CN114954822A

CN114954822A - Full-submersible tension leg platform and underwater oil production method based on device

Info

Publication number: CN114954822A
Application number: CN202210816034.2A
Authority: CN
Inventors: 雷振东
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-07-16
Filing date: 2022-07-16
Publication date: 2022-08-30

Abstract

The invention relates to a fully submersible tension leg platform and an underwater oil extraction method based on the device. The tension leg platform comprises a platform main body, tension leg tendons and an anchoring foundation; the top of the tension leg tendon is connected with the edge of the platform main body, and the bottom of the tension leg tendon is connected with the anchoring foundation; the platform main body comprises a buoyancy tank for providing buoyancy and a platform deck; the buoyancy generated by the buoyancy tank is greater than the total gravity of the platform body. The platform body is located in a shallow water layer with a depth ranging from 30m to 100 m. The subsea production device is mounted on the platform body. And oil and gas exploitation of deep sea oil and gas fields is carried out through shallow water underwater oil extraction equipment. The tension leg platform and the underwater oil extraction method based on the tension leg platform have the advantages of low operation cost, high reliability and low manufacturing difficulty.

Description

Full-submersible tension leg platform and underwater oil production method based on device

Technical Field

The invention relates to a tension leg platform, in particular to a fully submersible tension leg platform and an underwater oil production method based on the device.

Background

The deep sea oil and gas exploitation modes are mainly divided into an above-water oil exploitation mode and an underwater oil exploitation mode. Wherein the above-water production mode is performed on the surface of the sea and the below-water production mode is performed on the bottom of the deep sea. The marine production mode requires the use of either a tension leg platform or a SPAR platform, both of which have high manufacturing difficulties and cost expenditures. Therefore, China is mainly inclined to use an underwater oil production mode for deep sea oil and gas production at present. At present, the maximum operation water depth of the deep water Christmas tree at home is 1480m, but the maximum operation water depth of the deep water Christmas tree at abroad reaches 2934 m. The deep water underwater oil extraction equipment in China still far does not meet the target of marine oil exploration and development in China, and the deep water underwater oil extraction equipment needs to be developed to the deeper sea area.

The underwater oil production equipment for the deep-sea oil and gas field comprises a deep-water manifold center, a deep-water transformer, a deep-water separator, a deep-water production tree and the like. The most representative of these is the deep water christmas tree. The description uses a deep water production tree as an example for background discussion, and other deep water production equipment has similar characteristics. The deepwater Christmas tree in the prior art has the following defects: 1. the cost is high. The price of a deep water christmas tree is twice the price of a shallow water christmas tree. More importantly, the daily maintenance cost and the maintenance cost of the deepwater Christmas tree are far higher than those of the shallow water Christmas tree. The shallow water Christmas tree only needs a diver to carry out maintenance operation, while the deep water Christmas tree only can carry out maintenance operation through an electro-hydraulic control mode and an ROV operation panel. This greatly increases the overhead required for normal operation of the deepwater Christmas tree; 2. the manufacturing difficulty is high. The subsea tree has exceptionally strict manufacturing process and technical requirements, which can be called the peak of the industrial manufacturing technology as in aerospace engineering. And the deepwater Christmas tree is installed on the deepwater seabed, so that the deepwater Christmas tree cannot be manually maintained once being installed, and needs to stably operate for decades. The manufacturing difficulty of the tree is higher than that of a shallow water Christmas tree, and the high temperature and high pressure resistance and corrosion resistance are more required to be considered; 3. the reliability requirement is high. Since the deepwater christmas tree is located on the seabed of deep sea or ultra-deep sea, remote operation can only be performed by an umbilical cable and an underwater robot. If the deep water Christmas tree breaks down, even oil leakage accidents happen, the maintenance operation is difficult. There are not small engineering obstacles to successfully solving accidents, rapidly reproducing and the like. At present, China sea oil is very strict in production safety, so that safe and reliable technical performance can be realized for underwater oil extraction equipment used for deep-sea oil and gas fields, and audiences prefer and like the oil extraction equipment.

