CN111197470A

CN111197470A - Deep sea natural gas hydrate non-riser exploration system and method

Info

Publication number: CN111197470A
Application number: CN201910220095.0A
Authority: CN
Inventors: 斯迈·格莱迪奇; 沈越
Original assignee: Paige Underwater Technology Guangzhou Co ltd
Current assignee: Paige Underwater Technology Guangzhou Co ltd
Priority date: 2019-03-21
Filing date: 2019-03-21
Publication date: 2020-05-26

Abstract

The present disclosure provides a deep sea natural gas hydrate water-riser-free exploration system, including: a drilling platform (11); a riser-free natural gas hydrate blowout preventer (5) installed in connection to a natural gas hydrate well; the underwater pump module (3) is installed and connected to the natural gas hydrate drilling base plate (17); a natural gas hydrate separator (4) connected to the riser-less natural gas hydrate blowout preventer (5) and the subsea pump module (3); wherein the drill pipe (15) is drilled directly through an open body of water. By using the system, the natural gas hydrate is ensured to be at a constant low pressure, the production stability and the low pressure are irrelevant to the yield, and the shallow buried hydrate can be continuously produced safely, reliably and economically.

Description

Deep sea natural gas hydrate non-riser exploration system and method

Technical Field

The disclosure relates to the field of deep sea natural gas hydrate drilling exploration, in particular to exploration drilling, testing and production of deep sea natural gas hydrate sediments.

Background

The natural gas hydrate is deposited under the shallow earth surface of the seabed, and the pressure gradient of the stratum where the deposit is located is similar to or identical to that of the seawater. Due to the short distance of the top of the natural gas hydrate deposit from the seabed, conventional drilling and production techniques do not conform to existing safety and integrity measures.

On the other hand, the depressurization process for natural gas hydrates generally reduces the pressure of natural gas hydrate deposits by inserting an electrical submersible pump into the natural gas hydrate wellbore. This submersible pump requires a minimum flow rate to maintain the depressurization process, which can no longer be maintained when gas hydrate production is slow for a number of reasons, resulting in production stoppage.

Currently, there is no commercially proven method for the recovery of natural gas from subsea hydrates, and in order to explore and recover natural gas from gas hydrate deposits, new methods must be introduced to provide a safe and reliable system. Thus, the present invention provides a unique method and innovative system for obtaining and recovering subsea hydrates.

Disclosure of Invention

Technical problem to be solved

The present disclosure provides a system and method for marine natural gas hydrate riser-free exploration to at least partially address the above-identified technical problems.

(II) technical scheme

According to an aspect of the present disclosure, there is provided a deep sea natural gas hydrate riser-free exploration system comprising:

a drilling platform 11;

a riser-free natural gas hydrate blowout preventer 5 installed to be connected to a natural gas hydrate well;

the underwater pump module 3 is installed and connected to the natural gas hydrate drilling base plate 17;

a natural gas hydrate separator 4 connected to the riser-less natural gas hydrate blowout preventer 5 and the underwater pump module 3;

the drill rod 15 of the deep-sea natural gas hydrate non-riser exploration system directly penetrates through an open water body to drill a well.

In some embodiments, the subsea pump module 3 comprises a riser-less drill pump 34, a de-pressuring pump 35, and a drilling fluid production fluid return line 1 and a gas production line 2 connecting subsea equipment of the deep sea natural gas hydrate riser-less exploration system and the drilling platform 11.

In some embodiments, the non-riser drill pump 34 and the reduced pressure pump 35 are two separate pump systems, wherein:

the riser-less drill pump 34 is used to pump drilling fluid and cuttings back to the rig during the riser-less drilling phase of the gas hydrate well;

the depressurization pump 35 is used to depressurize the formation of natural gas hydrates after the production of the natural gas hydrate well has begun.

In some embodiments, the depressurization pump 35 is used to control depressurization of the natural gas hydrate deposits by controlling the liquid level inside the gas production line 2.

In some embodiments, the drilling fluid production fluid return line 1 is used for returning drilling fluid and production fluid to the drilling platform; and/or as a kill line, pumping kill fluid from the rig 11 into the riser-less natural gas hydrate blowout preventer 5 and into the wellbore 19 for well control.

In some embodiments, the gas production line 2 is used to isolate the surrounding seawater, and the liquid in the gas production line 2 directly contacts the natural gas hydrate deposits.

In some embodiments, the gas production pipeline 2 is configured such that when the liquid level within the gas production pipeline 2 is below a predetermined threshold relative to the seawater surrounding the pipeline, the natural gas hydrate deposit is depressurized such that the natural gas hydrates are decomposed from a frozen state into natural gas and water.

In some embodiments, the drilling fluid production fluid return line 1 and the natural gas production line 2 are suspended from a drilling fluid production fluid return center 16 on the drilling vessel offset from the wellhead, and the drilling fluid production fluid return line 1 and the natural gas production line 2 are comprised of two separate lines or one double-deck concentric line.

In some embodiments, the drilling fluid production fluid return line 1 and the natural gas production line 2 are configured to participate in flushing one line to the other.

In some embodiments, the drilling fluid production fluid return line 1 and the natural gas production line 2 are connected at their lower ends to an emergency disconnect system 9 of the subsea pump module, the emergency disconnect system 9 being used to disconnect all cable and line connections including the drilling platform 11 and the subsea-mounted deep sea natural gas hydrate riser-less exploration system installation, and the emergency disconnect system 9 being reconnectable to the subsea pump module 3 after the emergency disconnect.

