Subsea carrier

Abstract

A subsea carrier (100) for transporting a fluid, e.g. CNG or crude, comprises a main body (101) for containing the fluid at a predetermined internal pressure, wherein the main body (101) preferably is made of concrete and designed to operate at a water depth where the external pressure substantially counteracts the internal pressure. The subsea carrier has a floating element (102) connected to the main body (101) by a stabilising cable (132), wherein the stabilising cable (132) comprises a first rope (321) for transmitting force and is attached to a first connector (134) that is movable with respect to the main body (101). A system wherein the subsea carrier is towed by a surface vessel (3) or is self-propelled and controlled remotely is also disclosed. The subsea carrier (100) reduces operational costs relative to subsea carriers with traditional control surfaces and ballasting systems at large cargo volumes, e.g. 150 000 m³ or more.

Description

BACKGROUND OF THE INVENTIONField of the Invention[0001]The present invention relates to a subsea carrier for a fluid, e.g. oil or compressed natural gas.Prior and Related Art[0002]In the following, hydrocarbons serves as an example of fluid cargo. However, embodiments of the carrier described herein can carry fresh water, inorganic gas or other fluid chemical compounds. Here, the term “hydrocarbons” means oil and gas, typically extracted from a subterranean reservoir. Natural gas, or NG, means hydrocarbons that are gaseous at normal conditions, i.e. 0° C. and 1 bar, such as methane, whereas the hydrocarbons also include components that are liquid at normal conditions, e.g. crude.[0003]Starting from a reservoir and a pressure of several hundred bar, a mixture of hydrocarbons, water and other substances, e.g. H2S, are brought to the surface under closely super-vised conditions. Temperature and pressure is controlled and chemicals may be added, e.g. to prevent or inhibit formation of h...

AI Technical Summary

Benefits of technology

[0022]The first connector is primarily movable in a longitudinal direction in order to adjust the pitch of the main body. The pitch should be adjusted such that the main body presents a minimum area perpendicular to the direction of travel at all times in order to minimise drag and thus operational costs. Equally important, e.g. a positive pitch causes the main body to move upward. This is undesired because the external pressure should exceed the internal pressure in order to compress the structure. The first connector may also be movable in a lateral direction in order to control roll, in particular at loading and unloading points.

[0023]In a preferred embodiment, the length of the stabilising cable exceeds the water depth. In this embodiment, the floating element floats on the surface, so that if the main body starts rising, the floating element rises out of the water. This reduces the buoyancy and thereby causes the main body to sink due to gravity. Opposite, if the main body starts sinking, an increased volume of the floating element is submerged. This increases the buoyancy and causes the main body to rise due to buoyancy transferred through the stabilising cable.

[0024]A preferred embodiment comprises a bridle...

Problems solved by technology

However, embodiments with a somewhat positive internal differential pressure are also anticipated because handling a limited dif...

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