In summary, the offshore platform in the above-water production mode and the deepwater production equipment in the underwater production mode both have the disadvantages of high cost and poor reliability. There is therefore a need for a fully submersible tension leg platform that is safe, reliable and low cost. The foreign enterprise has a profound technical accumulation on production equipment used on deep sea surfaces and deep sea floors. Therefore, it is necessary to design an underwater oil production method which can bypass the high skill of the external enterprises in the existing oil production mode.

Disclosure of Invention

The claimed invention is part to solve and improve: the invention aims to provide a fully-submersible tension leg platform and an underwater oil extraction method based on the device, so that shallow water oil extraction equipment borne by the tension leg platform can carry out oil extraction operation in a deep sea oil and gas field.

In order to achieve the above object, in some embodiments of the present invention, the following technical solutions are provided:

the invention provides a fully submersible tension leg platform, which comprises a platform main body for bearing underwater oil production equipment, tension leg tendons and an anchoring foundation, wherein the tension leg tendons are arranged on the platform main body; the top of the tension leg tendon is connected with the edge of the platform main body, and the bottom of the tension leg tendon is connected with the anchoring foundation; the platform body comprises a buoyancy tank for providing buoyancy; the buoyancy generated by the buoyancy tank is greater than the total gravity of the platform body.

In some embodiments, the pontoons of the tension leg platform of the present invention are flat; the buoyancy tank is used for bearing underwater oil production equipment; the tendon of the tension leg is connected to the edge of the buoyancy tank.

In some embodiments, the platform body of the tension leg platform of the present invention further comprises a platform deck; the buoyancy tank is positioned below the platform deck; the platform deck is used for bearing underwater oil production equipment.

In some embodiments, the tension leg tendons of the tension leg platform of the present invention are attached to the edge of the platform deck.

In some embodiments, the tension leg tendons of the tension leg platform of the present invention are attached to the edges of the pontoon.

In some embodiments, the tension leg tendons of the tension leg platform of the present invention are connected in a vertical configuration between the platform body and the anchor base.

In some embodiments, the tension leg tendons of the tension leg platform of the present invention are connected in an inclined configuration between the platform body and the anchoring base; the distance between the individual tension leg tendons increases with increasing water depth.

In some embodiments, the pontoons of the tension leg platform of the present invention further comprise reinforcing ribs that function to strengthen the pontoons against buckling; the reinforcing ribs are positioned in the buoyancy tank.

In some embodiments, the buoyancy tank of the tension leg platform of the present invention further comprises a staging wall; the chamber dividing wall is positioned in the floating box and used for dividing the floating box into independent sealed chambers.

The invention also provides an underwater oil production method based on the fully submersible tension leg platform, which comprises the following steps:

the method comprises the following steps: referring to fig. 1, a tension leg platform with full submergence and floatation capability is installed below the water surface with the platform body in the shallow water layer. The depth range of the shallow water layer is 30m-100 m;

step two: the bottom end of the top tension type vertical pipe is connected with a wellhead positioned on the seabed in a sealing manner; a tensioner on the platform body is mounted on top of the top-tensioned riser;

step three: the bottom end of the shallow water Christmas tree is connected with the top end of the top tension type vertical pipe in a sealing way;

step four: the shallow water Christmas tree and the underwater manifold center are connected in a sealing way through a jumper pipe; the shallow water Christmas tree transmits well fluid to the water and lower pipe gathering center through the jumper pipe;

step five: and the underwater manifold center finishes well fluid metering and pressurization, and then delivers the well fluid to a production system through an oil-gas pipeline for oil-gas treatment, storage and transportation.

In some embodiments, the production system is a floating production storage vessel (FPSO).

In some embodiments, the production system is a semi-submersible offshore platform.

In some embodiments, the production system is an oil and gas treatment plant located onshore.

In some embodiments, the platform body of the fully submersible tension leg platform of the present invention has other types of subsea production equipment mounted thereon, such as subsea manifold centers, subsea oil-water separators, and subsea transformers.

