JPH08189282A - Sea-bottom huydrocarbon production system,and installation method of sea-bottom source platform for producing hydrocarbon - Google Patents

Abstract

PURPOSE: To provide a petroleum production system, in which a semisubmersible type and the advantage of a tension-leg wellspring platform are combined by reducing cost and improving safety. CONSTITUTION: The production system 10 contains a small-sized tension-leg platform 24 connected on the sea bottom by a vertical tendon 50 and connected to a submachine oil field by vertical transport pipes 52. Accordingly, the overs and shorts of the tension of the tendon 50 and the vertical transport pipes 52 are avoided. Since movement in the mutually opposed horizontal direction of the tendon 50 and the vertical transport pipes 52 is prevented by constraint structure installed to the lower section of the platform, all the vertical transport pipes 52 and the tendon 50 are kept parallel mutually even when the platform 24 is drifted in the case of a storm wind.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for producing oil by boring an offshore oil well, and to a TLP (tension leg platform) thereof.

DESCRIPTION OF THE PRIOR ART Recently, attempts have been made to produce crude oil and gas from subterranean formations located deeper in the sea floor. As one approach, TLP (tension leg platform) anchored by multiple tendons that float on the sea surface and extend almost vertically to the sea floor.
There is use of. A vertical transport pipe extends down from the platform to the subsea well to carry hydrocarbons to the tree on the platform. The tree contains crude oil drains and valves that control the flow. The platform has a deck structure with one or more decks at or above sea level, and a lower hull in buoyant seawater that supports the deck structure and keeps the tenders and vertical transport tubes in tension. Includes hull and hull. Since the buoyancy of the hull is very large, the tension of the tendon is great, and the pitching, pitching and pitching are substantially reduced. The TLP is a stable, sway-resistant platform that provides a tree connected to a subsea well, where the tree is near, and preferably above, sea level and has all of its operational benefits.

Conventional TLP structures must remain in place and withstand the effects of severe ambient conditions such as storms such as hurricanes. By using a small platform anchored by a vertical tendon and connected by a vertical transport pipe, and by using a semi-submersible platform equipped with oil wells and production equipment that can move as storms approach, The platform's response to tidal currents can be minimized. The tendons and vertical transport tubes are correspondingly tensioned (that is, lengthened evenly) to prevent over-tensioning during a storm, and after the storm each one hits another tendon or vertical transport tube. The tension should be correspondingly reduced so that it has sufficient tension so that it does not.

[0004]

SUMMARY OF THE INVENTION In accordance with one embodiment of the present invention, a hydrocarbon production system is provided that includes a TLP that is a source platform that floats at sea level and is anchored by tension legs. The platform has a deck structure above or above sea level, and the source device, which is mainly the production tree on the platform, is connected to the upper end of a vertical transportation pipe that extends almost vertically to the oil well on the sea floor. A plurality of generally vertical tendons extending to the seabed and anchored there anchor the platform above the boring area or well. The platform keeps the tendon and the vertical transport tube under tension to prevent them from hitting each other. The platform has a hull structure that is mostly in seawater and supports the deck structure at or above sea level.

In order to ensure that the tension of the tendons and vertical transport pipes is changed correspondingly to the changes due to wave forces and platform offsets (drifts), the tendon and vertical transport pipes are placed near the bottom of the platform at the same depth in seawater. A folding lateral restraint structure is provided on the platform. As a result, during a storm, as the platform moves horizontally and vertically under wave forces, the vertical transport tube and tendon remain parallel, both increasing tension at the same rate. Since the tendons and vertical transport tubes share the increasing load, they are not over tensioned during heavy storms, and tendons and vertical transport tubes are properly tensioned during static conditions (zero platform drift). To be

The production system provides a very cost-saving and safety-improving isolation type that combines the advantages of a laterally (catenary) moored semi-submersible type with some of the advantages of a tension leg source platform. It can be a system. In that case, the system includes a small tension leg platform that is left on the area before the storm and a semi-submersible production support hull that is removed before the storm.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when taken in conjunction with the accompanying drawings.

