An experimental apparatus and method for the stability test at the wellhead of natural gas hydrate extraction.

Abstract

This invention discloses an experimental apparatus and method for testing the stability of natural gas hydrate wellheads. The experimental apparatus includes a drilling platform motion simulation subsystem, a wellhead assembly subsystem, and a hydrate simulation subsystem. The wellhead assembly subsystem includes a simulated wellhead and a conduit connected to the simulated wellhead. The hydrate simulation subsystem includes a fixed sleeve filled from bottom to top with a layer of backing soil and a hydrate simulation layer, and a soil pressurization simulation mechanism mounted on the fixed sleeve. The conduit passes through the backing soil layer of the soil pressurization simulation mechanism. This allows the force exerted by the backing soil layer on the conduit to more closely resemble actual conditions, thereby improving simulation accuracy.

Description

Technical Field

[0001] This invention relates to the field of natural gas hydrate extraction technology, and in particular to a test apparatus and method for wellhead stability testing in natural gas hydrate extraction. Background Technology

[0002] During the extraction of deep-water natural gas hydrates, thermal decomposition can easily damage the formation structure, reduce the strength of shallow seabed strata, and cause shallow seabed soil subsidence. As a key piece of equipment in deep-water drilling systems, wellheads are prone to tilting or sinking due to hydrate decomposition, which undermines the stability of the wellhead.

[0003] Currently, when conducting experimental simulations of wellhead stability, the guide pipe used in the experiment is usually the same as the guide pipe used in actual mining operations. Therefore, in order to ensure the accuracy of the simulation, the pressure of the soil layer on the guide pipe during the simulation must be the same as that during actual mining. However, the soil layer thickness during the simulation experiment is far less than the soil layer thickness into which the guide pipe extends during actual mining. This results in a situation where the pressure of the soil layer on the guide pipe in the current experimental device is seriously inconsistent with the actual situation, causing the simulation parameter to be seriously distorted. Summary of the Invention

[0004] In order to at least partially solve the technical problems existing in the prior art, the inventors made this invention, which provides a test device and test method for the stability of natural gas hydrate wellheads through specific implementation methods, which can make the force of the overburden layer on the guide pipe more consistent with the actual situation, thereby improving the simulation accuracy.

[0005] In a first aspect, embodiments of the present invention provide a wellhead stability test device for natural gas hydrate extraction, including a drilling platform motion simulation subsystem, a wellhead assembly subsystem, and a hydrate simulation subsystem, wherein the wellhead assembly subsystem includes a simulated wellhead and a conduit connected to the simulated wellhead;

[0006] The hydrate simulation subsystem includes a fixed sleeve filled with a cushion soil layer and a hydrate simulation layer from bottom to top, and a soil pressurization simulation mechanism disposed on the fixed sleeve.

[0007] The conduit passes through the topsoil layer of the soil pressure simulation device.

[0008] Secondly, embodiments of the present invention provide a method for testing the stability of natural gas hydrate extraction wellheads, including:

[0009] The stability simulation experiment of natural gas hydrate wellhead was conducted using the aforementioned natural gas hydrate wellhead stability test device.

[0010] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:

[0011] (1) The natural gas hydrate wellhead stability test device provided in this embodiment of the invention can be used to fill the overburden layer by installing a soil pressure simulation mechanism above the fixed sleeve. The various pressures applied to the overburden layer by the soil pressure simulation mechanism can simulate the pressure generated by the seabed soil layer on the guide pipe when it enters the hydrate layer during mining, so that the force of the overburden layer on the guide pipe is more consistent with the actual situation, thereby improving the simulation accuracy.

[0012] (2) The soil pressurization simulation mechanism includes a movable sleeve with pressure bladders distributed circumferentially inside the sleeve. The pressure bladders are connected to the external hydraulic system through inlet and outlet oil passages. By hydraulically pressurizing the pressure bladders, the expansion of the pressure bladders can circumferentially compress the filling soil layer, thereby increasing the compressive force and friction force generated by the soil layer on the guide pipe. In addition, this method can achieve the effect of circumferential compaction of the soil layer. Compared with the traditional method of downward compaction, this circumferential compaction will not disturb or damage the underlying hydrate simulation layer, reduce the adverse effects on the simulation experiment, and further improve the accuracy of the simulation experiment.

[0013] (3) The side wall of the pressure bladder away from the movable sleeve is an arc-shaped structure with a concave center, which makes it have a soil-gathering effect when it squeezes the cover layer, reducing the situation where the soil is squeezed upward.