Compared with the prior art, the technical scheme of the invention has the beneficial effects that:

(1) lower cost expenditure. Referring to fig. 1, the buoyancy generated by the buoyancy tanks of the tension leg platform of the present invention is greater than the total weight of the tension leg platform and the subsea production equipment mounted thereon. The residual buoyancy of the buoyancy tank is equal to the pretension of the tendon of the tension leg in magnitude and opposite in direction. Based on the stress analysis, the tension leg platform can realize the balance of a force system, so that the tension leg platform can stably submerge and float in seawater. The platform body of the tension leg platform is positioned in a shallow water layer of a deep sea area in a full submergence and floatation mode. Therefore, the underwater oil extraction equipment on the tension leg platform only needs to adapt to a shallow water environment, and how to adapt to the special extreme environment of the deep sea bottom does not need to be considered. For example, shallow water trees, shallow water umbilicals and shallow water manifold centers may be mounted on the tension leg platform of the present invention for deep sea oil and gas exploration. The manufacturing cost of the shallow water Christmas tree is half of that of the deep water Christmas tree, and the required length of the umbilical cable is short, so that the production cost is reduced. Moreover, the underwater oil production equipment used in the shallow water environment only needs to be maintained daily by divers, so that the problems of overhigh manufacturing cost and daily maintenance cost of the deepwater Christmas tree and other underwater oil production equipment used in the deepwater environment are solved;

(2) and (4) high reliability. Referring to fig. 1, the tension leg platform of the present invention is installed below the storm surface base. The water depth of the storm wave base surface is about 30m-50 m. Therefore, the underwater oil production method based on the fully-submersible tension leg platform does not belong to the sea surface oil production mode and the seabed oil production mode in the prior art, but belongs to the underwater shallow water oil production mode for deep-sea oil and gas fields. The inventors named it "storm recovery mode". The tension leg platform of the invention is almost never affected by storm waves, so that the six degrees of freedom to be considered by the sea surface floating body and the overturning risk caused by the rupture of the tendon of the tension leg do not need to be considered. Meanwhile, the tension leg platform of the invention adopts shallow underwater oil production equipment to mine deep-sea oil and gas fields, thus avoiding the problem of difficult maintenance of the deep underwater oil production equipment and further strengthening the reliable operation of the underwater oil production equipment;

(3) lower manufacturing difficulty. Referring to fig. 1, it can be seen from the first and second advantages that the tension leg platform and the underwater oil production equipment carried by the tension leg platform of the present invention have the advantages of low cost and high reliability. This means that the quality requirements for these subsea production devices are not critical, with the aim of reducing the manufacturing difficulties. Because the tension leg platform disclosed by the invention is fully submerged below the water surface and hardly influenced by extreme waves, the requirements of the residual buoyancy of the buoyancy tank and the pretension of the tension leg tendons are greatly reduced, and the requirements of the use quantity and the quality of the tension leg tendons are reduced. In some embodiments, the tension leg platform of the present invention may employ domestic polyester cables as the tension leg tendons. The tension leg platform can realize deep sea oil and gas exploitation by replacing a deep water Christmas tree with a shallow water Christmas tree, thereby reducing the manufacturing difficulty of the underwater Christmas tree. The maximum water depth of use of the most advanced umbilicals at present is less than 2500 m. According to the tension leg platform, the Christmas tree is arranged on a shallow water layer, so that the use water depth of the umbilical cable is greatly reduced, and the use of a domestic umbilical cable with low manufacturing difficulty is facilitated. The tension leg platform of the present invention can also be used to perform deep sea oil and gas treatment operations using a shallow water subsea manifold center, a shallow water oil-water separator, and a shallow water transformer. These subsea production devices for shallow water are relatively less difficult to manufacture.