[0008]

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a shut-off and mobile floating structure that includes a floating semi-submersible production structure or unit 20 that floats in the waters of the sea surface 22 and is connected to a small tension leg source platform or TLP 24. The production system is shown. The semi-submersible unit 20 includes a device 26 for the production of hydrocarbons and has a work deck 34 above the small TLP 24. This allows the slope to allow direct access between deck 34 and platform 24. The platform is located approximately in the center above the subsea well domain template. The platform deck structure 30 with the source 32 (mainly the tree at the top of the vertical transport pipe) is preferably above sea level, with the tree's valves and openings within 1.5 meters of sea level and using diving equipment. The platform deck structure should be within 3 meters of sea level so that it is accessible without access.

The work deck 34 of the unit 20 is supported by a buoyancy chamber 36 secured by a mooring system 40. The equipment on work deck 30 may include boring equipment 42 and production equipment 26. Buoyancy chamber 36
Supports one or more vertical struts 38 that support deck 34. As the unit 20 floats to the oil well region and the buoyancy chamber 36 can be partially submerged, the vertical struts 38 are partially located below the sea level 22 while keeping the work deck 34 above the platform 24.

The catenary mooring system 40, which secures the unit 20, is mounted at different locations around the unit and includes a number of mooring lines 44 and buoys 46 (approximately) extending in and along different directions with respect to the seabed 48. 8) are included. The area under the work deck 34 is substantially unobstructed so that the small platform 24 is placed under the work deck.

A miniature tension leg source platform 24, having a deck structure 30 thereon and preferably resting on the sea surface 22, is above the seabed or seabed well region template 28. The template 28 is placed on the seabed 48 above the well 58 and near the subsea oil field from which hydrocarbons are produced. Submarine template 28 is configured and anchored to seabed 48 so that the platform is sufficiently moored to withstand the forces resulting from the platform's response to wave and tide movements.
The upper ends of the plurality of tendons 50 are coupled to the platform, such as by coupling the platform to the deck structure 30. The tendon extends substantially perpendicular to the submarine template 28. The deck structure 30 has one or more decks, each preferably located above sea level, and further comprises a hull 51 including a plurality of corner struts 54 connecting the deck structure 30 to floating means 56 located below sea level. Have. The lower part 53 of the hull 51, which is always below sea level, may include the lower ends of the stanchions as well as the floating means. At least one vertical transport pipe 52 extends from the deck configuration 30 to the subsea template to connect the subsea well to the deck structure.

The production system is designed to function continuously under normal weather conditions. However, in extreme weather conditions, such as when a hurricane approaches, the semi-submersible hull or unit 20 ceases to function and moves.

The semi-submersible unit 20 is connected to the small platform 24 so that it can be conveniently and quickly disconnected from the platform 24 and the mooring system 40. The catenary mooring system 40 includes a mooring line 44 that is conveniently disconnected from the mooring buoy 46 and secured to the work deck 34 of the semi-submersible unit 20.

As shown in FIG. 4, the system for connecting the semi-submersible unit 20 to the platform 24 is a cross spring mooring system 72. Cables are used in system 72, which allows platform 2
Release the cable from 4 and place the cable 74 on the unit 20.
By fixing the unit 20, the unit 20 is disconnected. Both catenary and cross spring mooring systems may use mooring systems, quick release couplings, etc., standard for pipelines and umbilicals.

In one embodiment of the invention shown in FIG. 5,
A vertical transport pipe 52 extends through a hole in the lower hull 53. The lower hull includes a moonpool and template 60 in the center of the lower hull. The moon pool is also shown in Figure 2.
The vertical transport tube of FIG. 5 extends through a hole in the moonpool template 60. Also, the coach struts 54 are hollow,
It includes a tube 62 through which the tendon 50 passes.

FIGS. 6A and 6B are plan views showing different deck structures 30 of the source platform 24. The deck structure 30 is approximately 30 meters square (20
~ 40 meters square), and FIG.
FIG. 6 (B) shows an arrangement of up to about 13 oil wells. The platforms 24 are 24.
It is possible to have up to 33 vertical transport tubes with a diameter (inner diameter) of 5 cm. Each tendon can be a steel tube consisting of a thick wall with a diameter somewhat larger than the diameter of a vertical transport tube.

