

In fig. 1 and 3, the sea surface 1 and the seabed 12 are illustrated, the sea water being illustrated in a long and short double-dashed line, and the sea water 13 being illustrated in a black dot.

Referring to fig. 1 and 3, an offshore non-riser drilling fluid return system of the present disclosure includes: the drilling fluid volume control unit 212, the open water drilling pipe 211, a drilling fluid return line 221 arranged at an interval from the drilling fluid volume control unit 212, a drilling fluid return pump 222 installed at one pipe section of the drilling fluid return line 221, and the drilling fluid processing device 206.

The drilling fluid volume control unit 212 is located in the sea water and the top of the drilling fluid volume control unit 212 is open towards the sea water and the bottom of the drilling fluid volume control unit 212 is towards the drilling location. Open water drilling pipe 211 is used to lower from a floating rig 201 and drill through drilling fluid volume control unit 212 and drilling fluid is pumped from rig 201 through the bore hole inside pipe 211 to wellbore 31. The drilling fluid return line 221 is connected to the drilling fluid volume control unit 212 by a hose. The drilling fluid return pump 222 is used for pumping the drilling fluid 50 flowing from the drilling fluid volume control unit 212 into the drilling fluid return line 221 back to the drilling platform 201, and is recycled after being processed by the drilling fluid processing device 206.

In accordance with an embodiment of the present disclosure, referring to fig. 1 and 3, when the non-riser subsea blowout preventer 218 is not installed, the drilling fluid volume control unit 212 is disposed toward a drilling location, such as may be installed on a wellhead of a drilling template 231; when the drilling fluid volume control unit 212 is installed with a riser-less subsea blowout preventer 218, the drilling fluid volume control unit 212 is installed above the riser-less subsea blowout preventer 218. In either case, the top of the drilling fluid volume control unit 212 is open to the sea and the bottom is open to the drilling location. Although the kill hose emergency disconnect pipe segment 227 is illustrated in FIG. 1, in practice the kill hose emergency disconnect pipe segment 227 may not be installed in a system that does not include the riser-less subsea blowout preventer 218. During surface drilling, the wellbore is drilled at the drilling location without installing the riser-less subsea blowout preventer 218. When drilling deep sea, the riser-less subsea blowout preventer 218 may be installed as desired.

Floating rig 201, which is the load carrying and control platform for offshore drilling operations, may be a drill ship, such as a semi-submersible drill ship with the bottom inside the sea as illustrated in the example of fig. 1. The floating rig 201 has two operating centers, drilling center 202 and drilling fluid return line center, the drilling center 202 corresponding to the axis of the drill pipe 221 and the drilling fluid return line center being shown with reference to the axis of the drilling fluid return line 221. There is a distance between the drilling center 202 and the axis of the fluid return line 221 to prevent interference between the drill pipe 221 and the fluid return line 221 during operation.

In accordance with an embodiment of the present disclosure, referring to fig. 1, a differential pressure sensor 214 is disposed 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 based on the height of the drilling fluid to sea water interface 32 within the drilling fluid volume control unit 212. The floating drilling system further includes: and 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 configured 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 including only a, only B, or both a and B. In this embodiment, the controller may be located on the drilling platform 201, and transmit the control signal to the differential pressure sensor 214 and the drilling fluid return pump 222 via an umbilical cable, or a wireless communication module is installed on the differential pressure sensor 214 and the drilling fluid return pump 222 to implement communication connection with the controller, or both of the foregoing cases are included.

Referring to fig. 1, in a riser-less drilling fluid return system, the wellbore is open to seawater so that the drilling fluid in the wellbore will be in direct contact with the seawater in the fluid volume control unit 212 and form a drilling fluid-seawater interface 32. One or more pressure differential sensors 214 mounted on the drilling fluid volume control unit 212 can monitor the interface 32 in real time and transmit a level signal to the controller in real time to control the real-time flow rate of the drilling fluid return pump 222 in the drilling fluid return line 221, thereby controlling the height of the drilling fluid-seawater interface 32 in real time and precisely. The controller may be a main controller disposed on the floating drilling platform 201, and the main controller can adjust the rotation speed of the drilling fluid reflux 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 controlling the height of the interface 32 between the drilling fluid and the seawater in real time.