In some embodiments, the system further comprises a well control isolation valve 44 disposed on the kill line 31 between the subsea pump module 4 and the non-riser natural gas hydrate blowout preventer 5, the well control isolation valve 44 being configured to open when well controlled such that kill fluid is pumped from the drilling rig 11 into the drilling fluid production fluid return line 1, through the kill line 31 bypassed by the subsea pump module 3 and the closed non-riser natural gas hydrate blowout preventer 5 into the well.

In some embodiments, the riser-less natural gas hydrate blowout preventer 5 is disposed at a drilling center 14 above a wellhead for drilling and production of shallow natural gas hydrate wells in deep water.

In some embodiments, the horizontal distance between the drilling center 14 and the drilling fluid production fluid return center 16 is greater than a predetermined threshold.

In some embodiments, the riser-less natural gas hydrate blowout preventer 5 is used to control the level of drilling fluid in the wellbore during drilling, and to isolate natural gas hydrate deposits from the pressure of the surrounding seawater during the production phase.

In some embodiments, the riser-less natural gas hydrate blowout preventer 5 is fitted with a blowout preventer natural gas hydrate sea chest valve 26, the blowout preventer natural gas hydrate sea chest valve 26 for allowing sea water outside the blowout preventer to enter the natural gas hydrate well.

In some embodiments, the gas hydrate separator 4 has an inner cavity 22, and the upper portion of the gas hydrate separator 4 is connected to the gas production line 2, and the inner cavity 22 is configured such that when the pressure reducing fluid in the gas hydrate well enters the inner cavity 22 of the gas hydrate separator 4, the fluid flows upward from the bottom of the inner cavity 22, and when the fluid flows out from the outlet 51 above the inner cavity 22, the direction is reversed downward, and the gas hydrate fluid is separated into a gas phase and a liquid phase.

In some embodiments, the gas hydrate separator 4, the depressurization pump 34, the drilling fluid production fluid return line 1, and the drilling platform 11 are connected in sequence, so that the liquid phase fluid separated by the gas hydrate separator 4 is pumped back to the drilling platform 11 through the depressurization pump 34 and the drilling fluid production fluid return line 1.

In some embodiments, the subsea pump module 3 is configured for isolating all pipelines between the subsea pump module 3 and the riser-less natural gas hydrate blowout preventer 5.

In some embodiments, a drilling fluid volume controller 6 is installed on top of the non-riser natural gas hydrate blowout preventer 5, and the drilling fluid volume controller 6 includes a level sensor for controlling the sea water and drilling fluid contact surface level 24 by controlling the rotational speed of the non-riser drill pump 34 during the drilling phase.

According to another aspect of the present disclosure, there is provided a deep sea natural gas hydrate exploration method, comprising the steps of:

s100, installing a natural gas hydrate underwater drilling base plate comprising a riser-free natural gas hydrate blowout preventer well head, an underwater pump module and a natural gas hydrate separator;

s200, completing the drilling and well completion operation of the natural gas hydrate well by using a closed-loop drilling fluid backflow system, realizing the volume control of the drilling fluid in the well hole through a drilling fluid volume controller 6 in the marine riser-free natural gas hydrate blowout preventer and a liquid level sensor inside the marine riser-free natural gas hydrate blowout preventer, and ensuring that seawater does not enter a drilling fluid backflow system;

s300, injecting ethylene glycol mixed solution into the gas production pipeline, reducing the liquid level inside the gas production pipeline, and reducing the pressure to be below a preset threshold value, so that the natural gas hydrate is decomposed into gas and water;

s400, stopping production by improving the liquid level control inside the gas production pipeline.

In some embodiments, the step S300 includes:

s301, when the test production plan starts, closing the natural gas hydrate blowout preventer without the marine riser, and replacing liquid in the gas production pipeline with glycol mixed liquid;

s302, starting a decompression pump of a pump module to reduce the liquid level in the gas production pipeline;

s303, when the sediment is sufficiently decompressed to be below a preset threshold value, the natural gas hydrate is decomposed into gas and water from a frozen state;

s304, the mixture of the produced gas and the water passes through a natural gas hydrate separator, sediment and water are pumped back to the drilling platform through a drilling fluid production liquid return pipe by a decompression pump, and the natural gas is conveyed to the drilling platform through a gas production pipeline.

In some embodiments, the step S100 further includes:

an emergency quick disconnect system is installed for disconnecting all cable and pipeline connections including the drilling platform and the subsea installed deep sea natural gas hydrate riser-less exploration system installation.

In some embodiments, the return system returns drilling fluid and cuttings to the drilling platform using a riser-less drilling pump of the subsea pump module and a drilling fluid production fluid return line in step S200.

(III) advantageous effects

According to the technical scheme, the deep sea natural gas hydrate riser-free exploration system and the deep sea natural gas hydrate riser-free exploration method have at least one of the following beneficial effects:

(1) by using the system, the shallow layer buried hydrate can be continuously produced safely, reliably and economically, the natural gas hydrate is ensured to be at a constant low pressure, the risk that free water in the natural gas hydrate deposit is frozen again is eliminated, and the fault-free production is ensured in the whole life cycle stage from the initial consumption to the first production and then to the end of the production during the hydrate exploitation;

(2) the system operates independent of actual production rates, the production of natural gas hydrate deposits is stable and low pressure independent of production, ensuring that the first depletion for initial production phase set up can be maintained for a sufficiently long time and the necessary depletion of the deposits by infiltration can continue.

(3) By reducing the liquid level in the natural gas production pipeline, the well drilling and production technology of natural gas hydrate sediments can simplify the well and casing program compared with the traditional underwater well technology, the ultra-deep sea bottom natural gas hydrate well drilling can be carried out on a small floating drilling platform, and the traditional well drilling marine riser system does not need technology any more and has obvious economic effect.

Drawings

FIG. 1 is a simplified layout of a riser-free natural gas hydrate riser-free exploration system of an embodiment of the present disclosure.