The platform 24 has a lower hull 56.
Means are included for laterally restraining tendon 50 and vertical transport tube 52 at or near the level of. As shown in FIG. 3, a system is constructed such that tendons 50 and vertical transport tubes 52 form a parallelogram in which all tendons and vertical transport tubes remain parallel in all weather conditions. That is, the lateral (horizontal) distance between the tendon 50 and the vertical transport pipe 52 is between the bottom of the platform 24 and the seabed 48 as the platform 24 moves laterally and downwards in water during a severe storm. Substantially unchanged at any position between. This will result in the same rate of increase in tension for all tendons and vertical conduits during severe storms and the same rate of decrease in tension after the storm has left. As a result, none of the tendons or vertical transport tubes are over-tensioned or under-tensioned.
Tensioned tendons or vertical transport tubes will likely "turn around", bumping into each other and damaging each other.

The deck structure 30 of the platform 24 is 1
It may include one deck, or it may include more than one deck.
The top of the tendon is preferably connected to one of the decks, but need not be, as the need for access to the tendon is rare. For the smallest size platform with a 20 meter square deck and a platform height of 25 meters, the bottom of the platform is stationary at about 15 meters below sea level and the tendons and vertical transport tubes are below sea level. At least 10
Be bound to the metric level. The top (tree) of a vertical transport tube is usually well above the platform and bottom.

FIGS. 7 and 8 show two mechanisms for laterally restraining tendons and vertical transport tubes at or near the horizontal level of the lower hull 56, where vertical transport tube 52 is shown. The case is shown. FIG. 7 shows a rectangular passage 6 surrounding the vertical transport pipe 52 and fixed thereto.
The lateral restraint structure formed by element 66 having 7 is shown. If platform drift is small, element 66 may move slightly laterally within hole 69 in the lower hull. If the platform drifts too much, as the platform 24 moves laterally in adverse weather conditions, the walls of the passageway 67 cause the vertical transport tube 52 to bend a small angle (up to about 8 °) with a large radius of curvature. The top 61 of the vertical transportation pipe is mounted on the deck structure 3 by the mount 63.
It is fixed to a deck 65 of 0 and a tree 67 extending on the deck. The guideway 67 causes the vertical transport pipe to bend with a radius of curvature greater than 10 times, preferably greater than 20 times the outer diameter of the vertical transport pipe. It is possible to secure the element 66 to the hull.

FIG. 8 shows a hollow tube (6 in FIG. 5) of the column 54.
A lateral restraint structure is shown, formed by a series of rings 68 attached to the wall 64 of the lower hull 56, such as 2). The inner diameter of the ring 68 gradually increases as it goes downward. The vertical transport tube 52 bends (up to about 8 °) due to the ring as the source platform moves laterally.

In prior art designs, any platform drift was addressed by pivoting in a tree such as 63 in FIG. 7, which required a large hole in the lower hull 56. With the tendon rotating at a lower level, the tension in the vertical transport tube was maintained by the hydraulic activator. In the present invention, since the vertical transport pipe in the lower portion of the hull well below the vertical transport pipe mount 63 is bent, a hydraulic activator and related devices are unnecessary.

For each tendon, a lateral restraint that allows for bending at or near the lower hull level is:
It can be achieved by the device or pivot joint of FIG. 7 or 8. Elastic pivot joints, which allow limited rotation in any direction, allow sharp bends and can be used for tendons as they do not carry fluid,
It cannot generally be used for vertical transport tubes that carry fluids (through tubes within vertical transport tubes). However, the applicant
It may be preferable to use the device of FIG. 7 or 8 to bend the tendon, avoiding the cost of the pivot joint and adapting the bending of the vertical transport pipe.

Since the platform 24 drifts only slightly during heavy storms, the vertical transport tube and tendon angles from the vertical are only about 8 °. The small platform 24 is practically unloaded by wind, which is a major factor limiting its drift during heavy storms.