Drawings

Various structural schematics corresponding to the embodiments of the present invention in the specification are shown in the drawings. The figures are not drawn to scale. The drawings may have enlarged details of certain structural features for clarity of presentation and may omit details of certain structural features. The shapes of the various parts and their relative sizes and positional relationships shown in the drawings are merely exemplary. The skilled person can additionally design parts with different shapes, sizes and relative positions according to the actual needs. In the drawings:

FIG. 1 is a force analysis schematic of a tension leg platform in some embodiments of the invention;

FIG. 2 is a perspective view of a tension leg platform in a first embodiment;

FIG. 3 is a vertical cross-sectional view of the tension leg platform taken at point A, B in FIG. 2;

FIG. 4 is a perspective view of several of the major components of the tension leg platform in a first embodiment;

FIG. 5 is a top perspective sectional view of the buoyancy tank in the first embodiment;

FIG. 6 is a side elevation, cross-sectional view of the buoyancy tank of the first embodiment;

FIG. 7 is a schematic perspective view of the connection of circumferential ribs and vertical ribs on the inner surface of the pontoon wall;

FIG. 8 is a schematic perspective view of the connection of vertical webs, radial webs and toggle plates at the corners of the pontoon walls;

FIG. 9 is a schematic perspective view of the structure of the pontoon truss;

FIG. 10 is a perspective view of a tension leg platform in a second embodiment;

FIG. 11 is a vertical cross-sectional view of the tension leg platform taken through point A, B in FIG. 10;

FIG. 12 is a top perspective cross-sectional view of the buoyancy tank in a second embodiment;

FIG. 13 is a side elevation, cross-sectional view of a buoyancy tank in a second embodiment;

FIG. 14 is a perspective view of a tension leg platform in a third embodiment;

FIG. 15 is a vertical cross-sectional view of the tension leg platform taken at point A, B in FIG. 14;

fig. 16 is a perspective view of several of the major components of the tension leg platform in a third embodiment.

Reference numbers for the tension leg platform of the present invention: buoyancy tank 1, buoyancy tank wall 101, circumferential rib 102, radial rib 103, vertical rib 104, toggle 105, buoyancy tank truss 106, sub-bay wall 107, tension leg connector 108, central buoyancy tank 109, edge buoyancy tank 110, tension leg tendon 2, platform deck 3, riser hole 301, top tensioned riser 302, shallow christmas tree 303, and tensioner 304.

Detailed Description

The following detailed description refers to the accompanying drawings that illustrate embodiments in which the invention may be practiced. It is to be noted that the various embodiments described herein are not necessarily mutually exclusive, so that features of different embodiments may be combined to form new embodiments. The functional and structural principles of the present invention have been shown and described in the embodiments. Any variations or modifications may be made to the embodiments of the invention without departing from the principles described. The dependent claims are hereby applied to the extent that the features of the different embodiments are combined together without conflict. The features of orientation of the individual parts described in the independent claims are defined with reference to the abstract drawing.

In the detailed description of the embodiments, words such as "top," "bottom," "ends," "bottom," "top," "bottom," and "above" are used in accordance with the directional characteristics of various parts in the accompanying drawings. The description of the orientation features of the different parts is used to illustrate the embodiments and is in no way limiting of the technical features. "Top end", "bottom end" and "ends" are used to describe the orientation features of the edges of an object. "Top" refers to the portion of the area near the top edge of the object being described. "bottom" refers to the portion of the area near the bottom edge of the object being described. "lower" and "upper" are used to describe the orientation features of one object that are outside the volumetric range of another object. That is, two objects whose orientation features are compared should be viewed as two objects, with no inclusion relationship.

In the description of the present invention, unless expressly defined otherwise, the terms "disposed," "mounted," "connected," and the like are to be construed broadly. The specific meaning of the above-mentioned words in the present invention can be reasonably determined by those skilled in the art in combination with the detailed contents of the technical solutions.

The fully submersible tension leg platform of the present invention may be referred to herein simply as the tension leg platform of the present invention.

The term "inboard side wall of the pontoon" refers to the pontoon wall on the side near the axle center of the tension leg platform of the invention.

The term "outboard wall of the pontoon" refers to the pontoon wall on the side away from the axle center of the tension leg platform of the invention.

The term "top wall of the buoyancy tank" refers to the tank wall at the top end of the buoyancy tank.

The term "bottom wall of the buoyancy tank" refers to the wall of the buoyancy tank at the bottom end of the buoyancy tank.

The term "submerged" means that the object is located below the water surface, but is floating in the water.

The term "circumferential rib" refers to a reinforcing rib distributed in the horizontal plane in the circumferential direction of the axis of the tension leg platform of the present invention.