Fig. 2 is a simplified layout of an embodiment of the present disclosure on a gas hydrate drilling template.

Fig. 3 is a layout view of an underwater pump module according to an embodiment of the present disclosure.

FIG. 4 is a simplified layout of a marine riser-less blowout preventer according to embodiments of the present disclosure.

Fig. 5 is a typical valve arrangement for an underwater pump module during a natural gas hydrate drilling phase according to an embodiment of the disclosure.

Fig. 6 is a typical valve arrangement for an underwater pump module during a natural gas hydrate production phase according to an embodiment of the disclosure.

FIG. 7 illustrates an exemplary valve arrangement for a subsea pump module during well control according to embodiments of the present disclosure.

FIG. 8 is a schematic diagram of a circuit of drilling fluid during a drilling phase of an embodiment of the disclosure.

Fig. 9 is a schematic diagram of a circuit for producing fluids and gases during a natural gas hydrate production phase in accordance with an embodiment of the disclosure.

[ description of main reference numerals in the drawings ] of the embodiments of the present disclosure

1. Drilling fluid production fluid return line

2. Gas production line

3. Underwater pump module

4. Natural gas hydrate separator

5. Natural gas hydrate blowout preventer without marine riser

6. Drilling fluid volume controller

7. Control and power umbilical

8. Tension rope

9. Emergency disconnect system

10. Control and power supply module

11. Drilling platform

12. Sea surface

13. Seabed

14. Well drilling center

15. Drill rod

16. Drilling fluid production fluid backflow center

17. Natural gas hydrate base plate

18. Well head

19. Wellbore

20. Natural gas hydrate deposits

21. Drilling fluid return line

22. Separator inner chamber

23. Hydrostatic pressure of seawater

24. Contact surface level

25. Level of natural gas hydrates

26. Natural gas hydrate sea valve of blowout preventer

27. Kill valve entry

28. Upper kill valve inlet

29. Shear gate

30. Tubular clamping sealing flashboard

31. Kill line

32. Blowout preventer control line

33. Well head connector of blowout preventer

34. Drilling pump without marine riser

35. Pressure reducing pump

36. Natural gas hydrate inlet joint

37. Gas production pipeline connecting hose

38. Drilling fluid production liquid backflow pipeline connecting hose

39. Natural gas hydrate production valve

40. Pressure reducing control valve

41. Well killing by-pass valve

42. Surface well section drilling valve

43a, 43b, 43c, pump module inlet connection

44. Well control isolation valve

45. Separator bypass valve

46. Drilling fluid

47. Backflushing circulating valve

48. Lower gas production line

49. Well fluid pipeline

50. Unfrozen free gas

51. An outlet

Detailed Description

The present disclosure provides a deepwater natural gas hydrate riser-free exploration system operating from a floating drilling platform or vessel that enables the pressure deep inside the natural gas hydrate deposit to be permanently reduced. The system comprises a riser-free natural gas hydrate blowout preventer, a deep sea natural gas hydrate separator and a pump unit. The system does not use a marine riser, and the drill pipe directly penetrates through an open water body to drill a well. The system reduces the natural gas hydrate pressure by reducing the liquid level of the gas production line so that the pressure in the gas production line is less than the pressure of the surrounding seawater, and when the hydrostatic pressure of the natural gas hydrate is reduced to a sufficient level, the natural gas hydrate can be converted from a frozen state into gas and water and starts to flow to the production system.

Because the conventional electric submersible pump needs a minimum flow rate of the hydrate for decompression, namely enough liquid needs to be in the hydrate deposit, and continuous decompression cannot be realized when the liquid is not enough. Therefore, in the natural gas production process, if the pressure of the deposit is increased again due to the performance problem of the electric submersible pump or the pressure reduction stop caused by the unexpected stop of the power failure, the natural gas hydrate decomposed by the pressure reduction may be frozen into the hydrate again, so that the production is stopped. The deepwater natural gas hydrate marine riser-free exploration system can maintain the pressure of the natural gas hydrate at constant low pressure for a long time, does not depend on the decompression of an electric submersible pump inserted into a natural gas hydrate well in the prior art, does not stop decompression due to the performance of the electric submersible pump or accidental shutdown, and eliminates the risk of refreezing free water in natural gas hydrate sediments.

In particular, the deep sea natural gas hydrate riser-less exploration system of the present disclosure, at an initial stage, natural gas and water are produced together, will support the pressure wave consumption as the decomposition fluid is produced, and the pressure wave will propagate deeper down to the entire natural gas hydrate deposit reservoir. The pressure of the natural gas hydrate deposit in the system can thus be constantly maintained low enough to allow the natural gas hydrate to decompose into gas and water.

On the other hand, the deep sea natural gas hydrate riser-less exploration system of the present disclosure does not require an electrical submersible pump to maintain reduced pressure with minimal flow rates, so that stable and low pressure production from natural gas hydrate deposits production zones is independent of circulation or gas and water production. In this way, the present system can maintain a low yield of natural gas or water even if the yield is low.

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.

Certain embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the disclosure are shown. Indeed, various embodiments of the disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

In an exemplary embodiment of the present disclosure, a deep sea natural gas hydrate riser-free exploration system is provided. FIG. 1 is a simplified layout of a gas hydrate riser-less exploration system according to an embodiment of the disclosure. As shown in fig. 1, a deep sea natural gas hydrate riser-less exploration system is deployed and operated on a floating drilling platform 11 at the sea surface 12. The deep sea natural gas hydrate water-riser-free exploration system comprises: a riser-free natural gas hydrate blowout preventer 5 connected to a natural gas hydrate well, a natural gas hydrate separator 4 and a subsea pump module 3 connected to a natural gas hydrate drilling template 17 are installed.

