FR2476715A2 - Marine platform on top end of tower resting on sea-bed - where tower is towed to site via main and auxiliary floats, and main float is then lowered to sea-bed - Google Patents

Abstract

This is an addn. to 75.34950, which described a platform on a tower resting on a main float while being towed to a desired site, at which the main float is sunk. The novelty in the present invention is that the tower is located inside a guide structure, in which the tower can slide vertically, the structure is carried by a row of auxiliary floats while being towed with the tower to a site. At the site, the main float and the tower are lowered until the float rests on the seabed. The guide structure then forms the platform at the top end of the tower; and the auxiliary floats are towed away. Platform is used in offshore winning of petroleum or natural gas, where the presinvention provides an alternative to the main patent.

Description

 This addendum refers to patent application N075 34950 published as a Utility Certificate under "2 331 645.

 Its purpose is to describe an alternative embodiment of the principle of marine platform which was proposed in the initial request and to explain the corresponding laying method.

 The platform always consists of a sealed lower float (1), supporting in its center a tower (2) whose uprights such as (3) are all vertical.

 Under the lower float, spades (10) delimit cells (11) for possible injection for leveling.

 In this new embodiment the tower (2) and the lower float (1) preferably have an octagonal or hexagonal section but can also be of quadrangular section as in the embodiment described in the initial request.

The stabilizing role played in the initial request by the upper float (reference (3) of this request) is held in this new embodiment by a ring of auxiliary floats such as (4) connected at support points such that (5) to a guide structure (6) surrounding the tower and in which this tower can slide freely from top to bottom. (Fig I and Fig II)
There are eight auxiliary floats If the tower is octagonal, six if it is hexagonal.

 The support points such as (5) are organized in a known manner so that the structure (6) is integral with the floats (4) as long as it rests on them, but that it disconnects as soon as its weight is no longer transferred to them.

 The guide structure can receive at its upper part, on the construction site, all or only part of the final equipment (7) of the tower.

The stabilizing floats (4) are kept equidistant by tie rods such as (12) connecting them together.

 In the end of construction or transport position, oG the auxiliary floats (4) support the loaded guide structure, their draft is the same as that of the lower float supporting the tower.

 The lower float supports the weight of the tower and also has a residual positive buoyancy of around 400 tonnes balanced by the traction of winches such as (8) placed at the top of the tower and exerting this traction on the guide structure (6) by 1 intermediate cables such as (9).

 The platform with its equipped guide structure leaves the construction site in the position of board I which is the towing and transport position.

Arrival at the installation site the lower float (1) and the tower (2) are gradually immersed by traction on the cables (9t until approaching the bottom at a short distance. In this position (board II) the top of the tower and that of the guide structure are at the same level
The guide structure is then made integral with the tower by known means and then the slow and simultaneous ballasting of all the auxiliary floats (4) is carried out, which causes the final descent of the tower and its lower float and their provisional support on the bottom.

 We proceed to leveling the platform by injecting differential cement between the ground and the bottom of the lower float in the alveoli of the spades (11), we ballast the lower float then we continue to ballast the auxiliary floats which results in clearing them their fasteners such as (5) and allow their removal by tugs.

 Part of the equipment initially placed on the guide structure is then swiped over the top of the tower (Plate III) and the last modules are replaced by pontoon-crane.

 The platform as described by this embodiment can optionally be removed from the site and moved by following the same procedure in reverse.

 Such a platform can be used in the petroleum industry or in setting up installations at sea.

Claims (1)

Claims 1 / - Gravity platform for installation at sea in which a vertical tower is supported by a lower float and is stabilized by a guide structure supported by auxiliary floats, structure through which the tower can slide freely from top to bottom. 20 / - Platform produced according to 1 / in which the connection between  the guide structure and the auxiliary floats cease  to exist when the guide structure no longer presses on the  auxiliary floats.  3 / - Platform made according to 10 / in which the floats  auxiliaries are distributed symmetrically under the structure of  guiding so that they offer minimal resistance  in swell.  4 / - Platform made according to 20 / in which we can place on  the top of the guide structure part or all of the equi  final part of this platform.