The term "vertical rib" refers to a reinforcing rib that runs in the vertical direction.

The term "radial web" refers to a reinforcement rib that is distributed radially along the axis of the tension leg platform of the present invention in the horizontal plane.

The term "platform body" refers to the buoyancy tanks of the tension leg platform of the present invention or to the combination of the buoyancy tanks and platform deck of the tension leg platform of the present invention.

The term "subsea production facility" generally refers to one or more devices used for subsea hydrocarbon production. The device for underwater oil and gas exploitation comprises a shallow water Christmas tree, an underwater oil-water separator, an underwater oil and gas manifold center, an underwater transformer, a top tensioning type vertical pipe, a tensioner and the like.

The term "total weight of the platform body" refers to the total weight of the platform body and the subsea production equipment carried thereon.

The term "subsea shallow water production unit" refers to a subsea production unit for use in a shallow water environment.

The term "deepwater subsea production facility" refers to a subsea production facility for use in a deepwater environment.

A first embodiment of the tension leg platform of the present invention, which can be used to describe with reference to fig. 1 to 8, comprises a platform body, tension leg tendons 2, tension leg connectors 108 and an anchoring base. Wherein the platform main body comprises a buoyancy tank 1 and a platform deck 3; the buoyancy tank 1 comprises a buoyancy tank wall 101 and reinforcing ribs; the reinforcing ribs comprise circumferential ribs 102, radial ribs 103, vertical ribs 104 and toggle plates 105.

Referring to fig. 4 and 5, the buoyancy tank 1 is in the form of a ring, located below the edge region of the platform deck 3. The tension leg connectors 108 are symmetrically distributed with respect to the centroid of the buoyancy tank 1.

Referring to fig. 4, 3 and 2, the top end of the buoyancy tank 1 is fixedly connected to the bottom end of the platform deck 3 by welding. The tension leg connectors 108 are fixedly attached to the edges of the buoyancy tank 1 by welding.

Referring to fig. 2 and 1, the top of the tension leg tendon 2 is attached to a tension leg connector 108. The bottom of the tension leg tendon 2 is connected to an anchoring base (not shown) located at the sea bottom. The tension leg tendon 2 is connected in a vertical configuration between the platform body and the anchoring base. The tension leg tendon 2 is made of a corrosion resistant steel wire rope. The prior art is used with respect to the tension leg tendon 2, the tension leg connector 108 and the anchoring foundation. For clarity and conciseness, the description of the present invention will not be repeated.

Referring to fig. 2, the central region of the platform deck 3 contains riser holes 301. This is provided to enable a top-tensioned riser 302 to be passed through riser bore 301 and then connected to tensioners 304 on platform deck 3. The tensioner 304 can be referred to in published journal "vibration and shock" article "numerical simulation of top-tensioned riser hydro-pneumatic tensioner".

The tension leg platform of this embodiment is mounted below the water surface in a fully submerged fashion with the platform body at a depth of 50 m. The buoyancy of the buoyancy tank 1 is greater than the total gravity of the platform body. The residual buoyancy of the buoyancy tank 1 is equal to the pretension of the tendon 2 of the tension leg in magnitude and opposite in direction, so that the force system balance of the tension leg platform is realized.

Referring to fig. 5 and 6, the inner surfaces of the inner and outer sides of the buoyancy tank walls 101 are provided with circumferential ribs 102 and vertical ribs 104, and the inner surfaces of the top and bottom walls of the buoyancy tank are provided with radial ribs 103. Circumferential rib 102, radial rib 103, and vertical rib 104 are all fixed to the inner surface of the pontoon wall 101 by welding. The steel of the buoyancy tank 1 is made of an alloy material for a bilge water system of an ocean drilling platform with the reference patent application number of 201610069890.0 and a preparation method thereof.

Referring to fig. 7, vertical webs 104 extend vertically through circumferential web 102 and are welded thereto. The profile type of circumferential rib plate 102 is T-shaped steel. The profile types of the vertical rib plates 104 and the radial rib plates 103 are flanged steel.