The following detailed description of the various parts of the disclosed deep sea natural gas hydrate riser-free exploration system is made with reference to the accompanying drawings:

the natural gas hydrate riser-free exploration system is deployed in two areas. Wherein the first zone comprises a drilling center 14 for deploying a natural gas hydrate drilling template 17 and a riser-less natural gas hydrate blowout preventer 5, and for tripping a drill pipe 15; the second zone includes a production and fluid return center 16 positioned offset from the drilling center 14 for deployment and operation of the production and drilling fluid return system, including the drilling fluid production fluid return line 1 and the gas production line 2. The two centers are located far enough apart to avoid interference between the drill pipe 15 and the production and liquid return center 16 lines when the system is used in deep sea and high sea currents.

Fig. 2 is a simplified layout of an embodiment of the present disclosure on a gas hydrate drilling template. As shown in fig. 2, an underwater pump module 3, a gas hydrate separator 4 and a riser-free gas hydrate blowout preventer 5 are arranged above the gas hydrate drilling template 17, and a drilling fluid volume controller 6 is connected to the top of the riser-free gas hydrate blowout preventer 5. The natural gas hydrate production liquid is processed in a natural gas hydrate separator 4, and the gas part and the liquid part are respectively conveyed to a drilling platform through a gas production pipeline 2 and a drilling fluid production liquid return pipeline 1.

Fig. 3 is a layout view of an underwater pump module according to an embodiment of the present disclosure. As shown in fig. 3, the subsea pump module 3 comprises a riser-free drill pump 34 for drilling fluid return, a depressurisation pump 35 for natural gas hydrate deposits, and a gas production line 2 and a drilling fluid production return line 1 connecting subsea equipment and a drilling platform. The reduced pressure pump 35 is used to reduce the pressure within the natural gas hydrate deposit to a lower level that allows the natural gas hydrates to decompose to gas; the riser-less drill pump 34 is used to pump drilling mud back onto the drilling platform. Additionally, a kill bypass system is used to pump kill fluid into the well when the riser-less natural gas hydrate blowout preventer is closed.

The underwater pump module 3 is mounted on a gas hydrate base plate 17, which is a recoverable module. Referring to fig. 2 and 3, if it is desired to retrieve the subsea pump module 3 to the drilling rig for servicing 17, the pump module inlet connections (43a, 43b, 43c), and the gas hydrate inlet connection 36 may be disconnected from the gas hydrate template 17.

The underwater pump module 3 is composed of an upper part and a lower part, the upper part of the underwater pump module 3 is provided with a control and power supply module 10 which is controlled by a tension rope 8 in a tension state and can be disconnected quickly in an emergency. All connections between the rig and the gas hydrate drilling template are located at this point and controlled by the control and power module 10. The control and power supply module 10 is connected directly to the lower part of the underwater pump module by means of an emergency disconnection system 9 connection. The emergency disconnection system 9 comprises all cables and pipelines of the control system and the deep sea natural gas hydrate non-riser exploration system connected with the drilling ship

The lower part of the underwater pump module 3 comprises a non-riser drill pump 34, a relief pump 35, a kill bypass valve 41, a relief control valve 40, a surface interval drill valve 42 and a recoil circulation valve 47, instruments, a manifold and the like. Wherein the riser-less drill pump 34 and the depressurization pump 35 are two separate pump systems, wherein the riser-less drill pump 34 is configured to pump drilling fluid and cuttings back to the drilling platform during the riser-less drilling phase of the natural gas hydrate well; the depressurization pump 35 is used to depressurize the formation of natural gas hydrates after the production of the natural gas hydrate well has begun. The depressurisation pump 35 controls the depressurisation of the natural gas hydrate deposits by controlling the liquid level inside the gas production line 2.

The recoil circulation valve 47 functions to reversely clean the drilling fluid production fluid return line 1 and the gas production line, and the cleaning fluid is pumped from the drilling platform 11 to one line and returned from the other line as required. In the event that kill fluid should be pumped into the wellbore 19, the marine riser-less drill pump 34, the de-ballast pump 35, the recoil circulation valve 47, and the separator bypass valve 45 are all closed. The kill fluid passes through the kill bypass valve 41, exits the subsea pump module 43 through the second port 43b at the pump module inlet, passes through the well control isolation valve 44, and enters the riser-less natural gas hydrate blowout preventer 5 through the kill line 31.

In order to ensure the safety of all cables and pipelines connected to the drilling platform and the gas hydrate drilling base plate 17 and to enable quick disconnection of the connection to the underwater pump module 3, a control and power umbilical 7 is fixed to an emergency quick disconnect tension line 8, and the tension line 8 is always in tension. After an emergency disconnection of the system, the control and power module 10 may be reconnected to the subsea pump module 3 in order to resume gas hydrate exploration.

The drilling fluid production fluid return line 1 and the gas production line 2 are suspended from a gimbaled base 16 in the operational area of the rig 11. The drilling fluid production fluid return line 1 and the gas production line 2 may be used together as concentric pipes or clamped by two separate lines.

Further, the drilling fluid production fluid return line 1 is connected to the emergency disconnect system 9 of the subsea pump module 3 by a drilling fluid production fluid return line connection hose 38, said drilling fluid production fluid return line 1 having a dual function: one function is for drilling and production fluids to be lifted back to the floating rig; another function is to pump the kill fluid from the rig 11 into the wellbore 19, and also to perform well control, such as the accidental encounter of free gas during the drilling phase, as a kill line that can be used to pump the kill fluid into a non-riser natural gas hydrate blowout preventer.

