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Periscoping Low-Drag, Disconnectable Turret (PLDDT)

IP.com Disclosure Number: IPCOM000208818D
Publication Date: 2011-Jul-19
Document File: 3 page(s) / 167K

Publishing Venue

The IP.com Prior Art Database

Abstract

The proposed invention provides a disconnectable turret concept for ships and offshore production vessels. It is intended for use in the offshore loading and offloading of liquid hydrocarbons such as oil, Liquefied Natural Gas (LNG) or other fluids and in the production of hydrocarbons from an offshore reservoir through risers to a floating production vessel and or a floating LNG vessel. The primary features of this invention include a periscoping turret (the PLDDT device), a rotating turret sleeve and a Disconnectable Turret Buoy (DTB). The proposed concept introduces a reduction in the additional or parasitic drag and an increase in the number of flow paths that can be incorporated in the turret.

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Periscoping Low-Drag, Disconnectable Turret (PLDDT)

Statement of the Problem

Disconnectable turret systems are often used in offshore areas of the world subjected to harsh environments. Disconnectable turrets were first used in the

North Sea

in the mid-1990s for the offloading of produced crude oil to shuttle tankers. This use of disconnectable turrets enabled offloading in higher seastates than Catenary Anchor Leg Mooring (CALM) buoys. Since then, disconnectable turrets have been employed in oil production developments in locations where environmental conditions such as typhoons, sea ice or icebergs pose an unacceptable hazard to the vessel. Additionally, disconnectable turret capability has been installed in some Liquefied Natural Gas (LNG) carriers equipped with regassification facilities, thus providing a low-cost offshore LNG import terminal solution. It is also feasible to conceive of LNG carriers loading or discharging either gaseous methane or LNG through a disconnectable turret located some distance offshore that is connected via pipeline to an onshore LNG export or import facility.

In all crude and LNG loading/offloading scenarios, the state of the art of disconnectable turrets involves the turret being pulled up into a recess in the bottom of the ship at the bow.  This recess is essentially around ten meters in diameter and can cause considerable parasitic drag when the ship is underway. The drag must be overcome by additional power, which results in higher fuel cost than that of a ship without the disconnectable turret recess.  It is desirable to reduce the parasitic drag  for disconnectable turret systems on oil shuttle tankers and LNG carriers.

Description of the Invention

This invention provides a disconnectable turret concept for ships and offshore production vessels. It is intended for use in the offshore loading and offloading of liquid hydrocarbons such as oil, LNG or other fluids and in the production of hydrocarbons from an offshore reservoir through risers to a floating production vessel and or a floating LNG vessel. 

The primary features of the invention are (see Figure 1):

·         A periscoping turret (the PLDDT device), which is housed within a cylinder or sleeve within the floating vessel or ship.  The PLDDT is equipped with a device (to be engineered) that enables it to be lowered and raised within the sleeve so as to extend beneath the keel of the vessel. When lo...