Referring to fig. 8 and 6, the toggle plate 105 is located at the corner of the buoyancy tank 1, and the toggle plate 105 has a triangular plate shape. One side of the toggle plate 105 is connected to the radial rib 103 and the other side of the toggle plate 105 is connected to the vertical rib 104. This is done to increase the strength of the connection point between vertical rib 104 and radial rib 103.

A second embodiment of the tension leg platform of the present invention, which can be used to describe with reference to fig. 7 to 13, comprises a platform body, tension leg tendons 2, tension leg connectors 108 and an anchoring base. Wherein the platform body comprises a buoyancy tank 1; the buoyancy tank 1 comprises a buoyancy tank wall 101, a sub-bin wall 107 and reinforcing ribs; the stiffeners include circumferential stiffeners 102, radial stiffeners 103, vertical stiffeners 104, toggle plates 105, and pontoon trusses 106.

Referring to fig. 10 and 12, the buoyancy tank 1 is flat. This is provided in order to enable the installation of subsea production equipment on the buoyancy tank 1. The tension leg connectors 108 are symmetrically distributed with respect to the centroid of the buoyancy tank 1 and are fixedly connected to the edge of the buoyancy tank 1 by welding.

Referring to fig. 10, the top of the tension leg tendon 2 is attached to a tension leg connector 108. The bottom of the tension leg tendon 2 is connected to an anchoring base (not shown) located at the sea bottom. The tension leg tendon 2 is connected in a vertical configuration between the platform body and the anchoring base. The tension leg tendon 2 is made of a corrosion resistant hollow steel tube (refer to the tension leg platform tendon installation and temporary buoy design, published in journal, ocean engineering equipment and technology). The prior art is used with respect to the tension leg tendon 2, the tension leg connector 108 and the anchoring foundation. For clarity and conciseness, the description of the present invention will not be repeated.

Referring to fig. 10, the central region of the buoyancy tank 1 contains riser holes 301. This is provided to enable a top-tensioned riser 302 to be passed through riser bore 301 and then connected to tensioners 304 on the buoyancy tank 1 (see figure 1). The tensioner 304 can be referred to in published journal "vibration and shock" article "numerical simulation of top-tensioned riser hydro-pneumatic tensioner".

The tension leg platform of this embodiment is mounted below the water surface in a fully submerged fashion with the platform body at a depth of 30 m. The buoyancy of the buoyancy tank 1 is greater than the total gravity of the platform body. The residual buoyancy of the buoyancy tank 1 is equal to the pretension of the tendon 2 of the tension leg in magnitude and opposite in direction, so that the force system balance of the tension leg platform is realized.

Referring to fig. 13 and 12, the inner surfaces of the inner and outer sides of the pontoon wall 101 are provided with circumferential ribs 102 and vertical ribs 104, and the inner surfaces of the top and bottom walls of the pontoon are provided with radial ribs 103. Circumferential rib 102, radial rib 103, and vertical rib 104 are all fixed to the inner surface of the pontoon wall 101 by welding. The steel of the buoyancy tank 1 is made of an alloy material for a bilge water system of an ocean drilling platform with the reference patent application number of 201610069890.0 and a preparation method thereof.

Referring to fig. 7, vertical webs 104 extend vertically through circumferential web 102 and are welded thereto. The section type of the circumferential rib plate 102 is I-shaped steel; the profile types of the vertical rib 104 and the radial rib 103 are channel steel.

Referring to fig. 13 and 8, the toggle plate 105 is located at the corner of the buoyancy tank 1, and the toggle plate 105 has a triangular plate shape. One side of the toggle plate 105 is connected to the radial rib 103 and the other side of the toggle plate 105 is connected to the vertical rib 104. This is done to increase the strength of the connection point between vertical rib 104 and radial rib 103.

Referring to fig. 12, 13 and 9, the pontoon truss 106 is ring-shaped and is located inside the pontoon 1. The top end of the buoyancy tank truss 106 is connected with the buoyancy tank top wall in a welding mode, and the bottom end of the buoyancy tank truss 106 is connected with the buoyancy tank bottom wall in a welding mode. This is provided to increase the buckling resistance of the buoyancy tank 1.