The gas production line 2 is located at an off-wellhead location and is connected to the emergency disconnect system 9 of the underwater pump module 3 by a gas production line connection hose 37, which isolates the surrounding seawater and the liquid in the pipe directly contacts the gas hydrate deposits. When the liquid level in the gas production line is sufficiently lower than the seawater surrounding the line, the natural gas hydrate deposit will be depressurized so that the natural gas hydrates can decompose from a frozen state into natural gas and water. The liquid level inside the gas production line 2 may be lowered to a sufficiently low level 25 for depressurization of the natural gas hydrate deposit 20 and transport of the produced gas from the seabed to the surface drilling platform 11. The liquid level inside the gas production line decreases so that the pressure inside the line is less than the pressure of the seawater surrounding the line. When the liquid level is lowered to allow the hydrostatic pressure within the gas hydrates to be sufficiently low, the gas hydrates are converted from a frozen state to gas and water and begin to flow to the production system.

Preferably, the gas production line 2 and drilling fluid production return line 1 and control umbilical 7 are connected to an emergency disconnect system 9, which emergency disconnect system 9 is installed on top of the subsea pump module 3.

It is further preferred that the drilling fluid production return line 1 and the natural gas production line 2 are configured to participate in flushing one line to the other in order to prevent the reverse circulation means of the submersible pump module 3 from malfunctioning and causing a blockage.

FIG. 4 is a simplified layout of a marine riser-less blowout preventer according to embodiments of the present disclosure. Referring to fig. 4, a riser-less natural gas hydrate blowout preventer 5 is deployed below the drilling center 14 for drilling and production of shallow natural gas hydrate wells in deep water. The primary function of the drilling fluid accumulation controller 6 is to control the level of drilling fluid in the wellbore during initial drilling, and the riser-less natural gas hydrate blowout preventer 5 can safely shut down the wellbore 19 when drilling a natural gas hydrate exploration well. The process of safely closing the wellhead during the drilling phase comprises: firstly, the drill rod 15 is tightly buckled and sealed by closing the tubular clamping and sealing flashboard 30; the drill pipe 15 is then sheared off by closing the shear rams 29 while the wellbore 19 is completely closed; the sheared drill pipe 15 is clamped locked inside the riser-less natural gas hydrate blowout preventer 5 and may be retrieved for continued drilling operations. Wherein, a connector used for installing a drilling fluid volume controller 6 is arranged at the top of the marine riser-free natural gas hydrate blowout preventer 5.

The second primary function of the riser-less natural gas hydrate blowout preventer 5 is to isolate the natural gas hydrate deposit 20 from the seawater hydrostatic pressure 23 while simultaneously connecting the natural gas hydrate deposit 20 to the gas production pipeline 2 and the de-pressurization pump 35.

The third primary function of the non-riser natural gas hydrate blowout preventer 5 is to allow seawater to enter the natural gas hydrate wellbore 19 to reestablish the hydrostatic head of the natural gas hydrate deposit 20 and stop any natural gas hydrate breakdown when some of the fluid in the gas production line 2 is empty or the natural gas is full.

The fourth primary function of the riser-less natural gas hydrate blowout preventer 5 is to control free gas 50 that is not frozen below the natural gas hydrates that is accidentally encountered.

In some preferred embodiments, the functions of the valves and rams of the riser-less natural gas hydrate blowout preventer 5 may be electrically or hydraulically operated.

Referring again to fig. 4, the riser-less subsea blowout preventer 5 is typically equipped with a production fluid outlet and an upper kill valve inlet 28 and a lower kill valve inlet 27, which will be used when the natural gas hydrate blowout preventer 5 is closed off the wellhead. When the natural gas hydrate deposit 2050 of the borehole 19 is accidentally overpressurized with liquid or gas, the riser-less natural gas hydrate blowout preventer 5 closes the borehole head, and the rig is now without a drill pipe 15 into the borehole, kill fluid may be pumped into the borehole 19 from the lower kill valve inlet in order to regain pressure control in the borehole. The same production fluid outlet and upper kill valve inlet 28 are primarily used for the flow of natural gas hydrate production fluid out of the wellbore 19 into the natural gas hydrate separator 4.

As shown in fig. 4, a blowout preventer gas hydrate sea chest valve 26 is provided on the marine riser-less blowout preventer 5, which allows seawater 23 to rapidly flood into the depressurized gas hydrate deposit 20, restoring the original hydrostatic pressure conditions of the gas hydrate deposit 20, and rapidly stopping gas hydrate production.

In addition to the rig 11 riser natural gas hydrate blowout preventer 5 handling system, all components of the riser-less subsea blowout preventer 5 are mounted within the frame module and further configured with a blowout preventer wellhead connector 33.

And a drilling fluid volume controller 6 is arranged at the top of the riser-free natural gas hydrate blowout preventer 5. The drilling fluid volume controller 6 achieves precise control of the sea and drilling fluid contact surface level 24 by controlling the rotational speed of a non-riser drill pump 34 mounted within the pump module. Specifically, the drilling fluid volume controller 6 adjusts the rotation speed of the drilling pump through the reading of a liquid level sensor in the drilling fluid volume controller, in this embodiment, the liquid level sensor is a pressure sensor, and is installed in the drilling fluid volume controller and used for measuring the liquid level of the drilling fluid in the drilling fluid volume controller 6, and the rotation speed of the drilling pump 34 without the marine riser is controlled according to the reading of the group of sensors, so that the drilling fluid is ensured not to fill the volume controller and overflow the sea, and the drilling fluid in the volume controller 6 is not pumped out, so that the seawater is sucked into the system.