Referring to fig. 1 and 2, the drilling fluid volume control unit 212 is located in seawater and is open at both ends to seawater and a drilling location (after drilling the borehole 31 at the drilling location by the drill pipe 211, the drilling location corresponding to the borehole 31), respectively, and has a certain level height within the drilling fluid volume control unit 212 based on the equilibrium between the hydrostatic pressure, the atmospheric pressure and the drilling fluid 50 gushing out of the borehole 31, and the hydrostatic pressure gradient 131, the atmospheric pressure 41 and the hydrostatic pressure gradient 51 of the drilling fluid in the volume control unit caused by the drilling fluid 50 are illustrated in fig. 2. Based on the U-tube principle, the drilling fluid 50 in the drilling fluid volume control unit 212 enters the drilling fluid return line 221 through a hose and has a certain fluid level. To distinguish the drilling fluid entering the drilling fluid return line as being balanced by the combined effect of the seawater static pressure, the atmospheric pressure and the drilling fluid 50 flowing out of the borehole 31, reference numeral 61 is used to illustrate the drilling fluid static pressure gradient in the drilling fluid return line, the drilling fluid static pressure gradient 61 in the drilling fluid return line being the balancing effect of the seawater static pressure gradient 131, the atmospheric pressure 41 and the drilling fluid static pressure gradient 51 in the volume control unit. Figure 2 also illustrates a return pump inlet pressure 71, a return pump outlet pressure 72 and a return pump outlet flow 73, the drilling fluid return pump 222 being slightly lower than the level of drilling fluid 50 entering the drilling fluid return line 221 through the hose, pumping the drilling fluid 50 flowing into the drilling fluid return line 221 from the drilling fluid volume control unit 212 above the surface of the sea.

A drilling fluid return pump 222 is axially mounted on a section of the drilling fluid return line 221. For example, there may be one or more drilling fluid return pumps 222, with a plurality of drilling fluid return pumps 222 arranged in axial sequence along a section of drilling fluid return line 221. The drilling fluid return pump 222 is positioned below the level of drilling fluid 50 in the drilling fluid return line 221, which level is determined by the atmospheric pressure, seawater, and the hydrostatic pressure balance of the drilling fluid. The setting position of the drilling fluid return pump can be set according to the number of the drilling fluid return pumps, the pumping capacity, the diameter of a drilling fluid return pipeline and the pumping requirement.

According to an embodiment of the present disclosure, referring to fig. 1, the drilling fluid treatment device 206 in the above-mentioned offshore non-riser drilling fluid return system is configured to be disposed on a floating drilling platform 201. The drilling fluid treatment device 206 is connected to a drilling fluid return line 221. The drilling fluid return pump 222 pumps the drilling fluid 50 in the drilling fluid return line 221 to the drilling fluid treatment device 206, and the drilling fluid treatment device 206 is used for treating the drilling fluid 50 so as to recycle the treated drilling fluid 50.

The drilling fluid treated by the drilling fluid treatment device 206 is sent to the borehole 31 through the drilling rod 211 in the open water again for drilling operation.

The offshore non-riser drilling fluid backflow system is not limited by the size or the water depth capacity of a drilling ship when drilling operation is performed, and can be suitable for deep water and ultra-deep water drilling operation. And the drilling fluid return pump does not need to be installed on the seabed, and the drilling depth is deeper than that of a conventional drilling system, so that the drilling fluid return pump can be applied to a full-depth water area, and the limitation of recovering the drilling fluid in the deep-sea water area in the traditional technology is broken through.

In deep sea scientific drilling operations, the offshore riser-less drilling fluid return system of the present disclosure has considerable economic value because it enables the drilling fluid used in the drilling operation to be recycled rather than being discarded in seawater as in previous drilling operations not equipped with such a system. The cyclic utilization of the drilling fluid can reduce the space of the drilling platform for storing the drilling fluid and chemical agents thereof, thereby reducing the cost of drilling operation.

The offshore drilling fluid backflow system for the non-riser drilling adopts a drilling structure for drilling without a riser, a heavy riser and a tension system of the riser are not required to be installed, and the drilling fluid backflow pipeline with a small diameter is used for replacing a traditional large-aperture riser for mud backflow, so that the requirement of a drilling platform on the drilling fluid demand is reduced by 70-90%. In addition, the present disclosure allows for a larger offset of the floating rig relative to the wellbore, and in addition, the present disclosure allows for a larger offset of the rig relative to the wellbore, unlike using conventional hard risers, which use flexible connections between the drilling fluid return line and the volume control unit, since the floating rig is not required to maintain a very precise positioning, the amount of fuel used is greatly reduced.

In the case that the pressure control of the borehole is not required, the drilling fluid volume control unit 212 may be fixed to the drilling template by using a drilling fluid volume control unit with a borehole head to perform a drilling operation at a well-positioned borehole position without installing a riser sub-sea blowout preventer (riser blowout preventer), so as to realize the backflow of the drilling fluid during the drilling of the borehole. In additional embodiments described later, the drilling fluid volume control unit 212 described above may also be installed above the non-riser subsea blowout preventer to enable pressure control of the wellbore based on the non-riser subsea blowout preventer.

According to an embodiment of the present disclosure, referring to fig. 1, a drill pipe U-tube blocking valve 213 is provided on a drill pipe 211; a controllable U-shaped pipe blocking valve 223 of the drilling fluid return line is arranged on the drilling fluid return line 221.