[0014] (4) Multiple shaping wires are connected inside the pressure bladder, so that the shape of the pressure bladder can be maintained more stably after it is pressurized and expanded, ensuring that the squeezing effect on the soil layer is more stable during the simulation experiment.

[0015] (5) The overflow stop strip is set along the circumference of the side wall of the pressure bladder. The vertical cross section of the overflow stop strip is an inverted triangle. When the pressure bladder squeezes the soil layer, the structure of the overflow stop strip enables it to push the soil downward, thereby reducing the soil overflow.

[0016] (6) At least two pressure bladders are set. By pressurizing and controlling different pressure bladders separately (for example, one is pressurized and expanded while the other is not pressurized), the lateral thrust of the overburden layer on the guide pipe can be controlled, and the lateral forces in different directions between the upper and lower overburden layers can be controlled, which can produce a shear force effect on the guide pipe. The more pressure bladders there are, the more directions the lateral force and shear force can be changed, and the more comprehensive the situation can be simulated. In the simulation experiment, the number of pressure bladders can be selected according to the needs.

[0017] (7) The guide strip on the upper part of the outer wall of the movable sleeve can play a guiding role when the movable sleeve is added.

[0018] (8) The grid cover can shield the soil layer and reduce the problem of soil leakage upward when the pressure bladder squeezes the soil layer.

[0019] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0022] Figure 1 This is a cross-sectional view of the experimental device for the stability test of natural gas hydrate extraction wellhead in an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of the hydrate simulation subsystem in an embodiment of the present invention;

[0024] Figure 3 This is an exploded view of the movable sleeve in an embodiment of the present invention. Detailed Implementation

[0025] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0026] In the description of this invention, it should be noted that the terms "comprising", "including", "having", "containing", etc., are all open-ended terms, meaning that they include but are not limited to.

[0027] To address the problem in existing technologies where the pressure exerted by the overburden layer on the guide pipe during deep-water natural gas hydrate extraction operations is significantly inconsistent with actual conditions, this invention provides a wellhead stability testing device and method for natural gas hydrate extraction. This method enables the force exerted by the overburden layer on the guide pipe to better reflect actual conditions, thereby improving simulation accuracy.

[0028] Example

[0029] This invention provides a wellhead stability test device for natural gas hydrate extraction, comprising a drilling platform motion simulation subsystem, a wellhead assembly subsystem, and a hydrate simulation subsystem.

[0030] Its cross-sectional structure is as follows Figure 1 As shown, the wellhead assembly subsystem includes a simulated wellhead 1 and a conduit 2 connected to the simulated wellhead 1.

[0031] Furthermore, the conduit 2 includes multiple conduit segments connected by threads, with the uppermost end of the conduit 2 threadedly connected to the simulated wellhead 1.

[0032] The simulated wellhead 1 is equipped with a counterweight module 3 for simulating vertical loads and a loading component 4 for simulating lateral loads. The loading component 4 belongs to the drilling platform motion simulation subsystem and is used to simulate the rotation of the drilling platform.

[0033] The hydrate simulation subsystem includes a fixed sleeve 6 and a soil pressurization simulation mechanism on the fixed sleeve 6. The conduit 2 passes through the overburden layer 11 of the soil pressurization simulation mechanism.

[0034] The fixed sleeve 6 is filled with a soil layer 7 and a hydrate simulation layer 8 from bottom to top.

[0035] Yes, the hydrate simulation subsystem includes an experimental soil tank, which includes a base 5, a fixed sleeve 6 installed on the base 5, and a soil pressure simulation mechanism on top of it.

[0036] The guide pipe used in the simulation experiment is the same as that used in actual mining. However, it is impossible to truly fill a soil layer hundreds of meters deep to simulate the real seabed soil layer in the simulation experiment. This leads to a significant discrepancy between the pressure and friction forces between the soil layer and the guide pipe and the actual situation, resulting in serious distortion of the related simulation parameters. The experimental device provided in this embodiment of the invention, by installing a soil pressurization simulation mechanism above the fixed sleeve, can be used to fill the soil layer. The various pressures applied to the soil layer by the soil pressurization simulation mechanism simulate the pressure exerted on the guide pipe by the seabed soil layer when the guide pipe penetrates the hydrate layer during mining, making the forces exerted by the soil layer on the guide pipe more consistent with the actual situation, thereby improving the simulation accuracy.

[0037] In some embodiments, the soil pressurization simulation mechanism may be implemented by including a movable sleeve 9, with pressure bladders 10 distributed circumferentially inside the movable sleeve 9, and a soil cover layer 11 filling the cavity enclosed by the pressure bladders 10; the pressure bladders 10 are connected to the external hydraulic system through inlet and outlet oil passages.