A low pressure bottom drilling fluid return line 21 is provided between the natural gas hydrate blowout preventer 5 and the non-riser drill pump 34 of the subsea pump module 3, the suction line connection being connected by ROV operation to the natural gas non-riser subsea blowout preventer 5, the other end of the line being fitted with a third connection 43c to the inlet of the subsea pump module 3. In the event that the rig 11 leaves the wellsite and the control and power module 10 is disconnected urgently, the drilling fluid return line 21 can ensure that the subsea pump module 3 and the gas hydrate blowout preventer will remain connected.

Referring to fig. 2 and 3, a lower gas production line 48 is provided between the gas hydrate separator 4 and the underwater pump module 3, one end of the line is connected to the gas hydrate inlet joint 36 of the gas hydrate separator 4, and a well fluid line 49 is connected to the first joint 43a of the pump module inlet. In the event that the rig 11 leaves the well site, the control and power module 10 is disconnected urgently, the subsea pump module 3 and the non-riser natural gas hydrate blowout preventer 5 remain connected.

In addition, referring to fig. 2 and 4 again, a well control isolation valve 44 at the inlet of the gas hydrate separator 4 and the kill line 31 are arranged between the riser-free gas hydrate blowout preventer 5 and the gas hydrate separator 4, and the plug-in connector of the kill line is connected to the riser-free gas hydrate blowout preventer 5 through an ROV operation.

The kill line 31 led out by the marine riser-free natural gas hydrate blowout preventer 5 is divided into two paths, one path of the kill line 31 is connected between the marine riser-free natural gas hydrate blowout preventer 5 and the second joint 43b at the inlet of the underwater pump module 3, and the other path of the kill line 31 is connected between the marine riser-free natural gas hydrate blowout preventer 5 and the inlet of the natural gas hydrate separator 4 through a separator bypass valve 45. In the event that the rig 11 leaves the well site and the control and power module 10 is disconnected urgently, the kill line 31 will maintain a connection between the subsea pump module 3 and the riser-less natural gas hydrate blowout preventer 5.

A gas hydrate separator 4 is also installed in the gas hydrate drilling template 17 for transporting the gas hydrate deposits 20 to the drilling platform 11. The separator separates the natural gas hydrate mixed liquid into a gas phase and a liquid phase. Inside the natural gas hydrate separator 4 is installed a separator inner chamber 22. The natural gas hydrate solution passes from the bottom of the natural gas hydrate separator through the blowout preventer 5 and the kill line 31 into the separator inner chamber 22. At the top of the separator inner chamber 22, a set of inner chamber outlets 51 is provided, from which outlets 51 the natural gas hydrate deposits 20 flow out of the separator inner chamber 22 and move in reverse downwards, the gas portion of the natural gas hydrates are released from the fluid, the liquid portion leaves the separator 4 through the well fluid line 49, the gas portion moves upwards in the natural gas hydrate separator 4, through the fluid inside the gas production line 2 through the lower gas production line 48 and the natural gas hydrate inlet connection 36, until passing through the level 25 of natural gas hydrates depressurized inside the tube. The natural gas expands in the fluid in the gas production line 1, and the expansion effect of the gas is adjusted by controlling the production liquid level in the gas production line 2 by the decompression pump 35.

Fig. 5 is a typical valve arrangement for an underwater pump module during a natural gas hydrate drilling phase according to an embodiment of the disclosure. As shown in fig. 5, where the surface interval drilling valve is opened for pumping drilling fluid to the drilling fluid production fluid return line. Both the pressure relief system and the kill line system are closed. This arrangement is typically used for surface interval drilling where the wellhead returns drilling mud to the well pump without passing through the gas hydrate separator into the subsea pump module.

Fig. 6 is a typical valve arrangement for an underwater pump module during a natural gas hydrate production phase according to an embodiment of the disclosure. As shown in fig. 6, in which the depressurization control valve 40 is open, the surface interval drilling valve 42, the kill bypass valve 41, and the recoil circulation valve 47 are all closed.

FIG. 7 illustrates an exemplary valve arrangement for a subsea pump module during well control according to embodiments of the present disclosure. As shown in fig. 7, with kill bypass valve 41 open, kill control valve 40 closed, and surface interval drilling valve 42 closed. The system is provided with a well control isolation valve 44, and the killing mud is pumped from the drilling fluid production liquid return pipeline 1 and enters the well through the killing pipeline of the underwater pump module 3 and the killing pipeline of the drilling base plate 17. Specifically, the well control isolation valve 44 is arranged on the well control pipeline 31, when well control is performed, the well control isolation valve 44 is opened, well control fluid is pumped into the drilling fluid production fluid return pipeline 1 from the drilling platform 11, and enters the well through the bypass well control pipeline 31 of the underwater pump module 3 and the closed blowout preventer 5. The recoil valve 47 is also shown closed. The recoil recirculation valve 47 functions to unblock one of the lines when it is blocked by pumping seawater from the gas production line 2 or from the drilling fluid production line 1 from the rig.

FIG. 8 is a schematic diagram of a circuit of drilling fluid during a drilling phase of an embodiment of the disclosure. As shown in fig. 8, drilling fluid is pumped into the well through drill pipe 15, drilling fluid control volume 6 controls the return drilling fluid from the well, bypassing gas hydrate separator 4 and pumped back to the platform through a riser-less drilling pump 34 and drilling fluid production fluid return line 1.

Fig. 9 is a schematic diagram of a circuit for producing fluids and gases during a natural gas hydrate production phase in accordance with an embodiment of the disclosure. As shown in fig. 9, with the non-riser drill pump 43 line closed, the non-riser natural gas hydrate blowout preventer 5 is closed to isolate the hydrostatic pressure in the well and seawater. When the pressure inside the natural gas hydrate separator is low, the formation pressure presses the mixture of gas, hydrate and water together into the natural gas hydrate separator 4. The natural gas hydrate separator 4 separates natural gas hydrate into gas and production liquid. Gas is delivered to the platform via gas production line 2 and production fluid is delivered to the drilling platform via reduced pressure pump 35.