A third embodiment of the tension leg platform of the present invention, which can be used to describe with reference to fig. 14 to 16, comprises a platform body, tension leg tendons 2, tension leg connectors 108 and an anchoring base. The platform main body comprises a buoyancy tank 1 and a platform deck 3; buoyancy tank 1 includes a central buoyancy tank 109 and an edge buoyancy tank 110.

Referring to fig. 16 and 15, the edge pontoons 110 are located below the edge region of the platform deck 3 and the central pontoons 109 are located below the central region of the platform deck 3. The central buoyancy tank 109 is annular and the hole in the centre of the central buoyancy tank 109 corresponds to the riser hole 301 of the platform deck. This is provided to enable top-tensioned risers 302 to pass through the central region of central buoyancy tank 109 and riser apertures 301 and then connect to tensioners 304 on platform deck 3 (see figure 1). The tensioner 304 can be referred to in published journal "vibration and shock" article "numerical simulation of top-tensioned riser hydro-pneumatic tensioner".

Referring to fig. 15 and 14, the top end of the buoyancy tank 1 is fixedly attached to the bottom end of the platform deck 3 by welding. The tension leg connectors 108 are symmetrically distributed with respect to the centroid of the platform deck 3. The tension leg connectors 108 are fixedly attached to the edges of the platform deck 3 by welding.

Referring to fig. 14, the top of the tension leg tendon 2 is attached to a tension leg connector 108. The bottom of the tension leg tendon 2 is connected to an anchoring base (not shown) located at the sea bottom. The tension leg tendons 2 are connected in an inclined configuration between the platform body and the anchoring base. The distance between the individual tension leg tendons 2 increases with increasing water depth. The tension leg tendon 2 is made of a polyester cable. The prior art is used with respect to the tension leg tendon 2, the tension leg connector 108 and the anchoring foundation. For clarity and conciseness, the description of the present invention will not be repeated.

The tension leg platform of this embodiment is mounted below the water surface in a fully submerged fashion with the platform body at a depth of 100 m. The buoyancy of the buoyancy tank 1 is greater than the total gravity of the platform body. The residual buoyancy of the buoyancy tank 1 and the resultant force of the pretension of the tendon 2 of the tension leg have the same direction and the opposite direction, thereby realizing the force system balance of the tension leg platform.

The buoyancy walls 101 of the central buoyancy tank 109 and the edge buoyancy tanks 110 are formed using 5cm thick titanium alloy sheet material, and are arranged to enhance the buckling resistance of the buoyancy tank 1.

The invention relates to a mounting method of a fully-submersible tension leg platform, which comprises the following steps:

the method comprises the following steps: and fixedly installing the anchoring foundation on the seabed. The bottom of the tension leg tendon 2 is connected with an anchoring foundation, and the top of the tension leg tendon 2 is connected with a temporary buoy;

step two: ballast water is injected into a buoyancy tank 1 of the platform main body, and meanwhile, a large crane ship hoists the platform main body, so that the platform main body slowly and stably sinks below the water surface and reaches a preassembly position;

step three: the tension leg tendon 2 is connected with the tension leg connector 108 of the platform body, and then the tension leg tendon 2 unloads the temporary buoy;

step four: discharging a part of ballast water in the buoyancy tank 1, so that the buoyancy generated by the buoyancy tank 1 is larger than the gravity of the platform body. The residual buoyancy of the buoyancy tank 1 and the pretension of the tension leg tendon 2 keep balance, so that the platform main body stably submerges in seawater;

step five: the subsea production device is mounted above the platform body. When the underwater oil production equipment is installed, the ballast water in the buoyancy tank 1 is further discharged, and the buoyancy generated by the buoyancy tank 1 is always kept larger than the total weight of the platform body and the underwater oil production equipment installed thereon.

The temporary pontoons referred to in this specification may be referred to as temporary buoyancy devices for the tension leg platform tendons in patent application No. 201720183142.5. For the method of installing the tendon of the tension leg, refer to the method of joining the segmented groups of tendon of the tension leg platform of patent application No. 201811086011.0.

The methods of manufacture and installation of the tension leg tendon 2, tension leg tendon connector 108 and anchor foundation referred to in the present specification are all prior art.