As shown in FIG. 1, a method for installing a production system is provided that includes setting a seabed template on the seabed 48 proximate to a subsea well. The seabed template 28 is anchored on the seabed. Tendon is installed by anchoring on the template,
The buoy is temporarily attached to the top of the tendon. The platform 24 is then pulled into position on the template and the top of the tendon is attached and tensioned to the platform. Using the boring device 52, at least one oil well 58 is formed in the subsea template 28.
Drilled into the subsea oil well. Vertical transportation pipes will be installed to connect the tree on the platform structure to the oil well. The tendons and vertical transport tubes are constrained to move substantially horizontally relative to each other at the bottom of the hull below the deck structure.

The production system is designed so that all installation work can be done without resorting to costly, heavy crane vessels. By connecting the upper end of the tendon 50 to the platform, preferably to the deck structure 30 of the platform, the platform 24
Is installed above the seabed template 28. The semi-submersible unit 20 includes a platform 24 and an oil well region 2
Directly access 8 directly. The unit 20 is connected to the platform using a cross spring mooring system 72 using cables 74. Then the vertical transport pipe 52
Submarine template 28 via platform 24
It is installed from the semi-submersible unit 20 up to. The vertical transport pipe 52 is attached to the deck structure 30 of the platform. At least one flexible flow line 70 extending from the upper deck structure 30 to the production device 26 on the working deck 34 of the unit 20 is provided for the transfer of hydrocarbons from the subsea well to the semi-submersible unit 20. It Flexible flow line 70 includes a plurality of lines for passing oil and gas and may further include one or more controlled umbilicals for source control.

Thus, the present invention provides an apparatus for boring subsea wells to produce oil with reduced complexity and cost. A vertical transport pipe extending from near the seabed to the tree on a small tension leg platform and a tendon extending from the seabed to the platform extend through a lateral guide structure at the bottom of the platform under the hull in seawater. A lateral guide structure ensures that the tendons and vertical conduits extend substantially parallel to each other between the bottom of the platform and the end position near the seabed, with the lateral direction of the vertical conduits and tendons relative to each other at the bottom of the platform. (Horizontal) movement of is blocked. A lateral guide structure for a vertical transport pipe includes a guide that guides the vertical transport pipe to bend at a large radius at the bottom of the platform.

While particular embodiments of the present invention have been illustrated and shown, it will be appreciated that modifications and variations will readily occur to those skilled in the art, and as such the claims are entitled to such modifications. And equivalents are intended to be included.

[Brief description of drawings]

FIG. 1 is an elevational view of a submarine platform system showing a semi-submersible production structure and a compact tension leg source platform.

2 is an isometric view of the platform of FIG. 1. FIG.

FIG. 3 shows the lateral movement of a small platform in which a parallelogram configuration is formed by tendons and vertical transport tubes.

FIG. 4 is a plan view taken at line 4-4 of FIG. 1 showing the means for connecting the semi-submersible structure to the platform using the cross spring mooring system.

FIG. 5 is a plan view of the undercarriage of the platform of another embodiment of the present invention.

6A and 6B are plan views of the deck structure of an example platform having 20 vertical transport tubes and 12 vertical transport tubes.

FIG. 7 is a cross-sectional view of a lateral restraint structure that restrains a vertical transport pipe.

FIG. 8 is a sectional view of a lateral restraint structure according to another embodiment of the present invention.

[Explanation of symbols]

 10 Production System 24 Platform 50 Tendon 51 Hull 52 Vertical Transport Pipe

Claims (11)