[0038] The pressure bladder is used to circumferentially compress the cover layer, thus supplementing the force exerted on the guide pipe and compensating for the insufficient depth of the cover layer. Although the expansion of the pressure bladder is limited, the cover layer can be "tightened" through repeated compression using a "one-inflation-one-release" method (this operation requires continuous replenishment of soil from the outside to the cover layer), gradually increasing the force exerted by the cover layer on the guide pipe and ultimately meeting the simulation requirements.

[0039] The expansion of the pressure bladder can compress the filling soil layer circumferentially, increasing the compressive and frictional forces exerted by the soil layer on the guide pipe. In addition, this method can achieve the effect of circumferential compaction of the soil layer. Compared with the traditional method of downward compaction, this circumferential compaction will not disturb or damage the underlying hydrate simulation layer, reducing the adverse effects on the simulation experiment and further improving the accuracy of the simulation experiment.

[0040] Compared to fixed sleeves, movable sleeves are easy to assemble and disassemble. Movable sleeves can be a single section or multiple sections connected vertically, thus enabling flexible simulation of the thickness of the overburden layer.

[0041] See Figure 2 As shown, the lower end of the movable sleeve 9 is fitted onto the fixed sleeve 6, and the movable sleeve 9 and the fixed sleeve 6 are connected and fixed by a latch 15; when the movable sleeve 9 has multiple sections, the upper and lower adjacent movable sleeves 9 are also connected and fixed by a latch 15.

[0042] In some embodiments, multiple guide strips 16 are distributed circumferentially on the upper end of the outer wall of the movable sleeve 9, which can play a guiding role when the movable sleeve 9 is added.

[0043] In some embodiments, refer to Figure 3 As shown, a mesh cover 14 is provided at the upper end of the movable sleeve 9; the mesh cover 14 is fixedly connected to the movable sleeve 9 by a latch 15, and a through hole 17 for the conduit to pass through is opened in the middle of the mesh cover.

[0044] The mesh cover can shield the soil layer and reduce the problem of soil leakage upwards when the pressure bladder squeezes the soil layer.

[0045] In a specific embodiment, the performance of the pressure bladder can be further optimized in the following ways:

[0046] (1) Arc-shaped structure

[0047] See Figure 1 As shown, the side wall of the pressure bladder away from the movable sleeve has an arc-shaped structure with a concave center. This allows it to gather the soil when compressing the cover layer, reducing the upward extrusion of soil.

[0048] (2) Shaping wire

[0049] See Figure 3 As shown, the pressure bladder 10 is connected to multiple shaping wires 12, which are used to maintain the shape of the pressure bladder 10 when it is inflated.

[0050] Multiple shaping wires are connected inside the pressure bladder, which allows the shape of the pressure bladder to be maintained more stably after it is pressurized and expanded, ensuring a more stable compression effect on the soil layer during the simulation experiment.

[0051] Furthermore, the shaping guide wire 12 is perpendicular to the side wall of the movable sleeve 9.

[0052] (3) Overflow stop strip

[0053] The pressure bladder 10 has multiple overflow prevention strips 13 arranged vertically along the circumferential direction on the side wall away from the movable sleeve 9.

[0054] Furthermore, the vertical cross-section of the overflow stop strip 13 is an inverted triangle.

[0055] The overflow stop strip is installed circumferentially along the side wall of the pressure bladder. The vertical cross-section of the overflow stop strip is an inverted triangle. When the pressure bladder compresses the cover soil layer, the structure of the overflow stop strip enables it to push the soil downward, thereby reducing soil overflow.

[0056] The overflow-stop strip, the aforementioned mesh cover, and the concave arc-shaped structure in the side wall of the pressure bladder all mitigate the overflow problem of the cover soil layer when the pressure bladder is pressurized and expanded.

[0057] (4) Setting of multiple pressure bladders

[0058] The movable sleeve has multiple pressure bladders arranged vertically inside. Figure 1 Taking two pressure bags as an example.

[0059] At least two pressure bladders are used. By controlling the pressure of different bladders individually (e.g., one is inflated while the other is not), the lateral thrust exerted by the overburden layer on the guide pipe can be controlled. Furthermore, controlling the lateral forces in different directions between the upper and lower overburden layers can generate shear forces on the guide pipe. The more pressure bladders there are, the more directions the lateral and shear forces can be changed, resulting in a more comprehensive range of simulated scenarios. The number of pressure bladders can be selected according to requirements in simulation experiments. Additionally, by combining this with the intermittent impact effect of the pressure bladders' "inflation and deflating," this shearing action can effectively simulate earthquake conditions, further increasing the parameters that the experimental device can simulate and making the simulation effect more outstanding.