The deep sea natural gas hydrate riser-less exploration system of the present disclosure ensures that the natural gas hydrate is at a constant low pressure independent of circulation or gas and water production. The risk of free water in the gas hydrate deposit freezing again is thereby eliminated and the dissipative pressure wave can penetrate deep into the reservoir of gas hydrates over the course of production time.

In a second exemplary embodiment of the present disclosure, there is provided a deep sea natural gas hydrate exploration method, comprising the steps of:

s100, installing a natural gas hydrate underwater drilling base plate comprising a natural gas hydrate blowout preventer well head, an underwater pump module, a natural gas hydrate separator and a remote control operation pipe.

Preferably, the step S100 further includes:

an emergency quick disconnect system is installed that includes all cables and pipelines that the control system and the deep sea natural gas hydrate riser-less exploration system are connected to the drilling vessel.

S200, completing the drilling and well completion operation of the natural gas hydrate well by using a closed-loop drilling fluid backflow system, realizing the volume control of the drilling fluid in the well hole through a pressure sensor and a volume control system in the marine riser-free natural gas hydrate blowout preventer, and ensuring that no seawater enters the drilling fluid backflow system.

The return system returns drilling fluid and drill cuttings to the drilling platform using a riser-less drilling pump of the subsea pump module and a drilling fluid production fluid return line.

S300, injecting ethylene glycol mixed liquid into the gas production pipeline, reducing the liquid level inside the gas production pipeline, and decomposing the natural gas hydrate into gas and water after full pressure reduction.

Specifically, the step S300 includes:

s301, when the test production plan starts, the marine riser-free natural gas hydrate blowout preventer is closed, and liquid in the gas production pipeline is replaced by the ethylene glycol mixed liquid.

And S302, starting a decompression pump of the pump module to reduce the liquid level inside the gas production pipeline so as to reduce the hydrostatic pressure of the natural gas hydrate deposit.

And S303, when the sediment is sufficiently decompressed, the natural gas hydrate is decomposed into gas and water from a frozen state.

S304, pumping the sediment and the water back to the drilling platform through a drilling fluid production liquid return pipe by a decompression pump according to the mixture of the production gas and the water through a natural gas hydrate separator, and conveying the other part of the natural gas to the drilling platform through a gas production pipeline.

S400, the liquid level in the gas production pipeline is increased, so that the production is stopped at any time.

For the purpose of brief description, any technical features of the first embodiment that can be applied to the same are described herein, and the same description is not repeated.

So far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. Further, the above definitions of the various elements and methods are not limited to the various specific structures, shapes or arrangements of parts mentioned in the examples, which may be easily modified or substituted by those of ordinary skill in the art.

It should also be noted that directional terms, such as "upper", "lower", "front", "rear", "left", "right", and the like, used in the embodiments are only directions referring to the 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.

Furthermore, the word "comprising" 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.

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.

In addition, unless steps are specifically described or must occur in sequence, the order of the steps is not limited to that listed above and may be changed or rearranged as desired by the desired design. The embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e., technical features in different embodiments may be freely combined to form further embodiments.

Those skilled in the art will appreciate that the modules in the device in an embodiment may be adaptively changed and disposed in one or more devices different from the embodiment. The modules or units or components of the embodiments may be combined into one module or unit or component, and furthermore they may be divided into a plurality of sub-modules or sub-units or sub-components. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where at least some of such features and/or processes or elements are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Also in the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware.

Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various disclosed aspects. However, the disclosed method should not be interpreted as reflecting an intention that: that is, the claimed disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, disclosed aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this 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

1. A deep sea natural gas hydrate riser-free exploration system, comprising:

a drilling platform (11);

a riser-free natural gas hydrate blowout preventer (5) installed in connection to a natural gas hydrate well;

the underwater pump module (3) is installed and connected to the natural gas hydrate drilling base plate (17);

a natural gas hydrate separator (4) connected to the riser-less natural gas hydrate blowout preventer (5) and the subsea pump module (3);

the drill rod (15) of the deep-sea natural gas hydrate non-riser exploration system directly penetrates through an open water body to drill a well.

2. The deep sea natural gas hydrate riser-free exploration system of claim 1,

the underwater pump module (3) comprises a non-riser drilling pump (34), a decompression pump (35), and a drilling fluid production liquid return pipeline (1) and a gas production pipeline (2) which are connected with seabed equipment of the deep-sea natural gas hydrate non-riser exploration system and a drilling platform (11).

3. The deep sea natural gas hydrate riser-free exploration system according to claim 2,

the riser-less drilling pump (34) and the depressurization pump (35) are two separate pump systems, wherein:

the riser-less drilling pump (34) is for pumping drilling fluid and cuttings back to the drilling platform during a riser-less drilling phase of the natural gas hydrate well;

the depressurization pump (35) is used to depressurize the formation of natural gas hydrates after production of the natural gas hydrate well has begun.

4. The deep sea natural gas hydrate riser-free exploration system of claim 3,

the depressurisation pump (35) is for controlling depressurisation of the natural gas hydrate deposits by controlling the liquid level inside the gas production line (2).

5. The deep sea natural gas hydrate riser-free exploration system according to claim 2,

the drilling fluid production fluid return line (1) is used for returning drilling fluid and production fluid to a drilling platform; and/or

For use as a kill line, kill fluid is pumped from a drilling platform (11) into a riser-less natural gas hydrate blowout preventer (5) and into a wellbore (19) for well control.