When surface layer drilling begins, drilling fluid enters a borehole through a drill rod 211, when a new drill rod part is added on the drill rod, the static pressure gradient of the drilling fluid in the drill rod is higher than that of an open water area outside the drill rod, according to the U-shaped pipe principle, a large amount of heavy drilling fluid can gush out of the drill rod from the bottom of the drill rod, and through the arrangement of a drill rod U-shaped pipe blocking valve arranged on the drill rod, part of drilling fluid gushed out due to the U-shaped pipe principle can be effectively prevented, meanwhile, the drill rod U-shaped pipe blocking valve is also beneficial to avoiding air entering caused when the drill rod is added, and the loss of the drilling fluid is reduced; through setting up the controllable U-shaped pipe of drilling fluid return line and blocking the valve, can prevent because of the partial drilling fluid that U type pipe principle was gushed, reduce the loss of drilling fluid.

To further optimize emergency situations, the above-described offshore non-riser drilling fluid return system without or with the non-riser subsea blowout preventer 218, according to an embodiment of the present disclosure, and as illustrated with reference to fig. 1 and 3, further comprises: separable connection structure sets up on one of them or between the two of drilling fluid volume control unit 212 and drilling fluid return line 221, and separable connection structure and drilling fluid volume control unit 212 and drilling fluid return line 221 all are connected through above-mentioned hose between them, and this separable connection structure includes: the fixed part to and with the detachable separation portion of being connected of above-mentioned fixed part, the mode that control separation portion realized the separation includes: external forces or electrical control signals. For example, the electrical control signal may be in the form of, for example, a controller sending a disconnection control signal to the emergency disconnection structure 233 based on the umbilical 235 to the disconnection portion, which performs a structural change under the control of the disconnection control signal to effect disconnection from the fixed portion. The manner in which the external force is controlled can be found in the manner described later in which tension control is based on the tension link 234.

In one embodiment, the separable connecting structure includes: the drilling base plate emergency disconnection unit 232 is arranged between the drilling fluid volume control unit 212 and the drilling fluid return pipeline 221, is used for being installed on the drilling base plate 231 and is arranged at intervals with the area where the well bore 31 is located; an emergency disconnection structure 233 detachably connected to the drilling template emergency disconnection unit 232; an umbilical 235 and a tension connector 234 connected between the floating rig 201 and the emergency disconnect structure 233, the umbilical 235 and tension connector 234 being secured to each other. Wherein the emergency disconnection structure 233 is controlled by a tension force of the tension connector 234, and when the tension force reaches or is greater than a preset tension force of the tension connector 234, the emergency disconnection structure 233 is disconnected from the drilling template emergency disconnection unit 232.

For example, the securing of the umbilical 235 and the tension connector 234 is accomplished by an umbilical fastener 236. In one embodiment, the tension connector 234 may be a tension cable, and the tension connector 234 of the present disclosure may be a connector having a certain mechanical strength and flexibility capable of providing a tensile force, not limited to a cable.

The drilling template emergency disconnect unit 232 is adapted to be fixedly arranged on the drilling template 231, the drilling template 231 is adapted to be fixed to the seabed 12, and a part of the area of the drilling template 231 is located above the borehole 31. The drilling template emergency disconnect unit 232 is spaced from the region of the borehole 31. When the tension of the tension connector 234 reaches or exceeds the preset tension of the tension connector 234, the emergency disconnect structure 233 is disengaged from the drilling template emergency disconnect unit 232.

In the offshore non-riser drilling fluid backflow system comprising or not comprising a non-riser underwater blowout preventer, by arranging the drilling base plate emergency disconnection unit and the emergency disconnection structural member, the control signal based on the umbilical cable can disconnect the pipeline connection between the drilling fluid backflow device and the drilling fluid volume control unit in case of emergency and reconnect the drilling fluid backflow device and the drilling fluid volume control unit after emergency release, the pipeline between the drilling fluid volume control unit and the emergency disconnection unit on the drilling base plate is not disconnected in case of emergency, the pipeline connection of a drilling part cannot be influenced, and the borehole is prevented from being relocated; and the pipeline between the emergency disconnection structural member and the drilling fluid return line can be disconnected along with the separation of the emergency disconnection structural member from the drilling base plate emergency disconnection unit under the emergency condition, and is reconnected after the subsequent emergency is relieved, so that the drilling fluid return line is effectively prevented from being influenced under the emergency condition.

The disconnection and reconnection functions of the present disclosure are realized based on the structural arrangement of the drilling base plate emergency disconnection unit and the emergency disconnection structure of the above examples, and any separable connection structure installed between the drilling fluid volume control unit and the drilling fluid return line is within the scope of the present disclosure. In other embodiments, the separable connection structure may be placed at the bottom of the drilling fluid return line, or on the drilling fluid volume control unit, or on the riser-less subsea blowout preventer.