[0060] In some embodiments, both the fixed sleeve 6 and the movable sleeve 9 are provided with through holes 18 for fluid to flow out.

[0061] In some embodiments, the experimental apparatus further includes a data processing and control subsystem for controlling and acquiring data from the aforementioned subsystem.

[0062] In some embodiments, the above-described experimental apparatus includes multiple wellhead assembly subsystems.

[0063] Based on the inventive concept of this invention, this embodiment of the invention also provides a method for testing the stability of natural gas hydrate extraction wellheads, including:

[0064] The stability simulation experiment of natural gas hydrate wellhead was conducted using the aforementioned natural gas hydrate wellhead stability test device.

[0065] The core technical point of this invention is to make the force exerted by the overburden layer on the guide pipe during the simulation experiment more consistent with the actual situation. Therefore, the description of other aspects will not be repeated in this example. Even if the experimental process is not specifically described, other components of the experimental device and other details of the experimental method can be referred to a known prior art (such as a deep-water natural gas hydrate wellhead stability experimental device disclosed in Chinese patent application No. 201811135589.0). This will not cause any problems for those skilled in the art, such as unclear explanations that would prevent the solution from being implemented.

[0066] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process may be rearranged without departing from the scope of this disclosure. The appended method claims provide elements of various steps in an exemplary order and are not intended to limit the scope to the specific order or hierarchy described.

[0067] In the detailed description above, various features are combined together in a single embodiment to simplify this disclosure. This approach to disclosure should not be construed as reflecting an intention that embodiments of the claimed subject matter require more features than are explicitly stated in each claim. Rather, as reflected in the appended claims, the invention is presented with fewer features than all of the features in a single disclosed embodiment. Therefore, the appended claims are hereby explicitly incorporated into the detailed description, with each claim representing a separate preferred embodiment of the invention.

[0068] The foregoing description includes examples of one or more embodiments. It is certainly impossible to describe all possible combinations of components or methods in order to describe the above embodiments; however, those skilled in the art will recognize that further combinations and arrangements of the various embodiments are possible. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims.

Claims

1. A wellhead stability testing device for natural gas hydrate extraction, comprising a drilling platform motion simulation subsystem, a wellhead assembly subsystem, and a hydrate simulation subsystem, characterized in that, The wellhead assembly subsystem includes a simulated wellhead and a conduit connected to the simulated wellhead; The hydrate simulation subsystem includes a fixed sleeve filled with a cushion soil layer and a hydrate simulation layer from bottom to top, and a soil pressurization simulation mechanism disposed on the fixed sleeve. The conduit passes through the topsoil layer of the soil pressure simulation mechanism; The soil pressurization simulation mechanism includes multiple movable sleeves connected vertically. Inside each movable sleeve, multiple pressure bladders are arranged vertically along the circumference. The soil cover layer is filled in the cavity enclosed by the pressure bladders. The pressure bladders are connected to an external hydraulic system through inlet and outlet oil passages. The sidewall of the pressure bladder away from the movable sleeve has an arc-shaped structure with a concave center; The pressure bladder is connected to multiple shaping cables, which are used to maintain the shape of the pressure bladder when it is inflated; the shaping cables are perpendicular to the side wall of the movable sleeve. The pressure bladder has multiple overflow prevention strips arranged vertically along its circumferential sidewall away from the movable sleeve.

2. The apparatus as claimed in claim 1, characterized in that, The vertical cross-section of the overflow stop strip is an inverted triangle.

3. The apparatus as described in claim 1, characterized in that, The upper end of the outer wall of the movable sleeve has multiple guide strips distributed circumferentially.

4. The apparatus according to any one of claims 1 to 3, characterized in that, The uppermost movable sleeve is equipped with a mesh cover; The mesh cover and the uppermost movable sleeve are fixedly connected by a latch, and the mesh cover has a through hole in the middle for the conduit to pass through.

5. The apparatus as claimed in claim 1, characterized in that, The drilling platform motion simulation subsystem includes a loading component for simulating lateral loads connected to the simulated wellhead; The simulated wellhead is also connected to a counterweight module for simulating vertical loads.

6. The apparatus as claimed in any one of claims 1 to 3 and 5, characterized in that, The catheter comprises multiple catheter segments connected by threads; The upper end of the guide tube is threadedly connected to the simulated wellhead.

7. A method for testing the stability of natural gas hydrate extraction wellheads, characterized in that, include: A wellhead stability simulation experiment for natural gas hydrate extraction was conducted using the wellhead stability test apparatus described in any one of claims 1 to 6.

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