6. The deep sea natural gas hydrate riser-free exploration system according to claim 2,

the gas production line (2) is used for isolating surrounding seawater, and liquid in the gas production line (2) directly contacts natural gas hydrate deposits.

7. The deep sea natural gas hydrate riser-free exploration system of claim 6,

the gas production line (2) is configured such that when the liquid level within the gas production line (2) is below a predetermined threshold value compared to the seawater surrounding the line, the natural gas hydrate deposit is depressurized such that the natural gas hydrates are decomposed from a frozen state into natural gas and water.

8. The deep sea natural gas hydrate riser-free exploration system according to claim 2,

the drilling fluid production fluid return line (1) and the natural gas production line (2) are suspended from a drilling fluid production fluid return center (16) deviated from a wellhead on a drilling ship, and the drilling fluid production fluid return line (1) and the natural gas production line (2) are composed of two separation lines or a double-layer concentric line.

9. The deep sea natural gas hydrate riser-free exploration system according to claim 2,

the drilling fluid production fluid return line (1) and the natural gas production line (2) are configured to be able to participate in flushing one line to the other.

10. The deep sea natural gas hydrate riser-free exploration system according to claim 2,

the drilling fluid production fluid return line (1) and the natural gas production line (2) are connected at their lower ends to an emergency disconnect system (9) of the underwater pump module, the emergency disconnect system (9) being adapted to disconnect all cable and line connections including the drilling platform (11) and the subsea-mounted deep sea natural gas hydrate riser-less exploration system installation, and the emergency disconnect system (9) being re-connectable to the underwater pump module (3) after the emergency disconnect.

11. The deep sea natural gas hydrate riser-free exploration system according to claim 1, further comprising a well control isolation valve (44) disposed on the kill line (31) between the subsea pump module (4) and the riser-free natural gas hydrate blowout preventer (5), the well control isolation valve (44) being configured to open upon well control such that kill fluid is pumped from the drilling platform (11) into the drilling fluid production fluid return line (1) through the kill line (31) bypassed by the subsea pump module (3) and the closed riser-free natural gas hydrate blowout preventer (5).

12. The deep sea natural gas hydrate riser-free exploration system of claim 1,

the marine riser-free natural gas hydrate blowout preventer (5) is arranged in a drilling center (14) above a well head and used for drilling and producing shallow natural gas hydrate wells in deep water.

13. The deep sea natural gas hydrate riser-free exploration system according to claim 12, wherein a horizontal distance between the drilling center (14) and the drilling fluid production fluid return center (16) is greater than a predetermined threshold value.

14. The deep sea natural gas hydrate riser-free exploration system of claim 12,

the riser-less natural gas hydrate blowout preventer (5) is used for controlling the level of drilling fluid in a wellbore during drilling and for isolating natural gas hydrate deposits from the pressure of surrounding seawater during production.

15. The deep sea natural gas hydrate riser-free exploration system of claim 12,

the riser-free natural gas hydrate blowout preventer (5) is provided with a blowout preventer natural gas hydrate sea valve (26), and the blowout preventer natural gas hydrate sea valve (26) is used for allowing seawater outside the blowout preventer to enter a natural gas hydrate well.

16. The deep sea natural gas hydrate riser-free exploration system of claim 1,

the natural gas hydrate separator (4) is provided with an inner cavity (22), the upper part of the natural gas hydrate separator (4) is connected with the gas production pipeline (2), the inner cavity (22) is configured to enable the fluid to flow upwards from the bottom of the inner cavity (22) when the pressure reducing fluid in the natural gas hydrate well enters the inner cavity (22) of the natural gas hydrate separator (4), the direction of the fluid is reversed downwards when the fluid flows out from an outlet (51) above the inner cavity (22), and the natural gas hydrate fluid is separated into a gas phase and a liquid phase.

17. The deep sea natural gas hydrate riser-free exploration system of claim 16,

the natural gas hydrate separator (4), the decompression pump (34), the drilling fluid production liquid backflow pipeline (1) and the drilling platform (11) are sequentially connected and used for enabling liquid phase fluid separated by the natural gas hydrate separator (4) to be pumped back to the drilling platform (11) through the decompression pump (34) and the drilling fluid production liquid backflow pipeline (1).

18. The deep sea natural gas hydrate riser-free exploration system of claim 1,

the subsea pump module (3) is configured for isolating all pipelines between the subsea pump module (3) and the riser-less natural gas hydrate blowout preventer (5).

19. The deep sea natural gas hydrate riser-free exploration system of claim 1,

and a drilling fluid volume controller (6) is installed at the top of the marine riser-free natural gas hydrate blowout preventer (5), and the drilling fluid volume controller (6) comprises a liquid level sensor and is used for controlling the liquid level (24) of the contact surface of seawater and drilling fluid by controlling the rotating speed of a marine riser-free drilling pump (34) in a drilling stage.

20. A deep sea natural gas hydrate exploration method is characterized by comprising the following steps:

s200, completing the drilling and well completion operation of the natural gas hydrate well by using a closed-loop drilling fluid backflow system, realizing the volume control of the drilling fluid in the well hole through a drilling fluid volume controller (6) in the marine riser-free natural gas hydrate blowout preventer and a liquid level sensor inside the marine riser-free natural gas hydrate blowout preventer, and ensuring that seawater does not enter a drilling fluid backflow system;

21. The deep sea natural gas hydrate exploration method according to claim 20, wherein said step S300 comprises:

22. The deep sea natural gas hydrate exploration method according to claim 20, wherein said step S100 further comprises:

23. The deep sea natural gas hydrate exploration method of claim 20,

in step S200, the return system returns the drilling fluid and the drill cuttings to the drilling platform by using the non-riser drilling pump of the underwater pump module and the drilling fluid production fluid return pipe.