Referring to fig. 1, the underwater oil production method based on the fully submersible tension leg platform of the present invention includes the following steps:

the method comprises the following steps: the tension leg platform with the full submerging and floating function is installed below the water surface, so that the platform main body is located in a shallow water layer. The depth range of the shallow water layer is 30m-100 m;

step two: the bottom end 302 of the top tension type riser is hermetically connected with a wellhead positioned on the seabed; tensioners 304 on the platform body are mounted on top of the top-tensioned riser 302;

step three: the bottom end of the shallow water Christmas tree 303 is hermetically connected with the top end of the top tensioning type riser 302;

step four: the shallow water christmas tree 303 is sealingly connected to the subsea manifold center by a jumper. The shallow tree 303 delivers well fluid to a subsea manifold (not shown) via the jumper;

step five: the subsea manifold center performs well fluid metering and pressurization, and then delivers the well fluid to a production system for oil and gas processing and storage (not shown in the figure) via an oil and gas pipeline.

The top-tensioned riser 302 and tensioner 304 described in this specification all employ prior art techniques.

The underwater oil production equipment mentioned in the underwater oil production method adopts the prior art. For clarity and conciseness, the description of the invention is not repeated.

Claims

1. A fully submersible tension leg platform is characterized by comprising a platform main body for bearing underwater oil production equipment, tension leg tendons (2) and an anchoring foundation; the top of the tension leg tendon (2) is connected with the edge of the platform main body, and the bottom of the tension leg tendon (2) is connected with an anchoring foundation; the platform body comprises a buoyancy tank (1) for providing buoyancy; the buoyancy generated by the buoyancy tank 1 is greater than the total gravity of the platform body.

2. A fully submersible tension leg platform according to claim 1 wherein the pontoon (1) is flat; the buoyancy tank (1) is used for bearing underwater oil production equipment; the tension leg tendon (2) is connected to the edge of the buoyancy tank (1).

3. A fully submersible tension leg platform according to claim 1 wherein the platform body further comprises a platform deck (3); the buoyancy tank (1) is positioned below the platform deck (3); the platform deck (3) is used for bearing underwater oil production equipment.

4. A fully submersible tension leg platform according to claim 3 wherein the tension leg tendons (2) are attached to the edge of the platform deck (3).

5. A fully submersible tension leg platform according to claim 3 wherein the tension leg tendons (2) are attached to the edges of the pontoon (1).

6. A fully submersible tension leg platform according to any one of claims 1 to 5 in which the tension leg tendons (2) are connected in an upright configuration between the platform body and the anchoring base.

7. A fully submersible tension leg platform according to any one of claims 1 to 5 in which the tension leg tendons (2) are connected in an inclined configuration between the platform body and the anchoring base; the distance between the individual tension leg tendons (2) increases with increasing water depth.

8. A fully submersible tension leg platform according to any one of claims 1 to 5 further comprising stiffeners having the function of strengthening the buoyancy tank (1) against buckling; the reinforcing ribs are positioned in the buoyancy tank (1).

9. A fully submersible tension leg platform according to any one of claims 1 to 5 further comprising a binning wall (107); the chamber dividing wall (107) is positioned inside the floating box (1) and is used for dividing the floating box (1) into independent sealed chambers.

10. A method of subsea production based on a fully submersible tension leg platform according to any of claims 1 to 9, comprising the steps of:

the method comprises the following steps: installing a tension leg platform with a full submerging and surfacing function below the water surface to enable a platform main body to be positioned in a shallow water layer;

the depth range of the shallow water layer is 30m-100 m;

step two: the bottom end (302) of the top tensioning type riser is hermetically connected with a wellhead positioned on the seabed; a tensioner (304) on the platform body is mounted on top of the top-tensioned riser (302);

step three: the bottom end of the shallow water Christmas tree (303) is hermetically connected with the top end of the top tensioning type vertical pipe (302);

step four: the shallow water Christmas tree (303) is hermetically connected with the underwater manifold center through a jumper pipe; the shallow water Christmas tree (303) conveys well fluid to a water and lower pipe junction center through the jumper pipe;