In an offshore non-riser drilling fluid return system that does not include a non-riser subsea blowout preventer 218, according to an embodiment of the present disclosure, and as illustrated with reference to fig. 1, the hose connected between the fluid return line 221 and the fluid volume control unit 212 comprises: a drilling fluid intake hose non-emergency disconnect pipe section 216 connected between the drilling fluid volume control unit 212 and the drilling template emergency disconnect unit 232; and a drilling fluid intake hose emergency disconnect pipe section 226 connected between the emergency disconnect structure 233 and the drilling fluid return line 221. In this embodiment, the drilling fluid intake hose non-emergency disconnect section 216 and the drilling fluid intake hose emergency disconnect section 226 are used to transport the drilling fluid 50.

In an offshore non-riser drilling fluid return system, with or without a non-riser subsea blowout preventer, according to an embodiment of the present disclosure, and as illustrated with reference to fig. 1 and 3, the hose between the above-described fluid return line 221 and the fluid volume control unit 212 comprises: a drilling fluid intake hose non-emergency disconnect pipe section 216 connected between the drilling fluid volume control unit 212 and the drilling template emergency disconnect unit 232; and a drilling fluid intake hose emergency disconnect pipe section 226 connected between the emergency disconnect structure 233 and the drilling fluid return line 221. Wherein the drilling fluid intake hose non-emergency disconnect section 216 and the drilling fluid intake hose emergency disconnect section 226 are used to transport the drilling fluid 50.

In an offshore non-riser drilling fluid return system including a non-riser subsea blowout preventer 218, the non-riser subsea blowout preventer 218 is connected between the fluid volume control unit 212 and the wellbore 31, according to an embodiment of the present disclosure, illustrated with reference to fig. 3.

Referring to fig. 3, in an offshore non-riser drilling fluid return system including a non-riser subsea blowout preventer 218, the hose between the fluid return line 221 and the fluid volume control unit 212 includes, in addition to the fluid intake hose non-emergency disconnect section 216 and the fluid intake hose emergency disconnect section 226: a kill hose non-emergency disconnect pipe section 217 connected between the riser-less subsea blowout preventer 218 and the drilling template emergency disconnect unit 232; and a kill hose emergency disconnect pipe segment 227 connected between the emergency disconnect structure 233 and the fixed end of the kill line hot stab connection 225 attached to the drilling fluid return line 221. Wherein the kill hose non-emergency disconnect section 217 and the kill hose emergency disconnect section 227 are used to transport kill fluid that is pumped through a kill umbilical connected to the free end of the kill line hot stab connection 225.

FIG. 4 is a schematic diagram of the main components, valves and piping of an offshore non-riser drilling fluid return system according to an embodiment of the present disclosure. Although FIG. 4 illustrates a system including a non-riser subsea blowout preventer, the same component details apply equally to a system that does not include a non-riser subsea blowout preventer.

Referring to fig. 1, 3 and 4, in an offshore non-riser drilling fluid return system with or without a non-riser subsea blowout preventer 218, further comprising: a counterweight unit 224 mounted at the bottom of the drilling fluid return line 221. The weight unit 224 has mounted therein a drilling fluid return inlet valve 228 and a control fluid outlet valve 229. The kill line hot stab 225 is secured to the counterweight unit 224. Wherein the drilling fluid intake hose emergency disconnect pipe section 226 is in communication with the drilling fluid return line 221 via a drilling fluid return inlet valve 228; kill hose emergency disconnect pipe segment 227 communicates with the kill umbilical via kill fluid outlet valve 229 and kill line hot stab connection 225.

In accordance with an embodiment of the present disclosure, shown with reference to FIG. 4, a riser-less subsea blowout preventer 218 includes: a gate valve set. The ram valve set comprises a blowout preventer shear ram valve 2182 and a blowout preventer clamping ram valve 2183 which are arranged from top to bottom at intervals. The blowout preventer clamp ram valve 2183 is used to clamp the drill pipe 211 when it is desired to safely close the wellbore 31. Blowout preventer shear ram valve 2182 is used to sever drill pipe 211 while allowing wellbore 31 to be sealed after blowout preventer clamp ram valve 2183 clamps drill pipe 211.

FIG. 5 is a schematic diagram of a structure of a riser-less subsea blowout preventer and a drilling fluid volume control unit according to an embodiment of the present disclosure.

Referring to fig. 5, the drilling fluid volume control unit 212 is provided with a suction line sub 2121 operable by an ROV, an ROV auxiliary control panel 2122, and a blowout preventer control fluid accumulator 2123, and an accumulator fluid replacement pipe 2124 connected to the blowout preventer control fluid accumulator 2123. A ROV-operable suction line fitting 2121 is used to connect with the drilling fluid suction hose non-emergency disconnect section 216.