[Claims] 1. A subsea offshore hydrocarbon production system of known depth for producing hydrocarbons from at least one offshore subsea well, the submerged hydrocarbon production system being substantially above sea level. A platform including a deck structure including two decks, and a floating hull supporting the deck structure and extending below 3 meters below the sea level but including a lower part of the underwater sea near the sea floor, and an upper end of the platform. A plurality of substantially vertical tendons connected to the bottom of the sea floor and at least one vertical transport pipe connected to the deck structure at the top and to the bottom of the sea, and at least 3 meters below sea level. Position, mounted on the lower portion of the hull and constraining each of the tendons and the vertical transport tubes in a horizontal direction with respect to substantially horizontal movement with respect to the hull. And a lateral confinement structure that, undersea hydrocarbon production systems. 2. The lateral restraint structure includes a guide to bend the vertical transport tube up to about 8 ° with a radius of curvature greater than 10 times the diameter of the vertical transport tube. Undersea system. 3. The submarine system of claim 1, wherein the restraint structure includes an element having a passage that gradually widens downwardly, the vertical transport pipe extending through the passage. 4. The submarine system of claim 3, wherein the restraint structure includes a plurality of angular guides, each tendon extending through one of the guides. 5. The restraint structure includes a series of rings having different inner diameters attached to the lower hull structure, and the rings are arranged such that the inner diameters thereof become larger as they go downward. Submarine system described in. 6. The system of claim 1, wherein an upper end of the vertical transport pipe is connected to a tree above sea level and the lateral restraint structure is at least 3 meters below sea level. 7. A subsea, offshore hydrocarbon production system for producing hydrocarbons from an offshore well, comprising a platform floating above sea level and capable of drifting from rest to about 8 °. The lower part has the bottom of the hull below the sea level, the upper part is above the sea level, and the lower end is at a height of several meters above the bottom of the hull. A tree and a plurality of generally vertical tendons extending to the seabed, the tendons having a lower end anchored to the seabed, an upper end attached to the platform, a lower end attached to the seabed and coupled to the well, and A plurality of substantially vertical vertical transport pipes having an upper end attached to the lower end of the tree on the platform; The boom has a lateral guide structure for bending each of the vertical transportation pipes at a position several meters below the lower end of the tree when the hull drifts from the stationary state to about 8 °. Also, pivoting at a position selected to extend the vertical transport tube and tendon substantially parallel to each other when a plurality of meters below the level of the bottom of the tree and when the platform drifts from the rest to about 8 °. A submarine hydrocarbon production system. 8. The lateral guide structure includes a plurality of guides, each of which has a diameter of two vertical transport tubes for platform drift from the rest to about 8 °.
8. The system of claim 7, adapted to bend one of the vertical transport tubes with a radius of curvature greater than zero. 9. A method for installing a submarine source platform for hydrocarbon production in the sea, comprising boring at least one oil well to the seabed, a deck structure and an undersea supporting said deck structure. Installing a small tension leg source platform including a hull having a lower hull with the platform floating near the surface of the sea, the step of anchoring each lower end of a plurality of tendons to the seabed, and Connecting the upper end of the vertical transport pipe to the platform, and further comprising the step of installing at least one vertical transport pipe, which comprises connecting the lower end of the vertical transport pipe to the well and the deck structure of the platform. And connecting the upper end of the vertical transportation pipe to the hull. A method for installing a submarine source platform, comprising constraining the vertical transport pipe and the tendon from substantially horizontal movement of each other at a level in seawater substantially the same as the undercarriage. 10. The step of constraining the vertical transport tube comprises the step of bending the vertical transport tube with a radius of curvature greater than 10 times the diameter of the vertical transport tube when the platform drifts. 10. The method of claim 9 included. 11. A method for installing an offshore well platform for production from an undersea oil well, comprising anchoring a lower end of each of a plurality of tendons to the seabed near said offshore oil well, and Mounting at least one buoy on the upper end of the tendon, and after mounting the at least one buoy on the tendon, transferring a small tension leg source platform floating on the sea surface to the tendon, the platform comprising: It has a deck structure at least approximately at the same height and a lower hull below sea level and below the deck structure, and further picks up the upper end of the tendon and places the tendon at a position spaced from the platform. Including the step of mounting the upper end, the step including the tendon A tensioning step, further comprising boring at least one well into the subsea well and installing at least one vertical transport pipe, the step comprising: vertically transporting the well connected to the well. Connecting the lower ends of the pipes and connecting the upper ends of the vertical transport pipes to the deck structure, further comprising connecting the vertical transport pipes and the tendons at approximately the same level as the lower hull and in a substantially horizontal direction relative to each other. A method for installing a submarine source platform including the step of restraining from movement.