Based on the setting of the marine riser-free subsea blowout preventer 218, when the floating drilling platform unexpectedly drifts a predetermined position, the connection between the drill pipe 211 and the floating drilling platform 201 can be cut off, and the well bore 31 is sealed, so that effective well control is realized. The pinched-off drill pipe 211 can be quickly fished out of the wellbore 31 after the floating rig 201 is returned directly above the wellbore 31, otherwise reconnection would be difficult.

In one example, referring to fig. 5, the above-described offshore non-riser drilling fluid return system including the non-riser subsea blowout preventer 218 further comprises: a main controller and an ROV auxiliary control panel 2122. The main controller is disposed on the floating rig 201 and is electrically and/or communicatively coupled to the non-riser subsea blowout preventer 218. An ROV auxiliary control panel 2122 is provided on the drilling fluid volume control unit 212 and is electrically connected to the riser-less subsea blowout preventer 218. The ROV auxiliary control panel 2122 is electrically and/or communicatively coupled to the main controller. Fig. 5 illustrates an ROV auxiliary control panel 2122, which may control an underwater Robot (ROV) 2122 to implement installation of an underwater pipeline.

The valves of the non-riser subsea blowout preventer 218 may be controlled by voice, electrical, or fluid control, by the controller of the floating rig 201 and/or the ROV auxiliary control panel 2122. The control fluid of the ROV auxiliary control panel 2122 is supplied from a bop control fluid accumulator 2123, and when the amount of control fluid stored in the bop control fluid accumulator 2123 is insufficient, fluid can be replenished through an accumulator fluid replenishing pipe 2124.

Referring to fig. 4 and 5, the above-described riser-less subsea blowout preventer 218 further comprises: an upper kill valve 2184 connected with a blowout preventer shear gate valve 2182, a lower kill valve 2185 connected with a blowout preventer clamp gate valve 2183, and a kill hose access coupling 2181 connected with both the upper kill valve 2184 and the lower kill valve 2185. Kill hose access nipple 2181 is used to connect with kill hose non-emergency disconnect tube section 217. The marine riser-free underwater blowout preventer 218 can control the control fluid in the control hose non-emergency disconnection pipe section 217 accessed from the control hose access joint 2181 to be sent to the well bore 31 through the opening and closing of the upper control valve 2184 and the lower control valve 2185, then the blowout preventer clamping gate valve 2183 is closed, the pressure in the well bore 31 is regulated and controlled based on the control fluid while the drill pipe 211 is cut off, and the safety of drilling operation is further ensured.

The non-riser subsea blowout preventer 218 is equipped with a kill hose access connection 2181, and the kill line is connected to the kill hose access connection 2181 of the non-riser subsea blowout preventer 218 by a remote control device, for example, a subsea robot or other kill line access method may be used to perform the connection operation.

Referring to FIG. 5, the above-described riser-less subsea blowout preventer 218 may further include a wellhead connector 2186 for connection with the wellbore 31. In one embodiment, the kill line may be a flexible kill umbilical, with a kill valve disposed on the kill line.

According to the embodiment of the disclosure, a turntable and a derrick located above the turntable are arranged on the floating drilling platform 201, the turntable is provided with a turntable opening 208, a hollow area is arranged below a drilling center 202 of the derrick, the hollow area is a moon pool 207, and a moon pool vehicle 204 moves around the moon pool 207; the derrick is provided with a hoisting device 203. Wherein the drilling fluid return line 221, when assembled with the drilling fluid return pump 222, can be lowered below the moon pool 207 through the turntable opening 208 based on the hoist 203. The drilling fluid return line 221 and the drilling fluid return pump 222 are suspended and fixed in the universal hanger 205 of the moonpool vehicle 204 and can move with the moonpool vehicle 204 to free the drilling center 202 for the drill pipe 211 to operate. By mounting the drilling fluid return pump 222 axially to the section of the drilling fluid return line 221, the diameter size of the drilling fluid return line is reduced, allowing for lowering and retrieval through smaller sized rotary table openings.

Based on the above, drilling fluid backwash pump has reduced the diameter size of drilling fluid backflow pipeline along the axial installation on drilling fluid backflow pipeline, can pass the carousel opening of small-size and transfer to below the moon pool after floating drilling platform installs, has avoided among the prior art because contain the big degree of difficulty and the insecurity that can only install under water that leads to of marine riser system size. In addition, the drilling fluid return pipeline can be installed and deployed through a hoisting device of the derrick, and the arrangement can remarkably reduce the operation time of drilling operation.

A second exemplary embodiment of the present disclosure provides a method of assembling a floating drilling system. The floating drilling system of the present embodiment may be a floating drilling system that does not include or includes a riser-less subsea blowout preventer 218.

Fig. 6 is a flow chart of an assembly method of an offshore non-riser drilling fluid return system according to an embodiment of the present disclosure. Fig. 7 is a schematic diagram of a process of passing a drilling fluid return line and a drilling fluid return pump through a small bore turntable opening and suspending the drilling fluid return line on a gimbal hanger in a moonpool vehicle according to an embodiment of the present disclosure.

Referring to fig. 6, the assembling method of the present embodiment includes the following operations: s21, S22, S23, S24, S25 and S26. The implementation of the above operations S22, S23, S24, and S26 may be as described with reference to fig. 7.

At operation S21, the drilling fluid return line 221 and the drilling fluid return pump 222 are assembled on the floating drilling platform 201.

In operation S22, the assembled fluid return line 221 and fluid return pump 222 are lowered through the carousel opening 208 to below the moon pool 207 based on the hoist 203, as shown with reference to fig. 7.

The rotary table opening 208 is here a small sized rotary table opening for the drill rod lowering and retrieving operations. Because the drilling fluid reflux pump is axially installed on one pipe section of the drilling fluid reflux pipeline, the diameter size of the drilling fluid reflux pipeline is reduced, the drilling fluid reflux pipeline 221 and the drilling fluid reflux pump 222 in the drilling fluid reflux device are firstly assembled on the floating drilling platform 201 and then are placed below the moon pool 207 through the small-sized turntable opening 208, compared with the situation that in the prior art, the reflux system with the marine riser cannot pass through the small-sized turntable opening and can only be installed underwater, the installation difficulty is greatly reduced, the arrangement and installation efficiency of each device/device is improved, the operation time of drilling operation is saved, and meanwhile, the installation accuracy is also improved.

In operation S23, the lowered drilling fluid return line 221 and the drilling fluid return pump 222 are suspended and fixed in the universal suspension 205 of the moon pool vehicle 204, as shown with reference to fig. 7.

In operation S24, the moon pool vehicle 204 is moved to free up the location of the drilling center 202. Fig. 6 shows the direction of the positional change of the moon pool vehicle by a double arrow.

At operation S25, the drill pipe 211 and the drilling fluid volume control unit 212 are assembled on the floating drilling platform 201. The operations S25 and S21 may be executed in parallel or sequentially, and the execution order is not limited.

In operation S26, the assembled drill pipe 211 and the drilling fluid volume control unit 212 are lowered at the drilling center 202 through the turntable opening 208 to below the moon pool 207 based on the hoist 203 such that the drilling fluid volume control unit 212 is connected to the wellbore 31, the drilling fluid volume control unit 212 being located in the seawater and being open at both ends to the seawater and the wellbore 31, respectively, as shown with reference to fig. 7.

After the drilling fluid backflow pipeline 221 and the drilling fluid backflow pump 222 are installed, the drilling fluid backflow pipeline can be hung on the moon pool vehicle 204 around the moon pool 207, the moon pool vehicle 204 can bear the weight of the pipelines and the pumps in the drilling fluid backflow device, and the drilling fluid backflow device is transferred to one side of the edge of the moon pool to free the position of the drilling center 202, so that the drilling operation in the open water area is not affected.

The present embodiment is illustrated in a floating drilling system without the riser-less subsea blowout preventer 218, and it should be noted that in a floating drilling system including the riser-less subsea blowout preventer 218, the above operation S25 further requires assembling the riser-less subsea blowout preventer 218, the drill pipe 211, and the drilling fluid volume control unit 212.

The assembling method further comprises the following steps: assembling a separable connecting structure, and respectively connecting the separable connecting structure, the volume control unit and the drilling fluid return pipeline. The assembly of other detailed structures is not described, and the underwater pipeline can be assembled by using the underwater robot according to the description of the first embodiment.

Fig. 8 is a flow chart of a drilling fluid recovery method based on an offshore non-riser drilling fluid return system according to an embodiment of the present disclosure.

Referring to fig. 8, 1 and 2, the method for recovering drilling fluid of the present embodiment includes the following operations: s31, S32, and S33.

In operation S31, the height of the drilling fluid to sea water interface 32 within the drilling fluid volume control unit 212 is obtained.

In operation S32, a real-time rotational speed of the fluid return pump 222 is determined based on a height of the drilling fluid-sea water interface 32.

In operation S33, the real-time rotational 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 line 221, so as to achieve the recovery of the drilling fluid 50 and to maintain the interface 32 between the drilling fluid and the seawater at a preset height.

For floating drilling systems that include a separable connection structure, with or without a riser-less subsea blowout preventer, during drilling fluid recovery, a controller (e.g., a master controller) controls whether the emergency disconnect structure 233 is disengaged from the drilling template emergency disconnect unit 232 based on tension of the tension connection 234 for an emergency situation such that the separable connection structure disconnects between the drilling fluid volume control unit and the drilling fluid return line when an emergency situation arises. At this time, the pipelines from the drilling fluid volume control unit to the drilling base plate emergency disconnection unit, such as the first pipeline 216 and the second pipeline 217, are not disconnected in an emergency, so that the pipeline connection of the drilling part is not affected, and the borehole is prevented from being repositioned. While the lines between the emergency disconnect structure and the drilling fluid return line, such as the third line 226 and the fourth line 227, may be disconnected in an emergency with the disconnection of the emergency disconnect structure from the drilling template emergency disconnect unit. After the emergency is relieved, the emergency disconnection structural member 233 is connected with the drilling base plate emergency disconnection unit 232 again, so that the drilling fluid backflow pipeline is effectively prevented from being influenced due to emergency, and the drilling fluid backflow pipeline is protected.

In summary, embodiments of the present disclosure provide an offshore drilling fluid backflow system without a riser and an assembly method thereof, which do not require installation of a heavy riser and a tension system thereof, achieve recovery and cyclic utilization of drilling fluid, and can be applied to deep water and ultra-deep water drilling operations, so that the requirement of a drilling platform on the drilling fluid demand is reduced by 70 to 90%; and allows a greater offset of the drilling platform relative to the wellbore, by using a flexible connection between the drilling fluid return line and the drilling fluid volume control unit connection, the amount of fuel used is greatly reduced as there is no need for a floating drilling platform to maintain a very precise positioning. The drilling fluid return pump is axially mounted on one pipe section of the drilling fluid return pipeline, so that the diameter size of the drilling fluid return pipeline is reduced, the drilling fluid return pipeline can be mounted and deployed through the lifting device, and the arrangement can obviously reduce the operation time of drilling operation. Based on the arrangement of the underwater blowout preventer without the marine riser, when the floating type drilling platform is accidentally drifted to a preset position, the connection between the drill rod and the floating type drilling platform is cut off, a well hole is sealed, and effective well control is realized. By arranging the separable connecting structure, the umbilical cable-based control signal can disconnect the connection between the drilling fluid backflow pipeline and the drilling fluid volume control unit in case of emergency and reconnect the umbilical cable-based control signal after emergency release, and a pipeline between the drilling device and the drilling base plate emergency disconnection unit is not disconnected in case of emergency, so that the pipeline connection of a drilling part is not influenced, and the borehole is prevented from being repositioned; and the pipeline between the emergency disconnection structure and the drilling fluid return line can be disconnected along with the separation of the emergency disconnection structure from the drilling base plate emergency disconnection unit under the emergency condition, and is reconnected after the subsequent emergency release, so that the drilling fluid return line is effectively prevented from being influenced under the emergency condition.

It should also be noted that while the present disclosure has been described in connection with the accompanying drawings, the embodiments disclosed in the drawings are intended to be illustrative of the preferred embodiments of the present disclosure and should not be construed as limiting the present disclosure. The dimensional proportions in the drawings are merely schematic and are not to be understood as limiting the disclosure. Directional phrases used in the embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., refer only to the direction of the attached drawings and are not intended to limit the scope of the present disclosure. Throughout the drawings, like elements are represented by like or similar reference numerals. Conventional structures or constructions will be omitted when they may obscure the understanding of the present disclosure.

And the shapes and sizes of the respective components in the drawings do not reflect actual sizes and proportions, but merely illustrate the contents of the embodiments of the present disclosure. Furthermore, in the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

The use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify a corresponding element does not by itself connote any ordinal number of the element or any ordering of one element from another or the order of manufacture, and the use of the ordinal numbers is only used to distinguish one element having a certain name from another element having a same name.

Furthermore, the word "comprising" or "comprises" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Unless a technical obstacle or contradiction exists, the above-described various embodiments of the present disclosure may be freely combined to form further embodiments, which are all within the scope of protection of the present disclosure.

The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

Claims (10)

1. An offshore non-riser drilling fluid return system, comprising:

a drilling fluid volume control unit (212) located within seawater with a top of the drilling fluid volume control unit (212) open to the seawater, a bottom of the drilling fluid volume control unit (212) facing a drilling location;

open water drilling pipe (211) for lowering from a floating drilling platform (201) and performing drilling operations through the drilling fluid volume control unit (212), and drilling fluid is pumped from the drilling platform (201) through the bore hole inside the pipe (211) to the borehole (31); and

and the drilling fluid return pipeline (221) is connected with the drilling fluid volume control unit (212) through a hose, and a drilling fluid return pump (222) is arranged on one of the sections of the drilling fluid return pipeline (221) and is used for pumping the drilling fluid (50) flowing into the drilling fluid return pipeline (221) from the drilling fluid volume control unit (212) back to the drilling platform (201) for circulation treatment.

2. The offshore non-riser drilling fluid return system of claim 1,

a differential pressure sensor (214) is installed on the drilling fluid volume control unit (212), and the differential pressure sensor (214) is used for sensing a differential pressure value inside and outside the drilling fluid volume control unit (212) according to the height of an interface (32) of the drilling fluid and the seawater in the drilling fluid volume control unit (212);

the system further comprises: a control unit, electrically and/or communicatively connected with the differential pressure sensor (214) and the drilling fluid return pump (222), for controlling the drilling fluid return pump (222) according to the differential pressure value fed back by the differential pressure sensor (214) so that an interface (32) of drilling fluid and seawater in the drilling fluid volume control unit (212) is at a preset height.

3. The offshore non-riser drilling fluid return system of claim 1,

a drill pipe U-shaped pipe blocking valve (213) is arranged on the drill pipe (211);

and a drilling fluid return pipeline (221) is provided with a controllable U-shaped pipe blocking valve (223) of the drilling fluid return pipeline.

4. The offshore non-riser drilling fluid return system of claim 1, further comprising: a separable connection structure disposed on one or both of the drilling fluid volume control unit (212) and the drilling fluid return line (221), the separable connection structure being connected to the drilling fluid volume control unit (212) and the drilling fluid return line (221) by the hose; the separable connection structure includes: the fixing part is detachably connected with the separation part, and the separation part is separated from the fixing part under the control of an external force or an electrical control signal.

5. The offshore non-riser drilling fluid return system of claim 4, wherein the separable connection structure comprises:

the drilling template emergency disconnection unit (232) is arranged between the drilling fluid volume control unit (212) and the drilling fluid return pipeline (221), is used for being installed on a drilling template (231) and is arranged at intervals with an area where the well hole (31) is located, and the drilling template emergency disconnection unit (232) serves as the fixing part;

an emergency disconnection structure (233) detachably connected to the drilling template emergency disconnection unit (232), the emergency disconnection structure (233) serving as the disconnection part;

an umbilical (235) and a tensioning connector (234) for connection between the drilling platform (201) and the emergency disconnect structure (233), the umbilical (235) and the tensioning connector (234) being secured to one another;

the emergency disconnection structure (233) is controlled by the tension of the tension connector (234), and when the tension reaches or is greater than the preset tension of the tension connector (234), the emergency disconnection structure (233) is disconnected from the drilling template emergency disconnection unit (232).

6. The offshore non-riser drilling fluid return system of claim 5, wherein the hose comprises:

a drilling fluid intake hose non-emergency disconnect section (216) connected between the drilling fluid volume control unit (212) and the drilling template emergency disconnect unit (232); and

an emergency disconnect pipe section (226) of a drilling fluid suction hose connected between the emergency disconnect structure (233) and the drilling fluid return line (221);

wherein the drilling fluid intake hose non-emergency disconnect section (216) and the drilling fluid intake hose emergency disconnect section (226) are for conveying the drilling fluid (50).

7. The offshore non-riser drilling fluid return system of claim 6, further comprising:

a riser-less subsea blowout preventer (218), the riser-less subsea blowout preventer (218) connected between the drilling fluid volume control unit (212) and the wellbore (31).

8. The offshore non-riser drilling fluid return system of claim 7, wherein the hose further comprises:

a kill hose non-emergency disconnect pipe section (217) connected between the riser-less subsea blowout preventer (218) and the drilling template emergency disconnect unit (232); and

a kill hose emergency disconnect section (227) connected between the emergency disconnect structure (233) and a fixed end of a kill line hot stab sub (225) attached to the drilling fluid return line (221);

wherein the kill hose non-emergency disconnect section (217) and the kill hose emergency disconnect section (227) are used to transport kill fluid that is pumped through a kill umbilical connected to the free end of the kill line hot stab sub (225).

9. The offshore non-riser drilling fluid return system of claim 8, further comprising:

a weight unit (224) installed at the bottom of the drilling fluid return line (221), wherein a drilling fluid return inlet valve (228) and a killing fluid outlet valve (229) are installed in the weight unit (224);

the kill line hot stab sub (225) is fixed with the counterweight unit (224);

wherein the drilling fluid intake hose emergency disconnect pipe segment (226) communicates with the drilling fluid return line (221) via the drilling fluid return inlet valve (228); the kill hose emergency disconnect section (227) is in communication with the kill umbilical via the kill fluid outlet valve (229) and the kill line hot stab connection (225).

10. The offshore riser-less drilling fluid return system of any of claims 7-9, wherein the riser-less subsea blowout preventer (218) comprises:

the ram valve group comprises a blowout preventer shear ram valve (2182) and a blowout preventer clamping ram valve (2183) which are arranged from top to bottom at intervals; the blowout preventer clamping gate valve (2183) is used to clamp the drill pipe (211) when safe shut-off of the wellbore (31) is required; the blowout preventer shear gate valve (2182) is used for cutting off the drill pipe (211) after the blowout preventer clamping gate valve (2183) clamps the drill pipe (211), and meanwhile, the well bore (31) is sealed.

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